KR20190028481A - High yield strength steel plate - Google Patents

Abstract

The present invention relates to a high yield strength steel sheet wherein the yield strength can be increased without significantly affecting the ultimate tensile strength (UTS) and, as the case may be, a higher yield Strength can be obtained.

Description

High yield strength steel plate

The present application relates to high yield strength steels. Due to its inherent structure and mechanism, the yield strength can be increased without significantly affecting the ultimate tensile strength (UTS). In some cases, higher yield strengths can be obtained without significant reduction in ultimate tensile strength and total elongation. These new steels can be advantageous for a myriad of applications where relatively high tensile strength and total elongation as well as comparatively high yield strengths are required, such as passenger cages in automobiles.

The third generation of Advanced High Strength Steels (AHSS) is currently being developed for automotive applications, particularly automotive applications. Advanced high strength steels (AHSS) are classified into 4% to 30% elongation and tensile strength in excess of 700 MPa and are classified into martensitic steel, dual phase steel, TRIP (transformation induced plasticity steel) Organic sintered steel) and complex phase steel (CP). The object of the third generation AHSS can be seen on a banana chart of automotive steels announced at World Auto Steel (Fig. 1).

Tensile properties such as ultimate tensile strength (UTS) and total elongation are important criteria for establishing combinations of properties. However, AHSS steels are generally not classified by yield strength (YS). The yield strength of steels is important to automotive designers because once the part is working and the part is stressed beyond yielding, the part will be permanently deformed (plastically deformed). Steels with high yield strength resist permanent deformation at higher stress levels than steels with low yield strength. The resistance to this deformation is important to allow structures made of steels that can withstand larger loads before the structure is permanently deflected and deformed. This allows the automotive designer to reduce the weight of the associated parts by reducing the gauge while maintaining the same resistance to deformation of the part. Third generation AHSS of various types of grades suffer from low initial yield strengths despite having various combinations of tensile strength and ductility.

Automotive parts that cause premature yielding and permanent plastic deformation during normal operation will not be acceptable according to most design criteria. However, the lower the yield strength, especially when combined with a high strain hardening coefficient, can be advantageous in crashes. This is especially true at the front and rear ends of the car, often referred to as the crumple zone. In this area, a low yield strength material with higher ductility can enhance the strength that causes deformation and process deformation during impact, resulting in a high level of energy absorption due to high initial ductility.

Low yield strengths in other parts of the vehicle are not acceptable. Specifically, a car front passenger seat cage is included. Materials used as passenger cages must have a high yield strength, as deformation / intrusion to the passenger cage is extremely limited. Passage through the passenger seat cage can cause injury or death to a person in the car. Therefore, a material having a high yield strength is needed for such a portion.

The yield strength of the material can be increased in several ways on an industrial scale. The material is a process called temper rolling, which enables a small amount of cold rolling (less than 2% reduction (rolled amount)). The process causes a small amount of plastic deformation in the material and the yield strength of the material increases slightly corresponding to the deformation applied to the material during the temper rolling. Another way to increase the yield strength of a material is to reduce the grain size of the material known as Hall-Petch strengthening. If the grain size is small, the shear stress required for the initial dislocation movement of the material increases, and the initial strain is delayed until a high load is applied. The grain size can be reduced through process modifications such as recrystallization occurring during annealing after plastic deformation and altered annealing to limit grain growth in the growth process. It is possible to increase the yield strength of a compositionally deformable material to an alloy such as the addition of an alloying element present in a solid solution. However, the addition of such an alloying element must occur while the material is being melted and may lead to an increase in cost.

It is possible to develop a passive cage of high yield strength from AHSS having a low yield strength. However, it is difficult to uniformly strain-cure the final part in many metalworking operations. This means that there is a lower yield strength zone that can still be deformed, thereby causing unacceptable intrusion into the passenger seat cage, while the heavily cold worked area of the part has a much higher yield strength do.

Cold finished steels in a fully annealed state are known to increase yield strength and tensile strength. It can be uniformly applied to the entire sheet during cold rolling to increase yield strength and tensile strength. However, the process reduces the total elongation and often reduces it to levels far below 20%. As the elongation decreases, the cold forming ability decreases and the ability to produce components with complex shapes decreases, which also reduces the usefulness of AHSS. A high ductility of at least 30% elongation is generally required to form a composite shape through a cold stamping process. Processes such as roll forming can be used to produce parts with low elongation rates, but these processes have limitations in forming complex shapes of parts. Cold rolling can introduce anisotropy into the material, resulting in reduced cold formability.

a. Of at least 70 atomic% Fe and Si, Mn, Cr, Ni, and supplying a metal alloy comprising at least four or more element selected from Cu, or C, to melt the alloy, 10 ^-4 K / sec to 10 ³ Cooling at a rate of K / sec and solidifying to a thickness of > 5.0 mm to 500 mm;

b. Processing the alloy into a first sheet form having a thickness of 0.5 to 5.0 mm, the first sheet having a total elongation of X ₁ (%), an ultimate tensile strength of Y ₁ (MPa), and an ultimate tensile strength of Z ₁ Have yield strength;

c. Permanently deforming said alloy in a temperature range of from 150 DEG C to 400 DEG C to a second sheet form exhibiting one of the following tensile properties combinations A or B. < Desc / Clms Page number 13 >

A. (1) Total elongation X ₂ = X ₁ ± 7.5%;

(2) Ultimate tensile strength Y ₂ = Y ₁ ± 100 MPa; And

(3) Yield strength Z ₂ > Z ₁ + 100 MPa

B. (1) Ultimate tensile strength Y ₃ = Y ₁ ± 100 MPa; And

(2) Yield strength Z ₃ > Z ₁ + 200 MPa.

Optionally, the second sheet formed in step (c) exhibiting said tensile property combination A or B may be exposed to permanent deformation at a temperature of 150 ° C or lower.

Therefore,

a. Of at least 70 atomic% Fe and Si, Mn, Cr, Ni, and supplying a metal alloy comprising at least four or more element selected from Cu, or C, to melt the alloy, 10 ^-4 K / sec to 10 ³ Cooling at a rate of K / sec and solidifying to a thickness of > 5.0 mm to 500 mm;

b. Processing the alloy into a first sheet form having a thickness of 0.5 to 5.0 mm;

c. Permanently deforming said alloy in the form of a second sheet in a temperature range of from 150 캜 to 400 캜;

d. And permanently deforming said alloy in a second sheet form exhibiting the following combination of tensile properties at a temperature less than 150 < 0 > C.

(1) total elongation = 10.0 to 40.0%;

(2) Ultimate tensile strength = 1150 to 2000 MPa;

(3) Yield strength = 550 to 1600 MPa.

The metallic alloy produced in the present invention is particularly useful in vehicles, railway vehicles, railway tank cars / wagons, drill collars, drill pipes, pipe casings, welded joints, wellheads, compressed gas storage tanks or liquefied natural gas vessels. More specifically, the alloy is useful for white vehicle bodies, vehicle frames, chassis or panels.

The following detailed description is provided for purposes of illustration and is not to be construed as limiting the invention in any way, and may be better understood with reference to the accompanying drawings.
Figure 1 "Banana Plot" of World Auto Steel with the target characteristics of the third generation AHSS.
2 Summary of Method 1 for making high yield strength of the alloy of the present application.
Figure 3 Summary of Method 2 for making a combination of high yield strength and desired properties of the alloy of the present application.
Fig. 4 Ultimate tensile strength of an alloy before and after cold rolling.
Fig. 5 Tensile elongation of alloys before and after cold rolling.
Fig. 6 Yield strength of alloy before and after cold rolling.
7: Magnetic phase volume percent of the alloy before and after cold rolling.
Figure 8 Tensile stress-strain curves for alloy 2 after cold rolling with various reductions.
Fig. 9 Backscattering SEM picture of the microstructure of the hot band from alloy 2: a) low magnification image; b) High magnification image.
Figure 10 bright-field TEM photograph of the microstructure of the hot band from Alloy 2: a) low magnification image; b) High magnification image.
Figure 11 TEM photograph showing nanoparticles in a hot band from alloy 2.
Figure 12 Backscattering SEM picture of the microstructure of the cold rolled sheet from alloy 2: a) low magnification image; b) High magnification image.
Figure 13 TEM photograph of the microstructure of the cold rolled sheet from alloy 2: a) low magnification image; b) High magnification image.
Figure 14 TEM photograph showing nanoparticles found in two sheets of alloy after cold deformation.
Fig. 15 Engineering tensile stress-strain curves for alloy 2 after rolling with a 20% reduction at different temperatures.
Figure 16 Change in magnetic phase volume percent (Fe%) during tensile test of alloy 2.
Figure 17 Engineering strain-strain curves for alloy 7 after rolling with a 20% reduction at different temperatures.
Figure 18 Engineering stress-strain curve for alloy 18 after rolling with a 20% reduction at different temperatures.
Figure 19 Engineering stress-strain curve for alloy 34 after rolling with a 20% reduction at different temperatures.
Figure 20 Engineering strain-strain curve for alloy 37 after rolling with a 20% reduction at different temperatures.
Fig. 21 Representative engineering stress-strain curves for alloy 2 rolled at various degrees of rolling at 200 < 0 > C.
22 shows the yield strength and ultimate tensile strength of alloy 2 at 200 DEG C as a function of the rolling amount.
23 shows the yield strength and total elongation of alloy 2 at 200 DEG C as a function of rolling amount.
24 shows the effect of rolling at 200 DEG C on the strain-induced phase deformation of alloy 2 as a function of the rolling amount.
Figure 25 Backscatter SEM picture of the microstructure of the hot bands from Alloy 2: a) low magnification image; b) High magnification image.
Fig. 26 Backscattering SEM image of microstructure of alloy 2 after rolling at 200% at 30% rolling amount SEM photograph: a) low magnification image; b) High magnification image.
Fig. 27 Backscattering SEM picture of the microstructure of alloy 2 after rolling at 70% rolling at 200 DEG C SEM photograph: a) low magnification image; b) High magnification image.
FIG. 28 Bright TEM photographs of the microstructure of alloy 2 after rolling at a temperature of 200% at 10% rolling. TEM photograph: a) low magnification image; b) High magnification image.
FIG. 29 Bright TEM image of microstructure of alloy 2 after rolling at 200% at 30% rolling. TEM photograph: a) low magnification image; b) High magnification image.
Fig. 30 Bright TEM photograph of the microstructure of alloy 2 after rolling at 70% rolling at 200 DEG C TEM photograph: a) low magnification image; b) High magnification image.
Fig. 31 Engineering strain-strain curve of alloy 2 machined with a combination of rolling methods.
Fig. 32 Engineering strain-strain curve of alloy 7 machined with a combination of rolling methods.
Fig. 33 Engineering stress-strain curve of alloy 18 processed with a combination of rolling methods.
Fig. 34 Engineering strain-strain curve of alloy 34 machined in combination of rolling methods.
35 Comparison of engineering stress-strain curves of two alloy sheets processed in different methods and combinations thereof.
Figure 36 Tensile elongation and magnetic phase volume percent of tensile sample gauge after testing of alloy 2 at different temperatures.
Figure 37 The magnetic phase volume percentage at room temperature and 200 ° C is expressed as a function of the rolling amount.
Fig. 38 Engineering stress-strain curves of annealed sheets processed by cold rolling and rolling at 200 ^o C;
Fig. 39 Maximum rolling amount of alloy 2 vs rolling temperature.

This application is a priority application to U.S. Provisional Application No. 62 / 359,844, filed July 8, 2016, and U.S. Provisional Application No. 62 / 482,954, filed April 7, This application is herein incorporated by reference in its entirety.

Figure 2 shows a summary of a preferred method 1 for producing a high yield strength from a low yield strength material by a path leading to one of two conditions as provided in condition 3a or 3b. The starting condition in step 1 of method 1 is to supply a metallic alloy. Such a metallic alloy will comprise at least 4 atomic percent of at least 70 atomic percent iron and Si, Mn, Cr, Ni, Cu, The alloy composition is melted, preferably cooled at a rate of 10 ^-4 K / s to 10 ³ K / s, and solidified to a thickness of> 5.0 mm to 500 mm. The casting process may be carried out in various processes such as ingot casting, bloom casting, continuous casting, thin slab casting, thick slab casting, thin strip casting, belt casting, . A preferred method is continuous casting in sheet form by thin slab casting, thick slab casting, and sheet metal casting. Preferred alloys will exhibit an austenite fraction (? -Fe) of 10% to 100% by volume and all increments therebetween in the temperature range of 150 to 400 占 폚.

In step 2 of method 1, the alloy is processed into a sheet form preferably having a thickness of 0.5 to 5.0 mm. Step 2 may include hot rolling or hot rolling and cold rolling. For hot rolling, the preferred temperature range will be in the range of 700 占 폚 to less than the Tm of the alloy. In the case of cold rolling, the preferred temperature is understood as room temperature. After hot rolling or hot rolling and cold rolling, the sheet may be further heat treated, preferably at a temperature of 650 ° C to a temperature below the melting point (Tm) of the alloy.

Thus, the step of producing the sheet from the cast product may vary depending on the particular manufacturing route and the particular target object. For example, consider a thick slab cast as one process path to obtain a sheet of target thickness. The alloy is typically cast through a water-cooled mold having a thickness of 150 to 300 mm. After cooling, the cast ingot is preferably prepared for hot rolling, which may include some surface treatment to remove surface defects, including oxides. The ingot will then pass through a roughing mill hot roller, which may include several steps, typically resulting in a transfer bar slab of 15 to 100 mm thickness. The transfer bar then passes through successive / tandem hot rolling finishing stands to produce a hot band coil, typically 1.5 to 5.0 mm thick. If additional gauge reduction is desired, cold rolling may be performed at various mills, including various reductions per step, various steps and tandem mill, Z-mill and reversing mill. Typically the cold rolled thickness will be 0.5 to 2.5 mm thick. Preferably, the cold-rolled material is annealed to recover ductility lost partially or completely from the cold-rolling process in the temperature range of 650 ° C to below the melting point (Tm) of the alloy.

Another example is the preferred processing of the casting material through a thin slab casting process. In this case, the newly formed slab having a thickness of 35 to 150 mm after casting through a water cooled mold can be directly heated in a tunnel furnace or by direct heating using induction heating to feed the slab directly to the target It is moved to hot rolling. The slabs are preferably hot-rolled in one to ten multi-stand finishing mills. After hot rolling, the strip is rolled into a hot band coil of typical thickness 1-5 mm. If an additional process is required, cold rolling may be applied in a manner similar to the above. The bloom casting is similar to the above example, but with a thicker thickness, typically 200 to 500 mm thick, which can be cast and used in an initial breaker stage (initial) to allow the initial cast thickness to be reduced and passed through a hot rolling roughing mill. breaker steps may be required.

Notwithstanding the specific process proceeding from step 1 to step 2, once the sheet is formed in the preferred range of 0.5 mm to 5.0 mm, the sheet has a total elongation of X ₁ (%), an ultimate tensile strength of Y ₁ (MPa) And Z ₁ (MPa). A preferred characteristic of the alloy is an ultimate tensile strength of 900 to 2050 MPa, a tensile elongation of 10 to 70% and a yield strength in the range of 200 to 750 MPa.

In step 3 of method 1, the alloy is permanently deformed (i.e., plastically deformed) in the temperature range of 150 ° C to 400 ° C. Such permanent deformation can be provided by rolling to reduce the thickness. This can be done, for example, at the end of the creation of a steel coil. Rather than conventional cold rolling for final gauge reduction to sheets starting at room temperature, preferably hot rolling is carried out at a target temperature range of 150 to 400 占 폚. One method is to heat the sheet to the target temperature range before passing through the cold rolling mill.

The sheet may be heated by a variety of methods including passing through a tunnel mill, a radioactive heater, a resistive heater, or an induction heater. Alternatively, the reduction roller is heated directly. A third example for illustration is to anneal the sheet to a low temperature batch and then pass it through the cold rolling mill in the target temperature range. The sheet may also be deformed into parts in an elevated temperature range using a variety of processes that provide permanent deformation during the manufacture of the component in a variety of ways including roll forming, metal stamping, metal drawing, hydroforming, and the like.

Despite the particular process of permanently deforming the alloy in the temperature range of 150 to 400 DEG C, two distinct conditions can be formed as shown in conditions 3a and 3b of FIG. In condition 3a, when comparing the alloy in step 2 and the alloy after step 3, the total elongation and the ultimate tensile strength are relatively unaffected, but the yield strength increases. Specifically, the total elongation X ₂ is X ₁ ± 7.5%, the tensile strength Y ₂ is Y ₁ ± 100 MPa, and the yield strength Z ₂ is = Z ₁ + 100 MPa. A preferred characteristic of the alloy in condition 3a is an ultimate tensile strength value (Y ₂ ) of 800 to 2150 MPa, a tensile elongation (X ₂ ) of 2.5% to 77.5%, and a yield strength (Z ₂ ) of 300 MPa. More preferably, the yield strength may range from 300 to 1000 MPa.

In condition 3b, when comparing the alloy in step 2 and the alloy after step 3, the ultimate tensile strength is relatively unaffected, but the yield strength increases. Specifically, the ultimate tensile strength Y ₃ is Y ₁ ± 100 MPa and the yield strength (Z ₃ ) is 400 MPa. Conditions is a desirable characteristic of the alloy is 800 at the 3b to the ultimate tensile strength value of 2150 MPa (Y ₃₎ and (Z3) at least 400 MPa yield strength. More preferably, the yield strength can be in the range of 400 to 1200 MPa. Also unlike the conditions 3a total elongation decrease is greater than 7.5%, that the total elongation (X ₃₎ is defined as follows: in step _{B: X 3 <X 1 -} 7.5%.

As can be seen from various examples, with normal deformation, the metal material will be strain hardened / work hardened. For example, it is expressed as strain hardening exponent (n) at the relationship between stress (τ) and strain (ε) τ = K ε ⁿ . The ripple effect of this is that if the material is permanently deformed, the basic properties change. Comparing initial and final conditions, typical predicted properties of increasing yield strength and tensile strength with decreasing total ductility will be seen. To illustrate this effect, a specific case example is provided, which will show contrast with the new material properties specified in this application.

Figure 3 shows a summary of Method 2 of the present invention. The first three steps of Method 2 are the same as Method 1, and Step 4 is an additional step of Method 2. As shown, Step 4 can be applied to the alloy of Condition 3a or Condition 3b.

As previously indicated, in the description of FIG. 2, a combination of various properties (e.g., total elongation, ultimate tensile strength, and yield strength) is provided for each condition 3a or 3b. As further described in the detailed description and in the case of the subsequent embodiments, the alloy of the condition 3a or 3b can be further characterized by its particular structure. The final properties can be further adjusted using a further optional step of permanently deforming the alloy at temperatures between room temperature and 150 ° C, more preferably between 0 ° C and 150 ° C. This can be done by adding another step during iron coil manufacture as illustrated in Fig.

In this case, step 4 may be reduced by a 0.5 to 2.0% reduction or > 2% to 50% to a skin pass (e.g., a small reduced rolling pass, sometimes used for surface quality or leveling improvement) For example, another method may be performed to produce a part from a sheet processed by method 1. In optional step 4 of method 2, the sheet may be roll formed, metal stamped, Drawing, hydroforming, etc. In spite of the precise process activating step 4 of method 2, the final properties are tensile elongation of 10 to 40%, extreme values of 1150 to 2000 MPa Tensile strength and yield strength of 550 to 1600 MPa.

alloy

The structure and mechanism in the present application leading to a new process path for developing a high yield strength is related to the chemical composition of the compound given in Table 1 below.

As can be seen in Table 1, the alloy of the present invention is an iron-based metallic alloy having Fe of more than 70 atomic%. It is also understood that the alloy of the present invention includes at least four or more, or five or more, or six elements selected from Fe and Si, Mn, Cr, Ni, Cu, Thus, depending on the presence of four or more elements selected from Si, Mn, Cr, Ni, Cu or C, the elements are present in the indicated atomic percentages as follows: Si (0 to 6.13 atomic%); Mn (0 to 15.17 atom%); Cr (0 to 8.64 atomic%); Ni (0 to 9.94 atomic%); Cu (0 to 1.86 atomic%); And C (0 to 3.68 at%). Most preferably, the alloy of the present invention contains 70 atom% or more of Fe together with Si, Mn, Cr, Ni, Cu and C, or contains 70 atom% or more of Fe together with Si, Mn, Cr, Ni, Or 70 atomic% or more Fe together with Si, Mn, Cr, Ni, Cu and C, and the other impurities are in the range of 0 to 5000 ppm.

Laboratory slab casting

The alloy was measured at an input of 3,400 grams using a commercially available reinforcing additive powder and a base steel feedstock having a composition according to the atomic ratios in Table 1. As mentioned above, the impurities can be present at various levels depending on the feedstock used. Impurities generally include the following elements; Co, Mo, N, Nb, P, Ti, V, W and S. If 0,5,000 parts per million, preferably 0 to 500 ppm,

The feed was introduced into a zirconia-coated silica crucible located on an Indutherm VTC 800V vacuum tilt casting machine (Indutherm VTC 800V). The casting machine was then flushed with argon at atmospheric pressure twice before casting to empty the casting and melting chamber and prevent oxidation of the melt. The melt was heated to a 14 kHz RF induction coil for about 5 minutes to 7 minutes, depending on alloy composition and input mass, until fully melted. After the final solids were melted, they were further heated for 30 to 45 seconds to ensure superheat and melt homogeneity. The chamber is then emptied, the crucible is tilted and the melt is poured into a channel 50 mm thick, 75-80 mm wide, and 125 mm deep, of a water cooled copper die, Step 1 of FIG. The process can be applied to preferred casting thicknesses in the range of > 5.0 to 500 mm. The melt was cooled under vacuum for 200 seconds before filling with argon at atmospheric pressure.

Laboratory Hot rolling

The alloy of the present invention is preferably processed into a laboratory sheet. A laboratory alloy process has been developed to activate hot bands from the slabs produced by continuous casting, which represents step 2 of Figures 2 and 3. Industrial hot rolling involves heating the slab in a tunnel furnace to a target temperature and then passing it through a reversible mill or a multi-stand mill or a combination thereof to a desired gauge at a temperature in the range of 700 ° C to the melting point (Tm) As shown in FIG. During rolling to one of the mill types, the temperature of the slab becomes steadily low due to heat loss to air and work rolls, resulting in much lower temperature of the final hot band. This is simulated in the laboratory by heating to a temperature of 1100 ° C to 1250 ° C in a tunnel furnace followed by hot rolling. Since laboratory mills are slower than industrial mills, the heat loss is greater during each hot rolling pass, so the slabs are reheated between each pass for 4 minutes to reduce the temperature drop, and the final temperature of the target gauge discharged from the laboratory mill is typically Depending on the furnace temperature and the final thickness.

Prior to hot rolling, the laboratory slabs were preheated by heating in a Lucifer EHS3GT-B18 furnace. The furnace setting temperature varies from 1100 ° C to 1250 ° C depending on the alloy melting point and the temperature of the hot rolling process. The initial temperature is set high to facilitate higher reduction and the subsequent temperature is set low to minimize surface oxidation in the hot band. The slab is soaked for 40 minutes prior to hot rolling to reach the target temperature and then sent to the Fenn Model 061 2 high-mill in a tunnel. The 50 mm castings are hot rolled for 5 to 10 passes through a mill and then cooled in the atmosphere. The final thickness range after hot rolling is preferably from 1.8 mm to 4.0 mm and the variable reduction per pass is from 20% to 50%.

After hot rolling, the slab thickness was reduced to the final thickness of the hot band of 1.8 to 2.3 mm. The processing conditions can be adjusted by varying the amount of hot rolling and / or by adding a cold rolling step to produce a preferred thickness range of 0.5 to 5.0 mm. The tensile specimen was prepared by cutting the laboratory hot band using a wire EDM. Tensile properties were measured with an Instron mechanical test frame (Model 3369) using Instron's Bluehill control and analysis software. The tensile properties of the alloys at the hot rolling conditions are listed in Table 2 and processed to a thickness of 1.8 to 2.3 mm.

The ultimate tensile strength value ranges from 913 to 2000 MPa and the tensile elongation varies from 13.8 to 68.5%. The yield strength is in the range of 250 to 711 MPa. The mechanical properties of the hot bands from the steel alloys herein depend on the alloy composition, the processing conditions and the material mechanical response to the processing conditions.

Example

Comparative Example  # 1 Conventional Properties for Rolling at Room Temperature

Hot bands from the inventive alloys listed in Table 1 were cold rolled to a final target gauge thickness of 1.2 mm through multiple cold rolling passes for comparison purposes. The tensile specimens were prepared by cutting from each cold-rolled sheet using wire EDM. Tensile properties were measured with an Instron mechanical test frame (Model 3369) using Instron's Bluehill control and analysis software. All tests were carried out at room temperature with displacement control.

The tensile properties of the alloys of this invention after cold rolling are listed in Table 3. As listed, the yield strength increases significantly in the hot band to a maximum of 711 MPa (Table 2). The yield strength after cold rolling varies from 1037 to 2000 MPa. The ultimate tensile strength value after cold rolling ranges from 1431 to 2222 MPa. However, for each alloy after cold rolling, the tensile elongation is variously reduced to 4.2 to 31.1%. The general trend of the effect of cold rolling on the tensile properties of the alloys of the present application is shown in Figs. 4-6.

Relative magnetic phase percentages were measured by ferrite scopes after hot-bending and cold rolling for each alloy of the present application, and are listed in Table 1 and for the selected alloys are shown in FIG. The magnetic phase volume percent of 0.1 to 56.4 Fe% of the hot band increases from 1.6 to 84.9 Fe% after cold rolling to show phase transformation during deformation.

The comparative example shows that the yield strength of the present alloys can be increased by cold rolling (i.e., at room temperature). The ultimate tensile strength also increases, but cold rolling leads to a significant reduction in the ductility of the alloy, which is indicated by a decrease in tensile elongation, which can be a limiting factor in certain applications. As indicated by the increase in ultimate tensile strength, strength reinforcement is related to the phase transformation of austenite into ferrite, as described by measurement at the magnetic phase volume percentages before and after cold rolling.

Comparative Example  #2 Cold The rolling amount  Effect on yield strength of alloy 2

Alloy 2 was processed into a 4.4 mm thick hot band. The hot bands were cold rolled through different cold rolling (i. E., At room temperature) passes and with different rolling reductions. After cold rolling, the samples were heat treated at 850 ° C for 10 minutes by intermediate annealing. This represents the start condition of each sample, indicating a fully annealed condition to remove the previous cold work. In the starting conditions, subsequent cold rolling at different degrees (e.g., 0%, 4.4%, 9.0%, 15.1%, 20.1%, 25.1% and 29.7%) were applied as shown in Table 5, The final gauge shall be at a constant thickness of 1.2 mm. The increase in the yield strength of the material as the cold reduction increases in the final stage after annealing is evidenced by the tensile stress-strain curve of FIG. The tensile properties in the test are listed in Table 5. The yield strength of Alloy 2 is increased to a range of 666 to 1140 MPa depending on the degree of reduction compared to the initial value of the annealing condition (Table 5).

In addition, the magnetic phase volume percent measured by the ferrite scope increases to 12.9 Fe% as shown in Table 5, compared with the initial value of 1.0 Fe% in the annealed state. It should be noted that the yield strength increases as the tensile elongation after cold rolling decreases and the ductility of the alloy is lost.

Comparative Example # 2 shows that in order to achieve a relatively high yield strength value with an increase in tensile strength but with a decrease in ductility, the yield strength of the alloy can be varied by a cold rolling reduction. The higher the cold rolling applied, the higher the yield strength and the lower the tensile elongation.

Comparative Example  # 3 from alloy 2 Hot-band  Structural transformation during cold rolling

The hot bands of alloy 2 with a thickness of 4 mm were cold rolled to a final thickness of 1.2 mm via multiple cold rolling passes with intermediate annealing at 850 占 폚 for 10 minutes. The microstructure of the hot-band and cold rolled sheet was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

To prepare the SEM samples, the pieces were cut into EDM, mounted to epoxy, gradually polished with 9, 6, and 1 micron diamond suspensions, and finally polished with 0.02 micron silica. To prepare the TEM specimens, the samples were cut from the sheet with EDM and then thinned to a reduced grit size pad each time. Thinning to a thickness of 60 to 70 μm is performed by grinding with a 9 μm, 3 μm and 1 μm diamond suspension, respectively. Discs with a diameter of 3 mm were drilled from the foil and final polishing was performed by electropolishing using a twin-jet grinder. The chemical solution used was 30% nitric acid mixed in methanol. If the thin area for TEM observation is not sufficient, TEM specimens can be ion-milled using a Gatan PIPS (Precision Ion Polishing System). Ion-milling is usually done at 4.5 keV and the tilt angle is reduced from 4 ° to 2 ° to open the thinner part. TEM studies were performed using a JEOL 2100 high-resolution microscope operating at 200 kV.

SEM analysis of the hot band structure shows relatively large austenite grain boundaries with straight boundaries (Figure 9). Bright field TEM images show that the hot band structure contains very low dislocations and grain boundaries are typical of linearity and sharpness in the recrystallization structure (FIG. 10). TEM studies also showed that nanoprecipitates were present in the microstructure (Figure 11).

When the hot band is cold rolled, the austenite phase in the selected region of the hot band structure is transformed into a reffered ferrite phase under stress. The backscatter SEM image of the cold rolled sheet shows the presence of deformed and refined structures and deformation twins (FIG. 12). As shown in the TEM image of Fig. 13, a high dislocation density is generated in the retained austenite grains, and a purified ferrite grains having a size of 200 to 300 nm are formed. Deformation twinning was also observed in the residual austenite grains. Further nano precipitation was observed as part of the phase transformation process during cold rolling (FIG. 14).

This example demonstrates microstructural evolution from the initial hot band austenite structure during cold rolling, which is not only a refinement of the structure due to phase transformation into ferrite with nano precipitation, but also an increase in dislocation density and alloy strengthening by modified twinning, An increase in ultimate tensile strength).

Example  # 4 Effect of Rolling Temperature on Yield Strength of Alloy 2

The starting material was a hot band from alloy 2.5 with a thickness of about 2.5 mm made by hot rolling a 50 mm thick laboratory cast slab according to a commercial hot band manufacturing process. The starting material had an average ultimate tensile strength of 1166 MPa, an average tensile elongation of 53.0% and an average yield strength of 304 MPa. The starting material also had a magnetic phase volume fraction of 0.9 Fe%.

The hot bands were media blast treated to remove oxides and were placed in a Yamato DKN810 machine-convection oven for 30 minutes or more before rolling and allowed to reach plate temperature. The hot bands were rolled in a Fenn Model 061 mill with a steadily decreasing roll gap and a constant starting temperature (for example, 50, 100, 150, 200, 250 ° C, 300 Lt; 0 &gt; C, 350 &lt; 0 &gt; C, and 400 [deg.] C) for at least 10 minutes between passes. The samples were EDM cut into ASTM E8 standard shapes. Tensile properties were measured with an Instron mechanical test frame (Model 5984) using Instron's Bluehill control and analysis software. All tensile tests were carried out at room temperature under displacement control by holding the lower fixture firmly and moving the upper fixture: the load cell is connected to the upper fixture.

The tensile properties of alloy 2 after rolling at the specified temperature are listed in Table 6. Depending on the rolling temperature, the yield strength is increased to a range of 589 to 945 MPa compared to a value of 250 to 711 MPa of hot bands (Table 2). The ultimate tensile strength of Alloy 2 is 1132 to 1485 MPa and the tensile elongation is 21.2 to 60.5%. An example of a stress-strain curve is shown in Fig. As shown, the rolling of the hot bands from Alloy 2 at a temperature of 200 ^° C shows the possibility of increasing the yield strength with a minimum change in ductility and ultimate strength consistent with step (3a) of FIG.

The magnetic phase volume percent (Fe%) of the tensile gage of at least 10 mm from the wave front after rolling was measured and reported in Table 7. As shown, the magnetic phase volume percent of alloy 2 at a temperature of 100 ° C or higher after rolling is significantly lower in the range of 0.3 to 9.7 Fe% compared to that of (18.0 Fe%, Table 4) at room temperature after cold rolling. A significant increase in the magnetic phase volume percent of alloy 2 after rolling at temperature and after tensile testing was measured (Table 7, Fig. 16). After tensile testing, the magnetic phase volume percent of the tensile gauge of the sample varies from 25.2 to 52.1 Fe%, depending on the rolling temperature.

In this example, the yield strength of the present alloys is increased by rolling at elevated temperatures, which shows that the phase transformation from austenite to ferrite is reduced. A significant reduction in Fe% occurs when the rolling temperature is higher than 100 ^° C. In addition, rolling the hot bands from the present alloy at a temperature of 150 ° C to 400 ° C allows the extreme tensile strength to remain at approximately the same level without significant changes in ductility (eg, limited change to ± 7.5 Fe%) (For example, by increasing the yield strength by at least 100 MPa or more compared to the initial value) of the yield strength (for example, ± 100 MPa compared to the initial value).

Example  # 5 Effect of Rolling Temperature on Yield Strength of Alloy 7, Alloy 18, Alloy 34 and Alloy 37

 The starting material was a hot band from alloy 7, alloy 18, alloy 34, and alloy 37, respectively, of about 2.5 mm initial thickness made by hot rolling a 50 mm thick laboratory cast slab according to a commercial hot band manufacturing process. Alloy 7, Alloy 18, Alloy 34, and Alloy 37 were treated with hot bands having a thickness of about 2.5 mm by hot rolling at a temperature of 1100 DEG C to 1250 DEG C, and then subjected to medium blast treatment to remove the oxide. The tensile properties of the hot band material are described previously in Table 2. The hot bands were media blast treated to remove oxides and were placed in a Yamato DKN810 machine-convection oven for 30 minutes or more before rolling to allow the plate to reach the desired temperature.

The produced and refined hot bands were rolled in a Fenn Model 061 mill with a steadily decreasing roll gap and placed in a furnace for at least 10 minutes between passes to ensure a constant temperature. The samples were EDM cut into ASTM E8 standard shapes. Tensile properties were measured with an Instron mechanical test frame (Model 5984) using Instron's Bluehill control and analysis software. All tensile tests were carried out at room temperature under displacement control by holding the lower fixture firmly and moving the upper fixture: the load cell is connected to the upper fixture.

The properties of each alloy, especially elongation, yield strength, and ultimate tensile strength, were monitored over the entire temperature range examined. Each alloy was tested after rolling in a temperature range of from 100 ^o C up to 400 ^o C. Alloy 7 showed a tensile elongation of 14.7% to 35.5%, an ultimate tensile strength in the range of 1218 MPa to 1601 MPa, and a yield strength in the range of 557 MPa to 678 MPa (Table 8) over the entire temperature range examined, Of Fe was 29.9 to 41.7 and after the tensile test was 31.5 to 39.6 (Table 9). Alloy 18 exhibited a tensile elongation in the range of 43.0% to 51.9%, an ultimate tensile strength in the range of 1083 MPa to 1263 MPa, and a yield strength in the range of 772 MPa to 924 MPa at 150 to 400 ^o C (Table 10) Of Fe was 6.8 to 12.3 in the range of 150 to 400 ^° C and 31.5 to 39.6 after the tensile test (Table 11). Alloy 34 exhibited a tensile elongation in the range of from 21.1% to 31.1%, an ultimate tensile strength in the range of 1080 MPa to 1140 MPa, and a yield strength in the range of 869 MPa to 966 MPa in the range of 150 to 400 ^o C (Table 12) The previous Fe% was 0.4 to 1.0 and after the tensile test was 0.8 to 2.1 (Table 13). Alloy 38 exhibited a tensile elongation in the range of 1.5 to 9.0%, an ultimate tensile strength in the range of 1537 MPa to 1750 MPa, and a yield strength in the range of 1384 MPa to 1708 MPa in the range of 150 to 400 ^o C (Table 14) The previous Fe% was 74.5 to 84.3 and after the tensile test was 71.1 to 85.6 (Table 15).

The curves which are the targets for each alloy of the present application are shown in Figs. 17 to 20, and the tested hot bands and reference curves after cold rolling are shown in parallel comparison for the same about 20% reduction.

In this example, the phase transformation from the austenite to the ferrite of the alloy of the present invention is reduced, but the yield strength is increased when rolled at a temperature of 100 ° C to 400 ° C. Examples of changes in yield strength, ultimate tensile strength and tensile elongation are shown in steps 3a and 3b of FIG.

Example  # 6 at 200 ° C The rolling amount  Effect on yield strength of alloy 2

Alloy 2 was machined into a hot-band about 2.5 mm thick in a laboratory casting. After hot rolling, alloy 2 was rolled at 200 &lt; 0 &gt; C at various rolling amounts of about 10% to 40%. Between the rolling passes, the alloy 2 sheet material was placed in a convection furnace at 200 ° C for 10 minutes to maintain the temperature. Once the desired rolling amount was achieved, the ASTM E8 tensile sample was cut through wire-EMBM and used for testing.

The tensile properties of alloy 2 after rolling at 200 DEG C in different rolling amounts (0.0 to 70.0%) are listed in Table 16 and the table also includes data prior to rolling experiments. 21 shows the typical tensile curve of alloy 2 as a function of the rolling amount at 200 占 폚. As the reduction increases, the ultimate tensile strength of the material (ie, a change of ± 100 MPa) is not changed until the 30% rolling amount, but the yield strength is observed to increase sharply. 22 compares the yield strength and the ultimate tensile strength trend at 200 캜 according to the rolling amount, and the increase in the yield strength is comparatively fast, while the ultimate tensile strength change corresponds to the characteristic of the step 3a in Fig. 2 , And it is consistent with the characteristic change of step 3b at the rolling amount of 39.0%.

The total elongation of alloy 2 is shown as a function of the rolling amount at 200 캜 in FIG. This shows that the yield strength of Alloy 2 increases as the further rolling amount increases during rolling at 200 ° C, but ductility does not decrease sharply until> 30% rolling. This was simulated using commercial rolling methods including laboratory rolling and tandem milling, Z-milling, and reversible milling, and the precise amount of reduction in ductility can be changed by further application of strip tension during rolling. Please refer to.

The magnetic phase volume percent (Fe%) was again measured after rolling at 200 ° C and again using a Fischer Feritscope FMP30 after tensile testing of the tensile gage (ie, the reduced gage portion present in the tensile specimen). The measurements shown in Table 17 show the amount of phase transformation due to the deformation occurring in the alloy during the rolling process and the subsequent tensile test. The phase transformation due to the deformation of the alloy 2 after the rolling and tensile tests is shown in Fig. Since the volume percentage of magnetic phase increases slightly with increasing rolling amount, the phase transformation due to deformation is greatly suppressed at 200 ° C. Rolling at 200 캜 shows that as the amount of rolling that suppresses the amount of transformation of the material increases, it affects phase transformation due to deformation during tensile testing.

Another process was applied: Alloy 2 was machined to a hot band of about 9.3 mm in thickness at 1250 ° C, followed by removal of the oxide by medium blasting followed by rolling (~ 50% reduction) to 4.6 mm at 200 ° C. It was then heat treated at 850 ° C for 10 minutes and rolled at about 50.4, 60.1 and 70% rolled at 200 ° C.

As in the case of alloy 2 by rolling at 200 DEG C, this example shows that the yield strength of the present alloy can be controlled by varying the amount of rolling at a temperature higher than the atmospheric temperature. In the broad context of the present invention, the temperature range is considered between 150 [deg.] C and 400 [deg.] C, as provided in the example for Table 7. [ During rolling, the strain path is changed, resulting in a phase transformation due to a relatively limited strain, increasing the yield strength in the cold rolling state while maintaining soft and ultimate tensile strength. Thus, the parameters of rolling can be optimized to improve the yield strength of the material without sacrificing ductile or ultimate tensile strength.

Example  # 7  Microstructure of alloy 2 after rolling

Alloy 2 was processed into a 9 mm thick hot band from the laboratory castings according to the commercial hot band manufacturing process. The hot bands were cold rolled with a 50% rolling amount according to the cold rolling of the commercial sheet manufacturing process and annealed by air cooling at 850 캜 for 10 minutes. And subjected to medium-blast treatment to remove the oxide formed during the annealing. Thereafter, the alloy was cold rolled to the point of failure or limited rolling of the mill. The sample was heated to 200 DEG C in a convection oven for at least 30 minutes prior to cold rolling to maintain a uniform temperature and reheated between passes for 10 minutes to maintain a constant temperature. Two sheets of the alloy were first cold-rolled at a reduction of 30% (rolled amount) and then cold-rolled at a maximum reduction of 70%. Microstructure was observed by scanning electron microscopy (SEM) after initial and rolling. To prepare the SEM samples, the slices were cut into EDM, mounted to epoxy, gradually polished with 9 μm, 6 μm and 1 μm diamond suspensions, and finally polished with 0.02 μm silica.

Figure 25 shows a backscatter SEM image of microstructure prior to cold rolling, which is mostly austenitic with heat-treated twins in micron-sized grains. As shown in Fig. 26, band structures can be seen in different regions in different directions after 30% reduced cold rolling. Perhaps the bands with similar orientations are twisted twins in one austenite grain, while the bands in the other direction are twins in other crystal orientation grains. Some tissue refinement can be observed in selected areas.

After the rolling amount has increased to 70%, the band is no longer visible and the refined structure can be seen through the bloom (Fig. 27). As can be seen in the high magnification image of Figure 27B, a fine island that is much smaller than 10 [mu] m can be identified. Considering the high strain exhibited by the stable austenite during the rolling process, the austenite can typically be significantly purified in the range of 100 to 500 nm. Ferrite scope measurements show that the austenite is stable at 200 [deg.] C, where almost 100% austenite is retained after rolling.

This example demonstrates that while the refinement is rolled at 200 占 폚 at a high rolling amount of 70% as opposed to cold rolling occurring at the austenite to ferrite transformation, the austenite stabilization in the alloy (e.g., Resistance to transformation) and microstructural refinement of the austenite.

Example  # 8 &lt; SEP &gt; The rolling amount  Microstructure of Alloy 2 Effect

The rolling of temperature greatly increases the yield strength of alloy 2, while the tensile elongation is maintained. The TEM study was conducted on alloy 2 rolled at 200 ° C to analyze the structural changes due to rolling deformation during rolling at 200 ° C. In this case, the 50 mm thick laboratory casting slab was first hot rolled and the resulting hot bands were rolled at 200 DEG C at different strains. The microstructure of the rolled sheet was studied by transmission electron microscopy (TEM) to observe structural changes. To prepare the TEM specimens, the samples were cut using a wire EDM, and each was made thin by polishing with a pad of reduced grit size. Samples with thinner thicknesses of 60-70 μm were performed by polishing with 9 μm, 3 μm and 1 μm diamond suspensions, respectively. Discs with a diameter of 3 mm were drilled from the foil and final polishing was performed by electropolishing using a twin-jet grinder. The chemical solution used was 30% nitric acid mixed in methanol. If the thin area for TEM observation is not sufficient, TEM specimens can be ion-milled using a Gatan PIPS (Precision Ion Polishing System). Ion milling is typically done at 4.5 keV and the tilt angle is reduced from 4 ° to 2 ° to open the thinner part. TEM studies were performed using a JEOL 2100 high-resolution microscope operating at 200 kV.

Figure 28 shows a bright-field TEM image of the microstructure of alloy 2 rolled at 200 캜 with a 10% reduction (rolling amount). The austenite grains are filled with entangled dislocations, and a dislocation cell structure appears. However, the original austenite grain boundaries are still visible due to the relatively low rolling strain. Austenite is stable during rolling at 200 &lt; 0 &gt; C. Electron diffraction indicates that the austenite is predominant in agreement with the ferrite scope measurement. Rolling at a rolling rate of 10% at 200 ° C increases the average yield strength of the hot band from 303 MPa to 529 MPA (see Table 16). When the sheet is rolled at a rolling amount of 30%, the TEM exhibits a higher dislocation density in the crystal grains, and a distinct dislocation cell structure appears, as shown in Fig. Some modified twins also appear in the austenite grains. Similar to the 10% rolled sample, the austenite phase is retained as confirmed by electron diffraction. However, the original grain boundaries of austenite are no longer visible. Rolling at 200 ° C with a 30% reduction results in an average yield strength of 968 MPa (Table 16). After rolling to a 70% reduction (Figure 30), a higher dislocation density continues from the TEM, and the dislocation cell is similar to the 30% rolled sample (Figure 29). Deformation pairs are also present in the sample. Similar to the 30% rolled sample, the austenite still remained in rolling, which was confirmed by electron diffraction.

This example demonstrates that the alloy herein retains the austenite structure during rolling at 200 &lt; 0 &gt; C at a rolling amount of 70%. Tissue changes, including dislocation cell formation and twinning, increase the yield strength after rolling at 200 ° C.

Example  # 9 Process method by combination of rolling method

Alloy 2, Alloy 7, Alloy 18, and Alloy 34 were processed into hot bands having a thickness of about 2.7 mm, then subjected to media blasting to remove oxides and rolled at 200 ° C in a 20% rolled amount. The sample was sectioned and rolled to a range of rolling temperatures at room temperature. The ASTM E8 tensile samples were cut into wire EDM and tested on an Instron 5984 frame using Instron's Bluehill software.

The tensile properties of the selected alloys after combined rolling are listed in Tables 18 to 21. Significant increases in yield strength were observed in all three alloys after combination of rolling methods compared to hot band conditions or immediately after rolling at 200 &lt; 0 &gt; C and about 20% reduction at rolling and subsequent reduction at room temperature. The yield strength for alloy 2 is less than 1216 MPa (the yield strength of the hot band is 309 MPa and 803 MPa after rolling at 200 ° C), alloy 7 is less than 1571 MPa (the yield strength of the hot band is 333 MPa And 575 MPa after rolling at 200 ° C), the alloy 18 is 1080 MPa or less (the yield strength of the hot band is 390 MPa and 834 MPa after rolling at 200 ° C), and the alloy 34 is 1248 MPa or less The yield strength of the hot band is 970 MPa and after rolling at 200 DEG C is 1120 MPa). 31 to 34 show respective tensile curves for Alloy 2, Alloy 7, Alloy 18, and Alloy 34, respectively. Increases in ultimate tensile strength and reduction in tensile elongation after cold rolling were observed in all alloys (see Tables 18-21). The analysis of the magnetic phase volume percent of the alloy selected for each experimental condition before and after the tensile test is listed in Tables 22 to 25. Cold rolling shows a higher Fe% in the treated sheet from the alloy of the present application and further Fe% is increased due to the occurrence of the transformation during the tensile test.

This embodiment shows a path for creating a third distinct property combination, which is a process in which the sheet is processed to a thickness of 0.5 mm to 5.0 mm and then deformed (rolled) and heated at a temperature in the range of 150 &lt; 0 & By reducing the thickness at the pass of &lt; RTI ID = 0.0 &gt; 150 C &lt; / RTI &gt; It has been observed that this provides a relatively high yield strength as compared to cold rolling alone and has a higher tensile strength compared to hot rolling alone.

Example  # 10 to control the combination of characteristics Method Example

The hot bands from Alloy 2 were processed into sheets with higher yield strengths and combinations of properties by different methods according to the steps provided in Figures 2 and 3. Alloy 2 was first cast and then hot rolled into 2.5 to 2.7 mm thick sheets. For comparison of the tensile strength, the reference hot-band material was hot-rolled to ~ 1.8 mm to reduce the gauge before testing. In the example of Fig. 2 (i.e., 20% rolled at 200 캜), the hot band was rolled at 200 캜 with a 20% reduction. Heated at 200 ° C for 30 minutes before being rolled 20% at 200 ° C and reheated for 10 minutes between rolling passes to maintain the temperature. In the example of Fig. 3 (for example, 10% cold rolling at room temperature after 20% rolling at 200 캜), processing steps including a 20% reduction at 200 캜 and a 10% reduction at room temperature were repeated. The tensile specimens were prepared by cutting the worked sheet by each method using wire EDM. Tensile properties were measured with an Instron mechanical test frame (Model 5984) using Instron's Bluehill control and analysis software. All tests were carried out at room temperature under displacement control.

A representative stress-strain curve having the combination of characteristics obtained in each processing method close to the optimum is shown in Fig. As shown, the yield strength can be increased significantly (i. E., 469 MPa increase) by rolling at 200 DEG C and the ultimate tensile strength (e. G., 34 MPa increase) and elongation (e. Can be minimized. This is provided by the exemplary embodiment 3a of FIG. A further 10% rolled sample at room temperature from the start conditions of step 3 will also satisfy step 4 of FIG. As can be seen in this case, this increases the yield strength (i.e., 688 MPa increase) and the tensile strength (increase 224 MPa), but the total elongation decreases (i.e., 25.1% decrease). Meeting the step 4 of FIG. 3 can be done by cold stamping the part by various processes, which results in the area of the stamped part having a higher yield strength and tensile strength and correspondingly lower ductility, It is used to make. The alloys herein demonstrate high yield strength by various methods or combinations thereof which provide various combinations of strength / elongation of the sheet produced from the alloys herein.

Example  # 11 Effect of Test Temperature on Tensile Properties of Alloy 2

Alloy 2 was prepared in the form of a sheet having a thickness of 1.4 mm by hot rolling and cold rolling the slab to the desired thickness and subsequent annealing. The tensile specimen was prepared by cutting two sheets of alloy with wire EDM. Tensile properties were measured at different temperatures ranging from -40 占 폚 to 200 占 폚.

The tensile properties of two sheets of alloys at different temperatures are shown in Table 26. [ The tensile sample gauge was measured after testing the magnetic phase volume percentage at each temperature using the ferrite scope also listed in Table 26. As can be seen, as the test temperature increases, the tensile elongation increases while the yield strength and ultimate tensile strength decrease.

The tensile elongation and magnetic phase volume percent (Fe%) are shown in Figure 36 as a function of the test temperature, and although the elongation at elevated temperatures is higher, the magnetic phase volume percentage of the post-test tensile sample gauge is significantly reduced and 200 After the test at &lt; RTI ID = 0.0 &gt; 0 C, &lt; / RTI &gt; The decrease in the magnetic phase volume percentage in the tensile sample gauge after testing indicates that the austenite stability at the elevated temperature suppresses the transformation from ferrite to stress.

As compared to cold rolling, as clearly shown in the last column of Table 26 in this example, the multicomponent alloy of the present invention during rolling at high temperature shows that the austenite stability is significantly increased and the transformation into ferrite is suppressed. Provide higher ductility during rolling and provide higher formability in subsequent sheet forming operations such as stamping, drawing, and the like.

Example  # 12 Decrease in process steps for the desired gauge

Alloy 2 was processed into a 4.4 mm thick hot band. Two sections of hot bands were rolled at 200 ° C, one at room temperature and the other one. The plates were heated in a mechanical convection oven at 200 DEG C for 30 minutes before being rolled and reheated for 10 minutes between passes to maintain a constant temperature.

The failure at rolling at room temperature occurred at a reduction of about 42%, while a reduction of more than 70% was applied during rolling at 200 ° C, reaching the limit of the mill without breakage. The limit of the mill occurs when the Fenn Model 061 mill can no longer carry out a significant amount of rolling per pass during cold rolling, as the material can continue rolling down.

Percent magnetic phase (Fe%) was measured with ferrite scopes at different levels of rolling during cold rolling and rolling at 200 ^° C. The result is shown in Fig. As shown, the percentage of magnetic phase volume (Fe%) increases sharply in the case of reduction at room temperature, resulting in a material limit for rolling at about 42%. For rolling at 200 ^° C, the magnetic phase volume percent (Fe%) remains below 3 Fe% even at a maximum rolling amount of> 70%.

Two sheets of the alloy with a final thickness of 1.2 mm were produced using both cold rolling and rolling at 200 &lt; ⁰ &gt; C. In the case of cold rolling, the target thickness was obtained with a reduction of 29% in the final rolling step by cyclic rolling through the intermediate annealing treatment to recover the alloy ductility. Tensile samples were prepared by EDM cutting a 1.2 mm thick sheet produced by both rolling methods and annealed at 1000 占 폚 for 135 seconds. Tensile properties were measured with an Instron mechanical test frame (Model 3369) using Instron's Bluehill control and analysis software. All tensile tests were carried out at room temperature under displacement control by holding the lower fixture firmly and moving the upper fixture: the load cell is connected to the upper fixture.

An example of an engineering stress-strain curve of an annealed sheet produced by cold rolling and rolling at 200 DEG C is shown in FIG. As shown, despite the different rolling methods for the desired thickness, the final properties of the sheet after annealing were similar.

This example demonstrates that rolling, which is austenite stable and not transformed into ferrite, significantly improves the rolling performance of the alloy, as described for alloy 2 at 200 ° C, which is a process for obtaining the desired sheet gauge Decrease the step. Thus, such hot rolling can be used to obtain a final target gauge with a high cold rolling amount of greater than 70%. The final gauge material may be annealed to restore the initial properties (i.e., initial conditions). The final target gauge can then be obtained by rolling in the temperature range of 150 to 400 占 폚 and following the steps and procedures of Fig. 2 or Fig.

Example  # 13 Max Rolling amount  change

The hot band was produced from Alloy 2 to a thickness of about 9 mm. After heating for 60 minutes at 200-250 占 폚, it was reheated between rolling passes for 10 minutes to maintain a constant temperature and rolled to about 4.5 mm. Once rolled to 4.5 mm, it was cut and heat treated at 850 ° C for 10 minutes and air cooled. The material was media blasted to remove the oxide, heated to the desired temperature for at least 30 minutes before rolling, and reheated for 10 minutes between passes to maintain a constant temperature. The material was rolled until there was a defect (visible crack) characterized by a visible crack propagating at least 2 inches from the end of the sheet. This is not the limit (maximum) of the equipment or the limit of the material (maximum) when the rolling mill has difficulties in obtaining the load required to reduce the material and the rolling is stopped by about 70% of rolling. The rolling control material at room temperature was a 4.4 mm thick hot band which was rolled until it broke at room temperature. The results of the maximum rolling amount as a function of the rolling temperature are given in Tables 27 and 39.

This embodiment demonstrates our alloy that the maximum amount of rolling increases as the temperature increases. Thus, alloys of the present invention can be considered to permit permanent deformation with a thickness reduction of more than 20% before being broken when heated to a temperature in the range of 150 ° C to 400 ° C. More preferably, the alloy of the present disclosure is considered to be permanently deformable with a thickness reduction of greater than 40% before being broken when heated in the temperature range. This provides a much larger potential variant for rolling operations, including processing industrial materials to reach the target gauge. A larger reduction before cracking means that fewer steps (ie, cold rolling and recrystallization annealing) may be required to obtain a particular target gauge during steel production. In addition, greater moldability proven at higher temperatures can be beneficial for manufacturing parts in a variety of molding operations including stamping, roll forming, drawing, hydroforming, and the like.

Claims (19)

a. Of at least 70 atomic% Fe and Si, Mn, Cr, Ni, and supplying a metal alloy comprising at least four or more element selected from Cu, or C, to melt the alloy, 10 ^-4 K / sec to 10 ³ Cooling at a rate of K / sec and solidifying to a thickness of > 5.0 mm to 500 mm;
b. Processing the alloy into a first sheet form having a thickness of 0.5 to 5.0 mm, the first sheet having a total elongation of X ₁ (%), an ultimate tensile strength of Y ₁ (MPa), and an ultimate tensile strength of Z ₁ Have yield strength;
c. Permanently deforming said alloy in a temperature range of from 150 DEG C to 400 DEG C to a second sheet form exhibiting one of the following tensile properties combinations A or B. &lt; Desc / Clms Page number 13 >
A. (1) Total elongation X ₂ = X ₁ ± 7.5%;
(2) Ultimate tensile strength Y ₂ = Y ₁ ± 100 MPa; And
(3) Yield strength Z ₂ > Z ₁ + 100 MPa.
B. (1) Ultimate tensile strength Y ₃ = Y ₁ ± 100 MPa; And
(2) Yield strength Z ₃ > Z ₁ + 200 MPa
The method according to claim 1,
Wherein the alloy comprises at least 70 atomic percent of iron and at least 5 elements selected from Si, Mn, Cr, Ni, Cu or C;
The method according to claim 1,
Wherein the alloy comprises at least 70 atomic percent iron and Si, Mn, Cr, Ni, Cu, and C.
The method according to claim 1,
Wherein the alloy formed in step (b) exhibits an X ₁ value of 10.0 to 70.0%, a Y ₁ value of 900 to 2050 MPa, and a Z ₁ value of 200 to 750 MPa.
The method according to claim 1,
The tensile properties A combination method is X ₂ = 2.5% to 77.5%, Y ₂ = 800 MPa to 2150 MPa, and Z _2> 300 MPa.
The method according to claim 1,
The tensile properties combined B is a method Y ₃ = 800 MPa to 2150 MPa, and Z _3> 300 MPa.
The method according to claim 1,
Wherein the first sheet formed in step (c) is permanently deformed into the second alloy sheet by reducing the thickness of the first alloy sheet.
The method according to claim 1,
Wherein step (b) is carried out at a temperature of from 700 [deg.] C to a temperature below the melting point (Tm) of said alloy.
The method according to claim 1,
Wherein after step (b), the alloy is heat treated at a temperature from 650 캜 to less than the melting point (Tm) of the alloy.
The method according to claim 1,
Wherein in step (c) the alloy is permanently deformed to a thickness reduction of greater than 20% before fracture.
The method according to claim 1,
Wherein the first sheet formed in step (c) is permanently deformed into the second alloy sheet by roll forming, metal stamping, metal drawing or hydroforming.
The method according to claim 1,
Wherein the alloy formed to a thickness of > 5.0 mm to 500 mm contains greater than 10% by volume of austenite.
The method according to claim 1,
Wherein the second sheet is permanently deformed in the temperature range of 150 DEG C or below after permanently deforming the alloy with the second sheet in the temperature range of 150 DEG C to 400 DEG C in step (c).
a. Supplying a metallic alloy containing at least 70 atomic% of iron and at least four or more elements selected from Si, Mn, Cr, Ni, Cu or C, melting the alloy,^-4K / sec to 10³ Cooling at a rate of K / sec and solidifying to a thickness of > 5.0 mm to 500 mm;
b. Processing the alloy into a first sheet form having a thickness of 0.5 to 5.0 mm;
c. Permanently deforming said alloy in the form of a second sheet in a temperature range of from 150 캜 to 400 캜; And
d. Permanently deforming said alloy in a second sheet form exhibiting the following combination of tensile properties at a temperature of less than 150 ° C.
(1) total elongation = 10.0 to 40.0%;
(2) Ultimate tensile strength = 1150 to 2000 MPa;
(3) Yield strength = 550 to 1600 MPa.
15. The method of claim 14,
Wherein step (b) is carried out at a temperature of from 700 [deg.] C to a temperature below the melting point (Tm) of said alloy.
15. The method of claim 14,
Wherein after step (b), the alloy is heat treated at a temperature from 650 캜 to less than the melting point (Tm) of the alloy.
15. The method of claim 14,
Wherein the permanently deforming step includes roll forming, metal stamping, metal drawing or hydroforming.
15. The method of claim 14,
Wherein the permanently deformed portion formed in step (d) is located in a car frame, an automotive chassis or an automotive panel.
15. The method of claim 14,
Wherein the permanently deformed portion formed in step (d) is one of a drill collar, a drill pipe, a pipe casing, a tool joint, a wellhead, a compressed gas storage tank, a railway tank car / tank wagon, .

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