Grain-oriented electrical steel sheet and manufacturing method of grain-oriented electrical steel sheet

A manufacturing method of a grain-oriented electrical steel sheet, the method comprising:

• a hot rolling step of heating a slab and hot rolling the heated slab to obtain a hot-rolled steel sheet, the slab including, in terms of mass %,
• 2.50 to 4.00% of Si,
• 0.01 to 0.30% of Mn,
• 0.0030 to 0.0150% of N,
• 0.010 to 0.100% of C,
• 0.010 to 0.050% of sol. Al,
• 0.010 to 0.050% in total of at least one of S and Se,
• 0.001 to 0.010% of Ti,
• 0 to 0.50% of Ni,
• 0 to 0.50% of Cu,
• 0 to 0.30% of Sb,
• 0 to 0.30% of Sn,
• 0 to 0.50% of Cr,
• 0 to 0.05% of P,
• 0 to 0.05% of Mo,
• 0 to 0.05% of Ta,
• 0 to 0.010% of Nb,
• 0 to 0.50% of V,
• 0 to 0.010% of B,
• 0 to 0.0200% of Bi,
• 0 to 0.0200% of Te, and
• a balance including Fe and impurities;
• a hot-band annealing step of annealing the hot-rolled steel sheet;
• a cold rolling step of cold rolling the hot-rolled steel sheet after the hot-band annealing step to obtain a cold-rolled steel sheet;
• a decarburization annealing step of decarburization annealing the cold-rolled steel sheet to obtain a decarburization-annealed steel sheet;
• a final annealing step of applying an annealing separator on the decarburization-annealed steel sheet, followed by final annealing, to form a primary coating on a surface of the decarburization-annealed steel sheet, thereby obtaining a final-annealed steel sheet;
• and
• an insulating coating forming step of forming an insulating coating on a surface of the final-annealed steel sheet, wherein
• a total rolling reduction is 89% or more in the cold rolling step,
• the decarburization annealing step includes:
• a local heating process of partly heating a surface of the cold-rolled steel sheet by irradiating with a laser beam in an air atmosphere at an interval of 5 to 30 mm in a direction that forms 30 to 150° with respect to a rolling direction;
• a temperature rising process of raising a temperature of the cold-rolled steel sheet after the local heating process in a non-oxidizing atmosphere from a temperature range of 450° C. or lower to a temperature range of 750 to 950° C., which is a temperature for decarburization annealing, at an average heating rate of 80° C./sec or more and 2000° C./sec or less;
• and
• a heat equalizing process of decarburization annealing the cold-rolled steel sheet after the temperature rising process at an oxygen potential PO satisfying equation (1) below, when, in irradiation conditions of the laser beam in the local heating process,
• an average intensity of the laser beam is defined as P, in terms of a unit of W,
• a focused spot diameter of a focused spot in the rolling direction is defined as Dl, in terms of a unit of mm,
• a focused spot diameter of the focused spot in a width direction orthogonal to the rolling direction is defined as Dc, in terms of a unit of mm,
• an irradiation time is defined as t, in terms of a unit of sec, and
• an instantaneous input energy represented by 4/π×P/(Dl×Dc)×t is defined as Up, in terms of a unit of J/mm2,
• a following equation (2) is satisfied:
• P
• O
• ≤
• 0.6
• -
• 0.04
• Up
• (
• 1
• )
• 1
• ≤
• Up
• ≤
• 5.
• (
• 2
• )