Influence of intrinsic manufacturing defects on corrosion behavior of AISI 420 stainless steel fabricated by laser powder bed fusion

In this study, 420 stainless steel (SS) was fabricated by L-PBF with specific processing parameters: 140 W laser power, 550 mm/s scanning speed, 80 mu m spot size, and 50 mu m layer thickness. The resulting specimens exhibited 0.42% porosity and an average size of 18 mu m for Lack-of-fusion (LOF) pores, with elemental C and Cr ablation at approximately 35.9% and 18.0%, respectively. A comparative analysis between the corrosion resistance of L-PBF specimens and cast 420 SS was conducted. Despite exhibiting extraordinary mechanical properties, L-PBF specimen displayed lower corrosion resistance and failed to produce a passive region. LOF pores and elemental ablation from intrinsic laser additive manufacturing process were the primary reasons for this outcome. Two distinct corrosion mechanisms were observed in the study. The LOF pores exhibited a higher susceptibility to pitting corrosion, leading to the formation of larger pitting pits with an approximate size of 100 mu m. Conversely, the LOF-free areas displayed the presence of smaller pitting nucleation, measuring < 2 mu m. This observation was attributed to the ablation of C element, leading to a 28% increase in the Cr/C content. The higher Cr/C in the LOF-free areas offered enhanced protection, thus preventing the formation of larger pitting pits in these regions.