Formation Behavior of M₂C and M₆C Eutectic Carbides in M42 High-Speed Steel

Abstract

High-Speed SteelSynopsis M 2 C eutectic carbide favours the mechanical properties of high-speed steels, but is often largely replaced by coarse M 6 C eutectic carbide in as-cast M42 steel. To deeply understand the formation behavior of M 2 C and M 6 C carbides, M 2 C and M 6 C eutectic alloys were prepared according to the composition of M 2 C and M 6 C eutectic mixtures in M42 steel, and their solidification behavior was investigated. Only one type of eutectic carbide is formed in water-quenched M 2 C and M 6 C eutectic alloys, i.e., M 2 C and M 6 C, respectively. Both M 2 C and M 6 C carbides appear in the alloys cooled at 3°C/min. However, the M 2 C eutectic alloy was more significantly affected in terms of carbide type by the low cooling rate. According to thermodynamic calculation, M 6 C carbide in the M 2 C eutectic alloy is only slightly more stable in thermodynamics above 1210.1 °C, below which M 2 C carbide becomes stable. For the M 6 C eutectic alloy, however, only M 6 C eutectic carbide is thermodynamically stable. Furthermore, thermodynamic results reveal that besides raising the content of C and V, reducing the content of Mo can also greatly promote the formation of M 2 C carbide in M42 steel, which updates the traditional opinion on the influence of Mo element. The results in this work provide the underlying insights needed to promote the formation of M 2 C carbide in M42 steel by fine-tuning the composition.

Microstructure, Strengthening Mechanism and Mechanical Properties of Vanadis 60-Ta_0.5Nb_0.5C-B₄C High-speed Steel Composite via Vacuum Sintering, Sub-zero, and Heat Treatments

“…In other words, M 6 Ctype carbides can more effectively increase hardness and strength than MC-type precipitates. 7,13,[29][30][31] This finding suggests a positive relationship between the increased hardness and TRS and the quantity of M 6 C-type carbides.…”

Effect of Alloying and Microalloying Elements on Carbides of High-Speed Steel: An Overview

“…Figure 3 illustrates a hexagonal close-packed (HCP) crystal structure of M2C carbide. Mo, W, V, Cr, Fe, and other metal atoms generate M2C [14]. The metastable condition of M2C eutectic carbides causes them to break down at high temperatures.…”

“…The metastable condition of M2C eutectic carbides causes them to break down at high temperatures. M6C shaped like a fishbone (Figure 4) is a carbide found mostly in W-series and W-Mo-series high-speed steels and has a complicated cubic lattice structure [14,15]. M7C3 is a complicated orthogonal structure that is mainly found in steels with high carbon and chromium content, appearing as a fishbone or strip.…”