Deformation and fracture behavior of 316L sintered stainless steel under various strain rate and relative sintered density conditions

Abstract

This study investigates the effects of the strain rate and the relative sintered density on the mechanical response and fracture behavior of 316L sintered stainless steel. Low strain rate compression tests are conducted on an MTS 810 servohydraulic machine at strain rates of 10−3 to 10−1 s−1, while dynamic impact tests are performed using a split-Hopkinson bar at strain, rates of 3×103 to 9×103 s−1. The Taguchi method with an L9 orthogonal array is used to characterize and optimize the sintering process control factors such that the specimens have three different relative sintered densities, i.e., 83, 88, and 93 pct. It is found that the strain rate and relative sintered density have significant effects on the flow stress, fracture strain, strain rate sensitivity, and activation volume. The significant differences observed in the strain rate sensitivity and activation volume in the high and low strain rate tests indicate that the corresponding deformation is dominated by different rate controlling mechanisms. Furthermore, the changes in strain rate sensitivity and thermal activation volume observed at different levels of the relative sintered density are related to the work hardening stress. At high strain rate and relative sintered densities slip deformation in the form of slip bands is frequently observed within the grains. Therefore, it appears that higher strain rates and relative sintered densities represent favorable conditions for the formation of shear bands and cracking, and hence lead to premature specimen fracture. The fracture surfaces contain dimplelike structures, which are indicative of a ductile fracture mode. The depth and the density of these dimples decrease as the strain rate and relative sintered density increase, indicating a loss of ductility.