Investigation of cyclic deformation behavior in the surface layer of 18Cr–8Ni austenitic stainless steel based on Vickers microhardness measurement

Abstract

The physical basis of the cyclic deformation behavior detection based on Vickers hardness measurement was introduced briefly. The fatigue hardening/softening behavior of the bulk material of 18Cr–8Ni austenitic stainless steel was determined in terms of the cycle-dependent changes in stress amplitude under total-strain-control low-cycle fatigue (LCF) testing and its micromechanisms were discussed preliminarily. The values of Vickers microhardness on the surface of the specimens were measured periodically during the course of fatigue failure and the cyclic deformation resistance changes in the surface layer was analyzed according to the physical character of the Vickers hardness. It is shown, by comparing the cyclic deformation behavior in the near-surface regions with that in the bulk material, that at a high strain amplitude both the surface layer and the bulk undergo a similar hardening behavior within the whole fatigue life, while at a low strain amplitude the surface layer undergoes a continuous hardening process, whereas in the bulk a slight softening occurs after an increasing hardening to a maximum value during initial cycles. Microstructure observations in both the near-surface regions and the interior of the cyclically deformed specimens as well as SEM examinations of the fracture surface were performed to explain the above experimental results.