Machining processes for metal workpieces

Abstract

This invention discloses a processing technology for metal workpieces. The processing technology includes: carburizing a metal workpiece to obtain a first metal workpiece; subjecting the first metal workpiece to a first tempering treatment to obtain a second metal workpiece; quenching the second metal workpiece to obtain a third metal workpiece; subjecting the third metal workpiece to a second tempering treatment to obtain a fourth metal workpiece; and subjecting the fourth metal workpiece to a nitriding and carburizing treatment to obtain the finished metal workpiece. The metal workpiece obtained using the processing technology provided in this application exhibits high surface hardness while maintaining a hardness gradient.

Description

Technical Field

[0001] This invention belongs to the field of metal workpiece processing technology, and more specifically, relates to a metal workpiece processing technology. Background Technology

[0002] Metallic materials are widely used in construction and decoration, machinery industry, automotive industry, food industry, instrumentation, aerospace and other fields. The performance of metallic workpieces also has a crucial impact on their use and lifespan. Therefore, in the manufacturing of metallic workpieces, in addition to general quenching and tempering heat treatment processes, various surface hardening treatments such as carburizing, nitriding, and high-frequency quenching are also required.

[0003] Currently, heat treatment processes for metal workpieces are generally limited to single carburizing and quenching processes or ion diffusion processes. There are no widely used technologies for further strengthening carburized and quenched workpieces; generally, workpieces can be used directly after carburizing and quenching (or directly after finishing). This treatment method can achieve a very deep carburized layer, but the workpiece's load-bearing capacity is relatively low, its wear resistance is poor, and it is prone to fatigue failure under heavy loads, resulting in a short lifespan. It is widely used in some fields where reliability requirements are not very high. Ion diffusion processes are more efficient and have better surface strengthening effects, but the carburized layer depth is shallower, and the diffusion process can lead to a decrease in the core hardness of the material.

[0004] Therefore, developing a process that can both improve the surface hardness of metal workpieces and maintain the hardness gradient, thereby effectively improving the wear resistance and fatigue resistance of metal workpieces, has significant theoretical research value and practical application value. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide a processing technology for metal workpieces, wherein the metal workpieces obtained using the processing technology provided in this application have high surface hardness while maintaining a hardness gradient.

[0006] This invention proposes a heat treatment process for metal workpieces. According to an embodiment of the invention, the method includes: carburizing the metal workpiece to obtain a first metal workpiece; performing a first tempering treatment on the first metal workpiece to obtain a second metal workpiece; quenching the second metal workpiece to obtain a third metal workpiece; performing a second tempering treatment on the third metal workpiece to obtain a fourth metal workpiece; and performing a nitriding and carbonizing treatment on the fourth metal workpiece to obtain a finished metal workpiece.

[0007] According to the heat treatment process of the above embodiments of the present invention, more time and temperature conditions can be provided during the second tempering process, allowing the metal to relax residual stress through internal local plastic deformation or local relaxation processes. Furthermore, the retained austenite in the metal workpiece is distributed in a thin film at the grain boundaries during the second tempering process. When the martensitic lath cracks formed during the second tempering extend to the grain boundaries and encounter the retained austenite, the crack tips undergo plastic deformation, which helps to prevent further crack propagation, thereby improving the toughness of the material. During the nitrocarburizing process, nitrogen and carbon are simultaneously diffused into the surface of the metal workpiece, forming a nitrocarburite diffusion layer. Nitrocarburites have extremely high hardness, resulting in high surface hardness of the workpiece. Moreover, carbon atoms can also form alloy cementite with strong carbide-forming elements (such as Cr, W, Mo, V, etc.) in the workpiece, increasing the hardness of the metal diffusion layer and also helping to maintain the hardness gradient of the workpiece. Therefore, the metal workpiece obtained using the processing technology provided in this application has high surface hardness while maintaining a hardness gradient.

[0008] In addition, the processing technology according to the above embodiments of the present invention may also have the following additional technical features:

[0009] In some embodiments of the present invention, after the third metal workpiece undergoes a second tempering treatment to obtain a fourth metal workpiece, and before the fourth metal workpiece undergoes ion co-diffusion treatment to obtain a strengthened metal workpiece, the method further includes grinding, polishing, and cleaning the fourth metal workpiece. This facilitates the uniform distribution and penetration of carbon and nitrogen elements during the nitrocarburizing process, avoids arcing and other phenomena during the diffusion process, and improves the co-diffusion effect.

[0010] In some embodiments of the present invention, the material of the metal workpiece includes at least one of low-carbon steel and low-carbon alloy steel.

[0011] In some embodiments of the present invention, the carburizing process includes at least one of gas carburizing, vacuum carburizing, and plasma carburizing.

[0012] In some embodiments of the present invention, the carburizing temperature is 900°C-950°C. This ensures the formation of austenite and maintains its stability, thereby promoting uniform diffusion of carbon atoms.

[0013] In some embodiments of the present invention, the carburizing time is 1 hour to 30 hours. This is beneficial for improving the surface hardness of the metal workpiece.

[0014] In some embodiments of the present invention, the first tempering process includes first holding at 600℃-700℃ for 2-4 hours, and then holding at 600℃-700℃ for another 2-4 hours. This helps to adjust the balance between the hardness and toughness of the workpiece, ensuring that the workpiece maintains sufficient hardness while also possessing good toughness to meet the requirements of use in complex working environments.

[0015] In some embodiments of the present invention, the quenching temperature is 700℃-900℃. This improves the hardness and strength of the metal workpiece.

[0016] In some embodiments of the present invention, the quenching time is 3-4 hours. This improves the surface hardness of the metal workpiece.

[0017] In some embodiments of the present invention, the temperature of the second tempering is 150°C-460°C. This maintains the surface hardness of the workpiece while also improving its toughness.

[0018] In some embodiments of the present invention, the second tempering time is 2-8 hours. This is beneficial for improving the strength and toughness of the workpiece.

[0019] In some embodiments of the present invention, the surface roughness of the fourth metal workpiece is less than 0.08 μm. This facilitates the uniform distribution and penetration of carbon and nitrogen elements during the nitrocarburizing process, thereby improving the nitrocarburizing effect.

[0020] In some embodiments of the present invention, the temperature of the nitriding and carbonizing process is 160°C-460°C. This is beneficial for improving the surface hardness of the workpiece.

[0021] In some embodiments of the present invention, the nitriding and carbonizing time is 1 hour to 30 hours. This is beneficial for improving the surface hardness of the workpiece.

[0022] In some embodiments of the present invention, the vacuum degree of the nitriding and carbonization process is 10 Pa to 400 Pa. This is beneficial for improving the surface hardness of the workpiece.

[0023] In some embodiments of the present invention, the temperature of the second tempering is not lower than the temperature of the nitriding and carburizing process. This allows the resulting metal workpiece to have high surface hardness while maintaining a hardness gradient.

[0024] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0025] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0026] Figure 1 A process flow diagram of the metal workpiece processing according to an embodiment of this application is shown;

[0027] Figure 2 The images show a comparison of the surface microhardness of the finished metal workpieces obtained in Example 1, Comparative Example 1, and Comparative Example 2 of this application.

[0028] Figure 3 This paper displays a comparison chart of the hardness gradient curves of the finished metal workpieces obtained in Embodiment 1, Comparative Example 1, and Comparative Example 2 of this application.

[0029] Figure 4 The images show a comparison of the surface microhardness of the finished metal workpieces obtained in Examples 2, 3, and 4 of this application.

[0030] Figure 5 The diagram shows a comparison of the hardness gradient curves of the finished metal workpieces obtained in Examples 2, 3, and 4 of this application. Detailed Implementation

[0031] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0032] This invention proposes a processing technology for metal workpieces. According to an embodiment of the invention, refer to... Figure 1 The processing technology includes:

[0033] S1. Carburize the metal workpiece. First metal workpiece.

[0034] In this step, a first metal workpiece is obtained by carburizing the metal workpiece. Specifically, the metal workpiece is placed in a carburizing medium, heated to the single-phase austenite region, and held at that temperature for a sufficient time. The active carbon atoms in the carburizing medium can penetrate into the surface layer of the metal workpiece, increasing the carbon content on the surface and forming a certain carbon concentration gradient, which can improve the hardness of the workpiece and enhance its scratch resistance and wear resistance.

[0035] As an example, the carburizing process includes, but is not limited to, at least one of gas carburizing, vacuum carburizing, and plasma carburizing.

[0036] According to some specific embodiments of the present invention, the material of the metal workpiece includes at least one of low-carbon steel and low-carbon alloy steel. The material of the aforementioned metal workpiece possesses excellent toughness and machinability, allowing it to deform more easily during processing without easily cracking or breaking.

[0037] According to some specific embodiments of the present invention, the carburizing temperature is 900℃-950℃. For example, it can be 900℃, 920℃, 940℃, 950℃, etc. By limiting the carburizing temperature within the above range, the formation of austenite can be ensured and its stability maintained, thereby promoting the uniform diffusion of carbon atoms and improving the surface hardness of the metal workpiece.

[0038] According to some specific embodiments of the present invention, the carburizing time is 1 hour to 30 hours. For example, 1 hour, 10 hours, 20 hours, 30 hours, etc. By limiting the carburizing time within the above range, the gradient of carbon concentration can be precisely controlled, ensuring that the surface carbon content reaches the predetermined requirements, thereby improving the surface hardness of the metal workpiece.

[0039] S2. Perform a first tempering treatment on the first metal workpiece to obtain a second metal workpiece.

[0040] In this step, the second metal workpiece is obtained by subjecting the first metal workpiece to a first tempering treatment. Specifically, the first metal workpiece is heated to a certain temperature, causing its microstructure to transform into a tempered microstructure. This effectively eliminates residual stress and brittleness generated during carburizing, making the workpiece microstructure more stable and preventing deformation and cracking. Simultaneously, the first tempering treatment can further refine the grains, improving the toughness and plasticity of the workpiece core, enabling it to withstand larger impact loads and deformations.

[0041] According to some specific embodiments of the present invention, the first tempering process includes first holding at a temperature of 600℃-700℃ for 2h-4h, for example, the temperature can be 600℃, 650℃, 700℃, etc., and the time can be 2h, 3h, 4h, etc., followed by holding at a temperature of 600℃-700℃ for 2h-4h, for example, the temperature can be 600℃, 650℃, 700℃, etc., and the time can be 2h, 3h, 4h, etc. The first high-temperature tempering can promote the initial homogenization and stabilization of the workpiece's microstructure, while eliminating some residual stress and improving the workpiece's toughness. The second high-temperature tempering can further refine the grains, making the microstructure more uniform, improving the workpiece's mechanical properties and thermal stability, and also further eliminating any residual internal stress that may have remained during the first high-temperature tempering process, thereby ensuring that the workpiece has better dimensional stability and resistance to deformation during subsequent use. Therefore, by performing two consecutive high-temperature tempering processes, it is beneficial to adjust the balance between the hardness and toughness of the workpiece, so that the workpiece can maintain sufficient hardness while also having good toughness, in order to meet the usage requirements in complex working environments.

[0042] S3. The second metal workpiece is quenched to obtain the third metal workpiece.

[0043] In this step, the third metal workpiece can be obtained by quenching the second metal workpiece. Specifically, the second metal workpiece is heated and then rapidly cooled, which can promote the full diffusion and penetration of carbon atoms on the surface of the workpiece, and can combine with iron atoms in the workpiece to form a high-hardness martensitic structure, while maintaining a certain strength and toughness in the core of the workpiece.

[0044] According to some specific embodiments of the present invention, the quenching temperature is 700℃-900℃. For example, it can be 700℃, 750℃, 800℃, 850℃, 900℃, etc. During the quenching process, austenite can be rapidly cooled and transformed into martensite. By limiting the quenching temperature within the above range, on the one hand, finer and more uniform martensite can be formed, which can improve the hardness and strength of the metal workpiece. On the other hand, the amount of retained austenite can be controlled, avoiding the adverse effects of too much or too little retained austenite on the workpiece performance.

[0045] According to some specific embodiments of the present invention, the quenching time is 3-4 hours. For example, it can be 3 hours, 3.5 hours, 4 hours, etc. By limiting the quenching time within the above range, the transformation of austenite to martensite can be completed within the optimal time window, ensuring the quantity and quality of martensite formation, which is beneficial to the formation of fine and uniform martensite structure, reducing the occurrence of coarse martensite or martensite laths, and thus improving the surface hardness of the metal workpiece.

[0046] S4. Perform a second tempering treatment on the third metal workpiece to obtain the fourth metal workpiece.

[0047] In this step, the fourth metal workpiece is obtained by subjecting the third metal workpiece to a second tempering treatment. Specifically, heating the third metal workpiece to a certain temperature and holding it there eliminates residual stress generated during quenching, preventing deformation and cracking. Furthermore, the retained austenite in the metal workpiece is distributed in a thin film at the grain boundaries during the second tempering process. When the martensitic lath cracks formed during the second tempering extend to the grain boundaries and encounter the retained austenite, plastic deformation occurs at the crack tip. This plastic deformation helps to prevent further crack propagation, thereby improving the toughness of the metal workpiece.

[0048] According to some specific embodiments of the present invention, the temperature of the second tempering is 150℃-460℃. For example, it can be 150℃, 200℃, 300℃, 460℃, etc. By limiting the temperature of the second tempering within the above range, residual stress inside the workpiece can be substantially eliminated, while controlling the transformation of martensite, thereby maximizing the maintenance of the hardness gradient of the workpiece and improving the toughness of the metal workpiece.

[0049] According to some specific embodiments of the present invention, the second tempering time is 2h-8h. For example, it can be 2h, 4h, 6h, 8h, etc. By limiting the second tempering time within the above range, on the one hand, residual stress in the workpiece can be further eliminated, making the microstructure more stable, thereby improving the performance stability of the workpiece. On the other hand, it can ensure that carbides are uniformly dispersed in the workpiece, which is beneficial to improving the strength and toughness of the workpiece.

[0050] S5. The fourth metal workpiece is subjected to nitrocarburizing treatment to obtain the finished metal workpiece.

[0051] In this step, by subjecting the fourth metal workpiece to nitrocarburizing treatment, a finished metal workpiece can be obtained. Specifically, the fourth metal is subjected to nitrocarburizing treatment using a hollow cathode ion source diffusion strengthening device. During the nitrocarburizing treatment, nitrogen and carbon are simultaneously diffused into the surface of the metal workpiece to form a nitrocarburized diffusion layer. Moreover, carbon atoms can also form alloy cementite with strong carbide-forming elements (such as Cr, W, Mo, V, etc.) in the workpiece, which can form a relatively uniform hardness distribution in the workpiece, which is beneficial to maintaining the hardness gradient of the workpiece and thus improving the hardness of the metal workpiece.

[0052] It should be noted that the hollow cathode ion source diffusion strengthening equipment includes the equipment body, an active screen, a pulse power supply, and a cathode disk. The furnace body of the hollow cathode ion source diffusion strengthening equipment has a vacuum chamber inside. When the workpiece is subjected to nitriding and carburizing, the workpiece is placed on the cathode disk, and the active screen is placed outside the cathode disk. The furnace body is closed and evacuated to a vacuum (10Pa-30Pa). At this time, a bias voltage is applied to the cathode disk, so that the cathode disk and the workpiece are in a cathode state. At the same time, a bias voltage is applied to the active screen, so that the active screen is also in a cathode state. Hydrogen, nitrogen, and methane are introduced into the hollow cathode ion source diffusion strengthening equipment body. The plasma generated after the gas is ionized will bombard the active screen under the action of the electric field, forming iron-nitrogen-carbon compounds that are then deposited on the workpiece surface. The other part will bombard the workpiece surface. The metal atoms sputtered from the workpiece surface will combine with the active gas atoms and be deposited on the workpiece surface. The gas atoms will continue to diffuse into the interior of the workpiece, forming a nitriding and carburizing strengthening layer. Furthermore, this diffusion enhancement equipment is equipped with two independent power supplies, one for the active screen and the other for the cathode disk, which effectively improves the gas ionization rate. The high-concentration plasma generated by the hollow cathode effect bombards the workpiece surface under bias voltage, enhancing the diffusion efficiency and effect.

[0053] According to some specific embodiments of the present invention, between step S4 and step S5, the process further includes grinding, polishing, and cleaning the fourth metal workpiece. Grinding, polishing, and cleaning the fourth metal workpiece removes oil, dust, and other impurities from its surface, ensuring a clean and uncontaminated surface during subsequent nitriding and carbonizing processes. Grinding and polishing significantly reduce the surface roughness of the workpiece, making it smoother, which is beneficial for the uniform distribution and penetration of carbon and nitrogen elements during nitriding and improves the co-diffusion effect.

[0054] According to some specific embodiments of the present invention, the surface roughness of the fourth metal workpiece is less than 0.08 μm. For example, it can be 0.07 μm, 0.05 μm, 0.04 μm, 0.03 μm, 0.01 μm, etc. By limiting the surface roughness of the fourth metal workpiece within the above range, the surface of the metal workpiece is made smoother, which helps to avoid arcing and other problems during the nitrocarburizing process, and also facilitates the uniform distribution of carbon and nitrogen elements, thereby improving the co-burdening effect.

[0055] According to some specific embodiments of the present invention, the temperature of nitriding and carburizing is 150℃-460℃. For example, it can be 150℃, 200℃, 300℃, 400℃, 460℃, etc. By limiting the temperature of nitriding and carburizing within the above range, nitrogen and carbon can be simultaneously diffused into the surface of the metal workpiece to form a nitriding and carburizing compound diffusion layer. The nitriding and carburizing compound has extremely high hardness, resulting in a high surface hardness of the workpiece. Moreover, carbon atoms can also form alloy cementite with strong carbide-forming elements (such as Cr, W, Mo, V, etc.) in the workpiece, increasing the hardness of the metal diffusion layer and helping to maintain the hardness gradient of the workpiece.

[0056] According to some specific embodiments of the present invention, the nitriding and carbonizing time is 1 hour to 30 hours. For example, the time can be 1 hour, 5 hours, 10 hours, 15 hours, 20 hours, 30 hours, etc. By limiting the nitriding and carbonizing time within the above range, nitrogen and carbon can be simultaneously diffused into the surface of the metal workpiece to form a nitriding and carbonaceous compound diffusion layer. The nitriding and carbonaceous compounds have extremely high hardness, resulting in a high surface hardness of the workpiece. Moreover, carbon atoms can also form alloy cementite with strong carbide-forming elements (such as Cr, W, Mo, V, etc.) in the workpiece, which also increases the hardness of the metal diffusion layer and helps maintain the hardness gradient of the workpiece.

[0057] According to some specific embodiments of the present invention, the vacuum degree of the nitriding and carbonizing process is 10 Pa to 400 Pa. For example, it can be 10 Pa, 50 Pa, 100 Pa, 200 Pa, 400 Pa, etc. By limiting the vacuum degree of the nitriding and carbonizing process to the above range, on the one hand, the oxygen content during the nitriding and carbonizing process can be effectively reduced, thus reducing the oxidation reaction on the workpiece surface. On the other hand, the plasma density can be increased, accelerating the nitriding and carbonizing process, allowing nitrogen and carbon to penetrate more uniformly into the workpiece, thereby obtaining a uniform diffusion layer. This is beneficial to the diffusion and strengthening effect.

[0058] According to some specific embodiments of the present invention, the temperature of the second tempering is not lower than the temperature of the carbonitriding process, that is, the temperature of the carbonitriding process generally does not exceed the temperature of the second tempering process. When the temperature of the carbonitriding process does not exceed the temperature of the second tempering process, the tempering process provides sufficient microstructure preparation for the carbonitriding process, and the microstructure transformation does not occur significantly during the carbonitriding process. Therefore, it is possible to achieve high surface hardness in the obtained metal workpiece while maintaining a hardness gradient.

[0059] According to the heat treatment process of the above embodiments of the present invention, the metal workpiece is first subjected to carburizing treatment. During the carburizing process, active carbon atoms are absorbed by the surface of the metal workpiece and dissolve into the austenite in the surface layer of the workpiece, thereby increasing the carbon content in the austenite and enabling the workpiece surface to obtain higher hardness and wear resistance, thus improving its service life and performance. The metal workpiece is then subjected to a first tempering treatment. During the tempering process after carburizing, the uniform diffusion of surface carbon atoms is promoted. At the same time, carbon atoms and alloying elements in the metal workpiece can precipitate in the form of carbides, reducing the carbon concentration gradient inside the workpiece, making the internal structure of the metal workpiece more uniform and stable, which is beneficial for reducing internal stress and brittleness, and improving the toughness of the workpiece. During the quenching process, due to the very fast cooling rate, the austenite in the metal workpiece cannot transform into stable ferrite and can instead transform into martensite, further improving the hardness and strength of the metal workpiece. During the second tempering process, more time and temperature conditions are provided, allowing the metal to relax residual stress through internal localized plastic deformation or localized relaxation processes. Furthermore, the retained austenite in the metal workpiece is distributed in a thin film at the grain boundaries during the second tempering. When the martensitic lath cracks formed during the second tempering propagate to the grain boundaries and encounter the retained austenite, the crack tips undergo plastic deformation, which helps to prevent further crack propagation and thus improves the material's toughness. In the nitriding and carburizing process, nitrogen and carbon are simultaneously diffused into the surface of the metal workpiece, forming a nitriding and carburizing compound diffusion layer. Nitrogen and carburizing compounds have extremely high hardness, resulting in a high surface hardness for the workpiece. Moreover, carbon atoms can also form alloy cementite with strong carbide-forming elements (such as Cr, W, Mo, V, etc.) in the workpiece, increasing the hardness of the diffusion layer and also helping to maintain the hardness gradient of the workpiece. Therefore, the metal workpiece obtained using the processing technology provided in this application has high surface hardness while maintaining a hardness gradient.

[0060] The present disclosure will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0061] Example 1

[0062] The metal workpiece used in Example 1 is made of 18Cr2Ni4WA material.

[0063] 1) Carburize the metal workpiece to obtain the first metal workpiece: Place the metal workpiece made of 18Cr2Ni4WA in a carburizing furnace for carburizing treatment. The carburizing process is gas carburizing, the carburizing temperature is 920℃, and the carburizing time is 3.5h.

[0064] 2) The first metal workpiece obtained in 1) is subjected to a first tempering treatment to obtain a second metal workpiece. The first tempering treatment process is to first hold at 680℃ for 3 hours, and then hold at 680℃ for 3 hours to obtain the second metal workpiece.

[0065] 3) The second metal workpiece obtained in 2) is subjected to quenching treatment, wherein the quenching temperature is 800℃ and the quenching time is 3.5h, to obtain the third metal workpiece.

[0066] 4) The third metal workpiece obtained in 3) is subjected to a second tempering treatment. The temperature of the second tempering is 180℃ and the time of the second tempering is 3h, to obtain the fourth metal workpiece.

[0067] 5) After the fourth metal workpiece obtained in 4) is coarsely ground and finely ground with 800#~2000# sandpaper, it is polished to a mirror finish with a surface roughness of less than 0.08μm. It is then ultrasonically cleaned with acetone and anhydrous ethanol in sequence. The workpiece is then placed in the vacuum chamber of the magnetic field-assisted hollow cathode ion source diffusion enhancement device. The vacuum pump is turned on to evacuate the vacuum chamber to a vacuum (10Pa). After maintaining the vacuum for 15 minutes, the vacuum pump is turned off and inert gas is introduced to stabilize the equipment pressure at the first stage pressure (90000Pa). Then, the inert gas is stopped. The upper and lower auxiliary heating zones are turned on and the heating temperature is set to the first stage temperature (300℃). Heating begins, and the equipment is allowed to reach the second stage temperature (150℃). The vacuum pump is then turned on and nitrogen, hydrogen, and methane are introduced in a ratio (95:285:5) to bring the equipment pressure to the second stage pressure (40Pa). The process temperature is then set to 400℃. Turn on the cathode disk bias power supply and the active screen bias power supply, and set their frequencies (20kHz). Set the second-stage cathode disk bias voltage (550V) and the second-stage cathode disk duty cycle (30%); set the second-stage active screen bias voltage (550V) and the second-stage active screen duty cycle (30%). Continue heating to ensure stable glow discharge within the equipment; wait for the equipment temperature to reach the third-stage temperature (250℃), then continue introducing nitrogen, hydrogen, and methane in a ratio of 95:285:5 to bring the equipment pressure to the third-stage pressure (200Pa). Set the third-stage cathode disk bias voltage (650V) and the third-stage cathode disk duty cycle (50%); set the third-stage active screen bias voltage (650V) and the third-stage active screen duty cycle (50%). Once the temperature inside the equipment reaches the fourth stage temperature (300℃), continue to introduce nitrogen, hydrogen, and methane in a ratio of 95:285:5 to bring the equipment pressure to the fourth stage pressure (300Pa). Set the fourth stage cathode disk bias voltage (700V) and the fourth stage cathode disk duty cycle (72%); set the fourth stage active screen bias voltage (700V) and the fourth stage active screen duty cycle (72%). After the equipment reaches the process temperature (380℃), maintain this temperature for 3 hours. After the maintenance period, turn off the cathode disk bias power supply and the active screen bias power supply, turn off the upper and lower auxiliary heating, and stop heating. Turn off the vacuum pump, stop introducing nitrogen, hydrogen, and methane, and start introducing inert gas until the equipment pressure reaches the fifth stage pressure (90000Pa), then stop introducing inert gas. Turn on the upper and lower cooling fans to begin cooling. When the temperature inside the equipment reaches the sixth stage temperature (50°C), turn off the upper and lower cooling fans and remove the workpiece.

[0068] Example 2

[0069] The metal workpiece used in Example 2 is made of 20Cr2Ni4A.

[0070] The operation methods and process parameters of steps 1), 2) and 3) are the same as those in Example 1.

[0071] 4) The third metal workpiece obtained in 3) is subjected to a second tempering treatment. The temperature of the second tempering is 400℃ and the time of the second tempering is 8h, to obtain the fourth metal workpiece.

[0072] 5) After rough and fine grinding with 800# to 2000# sandpaper, the fourth metal workpiece obtained in step 4) is polished to a mirror finish with a surface roughness of less than 0.08 μm. It is then ultrasonically cleaned sequentially with acetone and anhydrous ethanol. The workpiece is then placed in the vacuum chamber of the magnetic field-assisted hollow cathode ion source diffusion enhancement device. The vacuum pump is turned on to evacuate the chamber to a vacuum level of 5 Pa, which is maintained for 15 minutes before being turned off. Inert gas is introduced to stabilize the equipment pressure at the first stage pressure (90000 Pa), at which point the inert gas supply is stopped. The upper and lower auxiliary heating zones are then turned on, and the heating temperature is set to the first stage temperature (320℃). Heating begins, and the equipment is allowed to reach the second stage temperature (150℃). The vacuum pump is then turned on, and nitrogen, hydrogen, and methane are introduced in a ratio of 95:285:5 to bring the equipment pressure to the second stage pressure (30 Pa). The process temperature is then set to 420℃. Turn on the cathode disk bias power supply and the active screen bias power supply, and set their frequencies (20kHz). Set the second-stage cathode disk bias voltage (550V) and the second-stage cathode disk duty cycle (30%); set the second-stage active screen bias voltage (550V) and the second-stage active screen duty cycle (30%). Continue heating to ensure stable glow discharge within the equipment; wait for the equipment temperature to reach the third-stage temperature (250℃), then continue introducing nitrogen, hydrogen, and methane in a ratio of 95:285:5 to bring the equipment pressure to the third-stage pressure (150Pa). Set the third-stage cathode disk bias voltage (650V) and the third-stage cathode disk duty cycle (50%); set the third-stage active screen bias voltage (650V) and the third-stage active screen duty cycle (50%). Once the temperature inside the equipment reaches the fourth stage temperature (300℃), continue to introduce nitrogen, hydrogen, and methane in a ratio of 95:285:5 to bring the equipment pressure to the fourth stage pressure (300Pa). Set the fourth stage cathode disk bias voltage (700V) and the fourth stage cathode disk duty cycle (72%); set the fourth stage active screen bias voltage (700V) and the fourth stage active screen duty cycle (72%). After the equipment reaches the process temperature (380℃), maintain this temperature for 3 hours. After the maintenance period, turn off the cathode disk bias power supply and the active screen bias power supply, turn off the upper and lower auxiliary heating, and stop heating. Turn off the vacuum pump, stop introducing nitrogen, hydrogen, and methane, and start introducing inert gas until the equipment pressure reaches the fifth stage pressure (90000Pa), then stop introducing inert gas. Turn on the upper and lower cooling fans to begin cooling. When the temperature inside the equipment reaches the sixth stage temperature (50°C), turn off the upper and lower cooling fans, remove the workpiece, and obtain the finished metal workpiece.

[0073] Comparative Example 1

[0074] The metal workpiece used in Comparative Example 1 was made of 18Cr2Ni4WA material.

[0075] The metal workpiece was heat-treated and used as a blank control; no further operations were performed.

[0076] Comparative Example 2

[0077] The metal workpiece used in Comparative Example 2 was made of 18Cr2Ni4WA material.

[0078] Steps 4) and 5) in Example 1 are deleted, and the rest is the same as in Example 1.

[0079] Comparative Example 3

[0080] The metal workpiece used in Comparative Example 3 was made of 20Cr2Ni4A.

[0081] The metal workpiece was heat-treated and used as a blank control; no further operations were performed.

[0082] Comparative Example 4

[0083] The metal workpiece used in Comparative Example 4 was made of 20Cr2Ni4A.

[0084] Steps 4) and 5) in Example 1 are deleted, and the rest is the same as in Example 2.

[0085] The processing techniques of Examples 3-12 and Comparative Examples 5-6 are the same as those of Example 1, except for some different process parameters (see Table 1).

[0086] The processing parameters of the finished metal workpieces obtained in Examples 1-12 and Comparative Examples 1-2 of this application are shown in Table 1.

[0087]

[0088] " / " indicates no

[0089] Testing and Analysis

[0090] Under the same conditions, the finished metal workpieces obtained in Examples 1-10 and Comparative Examples 1-6 were subjected to surface microhardness tests and hardness gradient tests, respectively. The specific calculation methods are as follows:

[0091] Surface microhardness test:

[0092] 1. The hardness tester shall comply with the requirements of GB / T 4340.2, and the specified test force shall be applied within the required test force range. The indenter shall be a diamond cone with a square base and comply with the requirements of GB / T 4340.2.

[0093] 2. The surface of the sample should be flat and smooth, and free of oxide scale and foreign contaminants. The thickness of the sample or test layer should be at least 1.5 times the diagonal length of the indentation.

[0094] 3. The test is generally conducted at room temperature between 10℃ and 35℃. The test platform should be clean and free of other contaminants. The specimen should be placed securely on a rigid test platform to ensure that the specimen does not shift during the test.

[0095] 4. The indenter contacts the sample surface and applies the test force perpendicular to the test surface. There should be no impact or vibration during the application of force until the test force reaches the specified value. For micro Vickers hardness testing, the application of force should not exceed 10 seconds and the indenter descent speed should be between 15 μm / s and 70 μm / s.

[0096] 5. The test force holding time is 10s to 15s. The distance from any indentation to the edge of the specimen should be at least 2.5 times the length of the indentation diagonal. The distance between two adjacent indentations should be at least 3 times the length of the indentation diagonal. On a plane, the difference between the lengths of the two diagonals of the indentation should not exceed 5% of the average length of the diagonals.

[0097] 6. Measure the lengths of the two diagonals of the indentation and calculate the Vickers hardness value using the arithmetic mean according to Table 2 of GB / T 4340.2-2009.

[0098] Figure 2 The images show a comparison of the surface microhardness of the finished metal workpieces obtained in Example 1, Comparative Example 1, and Comparative Example 2 of this application. From the images, it can be seen that the hardness of Example 1 is 902 HV. 0.1 Comparative Example 1 has a hardness of 316 HV. 0.1 Comparative Example 2 has a hardness of 555 HV. 0.1 Compared with the comparative example, the surface hardness of Example 1 was significantly improved.

[0099] Figure 4 The images show a comparison of the surface microhardness of the finished metal workpieces obtained in Examples 2, 3, and 4 of this application. From the images, it can be seen that the hardness of Example 2 is 873 HV. 0.1 Comparative Example 3 has a hardness of 287 HV. 0.1 Comparative Example 4 has a hardness of 632 HV. 0.1 Compared with the comparative example, the surface hardness of Example 2 was significantly improved.

[0100] Hardness gradient test:

[0101] 1. The indenter contacts the sample surface and applies the test force perpendicular to the test surface. There should be no impact or vibration during the application of force until the test force reaches the specified value. For micro Vickers hardness testing, the application of force should not exceed 10 seconds and the indenter descent speed should be between 15 μm / s and 70 μm / s.

[0102] 2. The test force holding time is 10s to 15s. The distance from any indentation to the edge of the specimen should be at least 2.5 times the length of the indentation diagonal. The distance between two adjacent indentations should be at least 3 times the length of the indentation diagonal. On a plane, the difference between the lengths of the two diagonals of the indentation should not exceed 5% of the average length of the diagonals.

[0103] 3. Measure the lengths of the two diagonals of the indentation and calculate the Vickers hardness value using the arithmetic mean according to Table 2 of GB / T 4340.2-2009.

[0104] 4. The hardness gradient of the cross-section is measured with adjacent test points spaced 25 μm apart, for a total of 20 test points. All test points are located on the same straight line perpendicular to the surface. The test load is 0.1 kgf.

[0105] Figure 3 The graph shows a comparison of the hardness gradient curves of the finished metal workpieces obtained in Example 1, Comparative Example 1, and Comparative Example 2 of this application. It can be seen from the graph that the hardness gradient of Example 1 is stable at 535 HV. 0.1 Comparative Example 1 shows a hardness gradient that is stable at 335 HV. 0.1 Comparative Example 2 shows a hardness gradient that stabilizes at 550 HV. 0.1 .

[0106] Figure 5 The graph shows a comparison of the hardness gradient curves of the finished metal workpieces obtained in Examples 2, 3, and 4 of this application. From the graph, it can be seen that the hardness gradient of Example 2 is stable at 520 HV. 0.1 Comparative Example 3 shows that the hardness gradient is stable at 300 HV. 0.1 Comparative Example 4 shows a hardness gradient that stabilizes at 555 HV. 0.1 .

[0107] The calculation results are shown in Table 2.

[0108] Table 2

[0109] Example 1 912 535 Example 2 905 524 Example 3 909 535 Example 4 860 541 Example 5 922 530 Example 6 919 532 Example 7 926 491 Example 8 931 495 Example 9 914 537 Example 10 835 548 Example 11 780 538 Example 12 925 497 Comparative Example 1 316 335 Comparative Example 2 555 550 Comparative Example 3 287 300 Comparative Example 4 632 555 Comparative Example 5 730 290 Comparative Example 6 281 275

[0110] As shown in Table 2, compared with Comparative Examples 1-6, the surface hardness of the finished metal workpieces in Examples 1-12 was significantly improved. Furthermore, since theoretically, the hardness gradient of a carburized and quenched workpiece after carbonitriding treatment should not exceed that of the carburized and quenched workpiece, the hardness gradient of the finished metal workpieces in Comparative Examples 2 and 4 is better than that of the finished metal workpieces in Examples 1-12. The relatively poor surface hardness and hardness gradient of the samples in Examples 2, 9-10, and 12 are mainly due to their carbonitriding temperature exceeding their second tempering temperature. This demonstrates that a good strengthening effect is achieved when the carbonitriding temperature does not exceed the second tempering temperature.

[0111] In Example 6, both the second tempering and nitriding temperatures were relatively high, resulting in a slightly lower hardness gradient stability value. In Example 2, the nitriding temperature exceeded the second tempering temperature, causing a decrease in surface hardness. However, the lowest of the nitriding and second tempering temperatures in Example 2 was still lower than either of the temperatures in Example 6. Therefore, the hardness gradient stability of Example 2 after the decrease was still slightly higher than that of Example 6.

[0112] In Example 10, the second tempering and nitrocarburizing temperatures are both very low. The highest temperature among the second tempering and nitrocarburizing temperatures is also lower than the highest temperature in other examples. Therefore, its hardness gradient stability is the greatest. The second tempering temperature is lower than the nitrocarburizing temperature, resulting in a poor strengthening effect of nitrocarburizing on surface hardness. Compared with Example 4, its hardness gradient stability is also slightly lower.

[0113] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," "some implementations," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0114] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A process for machining a metal workpiece, characterized in that, include: The metal workpiece is carburized to obtain the first metal workpiece. The carburizing temperature is 900℃-950℃; The first metal workpiece is subjected to a first tempering treatment to obtain a second metal workpiece; the temperature of the first tempering is 600℃-700℃. The second metal workpiece is quenched to obtain the third metal workpiece; the quenching temperature is 700℃-900℃. The third metal workpiece is subjected to a second tempering treatment to obtain a fourth metal workpiece; the temperature of the second tempering is 150℃-460℃. The fourth metal workpiece is subjected to nitrocarburizing treatment to obtain the finished metal workpiece; the temperature of nitrocarburizing is 150℃-460℃. The temperature of the second tempering is not lower than the temperature of the nitriding and carbonizing process.

2. The process of claim 1, wherein, After the third metal workpiece undergoes a second tempering treatment to obtain the fourth metal workpiece, and before the fourth metal workpiece undergoes ion co-diffusion treatment to obtain the strengthened metal workpiece, the process further includes grinding, polishing, and cleaning the fourth metal workpiece.

3. The process according to claim 1 or 2, characterized in that, The material of the metal workpiece includes at least one of low-carbon steel and low-carbon alloy steel. And / or, the carburizing process includes at least one of gas carburizing, vacuum carburizing, and plasma carburizing.

4. The processing technology according to claim 1 or 2, characterized in that, The carburizing time is 1 hour to 30 hours.

5. The processing technology according to claim 1 or 2, characterized in that, The first tempering time is 2-8 hours.

6. The processing technology according to claim 1 or 2, characterized in that, The quenching time is 3-4 hours.

7. The processing technology according to claim 1 or 2, characterized in that, The second tempering time is 2-8 hours.

8. The processing technology according to claim 1 or 2, characterized in that, The surface roughness of the fourth metal workpiece is less than 0.08 μm.

9. The processing technology according to claim 1 or 2, characterized in that, The nitrogen-carbon co-infiltration time is 1h-30h; And / or, the vacuum degree of the nitrocarburizing is 10Pa-400Pa.

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