Carbonitriding salt bath composite process and carbonitriding clamp

Abstract

The invention provides a carbonitriding salt bath composite technology and a carbonitriding clamp. The carbonitriding salt bath composite technology comprises the following steps that S1, pre-cleaning is conducted, specifically, a workpiece is cleaned and dried; and S2, preheating is conducted, specifically, the workpiece is heated to 300-350 DEG C to be preheated. And S3, carbonitriding, wherein carbonitriding is conducted on the workpiece through a salt bath. And S4, quenching is conducted, specifically, the workpiece is immersed in molten salt to be rapidly cooled, and bainite quenching is conducted. And S5, tempering. And S6, post-cleaning. The workpiece processed by the heat treatment process disclosed by the invention has the advantages of good toughness, strong impact resistance, good fatigue resistance, high surface hardness, good wear resistance and corrosion resistance and long service life.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat treatment, and particularly relates to a carbonitriding salt bath composite process. Background Art

[0002] In recent years, China has accelerated the construction of a clean and low-carbon energy system, and the proportion of clean energy and non-fossil energy consumption has gradually increased. As a clean energy source, wind power is playing an increasingly important role in China's energy structure adjustment. With the progress of technology, wind turbines have evolved from 10 MW to 18 MW, with blades up to 126 meters long and hub heights of 170 meters. The structure of wind turbines is relatively complex, consisting of a wind wheel (blades, hub), main bearings, wind turbine main shafts, gearboxes, generators, etc. Among them, the hub, main shaft, gearbox, generator, etc. constitute the transmission system of the wind turbine generator set. The wind turbine main shaft plays a role in connecting the blade hub and the gearbox and transmitting kinetic energy in the wind turbine. As the main load-bearing component in the wind turbine, the wind turbine main shaft needs to bear continuously changing axial and radial loads, requires high load-bearing capacity, continuous operation, and is difficult and costly to replace. It needs to have high hardness and good wear resistance. It serves in a harsh environment for a long time and is easily exposed to corrosive seawater, so it is required to have good corrosion resistance.

[0003] Therefore, the above problems need to be solved urgently. Summary of the Invention

[0004] Object of the Invention: In order to overcome the above deficiencies, the present invention provides a carbonitriding salt bath composite process for heat-treating workpieces, including carbonitriding, salt bath quenching, and tempering to form a mixed structure of lower bainite and a small amount of martensite in the workpiece, so that the workpiece has good toughness and mechanical strength, improves the impact resistance and fatigue resistance of the workpiece, enhances the surface hardness of the workpiece, enhances wear resistance, and extends the service life of the workpiece.

[0005] Technical Solution: In order to achieve the above object, the present invention provides a carbonitriding salt bath composite process, including the following steps: S1: Pre-cleaning, heating the workpiece to 60°C, cleaning the workpiece with a cleaning agent to remove stains on the surface of the workpiece, and after cleaning, the workpiece should be dried to remove surface moisture.

[0006] S2: Preheating, heating the workpiece to 300 - 350°C for preheating, and the preheating speed is 40 - 50°C / min.

[0007] S3: Carbonitriding, using a salt bath to perform carbonitriding on the workpiece.

[0008] S4: Quenching, immersing the workpiece in molten salt for rapid cooling to perform bainite quenching.

[0009] S5: Tempering. Put the workpiece into a tempering furnace, heat the workpiece to 200 °C, hold for 2 h, and then cool it naturally.

[0010] S6: Post-cleaning. Heat the workpiece to 60 °C, and use a cleaning agent to clean the surface of the workpiece to remove the residual stains on the surface of the workpiece.

[0011] The heat treatment process disclosed by the present invention is applied to the main shaft of a large wind turbine made of 42CrMo4 high-strength alloy steel. In order to remove the residues on the surface of the workpiece, avoid polluting the furnace during the subsequent heat treatment process, and affect the carbonitriding and quenching effects, it is necessary to clean the surface of the workpiece to improve the heat treatment effect and ensure the quality and performance of the workpiece. After the workpiece is cleaned, in order to reduce the deformation of the workpiece, the workpiece should be put into a heating furnace and heated to 300 - 350 °C for preheating. The preheating speed is 40 - 50 °C / min. Preheating can reduce stress and reduce the deformation of the workpiece. Preheating can enable the workpiece to reach the carburizing temperature faster and shorten the carbonitriding cycle. The preheated workpiece is subjected to carbonitriding treatment. Select a suitable molten salt, heat the molten salt to a molten state, place the preheated workpiece into the molten salt, and select urea and ammonium chloride together as the carburizing and nitriding agents. Then, heat the workpiece after carbonitriding to the austenitizing temperature, and then immerse the workpiece into the molten salt for rapid cooling for bainite quenching. Carbonitriding can significantly improve the surface hardness of the workpiece and enhance wear resistance. Bainite quenching enables the core of the workpiece to have good toughness, improves the impact resistance and fatigue resistance of the workpiece, and extends the service life of the workpiece. Finally, temper the workpiece to eliminate the residual stress of the workpiece, improve the toughness and tissue stability of the material, and extend the service life of the workpiece.

[0012] Further, in the above carbonitriding salt bath composite process, in S3, it includes: S31: Nitrocarburizing treatment of the workpiece in a low-temperature salt bath. The carbonitriding temperature is 500 - 600 °C, and the time is 300 - 360 min; S32: Carbonitriding treatment of the workpiece in a medium-temperature salt bath. The carbonitriding temperature is 600 - 700 °C, and the time is 40 - 60 min.

[0013] First, perform carbonitriding at a lower temperature and maintain it for a longer time to ensure that carbon and nitrogen can penetrate evenly into the surface of the workpiece and ensure the penetration depth of carbon and nitrogen. Then, move the workpiece to a molten salt at a higher temperature for carbonitriding. Performing carbonitriding at a higher temperature can form a high-hardness surface layer on the surface of the workpiece. By performing low-temperature and medium-temperature carbonitriding treatments step by step, the deformation of the workpiece is reduced while ensuring the penetration depth of carbon and nitrogen and the surface hardness.

[0014] Further, in the above nitrocarburizing salt bath composite process, the S32 step further includes adding a titanium accelerating agent during the nitrocarburizing process to form a high-quality carburized layer. The titanium accelerating agent can promote the infiltration of nitrogen atoms and carbon atoms, and can form compounds rich in nitrogen, carbon and titanium on the surface of the workpiece, improving the hardness and wear resistance of the workpiece, and significantly improving the thermal fatigue resistance of the workpiece.

[0015] Further, in the above nitrocarburizing salt bath composite process, the S4 includes: S41: First, slowly heat the workpiece to 850 - 900 °C, hold for 45 - 90 min, and then place the workpiece in an isothermal molten salt at 280 °C - 300 °C for pre-cooling for 30 s. During the quenching process, pre-cool the workpiece first to reduce workpiece deformation, rapidly reduce the workpiece temperature, reduce the generation of pearlite, and prepare for subsequent bainite transformation.

[0016] S42: Then place the workpiece in an isothermal molten salt at 180 °C - 200 °C for rapid cooling, hold for 30 min, to obtain a duplex structure of lower bainite, a small amount of martensite and retained austenite. Strictly control the heating rate and cooling rate of the workpiece to reduce workpiece deformation.

[0017] Further, in the above nitrocarburizing salt bath composite process, the S4 includes: S43: Natural aging. Naturally cool the quenched workpiece in the air.

[0018] Further, in the above nitrocarburizing salt bath composite process, the S4 includes: S44: Place the workpiece in liquid nitrogen and cool it to below - 100 °C, hold for 8 - 10 h to transform the retained austenite into martensite, and then slowly warm the workpiece back to room temperature. Transform the retained austenite into martensite. At the same time, there is more retained austenite in the surface area. After transformation into martensite, it further improves the surface hardness and wear resistance of the workpiece and increases the workpiece strength. Placing the workpiece in liquid nitrogen can release the workpiece stress and reduce workpiece deformation.

[0019] Further, in the above nitrocarburizing salt bath composite process, continuously stir the molten salt in the S4 to reduce the temperature difference in the salt bath, avoid local overheating or overcooling, ensure uniform surface treatment of the workpiece, and improve the treatment efficiency.

[0020] Further, in the above nitrocarburizing salt bath composite process, in the nitrocarburizing salt bath composite process, the workpiece is heat-treated individually or in batches, and contact between workpieces and between workpieces and the furnace wall is prohibited to prevent local overheating of the workpiece, ensure uniform heating of the workpiece, avoid deformation, and the contact parts of the workpiece are prone to adhesion, affecting the nitrocarburizing effect.

[0021] Further, in the above nitrocarburizing salt bath composite process, the S6 includes: S61: Dry the workpiece.

[0022] S62: After the workpiece is dried, the surface of the workpiece is oxidized to form an oxide film.

[0023] S63: After the workpiece is polished, it is oxidized again to form a multi-layer oxide film.

[0024] After the workpiece is subjected to bainite quenching and tempering, the surface of the workpiece is oxidized to improve the wear resistance, corrosion resistance and appearance quality of the workpiece. And the oxidation treatment is usually carried out at a lower temperature and will not affect the formed carbonitriding layer. The oxide film obtained after a single oxidation treatment is relatively thin. After the workpiece is oxidized, it is polished and then subjected to a secondary oxidation treatment to form a multi-layer oxide film, improving the overall corrosion resistance and wear resistance.

[0025] A carbonitriding fixture applied to the above carbonitriding salt bath composite process, comprising a bottom plate and a top plate. The bottom plate and the top plate are arranged in parallel, and the bottom plate and the top plate are connected by connecting columns. A clamping device is connected between the bottom plate and the top plate. The clamping device includes a first clamping block and a second clamping block. A driving plate is provided on one side of the bottom plate away from the top plate. The driving plate is respectively drivingly connected to the first clamping block and the second clamping block, and the driving plate drives the first clamping block and the second clamping block to alternately clamp the workpiece. A driving shaft sleeve is connected to one side of the driving plate away from the bottom plate, and the driving shaft sleeve is provided with a clamping groove. The driving shaft sleeve is connected to a driving device, and the driving device drives the driving shaft sleeve to reciprocate.

[0026] Further, in the above carbonitriding fixture, the driving plate is provided with a driving groove, the driving groove is arranged in a V shape, and the driving grooves are arranged in an array around the axis of the driving plate.

[0027] Further, in the above carbonitriding fixture, the first clamping blocks are arranged in an array around the axis of the driving plate. One end of the first clamping block close to the center of the driving plate is arc-shaped. The first clamping block is provided with a first sliding shaft, and both ends of the first sliding shaft are respectively slidably connected to through grooves provided on the bottom plate and the top plate. The first sliding shaft is slidably connected to the corner part of the driving groove. Both ends of the first clamping block are connected with first positioning shafts, and the first positioning shafts are respectively slidably connected to through grooves provided on the bottom plate and the top plate. The second clamping blocks are arranged in an array around the axis of the driving plate. One end of the second clamping block close to the center of the driving plate is arc-shaped. The second clamping block is provided with a second sliding shaft, and both ends of the second sliding shaft are respectively slidably connected to through grooves provided on the bottom plate and the top plate. The second sliding shaft is slidably connected to one end of the driving groove. Both ends of the second clamping block are connected with second positioning shafts, and the second positioning shafts are respectively slidably connected to through grooves provided on the bottom plate and the top plate.

[0028] During the heat treatment process, the workpiece is placed between the bottom plate and the top plate. The bottom of the workpiece is supported by the ejector pins provided on the bottom plate, and then the entire device and the workpiece are preheated. During the carbonitriding process, a rotating device is provided at the bottom of the carbonitriding furnace. Then, the drive shaft sleeve of the above fixture is clamped to the rotating device. The rotating device rotates reciprocally to drive the drive plate to rotate reciprocally. The first sliding shaft provided on the first clamping block and the second sliding shaft provided on the second clamping block slide along the drive groove. Due to the special V-shaped design of the drive groove, the first clamping block and the second clamping block alternately clamp the workpiece, enabling the surface of the workpiece to fully contact carbon atoms and nitrogen atoms. Moreover, the alternately moving first clamping block and second clamping block can fully stir the molten salt, making the distribution of nitrogen atoms and carbon atoms in the molten salt uniform, reducing the problem of uneven local temperature, facilitating heat transfer, avoiding insufficient carburized layer, ensuring a uniform carburized layer and consistent hardness, and ensuring surface quality. During the quenching or tempering stage, the workpiece and the fixture are quenched or tempered together. The drive device at the bottom of the furnace drives the drive plate to rotate reciprocally, agitating the cooling medium (molten salt), increasing the thermal conductivity. The intermittent and alternating contact between the workpiece and the first clamping block and the second clamping block can quickly dissipate the heat on the surface of the workpiece into the molten salt, reducing the fixed contact area between the workpiece and the fixture, ensuring rapid and uniform cooling of the workpiece, ensuring consistent tissue transformation, reducing part deformation, and ensuring the treatment effect. During the entire treatment process, the volume of the workpiece will change. According to the heat treatment temperature and different heat treatment processes, the rotation angle of the drive plate is adjusted to ensure that the first clamping block and the second clamping block are in reasonable positions, which can ensure that the workpiece is straightened. Moreover, the reciprocating movement distance of the first clamping block and the second clamping block should not be too large to avoid squeezing the workpiece by the first clamping block and the second clamping block, affecting the heat treatment effect and the quality of the workpiece.

[0029] As can be seen from the above technical solutions, the present invention has the following beneficial effects: ① For the carbonitriding salt bath composite process and the carbonitriding fixture of the present invention, preheating is carried out to reduce stress, reduce workpiece deformation, enable the workpiece to reach the carburizing temperature faster, and shorten the carbonitriding cycle.

[0030] ② For the carbonitriding salt bath composite process and the carbonitriding fixture of the present invention, during the carbonitriding process, carbonitriding is first carried out at a lower temperature and maintained for a longer time to ensure that carbon and nitrogen can uniformly penetrate into the surface of the workpiece and ensure the penetration depth of carbon and nitrogen. Then, the workpiece is moved to the molten salt at a higher temperature for carbonitriding. Performing carbonitriding at a higher temperature can form a high-hardness surface layer on the surface of the workpiece. By performing low-temperature and medium-temperature carbonitriding treatments step by step, while ensuring the penetration depth of carbon and nitrogen and the surface hardness, workpiece deformation is reduced.

[0031] ③ The carbonitriding salt bath composite process and carbonitriding fixture of the present invention, after carbonitriding, first austenitize the workpiece, and then quickly cool it in the molten salt for bainite quenching, which can form fine bainite structure, making the workpiece have good toughness and ductility. The surface hardness of the treated workpiece is high, the core toughness is good, and the mechanical properties are excellent.

[0032] ④ The carbonitriding salt bath composite process and carbonitriding fixture of the present invention use molten salt cooling during quenching, which can provide a uniform cooling environment, reduce the temperature gradient, and reduce deformation. During the quenching process, first pre-cool the workpiece to quickly reduce its temperature, reduce the generation of pearlite, and prepare for subsequent bainite transformation. Then transfer the workpiece to an isothermal molten salt at 180°C - 200°C for rapid cooling to further reduce the formation of pearlite and promote the transformation of austenite to bainite. Stepwise cooling can reduce stress generation and workpiece deformation.

[0033] ⑤ The carbonitriding salt bath composite process and carbonitriding fixture of the present invention cool the workpiece in liquid nitrogen to below -100°C to transform retained austenite into martensite. Since there is more retained austenite in the surface area, after transformation into martensite, it further improves the surface hardness and wear resistance of the workpiece and increases the strength of the workpiece. Placing the workpiece in liquid nitrogen can release the stress of the workpiece and reduce workpiece deformation.

[0034] ⑥ The carbonitriding salt bath composite process and carbonitriding fixture of the present invention alternately clamp the workpiece with the first clamping block and the second clamping block, enabling the surface of the workpiece to fully contact carbon atoms and nitrogen atoms. Moreover, the alternately operating first clamping block and second clamping block can fully stir the molten salt, making the distribution of nitrogen atoms and carbon atoms in the molten salt uniform, reducing the problem of uneven local temperature, facilitating heat transfer, avoiding insufficient carburized layer, ensuring uniform carburized layer and consistent hardness, and ensuring surface quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the process diagram of the carbonitriding salt bath composite process of the present invention; Figure 2 is the temperature curve diagram of the heat treatment process of the present invention; Figure 3 is the structural schematic diagram of the fixture of the present invention; Figure 4 is the bottom view of the fixture of the present invention.

[0036] In the figure: 1, bottom plate; 2, top plate; 3, connecting column; 4, first clamping block; 42, first sliding shaft; 43, first positioning shaft; 5, second clamping block; 52, second sliding shaft; 53, second positioning shaft; 6, driving plate; 61, driving groove; 7, driving shaft sleeve; 71, clamping groove; 61, driving groove. DETAILED DESCRIPTION OF THE INVENTION

[0037] Example 1 As Figure 1 shown, a carbonitriding salt bath composite process includes the following steps: S1: Pre-cleaning. Heat the workpiece to 60°C, clean the workpiece with a cleaning agent to remove stains on the workpiece surface, and after cleaning, dry the workpiece to remove surface moisture.

[0038] S2: Preheating. Heat the workpiece to 300 - 350°C for preheating, and the preheating speed is 40 - 50°C / min; S3: Carbonitriding. Perform carbonitriding on the workpiece using a salt bath; In S3, it includes: S31: Nitrocarburizing treatment of the workpiece in a low-temperature salt bath. The carbonitriding temperature is 500 - 600°C, and the time is 300 - 360 min.

[0039] S32: Carbonitriding treatment of the workpiece in a medium-temperature salt bath. The carbonitriding temperature is 600 - 700°C, and the time is 40 - 60 min.

[0040] Step S32 also includes adding a titanium accelerating agent during the carbonitriding treatment to form a high-quality infiltration layer.

[0041] S4: Quenching; Immerse the workpiece in molten salt for rapid cooling to perform bainite quenching; S4 includes: S41: First, slowly heat the workpiece to 850 - 900°C, hold for 45 - 90 min, place the workpiece in an isothermal molten salt at 280°C - 300°C for pre-cooling for 30 s, and continuously stir the molten salt.

[0042] S42: Then place the workpiece in an isothermal molten salt at 180°C - 200°C for rapid cooling, hold for 30 min, to obtain a complex structure of lower bainite, a small amount of martensite, and retained austenite.

[0043] S43: Naturally cool the quenched workpiece in the air.

[0044] S44: Cool the workpiece in liquid nitrogen to below -100°C, hold for 8 h - 10 h, transform the retained austenite into martensite, and then slowly warm the workpiece back to room temperature.

[0045] S5: Tempering; Put the workpiece into a tempering furnace, heat the workpiece to 200°C, hold for 2 h, and then cool naturally; S6: Post-cleaning; Heat the workpiece to 60°C, clean the workpiece surface with a cleaning agent to remove residual stains on the workpiece surface.

[0046] S6 includes: S61: Dry the workpiece; S62: After the workpiece is dried, an oxidation treatment is performed on the surface of the workpiece to form an oxide film.

[0047] S63: After the workpiece is polished, an oxidation treatment is performed again to form a multi-layer oxide film.

[0048] In the above carbonitriding salt bath composite process, the workpiece is heat-treated individually or in batches.

[0049] The titanium catalyst can promote the infiltration of nitrogen atoms and carbon atoms, and can form compounds rich in nitrogen, carbon and titanium on the surface of the workpiece, improving the hardness and wear resistance of the workpiece, and significantly improving the thermal fatigue resistance of the workpiece.

[0050] Transform the retained austenite into martensite. At the same time, there is more retained austenite in the surface area. After transformation into martensite, it further improves the hardness and wear resistance of the workpiece surface and increases the strength of the workpiece. Placing the workpiece in liquid nitrogen can release the stress of the workpiece and reduce the deformation of the workpiece.

[0051] Further, in the above carbonitriding salt bath composite process, in S4, reduce the temperature difference in the salt bath, avoid local overheating or overcooling, ensure uniform surface treatment of the workpiece, and improve the treatment efficiency.

[0052] Further, in the above carbonitriding salt bath composite process, in the carbonitriding salt bath composite process, the workpiece is heat-treated individually or in batches, and contact between workpieces and between the workpiece and the furnace wall is prohibited to prevent local overheating of the workpiece, ensure uniform heating of the workpiece, avoid deformation, and the contact parts of the workpiece are prone to adhesion, affecting the carbonitriding effect.

[0053] Further, in the above carbonitriding salt bath composite process, S6 includes: After the workpiece is subjected to bainite quenching and tempering, an oxidation treatment is performed on the surface of the workpiece to improve the wear resistance, corrosion resistance and appearance quality of the workpiece, and the oxidation treatment is usually carried out at a lower temperature and will not affect the already formed carbonitriding layer.

[0054] Further, in the above carbonitriding salt bath composite process, S6 includes: The oxide film obtained after a single oxidation treatment is relatively thin. After the workpiece is oxidized, it is polished and then subjected to a secondary oxidation treatment to form a multi-layer oxide film, improving the overall corrosion resistance and wear resistance.

[0055] The process disclosed by the present invention is applied to the main shaft of a large wind turbine made of 42CrMo4 high-strength alloy steel. In order to remove the residues on the surface of the workpiece and avoid polluting the furnace during the subsequent heat treatment process, which may affect the carbonitriding and quenching effects, the surface of the workpiece is cleaned. After the workpiece is cleaned, it is placed in a heating furnace and heated to 300 - 350 °C for preheating, and the preheating speed is 40 - 50 °C / min. The preheated workpiece is subjected to carbonitriding treatment. A suitable molten salt is selected and heated to the molten state. The preheated workpiece is placed into the molten salt, and urea and ammonium chloride are jointly selected as the carburizing and nitriding agents. During the carbonitriding process, the workpiece first undergoes carbonitriding at a lower temperature and is maintained for 300 - 360 min, and then the workpiece is moved to a molten salt at a higher temperature for carbonitriding and is maintained for 40 - 60 min to form a high-hardness surface layer. During the carbonitriding treatment process, a titanium accelerating agent is added to further improve the surface hardness, wear resistance, and corrosion resistance. Then the workpiece after carbonitriding is heated to the austenitizing temperature, and then the workpiece is immersed in the molten salt for bainite quenching. During the bainite quenching process, the workpiece is first slowly heated to 850 - 900 °C and held for 45 - 90 min for austenitization. Then the workpiece is placed into an isothermal molten salt at 280 °C - 300 °C for pre-cooling for 30 s. Then the workpiece is placed into an isothermal molten salt at 180 °C - 200 °C for rapid cooling and held for 30 min to obtain a duplex structure of lower bainite, a small amount of martensite, and retained austenite. After quenching, the workpiece is naturally cooled, and then placed into liquid nitrogen and cooled to below -100 °C and held for 8 h - 10 h to transform the retained austenite into martensite, and then the workpiece is slowly warmed back to room temperature. Then the workpiece is placed into a tempering furnace, the workpiece is heated to 200 °C and held for 2 h, and then naturally cooled. The workpiece is heated to 60 °C, and a cleaning agent is used to clean the surface of the workpiece to remove the stains remaining on the surface of the workpiece. The workpiece is dried, and the surface of the workpiece is subjected to oxidation treatment to form an oxide film. After the workpiece is polished, oxidation treatment is carried out again to form a multi-layer oxide film.

[0056] Comparative Example 1 Select the same materials as in Example 1 and perform heat treatment according to the traditional method, specifically including 1. Carbonitriding; 2. Oil immersion quenching; 3. Tempering. Other steps can adopt conventional conditions.

[0057] Relevant tests are carried out after the treatment, and the results are as follows: Surface hardness HRC Core hardness HRC Impact energy / J Flexural strength / Mpa Comparative example 58.7 42.3 13.6 1755.29 Example 1 63.4 44.2 20.3 1965.05 After the treatment of the present invention, the surface hardness and core hardness of the workpiece are higher, the impact resistance is better, and the bending performance is stronger.

[0058] As Figure 3-4A carbonitriding fixture shown is applied to the above carbonitriding salt bath composite process, and includes a bottom plate 1 and a top plate 2. The bottom plate 1 and the top plate 2 are arranged in parallel, and the bottom plate 1 and the top plate 2 are connected by a connecting column 3. A clamping device is connected between the bottom plate 1 and the top plate 2, and the clamping device includes a first clamping block 4 and a second clamping block 5. A driving plate 6 is provided on one side of the bottom plate 1 away from the top plate 2. The driving plate 6 is respectively drivingly connected to the first clamping block 4 and the second clamping block 5, and the driving plate 6 drives the first clamping block 4 and the second clamping block 5 to alternately clamp the workpiece. A driving shaft sleeve 7 is connected to one side of the driving plate 6 away from the bottom plate 1, and the driving shaft sleeve 7 is provided with a clamping groove 71. The driving shaft sleeve 7 is connected to a driving device, and the driving device drives the driving shaft sleeve 7 to reciprocally rotate. The driving plate 6 is provided with a driving groove 61, the driving groove 61 is arranged in a V shape, and the driving grooves 61 are arranged in an array around the axis of the driving plate 6.

[0059] The first clamping blocks 4 are arranged in an array around the axis of the driving plate 6. One end of the first clamping block 4 close to the center of the driving plate 6 is arc-shaped. A first sliding shaft 42 is arranged through the first clamping block 4. Both ends of the first sliding shaft 42 are respectively slidably connected to through grooves provided on the bottom plate 1 and the top plate 2. The first sliding shaft 42 is slidably connected to the corner part of the driving groove 61. Both ends of the first clamping block 4 are connected with first positioning shafts 43, and the first positioning shafts 43 are respectively slidably connected to through grooves provided on the bottom plate 1 and the top plate 2. The second clamping blocks 5 are arranged in an array around the axis of the driving plate 6. One end of the second clamping block 5 close to the center of the driving plate 6 is arc-shaped. A second sliding shaft 52 is arranged through the second clamping block 5. Both ends of the second sliding shaft 52 are respectively slidably connected to through grooves provided on the bottom plate 1 and the top plate 2. The second sliding shaft 52 is slidably connected to one end of the driving groove 61. Both ends of the second clamping block 5 are connected with second positioning shafts 53, and the second positioning shafts 53 are respectively slidably connected to through grooves provided on the bottom plate 1 and the top plate 2.

[0060] During the heat treatment process, the workpiece is placed between the bottom plate 1 and the top plate 2. The bottom of the workpiece is supported by the ejector pins provided on the bottom plate 1, and then the entire device and the workpiece are preheated. During the carbonitriding process, a rotating device is provided at the bottom of the carbonitriding furnace. Then, the drive shaft sleeve 7 of the above fixture is clamped to the rotating device. The rotating device reciprocally rotates to drive the drive plate 6 to reciprocally rotate. The first sliding shaft 42 provided on the first clamping block 4 and the second sliding shaft 52 provided on the second clamping block 5 slide along the drive groove 61. Due to the special V-shaped design of the drive groove 6, the first clamping block 4 and the second clamping block 5 alternately clamp the workpiece, enabling the surface of the workpiece to fully contact carbon atoms and nitrogen atoms. Moreover, the alternately operating first clamping block 4 and second clamping block 5 can fully stir the molten salt, making the distribution of nitrogen atoms and carbon atoms in the molten salt uniform. During the quenching or tempering stage, the workpiece and the fixture are quenched or tempered together. The drive device at the bottom of the furnace drives the drive plate 6 to reciprocally rotate, agitating the cooling medium (molten salt), and intermittently and alternately contacting the workpiece with the first clamping block 4 and the second clamping block 5, so as to quickly dissipate the heat on the surface of the workpiece into the molten salt and reduce the fixed contact area between the workpiece and the fixture. During the entire processing process, the volume of the workpiece will change. According to the heat treatment temperature and different heat treatment processes, the rotation angle of the drive plate 6 is adjusted to make the first clamping block 4 and the second clamping block 5 in a reasonable position, which can ensure that the workpiece is straightened. Moreover, the reciprocating movement distance of the first clamping block 4 and the second clamping block 5 should not be too large to avoid the first clamping block 4 and the second clamping block 5 squeezing the workpiece and affecting the heat treatment effect.

[0061] The above embodiments are exemplary, and their purpose is to illustrate the technical concept and characteristics of the present invention, so that those skilled in this field can understand the content of the present invention and implement it accordingly. However, the protection scope of the present invention cannot be limited thereby. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A carbonitriding salt bath composite process, characterized in that: It includes the following steps: S1: Pre-cleaning, heating the workpiece to 60°C, cleaning the workpiece with a cleaning agent to remove stains on the surface of the workpiece, and drying the workpiece after cleaning to remove surface moisture; S2: Preheating, heating the workpiece to 300 - 350°C for preheating, and the preheating speed is 40 - 50°C / min; S3: Carbonitriding, carbonitriding the workpiece using a salt bath; S4: Quenching, immersing the workpiece in molten salt for rapid cooling to perform bainite quenching; S5: Tempering, putting the workpiece into a tempering furnace, heating the workpiece to 200°C, holding for 2h, and then naturally cooling; S6: Post-cleaning, heating the workpiece to 60°C, cleaning the surface of the workpiece with a cleaning agent to remove residual stains on the surface of the workpiece.

2. The carbonitriding salt bath composite process according to claim 1, wherein: In S3, it includes: S31: Low-temperature salt bath nitrocarburizing treatment of the workpiece, the carbonitriding temperature is 500 - 600°C, and the time is 300 - 360min; S32: Medium-temperature salt bath carbonitriding treatment of the workpiece, the carbonitriding temperature is 600 - 700°C, and the time is 40 - 60min.

3. The carbonitriding salt bath composite process according to claim 2, characterized in that: The S32 step also includes adding a titanium accelerating agent during the carbonitriding treatment to form a high-quality infiltration layer.

4. The carbonitriding salt bath composite process according to claim 1, characterized in that: S4 includes: S41: First, slowly heat the workpiece to 850 - 900°C, hold for 45 - 90min, place the workpiece in an isothermal molten salt at 280°C - 300°C for precooling for 30s; S42: Then place the workpiece in an isothermal molten salt at 180°C - 200°C for rapid cooling, hold for 30min, and obtain a complex phase structure of lower bainite, a small amount of martensite, and retained austenite.

5. The carbonitriding salt bath composite process according to claim 4, characterized in that: S4 includes: S43: Naturally cooling the quenched workpiece in the air.

6. The carbonitriding salt bath composite process according to claim 5, characterized in that: S4 includes: S44: Cooling the workpiece in liquid nitrogen to below -100°C, holding for 4h - 8h, and transforming the retained austenite into martensite.

7. The nitrocarburizing salt bath composite process according to claim 1, characterized in that: S6 includes: S61: Cleaning and drying the workpiece; S62: After drying the workpiece, performing an oxidation treatment on the surface of the workpiece to form an oxide film; S63: After polishing the workpiece, performing an oxidation treatment again to form a multi-layer oxide film.

8. A carbonitriding fixture, characterized in that: Applied to the nitrocarburizing salt bath composite process according to any one of claim 1, it includes a bottom plate (1) and a top plate (2), the bottom plate (1) and the top plate (2) are arranged in parallel, and the bottom plate (1) and the top plate (2) are connected by a connecting column (3); a clamping device is connected between the bottom plate (1) and the top plate (2), and the clamping device includes a first clamping block (4) and a second clamping block (5); a driving plate (6) is provided on one side of the bottom plate (1) away from the top plate (2), the driving plate (6) is respectively drivingly connected to the first clamping block (4) and the second clamping block (5), and the driving plate (6) drives the first clamping block (4) and the second clamping block (5) to alternately clamp the workpiece; a driving shaft sleeve (7) is connected to one side of the driving plate (6) away from the bottom plate (1), and the driving shaft sleeve (7) is provided with a card slot (71); the driving shaft sleeve (7) is connected to a driving device, and the driving device drives the driving shaft sleeve (7) to perform a reciprocating rotational motion.

9. The carbonitriding fixture according to claim 8, characterized in that: The driving board (6) is provided with a driving groove (61), the driving groove (61) is arranged in a V shape, and the driving grooves (61) are arranged in an array around the axis of the driving board (6).

10. The carbonitriding jig according to claim 9, characterized in that: The first clamping block (4) is arranged in an array around the axis of the driving board (6). One end of the first clamping block (4) close to the center of the driving board (6) is arc-shaped. A first sliding shaft (42) is arranged through the first clamping block (4). Two ends of the first sliding shaft (42) are respectively and slidably connected in through grooves provided on the bottom plate (1) and the top plate (2). The first sliding shaft (42) is slidably connected to the corner part of the driving groove (61). Two ends of the first clamping block (4) are connected with first positioning shafts (43), and the first positioning shafts (43) are respectively slidably connected in through grooves provided on the bottom plate (1) and the top plate (2). The second clamping block (5) is arranged in an array around the axis of the driving board (6). One end of the second clamping block (5) close to the center of the driving board (6) is arc-shaped. A second sliding shaft (52) is arranged through the second clamping block (5). Two ends of the second sliding shaft (52) are respectively and slidably connected in through grooves provided on the bottom plate (1) and the top plate (2). The second sliding shaft (52) is slidably connected to one end of the driving groove (61). Two ends of the second clamping block (5) are connected with second positioning shafts (53), and the second positioning shafts (53) are respectively slidably connected in through grooves provided on the bottom plate (1) and the top plate (2).

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