Effect of Build Orientation and Annealing on Corrosion Resistance of Additively Manufactured Duplex Stainless Steel in 3.5% NaCl

Abstract

Grade 2205 Duplex stainless steel (DSS) components were built via selective laser melting (SLM) with gas atomized powder (D90 < 45μm) using a 250 W laser in a nitrogen environment. The relative density was 99.1 ± 0.3%, and the ferrite/austenite phase ratio after annealing was 53.0/47.0 ± 4.8%. Two build orientations (parallel and perpendicular to build direction), as well as as-built SLM (no heat treatment) and annealed conditions, were studied. Corrosion properties were characterized in a 3.5% NaCl electrolyte and compared to 2205 wrought. The charge transfer resistance was > 500 kohm.cm2, and the corrosion rate was < 100 nA cm−2 for all alloys, which suggest passivity. No stable pit formation occurred during cyclic polarization tests although the as-built perpendicular and annealed SLM conditions showed metastable pitting, likely due to surface porosity and/or chemical inhomogeneity. The as-built parallel condition did not show metastable pitting and had the highest average charge transfer resistance, which is evidence of possible improvements from laser melted material, but not conclusive. Ultimately, all SLM DSS 2205 was similar to 2205 wrought, implying that the build orientation and annealing were not as significant of factors as the chemical composition in predicting the passivity and pitting resistance.