Microstructure analysis of novel LPBF-processed duplex stainless steels correlated to their mechanical and corrosion properties

Abstract

The austenitic steel AISI 316L has recently become one of the most popular alloys for laser powder bed fusion as it shows good mechanical properties along with sufficient corrosion resistance. For duplex stainless steels the LPBF process does not seem to be as attractive as a solution annealing treatment is required to attain the desired austenite and ferrite microstructure. The goal of this study is to identify a chemical composition that shows enhanced corrosion resistance and tensile strength compared to AISI 316L without requiring a post-process heat treatment like the conventional duplex stainless steels. Based on thermodynamic simulations powder mixtures of austenitic stainless steel AISI 316L and duplex stainless steel AISI 318LN in three mixing ratios have been processed. The influence of the chemical composition and LPBF processing parameters on the resulting microstructure are investigated by light optical microscopy and electron backscatter diffraction. Tensile tests were conducted and polarization curves recorded to evaluate the potential of the most promising alloy. 30 wt.-% of AISI 318LN added to AISI 316L lead to an austenite/ferrite microstructure in the as-built condition. The phase fractions vary with the LPBF processing parameters. The strength as well as corrosion resistance of this new alloy is superior to that of pure AISI 316L, while the ductility is lower.