Effect of thermo-elasto-plastic strain on the mechanism of twin-free microstructure formation in the stainless steel

The stainless steel with grain growth stagnant microstructure was subjected to rapid heating and quenching cycles repetitively to induce thermo-elasto-plastic strain. The evolving microstructure and grain orientation were analysed using electron microscopy equipped with an EBSD facility. A special emphasis was laid on elucidating the twin evolution mechanism. Multi variant primary and secondary twin (s) formation associated with {001}, {011, {111} and {122} slip planes have been observed by electron microscopy. The possible role of vacancies accumulated during the quenching process and the boundary characteristics on the formation of stacking faults especially in the non-preferred slip planes have been discussed and a logical correlation has also been made on the evolution of crystallographic multi-variant twin (s) within the austenite grains. The result also suggests that the thermo-elasto-plastic strain can have a profound effect in altering the true-twin crystallographic relation of the multi-variant twin(s) within the austenite grains. It has been observed that the grain rotation towards < 110 > preferred orientation resulted in the formation of twin-free refined grain microstructure at some instances of annealing cycles. The absence of twin(s) was correlated with the rotation and widening of the twinned region to a new grain formation. On further subjecting, this twin free microstructure to annealing cycle, reappearance of the new twin(s) noted.