The optimal combination of current intensity and frequency of mould electromagnetic stirring (M-EMS) in continuous casting billet was a crucial compromise for improving inner quality of cast billet such as reduction in center segregation and porosity of medium-high carbon steel. In the present study, a decoupled three-dimensional mathematic model of electromagnetic field, fluid flow and heat transfer in continue casting billet mould with EMS has been developed, and the effects of current intensity and frequency on the system were also discussed. In addition, the industrial trials were carried out to investigate the magnetic field characteristics in the mould with M-EMS and the influence of M-EMS on the solidification structure of 55SiCr. According to the calculations and analysis, the optimal combination range of current intensity and frequency was 300–320 A and 3–4 Hz, respectively. The results showed that inner quality in as-cast billet of 55SiCr has been improved significantly with optimal parameter of 320 A and 3 Hz. For instance, central equiaxed zone increased from 19% to 33%, the center carbon segregation ratio decreased from 1.13 to 1.05 as well as center porosity has nearly disappeared.
