Inhomogeneity of Microstructure along the Thickness Direction in Stir Zone of Friction Stir Welded Duplex Stainless Steel

Inhomogeneity in microstructures along the thickness direction stir zone of a duplex stainless steel (SUS329J4L) welded at rotational speeds 275 rpm, 400 and 800 rpm were investigated using electron back scattered diffraction method. The changes volume fractions average grain sizes ferrite austenite may reflect temperature gradient direction. However, near top surface, significant refinement occurred presumably due to introduction additional strain by shoulder. KAM values exhibited higher value than through all direction, which is inferred be related difference dynamic recrystallization behavior governed stacking fault energy; i.e., lower phase phase. layer per unit length layered structure became smaller that base metal as speed FSW was reduced implies new grains nucleate during FSW. Furthermore, some nucleated austenite/austenite boundaries confirmed satisfy Kurdjumov-Sachs orientation relationship. assumed promote nucleation with different phases probably owing stirring effect elements In formed FSW, linear relationship between found hold irrespective speeds.