Laser Directed Energy Deposition of High-Carbon High-Chromium D2 Tool Steel Structures: Processing, Heat Treatment and Material Behavior

The tooling industry is one of the sectors that demands the deployment of advanced manufacturing techniques, like-laser directed energy deposition (LDED) for building customized tools. D2 tool steel, a high-carbon high-chromium alloy, is among the various alloys used for tooling applications, but LDED processing of D2 tool steel is challenging due to its higher hot cracking susceptibility. In the present work, a full factorial experiment is carried out to identify process window for building defect-free D2 tool steel structures, and thereafter, microstructural and mechanical properties of the bulk D2 tool steel structures are characterized in as-built and the heat-treated conditions. The LDED built D2 bulk structures at identified process parameters are found to be crack-free with high relative area density (> 99.9%). It is observed that the heat-treatment of LDED built D2 tool steel leads to formation of cementite (Fe3C) phase along with retained austenite and other eutectic phases. This leads to an increase in the micro-hardness, wear-resistance and compressive yield strength of heat-treated D2 tool steel at room temperature. However, reduction in the wear resistance at elevated temperatures is observed in the heat-treated sample. This study establishes LDED as a fabrication technique for defect-free processing of D2 tool steel for potential tooling applications.