Grain oriented electrical steel having high volume resistivity and method for producing same

A method of producing grain oriented electrical steel having an aluminum nitride inhibitor system, said method comprising the steps of:

• a) providing a hot rolled strip which consists essentially of, in weight percent, 2.25 to 7% Si, 0.01-0.08% C, 0.015-0.05% Al, up to 0.01% S, greater than 0.5% Mn.sub.eq, 0.001-0.011% N and balance being essentially iron and unavoidable impurities to provide a volume resistivity of at least 50 micro-ohm-cm., said steel composition balanced such that 2.ltoreq.{(% Si)-0.45(% Mn.sub.eq)}.ltoreq.4.4;
• said % Mn.sub.eq defined as (% Mn)+1.5 (% Ni)+0.5(% Cu)+0.1(% Cr);
• b) providing .gamma..sub.1150.degree. C. in said strip of at least 5%;
• said .gamma..sub.1150.degree. C. defined as austenite volume percent;
• c) initial annealing said strip by heating said strip to a temperature of 950.degree. to 1150.degree. C. for a soak time of 180 seconds or less and heating said strip to a secondary soaking temperature of 775.degree.-950.degree. C. for a soak time of from 0-300 seconds and cooling;
• d) cold rolling said annealed strip to a final thickness;
• e) decarburizing said cold rolled strip to a carbon level below 0.005%;
• f) nitriding said strip in one or more steps following primary recrystallization during said decarburizing and prior to secondary grain growth to provide excess nitrogen;
• g) providing said strip with an annealing separator coating at a stage selected from the group of before nitriding, after nitriding or between nitriding treatments;
• and
• h) final annealing said coated strip at a temperature of at least 1100.degree. C. for at least 5 hours to effect secondary grain growth and purification.