On the Laser Powder Bed Fusion of a Modified AISI S2 Tool Steel Enriched with SiC

Over recent years, the development of modified and new metallic alloys manufactured by Laser Powder Bed Fusion (LPBF) has been the object of ever increasing attention. Indeed, the ultra-fast heating and cooling rates that characterize LPBF are responsible for the formation of strongly out-of-equilibrium microstructures, involving supersaturated solid solution as well as new metastable phases, thus offering new possibilities in terms of usage properties (hardness, tribological properties…).
This work focuses in particular on the development of a modified AISI S2 tool steel enriched with silicon carbide (SiC). The complete dissolution of SiC within the melt pool leads to an enrichment of the alloy with both Si and C, thus changing its solidification sequence. Moreover, the in-situ thermal cycles that affect the previous layers during the deposition of a new layer leads to the formation of a complex microstructure depending on the specific phase transformations induced by the local thermal history. Martensite (untempered or tempered), bainite and retained austenite have been differentiated by combining optical and scanning electron microscopy (including EDS and EBSD analysis), Differential Thermal Analysis, as well as macro- and nano-hardness.