A high yield strength and high strength-plasticity TWIP steel and its preparation method

Abstract

The invention discloses a high yield strength and high strength and plasticity TWIP steel and a preparation method thereof, which belongs to the technical field of TWIP steel, and solves the problem that the mechanical properties of TWIP steel in the prior art cannot meet the demand or the process is difficult and the cost is high. The components of the high yield strength and high strength and plasticity TWIP steel include by mass percentage: Mn: 15% to 20%, C: 0.3% to 0.9%, Al: 0.8% to 2.5%, Si: 0.8% to 2.5%, Cr: 0.1% to 2.4%, V: 0.001% to 0.5%, Nb: 0.001% to 0.3%, Ti: 0.001% to 0.07%, P≤0.01%, S≤0.008%, and the balance is Fe and unavoidable impurities. The high yield strength and high strength and plasticity TWIP steel of the invention has high yield strength and high strength and plasticity.

Description

Technical Field

[0001] The invention relates to the technical field of TWIP steel, and in particular to a high-yield strength and high-strength-plasticity TWIP steel and a preparation method thereof. Background Art

[0002] Relevant data show that if the overall weight of the car is reduced by 10%, the corresponding fuel consumption will be reduced by 3% to 7%. Therefore, while ensuring the safety of the car, the use of a large amount of high-strength steel to make the car body lightweight is the future development direction of the automotive industry. Twinning induced plasticity (TWIP) steel is a second-generation high-strength steel for automobiles. It has excellent plasticity, high strain hardening and high energy absorption capacity. It is an ideal impact-resistant structural material for automobiles and has attracted widespread attention from the steel and automobile industries. However, compared with other advanced high-strength steels for automobiles, TWIP steel has a lower yield strength, which limits the goal of using TWIP steel to reduce the wall thickness and weight of parts in engineering designs based on yield strength.

[0003] To solve the above problems, researchers have conducted a lot of research on the strengthening mechanism and processing technology of TWIP steel, and found that the main strengthening mechanisms in TWIP steel are: solid solution strengthening, grain boundary strengthening, dislocation strengthening, and precipitation phase strengthening. As a result, a variety of technologies to improve the yield strength of TWIP steel have been developed, including: partial recrystallization, pre-deformation, grain refinement, precipitation strengthening, and microalloying. Among them, partial recrystallization and pre-deformation processes can improve the yield strength of TWIP steel with the help of dislocation strengthening, but the plasticity of TWIP steel will be significantly reduced. Although grain refinement is an effective means to effectively improve the yield strength of TWIP steel, there is a limit to improving the yield strength simply by grain refinement. In actual industrial production, it is very difficult to obtain TWIP steel with a grain size of less than 3μm. For example, in CN106191404A and CN113930659A, in order to obtain a grain size of about 1 μm for TWIP steel, it is necessary to undergo hot rolling + warm rolling + asynchronous rolling + cold rolling + high temperature short-time annealing process or hot rolling + low temperature cold rolling + instantaneous annealing + tempering process, respectively, and the industrial production process is very difficult. It can be seen that the existing TWIP steel cannot meet the industrial application requirements of both mechanical properties and process feasibility, which limits the wider application of TWIP steel in the fields of automotive steel and petrochemical industry. Summary of the invention

[0004] In view of the above situation, the present invention aims to provide a high yield strength and high strength-plasticity TWIP steel and a preparation method thereof, so as to solve the problem that the mechanical properties of the existing TWIP steel cannot meet the requirements or the process is difficult and the cost is high.

[0005] The purpose of the present invention is mainly achieved through the following technical solutions:

[0006] On the one hand, the present invention provides a high yield strength and high strength and plasticity TWIP steel, wherein the components of the high yield strength and high strength and plasticity TWIP steel include, by mass percentage: Mn: 15% to 20%, C: 0.3% to 0.9%, Al: 0.8% to 2.5%, Si: 0.8% to 2.5%, Cr: 0.1% to 2.4%, V: 0.001% to 0.5%, Nb: 0.001% to 0.3%, Ti: 0.001% to 0.07%, P≤0.01%, S≤0.008%, and the balance is Fe and unavoidable impurities.

[0007] Furthermore, the components of the high yield strength and high strength-plasticity TWIP steel are, by mass percentage, Mn: 16% to 20%, C: 0.4% to 0.9%, Al: 0.85% to 2.5%, Si: 0.9% to 2.5%, Cr: 0.1% to 2.4%, V: 0.1% to 0.5%, Nb: 0.005% to 0.3%, Ti: 0.03% to 0.07%, P≤0.01%, S≤0.008%, and the remainder is Fe and unavoidable impurities.

[0008] Furthermore, the microstructure of the high yield strength and high strength-ductility TWIP steel is completely recrystallized austenite grains + carbide precipitation phase.

[0009] Furthermore, in the microstructure of high yield strength and high strength-ductility TWIP steel, carbides mainly include (Ti,Nb)C and V4C3.

[0010] The present invention also provides a method for preparing the above-mentioned high yield strength and high strength-plasticity TWIP steel, comprising the following steps:

[0011] Step 1, smelting and pouring into steel ingots;

[0012] Step 2: Two-stage homogenization treatment;

[0013] Step 3: Forging;

[0014] Step 4, air cooling to room temperature after multiple hot rolling;

[0015] Step 5, performing multiple cold rolling on the hot rolled plate;

[0016] Step 6: Recrystallization annealing treatment to obtain high yield strength and high strength-ductility TWIP steel.

[0017] Furthermore, in step 2, the two-stage homogenization process includes:

[0018] S201, heat to 640-660°C, keep warm for 1-2h;

[0019] S202. Continue to raise the temperature to 1140-1160°C, keep warm for 17-25 hours and then air cool.

[0020] Furthermore, the heating rate in S201 is lower than the heating rate in S202.

[0021] Furthermore, in step 3, the initial forging temperature is controlled to be 1080-1130°C, and the final forging temperature is controlled to be 960-1010°C.

[0022] Furthermore, in step 4, the starting temperature of hot rolling is 1080-1130°C, and the final rolling temperature is 960-1010°C.

[0023] Furthermore, in step 6, the step of recrystallization annealing treatment includes: keeping the temperature at 950-1150° C. for 5-80 minutes.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] a) The high yield strength and high strength and plasticity TWIP steel of the present invention adopts the Fe-Mn-C-Al-Si-Cr component system as the matrix component, and the content of each element is precisely controlled to ensure that the TWIP steel of the present invention has good austenite stability. The microstructure after complete recrystallization annealing is completely recrystallized austenite grains + carbide precipitation phase, the average grain size of the austenite grains is 3-40 μm, the carbides mainly include (Ti, Nb) C and V4C3, the size of (Ti, Nb) C is 10-30 μm, the size of V4C3 is 5-40 nm, and the stacking fault energy is 20-30 J / m 2 Within this range, it is ensured that the TWIP steel of the present invention has high yield strength and high strength-ductility product.

[0026] b) The TWIP steel of the present invention is compositely alloyed with V, Nb and Ti, so that a relatively large (Ti, Nb)C precipitate phase and a dispersed nano-scale precipitate phase V4C3 are present in the TWIP steel; the (Ti, Nb)C has a size of about 10 to 30 μm and precipitates at high temperature, which can pin the grains and hinder the growth of austenite grains during hot rolling; and the nano-scale precipitate phase V4C3 has a size of about 5 to 40 nm and hinders the movement of dislocations during deformation, thereby significantly improving the strength and plasticity of the TWIP steel.

[0027] c) The multi-pass hot rolling + cold rolling + recrystallization annealing process used in the preparation method of the high yield strength and high strength and plasticity TWIP steel of the present invention is simple and economical, has high process feasibility, and can be used to achieve large-scale industrial production based on existing production lines.

[0028] d) The high yield strength and high strength-plasticity product TWIP steel of the present invention has high yield strength and high strength-plasticity product. The specific properties are as follows: yield strength is 540MPa or more (e.g., 545-680MPa), tensile strength is 960MPa or more (e.g., 967-1110MPa), elongation is 50% or more (e.g., 51%-60%), and strength-plasticity product is 52730MPa% or more (e.g., 52730-64410MPa%).

[0029] Other features and advantages of the present invention will be described in the following description, and part of them will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the contents particularly pointed out in the written description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0031] Figure 1 is the grain structure of the TWIP steel after annealing in Example 2;

[0032] Figure 2 This is the precipitation phase morphology of the TWIP steel in Example 2. DETAILED DESCRIPTION

[0033] Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used to explain the principles of the present invention together with the embodiments of the present invention.

[0034] The invention provides a high yield strength and high strength and plasticity TWIP steel. The components of the high yield strength and high strength and plasticity TWIP steel include, by mass percentage, Mn: 15% to 20%, C: 0.3% to 0.9%, Al: 0.8% to 2.5%, Si: 0.8% to 2.5%, Cr: 0.1% to 2.4%, V: 0.001% to 0.5%, Nb: 0.001% to 0.3%, Ti: 0.001% to 0.07%, P≤0.01%, S≤0.008%, and the balance is Fe and unavoidable impurities.

[0035] The following is a detailed description of the effects and dosage of the components in the present invention:

[0036] Mn: The role of Mn is to expand the austenite phase region and reduce the transformation temperature Ms of martensite, so that TWIP steel has a stable austenite structure at room temperature. At the same time, manganese can significantly increase the stacking fault energy and reduce the tendency of deformation-induced martensite phase transformation. However, since Mn can cause the yield strength of TWIP steel to decrease and the plasticity to increase, the Mn element in the present invention is controlled at 15% to 20%.

[0037] C: C can increase the stacking fault energy, which helps to maintain single-phase austenite at room temperature. Secondly, carbon atoms are dissolved in the lattice gaps of iron atoms, and the strength and hardness of TWIP steel are improved through lattice distortion. However, when the carbon content is too high, exceeding the solid solubility in the lattice, carbon atoms often combine with strong carbide elements and precipitate in the form of carbides. Since such carbides have high binding energy, they are difficult to eliminate once precipitated and are distributed along the grain boundaries, resulting in reduced plasticity and toughness. At the same time, the welding performance will also be affected. Therefore, the C element in the present invention is controlled at 0.3% to 0.9%.

[0038] Al: The addition of aluminum can increase the stacking fault energy, help the twinning process, and improve the plastic deformation ability. At the same time, the aluminum atoms have weak bonding force, which can alleviate the degree of work hardening. However, since aluminum is easily oxidized, it is easy to generate oxide residues to block the casting port during steel plate casting, so high aluminum content is not conducive to the industrial production of TWIP steel. Therefore, in the present invention, the Al element is controlled at 0.8% to 2.5%.

[0039] Si: Silicon can be dissolved in the austenite matrix of high manganese steel. On the one hand, silicon atoms can play a solid solution strengthening effect, and in the process of dissolution, due to competition with carbon atoms, the solubility of carbon in austenite can be changed; on the other hand, when the silicon content increases, the stacking fault energy is reduced, which is conducive to the transformation from face-centered cubic to body-centered cubic during deformation. However, too high silicon content will affect the surface quality of the steel plate and reduce the hot rolling performance of the steel plate. Therefore, the Si element in the present invention is controlled at 0.8% to 2.5%.

[0040] Cr: Cr can reduce the stacking fault energy of TWIP steel and refine the width and spacing of deformation twins during deformation, which can improve strength and elongation at the same time. However, Cr is a strong ferrite forming element, which will reduce the austenite phase area and easily combine with C to form Cr. 23 C6 carbide seriously deteriorates various properties of steel, so the Cr element is controlled within 0.1% to 2.4% in the present invention.

[0041] V: When V, Nb, and Ti are added to the steel, Nb and Ti will combine with C to form MC carbides, which can hinder the growth of austenite grains during recrystallization of TWIP steel and play a role in refining grains; V and C combine to form V4C3 nanoscale precipitation phases, which can improve the strength and plasticity of TWIP steel through precipitation strengthening. Therefore, in the present invention, V, Nb, and Ti elements are added in combination, and the grains are refined by Nb and Ti. The precipitation of nanoparticles is controlled by an appropriate amount of V element to ensure that nano-sized hard phase particles are precipitated in fine austenite grains to improve strength. Since the Ti element content is greater than 0.07%, it is easy to form coarse TiC, and the grain refining effect is weakened. Therefore, in the present invention, V is controlled within the range of 0.001% to 0.5%, Nb is controlled within the range of 0.001% to 0.3%, and Ti is controlled within the range of 0.001% to 0.07%.

[0042] P, S: P and S are impurity elements in TWIP steel, which will deteriorate the mechanical properties of the alloy. Therefore, in the present invention, P is controlled to be ≤ 0.01% and S to be ≤ 0.008%.

[0043] In order to further improve the comprehensive properties of the above-mentioned high yield strength and high strength and plasticity TWIP steel, the components of the above-mentioned high yield strength and high strength and plasticity TWIP steel are calculated by mass percentage: Mn: 16%~20%, C: 0.4%~0.9%, Al: 0.85%~2.5%, Si: 0.9%~2.5%, Cr: 0.1%~2.4%, V: 0.1%~0.5%, Nb: 0.005%~0.3%, Ti: 0.03%~0.07%, P≤0.01%, S≤0.008%, and the balance is Fe and unavoidable impurities.

[0044] Specifically, the microstructure of the high yield strength and high strength and plasticity TWIP steel of the present invention is a completely recrystallized austenite grain + carbide precipitation phase, the average grain size of the austenite grain is 3 to 40 μm (for example, 4 to 15 μm), the carbides mainly include (Ti, Nb) C and V4C3, the size of (Ti, Nb) C is 10 to 30 μm, and the size of V4C3 is 5 to 40 nm (for example, 10 to 30 nm); the stacking fault energy is 20 to 30 J / m 2 within the range.

[0045] On the other hand, the present invention also provides a method for preparing TWIP steel with high yield strength and high strength-plasticity product, which includes smelting, homogenization treatment, forging, hot rolling, cold rolling and heat treatment.

[0046] Specifically, the preparation method of the high yield strength and high strength-plasticity TWIP steel comprises the following steps:

[0047] Step 1, smelting: raw materials are mixed in proportion, and protective gas is introduced into a vacuum furnace for smelting, and then the smelting is followed by pouring into a steel ingot;

[0048] Step 2: Two-stage homogenization treatment;

[0049] Step 3: Forging;

[0050] Step 4, air cooling to room temperature after multiple hot rolling;

[0051] Step 5, pickling the hot-rolled plate and then cold-rolling it for multiple passes;

[0052] Step 6: Recrystallization annealing treatment to obtain high yield strength and high strength-ductility TWIP steel.

[0053] Specifically, in the above step 1, the protective gas may be argon.

[0054] Specifically, in the above step 2, since the high manganese TWIP steel has low thermal conductivity but a large thermal expansion coefficient, the temperature difference during the heat treatment process will cause large thermal stress, and the simultaneous action of casting stress and thermal stress will cause cracks. Therefore, during the heat treatment process, the TWIP steel needs to control the heating rate and perform a two-stage homogenization treatment to control the internal and external temperature difference. Specifically, the steps of the two-stage homogenization treatment include:

[0055] S201, heat to 640-660°C, keep warm for 1-2h;

[0056] S202. Continue to raise the temperature to 1140-1160°C, keep warm for 17-25 hours and then air cool.

[0057] Specifically, considering that thermal stress is more easily accumulated at low temperatures, the heating rate in S201 is lower than the heating rate in S202 .

[0058] Specifically, the heating rate in S201 is 55-65° C. / min.

[0059] Specifically, the heating rate in S202 is 140-160° C. / min.

[0060] Specifically, in the above step 3, considering that high manganese steel is prone to precipitate carbides below 960°C, and the lower the temperature, the faster the precipitation rate, the initial forging temperature is controlled to be 1080-1130°C, and the final forging temperature is controlled to be 960-1010°C.

[0061] Specifically, in the above step 4, the number of hot rolling is 4 to 8 times, and the deformation amount of each pass is 15% to 25%.

[0062] Specifically, in the above step 4, the starting temperature of hot rolling is 1080-1130°C, and the finishing temperature is 960-1010°C.

[0063] Specifically, in the above step 5, the purpose of pickling is to wash away the oxide scale on the surface of the rolled plate.

[0064] Specifically, in the above step 5, the number of cold rolling passes is 5 to 10, and the deformation amount of each pass is between 2% and 15%.

[0065] Specifically, in the above step 6, the step of recrystallization annealing treatment includes: keeping the temperature at 950-1150° C. for 5-80 minutes.

[0066] The high yield strength and high strength-ductility product TWIP steel of the present invention has a yield strength of 540 MPa or more (e.g., 545-680 MPa), a tensile strength of 960 MPa or more (e.g., 967-1110 MPa), an elongation of 50% or more (e.g., 51%-60%), and a strength-ductility product of 52730 MPa% or more (e.g., 52730-64410 MPa%).

[0067] The high yield strength and high strength and plasticity TWIP steel of the present invention adopts the Fe-Mn-C-Al-Si-Cr component system as the matrix component, and the content of each element is precisely controlled to ensure that the TWIP steel of the present invention has good austenite stability, and the microstructure after complete recrystallization annealing is completely recrystallized austenite grains + carbide precipitation phase, the average grain size of the austenite grains is 3-40 μm, the carbides mainly include (Ti, Nb) C and V4C3, the size of (Ti, Nb) C is 10-30 μm, the size of V4C3 is 5-40 nm, and the stacking fault energy is 20-30 J / m 2 Within this range, it is ensured that the TWIP steel of the present invention has high yield strength and high strength-ductility product.

[0068] The TWIP steel of the present invention is compositely alloyed with V, Nb and Ti, so that a relatively large (Ti, Nb)C precipitation phase and a dispersedly distributed nano-scale precipitation phase V4C3 exist in the TWIP steel; the (Ti, Nb)C has a size of about 10 to 30 μm and precipitates at high temperature, which can pin the grains and hinder the growth of austenite grains during hot rolling; and the nano-scale precipitation phase V4C3 has a size of about 5 to 40 nm and hinders the movement of dislocations during deformation, thereby significantly improving the strength and plasticity of the TWIP steel.

[0069] The multi-pass hot rolling + cold rolling + recrystallization annealing process adopted in the preparation method of the high yield strength and high strength and plasticity TWIP steel of the present invention is simple and economical, has high process feasibility, and can realize large-scale industrial production based on existing production lines.

[0070] Examples 1-5

[0071] The advantages of precise control of the composition and process parameters of the steel of the present invention are demonstrated below with specific examples and comparative examples.

[0072] Examples 1-5 of the present invention provide a high yield strength and high strength-ductility TWIP steel. The chemical compositions of the steels of Examples 1-5 are shown in Table 1.

[0073] Example 1

[0074] The method for preparing the steel of Example 1 comprises:

[0075] 1. Melting: Mix the raw materials of each component according to the proportion, introduce protective gas argon into the vacuum furnace for melting, and cast into steel ingots after melting;

[0076] 2. Homogenization treatment: heat up to 650℃ at 60℃ / min, keep warm for 1.5h, then heat up to 1150℃ at 150℃ / min, keep warm for 20h, then air cool;

[0077] 3. Forging: The starting forging temperature is 1100℃, the final forging temperature is 1000℃, and the forging is made into a 30mm thick square forging billet;

[0078] 4. Hot rolling: The starting temperature of hot rolling is 1100℃, the final rolling temperature is 1000℃, and after 8 passes of hot rolling to 6mm, it is air-cooled to room temperature;

[0079] 5. Cold rolling: The hot rolled plate is pickled to remove the oxide scale on the surface of the rolled plate, and then cold rolled for 10 passes to 2mm;

[0080] 6. Heat treatment: annealing at 950°C for 40 min.

[0081] Example 2

[0082] This embodiment provides a TWIP steel, which has the same composition as that of Example 1 and is prepared in substantially the same manner as that of Example 1, except that the final heat treatment process is annealing at 950° C. for 10 min.

[0083] Example 3

[0084] This embodiment provides a TWIP steel, and its composition is shown in Table 1. The preparation method is substantially the same as that of Embodiment 1, but in order to control the grain size substantially the same as that of Embodiment 1, the final heat treatment process is annealing at 950°C for 30 minutes.

[0085] Example 4

[0086] This embodiment provides a TWIP steel, the composition of which is shown in Table 1 above.

[0087] The method for preparing the steel of Example 4 comprises:

[0088] 1. Melting: Mix the raw materials of each component according to the proportion, introduce protective gas argon into the vacuum furnace for melting, and cast into steel ingots after melting;

[0089] 2. Homogenization treatment: heat up to 650℃ at 60℃ / min, keep warm for 1.5h, then heat up to 1150℃ at 150℃ / min, keep warm for 20h, then air cool;

[0090] 3. Forging: The starting temperature of forging is 1080℃, the final forging temperature is 960℃, and the forging is made into a 30mm thick square forging billet;

[0091] 4. Hot rolling: The starting temperature of hot rolling is 1100℃, the final rolling temperature is 960℃, hot rolling is performed for 8 passes to 4mm, and then air-cooled to room temperature;

[0092] 5. Cold rolling: The hot rolled plate is pickled to remove the oxide scale on the surface of the rolled plate, and then cold rolled for 10 passes to 2mm;

[0093] 6. Heat treatment: annealing at 1050°C for 20 min.

[0094] Example 5

[0095] This embodiment provides a TWIP steel, the composition of which is shown in Table 1 above.

[0096] The method for preparing the steel of Example 5 comprises:

[0097] 1. Melting: Mix the raw materials of each component according to the proportion, introduce protective gas argon into the vacuum furnace for melting, and cast into steel ingots after melting;

[0098] 2. Homogenization treatment: heat up to 650℃ at 60℃ / min, keep warm for 1.5h, then heat up to 1150℃ at 150℃ / min, keep warm for 20h, then air cool;

[0099] 3. Forging: The starting forging temperature is 1100℃, the final forging temperature is 1000℃, and the forging is made into a 30mm thick square forging billet;

[0100] 4. Hot rolling: The starting temperature of hot rolling is 1080℃, the final rolling temperature is 1010℃, and it is hot rolled for 5 times to 6mm and then air-cooled to room temperature;

[0101] 5. Cold rolling: The hot rolled plate is pickled to remove the oxide scale on the surface of the rolled plate, and then cold rolled for 6 passes to 2mm;

[0102] 6. Heat treatment: annealing at 1000°C for 30 minutes.

[0103] Example 6

[0104] This embodiment provides a TWIP steel, the composition of which is shown in Table 1 above.

[0105] The method for preparing the steel of Example 6 comprises:

[0106] 1. Melting: Mix the raw materials of each component according to the proportion, introduce protective gas argon into the vacuum furnace for melting, and cast into steel ingots after melting;

[0107] 2. Homogenization treatment: heat up to 650℃ at 60℃ / min, keep warm for 1.5h, then heat up to 1150℃ at 150℃ / min, keep warm for 25h, then air cool;

[0108] 3. Forging: The starting forging temperature is 1100℃, the final forging temperature is 1000℃, and the forging is made into a 30mm thick square forging billet;

[0109] 4. Hot rolling: The starting temperature of hot rolling is 1100℃, the final rolling temperature is 1000℃, and after 8 passes of hot rolling to 6mm, it is air-cooled to room temperature;

[0110] 5. Cold rolling: The hot rolled plate is pickled to remove the oxide scale on the surface of the rolled plate, and then cold rolled for 10 passes to 2mm;

[0111] 6. Heat treatment: annealing at 1100°C for 10 min.

[0112] The inventor has conducted a large number of experimental studies during the research process, and now uses some solutions with poor performance as comparative examples.

[0113] Comparative Example 1

[0114] This comparative example provides a TWIP steel, the components of which are shown in Table 1. The preparation method is substantially the same as that of Example 1, but in order to control the grain size substantially the same as that of Example 1, the final heat treatment process is annealing at 950° C. for 20 min.

[0115] Comparative Example 2

[0116] This comparative example provides a TWIP steel, the components of which are shown in Table 1. The preparation method is the same as that of Example 3, which will not be repeated here.

[0117] The components of the embodiments and comparative examples are shown in Table 1 below, and the microstructure and main performance test results of the embodiments and comparative examples are shown in Table 2. Figure 1 The grain structure of the TWIP steel in Example 2 after annealing is shown. Figure 2 Shown is the precipitation phase morphology of the TWIP steel in Example 2.

[0118] Table 1 Chemical composition, wt%

[0119]

[0120] Table 2 Partial performance test results and organization

[0121]

[0122]

[0123] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A high yield strength and high strength-plasticity TWIP steel, characterized in that: The components of the high yield strength and high strength and plasticity TWIP steel are as follows by mass percentage: Mn: 15%-20%, C: 0.3%-0.9%, Al: 0.8%-2.5%, Si: 0.8%-2.5%, Cr: 0.1%-2.4%, V: 0.001%-0.5%, Nb: 0.001%-0.283%, Ti: 0.001%-0.07%, P≤0.01%, S≤0.008%, and the balance is Fe and unavoidable impurities; The microstructure of the high yield strength and high strength and plasticity TWIP steel is completely recrystallized austenite grains + carbide precipitation phase; the average grain size of the austenite grains is 3-40 μm; Carbides include (Ti, Nb) C and V4C3; the size of (Ti, Nb) C is 10~30μm, and the size of V4C3 is 5~40nm; The high yield strength and high strength-plasticity product TWIP steel has a yield strength of more than 540 MPa, a tensile strength of more than 960 MPa, an elongation of more than 50%, and a strength-plasticity product of more than 52730 MPa%.

2. The high yield strength and high strength-ductility TWIP steel according to claim 1, characterized in that: The components of the high yield strength and high strength and plasticity TWIP steel are, by mass percentage, Mn: 16%~20%, C: 0.4%~0.9%, Al: 0.85%~2.5%, Si: 0.9%~2.5%, Cr: 0.1%~2.4%, V: 0.1%~0.5%, Nb: 0.005%~0.283%, Ti: 0.03%~0.07%, P≤0.01%, S≤0.008%, and the balance is Fe and unavoidable impurities.

3. A method for preparing the high yield strength and high strength-plasticity TWIP steel according to claim 1 or 2, characterized in that: The following steps are involved: Step 1, smelting and pouring into steel ingots; Step 2: Two-stage homogenization treatment; Step 3: Forging; Step 4, air cooling to room temperature after multiple hot rolling; Step 5, performing multiple cold rolling on the hot rolled plate; Step 6: Recrystallization annealing treatment to obtain high yield strength and high strength-ductility TWIP steel.

4. The preparation method according to claim 3, characterized in that: In step 2, the two-stage homogenization process comprises: S201, heat up to 640~660℃, keep warm for 1~2h; S202. Continue to raise the temperature to 1140~1160℃, keep warm for 17~25h and then air cool.

5. The preparation method according to claim 4, characterized in that: The heating rate in S201 is lower than the heating rate in S202.

6. The preparation method according to claim 3, characterized in that: In step 3, the initial forging temperature is controlled to be 1080-1130°C, and the final forging temperature is controlled to be 960-1010°C.

7. The preparation method according to claim 3, characterized in that: In step 4, the starting temperature of hot rolling is 1080-1130° C., and the final rolling temperature is 960-1010° C.

8. The preparation method according to any one of claims 3 to 7, characterized in that: In step 6, the recrystallization annealing step includes: keeping the temperature at 950-1150° C. for 5-80 minutes.

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