Microstructure and Properties of a Novel Carbon‐Martensitic Hot Work Tool Steel Processed by Laser Additive Manufacturing without Preheating

Abstract

Laser additive manufacturing (LAM) techniques, such as laser‐powder bed fusion (L‐PBF) or laser‐directed energy deposition (L‐DED), allow for the production of complex‐shaped parts by either the local melting of a metallic powder bed by a laser beam (L‐PBF) or a local application and laser beam melting of powder material by a nozzle (L‐DED). In the case of carbon‐martensitic tool steels, their cold crack susceptibility limits their LAM processability and is usually counteracted by substrate preheating. As preheating can increase the oxygen take‐up of the powder and alter the part microstructure, it can be disadvantageous for part quality and powder reusability. In this study, it is investigated a carbon‐martensitic steel designed for the production of parts with low crack density by LAM without preheating, focusing on the microstructure and hardness of the L‐PBF‐ and L‐DED‐manufactured steel. The steel can be LAM‐processed without preheating, resulting in specimens with low crack densities and martensitic microstructure with retained austenite. The hardness of the as‐built material (L‐PBF: 542HV30 and L‐DED: 623HV30) is increased by quenching and tempering up to 693HV30. Direct tempering of the as‐built specimen without previous quenching leads to a shift of the secondary hardness maximum from 500 to 530 °C.