Decarburization degree and the change in magnetic properties after forsterite coating in grain-oriented silicon steel has been studied.
Decarburization temperatures ranged from 800℃ to 950℃ and dew-points from 20℃ to 50℃, respectively in $80%N_2-20%H_2$ gas atmosphere.
Forsterite coating was performed by dipping the decarburized specimens into MgO slurry and annealing at high temperature after drying.
The oxide films were formed on the surface during decarburization anneal, and changed in morphology and structure as decarburization atmosphere varied. Changes in magnetic properties after forsterite coating which was performed by the reaction of MgO with $SiO_2$ in the oxide films are believed to be due to the difference in effective residual tensile stress-state and surface roughness.
Residual carbon contents increased with decarburization temperature and decreased with dew-point in the ranges considered. So the best conditions for decarburization in $80%N_2-20%H_2$ gas atmosphere are decarburization temperature of 800℃ and dew-point of 50℃.
However, the specimen which decarburized at temperature of 850℃ with dew-point of 40℃ in 80%N-20%H gas atmosphere has shown the best magnetic properties.
