Abnormal martensitic transformation and morphology induced by chemical heterogeneity in additively manufactured maraging steel

Abstract

We report on the effect of chemical heterogeneity on martensitic transformation in a maraging steel produced through laser-based directed energy deposition. Unlike conventional maraging steels with lath martensitic microstructures, the maraging steel exhibited an abnormal morphology, which was refined and elongated in the building direction. The growth direction of the abnormal lath martensite did not occur along the habit plane, while the lath martensite morphology corresponded to the cellular dendritic microstructure of the maraging steel. Among the elements partitioned to the interdendritic region, Ni played a major role in the reduction of the martensitic transformation start temperature (Ms temperature), thereby interfering with the martensitic transformation across the interdendritic region. The interdendritic region acted as a new domain boundary of martensitic transformation, where incomplete martensitic transformation in the region resulted in the retention of austenite.