An in situ study on austenite memory and austenitic spontaneous recrystallization of a martensitic steel

▶ In situ observation showed direct understanding of austenite memory. ▶ Coherent interface between acicular austenite and martensite caused austenite memory. ▶ Austenitic spontaneous recrystallization occurred 70 °C higher than A f temperature. ▶ Austenite change was affected by interfacial and phase transformation stored energy. The phenomenon of austenite memory in 13Cr–5Ni martensitic steel during the reverse transformation from martensite to austenite has been observed in situ by confocal laser scanning microscope. The mechanisms of austenite memory and austenitic spontaneous recrystallization in relation to the austenite nucleation and growth characteristics from martensite during the reverse transformation have been studied. The results indicated that, acicular austenite led preferably to the recovery of the initial grain size and orientation and exhibited austenite memory when heated to A f temperature. Furthermore, it is proposed that the coherent interface formed between acicular austenite and lath martensite was the direct cause of austenite memory. Grain refinement was induced by nucleation of globular austenite based on austenitic spontaneous recrystallization, which occurred from 900 °C to 950 °C in austenite single phase region driven by phase transformation stored energy. 950 °C was the most appropriate temperature for grain refinement of 13Cr–5Ni steel.