The effect of alternative magnetic field on solidification structure improvement and primary carbide refinement in M50 ingots produced by vacuum arc remelting

Abstract

In the present study, the effect of the alternative magnetic field (AMF) on the metal pool shape, primary carbides formation, and mechanical properties during vacuum arc remelting (VAR) process was investigated by experiments and numerical simulations. Without AMF, the original depth of the molten pool was 87.74 mm. The application of the AMF decreased the depth of the metal pool, to various degrees (86.46 mm at 40 Gs 0.5 Hz, 78.96 mm at 40 Gs 0.1 Hz, 69.82 mm at 40 Gs 0.05 Hz). As a consequence, the primary carbides became more refined average size reduced by 20.66%∼25.72%. After modification, uniformly distributed hardness and improved wear resistance was achieved. Meanwhile, compared with 0.5 and 0.1 Hz cases, the strengthening effect was more obvious at 0.05 Hz. The numerical simulation results showed that, the AMF and the melting current in the molten steel produced Lorentz force, which caused the horizontal circulation. Therefore, the temperature of metal pool became more homogenized under the horizontal circulation. When the frequency was 0.05 Hz, the horizontal circulation in liquid steel was more intense, which makes the temperature field more uniform. Horizontal circulation can also reduce the segregation of alloying elements, which restrains the precipitation condition and refines primary carbides. The hardness uniformity can also be attributed to the uniform distribution of alloying elements. The improvement in wear resistance is attributed to the refinement of the primary carbide, thereby reducing the occurrence of primary carbide spalling during friction.

Keywords

• M50 bearing steel
• Primary carbide
• VAR
• Alternative magnetic field
• Mechanical properties