Influence of carbon concentration on martensitic transformation in metastable austenitic steels under cyclic loading conditions

Metastable austenitic steels reveal a partial martensitic transformation during monotonic and cyclic loading. The volume fraction of martensite formed depends strongly on the amplitude and frequency of plastic strain, specimen geometry, the temperature, grain size, and the chemical composition. Particularly the latter has been varied by a carburization/decarburization treatment applied to the three austenitic steels AISI 304, AISI 304L, and AISI 301 (corresponding German designations: X5 CrNi 18 9, X2 CrNi 18 11, X12 CrNi 17 7) in the present study. Fatigue testing of the carbon-modified alloys showed that the martensite formation manifests itself by cyclic hardening which increases clearly by lowering the carbon concentration and vice versa. Since the martensite content within a specimen can be measured easily by determining the magnetic volume fraction, in this study the possibility is evaluated to apply thin foils of austenitic steel on cyclically loaded components, so that the martensite content monitors the damage history of such a component.