Heat treatment method for improving structure performance of GCr15

Abstract

The invention discloses a heat treatment method for improving the structure performance of GCr15, which comprises the following steps: preparing a bearing turning part made of a high-grade high-quality steel GCr15 material meeting the GB / T 18254 standard, and carrying out primary nitriding treatment; carrying out primary quenching treatment on the bearing turning part; and the bearing turning part is subjected to high-temperature tempering treatment. According to the method, after the GCr15 material is subjected to heat treatment, the surface hardness, the wear resistance and the tempering resistance can be improved.

Description

Technical Field

[0001] The present invention relates to a heat treatment method for improving the tissue performance of GCr15. Background Art

[0002] As a bearing steel material with a large usage amount, the structure obtained after martensite quenching and low-temperature tempering at 180°C for GCr15 is cryptocrystalline martensite, a small amount of carbides, and retained austenite, and the hardness is about 59 - 64 HRC. Through carbonitriding heat treatment, a higher surface hardness of 61 - 63 HRC and tempering resistance can be obtained. However, for thin-walled products, it will cause deformation problems and also have a high scrap rate. When the precision machine tool bearings made of GCr15 material operate at high speed, local temperature rise and wear will occur due to lubrication problems. Therefore, a process method is needed to reduce deformation problems while improving surface hardness, wear resistance, and tempering resistance. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the present invention provides a heat treatment method for improving the tissue performance of GCr15, which can improve the wear resistance and tempering resistance of GCr15 material after heat treatment.

[0004] To achieve the above object, the present invention provides a heat treatment method for improving the tissue performance of GCr15. Step 1: Prepare high-quality steel GCr15 material that meets the GB / T 18254 standard, and complete spheroidizing annealing heat treatment and turning processing; Step 2: Perform a nitriding treatment on the bearing turned part once; Step 3: Perform a quenching treatment on the bearing turned part once; Step 4: Perform a high-temperature tempering treatment on the bearing turned part.

[0005] As a further setting of the present invention, in Step 2, carburizing treatment is carried out in a vacuum gas nitriding furnace. First, heat up to 540 - 560°C at a heating rate of 10 - 30°C / min along with the furnace, the furnace pressure is 3 - 7×10 4 Pa, keep warm for 4 - 6 h, control the ammonia decomposition rate at 15 - 25%, then heat up to 550 - 600°C along with the furnace, keep warm for 4 - 6 h, control the ammonia decomposition rate at 80 - 85%, and then cool to 150 - 250°C along with the furnace and take out the furnace for air cooling.

[0006] As a further setting of the present invention, in Step 3, quenching is carried out in a mesh belt furnace. First, heat up to 830 - 850°C along with the furnace, set the carbon potential at 0.85 - 0.95%, and keep warm for 30 - 150 min; then perform quenching, the oil temperature is 50 - 100°C, and the quenching time is 2 - 10 min.

[0007] As a further setting of the present invention, in step four, high-temperature tempering is carried out in a mesh belt furnace. First, the temperature is raised with the furnace to 200 - 250 °C and held for 2 - 4 h.

[0008] The beneficial effects of such a setting are as follows: By setting in this way, the surface hardness can be improved after heat treatment of GCr15 material, the deformation problem of thin-walled products can be reduced compared with carbonitriding, the wear resistance, grain size and tempering resistance can be improved. In the first nitriding treatment, the temperature, furnace pressure and ammonia decomposition rate are controlled in stages. In the low-temperature stage of 540 - 560 °C, nitrogen atoms slowly penetrate into the material surface to form a dense nitride layer, effectively improving the surface hardness and enabling it to better resist external friction and wear; after the temperature is raised to 550 - 600 °C, the nitride structure is further optimized, while enhancing the surface hardness, the wear resistance is improved, and the service life of the bearing is extended. During the step-by-step nitriding treatment process, the temperature and pressure change gently, and the thermal stress distribution is uniform, greatly reducing the deformation risk of thin-walled products caused by stress concentration, and ensuring the dimensional accuracy and shape stability of the products. Quenching treatment transforms the internal structure of the material into martensite, improving the hardness and strength; high-temperature tempering treatment eliminates the quenching stress and improves the toughness. The combination of the two optimizes the grain size, making the grains refined and uniform, and enhancing the comprehensive mechanical properties of the material. At the same time, the high-temperature tempering treatment improves the tempering resistance of the material. In subsequent use, even in a high-temperature environment, the material can maintain stable hardness and strength, ensuring the reliable operation of the bearing under complex working conditions. Description of the Drawings

[0009] Figure 1 It is the surface metallographic structure diagram after being treated by the prior art; Figure 2 It is the surface metallographic structure diagram after heat treatment of the embodiment of the present invention; Figure 3 It is the hardness gradient data diagram of the embodiment of the present invention and the prior art; Figure 4 It is the hardness gradient data diagram after tempering at 250 °C of the embodiment of the present invention and the prior art 2. Detailed Embodiment

[0010] The embodiment of the heat treatment method for improving the tissue performance of GCr15 of the present invention is as Figures 1 to 4 shown: The material is high-quality steel GCr15 material in accordance with the GB / T 18254 standard, and spheroidizing annealing heat treatment and turning are completed. The outer diameter of the bearing is 100 mm, and the effective wall thickness is 10 mm. Its heat treatment steps are as follows: 1. Nitriding treatment of the bearing turning parts is carried out in a vacuum gas nitriding furnace. First, the temperature is raised with the furnace to 550 °C at a heating rate of 20 °C, and the furnace pressure is 4×10 4Heat preservation at Pa for 5 h, control the ammonia decomposition rate at 20%, then heat up to 580 °C with the furnace, keep warm for 5 h, and control the ammonia decomposition rate at 80%. Then cool with the furnace to 200 °C and air cool after taking out of the furnace.

[0011] 2. Perform quenching treatment in a mesh belt furnace. The process is to first heat up to 840 °C with the furnace, set the carbon potential at 0.90%, and keep warm for 40 min. Then perform quenching, with the oil temperature at 100 °C and the quenching time at 5 min.

[0012] 3. Perform high-temperature tempering treatment in a mesh belt furnace. The process is to first heat up to 225 °C with the furnace and keep warm for 3 h.

[0013] For the final inspection, using the existing heat treatment process, the overall hardness is 59.5 - 60.5 HRC, and the hardness gradient data is as Figure 3 shown, and the surface microstructure is as Figure 1 shown, which is cryptocrystalline martensite, a small amount of carbides, and a small amount of retained austenite. For the result of implementing the present invention, the microstructure is as Figure 2 shown, which is cryptocrystalline martensite, a large amount of carbides, and a small amount of retained austenite. The surface hardness is 61.5 - 62.5 HRC. At the same time, after tempering at 250 °C, the surface of the technology of the present invention still has a hardness above 60 HRC.

[0014] The above examples are only one of the preferred specific examples of the present invention. The common variations and substitutions made by those skilled in the art within the scope of the technical solution of the present invention are included in the protection scope of the present invention.

Claims

1. A heat treatment method for improving the tissue performance of GCr15, characterized in that: It includes the following steps: Step 1: Prepare high-quality steel GCr15 material that meets the GB / T 18254 standard, and complete spheroidizing annealing heat treatment and turning machining; Step 2: Conduct a nitriding treatment on the bearing turned parts once; Step 3: Conduct a quenching treatment on the bearing turned parts once; Step 4: Conduct a high-temperature tempering treatment on the bearing turned parts.

2. The heat treatment method for improving the tissue performance of GCr15 according to claim 1, characterized in that: In the second step, carburizing treatment is carried out in a vacuum gas nitriding furnace. First, the furnace is heated to 540 - 560 °C at a heating rate of 10 - 30 °C / min, the furnace pressure is 3 - 7×10 4 Pa, keep the temperature for 4 - 6 h, control the ammonia decomposition rate at 15 - 25%, then heat the furnace to 550 - 600 °C, keep the temperature for 4 - 6 h, control the ammonia decomposition rate at 80 - 85%, and then cool the furnace to 150 - 250 °C, and take out the furnace for air cooling.

3. The heat treatment method for improving the tissue performance of GCr15 according to claim 1, characterized in that: In Step 3, quenching is carried out in a mesh belt furnace. First, heat up with the furnace to 830 - 850 °C, set the carbon potential to 0.85 - 0.95%, and hold for 30 - 150 min; then conduct quenching, with the oil temperature at 50 - 100 °C and the quenching time at 2 - 10 min.

4. The heat treatment method for improving the tissue performance of GCr15 according to claim 1, characterized in that: In Step 4, high-temperature tempering is carried out in a mesh belt furnace. First, heat up with the furnace to 200 - 250 °C and hold for 2 - 4 h.

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