Method for producing a grain-oriented electrical steel strip and grain-oriented electrical steel strip

Abstract

A method is used to produce a grain-oriented electrical steel strip having optimized magnetic properties. The method may utilize a steel comprising in percent by weight 2.0-4.0% Si, 0.010-0.100% C, at most 0.065% Al, at most 0.02% N, and optionally further constituents, the balance being iron and unavoidable impurities. The steel may be processed to give a cold strip, which may then be subjected to oxidation/primary recrystallization annealing. The resultant cold strip may have an oxide layer to which an annealing separator layer is applied. In a subsequent high-temperature anneal, a forsterite layer forms therefrom, and an insulation layer may be applied thereto prior to a final anneal. After the oxidation/primary recrystallization anneal, a spectrum of the oxide layer obtained is determined by way of FTIR, and an area (Fe2SiO4) is determined for a peak representing Fe2SiO4 molecules present in the oxide layer and is at 980 cm−1, and an area (αSiO2) for a peak representing αSiO2 molecules present in the oxide layer and is at 1250 cm−1. Then the composition of the steel, parameters for the cold rolling, parameters for the oxidation/primary recrystallization anneal, or parameters for a hot strip anneal are adjusted such that 0.5×area (Fe2SiO4)≤area (αSiO2)≤2×area (Fe2SiO4).

1 .- 10 . (canceled) 
     
     
         11 . A method of producing a grain-oriented electrical steel strip, the method comprising:
 smelting a steel melt comprising 2.0-4.0% by weight Si, 0.010-0.100% by weight C, up to 0.065% by weight Al, up to 0.02% by weight N, iron, and unavoidable impurities;   casting the steel melt to give a preliminary material;   hot rolling the preliminary material to give a hot strip;   coiling the hot strip to give a coil;   cold rolling the hot strip to give a cold strip;   oxidation/primary recrystallization annealing the cold strip, wherein a surface of the cold strip includes an oxide layer after the oxidation/primary recrystallization annealing;   recording a spectrum of the oxide layer by way of diffuse reflectance Fourier transformation infrared spectroscopy;   determining an area (Fe 2 SiO 4 ) by integrating for a peak present in the spectrum obtained at 980 cm −1 , which represents Fe 2 SiO 4  molecules present in the oxide layer;   determining an area (αSiO 2 ) by integrating for a peak present in the spectrum obtained at 1250 cm −1 , which represents αSiO 2  molecules present in the oxide layer;   adjusting a composition of the steel melt, parameters of the cold rolling of the hot strip, or parameters of the oxidation/primary recrystallization annealing so that 0.5×the area (Fe 2 SiO 4 )≤the area (αSiO 2 )≤2×the area (Fe 2 SiO 4 );   applying an annealing separator layer to the surface of the cold strip that includes the oxide layer;   high-temperature annealing the cold strip coated with the annealing separator layer to form a forsterite layer on the surface of the calcined cold strip;   applying an insulation layer to the surface of the cold strip having the forsterite layer; and   annealing the cold strip.   
     
     
         12 . The method of  claim 11  wherein the steel melt further comprises:
 up to 0.5% by weight Cu; 
 up to 0.060% by weight S; and 
 up to 0.3% by weight Cr, Mn, Ni, Mo, P, As, Sn, Sb, Se, Te, B or Bi. 
 
     
     
         13 . The method of  claim 11  wherein the oxidation/primary recrystallization annealing comprises at least one of a decarburizing treatment or a nitriding treatment. 
     
     
         14 . The method of  claim 11  comprising laser-treating the cold strip after the cold strip is annealed. 
     
     
         15 . The method of  claim 11  wherein the cold rolling of the hot strip to give the cold strip is performed in at least three cold rolling steps. 
     
     
         16 . The method of  claim 11  comprising annealing the hot strip after the coiling of the hot strip. 
     
     
         17 . The method of  claim 16  wherein the adjustment comprises adjusting the composition of the steel melt, the parameters of the cold rolling of the hot strip, the parameters of the oxidation/primary recrystallization annealing, or parameters of the annealing of the hot strip so that 0.5×the area (Fe 2 SiO 4 )≤the area (αSiO 2 )≤2×the area (Fe 2 SiO 4 ). 
     
     
         18 . The method of  claim 11  wherein the steel melt further comprises up to 0.5% by weight Cu; up to 0.060% by weight S; and up to 0.3% by weight Cr, Mn, Ni, Mo, P, As, Sn, Sb, Se, Te, B or Bi; wherein the cold rolling of the hot strip to give the cold strip is performed in at least three cold rolling steps, the method further comprising:
 annealing the hot strip after the coiling of the hot strip; 
 determining an index kC for the cold rolling wherein kC=T ob /(2×Ab), wherein T ob  is an average surface temperature in degrees Celsius during a last three passes of the at least three cold rolling steps, wherein Ab is a total percent decrease in a thickness of the cold strip achieved over the last three cold rolling passes; 
 determining an index kOx for the oxidation/primary recrystallization annealing wherein kOx=T ox /(5×DP ox ), wherein T ox  is a maximum temperature in degrees Celsius achieved during the oxidation/primary recrystallization annealing, wherein DP ox  is a maximum dew point in degrees Celsius achieved in an atmosphere under which the oxidation/primary recrystallization annealing occurs; 
 determining an index kH for the annealing of the hot strip wherein kH=T max /(8×DP max +10×K), wherein T max  is a maximum temperature in degrees Celsius in the annealing of the hot strip, wherein DP max  is a maximum dew point in degrees Celsius achieved in an atmosphere in which the annealing of the hot strip occurs, wherein K is a cooling rate in degrees Celsius per second while cooling within a temperature range of 700° C.-400° C. after the hot strip annealing; and 
 adjusting T max , DP max , K, T ob , Ab, T ox  and DP ox  such that
   percent by weight Sn/percent by weight Cu≤ k C≤3×(percent by weight Sn/percent by weight Cu+percent by weight Cr+ k H),  (1)
 
   ¼×( k H+ k C+percent by weight Sn/percent by weight Cu)≤ k O x≤ 2×( k H +   k C+percent by weight Sn/percent by weight Cu+percent by weight Cr), and  (2)
 
   γ 1150 /100×3≤ k H≤γ 1150 /100×15, wherein γ 1150 =694×percent by weight C−23×percent by weight Si+64.8,  (3)
 
 wherein the percentages by weight in the adjustment of T max , DP max , K, T ob , Ab, T ox  and DP ox  are with respect to the steel melt. 
 
 
     
     
         19 . The method of  claim 11  wherein the annealing separator layer comprises predominantly MgO. 
     
     
         20 . The method of  claim 11  wherein the high-temperature annealing is a bell anneal. 
     
     
         21 . The method of  claim 20  wherein a temperature in the high-temperature annealing is more than 1150° C. 
     
     
         22 . A grain-oriented electrical steel strip comprising:
 a forsterite film disposed on a cold-rolled steel substrate comprised of a steel comprising:
 2.0-4.0% by weight Si, 
 up to 0.100% by weight C, 
 up to 0.065% by weight Al, 
 up to 0.020% by weight N, 
 iron, and 
 unavoidable impurities, 
   wherein the forsterite film has a higher peak at a wavenumber of 977 cm −1  than at a wavenumber of 984 cm −1  in a spectrum recorded by way of diffuse reflectance Fourier transformation infrared spectroscopy.   
     
     
         23 . The grain-oriented electrical steel strip of  claim 22  comprising:
 up to 0.5% by weigh Cu; 
 up to 0.060% by weight S; and 
 up to 0.3% by weight Cr, Mn, Ni, Mo, P, As, Sn, Sb, Se, Te, B or Bi. 
 
     
     
         24 . The grain-oriented electrical steel strip of  claim 23  comprising a carbon content of at least 0.010% by weight. 
     
     
         25 . The grain-oriented electrical steel strip of  claim 23  produced by the method of  claim 11 .