Stabilization of austenitic structure in transition zone of 'austenitic stainless steel/NiCr alloy' joint fabricated by wire-feed electron beam melting

摘要

The gradient material "stainless steel/NiCr alloy" has been designed using the additive manufacturing method - double wire-feed electron-beam melting. The effect of gradual addition of Ni-based alloy on phase transformation and microstructure in additively-fabricated "stainless steel/NiCr alloy" joint has been revealed. Despite the abrupt change in wire composition during the fabrication of the joint, the wide transition zone is formed between two parts of the additively-manufactured billet: gamma-austenitic matrix and dendritic delta-ferrite in steel part gradually passing into Fe-based austenite, then into Ni-based austenite, and, finally, into gamma-(Ni,Cr) austenite with cellular-shape dendrites in NiCr part. The steel-based transition zone of the as-built joint possesses pure austenitic structure stabilized by nickel in comparison with two-phase dendritic microstructure typical for additively-manufactured CrNi stainless steel. The increased microhardness (2.3-2.4 GPa) corresponds to stable austenitic steel structure of the joint. (C) 2020 Elsevier B.V. All rights reserved.