Effect of nitrogen on high temperature low cycle fatigue behaviors in type 316L stainless steel

Abstract

Strain-controlled low cycle fatigue (LCF) tests were conducted in the temperature range of RT-600 degrees C and air atmosphere to investigate the nitrogen effect on LCF behavior of type 316L stainless steels with different nitrogen contents (0.01-0.15%). The waveform of LCF was a symmetrical triangle with a strain amplitude of +/- 0.5% and a constant strain rate of 2 x 10(-3)/s was employed for most tests. Cyclic stress response of the alloys exhibited a gradual cyclic softening at RT, but a cyclic hardening at an early stage of fatigue life at 300-600 degrees C. The hardening at high temperature was attributed to dynamic strain aging (DSA). Nitrogen addition decreased hardening magnitude (maximum cyclic stress - first cyclic stress) because nitrogen retarded DSA for these conditions. The dislocation structures were changed from cell to planar structure with increasing temperature and nitrogen addition by DSA and short range order (SRO), Fatigue life was a maximum at 0.1% nitrogen content, which was attributed to the balance between DSA and SRO. (C) 1998 Elsevier Science B.V.