Austenite-based lightweight high-strength steel and large strain warm rolling preparation method thereof

Abstract

The present invention discloses an austenitic-based lightweight high-strength steel and a large strain warm rolling preparation method thereof, belonging to the field of cold-rolled plate and strip production. The preparation method comprises: a smelting process: smelting and casting into slabs according to the following chemical composition: by weight percentage, C: 0.32% to 0.50%, Si: 0.20% to 0.50%, Mn: 12.0% to 16.0%, P≤0.020%, S≤0.010%, Als: 6.0% to 9.0%, Ti: 0.020% to 0.050%, the balance being Fe and unavoidable impurities; a hot rolling process: The slab is heated to 1230℃~1270℃ and kept warm for 3~7 hours before being taken out of the furnace and hot rolled into strip steel. The final rolling temperature is 830℃~900℃ and then air-cooled to room temperature. Warm rolling process: the hot-rolled strip steel is heated to 400℃~460℃ and then warm rolled. The reduction rate of each pass is ≥15%. Heat treatment process: the warm-rolled strip steel is heated to 900℃~980℃ and kept warm for 1~4 hours. After solution treatment, it is cooled to room temperature to obtain austenitic light-weight high-strength steel. The austenitic light-weight high-strength steel prepared by the method of the present invention has a yield strength of 550~650MPa, a tensile strength of 950~1030MPa, and an elongation A 50 Reach 34.0~40.0%.

Description

Technical Field

[0001] The present invention belongs to the field of cold-rolled plate and strip production, and specifically relates to a method for preparing austenite-based lightweight high-strength steel by large-strain warm rolling and the austenite-based lightweight high-strength steel prepared thereby. Background Art

[0002] The automotive manufacturing industry is a pillar of the national economy. With energy shortages and environmental pollution becoming increasingly prominent, and under the constraints of the nation's "dual carbon" goals, lightweighting has become a key focus for carbon emission reduction in the automotive industry. Currently, there are three main approaches to achieving vehicle lightweighting: First, the use of lightweight raw materials, such as aluminum alloys, magnesium alloys, and carbon fiber composites. While the use of lightweight raw materials can reduce overall vehicle weight, these materials suffer from limitations such as complex forming processes, poor welding performance, low crash absorption, high prices, and low production volumes, limiting their market adoption. Second, the use of ultra-high-strength steel in place of conventional automotive steel reduces vehicle weight by reducing sheet thickness. However, as sheet strength increases, forming capacity decreases, leading to cracking, wrinkling, and excessive springback. Furthermore, as sheet thickness decreases, the stiffness of certain vehicle components decreases excessively, leading to acoustic issues that create uncomfortable conditions for passengers, limiting their widespread adoption. Third, the development of a steel grade that combines high strength, high elongation, and low density. Low-density steel offers excellent mechanical and physical properties and significant weight reduction, making it a hot research topic for automakers and their suppliers.

[0003] The following literature is available on the preparation of steel grades that combine high strength, high elongation and low density:

[0004] CN 115537672 A discloses a low-cost austenitic steel with a yield strength greater than 1000 MPa and its warm rolling preparation process. The chemical composition of the steel, in terms of weight percentage, is as follows: Mn: 31.7-32.2%, C: 0.58-0.69%, with the remainder being Fe and other unavoidable impurities. The processing of the smelted high-manganese austenitic steel is divided into two forging steps and warm rolling. The first forging step involves solution treatment of the high-manganese steel ingot at a solution temperature of 1000-1200°C for 3-5 hours; followed by the first forging step at an initial forging temperature of ≥800°C and a final forging temperature of ≥600°C. The thickness of the slab after forging is 100-105 mm. The second forging step involves the slab obtained from the first forging step being kept at 800-900°C for 2-4 hours. h; then a second forging is performed, with an initial forging temperature of 700-800°C and a final forging temperature of ≥600°C. The thickness of the slab after forging is 50-60mm; warm rolling of the slab: the slab obtained after the two forging passes is kept at a temperature of 500-600°C for 20-40 minutes; then rolling is performed, with an initial rolling temperature of 500-550°C and a final rolling temperature of ≥400°C. The thickness of the steel plate after rolling is 7-7.6mm, and the rolling deformation is more than 80%. This patented warm rolling is performed after heating to 500-600°C. As the rolling passes proceed, the temperature gradually decreases, which is not conducive to obtaining good edge quality or uniform microstructure and properties.

[0005] CN 111593263 A discloses a preparation method of high-strength low-density steel and a manufacturing method thereof. The chemical composition of the high-strength low-density steel, calculated by weight percentage, is as follows: Mn: 18% to 20%, Al: 5% to 7%, C: 0.03% to 0.04%, Ni: 7% to 8%, Si: 1.0% to 1.2%, Mo: 1.0% to 1.5%, Ti: 1.0% to 1.2%, the balance being Fe, and no other impurity elements. The preparation scheme is as follows: mixing: according to the material composition of step (1), the components are mixed to obtain a mixed powder; the microstructure of the mixed powder is nearly spherical, and the purity is above 99.5%, wherein the particle size of the iron powder is 75-100 μm, the particle size of the manganese powder is 60-80 μm, the particle size of the aluminum powder is 75-100 μm, the particle size of the nickel powder is 60-80 μm, the particle size of the silicon powder is 20-40 μm, the particle size of the titanium powder is 20-30 μm, the particle size of the molybdenum powder is 60-80 μm, and the particle size of the carbon powder is 20-30 μm; grinding: grinding the mixed powder obtained in step (2) for 10-15 hours, and filling with a protective atmosphere at the same time; filling powder: fixing the powder into shape through a set of graphite molds, the composition of the mold is graphite, and no other Impurities, which include an upper pressure head, a lower pressure head and a hollow female mold with a temperature measuring hole. The upper pressure head and the lower pressure head have the same structure and are both columnar structures. The graphite female mold is a sleeve-shaped hollow structure, and a temperature measuring hole is opened on the side wall of the graphite female mold; the lower pressure head is first inserted into the inner hole of the female mold, and a graphite sheet is placed. Then, the mixed powder obtained in step (3) is filled on the lower pressure head inside the female mold, and a graphite sheet is also placed. Then, the upper pressure head is inserted into the inner hole from above the female mold, and the mixed metal powder is pressed tightly by the upper and lower pressure heads; press sintering: the mold to be sintered obtained in step (4) is placed in the furnace of the spark plasma sintering system, and the air in the furnace is extracted to a vacuum state; then, the pressure system is adjusted so that the pressure head maintains a constant pressure on the mold; then, an electric current is passed to sinter the metal powder to obtain high-strength low-density steel. This patent only introduces the raw material smelting process (mixing, grinding, powder filling and press sintering), and the process is vague and not referenceable. Moreover, a large amount of Ni element (7% to 8%) is added, which is inconsistent with the current situation of nickel deficiency in my country. The large amount of Mo, Mn and other alloys will greatly increase the cost.

[0006] CN 111235484 A discloses a high-strength, high-hardness, low-density steel and a preparation method thereof. The chemical composition of the steel, calculated by weight percentage, is as follows: C: 0.70-1.8%, Al: 8.0-12.0%, Si: 0.3-0.9%, Mn: 25-34%, Cr: 0.3-1.2%, V: 0.1-0.7%, Ti: 0.1-0.8%, Mo: 0.7-1.3%, and the balance is Fe and unavoidable impurities. The ingot is subjected to water toughening treatment: the temperature of the water toughening treatment is 1050-1100°C, and the time is 20-30 minutes; the temperature of the hot rolling treatment is 1000-1120°C, and the time is 120-180 minutes, the hot rolling treatment is multi-pass rolling deformation, and the total deformation of the hot rolling treatment is 60-65%; the temperature of the aging treatment is 350-450°C, and the time is 6-12 hours; the temperature of the nitriding treatment is 570-580°C, and the time is 47-50 hours, and the heating rate to the nitriding treatment temperature is 10-20°C / min; the temperature of the denitriding treatment is 620-630°C, and the time is 2-4 hours, and the heating rate to the denitriding treatment temperature is 5-10°C / min. The obtained high-strength, high-hardness, low-density steel has a yield strength of 870.21-1077.36 MPa, a tensile strength of 950.35-1127.7 MPa, a hardness of 62-68 HRC, and a density of 6.63-7.19 g / cm 3 However, its high carbon content (0.70-1.80%) is detrimental to weldability, and the addition of large amounts of manganese (25-34%) and precious metal elements such as molybdenum (0.7-13%) and vanadium (0.1-0.7%) makes the alloy costly. Furthermore, the patented method has complex procedures (aging and nitriding), poor operability, and increased process costs.

[0007] In view of this, the existing technology needs to be improved. Summary of the Invention

[0008] In view of at least one of the problems in the above-mentioned prior art, an object of the present invention is to provide an austenite-based lightweight high-strength steel and a large strain warm rolling preparation method thereof.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] According to a first aspect of the present invention, there is provided a method for preparing austenitic lightweight high-strength steel by large strain warm rolling, comprising the following steps:

[0011] (a) Smelting process: Smelting and casting into slabs according to the chemical composition of austenitic lightweight high-strength steel, wherein the chemical composition of the austenitic lightweight high-strength steel comprises, by weight percentage, C: 0.32% to 0.50%, Si: 0.20% to 0.50%, Mn: 12.0% to 16.0%, P ≤ 0.020%, S ≤ 0.010%, Als: 6.0% to 9.0%, Ti: 0.020% to 0.050%, and the balance being Fe and unavoidable impurities;

[0012] (b) hot rolling process: the slab obtained in step (a) is heated to 1230° C. to 1270° C. and kept at this temperature for 3 to 7 hours before being removed from the furnace, the slab surface is descaled using a descaling device, and then hot rolled into a strip of the first thickness specification, with a finishing temperature of 830° C. to 900° C.;

[0013] (c) Warm rolling process: After pickling, the steel strip obtained in step (b) is heated to 400° C. to 460° C. and warm rolled to form a steel strip of the second thickness specification, with a reduction ratio of ≥15% per pass;

[0014] (d) Heat treatment process: The steel strip obtained in step (c) is heated to 900° C. to 980° C. for solution treatment, kept at this temperature for 1 to 4 hours, and then cooled to room temperature to obtain austenitic lightweight high-strength steel.

[0015] Preferably, the chemical composition of the austenitic lightweight high-strength steel includes, by weight percentage: C: 0.35% to 0.46%, Si: 0.30% to 0.45%, Mn: 12.5% ​​to 14.0%, P≤0.015%, S≤0.010%, Als: 6.5% to 8.0%, Ti: 0.025% to 0.040%, and the balance is Fe and unavoidable impurities.

[0016] According to some embodiments of the present invention, in step (b), the slab is heated to 1230° C. to 1270° C. at a rate of 5° C. / min.

[0017] According to some embodiments of the present invention, the first thickness specification is 5 mm to 8.0 mm, and the second thickness specification is 0.8 mm to 2.0 mm.

[0018] According to some embodiments of the present invention, in step (c), the steel strip is electrically heated to 400-460° C. using the steel strip clamping end.

[0019] According to some embodiments of the present invention, in step (d), the solution treatment is followed by air cooling to room temperature.

[0020] According to a second aspect of the present invention, there is provided an austenite-based lightweight high-strength steel, which is prepared by using the method according to the first aspect of the present invention.

[0021] According to some embodiments of the present invention, the yield strength of the austenite-based lightweight high-strength steel is 550-650 MPa, the tensile strength is 950-1030 MPa, and the elongation A 50 It is 34.0~40.0%.

[0022] According to some embodiments of the present invention, the microstructure of the austenite-based lightweight high-strength steel consists of strip-shaped delta ferrite and austenite.

[0023] According to some embodiments of the present invention, in the structure of the austenite-based lightweight high-strength steel, the banded delta ferrite accounts for 25% to 30%, and the austenite accounts for 70% to 75%.

[0024] By adopting the above technical solution, the present invention has the following beneficial effects:

[0025] The present invention prepares austenite-based lightweight high-strength steel by designing the composition of alloy elements and their contents and combining the process of smelting process + hot rolling process + warm rolling process + heat treatment process, and its yield strength reaches 550-650MPa, tensile strength reaches 950-1030MPa, and elongation A 50 Reach 34.0~40.0%.

[0026] The present invention reduces the density of the steel by adding the lightweight element Al, thereby reducing the material density while ensuring strong plasticity; by adding Mn to expand the austenite phase region and stability, heating is performed during the warm rolling process to recover the work hardening to a certain extent, ensuring the feasibility of large reductions in each rolling pass; at the same time, the relatively low heating temperature suppresses recrystallization, which is conducive to further grain refinement, providing raw materials with good plate shape / thickness accuracy for subsequent heat treatment, and providing technical support for the development of high-strength, low-density automotive steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A flow chart of the method for preparing austenite-based lightweight high-strength steel by large strain warm rolling provided by the present invention;

[0028] Figure 2 A metallographic microscope photograph of austenitic lightweight high-strength steel produced by the method for producing austenitic lightweight high-strength steel by large strain warm rolling provided in Example 1;

[0029] Figure 3 This is a scanning electron microscope photograph of austenitic lightweight high-strength steel prepared by the method for preparing austenitic lightweight high-strength steel by large strain warm rolling provided in Example 1. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] As required, specific embodiments of the present invention are disclosed in this specification; however, it should be understood that the disclosed embodiments are merely illustrative of the invention, which may be implemented in various alternative forms. In the following description, various operating parameters and components are described in connection with various contemplated embodiments. These specific parameters and components are provided herein as examples only and are not intended to be limiting.

[0032] According to a first aspect of the present invention, a method for preparing austenite-based lightweight high-strength steel by high strain warm rolling is provided. Figure 1 As shown, the method includes the following steps:

[0033] (a) Smelting process: Smelting and casting into slabs according to the chemical composition of austenitic lightweight high-strength steel, wherein the chemical composition of the austenitic lightweight high-strength steel comprises, by weight percentage, C: 0.32% to 0.50%, Si: 0.20% to 0.50%, Mn: 12.0% to 16.0%, P ≤ 0.020%, S ≤ 0.010%, Als: 6.0% to 9.0%, Ti: 0.020% to 0.050%, and the balance being Fe and unavoidable impurities;

[0034] (b) hot rolling process: the slab obtained in step (a) is heated to 1230°C to 1270°C and kept at this temperature for 3 to 7 hours before being removed from the furnace, the slab is descaled to remove the iron oxide scale on the surface of the slab, and then hot rolled into a strip of the first thickness specification at a finishing temperature of 830°C to 900°C, and then air-cooled to room temperature;

[0035] (c) warm rolling process: the steel strip obtained in step (b) is pickled, heated to 400°C to 460°C, and warm rolled to form a steel strip of the second thickness specification, with a reduction ratio of ≥15% per pass and a total reduction ratio of 60% to 90%;

[0036] (d) Heat treatment process: The steel strip obtained in step (c) is heated to 900° C. to 980° C. for solution treatment, kept at this temperature for 1 to 4 hours, and then cooled to room temperature to obtain austenitic lightweight high-strength steel.

[0037] Preferably, the chemical composition of the austenitic lightweight high-strength steel includes, by weight percentage: C: 0.35% to 0.46%, Si: 0.30% to 0.45%, Mn: 12.5% ​​to 14.0%, P≤0.015%, S≤0.010%, Als: 6.5% to 8.0%, Ti: 0.025% to 0.040%, and the balance is Fe and unavoidable impurities.

[0038] The roles of alloying elements in this austenitic lightweight high-strength steel are as follows:

[0039] Carbon: C is an important austenitic element in steel, which can stabilize the austenite structure and promote density reduction. At the same time, C can work together with the Mn and Al elements in the steel to form κ-carbide ((Fe,Mn)3AlC). The two work together to produce precipitation strengthening, increasing the strength of the steel. Too low a C content will cause the austenite structure in the steel to be unstable, but too high a C content will promote the coarsening of austenite grain boundaries and the formation of κ-carbide, which will damage the elongation of low-density steel. Therefore, the C content of the present invention is 0.32% to 0.50%, preferably 0.35% to 0.46%.

[0040] Silicon: Si can dissolve in ferrite and austenite to increase the strength of steel. Its effect is second only to that of C and P, and is stronger than that of elements such as Mn, Cr, Ti, and Ni. Si can also inhibit the precipitation of carbides in ferrite, allowing dissolved carbon atoms to fully accumulate in austenite, thereby improving its stability. Too low a Si content makes it difficult to obtain retained austenite at room temperature. However, when the Si content is too high, the surface oxide scale formed by Si in the heating furnace is difficult to remove, increasing the difficulty of dephosphorization. Furthermore, during annealing, SiO2 is easily accumulated on the surface, leading to surface defects such as plating defects. Therefore, the Si content of the present invention is 0.20% to 0.50%, preferably 0.30% to 0.45%.

[0041] Manganese: Mn is an austenitizing element. Adding Mn expands the austenite phase and increases the austenite content, improving the stacking fault energy of the steel, inhibiting martensitic transformation, causing dense twins to form during deformation, and effectively increasing the steel's elongation. However, a significant increase in Mn content increases costs and can also cause severe segregation. Therefore, in the present invention, the Mn content is 12.0% to 16.0%, preferably 12.5% ​​to 14.0%.

[0042] Aluminum: The density of Als is 2.7g / cm 3 , much lower than 7.85g / cm 3 The Fe density can significantly reduce the material density. A certain Als content can also significantly improve the hot deformation resistance of steel, improve the corrosion resistance of steel, and delay dynamic cracking. Als can also significantly increase the stacking fault energy of steel and change the deformation mechanism. Medium manganese steel containing Als can have a certain buffering effect in the event of a violent collision. However, considering that Als is a strong ferritizing element, an excessively high Als content can easily promote the formation of ferrite phase and reduce the austenite phase content. Therefore, the Als content in the present invention is 6.0% to 9.0%, preferably 6.5% to 8.0%.

[0043] Phosphorus and sulfur: P and S increase the brittleness of steel products, so their content must be strictly controlled. Therefore, P ≤ 0.020%, S ≤ 0.010%, preferably P ≤ 0.015%, S ≤ 0.010%.

[0044] Titanium: The Ti element is very active and easily combines with O. During the smelting process, a portion of Ti can act as a deoxidizer. Secondly, it has a strong affinity with C and is a strong carbide-forming element. Titanium carbide in steel can play a role in refinement strengthening and precipitation strengthening, which can improve the strength of the steel. However, if the content is too high, it can significantly reduce the diffusion rate of C in austenite, reduce the C content in austenite, lead to a decrease in matrix stability and reduce plasticity. Therefore, the Ti content is set in the range of 0.020-0.050% by weight, preferably 0.025-0.040%.

[0045] In the present invention, by designing the composition of alloying elements and their contents in conjunction with the corresponding process flow, an austenitic-based lightweight high-strength steel is obtained. In particular, the density of the steel is reduced by adding the lightweight element Al, and the material density is reduced while ensuring strong plasticity. The austenitic phase region and stability are expanded by adding Mn.

[0046] In step (b), the slab heating temperature is typically but not limited to, for example, 1230°C, 1240°C, 1250°C, 1260°C or 1270°C, the slab holding time is typically but not limited to, for example, 3 hours, 4 hours, 5 hours, 6 hours or 7 hours, and the final rolling temperature is typically but not limited to, for example, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C or 900°C.

[0047] In some embodiments, in step (b), the slab is slowly heated to 1250±20°C and held at that temperature for 5 hours before being removed from the furnace. Surface scale is removed using a descaling device, and the slab is then strip-rolled to a first thickness using a hot rolling mill. The final rolling temperature is 830-900°C, followed by air cooling to room temperature. The slow heating is performed to achieve a uniform microstructure in each microregion of the strip during heating. Slow heating refers to heating at a rate of 5°C / min.

[0048] In step (c), the warm rolling temperature is typically but not limited to 400°C, 410°C, 420°C, 430°C, 440°C, 450°C or 460°C, the reduction ratio of each pass is typically but not limited to 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%, and the total reduction ratio is typically but not limited to 60%, 65%, 70%, 75%, 80%, 85% or 90%.

[0049] In some embodiments, the first thickness specification is 5 mm to 8 mm, and the second thickness specification is 0.8 mm to 2.0 mm.

[0050] In some embodiments, in step (c), after pickling the hot-rolled coil, the strip is warm-rolled to a thickness of 0.8-2.0 mm using a four-roll cold / warm rolling mill. The strip is then heated to 400-460°C using a clamping end and then warm-rolled, with a reduction of 15% or greater per pass. Electric heating is performed using an electric heating device at the clamping end of the strip to recover some work hardening, ensuring the feasibility of large reductions (large strains) in each rolling pass and accumulating distortion energy. Furthermore, the relatively low heating temperature suppresses recrystallization, facilitating further grain refinement and providing raw material with excellent shape and thickness accuracy for subsequent heat treatment, providing technical support for the development of high-strength, low-density automotive steel.

[0051] In step (d), the strip heating temperature is typically but not limited to 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C or 980°C, and the strip holding time is typically but not limited to 1 hour, 2 hours, 3 hours or 4 hours.

[0052] In some embodiments, in step (d), after the solution treatment, the steel strip is slowly cooled to room temperature, for example, air-cooled to room temperature, so that the microstructure of each micro-region is uniform.

[0053] According to a second aspect of the present invention, there is provided an austenite-based lightweight high-strength steel, which is prepared by using the method according to the first aspect of the present invention.

[0054] The yield strength of austenitic lightweight high-strength steel is 550-650MPa, the tensile strength is 950-1030MPa, and the elongation A 50 It is 34.0~40.0%.

[0055] The microstructure of the austenite-based lightweight high-strength steel is composed of banded delta ferrite and austenite, wherein the banded delta ferrite accounts for 25% to 30% and the austenite accounts for 70% to 75%.

[0056] The present invention will be described in detail below through specific examples.

[0057] Example

[0058] The following provides seven groups of austenitic lightweight high-strength steels produced by large strain warm rolling, and their chemical compositions are shown in Table 1.

[0059] Table 1 Chemical composition (wt.%) of austenitic lightweight high-strength steel produced by large strain warm rolling

[0060] serial number C Si Mn P S Als Ti Example 1 0.42 0.42 13.2 0.012 0.004 7.0 0.032 Example 2 0.39 0.44 12.8 0.010 0.005 6.8 0.028 Example 3 0.40 0.40 13.4 0.009 0.003 7.3 0.035 Example 4 0.32 0.20 12.5 0.020 0.008 9.0 0.025 Example 5 0.50 0.50 14.0 0.015 0.010 6.0 0.050 Example 6 0.35 0.30 12.0 0.010 0.007 6.5 0.040 Example 7 0.46 0.45 16.0 0.012 0.003 8.0 0.020

[0061] The specific process of the preparation method of the austenite-based lightweight high-strength steel prepared by the large strain warm rolling is as follows:

[0062] a. Smelting process: After smelting process, austenite-based high-strength steel slabs with the chemical composition shown in Table 1 are prepared;

[0063] b. Hot rolling process: The slab is slowly heated to 1250±20℃ and kept at this temperature for 5 hours before being taken out of the furnace. The surface oxide scale is removed by descaling equipment. The hot rolling unit rolls the strip to the set thickness specification. The final rolling temperature is 830-900℃, and then air-cooled to room temperature;

[0064] c. Warm rolling process: After pickling the hot-rolled coil, the strip is warm-rolled to 0.8-2.0 mm using a four-roll cold / warm rolling mill. The strip is heated to 400-460°C using the clamping end and then warm-rolled. The reduction rate for each pass is ≥15%. By recovering the work hardening to a certain extent, the feasibility of large reduction (large strain) in each rolling pass is ensured, and distortion energy is accumulated. At the same time, the relatively low heating temperature suppresses recrystallization, which is conducive to further grain refinement.

[0065] d. Heat treatment process: Heat the strip to 900-980℃ and keep it at this temperature for 1-4 hours for solution treatment, then slowly cool it to room temperature.

[0066] The specific process parameters are shown in Table 2.

[0067] Table 2 Main process parameters of rolling and heat treatment of austenitic lightweight high-strength steel produced by large strain warm rolling

[0068]

[0069] Comparative Example

[0070] Corresponding products were prepared as comparative examples according to the processes disclosed in documents CN 115537672 A, CN 111593263 A, and CN105803334A.

[0071] The preparation process of CN 115537672 A is as follows: 1) smelting high-manganese austenitic steel; 2) primary forging: subjecting the high-manganese steel ingot to a solution treatment at a solution temperature of 1000-1200°C and a holding time of 3-5 hours; then performing a first forging at an initial forging temperature of ≥800°C and a final forging temperature of ≥600°C, with the thickness of the slab after forging being 100-105 mm; 3) secondary forging: subjecting the slab obtained in step 2) to a holding temperature of 800-900°C for 2-4 hours; A second forging process is then performed, with an initial forging temperature of 700-800°C and a final forging temperature of ≥600°C. The thickness of the slab after forging is 50-60mm. 4) Warm rolling of the slab: The slab obtained in step 3) is held at 500-600°C for 20-40 minutes. Rolling is then performed, with an initial rolling temperature of 500-550°C and a final rolling temperature of ≥400°C. The thickness of the steel plate after rolling is 7-7.6mm, and the rolling deformation is greater than 80%. This process uses a two-step forging + warm rolling process, with the warm rolling process first heating the steel plate and then rolling it using a hot rolling mill.

[0072] The preparation process of CN 111593263 A is as follows: (1) Mixing: Mixing the components to obtain a mixed powder; (2) Grinding: Grinding the mixed powder for 10-15 hours while filling with a protective atmosphere; (3) Filling: Fixing the powder in a graphite mold to form the powder; (4) Pressing: Sintering the metal powder to obtain high-strength, low-density steel. This patent primarily produces experimental steel through batching and roasting, without forging, rolling, or heat treatment.

[0073] The preparation process of CN105803334 A is as follows: (1) subjecting the ingot to water toughening treatment: the water toughening treatment temperature is 1050-1100°C, and the time is 20-30 min; (2) hot rolling: the hot rolling treatment temperature is 1000-1120°C, and the time is 120-180 min. The hot rolling treatment is a multi-pass rolling deformation, and the total deformation of the hot rolling treatment is 60-65%; (3) solution treatment: the solution treatment temperature is 1000-1100°C, and the time is 120- 180min; (4) aging treatment: the aging treatment temperature is 350-450℃, and the time is 6-12h; (5) nitriding treatment: the nitriding treatment temperature is 570-580℃, and the time is 47-50h, and the heating rate to the nitriding treatment temperature is 10-20℃ / min; wherein the denitriding treatment temperature is 620-630℃, and the time is 2-4h, and the heating rate to the denitriding treatment temperature is 5-10℃ / min.

[0074] Table 3 Main process parameters of comparative example

[0075]

[0076] Performance Characterization

[0077] The microstructure of the lightweight high-strength steel plate (corresponding to Example 1) prepared by the process of the present invention is as follows: Figures 2 to 3 As shown, from Figure 2 and Figure 3 It can be seen from the figure that the microstructure of the lightweight high-strength steel plate prepared by the present invention is strip-shaped delta ferrite and austenite, and the structure is uniform.

[0078] The properties of the above-mentioned austenitic lightweight high-strength steel plates and comparative steel plates were tested in accordance with GB / T228-2010 "Metallic Materials Room Temperature Tensile Test Methods", as shown in Table 4.

[0079] Table 4 Mechanical properties of austenitic lightweight high-strength steel prepared by large strain warm rolling

[0080]

[0081] As shown in Table 4, compared with the prior art, the lightweight high-strength steel prepared by the process of the present invention has excellent elongation and density while ensuring higher yield strength and tensile strength.

Claims

1. A method for preparing austenitic lightweight high-strength steel by large strain warm rolling, characterized in that: The following steps are involved: (a) Smelting process: Smelting and casting into slabs according to the chemical composition of austenitic lightweight high-strength steel. The chemical composition of austenitic lightweight high-strength steel includes, by weight percentage: C: 0.32%~0.50%, Si: 0.20%~0.50%, Mn: 12.0%~16.0%, P≤0.020%, S≤0.010%, Als: 6.0%~9.0%, Ti: 0.020%~0.050%, the balance is Fe and unavoidable impurities; (b) hot rolling process: the slab obtained in step (a) is heated to 1230° C. to 1270° C. and kept at this temperature for 3 to 7 hours before being removed from the furnace, the slab surface is descaled using a descaling device, and then hot rolled into a strip of the first thickness specification, with a finishing temperature of 830° C. to 900° C.; (c) Warm rolling process: After pickling, the steel strip obtained in step (b) is heated to 400° C. to 460° C. and warm rolled to form a steel strip of the second thickness specification, with a reduction ratio of ≥15% per pass; (d) Heat treatment process: The steel strip obtained in step (c) is heated to 900° C. to 980° C. for solution treatment, kept at this temperature for 1 to 4 hours, and then cooled to room temperature to obtain austenitic lightweight high-strength steel.

2. The method for preparing austenite-based lightweight high-strength steel by large strain warm rolling according to claim 1, characterized in that: The chemical composition of the austenitic lightweight high-strength steel includes, by weight percentage, C: 0.35% to 0.46%, Si: 0.30% to 0.45%, Mn: 12.5% ​​to 14.0%, P≤0.015%, S≤0.010%, Als: 6.5% to 8.0%, Ti: 0.025% to 0.040%, and the balance is Fe and unavoidable impurities.

3. The method for preparing austenite-based lightweight high-strength steel by large strain warm rolling according to claim 1, characterized in that: In step (b), the slab obtained in step (a) is heated to 1230° C. to 1270° C. at a rate of 5° C. / min.

4. The method for preparing austenite-based lightweight high-strength steel by large strain warm rolling according to claim 1, characterized in that: The first thickness specification is 5mm~8.0mm, and the second thickness specification is 0.8mm~2.0mm.

5. The method for preparing austenite-based lightweight high-strength steel by large strain warm rolling according to claim 1, characterized in that: In step (c), the steel strip is electrically heated to 400-460° C. using an electric heating device at the clamping end of the steel strip.

6. The method for preparing austenite-based lightweight high-strength steel by large strain warm rolling according to claim 1, characterized in that: In step (d), the solution treatment is followed by air cooling to room temperature.

7. An austenite-based lightweight high-strength steel, characterized in that: It is prepared by the method according to any one of claims 1 to 6.

8. The austenite-based lightweight high-strength steel according to claim 7, characterized in that: The yield strength of the austenite-based lightweight high-strength steel is 550-650 MPa, the tensile strength is 950-1030 MPa, and the elongation A 50 It is 34.0~40.0%.

9. The austenite-based lightweight high-strength steel according to claim 7, characterized in that: The structure of the austenite-based lightweight high-strength steel consists of strip-shaped delta ferrite and austenite.

10. The austenite-based lightweight high-strength steel according to claim 9, characterized in that: In the structure of the austenite-based lightweight high-strength steel, the strip-shaped delta ferrite accounts for 25% to 30%, and the austenite accounts for 70% to 75%.

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