Influence of Different Heat Treatments on Microstructure Evolution and High-Temperature Tensile Properties of LPBF-Fabricated H13 Hot Work Steel

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Abstract
This study investigates the effect of tensile test temperatures, ranging from 300 °C to 600 °C, on the microstructure, mechanical properties, and fracture behavior of AISI H13 11 tool steel manufactured by laser powder bed fusion (LPBF) under three material conditions: As-Built (AB), Direct Double-Tempered (DTT), and 13 Quenched and Double-Tempered (QTT). Optical and SEM observations show that quenching before tempering leads to a more homogeneous microstructure. Full austenitization during quenching eliminates the laser track patterns and cellular structures characteristic of the AB and DTT conditions, resulting in a microstructure like that of conventionally processed material. Tensile test results reveal that, while all material conditions (AB, DTT, and QTT) perform similarly at lower temperatures (up to 300 °C), significant differences emerge at elevated temperatures. At 300 °C, AB, DTT, and QTT maintain 87.5%, 85.8%, and 83.1% of their room-temperature yield strength, respectively. However, beyond this point, the DTT condition clearly outperforms the others. QTT shows a sharp decline above 300 °C, retaining only ~24% of its yield strength, whereas AB and DTT maintain approximately 80%. The superior performance of DTT becomes more evident at higher temperatures: it retains 25% and 20% of its yield strength at 500 °C and 600 °C, respectively, higher than both AB and QTT.

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