Mechanical properties and microstructure evolution of additive manufactured 316L stainless steel under dynamic loading

Abstract

Stainless steel 316L alloy with a complete austenite phase was manufactured using the Laser Engineered Net Shaping (LENS) technique. The microstructure of LENS-316L from the sub-millimeter to nanometer domains was analyzed using multi-scale characterization methods. The dynamic behavior of LENS-316L was studied by the Split Hopkinson Pressure Bar (SHPB) test. In this study, the dominating strengthening mechanism of the microstructure in LENS-316L was the dislocation strengthening mechanism, providing approximately 153 MPa. The molten pool deforms significantly after the material was dynamically compressed. When the strain rate reached 5000 s−1, the material exhibited an adiabatic shear phenomenon and formed adiabatic shear bands. The width of the shear band decreased with the increase in the strain rate. When the strain rate increases from 3000 s−1 to 4000 s−1, the dislocation density increases, the number of twins increases, and the twin thickness decreases. The effect of varying strain rates (3000, 4000, 5000, 6000 s−1) and varying temperatures (20, 150, 272, 450, 620 °C), on the stress–strain curves of the material were studied through the SHPB test. Additionally, the traditional Johnson–Cook (JC) constitutive model was modified. The modified constitutive model considers the effects of the strain rate and temperature softening coefficients in the strain hardening stage to predict the mechanical behavior of LENS-316L at high temperature and strain rates. Model predictions were in agreement with the experimental data. This study provides important insights for applying the LENS-316L complex construction in a dynamic load impact environment.