Method of producing stable magnetic domain refinement of electrical steels by metallic contaminants

A method of refining the magnetic domain wall spacing of grain-oriented silicon steel sheet having an insulation base coating thereon, the method comprising:

• removing portions of the base coating to expose a line pattern of the underlying silicon steel;
• thereafter applying a metallic contaminant to the exposed silicon steel, the metallic contaminant selected from the group of copper, tin, nickel, zinc, antimony, combinations and compounds thereof, the exposed steel being free of thermal and plastic stresses;
• thereafter annealing the steel and contaminant thereon at time and temperature of about 1400.degree. to 2100.degree. F. in a protective atmosphere to diffuse sufficient and controlled amounts of contaminant into the exposed steel to provide a substantially homogeneous steel sheet throughout its thickness having developed stable pores in the line pattern to effect heat resistant domain refinement and reduced core loss in a substantially stress-free sheet.