Microstructure engineering in duplex stainless steels via laser powder-bed fusion additive manufacturing

Duplex stainless steels, characterized by approximately equal fractions of austenite and ferrite in their equilibrium state, exhibit an exceptional combination of superior corrosion resistance and mechanical properties. However, when these steels are produced using laser powder bed fusion additive manufacturing, the rapid cooling rates typically lead to a non-equilibrium microstructure dominated by delta-ferrite. Additionally, fluctuations in energy distribution contribute to chemical and interfacial instabilities. While this metastable microstructure results in lower ductility and toughness in the as-built state, it serves as an optimal precursor for a controlled transformation into ultrafine austenite during heat treatment. Here, we uncover critical insights into how printing parameters influence the morphology, size, and dislocation density of solidified delta-ferrite, as well as their impact on the phase transformation pathway, morphology, size, and interface characteristics of the resulting austenite. These findings offer a framework for tailoring microstructures in multi-phase materials fabricated through additive manufacturing.