Characterization and mechanical behavior of AISI 316L/Incoloy 825 dissimilar welds processed by friction stir welding

This work explored the feasibility of friction stir welding between Incoloy 825 Ni-based superalloy and AISI 316 L stainless steel. Microstructure, microtexture, and mechanical properties of the weldments were investigated as well. By using a range of FSW parameters including the rotation speed (ω) of 400-500 rpm and the travel speed (v) of 18-24 mm/min, sound welds were obtained. Optical and electron microscopy examinations revealed that the formation of equiaxed recrystallized austenite and ferrite grains in the stir zones led to an increase in microharness of the welds. Elongated grains with uncompleted recrystallization forms were observed in thermo-mechanically affected zones, too. According to the results of electron backscatter diffraction analysis, a fiber texture with {111} ǁ welding direction relationship for ferrite phase formed in AISI 316 L base metal and stir zones while the orientations of austenite grains in the stir zones were highly dependent on the ω/v ratio. Upon tensile testing, the samples underwent ductile fracture mode, and the tensile strength of the weldments was similar to that of the weaker base metal (i.e. AISI 316 L). Based on the obtained results, the welding conditions including ω =500 rpm and v = 24 mm/min by positioning the stainless steel on the advancing side were recommended.