Refining the Carbide Size in AISI M50 High-Speed Steel Through Tailored Compositional Modifications

The present study focuses on redesigning the composition of the conventional M50 steel grade, which is widely used for high-temperature bearings. Through thermodynamic calculations, a new steel variant was developed in the laboratory with the aim of refining carbides and improving hardness. After undergoing quenching at 1070 °C and triple tempering at 540 °C, the hardness reached 66 HRC, which is 7.57% higher than that of M50 steel (61 HRC). Meanwhile, the hardness at 400 °C reached 60 HRC. In addition to the typical M₂C and M₆C carbides found in M50 steel, the presence of Fe and Cr-rich M₂₃C₆ carbides was detected in the redesigned steel after triple tempering. These carbides play a significant role in enhancing hardness. Furthermore, the heat treatment process effectively eliminated the uneven and coarse carbides. The average size of primary carbides is 4.6 ± 0.6 μm, which represents a 27.0% reduction compared to M50 steel (6.3 ± 0.1 μm). The detrimental V-rich MC carbides commonly found in M50 were eliminated.