On the origin of grain refinement and twin boundaries in as-fabricated austenitic stainless steels produced by laser powder bed fusion

Abstract

316 L austenitic stainless steel samples have been fabricated by laser powder bed fusion using two powder batches of slightly different compositions but keeping the same processing parameters. Compared to the first powder batch, the second powder batch led to a finer grain structure, a more random texture, and an extremely high density of Σ3 twin boundaries. A review of the literature shows that these two kinds of microstructures had been observed in previous works, but separately and not connected to changes in composition. Several hypotheses are reviewed to explain these microstructure differences. We conclude that local liquid ordering, also described as icosahedral short range order (ISRO) can have an effect on the microstructure formation during solidification. ISRO in the liquid is thought to be stronger in the second powder batch. Finding ways to enhance the influence of the ISRO in the liquid on the microstructure formation can be seen as a promising strategy to design alloys for additive manufacturing.