Method for carbonitriding heat treatment of screws

[0021] Example 1

[0022] The screws to be heat treated are cleaned with warm water and high pressure spray to remove the residual oil and diesel in the screw threading process, reduce the pollution of the equipment, and ensure even carburization of the parts. The water pressure during the cleaning process is controlled to 1kgf/cm 2.

[0023] The feeder speed is adjusted to 30Hz/rpm, the feeder transports the screws to the continuous furnace for continuous preheating and carbonitriding treatment, adjusts the main speed of the continuous furnace for continuous preheating, and the preheating is a two-stage type Preheating, the first stage of preheating temperature is 600℃, and the holding time is 10 minutes to reduce the internal stress caused by screw heading and threading, reduce the temperature difference between the inside and outside of the screw, and eliminate the cracking and cracking caused by work hardening. Deformation, the second stage of preheating temperature is 860℃, and the holding time is 25 minutes, so that the inner and outer temperature of the heating screw are consistent. The inner and outer parts of the screw have completed the structure transformation, carbide dissolution and austenite composition uniformity, which can make the screw Obtain ideal properties such as hardness, toughness, elasticity, and plasticity. After preheating, the screws are carbonitrided. The carbonitriding temperature is controlled at 860℃, and the carbonitriding time is controlled at 15 minutes. The carbon source is a mixture of propane and butane. The carbon potential is 1%. Air flow is 0.2nm 3 /h, pretreated vaporized methanol is used as the protective gas, and the flow rate of vaporized methanol is 6000CC/h. The carbonitriding is mainly carburizing and nitrogen is infiltrated at the same time, which overcomes the nitriding layer to a certain extent Although the hardness is high, the carburized layer is shallow, and the carburized layer has a large hardening depth, but the surface hardness is lower. The carbonitrided layer has higher hardness, wear resistance, corrosion resistance, and bending than the carburized layer. Strength and contact fatigue strength. After carbonitriding, a quenching is performed, and the quenching temperature is 820°C. Then use fast bright oil to quench the screw twice. During the second quenching process, the temperature of fast bright oil is controlled at 60°C, and the quenching time is 3 seconds. The above-mentioned preheating, carbonitriding and one-time quenching are all carried out in a continuous furnace, and the whole process lasts for 53 minutes.

[0024] The quenched screws are cleaned on the surface, using warm water and high pressure spray cleaning, the water pressure is controlled at 1kgf/cm 2 , The quenching oil remaining on the surface after quenching is removed by cleaning to ensure that the screw is heated evenly and the hardness is stable during the tempering process.

[0025] The quenched screw is tempered, the tempering temperature is controlled at 370℃, and the tempering time is 90 minutes, because the structure after quenching is martensite and retained austenite, and internal stress is generated, although the strength of martensite Strong, high hardness, but poor plasticity, high brittleness, and easy to deform and crack under the action of internal stress. In addition, the structure after quenching is unstable and can slowly decompose at room temperature, resulting in volume change and deformation. Therefore, The quenched parts must be tempered before they can be used. The purpose of tempering is to reduce or eliminate the internal stress of quenching, stabilize the structure, stabilize the size, reduce brittleness, and obtain the required mechanical properties.

[0026] Example 2

[0027] The screws to be heat treated are cleaned with warm water and high pressure spray to remove the residual oil and diesel in the screw threading process, reduce the pollution of the equipment, and ensure even carburization of the parts. The water pressure during the cleaning process is controlled to 1.2kgf/cm 2.

[0028] The feeder speed is adjusted to 45Hz/rpm, the feeder transports the screws to the continuous furnace for continuous preheating and carbonitriding treatment, adjusts the main speed of the continuous furnace for continuous preheating, and the preheating is a two-stage type Preheating, the first stage of preheating temperature is 600℃, and the holding time is 13 minutes to reduce the internal stress caused by screw heading and threading, reduce the temperature difference between the inside and outside of the screw, and eliminate the cracking and cracking caused by work hardening. Deformation, the second stage of preheating temperature is 870℃, holding time is 22 minutes, so that the inner and outer temperature of the heating screw are consistent, the inner and outer parts of the screw have completed the structural transformation, carbide dissolution and austenite composition uniformity, which can make the screw Obtain ideal properties such as hardness, toughness, elasticity, and plasticity. After preheating, the screws are carbonitrided. The carbonitriding temperature is controlled at 870℃, and the carbonitriding time is controlled at 10 minutes. The carbon source is a mixture of propane and butane. The carbon potential is 1.1%. Air flow is 0.4nm 3 /h, pretreated gasified methanol is used as the protective gas, and the flow of gasified methanol is 8000CC/h. The carbonitriding is mainly carburizing, while infiltration of nitrogen, which overcomes the nitriding layer to a certain extent Although the hardness is high, the carburized layer is shallow, and the carburized layer has a large hardening depth, but the surface hardness is lower. The carbonitrided layer has higher hardness, wear resistance, corrosion resistance, and bending than the carburized layer. Strength and contact fatigue strength. After carbonitriding, a quenching is performed, and the quenching temperature is 840°C. Then use fast bright oil to quench the screw twice. During the second quenching process, the temperature of fast bright oil is controlled at 70℃, and the quenching time is 6 seconds. The above-mentioned preheating, carbonitriding and one-time quenching are all carried out in a continuous furnace, and the whole process lasts 51 minutes.

[0029] Clean the surface of the quenched screws, using warm water and high pressure spray cleaning, the water pressure is controlled at 1.2kgf/cm 2 , The quenching oil remaining on the surface after quenching is removed by cleaning to ensure that the screw is heated evenly and the hardness is stable during the tempering process.

[0030] The quenched screw is tempered, the tempering temperature is controlled at 400℃, and the tempering time is 80 minutes, because the structure after quenching is martensite and retained austenite, and internal stress is generated, although the strength of martensite Strong, high hardness, but poor plasticity, high brittleness, and easy to deform and crack under the action of internal stress. In addition, the structure after quenching is unstable and can slowly decompose at room temperature, resulting in volume change and deformation. Therefore, The quenched parts must be tempered before they can be used. The purpose of tempering is to reduce or eliminate quenching internal stress, stabilize the structure, stabilize the size, reduce brittleness, and obtain the required mechanical properties.

[0031] Example 3

[0032] The screws to be heat treated are cleaned with warm water and high pressure spray to remove the residual oil and diesel in the screw threading process, reduce the pollution of the equipment, and ensure even carburization of the parts. The water pressure during the cleaning process is controlled to 1.5kgf/cm 2.

[0033] The feeder speed is adjusted to 60Hz/rpm, the feeder transports the screws to the continuous furnace for continuous preheating and carbonitriding treatment, adjusts the main speed of the continuous furnace for continuous preheating, and the preheating is a two-stage type Preheating, the first stage of preheating temperature is 600℃, and the holding time is 15 minutes to reduce the internal stress caused by the screw heading and threading, reduce the temperature difference between the inside and outside of the screw, and eliminate the cracking and cracking caused by the work hardening of the screw. Deformation, the second stage of preheating temperature is 890℃, and the holding time is 25 minutes, so that the inner and outer temperature of the heating screw are consistent. The inner and outer parts of the screw have completed the structure transformation, carbide dissolution and austenite composition uniformity, which can make the screw Obtain ideal properties such as hardness, toughness, elasticity, and plasticity. After preheating, the screws are carbonitrided. The carbonitriding temperature is controlled at 890℃, and the carbonitriding time is controlled at 10 minutes. The carbon source is a mixture of propane and butane. The carbon potential is 1.2%. Air flow is 0.5nm 3 /h, pretreated gasified methanol is used as the protective gas. The flow rate of gasified methanol is 9000CC/h. The carbonitriding is mainly carburizing and nitrogen is infiltrated at the same time, which overcomes the nitriding layer to a certain extent. Although the hardness is high, the carburized layer is shallow, and the carburized layer has a large hardening depth, but the surface hardness is lower. The carbonitrided layer has higher hardness, wear resistance, corrosion resistance, and bending than the carburized layer. Strength and contact fatigue strength. After carbonitriding, a quenching is performed, and the quenching temperature is 850℃. Then use fast bright oil to quench the screw twice. During the second quenching, the temperature of fast bright oil is controlled at 75°C, and the quenching time is 10 seconds. The above-mentioned preheating, carbonitriding and one-time quenching are all carried out in a continuous furnace, and the whole process lasts 60 minutes.

[0034] The quenched screws are cleaned on the surface, using warm water and high pressure spray cleaning, and the water pressure is controlled at 1.5kgf/cm 2 , The quenching oil remaining on the surface after quenching is removed by cleaning to ensure that the screw is heated evenly and the hardness is stable during the tempering process.

[0035] The quenched screw is tempered, the tempering temperature is controlled at 420℃, and the tempering time is 90 minutes, because the structure after quenching is martensite and retained austenite, and internal stress is generated, although the strength of martensite Strong, high hardness, but poor plasticity, high brittleness, easy to deform and crack under the action of internal stress, in addition, the structure after quenching is unstable, and it can slowly decompose at room temperature, resulting in volume change and deformation. Therefore, The quenched parts must be tempered before they can be used. The purpose of tempering is to reduce or eliminate quenching internal stress, stabilize the structure, stabilize the size, reduce brittleness, and obtain the required mechanical properties.