Nanoindentation Investigation on the Relation Between Local Mechanical Properties and Cyclic Hardening/Softening Behavior of 310S Stainless Steel

ABSTRACT The fatigue behaviors of 310S stainless steel contained initial hardening, cyclic softening, and secondary hardening, which are complex and hard to characterize. In this work, the fully reversed strain‐controlled fatigue tests were conducted at constant strain amplitudes ranging from 0.25% to 1.0%. Scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD) were used to observe microstructures. The mechanisms of initial hardening, cyclic softening and secondary hardening behaviors were dominated by the interaction between dislocation and grain boundary, recovery of grain boundary, and formation of substructure such as dislocation cell within the grain, respectively. Nanoindentation measurements of hardness and elastic modulus showed that the hardness of specimens increased at low strain amplitudes due to higher geometrically necessary dislocations (GND) density near grain boundaries. When the strain amplitude further increases (above 0.5%), the recovery of grain boundary reaches a limitation, and the hardness of the tested specimen is saturated at 2.45 GPa.