Thermal and mechanical properties of selective laser melted and heat treated H13 hot work tool steel

It is attractive to fabricate molds and dies using additive manufacturing (AM) technology because the increased freedom of design makes higher cooling efficiency possible. However, little is known so far about the thermal properties of the tool steels fabricated by AM, as well as how to balance between the thermal and mechanical properties. In this work, an H13 tool steel was processed by selective laser melting (SLM) followed by heat treatments and the thermal and mechanical properties in relation to microstructure were investigated. The as-built H13 showed lower thermal conductivities compared with conventional counterparts and exhibited anisotropy with a lower thermal conductivity along the building direction. Heat treatments generally increased the values of thermal conductivities and largely reduced anisotropy, but the final thermal conductivity differed when using different heat-treating schedules. It was found that porosity, retained austenite, the melt-pool structure and the ultra-fine cellular-columnar microstructure, which were functions of SLM and heat-treating parameters, were factors determining the thermal conductivity of H13. Based on the present study of SLMed H13, it is proposed that a trade-off is necessary between thermal and mechanical properties when designing the processing route