Influence of Preheating Temperature on Microstructure Evolution and Hardness of High‐Speed Steel AISI M50 Processed by Laser Powder Bed Fusion

Abstract

The laser powder bed fusion (LPBF) technology has been involved in the tooling industry to produce tools with complex geometry and integrated functions. However, tool steels with high carbon content tend to crack due to the thermal stresses during the LPBF process. One solution is increasing the powder bed temperature to avoid large thermal gradients. In the present study, the influence of the preheating temperature on microstructure and corresponding hardness is systematically investigated. With the help of time–temperature–transformation diagram, the phase evolution during the LPBF process is systematically explained. AISI M50 samples are produced by LPBF from room temperature to a preheating temperature of 650 °C. Higher preheating temperatures shift the optimal laser parameter window to lower volume energy densities. A cellular/dendritic microstructure formed during the rapid solidification with retained austenite is located at the interdendritic regions. Moreover, a high preheating temperature reduces the retained austenite fraction, specifically from 39% without preheating to 7.6% at 650 °C preheating temperature.

Laser Powder Bed Fusion of Hard‐Phase Containing Co‐Base Alloy

“…If soft martensitic steels can be processed into dense samples using the PBF-LB/M process, the AM of carbon martensitic steels is only possible via the design of appropriate alloys [1][2][3][4] or additional measures, such as preheating. [5][6][7] The maximum application temperature of soft-martensitic or C-martensitic hardening tool steels is limited by Ostwald ripening of the corresponding precipitations and recovery and recrystallization of the metal matrix. In addition to precipitationhardening austenites, hard phasecontaining Co-base materials offer a high potential for wear protection applications at higher temperatures.…”

“…If soft martensitic steels can be processed into dense samples using the PBF‐LB/M process, the AM of carbon martensitic steels is only possible via the design of appropriate alloys [ 1–4 ] or additional measures, such as preheating. [ 5–7 ]…”