A treatment method for improving impact toughness and fatigue resistance of cast steel axle housings

Abstract

The application 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 cast steel bridge housing. The method comprises the following steps: subjecting the initial cast steel bridge housing to normalizing treatment at 880-930 DEG C, obtaining the normalized bridge housing after the normalizing treatment; subjecting the normalized bridge housing to quenching treatment at 880-950 DEG C, obtaining the quenched bridge housing after the quenching treatment; subjecting the quenched bridge housing to tempering treatment at 250-600 DEG C, obtaining the tempered bridge housing after the tempering treatment; taking the normalizing treatment, the quenching treatment and the tempering treatment as a cycle unit, and performing 2-3 cycles to obtain the cast steel bridge housing with high strength and toughness and fatigue resistance. The application optimizes the sequence and cycle unit number of the normalizing treatment, the quenching treatment and the tempering treatment, significantly refines the microstructure, reduces stress concentration, and improves the overall toughness and fatigue resistance, so as to solve the problem that the strength and toughness are difficult to be considered in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology for metallic materials, specifically relating to a treatment method for improving the impact toughness and fatigue resistance of cast steel bridge shells. Background Technology

[0002] As a key component for load bearing and force transmission in advanced heavy-duty mining trucks, cast steel axle housings, made from traditional C-grade cast steel, no longer meet the market's requirements for high strength, toughness, and lightweight construction in mining dump trucks. Mining dump trucks and other heavy-duty mining vehicles need components capable of withstanding extremely high impacts and complex loads, demanding cast steel axle housings with higher strength, toughness, and fatigue resistance to ensure long-term stability and reliability under high-stress environments.

[0003] Traditional cast steel materials, such as Grade C cast steel, while possessing a certain strength, exhibit low toughness and fatigue resistance when facing complex mechanical stresses, especially impact loads. To address this issue, current research primarily focuses on improving the overall performance of steel by altering alloy composition and optimizing heat treatment processes. However, traditional heat treatment processes often only increase strength while simultaneously reducing toughness and fatigue life. Therefore, developing high-strength, high-toughness cast steel materials that significantly improve impact toughness and fatigue resistance while maintaining high strength is crucial for enhancing the performance of cast steel bridge housings. Summary of the Invention

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

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

[0006] The purpose of this invention is to provide a method for improving the impact toughness and fatigue resistance of cast steel bridge shells, comprising the following steps:

[0007] S1. The initial material of cast steel bridge housing is normalized at 880℃~930℃. After the normalizing treatment is completed, it is cooled to room temperature to obtain the normalized bridge housing.

[0008] S2. The normalized rear axle housing is subjected to a first quenching treatment at 880℃~950℃. The first quenching is carried out by water cooling. After the first quenching, the normalized rear axle housing is heated to 880℃~950℃ and then subjected to a second quenching treatment by oil cooling. After the second quenching treatment, the quenched rear axle housing is obtained.

[0009] S3. Temper the quenched axle housing at 250℃~650℃, and then temper the axle housing after cooling to room temperature.

[0010] S4. Using normalizing, quenching and tempering as cyclic units, perform 2 to 3 cycles to obtain a cast steel bridge shell with high strength, toughness and fatigue resistance.

[0011] It should be noted that high-strength and high-toughness cast steel bridge housings, as crucial load-bearing components of advanced heavy-duty mining trucks, require materials with extremely high strength, toughness, and fatigue resistance to cope with complex working environments and heavy loads. Based on this, this invention designs a novel cyclic heat treatment process. This method optimizes the sequence of normalizing, quenching, and tempering, using normalizing, quenching, and tempering as cyclic units. By precisely controlling the temperatures of normalizing, quenching, and tempering, and performing multiple cycles, the microstructure is significantly refined, stress concentration is reduced, and the toughness and fatigue resistance of the cast steel bridge housing are greatly improved while maintaining high strength. This method is suitable for manufacturing cast steel bridge housings for heavy-duty mining trucks, solving the problem of balancing strength and toughness in existing technologies for cast steel bridge housings.

[0012] It should be noted that the present invention forms fine residual austenite, lath martensite and bainite structures through multiple quenching processes, thereby maximizing the strength of the material.

[0013] In some specific embodiments, the holding time for normalizing is 1 to 2 hours, and the cooling method is air cooling. It should be noted that the present invention uses normalizing treatment to refine the original grains and reduce segregation within the microstructure and the formation of coarse martensite and bainite.

[0014] In some specific embodiments, before the first and second quenching processes, the temperature is maintained at 880℃~950℃ for 30min~60min.

[0015] In some specific embodiments, the holding time for tempering is 1 to 2 hours, and the cooling method is air cooling or oil cooling. It should be noted that the present invention eliminates residual stress formed during quenching through the tempering process, thereby improving the toughness and fatigue life of the material.

[0016] In summary, this invention uses normalizing, quenching, and tempering as cyclic units. Through multiple cycles, normalizing and quenching significantly refine the grains, reduce the occurrence of coarse martensite, improve the microhardness distribution of the material, and effectively increase the overall strength. The cyclic tempering process fully releases the residual stress generated during quenching, which helps to improve the fatigue resistance and impact resistance of the cast steel bridge shell, thereby extending its service life. The resulting high-strength and tough cast steel has an impact absorption energy that is more than 30% higher than that of materials treated with traditional single quenching and tempering at room temperature and low temperature, enabling it to better cope with high impact and complex working conditions.

[0017] In some specific embodiments, the tempering temperature is 550°C to 650°C.

[0018] In some specific embodiments, the initial chemical composition of the cast steel bridge shell material, by mass percentage, includes:

[0019] 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%, with the balance being Fe and unavoidable impurities, totaling 100%. This invention is based on low-carbon, low-alloy cast steel with high silicon content. By introducing trace amounts of rare earth elements and trace amounts of alloying element Nb, and through a cyclic heat treatment process, the impact toughness and comprehensive mechanical properties of the material are significantly improved.

[0020] In some specific embodiments, the rare earth element is La.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) This invention provides a treatment method to improve the impact toughness and fatigue resistance of cast steel bridge shells. This method optimizes the order of normalizing, quenching and tempering treatments and designs a new type of cyclic heat treatment process. Normalizing, quenching and tempering treatments are used as cyclic units. The temperature of normalizing, quenching and tempering is precisely controlled and multiple cycles are performed. This significantly refines the microstructure and reduces stress concentration. At the same time, while maintaining high strength, the toughness and fatigue resistance of cast steel bridge shells are greatly improved. This method is suitable for the manufacture of cast steel bridge shells for heavy mining vehicles, so as to solve the problem that it is difficult to balance strength and toughness in the prior art.

[0023] (2) This invention uses normalizing, quenching and tempering as cyclic units. Through multiple cycles, normalizing and quenching significantly refine the grains, reduce the occurrence of coarse martensite, improve the microhardness distribution of the material, and effectively improve the overall strength. The cyclic tempering process fully releases the residual stress generated during quenching, 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 under room temperature and low temperature conditions is more than 30% higher than that of the material treated by traditional single quenching and tempering, enabling it to better cope with high impact and complex working conditions. Attached Figure Description

[0024] Figure 1 This is a diagram showing the original austenite grain size of the cast steel bridge housing of the present invention before heat treatment.

[0025] Figure 2 This is a grain size microstructure diagram of the cast steel bridge shell with high strength, toughness, and fatigue resistance in Embodiment 1 of the present invention.

[0026] Figure 3 This is a metallographic diagram of the high-strength, high-toughness, and fatigue-resistant cast steel bridge shell of Embodiment 1 of the present invention. Figure 3 In the diagram, 'a' is a metallographic structure diagram magnified 1000 times, and 'b' is a metallographic structure diagram magnified 2000 times. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] It should be noted that the technical terminology used in this invention is for the purpose of describing specific embodiments only and is not intended to limit the scope of protection of this invention. Certain terms are used in this invention to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This invention does not distinguish components based on differences in terminology, but rather on differences in their functions.

[0029] The following specific examples will provide further explanation.

[0030] Example 1

[0031] A method for improving the impact toughness and fatigue resistance of cast steel bridge housings, wherein the initial material used for the cast steel bridge housing is a high-silicon, low-carbon, low-alloy steel, whose 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%, with the balance being Fe and unavoidable impurities, totaling 100%. The method includes the following steps:

[0032] S1. Normalizing treatment: The initial material of the cast steel bridge shell is placed in a heating furnace and heated to 900°C. The normalizing temperature is maintained for 1.5 hours until the internal temperature of the initial material of the cast steel bridge shell is uniform. Then it is placed in the air to cool to room temperature to complete the normalizing process. During the normalizing process, the grains of the cast steel are refined and the structure is made uniform, which improves the comprehensive mechanical properties of the material and obtains the normalized bridge shell.

[0033] S2. Quenching Treatment: The normalized rear axle housing is placed in a heating furnace, and the furnace temperature is raised to 950℃. This quenching temperature is maintained for 60 minutes until the internal temperature of the normalized rear axle housing is uniform and the austenite is completely transformed. Then, the first quenching treatment is performed. During the quenching process, water quenching fluid is used for rapid cooling. After quenching, the internal structure of the cast steel part is mainly a mixture of fine martensite and bainite. Then, the second quenching treatment is performed. The normalized rear axle housing after the first quenching treatment is placed in a heating furnace, and the furnace temperature is raised to 920℃. This temperature is maintained for 45 minutes. After maintaining a uniform temperature, oil quenching fluid is used for cooling. The second quenching further refines the microstructure of the axle housing and further enhances its strength, resulting in the quenched rear axle housing.

[0034] S3. Tempering Treatment: After quenching, the axle housing is placed in a heating furnace and heated to 600℃ for 1 hour. It is then oil-cooled to room temperature. Tempering eliminates residual stress generated during quenching and optimizes 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 significantly improved.

[0035] S4. The process is repeated twice, with normalizing, quenching and tempering as the cycle units. In each cycle, the operation steps and process parameters of normalizing, quenching and tempering are kept consistent to ensure the uniformity of the microstructure and the stability of the microstructure properties. After each cycle, the cast steel bridge shell is observed under a microscope to have a uniform microstructure with fine grains and a stable microstructure, resulting in a cast steel bridge shell with high strength, toughness and fatigue resistance.

[0036] Example 2

[0037] A method for improving the impact toughness and fatigue resistance of cast steel bridge housings, wherein the initial material used for the cast steel bridge housing is a high-silicon, low-carbon, low-alloy steel, whose 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%, with the balance being Fe and unavoidable impurities, totaling 100%. The method includes the following steps:

[0038] S1. Normalizing treatment: The initial material of cast steel bridge shell is placed in a heating furnace and heated to 900°C. The normalizing temperature is maintained for 1.5 hours until the internal temperature of the initial material of cast steel bridge shell is uniform. Then it is placed in air to cool to room temperature to complete the normalizing process. During the normalizing process, the grains of the bridge shell are refined and the structure is uniform, which improves the comprehensive mechanical properties of the material and obtains the normalized bridge shell.

[0039] S2. Quenching Treatment: The normalized rear axle housing is placed in a heating furnace, and the furnace temperature is raised to 950℃. This temperature is maintained until the internal temperature of the normalized rear axle housing is uniform and the austenite is completely transformed. Then, the first quenching treatment is performed. During the quenching process, water quenching fluid is used for rapid cooling. After quenching, the internal structure of the cast steel part is mainly a mixture of fine martensite and bainite. Then, the second quenching treatment is performed. The normalized rear axle housing after the first quenching is placed in a heating furnace, and the furnace temperature is raised to 920℃ and held for 45 minutes. After maintaining a uniform temperature, oil quenching fluid is used for cooling. The second quenching further refines the microstructure of the cast steel and further enhances the strength of the material, resulting in the quenched rear axle housing.

[0040] S3. Tempering Treatment: After quenching, the axle housing is placed in a heating furnace, and the temperature inside the furnace is raised to 650℃ and held for 1 hour. It is then air-cooled to room temperature. The purpose of tempering is to eliminate residual stress generated during quenching and to optimize 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.

[0041] S4. The process is carried out twice, with normalizing, quenching and tempering as the cycle unit. 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 microstructure properties. After each cycle, the cast steel parts are observed under a microscope and their microstructure is uniform with fine grains and stable microstructure, resulting in a cast steel bridge shell with high strength, toughness and fatigue resistance.

[0042] Example 3

[0043] A method for improving the impact toughness and fatigue resistance of cast steel bridge housings, wherein the initial material used for the cast steel bridge housing is a high-silicon, low-carbon, low-alloy steel, whose 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%, with the balance being Fe and unavoidable impurities, totaling 100%. The method includes the following steps:

[0044] S1. Normalizing Treatment: The initial cast steel bridge shell material is placed in a heating furnace, and the furnace temperature is raised to 900℃. This normalizing temperature is maintained for 1.5 hours until the internal temperature of the initial cast steel bridge shell material is uniform. Subsequently, the bridge shell is placed in air to cool to room temperature, completing the normalizing process. During the normalizing process, the grains of the cast steel bridge shell are refined, the microstructure is made uniform, and the comprehensive mechanical properties of the cast steel bridge shell are improved, resulting in a normalized bridge shell.

[0045] S2. Quenching Treatment: After normalizing, the axle housing is placed in a heating furnace, and the furnace temperature is raised to 950℃. This quenching temperature is maintained for 60 minutes until the internal temperature of the normalized axle housing is uniform and the austenite is completely transformed. Then, the first quenching treatment is performed. During the quenching process, water quenching fluid is used for rapid cooling. After quenching, the internal structure of the axle housing is mainly a mixture of fine martensite and bainite. Then, the second quenching treatment is performed. The normalized axle housing after the first quenching treatment is placed in a heating furnace, and the furnace temperature is raised to 920℃. This uniform temperature is maintained for 45 minutes, and then oil quenching fluid is used for cooling. The second quenching further refines the microstructure of the axle housing and further enhances its strength, resulting in the quenched axle housing.

[0046] S3. Tempering Treatment: After quenching, the bridge housing is placed in a heating furnace and heated to 650℃ for 1 hour. It is then air-cooled to room temperature. Tempering eliminates residual stress generated during quenching and optimizes toughness by precipitating fine carbides. Due to the appropriate control of tempering temperature and holding time, the impact toughness of the cast steel bridge housing is significantly improved.

[0047] S4. The process is repeated twice, with normalizing, quenching and tempering as the cycle units. In each cycle, the operation steps and process parameters of normalizing, quenching and tempering are kept consistent to ensure the uniformity of the microstructure and the stability of the microstructure properties. After each cycle, the cast steel bridge shell is observed under a microscope to have a uniform microstructure with fine grains and a stable microstructure, resulting in a cast steel bridge shell with high strength, toughness and fatigue resistance.

[0048] Comparative Example 1

[0049] A method for processing cast steel bridge shells includes the following steps:

[0050] The initial material used for the cast steel bridge housing is the same as in Example 2. The initial material 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%, with the balance being Fe and unavoidable impurities, totaling 100%. The process includes the following steps:

[0051] S1. Normalizing Treatment: The initial cast steel bridge shell material is placed in a heating furnace, and the furnace temperature is raised to 900℃. This normalizing temperature is maintained for 1.5 hours until the internal temperature of the initial cast steel bridge shell material is uniform. Subsequently, it is cooled to room temperature in air to complete the normalizing process. During the normalizing process, the grains of the bridge shell are refined, the microstructure is made uniform, and the overall mechanical properties of the material are improved, resulting in a normalized bridge shell.

[0052] S2. Quenching treatment: The normalized rear axle housing is placed in a heating furnace, and the temperature inside the furnace is raised to 950℃. This quenching temperature is maintained for 60 minutes until the internal temperature of the normalized rear axle housing is uniform and the austenite is completely transformed. The first quenching treatment is then performed. During the quenching process, water quenching fluid is used for rapid cooling. After quenching, the internal structure of the cast steel part is mainly a mixture of fine martensite and bainite, resulting in the quenched rear axle housing.

[0053] S3. Tempering treatment: After quenching, the bridge housing is placed in a heating furnace and heated to 650°C. The temperature is held for 1 hour, and then air-cooled to room temperature. The purpose of tempering is to eliminate the residual stress generated during the quenching process and obtain the treated cast steel bridge housing.

[0054] Comparative Example 2

[0055] A method for processing cast steel bridge shells includes the following steps:

[0056] The initial material used for the cast steel bridge housing is the same as in Example 2. The initial material 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%, with the balance being Fe and unavoidable impurities, totaling 100%. The process includes the following steps:

[0057] S1. Normalizing treatment: The initial material of cast steel bridge shell is placed in a heating furnace and heated to 900°C. The normalizing temperature is maintained for 1.5 hours until the internal temperature of the initial material of cast steel bridge shell is uniform. Then it is placed in air to cool to room temperature to complete the normalizing process. During the normalizing process, the grains of the bridge shell are refined and the structure is uniform, which improves the comprehensive mechanical properties of the material and obtains the normalized bridge shell.

[0058] S2. Quenching Treatment: The normalized rear axle housing is placed in a heating furnace, and the furnace temperature is raised to 950℃. This temperature is maintained until the internal temperature of the normalized rear axle housing is uniform and the austenite is completely transformed. Then, the first quenching treatment is performed. During the quenching process, water quenching fluid is used for rapid cooling. After quenching, the internal structure of the cast steel part is mainly a mixture of fine martensite and bainite. Then, the second quenching treatment is performed. The material is heated to 920℃ and held for 45 minutes. After maintaining a uniform temperature, oil quenching fluid is used for cooling. The second quenching further refines the microstructure of the cast steel and further enhances the strength of the material, resulting in the quenched rear axle housing.

[0059] S3. Tempering treatment: After quenching, the bridge housing is placed in a heating furnace and heated to 650°C. The temperature is held for 1 hour, and then air-cooled to room temperature. The purpose of tempering is to eliminate the residual stress generated during the quenching process and obtain the treated cast steel bridge housing.

[0060] Comparative Example 3

[0061] A method for processing cast steel bridge shells includes the following steps:

[0062] The initial material used for the cast steel bridge housing is the same as in Example 2. The initial material 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%, with the balance being Fe and unavoidable impurities, totaling 100%. The process includes the following steps:

[0063] S1. Normalizing treatment: The initial material of cast steel bridge shell is placed in a heating furnace and heated to 900°C. The normalizing temperature is maintained for 1.5 hours until the internal temperature of the initial material of cast steel bridge shell is uniform. Then it is placed in air to cool to room temperature to complete the normalizing process. During the normalizing process, the grains of the bridge shell are refined and the structure is uniform, which improves the comprehensive mechanical properties of the material and obtains the normalized bridge shell.

[0064] S2. Quenching treatment: The normalized rear axle housing is placed in a heating furnace, and the temperature inside the furnace is raised to 950℃. This quenching temperature is maintained for 60 minutes until the internal temperature of the normalized rear axle housing is uniform and the austenite is completely transformed. The first quenching treatment is then performed. During the quenching process, water quenching fluid is used for rapid cooling. After quenching, the internal structure of the cast steel part is mainly a mixture of fine martensite and bainite, resulting in the quenched rear axle housing.

[0065] S3. Tempering treatment: After quenching, the axle housing is placed in a heating furnace and heated to 650°C. The temperature is held for 1 hour, and then air-cooled to room temperature. The purpose of tempering is to eliminate the residual stress generated during the quenching process and obtain the tempered axle housing.

[0066] S4. Using normalizing, quenching and tempering as cyclic units, perform 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.

[0067] The microstructure of the cast steel bridge shells prepared in Examples 1 to 3 was observed, and the results are as follows:

[0068] Figure 1 This is a diagram showing the original austenite grain size of the cast steel bridge housing of this invention before heat treatment. Figure 1 As shown, the original austenite grains are coarse, with a grain size of 3.5 to 4.

[0069] Using the treatment method described in Comparative Example 1, i.e., the heat treatment process involves only one normalizing + quenching + tempering heat treatment, the resulting microstructure is relatively coarse, with a grain size of 3.5 to 4, and low plastic mechanical properties.

[0070] Figure 2 This is a grain size microstructure diagram of the cast steel bridge shell with high strength, toughness, and fatigue resistance in Embodiment 1 of the present invention. Figure 2 As shown, after two cycles of heat treatment, the grain size is significantly reduced, with a grain size of 7.0 to 7.5 grade.

[0071] Figure 3 This is a metallographic diagram of the high-strength, high-toughness, and fatigue-resistant cast steel bridge shell of Embodiment 1 of the present invention. Figure 3 In the diagram, 'a' is a metallographic image magnified 1000 times, and 'b' is a metallographic image magnified 2000 times. For example... Figure 3 As shown, the microstructure of the cast steel bridge shell treated in Example 1 was observed under a metallographic microscope. The microstructure was uniform with fine grains and was a tempered sorbite structure.

[0072] 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.

[0073] Table 1. Mechanical properties of cast steel bridge shells treated in Examples 1-3 and Comparative Examples 1-3

[0074]

[0075] As shown in Table 1, the impact absorption energy of the cast steel bridge shells in Examples 1 to 3 of the present invention is 35J to 41J at -40℃, while the impact absorption energy of the cast steel bridge shell in Comparative Example 1, which is treated with conventional heat treatment, is 25J. The impact absorption energy of the present invention is increased by 40% compared with the conventional heat treatment method in Comparative Example 1. The tensile strength is ≥950 MPa; the elongation is ≥20%; and the hardness is HBW 260-280. In conventional heat treatment methods, such as Comparative Example 2, which involves one water quenching and one oil quenching during the quenching process, the impact absorption energy, tensile strength, elongation, and hardness can be improved. However, the impact absorption energy, tensile strength, elongation, and hardness are still not ideal. In contrast, in conventional heat treatment methods, such as Comparative Example 3, which involves two cyclic units, the impact absorption energy decreases while the tensile strength increases. This is because 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, the presence of high-density dislocations and residual stress inside the martensite leads to increased brittleness and a decrease in impact toughness. In summary, the multi-cycle heat treatment process provided by this invention can significantly improve the impact toughness, strength, and fatigue resistance of cast steel bridge housings, and the process is simple and easy to operate. This method has broad application prospects, and is particularly suitable for applications such as heavy-duty mining trucks, construction machinery, and transportation vehicles where materials must maintain long-term high performance under complex working conditions.

[0076] It should be noted that when numerical ranges are involved in this invention, it should be understood that both 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 in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0077] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for improving the impact toughness and fatigue resistance of cast steel bridge shells, characterized in that, Includes the following steps: The initial material of cast steel bridge housing was normalized at 880℃~930℃ for 1h~2h. After the normalizing treatment, it was cooled to room temperature to obtain the normalized bridge housing. The cooling method was air cooling. The normalized rear axle housing is held at 880℃~950℃ for 30min~60min and then subjected to a first quenching treatment at 880℃~950℃ using water cooling. After the first quenching, the normalized rear axle housing is heated to 880℃~950℃ and held for 30min~60min, and then subjected to a second quenching treatment using oil cooling. After the second quenching treatment, the quenched rear axle housing is obtained. The quenched axle housing is tempered at 550℃~650℃ for 1h~2h. After the tempering treatment is completed, it is cooled to room temperature to obtain the tempered axle housing. The cooling method is air cooling or oil cooling. By using normalizing, quenching and tempering as cyclic units, and performing two cycles, a cast steel bridge shell with high strength, toughness and fatigue resistance is obtained.

2. The method for improving the impact toughness and fatigue resistance of cast steel bridge shells according to claim 1, characterized in that, The initial chemical composition of the cast steel bridge shell material, by mass percentage, includes: 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%, with the balance being Fe and unavoidable impurities, totaling 100%.

3. The method for improving the impact toughness and fatigue resistance of cast steel bridge shells according to claim 2, characterized in that, The rare earth element is La.

Images