Effect of Grain Boundary Engineering on the Work Hardening Behavior of AL6XN Super-Austenitic Stainless Steel

To examine the influence of grain boundary engineering (GBE) on the work hardening behavior, the tensile tests were carried out on the non-GBE and GBE AL6XN super-austenitic stainless steel (ASS) samples with a comparable grain size at two strain rates of 10(-2) s(-1) and 10(-4) s(-1). The evolution of deformation microstructures was revealed by transmission electron microscopy (TEM) and quasi-in situ electron backscatter diffraction (EBSD) observations. The results show that the influence of GBE on the mechanical properties of AL6XN super-ASS is mainly manifested in the change of work hardening behavior. At the early stage of plastic deformation, GBE samples show a slightly lowered work hardening rate, since the special grain boundaries (SBs) of a high fraction induce a higher dislocation free path and a weaker back stress; however, with increasing plastic deformation amount, the work hardening rate of GBE samples gradually surpasses that of non-GBE samples due to the better capacity of maintainable work hardening that is profited from the inhibited dislocation annihilation by SBs. In a word, the enhanced capacity of sustained work hardening effectively postpones the appearance of necking point and thus efficaciously ameliorates the ductility of GBE samples under the premise of little changes in yield strength and ultimate tensile strength.