Strength and ductility of additively manufactured 310 austenitic stainless steel via wire-arc directed energy deposition: The role of columnar grain growth and ductility-dip cracking

This study investigates the underlying factors governing the mechanical properties of single-wall additively manufactured SS 310 austenitic stainless steel via wire-arc directed energy deposition. It demonstrates the predominant microstructural feature in the printed SS 310 stainless steel is the formation of epitaxial large columnar austenite grains, which promotes the occurrence of sub-solidus solid-state ductility-dip cracking (DDC) during the multi-layer additive manufacturing process. While the yield strength and tensile strength of wire-arc additively manufactured SS 310 are comparable to those of wrought annealed AISI 310, the short micro-cracks and the presence of δ-ferrite hinder the work hardening rate and uniform elongation. Additionally, micro-cracks promote void nucleation during the ductile fracture process, resulting in a noteworthy reduction in post-necking elongation and energy absorption capability. The stress-strain behavior of the manufactured part exhibits anisotropy due to the growth of columnar grains, the heterogeneous periodic microstructure, and the orientation of the ductility-dip cracks. To fully harness the potential of wire-arc additive manufacturing as a cost-effective and sustainable manufacturing process, it is imperative to optimize the grain structure and minimize residual stress to eliminate the occurrence of DDC in the production of SS 310 austenitic stainless steel.