Annealing twin evolution in the grain-growth stagnant austenitic stainless steel microstructure

Abstract

Twin evolution mechanism in the growing and otherwise growth-stagnant grains of austenitic stainless steel was studied here during isothermal annealing and repetitive anneal-quench cycle. Specimens were subjected to two different types of annealing treattnent; a) isothermal annealing for different durations at 1200 degrees C and b) also repetitively annealed at 1200 degrees C and then water quenched. Under isothermal annealing conditions a critical grain growth kinetics was found responsible for the occurrence of high twin frequency. Interestingly, almost negligible twinning tendency was seen after grain growth becomes stagnant. However, reoccurence of twinning activity was seen in growth-stagnant grains when subjected to the repetitive anneal-quench cycles. Reoccurrence of twinning, in otherwise growth stagnant grains, behaviour is attributed to thermo-elastoplastic strain generation due to repetitive thermal volume expansion and contraction. It is proposed in this study that quenching from high temperature resulted in interface stress generation due to rigid body rotation of grains and also local modified stacking fault energy sites at grain boundary.