Abstract: The microstructures and mechanical properties of 31CrMoV9 steel electron beam welded joints with different post-weld heat treatment (PWHT), including stress relief annealing and quenching and tempering, were investigated and compared to the matrix with the same strength level. The results indicate that the microstructure of the electron beam welded joints is lath martensite and a small amount of retained austenite. After quenching and tempering treatment, the microstructure of the welded joint is relatively uniform tempered sorbite. And the mechanical properties of the joint are equivalent to that of the matrix. Compared with post-weld stress relief annealing treatment, the Charpy impact properties of the quenched and tempered welded joints are improved significantly. The two types of post-weld heat treatment cannot eliminate the solidification structure morphology such as columnar dendrites. The post-weld quenching and tempering process can reduce the segregation of the columnar dendrite structure of the weld and refine it, making the structure and hardness of the weld and the base metal are more uniform. No cracking is found in the electron beam welded joint, by several repeated quenching, which indicates that the post-weld quenching and tempering process is feasible. Therefore, PWHT provides a practical process route for improving the properties of the welded joint.

Key words: 31CrMoV9 steel, electron beam welding, post-weld heat treatment (PWHT), microstructure of welded joint, properties