Hybrid additive manufacturing (HAM) has emerged as a promising strategy for tooling construction and repair, integrating conventional machining routes with additive processes. In this context, laser-directed energy deposition (DED) stands out for its ability to repair and functionalize high-value metallic components and automotive industry tooling. In particular, the deposition of 316L stainless steel onto gray cast iron not only locally enhances corrosion resistance properties but also acts as a buttering layer, promoting adhesion of subsequent functional layers and mitigating the formation of brittle phases at the interface.

This study investigates the influence of energy density on the metallurgical quality of single-layer 316L coatings deposited on machined gray cast iron substrates. Depositions were carried out with constant laser power of 1000 W and a powder feed rate of 10.91 g/min, while scan speed was varied between 600, 720, and 1020 mm/min. These processing conditions resulted in different volumetric energy densities (VED) of 14.14, 11.79, and 8.32 J/mm³, respectively. Metallographic analysis revealed that higher energy densities increased porosity and microstructural heterogeneity, whereas the intermediate condition provided the best compromise between layer thickness, reduced porosity, and microhardness homogeneity.

Microhardness mapping also revealed the formation of a localized region within the heat-affected zone (HAZ) exhibiting values close to 650 HV for all tested conditions. Such a hard region may embrittle the deposited layer and compromise long-term performance, highlighting the need for further investigations into phase formation mechanisms and potential post-processing strategies. These results confirm the potential of this approach for hybrid tooling applications, provided that process parameters are carefully optimized to minimize porosity and ensure stable metallurgical bonding.