Super duplex stainless steel (AWS A5.9 ER2594) fabricated via arc-based directed energy deposition: tensile behavior and fracture toughness at −30 °C

Super duplex stainless steel (SDSS; AWS A5.9 ER2594; UNS S32750) combines high fracture toughness, tensile strength, and corrosion resistance due to its ∼50/50 balance of δ-ferrite and austenite and rich chemical composition (high Cr and Mo content). This combination offers a suitable cost and competitive performance compared with other corrosion-resistant alloys. However, when SDSS is fabricated via arc-based directed energy deposition (SDSS DED-arc), low performance is usually reported, attributed to the non-optimized microstructure and the formation of deleterious phases. In addition, due to the use of SDSS in structural applications (e.g., piping systems) and the ferrite ductile-to-brittle transition, SDSS DED-arc must also ensure adequate fracture toughness at sub-zero temperatures. In this regard, this work evaluated the tensile properties and fracture toughness of an SDSS DED-arc at -30 °C and compared its performance with that of the traditional material (wrought SDSS). SDSS DED-arc parts were printed and subsequently heat-treated (1150 °C / 1 h) to improve the microstructure. In sequence, both additively manufactured and wrought materials were microstructurally characterized and mechanically tested. DED-arc exhibited a microstructure composed of coarse and oriented δ-ferrite with a fine austenite phase distributed within the matrix. In contrast, the wrought material showed a banded microstructure composed of fine and non-oriented grains of δ-ferrite and austenite. The SDSS DED-arc exhibited isotropic behavior, with tensile strength and fracture toughness comparable to (or even exceeding) those of the wrought material, meeting the tensile strength requirements (ASTM A182 UNS S32750) and the fracture toughness engineering benchmark (DNVGL-OS-B101).