Investigation on the Effect of Mg Treatment on the Microstructure of High‐Speed Steel

The effect of magnesium treatment on the microstructure, primary carbides, and thermoplasticity of M2 high‐speed steel (M2 HSS) is investigated. The results show that magnesium treatment has a positive effect on improving the microstructure and properties of M2 HSS. It is mainly manifested in the refinement of secondary dendritic arm spacing (SDAS) and inclusions of M2 HSS. Compared with the free magnesium addition, the SDAS from 69.3 to 59 μm. The 3D reconstruction results show that compared with the free magnesium, the volume percentage of carbide in magnesium steel decreases by 24%. The MgAl 2 O 4 spinel can act as a nucleation core to promote heterogeneous carbide nucleation in HSS steel, resulting in a 14.8% thinning of the secondary dendrite arm spacing. Moreover, the thermoplasticity of M2 HSS with magnesium treatment is increased. Compared with the free magnesium addition, the number of creaks in forged HSS decrease from 6 to 2, and the creak depth reduces from 7 to 1 mm, which improves the thermoplasticity of M2 HSS. Magnesium treatment can effectively improve the as‐cast microstructure and thermoplasticity of M2 HSS by refining dendrites and optimizing the morphology and distribution of carbides. The present study will provide a new pathway for enhancing comprehensive performance through alloying in industrial applications.