Improvement of Magnetic Properties of a Reversible Hot Rolled Grain-Oriented Electrical Steel

The obtaining of excellence in magnetic properties of grain-oriented silicon steel processed through Steckel mill has been a big challenge to APERAM. Due to the characteristics of this process, with larger susceptibility to temperature variation, and consequently, the variation of properties along the length, a precise control of the process and product parameters is required. This paper will focus on the effect of hot rolling temperature and chemical composition, specifically the carbon content and Mn/S ratio, on the behavior of manganese sulfide precipitates. Evaluating the process data, it was identified that an adjustment in the range of hot rolling temperature could contribute to reduce the observed occurrence of variation in magnetic loss, concentrated in regions near the head of the hot rolled coil, that appeared as a bulge at the core loss charts. Precipitation-time-temperature curves were obtained, considering the typical chemical composition to this steel, based on the literature and experimental models, and comparisons with current practices were done. Experiments were carried out at the plant, searching the temperature setting, in which the rolling process would be started within the range of sulfide precipitation, according to the theoretical prediction. The results of the first tests have already indicated a trend of decline in the occurrence of the phenomenon mentioned. Additional chemical composition and process adjustments were done to guarantee stabilization of magnetic properties along the coil length.