From arc to alloy: Impact of directed energy deposition-arc/M on the microstructure and thermophysical properties of hot-work tool steels

Directed Energy Deposition-Arc (DED-Arc/M) offers a promising method for producing complex shaped and medium-sized parts without the need for specific tooling, thereby minimizing resource consumption. However, the unique thermal conditions of DED-Arc/M, characterized by high cooling rates and successive re-heating cycles, lead to microstructures differing significantly from those of conventionally processed material. This results in pronounced segregation and high states of solid solution of alloying elements, leading to a high degree of chemical inhomogeneity and retained austenite. Thus, a direct application of additively manufactured parts in as-built condition is not desirable, rendering thermal post-processing necessary. Direct tempering of additively manufactured tool steels can preserve a fine microstructure, reduce retained austenite and utilize high solution states for precipitation hardening, which enhances the mechanical properties compared to conventionally processed materials. Conventional heat-treatment, i.e. austenitizing, quenching and subsequent tempering of additive manufactured tool steels, results in effective chemical homogenization. However, this process has also been observed to coarsen the fine microstructure that is characteristic of additive manufacturing, thereby diminishing its advantageous properties, such as high solution state. Consequently, the mechanical properties of additively manufactured and conventionally processed materials become comparable. While these effects have been investigated regarding mechanical properties, the impact on thermophysical properties has not been sufficiently explored. This work examines the interaction between DED-Arc/M-induced microstructure and thermal post-processing, focusing on the thermophysical properties of hot-work tool steel AISI H13 (X40CrMoV5-1). Thermal conductivity is studied from 50 °C to 500 °C, covering a temperature interval typical for hot working applications. This study offers a comprehensive understanding of DED-Arc/M-induced microstructural features, providing insights into the material’s thermophysical properties. The findings indicate that DED-Arc/M processed and heat-treated AISI H13 tool steel can achieve thermal conductivity similar to conventional material, emphasizing that DED-Arc/M is a promising technique for manufacturing efficient tools for hot working applications.