Effect of Heat Treatments on Residual Stress and Properties of AISI 316L Steel Processed by Directed Energy Deposition

AISI 316L stainless steel samples were produced by means of laser powder-directed energy deposition using optimized building conditions with two different deposition strategies. The samples, in the as-built state, were at first characterized in terms of microstructure, hardness and residual stresses by the incremental hole-drilling strain-gauge method. The results highlighted that the deposition strategy mainly affects the residual stress values, while the material hardness value is not strongly varied. The distribution of the residual stresses along the sample height was also evaluated by measuring the stress at different distances from the building platform. Furthermore, some samples underwent a homogenizing heat treatment for 2 h at 600 and 800 °C and were characterized and compared with the as-built ones. The results showed that the suggested heat treatments allow not only a reduction in residual stresses but also the homogenization of the microstructure confirmed by comparing the variations of the Vickers hardness values along the building direction. Tensile tests were also performed on the as-built and heat-treated samples in order to investigate the effect of the heat treatment on the tensile properties of the material.