Discussing the precipitation behavior of σ phase using diffusion equation and thermodynamic simulation in dissimilar stainless steels

This study performed a precipitation examination of the σ phase using the Vitek diffusion equation and thermodynamic simulation in dissimilar stainless steels during multi-pass welding. The results of the experiment demonstrate that the diffusion rates (DCrδ and DNiδ) of Cr and Ni are higher in δ-ferrite than (DCrγ and DNiγ) in the γ phase and that they facilitate the precipitation of σ phase in the third pass fusion zone. When the diffusion activation energy of Cr in δ-ferrite is equal to that of Ni in δ-ferrite (Qd Crδ≒Qd Niδ), phase transformation of the δ → σ can be occurred.

Research highlightsThis article concentrates the phase transformation in δ → σ in dissimilar stainless steels using the Vitek equation and thermodynamics simulation during the multi-pass welding. The phase transformation in δ → σ is very important to the properties of stainless steel composites. In this study, the diffusion behavior of Cr, Ni and Si in the δ, σ, and γ phases were discussed using the DSC analysis and diffusion equation calculation. This method has a novelty for discussing the phase transformation in δ → σ in the dissimilar stainless steel. We hope that we can give a scientific contribution for the phase transformation of the dissimilar stainless steels during the multi-pass welding.