Microstructural characterization of AISI 440C stainless tool steel fabricated by laser powder bed fusion

The microstructure of a stainless tool steel AISI 440C fabricated by laser powder bed fusion (L-PBF) without pre-heating of the build plate was characterized by multi-scale experimental methods. In combination with thermodynamic calculations, the solidification and cooling-down procedures were analyzed with the intention to understand the cracking behavior of high carbon tool steels processed by L-PBF. The results showed a fully austenitic structure in the as-built sample with sub-micro cellular structures and nano-sized carbides decorating the cell walls. Significant segregation exists merely at the intersection of cell walls while it is absent along high angle grain boundaries. Factors contributing to crack-free AISI 440C are discussed, providing guidelines for future L-PBF fabrication of high-carbon tool steels.