Thermal flattening semi-processed electrical steel

Abstract

The thermal flattening of grain oriented silicon steel which is in the semi-processed condition has improved magnetic properties after a stress relief anneal by using a low temperature and high tension flattening anneal. The flattening process is conducted at a temperature between 1000.degree. to 1435.degree. F. (540.degree. to 780.degree. C.) with a tension selected to produce a yield strength/tension ratio from above 5 to about 20 and preferably from 7 to 13. The yield strength of the material will vary depending on the length of the time at peak temperature but are typically from 400 to 4000 psi (29,200 to 292,000 gm/cm.sup.2). The material as thermally flattened will have at least about 10% stress. After a stress relief anneal above about 1450.degree. F. (785.degree. C.), the material has significantly improved core loss compared to conventional thermally flattened material. The material is particularly suited for wound transformer core applications.

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