The effect of phase composition and phase distribution on the peculiarities of crack formation and fracture mechanism in Cr-Ni steels obtained by electron beam 3D-printing

The peculiarities of crack formation near the fracture region and fracture micromechanism at uniaxial tension of specimens of stainless Ni-Cr steels, obtained by the method of electron beam 3D-printing, were investigated depending on phase composition and phase distribution in the structure. It was found that in specimens with a two-phase (austenite / δ-ferrite) microstructure, the morphology of ferrite and its volume fraction (up to 25%) affect the distribution of plastic shear in austenite and ferrite, have a weak effect on the behavior of the formation of micro- and macroscopic localized deformation bands in pre-fracture stage of plastic flow. The mechanism of crack formation is similar to that observed in cast stainless steels of similar compositions exhibited a single-phase austenitic structure. In additive-grown steel containing niobium, the brittle intermetallic phases based on niobium and iron promote the formation of pores and microcracks at the “austenite / NbFeCrNi-phase” or “δ-ferrite / NbFeCrNi-phase” interfaces, and the formation of cracks in the localized deformation bands (and their formation) is suppressed. Regardless of the elemental and phase composition of the steel specimens obtained by the additive 3D-printing method, their main fracture micromechanism, a transgranular dimpled fracture, is similar to that observed in cast specimens of austenitic stainless steels.

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