UC Irvine

High pressure die casting remains a fast, cost-effective technique for manufacturing complex automotive parts. The harsh working conditions that the molds endure make them susceptible to corrosion and thermal fatigue. The metals utilized in molds are often expensive and difficult to machine, necessitating proper maintenance to extend their lifespans. Straight cooling channels in molds have been effective in extending the lifespans of these molds by managing the temperature of vulnerable spots. However, straight channels are ineffective when cooling complex geometries. In recent years, additive manufacturing (AM) has been deemed a promising solution due to its ability to create near net shape parts with complex internal geometries. Leveraging this ability, complex cooling channels can be created that conform to the geometry of the mold. Research has been done on the additive manufacturing of a popular mold material, H13 tool steel, using laser powder bed fusion. Unfortunately, the resulting parts have issues with cracks and delamination from the substrate plate. An emerging AM technique known as wire arc additive manufacturing (WAAM) has demonstrated its ability to print H13 tool steel without cracks. Although successful, no work has been done on heat treating these as-built structures to achieve the desired microstructure needed for use in high pressure die casting applications. In addition, most of the research has been done solely on H13. In this study, H13 tool steel and two other hot-work chromium tool steels were manufactured with WAAM and subjected to a conventional heat treatment consisting of: annealing, austenitizing, and tempering. Due to the high hardness of the as-built condition, samples were also taken directly through a tempering cycle after printing to determine the viability of reducing the post processing time by more than 30 hours. The microstructures after each heat treatment condition were analyzed and hardness tested. Despite their microstructural differences when compared to the wrought state, the tool steels studied were able to be heat treated conventionally and directly from the as-built condition to a desired range of 44 to 48. The size of the alloy carbides strongly influenced the hardness of each tool steel after each heat treatment.