Effect of alternative magnetic fields with different intensities on microstructure and mechanical properties of M50 steel during vacuum arc remelting

The use of an alternative magnetic field during vacuum arc remelting (VAR) can have significant effects on the primary carbide and mechanical properties of M50-bearing steel. The solidification structure and the primary carbide morphology of the VAR ingot were analyzed by optical microscopy and scanning electron microscopy. Characterization and analysis of the growth direction of primary carbides were conducted using high-resolution rapid electron backscatter diffraction. Solute elements segregation was analyzed using an electron probe microanalyzer. FLUENT was utilized to conduct numerical simulations to validate the experimental findings and elucidate the underlying mechanism. Compared to traditional VAR, magnetic-controlled VAR generates a horizontal circulation, which makes a shallower and flatter molten pool and a more even temperature distribution. In the time dimension, the local solidification time is shortened, and the concentration of solute elements will be alleviated. In the spatial dimension, the secondary dendrite arm spacing decreases, alleviating the degree of inter-dendritic segregation. Consequently, the possibility of forming a segregation diminishes. Both aspects promote the even distribution of solute atoms, resulting in less segregation and hindering the development of primary carbide. This leads to the refinement of primary carbide size and its uniform distribution. The magnetic-controlled vacuum arc melting not only refines the dendritic structure in the M50 ingot, causing it to expand more axially along the ingot, but also refines primary carbides and improves tensile and wear-resistant mechanical properties.