Treatment method for improving impact toughness and fatigue resistance of cast steel axle housing

Abstract

The invention belongs to the technical field of metal material heat treatment, and particularly relates to a treatment method for improving impact toughness and fatigue resistance of a cast steel axle housing. Comprising the following steps that a cast steel axle housing initial material is subjected to normalizing treatment at the temperature of 880-930 DEG C, and a normalized axle housing is obtained after normalizing treatment is finished; the normalized axle housing is subjected to quenching treatment at the temperature of 880-950 DEG C, and a quenched axle housing is obtained after quenching treatment is finished; the quenched axle housing is subjected to tempering treatment at the temperature of 250-600 DEG C, and a tempered axle housing is obtained after tempering treatment is finished; normalizing treatment, quenching treatment and tempering treatment are used as circulation units, circulation is conducted for 2-3 times, and the cast steel axle housing with high strength, toughness and fatigue resistance is obtained. By optimizing the sequence of normalizing, quenching and tempering and the number of circulating units, the microstructure is remarkably refined, stress concentration is reduced, the overall toughness and fatigue resistance are improved, and the problem that strength and toughness are difficult to consider at the same time in the prior art is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment of metal materials, and in particular relates to a treatment method for improving the impact toughness and fatigue resistance of a cast steel bridge housing. Background Art

[0002] As one of the key components for load-bearing and force-transmitting of advanced heavy-duty mining vehicles, the strength level and variety quality of the traditional C-grade cast steel can no longer meet the market's requirements for high-strength and toughness mechanical properties and lightweight for mining dump trucks. Mining dump trucks and other heavy-duty mining vehicles require components that can withstand extremely high impacts and complex loads, requiring cast steel bridge housings to have higher strength, toughness and fatigue resistance to ensure their long-term stability and reliability in high-stress environments.

[0003] Traditional cast steel materials, such as C-grade cast steel, have certain strength, but they show low toughness and fatigue resistance when facing complex mechanical stresses, especially impact loads. To solve this problem, current research focuses on improving the comprehensive performance of steel by changing alloy composition and optimizing heat treatment processes. However, traditional heat treatment processes can only increase strength while reducing toughness and fatigue life. Therefore, how to ensure high strength while significantly improving impact toughness and fatigue resistance of high-strength and tough cast steel materials has become the key to improving the performance of cast steel bridge shells. Summary of the invention

[0004] The purpose of the present invention is to provide a treatment method for improving the impact toughness and fatigue resistance of a cast steel bridge shell. In order to solve the problem in the prior art that it is difficult to strike a balance between strength and toughness, the present invention improves the impact toughness of a cast steel bridge shell through cyclic heat treatment. This method significantly refines the microstructure and reduces stress concentration by optimizing the sequence and number of cycle units of normalizing, quenching and tempering, thereby improving the overall toughness and fatigue resistance.

[0005] The present invention solves the above technical problems through the following technical solutions.

[0006] The object of the present invention is to provide a method for improving the impact toughness and fatigue resistance of a cast steel bridge housing, comprising the following steps: S1. The initial material of the cast steel bridge housing is normalized at 880°C to 930°C. After the normalizing treatment, it is cooled to room temperature to obtain the normalized bridge housing.

[0007] S2. The normalized rear axle housing is subjected to a first quenching treatment at 880°C to 950°C, and the first quenching is performed by water cooling. After the first quenching, the normalized rear axle housing is heated to 880°C to 950°C, and then subjected to a second quenching treatment, and the second quenching is performed by oil cooling. After the second quenching treatment is completed, a quenched rear axle housing is obtained.

[0008] S3. Temper the quenched axle housing at 250°C to 650°C, and then temper the axle housing after cooling to room temperature.

[0009] S4. Normalizing, quenching and tempering are performed as a cycle unit for 2 to 3 cycles to obtain a cast steel bridge shell with high strength, toughness and fatigue resistance.

[0010] It should be noted that high-strength and tough cast steel bridge shells, as important load-bearing components of advanced heavy-duty mining vehicles, require materials with extremely high strength, toughness and fatigue resistance to cope with complex working environments and heavy loads. Based on this, the present invention designs a new type of cyclic heat treatment process, which optimizes the order of normalizing, quenching and tempering, takes normalizing, quenching and tempering as cycle units, accurately controls the temperature of normalizing, quenching and tempering, and performs multiple cyclic treatments to significantly refine the microstructure and reduce stress concentration. At the same time, the toughness and fatigue resistance of the cast steel bridge shell are greatly improved while maintaining high strength. It is suitable for the manufacture of cast steel bridge shells for heavy-duty mining vehicles to solve the problem that the strength and toughness of cast steel bridge shells in the prior art are difficult to balance.

[0011] It should be noted that the present invention forms fine residual austenite, lath-shaped martensite and bainite structures through multiple quenching processes, thereby maximizing the strength of the material.

[0012] In some specific embodiments, the holding time of the normalizing treatment is 1 hour to 2 hours, and the cooling method is air cooling. It should be noted that the present invention adopts normalizing treatment to refine the original grains, reduce internal segregation of the organization and the formation of coarse martensite and bainite.

[0013] In some specific embodiments, before the first quenching and the second quenching, the temperature is kept at 880° C. to 950° C. for 30 min to 60 min.

[0014] In some specific embodiments, the holding time of the tempering treatment is 1h to 2h, and the cooling method is air cooling or oil cooling. It should be noted that the present invention eliminates the residual stress formed by quenching through the tempering process, thereby improving the toughness and fatigue life of the material.

[0015] In summary, the present invention uses normalizing, quenching and tempering as a cycle unit. After multiple cycles, normalizing and quenching significantly refine the grains, reduce the appearance of coarse martensite, improve the microhardness distribution of the material, and effectively improve the overall strength. The cyclic tempering treatment allows the residual stress generated during the quenching process to be fully released, which helps to improve the fatigue resistance and impact resistance of the cast steel bridge shell, thereby extending the service life of the cast steel bridge shell. The impact absorption energy of the high-strength and tough cast steel at room temperature and low temperature conditions is increased by more than 30% compared with the traditional single quenching and tempering materials, so that it can better cope with high impact and complex working conditions.

[0016] In some specific embodiments, the tempering temperature is 550°C to 650°C.

[0017] In some specific embodiments, the chemical composition of the initial material of the cast steel bridge housing includes, by mass percentage: C: 0.18% to 0.25%, Si: 1.2% to 1.5%, Mn: 0.75% to 0.85%, Ni: 0.8% to 1.2%, Cr: 0.8% to 1.0%, Mo: 0.15% to 0.3%, rare earth elements: 0.03% to 0.07%, Nb: 0.02% to 0.04%, the remainder is Fe and unavoidable impurities, which add up to 100%. The present invention is based on low-carbon low-alloy cast steel with high silicon content, and significantly improves the impact toughness and comprehensive mechanical properties of the material by introducing trace rare earth elements and trace alloying elements Nb and by a cyclic heat treatment process.

[0018] In some specific embodiments, the rare earth element is La.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a treatment method for improving the impact toughness and fatigue resistance of a cast steel bridge shell. The method optimizes the order of normalizing, quenching and tempering treatments, designs a new type of cyclic heat treatment process, takes normalizing, quenching and tempering treatments as cyclic units, accurately controls the temperatures of normalizing, quenching and tempering, and performs multiple cyclic treatments to significantly refine the microstructure and reduce stress concentration. At the same time, the toughness and fatigue resistance of the cast steel bridge shell are greatly improved while maintaining high strength. The method is suitable for the manufacture of cast steel bridge shells for heavy mining vehicles, so as to solve the problem of difficulty in balancing strength and toughness in the prior art.

[0020] (2) The present invention uses normalizing, quenching and tempering as a cycle unit. After multiple cycles, normalizing and quenching significantly refine the grains, reduce the appearance of coarse martensite, improve the microhardness distribution of the material, and effectively improve the overall strength. The cyclic tempering treatment allows the residual stress generated during the quenching process to be fully released, which helps to improve the fatigue resistance and impact resistance of the cast steel bridge shell, thereby extending the service life of the cast steel bridge shell. The impact absorption energy of the cast steel bridge shell at room temperature and low temperature conditions is increased by more than 30% compared with the material subjected to traditional single quenching and tempering treatment, so that it can better cope with high impact and complex working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a diagram of the original austenite grain size of the cast steel bridge housing casting of the present invention without heat treatment.

[0022] Figure 2 This is a grain size microstructure diagram of the high-strength, toughness and fatigue-resistant cast steel bridge housing of Example 1 of the present invention.

[0023] Figure 3 This is the metallographic structure diagram of the cast steel bridge housing with high toughness and fatigue resistance in Example 1 of the present invention. Figure 3 In the figure, a is the metallographic structure diagram at a magnification of 1000, and b is the metallographic structure diagram at a magnification of 2000. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Certain words are used in the present invention to refer to specific components. It should be understood by those skilled in the art that technicians will use different nouns to refer to the same component. The present invention does not distinguish the components by the difference in nouns, but by the difference in functions of the components.

[0026] The invention is further described below through specific examples.

[0027] Example 1 A treatment method for improving the impact toughness and fatigue resistance of a cast steel bridge housing, wherein the initial material of the cast steel bridge housing is a high-silicon, low-carbon, low-alloy steel, and its chemical composition, by mass percentage, includes: C: 0.18%, Si: 1.4%, Mn: 0.8%, Ni: 0.8%, Cr: 0.8%, Mo: 0.2%, rare earth element La: 0.05%, Nb: 0.02%, and the balance is Fe and unavoidable impurities, which total 100%. The method comprises the following steps: S1. Normalizing treatment: Place the initial material of the cast steel bridge shell into a heating furnace, raise the temperature in the heating furnace to 900°C, maintain the normalizing temperature for 1.5 hours until the internal temperature of the initial material of the cast steel bridge shell is uniform, and then place it in the air to cool to room temperature to complete the normalizing process. During the normalizing process, the grains of the cast steel parts are refined, the structure is uniform, and the comprehensive mechanical properties of the material are improved to obtain the normalized bridge shell.

[0028] S2, quenching treatment: put the normalized rear axle housing into a heating furnace, raise the temperature in the heating furnace to 950℃, maintain the quenching temperature for 60 minutes until the internal temperature of the normalized rear axle housing is uniform and the austenite is completely transformed, and then perform the first quenching treatment. During the quenching process, use water quenching coolant for rapid cooling. After quenching, the internal structure of the steel casting is mainly a mixed structure of fine martensite and bainite; then perform the second quenching treatment, put the normalized rear axle housing after the first quenching treatment into a heating furnace, raise the temperature in the heating furnace to 920℃, keep it warm for 45 minutes, maintain a uniform temperature, and then use oil quenching coolant for cooling. The second quenching further refines the microstructure of the axle housing, further enhances the strength of the axle housing, and obtains the quenched rear axle housing.

[0029] S3, tempering treatment: put the quenched axle housing into a heating furnace, heat it to 600℃, keep it warm for 1 hour, and then cool it to room temperature with oil. The purpose of tempering is to eliminate the residual stress generated during the quenching process and optimize the toughness by precipitating fine carbides. Due to the proper control of tempering temperature and holding time, the impact toughness of the cast steel axle housing is greatly improved.

[0030] S4. Take normalizing, quenching and tempering as the cycle unit and carry out 2 cycles. In each cycle, the operation steps and process parameters of normalizing, quenching and tempering are kept consistent to ensure the uniformity of microstructure and the stability of organizational properties. The cast steel bridge shell after each cycle is observed under a microscope. Its microstructure is uniform, the grains are fine, and the organizational structure is stable, so that a cast steel bridge shell with high strength, toughness and fatigue resistance is obtained.

[0031] Example 2 A treatment method for improving the impact toughness and fatigue resistance of a cast steel bridge housing, wherein the initial material of the cast steel bridge housing is a high-silicon, low-carbon, low-alloy steel, and its chemical composition, by mass percentage, includes: C: 0.2%, Si: 1.2%, Mn: 0.85%, Ni: 0.9%, Cr: 0.9%, Mo: 0.15%, rare earth element La: 0.03%, Nb: 0.02%, and the balance is Fe and unavoidable impurities, which total 100%. The method comprises the following steps: S1. Normalizing treatment: Place the initial material of the cast steel bridge shell into a heating furnace, raise the temperature in the heating furnace to 900°C, maintain the normalizing temperature for 1.5 hours until the internal temperature of the initial material of the cast steel bridge shell is uniform, and then place it in the air to cool to room temperature to complete the normalizing process. During the normalizing process, the grains of the bridge shell are refined, the structure is uniform, the comprehensive mechanical properties of the material are improved, and the normalized bridge shell is obtained.

[0032] S2. Quenching treatment: put the normalized rear axle housing into a heating furnace, raise the temperature in the heating furnace to 950℃, maintain this temperature until the internal temperature of the normalized rear axle housing is uniform and the austenite is completely transformed, and then carry out the first quenching treatment. During the quenching process, use water quenching coolant for rapid cooling. After quenching, the internal structure of the steel casting is mainly a mixed structure of fine martensite and bainite; then carry out the second quenching treatment, put the normalized rear axle housing after the first quenching into a heating furnace, raise the temperature in the heating furnace to 920℃, keep it warm for 45 minutes, maintain a uniform temperature, and then use oil quenching coolant for cooling. The second quenching further refines the microstructure of the cast steel and further enhances the strength of the material to obtain a quenched rear axle housing.

[0033] S3, tempering treatment: put the quenched axle housing into a heating furnace, raise the temperature in the heating furnace to 650℃, keep it warm for 1 hour, and then air cool it to room temperature. The purpose of tempering is to eliminate the residual stress generated during the quenching process and optimize the toughness by precipitating fine carbides. Due to the proper control of tempering temperature and holding time, the impact toughness of the cast steel axle housing is greatly improved.

[0034] S4. Take normalizing, quenching and tempering as the cycle unit and carry out 2 cycles. In each cycle, the operation steps and process parameters of normalizing, quenching and tempering are kept consistent to ensure the uniformity of microstructure and the stability of organizational properties. The steel castings after each cycle are observed under a microscope. The microstructure is uniform, the grains are fine, and the organizational structure is stable, so that a cast steel bridge shell with high strength, toughness and fatigue resistance is obtained.

[0035] Example 3 A treatment method for improving the impact toughness and fatigue resistance of a cast steel bridge housing, wherein the initial material of the cast steel bridge housing is a high-silicon, low-carbon, low-alloy steel, and its chemical composition, by mass percentage, includes: C: 0.25%, Si: 1.5%, Mn: 0.75%, Ni: 1.0%, Cr: 1.0%, Mo: 0.3%, rare earth element La: 0.07%, Nb: 0.02%, and the balance is Fe and unavoidable impurities, which total 100%. The method comprises the following steps: S1. Normalizing treatment: Put the initial material of the cast steel bridge shell into a heating furnace, raise the temperature in the heating furnace to 900℃, maintain the normalizing temperature for 1.5 hours until the temperature inside the initial material of the cast steel bridge shell is uniform, and then cool the bridge shell to room temperature in the air to complete the normalizing process. During the normalizing process, the grains of the cast steel bridge shell are refined, the structure is uniform, the comprehensive mechanical properties of the cast steel bridge shell are improved, and the normalized bridge shell is obtained.

[0036] S2, quenching treatment: put the normalized rear axle housing into a heating furnace, raise the temperature in the heating furnace to 950℃, maintain the quenching temperature for 60 minutes until the internal temperature of the normalized rear axle housing is uniform and the austenite is completely transformed, and then perform the first quenching treatment. During the quenching process, use water quenching coolant for rapid cooling. After quenching, the internal structure of the axle housing is mainly a mixed structure of fine martensite and bainite; then perform the second quenching treatment, put the normalized rear axle housing after the first quenching treatment into a heating furnace, raise the temperature in the heating furnace to 920℃, maintain the uniform temperature for 45 minutes, and then use oil quenching coolant for cooling. The second quenching further refines the microstructure of the axle housing, further enhances the strength of the axle housing, and obtains the quenched rear axle housing.

[0037] S3, tempering treatment: put the quenched axle housing into a heating furnace, heat it to 650℃, keep it warm for 1 hour, and then air cool it to room temperature. The purpose of tempering is to eliminate the residual stress generated during the quenching process and optimize the toughness by precipitating fine carbides. Due to the proper control of tempering temperature and holding time, the impact toughness of the cast steel axle housing is greatly improved.

[0038] S4. Take normalizing, quenching and tempering as the cycle unit and carry out 2 cycles. In each cycle, the operation steps and process parameters of normalizing, quenching and tempering are kept consistent to ensure the uniformity of microstructure and the stability of organizational properties. The cast steel bridge shell after each cycle is observed under a microscope. Its microstructure is uniform, the grains are fine, and the organizational structure is stable, so that a cast steel bridge shell with high strength, toughness and fatigue resistance is obtained.

[0039] Comparative Example 1 A method for processing a cast steel bridge housing comprises the following steps: The initial material of the cast steel bridge housing is the same as that of Example 2. The initial material of the cast steel bridge housing is a high-silicon, low-carbon, low-alloy steel, and its chemical composition includes, by mass percentage: C: 0.2%, Si: 1.2%, Mn: 0.85%, Ni: 0.9%, Cr: 0.9%, Mo: 0.15%, rare earth element La: 0.03%, Nb: 0.02%, and the balance is Fe and unavoidable impurities, which total 100%. The following steps are included: S1. Normalizing treatment: Put the initial material of the cast steel bridge shell into a heating furnace, raise the temperature in the heating furnace to 900℃, maintain the normalizing temperature for 1.5 hours until the internal temperature of the initial material of the cast steel bridge shell is uniform, and then cool it to room temperature in the air to complete the normalizing process. During the normalizing process, the grains of the bridge shell are refined, the structure is uniform, the comprehensive mechanical properties of the material are improved, and the bridge shell after normalization is obtained.

[0040] S2. Quenching treatment: put the normalized rear axle housing into a heating furnace, raise the temperature in the heating furnace to 950°C, maintain the quenching temperature for 60 minutes until the internal temperature of the normalized rear axle housing is uniform and the austenite is completely transformed, and perform the first quenching treatment. During the quenching process, use water quenching coolant for rapid cooling. After quenching, the internal structure of the steel casting is mainly a mixed structure of fine martensite and bainite, and a quenched rear axle housing is obtained.

[0041] S3. Tempering treatment: put the quenched axle housing into a heating furnace, raise the temperature in the heating furnace to 650°C, keep it warm for 1 hour, and then air-cool it to room temperature. The purpose of tempering is to eliminate the residual stress generated during the quenching process and obtain the treated cast steel axle housing.

[0042] Comparative Example 2 A method for processing a cast steel bridge housing comprises the following steps: The initial material of the cast steel bridge housing is the same as that of Example 2. The initial material of the cast steel bridge housing is a high-silicon, low-carbon, low-alloy steel, and its chemical composition includes, by mass percentage: C: 0.2%, Si: 1.2%, Mn: 0.85%, Ni: 0.9%, Cr: 0.9%, Mo: 0.15%, rare earth element La: 0.03%, Nb: 0.02%, and the balance is Fe and unavoidable impurities, which total 100%. The following steps are included: S1. Normalizing treatment: Place the initial material of the cast steel bridge shell into a heating furnace, raise the temperature in the heating furnace to 900°C, maintain the normalizing temperature for 1.5 hours until the internal temperature of the initial material of the cast steel bridge shell is uniform, and then place it in the air to cool to room temperature to complete the normalizing process. During the normalizing process, the grains of the bridge shell are refined, the structure is uniform, the comprehensive mechanical properties of the material are improved, and the normalized bridge shell is obtained.

[0043] S2. Quenching treatment: put the normalized rear axle housing into a heating furnace, raise the temperature in the heating furnace to 950℃, maintain this temperature until the internal temperature of the normalized rear axle housing is uniform and the austenite is completely transformed, and then perform the first quenching treatment. During the quenching process, use water quenching coolant for rapid cooling. After quenching, the internal structure of the steel casting is mainly a mixture of fine martensite and bainite; then perform the second quenching treatment, heat the material to 920℃, keep it warm for 45 minutes, maintain a uniform temperature, and then use oil quenching coolant for cooling. The second quenching further refines the microstructure of the cast steel and further enhances the strength of the material to obtain a quenched rear axle housing.

[0044] S3. Tempering treatment: put the quenched axle housing into a heating furnace, raise the temperature in the heating furnace to 650°C, keep it warm for 1 hour, and then air-cool it to room temperature. The purpose of tempering is to eliminate the residual stress generated during the quenching process and obtain the treated cast steel axle housing.

[0045] Comparative Example 3 A method for processing a cast steel bridge housing comprises the following steps: The initial material of the cast steel bridge housing is the same as that of Example 2. The initial material of the cast steel bridge housing is a high-silicon, low-carbon, low-alloy steel, and its chemical composition includes, by mass percentage: C: 0.2%, Si: 1.2%, Mn: 0.85%, Ni: 0.9%, Cr: 0.9%, Mo: 0.15%, rare earth element La: 0.03%, Nb: 0.02%, and the balance is Fe and unavoidable impurities, which total 100%. The following steps are included: S1. Normalizing treatment: Place the initial material of the cast steel bridge shell into a heating furnace, raise the temperature in the heating furnace to 900°C, maintain the normalizing temperature for 1.5 hours until the internal temperature of the initial material of the cast steel bridge shell is uniform, and then place it in the air to cool to room temperature to complete the normalizing process. During the normalizing process, the grains of the bridge shell are refined, the structure is uniform, the comprehensive mechanical properties of the material are improved, and the normalized bridge shell is obtained.

[0046] S2. Quenching treatment: put the normalized rear axle housing into a heating furnace, raise the temperature in the heating furnace to 950°C, maintain the quenching temperature for 60 minutes until the internal temperature of the normalized rear axle housing is uniform and the austenite is completely transformed, and perform the first quenching treatment. During the quenching process, use water quenching coolant for rapid cooling. After quenching, the internal structure of the steel casting is mainly a mixed structure of fine martensite and bainite, and a quenched rear axle housing is obtained.

[0047] S3. Tempering treatment: put the quenched axle housing into a heating furnace, raise the temperature in the heating furnace to 650°C, keep it warm for 1 hour, and then air-cool it to room temperature. The purpose of tempering is to eliminate the residual stress generated during the quenching process and obtain a tempered axle housing.

[0048] S4. Take normalizing, quenching and tempering as the cycle unit and carry out 2 cycles. In each cycle, the operation steps and process parameters of normalizing, quenching and tempering are kept consistent to obtain a cast steel bridge shell with high strength, toughness and fatigue resistance.

[0049] The microstructure of the cast steel axle housings prepared in Examples 1 to 3 was observed, and the results are as follows: Figure 1 This is a diagram of the original austenite grain size of the cast steel bridge housing casting of the present invention without heat treatment. Figure 1 As shown, the original austenite grains are coarse and the grain size is 3.5 to 4.

[0050] The above treatment method of comparative example 1 is adopted, that is, the heat treatment process is only one normalizing + quenching + tempering heat treatment, the obtained structure is relatively coarse, the grain size is also level 3.5 to level 4, and the plastic mechanical properties are relatively low.

[0051] Figure 2 This is a microstructure diagram of the grain size of the cast steel bridge housing with high toughness and fatigue resistance in Example 1 of the present invention. Figure 2 As shown in the figure, after two cycles of heat treatment, the grain size is significantly reduced, and the grain size is 7.0 to 7.5.

[0052] Figure 3 This is the metallographic structure diagram of the cast steel bridge housing with high toughness and fatigue resistance in Example 1 of the present invention. Figure 3 In the figure, a is a metallographic structure diagram magnified by 1000, and b is a metallographic structure diagram magnified by 2000. Figure 3 As shown, by observing its organizational structure through a metallographic microscope, the microstructure of the cast steel bridge housing treated in Example 1 is uniform, the grains are fine, and it is a tempered troostite structure.

[0053] The mechanical properties of the cast steel bridge shells treated in Examples 1 to 3 and the cast steel bridge shells treated in Comparative Examples 1 to 3 were tested, and the results are shown in Table 1.

[0054] Table 1 Mechanical properties of cast steel bridge shells treated in Examples 1 to 3 and Comparative Examples 1 to 3

[0055] As shown in Table 1, the impact absorption energy of the cast steel bridge shells of Examples 1 to 3 of the present invention is 35J to 41J at -40°C, while the impact absorption energy of the cast steel bridge shell of Comparative Example 1 subjected to conventional heat treatment is 25J. Compared with the conventional heat treatment method of Comparative Example 1, the impact absorption energy of the present invention is increased by 40%, and the tensile strength is ≥950 MPa; the elongation is ≥20%; and the hardness is HBW 260-280. In the conventional heat treatment method, as in Comparative Example 2, one water quenching + one oil quenching are performed in the quenching treatment, which can improve the impact absorption energy, tensile strength, elongation and hardness, but the impact absorption energy, tensile strength, elongation and hardness are still not ideal. In the conventional heat treatment method, two cycle units are performed, such as Comparative Example 3, and its impact absorption energy decreases and the tensile strength increases. This is because the rapid cooling after water quenching forms high-hardness martensite, which leads to a decrease in impact absorption energy and an increase in tensile strength. However, there are high-density dislocations and residual stresses inside the martensite, which leads to an increase in brittleness and a decrease in impact toughness. In summary, the impact toughness, strength and fatigue resistance of the cast steel bridge shell can be significantly improved through the multiple cycle heat treatment process provided by the present invention, and the process is simple and easy to operate. The method has a wide range of application prospects, and is particularly suitable for heavy mining vehicles, construction machinery, transportation tools and other occasions that require materials to maintain long-term high performance under complex working conditions.

[0056] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0057] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for improving the impact toughness and fatigue resistance of a cast steel bridge housing, characterized in that: The following steps are involved: The initial material of the cast steel axle housing is normalized at 880°C to 930°C, and after the normalization treatment, it is cooled to room temperature to obtain a normalized axle housing; The normalized rear axle housing is subjected to a first quenching treatment at 880°C to 950°C, the first quenching is performed by water cooling, the normalized rear axle housing subjected to the first quenching is heated to 880°C to 950°C after the first quenching is completed, and then subjected to a second quenching treatment, the second quenching is performed by oil cooling, and after the second quenching treatment is completed, a quenched rear axle housing is obtained; The quenched axle housing is tempered at 250°C to 650°C, and after the tempering treatment is completed, it is cooled to room temperature to obtain a tempered axle housing; Normalizing, quenching and tempering are performed as a cycle unit for 2 to 3 cycles to obtain a cast steel bridge shell with high strength, toughness and fatigue resistance.

2. The method for improving the impact toughness and fatigue resistance of a cast steel bridge housing according to claim 1, characterized in that: The normalizing time is 1h to 2h, and the cooling method is air cooling.

3. The method for improving the impact toughness and fatigue resistance of a cast steel bridge housing according to claim 1, characterized in that: Before the first quenching and the second quenching, keep warm at 880℃~950℃ for 30min~60min.

4. The method for improving the impact toughness and fatigue resistance of a cast steel bridge housing according to claim 1, characterized in that: The holding time for tempering treatment is 1h to 2h, and the cooling method is air cooling or oil cooling.

5. The method for improving the impact toughness and fatigue resistance of a cast steel bridge housing according to claim 4, characterized in that: The holding temperature of the tempering treatment is 550℃~650℃.

6. The method for improving the impact toughness and fatigue resistance of a cast steel bridge housing according to claim 1, characterized in that: The chemical composition of the initial material of the cast steel bridge shell is calculated by mass percentage: C: 0.18%~0.25%, Si: 1.2%~1.5%, Mn: 0.75%~0.85%, Ni: 0.8%~1.2%, Cr: 0.8%~1.0%, Mo: 0.15%~0.3%, rare earth elements: 0.03%~0.07%, Nb: 0.02%~0.04%, the remainder is Fe and unavoidable impurities, totaling 100%.

7. The method for improving the impact toughness and fatigue resistance of a cast steel bridge housing according to claim 6, characterized in that: The rare earth element is La.

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