Effect of heat treatment on microstructure, mechanical and corrosion properties of austenitic stainless steel 316L using arc additive manufacturing

The mechanical and corrosion properties of gas metal arc additive manufacturing (GMA-AM) 316L could be optimized by modifying the volume fractions of sigma (sigma) and delta-ferrite (delta) phases through heat treatment. Results show that the heat treatment at 1000 degrees C to 1200 degrees C for one hour will not obvious influence the morphology of grains in steel but largely influence the contents of sigma and delta phases. The heat treatment at 1000 degrees C effectively increases the amount of sigma phase in steel, causing both increase of UTS and YS but decrease of El and RA. The heat treatment at 1100 degrees C to 1200 degrees C completely eliminates a phase, leading to the decrease of UTS and YS but increase of El and RA. The sigma phase has better strengthening effect than delta phase, but which may degrade ductility and increase the possibility for cracks generation in steel. Meanwhile, limiting the number of both sigma and delta phases through heat treatment can improve the corrosion resistance of steel. And sigma phase appears more detrimental impact on degradation the corrosion resistance of steel than delta phase.