mechanicalproperties, usually involving complex, multi-step heat treatment procedures. This study investigates themicrostructural evolution and its impact on mechanical properties of an AM tool steel through successive heattreatment steps, including the as-built, spheroidized, quenched, sub-zero treated, and three repeated temperedconditions. For the first time, the dynamic mechanisms of phase transformation and carbide evolution duringheat treatment of an AM tool steel are systematically revealed through the combined application of in situsynchrotron X-ray diffraction and multi-scale characterization techniques. (Cr,Mo,Mn,V)23C6 carbide precipitationwas revealed alongside (retained) austenite, martensite and δ-ferrite, with the phase contents varying acrossthe individual heat treatment steps. A strong correlation between (retained) austenite, (tempered) martensite andVickers hardness was observed, with a final Vickers hardness of 577 ± 5 HV10 in the fully heat-treated condition.Furthermore, the as-built microstructure strongly influenced the subsequent thermal processing behavior asindicated by the stability of δ-ferrite throughout heat treatment, originating from austenite by-passing during LBPBF,and the early formation of M23C6 carbides during spheroidizing, driven by Cr segregation resulting from theLB-PBF process. Therefore, this study highlights the influence of AM microstructures on heat treatment responsesand offers new insights into carbide formation and phase transformations of AM tool steels. The findingsemphasize the critical role of post-printing heat treatments in tailoring the microstructural and mechanicalproperties of tool steels, thus advancing the understanding of specific heat treatment strategies for AMcomponents.
Ofner et al. (Wed,) studied this question.