Heat treatment method for powder metallurgy high-speed steel gear
By combining tempering, stabilization, sandblasting, and nitriding processes, the problem of matching the core and surface hardness of powder metallurgy high-speed steel gears was solved, achieving high-quality hardness and wear resistance, and expanding its application in aero-engine transmission systems.
Patent Information
- Application Number
- CN202511184779.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-22
- Publication Date
- 2025-11-25
AI Technical Summary
Existing technologies cannot simultaneously meet the core hardness and surface hardness requirements of powder metallurgy high-speed steel gears. Conventional heat treatment processes are also unable to achieve a core hardness of 31-45 HRC and a surface hardness of ≥90 HR15 N.
The process employs a combination of quenching and tempering heat treatment, stabilization treatment, sandblasting treatment, and nitriding heat treatment. The quenching and tempering treatment achieves a core hardness of 31-45 HRC. The nitriding treatment forms a high-quality nitriding layer at 490-550℃ to improve surface hardness. The sandblasting treatment activates the material surface and enhances the adhesion between the nitriding layer and the substrate.
Effective control of the core hardness and surface hardness of powder metallurgy high-speed steel gears has been achieved, meeting the stringent performance requirements of aero-engine transmission systems and improving the stability and wear resistance of the material.
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Figure CN121006505A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of metal heat treatment technology, and in particular to a heat treatment method for powder metallurgy high-speed steel gears. Background Technology
[0002] Powder metallurgy high-speed steel is a new type of high-speed steel produced using powder metallurgy technology. Compared with traditional cast high-speed steel, it overcomes the shortcomings of macroscopic segregation of alloying elements and coarse carbides, exhibiting high bending strength and impact toughness, making it suitable for cold and hot operations under conditions of severe friction, impact, and vibration. Currently, third-generation powder metallurgy high-speed steel has been developed abroad and applied to transmission components such as camshafts, bearings, and turbine shafts. my country's powder metallurgy high-speed steel industry started late, developed slowly, has outdated equipment, and offers limited varieties and specifications, still lagging significantly behind foreign countries. Technical challenges in the preparation and processing of powder metallurgy high-speed steel restrict its application; currently, powder metallurgy high-speed steel is mainly used in cutting tools and precision punching tools.
[0003] The excellent bending strength and impact toughness of powder metallurgy high-speed steel are essential characteristics in the field of transmission gears. However, since the hardness of powder metallurgy steel after conventional heat treatment is approximately 55-60 HRC, it is not suitable for the performance requirements of most gears. By researching and controlling the material's properties through a reasonable heat treatment process, the core can achieve excellent toughness while the surface possesses good strength and wear resistance, thus expanding the material's application to the transmission system field. To apply powder metallurgy high-speed steel CPM 10V to advanced equipment manufacturing, a certain type of engine was designed to manufacture gears using this material, requiring a core hardness of 31-45 HRC and a surface hardness ≥90 HR15 N. Conventional existing heat treatment processes cannot simultaneously achieve the required core and surface hardness. Summary of the Invention
[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a heat treatment method for powder metallurgy high-speed steel gears that is simple in process and produces high-quality products.
[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A heat treatment method for powder metallurgy high-speed steel gears includes the following steps: S1. The powder metallurgy high-speed steel bar is subjected to quenching and tempering heat treatment to obtain a powder metallurgy high-speed steel bar with a core hardness of 31-45HRC; the microstructure of the powder metallurgy high-speed steel bar is transformed into martensitic microstructure and granular carbides. S2. Powder metallurgy high-speed steel bars are semi-finished to obtain semi-finished gear parts; S3. Stabilize the semi-finished gear parts to eliminate internal stress and processing stress and homogenize the martensitic structure. S4. The semi-finished gear parts to be nitrided are sandblasted to activate the material surface, remove the surface passivation film, and increase the surface roughness. S5. The semi-finished gear parts after sandblasting are subjected to nitriding heat treatment, which includes the following steps: The semi-finished gear parts were placed in an ammonia atmosphere and heated to 490–550°C and held at that temperature. During the heating process, the ammonia decomposition rate was 35–45%. S6. The semi-finished gear parts after nitriding heat treatment are precision machined to obtain powder metallurgy high-speed steel gears.
[0006] As a further improvement to the above technical solution: In step S1, the conditioning process includes the following steps: A1. Heat treatment of powder metallurgy high-speed steel at 980-1120℃ to transform the microstructure of powder metallurgy high-speed steel into austenitic microstructure. A2. Powder metallurgy high-speed steel is quenched in quenching oil at a temperature of 30-90℃ to transform the austenitic structure into quenched martensite and granular carbides. A3. The powder metallurgy high-speed steel is tempered at 600-700℃ to homogenize the martensitic structure. After quenching in the tempering process, it is tempered at 600-700℃ to cause the martensite to decompose and the carbides to precipitate, thereby adjusting the hardness to the range of 30-50 HRC required for conventional transmission components, meeting the core hardness requirements of conventional transmission components.
[0007] Preferably, the standard tempering temperature for powder metallurgy steel is generally 500-560℃, after which secondary hardening occurs, and the hardness can reach 60HRC. This invention uses tempering at 600-700℃, causing martensite decomposition and carbide precipitation, thereby controlling the hardness to the 30-50HRC range required for conventional transmission components. Furthermore, to fully eliminate abnormal microstructures such as residual austenite, preferably, 2-3 tempering cycles should be performed.
[0008] In step A1, the heat preservation treatment time is 90-210 minutes; In step A1, the heat preservation treatment time is 130-150 minutes.
[0009] To prevent cracking, tempering should be performed within 1 hour after quenching.
[0010] In step A3, the tempering process is performed 2-3 times.
[0011] In step S3, the stabilization treatment temperature is 500-600℃ and the time is 120-240 min.
[0012] In step S4, during the sandblasting process, corundum sand with a mesh size ≥ 80 is used as the sandblasting sand particles.
[0013] In step S5, the holding time for the nitriding heat treatment is 5-100 hours.
[0014] Preferably, the nitriding treatment adopts a two-stage nitriding process. The temperature of the first stage nitriding process is 520-550℃, the nitrogen potential is 0.45%-0.55%, and the time is 20-30h. The temperature of the second stage nitriding process is 520-550℃, the nitrogen potential is 0.25%-0.35%, and the time is 15-20h.
[0015] The powder metallurgical high-speed steel is CPM 10V or HOP 10V.
[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention discloses a heat treatment method for powder metallurgy high-speed steel gears, comprising quenching and tempering, stabilization, sandblasting, and nitriding. The stabilization treatment effectively eliminates residual stress, resulting in a more uniform microstructure and improved material stability, facilitating the smooth progress of nitriding and enhancing the bonding force between the nitrided layer and the substrate. The sandblasting treatment activates the nitrided surface, increasing the contact area between nitrogen atoms and the workpiece surface, further improving the uniformity of the nitrided surface. The nitriding treatment is carried out at a temperature of 490–550°C and an ammonia decomposition rate of 35–45%, which enables the formation of a high-quality nitrided layer, significantly improving the surface hardness, wear resistance, and corrosion resistance of the powder metallurgy high-speed steel, meeting the stringent requirements for material surface properties in the field of aero-engine transmission systems. Attached Figure Description
[0017] Figure 1 This is a surface microstructure diagram of powder metallurgy high-speed steel after nitriding heat treatment according to Embodiment 1 of the present invention. Detailed Implementation
[0018] The present invention will be further described in detail below. Unless otherwise specified, the instruments or materials used in the present invention are commercially available.
[0019] Example 1 The transmission gear of a certain type of engine is made of powder metallurgy high-speed steel CPM10V. The heat treatment requirements are: nitriding of the gear surface, with a surface hardness ≥90HR15N and a core hardness of 31-45HRC.
[0020] This embodiment describes a heat treatment method for powder metallurgy high-speed steel gears, the specific implementation steps of which include: S1. The powder metallurgy high-speed steel bar is subjected to quenching and tempering heat treatment to obtain the properties required for conventional transmission components by controlling the material microstructure, including the following steps: A1. Heat the powder metallurgy high-speed steel bar to 1100℃ and hold for 140 minutes to obtain a stable high-alloy austenitic structure, which helps to form a high-alloy martensite structure after quenching, thereby producing a secondary hardening effect by precipitating alloy carbides during tempering.
[0021] A2. The powder metallurgy high-speed steel bar is quenched and cooled in quenching oil at 50℃. The quenching and cooling method is oil cooling to obtain a high-hardness martensitic structure. In order to release the internal pressure of the material as soon as possible, tempering is performed after 40 minutes of oil cooling. The core hardness of the powder metallurgy high-speed steel bar is 31-45HRC and the surface hardness is ≥60HRC.
[0022] A3. The powder metallurgy high-speed steel bar is subjected to two tempering treatments, with the temperature needing to be reduced to room temperature between the two tempering treatments. The tempering temperature is 660℃, and the holding time is 210 minutes. After meeting the holding time requirements for both tempering treatments, the bar is air-cooled to room temperature. This invention uses tempering at a temperature of 500-700℃, which causes the martensite to decompose and the carbides to precipitate, thereby controlling the hardness to the range of 30-50 HRC required for conventional transmission components, meeting the core hardness requirements of conventional transmission components.
[0023] S2. According to the design requirements, the powder metallurgy high-speed steel bar is semi-finished to obtain the semi-finished gear parts.
[0024] S3. The semi-finished gear part is heated to 550℃ for stabilization treatment and held at that temperature for 180 minutes. After holding, it is cooled to room temperature. Nitrogen gas is introduced for protection during the heating and cooling process.
[0025] S4. The nitrided surface of the semi-finished gear parts is sandblasted. Corundum sand with a mesh size of 80 is used for sandblasting. The sandblasting pressure is 0.2MPa. After sandblasting, the nitrided surface has a uniform sandblasted color and no metallic luster.
[0026] S5, nitriding treatment B1. Place the semi-finished gear parts after sandblasting into a controlled atmosphere furnace. After sealing the furnace, perform a vacuum process to remove air and impurities from the furnace.
[0027] B2. Ammonia gas is introduced, and the furnace pressure is adjusted to 10 MPa. The furnace temperature is raised to 510℃ at a heating rate of 3℃ / min and held at that temperature. During the heating process, the ammonia decomposition rate is 35-45%. A two-stage nitriding process is adopted: the first stage nitriding process is carried out at a temperature of 510℃, a nitrogen potential of 0.5%, and a time of 35 hours; the second stage nitriding process is carried out at a temperature of 510℃, a nitrogen potential of 0.3%, and a holding time of 20 hours. The two-stage nitriding process and the change in nitrogen potential result in the formation of fine nitride structures on the surface of the semi-finished gear parts, achieving high hardness and excellent wear resistance.
[0028] B3. Stop the supply of ammonia gas, gradually reduce the pressure inside the furnace, and after the furnace temperature cools down to room temperature, remove the semi-finished gear parts to complete the nitriding treatment.
[0029] S6. The semi-finished gear parts after nitriding heat treatment are precision machined to obtain powder metallurgy high-speed steel gears.
[0030] Physicochemical testing of powder metallurgy high-speed steel gears: The microstructure consists of fine nitrides (martensite) + uniformly distributed carbides, and the microstructure is qualified (see...). Figure 1 In this embodiment, the effective hardened layer depth of the powder metallurgy steel is 0.45 mm (measured to a core hardness of +50 HV), the surface hardness is 92.5 HR15 N, the core hardness is 41.0 HRC, and the brittleness is grade I, which meets the technical requirements.
[0031] The powder metallurgical high-speed steel gears prepared have excellent wear resistance and fatigue resistance, as well as high toughness, high strength and impact resistance.
[0032] Comparative Example 1 This comparative example describes a heat treatment method for powder metallurgy high-speed steel gears. The transmission gears of a certain type of engine are made of powder metallurgy high-speed steel CPM10V. The materials and machining routes are largely the same as in Example 1, except that nitriding heat treatment and pre-nitriding sandblasting treatment are not performed. Specific implementation steps include: S1, Powder metallurgy high-speed steel bars undergo quenching and tempering heat treatment, including the following steps: A1. Heat the workpiece to 1100℃ and hold for 140 minutes to fully austenitize the microstructure of the powder metallurgy high-speed steel bar.
[0033] A2. The powder metallurgy high-speed steel bar is quenched and cooled in quenching oil at 50℃ using oil cooling to obtain a quenched martensitic structure. The core hardness of the powder metallurgy high-speed steel bar is 31-45 HRC and the surface hardness is ≥60 HRC.
[0034] A3. The workpiece is subjected to two tempering treatments. It needs to be returned to room temperature between the two tempering treatments. The tempering temperature is 660℃ and the holding time is 210min. After the tempering holding time is met, it is air-cooled to room temperature.
[0035] S2. According to the design requirements, the powder metallurgy high-speed steel bar is semi-finished to obtain the semi-finished gear parts.
[0036] S3. Heat the workpiece to 550℃ for stabilization treatment and hold for 180 minutes. Nitrogen gas is introduced for protection during the heating and cooling process.
[0037] S4. Perform finishing on the semi-finished gear components to obtain powder metallurgy high-speed steel gears.
[0038] This comparative example compares the finished gear processed using the quenching and tempering parameters of this invention with a gear that has undergone nitriding heat treatment to verify the advantages of the nitriding process. The powder metallurgy high-speed steel gear from this comparative example was subjected to hardness testing; the hardness from surface to core was 39-41 HRC. The surface hardness is low, failing to meet the design requirement of a surface hardness greater than or equal to 90 HRC 15 N. During high-speed operation, the gear surface is prone to spalling, leading to transmission system failure.
[0039] Comparative Example 2 The heat treatment method for a powder metallurgy high-speed steel gear in Comparative Example 2 is largely the same as that in Example 1, except that step B2 is different and specifically includes the following steps: B2. Introduce ammonia gas and adjust the furnace pressure to 10 MPa. Increase the furnace temperature to 510℃ at a heating rate of 3℃ / min. During the heating process, a one-stage nitriding process is adopted at a temperature of 510℃ to stabilize the ammonia decomposition rate at 30% for 48 hours.
[0040] This comparative example aims to verify whether the microstructure and hardness of the workpiece after nitriding using a traditional single-stage nitriding process meet the requirements for transmission gears.
[0041] Physicochemical testing: The microstructure of the powder metallurgy high-speed steel gear in this comparative example is a coarse nitride (martensite) + carbide structure, with brittleness grade II. The effective hardened layer depth of the powder metallurgy high-speed steel gear in this comparative example is 0.48 mm (measured to a core hardness of +50 HV), the surface hardness is 94.5 HR15 N, and the core hardness is 42.0 HRC. The presence of coarse nitrides in the microstructure does not meet the technical requirements.
[0042] Comparative Example 3 The heat treatment method for a powder metallurgy high-speed steel gear in Comparative Example 3 is largely the same as that in Example 1, except that step A3 is different. Step A3 specifically includes the following steps: A3. The powder metallurgy high-speed steel bar is subjected to two tempering treatments. It needs to be returned to room temperature between the two tempering treatments. The tempering temperature adopts the traditional standard requirement of 520℃ and the holding time is 210min. After the holding time of the two tempering treatments is met, it is air-cooled to room temperature.
[0043] This comparative example verifies whether the hardness index of products processed at traditional tempering temperatures meets the design requirements. Physical and chemical testing: The powder metallurgy high-speed steel gears used in this comparative example were subjected to hardness testing. The hardness from the surface to the core was 57-59 HRC. This does not meet the design hardness requirement of 31-45 HRC.
[0044] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, should fall within the protection scope of the present invention.
Claims
1. A heat treatment method for powder metallurgy high-speed steel gears, characterized in that: Includes the following steps: S1. Powder metallurgy high-speed steel bars are subjected to quenching and tempering heat treatment to obtain powder metallurgy high-speed steel bars with a core hardness of 31-45HRC. S2. Semi-finishing powder metallurgy high-speed steel bars is performed to obtain semi-finished gear parts. S3. Stabilize the semi-finished gear parts to eliminate internal stress and homogenize the structure. S4. The surface of the semi-finished gear parts to be nitrided is sandblasted to activate the material surface; S5. The semi-finished gear parts after sandblasting are subjected to nitriding heat treatment, which includes the following steps: The semi-finished gear parts were placed in an ammonia atmosphere and heated to 490–550°C and held at that temperature. During the heating process, the ammonia decomposition rate was 35–45%. S6. The semi-finished gear parts after nitriding heat treatment are precision machined to obtain powder metallurgy high-speed steel gears.
2. The heat treatment method for powder metallurgy high-speed steel gears according to claim 1, characterized in that: In step S1, the quenching and tempering heat treatment includes the following steps: A1. Heat treatment of powder metallurgy high-speed steel bars at 980-1120℃ to transform the microstructure of powder metallurgy high-speed steel bars into austenitic microstructure. A2. The powder metallurgy high-speed steel bar is quenched in quenching oil at a temperature of 30-90℃ to transform the austenitic structure into a martensite structure and granular carbides. A3. Temper the powder metallurgy high-speed steel bar at a temperature of 500-700℃ to homogenize the martensitic structure.
3. The heat treatment method for powder metallurgy high-speed steel gears according to claim 2, characterized in that: In step A1, the heat preservation treatment time is 90-210 minutes.
4. The heat treatment method for powder metallurgy high-speed steel gears according to claim 3, characterized in that: In step A1, the heat preservation treatment time is 130-150 minutes.
5. The heat treatment method for powder metallurgy high-speed steel gears according to claim 2, characterized in that: The quenching process is followed by oil cooling within 1 hour.
6. The heat treatment method for powder metallurgy high-speed steel gears according to claim 2, characterized in that: In step A3, the tempering process is performed 2-3 times.
7. The heat treatment method for powder metallurgy high-speed steel gears according to any one of claims 1 to 6, characterized in that: In step S3, the stabilization treatment temperature is 500-600℃ and the time is 120-240 min.
8. The heat treatment method for powder metallurgy high-speed steel gears according to any one of claims 1 to 6, characterized in that: In step S4, during the sandblasting process, corundum sand with a mesh size ≥ 80 is used as the sandblasting sand particles.
9. The heat treatment method for powder metallurgy high-speed steel gears according to any one of claims 1 to 6, characterized in that: In step S5, the holding time for the nitriding heat treatment is 5-100h, and a two-stage nitriding process is adopted; the temperature of the first stage nitriding process is 520-550℃, and the nitrogen potential is 0.45%-0.55%; the temperature of the second stage nitriding process is 520-550℃, and the nitrogen potential is 0.25%-0.35%.
10. The heat treatment method for powder metallurgy high-speed steel gears according to any one of claims 1 to 6, characterized in that: The powder metallurgical high-speed steel is CPM 10V or HOP 10V.