Mechanical Properties of High-Speed Steel AISI M50 Produced by Laser Powder Bed Fusion

The microstructure and mechanical properties of high-speed steel AISI M50 (80MoCrV42-16, Mat. Nr. 1.3551), produced by laser powder bed fusion (LPBF), are analyzed. The mechanical properties in hardened and tempered condition are characterized by hardness, fatigue strength, and toughness and compared with the properties of conventionally produced samples. Moreover, the effects of an additional posttreatment by hot isostatic pressing (HIP) on the microstructure and mechanical properties are investigated. Dilatometric testing is used to investigate the influence of the different initial microstructures on hardening. All heat-treated samples expose a fine martensitic microstructure with high hardness. The conventionally produced samples show a band-like orientation of carbides due to the production by vacuum induction melting and vacuum arc remelting followed by a hot working process. This carbide structure is bypassed by the rapid cooling in the LPBF process. The LPBF samples show a comparable hardness after hardening and tempering to the conventionally produced material. In heat-treated state, the LPBF samples show a low fatigue strength. Posttreatment by HIP included in the heat-treatment chain significantly increases the fatigue strength. Nevertheless, the fatigue strength is still lower compared with the reference material. Both LPBF grades show a low toughness compared with the reference material.