Heat treatment process for wear-resistant accessory for multi-stage surface modification oversized digging bucket

Abstract

The invention discloses a heat treatment process for a wear-resistant accessory for a multi-stage surface modification oversized digging bucket. The heat treatment process comprises the steps of multi-stage gradient normalizing treatment, primary quenching, austenitizing treatment, multi-stage quenching and tempering treatment, optional subzero treatment and high-energy shot blasting. The material comprises the following components in percentage by weight: 0.20%-0.50% of C, 0.10%-0.50% of Si, 0.50%-1.50% of Mn, 0.80%-2.00% of Cr, 0.50%-1.50% of Ni, 0.10%-0.50% of Mo, less than or equal to 0.030% of S, less than or equal to 0.030% of P and the balance of Fe and inevitable impurities. Fine-grain martensite is formed on the surface layer through gradient heat treatment, the grain size is larger than or equal to 8 grades, a martensite / bainite mixed structure is obtained in a transition area, and 5-15% of retained austenite is reserved in the core. The final product has the surface high hardness of 58-63 HRC, the core toughness of 45-50 HRC and the excellent low-temperature impact property that Akv is larger than or equal to 25 J at the temperature of-40 DEG C, and is particularly suitable for mining machinery wear-resisting parts under the extreme working condition.

Description

Technical Field

[0001] This invention relates to materials for wear-resistant parts of engineering machinery, and more particularly to a heat treatment process for wear-resistant parts of ultra-large excavator buckets with multi-stage surface modification. Background Technology

[0002] As large-scale mining operations become deeper and more extensive, wear-resistant components for construction machinery face increasingly demanding service environments. As core load-bearing components, the wear-resistant parts of extra-large excavator buckets must operate for extended periods under extreme conditions such as -40°C low-temperature impact, high-stress abrasive wear, and frequent impact loads. While traditional heat treatment processes can achieve high surface hardness through single quenching, insufficient hardenability often results in a sharp drop in core hardness below 35 HRC, and the low-temperature impact energy is generally below 15 J, easily leading to hardened layer peeling or overall brittle fracture.

[0003] In existing technologies, conventional gradient heat treatment attempts to balance strength and toughness through staged temperature control, but it still has significant limitations in practical applications: the thickness of the fine-grained martensite layer on the surface is insufficient, and the grain size is difficult to stably reach level 8 or above; while deep strengthening processes are prone to forming brittle carbide bands in the transition zone, leading to a decrease in interfacial bonding strength. In terms of material systems, although mainstream high-carbon high-chromium alloys have excellent wear resistance, they also have high hardness and high brittleness, making welding repair difficult, and their low-temperature impact toughness is difficult to exceed 20J; although material designs with reduced carbon content can improve toughness, the lack of supporting heat treatment processes results in insufficient surface hardness and significantly deteriorated wear resistance.

[0004] Patent CN111500830B proposes an optimized solution for the tempering process of carburized parts. It precisely controls the tempering temperature and time using the mathematical formula T×logt=A, aiming to form a microstructure dominated by low-carbon tempered martensite (volume fraction ≥90%) and retained austenite (2-10%), while suppressing the formation of the brittle Fe3C phase. This solves the problems of excessively high-carbon martensite content, poor strength and plasticity, and low contact fatigue performance caused by traditional processes. The patent has significant advantages: First, it achieves optimized strength-plasticity matching, maintaining a surface hardness of 650-750HV1.0, improving wear resistance and increasing plasticity by 5-30%, while avoiding temper brittleness and improving contact fatigue life; second, it improves process efficiency, shortening furnace time by more than 20%, reducing energy consumption, and making it suitable for large-scale production; third, it has wide applicability, suitable for various carburized steels, especially heavy-duty parts. However, this patent also has some drawbacks and challenges: the process is highly complex, requiring strict adherence to parameter relationships, and demanding high precision in equipment temperature control and skilled operation; the A value varies significantly across different temperature ranges, which may increase the difficulty of parameter optimization; if the residual austenite content is too high, additional cryogenic treatment is required, increasing the number of processes and costs; in addition, the testing threshold is high, requiring equipment such as transmission electron microscopy to verify substructure carbides, and its applicability is mainly limited to carburized parts.

[0005] Patent CN116121493B proposes a heat treatment method for high-strength, tough, lightweight, and wear-resistant high-manganese steel castings, applicable to Fe-Mn-Al-C or Fe-Mn-C series high-manganese steels. The method comprises five steps: pretreatment, water quenching, cryogenic treatment, aging treatment, and shot peening. This method prevents high-temperature decarburization and oxidation by coating the surface with an Al2O3-SiO2-Na2O-based anti-oxidation coating. Water quenching is then performed at a rate of ≥100℃ / h to 1040-1200℃ to form a single austenitic structure. Subsequently, cryogenic treatment at -130℃ to -196℃ for 1-48 hours induces the dispersion and precipitation of nano-sized carbides. Aging treatment at 450-650℃ further refines the microstructure. Finally, shot peening strengthens the surface, improving hardness and wear resistance. The advantages of this patent lie in significantly improving the overall performance of the material, such as reducing density, increasing tensile strength and elongation, while simplifying the process, being environmentally friendly, and improving surface quality. However, this method also has drawbacks such as high cost, strict process control, potential limitations, and the possibility of sacrificing some plasticity. Overall, this patent significantly improves the comprehensive performance of high-manganese steel through innovative process combinations, but a trade-off between cost and process complexity is necessary, making it suitable for industrial scenarios with high requirements for wear resistance and lightweighting. Summary of the Invention

[0006] This invention aims to solve the problems of insufficient surface hardness, poor core toughness, and low-temperature brittleness in wear-resistant parts of ultra-large excavator buckets under extreme working conditions through a multi-stage gradient heat treatment process and specific material composition design. Specifically, this is achieved through the following means:

[0007] A multi-stage surface-modified heat treatment process for wear-resistant parts of ultra-large excavator buckets includes the following steps:

[0008] Step 1: Multi-stage gradient normalizing treatment

[0009] The wear-resistant parts of the extra-large excavator bucket are heated to a high austenitizing temperature and subjected to multi-stage gradient normalizing treatment.

[0010] Step 2: First quenching treatment

[0011] The normalized extra-large excavator bucket is quenched to room temperature using wear-resistant parts.

[0012] Step 3: Austenitizing treatment

[0013] The wear-resistant parts of the extra-large excavator bucket are heated to a lower austenitizing temperature for austenitizing treatment.

[0014] Step 4: Multi-stage quenching treatment

[0015] The austenitized super-large excavating bucket is quenched to room temperature using wear-resistant parts.

[0016] Step 5: Tempering

[0017] The super-large excavating bucket, after undergoing multi-stage quenching treatment, is then tempered using wear-resistant parts.

[0018] Further steps include the following:

[0019] Step 1: Multi-stage gradient normalizing treatment;

[0020] The wear-resistant parts of the extra-large excavator bucket are heated to a high austenitizing temperature. The multi-stage gradient normalizing treatment includes the following steps: the first stage is held at 650-720℃ for 1.0-2.0h, the second stage is held at 780-820℃ for 0.5-1.0h, and the third stage is held at 900-950℃ for 15-30min.

[0021] Step 2: First quenching treatment

[0022] The super-large excavator bucket after normalizing is quenched to room temperature using wear-resistant parts, with a quenching temperature of 850-880℃.

[0023] Step 3: Austenitizing treatment

[0024] The extra-large excavator bucket is heated to a relatively low austenitizing temperature using wear-resistant parts, and then subjected to austenitizing treatment. The austenitizing treatment temperature is 920-980℃.

[0025] Step 4: Multi-stage quenching treatment

[0026] The austenitized super-large excavating bucket is quenched to room temperature using wear-resistant parts. The workpiece is then immersed in the quenching medium for 15-30 seconds and then removed. It is left in the air for 5-15 seconds. The immersion-removal process is repeated twice.

[0027] Step 5: Tempering

[0028] The super-large excavating bucket after multi-stage quenching is tempered with wear-resistant parts at a temperature of 200-300℃.

[0029] Furthermore, by mass percentage, the wear-resistant component comprises: C 0.20%–0.50%, Si 0.10%–0.50%, Mn 0.50%–1.50%, Cr 0.80%–2.00%, Ni 0.50%–1.50%, Mo 0.10%–0.50%, S ≤0.030%, P ≤0.030%, with the balance being Fe and unavoidable impurities.

[0030] Furthermore, by mass percentage, C 0.25%–0.40%, Si 0.15%–0.30%, Mn 0.80%–1.20%, Cr 1.00%–1.80%, Ni 0.80%–1.20%, Mo 0.15%–0.35%, S≤0.025%, P≤0.025%, with the balance being Fe and unavoidable impurities.

[0031] Furthermore, in terms of mass percentage, P ≤ 0.01%, S ≤ 0.01%.

[0032] Furthermore, the heating rate of the multi-stage gradient normalizing treatment is as follows: in the first stage, the temperature is increased to 650-720℃ at 80-100℃ / h; in the second stage, the temperature is increased to 780-820℃ at 50-70℃ / h; and in the third stage, the temperature is increased to 900-950℃ at 30-50℃ / h.

[0033] Furthermore, in the multi-stage quenching treatment, the quenching medium temperature is 20-30℃ during the first immersion, and the workpiece surface temperature rises to 400-450℃ after the first removal, and the quenching medium temperature is controlled at 40-50℃ during the second immersion.

[0034] Furthermore, after the multi-stage quenching treatment, a deep cryogenic treatment is added, which is maintained at -80℃ to -120℃ for 2.0-4.0 hours.

[0035] Furthermore, after the tempering treatment, high-energy shot peening is performed with a shot diameter of 0.2-0.5 mm and an impact pressure of 0.4-0.6 MPa.

[0036] Furthermore, the wear-resistant component has a fine-grained martensite layer with a thickness of 2-5 mm and a grain size grade of ≥8 on its surface; the transition zone is a mixed structure of lath martensite and lower bainite; and the core is a tempered martensite matrix containing 5-15% retained austenite.

[0037] Furthermore, the surface hardness of the wear-resistant parts reaches 58-63 HRC, the core hardness remains at 45-50 HRC, and the impact energy at -40℃ is ≥25J.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] 1. Through gradient normalizing and multi-stage quenching, a fine-grained martensite layer is formed on the surface, with a grain size ≥ 8 and a hardness of 58-63 HRC, exhibiting significantly better wear resistance than traditional processes. High core toughness: The core retains 5-15% residual austenite, maintaining a hardness of 45-50 HRC. Combined with a lath martensite / bainite transition layer, a gradient match between a "hard surface" and a "tough core" is achieved, preventing overall brittle fracture.

[0040] 2. Through composition design and residual austenite control, the impact energy at -40℃ is ≥25J, which is significantly improved compared with traditional processes, meeting the requirements of extreme low-temperature working conditions in deep mines.

[0041] 3. Optional cryogenic treatment and high-energy shot peening further enhance surface hardness, fatigue life, and resistance to stress corrosion. Gradient normalizing with staged temperature control, combined with segmented quenching, shortens the process cycle by more than 20%, reduces energy consumption, and is suitable for large-scale production. Attached Figure Description

[0042] Figure 1 A process flow diagram of the preparation method of the present invention is shown;

[0043] Figure 2 A photograph of the wear-resistant component structure of Example 1 is shown. Detailed Implementation

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should be noted that those skilled in the art can make various changes and modifications without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0045] This invention provides a multi-stage surface-modified heat treatment process for wear-resistant parts of ultra-large excavator buckets, which are mainly used in ultra-large excavator buckets for large-scale deep mining engineering machinery.

[0046] Example 1

[0047] The alloy material used for the wear-resistant parts has the following composition: C 0.30%, Si 0.20%, Mn 1.00%, Cr 1.50%, Ni 1.00%, Mo 0.25%, S≤0.020%, P≤0.015%, with the balance being Fe and impurities.

[0048] The method for preparing the wear-resistant parts first involves a multi-stage gradient normalizing treatment. The first stage involves heating to 700℃ at a rate of 90℃ / h and holding for 1.5 hours; the second stage involves heating to 800℃ at a rate of 60℃ / h and holding for 0.8 hours; and the third stage involves heating to 930℃ at a rate of 40℃ / h and holding for 20 minutes. Following this, a quenching treatment is performed, where the normalized workpiece is quenched at 870℃ using oil cooling to room temperature. Next, austenitizing treatment is carried out, involving heating to 950℃ and holding for 30 minutes. The workpiece was then air-cooled to room temperature. A multi-stage quenching process was then performed: first, the workpiece was immersed in a 20% PAG aqueous solution at 25°C for 25 seconds, then removed and held in air for 10 seconds, followed by a second immersion at 45°C for 20 seconds, then air-cooled to room temperature. The workpiece was then placed in a -100°C cryogenic chamber for 3 hours for cryogenic treatment. Afterward, it underwent tempering at 250°C for 2 hours and was cooled by water. Finally, high-energy shot peening was applied. The resulting wear-resistant part had a surface hardness of 59 HRC, a core hardness of 46 HRC, and an impact energy of 27 J at -40°C.

[0049] Example 2

[0050] The alloy material composition for wear-resistant parts is: C 0.28%, Si 0.18%, Mn 0.90%, Cr 1.30%, Ni 0.90%, Mo 0.20%, S≤0.018%, P≤0.012%, with the balance being Fe and impurities.

[0051] The method for preparing the wear-resistant parts first involves a multi-stage gradient normalizing treatment. The first stage involves heating to 720℃ at a rate of 100℃ / h and holding for 1.0 hour. The second stage involves heating to 820℃ at a rate of 50℃ / h and holding for 0.5 hours. The third stage involves heating to 950℃ at a rate of 30℃ / h and holding for 30 minutes. Following this, a quenching treatment is performed, where the normalized workpiece is quenched at 860℃ using oil cooling to room temperature. Next, austenitizing treatment is carried out, involving heating to 980℃ and holding for 30 minutes. After initial immersion in a 30°C 20% PAG aqueous solution quenching medium for 30 seconds, the workpiece was removed, left to stand in air for 5 seconds, and then subjected to a second immersion in a 50°C quenching medium for 20 seconds before air cooling to room temperature. The workpiece was then placed in a -120°C cryogenic chamber for 4 hours for cryogenic treatment. Following this, it underwent tempering at 280°C for 2 hours and was cooled by water. Finally, high-energy shot peening was applied. The resulting wear-resistant parts had a surface hardness of 60 HRC, a core hardness of 48 HRC, and an impact energy of 29 J at -40°C.

[0052] Example 3

[0053] The alloy material composition for wear-resistant parts is: C 0.35%, Si 0.25%, Mn 1.20%, Cr 1.80%, Ni 1.20%, Mo 0.35%, S≤0.025%, P≤0.025%, with the balance being Fe and impurities.

[0054] The method for preparing the wear-resistant parts first involves a multi-stage gradient normalizing treatment. The first stage involves heating to 650℃ at a rate of 80℃ / h and holding for 2.0 hours. The second stage involves heating to 780℃ at a rate of 70℃ / h and holding for 1.0 hour. The third stage involves heating to 900℃ at a rate of 50℃ / h and holding for 15 minutes. Following this, a quenching treatment is performed, where the normalized workpiece is quenched at 880℃ using oil cooling to room temperature. Next, austenitizing treatment is carried out, involving heating to 920℃ and holding for 30 minutes. After immersion in a 20% PAG aqueous solution at 20°C for 15 seconds, the workpiece is air-cooled to room temperature. Then, a multi-stage quenching process is performed. The workpiece is first immersed in a 20% PAG aqueous solution at 20°C for 15 seconds, then removed and left to stand in air for 15 seconds. A second immersion is then performed, this time with the quenching medium temperature raised to 40°C, for 20 seconds, followed by air cooling to room temperature. The workpiece is then placed in a -80°C cryogenic chamber for 2 hours for cryogenic treatment. Afterward, it undergoes tempering at 200°C for 2 hours and is cooled by water. Finally, high-energy shot peening is applied. The resulting wear-resistant part has a surface hardness of 58 HRC, a core hardness of 45 HRC, and an impact energy of 30 J at -40°C.

[0055] Example 4

[0056] The alloy material composition for wear-resistant parts is: C 0.30%, Si 0.20%, Mn 1.00%, Cr 1.50%, Ni 1.00%, Mo 0.25%, S≤0.010%, P≤0.010%, with the balance being Fe and impurities.

[0057] The method for preparing the wear-resistant parts first involves a multi-stage gradient normalizing treatment. The first stage involves heating to 700℃ at a rate of 90℃ / h and holding for 1.5 hours; the second stage involves heating to 800℃ at a rate of 60℃ / h and holding for 0.8 hours; and the third stage involves heating to 910℃ at a rate of 40℃ / h and holding for 25 minutes. Following this, a quenching treatment is performed, where the normalized workpiece is quenched at 870℃ using oil cooling to room temperature. Next, austenitizing treatment is carried out, involving heating to 950℃ and holding for 30 minutes. After initial immersion in a 20% PAG aqueous solution at 28°C for 20 seconds, the workpiece was air-cooled to room temperature. A multi-stage quenching process was then performed: first, the workpiece was immersed in the quenching medium at 28°C for 20 seconds, then removed and held in air for 12 seconds before a second immersion at 42°C for 20 seconds, followed by air cooling to room temperature. The workpiece was then placed in a -80°C cryogenic chamber for 2 hours for cryogenic treatment. Afterward, it underwent tempering at 230°C for 2 hours and was cooled by water. Finally, high-energy shot peening was applied. The resulting wear-resistant parts had a surface hardness of 62 HRC, a core hardness of 49 HRC, and an impact energy of 26 J at -40°C.

[0058] Example 5

[0059] The alloy material composition for wear-resistant parts is: C 0.30%, Si 0.20%, Mn 1.00%, Cr 1.50%, Ni 1.00%, Mo 0.25%, S≤0.020%, P≤0.015%, with the balance being Fe and impurities.

[0060] The method for preparing the wear-resistant parts first involves a multi-stage gradient normalizing treatment. The first stage involves heating to 700℃ at a rate of 90℃ / h and holding for 1.5 hours. The second stage involves heating to 800℃ at a rate of 60℃ / h and holding for 0.8 hours. The third stage involves heating to 930℃ at a rate of 40℃ / h and holding for 20 minutes. Following this, a quenching treatment is performed, where the normalized workpiece is quenched at 870℃ using oil cooling to room temperature. Next, austenitizing treatment is carried out, involving heating to 960℃ and holding for 30 minutes. The workpiece was then air-cooled to room temperature. A multi-stage quenching process was then performed: first, the workpiece was immersed in a 20% PAG aqueous solution at 25°C for 30 seconds, then removed and held in air for 10 seconds, followed by a second immersion at 50°C for 20 seconds, then air-cooled to room temperature. The workpiece was then placed in a -100°C cryogenic chamber for 3 hours for cryogenic treatment. Afterward, it underwent tempering at 260°C for 2 hours and was cooled by water. Finally, high-energy shot peening was applied. The resulting wear-resistant part had a surface hardness of 61 HRC, a core hardness of 47 HRC, and an impact energy of 28 J at -40°C.

[0061] Example 6

[0062] The alloy material composition for wear-resistant parts is: C 0.30%, Si 0.20%, Mn 1.00%, Cr 1.50%, Ni 1.00%, Mo 0.25%, S≤0.020%, P≤0.015%, with the balance being Fe and impurities.

[0063] The method for preparing the wear-resistant parts first involves a multi-stage gradient normalizing treatment. The first stage involves heating to 700℃ at a rate of 90℃ / h and holding for 1.5 hours; the second stage involves heating to 790℃ at a rate of 60℃ / h and holding for 0.7 hours; and the third stage involves heating to 930℃ at a rate of 40℃ / h and holding for 20 minutes. Following this, a quenching treatment is performed, where the normalized workpiece is quenched at 870℃ using oil cooling to room temperature. Then, before austenitizing treatment, a magnetic field of 1.5T is applied for 60 minutes, followed by heating to... After holding at 950℃ for 30 minutes, the parts were air-cooled to room temperature. A multi-stage quenching process was then performed: first, the parts were immersed in a 20% PAG aqueous solution at 25℃ for 25 seconds, then removed and held in air for 10 seconds, followed by a second immersion at 45℃ for 20 seconds, and then air-cooled to room temperature. The workpiece was then placed in a -110℃ cryogenic chamber for 3.5 hours for cryogenic treatment. Next, it underwent tempering at 250℃ for 2.0 hours and was cooled by water. Finally, high-energy shot peening was applied. The resulting wear-resistant parts had a surface hardness of 63 HRC, a core hardness of 50 HRC, and an impact energy of 25 J at -40℃.

[0064] Example 7

[0065] The alloy material composition for wear-resistant parts is: C 0.30%, Si 0.20%, Mn 1.00%, Cr 1.50%, Ni 1.00%, Mo 0.25%, S≤0.020%, P≤0.015%, with the balance being Fe and impurities.

[0066] The method for preparing the wear-resistant parts first involves a multi-stage gradient normalizing treatment. The first stage involves heating to 680℃ at a rate of 90℃ / h and holding for 1.8 hours. The second stage involves heating to 800℃ at a rate of 60℃ / h and holding for 0.8 hours. The third stage involves heating to 930℃ at a rate of 40℃ / h and holding for 20 minutes. Following this, a quenching treatment is performed, where the normalized workpiece is quenched at 855℃ using oil cooling to room temperature. Then, before austenitizing treatment, a magnetic field of 0.5T is applied for 30 minutes, followed by heating to... After holding at 950℃ for 30 minutes, the parts were air-cooled to room temperature. A multi-stage quenching process was then performed: first, the parts were immersed in a 20% PAG aqueous solution at 25℃ for 25 seconds, then removed and held in air for 10 seconds, followed by a second immersion at 45℃ for 20 seconds, and then air-cooled to room temperature. The workpiece was then placed in a -120℃ cryogenic chamber for 4 hours for cryogenic treatment. Afterward, it underwent tempering at 270℃ for 2 hours and was cooled by water. Finally, high-energy shot peening was applied. The resulting wear-resistant parts had a surface hardness of 59 HRC, a core hardness of 48 HRC, and an impact energy of 31 J at -40℃.

[0067] Example 8

[0068] The alloy material composition for wear-resistant parts is: C 0.30%, Si 0.20%, Mn 1.00%, Cr 1.50%, Ni 1.00%, Mo 0.25%, S≤0.020%, P≤0.015%, with the balance being Fe and impurities.

[0069] The method for preparing the wear-resistant parts first involves a multi-stage gradient normalizing treatment. The first stage involves heating to 700℃ at a rate of 90℃ / h and holding for 1.5 hours. The second stage involves heating to 800℃ at a rate of 60℃ / h and holding for 0.8 hours. The third stage involves heating to 930℃ at a rate of 40℃ / h and holding for 20 minutes. Following this, a quenching treatment is performed, where the normalized workpiece is quenched at 870℃ using oil cooling to room temperature. Next, austenitizing treatment is carried out, involving heating to 940℃ and holding for 30 minutes. After immersion in a 20% PAG aqueous solution at 22°C for 18 seconds, the workpiece is air-cooled to room temperature. Then, a multi-stage quenching process is performed. The workpiece is first immersed in a 20% PAG aqueous solution at 22°C for 18 seconds, then removed and held in air for 8 seconds before a second immersion. This time, the quenching medium temperature rises to 48°C, and the workpiece is immersed for 20 seconds before air-cooling to room temperature. The workpiece is then placed in a -100°C cryogenic chamber for 3 hours for cryogenic treatment. Afterward, it undergoes tempering at 300°C for 2.5 hours and is cooled by water. Finally, high-energy shot peening is applied. The resulting wear-resistant part has a surface hardness of 60 HRC, a core hardness of 46 HRC, and an impact energy of 32 J at -40°C.

[0070] Example 9

[0071] The alloy material composition for wear-resistant parts is: C 0.30%, Si 0.20%, Mn 1.00%, Cr 1.50%, Ni 1.00%, Mo 0.25%, S≤0.020%, P≤0.015%, with the balance being Fe and impurities.

[0072] The method for preparing the wear-resistant parts first involves a multi-stage gradient normalizing treatment. The first stage involves heating to 700℃ at a rate of 90℃ / h and holding for 1.5 hours. The second stage involves heating to 800℃ at a rate of 60℃ / h and holding for 0.8 hours. The third stage involves heating to 940℃ at a rate of 40℃ / h and holding for 22 minutes. Following this, a quenching treatment is performed, where the normalized workpiece is quenched at 870℃ using oil cooling to room temperature. Next, austenitizing treatment is carried out, involving heating to 970℃ and holding for 30 minutes. After immersion in a 20% PAG aqueous solution at 25°C for 25 seconds, the workpiece is air-cooled to room temperature. Then, a multi-stage quenching process is performed. The workpiece is first immersed in this quenching medium at 25°C for 25 seconds, then removed and left to stand in air for 10 seconds. A second immersion is then performed, this time with the quenching medium temperature raised to 45°C, for 20 seconds, followed by air cooling to room temperature. The workpiece is then placed in a -90°C cryogenic chamber for 2.5 hours for cryogenic treatment. Afterward, it undergoes tempering at 250°C for 2.0 hours and is cooled by water. Finally, high-energy shot peening is applied. The resulting wear-resistant part has a surface hardness of 61 HRC, a core hardness of 49 HRC, and an impact energy of 27 J at -40°C.

[0073] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A multi-stage surface-modified heat treatment process for wear-resistant parts of ultra-large excavator buckets, characterized in that, Includes the following steps: Step 1: Multi-stage gradient normalizing treatment The wear-resistant parts of the extra-large excavator bucket are heated to a high austenitizing temperature and subjected to multi-stage gradient normalizing treatment. Step 2: First quenching treatment The normalized extra-large excavator bucket is quenched to room temperature using wear-resistant parts. Step 3: Austenitizing treatment The wear-resistant parts of the extra-large excavator bucket are heated to a lower austenitizing temperature for austenitizing treatment. Step 4: Multi-stage quenching treatment The austenitized super-large excavating bucket is quenched to room temperature using wear-resistant parts. Step 5: Tempering The super-large excavating bucket, after undergoing multi-stage quenching treatment, is then tempered using wear-resistant parts.

2. The heat treatment process for multi-stage surface-modified wear-resistant parts for ultra-large excavator buckets according to claim 1, characterized in that, Includes the following steps: Step 1: Multi-stage gradient normalizing treatment; The wear-resistant parts of the extra-large excavator bucket are heated to a high austenitizing temperature. The multi-stage gradient normalizing treatment includes the following steps: the first stage is held at 650-720℃ for 1.0-2.0h, the second stage is held at 780-820℃ for 0.5-1.0h, and the third stage is held at 900-950℃ for 15-30min. Step 2: First quenching treatment The super-large excavator bucket after normalizing is quenched to room temperature using wear-resistant parts, with a quenching temperature of 850-880℃. Step 3: Austenitizing treatment The wear-resistant parts of the extra-large excavator bucket are heated to a relatively low austenitizing temperature for austenitizing treatment. The austenitizing treatment temperature is 920-980℃. Step 4: Multi-stage quenching treatment The austenitized super-large excavating bucket is quenched to room temperature using wear-resistant parts. The workpiece is then immersed in the quenching medium for 15-30 seconds and then removed. It is left in the air for 5-15 seconds. The immersion-removal process is repeated twice. Step 5: Tempering The super-large excavating bucket after multi-stage quenching is tempered with wear-resistant parts at a temperature of 200-300℃.

3. The wear-resistant parts for ultra-large excavator buckets prepared by the heat treatment process according to claim 1, characterized in that, The wear-resistant parts, by mass percentage, comprise: C 0.20%–0.50%, Si 0.10%–0.50%, Mn 0.50%–1.50%, Cr 0.80%–2.00%, Ni 0.50%–1.50%, Mo 0.10%–0.50%, S≤0.030%, P≤0.030%, with the balance being Fe and unavoidable impurities.

4. The wear-resistant part for an extra-large excavator bucket according to claim 3, characterized in that, By mass percentage, C 0.25%–0.40%, Si 0.15%–0.30%, Mn 0.80%–1.20%, Cr 1.00%–1.80%, Ni 0.80%–1.20%, Mo 0.15%–0.35%, S ≤0.025%, P ≤0.025%, with the balance being Fe and unavoidable impurities.

5. The wear-resistant part for an extra-large excavator bucket according to claim 3, characterized in that, In terms of mass percentage, P ≤ 0.01%, S ≤ 0.01%.

6. The heat treatment process for multi-stage surface-modified wear-resistant parts for ultra-large excavator buckets according to claim 1, characterized in that, The heating rate of the multi-stage gradient normalizing treatment is as follows: in the first stage, the temperature is increased from 80-100℃ / h to 650-720℃; in the second stage, the temperature is increased from 50-70℃ / h to 780-820℃; and in the third stage, the temperature is increased from 30-50℃ / h to 900-950℃.

7. The heat treatment process for multi-stage surface-modified wear-resistant parts for ultra-large excavator buckets according to claim 1, characterized in that, The multi-stage quenching process involves an initial immersion in a quenching medium at a temperature of 20-30°C. After the initial removal, the workpiece surface temperature rises to 400-450°C, at which point a second immersion is performed, with the quenching medium temperature controlled at 40-50°C.

8. The heat treatment process for multi-stage surface-modified wear-resistant parts for ultra-large excavator buckets according to claim 1, characterized in that, The multi-stage quenching process is followed by deep cryogenic treatment, which is maintained at -80℃ to -120℃ for 2.0-4.0 hours.

9. The heat treatment process for multi-stage surface-modified wear-resistant parts for ultra-large excavator buckets according to claim 1, characterized in that, After tempering, high-energy shot peening is performed with a shot diameter of 0.2-0.5 mm and an impact pressure of 0.4-0.6 MPa.

10. The microstructure characteristics obtained by the heat treatment process of multi-stage surface modification for wear-resistant parts of ultra-large excavator buckets according to any one of claims 1-10, characterized in that, The wear-resistant parts have a surface layer of 2-5 mm thick fine-grained martensite with a grain size grade ≥ 8; the transition zone is a mixed structure of lath martensite and lower bainite; and the core is a tempered martensite matrix containing 5-15% retained austenite.

11. The performance characteristics obtained by the heat treatment process for multi-stage surface modification of wear-resistant parts for ultra-large excavator buckets according to any one of claims 1-10, characterized in that, The wear-resistant parts have a surface hardness of 58-63 HRC, a core hardness of 45-50 HRC, and an impact energy of ≥25 J at -40℃.

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