Low cycle fatigue behavior and microstructure of a high alloyed metastable austenitic cast TRIP-steel

Abstract
Total strain-controlled low-cycle fatigue tests were performed at room temperature on a high alloyed metastable austenitic stainless cast steel in the range of 1x10^-3 ≤ Δ ε_t/2 ≤ 3×10^-2 at constant strain rate of 4×10^-3 s^-1. The cyclic stress response revealed combinations of cyclic hardening, saturation and cyclic softening, depending on the applied cyclic total strain amplitude. Total strain amplitudes higher than 8×10^-3 result in a pronounced secondary hardening up to fracture. In the case of metastable austenitic steels, at higher strain amplitudes the secondary hardening is an indicator for the austenitic-martensitic transformation. The deformation-induced α’-martensite content was detected using a nondestructive magnetic measuring technique (feritscope). The microstructure was investigated for different total strain amplitudes applying optical and scanning electron microscopy (SEM). It could be observed that with an increasing total strain amplitude the deformation band density increased considerably.