Effect of shock deformation on the residual strength and microstructure of nitronic 40 stainless steel

Abstract

The microstructure and mechanical properties of Nitronic 40 austenitic stainless steel were examined after shock deformation. Samples with a grain size of 25 μm were shock deformed to pressures ranging from 2.5 to 60 GPa at a constant pulse duration of 2 μs. Although the as-shock-loaded hardness and tensile flow properties of Nitronic 40 stainless steel generally increased with increasing shock pressure, the effect of shock pressure on the tensile ductility was more complex. For example, a decrease in tensile ductility with increasing pressure was observed at pressures up to 20 GPa. This was followed by a region where the tensile ductility was essentially independent of pressure. Finally, at shock pressures above 40 GPa, the tensile ductility again decreased with increasing shock pressure. Transmission electron microscopy has shown that these variations in mechanical behavior can be correlated to changes in microstructure, i.e. to the formation of coplanar dislocation arrays, stacking faults, deformation twins, ϵ martensite and second-phase particles, which occur in Nitronic 40 stainless steel as a consequence of shock loading.