ROLE OF MARTENSITE FORMATION ON CYCLIC STRESS-STRAIN BEHAVIOR OF 304LN-STAINLESS STEEL

In this investigation, experiments have been carried out at room temperature (RT); 300K, and at high temperature (HT); 573K to determine the role of martensite formation in the strain-controlled low cycle fatigue of 304LN (0.11%) stainless steel. Deformation-induced martensite was significantly present (0.7 to 2.3%) for RT, however, in trace amounts (0.05 to 0.07%) at HT. The presence of deformation-induced martensite at RT had detrimental effect on low cycle fatigue life of 304LN-SS. Significant drop in stress level was observed at HT (270-407 MPa) compared to value of stress at RT (395- 493 MPa) for cyclic stain amplitude values in the range (0.5 to 1.1%).The number of reversals to failure decreased with increasing strain amplitude (0.5 to 1.1%) from 17540.0 to 1046.0 at RT while at HT the number of cycles to failure decreased (15562 to 700). The maximum number of hardening cycles was found to increase from 15 to 55 for a temperature rise from 300K to 573K. The beneficial improvement in cyclic stress-strain response (hardening cycles) at 573K is attributed to absence of martensite. Effects of deformation-induced martensite and temperature have been invoked to account for changes that have been observed in the cyclic stress-strain behavior.