Effects of Tempering Holding Time on Microstructure and Mechanical Properties of Low-alloy CrMo Bainitic Steel Used for Electric Power Fittings

The effects of tempering holding time on the microstructure and mechanical properties of low-alloy CrMo bainitic steel for power fittings were studied by mechanical property testing and microstructure observation. The test results show that after isothermal quenching treatment, the microstructure of the material is bainite. During the tempering holding process, the M-A component on the bainite decomposes into ferrite（α） and M₃C. As the tempering holding time increases,M₃C is gradually spheroidizing and dissolving, M₂₃C₆ precipitates and grows at the grain boundary and sub-grain boundary.The spheroidizing and dissolving of M₃C result in the decrease of the tensile strength of the material and increase of the elongation. The precipitation of M₂₃C₆ at the grain boundary and sub-grain boundary is the main reason for the decrease in the impact performance of the material.