Influence of Heat Treatment and Scan Rotation on the Microstructure of Hot Work Tool Steel Manufactured using Laser Powder Bed Fusion

Abstract

Additive manufacturing provides a unique opportunity to have freedom in design. Often it is necessary to perform post treatment processes on the printed component to adjust the mechanical properties. This is particularly true for martensitic H13 tool steels manufactured with laser-powder bed fusion, where repeated thermal cycles as a result of the addition of the new top layer, can give rise to columnar growth and microstructural inhomogeneities. Considering the unit size and texture of martensitic microstructure as directly influenced by the size of the prior austenite grains (PAGs), the focus of the investigation lies in the PAG size of the as-built (AB) and heat-treated conditions. Furthermore, four types of samples with different scan rotations (0°, 45°, 67°, and 90°) are investigated. The AB material displays a characteristic cell structure with cell boundaries enriched in alloying elements as well as nanosized carbides at triple junctions and intercellular regions. A key finding of this research is that the heat treatment gives rise to PAG size refinement as a result of recrystallization and pinning effect from carbide hindering the grain growth during austenitization.