Grain oriented electrical steel with improved forsterite coating characteristics
Increasing the chromium content of an electrical steel substrate to a level greater than or equal to about 0.45 weight percent (wt %) produced a much improved forsterite coating having superior and more uniform coloration, thickness and adhesion. Moreover, the so-formed forsterite coating provides greater tension potentially reducing the relative importance of any secondary coating.
1. A grain oriented electrical steel sheet comprising chromium in a concentration of greater than about 1.2 wt. %, wherein during decarburization annealing the grain oriented electrical steel sheet has been rapidly heated at a rate in excess of 500° C/second to a temperature of about 700° C.; and wherein the grain oriented electrical steel sheet further comprises a forsterite coating formed on at least one surface of the grain oriented electrical steel sheet, wherein the forsterite coating has a free surface and wherein the forsterite coating is comprised of oxygen in a concentration greater than or equal to about 7.0 wt. % at one or more points in a region defined by a depth of about 2-3 μm below the free surface of the forsterite coating.
2. A grain oriented electrical steel sheet comprising chromium in a concentration of greater than about 1.2 wt. %, and at least one surface, the grain oriented electrical steel sheet comprising a surface region defined by a depth of less than or equal to 2.5 μm from the at least one surface and a bulk region defined by a depth greater than 2.5 μm from the at least one surface wherein the chromium concentration of said surface region is greater than the chromium concentration in said bulk region, when measured after decarburization annealing, wherein the grain oriented electrical steel sheet has been rapidly heated at a rate in excess of 500° C/second to a temperature of about 700° C., and before high temperature annealing.