A composite heat treatment process

Abstract

The present invention belongs to the field of metal heat treatment and relates to a composite heat treatment process. By using QPQ + multi-purpose furnace carburizing and quenching, a nitride and oxide structure is formed on the surface layer of the gear teeth, shortening the subsequent multi-purpose furnace carburizing and quenching time and improving production efficiency. By using integral salt bath nitriding, the surface passivation film is removed sufficiently, the carburized layer depth distribution is uniform, and the gear surface has higher anti-fatigue strength and wear resistance. The process has good repeatability and stable product quality.

Description

Technical Field

[0001] The present invention belongs to the field of metal heat treatment and relates to a composite heat treatment process. Background Art

[0002] 1Cr11Ni2W2MoV is a martensitic stainless steel. Due to its high carbon content (10.5 - 12%) and a certain amount of Ni (1.4 - 1.8%), a dense passivation film is extremely likely to form on the surface of the part, hindering the penetration of carbon atoms. Therefore, it is very difficult to meet the technical requirements of the part through ordinary carburizing and carbonitriding. To achieve carburizing of stainless steel, the passivation film problem must be solved first. This passivation film is an oxide film of stainless steel metal elements, with stable properties and is not easy to remove. The commonly used carburizing and quenching process for stainless steel is vacuum carburizing. The heating process of vacuum carburizing is in an oxygen-free vacuum state, which can effectively remove the passivation film on the surface of stainless steel. However, the temperature of vacuum carburizing is generally 950 - 1000°C. Due to the high temperature, the carburizing speed is fast, and over-carburizing is likely to occur at the sharp corners; network carbide is likely to appear in the carburized layer; when the loading amount in the furnace is too large, the problem of uneven carburized layer will occur. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a composite heat treatment process, which can ensure the uniformity of the carburized layer, carburized layer carbide, etc. of the tooth part, greatly improve the service life of the gear, and this process has good repeatability and stable product quality.

[0004] To achieve the above purpose, the present invention provides the following technical solution: A composite heat treatment process for the material 1Cr11Ni2W2MoV, including the following steps:

[0005] S1, according to the technical requirements of the workpiece, select appropriate process parameters for preliminary heat treatment, and then perform quenching and tempering treatment at 28 - 32 HRC;

[0006] S2, after quenching and tempering is completed, after the workpiece is subjected to precision turning and hobbing, perform QPQ treatment on the workpiece;

[0007] S3, after QPQ is completed, perform carburizing and quenching on the gear in a multi-purpose furnace;

[0008] S4, after carburizing is completed, cool down to 900 - 920°C, hold for 60 min and then take out of the furnace and cool in oil, use step quenching oil for cooling, and control the oil temperature at 110 - 120°C;

[0009] S5, perform low-temperature tempering at 180 - 210°C, hold for 180 - 240 min and then take out of the furnace and air-cool.

[0010] Optionally, the QPQ process flow in step S2 includes the following steps: cleaning → preheating at 380°C and holding for 20 min → salt bath nitriding at 540°C for 180 min and then air cooling after furnace discharging → oxidation at 450°C and holding for 10 min → cooling → cleaning → drying at 150°C and holding for 30 min → oil immersion.

[0011] Optionally, the cooling process of the QPQ process flow uses air cooling.

[0012] Optionally, in step S3, the carburizing temperature for carburizing and quenching is 930 - 940°C, the strong carburizing potential is 1.2%, the diffusion carburizing potential is 0.85%, and the carburizing holding time is determined according to the hardened layer depth.

[0013] Optionally, the ratio of the propane flow rate to the ammonia flow rate during the carburizing and quenching process is 1:1, and the specific value is 2 - 3 mL / min.

[0014] The beneficial effects of the present invention are as follows: A composite heat treatment process of the present invention uses QPQ + multi-purpose furnace carburizing and quenching, forming a layer of nitride and oxide tissues on the surface layer of the gear teeth, shortening the subsequent multi-purpose furnace carburizing and quenching time, and improving production efficiency; using integral salt bath nitriding, the surface passivation film is removed sufficiently, the carburized layer depth distribution is uniform, the gear surface has higher anti-fatigue strength and wear resistance, the process repeatability is good, and the product quality is stable.

[0015] Other advantages, objectives, and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0017] Figure 1 is a schematic diagram of the QPQ process for the material 1Cr11Ni2W2MoV of the present invention;

[0018] Figure 2 is a schematic diagram of the carburizing and quenching process for the material 1Cr11Ni2W2MoV of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0020] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and should not be construed as limitations on the present invention; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0021] In the drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and should not be construed as limitations on the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0022] Please refer to Figures 1 to 2 , in view of the uneven carburized layer and the out-of-tolerance carburide in the existing carburizing and quenching process of 1Cr11Ni2W2MoV, a composite heat treatment process for 1Cr11Ni2W2MoV is provided. Through this process, the uniformity of the carburized layer and the carburide in the tooth part can be ensured, the service life of the gear can be greatly improved, and the process has good repeatability and stable product quality;

[0023] To solve the above heat treatment production technical problems, the invention adopts the following technical solutions. The carburizing and quenching composite heat treatment process of the material 1Cr11Ni2W2MoV is carried out according to the following steps:

[0024] 1. According to the technical requirements of the workpiece, select appropriate process parameters for preliminary heat treatment - quenching and tempering at 28 - 32 HRC;

[0025] 2. After quenching and tempering is completed, and the workpiece has been subjected to finish turning and hobbing, the workpiece is subjected to QPQ treatment. The process flow is as follows: cleaning → preheating at 380°C for 20 minutes → salt bath nitriding at 540°C for 180 minutes, then taken out of the furnace and air-cooled → oxidation at 450°C for 10 minutes → cooling (air-cooling) → cleaning → drying at 150°C for 30 minutes → oil immersion. The QPQ process curve is as Figure 1 shown;

[0026] 3. After QPQ is completed, the gear is carburized and quenched in a multi-purpose furnace: carburizing temperature is 930 - 940°C, strong carburizing potential is 1.2%, diffusion carburizing potential is 0.85%, propane flow rate: ammonia flow rate = 1:1, and the specific value is 2 - 3 mL / min. The carburizing holding time is determined according to the case depth;

[0027] 4. After carburizing is completed, the temperature is reduced to 900 - 920°C, held for 60 minutes, then taken out of the furnace and oil-cooled. It is cooled using a step quenching oil, and the oil temperature is controlled at 110 - 120°C. Low-temperature tempering is carried out at 180 - 210°C for 180 - 240 minutes, then taken out of the furnace and air-cooled. The heat treatment curve is as Figure 2 shown.

[0028] This patent has the following advantages:

[0029] Compared with single carburizing and quenching, for the gear after composite heat treatment, the hardness at 0.1 mm can be increased by 50 - 80 HV on the basis of carburizing and quenching. At the same time, the carburizing time is shortened. The carbon, nitrogen concentration and hardness gradient of the carburized layer are improved. The composite heat treatment adopts salt bath nitriding + oxidation to ensure that a composite structure of nitrides and oxides with a thickness of more than 0.02 mm is formed on the entire tooth surface layer, and the passivation film on the gear surface is completely removed; for the multi-purpose furnace carburizing and quenching, an oxygen probe is used to control the carbon potential to ensure that the carburized layer carbides are distributed in a granular shape, improving the wear resistance of the product. The composite heat treatment makes up for the deficiencies such as uneven case depth and carbide out-of-tolerance of the carburized layer.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A composite heat treatment process for the material 1Cr11Ni2W2MoV, characterized in that, It includes the following steps: S1. According to the technical requirements of the workpiece, select appropriate process parameters for preliminary heat treatment, and then perform quenching and tempering treatment to 28 - 32 HRC. S2. After quenching and tempering is completed, and the workpiece is subjected to finish turning and hobbing, perform QPQ treatment on the workpiece. The QPQ process flow includes the following steps: cleaning → preheating at 380 °C for 20 min → salt bath nitriding at 540 °C for 180 min, then taking out and air cooling → oxidation at 450 °C for 10 min → cooling → cleaning → drying at 150 °C for 30 min → oil immersion. S4. After QPQ is completed, the gear is carburized and quenched in a multi-purpose furnace. S5. After carburizing is completed, cool down to 900 - 920 °C, hold for 60 min, then take out and oil cool, and use step quenching oil for cooling, with the oil temperature controlled at 110 - 120 °C. S6. Perform low-temperature tempering at 180 - 210 °C for 180 - 240 min, then take out and air cool.

2. The composite heat treatment process according to claim 1, characterized in that: The cooling process of the QPQ process flow adopts air cooling.

3. A composite heat treatment process according to claim 1, characterized in that: In step S3, the carburizing temperature for carburizing and quenching is 930 - 940 °C, the strong carburizing potential is 1.2%, the diffusion carburizing potential is 0.85%, and the carburizing holding time is determined according to the case depth.

4. A composite heat treatment process according to claim 3, characterized in that: The ratio of the propane flow rate to the ammonia flow rate during the carburizing and quenching process is 1:1, and the specific value is 2 - 3 mL / min.

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