Influence of Silicon Content and Strain Accumulation on Mean Flow-Stress Behavior and Microstructural Restoration of High-Silicon Electrical Steels

High-silicon Fe–Si steels are important soft magnetic materials for high-frequency electrical applications due to their high electrical resistivity, low core losses, and reduced magnetostriction. However, their broader industrial use is limited by low room-temperature ductility caused by atomic ordering and the formation of B2 and D0 3 superlattices. This study investigates the deformation behavior, and microstructural evolution of Fe–Si steels containing 2.89 to 6.35 wt pct Si using anisothermal multipass torsion tests from 1150 °C to 630 °C. Three phenomenological processing regimes were identified. Above approximately 930 °C, the MFS exhibits limited sensitivity to temperature and composition, consistent with efficient high-temperature restoration, including dynamic recovery and interpass recrystallization. Between approximately 930 °C and 710 °C, MFS increases rapidly, indicating increasing strain accumulation and reduced interpass restoration, particularly in the higher-Si alloys. Below approximately 710 °C, several MFS curves tend to stabilize. EBSD reveals extensive substructure development, progressive changes in the LAGB, MAGB and HAGB populations, and localized formation of fine HAGB-bounded grains, consistent with a contribution from CDRX. Increasing the strain per pass from 0.2 to 0.3 produces substantially greater grain refinement despite relatively similar MFS trajectories. Higher Si contents are associated with greater local misorientation and a more advanced refined microstructure after the complete schedule.