Characterizations of 21-4N to 4Cr9Si2 stainless steel dissimilar joint bonded by electric-resistance-heat-aided friction welding

A new welding process, electric-resistance-heat-aided friction welding (ERHAFW), was introduced in this study. To further improve the joint quality and energy-saving, electric resistance welding was combined with the conventional continuous-drive friction welding. 21-4N (austenitic stainless steel) and 4Cr9Si2 (martensitic stainless steel) valve steel rods of 4 mm diameter were used as base metals. The results show that electric-resistance-heat-aided friction welding can be applied to join thin rods within a relatively short time, which is very difficult for conventional friction welding (FW). The microstructure of ERHAFW bonded 21-4N to 4Cr9Si2 presents non-uniform across the joint. Different structure zones are observed from the weld line to both sides, which are the weld center, thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ). These regions exhibit different structures owing to the difference in the thermophysical and mechanical properties of these two steels under the fast heating and cooling during welding. The variation of microhardness in the joint is attributed to the microstructure change. The higher microhardness is obtained in the weld center and TMAZ of 4Cr9Si2 corresponding to the presence of fine tempered martensite and carbides.