Deformation-Induced γ → α'-Martensitic Transformation in Austenitic Stainless Steel Obtained by Electron Beam Additive Manufacturing

Abstract: The relationship between strain hardening and kinetics of deformation (Formula presented.) phase transformation in chromium–nickel steel Fe–19Cr–9Ni–0.7Ti–0.06C wt % obtained by electron beam additive manufacture was studied under uniaxial static tension at room temperature and at liquid nitrogen temperature. Additively-produced steel had a two-phase (γ + δ) structure with an increased content of δ-ferrite (≈14%). Post-production heat treatment at 1100°C (for 1 h) allowed to reduce its volume content down to 6%, which is, a predominantly austenitic structure in steel was close to those for analogues obtained by traditional metallurgical methods. Plastic deformation of additively-produced steel was accompanied by the formation of deformation (Formula presented.)-martensite, the volume fraction of which increased with an increase in the strain and with a decrease in the test temperature. Using the method of magnetophase analysis, it was shown that at room temperature, kinetics of the deformation (Formula presented.) transformation was sluggish and it, as well as the stage and magnitude of the strain hardening, weakly dependent on the content of δ-ferrite in the structure of steel obtained by the additive method. At the same time, increased content of the δ-phase under these deformation conditions contributed to an increase in the yield strength and reduced elongation to failure of the additively obtained samples. At low-temperature deformation, when the rapid kinetics of deformation (Formula presented.) transformation was observed, the formation rate of (Formula presented.)-martensite under plastic deformation was slower and strain hardening was weaker in steel with a larger volume fraction of δ-ferrite than those in the samples with low content of δ-phase. © 2022, Allerton Press, Inc.