Effect of repeated thermal cycling on the formation of retained austenite in 18%Ni 350 grade maraging steel

Samples of 18%Ni 350 grade maraging steel were repeatedly thermal-cycled between ambient temperature and 800 degrees C (above the austenizing finish temperature, A(f)). This heat treatment produced retained austenite in the microstructure, the volume fraction of which increased and decreased alternatively in relation to the number of thermal cycles. It was observed that the retained austenite (gamma), after having grown to a certain extent transformed back to the martensite phase (alpha(2)) and had the following orientation relationship with the parent martensite matrix (alpha(1)): (110)(alpha 1)//(110)(alpha 2) ((1) over bar 1 (2) over bar)(alpha 1)//((1) over bar 10)(alpha 2). This may be explained on the basis of the Nishiyama-Wassermann (N-W) and Kudjumov-Sachs (K-S) orientation relationships between austenite (gamma) and martensite (alpha) phases.