Hot-rolled steel sheet for grain-oriented electrical steel sheet and method of producing same, and method of producing grain-oriented electrical steel sheet

Abstract

Provided is a technique to reduce the variations in magnetic properties in a coil. A hot-rolled steel sheet for a grain-oriented electrical steel sheet having a chemical composition containing, by mass %, C: 0.002% or more and 0.080% or less, Si: 2.00% or more and 8.00% or less, Mn: 0.02% or more and 0.50% or less, acid-soluble Al: 0.003% or more and less than 0.010%, and at least one of S or Se: 0.001% or more and 0.010% or less in total, with N limited to less than 0.006%, and the balance being Fe and inevitable impurities, where regions from an outermost surface layer and a bottommost surface layer to a depth of 1/4 sheet thickness have a recrystallization ratio of 90% or less.

1 . A hot-rolled steel sheet for a grain-oriented electrical steel sheet, comprising:
 a chemical composition containing, by mass %,
 C: 0.002% or more and 0.080% or less, 
 Si: 2.00% or more and 8.00% or less, 
 Mn: 0.02% or more and 0.50% or less, 
 acid-soluble Al: 0.003% or more and less than 0.010%, and 
 at least one of S or Se: 0.001% or more and 0.010% or less in total, 
 with N limited to less than 0.006%, and the balance being Fe and inevitable impurities, wherein 
 regions from an outermost surface layer and a bottommost surface layer to a depth of 1/4 sheet thickness have a recrystallization ratio of 90% or less. 
   
     
     
         2 . The hot-rolled steel sheet for a grain-oriented electrical steel sheet according to  claim 1 , wherein the chemical composition further contains at least one selected from, by mass %,
 Ni: 0.005% or more and 1.5% or less,   Cu: 0.005% or more and 1.5% or less,   Sb: 0.005% or more and 0.5% or less,   Sn: 0.005% or more and 0.5% or less,   Cr: 0.005% or more and 0.1% or less,   P: 0.005% or more and 0.5% or less,   Mo: 0.005% or more and 0.5% or less,   Ti: 0.0005% or more and 0.1% or less,   Nb: 0.0005% or more and 0.1% or less,   V: 0.0005% or more and 0.1% or less,   B: 0.0002% or more and 0.0025% or less,   Bi: 0.005% or more and 0.1% or less,   Te: 0.0005% or more and 0.01% or less, and   Ta: 0.0005% or more and 0.01% or less.   
     
     
         3 . A hot-rolled and annealed sheet for a grain-oriented electrical steel sheet, comprising:
 a chemical composition containing, by mass %,
 C: 0.002% or more and 0.080% or less, 
 Si: 2.00% or more and 8.00% or less, 
 Mn: 0.02% or more and 0.50% or less, 
 acid-soluble Al: 0.003% or more and less than 0.010%, and 
 at least one of S or Se: 0.001% or more and 0.010% or less in total, 
 with N limited to less than 0.006%, and the balance being Fe and inevitable impurities, wherein 
   an average recrystallized grain size in regions from an outermost surface layer and a bottommost surface layer to a depth of 1/4 sheet thickness is three times or less an average recrystallized grain size in regions from a center of the sheet thickness to a length of less than 1/4 sheet thickness in directions to the outermost surface layer and the bottommost surface layer.   
     
     
         4 . The hot-rolled and annealed sheet for a grain-oriented electrical steel sheet according to  claim 3 , wherein the chemical composition further contains at least one selected from, by mass %,
 Ni: 0.005% or more and 1.5% or less,   Cu: 0.005% or more and 1.5% or less,   Sb: 0.005% or more and 0.5% or less,   Sn: 0.005% or more and 0.5% or less,   Cr: 0.005% or more and 0.1% or less,   P: 0.005% or more and 0.5% or less,   Mo: 0.005% or more and 0.5% or less,   Ti: 0.0005% or more and 0.1% or less,   Nb: 0.0005% or more and 0.1% or less,   V: 0.0005% or more and 0.1% or less,   B: 0.0002% or more and 0.0025% or less,   Bi: 0.005% or more and 0.1% or less,   Te: 0.0005% or more and 0.01% or less, and   Ta: 0.0005% or more and 0.01% or less.   
     
     
         5 . A method of producing a hot-rolled steel sheet for a grain-oriented electrical steel sheet, comprising:
 preparing a steel slab having a chemical composition containing, by mass %,
 C: 0.002% or more and 0.080% or less, 
 Si: 2.0% or more and 8.0% or less, 
 Mn: 0.02% or more and 0.50% or less, 
 acid-soluble Al: 0.003% or more and less than 0.010%, and 
 at least one of S or Se: 0.001% or more and 0.010% or less in total, 
 with N limited to less than 0.006%, and the balance being Fe and inevitable impurities; 
   heating the steel slab to 1300° C. or lower; and   subjecting the steel slab to hot rolling, wherein a friction coefficient in final pass of the hot rolling is 0.35 or less.   
     
     
         6 . The method of producing a hot-rolled steel sheet for a grain-oriented electrical steel sheet according to  claim 5 , wherein the chemical composition further contains at least one selected from, by mass %,
 Ni: 0.005% or more and 1.5% or less,   Cu: 0.005% or more and 1.5% or less,   Sb: 0.005% or more and 0.5% or less,   Sn: 0.005% or more and 0.5% or less,   Cr: 0.005% or more and 0.1% or less,   P: 0.005% or more and 0.5% or less,   Mo: 0.005% or more and 0.5% or less,   Ti: 0.0005% or more and 0.1% or less,   Nb: 0.0005% or more and 0.1% or less,   V: 0.0005% or more and 0.1% or less,   B: 0.0002% or more and 0.0025% or less,   Bi: 0.005% or more and 0.1% or less,   Te: 0.0005% or more and 0.01% or less, and   Ta: 0.0005% or more and 0.01% or less.   
     
     
         7 . A method of producing a grain-oriented electrical steel sheet, comprising:
 preparing a hot-rolled steel sheet with the method of producing a hot-rolled steel sheet for a grain-oriented electrical steel sheet according to  claim 5 ;   subjecting the hot-rolled steel sheet to hot band annealing, and to cold rolling once, or twice or more with intermediate annealing performed therebetween, to obtain a cold-rolled steel sheet with a final sheet thickness;   subjecting the cold-rolled steel sheet to primary recrystallization annealing;   applying an annealing separator to a surface of the cold-rolled steel sheet after subjection to the primary recrystallization annealing; and   then subjecting the cold-rolled steel sheet to secondary recrystallization annealing.   
     
     
         8 . A method of producing a grain-oriented electrical steel sheet, comprising:
 preparing a hot-rolled steel sheet with the method of producing a hot-rolled steel sheet for a grain-oriented electrical steel sheet according to  claim 6 ;   subjecting the hot-rolled steel sheet to hot band annealing, and to cold rolling once, or twice or more with intermediate annealing performed therebetween, to obtain a cold-rolled steel sheet with a final sheet thickness;   subjecting the cold-rolled steel sheet to primary recrystallization annealing;   applying an annealing separator to a surface of the cold-rolled steel sheet after subjection to the primary recrystallization annealing; and   then subjecting the cold-rolled steel sheet to secondary recrystallization annealing.