Microstructure and tensile behavior of friction-stir welded TRIP steel

Material softening in the heat-affected zone was deduced to be a combined result of dissolution and spheroidisation of retained austenite as well as recovery in bainitic ferrite. The stir zone martensite was characterized by significant orientation spread and therefore its orientation relationship with austenite essentially deviated from the ideal Kurdjumov-Sachs relation. Moreover, the martensite transformation was found to be influenced by variant selection.