The difference in fatigue crack growth induced by internal and external hydrogen in selective laser melted 304L stainless steel

The mechanical properties of selective-laser-melted (SLM) 304L steel under hydrogen charging and hydrogen environment were investigated by tensile and fatigue crack growth (FCG) tests. SLM samples showed higher mechanical properties and weaker hydrogen embrittlement compared with wrought samples, and the FCG rates of SLM 304L tested in a hydrogen environment were higher than hydrogen-charged samples. More obvious cleavage platforms and lamellar structures appeared and cracking tended to the multi-directional feature in the hydrogen gas environment. External hydrogen promotes slip planarity, deformation twinning, and plastic localization near the crack tip, and then causes the acceleration of FCG in SLM 304L steel.