Method for producing grain-oriented electrical steel sheet and hot-rolled sheet for grain-oriented electrical steel sheet

Abstract

A method for producing a grain-oriented electrical steel sheet is disclosed and includes performing hot rolling on a steel slab, which contains a certain composition, and then performing hot-rolled sheet annealing, cold rolling, decarburization annealing doubling as primary recrystallization annealing, and finishing annealing. Specifically, at least two consecutive passes of the hot rolling are performed in the temperature range of 1050 to 1150° C., the interval between the two passes is set to 60 seconds or less, the rolling reduction in each pass is set to 20% or more, and the strain rate in each pass is set to 15 s −1 or more so that fractures during the cold rolling are prevented. Also provided is a hot-rolled sheet used for such a production method.

1 . A method for producing a grain-oriented electrical steel sheet, comprising:
 performing hot rolling on a steel slab having a composition of components including C: 0.03 to 0.08 mass %, Si: 2.0 to 5.0 mass %, Mn: 0.005 to 1.0 mass %, Al: less than 0.010 mass %, N: 0.006 mass % or less, O: 0.0060 mass % or less, and S and Se (in terms of S+0.405×Se) in a range of 0.0015 to 0.0060 mass %, with a balance being Fe and unavoidable impurities so as to obtain a hot-rolled sheet, the hot rolling including at least two consecutive passes performed in a temperature range of 1050 to 1150° C. under conditions such that an interval between the two passes is 60 seconds or less, a rolling reduction in each pass is 20% or more, and a strain rate in each pass is 15 s −1  or more;   subjecting the hot-rolled sheet to hot-rolled sheet annealing;   performing cold rolling once or performing cold rolling two or more times with intermediate annealing interposed between each rolling to obtain a cold-rolled sheet;   subjecting the cold-rolled sheet to decarburization annealing which acts as primary recrystallization annealing; and   performing finishing annealing.   
     
     
         2 . The method for producing a grain-oriented electrical steel sheet according to  claim 1 ,
 wherein:   the hot rolling includes at least one pass performed in a temperature range of 850 to 950° C.,   the hot-rolled sheet annealing after the hot rolling is performed at a temperature of 850° C. or higher, and   a sum of a cooling time in a temperature range of 750° C. to 650° C. during a cooling process performed after the hot rolling and a heating time in a temperature range of 600° C. to 700° C. during a heating process of the hot-rolled sheet annealing is 20 seconds or less.   
     
     
         3 . The method for producing a grain-oriented electrical steel sheet according to  claim 2 , further comprising, after the at least one pass of the rolling performed in the temperature range of 850 to 950° C., holding the steel sheet as is for 1.0 second or longer. 
     
     
         4 . The method for producing a grain-oriented electrical steel sheet according to  claim 1 , wherein the steel slab further includes, in addition to the composition of components, at least one group of components selected from the following groups A to C:
 a group A: Ni: 1.50 mass % or less,   a group B: at least one element selected from the group consisting of Sn: 0.50 mass % or less, Sb: 0.50 mass % or less, Cu: 0.50 mass % or less, Mo: 0.50 mass % or less, Co: 0.0100 mass % or less, P: 0.50 mass % or less, Cr: 1.50 mass % or less, B: 0.0200 mass % or less, and Bi: 0.0200 mass % or less, and   a group C: at least one element selected from the group consisting of Nb: 0.0200 mass % or less, Ti: 0.0200 mass % or less, Te: 0.0200 mass % or less, Ga: 0.0100 mass % or less, and Zn: 0.500 mass % or less.   
     
     
         5 . A hot-rolled sheet for a grain-oriented electrical steel sheet, comprising a composition of components including C: 0.03 to 0.08 mass %, Si: 2.0 to 5.0 mass %, Mn: 0.005 to 1.0 mass %, Al: less than 0.010 mass %, N: 0.006 mass % or less, O: 0.0060 mass % or less, and S and Se (in terms of S+0.405×Se) in a range of 0.0015 to 0.0060 mass %, with a balance being Fe and unavoidable impurities,
 characterized in that: 
 the number density of precipitates each having a major axis of 4 μm or more among precipitates of sulfide and selenide and complex precipitates of such compounds is 0.30/mm 2  or less in a region with a size of 50 mm 2  including a central portion of a cross-section of the sheet in a thickness direction along a rolling direction, and having a width that is ⅕ a thickness of the sheet. 
 
     
     
         6 . The hot-rolled sheet for a grain-oriented electrical steel sheet according to  claim 5 , further comprising, in addition to the composition of components, at least one group of components selected from the following groups A to C:
 a group A: Ni: 1.50 mass % or less,   a group B: at least one element selected from the group consisting of Sn: 0.50 mass % or less, Sb: 0.50 mass % or less, Cu: 0.50 mass % or less, Mo: 0.50 mass % or less, Co: 0.0100 mass % or less, P: 0.50 mass % or less, Cr: 1.50 mass % or less, B: 0.0200 mass % or less, and Bi: 0.0200 mass % or less, and   a group C: at least one element selected from the group consisting of Nb: 0.0200 mass % or less, Ti: 0.0200 mass % or less, Te: 0.0200 mass % or less, Ga: 0.0100 mass % or less, and Zn: 0.500 mass % or less.   
     
     
         7 . The method for producing a grain-oriented electrical steel sheet according to  claim 2 , wherein the steel slab further includes, in addition to the composition of components, at least one group of components selected from the following groups A to C:
 a group A: Ni: 1.50 mass % or less,   a group B: at least one element selected from the group consisting of Sn: 0.50 mass % or less, Sb: 0.50 mass % or less, Cu: 0.50 mass % or less, Mo: 0.50 mass % or less, Co: 0.0100 mass % or less, P: 0.50 mass % or less, Cr: 1.50 mass % or less, B: 0.0200 mass % or less, and Bi: 0.0200 mass % or less, and   a group C: at least one element selected from the group consisting of Nb: 0.0200 mass % or less, Ti: 0.0200 mass % or less, Te: 0.0200 mass % or less, Ga: 0.0100 mass % or less, and Zn: 0.500 mass % or less.   
     
     
         8 . The method for producing a grain-oriented electrical steel sheet according to  claim 3 , wherein the steel slab further includes, in addition to the composition of components, at least one group of components selected from the following groups A to C:
 a group A: Ni: 1.50 mass % or less,   a group B: at least one element selected from the group consisting of Sn: 0.50 mass % or less, Sb: 0.50 mass % or less, Cu: 0.50 mass % or less, Mo: 0.50 mass % or less, Co: 0.0100 mass % or less, P: 0.50 mass % or less, Cr: 1.50 mass % or less, B: 0.0200 mass % or less, and Bi: 0.0200 mass % or less, and   a group C: at least one element selected from the group consisting of Nb: 0.0200 mass % or less, Ti: 0.0200 mass % or less, Te: 0.0200 mass % or less, Ga: 0.0100 mass % or less, and Zn: 0.500 mass % or less.