Method for controlling dimensional stability of high-alloy carburizing steel gear

Abstract

The invention relates to a method for controlling the dimensional stability of a high-alloy carburizing steel gear, and belongs to the field of surface treatment heat treatment. The gear test piece is subjected to carburizing treatment and heated to 930-950 DEG C, and the depth of a carburized layer is controlled to be 1.25-1.55 mm; quenching treatment is conducted, the quenching temperature ranges from 850 DEG C to 880 DEG C, oil quenching is conducted, and the oil temperature is controlled to be 80 DEG C; and after cleaning is completed, subzero treatment is rapidly conducted, the subzero treatment cooling rate is controlled to be smaller than or equal to 5 DEG C / min, the subzero treatment temperature is 120 DEG C below zero, the subzero treatment time is 4-6 h, then the temperature is slowly increased to the room temperature with the heating rate controlled to be 2-10 DEG C / min, and tempering treatment is conducted. The size stability of the high-alloy carburizing steel gear can be controlled, and the hardness, the abrasion resistance and the size stability are improved. The method has the advantages of simplicity in operation, no damage to workpieces, no pollution and cost saving.

Description

Technical Field

[0001] The invention belongs to the technical field of surface treatment and heat treatment, and in particular relates to a method for controlling the dimensional stability of a high-alloy carburizing steel gear. Background Art

[0002] The spindle gear material 18Cr2Ni4W is a high-quality high-alloy carburizing steel, which is widely used in the manufacture of key component gears in the manufacturing field. Compared with the application of mold steel in gears, high-alloy steel has better performance due to the addition of alloy elements. Since traditional cold treatment is to study the dimensional stability of high-alloy steel through dry ice, alcohol and other methods, the improvement of part dimensional stability is limited.

[0003] After traditional heat treatment, the material always has problems of incomplete structural transformation (metastable phase) or high residual stress, which directly results in low service life and poor dimensional stability of parts. The microstructure of the gear after quenching is retained austenite and martensite. Too much retained austenite affects the dimensional stability of the gear.

[0004] Therefore, inventing a method for controlling the stability of high alloy carburizing steel gears is an urgent problem to be solved. Summary of the invention

[0005] The invention provides a method for controlling the dimensional stability of a high-alloy carburizing steel gear, and the technical problem to be solved is: controlling the stability of the high-alloy carburizing steel gear.

[0006] In order to solve the above technical problems, the present invention provides a method for controlling the dimensional stability of high alloy carburizing steel gears, which is characterized by: nitriding, quenching, deep cryogenic treatment and low temperature tempering are performed on the gears in sequence to control the dimensional stability of the carburizing steel gears.

[0007] Preferably, the gear material is 18Cr2Ni4W high alloy carburizing steel.

[0008] Preferably, the carburizing is performed by atmosphere carburizing, the carburizing temperature is controlled at 930-950° C., and the depth of the carburized layer is controlled at 1.25-1.55 mm.

[0009] Preferably, the flatness requirement of the finished gear part is ≤0.014mm, leaving a machining allowance, and the flatness requirement after heat treatment is ≤0.35mm.

[0010] Preferably, during the quenching treatment, the quenching temperature is 850-880°C, and oil cooling is used. The increase in the quenching oil temperature increases the fluidity of the oil, making the temperature difference of various parts of the parts more consistent during cooling, the cooling is more uniform, and the quenching deformation can be appropriately reduced.

[0011] Preferably, during the quenching treatment, the oil temperature is controlled at 50-90°C.

[0012] Preferably, the carburized layer hardness is required to be 79-82.5HRA, the depth is 1.6-2.1mm, and the core hardness is 35-41HRC.

[0013] Preferably, the flatness of the gear after carburizing and quenching is controlled to be ≤0.35 mm, and deep cryogenic treatment is performed after completion.

[0014] Preferably, the cryogenic treatment is performed by placing the sample in a cryogenic device, introducing liquid nitrogen as a cooling medium, and slowly cooling the sample temperature to -120°C.

[0015] Preferably, the cryogenic treatment parameters are as follows:

[0016] (1) The cooling rate of cryogenic treatment is controlled within the range of ≤5℃ / min;

[0017] (2) The cryogenic treatment temperature is -110 to -130°C;

[0018] (3) The cryogenic treatment holding time is 4h-6h;

[0019] (4) Then slowly raise the temperature to room temperature at a heating rate within the range of 2-10°C / min, and perform low-temperature tempering.

[0020] Beneficial effects: In order to reduce the residual internal stress of materials and parts and improve the dimensional stability of parts, the present invention adds a cryogenic treatment method after quenching to control the cooling rate of the cryogenic treatment, and uses liquid nitrogen as the cooling medium to stabilize the precision parts, achieving good improvement effects.

[0021] The carbon content on the gear surface is increased by carburizing technology to form carbides, and the content of residual austenite is reduced by cryogenic treatment, thereby improving the dimensional stability, strength, toughness and wear resistance of the gear. This technology is easy to operate, does not damage the workpiece, is pollution-free, low-cost and highly efficient. Cryogenic treatment is to reduce the temperature of the material or part to a certain low temperature environment (≤-100℃), and promote the further transformation of the material microstructure or relaxation of residual stress through low temperature, thereby improving the performance of the material or part, and extending the service life and comprehensive mechanical properties of the gear. It solves the problem of restricting the dimensional stability of parts and components, releases residual stress and stabilizes the organization through cryogenic treatment, improves the dimensional stability of parts and components, reduces processing deformation, and improves the product qualification rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Spindle gear schematic

[0023] Figure 2 It is a time-temperature curve diagram of the process of the present invention. DETAILED DESCRIPTION

[0024] 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.

[0025] The invention proposes a method for controlling the dimensional stability of high alloy carburizing steel gears, which sequentially performs nitriding, quenching, cryogenic treatment and low temperature tempering on semi-finished gears to control the dimensional stability of carburizing steel gears. The gear material is 18Cr2Ni4W high alloy carburizing steel.

[0026] Preferably, the 18Cr2Ni4W high alloy carburizing steel is carburized by atmosphere carburizing, the carburizing temperature is controlled at 930-950℃, the carburizing layer depth is controlled at 1.25-1.55mm, the carburizing layer hardness is required to be 79-82.5HRA, the depth is 1.6-2.1mm, and the core hardness is 35-41HRC. This gear is a precision structural part, the flatness of the finished part is required to be ≤0.014mm, the machining margin is reserved, and the flatness after heat treatment is required to be ≤0.35mm. Due to the large size of the gear structure, the internal cavity structure, and the overall thin-walled complex structure.

[0027] Furthermore, the quenching treatment is carried out at a temperature of 850-880℃, and oil cooling is used. Generally, the oil temperature is 50-90℃. The upper limit of the oil temperature is used for cooling, and the oil temperature is controlled at about 80℃. The increase of the quenching oil temperature increases the fluidity of the oil, so that when cooling, the temperature difference of each part of the parts is more consistent, the cooling is more uniform, and the quenching deformation can be appropriately reduced. The flatness of the gear after carburizing and quenching is controlled to ≤0.35mm, and deep cryogenic treatment is carried out after completion.

[0028] Furthermore, after cleaning, a cryogenic treatment is quickly performed: the sample is placed in a cryogenic device, and after liquid nitrogen cooling medium is introduced, the sample temperature is slowly cooled to -120°C.

[0029] The cooling rate of the cryogenic treatment is controlled within the range of ≤5°C / min, the cryogenic treatment temperature is -110 to -130°C, preferably -120°C; the cryogenic treatment insulation time is 4h-6h; and then the temperature is slowly raised to room temperature at a heating rate controlled within the range of 2-10°C / min.

[0030] Furthermore, after the temperature is raised to room temperature, low-temperature tempering treatment is performed, and the temperature is controlled at 200° C. for tempering once.

[0031] Example:

[0032] 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;

[0033] Carburize the gears, heat to 930℃ and keep warm for about 15h, so that the surface depth of the carburized layer and the surface hardness meet the requirements;

[0034] The gear specimen is quenched by heating it to 850℃ and keeping it warm for 5-6 hours, and then oil quenched by vertical hanging clamping. The oil temperature is controlled at 80℃, which helps to ensure the uniformity of quenching and make it austenitized.

[0035] Use clean water and detergent to remove the oil stains on the gear surface, scrub it again with alcohol, and quickly perform deep freezing treatment after drying;

[0036] Put the gear specimen into a cryogenic device, introduce liquid nitrogen to slowly reduce the specimen temperature from room temperature to -120°C, and then keep it warm for 4 hours. The cooling rate is controlled within the range of ≤5°C / min, and the heating rate is controlled within the range of 2-10°C / min to slowly return to room temperature. The cooling rate should not be too fast, which may easily cause brittle cracking of the workpiece.

[0037] The gears were immediately tempered by heating to 200°C for 2 hours and then air-cooling to room temperature.

[0038] As a preferred embodiment of the above invention, the spindle gear material is 18Cr2Ni4W, which is a high alloy steel. After quenching, the residual austenite content is high, resulting in increased residual stress and easy deformation. Cryogenic treatment is an extension of quenching treatment. Through cryogenic treatment, the residual austenite inside the part is further transformed into martensite structure. The flatness of the gear after heat treatment changes from the original 0.5mm to about 0.3mm, and the flatness is increased by 0.2mm, thereby ensuring the uniformity of the internal structure of the part and greatly helping to stabilize the size. Therefore, adding cryogenic treatment after quenching can effectively promote organizational transformation and stabilize the size.

[0039] This technology can control the dimensional stability of gears, improve the toughness of the carburized layer, and extend the service life of gears. It can eliminate high-temperature tempering after carburizing, control the content of residual austenite in the carburized layer, and select the appropriate cryogenic temperature according to the composition of the material. It provides a reference for the control performance of precision parts in cryogenic treatment. Cryogenic treatment is simple to operate, pollution-free, and cost-saving. The appropriate cryogenic temperature helps to improve the mechanical properties and comprehensive properties of the material.

[0040] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for controlling the dimensional stability of high alloy carburizing steel gears, characterized in that: The gears are subjected to nitriding, quenching, cryogenic treatment and low-temperature tempering in sequence to control the dimensional stability of the carburized steel gears.

2. A method for controlling dimensional stability of high alloy carburizing steel gears according to claim 1, characterized in that: The gear material is 18Cr2Ni4W high alloy carburizing steel.

3. A method for controlling dimensional stability of high alloy carburizing steel gears according to claim 1, characterized in that: Carburizing adopts atmosphere carburizing, the carburizing temperature is controlled at 930-950℃, and the depth of carburizing layer is controlled at 1.25-1.55mm.

4. A method for controlling dimensional stability of high alloy carburizing steel gears according to claim 1, characterized in that: The flatness requirement for the finished gear part is ≤0.014mm, leaving a machining allowance, and the flatness requirement after heat treatment is ≤0.35mm.

5. The method for controlling the dimensional stability of high alloy carburizing steel gears according to claim 1, characterized in that: During the quenching treatment, the quenching temperature is 850-880℃, and oil cooling is used. The increase in the quenching oil temperature increases the fluidity of the oil, making the temperature difference of various parts of the parts more consistent during cooling, the cooling is more uniform, and the quenching deformation can be appropriately reduced.

6. A method for controlling dimensional stability of high alloy carburizing steel gears according to claim 5, characterized in that: During the quenching process, the oil temperature is controlled at 50-90°C.

7. A method for controlling dimensional stability of high alloy carburizing steel gears according to claim 3, characterized in that: The carburized layer hardness is required to be 79-82.5HRA, the depth is 1.6-2.1mm, and the core hardness is 35-41HRC.

8. The method for controlling the dimensional stability of high alloy carburizing steel gears according to claim 1, characterized in that: The flatness of the gear is controlled to ≤0.35mm after carburizing and quenching, and deep cryogenic treatment is performed after completion.

9. The method for controlling the dimensional stability of high alloy carburizing steel gears according to claim 1, characterized in that: Cryogenic treatment: Place the sample in a cryogenic device, introduce liquid nitrogen cooling medium, and slowly cool the sample temperature to -120°C.

10. The method for controlling the dimensional stability of high alloy carburizing steel gears according to claim 1, characterized in that: The cryogenic treatment steps are as follows: (1) The cooling rate of cryogenic treatment is controlled within the range of ≤5℃ / min; (2) The cryogenic treatment temperature is -110 to -130°C; (3) The cryogenic treatment holding time is 4h-6h; (4) Then slowly raise the temperature to room temperature at a heating rate within the range of 2-10°C / min, and perform low-temperature tempering.

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