Rate controlling deformation mechanisms in SS316L stainless steel manufactured using laser powder bed fusion technique

Abstract

We conducted uniaxial tensile strain rate jump tests to account for the strain rate controlling mechanisms in the additively manufactured SS316L stainless steel. Special emphasis is placed on the role of high dislocation density and chemical segregation on dictating the rate sensitive behavior. Lowest strain rate sensitivity is found, despite the highest dislocation density in the as build state, which signified the role of solute segregation at cell walls in increasing the activation volume and forms the strong basis for rejecting dislocation forest as the strain rate controlling obstacles. Consistent increase in the strain rate sensitivity with annealing is found consistent with the chemical homogenisation of the solutes causing smaller inter-obstacle spacing causing decreasing activation volume. Experimental findings are supported by CALPHAD simulations and mechanical threshold stress (MTS) modelling framework. Significant difference between the instantaneous and steady state rate sensitivity is understood using the dynamic pileup dislocation density readjustment mechanism causing considerable flow transient while adjusting the mobile dislocation density on strain rate change in the presence of solute decorated dislocation cells. Present investigation helps in gaining newer insights into the deformation mechanisms of the additively manufactured alloys featuring cellular microstructures.