Quenching partitioning and tempering heat treatment process for carburized workpieces

Abstract

The present invention discloses a quenching partitioning and tempering heat treatment process for carburized workpieces, including: ① putting the workpiece to be treated into a carburizing furnace, introducing a protective gas, maintaining the furnace temperature at 930 °C and the carbon potential at 1.0 - 1.2% C. After experiencing the strong carburizing period, the first diffusion period, and the second diffusion period, the furnace temperature is lowered to 820 - 830 °C for heat preservation treatment for 2.5 h and then air-cooled. After that, two tempering treatments are carried out at 650 °C, each tempering time is 5 h, and air cooling is used for temperature reduction after each tempering to obtain the carburized workpiece. ② Slowly heating the carburized workpiece obtained in the first step to 850 °C, with a carbon potential of 0.85% C, and keeping it for 0.5 h to make it fully austenitized. Then, it is immediately sent to a salt bath furnace at 210 - 270 °C for heat preservation for 5 - 10 min for partitioning, and then sent to a salt bath furnace at 510 - 570 °C for partitioning and tempering treatment for 10 - 20 min. After water cooling, cold treatment is carried out at -60 °C for 2 h. Finally, the workpiece is subjected to tempering treatment at 180 °C for 8 h and cooled to room temperature, thus completing all the technological processes. The workpiece obtained by the present invention can greatly reduce accidents such as tooth breakage failure and improve the working stability of underground engineering equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of heat treatment of metal materials, and particularly to a quenching partitioning and tempering heat treatment process for carburized workpieces. Background Art

[0002] Due to the action of extreme loads such as frequent overload, eccentric load, and impact, gears in the drive systems of underground engineering equipment such as shield machines and shearers often suffer from tooth breakage and other phenomena. Once tooth breakage failure occurs, it will directly lead to equipment shutdown or even scrapping, seriously affecting equipment and construction safety. Therefore, how to avoid tooth breakage failure of gears is of utmost importance in gear production.

[0003] The heat treatment processes of traditional gear steels mainly include carburizing and quenching, nitriding, induction quenching, etc. Among them, carburizing and quenching have a deep hardened layer and high tooth surface hardness. The gear core still maintains high toughness, and the gear teeth have high bending strength, high tooth surface contact strength, good wear resistance, high load-bearing capacity, and excellent comprehensive performance. Therefore, the carburizing and quenching heat treatment process is often selected for the production of gears in the drive systems of underground engineering equipment.

[0004] However, for gears in a strong impact environment, such as the cutting part gears of high-power shearers that are severely affected by impact loads and overloads, the impact toughness that can be achieved by the traditional carburizing and quenching process still cannot meet the requirements, and strong impact tooth breakage occurs frequently. Therefore, it is necessary to further improve the impact toughness of such gears.

[0005] Some scholars analyzed the tooth breakage surfaces of such gears and found that the fracture sites mostly occurred at the tooth roots. By macroscopically inspecting the tooth breakage fractures, they showed the characteristics of strong impact brittle fracture, and no fatigue propagation traces were seen. Other scholars studied the microstructure of the tooth breakage parts of the walking wheels of shearers after carburizing treatment and found that the high hardness of the core led to low impact resistance and fracture toughness of the walking wheels, which was one of the main reasons for tooth root fracture.

[0006] Therefore, the current research focus in the industry is concentrated on: how to further improve the toughness of the gear core while maintaining a high hardness on the gear surface, thereby reducing the probability of tooth breakage failure of the gear. Summary of the Invention

[0007] In order to solve the above problems, the present invention provides a quenching partitioning and tempering heat treatment process for carburized workpieces, and specifically the following technical solutions can be adopted:

[0008] The quenching partitioning and tempering heat treatment process for carburized workpieces according to the present invention includes the following steps:

[0009] First step: Place the workpiece to be processed into a carburizing furnace, introduce a protective gas, maintain the furnace temperature at 930 °C and the carbon potential at 1.0 - 1.2% C. After experiencing the strong carburizing period, the first diffusion period, and the second diffusion period, lower the furnace temperature to 820 - 830 °C, hold for heat treatment for 2.5 h and then air cool. After that, conduct two tempering treatments at 650 °C, with each tempering time being 5 h, and air cool for temperature reduction after each tempering to obtain a carburized workpiece.

[0010] Second step: Slowly heat the carburized workpiece obtained in the first step to 850 °C, with a carbon potential of 0.85% C, hold for 0.5 h to fully austenitize it, and then immediately send it into a salt bath furnace at 210 - 270 °C for partitioning for 5 - 10 min. Then send it into a salt bath furnace at 510 - 570 °C for partitioning tempering treatment for 10 - 20 min. After water cooling for temperature reduction, conduct cryogenic treatment at - 60 °C for 2 h. Finally, conduct a tempering treatment on the workpiece at 180 °C for 8 h and cool it to room temperature. Thus, the entire process flow is completed.

[0011] Preferably, the workpiece to be processed is a metal gear made of 18Cr2Ni4WA.

[0012] Preferably, the protective gas is nitrogen - methanol + propane, the strong carburizing period is 14 h, the first diffusion period is 5 h, and the second diffusion period is 8 h.

[0013] Furthermore, the carburized layer thickness of the carburized workpiece is 2.592 mm.

[0014] Preferably, the temperature for partitioning treatment of the carburized workpiece is 240 °C and the time is 10 min; the temperature for partitioning tempering is 570 °C and the time is 10 min.

[0015] Preferably, the temperature for partitioning treatment of the carburized workpiece is 210 °C and the time is 10 min; the temperature for partitioning tempering is 570 °C and the time is 15 min.

[0016] Preferably, the temperature for partitioning treatment of the carburized workpiece is 270 °C and the time is 5 min; the temperature for partitioning tempering is 570 °C and the time is 15 min.

[0017] The object of action of the present invention is mainly used for the traveling wheels of shearers. At present, for the gears in the cutting parts of high-power shearers in China that are severely affected by impact loads and overloading, 18Cr2Ni4WA with good hardenability, high load-bearing capacity and impact resistance is basically selected for manufacturing. Its carbon content is relatively low, between 0.1% and 0.25%. After carburizing treatment, a relatively high hardness and wear resistance can be obtained on the surface. However, the gears treated by the conventional carburizing and quenching process cannot meet the requirements of large loads and strong impacts, and tooth breakage still occurs. Researchers have comprehensively measured the carbon concentration from the surface to the core of carburized workpieces, and have breakthroughly combined the partitioning process commonly used for homogeneous materials with the carburizing process, fully considering the carbon concentration gradient of carburized workpieces. By using the fact that different carbon concentrations correspond to different martensite start temperatures (Ms) and martensite finish temperatures (Mf), the partitioning temperature is reasonably selected. As a result, in the process of temperature reduction, the core of the workpiece with a relatively low carbon concentration and a relatively high Ms temperature undergoes rapid martensite transformation. Since face-centered cubic austenite has a higher carbon solubility than body-centered cubic martensite, the carbon atoms in the supersaturated martensite phase will diffuse into the austenite phase at this time, enriching the carbon atoms in the austenite and obtaining carbon-rich austenite. This kind of structure has good plasticity and toughness. At the same time, the surface of the workpiece with a relatively high carbon concentration and a relatively low Ms temperature does not undergo martensite transformation at this temperature, that is, the surface of the workpiece is not affected by the partitioning process and does not reduce its hardness, while the core undergoes partitioning changes, the hardness decreases, and the toughness increases, enabling the workpiece to adapt to the working environment of high loads and high impacts.

[0018] The 18Cr2Ni4WA adopted in the present invention can ensure that the core of the carburized workpiece has excellent toughness and plasticity. In the subsequent partitioning process, alloying elements in low-carbon alloy steel such as Ni (<4.5%), Cr (<2%), Mn (<2%) etc. can effectively improve the hardenability of the steel, and improve the core structure and properties of the carburized workpiece. At the same time, Ni has a good influence on the quality of the carburized layer, and can greatly improve the strength, plasticity and toughness of the carburized layer, so that a good strengthening effect can be obtained in the core of the alloy carburized steel.

[0019] In summary, the quenching partitioning and tempering heat treatment process for carburized workpieces provided by the present invention first carburizes the metal workpiece to obtain a carburized workpiece with a large difference in Ms and Mf from the surface to the core (that is, the Ms and Mf of the surface of the carburized gear are high, and the Ms and Mf of the core are low) and a carbon concentration gradient. Then, cooling partitioning is carried out between the surface Ms and the core Ms, so as to obtain a workpiece with both a high-hardness carburized and quenched structure on the surface and a high-toughness partitioned structure in the core. This workpiece has a high surface contact strength, good wear resistance, high overall bending strength and load-bearing capacity, and strong impact toughness, which can greatly reduce accidents such as tooth breakage failure and improve the working stability of underground engineering equipment. Description of the Drawings

[0020] Figure 1 It is the T-t diagram of the carburizing treatment in Example 1.

[0021] Figure 2 It is the T-t diagram of the partitioning treatment in Example 1.

[0022] Figure 3 It is the T-t diagram of the quenching treatment in the comparative example.

[0023] Figure 4 It is the surface metallographic structure photograph of the specimen obtained in Example 1.

[0024] Figure 5 It is the core metallographic structure photograph of the specimen obtained in Example 1.

[0025] Figure 6 It is the surface metallographic structure photograph of the specimen obtained in the comparative example.

[0026] Figure 7 It is the core metallographic structure photograph of the specimen obtained in the comparative example. Detailed implementation manners

[0027] The following will make a detailed description of the embodiments of the present invention in conjunction with the accompanying drawings. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific construction processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0028] Example 1:

[0029] The quenching partitioning tempering heat treatment process for the carburized workpiece described in the present invention includes the following steps:

[0030] The first step, as Figure 1 shown, put the metal gear (i.e., the workpiece to be processed) made of 18Cr2Ni4WA into the carburizing furnace, introduce nitrogen methanol + propane as the protective gas, keep the furnace temperature at 930 °C, the carbon potential at 1.0 - 1.2% C. After experiencing the strong carburizing period (14 h), the first diffusion period (5 h), and the second diffusion period (8 h), lower the furnace temperature to 820 - 830 °C for heat preservation treatment for 2.5 h and then air cool. After that, perform two tempering treatments at 650 °C, each tempering time is 5 h, and air cooling is used for temperature reduction after each tempering to obtain the carburized workpiece, and the carburized layer thickness is 2.592 mm;

[0031] The second step, as Figure 2As shown, the carburized workpiece obtained in the first step is slowly heated to 850 °C. While the carbon potential is raised to 0.85% C, it is held for 0.5 h to complete austenitization. Then, it is immediately sent to a salt bath furnace at 240 °C for 10 min of partitioning, followed by being sent to a salt bath furnace at 570 °C for 10 min of partitioning and tempering treatment. After water cooling, it is then cryogenically treated at -60 °C for 2 h. Finally, the workpiece is tempered at 180 °C for 8 h and cooled to room temperature, thus completing all the process flows.

[0032] Example 2:

[0033] The quenching, partitioning and tempering heat treatment process for the carburized workpiece of the present invention includes the following steps:

[0034] First step, put the metal gear (i.e., the workpiece to be treated) made of 18Cr2Ni4WA into a carburizing furnace, introduce nitrogen methanol + propane as the protective gas, keep the furnace temperature at 930 °C, and the carbon potential at 1.0 - 1.2% C. After experiencing the strong carburizing period (14 h), the first diffusion period (5 h), and the second diffusion period (8 h), the furnace temperature is lowered to 820 - 830 °C, held for 2.5 h and then air-cooled. After that, two tempering treatments are carried out at 650 °C, each tempering time is 5 h, and air cooling is used for temperature reduction after each tempering, obtaining a carburized workpiece with a carburized layer thickness of 2.592 mm;

[0035] Second step, as Figure 2 shown, the carburized workpiece obtained in the first step is slowly heated to 850 °C. While the carbon potential is raised to 0.85% C, it is held for 0.5 h to complete austenitization. Then, it is immediately sent to a salt bath furnace at 210 °C for 5 min of partitioning, followed by being sent to a salt bath furnace at 510 °C for 10 min of partitioning and tempering treatment. After water cooling, it is then cryogenically treated at -60 °C for 2 h. Finally, the workpiece is tempered at 180 °C for 8 h and cooled to room temperature, thus completing all the process flows.

[0036] Example 3:

[0037] The quenching, partitioning and tempering heat treatment process for the carburized workpiece of the present invention includes the following steps:

[0038] First step, put the metal gear (i.e., the workpiece to be treated) made of 18Cr2Ni4WA into a carburizing furnace, introduce nitrogen methanol + propane as the protective gas, keep the furnace temperature at 930 °C, and the carbon potential at 1.0 - 1.2% C. After experiencing the strong carburizing period (14 h), the first diffusion period (5 h), and the second diffusion period (8 h), the furnace temperature is lowered to 820 - 830 °C, held for 2.5 h and then air-cooled. After that, two tempering treatments are carried out at 650 °C, each tempering time is 5 h, and air cooling is used for temperature reduction after each tempering, obtaining a carburized workpiece with a carburized layer thickness of 2.592 mm;

[0039] Step 2, as Figure 2 shown, slowly heat up the carburized workpiece obtained in the first step to 850 °C. While the carbon potential rises to 0.85% C, hold for 0.5 h to fully austenitize it. Then immediately send it into a salt bath furnace at 210 °C for 10 min for partitioning. Next, send it into a salt bath furnace at 570 °C for 15 min for partitioning and tempering treatment. After water cooling, perform cryogenic treatment at -60 °C for 2 h. Finally, perform tempering treatment on the workpiece at 180 °C for 8 h and cool it to room temperature. Thus, the entire process flow is completed.

[0040] Example 4:

[0041] The quenching, partitioning and tempering heat treatment process of the carburized workpiece described in the present invention comprises the following steps:

[0042] Step 1, put the metal gear (i.e., the workpiece to be processed) made of 18Cr2Ni4WA into a carburizing furnace, introduce nitrogen - methanol + propane as the protective gas, keep the furnace temperature at 930 °C, and the carbon potential at 1.0 - 1.2% C. After experiencing the strong carburizing period (14 h), the first diffusion period (5 h), and the second diffusion period (8 h), lower the furnace temperature to 820 - 830 °C, hold for 2.5 h and then air - cool. After that, perform two tempering treatments at 650 °C, each tempering time is 5 h, and after tempering, air - cool for temperature reduction to obtain the carburized workpiece, whose carburized layer thickness is 2.592 mm;

[0043] Step 2, as Figure 2 shown, slowly heat up the carburized workpiece obtained in the first step to 850 °C. While the carbon potential rises to 0.85% C, hold for 0.5 h to fully austenitize it. Then immediately send it into a salt bath furnace at 210 °C for 15 min for partitioning. Next, send it into a salt bath furnace at 540 °C for 20 min for partitioning and tempering treatment. After water cooling, perform cryogenic treatment at -60 °C for 2 h. Finally, perform tempering treatment on the workpiece at 180 °C for 8 h and cool it to room temperature. Thus, the entire process flow is completed.

[0044] Example 5:

[0045] The quenching, partitioning and tempering heat treatment process of the carburized workpiece described in the present invention comprises the following steps:

[0046] Step 1, put the metal gear (i.e., the workpiece to be processed) made of 18Cr2Ni4WA into a carburizing furnace, introduce nitrogen - methanol + propane as the protective gas, keep the furnace temperature at 930 °C, and the carbon potential at 1.0 - 1.2% C. After experiencing the strong carburizing period (14 h), the first diffusion period (5 h), and the second diffusion period (8 h), lower the furnace temperature to 820 - 830 °C, hold for 2.5 h and then air - cool. After that, perform two tempering treatments at 650 °C, each tempering time is 5 h, and after tempering, air - cool for temperature reduction to obtain the carburized workpiece, whose carburized layer thickness is 2.592 mm;

[0047] In the second step, as Figure 2 shown, the carburized workpiece obtained in the first step is slowly heated to 850 °C. While the carbon potential is increased to 0.85% C, it is held for 0.5 h to be fully austenitized. Then it is immediately sent to a salt bath furnace at 240 °C for 5 min of partitioning. Then it is sent to a salt bath furnace at 540 °C for 20 min of partitioning tempering treatment. After water cooling, it is then cryogenically treated at -60 °C for 2 h. Finally, the workpiece is tempered at 180 °C for 8 h and cooled to room temperature. Thus, the entire process flow is completed.

[0048] Example 6:

[0049] The quenching partitioning tempering heat treatment process of the carburized workpiece described in the present invention comprises the following steps:

[0050] In the first step, a metal gear made of 18Cr2Ni4WA (i.e., the workpiece to be treated) is placed in a carburizing furnace. Nitrogen methanol + propane is introduced as the protective gas. The temperature in the furnace is maintained at 930 °C and the carbon potential is 1.0 - 1.2% C. After experiencing the strong carburizing period (14 h), the first diffusion period (5 h), and the second diffusion period (8 h), the furnace temperature is lowered to 820 - 830 °C and held for 2.5 h and then air-cooled. Then, two tempering treatments are carried out at 650 °C, each with a tempering time of 5 h, and air cooling is used for temperature reduction after each tempering, obtaining a carburized workpiece with a carburized layer thickness of 2.592 mm;

[0051] In the second step, as Figure 2 shown, the carburized workpiece obtained in the first step is slowly heated to 850 °C. While the carbon potential is increased to 0.85% C, it is held for 0.5 h to be fully austenitized. Then it is immediately sent to a salt bath furnace at 240 °C for 15 min of partitioning. Then it is sent to a salt bath furnace at 510 °C for 15 min of partitioning tempering treatment. After water cooling, it is then cryogenically treated at -60 °C for 2 h. Finally, the workpiece is tempered at 180 °C for 8 h and cooled to room temperature. Thus, the entire process flow is completed.

[0052] Example 7:

[0053] The quenching partitioning tempering heat treatment process of the carburized workpiece described in the present invention comprises the following steps:

[0054] First step: Put the metal gear made of 18Cr2Ni4WA (i.e., the workpiece to be processed) into a carburizing furnace, introduce nitrogen methanol + propane as the protective gas, keep the furnace temperature at 930 °C, and the carbon potential at 1.0 - 1.2% C. After going through the strong carburizing period (14 h), the first diffusion period (5 h), and the second diffusion period (8 h), lower the furnace temperature to 820 - 830 °C, hold for 2.5 h and then air cool. After that, conduct two tempering treatments at 650 °C, with each tempering time being 5 h, and air cool after tempering to obtain the carburized workpiece, whose carburized layer thickness is 2.592 mm;

[0055] Second step: As Figure 2 shown, slowly heat up the carburized workpiece obtained in the first step to 850 °C, at the same time raise the carbon potential to 0.85% C, hold for 0.5 h to fully austenitize it, then immediately send it into a salt furnace at 270 °C and hold for 5 min for partitioning, then send it into a salt furnace at 570 °C for partitioning tempering treatment for 15 min, cool it by water cooling, then conduct cold treatment at -60 °C for 2 h, and finally conduct tempering treatment on the workpiece at 180 °C for 8 h and cool it to room temperature. Thus, the entire process flow is completed.

[0056] Example 8:

[0057] The quenching partitioning tempering heat treatment process for the carburized workpiece of the present invention includes the following steps:

[0058] First step: Put the metal gear made of 18Cr2Ni4WA (i.e., the workpiece to be processed) into a carburizing furnace, introduce nitrogen methanol + propane as the protective gas, keep the furnace temperature at 930 °C, and the carbon potential at 1.0 - 1.2% C. After going through the strong carburizing period (14 h), the first diffusion period (5 h), and the second diffusion period (8 h), lower the furnace temperature to 820 - 830 °C, hold for 2.5 h and then air cool. After that, conduct two tempering treatments at 650 °C, with each tempering time being 5 h, and air cool after tempering to obtain the carburized workpiece, whose carburized layer thickness is 2.592 mm;

[0059] Second step: As Figure 2 shown, slowly heat up the carburized workpiece obtained in the first step to 850 °C, at the same time raise the carbon potential to 0.85% C, hold for 0.5 h to fully austenitize it, then immediately send it into a salt furnace at 270 °C and hold for 10 min for partitioning, then send it into a salt furnace at 510 °C for partitioning tempering treatment for 20 min, cool it by water cooling, then conduct cold treatment at -60 °C for 2 h, and finally conduct tempering treatment on the workpiece at 180 °C for 8 h and cool it to room temperature. Thus, the entire process flow is completed.

[0060] Example 9:

[0061] The quenching partitioning tempering heat treatment process for the carburized workpiece of the present invention includes the following steps:

[0062] First step: Place the metal gear made of 18Cr2Ni4WA (i.e., the workpiece to be processed) into a carburizing furnace, introduce nitrogen methanol + propane as the protective gas, maintain the furnace temperature at 930 °C, and the carbon potential at 1.0 - 1.2% C. After going through the strong carburizing period (14 h), the first diffusion period (5 h), and the second diffusion period (8 h), lower the furnace temperature to 820 - 830 °C, hold for 2.5 h and then air cool. After that, conduct two tempering treatments at 650 °C, with each tempering time being 5 h, and air cool for temperature reduction after each tempering to obtain a carburized workpiece with a carburized layer thickness of 2.592 mm.

[0063] Second step: As Figure 2 shown, slowly heat the carburized workpiece obtained in the first step to 850 °C. At the same time, raise the carbon potential to 0.85% C, hold for 0.5 h to fully austenitize it, then immediately send it into a salt bath furnace at 270 °C and hold for 15 min for partitioning. Then send it into a salt bath furnace at 540 °C for partitioning and tempering treatment for 10 min. After water cooling, conduct cold treatment at -60 °C for 2 h. Finally, conduct a tempering treatment on the workpiece at 180 °C for 8 h and cool it to room temperature. Thus, the entire process flow is completed.

[0064] Comparative example:

[0065] Adopt a conventional quenching process, specifically as follows:

[0066] First step: Place the metal gear made of 18Cr2Ni4WA (i.e., the workpiece to be processed) into a carburizing furnace, introduce nitrogen methanol + propane as the protective gas, maintain the furnace temperature at 930 °C, and the carbon potential at 1.0 - 1.2% C. After going through the strong carburizing period (14 h), the first diffusion period (5 h), and the second diffusion period (8 h), lower the furnace temperature to 820 - 830 °C, hold for 2.5 h and then air cool. After that, conduct two tempering treatments at 650 °C, with each tempering time being 5 h, and air cool for temperature reduction after each tempering to obtain a carburized workpiece with a carburized layer thickness of 2.592 mm.

[0067] Second step: As Figure 3 shown, slowly heat the carburized workpiece obtained in the first step to 830 °C, hold for 2.5 h, with the carbon potential being 0.75% C. After oil cooling, conduct cold treatment at -60 °C for 2 h. Finally, conduct low-temperature tempering at 180 °C for 15 h. Thus, the entire process flow is completed.

[0068] After testing, the mechanical properties of the parts obtained in Examples 1 - 9 and the comparative example are shown in Table 1:

[0069] Table 1 Mechanical properties of the specimens

[0070]

[0071] As can be seen from the data shown in Table 1, the surface hardness of the specimens of the present invention is all above HRC 58, while the core hardness is significantly reduced. It shows that compared with the comparative example, after adding the partitioning treatment step, the present invention can improve the impact toughness of carburized steel without sacrificing the surface hardness. To corroborate this result, a group of example specimens and a group of comparative example specimens were selected, and the microstructural changes in the carburized layer and the core were determined by observing their microstructures with a LEICA DMI 3000M optical microscope (500 times magnification, specifically see Figures 4 - 7 ).

[0072] It can be seen from the metallographic pictures that the surfaces of the specimens of Example 1 and Comparative Document 1 are both composed of high-carbon martensite, retained austenite and carbides. However, the content of retained austenite in the surface structure of the specimen of Example 1 after the partitioning process treatment has increased significantly. Although this will cause a certain decrease in the hardness of the carburized layer, due to the refinement of the grains contained in the specimen after the partitioning process treatment, the fine-grain strengthening effect is generated. At the same time, fine and dispersed carbides are distributed in the carburized layer, and the distribution is relatively uniform, playing the role of precipitation strengthening. Therefore, the surface hardness of the specimen of Example 1 does not decrease due to the partitioning process treatment.

[0073] By observing the core tissue condition, it can be found that after the partitioning process treatment, the matrix structure of the specimen of Example 1 is more refined. This is because the increase in retained austenite divides the martensite / bainite and ferrite laths, refining the substructural units, and the crystallographic orientations of each tissue are in a disordered state. Martensite / bainite laths, ferrite and retained austenite are all factors affecting toughness. The layered structure of bainite and retained austenite with soft and hard phases has good toughening characteristics. Fine ferrite can coordinate martensite transformation and bainite deformation, playing the role of relaxing stress concentration and giving full play to the coordinated deformation of multi-phase tissues, making the core hardness all within 40-45HRC, and fully improving the impact toughness of the specimen.

[0074] It should be noted that in the description of the present invention, terms indicating orientation or positional relationship such as "front", "rear", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation to the present invention.

Claims

1. A quenching partitioning and tempering heat treatment process for carburized workpieces, characterized in that, The steps are as follows: In the first step, the workpiece to be processed is placed in a carburizing furnace, and a protective gas is introduced. The temperature in the furnace is maintained at 930 °C, and the carbon potential is 1.0 - 1.2% C. After going through the strong carburizing period, the first diffusion period, and the second diffusion period, the furnace temperature is lowered to 820 - 830 °C for heat preservation treatment for 2.5 h and then air-cooled. After that, two tempering treatments are carried out at 650 °C, with each tempering time being 5 h, and air cooling is used for temperature reduction after each tempering to obtain the carburized workpiece; In the second step, the carburized workpiece obtained in the first step is slowly heated to 850 °C, with a carbon potential of 0.85% C, and heat preservation is carried out for 0.5 h to make it fully austenitized. Then it is immediately sent to a salt bath furnace at 210 - 270 °C for heat preservation for 5 - 10 min for partitioning, and then sent to a salt bath furnace at 510 - 570 °C for partitioning tempering treatment for 10 - 20 min. After water cooling, cold treatment is carried out at - 60 °C for 2 h, and finally the workpiece is subjected to tempering treatment at 180 °C for 8 h and cooled to room temperature, thus completing the entire process flow; The workpiece to be processed is a metal gear made of 18Cr2Ni4WA; The protective gas is nitrogen - methanol + propane. The strong carburizing period is 14 h, the first diffusion period is 5 h, and the second diffusion period is 8 h; The carburized layer thickness of the carburized workpiece is 2.592 mm.

2. The quenching partitioning and tempering heat treatment process for carburized workpieces according to claim 1, characterized in that: For the carburized workpiece, the temperature for partitioning treatment is 240 °C and the time is 10 min; the temperature for partitioning tempering is 570 °C and the time is 10 min.

3. The quenching partitioning and tempering heat treatment process for carburized workpieces according to claim 1, characterized in that: For the carburized workpiece, the temperature for partitioning treatment is 210 °C and the time is 10 min; the temperature for partitioning tempering is 570 °C and the time is 15 min.

4. The quenching partitioning and tempering heat treatment process for carburized workpieces according to claim 1, characterized in that: For the carburized workpiece, the temperature for partitioning treatment is 270 °C and the time is 5 min; the temperature for partitioning tempering is 570 °C and the time is 15 min.

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