MARAGING BEHAVIOR IN AN FE-19.5NI-5MN ALLOY - I - PRECIPITATION CHARACTERISTICS (REPRINTED FROM METALLOGRAPHY, VOL 21, PG 399-423, 1988)

The aging behavior of an Fe-19.5Ni-5Mn alloy has been studied in detai l. A substantial maraging-hardening response was obtained upon aging a t between 300-550 degrees C, and it displayed classical hardening beha vior. The pronounced hardness was attributed to strain hardening cause d by coherent, fine spherical precipitates. The activation energy for precipitation, calculated from microhardness data, was 41 kcal/gmole. Ordered fct theta-NiMn precipitates were identified with two different shapes, depending on the aging temperature. Higher aging temperatures resulted in disk-shaped precipitates, while rod precipitates appeared at lower temperatures. Twin-related Widmanstatten austenite grains ap peared in a lenticular shape that were coupled together by a twin boun dary. Their orientation relationship with the parent martensite was fo und to be of the Kurdjumov-Sachs (K-S) type.