Increase of strength in metastable austenitic steels due to cyclic deformation-induced - martensite formation

Specimens of the austenitic steels AISI 304, 321 and 348 were investigated in total-strain control fatigue tests in the temperature range from -60°C to 25°C. The fatigue behavior and phase transformation from paramagnetic austenite to ferromagnetic martensitewere investigated by means of stress-strain hysteresis, electrical resistance and magnetic measurements. The influence of the testing temperature on the cyclic deformation behavior and phase transformation is shown in Fig. 1. Due to a decrease in temperature an increase of the stress amplitude occurs. The pronounced cyclic hard- ening can be correlated with two phenomena, an increase of the amount of martensiteand the cyclic hardening of not transformed austenite.