Novel carbonitriding process for bearing part

Abstract

The invention discloses a novel carbonitriding process for a bearing part. The novel carbonitriding process comprises the following steps: heating the bearing part in a carburizing furnace in a nitrogen protection state; the atmosphere of the replacement carburizing furnace is carbonitriding atmosphere; and carbonitriding and quenching the bearing part in a carburizing furnace under the atmosphere of methanol, propane and ammonia gas. According to the novel carbonitriding process for the bearing part, the phenomena that the surface of a product is oxidized and the color and luster are poor during treatment of a conventional atmosphere carbonitriding process are solved.

Description

Technical Field

[0001] The present invention relates to the field of heat treatment of metal materials, and particularly to a carbonitriding process for GCr15 parts. Background Art

[0002] Bearing products are widely used in many fields such as the automotive industry and the machinery industry. After carbonitriding and quenching treatment of bearing parts, the surface has properties such as high hardness, high wear resistance, and high fatigue strength.

[0003] The conventional gas carbonitriding process includes furnace charging, heating up, soaking, carbonitriding, quenching, and furnace discharging. Currently, the commonly used gas carbonitriding processes are all carried out in a carbonitrogen atmosphere. Since the carbonitriding process temperature of bearing parts is relatively low, the low-temperature time is relatively long during heating up. At low temperatures, due to the insufficient decomposition of methanol in the carbonitrogen atmosphere and the reversible reaction of carbon monoxide in the atmosphere (CO - C + CO2), oxidation and carbon deposition are likely to occur on the part surface, affecting the surface performance and appearance quality of the product. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a new carbonitriding process for bearing parts, which solves the problems of surface oxidation and poor appearance of products in the existing conventional gas carbonitriding process.

[0005] To solve the above technical problems, the present invention provides a new carburizing process for gear parts, including the following steps: S1. Replace the atmosphere in the carburizing furnace with nitrogen; S2. Load the bearing parts into the furnace; S3. Heat up the bearing parts under the protection of nitrogen; S4. Change the carbonitriding atmosphere and carry out carbonitriding and quenching in an atmosphere of methanol, propane, and ammonia; S5. Change to a nitrogen atmosphere and heat up again.

[0006] As a new carbonitriding process of the present invention, in the step S1, the oxygen content of the air in the furnace after nitrogen replacement is 0.3 - 0.8%; Further, in the step S1, the oxygen content of the air in the furnace after nitrogen replacement is 0.3 - 0.5%; Further, in the step S1, the replacement times are 1 - 3 times; Further, in the step S1, the replacement times are 2 times; As a new carbonitriding process for bearing parts of the present invention, in the step S3, the protective atmosphere during heating up is nitrogen, and the volume percentage is 99.9995%.

[0007] As a new carbonitriding process for a bearing part described in the present invention, in the S4 step, the carburizing atmosphere is methanol, propane, and ammonia; The new carbonitriding process described in the present invention can eliminate surface oxidation and poor appearance phenomena generated during the heating of the product. The thickness of the surface oxide layer, surface hardness, and gear deformation amount are reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a curve graph of a conventional carbonitriding process in the prior art; Figure 2 is a curve graph of the new carbonitriding process described in the present invention; Figure 3 is a block diagram of the steps of the carbonitriding process described in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] To make the technical solutions and beneficial effects of the present invention more obvious and understandable, the following will be described in detail by listing specific embodiments. Unless otherwise defined, the technical and scientific terms used herein have the same meanings as those in the technical and scientific fields to which the present application belongs.

[0010] Example 1:

[0011] A method for preparing a bearing product by carbonitriding, the method comprising the following steps: S1: Place a GCr15 part with dimensions of 10×10×15 mm in a carburizing furnace, heat the carburizing furnace at a rate of 10 °C / min, and then perform an equalizing treatment. The treatment temperature is 840 ± 10 °C, and the methanol flow rate is 3 L / h; S2: Perform carbonitriding treatment on the product in S1, wherein the carbonitriding atmosphere is methanol, propane, and ammonia, the carbon potential is controlled at 1.5 ± 0.05%, the ammonia flow rate is 2 M 3 / h, the ammonia concentration is about 22%, and the carbonitriding time is 240 ± 5 min; S3: Quench the product in S2.

[0012] Example 2: A method for preparing a bearing product by carbonitriding, the method comprising the following steps: S1: Replace the atmosphere in the carburizing furnace with nitrogen, introduce high-purity nitrogen (≥99.99%) into the furnace, replace the air in the furnace until the oxygen content is 0.5 - 0.8%, the replacement times is 1 time, and the pressure in the furnace rises to 200 - 500 Pa after replacement and is kept under pressure for 10 - 20 minutes; S2: Place a GCr15 part with dimensions of 10×10×15 mm in a carburizing furnace; S3. Under nitrogen protection, heat the carburizing furnace at a rate of 10 °C / min, and then perform a soaking treatment. The treatment temperature is 840 ± 10 °C, and the methanol flow rate is 3 L / h; S4: Perform a carbonitriding treatment on the product in S3. The carbonitriding atmosphere is methanol, propane, and ammonia. The carbon potential is controlled at 1.5 ± 0.05%, and the ammonia flow rate is 2M 3 / h, the ammonia concentration is about 22%, and the carbonitriding time is 240 ± 5 min; S5: Quench the product in S4; S6. Change the nitrogen atmosphere and then heat up.

[0013] Example 3: A method for preparing a bearing product by carbonitriding, the method comprising the following steps: S1: Replace the atmosphere in the carburizing furnace with nitrogen, introduce high-purity nitrogen (≥99.99%) into the furnace, replace the air in the furnace until the oxygen content is 0.3 - 0.5%, and the replacement times is 2 times. After each replacement, the pressure in the furnace is raised to 200 - 500 Pa and kept for 10 - 20 minutes; S2: Place a GCr15 part with dimensions of 10×10×15 mm in the carburizing furnace; S3. Heat the carburizing furnace at a rate of 10 °C / min, and then perform a soaking treatment. The treatment temperature is 840 ± 10 °C, and the methanol flow rate is 3 L / h; S4: Perform a carbonitriding treatment on the product in S3. The carbonitriding atmosphere is methanol, propane, and ammonia. The carbon potential is controlled at 1.5 ± 0.05%, and the ammonia flow rate is 2M 3 / h, the ammonia concentration is about 22%, and the carbonitriding time is 240 ± 5 min; S5: Quench the product in S4; S6: Change the nitrogen atmosphere and then heat up.

[0014] Example 4: Test the specimens of Examples 1 - 3: Oxidation defects and cracks: Oxide scale or decarburized layer (appearance of ferrite in the metallographic structure) can be seen on the surface; microcracks on the surface or near the surface (length ≥ 0.1 mm).

[0015] Measurement of case depth: Metallographic microscope method: Measure the vertical distance from the surface to the transition zone (where hardness or microstructure changes) at a magnification of 200× or 500×. Measure 3 times at each detection point, and take the average value as the case depth at that point.

[0016] The test results are shown in Table 1.

[0017] Table 1

[0018] As can be seen from Table 1, for the new carbonitriding process of the bearings described in the present invention, compared with the existing conventional process, nitrogen is used as the protective gas in the heating stage, which can eliminate the oxidation and appearance defects generated during the heating process of bearing parts, and improve the product performance and service life. In addition, by optimizing the nitrogen replacement parameters, the appearance performance of the product is improved, and the product performance of bearing parts is significantly optimized.

[0019] It should be understood that the above embodiments are all exemplary and do not cover all possible implementation manners included in the claims. Without departing from the scope of the present disclosure, various deformations and changes can also be made on the basis of the above embodiments.

Claims

1. A new carbonitriding process for bearing parts, characterized in that, It includes the following steps: Nitrogen replacement, furnace loading, carbonitriding and quenching, nitrogen replacement.

2. The new carbonitriding process for bearing parts as described in claim 1, characterized in that, The specific steps are as follows: S1. Replace the atmosphere in the carburizing furnace with nitrogen; S2. Load the bearing parts into the furnace; S3. Heat up the bearing parts under nitrogen protection; S4. Change the carbonitriding atmosphere and carry out carbonitriding and quenching in an atmosphere of methanol, propane, and ammonia; S5. Change the nitrogen atmosphere and then heat up.

3. The new process for carbonitriding of bearing parts as described in claim 1 is characterized in that: In step S1, the protective atmosphere during heating is nitrogen, and the nitrogen has a volume percentage of 99.9995%.

4. The new carbonitriding process for bearing parts as described in claim 1, characterized in that: In step S1, the oxygen content of the air in the furnace after nitrogen replacement is 0.3 - 0.8%.

5. The new process for carbonitriding of bearing parts as described in claim 1, characterized in that: In step S1, the oxygen content of the air in the furnace after nitrogen replacement is 0.3 - 0.5%.

6. The new process for carbonitriding of bearing parts as described in claim 1 is characterized in that: In step S1, the replacement is carried out 2 times.

7. The new carbonitriding process for bearing parts as described in claim 1, characterized in that: The carbonitriding atmosphere is methanol, propane, and ammonia.

8. A new carbonitriding process for bearing parts as described in claim 1, characterized in that: The nitrogen source is ammonia, and the carbon sources are methanol and propane.

9. A bearing part obtained by the new carbonitriding process according to any one of claims 1 - 8.

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