The peculiarities of hydrogen embrittlement of Nb-alloyed stainless steel fabricated by electron-beam additive manufacturing

Abstract

The peculiarities of hydrogen embrittlement of niobium-alloyed austenitic stainless steel produced by wire-feed electron-beam additive manufacturing (EBAM) method have been investigated. After EBAM-growth, the Nb-alloyed steel has had macroscopically and microscopically heterogeneous structure, which has been characterized by austenitic matrix with colonies of ferritic dendrites and Nb-enriched precipitates. Hydrogen-charging causes the increase in the yield strength and the ultimate tensile stress of EBAM-produced specimens relative to hydrogen-free specimens and assists to surface brittle cracking of the specimens. Fracture surface in hydrogen-charged specimens includes several characteristic regions: surface brittle layers (20-25 ȝm) fractured both in transgranular and intergranular modes, subsurface hydrogen-affected zone (35-45 ȝm) with elongated dimples and flat facets (transgranular mode), and ductile central part with dimple micromechanism of fracture (transgranular mode).