WO2020158823A1 - H-shaped steel having protrusions, and manufacturing method for same - Google Patents

Abstract

Provided are an H-shaped steel having protrusions and a production method for same, the H-shaped steel ensuring tensile strength, being capable of suppressing the occurrence of surface cracking during continuous casting, and having dramatically improved manufacturability.　A steel composition in which C: 0.05-0.20 mass%, Si: 0.05-0.60 mass%, Mn: 1.20-1.70 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, Nb: 0.005-0.050 mass%, V: 0.005-0.050 mass%, Ti: 0.005-0.030 mass% and N: 0.0020-0.0100 mass% are included in a range satisfying ([%S]/32)/([%Ti]/48)+4×([%N]/14)/([%Ti]/48)≤15.0, the remainder being Fe and unavoidable impurities, the tensile strength being at least 490 MPa, the yield strength being at least 355 MPa, and the impact absorption energy vE0 at O°C being at least 27J.

Description

H-section steel with protrusion and method for manufacturing the same

The present invention relates to a H-section steel with protrusions and a method for manufacturing the same, and in addition to being excellent in mechanical properties such as tensile strength and elongation, which is a substitute for a reinforcing bar used as a reinforcing material for a large structure such as a bridge pier, it has excellent toughness. Also relates to a H-shaped steel with protrusions and a method for manufacturing the same.

　For large structures such as bridge piers, reinforced concrete using reinforcing bars is widely used as a reinforcing material. Generally, the construction of a reinforced concrete structure is performed by assembling the reinforcing bars, installing a formwork, and placing concrete in the formwork. Here, when it is necessary to dispose the reinforcing bars densely in terms of strength, not only the filling property of concrete is deteriorated, the construction quality is deteriorated, but also the construction is prolonged, which is a major problem. In addition, the number of skilled workers engaged in the construction is declining year by year, and there is a further demand for the development of structural steel that contributes to labor saving on site work and shortening the construction period.

In response to such a request, various studies have been conducted on H-section steel with a protrusion that has a greater cross-sectional rigidity than rebar and can reduce the number of necessary members in the same structure. It is known that this H-section steel with a projection has a projection on the outer surface of the flange and has a high concrete adhesion performance equal to or higher than that of a reinforcing bar. In order to guarantee the performance as a structure, the H-section steel with protrusions used for a large structure as a substitute for a reinforcing bar is required to have toughness in addition to mechanical properties such as tensile strength and elongation.

In order to satisfy these requirements, for example, Patent Document 1 discloses a H-section steel with protrusions in which tensile strength and toughness are enhanced in a well-balanced manner by adjusting the addition amounts of Nb, V and Ni in the steel. There is. Further, in Patent Document 2, for the purpose of improving the toughness of the H-shaped steel with protrusions, there is a technique of setting an optimum cooling stop temperature according to the flange thickness and appropriately adjusting the amount of cooling water on the inner and outer surfaces of the flange. It is disclosed.

Japanese Patent No. 4045977 JP 2006-75883

However, the H-section steel with protrusions described in Patent Documents 1 and 2 described above has both high tensile strength and toughness by adding Nb and V that form carbonitride, but it is a rolled material by continuous casting. When manufacturing the steel, there is a problem that defects on the surface of the slab called so-called continuous casting cracks are likely to occur and the manufacturability is reduced. The present invention has been made in order to advantageously solve the above-mentioned problems. As compared with the conventional H-section steel with a projection, the H-section with a projection that can dramatically improve the productivity while ensuring a tensile strength equal to or higher than that of the conventional H-section steel with a projection. It is an object to provide a shaped steel together with its manufacturing method.

The present inventors have made H-shaped steel with protrusions in which the contents of C, Si, Mn, P, S, Nb, V, Ti and N are changed, and have made earnest investigations on tensile properties and toughness. As a result, it was found that the rate of continuous casting cracking was high when Nb or V was contained in the steel. Furthermore, by optimizing the amounts of S, Ti, and N contained in the steel, continuous casting cracks can be stabilized and suppressed even when Nb and V are contained. It has been found that by promoting the ferrite transformation, excellent toughness can be obtained.

The present invention is based on the above findings of the present invention, and its gist is as follows.
1. C: 0.05 to 0.20 mass%, Si: 0.05 to 0.60 mass%, Mn: 1.20 to 1.70 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, Nb: 0.005 to 0.050 mass%, V: 0.005 to 0.050% by mass, Ti: 0.005 to 0.030% by mass, and N: 0.0020 to 0.0100% by mass are contained within the range satisfying the following formula (1), and the balance has a steel composition of Fe and unavoidable impurities, and has a tensile strength. H-shaped steel with protrusions having a strength of 490 MPa or more, a yield strength of 355 MPa or more, and an impact absorption energy vE0 of 27 J or more at 0°C.
Note ([%S]/32)/([%Ti]/48)+4×([%N]/14)/([%Ti]/48)≦15.0 ・・・(1)
Here, [%S], [%Ti] and [%N] are the contents (mass %) of S, Ti and N in the steel, respectively.

2. The steel composition further comprises Cr: 1.0 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Mo: 1.0 mass% or less, Al: 0.10 mass% or less, B: 0.010 mass% or less, Ca. The protrusion H-shaped steel according to the above 1, containing one or more selected from the group consisting of: 0.10 mass% or less, Mg: 0.10 mass% or less, and REM: 0.10 mass% or less.

3. The H-shaped steel with a protrusion according to 1 or 2 above, wherein the protrusion has a height of 1.5 mm or more.

4. A method for producing a H-section steel with protrusions, comprising hot rolling a steel material having the steel composition according to any one of 1 or 2 above to form H-section steel with protrusions,
After the finish rolling of the hot rolling, protrusions are formed on the outer surface of the flange of the H-shaped steel, and after the finish rolling, the average cooling rate from the cooling start temperature of 750°C or higher to 500°C: 0.1 to 30°C/s. A method for manufacturing an H-section steel with protrusions, which is cooled under the conditions of.

5. 5. The method for producing a H-section steel with protrusions according to 4 above, wherein the finish rolling is performed at a temperature of 800° C. or higher.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to manufacture the H-section steel with a protrusion which has the outstanding toughness stably, it contributes to the rapid construction realization of a large-scale structure, and the quality improvement of a concrete construction product, and an industrially beneficial effect. Is brought about.

The sectional view of H-section steel with a projection is shown. It is a figure which shows H-section steel with a protrusion, (a) is the side view seen from the opposing direction of a web, (b) is the top view seen from the opposing direction of a flange outer surface, (c) is the upper surface of a flange outer surface. The figures are respectively shown.

The present invention will be specifically described below. First, in the present invention, the reason why the steel composition is limited to the above range will be described. In addition, "%" in the following description represents "mass %" unless otherwise specified.

C: 0.05 to 0.20%
C is an element necessary to secure the strength of the base material and needs to be contained at least 0.05%. However, if the C content exceeds 0.20%, not only the toughness of the base material is lowered but also the weldability is lowered. Therefore, in the present invention, the C content is set to 0.05 to 0.20%. The C content is preferably 0.10% or more. Further, the C content is preferably 0.15% or less.

Si: 0.05 to 0.60%
Si must be contained in the base metal at a strength of 0.05% or more as a deoxidizing agent, but if the Si content exceeds 0.60%, the toughness decreases and the high bond strength of Si with oxygen is high. Therefore, the weldability deteriorates. Therefore, in the present invention, the Si content is set to 0.05 to 0.60%. The Si content is preferably 0.20% or more. Further, the Si content is preferably 0.40% or less.

Mn: 1.20 ~ 1.70%
Like Si, Mn is a relatively inexpensive element that has the effect of increasing the strength of steel, so it is an important element for increasing strength. However, if the Mn content is less than 1.20%, the effect of addition is small, while if it exceeds 1.70%, the upper bainite transformation is promoted and the toughness is lowered, which is not preferable. Therefore, in the present invention, the Mn content is set to 1.20 to 1.70%. The Mn content is preferably 1.40% or more. Further, the Mn content is preferably 1.60% or less.

P: 0.035% or less When the content of P exceeds 0.035%, the ductility of steel deteriorates. Therefore, in the present invention, the amount of P in steel is 0.035% or less. It is preferably 0.020% or less. On the other hand, the smaller the P content, the more preferable, so the lower limit of the P content is not particularly limited and may be 0%. However, P is usually an element that is unavoidably contained in steel as an impurity, and excessive reduction in P causes an increase in refining time and an increase in cost, so the P content should be 0.005% or more. preferable.

S: 0.035% or less
When S is contained in steel, it is mainly present in the steel material in the form of A-type inclusions. If the S content exceeds 0.035%, the amount of the inclusions increases remarkably, and at the same time, coarse inclusions are formed, which greatly reduces the toughness of the steel. Therefore, in the present invention, the S content in steel is 0.035% or less. It is preferably 0.020% or less. On the other hand, the smaller the amount of S, the more preferable. Therefore, the lower limit of the S content is not particularly limited and may be 0%. Usually, S is an element that is unavoidably contained in steel as an impurity, and excessive reduction of S causes increase in refining time and cost, so the S content should be 0.002% or more. preferable.

Nb: 0.005 to 0.050%
Nb is an element having the effect of improving tensile strength and yield point by precipitating as carbonitride. To obtain this effect, the Nb content needs to be 0.005% or more. On the other hand, if the Nb content exceeds 0.050%, in addition to promoting precipitation embrittlement, it also promotes upper bainite transformation, so continuous casting cracks are likely to occur, and toughness is also reduced. Therefore, in the present invention, the Nb content is 0.005 to 0.050%. The Nb content is preferably 0.010% or more. Further, the Nb content is preferably 0.030% or less.

V: 0.005 to 0.050%
V is an element having the effect of improving tensile strength and yield point by precipitating as carbonitride. In order to obtain this effect, the V content needs to be 0.005% or more. On the other hand, when the V content exceeds 0.050%, precipitation embrittlement is promoted, and continuous casting cracks are likely to occur. Therefore, in the present invention, the V content is set to 0.005 to 0.050%. The V content is preferably 0.010% or more. Further, the V content is preferably 0.030% or less.

Ti: 0.005-0.030%
Ti is a useful element effective in preventing surface cracking during bending-unbending during continuous casting, and is positively added in the range of 0.005% or more. Further, Ti is an element effective in improving the toughness by forming TiN in the steel to refine the austenite grains and further promoting the intragranular ferrite transformation centered on TiN to refine the microstructure. On the other hand, if the Ti content exceeds 0.030%, coarse TiN is generated and the toughness of the steel is reduced, which is not preferable. Therefore, in the present invention, the Ti content is 0.005 to 0.030%. The Ti content is preferably 0.010% or more. Further, the Ti content is preferably 0.020% or less.

N: 0.0020-0.0100%
N is a useful element that forms carbonitrides in steel and improves the strength of steel, and its content must be 0.0020% or more. However, if the N content exceeds 0.0100%, the carbonitrides formed become coarse and the toughness of the steel decreases. Further, when the N content exceeds 0.0100%, surface cracking of the cast piece occurs, and the cast piece quality deteriorates, which is not preferable. Therefore, in the present invention, the N content is set to 0.0020 to 0.0100%. The N content is preferably 0.0030% or more. Further, the N content is preferably 0.0070% or less.

Further, in the present invention, it is not sufficient that each element simply satisfies the above range, and for S, Ti and N, [%S], [%Ti] and [%N] are respectively contained in the steel. When the contents of S, Ti and N (mass %) are set, it is important to satisfy the relationship of the following formula (1).
([%S]/32)/([%Ti]/48)+4×([%N]/14)/([%Ti]/48)≦15.0・・・(1)

The inventors investigated the cause of cracking in steel during continuous casting, and found that coarse MnS and V and Nb carbonitride precipitates on ferrite formed in austenite grain boundaries during continuous casting. I got the knowledge that it was the cause. Therefore, a study was conducted to suppress the precipitation of MnS and V and Nb-based carbonitrides in the ferrite, and by adjusting the contents of S, Ti and N in the steel, it was found that It has been found that the precipitation of MnS with V and Nb-based carbonitrides can be suppressed to suppress cracking during continuous casting. That is, the value calculated by the left side of the above equation (1), which is a parameter based on the contents of S, Ti, and N, does not exceed 15.0, so that S is precipitated as Ti carbosulfide and N is precipitated as TiN. Thus, precipitation of coarse MnS and V and Nb-based carbonitrides on ferrite generated in the austenite grain boundaries during continuous casting can be suppressed, and continuous casting cracks can be stably suppressed. It is more preferable that the right side of the above formula (1) is 10.0 or less, that is, the following formula (1)′ is satisfied.
([%S]/32)/([%Ti]/48)+4×([%N]/14)/([%Ti]/48)≦10.0・・・(1)'

In the steel composition of the H-section steel with protrusions used in the present invention, the balance other than the components described above is Fe and inevitable impurities.
Further, in the H-section steel with protrusions of the present invention, in addition to the components described above, Cr: 1.0% or less, Cu: 1.0% or less, Ni: 1.0% or less for the purpose of improving strength, ductility, toughness, and weld property. % Or less, Mo: 1.0% or less, Al: 0.10% or less, B: 0.010% or less, Ca: 0.10% or less, Mg: 0.10% or less, REM: 0.10% or less. It may optionally contain.
Hereinafter, the reasons for specifying the contents of the above elements will be described.

Cr: 1.0% or less Cr is an element that can further strengthen the steel by solid solution strengthening. However, if its content exceeds 1.0%, the upper bainite transformation is promoted and the toughness is lowered, which is not preferable. Therefore, when the chemical composition of steel contains Cr, the Cr content is 1.0% or less. It is more preferably 0.005% or more and 0.5% or less.

Cu: 1.0% or less Cu is an element that can further strengthen the steel by solid solution strengthening. However, if the content exceeds 1.0%, Cu cracking tends to occur. Therefore, if the composition of the steel contains Cu, the Cu content should be 1.0% or less. It is more preferably 0.005% or more and 0.5% or less.

Ni: 1.0% or less Ni is an element that can increase the strength of steel without deteriorating ductility. Moreover, since Cu cracking can be suppressed by adding Cu together, it is desirable that Ni is also contained when the steel composition contains Cu. However, if the Ni content exceeds 1.0%, the hardenability of steel further increases and the toughness tends to decrease. Therefore, when the steel composition contains Ni, the Ni content is 1.0% or less. It is more preferably 0.005% or more and 0.5% or less.

Mo: 1.0% or less Mo is an element that can further strengthen the steel by solid solution strengthening. However, if the content exceeds 1.0%, a large amount of upper bainite is generated in the steel, and the toughness tends to decrease. Therefore, when the component composition contains Mo, the Mo content is 1.0% or less. It is more preferably 0.005% or more and 0.5% or less.

Al: 0.10% or less Al is an element that can be added as a deoxidizing agent. However, when the Al content exceeds 0.10%, a large amount of oxide inclusions are generated in the steel due to the high binding force of Al with oxygen, and as a result, the ductility of the steel decreases. Therefore, when the steel composition contains Al, the Al content is preferably 0.10% or less. On the other hand, the lower limit of the Al content is not particularly limited, but it is preferably 0.001% or more for deoxidation. More preferably, it is 0.001% or more and 0.03% or less.

B: 0.010% or less B is an element having the effect of segregating to the grain boundaries in steel and improving the grain boundary strength. It is also an element effective for improving toughness by forming a composite precipitate with TiN, which becomes the nucleation site of intragranular ferrite, and refining the microstructure. On the other hand, if its content exceeds 0.010%, the toughness decreases due to the precipitation of coarse carbonitrides at the grain boundaries. Therefore, when the steel composition contains B, the B content is 0.010% or less. It is more preferably 0.001% or more and 0.003% or less.

Ca: 0.10% or less Ca has a function of converting the oxides and sulfides in the sulfide-based inclusions into those having high stability at high temperatures, and granulating the sulfide-based inclusions. The toughness and ductility of the steel can be improved by the effect of Ca to control the morphology of inclusions. However, if the Ca content exceeds 0.10%, the cleanliness tends to decrease and the toughness tends to decrease. Therefore, when the steel composition contains Ca, the Ca content is 0.10% or less. It is more preferably 0.0010% or more and 0.0050% or less.

Mg: 0.10% or less Mg has the function of transforming the oxides and sulfides in the sulfide-based inclusions into those having high stability at high temperatures and granulating them. Then, the toughness and ductility of the steel can be improved by the effect of controlling the morphology of inclusions by this Mg. However, if the Mg content exceeds 0.10%, the cleanliness tends to decrease and the toughness tends to decrease. Therefore, when the steel composition contains Mg, the Mg content is 0.10% or less. It is more preferably 0.0010% or more and 0.0050% or less.

REM: 0.10% or less REM (rare earth metal) has the effect of transforming oxides and sulfides in sulfide-based inclusions into those with high stability at high temperatures, and granulating sulfide-based inclusions. .. Then, the toughness and ductility of the steel can be improved by the effect of controlling the morphology of inclusions by the REM. However, if the REM content exceeds 0.10%, the cleanliness tends to decrease and the toughness tends to decrease. Therefore, if the steel composition contains REM, the REM content should be 0.10% or less. It is more preferably 0.0010% or more and 0.0050% or less.
The balance other than the elements described above is Fe and inevitable impurities.

The H-shaped steel with protrusions of the present invention will be described in detail. That is, as shown in FIG. 1, the H-section steel with protrusions is formed by connecting a pair of flanges 2 with a web 3 similarly to a general H-section steel. The H-section steel with protrusions has protrusions 4 on the outer surface of the flange 2. The projections 4 are provided to give concrete adhesion performance. In the H-shaped steel with projection 1 provided with the projection 4 for this purpose, the location where the projection 4 is provided is the outer surface of the flange 2 as shown in FIG. In the illustrated example, the entire outer surface of the flange 2 is an enlarged view of a portion surrounded by a square in FIG. 2A. The protrusions 4 are formed so as to be arranged in the longitudinal direction of the flange 2.

Note that the shape, size, and number of protrusions can be set arbitrarily according to the specifications required for H-section steel with protrusions. Therefore, although not limited to the illustrated example, for example, the height h of the projection 4 is preferably 1.5 mm or more in consideration of the concrete adhesion performance. On the other hand, the upper limit of the height h is preferably 6 mm from the viewpoint of preventing roll breakage. Further, the distance d between the protrusions 4 preferably satisfies the relationship of h/d≧0.05 with the height h in consideration of the concrete adhesion performance.

Next, a method for manufacturing the H-section steel with protrusions of the present invention will be described. There is no particular limitation on the melting method and the casting method of steel (slab or beam blank), and any conventionally known method is suitable. Further, the hot rolling conditions for forming the H-shaped steel are not particularly limited and may be carried out according to a conventional method. In the finish rolling of the hot rolling, the protrusion can be formed by using a roll having a groove corresponding to the protrusion to be formed on the surface of the roll as a roll for rolling down the portion (flange outer surface) where the protrusion is formed. After finish rolling, it is necessary to perform cooling satisfying the following conditions.

Flange temperature at the start of cooling: 750°C or higher In the present invention, the flange temperature at the start of cooling is set to 750°C or higher in order to prevent a decrease in production efficiency by starting cooling of the steel material immediately after finish rolling. To do. On the other hand, if the flange temperature at the start of cooling is less than the Ar ₃ temperature, it becomes difficult to obtain sufficient strength, so it is preferable to further set the flange temperature at the start of cooling to the Ar ₃ temperature or higher. The Ar ₃ transformation temperature is simply shown in relation to the steel composition by the following equation (2), for example.
Ar ₃ =910-310×[%C]+25×([%Si]+2×[%Al])-80×[Mneq] ・・・(2)
Here, [Mneq] is a value calculated by the following equation (3).
[Mneq]=[%Mn]+[%Cr]+[%Cu]+[%Mo]+[%Ni]/2+10×([%Nb]-0.02)・・・(3)
In the expressions (2) and (3), [%M] means the content (mass %) of the element M in the steel. Here, in calculating Ar ₃ by the above formulas (2) and (3), regarding the content of the element M not positively contained, the content of the element M contained as an unavoidable impurity ( It should be calculated using the analysis value).

Average cooling rate from cooling start temperature to 500℃: 0.1～30℃/s
If the average cooling rate from the cooling start temperature to 500°C is less than 0.1°C/s, it is difficult to secure the predetermined tensile properties and toughness, so the cooling rate is 0.1°C/s or more. On the other hand, when the cooling rate becomes higher than 30°C/s, adverse effects such as decrease in toughness and excessive increase in tensile strength occur due to the formation of bainite or martensite. The cooling rate is in the range of 0.1 to 30°C/s. The preferable average cooling rate is in the range of 0.5 to 10°C/s.

By adjusting the above-mentioned composition and rolling and cooling according to the above conditions, the H-shaped steel with projections has a tensile strength of 490 MPa or more, a yield strength of 355 MPa or more, and an impact absorption energy vE0 of 27 J at 0°C. As described above, excellent mechanical performance can be obtained. Although it is not necessary to specify the upper limit for any of the characteristics, practically, the tensile strength is 640 MPa, the yield strength is 475 MPa, and the impact absorption energy vE0 at 0° C. is about 350 J.

Here, the flange thickness of the H-section steel with protrusions that is the subject of the present invention is not particularly limited. The protrusion on the outer surface of the flange is formed by using a grooved roll in the finish rolling process. That is, it is necessary to increase the amount of reduction of the flange portion as much as possible in order to give a desired protrusion height. Therefore, a protruding H-section steel with a thick flange requires greater reduction. As will be described later, in the present invention, by controlling the rolling temperature within an appropriate range, it is said that the formation efficiency of the projection height is lowered. Even in the case of a thick H-section steel with a flange thickness of 16 mm or more, a sufficient projection height can be obtained. Can be granted.

In finish rolling for forming protrusions during hot rolling, the finish rolling temperature is preferably 800°C or higher from the viewpoint of forming protrusions having a sufficient protrusion height. If the finishing rolling temperature is less than 800°C, it is difficult to stably form protrusions of sufficient height. On the other hand, the upper limit of the finishing temperature is not particularly limited, but if it exceeds 1050° C., the austenite grain size becomes coarse and the toughness tends to decrease. Therefore, the finishing temperature is preferably 1050° C. or lower.

Hereinafter, the configuration and operational effects of the present invention will be described more specifically according to the examples. However, the present invention is not limited by the following examples, and can be appropriately modified within a range compatible with the spirit of the present invention, and these are all included in the technical scope of the present invention. Be done.

A steel blank having the composition shown in Table 1 was used as a beam blank having a cross section of 400 mm×560 mm×length of 8000 mm by a continuous casting machine, and the presence or absence of cracks on the surface was examined. That is, the surface of the beam blank was observed in the longitudinal direction and examined for cracks having a length of 10 mm or more. Surface cracks obtains the number of cracks per 1 m ^2, A: no cracks, B: 1 ~ 4 pieces ^/ m 2, C: evaluated using an index of 5 or more / ^{m 2,} A or B in the index Those judged were accepted. Table 1 also shows the results of surface crack determination. In the steel having a steel composition satisfying the above formula (1), the surface cracking judgment result was A or B.

Next, among these beam blanks, those having a surface crack determination result of A or B were heated at 1250° C. for 2 hours, then hot-rolled and cooled under the conditions shown in Table 2, and shown in FIG. A H-section steel 1 with a protrusion having a cross-sectional shape, that is, a shape having a web 3 and a pair of flanges 2 arranged at both ends of the web was manufactured. Here, the cross-sectional dimension (web height x flange width x web thickness x flange thickness) is one of two types of 320 x 323 x 25 x 25 mm and 350 x 333 x 35 x 40 mm. Manufactured steel. In finish rolling, a rolling roll having a groove corresponding to the projection shape to be formed on the flange outer surface is used as a rolling roll for rolling down the flange outer surface, and the flange outer surface extends in the width direction of the flange 2 as shown in FIG. The existing projections 6 were formed. Here, the finish rolling roll that rolls down the outer surface of the flange is provided with a groove capable of forming a protrusion having a protrusion width w of 15 mm and a protrusion height h of 1.5 mm or more. The cooling rate after finish rolling is measured by measuring the temperature of the outer surface of the flange with a radiation thermometer and converting the temperature change from the start of cooling to the end of cooling per unit time (seconds) to obtain the cooling rate (°C/ s) was calculated.

The obtained H-section steel with protrusions was subjected to protrusion height evaluation, tensile test and toughness test. The details of each evaluation will be described below in detail.

<Evaluation of protrusion height>
With respect to the obtained H-section steel with protrusions, the protrusion height h on the outer surface of the flange shown in FIG. 2 was measured. Such a value was measured at three points in the rolling direction of the H-section steel with protrusions after finish rolling in the rolling direction, the center portion and the tail end portion, and the average value was adopted. The lower limit of the required performance of the protrusion height was set to 1.5 mm, and a value above this value was defined as a suitable range of the protrusion height h. Further, the manufacturing conditions under which the H-shaped steel with protrusions having the protrusion height h of not less than this value are obtained can be evaluated as particularly preferable conditions from the viewpoint of ease of forming the protrusions.

<Tensile test>
JIS 1A test specified in JIS Z 2201 so that the tensile direction is the flange longitudinal direction of H-section steel from the flange 1/6B part (60 mm in the flange width direction sandwiching 1/6B) shown as reference numeral 5 in FIG. A piece (flange full-thickness test piece) was sampled, a tensile test was performed according to JIS Z2241, and the yield strength (yield stress YS or 0.2% proof stress) and the tensile strength were measured.

<Toughness test>
A 2mmV notch Charpy impact test piece specified in JIS Z2202 was sampled from the back surface of the flange 1/6B portion 5 shown in FIG. A Charpy impact test was performed to measure the absorbed energy at 0°C.

Table 2 also shows the results of the above survey. Test results of the H-section steel with protrusions produced by the manufacturing method within the scope of the present invention (the average cooling rate of the outer surface of the flange is within the scope of the present invention) using a compatible steel satisfying the steel composition of the present invention (test No. in Table 2). .1 to 19, 31) all satisfied the desired properties (tensile strength: 490 MPa or more, yield strength: 355 MPa or more and impact absorption energy vE0: 27 J or more at 0° C.). Although Test No. 33 satisfied the desired properties with respect to tensile strength, yield strength, and impact absorption energy at 0°C, since the finishing rolling temperature was below the suitable lower limit of 800°C, the protrusion height Was 1.4 mm, which was less than the preferred range (1.5 mm or more).

On the other hand, comparative examples (test Nos. 20 to 30, 32 to 34 in Table 2) in which the steel composition of the H-section steel did not satisfy the conditions of the present invention or the manufacturing method within the scope of the present invention was not applied , Tensile strength, yield strength, or toughness does not satisfy the required characteristics.

1 H-section steel with protrusions (rolled H-section steel)
2 Flange 3 Web 4 Protrusion 5 Flange 1/6B part (test piece sampling position)

Claims (5)

C: 0.05 to 0.20 mass%, Si: 0.05 to 0.60 mass%, Mn: 1.20 to 1.70 mass%, P: 0.035 mass% or less, S: 0.035 mass% or less, Nb: 0.005 to 0.050 mass%, V: 0.005 to 0.050% by mass, Ti: 0.005 to 0.030% by mass, and N: 0.0020 to 0.0100% by mass are contained within the range satisfying the following formula (1), and the balance has a steel composition of Fe and unavoidable impurities, and has a tensile strength. H-shaped steel with protrusions having a strength of 490 MPa or more, a yield strength of 355 MPa or more, and an impact absorption energy vE0 of 27 J or more at 0°C.
Note ([%S]/32)/([%Ti]/48)+4×([%N]/14)/([%Ti]/48)≦15.0 ・・・(1)
Here, [%S], [%Ti] and [%N] are the contents (mass %) of S, Ti and N in the steel, respectively. The steel composition further comprises Cr: 1.0 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Mo: 1.0 mass% or less, Al: 0.10 mass% or less, B: 0.010 mass% or less, Ca. The protrusion H-shaped steel according to claim 1, containing one or more selected from the group consisting of: 0.10 mass% or less, Mg: 0.10 mass% or less, and REM: 0.10 mass% or less. The H-shaped steel with protrusion according to claim 1 or 2, wherein the protrusion has a height of 1.5 mm or more. A method for producing a H-section steel with protrusions, comprising hot rolling a steel material having the steel composition according to claim 1 or 2 to form H-section steel with protrusions,
After the finish rolling of the hot rolling, protrusions are formed on the outer surface of the flange of the H-shaped steel, and after the finish rolling, the average cooling rate from the cooling start temperature of 750°C or higher to 500°C: 0.1 to 30°C/s. A method for manufacturing an H-section steel with protrusions, which is cooled under the conditions of. The method for manufacturing a H-section steel with protrusions according to claim 4, wherein the finish rolling is performed at a temperature of 800°C or higher.

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