Restricted variant selection in martensite transformation of maraging steel during additive manufacturing

Abstract

Abnormal martensitic microstructures have been observed in additively manufactured (AMed) maraging steels. We find that AMed martensite exhibits a highly biased selection of variants, predominantly concentrated on a few variants within a single prior austenite grain. Variant selection follows orientation-dependent trends, with restricted variants exhibiting Bain axes closely aligned with specific coordinate directions. Through the thermomechanical finite element analysis, thermal strains during the deposition process are computed, and it is revealed that the tensile residual thermal strain was dominant along a specific orientation. Moreover, the orientation along which the tensile strain was applied is consistent with the Bain axis of the variants that exhibited the restricted selection behavior. We conclude that the direction-dependent distribution of thermal strain during additive manufacturing suppresses the martensitic transformation when the strain is applied in tension. This finding demonstrates potential pathways for intelligent process design, enabling spatial control of microstructure and properties for specific applications.