High-strength non-oriented electrical steel sheet and method of manufacturing the same

Abstract

A high-strength non-oriented electrical steel sheet contains: by mass %, C: not less than 0.002% nor more than 0.05%; Si: not less than 2.0% nor more than 4.0%; Mn: not less than 0.05% nor more than 1.0%; N: not less than 0.002% nor more than 0.05%; and Cu: not less than 0.5% nor more than 3.0%. An Al content is 3.0% or less, and when a Nb content (%) is set to [Nb], a Zr content (%) is set to [Zr], a Ti content (%) is set to [Ti], a V content (%) is set to [V], a C content (%) is set to [C], and an N content (%) is set to [N], Formula (1) and Formula (2) are satisfied. A balance is composed of Fe and inevitable impurities, a recrystallization area ratio is 50% or more, yield stress at a tensile test is 700 MPa or more, fracture elongation is 10% or more, and an eddy current loss We 10/400 (W/kg) satisfies Formula (3) in relation to a sheet thickness t (mm) of the steel sheet. 2.0×10 −4 ≦[Nb]/ 93 +[Zr]/ 91 +[Ti]/ 48 +[V]/ 51   (1) 1.0×10 −3 ≦[C]/ 12 +[N]/ 14 −([Nb]/ 93 +[Zr]/ 91 +[Ti]/ 48 +[V]/ 51 )≦ 3.0×10 −3   (2) We 10/400 ≦70× t 2   (3)

What is claimed is: 
     
         1 . A high-strength non-oriented electrical steel sheet containing:
 by mass %,   C: not less than 0.002% nor more than 0.05%;   Si: not less than 2.0% nor more than 4.0%;   Mn: not less than 0.05% nor more than 1.0%;   N: not less than 0.002% nor more than 0.05%; and   Cu: not less than 0.5% nor more than 3.0%, and wherein   an Al content is 3.0% or less,   when a Nb content (%) is set to [Nb], a Zr content (%) is set to [Zr], a Ti content (%) is set to [Ti], a V content (%) is set to [V], a C content (%) is set to [C], and an N content (%) is set to [N], Formula (1) and Formula (2) are satisfied,   a balance is composed of Fe and inevitable impurities,   a recrystallization area ratio is 50% or more,   yield stress at a tensile test is 700 MPa or more,   fracture elongation is 10% or more, and   an eddy current loss We 10/400  (W/kg) satisfies Formula (3) in relation to a sheet thickness t (mm) of the steel sheet.
   2.0×10 −4 ≦[Nb]/93+[Zr]/91+[Ti]/48+[V]/51   (1)
 
   1.0×10 −3 ≦[C]/12+[N]/14−([Nb]/93+[Zr]/91+[Ti]/48+[V]/51)≦3.0×10 −3    (2)
 
   We 10/400 ≦70 ×t   2    (3)
 
   
     
     
         2 . The high-strength non-oriented electrical steel sheet according to  claim 1 , further containing, by mass %, Ni: not less than 0.5% nor more than 3.0%. 
     
     
         3 . The high-strength non-oriented electrical steel sheet according to  claim 1 , further containing, by mass %, Sn: not less than 0.01% nor more than 0.10%. 
     
     
         4 . The high-strength non-oriented electrical steel sheet according to  claim 2 , further containing, by mass %, Sn: not less than 0.01% nor more than 0.10%. 
     
     
         5 . The high-strength non-oriented electrical steel sheet according to  claim 1 , further containing, by mass %, B: not less than 0.0010% nor more than 0.0050%. 
     
     
         6 . The high-strength non-oriented electrical steel sheet according to  claim 2 , further containing, by mass %, B: not less than 0.0010% nor more than 0.0050%. 
     
     
         7 . The high-strength non-oriented electrical steel sheet according to  claim 3 , further containing, by mass %, B: not less than 0.0010% nor more than 0.0050%. 
     
     
         8 . The high-strength non-oriented electrical steel sheet according to  claim 4 , further containing, by mass %, B: not less than 0.0010% nor more than 0.0050%. 
     
     
         9 . A method of manufacturing a high-strength non-oriented electrical steel sheet comprising:
 manufacturing a slab containing:   by mass %,   C: not less than 0.002% nor more than 0.05%;   Si: not less than 2.0% nor more than 4.0%;   Mn: not less than 0.05% nor more than 1.0%;   N: not less than 0.002% nor more than 0.05%; and   Cu: not less than 0.5% nor more than 3.0%   and in which   an Al content is 3.0% or less,   when a Nb content (%) is set to [Nb], a Zr content (%) is set to [Zr], a Ti content (%) is set to [Ti], a V content (%) is set to [V], a C content (%) is set to [C], and an N content (%) is set to [N], Formula (1) and Formula (2) are satisfied, and a balance is composed of Fe and inevitable impurities;   obtaining a hot-rolled sheet by hot rolling the slab;   pickling the hot-rolled sheet;   next, obtaining a cold-rolled sheet by cold rolling the hot-rolled sheet; and   finish-annealing the cold-rolled sheet, wherein   a soaking temperature T (° C.) of said finish-annealing and a Cu content “a” (mass %) of the cold-rolled sheet satisfy Formula (4).
   2.0×10 −4 [Nb]/93+[Zr]/91+[Ti]/48+[V]/51   (1)
 
   1.0×10 −3 ≦[C]/12+[N]/14−([Nb]/93+[Zr]/91+[Ti]/48+[V]/51)≦3.0×10 −3    (2)
 
   T≦200× a+ 500   (4)
 
   
     
     
         10 . The method of manufacturing a high-strength non-oriented electrical steel sheet according to  claim 9 , further comprising annealing the hot-rolled sheet between said obtaining the hot-rolled sheet and said pickling the hot-rolled sheet. 
     
     
         11 . A method of manufacturing a high-strength non-oriented electrical steel sheet comprising:
 manufacturing a slab containing:   by mass %,   C: not less than 0.002% nor more than 0.05%;   Si: not less than 2.0% nor more than 4.0%;   Mn: not less than 0.05% nor more than 1.0%;   N: not less than 0.002% nor more than 0.05%; and   Cu: not less than 0.5% nor more than 3.0%   and in which   an Al content is 3.0% or less,   when a Nb content (%) is set to [Nb], a Zr content (%) is set to [Zr], a Ti content (%) is set to [Ti], a V content (%) is set to [V], a C content (%) is set to [C], and an N content (%) is set to [N], Formula (1) and Formula (2) are satisfied, and   a balance is composed of Fe and inevitable impurities;   obtaining a hot-rolled sheet by hot rolling the slab;   next, pickling the hot-rolled sheet;   next, obtaining a cold-rolled sheet by cold rolling the hot-rolled sheet; and   finish-annealing the cold-rolled sheet, wherein   a coiling temperature of said hot rolling is 550° C. or less, and a ductile/brittle fracture transition temperature at a Charpy impact test of the hot-rolled sheet is 70° C. or less.
   2.0×10 −4 [Nb]/93+[Zr]/91+[Ti]/48+[V]/51   (1)
 
   1.0×10 −3 ≦[C]/12+[N]/14−([Nb]/93+[Zr]/91+[Ti]/48+[V]/51)≦3.0×10 −3    (2)
 
   
     
     
         12 . A method of manufacturing a high-strength non-oriented electrical steel sheet comprising:
 manufacturing a slab containing:   by mass %,   C: not less than 0.002% nor more than 0.05%;   Si: not less than 2.0% nor more than 4.0%;   Mn: not less than 0.05% nor more than 1.0%;   N: not less than 0.002% nor more than 0.05%; and   Cu: not less than 0.5% nor more than 3.0%   and in which   an Al content is 3.0% or less,   when a Nb content (%) is set to [Nb], a Zr content (%) is set to [Zr], a Ti content (%) is set to [Ti], a V content (%) is set to [V], a C content (%) is set to [C], and an N content (%) is set to [N], Formula (1) and Formula (2) are satisfied, and   a balance is composed of Fe and inevitable impurities;   obtaining a hot-rolled sheet by hot rolling the slab;   next, annealing the hot-rolled sheet;   next, pickling the hot-rolled sheet;   next, obtaining a cold-rolled sheet by cold rolling the hot-rolled sheet; and   finish-annealing the cold-rolled sheet, wherein   a cooling rate from 900° C. to 500° C. of said annealing is 50° C./sec or more, and a ductile/brittle fracture transition temperature at a Charpy impact test of the hot-rolled sheet is 70° C. or less.
   2.0×10 −4 [Nb]/93+[Zr]/91+[Ti]/48+[V]/51   (1)
 
   1.0×10 −3 ≦[C]/12+[N]/14−([Nb]/93+[Zr]/91+[Ti]/48+[V]/51)≦3.0×10 −3  (2)