A comparative study of isothermal and thermomechanical fatigue on type 316L(N) austenitic stainless steel

Thermomechanical fatigue (TMF) behaviour of a nitrogen-alloyed type 316L austenitic stainless steel under in-phase (IP) and out-of-phase (OP) cycling conditions in different temperature domains has been reported. Tests were performed under mechanical strain control mode, at a fixed strain rate of 6.4 × 10−5 s−1 and a strain amplitude of ±0.4%. It was observed that OP TMF yielded lower lives compared to IP TMF in the sub-creep regimes, whereas the reverse was found true in the creep temperature domain. The variations observed in cyclic lives and the cyclic stress response behaviour under isothermal and TMF were examined in relation to the dynamic strain ageing (DSA) effects occurring in the intermediate temperature ranges. The development of dislocation substructures under TMF cycling was evaluated and discussed in relation to the DSA and creep processes. Extensive carbide precipitation was observed under TMF cycling that contributed to an enhanced stress response compared to isothermal cycling at the peak temperature.