Sensitivity of a high nitrogen austenitic stainless steel to fatigue crack initiation

The low cycle fatigue behaviour of a 0.9%NCr-Mn austenitic stainless has been investigated at room temperature and at 77 K at total strains ranging from Delta epsilon(t) = 0.6 to 2.5%. The macroscopic behaviour, cyclic stress amplitude and accommodation period, is strongly influenced by the test temperature. The fatigue resistance has been associated to surface plasticity and to crack initiation. Cycling at low temperature or st room temperature at high strain amplitude favours crack initiation at grain boundaries which is detrimental for fatigue resistance. However, it is found that the fatigue cracks tend to initiate transgranularly which is beneficial for fatigue resistance when the alloy is previously aged at 350 degrees C.