REVERTED AUSTENITE DURING AGING IN 18NI(350) MARAGING-STEEL

The evolution of reverted austenite in 18Ni(350) maraging steel was examined using transmission electron microscopy. The types of reverted austenite observed were determined by the aging temperature and time. On aging at 500 and 570 degrees C, lath-like austenite appears at the prior grain boundaries and the martensite lath-boundaries, but after aging for 4 h at 570 degrees C, plate-like austenite was observed within the martensite laths. These two types of austenite contain a high density of dislocations. During heating to 640 degrees C, Widmanstatten austenite forms within the martensite laths along with lath-like austenite at the prior austenite grain boundaries and the martensite lath-boundaries. The formation of the austenite formed at 640 degrees C appears to be shear dominated but aided by a prior or simultaneous diffusion-controlled process. The orientation relationship of the martensite with the different types of austenite is the Kurdjumov-Sachs (KS) relation.