Effect of microstructure and hardness on non-proportional cyclic hardening coefficient and predictions

This paper investigates the effects of microstructure and hardness on non-proportional cyclic hardening of metallic materials. Constant amplitude in-phase and 90° out-of-phase strain-controlled axial-torsion cyclic tests were conducted to evaluate the hardening. Tubular specimens made from 1050 steel in normalized, quenched and tempered, and induction hardened conditions as well as 304L stainless steel were used to study the effect of microstructure on multiaxial cyclic deformation. Reductions in the non-proportional cyclic hardening were observed as the microstructure of 1050 steel changed form pearlitic–ferritic with lower hardness to tempered martensite with higher hardness. Significant non-proportional cyclic hardening was also observed for 304L stainless steel with austenitic microstructure. Multiaxial data generated in this study as well as multiaxial deformation data of several materials from literature suggest non-proportional cyclic hardening can be related to uniaxial cyclic hardening. Non-proportional hardening coefficients predicted from a proposed equation based on this observation were found to be in very good agreement with the experimental values in this study and from the literature.