Effect of tempering treatment on microstructure and properties of supermartensitic stainless steel deposited metal

The welding of large-scale impluse turbine runners is a significant engineering challenge that needs urgent resolution in China. This presents elevated demands for the impact performance of supermartensitic stainless steel welding materials. The optimization of the post-weld heat treatment process is a crucial method to address this issue. For this purpose, the effect of various tempering treatment on the microstructure and mechanical properties of supermartensitic stainless steel deposited metal was investigated. The chemical composition, microstructure, tensile strength, impact and hardness of the deposited metal were tested and characterized. The results show that the tempering microstructure of the deposited metal consists of fine tempered martensite and reversed austenite. Compared with the one-stage tempering at 590 ℃ for 8 hours, the two-stage tempering can increase the content of the reversed austenite. The content of the reversed austenite further increases with the increase in the two-stage tempering temperature. The increase in the soft and ductile reversed austenite improves the impact performance of the deposited metal. After the two-stage tempering at 650 ℃ for 2 hours followed by 590 ℃ for 8 hours, a 16% volume fraction of reversed austenite can be obtained. The impact absorption energy of the deposited metal at 0 ℃ reaches 90 J, which is about 23% higher than the one-stage tempering. The corresponding impact fracture characteristics change from ductile + partially brittle fracture to complete ductile fracture.