Cyclic Deformation Behavior of a New N+C Alloying Austenitic Manganese Steel

Abstract

The cyclic deformation behavior and fatigue characteristics of a new austenitic manganese steel with composition FeMn18Cr7C0.8N0.2 (wt%) have been explored and analyzed based on the partition of hysteresis loops linked with microstructure by low cycle testing in the total strain amplitudes 0.3% - 1.0%. The new N+C austenitic manganese steel exhibited immediate cyclic softening for small strain amplitude and initial hardening at the onset of fatigue life followed by softening for medium and high strain amplitudes. For low and high strain amplitudes the evolution of internal stress and effective stress partitioned from the hysteresis loop with the prolonged cycles both corresponded to the change in the total stress amplitudes. With the exception of 316LN0.2 austenitic stainless steel, the effective stress and internal stress made a contribution to the cyclic deformation behavior with similar effect. The markedly improved contribution of effective stress in the new N+C austenitic manganese steel was attributed to the enhanced short range order caused by N+C alloying whereas the decreasing of effective stress with the number of cycles was because of this broken short range interaction. TEM observations showed that the significantly increased planar dislocation structures due to the presence of N+C were responsible for the strong tendency to cyclic softening, in association with the decrease of effective stress and internal stress simultaneously. Moreover the fatigue short crack could be observed on the fractured sample surface at high strain amplitude.