Grain-oriented electrical steel sheet, manufacturing method therefor, and method for predicting transformer noise property

Abstract

Provided is a grain-oriented electrical steel sheet having an excellent noise property in an actual transformer. Magnetostrictive properties of the grain-oriented electrical steel sheet are set such that the number of acceleration/deceleration points that are present in the magnetostriction velocity level dλ/dt in one period of magnetostrictive vibration is 4 and the magnitude of velocity level change between adjacent velocity change points in an acceleration zone or deceleration zone of magnetostrictive vibration is 3.0×10 −4 sec −1 or less.

1 . A grain-oriented electrical steel sheet comprising a forsterite film and an insulating coating at a surface thereof, wherein
 magnetostrictive properties of the grain-oriented electrical steel sheet satisfy conditions I and II, shown below,
 I: the number of acceleration/deceleration points that are present in a magnetostriction velocity level dλ/dt in one period of magnetostrictive vibration is 4, 
 II: the magnitude of velocity level change between adjacent magnetostriction velocity level change points in an acceleration zone or deceleration zone of magnetostrictive vibration is 3.0×10 −4  sec −1  or less, 
   a front/rear difference in total tension of the forsterite film and the insulating coating is less than 0.5 MPa, and   a front/rear difference in tension of the forsterite film is 0.5 MPa or more.   
     
     
         2 . A method for manufacturing a grain-oriented electrical steel sheet, for use in manufacturing the grain-oriented electrical steel sheet according to  claim 1 , comprising:
 hot rolling a slab to obtain a hot rolled sheet;   subjecting the hot rolled sheet to hot band annealing as necessary;   subsequently subjecting the hot rolled sheet to cold rolling once, or twice or more with intermediate annealing in-between, to obtain a cold rolled sheet of final sheet thickness;   subsequently subjecting the cold rolled sheet to decarburization annealing to obtain a decarburization annealed sheet;   subsequently applying an annealing separator having MgO as a main component onto a surface of the decarburization annealed sheet and then subjecting the decarburization annealed sheet to final annealing to form the forsterite film and obtain a final annealed sheet; and   subsequently applying an insulating coating treatment liquid onto the final annealed sheet and then subjecting the final annealed sheet to flattening annealing that also serves as baking to form the insulating coating, wherein   in formation of the forsterite film and the insulating coating, a front/rear difference in total tension of the forsterite film and the insulating coating is adjusted to less than 0.5 MPa, and a front/rear difference in tension of the forsterite film is adjusted to 0.5 MPa or more.   
     
     
         3 . The method for manufacturing a grain-oriented electrical steel sheet according to  claim 2 , wherein
 tension of the forsterite film is adjusted through at least one of: changing formation conditions of an internal oxidation layer at front and rear steel sheet surfaces in the decarburization annealing; changing the annealing separator in terms of type; changing the annealing separator in terms of application amount; and changing an amount of electrodeposition in electrodeposition treatment performed before the final annealing.   
     
     
         4 . The method for manufacturing a grain-oriented electrical steel sheet according to  claim 2 , wherein
 tension of the insulating coating is adjusted through at least one of: changing the insulating coating in terms of thickness; and changing the insulating coating in terms of composition.   
     
     
         5 . A method for predicting a transformer noise property, comprising
 predicting a noise property of a transformer in which a grain-oriented electrical steel sheet including a forsterite film and an insulating coating at a surface thereof is used by using a magnetostrictive property III and a magnetostrictive property VI of the transformer, shown below,
 magnetostrictive property III: the number of acceleration/deceleration points present in a magnetostriction velocity level dλ/dt in one period of magnetostrictive vibration, 
 magnetostrictive property VI: the magnitude of velocity level change between adjacent magnetostriction velocity level change points in an acceleration zone or deceleration zone of magnetostrictive vibration. 
   
     
     
         6 . The method for manufacturing a grain-oriented electrical steel sheet according to  claim 3 , wherein
 tension of the insulating coating is adjusted through at least one of: changing the insulating coating in terms of thickness; and changing the insulating coating in terms of composition.