，介绍65Mn830℃淬火（油冷）金相...
65Mn830℃quenching (oil cooling) metallography
This paper mainly studies 65Mn830℃quenching (oil cooling) metallography. Quenching is a thermal treatment process of heating, holding, and cooling metal materials at different temperatures to obtain different properties from its hardened state. Quenching is divided into three types: Oil quenching, water quenching and quenching. Oil quenching is commonly used for surface hardening of high carbon steel and its alloys, especially for the surface hardening of large forgings and castings. 65Mn is a kind of spring steel with high strength, but low hardenability. When carbon steel containing 0.62-0.70% of C at 830℃ high temperature quenching (oil cooling) of 65Mn, the temperature range of austenitic transformation temperature (A1) is 727-799℃ (may produce brinell hardness of more than 120).
Metallographic examination consists of polished specimen, etching, observation and diagnosis. The preparation of the sample should be carried out in strict accordance with the technical requirements to ensure the accuracy of the observation results. The metallography of 65Mn830℃ quenching (oil cooled) mainly includes: surface morphology observation and internal structure analysis. The surface of steel after quenching is generally complete, smooth and non-porous, with a large number of white patches, known as white spots. The degree of white spots and the area covered by Fe3C distribution are the key indicators for evaluating the influence of quenching temperature, soaking time and quenching media on the quenching quality of 65Mn steel. Internally, it can find pearlite, martensite, austenite, graphite and other structures, and also can find some overheating and incomplete martensite, that is, the mixture of martensite and untransformed austenite (M + U).M can be further divided into three subgroups according to the carbon content, namely, low carbon martensite, medium carbon martensite and high carbon martensite, which can be judged by means of differential optical microscope.
The wear resistance and toughness of 65Mn steel after quenching are closely related to quenching temperature. When the temperature is too low, only low carbon martensite is formed in the internal structure, which generally has poor wear resistance and low toughness; when the temperature is too high, white spots and M+U structure will appear on the surface of the steel, and its wear resistance and toughness will naturally decrease; when the temperature reaches the best range, the wear resistance and toughness are obviously improved.
To sum up, 65Mn830℃quenching (oil cooling) metallography has important application significance for optimizing the quenching process and improving the performance of 65Mn steel.
