Abstract:
Two heats of M2 high-speed steel with different contents of rare earth (Ce) were produced by a domestic steel plant, optical microscopy, scanning electron microscopy, X-ray diffraction analysis, and high-temperature confocal microscopy are used to explore the effects of Ce on the inclusions and carbides in M2 high-speed steel. After adding Ce, the S content in the electroslag ingot decreases. The inclusions are modified from large-sized and irregular Al2O3 to small-sized and globular CeAlO3. The inclusions are completely modified. Meanwhile, the number density of the inclusions decreases, and the average size is reduced. Thermodynamic calculations show that CeAlO3 inclusions are most likely to be generated in the electroslag ingot, which is consistent with the test results. The eutectic carbides in the as-cast structure of the electroslag ingot are significantly refined. Mismatch calculations show that the mismatch between (001)CeAlO3 and (100)γ-Fe is 4.49%. It can serve as a heterogeneous nucleation core for γ-Fe, promoting the increase of nucleation sites during the solidification process of the molten steel and greatly reducing the growth space of the eutectic carbides. The addition of Ce does not change the type of carbides in the wire rod. The statistical results of carbides in the longitudinal section of the wire rod show that after the addition of Ce, the number of carbides in the same area (1000μm2) increases significantly, while the proportion of the carbide area decreases. The influence of rare earth Ce on inclusions and carbides is beneficial to the improvement of the properties of M2 high-speed steel. The research results provide a theoretical support for the production of high-quality M2 high-speed steel.