Effect of the as-built microstructure on the martensite to austenite transformation in a 18Ni maraging steel after laser-based powder bed fusion

During laser-based powder bed fusion, the non-equilibrium solidification conditions promote local elemental segregation, leading to a characteristic microstructure composed of cellular walls. These walls can display either low carbon BCC martensite or FCC retained austenite crystal structures, thus affecting subsequent isochronal isothermal phase transformation mechanisms. In present study, effect non-homogeneous as-built on martensite-to-austenite reversion phenomena was studied for 18Ni maraging steel fabricated by fusion. In-situ synchrotron X-ray diffraction used retrieve volume fraction and lattice parameter evolution during physical simulation continuous heating cycles austenitic field; tempering throughout inter-critical tempered + (?’ ?) field. The resulted in expansion ?’ ? field very slow rates. This associated synergic effects compositional segregations (anticipating reversion) pre-existing (delaying solubilization). conventional tempering, did not fundamentally alter kinetics, resulting similar high temperature microstructures at end stage relative solution treated state.