EFFECT OF CRACK INITIATION MODE ON LOW-CYCLE FATIGUE LIFE OF TYPE 304 STAINLESS-STEEL WITH SURFACE-ROUGHNESS

To investigate the effect of surface roughness and grain size on the fatigue life, low cycle fatigue (LCF) tests were carried out on type 304 stainless-steel specimens with three different modes of surface roughness and two different grain sizes (50-mu-m, 500-mu-m) at the test temperatures of 300 and 873 K. The fatigue cracks for an electropolished specimen are initiated at grain boundaries regardless of grain size and testing temperature. But the fatigue crack initiation site for a rough-surface specimen depends on the grain size, surface roughness and temperature. The surface roughness effect is decreased with increasing grain size and temperature because of the change in the crack initiation mode.