Method for improving comprehensive performance of main shaft gear

Abstract

The invention relates to a method for improving the comprehensive performance of a main shaft gear, which adopts the treatment process of cleaning, preheating, carburizing, high-temperature tempering, quenching preheating, quenching, subzero treatment, low-temperature tempering and gear grinding, so that not only can the depth of a carburized layer be accurately controlled, but also the use performance of a carburized part can be ensured. Wherein the preheating treatment before carburizing can refine grains, obtain a uniform metallographic structure and reduce thermal distortion of parts, the effect of controlling the size stability of the gear is achieved, then the toughness of a carburized layer is improved, and the service life of the gear is prolonged. And then high-temperature tempering after carburization can promote further uniform diffusion of carbon elements on the surface layer, the structure is balanced, and the internal stress of gear parts is reduced. And the preheating treatment before quenching can prevent the part from cracking in the subsequent quenching process. And a proper subzero treatment temperature gradient is selected according to material components, so that the content of retained austenite in a carburized layer is controlled, and the mechanical property and the comprehensive property of the material are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of gears, and in particular relates to a method for improving the comprehensive performance of a main shaft gear, in particular to a method for improving the comprehensive performance of a main shaft gear of a transmission box. Background Art

[0002] The transmission box spindle gear is an important part of the transmission system of the transmission box. It not only transmits motion but also torque during the transmission process. Therefore, it is very important to study the technology to improve the comprehensive performance of the transmission box spindle gear. The spindle gear material 18Cr2Ni4W is a high-quality alloy carburizing steel. Compared with the application of mold steel in gears, alloy steel has better performance due to the addition of alloy elements and is more widely used in the transmission box field. A large number of related studies have shown that the spindle gear needs to be comprehensively processed to ensure its dimensional stability and surface hardness, thereby improving its comprehensive performance.

[0003] The traditional comprehensive performance treatment method for the transmission box main shaft gear is: carburizing → quenching → Tempering. During the carburizing process, the depth of the carburized layer should be controlled at 1.25-1.55mm, and the hardness of the carburized layer on the tooth surface is required to be 56-62HRC, and the hardness of the core is 35-41HRC. However, when the depth of the carburized layer is greater than 1mm, it is difficult to accurately control the depth of the carburized layer, resulting in uneven surface hardness of the transmission box main shaft gear, thereby affecting the performance of the gear. The transmission box main shaft gear is a precision structural part with a large overall size and a cavity structure inside. It is very easy to deform during the quenching process, affecting the dimensional accuracy of the gear and ultimately affecting the performance of the transmission box. Summary of the invention

[0004] The present invention provides a method for improving the comprehensive performance of a main shaft gear, which solves the problems that the depth of the carburized layer of a transmission box component gear is difficult to accurately control and the dimensional stability is difficult to ensure due to traditional heat treatment, and improves the comprehensive performance of an 18Cr2Ni4W alloy carburized steel transmission box main shaft gear.

[0005] In order to solve the above technical problems, the present invention provides a method for improving the comprehensive performance of the main shaft gear of the transmission box, which is characterized by a processing process of cleaning → preheating → carburizing → high temperature tempering → quenching preheating → quenching → deep cold treatment → low temperature tempering → gear grinding.

[0006] Specifically, the process includes the following steps: cleaning the gear surface, and then performing preheating treatment before carburizing, with the preheating temperature being 800℃±20℃; performing carburizing treatment after the preheating treatment, with the carbon potential fraction being 0.9~1.1Cp and the temperature being 920℃±20℃; then performing high-temperature tempering at a temperature of 610℃±20℃; the quenching preheating temperature being 500℃±20℃, the quenching temperature being 800℃±20℃, using oil quenching, controlling the oil temperature at 50℃~90℃, controlling the cooling rate of deep cold treatment at a range of ≤5℃ / min, and finally returning the gear temperature to room temperature, and then performing tempering treatment, with the tempering temperature being 200℃±20℃.

[0007] Furthermore, before carburizing, the parts of the gear that do not need to be carburized need to be copper-plated for protection, and the thickness of the copper layer is 0.03 to 0.05 mm.

[0008] Furthermore, the heating rate of preheating before carburizing is gradient controlled. First, the furnace temperature is quickly raised from room temperature to 600°C, and then the gear workpiece is placed in it. The heating rate is 100°C / hour, the temperature is raised to 800±20°C, and then it is kept warm for 1 hour.

[0009] Furthermore, the heating rate of high temperature tempering is gradient controlled. First, the furnace temperature is quickly raised from room temperature to 500°C, and then the gear workpiece is placed in it. The heating rate is 100°C / hour, the temperature is raised to 610±20°C, and then it is kept warm for 3.5 hours.

[0010] Furthermore, the furnace temperature is first rapidly raised from room temperature to 400°C, and then the gear workpiece is placed therein, with a heating rate of 100°C / hour, the temperature is raised to 500±20°C, and the temperature is kept for 2 hours.

[0011] Furthermore, the quenching treatment has a heating rate of 100°C / hour, from 500±20°C to 800±20°C, and is kept warm for 3 hours, followed by oil cooling, the oil bath temperature is 50°C to 90°C, the oil bath cooling time is 0.5 hours, and then taken out for air cooling.

[0012] Furthermore, the cryogenic treatment process is as follows: the first cryogenic treatment temperature is -80°C ± 10°C, and the time is 0.5 hour; and then the second cryogenic treatment is performed at a temperature of -180°C ± 10°C, and the time is 2 hours.

[0013] Beneficial effects: The present invention adopts the processing technology of cleaning → preheating → carburizing → high temperature tempering → quenching preheating → quenching → cryogenic treatment → low temperature tempering → gear grinding, which can not only accurately control the depth of the carburized layer, but also ensure the performance of the parts after carburizing. The preheating treatment before carburizing can refine the grains, obtain a uniform metallographic structure, and can also reduce the thermal distortion of the parts, thereby achieving the function of controlling the dimensional stability of the gear, and then improve the toughness of the carburized layer and extend the service life of the gear. Then the high temperature tempering after carburizing can promote the further uniform diffusion of the surface carbon elements, balance the structure, and reduce the internal stress of the gear parts. The preheating treatment before quenching can prevent the parts from cracking during subsequent quenching. According to the material composition, a suitable cryogenic treatment temperature gradient is selected to control the content of residual austenite in the carburized layer, thereby improving the mechanical properties and comprehensive properties of the material.

[0014] The invention can accurately control the depth of the carburized layer of the 18Cr2Ni4W alloy carburized steel, and can ensure the dimensional stability of the gear, improve its hardness and wear resistance, and also has the advantages of simple operation, no damage to the workpiece, no pollution, low cost, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A flow chart of a comprehensive process for the main shaft gear of an 18Cr2Ni4W transmission box provided by an example of the present invention;

[0016] Figure 2 A time-temperature curve diagram of the comprehensive process of the main shaft gear of the 18Cr2Ni4W transmission box provided by an example of the present invention;

[0017] Figure 3 This is a comparison chart of the surface hardness of the gear before and after the comprehensive process treatment of the present invention.

[0018] Figure 4 This is a comparison chart of the gear size changes before and after the comprehensive process treatment of the present invention.

[0019] Figure 5 This is a comparison diagram of the gear flatness before and after the comprehensive process treatment of the present invention.

[0020] Figure 6 (1) and (2) are respectively the comparison diagrams of the microstructure of the carburized layer on the gear tooth surface before and after the comprehensive process treatment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below.

[0022] The present invention proposes a method for improving the comprehensive performance of the main shaft gear, and the specific steps are as follows:

[0023] (1) Cleaning the 18Cr2Ni4W alloy steel gear workpiece;

[0024] The gear surface is cleaned with a cleaning agent, wherein the cleaning agent is a mixed solution of n-butanol and xylene with a mixing ratio of 7:3.

[0025] (2) Gear workpieces are copper-plated for protection, and the copper-plated areas are other parts except the teeth.

[0026] That is, before carburizing, the parts of the gear that do not need to be carburized need to be copper-plated for protection, and the thickness of the copper layer is 0.03 to 0.05 mm.

[0027] (3) Preheating treatment of gear workpiece before carburizing: preheating temperature is 800℃±20℃, keep warm for 1 hour.

[0028] Specifically, the heating rate of preheating before carburizing is gradient controlled. First, the furnace temperature is quickly raised from room temperature to 600°C, and then the gear workpiece is placed in the furnace. The heating rate is 100°C / hour, the temperature is raised to 800°C, and then kept at this temperature for 1 hour. Preheating before carburizing can improve the dimensional stability of the gear during carburizing.

[0029] (4) Carburizing treatment of gear workpieces.

[0030] In the carburizing treatment, the carbon potential fraction is 0.9 to 1.1 Cp, the temperature is 920°C ± 20°C, and the carburizing time is 10 hours. The carburizing treatment is carried out in a controlled atmosphere multi-purpose furnace.

[0031] The controllable atmosphere is a mixed gas mainly composed of methane. Compared with other controllable atmospheres, methane has the characteristic of low cost.

[0032] (5) High temperature tempering treatment of gear workpieces.

[0033] The high temperature tempering treatment temperature is 610℃±20℃, kept at this temperature for 3.5 hours, then cooled to below 200℃ with the furnace and air-cooled.

[0034] Specifically, the heating rate of high temperature tempering is gradient controlled. First, the furnace temperature is quickly raised from room temperature to 500°C, and then the gear workpiece is placed in the furnace. The heating rate is 100°C / hour, the temperature is raised to 610°C, and then the temperature is kept for 3.5 hours. High temperature tempering after carburizing can improve the morphology of carbides on the surface of the gear and reduce the internal stress of the gear.

[0035] (6) Preheating treatment of gear workpieces before quenching.

[0036] The preheating treatment temperature before quenching is 500°C±20°C, and the temperature is kept for 2 hours.

[0037] The heating rate of preheating before quenching is gradient controlled. First, the furnace temperature is quickly raised from room temperature to 400°C, and then the gear workpiece is placed in the furnace. The heating rate is 100°C / hour, and the temperature is raised to 500±20°C. The temperature is kept for 2 hours. Preheating before quenching can solve the problem of dimensional instability caused by residual stress and improve the distribution of the hardened layer, and finally obtain the best microstructure of the gear surface.

[0038] (7) Quenching treatment of gear workpieces. The quenching temperature is 800℃±20℃, the temperature is kept for 3 hours, the oil bath temperature is 50℃~90℃, the oil bath cooling time is 0.5 hours, and then take out and air cool.

[0039] Specifically, the quenching treatment temperature rise rate is 100℃ / hour, from 500±20℃ to 800±20℃, kept at this temperature for 3 hours, then oil cooled, the oil bath temperature is 50℃~90℃, the oil bath cooling time is 0.5 hours, then taken out and air cooled. In this way, high carbon martensite can be formed on the gear tooth surface, and low carbon martensite can be formed in the gear core.

[0040] (8) Deep cryogenic treatment of gear workpieces.

[0041] The transmission box main shaft gear cooled to room temperature is cleaned and air-dried, and then placed in a deep freezing box. The temperature of the deep freezing treatment is a gradient change, and a deep freezing test with a temperature gradient is carried out at a constant rate of 4°C / min. The specific deep freezing treatment process is: the first deep freezing treatment temperature is -80°C±10°C, and the time is 0.5 hour; then the second deep freezing treatment is carried out at a temperature of -180°C±10°C, and the time is 2 hours. Finally, the gear is returned to room temperature with the box.

[0042] In the cryogenic treatment process, the residual austenite in the material is further transformed into martensite, and a large number of fine and dispersed carbides are precipitated inside the structure, which promotes the homogenization and densification of the alloy structure and can effectively increase the depth of the hardened layer, thereby improving the dimensional stability of the gear and the hardness of the tooth surface.

[0043] (9) Low temperature tempering treatment of gear workpiece: The low temperature tempering temperature is 200℃±20℃, keep warm for 3 hours, and then cool to room temperature with the furnace.

[0044] Specifically, the heating rate of low temperature tempering is 100°C / hour, the temperature is raised to 200°C, kept at this temperature for 3 hours, and then air-cooled to room temperature. Low temperature tempering can reduce the brittleness of the gear material and maintain its high hardness, which can further improve its wear resistance.

[0045] (10) Gear grinding of gear workpieces.

[0046] Gear grinding is performed on a gear grinding machine, and the final tooth surface roughness value is no more than 0.8.

[0047] Gear grinding is performed on a gear grinding machine. After carburizing and quenching, the gear will be deformed and its accuracy will drop by 2 levels. The purpose of gear grinding is to correct the deformation and further improve the accuracy of the gear and the roughness of the tooth surface, thereby improving the accuracy of gear transmission and ensuring the smooth operation of the gear.

[0048] Example:

[0049] The carburized layer depth of a transmission box main shaft 18Cr2Ni4W gear part is controlled at 1.25-1.55mm, and the hardness of the carburized layer on the tooth surface is required to be 56-62HRC, and the hardness of the core is required to be 35-41HRC.

[0050] After the sample gear is machined into a semi-finished gear, the gear must be pre-treated before heat treatment, and the steel chips and burrs on the gear surface must be polished with sandpaper of No. 0 or above;

[0051] The gear surface was cleaned with a mixed solution of n-butanol and xylene (mixing ratio was 7:3) and then air-dried naturally.

[0052] The gear workpiece is copper-plated for protection except for the tooth part, and the thickness of the copper layer is 0.05mm.

[0053] Heat the vacuum furnace to 600°C, then place the gear workpiece in the vacuum furnace for preheating at a heating rate of 100°C / hour, heat to 800°C±20°C, and keep warm for 1 hour.

[0054] The preheated gear workpiece is placed in a controlled atmosphere carburizing furnace. The controlled atmosphere is a mixed gas mainly composed of methane to ensure the stability of the gear workpiece. The workpiece spacing is not less than 100mm to ensure sufficient atmosphere circulation.

[0055] Carburize the gear workpiece, heat it to 920℃±20℃, keep it warm for 10 hours, and the carbon potential fraction is 1.0Cp, so that the surface meets the carburized layer depth and surface hardness requirements; cool it to below 200℃ in the furnace and air cool it out of the furnace.

[0056] Heat the high temperature tempering furnace to 500℃, place the gear workpiece in the high temperature tempering furnace, heat it to 610℃±20℃ at a heating rate of 100℃ / hour, keep it warm for 3.5 hours, then cool it to below 200℃ and air cool it out of the furnace.

[0057] Heat the high-temperature tempering furnace to 400°C, place the gear workpiece in a vacuum furnace, heat at a heating rate of 100°C / hour, heat to 500°C±20°C, and keep warm for 2 hours.

[0058] The vacuum furnace continues to heat to 800℃±20℃, keep warm for 3 hours, oil-cooled quenching, the oil bath temperature is 50℃~90℃, the oil bath cooling time is 0.5 hour, and then taken out for air cooling.

[0059] Place the gear workpiece in a cryogenic box with a constant cooling rate of 4°C / min. The first cryogenic treatment temperature is -80°C±10°C for 0.5 hour, and the second cryogenic treatment temperature is -180°C±10°C for 2 hours. Finally, return the gear workpiece to room temperature along with the box.

[0060] Place the gear workpiece in a low-temperature tempering furnace with a tempering temperature of 200℃±20℃ for 3 hours, and then air-cool to room temperature.

[0061] The gear workpiece grinding process ensures that the final surface roughness value of the tooth surface is no greater than 0.8.

[0062] Final inspection.

[0063] After the comprehensive treatment method of this embodiment, the carbon layer depth of the tooth surface of the transmission box main shaft 18Cr2Ni4W gear part is 1.53mm, the core hardness is 38HRC, and the carburized surface hardness is 62HRC, which is a qualified product.

[0064] The technical solution of the present invention has the following advantages over the prior art:

[0065] (1) The comprehensive treatment process technology of the present invention adopts treatment processes such as preheating before carburizing, high temperature tempering after carburizing, preheating before quenching, gradient deep cold treatment, and gear grinding, which not only meets the requirements of the gear for the depth of the carburized layer, but also can accurately control the depth of the carburized layer. At the same time, it can also meet the performance requirements after carburizing and the requirements of the tooth surface roughness, so that the 18Cr2Ni4W transmission box main shaft gear meets the technical requirements of the tooth surface carburized layer depth of 1.25-1.55mm, the tooth surface carburized layer hardness of 56-62HRC, the core hardness of 35-41HRC, and the tooth surface roughness value not less than 0.8. It solves the process control problem of different carburized layer depths in different parts of the prior art, and the problem of low tooth surface precision caused by carburizing and quenching. The process technology of the present invention is reasonable, effectively and accurately controls the depth of the carburized layer, and improves the tooth surface processing accuracy, providing a process technology reference for the comprehensive performance treatment of parts with the same material.

[0066] (2) Preheat treatment before carburizing can refine the grains, obtain uniform metallographic structure, and reduce the thermal deformation of parts, thus achieving the function of controlling the dimensional stability of gears. Then high-temperature tempering after carburizing can promote further uniform diffusion of carbon elements in the surface layer, balance the structure, and reduce the internal stress of gear parts. Preheat treatment before quenching can prevent parts from cracking during subsequent quenching. According to the material composition, the appropriate cryogenic treatment temperature gradient is selected to control the content of residual austenite in the carburized layer, thereby improving the mechanical properties and comprehensive properties of the material.

Claims

1. A method for improving the comprehensive performance of a transmission box main shaft gear, characterized in that: The processing technology includes cleaning → preheating → carburizing → high temperature tempering → quenching preheating → quenching → deep cryogenic treatment → low temperature tempering → gear grinding.

2. A method for improving the comprehensive performance of a transmission box main shaft gear according to claim 1, characterized in that: The gear is an 18Cr2Ni4W alloy steel gear.

3. A method for improving the comprehensive performance of a transmission box main shaft gear according to claim 1, characterized in that: The specific steps include: Clean the gear surface and then perform preheating treatment before carburizing at a temperature of 800℃±20℃; perform carburizing treatment after preheating treatment with a carbon potential fraction of 0.9~1.1Cp and a temperature of 920℃±20℃; then perform high-temperature tempering at a temperature of 610℃±20℃; the quenching preheating temperature is 500℃±20℃, the quenching temperature is 800℃±20℃, use oil quenching, control the oil temperature at 50℃~90℃, control the cooling rate of deep cold treatment at a range of ≤5℃ / min, and finally return the gear to room temperature before performing tempering treatment at a temperature of 200℃±20℃.

4. A method for improving the comprehensive performance of a transmission box main shaft gear according to claim 3, characterized in that: The gear surface is cleaned with a cleaning agent, wherein the cleaning agent is a mixed solution of n-butanol and xylene with a mixing ratio of 7:

3.

5. A method for improving the comprehensive performance of the main shaft gear of a transmission box according to claim 3, characterized in that: Before carburizing, the parts of the gear that do not need to be carburized need to be copper-plated for protection, and the thickness of the copper layer is 0.03 to 0.05 mm.

6. A method for improving the comprehensive performance of a transmission box main shaft gear according to claim 3, characterized in that: The heating rate of preheating before carburizing is gradient controlled. First, the furnace temperature is quickly raised from room temperature to 600°C, and then the gear workpiece is placed in it. The heating rate is 100°C / hour, the temperature is raised to 800±20°C, and then it is kept warm for 1 hour.

7. A method for improving the comprehensive performance of a transmission box main shaft gear according to claim 3, characterized in that: The heating rate of high temperature tempering is gradient controlled. First, the furnace temperature is quickly raised from room temperature to 500°C, and then the gear workpiece is placed in it. The heating rate is 100°C / hour, the temperature is raised to 610±20°C, and then it is kept warm for 3.5 hours.

8. The method for improving the comprehensive performance of the main shaft gear of a transmission box according to claim 3, characterized in that: First, the furnace temperature is quickly raised from room temperature to 400°C, and then the gear workpiece is placed in the furnace. The heating rate is 100°C / hour, and the temperature is raised to 500±20°C, and kept at this temperature for 2 hours.

9. A method for improving the comprehensive performance of a transmission box main shaft gear according to claim 3, characterized in that: The quenching treatment heating rate is 100℃ / hour, from 500±20℃ to 800±20℃, kept warm for 3 hours, then oil-cooled, the oil bath temperature is 50℃~90℃, the oil bath cooling time is 0.5 hour, and then taken out for air cooling.

10. A method for improving the comprehensive performance of a transmission box main shaft gear according to claim 3, characterized in that: The process of cryogenic treatment is as follows: the first cryogenic treatment temperature is -80℃±10℃, and the time is 0.5 hour; then the second cryogenic treatment is carried out, the temperature is -180℃±10℃, and the time is 2 hours.

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