Microstructural distribution and anisotropic tensile behavior in a 2Cr13 martensitic stainless steel thin wall fabricated by wire arc additive manufacturing

The anisotropic tensile behavior associated with different microstructural distributions in a thin wall of 2Cr13 martensitic stainless steel fabricated by wire arc additive manufacturing was examined. In the lower part of the thin wall, the vertical specimen had a lower strength and higher elongation than the horizontal specimen because of periodically distributed soft and hard bands of tempered martensitic structures toward the building direction. Tensile fracture preferentially occurred in the softest region when loading in the vertical direction, while inevitable crack propagation occurred in both soft and hard regions when horizontal loads were applied. In the upper part of the thin wall, no anisotropy in strength was detected, whereas significantly higher elongation was found in the vertical specimen than in the horizontal specimen. The anisotropic elongation mainly arose from the soft elongated δ-ferrite embedded in the hard quenched martensitic matrix along the building direction, because the elongated δ-ferrite served as a preferential site for crack initiation in the horizontal specimen, but not in the vertical specimen. This study suggests that heterogeneously distributed tempered martensite and elongated δ-ferrite should be appropriately controlled to diminish the anisotropy of the tensile behavior in wire arc additive manufactured martensitic stainless steel.