Abstract: Microstructure evolution and mechanical properties of 1.25Cr-0.5Mo steel with three different normalized microstructures during tempering and simulated post-weld heat treatment were analyzed by means of optical microscope, scanning electron microscope and mechanical testing machine. The results show that a large number of coarse carbides in coarse ferrite+pearlite structure of the 1.25Cr-0.5Mo steel precipitate along the grain boundary after simulated post-weld heat treatment, which reduces the impact property of the steel significantly, while the precipitation of finely dispersed carbides in the ferrite improves the strength of the steel slightly. In addition, the widening of bainite ferrite laths and coarsening of carbides in the bainite structure reduce the strength of the steel, but have little effect on impact property. With the increase of ferrite content, the comprehensive mechanical properties of the 1.25Cr-0.5Mo steel become worse. When the ferrite content is higher than 38%, the mechanical properties of the steel plate will not meet the requirements.

Key words: 1.25Cr-0.5Mo steel, heat treatment, microstructure, mechanical properties, carbides