Effect of carbon content in steel powder feedstock on impact toughness and microstructure of additively manufactured cast iron by directed energy deposition

Low- and medium-C steel powders were additively deposited on gray cast iron using a directed energy deposition (DED) process to identify the effect of the carbon content in the steel powder on the soundness of DED-processed cast iron in terms of the mechanical and microstructural properties. As a representative mechanical property, impact toughness tests of DED-processed cast iron specimens were performed, and then fractography was employed to understand the microstructure-dependent crack propagation resistance. Microstructural changes and chemical variations were investigated using multi-scale microstructure characterization as the layer-dependent properties. In particular, the microstructural characteristics across the interface were intensively analyzed to understand the effect of laser-heated low- and medium-C steel powders on a (high C) cast iron substrate. Elucidating the microstructural changes and the resulting mechanical properties of the deposits necessitated understanding the variations caused by the chemistry of the deposited powder and the effect of dilution with the substrate material. These layer-dependent properties and the resultant compatibility at the interface should be considered when selecting the feedstock material and designing the DED repair process.