Role of Si content on microstructural and mechanical responses of 16Cr–25Ni superaustenitic stainless steel weld metals

Abstract

In this work, three 16Cr–25Ni superaustenitic stainless steel weld metals with the Si content of 0.03 wt%, 1.22 wt% and 2.01 wt%, were prepared to study the microstructural evolution and its effect on mechanical properties. The results showed that with the increase of Si content, the size and number density of Mo-rich M6C carbide were increased in the weld metals. In particular, massive long strip shape M6C carbides were observed in the weld metal with the Si content of 2.01 wt%. For tensile tests, good match of strength and ductility was obtained in the weld metals with the Si content of 0.03 wt% and 1.22 wt%. However, the ductility of the weld metal was sharply decreased when the Si content further increased to 2.01 wt%, owing to the long strip shape M6C carbide that weakened the coordinated deformation with the matrix. The impact toughness was monotonously decreased from 185 J to 12 J with the increase of Si content, for the M6C carbide generated easier local stress concentration and fracture that the local stress concentration in the matrix was increasingly difficult to favor the twinning deformation. The results in this work are meaningful for the design of the weld metal with optimized microstructure and high mechanical performance for liquid lead-bismuth eutectic environment.