Segregation-dependent mechanical stability of reverted austenite and resultant tensile properties of Co-free maraging steel fabricated by wire-arc directed energy deposition

Abstract

The segregation-dependent mechanical stability of reverted austenite (RA) and resultant tensile properties was investigated on Co-free maraging steel fabricated by wire-arc directed energy deposition (DED). The results showed that the segregation in the interdendritic regions enabled the formation of gradient reverted austenite in Co-free maraging steel fabricated by wire-arc DED when subjected to aging heat treatment. The content and mechanical stability of reverted austenite and resultant tensile properties were strongly dependent on the degree and compositional gradient of segregation in the interdendritic regions as well as the post heat treatment process. The reverted austenite with compositional gradient inherited from the segregation, transformed into martensite successively from the edge to the interior within individual reverted austenite grain at different strain levels. Besides, the variations in the degree and compositional gradient of segregation in the interdendritic regions widened the range the mechanical stability of the reverted austenite and thereby activating martensite transformation over a broad strain regime. Annealing process prior to aging could modify the degree and compositional gradient of segregation in the interdendritic regions and accordingly tune the content and the range of mechanical stabilities of reverted austenite grains, thus attaining a gradual and consistent transformation induced plasticity effect over whole deformation regime and thereby increasing ductility without sacrificing strength of Co-free maraging steel fabricated by wire-arc DED.