Cyclic Thermal Dependent Microstructure Evolution During Laser Directed Energy Deposition of H13 Steel

The current study investigated evolution of fine-scale microstructure in H13 steel additively manufactured by laser directed energy deposition. X-ray diffraction, scanning electron microscopy, and site specific transmission electron microscopy were employed for the analysis. A multiphysics, multi-layer, and multi-track computational process model in conjuncture with time-temperature-transformation diagram provided variation in temperature as a function of time along with the corresponding phase transition pathways. The additively produced H13 steel sample exhibited cellular solidification of austenite grains followed by its near complete transformation into ferrite/martensite. Fine-scale observations indicated the presence of precipitates rich with carbide forming elements at the cell boundaries and junctions. Site specific transmission electron microscopy revealed these precipitates to be Mo–V and Cr rich carbides. The matrix consisted of martensite as the main phase. Small pockets of retained austenite were detected within the martensitic matrix.