A method for preparing high-hardness and high-toughness bainite wear-resistant steel

Abstract

The invention discloses a preparation method of a bainite wear-resistant steel with high hardness and high toughness, belonging to the technical field of wear-resistant steels. The preparation method of the bainite wear-resistant steel with high hardness and high toughness of the invention designs a deformation and heat treatment process, including melting, casting, forging treatment, rolling, heat treatment, cryogenic treatment, tempering treatment, and conducts deformation-induced precipitation, refinement of original austenite grains, transformation of austenite, tempering toughening, etc. on the steel, so as to enable the bainite wear-resistant steel with high hardness and high toughness to obtain high strength without losing plasticity and toughness. Its impact toughness is 50-60 J / cm<supgt;2< / supgt;, and its wear resistance is more than twice that of the commercially available wear-resistant steel.

Description

Technical Field

[0001] The invention belongs to the technical field of metal wear-resistant steel, and in particular relates to a preparation method of high-hardness and high-toughness bainite wear-resistant steel. Background Art

[0002] Mining machinery often faces severe service conditions, and materials usually fail prematurely due to insufficient wear resistance, resulting in serious economic losses and safety issues. In the past, high manganese steel was the mainstream choice for lining materials because it undergoes work hardening and increases hardness under large impacts, but it cannot fully exert its work hardening capabilities under medium and low load impact conditions, and its low initial hardness and yield strength lead to premature failure of the material. At the same time, high manganese steel liners are prone to plastic deformation during service, causing the liner to bite or deform and break the fixing bolts. The martensitic wear-resistant steel currently used has good strength and hardness, which meets the service conditions of mining machinery, but the toughness of martensitic steel has always been a problem, and cracks still occur during wear. Therefore, it is of great significance to develop a lining steel with high strength, high hardness and good plastic toughness.

[0003] Chinese invention patent CN115786665A discloses a method for ultrafine bainitic rail steel, whose chemical element composition and mass percentage are: C: 0.22-0.30, Mn: 1.0-1.8, Al: 0.4-1.0, Si: 1.5-Al, Cr: 0.8-1.3, Mo+Ni: <0.6, V+Nb+B: 0.06-0.20, P<0.02, S<0.02, and the balance is Fe. Rail steel also faces serious wear problems, which is consistent with the performance requirements required for the liner. In order to improve the performance of bainitic steel, nano-scale vanadium carbonitride is precipitated by multiple heat treatments. However, the cost of V and Nb is relatively high, and the amount of blocky residual austenite is relatively large, which affects the hardness of the wear surface.

[0004] Chinese invention patent CN114480806A discloses a method for manufacturing a thick TiC particle reinforced martensitic wear-resistant steel plate, the chemical element composition and its mass percentage are: C: 0.20-0.40%, Si: 0.20-0.30%, Mn: 0.50-1.00%, P≤0.0010%, S≤0.003%, Ti: 0.30-0.80%, Mo: 0.30-0.50%, Cr: 0.50-1.00%, B: 0.0008-0.002%, the balance is Fe and unavoidable impurity elements. The grain size is controlled by multi-pass rolling and micron-level TiC precipitates, but excessive addition of Ti content will inevitably lead to large pieces of born carbides, and the martensitic matrix is ​​accompanied by low toughness, which seriously affects the service life and economic safety of the wear-resistant steel plate.

[0005] Chinese invention patent CN101338399A discloses a carbide-free nano-bainite wear-resistant steel plate and its production process, the chemical element composition and its mass percentage are: C: 0.15-0.25, Mn: 1.5-2, Al: 0.2-0.6, Si: 1.5-2, Cr: 0.6-1, Mo: 0.25-0.5, Nb: 0.01-0.035, the balance is Fe. Although a large amount of alloy elements are used to obtain better performance, increasing economic costs, the comprehensive performance is relatively poor in the field of alloy wear-resistant steel, and it cannot be used in wear environments with complex working conditions and high-strength stress.

[0006] Obtaining high-strength and high-toughness bainitic steel has been a research hotspot in recent years. Hardness and toughness have always been in a competitive relationship, and traditional processes cannot solve this problem. Improving the performance of bainitic steel without increasing economic costs has always been a research topic. Summary of the invention

[0007] In view of the shortcomings of the above-mentioned prior art, the present invention provides a method for preparing high-hardness and high-toughness bainitic wear-resistant steel, which reduces the economic cost by adding alloy component elements with a lower mass fraction and improves the heat treatment process to obtain a wear-resistant lining with a smaller amount of film-like residual austenite and bainite structure, thereby significantly improving the wear resistance of the material.

[0008] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing high-hardness and high-toughness bainite wear-resistant steel, comprising the following steps:

[0009] (1) weighing raw materials according to the weight percentage of the chemical composition of high hardness and high toughness bainite wear-resistant steel, and then melting and casting into ingots; the high hardness and high toughness bainite wear-resistant steel comprises the following chemical components in weight percentage: C: 0.3-0.33%, Si: 1.0-1.4%, Mn: 0.6-0.7%, Cr: 0.9-1.0%, P<0.007%, S<0.001%, Ti: 0.3-0.4%, Ni: 1.3-1.5%, Mo: 0.3-0.5%, B: 0.001-0.002%, and the balance is Fe and unavoidable impurities;

[0010] (2) The ingot is heated and kept warm for a period of time, then heated and kept warm and then cooled, forged, and then air-cooled to room temperature;

[0011] (3) heating and heat-insulating the steel obtained in step (2), then cooling it, performing a first warm rolling, heating it after the rolling is completed, performing a second warm rolling, and then air cooling it to room temperature;

[0012] (4) The rolled steel is heated, kept warm for a period of time, air-cooled to room temperature, and then quenched to below zero for deep cooling and heat preservation, and then heated again for a certain period of time, and then air-cooled to room temperature to obtain high-hardness and high-toughness bainitic wear-resistant steel.

[0013] As a preferred embodiment of the present invention, the raw materials include pig iron, ferrosilicon, ferromanganese, ferrochrome and scrap steel.

[0014] As a preferred embodiment of the present invention, the pouring temperature is 1480-1530°C.

[0015] As a preferred embodiment of the present invention, in the step (2), the ingot is heated to 600±20°C and kept warm for 0.5h, and the heating rate is 30±20°C / min.

[0016] As a preferred embodiment of the present invention, in step (2), the temperature is raised to 1150-1200° C. and maintained for 1 hour.

[0017] As a preferred embodiment of the present invention, in step (2), the forging is started by air cooling to 950-1050° C., the steel thickness is forged from 300±20 mm to 220±20 mm, and the final forging temperature is 830-930° C. The forging process can crush large carbides and refine the grains.

[0018] As a preferred embodiment of the present invention, in the step (3), the steel obtained in the step (2) is heated to 860-920°C and kept warm for 1 hour, and the heating rate is 30±20°C / min.

[0019] As a preferred embodiment of the present invention, in the step (3), the steel is cooled to 700-750°C before the first warm rolling, and the first warm rolling reduces the thickness of the steel from 220±20 mm to 170±20 mm.

[0020] As a preferred embodiment of the present invention, in the step (3), after rolling is completed, the temperature is raised to 700-750°C and a second warm rolling is started. The second warm rolling reduces the thickness of the steel from 170±20 mm to 120±20 mm.

[0021] The present invention uses two rolling processes to precipitate micron-level precipitation phases close to the nanometer level in the steel, further refine the grains, and cooperate with the crushed eutectic carbides to strengthen the grain refinement and precipitation strengthening, thereby strengthening the matrix strength and hardness without sacrificing too much plasticity and toughness.

[0022] As a preferred embodiment of the present invention, in the step (4), the rolled steel is heated to 820-900°C at a rate of 30±20°C / min, kept at that temperature for 1 hour, and air-cooled to room temperature to obtain a bainite matrix.

[0023] As a preferred embodiment of the present invention, in step (4), after air cooling to room temperature, rapid quenching is performed using liquid nitrogen at a pressure of 5 bar, cooled to -80 to -60°C and kept warm for 1 hour, then heated again to 300-350°C and kept warm for 1 hour, and air cooled to room temperature.

[0024] During the heat treatment process of step (4) of the present invention, the transformation of bulk austenite to martensite at low temperature ensures that the steel obtains high hardness, while a small amount of film residual austenite ensures partial work hardening ability during strain. Subsequent tempering also provides a certain guarantee for obtaining high toughness.

[0025] Principle of the present invention: When the cast steel is heated to the forging temperature, the large carbides will first be forged and broken, so as to avoid the large carbides from deteriorating the toughness of the material. Secondly, the original austenite grains will be refined during the forging process. And the broken carbides will pin the grain boundaries to avoid the migration of grain boundaries during the deformation process. In the subsequent rolling process, the grains will be further refined, and this process will induce the precipitation of fine carbides, which will produce a multi-scale strengthening effect on the matrix together with the broken micron-sized eutectic carbides, and inhibit the growth of the grains of recovery recrystallization. The air cooling of the heat treatment process ensures that the main phase of the material is bainite structure, and the first formed bainite will cut the original austenite grains and control the austenite morphology. In the subsequent deep cooling process, the large pieces of residual austenite will first transform into martensite due to poor stability, and only a part of the film-like residual austenite with high stability will exist after the deep cooling. The tempering process after the deep cooling treatment obtains the tempered martensite structure to avoid low toughness caused by too high hardness. In addition, there is a large back stress in the martensite and bainite matrix, which can provide good back stress strengthening for the material during the deformation process. Under this process, the obtained bainite / martensite structure has high hardness, high strength and high toughness, thereby improving the wear resistance of the material.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: on the one hand, the present invention significantly reduces the production cost of high-hardness and high-toughness bainite wear-resistant steel by using a chemical composition with low alloy content and without adding high-priced alloy elements such as precious metals. On the other hand, the preparation process is optimized, and the forging process, rolling process, cryogenic treatment, and tempering treatment are combined; first, the carbide particles are refined by forging; secondly, the small-sized carbides are precipitated by the rolling process and the multi-scale matrix of the carbides in the forging process is strengthened, and finally, by cryogenic treatment and tempering treatment, it is ensured that only martensite, bainite, and a small amount of residual austenite with high stability exist in the steel matrix, and finally a high-hardness and high-toughness bainite wear-resistant steel with high hardness and toughness and excellent wear resistance is obtained, and the wear resistance of the high-hardness and high-toughness bainite wear-resistant steel is nearly 2 times higher than that of commercial wear-resistant steel under the same wear conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a process flow chart for preparing the high-hardness and high-toughness bainite wear-resistant steel described in the present invention.

[0028] Figure 2 This is the organizational diagram of the high-hardness and high-toughness bainite wear-resistant steel described in Example 1.

[0029] Figure 3 The wear comparison diagrams of the high hardness and high toughness bainitic wear-resistant steel and the commercial wear-resistant steel described in Example 1, wherein (a) is the wear diagram of the commercial wear-resistant steel, and (b) is the wear diagram of the high hardness and high toughness bainitic wear-resistant steel. DETAILED DESCRIPTION

[0030] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0031] Example 1

[0032] A method for producing high-hardness and high-toughness bainite wear-resistant steel, comprising the following steps:

[0033] (1) Ingredients: Calculate and weigh the raw materials such as pig iron, ferrosilicon, ferromanganese, ferrochrome and scrap steel according to the weight percentage of the chemical composition of high hardness and high toughness bainitic wear-resistant steel (C: 0.31%, Si: 1.2%, Mn: 0.61%, Cr: 0.97%, Ti: 0.3%, Ni: 1.3%, Mo: 0.35%, B: 0.001%, and the balance is Fe and inevitable impurities). Raw materials with larger volumes will prolong the melting time, and the raw materials with larger volumes are crushed into particles with a diameter not exceeding 5 mm.

[0034] (2) Melting: Use a medium frequency induction furnace with an acid lining for melting. Add the prepared raw materials into the furnace, heat to 1420°C, take samples for chemical composition analysis, reasonably control the chemical composition within the specified range, and then add pure aluminum for deoxidation;

[0035] (3) Pouring: Sand casting is adopted to take out the molten metal liquid of step (3) into a casting ladle and pour it at 1480°C. After pouring, a heat preservation agent is covered on the riser to cool it to room temperature to obtain a casting.

[0036] (4) Forging: The ingot was heated to 600°C at 10°C / min and kept at that temperature for 0.5 h. It was then heated to 1180°C for homogenization and kept at that temperature for 1 h. After being taken out of the furnace and cooled to 980°C, forging began. The thickness of the liner was forged from 300 mm to 220 mm. The final forging temperature was controlled at 880°C and then air-cooled to room temperature.

[0037] (5) Rolling: The forged steel plate is heated to 870°C at 10°C / min and kept at that temperature for 1h. After being taken out of the furnace and cooled to 730°C, the first rolling is started. The thickness of the liner is rolled from 220mm to 170mm. The temperature is raised to 730°C again and the second rolling is started. The thickness of the liner is rolled from 170mm to 120mm. The steel plate is then air-cooled to room temperature.

[0038] (6) Heat treatment: heat to 850°C at 10°C / min and keep warm for 1 h, then air cool to room temperature to obtain a bainite matrix, use liquid nitrogen at a pressure of 5 bar for rapid quenching, cool to -80°C and keep warm for 1 h, then heat to 330°C and keep warm for 1 h, and air cool to room temperature to obtain high hardness and high toughness bainite wear-resistant steel.

[0039] The high hardness and high toughness bainite wear-resistant steel is observed as Figure 1 The bainite / martensite multiphase structure shown in Figure 1 It can be seen that the high hardness and high toughness bainitic wear-resistant steel is mainly composed of bainite and martensite multiphase structure. The bainite and martensite structures are mainly lath-shaped. The surface hardness of high hardness and high toughness bainitic wear-resistant steel reaches 51HRC and the impact toughness is 58J / cm 2 ,Depend on Figure 3 It can be seen that the wear resistance of the high-hardness and high-toughness bainite wear-resistant steel under the same impact wear conditions is 2.3 times higher than that of commercial wear-resistant steel.

[0040] Example 2

[0041] A method for producing high-hardness and high-toughness bainite wear-resistant steel, comprising the following steps:

[0042] (1) Ingredients: According to the weight percentage of the chemical composition of high hardness and high toughness bainitic wear-resistant steel (C: 0.33%, Si: 1.0%, Mn: 0.67%, Cr: 1.0%, Ti: 0.35%, Ni: 1.4%, Mo: 0.38%, B: 0.001%, the balance is Fe and unavoidable impurities), the raw materials such as pig iron, ferrosilicon, ferromanganese, ferrochrome and scrap steel are calculated and weighed, and the larger raw materials are crushed into smaller particles.

[0043] (2) Melting: Use a medium frequency induction furnace with an acid lining for melting. Add the prepared raw materials into the furnace, heat to 1400°C, take samples for chemical composition analysis, reasonably control the chemical composition within the specified range, and then add pure aluminum for deoxidation;

[0044] (3) Pouring: Sand casting is adopted to take out the molten metal liquid of step (3) into a casting ladle and pour it at 1510°C. After pouring, a heat preservation agent is covered on the riser to cool it to room temperature to obtain a casting.

[0045] (4) Forging: The ingot was heated to 580°C at 20°C / min and kept at that temperature for 0.5 h. It was then heated to 1150°C for homogenization and kept at that temperature for 1 h. After being taken out of the furnace and cooled to 1000°C, forging began. The thickness of the liner was forged from 300 mm to 230 mm. The final forging temperature was controlled at 920°C and then air-cooled to room temperature.

[0046] (5) Rolling: The forged steel plate is heated to 880°C at 15°C / min and kept at that temperature for 1h. After being taken out of the furnace and cooled to 720°C, the first rolling is started. The thickness of the liner is rolled from 230 mm to 160 mm. The temperature is raised to 720°C again and the second rolling is started. The thickness of the liner is rolled from 160 mm to 110 mm. The steel plate is then air-cooled to room temperature.

[0047] (6) Heat treatment: heat to 860°C at 30°C / min and keep warm for 1 h, then air cool to room temperature to obtain a bainite matrix, use liquid nitrogen at a pressure of 5 bar for rapid quenching, cool to -70°C and keep warm for 1 h, then heat to 350°C and keep warm for 1 h, and air cool to room temperature to obtain high hardness and high toughness bainite wear-resistant steel.

[0048] The high hardness and high toughness bainite wear-resistant steel was observed. The bainite and martensite structures were mainly lath-shaped. The surface hardness of the high hardness and high toughness bainite wear-resistant steel reached 53HRC and the impact toughness was 55J / cm 2 The wear resistance of high hardness and high toughness bainitic wear-resistant steel under the same impact wear conditions is 2 times higher than that of commercial wear-resistant steel.

[0049] Example 3

[0050] A method for producing high-hardness and high-toughness bainite wear-resistant steel, comprising the following steps:

[0051] (1) Ingredients: According to the weight percentage of the chemical composition of high hardness and high toughness bainitic wear-resistant steel (C: 0.33%, Si: 1.4%, Mn: 0.64%, Cr: 0.9%, Ti: 0.3%, Ni: 1.47%, Mo: 0.35%, B: 0.001%, the balance is Fe and unavoidable impurities), the raw materials such as pig iron, ferrosilicon, ferromanganese, ferrochrome and scrap steel are calculated and weighed, and the larger raw materials are crushed into smaller particles.

[0052] (2) Melting: Use a medium frequency induction furnace with an acid lining for melting. Add the prepared raw materials into the furnace, heat to 1450°C, take samples for chemical composition analysis, reasonably control the chemical composition within the specified range, and then add pure aluminum for deoxidation;

[0053] (3) Pouring: Sand casting is used to pour the molten metal from step (3) into a ladle and pour it at 1530°C. After pouring, a heat preservation agent is covered on the riser to cool it to room temperature to obtain a cast billet.

[0054] (4) Forging: The ingot was heated to 610°C at 25°C / min and kept at that temperature for 0.5 h, then heated to 1200°C for homogenization and kept at that temperature for 1 h. After being taken out of the furnace and cooled to 950°C, forging began. The thickness of the liner was forged from 320 mm to 220 mm. The final forging temperature was controlled at 870°C and then air-cooled to room temperature.

[0055] (5) Rolling: The forged steel plate is heated to 890°C at 35°C / min and kept at that temperature for 1h. After being taken out of the furnace and cooled to 750°C, the first rolling is started. The thickness of the liner is rolled from 220mm to 150mm. The temperature is raised to 750°C again and the second rolling is started. The thickness of the liner is rolled from 150mm to 100mm. The steel plate is then air-cooled to room temperature.

[0056] (6) Heat treatment: heat to 860°C at 10°C / min and keep warm for 1 h, then air cool to room temperature to obtain a bainite matrix, use liquid nitrogen at a pressure of 5 bar for rapid quenching, cool to -60°C and keep warm for 1 h, then heat to 320°C and keep warm for 1 h, then air cool to room temperature to obtain high hardness and high toughness bainite wear-resistant steel.

[0057] The high hardness and high toughness bainite wear-resistant steel was observed after heat treatment. The bainite and martensite structures were mainly lath-shaped. The surface hardness of the high hardness and high toughness bainite wear-resistant steel reached 57HRC and the impact toughness was 50J / cm 2 The wear resistance of high hardness and high toughness bainitic wear-resistant steel under the same impact wear conditions is 2.7 times higher than that of commercial wear-resistant steel.

[0058] Example 4

[0059] A method for producing high-hardness and high-toughness bainite wear-resistant steel, comprising the following steps:

[0060] (1) Ingredients: Calculate and weigh the raw materials such as pig iron, ferrosilicon, ferromanganese, ferrochrome and scrap steel according to the weight percentage of the chemical composition of high hardness and high toughness bainitic wear-resistant steel (C: 0.32%, Si: 1.3%, Mn: 0.7%, Cr: 0.95%, Ti: 0.4%, Ni: 1.5%, Mo: 0.5%, B: 0.002%, and the balance is Fe and inevitable impurities), and crush the larger raw materials into smaller particles.

[0061] (2) Melting: Use a medium frequency induction furnace with an acid lining for melting. Add the prepared raw materials into the furnace, heat to 1420°C, take samples for chemical composition analysis, reasonably control the chemical composition within the specified range, and then add pure aluminum for deoxidation;

[0062] (3) Pouring: Sand casting is used to pour the molten metal from step (3) into a ladle and pour it at 1530°C. After pouring, a heat preservation agent is covered on the riser to cool it to room temperature to obtain a cast billet.

[0063] (4) Forging: The ingot was heated to 620°C at 50°C / min and kept at that temperature for 0.5 h, then heated to 1180°C for homogenization and kept at that temperature for 1 h. After being taken out of the furnace and cooled to 1050°C, forging began. The thickness of the liner was forged from 280 mm to 240 mm. The final forging temperature was controlled at 830°C and then air-cooled to room temperature.

[0064] (5) Rolling: The forged steel plate is heated to 920°C at 50°C / min and kept at this temperature for 1h. After being taken out of the furnace and cooled to 700°C, the first rolling is started. The thickness of the liner is rolled from 200mm to 190mm. The temperature is raised to 700°C again and the second rolling is started. The thickness of the liner is rolled from 190mm to 100mm. The liner is then air-cooled to room temperature.

[0065] (6) Heat treatment: heat to 900°C at 50°C / min and keep warm for 1 h, then air cool to room temperature to obtain a bainite matrix, use liquid nitrogen at a pressure of 5 bar for rapid quenching, cool to -80°C and keep warm for 1 h, then heat to 300°C and keep warm for 1 h, and air cool to room temperature to obtain high hardness and high toughness bainite wear-resistant steel.

[0066] The high hardness and high toughness bainite wear-resistant steel was observed after heat treatment. The bainite and martensite structures were mainly lath-shaped. The surface hardness of the high hardness and high toughness bainite wear-resistant steel reached 54HRC and the impact toughness was 49J / cm 2 The wear resistance of high hardness and high toughness bainitic wear-resistant steel under the same impact wear conditions is 2.9 times higher than that of commercial wear-resistant steel.

[0067] Comparative Example 1

[0068] A method for producing wear-resistant steel, comprising the following steps:

[0069] (1) Ingredients: Calculate and weigh raw materials such as pig iron, ferrosilicon, ferromanganese, ferrochrome and scrap steel according to the weight percentage of the chemical composition of high hardness and high toughness bainitic wear-resistant steel (C: 0.31%, Si: 1.2%, Mn: 0.61%, Cr: 0.97%, Ti: 0.3%, Ni: 1.3%, Mo: 0.35%, B: 0.001%, the balance is Fe and inevitable impurities), and crush the larger raw materials into smaller particles.

[0070] (2) Melting: Use a medium frequency induction furnace with an acid lining for melting. Add the prepared raw materials into the furnace, heat to 1420°C, take samples for chemical composition analysis, reasonably control the chemical composition within the specified range, and then add pure aluminum for deoxidation;

[0071] (3) Pouring: Sand casting is adopted to take out the molten metal liquid of step (3) into a casting ladle and pour it at 1480°C. After pouring, a heat preservation agent is covered on the riser to cool it to room temperature to obtain a casting.

[0072] (4) The ingot is heated to 860°C, then placed in a quenching liquid such as salt and directly cooled and isothermally treated at 330°C, and then cooled to room temperature in air to obtain wear-resistant steel.

[0073] The wear-resistant steel was subjected to color metallographic structure observation and performance testing. The wear-resistant steel formed bainite and martensite structures, but pearlite structures also existed inside the wear-resistant steel. Its surface hardness was 36HRC and its impact toughness was 27J / cm 2 The wear resistance of wear-resistant steel under the same impact wear conditions is nearly 1.1 times higher than that of commercial wear-resistant steel.

[0074] Comparative Example 2

[0075] A method for producing high-hardness and high-toughness bainite wear-resistant steel, comprising the following steps:

[0076] (1) Ingredients: According to the weight percentage of the chemical composition of high hardness and high toughness bainitic wear-resistant steel (C: 0.31%, Si: 1.2%, Mn: 0.61%, Cr: 0.97%, Ti: 0.3%, Ni: 1.3%, Mo: 0.35%, B: 0.001%, the balance is Fe and unavoidable impurities), the raw materials such as pig iron, ferrosilicon, ferromanganese, ferrochrome and scrap steel are calculated and weighed, and the larger raw materials are crushed into smaller particles.

[0077] (2) Melting: Use a medium frequency induction furnace with an acid lining for smelting. Add the prepared raw materials into the furnace and heat them to 1420°C before taking samples for chemical composition analysis. Rationally control the chemical compositions within the specified range and then add pure aluminum for deoxidation.

[0078] (3) Pouring: Sand casting is adopted to take out the molten metal liquid of step (3) into a casting ladle and pour it at 1480°C. After pouring, a heat preservation agent is covered on the riser to cool it to room temperature to obtain a casting.

[0079] (4) Forging: The ingot was heated to 600°C at 10°C / min and kept at that temperature for 0.5 h. It was then heated to 1180°C for homogenization and kept at that temperature for 1 h. After being taken out of the furnace and cooled to 980°C, forging began. The thickness of the liner was forged from 300 mm to 220 mm. The final forging temperature was controlled at 880°C and then air-cooled to room temperature.

[0080] (5) Rolling: The forged steel plate is heated to 870°C at 10°C / min and kept at that temperature for 1h. After being taken out of the furnace and cooled to 730°C, the first rolling is started. The thickness of the liner is rolled from 220mm to 170mm. The temperature is raised to 730°C again and the second rolling is started. The thickness of the liner is rolled from 170mm to 120mm. The steel plate is then air-cooled to room temperature.

[0081] (6) Heat treatment: Heat to 850℃ at 10℃ / min and keep warm for 1h, then put in 330℃ salt bath and keep warm for 1h, and air cool to room temperature to produce bainitic wear-resistant steel.

[0082] The sample was observed to be mainly composed of bainite and retained austenite, with a surface hardness of only 31HRC and an impact toughness of 41J / cm 2 The wear resistance of bainitic wear-resistant steel under the same impact wear conditions is 1.5 times higher than that of commercial wear-resistant steel.

[0083] Comparative Example 3

[0084] A method for producing high-hardness and high-toughness bainite wear-resistant steel, comprising the following steps:

[0085] (1) Ingredients: According to the weight percentage of the chemical composition of high hardness and high toughness bainitic wear-resistant steel (C: 0.31%, Si: 1.2%, Mn: 0.61%, Cr: 0.97%, Ti: 0.3%, Ni: 1.3%, Mo: 0.35%, B: 0.001%, the balance is Fe and unavoidable impurities), the raw materials such as pig iron, ferrosilicon, ferromanganese, ferrochrome and scrap steel are calculated and weighed, and the larger raw materials are crushed into smaller particles.

[0086] (2) Melting: Use a medium frequency induction furnace with an acid lining for smelting. Add the prepared raw materials into the furnace and heat them to 1420°C before taking samples for chemical composition analysis. Rationally control the chemical compositions within the specified range and then add pure aluminum for deoxidation.

[0087] (3) Pouring: Sand casting is adopted to take out the molten metal liquid of step (3) into a casting ladle and pour it at 1480°C. After pouring, a heat preservation agent is covered on the riser to cool it to room temperature to obtain a casting.

[0088] (4) Rolling: The ingot was heated to 870°C at 10°C / min and kept at that temperature for 1h. After being taken out of the furnace and cooled to 730°C, the first rolling was started. The thickness of the liner was rolled from 220mm to 170mm. The ingot was heated to 730°C again and the second rolling was started. The thickness of the liner was rolled from 170mm to 120mm. The ingot was then air-cooled to room temperature.

[0089] (5) Heat treatment: heat to 850°C at 10°C / min and keep warm for 1 h, then air cool to room temperature to obtain a bainite matrix, use liquid nitrogen at a pressure of 5 bar for rapid quenching, cool to -80°C and keep warm for 1 h, then heat to 330°C and keep warm for 1 h, and air cool to room temperature to obtain high hardness and high toughness bainite wear-resistant steel.

[0090] The sample was observed to be mainly composed of bainite and martensite, but the presence of large-sized primary carbides seriously affected the toughness. The surface hardness reached 47HRC and the impact toughness was 22J / cm 2 The wear resistance of bainitic wear-resistant steel under the same impact wear conditions is 1.3 times higher than that of commercial wear-resistant steel.

[0091] Comparative Example 4

[0092] A method for producing wear-resistant steel, comprising the following steps:

[0093] (1) Ingredients: Calculate and weigh the raw materials such as pig iron, ferrosilicon, ferromanganese, ferrochrome and scrap steel according to the weight percentage of the chemical components of the wear-resistant steel (C: 0.35%, Si: 1.18%, Mn: 1.35%, Cr: 1.08%, Ni: 1.14%, Al: 1.05%, Nb: 0.4%, the balance is Fe and inevitable impurities), and crush the larger raw materials into smaller particles.

[0094] (2) Melting: Use a medium frequency induction furnace with an acid lining for smelting. Add the prepared raw materials into the furnace and heat them to 1420°C before taking samples for chemical composition analysis. Rationally control the chemical compositions within the specified range and then add pure aluminum for deoxidation.

[0095] (3) Pouring: Sand casting is adopted to take out the molten metal liquid of step (3) into a casting ladle and pour it at 1480°C. After pouring, a heat preservation agent is covered on the riser to cool it to room temperature to obtain a casting.

[0096] (4) Forging: The ingot was heated to 600°C at 10°C / min and kept at that temperature for 0.5 h. It was then heated to 1180°C for homogenization and kept at that temperature for 1 h. After being taken out of the furnace and cooled to 980°C, forging began. The thickness of the liner was forged from 300 mm to 220 mm. The final forging temperature was controlled at 880°C and then air-cooled to room temperature.

[0097] (5) Rolling: The forged steel plate is heated to 870°C at 10°C / min and kept at that temperature for 1h. After being taken out of the furnace and cooled to 730°C, the first rolling is started. The thickness of the liner is rolled from 220mm to 170mm. The temperature is raised to 730°C again and the second rolling is started. The thickness of the liner is rolled from 170mm to 120mm. The steel plate is then air-cooled to room temperature.

[0098] (6) Heat treatment: heat to 850°C at 10°C / min and keep warm for 1 h, then air cool to room temperature to obtain a bainite matrix, use liquid nitrogen at a pressure of 5 bar for rapid quenching, cool to -80°C and keep warm for 1 h, then heat to 330°C and keep warm for 1 h, and air cool to room temperature to obtain high hardness and high toughness bainite wear-resistant steel.

[0099] The high hardness and high toughness bainitic wear-resistant steel was observed after heat treatment. The main phases of bainite and martensite were forged, and the large pieces of primary carbide were forged. The surface hardness of bainitic wear-resistant steel reached 44HRC and the impact toughness was 41J / cm 2 The wear resistance of bainitic wear-resistant steel under the same impact wear conditions is 1.6 times higher than that of commercial wear-resistant steel.

[0100] Table 1

[0101] Case Hardness (HRC) <![CDATA[Toughness (J / m 2 )]]> Example 1 51 58 Example 2 53 55 Example 3 57 50 Example 4 54 49 Comparative Example 1 36 27 Comparative Example 2 31 41 Comparative Example 3 47 22 Comparative Example 4 44 41

[0102] According to Examples 1-4 and Comparative Example 1, by comparing the conventional quenching and isothermal heat treatment methods of Comparative Example 1, it can be found that the high-hardness and high-toughness bainite wear-resistant steel treated by the present invention can obtain higher hardness and toughness and has better wear resistance due to the combined effect of multi-scale strengthening of the precipitated phase under large plastic deformation of the present invention and fine grain strengthening. In the subsequent deep cryogenic treatment, most of the residual austenite is transformed into martensite, further improving the surface hardness, and the subsequent tempering treatment improves the toughness of the material. The method of the present invention can obtain an ideal multiphase structure, which has very obvious advantages in improving hardness and toughness and improving wear resistance.

[0103] Compared with Example 1 and Comparative Example 2, the hardness and toughness of the wear-resistant steel prepared in Comparative Example 2 are poor. This is because the sample in Comparative Example 2 that has not undergone deep cryogenic treatment retains more residual austenite. Although the residual austenite has the ability to transform into martensite to increase the surface hardness, the initial hardness is low, resulting in low overall hardness of the sample.

[0104] Compared with Example 1 and Comparative Example 3, the hardness and toughness of the wear-resistant steel prepared in Comparative Example 3 are poor. This is because the deformation of Comparative Example 3 is insufficient, the primary large blocks of TiC cannot be broken, and the large blocks of carbides, especially near their sharp corners, are prone to stress concentration and cracks, resulting in a sharp deterioration in the toughness of the material, thereby exhibiting poor wear resistance.

[0105] According to Example 1, compared with Comparative Example 4, the hardness and toughness of the wear-resistant steel prepared in Comparative Example 4 are relatively poor. This is because Comparative Example 4 transforms the original TiC precipitation phase into NbC, but does not greatly change the performance of the bainitic wear-resistant steel, and the market price of Nb is 6 times that of Ti. Therefore, the high-hardness and high-toughness bainitic wear-resistant steel described in the present invention not only has strong wear resistance, but is also more economical.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing high-hardness and high-toughness bainite wear-resistant steel, characterized in that: The steps include: (1) weighing raw materials according to the weight percentage of the chemical composition of high hardness and high toughness bainite wear-resistant steel, and then melting and casting into ingots; the high hardness and high toughness bainite wear-resistant steel comprises the following chemical components in weight percentage: C: 0.3-0.33%, Si: 1.0-1.4%, Mn: 0.6-0.7%, Cr: 0.9-1.0%, P<0.007%, S<0.001%, Ti: 0.3-0.4%, Ni: 1.3-1.5%, Mo: 0.3-0.5%, B: 0.001-0.002%, and the balance is Fe and unavoidable impurities; (2) The ingot is heated and kept warm for a period of time, then the temperature is raised and kept warm and then cooled to 950-1050°C to start forging. The final forging temperature is 830-930°C, and then air-cooled to room temperature; (3) heating and heat-insulating the steel obtained in step (2) and then cooling it, cooling it to 700-750° C. after it is taken out of the furnace and then starting the first warm rolling, wherein the thickness of the steel is rolled from 220±20 mm to 170±20 mm in the first warm rolling, and after the rolling is completed, heating it to 700-750° C. and then starting the second warm rolling, wherein the thickness of the steel is rolled from 170±20 mm to 120±20 mm, and then air cooling it to room temperature; (4) The rolled steel is heated, kept warm for a period of time, air-cooled to room temperature, and then quenched to below zero for deep cooling and heat preservation, and then heated again for a certain period of time, and then air-cooled to room temperature to obtain high-hardness and high-toughness bainitic wear-resistant steel.

2. The method for preparing the high-hardness and high-toughness bainite wear-resistant steel according to claim 1, characterized in that: The pouring temperature is 1480-1530°C.

3. The method for preparing high-hardness and high-toughness bainite wear-resistant steel according to claim 1, characterized in that: In the step (2), the ingot is heated to 600±20°C and kept warm for 0.5h, and the heating rate is 30±20°C / min.

4. The method for preparing high-hardness and high-toughness bainite wear-resistant steel according to claim 1, characterized in that: In the step (2), the temperature is raised to 1150-1200° C. and maintained for 1 hour.

5. The method for preparing high-hardness and high-toughness bainite wear-resistant steel according to claim 1, characterized in that: In the step (2), the thickness of the steel material is forged from 300±20 mm to 220±20 mm.

6. The method for preparing high-hardness and high-toughness bainite wear-resistant steel according to claim 1, characterized in that: In the step (3), the steel obtained in the step (2) is heated to 860-920°C and kept warm for 1 hour, and the heating rate is 30±20°C / min.

7. The method for preparing high-hardness and high-toughness bainite wear-resistant steel according to claim 1, characterized in that: In the step (4), the rolled steel is heated to 820-900°C at a rate of 30±20°C / min, kept at that temperature for 1 hour, and air-cooled to room temperature to obtain a bainite matrix.

8. The method for preparing high-hardness and high-toughness bainite wear-resistant steel according to claim 1, characterized in that: In the step (4), liquid nitrogen at a pressure of 5 bar is used for quenching, and the mixture is cooled to -80 to -60°C and kept for 1 hour, then heated again to 300 to 350°C and kept for 1 hour, and then air-cooled to room temperature.

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