Processing Conditions Dependent Evolution of Microstructure in Laser Additive Manufactured HT-9 Ferritic Martensitic Steel

This study examined the effects of laser processing conditions on the evolution of microstructure and phase fractions in HT9 ferritic/martensitic (F/M) steels fabricated using laser powder bed fusion (L-PBF) and laser-directed energy deposition (L-DED). Electron backscattered diffraction (EBSD) micrographs of the cross-sections of the laser-processed builds showed the presence of α-ferrite, α′-martensite, and retained austenite (γ). Distinct differences were observed in the γ phase fraction between the L-PBF and L-DED microstructures. To correlate the observed phase fractions with process-induced thermokinetic effects, a multiscale multiphysics thermal model was used. The modeling results confirmed the experimental data and provided insight into the relationship between temperature changes during processing and phase evolution in HT9 steel.