Honors College Thesis

Selective Laser Melting of H13 Tool Steel for Rapid Tooling

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  • The current knowledge on the microstructural evolutions and mechanical properties of selective laser melting (SLM) produced H13 tool steel components is limited. This research is focused on optimization of SLM processing parameters for H13 tool steel and investigation of microstructure and mechanical properties of H13 tool steel components after SLM and heat treatment. H13 components with a relative density of ~99% were additively manufactured using the SLM process. The highest density part (relevant density 99%) with the lowest level of porosity (<0.01%) was made with a volumetric energy density (VED) of 760 J/mm3 (152 W laser power, 100 mm/s scanning speed, 40 m hatch spacing, and 50 m layer thickness). Wrought and SLM produced samples underwent tempering at 550, 600, and 650°C for two hours followed by furnace cooling. Both SLMed samples and austenitized followed by water quenched wrought samples presented martensitic microstructures with similar microhardness values of ~708 HV. No obvious trend was observed between VED and microhardness values. SLMed and tempered samples showed high microhardness value of 728.5±28.2 HV due to presence of high dislocation density caused by rapid solidification during SLM, finer grains and microstructure, and precipitation of second phase (carbides) during tempering. Tempered martensitic structure was observed in SLMed and tempered samples. These precipitates showed coarsening at 600 and 650°C leading to a decrease in microhardness. SLMed samples maintained higher microhardness values than wrought H13 samples at each tempering temperature likely due to higher dislocation density and finer grains present in SLMed parts (rapid solidification characteristics). High relative densities (99.9% or greater) were not achieved in SLMed parts, and further optimization deemed necessary to achieve full density parts. Furthermore, presence of cracks in the SLMed H13 tool steel parts is a problem that needs to be addressed before implementation of SLMed molds in applications that require high thermal fatigue resistance such as like plastic injection molding.
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