Abstract: For the iron cores of an electrical machinery and apparatuses, such as transformers, electric motors and generators, mostly a grain-oriented electromagnetic steel sheet is used. Since the grain-oriented electromagnetic steel sheet has a (110) [001]texture and is thus easily magnetized in the rolling direction, the direction of magnetic flux in the iron cores is required to be coincident with the rolling direction. However, this requirement cannot be completely fulfilled due to the shape and an operation efficiency of producing the iron cores as well as generation of a magnetic reluctance in the butted iron-core elements. Laser irradiation regions are formed, according to the present invention, for example, on the following: the parts of the iron core where the rotational magnetic field is generated; the entire surface of the I-type elements or: the major part of the E or C type element.

Abstract: In the conventional stacking method of the laminated core of a transformer, grain-oriented silicon steel sheet pieces of an identical grade or the identical magnetic properties are used as legs and yokes of the core. In a highly oriented silicon steel sheet having a high B.sub.8 value due to excellent magnetic properties in the rolling direction of the sheet, the excellent magnetic properties cannot be fully utilized for the watt loss reduction in the conventional stacking method. In a laminated core of the present invention, the transformer core comprises a grain-oriented silicon steel sheet having a higher orientation used for a leg(s) and a grain-oriented silicon steel sheet having a lower orientation used for a yoke(s). The former steel has the B.sub.8 value of generally 1.88 Tesla or higher and preferably 1.89 Tesla or higher. The latter steel has the B.sub.8 value of generally 1.86 Tesla or lower.