Hydrogen-enhanced densified deformation twins in 304L austenitic stainless steel fabricated by selective laser melting

Twin boundaries are the preferred site for crack nucleation and propagation in a hydrogen-rich environment. The relationship among hydrogen, cellular structure, and deformation twins is significant in further enhancing the resistance to hydrogen embrittlement of austenitic stainless steels produced by SLM. It has been demonstrated that cellular structures with high dislocation densities play a positive role in increasing stress above a critical level for deformation twin formation. The cellular structure affects the distribution of hydrogen, with hydrogen presence at cellular boundaries reducing its accumulation at grain boundaries. Hydrogen increases the density of deformation twins and reduces the thickness of individual deformation twins. This phenomenon can be attributed to an increase in nucleation sites for the deformation twin, which is closely related to the decrease in stacking fault energy and the increase in dislocation density caused by hydrogen. Both cellular structure and deformation twins play a positive role in improving the hydrogen embrittlement resistance of austenitic stainless steels.