Deoxidation of liquid steel is an essential process during steelmaking, and is usually carried out during tapping by adding into the ladle appropriate amounts of Fe-Mn, Fe-Si, Al or other special deoxidizers. Due to high affinity towards oxygen and relatively low price, Al deoxidizer is most commonly used in steelmaking. Deoxidation removes excessive dissolved oxygen in liquid steel, but it also causes the formation of non-metallic inclusions, i.e., deoxidation products. Depending on their characteristics, residual inclusions either positively or negatively affect steel properties. Large inclusions with irregular morphology are especially harmful to steel properties, such as ductility, toughness, fatigue strength and corrosion resistance. 1,2) On the contrary, small inclusions with suitable composition can serve as heterogeneous nucleation sites for phase transformation and precipitation, improving steel properties. 3) Therefore, controlling the inclusion characteristics is of great importance for the production of high-quality steel.

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.

No abstract