High-manganese wear-resistant steel with excellent fatigue resistance and production method thereof

Abstract

The invention discloses high-manganese wear-resistant steel with excellent fatigue resistance and a production method of the high-manganese wear-resistant steel. The high-manganese wear-resistant steel comprises the following chemical components in percentage by weight: 0.08-0.25% of C, 0.20-0.50% of Si, 12.0-14.0% of Mn, 3.0-5.0% of Cr, 0.10-0.20% of Nb + V, 0.01-0.04% of Y, less than or equal to 0.005% of O, less than or equal to 0.004% of N, less than or equal to 0.015% of P, less than or equal to 0.020% of S, 0.01-0.04% of Y and the balance of Fe and inevitable impurity elements. The production method comprises the steps of billet heating, forging and rolling, two-stage quenching and low-temperature tempering. The high-manganese wear-resistant steel provided by the invention has a uniform austenite and bainite structure, and has excellent wear resistance and fatigue resistance.

Description

Technical Field

[0001] The present invention belongs to the field of preparation technology, and particularly relates to a high manganese wear-resistant steel with excellent anti-fatigue performance and a production method thereof. Background Art

[0002] Due to its unique phenomenon that it can rapidly undergo work hardening on the surface layer after being subjected to impact and extrusion, high manganese wear-resistant steel has good wear resistance in the hardened layer while maintaining good toughness and plasticity of austenite in the core, becoming the best choice for wear-resistant steel. It is widely used in parts that are easily subjected to strong impact wear, such as shot blasting machines, ball mills, crushers, etc., and has been widely applied in industries such as shipbuilding, automobiles, machinery, power generation, cement, mines, and coal, becoming an inevitable development trend for the selection of new generation wear-resistant steel.

[0003] High manganese wear-resistant steel is usually used to manufacture components such as ball mill liners, hammer crusher hammers, jaw crusher jaws, and excavator bucket teeth. These components are repeatedly subjected to rolling and impact during service, resulting in cyclic plastic deformation and thus having the risk of fatigue failure. According to statistics, fatigue failure is one of the most common failure forms of steel, causing huge direct economic losses; in addition, fatigue failure can occur under loads higher than and far lower than the strength limit, resulting in extremely serious consequences, not only affecting the production progress but also potentially endangering the safety of personnel.

[0004] In view of the harsh service environment of high manganese wear-resistant steel, in order to fully ensure production stability and personnel safety, it is required that high manganese wear-resistant steel has excellent anti-fatigue performance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high manganese wear-resistant steel with excellent anti-fatigue performance. After the steel plate is subjected to two-stage quenching + tempering heat treatment, it has a uniform austenite + bainite structure, and has excellent wear resistance and excellent anti-fatigue performance at the same time.

[0006] To solve the above technical problem, the technical solution adopted by the present invention is: A high manganese wear-resistant steel with excellent anti-fatigue performance, its chemical composition and weight percentage content are: C: 0.08 - 0.25%, Si: 0.20 - 0.50%, Mn: 12.0 - 14.0%, Cr: 3.0 - 5.0%, Nb + V: 0.10 - 0.20%, Y: 0.01 - 0.04%, O ≤ 0.005%, N ≤ 0.004%, P ≤ 0.015%, S ≤ 0.020%, and the balance is Fe and inevitable impurity elements.

[0007] The basis for setting the components and contents in the high manganese wear-resistant steel with excellent anti-fatigue performance of the present invention is as follows: C: Carbon is the most effective element for improving the strength of steel plates, increasing surface hardness, slowing down the plastic deformation of steel after impact load, and hindering the formation of microcracks inside the steel, which is beneficial to improving the fatigue resistance of steel; however, too high a carbon content will lead to the formation of a brittle phase of network carbides, which is easy to initiate microcracks after being stressed, which is not conducive to the fatigue performance of steel. Therefore, the design range of carbon content is 0.08-0.25%.

[0008] Si: Silicon can be dissolved in the matrix, and solid solution strengthening improves the strength of steel. However, when the silicon content is too high, more hard and brittle large-sized silicon-containing precipitates will be formed, and stress concentration will occur at the sharp corners of the silicon phase, which will become microcrack nucleation points. The microcracks will expand instably and cause damage, thereby reducing fatigue performance. Therefore, the design range of silicon content is 0.20-0.50%.

[0009] Mn: Manganese can promote the formation of austenite, expand the austenite phase area, and make austenite exist at room temperature; but when the manganese content is too high, the stability of austenite is too high, and it needs to be transformed into martensite under strong impact to show wear resistance. The wear resistance of the steel plate cannot be reflected under low load impact. Therefore, the design range of manganese content is 12.0~14.0%.

[0010] Cr: Chromium is dissolved in the matrix, thereby increasing the matrix strength and the hardenability of the steel during quenching; it also has a secondary hardening effect, increasing the hardness and wear resistance of the steel. Therefore, the design range of chromium content is 3.0-5.0%.

[0011] Nb+V: Vanadium and niobium are commonly used elements for fine grain strengthening and precipitation strengthening, and Nb can change the shape of inclusions in steel, making sharp inclusions degenerate into elliptical shapes, reducing stress concentration around inclusions, which is beneficial to improving the fatigue performance of steel. Therefore, the vanadium + niobium content is designed to be 0.10-0.20%.

[0012] Y: The rare earth element yttrium can effectively modify inclusions to form small-sized rare earth inclusions containing yttrium. Such modified inclusions have good ductility and elasticity, low hardness, and reduce the stress concentration between the inclusions and the matrix, thereby effectively improving the fatigue resistance of the steel. Therefore, the rare earth element yttrium content is designed to be 0.01-0.04%.

[0013] O, N: In order to control the number and size of inclusions and improve the fatigue resistance of steel, the content of O and N elements is reduced as much as possible; at the same time, based on cost control, the oxygen content is designed to be ≤0.005% and the nitrogen content is ≤0.004%.

[0014] P, S: Phosphorus and sulfur are harmful elements, the lower the content, the better; based on production costs, the phosphorus content is designed to be ≤0.015%, and the sulfur content is designed to be ≤0.020%.

[0015] Furthermore, the high manganese wear-resistant steel with excellent anti-fatigue performance of the present invention has a microstructure of uniform austenite + bainite after two-stage quenching + tempering heat treatment.

[0016] Furthermore, for the high manganese wear-resistant steel with excellent anti-fatigue performance of the present invention, the wear amount ≤ 1 g, and the fatigue limit σ-1 of the smooth specimen ≥ 0.63Rm, where σ-1 is the fatigue limit of the smooth specimen and Rm is the tensile strength.

[0017] Furthermore, for the impact wear test, the specimen processing and testing are carried out in accordance with T∕CFA 010604-3-2016 "Test Method for Impact Abrasive Wear of Steel and Iron Materials". The impact hammer has a mass of 10 kg, the upper specimen is high manganese steel, the 45 steel with a hardness of 58HRC, and the counter-grinding is carried out at a rotational speed of 200 r / min; quartz sand with a particle size of 1-3 mm is used as the abrasive, and the flow rate is 15 kg / h; the selected impact energy is 2 J, and the impact time is 90 min. After the test, the specimens are cleaned in an ultrasonic cleaner with acetone solution and anhydrous ethanol solution for 60 s respectively, and weighed with an electronic balance with a precision of 0.1 mg. Each specimen is weighed 3 times, and the average value is taken as the wear result.

[0018] Furthermore, for the rotating bending fatigue test, the sampling and testing of the rotating bending fatigue test are carried out in accordance with GB / T 43337-2008 "Rotating Bending Method for Fatigue Testing of Metallic Materials". Smooth fatigue specimens are used, and the stress concentration coefficient Kt = 1. To reduce test errors, there should be no mechanical damage on the specimen surface. During the test, the rotational speed of the specimen is 5000 r / min, the cyclic characteristic R = -1, and the testing machine uses four-point loading. When the specimen breaks or the number of rotation cycles ≥ 1×107, in order to improve the credibility of the test, the fatigue limit σ-1 of the steel is measured by the staircase method (at least 3 pairs), and 3-5 stress levels are adopted. The stress increment at each level is about 3% of the fatigue limit σ-1.

[0019] The production method of the high manganese wear-resistant steel with excellent anti-fatigue performance of the present invention includes steel billet heating, forging + rolling, and two-stage quenching + tempering heat treatment processes; in the steel billet heating process, the steel billet is heated in an electromagnetic induction heating furnace, the heating-up time is 40-60 min, the heating temperature is 1220-1250 °C, and the holding time is 180-240 min to dissolve the chemical elements of the steel and make the composition and structure of the steel uniform.

[0020] Further, in the steel billet forging + rolling process of the present invention, the heated steel billet is forged into a slab with a thickness of 45 - 60 mm, and the final forging temperature is ≥ 850 °C. To simplify the production process and reduce energy consumption, the forged slab is directly subjected to warm rolling to roll the steel plate into a slab with a thickness of 15 - 25 mm, and the rolling temperature is between 800 - 700 °C, and it is cooled to room temperature by the method of burying sand.

[0021] Further, in the two-stage quenching + tempering heat treatment process of the present invention, the steel plate after warm rolling and forming is heated to 900 - 930 °C, held for 90 - 120 min, and forced air-cooled to 500 - 550 °C; the steel plate is reheated to 875 - 900 °C, held for 60 - 90 min, and water-quenched to room temperature; heating is carried out at the austenitizing temperature, and two-stage quenching can make the microstructure more uniform and regular, refine the grains, and improve the performance of the steel; the steel plate after two-stage quenching is heated to 400 - 500 °C, held for 130 - 150 min, and furnace-cooled to room temperature to obtain a uniform austenite + bainite structure.

[0022] The high manganese steel produced by the present invention has a uniform structure, has wear resistance, and at the same time has excellent anti-fatigue performance, improving the safety of wear-resistant components.

[0023] The beneficial effects produced by adopting the above technical solutions are as follows: 1. The high manganese wear-resistant steel provided by the present invention mainly uses C, Mn, and Cr as the main chemical components, and forms excellent anti-fatigue performance by adding trace alloying elements; warm rolling and forming have low equipment requirements and a simple production process.

[0024] 2. The high manganese wear-resistant steel liner provided by the present invention obtains an austenite + bainite structure after two-stage quenching + tempering heat treatment, with a uniform structure and excellent anti-wear ability. Description of the Drawings

[0025] Figure 1 It is a micrograph of the high manganese wear-resistant steel in Example 1. Detailed Description of the Invention

[0026] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following further describes the present invention in detail with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Example 1

[0027] A high manganese wear-resistant steel with excellent anti-fatigue performance is smelted using an electric furnace and cast into 50 kg ingots. The chemical composition and its weight percentage are determined using a direct-reading spectrometer as follows: C: 0.08%, Si: 0.20%, Mn: 12.0%, Cr: 3.0%, V+Nb: 0.10%, Y: 0.01%, O: 0.0048, N: 0.0032, P: 0.012%, S: 0.011%, and the balance is Fe and unavoidable impurities; its production process includes billet heating, forging + rolling, and two-stage quenching + tempering heat treatment processes. The specific process control is as follows: (1) Billet heating process: The billet is heated in an electromagnetic induction heating furnace. The heating furnace has a heating-up time of 40 min, a heating temperature of 1220 °C, and a billet holding time of 180 min.

[0028] (2) Forging and rolling process: The heated slab is forged into a 45 mm intermediate billet with a final forging temperature of 850 °C. Using an energy-saving production method, the forged intermediate billet is warm-rolled and multi-pass rolled into a 15 mm thick slab with a final rolling temperature of 718 °C, and then cooled to room temperature by burying it in sand.

[0029] (3) Two-stage quenching + tempering heat treatment process: The warm-rolled slab is heated to 900 °C, held for 90 min, forced air-cooled to 500 °C, reheated to 875 °C, held for 60 min, and then water-quenched to room temperature; the steel plate after two-stage quenching is heated to 400 °C, held for 130 min, and furnace-cooled to room temperature to obtain the product.

[0030] The high manganese wear-resistant steel obtained in this example has a uniform austenite + bainite structure, and the microstructure photograph is as Figure 1 shown. Other examples are the same and will not be given in sequence.

[0031] According to T∕CFA 010604-3-2016 "Test Method for Impact Abrasive Wear of Steel Materials", the wear resistance of the steel is detected, and the wear amount is 1.00 g; according to GB / T 43337-2008 "Rotating Bending Method for Fatigue Testing of Metallic Materials", the fatigue limit of the steel is measured to be 666 MPa, and the tensile strength Rm of the steel is 1057 MPa, that is, the fatigue limit σ-1≈0.63Rm. Example 2

[0032] A high manganese wear-resistant steel with excellent anti-fatigue performance is smelted using an electric furnace and cast into a 50 kg ingot. The chemical composition and its weight percentage are determined using a direct-reading spectrometer as follows: C: 0.10%, Si: 0.27%, Mn: 12.75%, Cr: 3.25%, V+Nb: 0.12%, Y: 0.017%, O: 0.0043, N: 0.0035, P: 0.010%, S: 0.015%, with the balance being Fe and unavoidable impurities; its production process includes billet heating, forging + rolling, two-stage quenching + tempering heat treatment processes, and the specific process control is as follows: (1) Billet heating process: The billet is heated in an electromagnetic induction heating furnace. The heating furnace has a heating-up time of 45 min, a heating temperature of 1225 °C, and a billet holding time of 190 min.

[0033] (2) Forging and rolling process: The heated slab is forged into an intermediate billet of 47 mm. The final forging temperature is 865 °C. Using an energy-saving production method, the forged intermediate billet is warm-rolled and multi-pass rolled into a slab with a thickness of 18 mm. The final rolling temperature is 730 °C, and it is cooled to room temperature by burying it in sand.

[0034] (3) Two-stage quenching + tempering heat treatment process: The warm-rolled slab is heated to 910 °C, held for 95 min, forced air-cooled to 510 °C, reheated to 880 °C, held for 65 min, and water-quenched to room temperature; the steel plate after two-stage quenching is heated to 420 °C, held for 135 min, and furnace-cooled to room temperature to obtain the product. The obtained high manganese wear-resistant steel has a uniform austenite + bainite structure.

[0035] According to T∕CFA 010604-3-2016 "Test Method for Impact Abrasive Wear of Steel Materials", the wear resistance of the steel is detected, and the wear amount is 0.68 g; according to GB / T 43337-2008 "Rotating Bending Method for Fatigue Testing of Metallic Materials", the fatigue limit of the steel is measured to be 695 MPa, and the tensile strength Rm of the steel is 1070 MPa, that is, the fatigue limit σ-1≈0.65Rm. Example 3

[0036] A high manganese wear-resistant steel with excellent anti-fatigue performance is smelted using an electric furnace and cast into a 50 kg ingot. The chemical composition and its weight percentage are determined using a direct-reading spectrometer as follows: C: 0.15%, Si: 0.30%, Mn: 12.30%, Cr: 3.50%, V+Nb: 0.15%, Y: 0.02%, O: 0.0038, N: 0.0027, P: 0.009%, S: 0.018%, with the balance being Fe and unavoidable impurities; its production process includes billet heating, forging + rolling, two-stage quenching + tempering heat treatment processes, and the specific process control is as follows: (1)Slab heating process: The slab is heated in an electromagnetic induction heating furnace. The heating furnace has a heating-up time of 50 min, a heating temperature of 1230 °C, and a holding time of 200 min for the slab.

[0037] (2)Forging and rolling process: The heated slab is forged into an intermediate blank of 50 mm. The final forging temperature is 857 °C. An energy-saving production method is adopted, and the forged intermediate blank is warm-rolled and multi-pass rolled into a slab with a thickness of 20 mm. The final rolling temperature is 727 °C, and it is cooled to room temperature by burying it in sand.

[0038] (3)Two-stage quenching + tempering heat treatment process: The warm-rolled slab is heated to 915 °C, held for 100 min, forced air-cooled to 520 °C, reheated to 878 °C, held for 70 min, and water-quenched to room temperature; the steel plate after two-stage quenching is heated to 450 °C, held for 140 min, and furnace-cooled to room temperature to obtain the product. The obtained high manganese wear-resistant steel has a uniform austenite + bainite structure.

[0039] The wear resistance of the steel is detected according to T∕CFA 010604-3-2016 "Test Method for Impact Abrasive Wear of Steel Materials", and the wear loss is 0.73 g; the fatigue limit of the steel is measured according to GB / T 43337-2008 "Rotating Bending Method for Fatigue Testing of Metallic Materials", the fatigue limit of the steel is 712 MPa, and the tensile strength Rm of the steel is 1063 MPa, that is, the fatigue limit σ-1≈0.67Rm. Example 4

[0040] A high manganese wear-resistant steel with excellent fatigue resistance is smelted using an electric furnace and cast into a 50 kg ingot. The chemical composition and its weight percentage are determined using a direct-reading spectrometer as follows: C: 0.18%, Si: 0.35%, Mn: 13.0%, Cr: 4.25%, V+Nb: 0.18%, Y: 0.025%, O: 0.0046, N: 0.0029, P: 0.015%, S: 0.014%, and the balance is Fe and unavoidable impurities; its production process includes slab heating, forging + rolling, and two-stage quenching + tempering heat treatment processes, which are specifically as follows: (1)Slab heating process: The slab is heated in an electromagnetic induction heating furnace. The heating furnace has a heating-up time of 52 min, a heating temperature of 1235 °C, and a holding time of 220 min for the slab.

[0041] (2)Forging and rolling process: The heated slab is forged into an intermediate blank of 53 mm. The final forging temperature is 860 °C. An energy-saving production method is adopted, and the forged intermediate blank is warm-rolled and multi-pass rolled into a slab with a thickness of 22 mm. The final rolling temperature is 724 °C, and it is cooled to room temperature by burying it in sand.

[0042] (3) Two-stage quenching + tempering heat treatment process: Heat the warm-rolled slab to 920 °C, hold for 105 min, air-cool forcibly to 530 °C, reheat to 883 °C, hold for 75 min, and water-quench to room temperature; Heat the steel plate after two-stage quenching to 475 °C, hold for 142 min, and furnace-cool to room temperature to obtain. The obtained high manganese wear-resistant steel has a uniform austenite + bainite structure.

[0043] According to T∕CFA 010604-3-2016 "Test Method for Impact Abrasive Wear of Steel Materials", the wear resistance of the steel is detected, and the wear loss is 0.86 g; According to GB / T 43337-2008 "Rotating Bending Method for Fatigue Test of Metallic Materials", the fatigue limit of the steel is measured to be 682 MPa, the tensile strength Rm of the steel is 1065 MPa, that is, the fatigue limit σ-1≈0.64Rm. Example 5

[0044] A high manganese wear-resistant steel with excellent fatigue resistance is smelted using an electric furnace and cast into a 50 kg ingot. The chemical composition and its weight percentage are determined using a direct-reading spectrometer as follows: C: 0.20%, Si: 0.42%, Mn: 13.5%, Cr: 4.75%, V+Nb: 0.19%, Y: 0.03%, O: 0.0041, N: 0.0038, P: 0.011%, S: 0.017%, and the balance is Fe and unavoidable impurities; Its production process includes steel billet heating, forging + rolling, two-stage quenching + tempering heat treatment process, and the specific process control is as follows: (1) Steel billet heating process: The steel billet is heated in an electromagnetic induction heating furnace. The heating furnace has a heating-up time of 58 min, a heating temperature of 1240 °C, and the steel billet has a holding time of 230 min.

[0045] (2) Forging and rolling process: Forge the heated slab into an intermediate billet of 55 mm, with a final forging temperature of 868 °C. Adopt an energy-saving production method, and warm-roll the forged intermediate billet into a slab with a thickness of 23 mm through multiple passes, with a final rolling temperature of 715 °C, and cool it to room temperature by burying it in sand.

[0046] (3) Two-stage quenching + tempering heat treatment process: Heat the warm-rolled slab to 925 °C, hold for 110 min, air-cool forcibly to 540 °C, reheat to 885 °C, hold for 80 min, and water-quench to room temperature; Heat the steel plate after two-stage quenching to 490 °C, hold for 145 min, and furnace-cool to room temperature to obtain. The obtained high manganese wear-resistant steel has a uniform austenite + bainite structure.

[0047] The wear resistance of the steel was tested according to T∕CFA 010604-3-2016 "Test Method for Impact Abrasive Wear of Steel Materials", and the wear loss was 0.85 g. The fatigue limit of the steel was measured as 679 MPa according to GB / T 43337-2008 "Rotating Bending Method for Fatigue Testing of Metallic Materials". The tensile strength Rm of the steel was 1078 MPa, that is, the fatigue limit σ-1≈0.63Rm. Example 6

[0048] A high manganese wear-resistant steel with excellent fatigue resistance was smelted in an electric furnace and cast into a 50 kg ingot. The chemical composition and its weight percentage were determined by a direct-reading spectrometer as follows: C: 0.25%, Si: 0.50%, Mn: 14.0%, Cr: 5.00%, V+Nb: 0.20%, Y: 0.04%, O: 0.0050, N: 0.0040, P: 0.008%, S: 0.016%, and the balance was Fe and unavoidable impurities. Its production process included steel billet heating, forging + rolling, two-stage quenching + tempering heat treatment processes. The specific process control was as follows: (1) Steel billet heating process: The steel billet was heated in an electromagnetic induction heating furnace. The heating furnace had a heating-up time of 60 min, a heating temperature of 1250 °C, and a holding time of 240 min for the steel billet.

[0049] (2) Forging and rolling process: The heated slab was forged into an intermediate billet of 60 mm. The final forging temperature was 855 °C. Using an energy-saving production method, the forged intermediate billet was warm-rolled and rolled into a 25 mm thick slab in multiple passes. The final rolling temperature was 700 °C, and it was cooled to room temperature by burying it in sand.

[0050] (3) Two-stage quenching + tempering heat treatment process: The warm-rolled slab was heated to 930 °C, held for 120 min, forced air-cooled to 550 °C, reheated to 900 °C, held for 90 min, and water-quenched to room temperature. The steel plate after two-stage quenching was heated to 500 °C, held for 150 min, and furnace-cooled to room temperature to obtain the product. The obtained high manganese wear-resistant steel had a uniform austenite + bainite structure.

[0051] The wear resistance of the steel was tested according to T∕CFA 010604-3-2016 "Test Method for Impact Abrasive Wear of Steel Materials", and the wear loss was 0.62 g. The fatigue limit of the steel was measured as 699 MPa according to GB / T 43337-2008 "Rotating Bending Method for Fatigue Testing of Metallic Materials". The tensile strength Rm of the steel was 1075 MPa, that is, the fatigue limit σ-1≈0.65Rm.

Claims

1. A high manganese wear-resistant steel with excellent fatigue resistance, characterized in that: The chemical composition and weight percentage of the high manganese wear-resistant steel are: C: 0.08-0.25%, Si: 0.20-0.50%, Mn: 12.0-14.0%, Cr: 3.0-5.0%, Nb+V: 0.10-0.20%, Y: 0.01-0.04%, O≤0.005%, N≤0.004%, P≤0.015%, S≤0.020%, and the balance is Fe and unavoidable impurity elements.

2. The high manganese wear-resistant steel with excellent fatigue resistance according to claim 1, characterized in that: The microstructure of the high manganese wear-resistant steel after two-stage quenching+tempering heat treatment is a uniform austenite+bainite structure.

3. The high manganese wear-resistant steel with excellent fatigue resistance according to claim 1, characterized in that: After the high manganese wear-resistant steel is subjected to two-stage quenching + tempering heat treatment, the wear loss is ≤1g, and the fatigue limit σ-1 of the smooth sample is ≥0.63Rm, wherein σ-1 is the fatigue limit of the smooth sample and Rm is the tensile strength.

4. A method for producing high manganese wear-resistant steel with excellent fatigue resistance according to any one of claims 1 to 3, characterized in that: It includes billet heating, forging + rolling, and two-stage quenching + tempering heat treatment processes.

5. The method for producing high manganese wear-resistant steel with excellent fatigue resistance according to claim 4, characterized in that: In the steel billet heating process, the heating temperature is 1220-1250° C. and the insulation time is 180-240 minutes.

6. The method for producing high manganese wear-resistant steel with excellent fatigue resistance according to claim 4, characterized in that: In the forging process, the heated steel billet is forged into a slab with a thickness of 45 to 60 mm, and the final forging temperature is ≥ 850°C.

7. The method for producing high manganese wear-resistant steel with excellent fatigue resistance according to claim 4, characterized in that: In the rolling process, the steel plate is warm rolled into a 15-25 mm thick slab at a rolling temperature between 800 and 700° C., and then buried in sand and cooled to room temperature.

8. The method for producing high manganese wear-resistant steel with excellent fatigue resistance according to claim 4, characterized in that: The two-stage quenching + tempering heat treatment process is as follows: the steel plate after warm rolling is heated to 900-930°C, kept warm for 90-120 minutes, and forced air-cooled to 500-550°C; the steel plate is reheated to 875-900°C, kept warm for 60-90 minutes, and water-quenched to room temperature; the steel plate after two-stage quenching is heated to 400-500°C, kept warm for 130-150 minutes, and cooled to room temperature with the furnace to obtain a uniform austenite + bainite structure.

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