Understanding The Impact of Laser Powder Bed Fusion Processing on the Sensitization of Austenitic 316L Stainless Steel Using Standardized Testing Procedures

The intergranular corrosion and degree of sensitization (DOS) of additively manufactured (AM) laser powder bed fusion (LPBF) 316L stainless steel (SS) was investigated and compared to conventional wrought 316L and 317L SS. Electrochemical testing and ASTM standard testing revealed that LPBF 316L microstructural features such as melt pool boundaries, cellular boundaries, and grain boundaries undergo preferential attack due to localized Cr and Mo depletion. In some cases, LPBF 316L SS showed improved intergranular corrosion and DOS in comparison to wrought 316L and 317L. ThermoCalc, X-ray diffraction, and transmission electron microscopy analysis showed that precipitation was similar in LPBF 316L SS and wrought 316L and 317L but the susceptibility of secondary phase formation was improved in LPBF 316L SS. Samples produced with the same volumetric energy density exhibited different degree of sensitization (DOS) revealing poor correlation but improved insight into the impact of higher scan speeds increasing cooling rates and promotion of heterogeneity leading to elevated DOS. Further, samples produced with high melt pool area and ratio of depth remelting showed the low DOS. ASTM standard boiling mass loss testing showed that the interlocking grain structure of LPBF 316L SS reduces grain fallout in comparison to wrought 316L and 317L SS. These findings show that AM 316L SS can have improved intergranular and DOS in comparison to conventional wrought materials.