A novel age-hardenable austenitic stainless steel with superb printability

Abstract

Precipitation-hardened high strength alloys, such as nickel-based alloys, aluminum alloys and stainless steels, are susceptible to hot cracking during 3D printing. This issue is typically mitigated by reducing solute segregation or promoting columnar-to-equiaxed transition. Here, we demonstrate an alternative approach by increasing segregation solutes, especially Ti element, to reduce hot cracking during laser powder bed fusion (LPBF) additive manufacturing of a new austenitic stainless steel (ASS). Enhanced segregation triggers peritectic-like reactions at cell/grain boundaries, forming multiple phases that bridge FCC dendrites. As a result, the new ASS exhibited excellent printability across a broad range of processing parameters. The as-built (AB) steel displayed a heterogeneous columnar grain microstructure with fine L2₁/BCC/C14 precipitates partially decorating cell structures, achieving a yield strength (σ_0.2) above 690 MPa and uniform elongation (ε_u) beyond 17.5 %. The epitaxial growth of the columnar grains was frequently interrupted by puddles of fine grains, leading to near-isotropic tensile properties. Following isochronal annealing at temperatures between 600 and 1150 °C for two hours, the AB steel underwent varying degrees of microstructure evolution, resulting in a broad range of mechanical properties (σ_0.2 from 300 to 1460 MPa and ε_u from 59.5 % to 7.6 %). This high strength is attributed to the formation of the L2₁/σ/η multiple phases at cell and grain boundaries, in combination with coherent L1₂-ordered (γ') nanoparticles precipitated within cell interiors during aging. This study explored that compositional design leveraging the unique solidification behavior of the LPBF process can produce hierarchical-structured stainless steels with excellent printability and tunable mechanical performance.