Thermodynamic Calculations and Heat Treatments on Phase Transformation Characteristics of 9Cr1Mo Steel

9Cr1Mo steels are widely used for high-temperature applications in thermal power plants, owing to their relatively high strengths and low costs. In the present study, thermodynamic calculations of equilibrium and nonequilibrium transformations are carried out by JMatPro software. In the equilibrium condition, the austenite transforms to ferrite with saturated amount of M23C6 carbides ((Cr,Fe)(23)C-6) at a temperature lower than 600?. By contrast, aus-tenite-martensite transformation accompanied by precipitation of a lesser amount of M23C6 carbides occurs lower than 340? under a certain cooling rate during the nonequilibrium process. Meanwhile, an experimental investigation on the effect of various cooling rates after aus-tenization on the microstructure and hardness of austenitized and tempered steel has been presented. The experimental results are close to the calculated ones. As the cooling rate after austenization increases, the ferrite transformation turns into martensite transformation, which could be verified by the variations of hardness, phase compositions, precipitation behaviors and grain boundary characteristics.