The effects of Cr and Ni equivalents on the microstructure and corrosion resistance of austenitic stainless steels fabricated by laser powder bed fusion

In this study, two gas-atomized austenitic stainless steel (ASS) powders with a predominant difference in Cr contents, Mod.-A (18Cr-14Ni-2.6Mo) and Mod.-B (22Cr-14Ni-2.5Mo), were applied in the laser powder bed fusion (LPBF) process. The two kinds of powders and the Mod.-B LPBF sample contained a certain amount of ferrite, whereas, the Mod.-A LPBF sample was found to contain no ferrite. Furthermore, the ferrite content of the Mod.-B LPBF sample determined by ferrite scope (about 5.5 %) was lower than that estimated by Schaeffler diagram (over 10 %). The rapid solidification of the LPBF process tended to reduce the ferrite contents of the fabricated sample as compared with the amount of ferrite present in the feedstock powder or estimated by Schaeffler diagram. It was noted that the chemical compositions of the austenite and ferrite in the Mod.-B LPBF sample had no noticeable differences. Moreover, few ferrites in the LPBF sample caused a significant grain refinement, which resulted in obvious increases in yield and ultimate tensile strength but a decrease in ductility. The corrosion behavior of the 316L plate and two LPBF samples was investigated in 3.5 wt% NaCl, 1 M HCl and 0.5 M H2SO4 solution in this work. The corrosion resistance of the LPBF samples were higher than that of 316L plate in 3.5 wt% NaCl and 1 M HCl solution. In 0.5 M H2SO4 solution, all three tested samples exhibited nearly the same potentiodynamic polarization curves. Overall, the Mod.-B LPBF sample exhibited corrosion resistance equivalent or superior to that of the 316L plate and Mod.-A LPBF sample.