Application of Direct Energy Deposition Additive Manufacturing for Hot Forging Die Repair

The United States Department of Defense heavily relies on forged components owing to their high yield strength, precision, and wear resistance. Forging dies are critical for shaping ingots or preforms into their final geometries under extreme thermo-mechanical cyclic loads. The severe operating environment leads to thermal fatigue, surface cracking, mechanical wear, and eventual failure of the forging die. This study proposes the direct energy deposition-based additive manufacturing processes as an innovative and effective solution for repairing forging dies. Eureka-450 and IN718 were deposited as repair alloys using wire arc additive manufacturing (WAAM) and wire laser additive manufacturing (WLAM) on an H-13 tool steel plate. The microstructural and mechanical properties of the interface, along with the bulk samples from the repair side, were examined using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray radiography, Vickers indentation, uniaxial tensile testing, and Charpy V-notch impact testing. The results indicated that WAAM and WLAM provided superior metallurgical bonding and significantly reduced the introduction of residual stresses compared to conventional methods. The grain and martensitic lath size in the H-13 steel gradually decreased when moving from the interface toward the H-13 substrate. This behavior is attributed to grain coarsening and the dispersion of martensitic laths caused by the thermal flux from the initially deposited layers. The ultimate tensile strength and ductility of the interface samples were consistently lower than the bulk samples in all the cases, likely due to the formation of hard and brittle heat-affected zones near the interface, which weakened the overall strength of the interface samples. Among Eureka-450 and IN718, the former exhibited higher tensile strength but low ductility and impact strength, while the latter depicted higher impact strength and ductility. This is attributed to the martensitic crystal structure of the Eureka-450 while austenitic crystal structure of the IN718.