Friction stir spot welding of single-crystal austenitic stainless steel

The high-resolution electron backscatter diffraction technique was employed to study the structural response of single-crystal austenitic stainless steel to friction stir spot welding. The strain-induced crystal rotations were found to be governed by simple-shear deformation. In contrast to aluminum alloys, the developed texture showed pronounced A/A {1 1 1}〈1 1 0〉 simple-shear texture components, this effect being attributed to the suppression of cross-slip. Grain boundary development was demonstrated to be closely linked with texture evolution. During pin plunging, at relatively low temperatures, microstructural evolution was shown to be dictated by continuous recrystallization. Due to this process, the single-crystal structure was broken up into an ultrafine-grained polycrystalline aggregate with a mean grain size of ∼0.2 μm. During shoulder contacting, however, the temperature rose and discontinuous recrystallization became predominant.