Grain-oriented electrical steel sheet and decarburized steel sheet used for manufacturing the same
A grain-oriented electrical steel sheet includes: a chemical composition represented by, in mass %, Si: 1.8% to 7.0%, Cu: 0.03% to 0.60%, and the balance: Fe and impurities; and a primary coating film containing forsterite on a surface of the steel sheet, in which a Cu/Fe light-emitting intensity ratio at an interface region between the primary coating film and the surface of the steel sheet is 0.30 or less.
1. A grain-oriented electrical steel sheet, comprising:
a chemical composition comprising
in mass %,
Si: 1.8% to 7.0%,
Cu: 0.03% to 0.60%, and
the balance: Fe and impurities, wherein the impurities comprise C; and
a primary coating film containing forsterite on a surface of the steel sheet, wherein
a Cu/Fe light-emitting intensity ratio at an interface region between the primary coating film and the surface of the steel sheet is 0.30 or less,
wherein the Cu/Fe light-emitting intensity ratio is evaluated by the average of (Cu light-emitting intensities/Fe light-emitting intensities), obtained by glow discharge optical emission spectrometry analysis, at respective measurement points in the interface region.
2. A manufacturing method of a grain-oriented electrical steel sheet, comprising:
a step of heating a slab in a temperature zone of 1300° C. to 1490° C.;
a step of obtaining a hot-rolled steel sheet by performing hot rolling of the slab;
a step of coiling the hot-rolled steel sheet in a temperature zone of 600° C. or less;
a step of performing hot-rolled sheet annealing of the hot-rolled steel sheet;
after the hot-rolled sheet annealing, a step of performing cold rolling and obtaining a cold-rolled steel sheet;
a step of performing decarburization annealing of the cold-rolled steel sheet; and
after the decarburization annealing, a step of applying an annealing separating agent containing MgO and performing finish annealing, wherein
the step of performing the hot rolling includes a step of performing rough rolling with a finishing temperature set to 1200° C. or less and a step of performing finish rolling with a start temperature set to 1000° C. or more and a finishing temperature set to 950° C. to 1100° C.,
in the hot rolling, the finish rolling is started within 300 seconds after start of the rough rolling,
cooling at a cooling rate of 50° C./second or more is started within 10 seconds after finish of the finish rolling,
pickling with a holding temperature set to 50° C. or more and a holding time period set to 30 seconds or more is performed in a pickling bath containing a nitric acid, a pickling inhibitor, and a surface active agent after the hot rolling and before finish of the cold rolling, and
the slab includes a chemical composition comprising,
in mass %,
C: 0.03% to 0.15%,
Si: 1.8% to 7.0%,
Mn: 0.02% to 0.30%,
S: 0.005% to 0.040%,
acid-soluble Al: 0.010% to 0.065%,
N: 0.0030% to 0.0150%,
Cu: 0.03% to 0.60%,
Sn: 0% to 0.5%,
Ge, Se, Sb, Te, Pb, or Bi, or an arbitrary combination of these: 0.0005% to 0.030% in total, and
the balance: Fe and impurities.
3. The manufacturing method of the grain-oriented electrical steel sheet according to claim 2 , wherein
the pickling bath further contains a nitrate.
4. A manufacturing method of a decarburized steel sheet for a grain-oriented electrical steel sheet, comprising:
a step of heating a slab in a temperature zone of 1300° C. to 1490° C.;
a step of obtaining a hot-rolled steel sheet by performing hot rolling of the slab;
a step of coiling the hot-rolled steel sheet in a temperature zone of 600° C. or less;
a step of performing hot-rolled sheet annealing of the hot-rolled steel sheet;
after the hot-rolled sheet annealing, a step of performing cold rolling and obtaining a cold-rolled steel sheet; and
a step of performing decarburization annealing of the cold-rolled steel sheet; wherein
the step of performing the hot rolling includes a step of performing rough rolling with a finishing temperature set to 1200° C. or less and a step of performing finish rolling with a start temperature set to 1000° C. or more and a finishing temperature set to 950° C. to 1100° C.,
in the hot rolling, the finish rolling is started within 300 seconds after start of the rough rolling,
cooling at a cooling rate of 50° C./second or more is started within 10 seconds after finish of the finish rolling,
pickling with a holding temperature set to 50° C. or more and a holding time period set to 30 seconds or more is performed in a pickling bath containing a nitric acid, a pickling inhibitor, and a surface active agent after the hot rolling and before finish of the cold rolling, and
the slab includes a chemical composition comprising,
in mass %
C: 0.03% to 0.15%,
Si: 1.8% to 7.0%,
Mn: 0.02% to 0.30%,
S: 0.005% to 0.040%,
acid-soluble Al: 0.010% to 0.065%,
N: 0.0030% to 0.0150%,
Cu: 0.03% to 0.60%,
Sn: 0% to 0.5%,
Ge, Se, Sb, Te, Pb, or Bi, or an arbitrary combination of these: 0.0005% to 0.030% in total, and
the balance: Fe and impurities.
5. The manufacturing method of the decarburized steel sheet for a grain-oriented electrical steel sheet according to claim 4 , wherein
the pickling bath further contains a nitrate.