A method for strengthening TWIP steel by precipitating β-Mn phase through warm rolling

Abstract

The present invention provides a method for strengthening TWIP steel by precipitating β-Mn phase by warm rolling, comprising the following steps performed in sequence: S1 homogenization annealing treatment; S2 hot rolling treatment; S3 warm rolling treatment: the hot-rolled TWIP steel is placed in a heat treatment furnace at 500-650°C for insulation, and then multiple warm rolling is performed until the total reduction of warm rolling is ≥80%, and after each warm rolling, it is placed in a heat treatment furnace at 500-650°C for insulation, and cooled to room temperature after the warm rolling. The present invention utilizes a warm rolling process to make the β-Mn phase precipitate and grow along the grain boundary instead of growing into the interior of the grain, that is, the growth direction of β-Mn is controlled by large deformation warm rolling, so that it can inhibit cracks initiated at the grain boundary, ensuring that the TWIP steel retains high elongation while improving the tensile strength.

Description

Technical Field

[0001] The invention relates to the technical field of steel rolling and heat treatment, in particular to a method for strengthening TWIP steel by using warm rolling to precipitate beta-Mn phase. Background Art

[0002] TWIP steel (twin induced plasticity steel) has attracted wide attention in the automotive industry due to its high tensile strength, excellent plastic deformation capacity, high strain hardening rate and high energy absorption rate. It is considered to be a new type of high-strength automotive steel with development potential and has been used in the manufacture of automotive safety parts, impact-resistant parts, chassis parts, etc. However, for working conditions with higher tensile strength requirements such as mine support, the yield strength and tensile strength of existing TWIP steel are still low, which limits its further application.

[0003] In order to improve its yield strength and tensile strength, severe plastic deformation and heat treatment methods are often used to strengthen TWIP steel. Among them, severe plastic deformation methods include cold rolling, high-pressure torsion, shot peening, etc. Although these methods can significantly improve the yield strength and tensile strength, they also reduce the plasticity of the material. In addition, processes such as high-pressure torsion and shot peening require special equipment and high production costs.

[0004] The common heat treatment method to improve the mechanical properties of TWIP steel is to use high-temperature solid solution and long-term (usually more than 10h) aging to precipitate strengthening phases such as κ' carbide and β-Mn phase in TWIP steel. Although this method can significantly improve the yield strength and tensile strength of TWIP steel, it is usually only applicable to TWIP steel with high Mn (mass percentage>30%) and high Al (mass percentage>9%) content, and the production cycle is long. At the same time, although κ' carbide can play a role in dispersion strengthening, the high-hardness β-Mn phase at the grain boundary grows into the interior of the austenite grain, resulting in stress concentration, which will cause the material to break prematurely in the elastic stage of tension and reduce the plasticity of the material.

[0005] Some researchers have also used the effect of warm rolling on the stacking fault energy of TWIP steel to regulate the effect of dislocations and twins on the strength and plasticity of TWIP steel: as the rolling temperature increases, the stacking fault energy of TWIP steel increases, and its deformation mechanism changes from twin-induced plasticity to dislocation plane slip, and the material retains a certain volume fraction of twins. During room temperature stretching, the twins retained by warm rolling can produce a TWIP effect, which is beneficial to the improvement of the plasticity of the material. However, the TWIP steel currently prepared by warm rolling, when its tensile strength reaches 1400MPa, its elongation at break is usually less than 20%. This high strength is formed by the formation of a large number of dislocation pileups and dislocation entanglements, which will reduce the movable dislocations in the material and reduce the plasticity of the material.

[0006] In summary, when the existing solid solution and aging heat treatment processes are used to strengthen TWIP steel, the β-Mn phase precipitated at the grain boundary will grow into the interior of the austenite grains, thereby splitting the grains and reducing the tensile properties; while when the existing warm rolling process is used to prepare TWIP steel, although the tensile strength of the material can be increased, its elongation is reduced. It is difficult to prepare high-strength and high-plasticity TWIP steel using the above two methods alone. Summary of the invention

[0007] In order to overcome the shortcomings of the prior art, the present invention provides a method for strengthening TWIP steel by precipitating β-Mn phase by warm rolling, which utilizes the warm rolling process to make the β-Mn phase precipitate and grow along the grain boundaries instead of growing inside the grains, that is, the growth direction of β-Mn is controlled by large deformation warm rolling, so that it can inhibit cracks initiated at the grain boundaries, thereby ensuring that the TWIP steel retains high elongation while improving the tensile strength.

[0008] The technical solution adopted by the present invention to solve the technical problem is: a method for strengthening TWIP steel by precipitating β-Mn phase by warm rolling, comprising the following steps performed in sequence:

[0009] S1 homogenization annealing treatment;

[0010] S2 hot rolling treatment;

[0011] S3 warm rolling treatment: the hot-rolled TWIP steel is cooled to room temperature, and then placed in a heat treatment furnace at 500-650°C for 20-40 minutes, followed by multiple warm rolling passes until the total warm rolling reduction is ≥80%, and after each warm rolling pass, it is placed back in a heat treatment furnace at 500-650°C for 3-8 minutes, and cooled to room temperature after the warm rolling.

[0012] As a further preferred embodiment, the specific operation of the homogenization annealing treatment is: placing the TWIP steel in a heat treatment furnace at 1100-1200° C. and keeping it at that temperature for 1-1.5 hours for homogenization annealing treatment.

[0013] As a further preferred embodiment, the specific operation of the hot rolling treatment is: taking out the TWIP steel after homogenization annealing treatment, performing multiple hot rolling, and after each hot rolling, putting it back into a 1100-1200° C. heat treatment furnace for 10-15 minutes.

[0014] As a further preferred embodiment, during the hot rolling process, the final rolling temperature of the TWIP steel is ensured to be greater than 900°C.

[0015] As a further preferred embodiment, the reduction in a single pass during hot rolling is 15-25%, and the hot rolling is terminated when the total reduction is ≥50%.

[0016] As a further preferred embodiment, the cooling method of the TWIP steel after hot rolling is air cooling to room temperature.

[0017] As a further preferred embodiment, the reduction in a single pass during the warm rolling process is 5 to 10%.

[0018] As a further preferred embodiment, the cooling method of the TWIP steel after the warm rolling is air cooling to room temperature.

[0019] Positive effects of the present invention:

[0020] (1) The present invention adopts a rolling process that is maturely used in the industry, and performs warm rolling with a large deformation amount at 500-650℃ for multiple passes: on the one hand, it ensures that the β-Mn phase generated at the grain boundary will not grow into the interior of the grain, avoiding the splitting effect of the brittle and hard phase on the grain; on the other hand, the higher warm rolling temperature increases the stacking fault energy of the TWIP steel, so that the deformation mechanism during warm rolling is dislocation plane slip, a large number of dislocations accumulate in the material, and a certain volume fraction of twins is retained for subsequent room temperature stretching. At the same time, the warm rolling treatment of the present invention forms strip-shaped grains in the TWIP steel, and the β-Mn phase at the grain boundary will induce the material to preferentially undergo delamination and cracking at the grain boundary, while the β-Mn phase will inhibit crack propagation during fracture.

[0021] The key implementation steps in the present invention are the combination of 500-650℃ warm rolling temperature and multi-pass large rolling reduction (≥80%), wherein the rolling temperature in the temperature range of 500-650℃ is conducive to the diffusion of elements such as C, Al, and Mn, and a C-poor zone and an Al-rich zone will be formed near the grain boundary. Al is a ferrite stabilizing element, and C is an austenite stabilizing element, so ferrite will be formed at the grain boundary, and C and Mn elements will be discharged, thereby facilitating the formation of β-Mn; single-pass small reduction warm rolling, and re-inserting into a heat treatment furnace for insulation after each rolling pass has a similar effect to aging. The total large deformation increases the accumulated dislocation density in TWIP steel and the deformation energy stored during the deformation process, and is also conducive to atomic diffusion during the insulation process between each pass, all of which are conducive to the formation of strengthening phases, and multi-pass large deformation can regulate the growth direction of the β-Mn phase, so that it does not grow into the interior of the grain, but only grows along the grain boundary, which is conducive to the improvement of elongation during the stretching process.

[0022] When the warm rolling temperature is lower than 500℃, the atomic activity is poor, the driving force for β-Mn nucleation is insufficient, and no β-Mn phase precipitates at this time. When the temperature is higher than 650℃, the β-Mn phase will dissolve in the austenite matrix due to the increased atomic activity. When the total rolling deformation is less than 80%, the stored deformation energy is small, which is not conducive to the precipitation of β-Mn. Even if a small amount of β-Mn phase is precipitated, it cannot grow along the grain boundary.

[0023] (2) The warm rolling process (higher temperature + multiple passes + large reduction) used in the present invention can promote the precipitation of β-Mn phase while increasing the dislocation density, and the growth direction of β-Mn is controlled by warm rolling, so that it can inhibit the cracks initiated at the grain boundary, ensuring that the TWIP steel retains high elongation while increasing the tensile strength. Therefore, the TWIP steel material after the warm rolling treatment of the present invention can be used directly, while the warm rolling / rolling process in patent documents such as the publication number CN 110951956 A can only be used as an intermediate process, because the purpose of the warm rolling is to refine the grains, and it is necessary to combine the subsequent annealing / aging treatment to control the grain size to increase the plasticity of the material. In summary, the warm rolling process and purpose of the present invention are different from the existing warm rolling process and purpose of the present invention. The warm rolling treatment of the present invention can be used as the final production process, while the existing warm rolling treatment can only be used as an intermediate processing process.

[0024] (3) The production and processing technology of the present invention is simple, and the TWIP steel containing β-Mn phase reinforcement can be obtained by homogenization annealing and subsequent rolling treatment.

[0025] (4) The preparation process of the present invention is clear and accurate, and has high production efficiency. A warm rolling temperature of 500-650° C. and a total pressing amount greater than 80% can produce a significant strengthening effect.

[0026] (5) The device for implementing the process design of the present invention has a simple structure, is easy to control and regulate parameters during the process, has low requirements on equipment and workers, and is convenient for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the metallographic diagram of the TWIP steel obtained in Example 1;

[0028] Figure 2a is the microstructure diagram of the TWIP steel obtained in Example 2;

[0029] Figure 2b is the microstructure diagram of the TWIP steel obtained in Example 3;

[0030] Figure 3a is the dislocation of the TWIP steel obtained in Example 2;

[0031] Figure 3b It is the twin crystal in the TWIP steel obtained in Example 2;

[0032] Figure 3c It is the morphology of the β-Mn strengthening phase and austenite matrix in the TWIP steel obtained in Example 2;

[0033] Figure 3d It is the diffraction spot of β-Mn strengthening phase in TWIP steel obtained in Example 2;

[0034] Figure 3e It is the austenite matrix diffraction spot in the TWIP steel obtained in Example 2;

[0035] Figure 4 1 is the room temperature tensile stress-strain curve of the TWIP steel obtained in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2.

[0036] Figure 5a This is the morphology of the TWIP steel obtained in Example 2 after being stretched at room temperature near the side of the fracture;

[0037] Figure 5b This is the morphology of the TWIP steel obtained in Example 2 after being stretched at room temperature and away from the side of the fracture;

[0038] Figure 5c This is the grain boundary crack propagation and inhibition morphology of the front area of ​​the fracture of the TWIP steel obtained in Example 2 after being stretched at room temperature;

[0039] Figure 5d This is the enlarged crack morphology of the front area of ​​the fracture of the TWIP steel obtained in Example 2 after being stretched at room temperature;

[0040] Figure 6 is a morphology diagram of the TWIP steel obtained in Comparative Example 1;

[0041] Figure 7 This is the morphology of the TWIP steel obtained in Comparative Example 2. DETAILED DESCRIPTION

[0042] The present invention provides a method for strengthening TWIP steel by precipitating a β-Mn phase through warm rolling, wherein the growth of the β-Mn phase is regulated by a simple rolling process, so that the β-Mn phase can be precipitated faster (compared with a solid solution + aging process), and the second phase (β-Mn phase) can be ensured not to grow inside the grains, not to split the grains, and to inhibit crack propagation at the grain boundaries. That is, the present invention utilizes a unique warm rolling process to regulate the contribution of dislocations and twins to the strengthening of TWIP steel, and finally forms a TWIP steel with high strength and high plasticity.

[0043] When TWIP steel is processed by the method of the present invention, only warm rolling treatment is required after hot rolling, and no subsequent processes such as annealing / aging treatment are required. The process is simple, less equipment is required and the equipment requirements are low, the performance is stable, and it has broad application prospects.

[0044] The specific embodiment of the present invention provides a method for strengthening TWIP steel by precipitating β-Mn phase by warm rolling, comprising the following steps performed in sequence:

[0045] S1 homogenization annealing treatment, the specific operation is: put the TWIP steel into a heat treatment furnace at 1100-1200℃ for 1h for homogenization annealing treatment to eliminate the unevenness of the casting structure;

[0046] S2 hot rolling treatment, the specific operation is: take out the TWIP steel after homogenization annealing treatment, carry out multiple hot rolling, and put it back into the 1100-1200℃ heat treatment furnace for 10 minutes after each hot rolling; during the hot rolling process, ensure that the final rolling temperature of the TWIP steel is greater than 900℃, and the single-pass reduction during hot rolling treatment is 15-25%, until the hot rolling is terminated when the total reduction is ≥50%. During the hot rolling process, the total hot rolling reduction and the single-pass reduction can be adjusted according to production, and are not limited to the above corresponding parameter ranges.

[0047] S3 warm rolling treatment: The hot-rolled TWIP steel is cooled to room temperature, and then placed in a heat treatment furnace at 500-650℃ for 20-40 minutes, followed by multiple warm rolling until the total reduction of warm rolling is ≥80%, and after each warm rolling, it is placed in a heat treatment furnace at 500-650℃ for 3-8 minutes, and cooled to room temperature after warm rolling. The reduction of a single pass is 5-10%. If the reduction of a single pass is too large, the roll will be lost. It is necessary to ensure that multiple passes of warm rolling with small reductions are carried out, and the total reduction of warm rolling reaches 80% or more. Only when warm rolling is carried out at 500-600℃ and the reduction is reached, will the strengthening phase be generated in the TWIP steel, and the growth direction of the strengthening phase is adjusted to grow only along the grain boundary.

[0048] The preferred embodiments of the present invention are described in detail below.

[0049] Example 1

[0050] Embodiment 1 of the present invention provides a method for processing TWIP steel, and the specific operations are as follows:

[0051] S1 Homogenization annealing treatment: Cut a rectangular sample of 30mm×40mm×24mm from the purchased hot-rolled commercial TWIP steel (Fe-0.6C-18Mn-2Al-0.5Si-0.016P-0.002S, wt%), and use sandpaper with a particle size of 200#~800# to polish the surface to remove the surface oxide scale. The box-type heat treatment furnace is heated to 1100℃, and then the TWIP steel sample is placed in a high-temperature heat treatment furnace at 1100℃ and kept warm for 1h for homogenization annealing treatment to eliminate the unevenness of the casting structure;

[0052] S2 hot rolling treatment, the specific operation is: take out the TWIP steel after homogenization annealing treatment, and carry out multiple hot rolling. The single pass reduction during hot rolling treatment is 20%. During the hot rolling process, the final rolling temperature of the TWIP steel is guaranteed to be greater than 900℃. After each single hot rolling, it is put back into the 1100℃ heat treatment furnace for 10 minutes; finally hot rolling to 12mm, the hot rolling reduction is 50%. After hot rolling, the TWIP steel is taken out and air-cooled to room temperature, recorded as TWIP-1, and its metallographic diagram is as follows Figure 1 As shown, it indicates that no strengthening phase has been formed at the grain boundaries of the material after hot rolling.

[0053] Example 2

[0054] Preferred embodiment 2 of the present invention provides a method for strengthening TWIP steel by precipitating β-Mn phase through warm rolling, wherein the processed sample is TWIP-1 obtained after being processed in embodiment 1, and the method comprises the following steps:

[0055] Warm rolling treatment: The TWIP-1 steel that has been air-cooled to room temperature is surface-polished with sandpaper of 200# to 800# to remove the surface oxide scale. The heat treatment furnace is heated to 600℃, and the TWIP-1 steel is placed in a 600℃ heat treatment furnace for insulation. After 30 minutes, it is taken out for warm rolling, in which the single-pass rolling reduction is 10%. After each warm rolling, it is put back into a 600℃ box furnace and re-insulated for 5 minutes. The final warm rolling is to 2.4mm, and the total warm rolling reduction is 80%. After warm rolling, the TWIP steel is taken out and air-cooled to room temperature to obtain a TWIP steel reinforced with β-Mn phase, which is recorded as TWIP-2. After testing, the tensile strength of TWIP-2 is as high as 1460MPa, and the elongation at break is 38.1%.

[0056] from Figure 4 The obvious sawtooth flow on the tensile curve indicates that TWIP-2 exhibits an obvious TWIP effect during room temperature stretching.

[0057] Depend on Figure 2a It can be seen from the microstructure diagram that the TWIP-2 obtained after the warm rolling treatment described in Example 2 precipitates a strengthening phase at the grain boundary, is distributed along the grain boundary, and does not grow into the interior of the grain.

[0058] Depend on Figure 3a From the TEM image, we can see that there are a lot of dislocations inside the TWIP-2 material. Figure 3b This indicates that there are twins inside the TWIP-2 material. Figure 3c Graph Combination Figure 3d Figure and Figure 3e The diffraction spots of β-Mn phase and the diffraction spots of austenite matrix were proved.

[0059] Depend on Figure 5a and Figure 5bIt can be clearly seen that both the cracks close to the fracture and the cracks far from the fracture are cracked along the grain boundary. There are small cracks between the β-Mn phases, but they do not extend for a long distance. Figure 5b It can be clearly seen that after the crack initiates, it stops at the strengthening phase. Figure 5c , Figure 5d It can be seen that the crack at the grain boundary expands in the direction of the lower left inclined arrow in the figure, and is suppressed when it encounters the adjacent grain boundary (indicated by the upper right inclined arrow).

[0060] In summary, it can be seen that the TWIP steel (TWIP-2) treated by the method of the present invention has an excellent strength-plasticity combination compared with the hot-rolled TWIP steel (TWIP-1), and the β-Mn phase plays a role in enhancing the strength and plasticity of the material, which can greatly promote industrial applications.

[0061] Example 3

[0062] Preferred embodiment 3 of the present invention provides a method for strengthening TWIP steel by precipitating β-Mn phase through warm rolling, wherein the processed sample is TWIP-1 obtained after being processed in embodiment 1, and the method comprises the following steps:

[0063] Warm rolling treatment: The TWIP-1 steel that has been air-cooled to room temperature is surface-polished with sandpaper of 200# to 800# to remove the surface oxide scale. The heat treatment furnace is heated to 650°C, and the TWIP-1 steel is placed in a 650°C heat treatment furnace for insulation. After 30 minutes, it is taken out for warm rolling. The single-pass rolling reduction is 10%. After each warm rolling, it is put back into a 650°C box furnace and re-insulated for 5 minutes. The final warm rolling is to 2.4mm, and the total warm rolling reduction is 80%. After warm rolling, the TWIP steel is taken out and air-cooled to room temperature to obtain a TWIP steel reinforced with β-Mn phase, which is recorded as TWIP-3. After testing, the tensile strength of TWIP-3 is as high as 1330MPa, and the elongation at break is 49.2%.

[0064] from Figure 4 The obvious sawtooth flow on the tensile curve indicates that TWIP-3 exhibits an obvious TWIP effect during room temperature stretching.

[0065] Depend on Figure 2b It can be seen from the microstructure diagram that the TWIP-3 obtained after the warm rolling treatment described in Example 3 precipitates a strengthening phase at the grain boundary, distributes along the grain boundary, and does not grow into the interior of the grain.

[0066] It can be seen that the TWIP steel (TWIP-3) treated by the method of the present invention has an excellent strength-plasticity combination compared with the hot-rolled TWIP steel (TWIP-1), and the β-Mn phase plays a role in enhancing the strength and plasticity of the material, which can greatly promote industrial applications.

[0067] Comparative Example 1

[0068] This comparative example 1 provides a method for strengthening TWIP steel. The processed sample is TWIP-1 obtained after being processed in Example 1. The method comprises the following steps:

[0069] Warm rolling treatment: The TWIP-1 steel that has been air-cooled to room temperature is surface-polished using sandpaper with a particle size of 200# to 800# to remove the surface oxide scale. The heat treatment furnace is heated to 400°C, and the TWIP-1 steel is placed in a 400°C heat treatment furnace for insulation. After 30 minutes, it is taken out for warm rolling. The single-pass rolling reduction is 10%. After each warm rolling pass, it is placed back in a 400°C box furnace and re-insulated for 5 minutes. The final warm rolling is to 2.4mm, and the total warm rolling reduction is 80%. After warm rolling, the TWIP steel is taken out and air-cooled to room temperature to obtain a TWIP steel that does not contain β-Mn phase reinforcement (such as Figure 6 The tensile strength of TWIP-4 is as high as 1900MPa, but the elongation at break is only 11%. Figure 4 The tensile curve shows that although the material TWIP-4 has high tensile strength, its plastic deformation ability is extremely poor, which has great limitations on the practical application of the material. It can be seen that simply ensuring the total warm rolling pressure and excessively reducing the warm rolling temperature cannot obtain the TWIP product with the beneficial effects of the present invention.

[0070] Comparative Example 2

[0071] This comparative example 2 provides a method for strengthening TWIP steel. The processed sample is TWIP-1 obtained after being processed in Example 1. The method comprises the following steps:

[0072] Warm rolling treatment: The TWIP-1 steel that has been air-cooled to room temperature is polished with sandpaper of 200# to 800# to remove the surface oxide scale. The heat treatment furnace is heated to 600°C, and the TWIP-1 steel is placed in a 600°C heat treatment furnace for insulation. After 30 minutes, it is taken out for warm rolling. The reduction for a single pass is 10%. After each warm rolling pass, it is placed back in a 600°C box furnace and kept warm for 5 minutes. The final warm rolling is to 7.2mm, and the total reduction for warm rolling is 60%. After warm rolling, the TWIP steel is taken out and air-cooled to room temperature. Figure 7 As shown, although a TWIP steel containing a small amount of β-Mn phase reinforcement is obtained, the β-Mn phase will grow inside the austenite grains, thereby splitting the grains and reducing the tensile properties. The tensile strength of the TWIP steel obtained in this comparative example 2 is about 1110 MPa, and the elongation at break is 30%.

[0073] Example 4

[0074] Embodiment 4 of the present invention provides a method for strengthening TWIP steel by precipitating β-Mn phase through warm rolling, and the specific operation is as follows:

[0075] S1 Homogenization annealing treatment: Cut a rectangular sample of 30mm×40mm×24mm from the purchased hot-rolled commercial TWIP steel (Fe-0.4C-20Mn-1.8Al-0.6Si-0.014P-0.002S, wt%), and use sandpaper with a particle size of 200#~800# to polish the surface to remove the surface oxide scale. The box-type heat treatment furnace is heated to 1200℃, and then the TWIP steel sample is placed in a high-temperature heat treatment furnace at 1200℃ and kept warm for 1.5h for homogenization annealing to eliminate the unevenness of the casting structure;

[0076] S2 hot rolling treatment, the specific operation is: take out the TWIP steel after homogenization annealing treatment, and carry out multiple hot rolling, the single pass reduction during hot rolling treatment is 15%, the final rolling temperature of TWIP steel is guaranteed to be greater than 900℃ during hot rolling, and after each single pass hot rolling, it is put back into the 1200℃ heat treatment furnace for 15 minutes; finally hot rolling to 9.6mm, the hot rolling reduction is 60%. After hot rolling, the TWIP steel is taken out and air-cooled to room temperature. Its metallographic diagram shows that no strengthening phase has been formed at the grain boundary of the material after this hot rolling.

[0077] S3 warm rolling treatment: The TWIP steel that has been air-cooled to room temperature is surface-polished with sandpaper of 200# to 800# to remove the surface oxide scale. The heat treatment furnace is heated to 500°C, and the TWIP-1 steel is placed in a 500°C heat treatment furnace for insulation. After 30 minutes, it is taken out for warm rolling, where the single-pass rolling reduction is 8%. After each warm rolling, it is put back into a 500°C box furnace and re-insulated for 3 minutes. The final warm rolling is to 1.44mm, and the total warm rolling reduction is 85%. After warm rolling, the TWIP steel is taken out and air-cooled to room temperature to obtain a TWIP steel reinforced with β-Mn phase, and the strengthening phase precipitates at the grain boundary, distributes along the grain boundary, and does not grow into the interior of the grain.

[0078] Example 5

[0079] Embodiment 5 of the present invention provides a method for strengthening TWIP steel by precipitating β-Mn phase through warm rolling, and the specific operation is as follows:

[0080] S1 Homogenization annealing treatment: Cut a rectangular sample of 30mm×40mm×24mm from the purchased hot-rolled commercial TWIP steel (Fe-0.35C-25Mn-2Al-0.6Si-0.015P-0.002S, wt%), and use sandpaper with a particle size of 200# to 800# to polish the surface to remove the surface oxide scale. The box-type heat treatment furnace is heated to 1150℃, and then the TWIP steel sample is placed in a high-temperature heat treatment furnace at 1150℃ and kept warm for 1.2h for homogenization annealing treatment to eliminate the unevenness of the casting structure;

[0081] S2 hot rolling treatment, the specific operation is: take out the TWIP steel after homogenization annealing treatment, and carry out multiple hot rolling, the single pass reduction during hot rolling treatment is 25%, the final rolling temperature of TWIP steel is guaranteed to be greater than 900℃ during hot rolling, and after each single pass hot rolling, it is put back into the 1150℃ heat treatment furnace for 12 minutes; finally hot rolling to 12mm, the hot rolling reduction is 50%. After hot rolling, the TWIP steel is taken out and air-cooled to room temperature. Its metallographic diagram shows that no strengthening phase has been formed at the grain boundary of the material after this hot rolling.

[0082] S3 warm rolling treatment: The TWIP steel that has been air-cooled to room temperature is surface-polished with sandpaper of 200# to 800# to remove the surface oxide scale. The heat treatment furnace is heated to 550°C, and the TWIP-1 steel is placed in a 550°C heat treatment furnace for insulation. After 30 minutes, it is taken out for warm rolling, where the single-pass rolling reduction is 5%. After each warm rolling, it is put back into a 550°C box furnace and re-insulated for 8 minutes. Finally, it is warm-rolled to 2.4mm, and the total warm rolling reduction is 80%. After warm rolling, the TWIP steel is taken out and air-cooled to room temperature to obtain a TWIP steel reinforced with β-Mn phase, and the strengthening phase precipitates at the grain boundary, distributes along the grain boundary, and does not grow into the interior of the grain.

[0083] The above are only preferred embodiments of the present invention. It should be understood that the description of the above embodiments is only used to help understand the method and core ideas of the present invention, and is not used to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, etc. made within the ideas and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for strengthening TWIP steel by precipitating β-Mn phase through warm rolling, characterized in that: The steps are as follows, in order: S1 homogenization annealing treatment; S2 hot rolling treatment; S3 warm rolling treatment: the hot-rolled TWIP steel is cooled to room temperature, and then placed in a heat treatment furnace at 500-650°C for 20-40 minutes, followed by multiple warm rolling passes until the total warm rolling reduction is ≥80%, and after each warm rolling pass, it is placed back in a heat treatment furnace at 500-650°C for 3-8 minutes, and cooled to room temperature after the warm rolling.

2. The method for strengthening TWIP steel by precipitating β-Mn phase by warm rolling according to claim 1, characterized in that: The specific operation of the homogenization annealing treatment is: putting the TWIP steel into a heat treatment furnace at 1100-1200° C. and keeping it at this temperature for 1-1.5 hours for homogenization annealing treatment.

3. The method for strengthening TWIP steel by precipitating β-Mn phase by warm rolling according to claim 1, characterized in that: The specific operation of the hot rolling treatment is: taking out the TWIP steel after the homogenization annealing treatment, performing multiple hot rolling, and after each hot rolling, putting it back into the 1100-1200° C. heat treatment furnace for 10-15 minutes.

4. The method for strengthening TWIP steel by precipitating β-Mn phase by warm rolling according to claim 3, characterized in that: During the hot rolling process, the final rolling temperature of TWIP steel is guaranteed to be greater than 900℃.

5. The method for strengthening TWIP steel by precipitating β-Mn phase by warm rolling according to claim 3, characterized in that: During the hot rolling process, the reduction in a single pass is 15-25%, and the hot rolling is terminated when the total reduction is ≥50%.

6. The method for strengthening TWIP steel by precipitating β-Mn phase by warm rolling according to claim 1, characterized in that: The cooling method of TWIP steel after hot rolling is air cooling to room temperature.

7. The method for strengthening TWIP steel by precipitating β-Mn phase by warm rolling according to claim 1, characterized in that: During warm rolling, the reduction in a single pass is 5 to 10%.

8. The method for strengthening TWIP steel by precipitating β-Mn phase by warm rolling according to claim 1, characterized in that: The cooling method of TWIP steel after warm rolling is air cooling to room temperature.

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