Analysis of Heat Treatment Process of Valve Plate

The valve plate is a component of the compressor, which is widely used in refrigeration equipment such as refrigerators and air conditioners. The valve plate is a powder metallurgical part, which is directly used after being polished after heat treatment. The valve plate is required not only to have a certain strength, ensure operational reliability, but also to make the parts have basically the same amount of distortion to ensure mass production. Because the valve plate material is iron-based powder metallurgy, the powder metallurgy material has porosity and is not as uniform as steel. At the same time, the weight of a single piece is less than 0.2 kg, so it is a small piece. After carbonitriding and quenching, there is a discrete amount of distortion. The Yamato crush test value tends to the lower limit and the dispersion is large. Through the analysis and improvement of the heat treatment process, the distortion amount is effectively reduced and the stability of the distortion amount is improved, and the crush test value is increased at the same time.

The temperature of carbonitriding is low, which reduces the amount of distortion in the process of carbonitriding. Because nitrogen infiltrates into the infiltrated layer in the carbonitriding process, the specific volume of martensite after quenching is larger, and the deformation caused by martensite transformation after carbonitriding and quenching of the valve plate is larger. Carbonitriding reduces the Ms point and increases the retained austenite in the layer structure after quenching, which affects the crush test value. Through the use of carburizing and quenching processes, the amount of distortion is reduced and the crush test value is increased. It effectively meets the technical index requirements and obtains good repeatability and reproducibility.

According to the characteristics of the parts, the process of carburizing instead of carbonitriding is used to effectively control the Ms point so that the amount of martensite obtained after quenching is large, and the amount of retained austenite is small, which effectively improves the crush test value. Substituting carbon-containing martensite with a relatively small specific volume instead of carbon-nitrogen-containing martensite with a relatively large specific volume effectively reduces the amount of deformation. Practice has proved that the deformation and crush test values of this part have obtained stable reproducibility.

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