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 h as 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 influe nced by the test temperature. The fatigue resistance has been associat ed to surface plasticity and to crack initiation. Cycling at low tempe rature or st room temperature at high strain amplitude favours crack i nitiation at grain boundaries which is detrimental for fatigue resista nce. However, it is found that the fatigue cracks tend to initiate tra nsgranularly which is beneficial for fatigue resistance when the alloy is previously aged at 350 degrees C.