Analysis of the Anomalous Effect of Heat Treatment on the Structure and Phase Transformations in High-Chromium Tool Steel

The effect of various heat treatments with heating to 1030 - 1250 degrees C on the structure and microhardness of high-chromium tool steel 160Kh12MF is studied. The chemical composition is determined, the microhardness is measured, and the microstructure of the steel is analyzed after quenching, normalizing and annealing. It is shown that the customary heat treatments (quenching from the austenitic range for hardening and annealing for softening) may have an effect opposite to the expected one. This phenomenon may be caused by phase transformations of the austenite during its cooling due to precipitation of carbides. It is established that super-cooled austenite is resistant to martensitic transformation, deformation, and cold treatment after rapid cooling. Aging of the martensite and its decomposition into martensite and carbides with growth of the microhardness are observed at the temperatures no lower than 750 degrees C.