Method of refining magnetic domains of barrier-coated electrical steels using metallic contaminants

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

• applying to the base coated steel a barrier coating having a primary constituent selected from the group of phosphorus, silicate, and combinations and compounds thereof for sealing the forsterite;
• thereafter removing portions of both the barrier and base coatings to expose a line pattern of the underlying silicon steel;
• then applying a metallic contaminant to the steel on the areas of exposed 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;
• and
• thereafter annealing the steel having the barrier coating and contaminant thereon at time and temperature of about 1400.degree. F. or more in a reducing atmosphere of substantially hydrogen to diffuse sufficient and controlled amounts of the metallic contaminant and an element from the barrier coating into the exposed steel to produce a line of permanent porosity to effect heat resistant domain refinement and reduced core loss.