Microstructure and mechanical properties of Nb-alloyed austenitic CrNi steel fabricated by wire-feed electron beam additive manufacturing

• Published in: Materials characterization 2022-08, Vol.190, p.112063, Article 112063
• Main Authors: Panchenko, Marina Yu, Maier, Galina G., Moskvina, Valentina A., Astafurov, Sergey V., Melnikov, Evgenii V., Reunova, Kseniya A., Kolubaev, Evgenii A., Astafurova, Elena G.
• Format: Article
• Language: English
• Subjects: Additive manufacturing; Microstructure; Nb-alloying; Solid-solution treatment; Stainless steel
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2022.112063

We investigated the phase composition, microstructure, mechanical properties, and fracture mechanisms of Nb-alloyed austenitic stainless steel produced by electron beam additive manufacturing (EBAM) after different regimes of the post-EBAM solid-solution treatments. As-build EBAM-produced steel has a predominantly austenitic structure, contains vermicular δ-ferrite (Vδ = 5–7%) and Nb-enriched precipitates (Laves phase Fe2Nb, FeNb and NbC). Niobium-alloying assists the stabilization of austenitic phase but does not suppress the columnar grain growth during EBAM-fabrication of austenitic stainless steels. Solid-solution treatments provide a change in morphology of δ-ferrite, a decrease in the ferrite volume fraction and the dissolution of intermetallic phases (Fe2Nb, FeNb), which all affect the tensile properties. Post-EBAM treatments contribute a decrease in the yield strength of the steel and improve the elongation-to-failure. All EBAM-produced specimens have good mechanical properties, which are comparable with those for steels produced by conventional methods. Irrespective of treatment regime, EBAM-fabricated specimens exhibit ductile transgranular fracture. For the EBAM-produced Nb-alloyed steel, the phase composition is described from the point of view solidification mode, and the effects of the precipitate hardening and solid-solution strengthening on the mechanical properties and fracture mechanisms were discussed. [Display omitted] •Nb-alloyed austenitic stainless steel was produced by electron beam additive manufacture.•As-build steel has austenitic structure with δ-ferrite and Nb-enriched precipitates.•NbC and intermetallic phases (Laves-Fe2Nb, FeNb) are typical of as-built material.•Mechanical properties of EBAM-produced steel are comparable with conventional steels.•EBAM-fabricated steel fracture in ductile transgranular mode.