Influence of Texture and Grain Size on Martensitic Transformations Occurring During Low-Cycle Fatigue of a Fine-Grained Austenitic Stainless Steel

The influence of grain size and texture on microstructural changes occurring during low-cycle fatigue of an austenitic stainless steel are investigated (grain size of 2 and 20 mu m). All the materials exhibited a strong secondary hardening at high strain range as a result of a fatigue-induced martensitic transformation. alpha' martensite is found to nucleate in austenitic grains containing a high density of dislocations but not at slip band intersections, as is usually reported for austenitic stainless steels. Considering the unstable composition of the steel studied and the decrease of the grain size, dislocations structures inside austenite grains are unchanged but cyclic solicitation promotes the induced transformation of austenitic phase. Localization of the martensite grains formed depends on the grain texture and the grain size inside which nucleus are formed.