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Oriented Si steel containing up to 6 percent Si was produced by gaseous siliconizing of oriented 3.25-percent Si steel strip. Dc magnetization curves in the with-grain (rolling) direction and ac core loss and magnetostriction measurements in both the with- and cross-grain (transverse) directions were obtained before and after magnetic annealing. Domain structures were photographed before and after the magnetic annealing treatments. Compared to the 3.25-percent Si starting material, the high Si strip exhibited improved dc permeability up to the knee of the magnetization curve, decreased losses, and decreased magnetostriction. The effects were approximately linear with increasing Si content and could be attributed to general magnetic softening. Magnetic annealing improved the properties further. When applied in the with-grain direction, the magnetic anneal led to a cleaner antiparallel domain structure; in the cross-grain direction, magnetic annealing established a completely transverse domain structure. These domain structure changes adequately accounted for the property improvements obtained from magnetic annealing.