Microstructure and phase composition of vanadium-alloyed high-nitrogen steel fabricated by additive manufacturing

The phase composition, microstructure and microhardness of the vanadium-alloyed high-nitrogen steel produced by electron beam additive manufacturing have been studied and compared with conventionally cast and solution-treated counterpart. It has been shown that phase composition of the high-nitrogen steel is dependent on the method of fabrication. The homogeneous coarse-grained austenitic structure with high concentration of interstitial atoms (N) in solid solution and coarse vanadium-based carbonitrides have been formed in conventionally produced specimens, but additive manufacturing provides the formation of heterogeneous dendritic microstructure of high-nitrogen austenite with numerous precipitates. Additively manufactured specimen has columnar coarse austenitic grains elongated in building direction, and vanadium and chromium carbonitrides are located preferably along grain boundaries. The microhardness of the additively fabricated steel (5.5 GPa) is close to the value for cast steel (5.3 GPa).