The precipitation control in aged alumina-forming austenitic stainless steels Fe-15Cr-25Ni-3Al-NbWCu by W addition and its effect on the mechanical properties

The effect of Tungsten (W) on the precipitate evolution and mechanical properties of the alumina-forming austenitic stainless steels (AFAs) Fe-15Cr-25Ni-3Al-NbWCu during aging at 700 °C was systematically investigated. After aging at 700 °C, microstructural characterization revealed that both of the secondary NbC and L12-ordered Ni-Cu-Al phases were precipitated in the matrix of the two steels for strengthening alloys, but W-added AFA (AFA-W) steel exhibited a smaller average size of Ni-Cu-Al phase than AFA steel. In addition, most of the precipitates in AFA steels were δ-ferrite phase with prolonging the aging time, and few Fe2Nb-type Laves phases were observed in the 1000 h-aged AFA samples. However, the addition of W promoted the precipitation of Fe2W-type Laves phases and increased its volume fraction during the aging period. The continuity of δ-ferrite at the grain boundary of AFA-W steels was also interrupted by the co-precipitated Fe2W Laves phase and B2-NiAl phase, avoiding the formation of detrimental δ-ferrite network. Compared to AFA steels, AFA-W steels exhibited higher room temperature tensile properties at the same aging time, which may be caused by the strengthening effect of more dispersed Fe2W phases and smaller sizes of Ni-Al-Cu phases in the grain interiors. Meanwhile, the stress concentration on the triple junctions caused by δ-ferrite was decreased by Fe2W precipitates; thus, further resulting in an increased ductility compared to the AFA steels without W addition. •W-added AFA (AFA-W) steel has a smaller average size of L12 Ni-Cu-Al phase.•W promotes the dispersed precipitation of Fe2W-type Laves phase in AFA-W matrix.•Combination of Fe2W Laves with Ni-Cu-Al phases enhances the strength of AFA-W.•W-added AFA (AFA-W) steel shown higher ductility than AFA without W addition.