Maraging Behavior in an Fe-19.5Ni-5Mn Alloy I: Precipitation Characteristics

The aging behavior of an Fe-19.5Ni-5Mn alloy has been studied in detail. A substantial maraging-hardening response was obtained upon aging at between 300–550°C, and it displayed classical hardening behavior. The pronounced hardness was attributed to strain hardening caused by coherent, fine spherical precipitates. The activation energy for precipitation, calculated from microhardness data, was 41 kcal/gmole. Ordered fct θ-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 Widmanstätten austenite grains appeared in a lenticular shape that were coupled together by a twin boundary. Their orientation relationship with the parent martensite was found to be of the Kurdjumov-Sachs (K-S) type.