Microstructure evolution and strengthening mechanisms in friction-stir welded TWIP steel

In this work, microstructure evolution during friction-stir welding (FSW) of TWIP steel was studied and the concomitant strengthening effect was elucidated. It was found that grain structure development resulted from competition between discontinuous- and continuous recrystallizations. Surprisingly, no clear evidences of extensive mechanical twinning were found, presumably due to high-temperature character of FSW process. The final microstructure evolved in stir zone was characterized by relatively high dislocation density and significant proportion of low-angle boundaries. From quantification of hardening mechanisms, it was shown that the substructure imparted significant strengthening effect.