CN1989267A - High young's modulus steel plate, zinc hot dip galvanized steel sheet using the same, alloyed zinc hot dip galvanized steel sheet, high young's modulus steel pipe, and method for production thereof - Google Patents

Abstract

An embodiment of a high Young's modulus steel sheet, wherein it has a chemical composition, in mass %, that C: 0.0005 to 0.30 %, Si: 2.5 % or less, Mn: 2.7 to 5.0 %, P: 0.15 % or less, S: 0.015 % or less, Mo: 0.15 to 1.5 %, B: 0.0006 to 0.01%, Al: 0.15 % or less, and the balance: Fe and inevitable impurities.

Description

High Young's modulus steel sheet, hot-dip galvanized steel sheet using the same, alloyed hot-dip galvanized steel sheet, and high Young's modulus steel pipe, and their manufacturing methods

technical field

The present invention relates to a high Young's modulus steel sheet, a hot-dip galvanized steel sheet using the same, an alloyed hot-dip galvanized steel sheet, a high Young's modulus steel pipe, and methods for producing them.

This application is to Japanese patent application 2004-218132 filed on July 27, 2004, Japanese patent application 2004-330578 filed on November 15, 2004, Japanese patent application 2005-019942 filed on January 27, 2005, 2005 Priority is claimed to Japanese Patent Application No. 2005-207043 filed on July 15, the contents of which are incorporated herein by reference.

Background technique

There have been many reports on techniques for increasing Young's modulus. Most of these relate to techniques for increasing Young's modulus in the rolling direction (RD) and in the width direction (TD) perpendicular to the rolling direction (RD).

Patent Documents 1 to 9 all disclose techniques for increasing Young's modulus in the TD direction by rolling in the α+γ ₂ phase region.

Patent Document 10 discloses a technique for increasing the Young's modulus in the TD direction by applying rolling to the surface layer at a temperature lower than the Ar ₃ transformation point.

On the other hand, there is also disclosed a technique for increasing the Young's modulus in the TD direction and also increasing the Young's modulus in the RD direction. That is, Patent Document 11 discloses that in addition to rolling in a certain direction, the Young's modulus of both is increased by performing rolling in a width direction perpendicular to the direction. However, in the continuous hot rolling process of a thin plate, changing the rolling direction in the middle obviously hinders productivity, so it is not practical.

Patent Document 12 discloses a cold-rolled steel sheet having a high Young's modulus, but this also has a high Young's modulus in the TD direction, not a high Young's modulus in the RD direction.

In addition, Patent Document 13 discloses the technology of increasing the Young's modulus by compositely adding Mo, Nb, and B. However, since the hot rolling conditions are completely different, the Young's modulus in the TD direction is high, and the Young's modulus in the RD direction is not high. High volume.

As described above, there have been steel sheets with a high Young's modulus, but all of them have a high Young's modulus in the width direction (TD) perpendicular to the rolling direction (RD). However, the width of the steel plate is about 2 m at most, and when the direction in which the Young's modulus is the largest is taken as the longitudinal direction of the member, the length cannot exceed the width. Therefore, for a long member, a steel plate having a high Young's modulus in the rolling direction is strongly desired. Furthermore, the production method also presupposes hot rolling in the α+γ region where the rolling reaction force tends to fluctuate, and there is a problem in terms of productivity.

When steel sheets are processed into parts for automobiles and building materials, shape freezing becomes the biggest problem. For example, when the load is removed after bending, there is a problem that the steel plate returns to its original shape due to springback, so that a desired shape cannot be obtained. This phenomenon becomes conspicuous with increasing strength, and becomes an obstacle when high-strength steel sheets are applied to members.

Patent Document 1: JP-A-59-83721

Patent Document 2: Japanese Unexamined Patent Publication No. 5-263191

Patent Document 3: JP-A-8-283842

Patent Document 4: Japanese Unexamined Patent Publication No. 8-311541

Patent Document 5: Japanese Unexamined Patent Publication No. 9-53118

Patent Document 6: JP-A-4-136120

Patent Document 7: JP-A-4-141519

Patent Document 8: Japanese Unexamined Patent Publication No. 4-147916

Patent Document 9: Japanese Unexamined Patent Publication No. 4-293719

Patent Document 10: JP-A-4-143216

Patent Document 11: JP-A-4-147917

Patent Document 12: Japanese Unexamined Patent Publication No. 5-255804

Patent Document 13: Japanese Unexamined Patent Publication No. 08-1311541

Contents of the invention

The present invention has been made in view of the above circumstances, and its object is to provide a steel sheet with a high Young's modulus excellent in the Young's modulus in the rolling direction (RD), a hot-dip galvanized steel sheet using the same, and an alloyed hot-dip coated steel sheet. Zinc steel sheet, and high Young's modulus steel pipe, and methods for their manufacture.

The inventors of the present invention have conducted intensive research in order to achieve the above objects, and have obtained the following unprecedented knowledge.

That is, by making C, Si, Mn, P, S, Mo, B, and Al containing predetermined amount, or containing C, Si, Mn, P, S, Mo, B, Al, N, Nb, and Ti The invention of a steel plate having a high Young's modulus in the rolling direction by developing a predetermined texture near the surface of the steel has been successful.

Furthermore, since the steel sheet obtained by the present invention has a particularly high Young's modulus of 240 GPa or more near the surface, the bending rigidity is remarkably improved, for example, the shape freezing property is remarkably improved. The reason why the degree of deficiencies in freezeability such as springback increases with high strength is that the amount of return after removal of the load applied when the press is deformed is large. Therefore, if the Young's modulus is increased, the return amount can be suppressed, and springback may be reduced. In addition, during bending deformation, the deformation behavior near the surface layer with a large bending moment has a significant influence on the shape freezing property, so it is possible to significantly improve the Young's modulus only by increasing the surface layer.

The present invention is based on such thoughts and new insights, and is an unprecedented new steel plate and its manufacturing method, and its gist is as follows.

(1). A high Young's modulus steel plate, characterized in that it contains C: 0.0005-0.30%, Si: 2.5% or less, Mn: 2.7-5.0%, P: 0.15% or less, and S: 0.015% or less, Mo: 0.15-1.5%, B: 0.0006-0.01%, Al: 0.15% or less, and the balance is composed of Fe and unavoidable impurities, {110}<223 in 1/8 layer of plate thickness >Any one or both of {110}<111> has a pole density of 10 or more, and the Young's modulus in the rolling direction exceeds 230GPa.

(2) The high Young's modulus steel sheet according to (1), wherein the pole density of {112}<110> of a layer half the thickness of the sheet is 6 or more.

(3) The high Young's modulus steel sheet according to (1), further comprising one or two of Ti: 0.001 to 0.20% by mass and Nb: 0.001 to 0.20% by mass.

(4). According to the high Young's modulus steel plate described in (1), it is characterized in that, after stretching 2%, implement heat treatment at 170 ℃ for 20 minutes and carry out stretching test again when the upper yield point minus the stretching The amount of BH (MPa) evaluated by the difference in flow stress at 2% is 5 MPa to 200 MPa.

(5). The high Young's modulus steel plate according to (1), further comprising Ca: 0.0005 to 0.01% by mass.

(6). The high Young's modulus steel plate according to (1), further comprising one or more of Sn, Co, Zn, W, Zr, V, Mg, and REM, and their The total content is 0.001 to 1.0% by mass.

(7) The high Young's modulus steel sheet according to (1), further containing one or more of Ni, Cu, and Cr, and the total content thereof is 0.001 to 4.0% by mass.

(8) A hot-dip galvanized steel sheet comprising the high Young's modulus steel sheet described in (1), and hot-dip galvanizing applied to the high Young's modulus steel sheet.

(9). An alloyed hot-dip galvanized steel sheet, characterized in that it has the high Young's modulus steel sheet described in (1) and the alloyed hot-dip coating applied on the high Young's modulus steel sheet zinc.

(10) A high Young's modulus steel pipe, comprising the high Young's modulus steel plate described in (1), and the high Young's modulus steel plate is wound in any direction.

(11) The method for producing a high Young's modulus steel sheet according to (1), which includes a step of heating a slab to a temperature of 950° C. or higher to perform hot rolling to produce a hot-rolled sheet, the The slab contains C: 0.0005-0.30%, Si: 2.5% or less, Mn: 2.7-5.0%, P: 0.15% or less, S: 0.015% or less, Mo: 0.15-1.5%, B: 0.0006- 0.01%, Al: 0.15% or less, and the balance is composed of Fe and unavoidable impurities; wherein the hot rolling process is carried out under the following conditions: below 800°C, the friction coefficient between the roll and the steel plate exceeds 0.2, and the total pressure Rolling was performed so that the down ratio was 50% or more, and the hot rolling was completed at a temperature from the Ar3 transformation point to 750°C.

(12). The method for manufacturing a high Young's modulus steel sheet according to (11), wherein, in the hot rolling step, at least one pass is carried out at a different circumferential speed of 1% or more. Peripheral speed rolling.

(13) The method for producing a high Young's modulus steel sheet according to (11), wherein at least one roll having a roll diameter of 700 mm or less is used in the hot rolling step.

(14). The method for producing a high Young's modulus steel sheet according to (11), further comprising the step of subjecting the hot-rolled steel sheet after the hot rolling to a maximum reaching temperature of The annealing step is performed under the condition of 500°C to 950°C.

(15). The method for manufacturing a high Young's modulus steel sheet according to (11), further comprising cold rolling the hot-rolled steel sheet after the hot rolling at a reduction ratio lower than 60%. process, and the process of annealing after the cold rolling process.

(16). The method for manufacturing a high Young's modulus steel sheet according to (11), further comprising: cold-rolling the hot-rolled steel sheet at a reduction ratio lower than 60%; A step of annealing at a maximum temperature of 500°C to 950°C after the cold rolling step; and a step of cooling to 550°C or less after the annealing step, followed by heat treatment at 150°C to 550°C.

(17). A method for manufacturing a hot-dip galvanized steel sheet, comprising: a step of manufacturing an annealed high Young's modulus steel sheet by the method for manufacturing a high Young's modulus steel sheet as described in (14); And a step of hot-dip galvanizing the high Young's modulus steel sheet.

(18). A method for manufacturing an alloyed hot-dip galvanized steel sheet, characterized in that it has: a step of manufacturing a hot-dip galvanized steel sheet by the method for manufacturing a hot-dip galvanized steel sheet described in (17); The process of heat-treating a hot-dip galvanized steel sheet at a temperature range of 450 to 600° C. for 10 seconds or longer.

(19). A method for manufacturing a hot-dip galvanized steel sheet, comprising: a step of manufacturing an annealed high Young's modulus steel sheet by the method for manufacturing a high Young's modulus steel sheet as described in (15); And a step of hot-dip galvanizing the high Young's modulus steel sheet.

(20). A method for manufacturing an alloyed hot-dip galvanized steel sheet, characterized in that it has: a step of manufacturing a hot-dip galvanized steel sheet by the method for manufacturing a hot-dip galvanized steel sheet described in (19); The process of heat-treating a hot-dip galvanized steel sheet at a temperature range of 450 to 600° C. for 10 seconds or longer.

(21). A method for manufacturing a high Young's modulus steel pipe, characterized in that it comprises: a step of manufacturing a high Young's modulus steel plate by the method for manufacturing a high Young's modulus steel plate described in (11); and The high Young's modulus steel plate is wound in any direction to form a steel pipe.

(22) A steel plate with a high Young's modulus, characterized by containing C: 0.0005-0.30%, Si: 2.5% or less, Mn: 0.1-5.0%, P: 0.15% or less, and S: 0.015% or less, Al: 0.15% or less, N: 0.01% or less; and also contains Mo: 0.005-1.5%, Nb: 0.005-0.20%, Ti: 48/14×N (mass%)-0.2%, B: One or more of 0.0001% to 0.01%, the total is 0.015% to 1.91% by mass; and the balance is composed of Fe and unavoidable impurities; among them, {110}<223> in the 1/8 layer of the plate thickness And/or the pole density of {110}<111> is 10 or more, and the Young's modulus in the rolling direction exceeds 230 GPa.

(23). The high Young's modulus steel plate according to (22), which is characterized in that it contains all of the above-mentioned Mo, Nb, Ti, and B, and their contents are Mo: 0.15% to 1.5%, Nb: 0.01%, respectively. ~ 0.20%, Ti: 48/14×N (mass %) ~ 0.2%, B: 0.0006 ~ 0.01%, and the pole density of {110}<001> of the 1/8 layer of plate thickness is 3 or less.

(24) The high Young's modulus steel plate according to (22), wherein the pole density of {110}<001> of the 1/8 layer of the plate thickness is 6 or less.

(25) The high Young's modulus steel sheet according to (22), wherein the Young's modulus in the rolling direction of at least 1/8 layer away from the surface layer of the plate thickness is 240 GPa or more.

(26). The high Young's modulus steel sheet according to (22), wherein the pole density of {211}<011> in a half layer of the sheet thickness is 6 or more.

(27). The high Young's modulus steel sheet according to (22), wherein the pole density of {332}<113> in a half layer of the sheet thickness is 6 or more.

(28). The high Young's modulus steel sheet according to (22), wherein the pole density of {100}<011> in a layer half the thickness of the sheet is 6 or less.

(29). The high Young's modulus steel plate according to (22), wherein the tensile strength is subtracted from the upper yield point when stretching 2% and heat-treating at 170° C. for 20 minutes and performing a stretching test again. The amount of BH evaluated by the difference of flow stress at 2% is 5MPa-200MPa.

(30). The high Young's modulus steel plate according to (22), further comprising Ca: 0.0005 to 0.01% by mass.

(31). The high Young's modulus steel plate according to (22), which further contains one or more of Sn, Co, Zn, W, Zr, V, Mg, and REM, and their The total content is 0.001 to 1.0% by mass.

(32). The high Young's modulus steel sheet according to (22), further containing one or more of Ni, Cu, and Cr, and the total content thereof is 0.001 to 4.0% by mass.

(33) A hot-dip galvanized steel sheet comprising the high Young's modulus steel sheet described in (22), and hot-dip galvanizing applied to the high Young's modulus steel sheet.

(34). An alloyed hot-dip galvanized steel sheet, characterized in that it has the high Young's modulus steel sheet described in (22), and an alloyed hot-dip coating applied on the high Young's modulus steel sheet zinc.

(35) A high Young's modulus steel pipe comprising the high Young's modulus steel plate according to (22), and the high Young's modulus steel plate is wound in an arbitrary direction.

(36). The method for producing a high Young's modulus steel sheet according to (22), which includes a step of heating a slab to a temperature of 1000° C. or higher to perform hot rolling to produce a hot-rolled sheet, and the The slab contains C: 0.0005% to 0.30%, Si: 2.5% or less, Mn: 0.1 to 5.0%, P: 0.15% or less, S: 0.015% or less, Al: 0.15% or less, N: 0.01% or less in mass % and also contain one or more of Mo: 0.005-1.5%, Nb: 0.005-0.20%, Ti: 48/14×N (mass%)-0.2%, B: 0.0001-0.01%, the total is 0.015% to 1.91% by mass; and the balance is composed of Fe and unavoidable impurities; wherein the hot rolling process is carried out under the following conditions: the friction coefficient between the roll and the steel plate exceeds 0.2, and the effective effect calculated by the following formula [1] Rolling is carried out so that the variable ε ^* is 0.4 or more and the total rolling reduction is 50% or more, and the hot rolling is completed at a temperature from the Ar ₃ transformation point to 900°C,

${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; -</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; j</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ]</span>$

In the formula, n is the number of stands in the finishing hot rolling mill, ε _j is the strain applied to the jth stand, ε _n is the strain applied to the nth stand, and t _i is the i-th stand to the i+1th stand The running time (seconds) between and τ _i can be calculated by the following formula [2] through the gas constant R (=1.987) and the rolling temperature T _i (K) of the i-th stand,

τ _i =8.46×10 ⁻⁹ ×exp{43800/R/T _i } [2].

(37). The method for manufacturing a high Young's modulus steel sheet according to (36), wherein, in the hot rolling step, at least one pass of a different circumferential velocity of 1% or more is applied. Peripheral speed rolling.

(38). The method for producing a high Young's modulus steel sheet according to (36), wherein at least one roll having a roll diameter of 700 mm or less is used in the hot rolling step.

(39). The method for producing a high Young's modulus steel sheet according to (36), further comprising the step of subjecting the hot-rolled steel sheet after the hot rolling to a maximum reaching temperature of The annealing step is performed under the condition of 500°C to 950°C.

(40). The method for manufacturing a high Young's modulus steel sheet according to (36), further comprising cold rolling the hot-rolled steel sheet after the hot rolling at a reduction ratio lower than 60%. process, and the process of annealing after the cold rolling process.

(41). The method for producing a high Young's modulus steel sheet according to (36), further comprising: cold-rolling the hot-rolled steel sheet at a rolling reduction lower than 60%; After the cold rolling step, annealing at a maximum temperature of 500°C to 950°C; and after the annealing step, cooling to 550°C or lower, followed by heat treatment at 150°C to 550°C.

(42) A method for producing a hot-dip galvanized steel sheet, comprising: a step of producing an annealed high Young's modulus steel sheet by the method for producing a high Young's modulus steel sheet as described in (39), And a step of hot-dip galvanizing the high Young's modulus steel sheet.

(43). A method for manufacturing an alloyed hot-dip galvanized steel sheet, comprising: a step of manufacturing a hot-dip galvanized steel sheet according to the method for manufacturing a hot-dip galvanized steel sheet described in (42); The process of heat-treating a hot-dip galvanized steel sheet at 450-600 degreeC for 10 seconds or more is mentioned above.

(44) A method for producing a hot-dip galvanized steel sheet, comprising: a step of producing an annealed high Young's modulus steel sheet by the method for producing a high Young's modulus steel sheet as described in (40), And a step of hot-dip galvanizing the high Young's modulus steel sheet.

(45). A method for manufacturing an alloyed hot-dip galvanized steel sheet, comprising: a step of manufacturing a hot-dip galvanized steel sheet by the method for manufacturing a hot-dip galvanized steel sheet described in (44), and The process of heat-treating a hot-dip galvanized steel sheet at 450-600 degreeC for 10 seconds or more is mentioned above.

(46). A method for producing a high Young's modulus steel pipe, comprising: a step of producing a high Young's modulus steel plate by the method for producing a high Young's modulus steel plate described in (36), and The high Young's modulus steel plate is wound in any direction to form a steel pipe.

According to the high Young's modulus steel sheet of the present invention, by specifying the composition described in (1) or (22) above, the shear texture near the surface layer can be developed in the low temperature γ range. Furthermore, by forming the texture described in (1) or (22) above, it is possible to realize an excellent Young's modulus especially in the rolling direction (RD direction).

According to the method for producing a high Young's modulus steel sheet of the present invention, by using the slab having the composition described in (11) or (36) above, the shear texture near the surface can be developed in the low temperature γ range. Furthermore, by performing hot rolling under the above-mentioned conditions, the texture described in (1) or (22) above can be obtained, and a steel sheet having an excellent Young's modulus in the rolling direction (RD direction) can be obtained in particular.

Description of drawings

Fig. 1 is a cross-sectional view showing a test piece used in a hat bending test.

Detailed ways

The reasons for limiting the steel composition and production conditions to those described above in the present invention are explained below.

(first embodiment)

The steel sheet according to the first embodiment contains C: 0.0005% to 0.30%, Si: 2.5% or less, Mn: 2.7 to 5.0%, P: 0.15% or less, S: 0.015% or less, Mo: 0.15% to 1.5% by mass %. %, B: 0.0006 to 0.01%, Al: 0.15% or less; and the balance is composed of Fe and unavoidable impurities. The pole density of either or both of {110}<223> and {110}<111> in the 1/8 layer of plate thickness is 10 or more, and the Young's modulus in the rolling direction exceeds 230GPa.

C is an inexpensive element that increases tensile strength, and its addition amount is adjusted according to the target strength level. When C is less than 0.0005% by mass, not only the steelmaking is technically difficult, but also the cost increases, and the fatigue properties of the weld zone deteriorate. Therefore, the lower limit was determined to be 0.0005% by mass. On the other hand, when the C content exceeds 0.30% by mass, it causes deterioration of formability or impairs weldability. Therefore, the upper limit is determined to be 0.30% by mass.

Si has an effect of increasing strength as a solid solution strengthening element, and is also effective in obtaining a structure including martensite, bainite, residual γ, and the like. The amount added is adjusted according to the target strength level. When the added amount exceeds 2.5% by mass, the press formability deteriorates, leading to a decrease in chemical conversion treatability. Therefore, the upper limit is determined to be 2.5% by mass.

When performing hot-dip galvanizing, problems such as decrease in productivity due to decrease in adhesion of the plating layer and delay in alloying reaction occur, so Si is preferably determined to be 1.2% by mass or less. The lower limit is not particularly set, but if it is determined to be 0.001 mass % or less, the production cost will increase, so exceeding 0.001 mass % is a substantial lower limit.

Mn is important for the present invention. That is, it is an essential element in order to obtain a high Young's modulus. In the present invention, the Young's modulus in the rolling direction (RD direction) can be developed by developing the shear texture near the surface layer of the steel sheet in the low-temperature γ region. Mn stabilizes the γ phase and expands the γ region to the low temperature region, so low-temperature rolling in the γ region is facilitated. Furthermore, there is also the possibility that Mn itself contributes favorably to the formation of the shear texture near the surface. From these points of view, Mn should be added at least 2.7% by mass. On the other hand, if it exceeds 5.0% by mass, the strength increases excessively, the ductility decreases, or the adhesion of galvanizing is hindered. Therefore, the upper limit is determined to be 5.0% by mass, preferably 2.9 to 4.0% by mass.

P is known to be an element that increases strength cheaply like Si, and when strength is required to be increased, it is more actively added. P has the effect of making the hot-rolled structure finer and improving workability. However, when the added amount exceeds 0.15% by mass, the fatigue strength after spot welding deteriorates, or the yield strength increases excessively, causing surface shape defects during pressing. Furthermore, the alloying reaction is extremely slow during continuous hot-dip galvanizing, and productivity decreases. Therefore, the upper limit thereof is determined to be 0.15% by mass.

When S exceeds 0.015% by mass, it causes hot cracking and deteriorates workability, so the upper limit is made 0.015% by mass.

Mo and B: important to the present invention. The addition of these elements made it possible for the first time to increase the Young's modulus in the rolling direction. Although the reason is not clear, it is considered that the rotation of the crystal due to the shear deformation due to the frictional force between the steel sheet and the roll is changed due to the effect of the composite addition of Mo, B, and Mn. As a result, a very sharp texture is formed in the range from the surface layer to the vicinity of the 1/4 layer of the hot-rolled sheet, and the Young's modulus in the rolling direction increases.

The lower limits of the Mo and B contents are Mo: 0.15% by mass and B: 0.0006% by mass, respectively. This is because it is added in a small amount. This is because the above-mentioned Young's modulus improvement effect is small. On the other hand, even if Mo and B are added over 1.5% by mass and over 0.01% by mass, respectively, the effect of improving the Young's modulus is saturated and the cost increases, so 1.5% by mass and 0.01% by mass are respectively determined as their upper limits.

In addition, the effect of improving the Young's modulus by adding these elements at the same time is further enhanced by the combination with C. Therefore, the amount of C is preferably determined to be 0.015% by mass or more.

Al can also be used as a deoxidation regulator. However, since Al significantly increases the transformation point, rolling in the low-temperature γ region becomes difficult, so the upper limit was determined to be 0.15% by mass.

In the steel sheet of the present embodiment, Ti and Nb are preferably contained in addition to the above composition. Ti and Nb have the effect of promoting the above-mentioned Mn, Mo, and B to further increase the Young's modulus. Furthermore, since it is effective in improving the workability and increasing the strength, and in refining and homogenizing the structure, it is added as required. However, the effect cannot be seen when the amount added is less than 0.001% by mass, and on the other hand, the effect tends to be saturated even if the added amount exceeds 0.20% by mass, so this was determined as the upper limit. Preferably it is 0.015-0.09 mass %.

Ca is useful as a deoxidizing element and is also effective in controlling the morphology of sulfides, so Ca may be added in the range of 0.0005 to 0.01% by mass. When it is less than 0.0005% by mass, the effect is insufficient, and when it is added in excess of 0.01% by mass, the workability deteriorates, so this range was determined.

A steel sheet containing these as main components may contain one or two or more of Sn, Co, Zn, W, Zr, Mg, and REM in a total of 0.001 to 1.0% by mass. Here, REM represents a rare earth metal element, which is one selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu above.

However, since Zr forms ZrN, solid solution N decreases, so it is preferable to make it 0.01 mass % or less.

Since Ni, Cu, and Cr are advantageous elements for performing low-temperature γ-region rolling, one or two or more of them may be added in a total range of 0.001 to 4.0% by mass. When it is less than 0.001% by mass, a remarkable effect cannot be obtained, and when it is added in excess of 4.0% by mass, workability deteriorates.

N: is a γ-stabilizing element, and thus is an advantageous element for performing low-temperature γ-zone rolling. Therefore, it may be added within 0.02% by mass. The reason why 0.02% by mass is determined as a substantial upper limit is that addition of more than this is difficult in manufacture.

The amounts of solid solution N and solid solution C are preferably 0.0005 to 0.004% by mass, respectively. When a steel plate containing them is processed as a member, strain aging also occurs at room temperature, and the Young's modulus increases. For example, when used in automobile applications, not only the yield strength of the steel sheet is increased but also the Young's modulus is increased by performing a coating and baking treatment after processing.

The amount of solid solution N and solid solution C can also be subtracted from the total amount of C and N by subtracting the amount of C and N present as compounds such as Fe, Al, Ti, B (quantified by chemical analysis of the extraction residue) Come and get it. Furthermore, it can also be obtained by an internal friction method and FIM (Field Ion Microscopy: Field Ion Microscopy).

When the amount of solid solution C and solid solution N is less than 0.0005% by mass, sufficient effect cannot be obtained, and even if it exceeds 0.004% by mass, the BH property tends to be saturated, so the upper limit was made 0.004% by mass.

Next, the texture, Young's modulus, and BH amount of the steel sheet will be described.

The pole density of {110}<223> and/or {110}<111> of the plate thickness/8 layer of the steel sheet according to the first embodiment is 10 or more. Thereby, the Young's modulus in the rolling direction can be improved. When the above pole density is less than 10, it is difficult for the Young's modulus in the rolling direction to exceed 230 GPa. The above-mentioned pole density is preferably 14 or more, and more preferably 20 or more.

The pole densities (random intensity ratios of X-rays) of these orientations are calculated according to the series expansion method based on the pole figures of {110}, {100}, {211}, and {310} measured by X-ray diffraction The 3-dimensional texture (ODF) can be calculated. That is, in order to obtain the pole density of each crystal orientation, the strength of (110)[2-23](110)[1-11] in the φ2=45° section of the three-dimensional texture is used as a representative.

An example of the above extreme density measurement is shown below.

The preparation of the sample for X-ray diffraction was performed as follows.

The steel plate is ground to a predetermined position in the thickness direction by mechanical grinding, chemical grinding, etc. After the polished surface is finished into a mirror surface by polishing, strain deformation is eliminated by means of electrolytic polishing and chemical polishing, and at the same time, 1/8 layer of plate thickness or 1/2 layer described later is adjusted as the measurement surface. For example, in the case of 1/8 layer, when the thickness of the steel plate is t, the surface of the steel plate is ground with a grinding amount of t/8 thickness, and the exposed ground surface is used as the measurement surface. In addition, it is difficult to accurately use the 1/8 layer and 1/2 layer of the plate thickness as the measurement surface, so the range of -3% to +3% of the relative plate thickness is used as the measurement surface centering on their target layers. Just sample. In addition, when segregation bands are confirmed in the center layer of the thickness of the steel plate, the measurement may be performed at a portion in the range of 3/8 to 5/8 of the thickness without segregation bands. In addition, when X-ray measurement is difficult, a statistically sufficient number of measurements are performed using the EBSP method and the ECP method.

The above {hkl}<uvw> means that the crystal orientation perpendicular to the plate surface is {hkl} and the crystal orientation in the longitudinal direction of the steel plate is <uvw> when the X-ray sample is taken by the above method.

The characteristics of the texture of the steel plate cannot be expressed only by the usual inverse pole diagram and positive pole diagram. For example, when the inverse pole diagram showing the crystal orientation in the normal direction of the steel plate surface is measured in the vicinity of 1/8 of the plate thickness Preferably, the surface intensity ratio (X-ray random intensity ratio) in each direction is <110>: 5 or more and <112>: 2 or more. Moreover, it is preferable that <112>: 4 or more and <332>: 1.5 or more about a 1/2 layer.

The limit of the above-mentioned extreme density should be satisfied at least for the 1/8 layer of the plate thickness, but preferably not only for the 1/8 layer of the plate thickness, but also for a wide range from the surface layer to the 1/4 layer of the plate thickness. For the 1/8 layer of plate thickness, {110}<001> and {110}<110> hardly exist, and their pole densities are preferably lower than 1.5, more preferably lower than 1.0. In the conventional steel sheet, this orientation exists to some extent in the surface layer, so the Young's modulus in the rolling direction cannot be improved.

In the first embodiment, it is further preferable that the pole density of {112}<110> ((112)[1-10] of the φ2=45° cross-section of the above-mentioned ODF) of the thickness 1/2 layer is 6 or more . If these orientations are developed, the <111> orientations in the width direction perpendicular to the rolling direction (hereinafter also referred to as TD direction) gather, so the Young's modulus in the TD direction increases. When the pole density is less than 6, it is difficult for the Young's modulus in the TD direction to exceed 230 GPa, so this is determined as the lower limit. The pole density is preferably 8 or more, more preferably 10 or more.

In addition, {554}<225> and {332}<113> of the 1/2 layer of plate thickness ((554)[-2-25] and (332)[-1- 13]) is expected to have some contribution to the Young's modulus in the rolling direction, so it is preferably 3 or more.

The crystallographic orientations mentioned above all allow dispersion fluctuations within -2.5° and +2.5°.

By simultaneously satisfying the requirements regarding the extreme density of the crystal orientations of the 1/8 layer and the 1/2 layer of the plate thickness described above, it is possible for the Young's modulus in both the rolling direction and the TD direction to exceed 230 GPa simultaneously.

The Young's modulus in the rolling direction of the steel sheet of the first embodiment exceeds 230 GPa. The measurement of the Young's modulus is carried out by the transverse resonance method at room temperature according to the Japanese Industrial Standard JISZ2280 High Temperature Young's Modulus Measurement Method for Metal Materials. That is, the material is not fixed, the sample is vibrated by an external vibrator in a floating state, the vibration frequency of the vibrator is slowly changed, and the primary resonance frequency of the above-mentioned sample is measured in the lateral vibration, by the following formula [3 ] Calculate Young's modulus.

E＝0.946×(1/h) ³ ×m/w×f ² [3]

In the formula, E: dynamic Young's modulus (N/m ² ), 1: length of test piece (m), h: thickness of test piece (m), m: mass (kg), w: width of test piece (m), f: primary resonance frequency (sec ^-1 ) of the transverse resonance method.

The BH amount of the steel sheet is preferably 5 MPa or more. That is, this is because the measured Young's modulus increases when movable dislocations are fixed by the coating and baking treatment. When the amount of BH is less than 5 MPa, its effect is lacking. And even if it exceeds 200MPa, no extra effect can be seen. Therefore, the range of the amount of BH is determined to be 5 to 200 MPa. The amount of BH is more preferably 30 to 100 MPa.

The so-called BH amount, the flow stress when the steel plate is stretched by 2% is σ ₂ (MPa), and the upper yield point when the steel plate is stretched by 2% and then heat-treated at 170°C for 20 minutes and stretched again is σ ₁ (MPa) , it is represented by the following formula [4].

BH＝σ ₁ -σ ₂ (MPa) [4]

Al-based plating and various plating may be applied to the above-mentioned hot-rolled steel sheet and cold-rolled steel sheet. For hot-rolled steel sheets, cold-rolled steel sheets, and steel sheets coated with various types of coatings, surface treatments such as organic coatings, inorganic coatings, and various paints can be performed according to the purpose.

Next, a method for manufacturing the steel plate of the first embodiment will be described.

In the first embodiment, there is a step of manufacturing a hot-rolled sheet by heating a slab to a temperature of 950° C. or higher, wherein the slab contains C: 0.0005 to 0.30% and Si: 2.5% by mass % Below, Mn: 2.7-5.0%, P: 0.15% or less, S: 0.015% or less, Mo: 0.15-1.5%, B: 0.0006-0.01%, Al: 0.15% or less, and the balance consists of Fe and unavoidable Impurities constitute.

The slab supplied for this hot rolling is not particularly limited. That is, the slabs produced by continuous casting slabs, thin slab casters, and the like may be used. Furthermore, a process such as continuous casting-direct rolling (CC-DR) in which hot rolling is performed immediately after casting is also suitable.

When the hot-rolled steel sheet is the final product, it is necessary to limit the production conditions as follows.

The heating temperature for hot rolling is above 950°C. This is because it is necessary to determine the finishing temperature of hot rolling described later to be equal to or higher than the Ar ₃ transformation point.

The hot rolling is performed so that the total reduction rate of each pass at 800° C. or lower is 50% or more. At this time, the friction coefficient between the roll and the steel plate exceeds 0.2. This is an essential condition for developing the shear texture of the surface layer and increasing the Young's modulus in the rolling direction.

The total reduction ratio is preferably 70% or more, more preferably 100% or more. The so-called total reduction rate is defined as R1+R2+... +Rn. Rn={slab thickness after (n-1) pass−slab thickness after n pass}/slab thickness after (n-1) pass×100%.

The finishing temperature of the hot rolling is not less than the Ar ₃ transformation point and not more than 750°C. Below the Ar ₃ transformation point, the {110}<001> texture, which is unfavorable for the Young's modulus in the rolling direction, develops. Furthermore, when the finish rolling temperature exceeds 750° C., it is difficult to develop a texture preferable for the rolling direction from the thickness surface layer to the vicinity of the 1/4 thickness layer.

The coiling temperature after rolling is not particularly limited, but the Young's modulus may increase in some cases when coiling is performed at 400 to 600°C, so it is preferable to coil within this range.

When performing hot rolling, it is preferable to perform rolling at a different peripheral speed with a different peripheral speed of the rolls of at least one pass or more being 1% or more. As a result, the formation of the texture near the surface layer is promoted, and thus the Young's modulus can be further improved compared to the case where rolling at different circumferential speeds is not performed. From this point of view, it is desirable to set the differential peripheral speed rolling to be preferably 1% or more, more preferably 5% or higher, and most preferably 10% or higher.

There is no special regulation on the upper limit of different peripheral speeds and the number of passes of different peripheral speed rolling, but there is no doubt that, from the above reasons, it can be seen that the greater the effect of improving the Young's modulus can be obtained. However, it is currently difficult to achieve a different peripheral speed of more than 50%, and the number of passes for hot finish rolling is usually about 8 passes.

Here, the differential peripheral velocity in the present invention is expressed as a percentage by dividing the difference in peripheral velocity of the upper and lower rolls by the peripheral velocity of the low-speed roll. In addition, in rolling at different circumferential speeds according to the present invention, there is no difference in the effect of improving Young's modulus regardless of which circumferential speed of the upper and lower rolls is greater.

In the rolling mill used for hot finish rolling, it is preferable to use one or more work rolls having a roll diameter of 700 mm or less. As a result, the formation of the texture near the surface layer can be promoted, and thus the Young's modulus can be further increased compared to the case where it is not used. From this point of view, the work roll diameter is determined to be 700 mm or less, preferably 600 mm or less, more preferably 500 mm or less. The lower limit of the work roll diameter is not particularly defined, but when it is 300 mm or less, it becomes difficult to control the plate passage. The upper limit of the number of passes using small-diameter rolls is not particularly specified, but as described above, the number of passes for hot finish rolling is usually about 8 passes.

It is preferable to heat-treat (anneal) the hot-rolled steel sheet produced in this way to a maximum temperature in the range of 500 to 950° C. after pickling. Accordingly, the Young's modulus in the rolling direction further increases. Although the reason for this has not been determined, it is presumed that dislocations introduced by the phase transformation after rolling are rearranged after heat treatment.

When the maximum reaching temperature is lower than 500°C, its effect is not significant. On the other hand, when it exceeds 950°C, the α→γ phase transition occurs, so as a result, the aggregation of the texture is the same or becomes weaker, and the Young's modulus also tends to deteriorate. Therefore, 500°C and 950°C were determined as the lower limit and the upper limit, respectively.

The range of the highest attained temperature is preferably 650°C to 850°C. The heat treatment method is not particularly limited, and may be performed on a usual continuous annealing line, box annealing, and continuous hot-dip galvanizing line described later.

Cold rolling and heat treatment (annealing) may be performed on the hot-rolled steel sheet. The cold rolling rate is less than 60%. This is because if the cold rolling ratio is 60% or more, the texture that increases the Young's modulus formed in the hot-rolled steel sheet will greatly change, and the Young's modulus in the rolling direction will decrease.

Heat treatment is performed after cold rolling. The maximum attainable temperature of this heat treatment is in the range of 500 to 950°C. When the temperature is lower than 500°C, the degree of improvement in Young's modulus decreases, and in some cases, processability deteriorates, so 500°C is determined as the lower limit.

On the other hand, when the heat treatment temperature exceeds 950°C, the α→γ transformation occurs, and as a result, the aggregation of the texture remains the same or becomes weaker, and the Young's modulus also tends to deteriorate. Therefore, 500°C and 950°C were determined as the lower limit and the upper limit, respectively. The preferable range of this maximum attainment temperature is 600 to 850 degreeC.

After the above-mentioned heat treatment, it is also possible to perform cooling up to 550°C, preferably up to 450°C, and heat treatment at 150 to 550°C once. This may be performed by selecting appropriate conditions for various purposes such as control of the amount of solid solution C, tempering of martensite, promotion of transformation of bainite, and other microstructure control.

According to the structure of the steel plate obtained by the method for producing a high Young's modulus steel plate of this embodiment, ferrite or bainite may be used as the main phase, and the two phases may be mixed. In the structure, martensite, austenite, Compounds based on carbides and nitrides are also acceptable. That is, it is only necessary to separately create structures according to required characteristics.

(second embodiment)

The steel sheet of the second embodiment contains C: 0.0005% to 0.30%, Si: 2.5% or less, Mn: 0.1 to 5.0%, P: 0.15% or less, S: 0.015% or less, Al: 0.15% or less in mass % , N: 0.01% or less; and one of Mo: 0.005 to 1.5%, Nb: 0.005 to 0.20%, Ti: 48/14×N (mass%) to 0.2%, and B: 0.0001 to 0.01% or Two or more kinds, the total is 0.015 to 1.91% by mass; and the balance is composed of Fe and unavoidable impurities. The pole density of {110}<223> and/or {110}<111> in the 1/8th layer of the plate thickness is 10 or more, and the Young's modulus in the rolling direction exceeds 230 GPa.

Here, the reasons for limiting the steel composition as described above will be described.

C is an element that increases the tensile strength inexpensively, and its addition amount is adjusted according to the target strength level. When C is less than 0.0005% by mass, not only steelmaking is technically difficult and the cost increases, but also the fatigue properties of the weld zone deteriorate. Therefore, the lower limit was determined to be 0.0005% by mass. On the other hand, when the C content exceeds 0.30% by mass, it causes deterioration of formability or impairs weldability, so the upper limit is determined to be 0.30% by mass.

Si has an effect of increasing strength as a solid solution strengthening element, and is also effective in obtaining a structure including martensite, bainite, residual γ, and the like. The amount added is adjusted according to the target strength level. When the added amount exceeds 2.5% by mass, the press formability deteriorates, leading to a decrease in chemical conversion treatability. Therefore, the upper limit is determined to be 2.5% by mass. In addition, when hot-dip galvanizing is performed, there are problems such as a decrease in the adhesion of the plating layer and a decrease in productivity due to a delay in the alloying reaction. Therefore, Si is preferably determined to be 1.2% by mass or less. Although the lower limit is not particularly set, it is a substantial lower limit since the production cost increases when it is determined to be 0.001% by mass or less.

Mn stabilizes the γ phase and expands the γ region to the low temperature region, so low-temperature rolling in the γ region is facilitated. Furthermore, there is also the possibility that Mn itself contributes favorably to the formation of the shear texture near the surface. From these viewpoints, the amount of Mn added is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 1.5% by mass or more. On the other hand, if it exceeds 5.0% by mass, the strength will increase too much, the ductility will decrease, and the adhesion of the galvanizing will be hindered, so 0.5% by mass is made the upper limit. Therefore, the added amount of Mn is preferably 2.9 to 4.0% by mass.

P is known to be an element that increases strength cheaply like Si, and when strength is required to be increased, it is more actively added. In addition, P also has the effect of making the hot-rolled structure finer and improving workability. However, if the added amount exceeds 0.15% by mass, the fatigue strength after spot welding deteriorates, the yield strength increases excessively, and surface shape defects occur during pressing. In addition, the alloying reaction is extremely slow during continuous hot-dip galvanizing, the productivity is lowered, and the secondary workability is also deteriorated. Therefore, the upper limit thereof is determined to be 0.15% by mass.

When S exceeds 0.015% by mass, it causes hot-rolling cracks and deteriorates workability, so the upper limit is made 0.015% by mass.

Mo, Nb, Ti, and B are important to the present invention. By adding one or more of these elements, it is possible to increase the Young's modulus in the rolling direction for the first time. Although the reason is not clear, the suppression of recrystallization during hot rolling and sharpening of the γ-phase work texture results in a change in the texture due to shear deformation of the steel sheet and the roll. As a result, a very sharp texture is formed from the surface layer of the hot-rolled sheet to the 1/4 layer of the sheet thickness, and the Young's modulus in the rolling direction increases.

The lower limits of Mo, Nb, Ti, and B content are 0.005 mass%, 0.005 mass%, 48/14×N mass%, and 0.0001 mass%, respectively; preferably 0.03 mass%, 0.01 mass%, 0.03 mass%, and 0.0003% by mass; more preferably 0.1% by mass, 0.03% by mass, 0.05% by mass, and 0.0006% by mass, respectively. This is because the above-mentioned effect of increasing Young's modulus becomes smaller than the addition of a small amount.

On the other hand, even if Mo, Nb, Ti, and B are added in excess of 1.5% by mass, 0.2% by mass, 0.2% by mass, and 0.01% by mass, respectively, the effect of improving Young's modulus is saturated and the cost increases. , therefore, 1.5 mass%, 0.2 mass%, 0.2 mass%, and 0.01 mass% are set as the upper limits of the addition amounts of Mo, Nb, Ti, and B, respectively.

Furthermore, if the total amount of addition of these elements is less than 0.015% by mass, a sufficient effect of improving Young's modulus cannot be obtained, so the lower limit of the total amount of addition is made 0.015% by mass. From this point of view, a preferable total addition amount is 0.035% by mass or more, and a more preferable total addition amount is 0.05% by mass or more. The upper limit of the total addition amount was determined as the sum of the upper limits of the respective addition amounts, that is, 1.91% by mass.

There is an interaction among Mo, Nb, Ti, and B, and the texture is enhanced by compound addition, and the Young's modulus increases. Therefore, it is more desirable to add at least two kinds or more in combination. In particular, Ti forms nitrides with N in the γ high temperature region, which can inhibit the formation of BN. Therefore, when B is added, Ti is also preferably added in an amount of 48/14×N mass % or more.

Furthermore, Mo, Nb, Ti, and B are all contained, and the respective elements are preferably added at 0.15% by mass, 0.01% by mass, 48/14×N% by mass, and 0.0006% by mass or more. In this case, the sharpening of the texture, in particular, the reduction of {110}<001> of the surface layer where the Young's modulus is lowered effectively increases the Young's modulus. Therefore, a high Young's modulus in the L direction can be achieved.

In addition, the effect of improving Young's modulus by simultaneous addition of these elements is further enhanced by the combination with C. Therefore, the amount of C is preferably determined to be 0.015% by mass or more.

The lower limits of the content of Mo, Nb, and B are 0.15% by mass, 0.01% by mass, and 0.0006% by mass, respectively. This is because the above-mentioned effect of improving Young's modulus decreases when a smaller amount is added. However, when only the Young's modulus of the surface layer is controlled, adding 0.1% by mass or more of Mo can sufficiently improve the Young's modulus, so this is set as the lower limit. On the other hand, when Mo, Nb, and B are respectively added in excess of 1.5 mass %, in excess of 0.2 mass %, and in excess of 0.01 mass %, the Young's modulus improvement effect is saturated and the cost increases, so 1.5 mass %, 0.2 mass %, respectively Mass % and 0.01 mass % are determined as these upper limits.

In addition, the effect of improving Young's modulus by simultaneous addition of these elements is further enhanced by the combination with C. Therefore, the amount of C is preferably determined to be 0.015% by mass or more.

Al can also be used as a deoxidation regulator. However, since Al significantly increases the transformation point, rolling in the low-temperature γ region becomes difficult, so the upper limit was determined to be 0.15% by mass. The lower limit of Al is not particularly limited, but it is preferably determined to be 0.01% by mass or more from the viewpoint of deoxidation.

N forms nitrides with B and reduces the recrystallization inhibitory effect of B, so it is controlled at 0.01% by mass or less. From this viewpoint, it is preferably 0.005% by mass or less, more preferably 0.002% by mass or less. The lower limit of N is not particularly set, but if it is less than 0.0005% by mass, not only is the cost incurred, but also there is little effect, so it is preferably determined to be 0.0005% by mass or more.

The amount of solid solution C is preferably determined to be 0.0005 to 0.004% by mass%. When a steel plate with solid solution C is processed into a member, strain aging occurs even at normal temperature, and the Young's modulus increases. For example, in the case of automotive applications, not only the yield strength of the steel sheet is improved but also the Young's modulus is increased by performing coating and baking after processing. The amount of solid solution C can also be obtained by subtracting the difference between the amount of C existing as a compound of Fe, Al, Nb, Ti, B, etc. (quantified by chemical analysis of the extraction residue) from the total amount of C. Furthermore, it can also be obtained by an internal friction method and FIM (Field Ion Microscopy: Field Ion Microscopy).

When the amount of solid-solution C is less than 0.0005% by mass, sufficient effect cannot be obtained, and even if it exceeds 0.004% by mass, the BH property tends to be saturated, so the upper limit was made 0.004% by mass.

In addition to the above composition, the steel sheet of the second embodiment preferably contains Ca: 0.0005 to 0.01% by mass in mass%.

Ca is useful as a deoxidizing element and is also effective in controlling the morphology of sulfides, so Ca may be added in the range of 0.0005 to 0.01% by mass. When it is less than 0.0005% by mass, the effect is insufficient, and when it is added in excess of 0.01% by mass, the workability deteriorates, so this range was determined.

One or two or more of Sn, Co, Zn, W, Zr, V, Mg, and REM may be contained in mass %, in a total of 0.001 to 1.0 mass %. In particular, W and V have an effect of suppressing the recrystallization of the γ region, so it is preferable to add 0.01% by mass or more of each. However, since Zr forms ZrN, solid solution N decreases, so it is preferable to make it 0.01 mass % or less.

In addition, one or two or more of Ni, Cu, and Cr may be contained in mass %, and the total is 0.001 to 4.0 mass %.

When the total amount of Ni, Cu, and Cr added is less than 0.001% by mass, no significant effect can be obtained, and when added in excess of 4.0% by mass, the workability deteriorates.

Next, the texture, Young's modulus, and BH amount of the steel sheet will be described.

Regarding the texture of the steel sheet according to the second embodiment, the pole density of {110}<223> and/or {110}<111> is 10 or more in a plate thickness/8 layer. Thereby, it is possible to increase the Young's modulus in the rolling direction. When the above-mentioned extreme density is less than 10, it is difficult for the Young's modulus in the rolling direction to exceed 230 GPa. The above-mentioned pole density is preferably 14 or more, and more preferably 20 or more.

The pole densities (random intensity ratios of X-rays) of these orientations are calculated based on the series expansion method based on the pole figures of {110}, {100}, {211}, and {310} measured by X-ray diffraction The 3-dimensional texture (ODF) can be calculated. That is, in order to obtain the pole density of each crystal orientation, the strength of (110)[2-23](110)[1-11] in the φ2=45° section of the three-dimensional texture is used as a representative.

The method described in the first embodiment can be applied to the measurement of the pole density.

The limit of the above extreme density is satisfied at least for the 1/8 layer of the board thickness, and actually not only the 1/8 layer, but preferably holds in a wide range from the surface layer to the 1/4 layer of the board thickness.

In the second embodiment, it is further preferable that the pole density of {110}<001> ((110)[001] in the φ2=45° cross-section of the above-mentioned ODF) orientation of the 1/8 layer of plate thickness is 3 or less. This orientation significantly reduces the Young's modulus in the rolling direction. Therefore, when the orientation exceeds 3, it is difficult for the Young's modulus in the rolling direction to exceed 230 GPa. Taking this into consideration, it is preferably 3 or less, more preferably less than 3 1.5.

The pole density of {211}<011> ((112)[1-10] of the φ2=45° cross-section of the above-mentioned ODF) of the 1/2 layer of the plate thickness is preferably 6 or more. If this orientation is developed, the <111> orientation in the width direction (TD direction) perpendicular to the rolling direction (RD direction) gathers, so the Young's modulus in the TD direction increases. When the pole density is less than 6, it is difficult for the Young's modulus in the TD direction to exceed 230 GPa, so this is determined as the lower limit. The pole density has a preferable range of 8 or more, and a more preferable range of 10 or more.

The pole density of {332}<113> and {332}<113> ((332)[-1-13] of the above-mentioned ODF φ2 = 45° section) of the 1/2 layer of the plate thickness has a significant effect on the poplar in the rolling direction The modulus is expected to have some contribution, so the pole density of {332}<113> of the 1/2 layer of the plate thickness is preferably 6 or more, more preferably 8 or more, and more preferably 10 or more.

In addition, the pole density of {100}<011> ((001)[1-10] in the φ2=45° section of the above-mentioned ODF) of the 1/2 layer of the plate thickness significantly reduces the Young's modulus in the 45° direction, Therefore, the pole density is preferably determined to be 6 or less. The pole density in this orientation is more preferably 3 or less, and most preferably 1.5 or less.

The crystallographic orientations mentioned above all allow dispersion fluctuations within the range of -2.5° and +2.5°.

The characteristics of the texture of the steel plate cannot be expressed only by the usual inverse pole diagram and positive pole diagram. For example, when the inverse pole diagram showing the crystal orientation in the normal direction of the steel plate surface is measured in the vicinity of 1/8 of the plate thickness It is preferable that the surface intensity ratio (X-ray random intensity ratio) in each direction is <110>: 5 or more and <112>: 2 or more. Moreover, it is preferable that it is <112>: 4 or more, <332>: 4 or more, and <100>: 3 or less about 1/2 layer.

Regarding the Young's modulus of the steel sheet, by satisfying the above-mentioned requirements for the extreme density of the crystal orientation of the 1/8 layer and the 1/2 layer of the plate thickness at the same time, not only the rolling direction (RD direction), but also the direction perpendicular to the rolling direction It is possible for the Young's modulus in one direction, that is, the width direction (TD direction) to exceed 230 GPa at the same time. For the measurement of Young's modulus, the method described in the first embodiment is applied.

The lower limit of the Young's modulus in the rolling direction from the surface layer to the 1/8th layer of the plate thickness is preferably 240 GPa or more. Thereby, a sufficient effect of improving shape freezing property can be obtained. The lower limit of the Young's modulus in the rolling direction from the surface layer to the 1/8 layer is more preferably 245 GPa, most preferably 250 GPa. The upper limit is not particularly limited, but in order to exceed 300 GPa, it is necessary to add a large amount of other alloy elements, and other properties such as processing deteriorate, so it is substantially 300 GPa or less. Even if the Young's modulus of the surface layer exceeds 240 GPa, the effect of sufficiently improving the shape freezing property cannot be exhibited when the layer thickness is less than 1/8. Needless to say, the thicker the thickness of the layer having a high Young's modulus, the higher the bending rigidity can be obtained.

In addition, the measurement of the Young's modulus of the surface layer was carried out by cutting out a test piece at a thickness of 1/8 or more from the surface layer, and performing it by the above-mentioned transverse vibration method.

The Young's modulus of the surface layer in the width direction of the plate is not particularly specified, and it is obvious that the higher the Young's modulus of the surface layer in the width direction of the plate, the higher the bending rigidity in the width direction. Contains all of the above-mentioned Mo, Nb, Ti, and B, and their contents are Mo: 0.15 to 1.5%, Nb: 0.01 to 0.20%, Ti: 48/14×N (mass%) to 0.2%, and B: 0.0006 to Composition of 0.01%, and the pole density of {110}<223> and/or {110}<111> made into 1/8 layer of plate thickness is 10 or more, and 1/8 layer of {110}<001 > In the case where the pole density is 3 or less, the Young's modulus of the surface layer in the width direction exceeds 240 GPa as in the rolling direction.

The BH amount of the steel sheet is preferably 5 MPa or more. That is, it is because the Young's modulus in the rolling direction (RD direction) increases when movable dislocations are fixed by the coating and baking treatment. When the amount of BH is less than 5 MPa, the effect is insufficient, and even if it exceeds 200 MPa, no extraordinary effect is observed. Therefore, the amount of BH is determined to be 5 to 200 MPa. The more preferable range of this BH amount is 30-100 MPa.

The amount of BH is represented by the formula [4] described in the first embodiment.

Next, a method for manufacturing the steel plate of the second embodiment will be described.

In the second embodiment, there is a step of heating a slab to a temperature of 1000° C. or higher and performing hot rolling to produce a hot-rolled sheet, wherein the slab contains C: 0.0005 to 0.30% and Si: 2.5% or less in mass % , Mn: 0.1-5.0%, P: 0.15% or less, S: 0.015% or less, Mo: 0.15-1.5%, B: 0.0006-0.01%, Al: 0.15% or less, Nb: 0.01-0.20%, N: 0.01 % or less, Ti: 48/14×N (mass %) to 0.2%, and the balance is composed of Fe and unavoidable impurities.

The slab supplied for this hot rolling is not particularly limited. That is, the slabs produced by continuous casting slabs, thin slab casters, and the like may be used. Furthermore, a process such as continuous casting-direct rolling (CC-DR) in which hot rolling is performed immediately after casting is also suitable.

In this hot rolling step, the hot rolling heating temperature is 1000° C. or higher. The hot-rolling heating temperature is 1000° C. or higher because it is necessary to set the hot-rolling finish temperature described later to be equal to or higher than the Ar ₃ transformation point.

Hot rolling is carried out under the conditions that the coefficient of friction between the roll and the steel plate exceeds 0.2, the effective variable ε ^* calculated by the following formula [5] is 0.4 or more, and the total reduction rate is 50% or more. The above conditions are for use The shear texture of the surface layer is developed and the Young's modulus in the rolling direction is increased.

${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; -</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; j</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; ]</span>$

In the formula, n is the number of stands in the finishing hot rolling mill, ε _j is the strain applied to the jth stand, ε _n is the strain applied to the nth stand, and t _i is the i-th stand to the i+1th stand The running time (seconds) between and τ _i can be calculated by the following formula (6) by means of the gas constant R (=1.987) and the rolling temperature T _i (K) of the i-th stand.

τ _i =8.46×10 _-9 ×exp{43800/R/T _i } [6]

The total reduction rate RT of the above-mentioned reduction rate, in the case of n-pass rolling, assuming that the reduction rates of the first pass to n pass are respectively R1 (%) to Rn (%), it can be obtained by the following formula [7] calculate.

RT＝R1+R2+...+Rn [7]

In the formula, Rn={slab thickness after (n-1) pass-slab thickness after n pass}/slab thickness after (n-1) pass×100%.

The above-mentioned effective variable ε ^* is 0.4 or more, preferably 0.5 or more, and more preferably 0.6 or more. The total reduction ratio is 50% or more, preferably 70% or more, and more preferably 100% or more.

The finishing temperature of this hot rolling is not less than the Ar ₃ transformation point and not more than 900°C.

When the finish rolling temperature is lower than the Ar ₃ transformation point, the {110}<001> texture, which is unfavorable for the Young's modulus in the rolling direction, develops. Furthermore, when the finish rolling temperature exceeds 900° C., it is difficult to develop a shear texture preferred in the rolling direction from the thickness surface layer to the vicinity of the 1/4 thickness layer. From this point of view, the finishing temperature of hot rolling is preferably 850°C or lower, more preferably 800°C or lower.

The coiling temperature after rolling is not particularly limited, but the Young's modulus may increase in some cases when coiling is performed at 400 to 600°C, so it is preferable to coil within this range.

When performing hot rolling, it is preferable to perform rolling at a different peripheral speed with a different peripheral speed of the rolls of at least one pass or more being 1% or more. As a result, the formation of the texture near the surface layer is promoted, and thus the Young's modulus can be further improved compared to the case where rolling at different circumferential speeds is not performed. From this point of view, it is desirable to set the differential peripheral speed rolling to be preferably 1% or higher, more preferably 5 or higher, and most preferably 10% or higher.

There is no special regulation on the upper limit of different peripheral speeds and the number of passes of different peripheral speed rolling, but there is no doubt that, from the above reasons, it can be seen that the greater the effect of improving the Young's modulus can be obtained. However, it is currently difficult to achieve a different peripheral speed of more than 50%, and the number of passes for hot finish rolling is usually about 8 passes.

Here, the differential peripheral velocity in the present invention is expressed as a percentage by dividing the difference in peripheral velocity of the upper and lower rolls by the peripheral velocity of the low-speed roll. In rolling at different circumferential speeds in the present invention, no matter which one of the circumferential speeds of the upper and lower rolls is greater, there is no difference in the effect of improving the Young's modulus.

In addition, it is preferable to use one or more work rolls having a roll diameter of 700 mm or less in the rolling mill used for the hot finish rolling. Thereby, the formation of the texture near the surface layer can be promoted, and thus the Young's modulus can be increased compared to the case where it is not used. From this point of view, the work roll diameter is determined to be 700 mm or less, preferably 600 mm or less, more preferably 500 mm or less. The lower limit of the work roll diameter is not particularly defined, but when it is 300 mm or less, it becomes difficult to control the plate passage. The upper limit of the number of passes using small-diameter rolls is not particularly specified, but as described above, the number of passes for hot finish rolling is usually about 8 passes.

It is preferable to heat-treat (anneal) the hot-rolled steel sheet produced in this way to a maximum temperature in the range of 500 to 950° C. after pickling. Accordingly, the Young's modulus in the rolling direction further increases. Although the reason for this has not been determined, it is presumed that dislocations introduced by the phase transformation after rolling are rearranged after heat treatment.

When the maximum reaching temperature is lower than 500°C, the effect is not significant. On the other hand, when the temperature exceeds 950°C, the α→γ phase transformation occurs, so as a result, the aggregation of the texture is the same or becomes weaker, and the Young's modulus also decreases. tendency to deteriorate. Therefore, 500°C and 950°C were determined as the lower limit and the upper limit, respectively.

The range of the highest attained temperature is preferably 650°C to 850°C.

The heat treatment method is not particularly limited, and may be performed on a usual continuous annealing line, box annealing, continuous hot-dip galvanizing line described later, or the like.

Cold rolling and heat treatment (annealing) may be performed after pickling the hot-rolled steel sheet. The cold rolling rate is less than 60%. This is because if the cold rolling ratio is 60% or more, the texture that increases the Young's modulus formed on the hot-rolled steel sheet will greatly change, and the Young's modulus in the rolling direction will decrease.

Heat treatment is carried out after cold rolling. The maximum attainable temperature of this heat treatment is in the range of 500 to 950°C. When the temperature is lower than 500°C, the degree of improvement in Young's modulus decreases, and in some cases, processability deteriorates, so 500°C is determined as the lower limit. On the other hand, when the heat treatment temperature exceeds 950°C, the α→γ transformation occurs, and as a result, the aggregation of the texture remains the same or becomes weaker, and the Young's modulus also tends to deteriorate. Therefore, 500°C and 950°C were determined as the lower limit and the upper limit, respectively.

The preferable range of this maximum attainment temperature is 600 to 850 degreeC.

The heating rate to reach the highest heating temperature is not particularly limited, but is preferably set within a range of 3 to 70°C/sec. When the heating rate is lower than 3°C/sec, recrystallization proceeds during heating, and the texture favorable to Young's modulus collapses. There is no particular change in material properties above 70° C./sec, so it is preferable to determine this value as the upper limit.

After the above heat treatment, it is also possible to perform cooling up to 550°C, preferably up to 450°C, and heat treatment at 150 to 550°C once. This may be performed by selecting appropriate conditions for various purposes such as control of the amount of solid solution C, tempering of martensite, promotion of transformation of bainite, and other microstructure control.

According to the structure of the steel plate obtained by the method for producing a high Young's modulus steel plate of this embodiment, ferrite or bainite may be used as the main phase, and the two phases may be mixed. In the structure, martensite, austenite, Compounds based on carbides and nitrides are also acceptable. That is, it is only necessary to separately create structures according to required characteristics.

(third embodiment)

In the third embodiment, a hot-dip galvanized steel sheet having a high Young's modulus, an alloyed hot-dip galvanized steel sheet, a high Young's modulus steel pipe, and a method for producing the same in the first and second embodiments described above An example of is described.

The hot-dip galvanized steel sheet includes the high Young's modulus steel sheet of the first and second embodiments, and the hot-dip galvanizing performed on the high Young's modulus steel sheet. The hot-dip galvanized steel sheet is produced by hot-dip galvanizing the annealed hot-rolled steel sheet or the cold-rolled cold-rolled steel sheet obtained in the first and second embodiments described above.

The composition of the galvanized layer is not particularly limited, and in addition to zinc, Fe, Al, Mn, Cr, Mg, Pb, Sn, Ni, etc. may be added as needed.

Heat treatment and galvanizing on a continuous hot-dip galvanizing line after cold rolling are also acceptable.

The galvannealed steel sheet includes the high Young's modulus steel sheet of the first and second embodiments, and the galvannealed steel sheet performed on the high Young's modulus steel sheet. The alloyed galvanized steel sheet is produced by alloying the above-mentioned hot-dip galvanized steel sheet.

This alloying treatment is performed by performing heat treatment in the range of 450 to 600°C. When the temperature is lower than 450°C, the alloying does not proceed sufficiently, and when the temperature exceeds 600°C, the alloying progresses excessively, and the plating becomes brittle. Therefore, problems such as peeling of the plating layer and the like arise due to processing such as pressing. The alloying treatment time is determined to be 10 seconds or more. At less than 10 seconds, alloying does not proceed sufficiently. When producing a galvannealed steel sheet, pickling may be carried out after hot rolling if necessary, and temper rolling at a reduction ratio of 10% or less may be performed on-line or off-line.

The high Young's modulus steel pipe is the steel plate having the high Young's modulus of the first and second embodiments, and is a steel pipe in which the high Young's modulus steel plate is wound in an arbitrary direction. For example, the high Young's modulus steel pipe is formed by winding the high Young's modulus steel sheet according to the first and second embodiments so that the angle between the rolling direction and the longitudinal direction of the steel pipe is within 0° to 30°. be manufactured. Accordingly, it is possible to manufacture a high Young's modulus steel pipe having a high Young's modulus in the longitudinal direction of the steel pipe.

Since the Young's modulus becomes the highest by winding parallel to the rolling direction, it is preferable that this angle be as small as possible. From this point of view, it is more preferable to wind at an angle of 15° or less. As long as the relationship between the rolling direction and the length direction of the steel pipe is satisfied, any method such as UO welded pipe, roll butt welded pipe, spiral welded pipe, etc. can be used for the pipe making method. Of course, the direction in which the Young's modulus is high is not necessarily limited to the direction parallel to the longitudinal direction of the steel pipe, and there is no problem in producing a steel pipe with a high Young's modulus in any direction depending on the application.

The above-mentioned high Young's modulus steel pipe may be subjected to Al-based plating and various platings. For hot-dip galvanized steel sheets, alloyed hot-dip galvanized steel sheets, and high Young's modulus steel pipes, surface treatments such as organic coatings, inorganic coatings, and various coatings can be performed according to the purpose.

Example

Next, the present invention will be described based on examples.

Examples related to the first and third embodiments are shown below.

(Example 1)

Steels having the compositions shown in Tables 1 and 2 were melted, and hot rolled under the conditions shown in Tables 3 and 4. All the heating temperatures at this time were 1250°C. In the finishing stand consisting of seven stages in total, the friction coefficient between the rolls and the steel plate was determined to be in the range of 0.21 to 0.24 in the last three stages, and the total reduction ratio of the last three stages was 70%. The temper rolling reduction rate is 0.3%.

The Young's modulus was measured by the above-mentioned transverse resonance method. Take a JIS No. 5 tensile test piece to evaluate the tensile properties in the TD direction. In addition, the texture of the 1/8 layer of the plate thickness was measured.

The results are shown in Table 3 and Table 4, from which it is known that when the steel having the chemical composition of the present invention is hot-rolled under appropriate conditions, the Young's modulus in the rolling direction can exceed 230 GPa.

Here, in the tables of the examples, FT represents the temperature at the exit side of the final finish rolling of hot rolling, CT represents the coiling temperature, TS represents the tensile strength, YS represents the yield strength, E1 represents the elongation, and E(RD) represents the RD direction The Young's modulus, E(D) indicates the Young's modulus in the direction 45° to the RD direction, and E(TD) indicates the Young's modulus in the TD direction. These notations are common to the following descriptions.

Table 1

Steel No. C Si Mn P S Al N A 0.0040 0.01 3.01 0.010 0.0019 0.031 0.0024 B 0.0044 0.01 2.44 0.011 0.0022 0.028 0.0026 C 0.0036 0.01 1.95 0.008 0.0019 0.033 0.0031 D. 0.0047 0.01 4.34 0.007 0.0025 0.029 0.0029 E. 0.050 0.02 3.26 0.005 0.0034 0.022 0.0033 f 0.051 0.02 3.33 0.005 0.0037 0.027 0.0032 G 0.050 0.01 2.27 0.006 0.0034 0.030 0.0030 h 0.055 0.55 3.58 0.007 0.0016 0.024 0.0025 I 0.103 0.09 3.04 0.011 0.0020 0.035 0.0027 J 0.112 0.84 3.00 0.010 0.0020 1.660 0.0034 K 0.100 0.08 3.04 0.009 0.0018 0.032 0.0028 L 0.010 0.22 3.63 0.005 0.0027 0.037 0.0026 m 0.009 0.04 3.50 0.009 0.0031 0.031 0.0034 N 0.011 0.01 0.52 0.022 0.0053 0.033 0.0019

Table 2

Steel No. Mo B Ti Nb other Ar ₃ (°C) Remark A 0.28 0.0025 - - - 630 Invention steel B 0.25 0.0016 0.011 0.008 - 690 compare steel C 0.17 0.0033 0.022 - - 712 compare steel D. 0.29 0.0022 0.009 0.013 - 526 Invention steel E. 0.52 0.0020 0.030 0.040 - 582 Invention steel f - - 0.029 0.038 - 649 compare steel G 0.53 0.0024 0.025 0.041 - 656 compare steel h 0.36 0.0037 0.014 0.022 Cr＝0.40 560 Invention steel I 0.40 0.0019 0.018 0.019 - 599 Invention steel J 0.39 0.0020 0.020 0.019 - 949 compare steel K 0.41 - 0.021 0.044 V＝0.010 627 compare steel L 0.33 0.0041 - 0.028 - 558 Invention steel m 0.42 0.0030 - - Cu＝0.42 571 Invention steel N - - - - - 887 compare steel

table 3

Sample No. Steel No. FT(°C) CT(°C) TS(MPa) YS(MPa) EI(%) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) {110}<223> {110}<111> Remark 1 A 840 500 525 377 29 216 195 228 5 3 comparative example 2 770 500 568 424 26 225 196 229 9 5 comparative example 3 700 500 607 459 twenty three 234 192 231 13 10 Example of the invention 4 B 880 400 491 354 30 220 202 226 5 4 comparative example 5 700 400 563 495 13 209 190 229 8 5 comparative example 6 580 400 722 683 7 198 195 218 2 3 comparative example 7 C 900 550 476 321 32 219 208 222 4 3 comparative example 8 800 550 495 338 30 223 201 225 6 4 comparative example 9 700 550 544 504 11 190 220 225 4 2 comparative example 10 D. 800 650 550 412 26 223 197 240 8 5 comparative example 11 740 600 572 429 25 242 194 236 16 15 Example of the invention 12 680 500 609 460 twenty one 242 189 243 twenty three 19 Example of the invention 13 E. 730 580 988 746 12 236 192 240 19 14 Example of the invention 14 700 550 1003 728 11 242 195 240 twenty two 16 Example of the invention 15 550 400 1110 650 13 208 203 237 6 6 comparative example 16 f 790 600 925 688 12 215 204 230 4 3 comparative example 17 710 550 977 651 13 224 199 232 6 4 comparative example 18 600 400 1046 622 14 195 193 229 4 3 comparative example 19 G 850 550 910 763 14 221 211 228 5 3 comparative example 20 760 550 934 779 13 217 212 224 4 3 comparative example twenty one 720 550 951 807 13 220 204 222 4 3 comparative example twenty two h 800 650 1243 1089 9 228 196 241 8 6 comparative example twenty three 690 550 1286 1101 8 248 191 243 26 twenty two Example of the invention twenty four 650 500 1355 1162 7 251 186 245 30 twenty three Example of the invention

Table 4

Sample No. Steel No. FT(°C) CT(°C) TS(MPa) YS(MPa) EI(%) E(RD)(GPa) E(D)(GPa) E{TD}(GPa) {110}<223> {110}<111> Remark 25 I 850 500 1093 879 12 227 203 229 8 7 comparative example 26 700 500 1152 926 11 242 194 239 20 15 Example of the invention 27 650 500 1189 947 11 244 192 240 twenty two 14 Example of the invention 28 J 950 700 774 478 19 218 213 223 4 3 comparative example 29 800 650 881 595 17 197 195 231 3 2 comparative example 30 700 550 1198 720 9 199 189 225 3 2 comparative example 31 K 850 550 1042 823 13 220 205 220 7 5 comparative example 32 700 550 1090 901 12 226 199 235 7 6 comparative example 33 650 550 1177 923 11 228 203 235 9 6 comparative example 34 L 740 600 754 627 17 239 197 236 16 11 Example of the invention 35 700 550 772 652 16 243 192 241 twenty one 18 Example of the invention 36 650 500 806 679 15 250 182 239 29 19 Example of the invention 37 m 780 630 721 597 19 228 210 233 8 4 comparative example 38 700 550 756 635 17 238 199 234 17 14 Example of the invention 39 650 500 779 658 16 244 192 246 twenty four twenty two Example of the invention 40 N 910 700 334 188 48 215 211 224 4 4 comparative example 41 800 650 329 165 50 218 207 225 3 3 comparative example 42 700 550 378 276 41 207 198 238 4 3 comparative example

(Example 2)

For steels E and L in the hot-rolled steel sheet of Example 1, implement continuous annealing (holding at 700°C for 90 seconds), box annealing (holding at 700°C for 6 hours), and continuous hot-dip galvanizing (the highest reaching temperature is 750°C). °C, alloying treatment at 500 °C for 20 seconds after immersion in a zinc plating bath), and the tensile properties and Young's modulus were measured.

The results are shown in Table 5. It is clear from the table that the Young's modulus increases by hot-rolling the steel having the chemical composition of the present invention under appropriate conditions and performing appropriate heat treatment.

(Example 3)

For steels E and L in the hot-rolled steel sheet of Example 1, after 30% reduction ratio cold rolling, implement continuous hot-dip galvanizing (make various changes in the maximum reaching temperature, dip in the galvanizing bath at 500 °C for 20 seconds of alloying treatment), and the tensile properties and Young's modulus were measured.

The results are shown in Table 6. It is clear from the table that by hot-rolling and cold-rolling the steel having the chemical composition of the present invention under appropriate conditions, and then through appropriate heat treatment, a cold-rolled steel sheet with excellent Young's modulus in the RD direction and the TD direction can be obtained . However, when the maximum attained temperature is remarkably high, the Young's modulus also slightly decreases.

table 5

Sample No. Steel No. FT(°C) CT(°C) Treatment after hot rolling TS(MPa) YS(MPa) EI(%) BH(MPa) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) {110}<223> {110}<111> Remark 43 E. 700 550 none 1003 728 11 68 242 195 240 twenty two 16 Example of the invention 44 E. 700 550 continuous annealing 980 751 11 95 245 196 242 20 17 Example of the invention 45 E. 700 550 Box annealing 943 777 12 56 250 197 242 16 11 Example of the invention 46 E. 700 550 Continuous alloying hot dip galvanizing 966 722 12 74 244 196 243 19 15 Example of the invention 47 L 700 550 none 772 652 16 60 243 192 241 twenty one 18 Example of the invention 48 L 700 550 continuous annealing 745 614 18 89 248 193 243 19 16 Example of the invention 49 L 700 550 Box annealing 712 633 20 47 252 195 246 17 12 Example of the invention 50 L 700 550 Continuous alloying hot dip galvanizing 739 620 19 66 249 195 242 18 15 Example of the invention

Table 6

Sample No. Steel No. FT(°C) CT(°C) Cold rolling rate (%) Maximum temperature (℃) TS(MPa) YS(MPa) EI(%) BH(Mpa) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) {110}<223> {110}<111> Remark 51 E 700 550 30 960 1058 784 10 53 231 194 233 11 8 Example of the invention 52 E 700 550 30 800 1181 695 13 94 237 198 235 14 10 Example of the invention 53 E 700 550 30 700 964 665 13 69 239 197 237 19 15 Example of the invention 54 L 700 550 30 970 810 679 15 57 231 199 232 11 7 Example of the invention 55 L 700 550 30 800 774 519 18 71 238 195 240 15 9 Example of the invention 56 L 700 550 30 700 711 536 18 65 240 194 239 16 11 Example of the invention

(Example 4)

Steels E and L among the hot-rolled steel sheets of Example 1 were subjected to the following treatments.

In the continuous hot-dip galvanizing line, the steel plate is heated to 650°C, cooled to about 470°C and dipped in a molten zinc bath at 460°C. The thickness of the zinc coating is 40 g/m ² on average on one side in terms of weight per unit area. After hot-dip galvanizing, (1) organic coating and (2) painting were performed on the surface of the steel sheet as follows, and tensile properties and Young's modulus were measured.

The results are shown in Table 7. It is clear from the table that the hot-dip galvanized steel sheet has a good Young's modulus after adding an organic film and paint to the surface.

(1) Organic film

When the solid content of the resin is 27.6% by mass, the viscosity of the dispersion is 1400mPa·s (25°C), the pH is 8.8, the content of the ammonium salt (-COONH ₄ ) of the carboxyl group is 9.5% by mass of the solid content of the entire resin, and the content of the carboxyl group is 4% by mass of corrosion inhibitor and 12% of colloidal silica were added to an aqueous resin having a solid content of 2.5% by mass of the entire resin and an average diameter of dispersed particles of about 0.030 μm to prepare a rust-preventive treatment liquid. This anti-rust treatment solution was applied to the above-mentioned steel plate by a roll coater, and dried so that the temperature reached on the surface of the steel plate was 120° C. to form a film with a thickness of about 1 μm.

(2) Coating

On the above degreased steel sheet, "ZM1300AN" manufactured by Nippon Pa-Calaging Co., Ltd. was applied as a chemical conversion treatment by a roll coater. Then, it was made to perform hot-air drying on the condition that the reaching temperature was 60 degreeC. The deposition amount of the chemical conversion treatment was 50 mg/m ² in terms of the deposition amount of Cr. Then, a primer was applied to one side of the steel sheet subjected to the chemical conversion treatment, and a backside coating was applied to the other side by a roll coater. Then it is dried and hardened in an induction heating furnace with hot air. The reaching temperature at this time was 210°C.

On the surface coated with the primer, a top coat is applied with a curtain coater, and then dried and hardened at a temperature of 230°C in an induction heating furnace with hot air. In addition, as a primer, "FL640EU primer" manufactured by Nippon Finco-Tingus Co., Ltd. was used, and the dry film thickness was applied so as to be 5 μm. As the back paint, "FL100HQ" manufactured by Nippon Finco-Tingus Co., Ltd. was used, and the dry film thickness was applied so as to be 5 μm. As a top coat, "FL100HQ" manufactured by Nippon Finco-Tingus Co., Ltd. was used, and it was applied so that the dry film thickness may be 15 micrometers.

Table 7

Sample No. Steel No. FT(°C) CT(°C) surface treatment TS(MPa) YS(MPa) EI(%) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) {110}<223> {110}<111> Remark 57 E. 700 550 hot-dip galvanized only 1010 775 11 237 194 239 18 15 Example of the invention 58 E. 700 550 Organic film 1016 763 11 240 196 240 19 14 Example of the invention 59 E. 700 550 painting 1042 822 10 245 200 243 18 15 Example of the invention 60 L 700 550 hot-dip galvanized only 781 654 15 238 192 238 16 12 Example of the invention 61 L 700 550 Organic film 789 679 14 239 194 240 16 11 Example of the invention 62 L 700 550 painting 838 707 13 247 203 246 17 12 Example of the invention

(Example 5)

Using steels E and L shown in Table 1, different peripheral speed rolling was performed. Table 8 shows the hot rolling conditions, tensile properties, and Young's modulus measurement results of changing the peripheral speed in the last three stages of the finishing stand consisting of seven stages in total. All hot rolling conditions not shown in Table 8 were the same as in Example 1.

It is clear from the table that when the steel having the chemical composition of the present invention is hot-rolled under suitable conditions, the texture near the surface can be promoted if the rolling is carried out at a different peripheral speed of 1% or more in one pass or more. The formation of Young's modulus further increased.

(Example 6)

Using steels E and L shown in Table 1, thin roll rolling was performed. Table 9 shows the hot rolling conditions, tensile properties, and Young's modulus measurement results of changing the roll diameter in the last three stages of the finishing stand consisting of seven stages in total. All hot rolling conditions not shown in Table 9 were the same as in Example 1.

It is clear from the table that when the steel having the chemical composition of the present invention is hot-rolled under suitable conditions, the texture near the surface layer can be promoted if rolling is carried out for more than one pass using rolls with a roll diameter of 700 mm or less. The formation of Young's modulus further increased.

Table 8

Sample No. Steel No. FT(°C) CT(°C) Different peripheral speed (%) TS(MPa) YS(MPa) EI(%) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) {110}<223> {110}<111> Remark 5 passes 6 passes 7 passes 63 E 700 550 0 0 0 1003 728 11 242 195 240 twenty two 16 Example of the invention 64 E 700 550 0 0 3 1005 733 11 245 193 240 twenty four 18 Example of the invention 65 E 700 550 1 2 3 1011 729 10 247 188 242 25 19 Example of the invention 66 E 700 550 10 5 5 1009 731 12 253 186 246 31 25 Example of the invention 67 L 700 550 0 0 0 772 652 16 243 192 241 twenty one 18 Example of the invention 68 L 700 550 3 3 3 773 655 15 245 189 242 twenty four 18 Example of the invention 69 L 700 550 0 0 10 775 650 15 249 190 244 26 19 Example of the invention 70 L 700 550 0 20 20 772 653 15 256 186 248 31 26 Example of the invention

Table 9

Sample No. Steel No. FT(°C) CT(°C) Roll diameter (mm) TS(MPa) YS(MPa) EI(%) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) {110}<223> {110}<111> Remark 5 passes 6 passes 7 passes 71 E 700 550 800 800 800 1003 728 11 242 195 240 twenty two 16 Example of the invention 72 E 700 550 800 800 600 1011 736 10 246 190 242 twenty four 19 Example of the invention 73 E 700 550 600 600 600 1009 725 11 251 187 244 28 twenty one Example of the invention 74 E 700 550 500 500 500 998 733 10 255 186 243 33 twenty four Example of the invention 75 L 700 550 800 800 800 772 652 16 243 192 241 twenty one 19 Example of the invention 76 L 700 550 800 800 600 783 658 14 247 189 243 25 17 Example of the invention 77 L 700 550 600 600 600 779 655 15 250 188 242 27 20 Example of the invention 78 L 700 550 500 500 500 768 649 16 253 186 245 30 25 Example of the invention

(Example 7)

Next, examples of the second and third embodiments are shown below.

Steels having the compositions shown in Tables 10-13 were melted, and hot-rolled under the conditions shown in Tables 14-19. All the heating temperatures at this time were determined to be 1230°C. In the finishing stand composed of 7 stages in total, the friction coefficient between the roll and the steel plate was determined to be in the range of 0.21 to 0.24 in the last 3 stages, and the total reduction ratio of the last 3 stages was 55%. All temper rolling reductions were 0.3%.

The Young's modulus was measured by the above-mentioned transverse resonance method. Take a JIS No. 5 tensile test piece to evaluate the tensile properties in the TD direction. Furthermore, the textures of the 1/8th layer of the plate thickness and the 7/16th layer of the plate thickness were measured.

The results are shown in Tables 14-19. In addition, Table 15 is a continuation of Table 14, Table 17 is a continuation of Table 16, and Table 19 is a continuation of Table 18. In the table and its continuation table, the values described in the same row represent the numerical values for the same sample. This is also common in the specification and in the tables that follow. Underlined values in the tables represent values outside the range of the present invention. This flag is also common in the description of the tables below.

It is clear from Tables 14 to 19 that the Young's modulus in the rolling direction can exceed 230 GPa when the steel having the chemical composition of the present invention is hot-rolled under appropriate conditions.

Table 10

Steel No. C Si Mn P S Al N Mo B A 0.0010 0.01 1.82 0.010 0.0023 0.036 0.0025 0.200 0.0010 B 0.0036 0.01 0.07 0.011 0.0019 0.042 0.0031 0.150 0.0008 C 0.038 0.01 2.98 0.007 0.0022 0.038 0.0042 0.300 0.0012 D 0.025 2.90 1.23 0.006 0.0035 0.035 0.0045 0.180 0.0001 E 0.050 0.02 0.52 0.007 0.0042 0.028 0.0036 0.250 0.0023 F 0.120 0.02 1.29 0.005 0.0023 1.050 0.0038 0.420 0.0016 G 0.055 0.01 2.30 0.006 0.0011 0.039 0.0038 0.010 0.0020 h 0.061 0.43 0.05 0.007 0.0016 0.045 0.0030 0.000 0.0002 I 0.011 0.42 0.51 0.012 0.0023 0.026 0.0045 0.004 0.0016 J 0.087 0.77 1.13 0.001 0.0025 0.035 0.0035 0.000 0.0000 K 0.102 0.03 2.35 0.021 0.0011 0.036 0.0036 0.320 0.0031 L 0.092 0.03 3.26 0.008 0.0016 0.036 0.0033 0.530 0.0018 m 0.053 0.22 2.05 0.009 0.0037 0.042 0.0042 0.000 0.0008 N 0.076 0.01 4.33 0.012 0.0025 0.038 0.0023 0.620 0.0016 o 0.032 0.06 3.50 0.010 0.0045 0.032 0.0021 0.000 0.0008 P 0.021 0.03 2.30 0.007 0.0036 0.033 0.0022 0.000 0.0012 Q 0.050 1.20 1.32 0.012 0.0087 0.042 0.0023 0.000 0.0011

Table 11

Steel No. Nb Ti Ti-48/14×N Mo+Nb+B+Ti other Ar ₃ (°C) Remark A 0.015 0.04 0.031 0.2560 756 Invention steel B 0.023 0.025 0.014 0.1988 903 Comparing steel C 0.042 0.031 0.017 0.3742 Cr: 0.2 641 Invention steel D 0.031 0.023 0.008 0.2341 906 Comparing steel E 0.023 0.023 0.011 0.2983 820 Invention steel F 0.028 0.018 0.005 0.4676 V: 0.04 995 Comparing steel G 0.025 0.023 0.010 0.0600 Cu: 0.3 701 Invention steel h 0.006 0.000 -0.010 0.0062 922 Comparing steel I 0.006 0.230 0.215 0.2416 876 Comparing steel J 0.000 0.000 -0.012 0.0000 840 Comparing steel K 0.044 0.042 0.030 0.4091 688 Invention steel L 0.025 0.053 0.042 0.6098 574 Invention steel m 0.004 0.004 -0.010 0.0088 Ca: 0.003 748 Comparing steel N 0.014 0.029 0.021 0.6646 563 Invention steel o 0.020 0.015 0.008 0.0358 W: 0.03 643 Invention steel P 0.038 0.023 0.015 0.0622 742 Invention steel Q 0.095 0.019 0.011 0.1151 852 Invention steel

Table 12

Steel No. C Si Mn P S Al N Mo B R 0.032 0.80 3.20 0.008 0.0042 0.031 0.0021 0.012 0.0006 S 0.048 0.30 1.57 0.010 0.0110 0.035 0.0018 0.036 0.0008 T 0.027 0.02 1.10 0.013 0.0078 0.042 0.0013 0.105 0.0003 u 0.036 0.50 2.05 0.008 0.0032 0.044 0.0023 0.520 0.0006 V 0.042 0.02 1.52 0.011 0.0051 0.023 0.0025 0.080 0.0021 W 0.033 0.60 0.97 0.006 0.0066 0.033 0.0020 0.020 0.0025 x 0.030 0.03 1.83 0.023 0.0035 0.035 0.0019 0.120 0.0016 Y 0.043 0.02 2.70 0.021 0.0022 0.032 0.0022 0.140 0.0027 Z 0.038 0.70 2.10 0.008 0.0067 0.040 0.0021 0.070 0.0009 AAA 0.049 0.02 0.98 0.010 0.0050 0.026 0.0013 0.000 0.0027 AB 0.047 0.03 1.23 0.009 0.0042 0.032 0.0019 0.100 0.0030 AC 0.030 0.02 1.92 0.013 0.0023 0.036 0.0021 0.000 0.0000 AD 0.028 0.03 1.63 0.006 0.0033 0.042 0.0024 0.000 0.0000 AE 0.049 0.40 2.48 0.009 0.0054 0.031 0.0019 0.500 0.0000 AF 0.035 0.02 1.20 0.012 0.0063 0.033 0.0023 0.000 0.0000

Table 13

Steel No. Nb Ti Ti-48/14×N Mo+Nb+B+Ti other Ar ₃ (°C) Remark R 0.000 0.009 0.002 0.0216 692 Invention steel S 0.000 0.011 0.005 0.0478 801 Invention steel T 0.000 0.030 0.026 0.1353 838 Invention steel u 0.000 0.025 0.017 0.5456 775 Invention steel V 0.042 0.015 0.006 0.1391 796 Invention steel W 0.065 0.020 0.013 0.1075 864 Invention steel x 0.030 0.012 0.005 0.1636 V: 0.02 777 Invention steel Y 0.012 0.019 0.011 0.1737 703 Invention steel Z 0.032 0.120 0.113 0.2229 776 Invention steel AA 0.035 0.000 -0.004 0.0377 837 Invention steel AB 0.000 0.000 -0.007 0.1030 819 Invention steel AC 0.042 0.000 -0.007 0.0420 770 Invention steel AD 0.000 0.096 0.088 0.0960 795 Invention steel AE 0.000 0.000 -0.007 0.5000 731 Invention steel AF 0.040 0.045 0.037 0.0850 825 Invention steel

Table 14

Sample No. Steel No. Ar ₃ (°C) ε ^* FT(°C) CT(°C) TS(MPa) YS(MPa) EI(%) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) 79 A 756 0.52 870 600 408 306 33 233 205 234 80 0.48 860 500 398 299 35 234 210 233 81 0.33 890 550 411 303 32 218 210 225 82 B 903 0.46 930 600 342 250 41 200 209 212 83 0.55 872 500 339 244 41 198 195 210 84 C 641 0.51 870 500 585 489 20 245 201 242 85 0.51 780 550 579 472 19 247 196 240 86 0.55 920 550 575 468 20 202 203 205 87 D. 906 0.49 830 550 383 295 34 210 212 217 88 0.31 880 550 394 297 33 208 200 205 89 E. 820 0.62 850 600 415 319 30 232 193 229 90 0.58 860 500 432 325 31 232 195 230 91 0.34 800 550 428 321 32 200 197 208 92 f 995 0.56 870 350 615 463 25 205 202 206 93 0.57 860 350 598 455 25 208 203 203 94 G 701 0.45 780 500 781 599 14 245 204 238 95 0.44 850 500 792 608 14 236 210 236 96 0.35 810 500 788 600 16 225 212 231

Table 15

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 79 13 13 1 9 10 4 Example of the invention 80 12 12 1 11 11 3 Example of the invention 81 6 7 2 5 4 2 comparative example 82 6 6 7 4 5 4 comparative example 83 7 8 9 6 5 5 comparative example 84 16 17 4 11 13 1 Example of the invention 85 18 18 2 10 11 1 Example of the invention 86 8 7 8 8 7 5 comparative example 87 8 8 7 7 5 2 comparative example 88 7 6 5 6 5 3 comparative example 89 12 12 1 8 11 1 Example of the invention 90 11 12 1 10 10 3 Example of the invention 91 6 6 5 5 5 6 comparative example 92 4 4 5 6 5 5 comparative example 93 4 4 3 6 6 6 comparative example 94 15 14 0 13 11 1 Example of the invention 95 11 13 1 10 8 1 Example of the invention 96 8 8 6 11 8 7 comparative example

Table 16

Sample No. Steel No. Ar ₃ (°C) ε ^* FT(°C) CT(°C) TS(MPa) YS(MPa) EI(%) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) 97 h 922 0.45 860 550 635 502 20 195 198 221 98 0.52 700 550 662 508 18 203 203 215 99 I 876 0.56 850 600 720 550 16 212 205 217 100 0.28 800 600 742 552 15 218 200 221 101 J 840 0.43 780 450 715 521 25 210 202 223 102 0.44 910 450 698 516 twenty four 215 212 218 103 K 688 0.56 750 500 890 688 14 247 198 243 104 0.49 850 550 875 670 15 245 203 240 105 0.3 880 500 865 670 13 206 203 209 106 L 574 0.5 700 550 942 730 12 251 212 240 107 0.5 850 550 925 712 10 248 210 240 108 0.29 830 550 899 689 9 220 195 225 109 m 748 0.51 820 600 860 660 11 223 211 235 110 0.37 930 600 851 653 11 210 206 221 111 N 563 0.46 780 500 1121 889 8 253 201 248 112 0.43 850 500 1101 895 6 250 207 241 113 0.38 920 500 1098 882 5 225 205 223

Table 17

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 97 5 5 4 4 4 2 comparative example 98 8 8 1O 7 6 8 comparative example 99 7 7 6 9 4 7 comparative example 1OO 8 8 6 7 5 8 comparative example 101 7 7 5 8 5 8 comparative example 102 6 6 4 5 4 5 comparative example 103 15 16 5 13 11 4 Example of the invention 104 15 15 3 13 12 5 Example of the invention 105 5 5 5 5 3 7 comparative example 106 18 19 0 17 15 O Example of the invention 107 17 17 0 15 14 O Example of the invention 108 9 8 7 7 8 1O comparative example 109 9 9 5 1O 7 2 comparative example 11O 5 5 3 8 4 9 comparative example 111 twenty one twenty two 0 15 18 O Example of the invention 112 18 18 0 13 15 0 Example of the invention 113 6 5 2 7 4 6 comparative example

Table 18

Sample No. Steel No. Ar ₃ (°C) ε ^* FT(°C) CT(°C) TS(MPa) YS(MPa) EI(%) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) 114 o 643 0.42 880 650 892 743 10 233 200 239 115 P 742 0.45 870 600 598 445 twenty two 238 197 235 116 Q 852 0.5 880 550 785 695 18 245 203 241 117 R 692 0.43 830 550 859 773 12 232 205 239 118 S 801 0.41 850 500 594 475 25 235 208 235 119 T 838 0.44 880 600 481 385 30 240 199 240 120 u 775 0.49 790 500 696 556 twenty three 243 202 239 121 V 796 0.56 810 550 719 559 20 241 205 239 122 W 864 0.51 890 600 762 553 21.04 245 208 241 123 x 777 0.42 830 600 592 474 20 239 193 235 124 Y 703 0.43 860 500 721 577 17 247 190 242 125 Z 776 0.49 880 550 779 657 15 243 200 243 126 AAA 837 0.44 870 500 463 298 26 239 203 237 127 AB 819 0.42 840 450 502 402 twenty four 237 201 237 128 AC 770 0.44 830 550 604 522 25 233 194 239 129 AD 795 0.52 800 250 562 326 26 237 203 239 130 AE 731 0.48 820 450 745 596 20 239 208 239 131 AF 825 0.5 890 550 652 495 15 241 200 237

Table 19

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 114 17 17 6 8 8 5 Example of the invention 115 15 16 5 11 11 4 Example of the invention 116 15 16 2 10 13 2 Example of the invention 117 13 14 6 8 10 6 Example of the invention 118 18 16 4 9 7 3 Example of the invention 119 12 12 1 12 9 1 Example of the invention 120 15 15 2 13 11 4 Example of the invention 121 16 15 1 10 13 2 Example of the invention 122 13 14 0 10 15 1 Example of the invention 123 14 13 1 9 11 3 Example of the invention 124 18 19 1 12 10 1 Example of the invention 125 17 16 0 9 8 1 Example of the invention 126 14 15 3 10 11 2 Example of the invention 127 13 13 3 8 8 4 Example of the invention 128 16 16 4 11 11 6 Example of the invention 129 15 14 3 13 13 5 Example of the invention 130 11 11 3 11 11 4 Example of the invention 131 13 13 2 15 14 2 Example of the invention

(Embodiment 8)

Steel slabs having the compositions of steel No.C and L in Tables 10 and 11 were melted, and hot-rolled under the conditions shown in Table 20. All the heating temperatures of the slabs were determined to be 1230°C. Regarding other rolling conditions, in the finishing stand consisting of 7 stages in total, the friction coefficient between the roll and the steel plate was determined to be in the range of 0.21 to 0.24 in the last 3 stages, and the total reduction ratio of the last 3 stages was 55%. All temper rolling reductions were 0.3%. In addition, Ar ₃ is the same as that in Tables 14 and 16.

After rolling, continuous annealing (holding at 700°C for 90 seconds), box annealing (holding at 700°C for 6 hours), and continuous hot-dip galvanizing (the highest reaching temperature is 750°C, after dipping in the zinc plating bath at 500 The tensile properties and Young's modulus were measured according to any of the treatments in which the alloying treatment was carried out at ℃ for 20 seconds.

The results are shown in Tables 20 and 21. In addition, Table 21 is a continuation of Table 20. It is clear from the table that the Young's modulus increases by hot rolling the steel having the chemical composition of the present invention under appropriate conditions and performing appropriate heat treatment.

Table 20

Sample No. Steel No. ε ^* FT(°C) CT(°C) Treatment after hot rolling TS(MPa) YS(MPa) EI(%) BH(MPa) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) 132 C 0.51 870 500 none 585 489 20 47 245 201 242 133 C 0.51 870 500 Continuous annealing 556 442 twenty three 65 243 203 240 134 C 0.51 870 500 Box annealing 530 418 25 48 248 201 243 135 C 0.51 870 500 Continuous alloying hot dip galvanizing 549 418 twenty two 62 241 201 240 136 L 0.5 850 550 none 925 712 10 62 248 210 240 137 L 0.5 850 550 Continuous annealing 898 716 14 79 245 211 242 138 L 0.5 850 550 Box annealing 867 694 15 52 251 208 247 139 L 0.5 850 550 Continuous alloying hot dip galvanizing 882 694 12 60 245 208 246

Table 21

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 132 16 17 0 11 13 1 Example of the invention 133 17 16 0 11 10 1 Example of the invention 134 17 18 0 13 12 0 Example of the invention 135 16 16 0 11 11 0 Example of the invention 136 17 17 0 15 14 0 Example of the invention 137 18 17 0 14 13 0 Example of the invention 138 19 18 0 14 15 0 Example of the invention 139 17 19 0 15 13 0 Example of the invention

(Example 9)

Steel slabs having the compositions of steel No.C and L in Tables 10 and 11 were melted, and hot rolled under the conditions shown in Table 22. All the heating temperatures of the slabs were determined to be 1230°C. Regarding other rolling conditions, in the finishing stand consisting of 7 stages in total, the friction coefficient between the roll and the steel plate was determined to be in the range of 0.21 to 0.24 in the last 3 stages, and the total reduction ratio of the last 3 stages was 55%. All temper rolling reductions were 0.3%. In addition, Ar ₃ is the same as that in Tables 14 and 16.

After hot rolling, cold rolling was performed, and then continuous hot-dip galvanizing was performed (variously changing the maximum attained temperature, and alloying treatment at 500° C. for 20 seconds after immersion in a galvanizing bath). Tensile properties and Young's modulus were then determined.

The results are shown in Tables 22 and 23. In addition, Table 23 is a continuation of Table 22. It is clear from the table that by hot-rolling and cold-rolling the steel having the chemical composition of the present invention under appropriate conditions and performing appropriate heat treatment, it is possible to obtain a cold-rolled steel sheet having excellent Young's modulus in the RD direction and the TD direction . However, when the maximum attained temperature is remarkably high, the Young's modulus also slightly decreases.

Table 22

Sample No. Steel No. ε ^* FT(°C) CT(°C)   Cold rolling rate (%) Maximum temperature (℃) TS(MPa) YS(MPa) EI(%) BH(MPa) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) 140 C 0.51 870 500 52 970 613 492 17 53 239 211 238 141 C 0.51 870 500 52 830 600 478 20 82 244 203 243 142 C 0.51 870 500 52 750 589 469 twenty one 65 245 201 203 143 L 0.5 850 550 30 970 1008 789 8 62 239 211 241 144 L 0.5 850 550 30 830 976 761 10 78 242 207 238 145 L 0.5 850 550 30 750 949 736 11 61 240 203 242

Table 23

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 140 15 14 0 10 10 2 Example of the invention 141 17 17 0 11 12 2 Example of the invention 142 16 17 1 10 11 1 Example of the invention 143 13 15 1 13 12 2 Example of the invention 144 16 17 0 15 15 1 Example of the invention 145 16 15 0 14 15 1 Example of the invention

(Example 10)

Steel slabs having compositions of steel No.C and L in Tables 10 and 11 were melted, and hot rolled under the conditions shown in Table 24. All the heating temperatures of the slabs were determined to be 1230°C. Regarding other rolling conditions, in the finishing stand consisting of 7 stages in total, the friction coefficient between the roll and the steel plate was determined to be in the range of 0.21 to 0.24 in the last 3 stages, and the total reduction ratio of the last 3 stages was 55%. All temper rolling reductions were 0.3%. In addition, Ar ₃ is the same as that in Tables 14 and 16.

After hot rolling, the steel sheet is heated to 650°C in a continuous hot-dip galvanizing line, cooled to about 470°C and dipped in a molten galvanizing bath at 460°C. The thickness of the zinc coating is 40 g/m ² on average on one side in terms of weight per unit area. After hot-dip galvanizing, (1) organic coating and (2) painting were performed on the surface of the steel sheet as follows, and tensile properties and Young's modulus were measured.

(1) Organic film

When the solid content of the resin is 27.6% by mass, the viscosity of the dispersion is 1400mPa.s (25°C), the pH is 8.8, the content of the ammonium salt (-COONH ₄ ) of the carboxyl group is 9.5% by mass of the solid content of the entire resin, and the content of the carboxyl group is 4% by mass of corrosion inhibitor and 12% of colloidal silica were added to an aqueous resin having a solid content of 2.5% by mass of the entire resin and an average diameter of dispersed particles of about 0.030 μm to prepare a rust-preventive treatment liquid. This anti-rust treatment solution was applied to the above-mentioned steel plate by a roll coater, and dried so that the temperature reached on the surface of the steel plate was 120° C. to form a film with a thickness of about 1 μm.

(2) Coating

On the above-mentioned degreased steel sheet, "ZM1300AN" manufactured by Nippon Parking Co., Ltd. was applied as a chemical conversion treatment by a roll coater, and it was dried with hot air at a temperature of 60°C. The deposition amount of the chemical conversion treatment was 50 mg/m ² in terms of the deposition amount of Cr. Then, the steel sheet subjected to the chemical conversion treatment is coated with a primer on one side of the steel sheet and a back coating on the other side by a roll coater, and dried and hardened in an induction heating furnace using hot air. The reaching temperature at this time was 210°C.

On the surface coated with the primer, a top coat is applied with a roller curtain coater, and then an induction heating furnace with hot air is used to reach a temperature of 230°C to dry and harden. As a primer, "FL640EU primer" manufactured by Nippon Finco-Tingus Co., Ltd. was used, and the dry film thickness was applied so as to be 5 μm. As the back paint, "FL100HQ" manufactured by Nippon Finco-Tingus Co., Ltd. was used, and the dry film thickness was applied so as to be 5 μm. As a top coat, "FL100HQ" manufactured by Nippon Finco-Tingus Co., Ltd. was used, and it was applied so that the dry film thickness may be 15 micrometers.

The results are shown in Tables 24 and 25. In addition, Table 25 is a continuation of Table 24. It is clear from the table that the hot-dip galvanized steel sheet and the steel sheet provided with an organic film and paint on the surface also have good Young's modulus.

Table 24

Sample No. Steel No. ε ^* FT(°C) CT(°C) surface treatment TS(MPa) YS(MPa) EI(%) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) 146 C 0.51 870 500 Only hot-dip galvanized 559 418 twenty two 243 201 242 147 C 0.51 870 500 Organic film 582 421 twenty two 245 208 243 148 C 0.51 870 500 painting 590 421 20 247 206 245 149 L 0.5 850 550 Only hot-dip galvanized 889 678 10 246 210 240 150 L 0.5 850 550 Organic film 912 687 9 249 210 243 151 L 0.5 850 550 painting 932 691 11 251 207 245

Table 25

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 146 16 17 0 11 13 1 Example of the invention 147 17 15 0 13 13 1 Example of the invention 148 19 16 1 12 14 0 Example of the invention 149 17 17 0 15 14 0 Example of the invention 150 19 18 0 15 14 1 Example of the invention 151 19 17 0 16 15 0 Example of the invention

(Example 11)

Steels No.C and L having Tables 10 and 11 were smelted and rolled at different circumferential speeds. In the finishing stand consisting of 7 stages in total, the peripheral speed is changed in the last 3 stages. Table 26 shows the hot rolling conditions and the measurement results of tensile properties and Young's modulus. The hot rolling conditions not shown in Table 26 were completely the same as in Example 7.

The results obtained are shown in Tables 26 and 27. In addition, Table 27 is a continuation of Table 26. It is clear from the table that when hot-rolling the steel having the chemical composition of the present invention under appropriate conditions, the formation of the texture near the surface layer can be promoted if the rolling is carried out at a different peripheral speed of 1% or more in one pass or more. , the Young's modulus is further increased.

Table 26

Sample No. Steel No. ε ^* FT(°C) CT(°C) Different peripheral speed (%) TS(MPa) YS(MPa) EI(%) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) 5 passes 6 passes 7 passes 152 C 0.51 870 500 0 0 0 585 489 20 245 201 242 153 C 0.49 868 500 0 0 3 591 446 20 247 203 242 154 C 0.5 872 500 1 2 3 589 445 20 248 202 240 155 C 0.51 875 500 10 5 5 597 451 twenty one 251 202 243 156 L 0.5 850 550 0 0 0 925 712 10 248 210 240 157 L 0.51 853 550 3 3 3 931 721 11 250 211 242 158 L 0.49 855 550 0 0 10 924 715 11 252 211 242 159 L 0.5 850 550 0 20 20 925 716 11 254 209 243

Table 27

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 152 16 17 0 11 13 1 Example of the invention 153 17 17 0 10 13 1 Example of the invention 154 18 16 0 10 14 0 Example of the invention 155 20 16 1 10 15 0 Example of the invention 156 17 17 0 15 14 0 Example of the invention 157 18 17 0 14 14 0 Example of the invention 158 20 16 1 15 15 0 Example of the invention 159 twenty two 16 0 13 16 0 Example of the invention

(Example 12)

Steel No.C and L steels in Tables 10 and 11 were used for thin roll rolling. In the finishing stand consisting of 7 stages in total, the diameter of the rolls is changed in the last 3 stages. Table 28 shows the hot rolling conditions and the measurement results of tensile properties and Young's modulus. The hot rolling conditions not shown in Table 28 were completely the same as in Example 7.

The results obtained are shown in Tables 28 and 29. In addition, Table 29 is a continuation of Table 28. Therefore, when the steel having the chemical composition of the present invention is hot-rolled under suitable conditions, if a roll with a roll diameter of 700 mm or more is used for more than one pass, the formation of texture near the surface layer can be promoted, and the Young's modulus can be further improved. improve.

Table 28

Sample No. Steel No. ε ^* FT(°C) CT(°C) Roll diameter (mm) TS(MPa) YS(MPa) EI(%) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) 5 passes 6 passes 7 passes 160 C 0.51 870 500 800 800 800 585 489 20 245 201 242 161 C 0.51 873 500 800 800 600 583 440 twenty two 246 202 243 162 C 0.53 870 500 600 600 600 585 442 20 249 203 243 163 C 0.53 867 500 500 500 500 589 445 19 253 203 243 164 L 0.5 850 550 800 800 800 925 712 10 248 210 243 165 L 0.51 855 550 800 800 600 927 718 11 251 210 245 166 L 0.52 853 550 600 600 600 931 721 11 253 210 246 167 L 0.52 852 550 500 500 500 933 723 10 256 212 243

Table 29

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 160 16 17 0 11 13 1 Example of the invention 161 18 16 0 10 14 0 Example of the invention 162 20 16 1 11 15 2 Example of the invention 163 twenty two 17 1 11 16 0 Example of the invention 164 17 17 0 15 14 0 Example of the invention 165 18 18 1 14 15 0 Example of the invention 166 20 17 0 15 15 0 Example of the invention 167 twenty three 16 0 13 17 0 Example of the invention

(Example 13)

The steel materials shown in Tables 30 to 33 were heated to 1200 to 1270° C., and hot rolled under the hot rolling conditions shown in Tables 34, 36, 38, and 40 to produce hot-rolled steel sheets with a thickness of 2 mm. Here, for the annealed hot-rolled steel sheet, "exist" was written in the column of hot-rolled sheet annealing (3 ^* ), and for the hot-rolled steel sheet that was not annealed, "none" was written. This annealing is performed at 600 to 700° C. for 60 minutes. This designation is used commonly in the description of the following tables.

The Young's modulus of the surface layer was measured by cutting out a sample at a thickness of 1/6 of the plate thickness from the surface layer, and measuring it by the above-mentioned resonance method. Regarding the tensile properties, JIS No. 5 tensile test pieces were used for evaluation in the width direction.

The evaluation of shape freezeability uses a rectangular sample of 260mm long x 50mm wide x plate thickness. The punch width is 78mm, the punch shoulder is R5mm, the die shoulder is R4mm, and it is formed into a cap with various thicknesses of anti-wrinkle platen. shape, and then use a 3-dimensional shape measuring device to measure the shape of the central area of the plate width. As shown in Figure 1, the average value of the left and right values subtracted from the angle between the line connecting point A and point B and the line connecting point C and point D minus 90° is used as the rebound amount, point C and point E The reciprocal of the radius of curvature ρ [mm] between them was multiplied by 1000 times and the value obtained by averaging the left and right was used as the amount of wall warpage to evaluate the shape freezing property. The smaller 1000/ρ, the better the shape freezing property. In addition, the bending is performed so as to introduce a fold line perpendicular to the rolling direction.

It is generally known that as the strength of the steel sheet increases, the shape freezing property deteriorates. Based on the results of actual part forming, the present inventors determined that the pressure of the anti-wrinkle platen measured by the above method was 70N of springback and 1000/ρ, and the tensile strength [MPa] of the steel plate was (0.015×TS-6 In the case of (°) or less and (0.01×TS-36 (mm ^-1 ) or less, since the freezeability at this time is good, satisfying both of them was evaluated as a good shape freeze condition.

The obtained results are shown in Tables 34-41. Table 35 is a continuation of Table 34, Table 37 is a continuation of Table 36, Table 39 is a continuation of Table 38, and Table 41 is a continuation of Table 40. In the table, regarding the rolling reduction (1 ^* ), when the total rolling reduction in hot rolling is 50% or more, it is rated as "suitable"; when it is less than 50%, it is rated as "unsuitable". Regarding the coefficient of friction (2 ^* ), when the average coefficient of friction in hot rolling exceeds 0.2, it is rated as "suitable", and when it is 0.2 or less, it is rated as "unsuitable". When the shape freezing property satisfies the above two conditions, it was rated as "good", and when it was not satisfied, it was rated as "poor". These notations are common to the descriptions of the following tables. 1000/ρ tends to decrease when the pressure of the anti-wrinkle platen increases. However, no matter what pressure of the anti-crease plate is selected, the level of the shape freezing property of the steel plate does not change. Therefore, the evaluation of the anti-wrinkle platen pressure of 70kN can well represent the shape freezing property of the steel plate.

Table 30

Steel No. C Si Mn P S Al N Mo B P1 0.003 0.01 1.50 0.080 0.0012 0.036 0.0025 0.200 0.0010 P2 0.031 0.75 0.50 0.013 0.0009 0.029 0.0027 0.420 0.0020 P3 0.023 0.02 0.60 0.009 0.0034 0.029 0.0025 0.350 0.0020 P4 0.042 0.36 0.32 0.008 0.0026 0.031 0.0036 0.430 0.0020 P5 0.020 0.09 1.45 0.015 0.0006 0.032 0.0024 0.180 0.0010 P6 0.045 0.53 1.85 0.010 0.0045 0.037 0.0041 0.170 0.0009 P7 0.080 1.30 1.70 0.028 0.0062 0.034 0.0031 0.210 0.0013 P8 0.160 0.07 0.98 0.013 0.0053 0.044 0.0024 0.300 0.0015 P9 0.110 0.05 2.12 0.010 0.0036 0.680 0.0024 0.290 0.0020 P10 0.150 1.80 1.95 0.018 0.0028 0.019 0.0031 0.320 0.0022 P11 0.007 0.08 1.22 0.030 0.0035 0.023 0.0021 0.070 0.0030 P12 0.130 0.11 1.52 0.009 0.0065 0.034 0.0022 0.000 0.0000 P13 0.020 0.06 0.98 0.012 0.0033 0.070 0.0033 0.000 0.0025 P14 0.079 0.06 0.73 0.013 0.0045 0.032 0.0028 0.300 0.0000 P15 0.060 0.20 0.77 0.040 0.0052 0.029 0.0022 0.140 0.0028

Table 31

Steel No. Nb Ti Ti-48/14×N Mo+Nb+Ti+B Ar ₃ (°C) Remark P1 0.030 0.018 0.0094 0.249 781 Invention steel P2 0.028 0.018 0.0087 0.468 842 Invention steel P3 0.018 0.020 0.0114 0.390 818 Invention steel P4 0.03 0.031 0.0187 0.493 840 Invention steel P5 0.042 0.010 0.0018 0.233 783 Invention steel P6 0.022 0.023 0.0089 0.216 Cr: 0.5 761 Invention steel P7 0.021 0.013 0.0024 0.245 778 Invention steel P8 0.033 0.021 0.0128 0.356 Ca: 0.0015 762 Invention steel P9 0.035 0.012 0.0038 0.339 V: 0.02 806 Invention steel P10 0.035 0.015 0.0044 0.372 727 Invention steel P11 0.022 0.021 0.0138 0.116 782 Invention steel P12 0.080 0.000 -0.0075 0.080 774 Invention steel P13 0.052 0.000 -0.0113 0.055 819 Invention steel P14 0.000 0.000 -0.0096 0.300 826 Invention steel P15 0.000 0.000 -0.0075 0.143 804 Invention steel

Table 32

Steel No. C Si Mn P S Al N Mo B P16 0.062 0.23 1.20 0.006 0.0066 0.042 0.0025 0.000 0.0000 P17 0.062 0.06 2.35 0.012 0.0003 0.033 0.0026 0.000 0.0000 P18 0.067 0.24 1.52 0.008 0.0045 0.035 0.0023 0.080 0.0011 P19 0.043 0.53 1.98 0.010 0.0036 0.042 0.0022 0.130 0.0020 C1 0.020 0.01 1.50 0.012 0.0017 0.032 0.0035 0.000 0.0001 C2 0.010 0.37 1.20 0.010 0.0003 0.023 0.0033 0.005 0.0023 C3 0.051 0.57 0.05 0.009 0.0026 0.026 0.0029 0.230 0.0001 C4 0.045 2.60 1.80 0.014 0.0042 0.027 0.0024 0.000 0.0010 C5 0.100 1.30 1.70 0.062 0.0056 1.200 0.0030 0.600 0.0008 C6 0.120 1.80 0.10 0.007 0.0029 0.620 0.0032 0.330 0.0004

Table 33

Steel No. Nb Ti Ti-48/14×N Mo+Nb+Ti+B other Ar ₃ (°C) Remark P16 0.040 0.080 0.0714 0.120 W: 0.01 826 Invention steel P17 0.000 0.110 0.1011 0.110 726 Invention steel P18 0.024 0.015 0.0071 0.120 775 Invention steel P19 0.033 0.020 0.0125 0.185 739 Invention steel C1 0.001 0.009 -0.0030 0.010 804 compare steel C2 0.002 0.000 -0.0113 0.009 808 compare steel C3 0.040 0.023 0.0131 0.293 909 compare steel C4 0.000 0.005 -0.0032 0.006 Cu: 0.2 843 compare steel C5 0.024 0.021 0.0107 0.646 981 compare steel C6 0.031 0.007 -0.0040 0.368 1031 compare steel

Table 34

Sample No. Steel No. Ar ₃ (°C) ε ^* Reduction rate(1*) Coefficient of friction (2*) FT(°C) CT(°C) Hot rolled sheet annealing (3*) TS (MPa E(RD)(GPa) E(D)(GPa) E(TD)(GPa) Surface Young's modulus in rolling direction (GPa) Surface Young's modulus in width direction (GPa) 168 P1 781 0.65 suitable suitable 835 500 none 469 246 205 240 255 255 169 0.57 suitable suitable 830 600 none 460 243 206 239 253 256 170 0.37 suitable suitable 850 550 none 467 212 205 235 221 239 171 P2 842 0.72 suitable suitable 860 400 none 500 245 199 239 259 263 172 0.59 suitable suitable 875 600 none 498 250 200 245 262 257 173 0.49 inappropriate suitable 880 600 none 503 204 205 218 218 229 174 P3 818 0.67 suitable suitable 840 450 none 446 242 203 238 253 255 175 0.82 suitable suitable 870 450 have 450 241 202 240 254 254 176 0.48 suitable inappropriate 850 450 none 449 213 206 239 225 235 177 P4 840 0.52 suitable suitable 860 500 have 479 246 198 40 256 261 178 0.59 suitable suitable 875 500 none 482 239 197 238 248 253 179 0.57 suitable suitable 750 500 none 485 214 200 230 223 223

Table 35

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Rebound(°) Wall warping (1000/ρ) shape freezing Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 168 13 13 3 10 10 2 0.0 0.4 good Example of the invention 169 13 12 2 9 9 1 0.5 0.4 Good Example of the invention 170 4 5 6 5 3 5 1.4 2.2 bad comparative example 171 13 12 3 11 10 2 0.1 0.7 good Example of the invention 172 16 15 3 10 12 3 0.3 0.8 Good Example of the invention 173 5 4 3 4 3 4 2.2 3.2 bad comparative example 174 12 12 0 9 10 3 0.1 0.9 good Example of the invention 175 13 13 0 8 9 2 0.0 0.9 good Example of the invention 176 5 6 4 5 3 5 1.4 1.9 Bad comparative example 177 14 15 1 10 10 2 0.0 0.8 Good Example of the invention 178 12 11 2 9 8 4 0.1 1.5 Good Example of the invention 179 6 5 6 5 3 5 1.3 2.8 bad comparative example

Table 36

Sample No. Steel No. Ar ₃ (°C) ε ^* Reduction rate(1*) Coefficient of friction (2*) FT(°C) CT(°C) Hot rolled sheet annealing (3*) TS (MPa E(RD)(GPa) E(D)(GPa) E(TD)(GPa) Young's modulus of surface layer in rolling direction (GPa) Young's modulus of the surface layer in the width direction (GPa) 180 P5 783 0.64 suitable suitable 820 600 none 590 239 206 237 245 241 181 0.63 suitable suitable 880 600 none 553 248 203 245 259 255 182 0.72 suitable suitable 920 600 none 567 209 200 218 231 253 183 P6 788 0.65 suitable suitable 880 350 none 632 248 197 243 268 257 184 0.52 suitable suitable 870 500 none 609 246 195 239 262 263 185 0.57 suitable suitable 860 730 none 578 216 201 229 225 229 186 P7 778 0.61 suitable suitable 830 450 none 782 246 203 238 255 255 187 0.76 suitable suitable 850 250 none 779 247 195 244 262 255 188 0.72 suitable suitable 930 400 none 749 203 199 213 209 219 189 P8 762 0.59 suitable suitable 830 350 none 792 235 200 239 249 238 190 0.54 suitable suitable 850 500 have 800 240 205 238 253 255 191 0.25 suitable inappropriate 850 400 none 803 210 203 220 219 220

Table 37

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Rebound(°) Wall warping (1000/ρ) shape freezing Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 180 11 10 1 9 8 1 1.0 2.1 good Example of the invention 181 14 13 3 11 11 0 0.6 1.5 good Example of the invention 182 4 5 5 4 3 6 3.0 3.0 bad comparative example 183 14 13 0 10 11 2 0.6 1.9 good Example of the invention 184 14 14 1 11 10 4 1.0 1.4 good Example of the invention 185 6 5 6 5 4 6 3.4 3.0 bad comparative example 186 14 15 0 10 10 2 4.6 4.0 Good Example of the invention 187 13 14 2 12 11 3 4.0 3.5 Good Example of the invention 188 5 4 2 5 3 7 6.5 5.8 bad comparative example 189 10 11 1 8 9 2 5.1 4.1 good Example of the invention 190 11 12 0 7 8 4 4.4 3.6 good Example of the invention 191 5 5 5 4 4 6 6.8 5.7 bad comparative example

Table 38

Sample No. Steel No. Ar ₃ (°C) ε ^* Reduction rate(1*) Coefficient of friction (2*) FT(°C) CT(°C) Annealing of hot-rolled sheet (3*) TS{MPa E(RD)(GPa) E(D)(GPa) E(TD)(GPa) Young's modulus of surface layer in rolling direction (GPa) Young's modulus of the surface layer in the width direction (GPa) 192 P9 806 0.67 suitable suitable 860 500 none 980 241 198 236 252 259 193 0.72 suitable suitable 870 400 none 997 239 209 235 250 253 194 0.71 inappropriate suitable 850 350 none 1029 213 210 219 225 245 195 P10 727 0.47 suitable suitable 780 300 none 1008 245 211 237 256 260 196 0.5 suitable suitable 830 350 none 1102 247 208 237 261 255 197 0.52 suitable inappropriate 850 500 none 904 206 203 230 215 219 198 P11 782 0.41 suitable suitable 840 500 none 498 241 211 236 250 249 199 P12 774 0.44 suitable suitable 860 550 none 605.8 240 206 236 253 243 200 P13 819 0.62 suitable suitable 830 500 none 652 239 209 239 249 246 201 P14 826 0.42 suitable suitable 860 600 none 723 242 196 238 256 247 202 P15 804 0.53 suitable suitable 850 500 none 525.7 239 200 236 262 249 203 P16 826 0.56 suitable suitable 880 550 none 581.5 237 202 238 246 242 204 P17 726 0.59 suitable suitable 800 450 none 700.5 245 200 237 253 253

Table 39

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Rebound(°) Wall warping (1000/ρ) shape freezing Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 192 12 12 3 9 9 3 7.9 5.8 good Example of the invention 193 11 10 1 10 8 1 8.0 6.4 Good Example of the invention 194 5 5 4 4 3 5 10.0 7.9 bad comparative example 195 13 12 2 10 10 2 7.8 6.2 good Example of the invention 196 14 13 0 11 11 3 8.7 6.8 Good Example of the invention 197 4 4 3 5 3 5 9.2 6.7 bad comparative example 198 12 12 6 10 9 5 0.5 0.0 good Example of the invention 199 13 12 4 9 8 4 1.9 2.0 good Example of the invention 200 11 12 3 9 8 3 2.5 3.0 Good Example of the invention 201 11 12 2 8 9 2 3.2 3.0 Good Example of the invention 202 11 10 0 10 8 4 0.9 1.2 Good Example of the invention 203 15 14 6 9 8 4 1.2 1.8 good Example of the invention 204 14 14 5 9 10 1 3.1 3.0 good Example of the invention

Table 40

Sample No. Steel No. Ar ₃ (°C) ε ^* Reduction rate(1*) Coefficient of friction (2*) FT(°C) CT(°C) Hot rolled sheet annealing (3*) TS (MPa E(RD)(GPa) E(D)(GPa) E(TD)(GPa) Surface Young's modulus in rolling direction (GPa) Surface Young's modulus in width direction (GPa) 205 P18 775 0.44 suitable suitable 880 400 none 621.6 249 199 239 260 255 206 P19 739 0.48 suitable suitable 860 500 none 712.7 243 200 235 256 250 207 C1 804 0.65 suitable suitable 880 400 have 439 204 205 205 210 225 208 0.68 inappropriate suitable 850 450 none 419 196 203 209 205 226 209 C2 808 0.78 suitable suitable 840 500 have 439 201 207 205 223 249 210 0.88 suitable suitable 850 750 none 447 200 205 203 209 231 211 C3 909 0.57 suitable suitable 820 600 none 567 208 207 219 227 246 212 0.67 suitable suitable 840 500 none 557 212 205 220 225 245 213 C4 843 0.95 suitable suitable 850 550 none 529 199 206 218 208 222 214 0.77 suitable suitable 880 550 have 549 200 206 223 203 220 215 C5 981 0.65 suitable suitable 870 450 none 780 205 199 209 198 221 216 0.32 suitable suitable 830 300 none 770 195 200 230 204 219 217 C6 1031 0.44 suitable suitable 850 300 none 790 222 205 207 231 237 218 0.7 inappropriate suitable 800 250 none 834 196 203 220 205 223

Table 41

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Rebound(°) Wall warping (1000/ρ) shape freezing Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 205 15 14 2 12 11 2 2.0 2.2 Good Example of the invention 206 12 13 4 10 9 3 3.4 3.1 Good Example of the invention 207 4 5 3 5 4 3 1.5 2.8 bad comparative example 208 8 9 7 4 3 6 2.0 2.8 bad comparative example 209 4 3 4 4 5 5 1.2 1.7 bad comparative example 210 4 5 3 5 3 6 2.5 3.2 bad comparative example 211 6 7 5 3 5 4 2.9 3.2 bad comparative example 212 5 4 4 5 2 3 2.9 3.0 bad comparative example 213 5 6 4 6 3 5 3.4 3.5 bad comparative example 214 7 8 5 4 5 4 4.0 4.3 bad comparative example 215 7 6 6 5 3 5 7.9 6.4 bad comparative example 216 5 4 3 5 3 7 7.7 6.5 bad comparative example 217 8 7 7 6 4 5 5.8 5.2 bad comparative example 218 5 6 5 3 6 5 8.4 6.5 bad comparative example

(Example 14)

Using the steels P5 and P8 shown in Tables 30 and 31, different peripheral speed rolling was performed. In the finishing mill stand composed of 6 stages in total, the circumferential speed is changed in the last 3 stages. Table 42 shows hot rolling conditions, tensile properties, measurement results of Young's modulus, and evaluation results of shape freezing properties. Manufacturing conditions not described in the table were the same as in Example 13.

The obtained results are shown in Tables 42 and 43. In addition, Table 43 is a continuation of Table 42. It is clearly shown in the table that when the steel with the chemical composition of the present invention is hot-rolled under suitable conditions, if rolling at a different peripheral speed of 1% or more in one pass or more is carried out, the Young's modulus near the surface layer will be further improved. Improvement, good shape freezing.

Table 42

Sample No. Steel No. Ar ₃ (°C) ε ^* Reduction rate(1*) Coefficient of friction (2*) FT(°C) CT(°C) Different circumferential velocity (%) Hot rolled sheet annealing (3*) TS(MPa) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) Young's modulus of surface layer in rolling direction (GPa) Surface Young's modulus in the width direction (GPa) 5 passes 6 passes 7 passes 219 P5 783 0.65 suitable suitable 870 500 0 0 0 none 582 239 205 236 245 247 220 0.67 suitable suitable 880 500 0 0 3 have 590 242 205 238 259 250 221 0.67 suitable suitable 860 500 1 2 3 none 598 244 202 240 252 252 222 0.66 suitable suitable 870 500 10 5 5 none 584 248 200 242 266 259 223 P8 762 0.65 suitable suitable 850 500 0 0 0 none 793 240 195 235 249 248 224 0.65 suitable suitable 860 500 3 3 3 have 775 241 198 237 257 249 225 0.67 suitable suitable 850 500 0 0 10 none 780 243 196 238 255 250 226 0.65 suitable suitable 850 500 0 20 20 none 789 246 197 240 263 252

Table 43

Sample No.   The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Rebound(°) Wall warping (1000/ρ) shape freezing Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 219 13 12 2 9 8 4 1.7 2.1 Good Example of the invention 220 12 11 1 9 9 3 1.1 1.8 Good Example of the invention 221 12 13 0 10 10 3 0.6 1.6 Good Example of the invention 222 14 15 0 11 12 1 0.1 1.3 good Example of the invention 223 11 12 2 10 9 3 5.2 4.1 Good Example of the invention 224 12 11 0 9 8 2 4.7 3.6 Good Example of the invention 225 12 13 0 11 9 2 4.2 3.3 Good Example of the invention 226 15 14 0 10 10 1 3.9 3 Good Example of the invention

(Example 15)

Using the steels P5 and P8 shown in Tables 30 and 31, thin roll rolling was performed. In the finishing mill stand composed of 6 stages in total, the diameter of the rolls is changed in the last 3 stages. Table 44 shows hot rolling conditions, tensile properties, measurement results of Young's modulus, and evaluation results of shape freezing properties. Manufacturing conditions not described in the table were the same as in Example 13.

The obtained results are shown in Tables 44 and 45. In addition, Table 45 is a continuation of Table 44. It is clearly shown in the table that when hot-rolling steel having the chemical composition of the present invention under suitable conditions, the Young's modulus near the surface layer is further increased, and the shape freezing property is improved by using rolls of 700 mm or less for one pass or more. .

Table 44

Sample No. Steel No. Ar ₃ (°C) ε ^* Reduction rate(1*) Coefficient of friction (2*) FT(°C) CT(°C) Roll diameter(mm) Hot rolled sheet annealing (3*) TS (MPa E(RD)(GPa) E(D)(GPa) E(TD)(GPa) Surface Young's modulus in rolling direction (GPa) Young's modulus of the surface layer in the width direction (GPa) 4 passes 5 passes 6 passes 227 P5 783 0.62 suitable suitable 850 550 800 800 800 none 579 238 205 239 246 249 228 0.67 suitable suitable 855 550 800 800 600 none 577 241 202 240 247 251 229 0.6 suitable suitable 860 550 600 600 600 none 592 245 205 240 253 253 230 0.73 suitable suitable 845 550 500 500 500 none 585 249 198 246 257 256 231 P8 762 0.65 suitable suitable 870 550 800 800 800 none 792 241 199 237 249 250 232 0.63 suitable suitable 860 550 800 800 600 have 783 245 200 239 255 249 233 0.67 suitable suitable 860 550 600 600 600 none 801 247 198 240 260 251 234 0.6 suitable suitable 865 550 500 500 500 none 803 251 202 241 265 260

Table 45

Sample No.   The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Rebound(°) Wall warping (1000/ρ) shape freezing Remark {110}<223> {110}<111> {110}<001> {211}<011> {332}<113> {100}<011> 227 11 11 2 9 7 3 1.9 2.1 good Example of the invention 228 12 12 1 9 8 0 1.2 1.8 Good Example of the invention 229 13 12 0 10 10 2 0.6 1.6 Good Example of the invention 230 14 15 0 11 12 3 0.1 1.3 Good Example of the invention 231 12 11 3 9 8 6 5.2 4.1 good Example of the invention 232 13 12 2 10 10 4 4.7 3.6 Good Example of the invention 233 14 15 1 11 10 4 4.2 3.3 good Example of the invention 234 15 16 0 12 12 3 3.9 3 Good Example of the invention

(Example 16)

Using steels P5 and P8 shown in Tables 30 and 31, cold-rolled annealed steel sheets were produced. Table 46 shows hot rolling, cold rolling, annealing conditions, tensile properties, measurement results of Young's modulus, and evaluation results of shape freezing properties. Manufacturing conditions not described in the table were the same as in Example 13.

The obtained results are shown in Tables 46 and 47. In addition, Table 47 is a continuation of Table 46. The table clearly shows that if the steel with the chemical composition of the present invention is hot-rolled, cold-rolled and annealed under proper conditions, the Young's modulus of the surface layer exceeds 245GPa, and the shape freezing property improves.

Table 46

Sample No. Steel No. Ar ₃ (°C) ε ^* Reduction rate(1*) Coefficient of friction (2*) FT(°C) CT(°C) Cold rolling rate (%) Maximum temperature (℃) TS(MPa) E(RD)(GPa) E(D)(GPa) E(TD)(GPa) Surface Young's modulus in rolling direction (GPa) Surface Young's modulus in width direction (GPa) 235 P5 783 0.65 suitable suitable 850 550 30 800 590 239 205 236 249 247 236 0.68 suitable suitable 850 550 60 780 585 242 205 238 257 255 237 0.72 suitable suitable 860 550 95 800 580 205 195 234 204 223 238 0.53 suitable suitable 870 550 40 960 598 205 210 216 205 210 239 0.59 suitable suitable 870 550 70 450 976 219 200 230 230 225 240 P8 762 0.55 suitable suitable 840 550 50 770 789 239 196 234 250 253 241 0.68 suitable suitable 860 550 60 780 820 242 205 237 253 249 242 0.67 suitable suitable 860 550 90 800 826 205 189 235 218 230 243 0.69 suitable suitable 850 550 40 980 795 205 205 209 208 216

Table 47

Sample No. The texture of the 1/8th layer of the plate thickness The texture of the central layer of the plate thickness Rebound(°) Wall warping (1000/ρ) shape freezing Remark {110}<223> <111>{110} {110}<001> {211}<011> {332}<113> {100}<011> 235 10 11 1 9 8 4 2.6 2.6 Good Example of the invention 236 11 12 2 9 9 3 2.5 2.5 Good Example of the invention 237 2 3 0 8 7 11 4.5 4.1 Bad comparative example 238 4 4 3 5 6 6 4.5 3.8 bad comparative example 239 5 6 3 6 4 8 * * bad comparative example 240 12 11 3 9 8 2 5.4 3.5 Good Example of the invention 241 13 12 1 9 9 6 5.8 3.7 good Example of the invention 242 4 4 0 5 3 4 8.5 6.3 bad comparative example 243 1 1 3 5 3 2 7.9 5.8 bad comparative example

The high Young's modulus steel plate of the present invention can be used in automobiles, household electrical appliances, buildings and the like. The high Young's modulus steel sheet of the present invention includes hot-rolled steel sheets and cold-rolled steel sheets in the narrow sense without surface treatment, and surface treatments such as hot-dip galvanizing, alloying hot-dip galvanizing, and electroplating for rust prevention. Generalized hot-rolled steel plate and cold-rolled steel plate. In addition, aluminum-based plated steel sheets are also included. These hot-rolled steel sheets, cold-rolled steel sheets, and various plated steel sheets have organic films, inorganic films, paints, etc. on their surfaces, and steel sheets that have various combinations thereof on their surfaces.

The high Young's modulus steel sheet of the present invention is a steel sheet having a high Young's modulus, and therefore can be used in a thinner thickness than conventional steel sheets, resulting in a reduction in weight. Therefore, it can be beneficial to the environment of the earth.

The use of the high Young's modulus steel sheet of the present invention can improve the shape freezing property, and the high-strength steel sheet can be easily applied to stamped parts such as automotive components. In addition, the steel sheet of the present invention is also excellent in impact energy absorption properties, and thus contributes to improvement of the safety of automobiles.

Claims (46)

1. A steel plate with a high Young's modulus, characterized in that it contains C: 0.0005% to 0.30%, Si: 2.5% or less, Mn: 2.7 to 5.0%, P: 0.15% or less, and S: 0.015% in mass % Below, Mo: 0.15-1.5%, B: 0.0006-0.01%, Al: 0.15% or less, and the balance is composed of Fe and unavoidable impurities. {110}<223> and Either or both of {110}<111> have an extreme density of 10 or more, and a Young's modulus in the rolling direction of more than 230GPa. 2 . The high Young's modulus steel sheet according to claim 1 , wherein the pole density of {112}<110> of a half layer of the sheet thickness is 6 or more. 3 . The high Young's modulus steel sheet according to claim 1 , further comprising one or two of Ti: 0.001 to 0.20% by mass and Nb: 0.001 to 0.20% by mass. 4. The high Young's modulus steel plate according to claim 1, characterized in that, after stretching by 2%, it is heat-treated at 170° C. for 20 minutes and the upper yield point when the tensile test is carried out again minus the stretching 2% The BH amount (MPa) evaluated by the difference of the flow stress at the time is 5MPa～200MPa. 5 . The high Young's modulus steel plate according to claim 1 , further comprising Ca: 0.0005 to 0.01% by mass. 6. The high Young's modulus steel plate according to claim 1, characterized in that it further contains one or more of Sn, Co, Zn, W, Zr, V, Mg, and REM, and their total content It is 0.001 to 1.0% by mass. 7 . The high Young's modulus steel sheet according to claim 1 , further comprising one or more of Ni, Cu, and Cr in a total content of 0.001 to 4.0% by mass. 8 . A hot-dip galvanized steel sheet comprising the high Young's modulus steel sheet according to claim 1 , and hot-dip galvanizing applied to the high Young's modulus steel sheet. 9. A galvanized alloyed steel sheet comprising the high Young's modulus steel sheet according to claim 1 and the galvanized alloyed steel sheet applied on the high Young's modulus steel sheet. 10. A steel pipe with a high Young's modulus, comprising the steel plate with a high Young's modulus according to claim 1, wherein the steel plate with a high Young's modulus is wound in any direction. 11. The method of manufacturing a high Young's modulus steel plate according to claim 1, comprising a step of heating a slab to a temperature of 950° C. or higher to perform hot rolling to produce a hot-rolled sheet, the slab Contains C: 0.0005-0.30%, Si: 2.5% or less, Mn: 2.7-5.0%, P: 0.15% or less, S: 0.015% or less, Mo: 0.15-1.5%, B: 0.0006-0.01% by mass % , Al: 0.15% or less, and the balance is composed of Fe and unavoidable impurities; wherein the hot rolling process is carried out under the following conditions: below 800°C, the friction coefficient between the roll and the steel plate exceeds 0.2, and the total reduction rate Rolling is performed so as to be 50% or more, and hot rolling is completed at a temperature from the Ar3 transformation point to 750°C. 12. The manufacturing method of the high Young's modulus steel plate according to claim 11, characterized in that, in the hot rolling process, at least one pass is carried out with a different circumferential rate of 1% or more. Speed rolling. 13. The method of manufacturing a high Young's modulus steel sheet according to claim 11, wherein at least one roll having a roll diameter of 700 mm or less is used in the hot rolling step. 14. The manufacturing method of high Young's modulus steel plate according to claim 11, characterized in that, it also has the step of using continuous annealing line or box annealing for the hot-rolled steel plate after the hot rolling to reach a maximum temperature of 500 The annealing process is carried out under the condition of ℃～950℃. 15. The method of manufacturing a high Young's modulus steel sheet according to claim 11, further comprising the step of cold rolling the hot-rolled steel sheet after the hot rolling at a reduction ratio lower than 60%. , and a step of annealing after the cold rolling step. 16. The manufacturing method of the high Young's modulus steel plate according to claim 11, further comprising the step of cold-rolling the hot-rolled steel plate at a reduction rate lower than 60%; a step of annealing at a maximum temperature of 500°C to 950°C after the cold rolling step; and a step of cooling to 550°C or less after the annealing step, and then heat-treating at 150°C to 550°C. 17. A method for manufacturing a hot-dip galvanized steel sheet, comprising: a step of manufacturing an annealed high Young's modulus steel sheet by the method for manufacturing a high Young's modulus steel sheet according to claim 14; The high Young's modulus steel plate is subjected to the process of hot-dip galvanizing. 18. A method for manufacturing an alloyed hot-dip galvanized steel sheet, characterized in that it has: a step of manufacturing a hot-dip galvanized steel sheet by the method for manufacturing a hot-dip galvanized steel sheet according to claim 17; A process in which a galvanized steel sheet is heat-treated at a temperature range of 450 to 600°C for 10 seconds or more. 19. A method for manufacturing a hot-dip galvanized steel sheet, comprising: a step of manufacturing an annealed high Young's modulus steel sheet by the method for manufacturing a high Young's modulus steel sheet according to claim 15; The high Young's modulus steel plate is subjected to the process of hot-dip galvanizing. 20. A method for manufacturing an alloyed hot-dip galvanized steel sheet, characterized in that it has: a step of manufacturing a hot-dip galvanized steel sheet by the method for manufacturing a hot-dip galvanized steel sheet according to claim 19; A process in which a galvanized steel sheet is heat-treated at a temperature range of 450 to 600°C for 10 seconds or more. 21. A method for manufacturing a high Young's modulus steel pipe, characterized in that, comprising: a step of manufacturing a high Young's modulus steel plate by the method for manufacturing a high Young's modulus steel plate according to claim 11; A high Young's modulus steel plate is wound in any direction to form a steel pipe. 22. A steel plate with a high Young's modulus, characterized by containing C: 0.0005% to 0.30%, Si: 2.5% or less, Mn: 0.1 to 5.0%, P: 0.15% or less, and S: 0.015% in mass % Below, Al: 0.15% or less, N: 0.01% or less; and also contains Mo: 0.005 to 1.5%, Nb: 0.005 to 0.20%, Ti: 48/14×N (mass%) to 0.2%, B: 0.0001 to 0.01% of one or more kinds, the total is 0.015 to 1.91% by mass; and the balance is composed of Fe and unavoidable impurities; among them, {110}<223> and/or in the 1/8 layer of the plate thickness Or the pole density of {110}<111> is 10 or more, and the Young's modulus in the rolling direction exceeds 230 GPa. 23. The high Young's modulus steel plate according to claim 22, characterized in that it contains all of said Mo, Nb, Ti, and B, and their contents are respectively Mo: 0.15-1.5%, Nb: 0.01-0.20 %, Ti: 48/14×N (mass %) to 0.2%, B: 0.0006 to 0.01%, and the pole density of {110}<001> of the 1/8 layer of the plate thickness is 3 or less. 24 . The high Young's modulus steel plate according to claim 22 , wherein the pole density of {110}<001> of the 1/8 layer of the plate thickness is 6 or less. 25. The high Young's modulus steel sheet according to claim 22, wherein the Young's modulus in the rolling direction at least 1/8 layer away from the surface layer of the plate thickness is 240 GPa or more. 26 . The high Young's modulus steel sheet according to claim 22 , wherein the pole density of {211}<011> in a half layer of the sheet thickness is 6 or more. 27 . The high Young's modulus steel plate according to claim 22 , wherein the pole density of {332}<113> in a half layer of the plate thickness is 6 or more. 28 . The high Young's modulus steel sheet according to claim 22 , wherein the pole density of {100}<011> of a half layer of the sheet thickness is 6 or less. 29. The high Young's modulus steel plate according to claim 22, characterized in that, after stretching by 2%, it is heat-treated at 170° C. for 20 minutes and the upper yield point when stretching again is performed minus 2% of stretching The BH amount evaluated by the difference of the flow stress at the time is 5MPa～200MPa. 30. The high Young's modulus steel plate according to claim 22, further comprising Ca: 0.0005 to 0.01% by mass. 31. The high Young's modulus steel plate according to claim 22, characterized in that it further contains one or more of Sn, Co, Zn, W, Zr, V, Mg, and REM, and their total content It is 0.001 to 1.0% by mass. 32. The high Young's modulus steel sheet according to claim 22, further comprising one or more of Ni, Cu, and Cr in a total content of 0.001 to 4.0% by mass. 33. A hot-dip galvanized steel sheet comprising the high Young's modulus steel sheet according to claim 22, and hot-dip galvanized coating applied to the high Young's modulus steel sheet. 34. An alloyed hot-dip galvanized steel sheet, characterized in that it has the high Young's modulus steel sheet according to claim 22, and an alloyed hot-dip galvanized steel sheet applied on the high Young's modulus steel sheet. 35. A steel pipe with a high Young's modulus, comprising the steel plate with a high Young's modulus according to claim 22, wherein the steel plate with a high Young's modulus is wound in any direction. 36. The method of manufacturing a high Young's modulus steel sheet according to claim 22, characterized in that it includes a step of heating a slab to a temperature of 1000° C. or higher to perform hot rolling to produce a hot-rolled sheet, the slab Contains C: 0.0005% to 0.30%, Si: 2.5% or less, Mn: 0.1 to 5.0%, P: 0.15% or less, S: 0.015% or less, Al: 0.15% or less, N: 0.01% or less; and Also contains one or more of Mo: 0.005-1.5%, Nb: 0.005-0.20%, Ti: 48/14×N (mass%)-0.2%, B: 0.0001-0.01%, totaling 0.01 5 ～1.91% by mass; and the balance is composed of Fe and unavoidable impurities; wherein the hot rolling process is carried out under the following conditions: the friction coefficient between the roll and the steel plate exceeds 0.2, and the effective variable calculated by the following formula [1] ε ^* is 0.4 or more and the total rolling reduction is 50% or more, and the hot rolling is completed at a temperature from the Ar ₃ transformation point to 900°C, $\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; *</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; -</span>\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ]</span>$ In the formula, n is the number of stands in the finishing hot rolling mill, ε _j is the strain applied to the jth stand, ε _n is the strain applied to the nth stand, and t _i is the i-th stand to the i+1th stand The running time (seconds) between and τ _i can be calculated by the following formula [2] through the gas constant R (=1.987) and the rolling temperature T _i (K) of the i-th stand, τ _i =8.46×10 ⁻⁹ ×exp{43800/R/T _i } [2]. 37. The method for manufacturing a high Young's modulus steel sheet according to claim 36, wherein, in the hot rolling process, at least one pass or more of a different circumferential rate of 1% or more is applied. Speed rolling. 38. The method of manufacturing a high Young's modulus steel sheet according to claim 36, wherein at least one roll having a roll diameter of 700 mm or less is used in the hot rolling step. 39. The manufacturing method of high Young's modulus steel plate according to claim 36, characterized in that, it also has the step of annealing the hot-rolled steel plate after the hot rolling with a continuous annealing line or box annealing at a maximum temperature of 500 The annealing process is carried out under the condition of ℃～950℃. 40. The method for manufacturing a high Young's modulus steel sheet according to claim 36, further comprising the step of cold rolling the hot-rolled steel sheet after the hot rolling at a reduction rate lower than 60%. , and a step of annealing after the cold rolling step. 41. The method for manufacturing a high Young's modulus steel sheet according to claim 36, further comprising: cold rolling the hot-rolled steel sheet at a reduction rate lower than 60%; After the cold rolling step, annealing is carried out under the condition that the maximum temperature reaches 500°C to 950°C; and after the annealing step, the temperature is cooled to 550°C or lower, followed by heat treatment at 150°C to 550°C. 42. A method for manufacturing a hot-dip galvanized steel sheet, comprising a step of manufacturing an annealed high Young's modulus steel sheet by the method for manufacturing a high Young's modulus steel sheet according to claim 39 , and The high Young's modulus steel plate is subjected to the process of hot-dip galvanizing. 43. A method for manufacturing an alloyed hot-dip galvanized steel sheet, comprising: a step of manufacturing a hot-dip galvanized steel sheet by the method for manufacturing a hot-dip galvanized steel sheet according to claim 42, and applying the heat to the hot-dip galvanized steel sheet A process in which a galvanized steel sheet is heat-treated at 450 to 600° C. for 10 seconds or more. 44. A method for manufacturing a hot-dip galvanized steel sheet, comprising a step of manufacturing an annealed high Young's modulus steel sheet by the method for manufacturing a high Young's modulus steel sheet according to claim 40, and The high Young's modulus steel plate is subjected to the process of hot-dip galvanizing. 45. A method for manufacturing an alloyed hot-dip galvanized steel sheet, comprising: a step of manufacturing a hot-dip galvanized steel sheet by the method for manufacturing a hot-dip galvanized steel sheet according to claim 44, and applying the heat to the hot-dip galvanized steel sheet A process in which a galvanized steel sheet is heat-treated at 450 to 600° C. for 10 seconds or more. 46. A method for manufacturing a high Young's modulus steel pipe, comprising: a step of manufacturing a high Young's modulus steel plate by the method for manufacturing a high Young's modulus steel plate according to claim 36, and said A high Young's modulus steel plate is wound in any direction to form a steel pipe.

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