Microstructural investigation of the fatigue behavior and phase transformation in metastable austenitic steels at ambient and lower temperatures

Microstructural investigations of the fatigue behavior and phase transformation in the metastable austenitic steels AISI 304 and 348 were performed. The specimens were cyclically loaded with a constant total-strain-amplitude in the temperature range −60 °C to 25 °C. By means of stress–strain hysteresis and magnetic measurements, the fatigue behavior and phase transformation were characterized. Microstructural changes were evaluated by transmission electron microscopy and by scanning electron microscopy by means of electron backscatter diffraction technique at defined fatigue states. The steels show differences in austenite stability, which lead to significant changes in the deformation induced martensite formation and the fatigue behavior. Dependent on the type of steel and the testing temperature similar α′-martensite fractions but different strengths developed.

► Fatigue behavior and phase transformation in metastable austenitic steels. ► Higher stability of AISI 304 against martensite formation compared to AISI 348. ► Different strength of martensite was proved experimentally. ► Microstructural characterization of martensite by EBSD, TEM and magnetic induction. ► The differences in strength of the martensite of AISI 304 and 348 were characterized and described.