Patent ID: 11866812
Assignee: NIPPON STEEL CORPORATION
Field: Materials, metallurgy (Chemistry)
Classification: CPC C  H | IPC C

Claim 2:
3. A producing method for a grain oriented electrical steel sheet according to claim 1 characterized in that
the producing method includes
a hot rolling process of heating and thereafter hot-rolling a steel piece to obtain a hot rolled steel sheet,
a hot band annealing process of optionally annealing the hot rolled steel sheet to obtain a hot band annealed steel sheet,
a cold rolling process of cold-rolling the hot rolled steel sheet or the hot band annealed steel sheet by cold-rolling once or by cold-rolling plural times with an intermediate annealing to obtain a cold rolled steel sheet,
a decarburization annealing process of decarburization-annealing the cold rolled steel sheet to obtain a decarburization annealed steel sheet,
a final annealing process of applying an annealing separator to the decarburization annealed steel sheet and thereafter final-annealing the decarburization annealed steel sheet to obtain a final annealed steel sheet,
an oxidizing process of conducting a washing treatment, a pickling treatment, and a heat treatment in turn for the final annealed steel sheet to obtain an oxidized steel sheet, and
an insulation coating forming process of applying a solution including a metal phosphate and a silica for forming a phosphate-silica mixed tension-insulation coating to a surface of the oxidized steel sheet and of baking the solution so as to form the tension-insulation coating with an average thickness of 1 to 3 μm,
wherein, in the hot rolling process,
the steel piece includes, as a chemical composition, by mass %,
2.5 to 4.0% of Si,
0.05 to 1.00% of Mn,
0.02 to 0.50% of Cr,
0.02 to 0.10% of C,
0.005 to 0.080% of S+Se,
0.010 to 0.07% of sol. A1,
0.005 to 0.020% of N,
0 to 0.03% of Bi,
0 to 0.03% of Te,
0 to 0.03% of Pb,
0 to 0,50% of Sb,
0 to 0.50% of Sn,
0 to 1.0% of Cu, and
a balance consisting of Fe and impurities, and
wherein,
in the decarburization annealing process,
the cold rolled steel sheet is held in a temperature ran e of 750 to 950° C. for 1 to 5 minutes in a moist atmosphere including hydrogen and nitrogen,
in the final annealing process,
at least one of an annealing separator in which MgO and Al2O3 of 85 mass % or more in total as percent solid are included, MgO: Al2O3which is a mass ratio of MgO and Al2O3satisfies 3:7 to 7:3, and a bismuth chloride of 0,5 to 15 mass % as compared with a total amount of MgO and Al2O3 as percent solid is included and an annealing separator in which MgO of 60 mass % or more as percent solid is included is applied to the decarburization annealed steel sheet, and
the steel sheet after applying the annealing separator is held in a temperature range of 1100 to 1300° C. for 10 to 30 hours in at least one of a nitrogen atmosphere and a mixed atmosphere of nitrogen and hydrogen,
in the oxidizing process,
as the washing treatment, a surface of the final annealed steel sheet is washed,
as the pickling treatment, the final annealed steel sheet is pickled using a sulfuric acid of 2 to 20 mass % at 70 to 90° C., and
as the heat treatment, the final annealed steel sheet is held in a temperature range of 700 to 900° C. for 10 to 60 seconds in a mixed atmosphere of nitrogen and hydrogen where a dew point is 10 to 30° C. and a hydrogen concentration is 0 to 4 volume %
in the insulation coating forming process,
the steel sheet after applying the solution for forming the tension-insulation coating is held at 850 to 950° C. for 10 to 60 seconds.