Provided is a linear groove formation pattern with which both an effect of reducing the building factor and a high magnetic flux density can be obtained. In a grain-oriented electrical steel sheet having a plurality of linear grooves extending in a direction crossing a rolling direction of the steel sheet on a surface of the steel sheet, a surface of the steel sheet between the linear grooves has a recessed defect that is recessed from the surface, a volume fraction of the recessed defect in the steel sheet is 0.0025 vol % or more and 0.01 vol % or less of a steel sheet without the recessed defect, and discontinuous portions that disrupt the extension of the linear grooves are provided at a frequency of 30 or more and 200 or less per square meter of the steel sheet.

Provided is a hot-band annealing method comprising subjecting a Si-containing hot rolled steel sheet, having an oxidized scale formed on a surface of the steel sheet by hot rolling, to hot-band annealing with a hot-band annealing equipment provided with a heating zone, a soaking zone, a cooling zone, and a rapid heating device at an upstream side of the heating zone and/or in an inlet side of the heating zone, wherein the hot rolled steel sheet is heated by not lower than 50° C. at a heating rate of not less than 15° C./s by using the rapid heating device to improve a descaling property. Also, provided is a descaling method characterized by subjecting the Si-containing hot rolled steel sheet, after the hot-band annealing, to descaling only by pickling without requiring mechanical descaling or heating the steel sheet in the pickling process.

In a grain-oriented electrical steel sheet manufacturing process of processing a steel slab having a predetermined composition to a final sheet thickness and then performing primary recrystallization annealing and nitriding treatment, the nitriding treatment is performed in at least two stages of temperatures including high-temperature nitriding and low-temperature nitriding, and a residence time in the high-temperature nitriding is 3 seconds or more and 600 seconds or less. In this way, nitrogen is efficiently diffused into the steel of the steel sheet before secondary recrystallization to precipitate AlN. Such a method can manufacture a grain-oriented electrical steel sheet having excellent magnetic property.

A linear groove formation method including forming a coated resist on a surface of a steel sheet, irradiating two or more laser beams onto the surface of the steel sheet while scanning the laser beams in a direction intersecting the rolling direction of the steel sheet cyclically in a rolling direction of the steel sheet, and forming linear grooves by etching portions of the steel sheet. In the laser irradiating process, the coated resist is removed continuously in a sheet transverse direction of the steel sheet by using the laser beams irradiated from respective ones of two or more laser irradiation devices arranged in the sheet transverse direction, and the laser beams are irradiated by shifting centers of two of the laser beams irradiated from two of the laser two of the laser irradiation devices adjacent to each other in the sheet transverse direction.

When a steel material is processed to produce a grain-oriented electrical steel sheet, conditions of a decarburization annealing process and conditions of a process before the decarburization annealing are adjusted so that a difference in concentration of O, Si, Al, Mn and P between the front and back surfaces of the steel sheet after the decarburization annealing is within a given range with respect to an average concentration between the front and back surfaces, and hence the difference in concentration of each of O, Si and Mg between the front and back surfaces of the product sheet is within ±5%, the difference in concentration of one or more of Al, Mn and P between the front and back surfaces is within ±15% and the difference in the concentration of one or more of Ca and Ti between the front and back surfaces is within ±20%.

An embodiment of the present invention provides a grain-oriented electrical steel sheet, including a groove including a bottom portion and a side portion positioned on a surface of the electrical steel sheet, a metal oxide layer positioned on the groove, and an insulating layer positioned on the metal oxide layer, wherein the steel sheet includes a normal groove in which thicknesses of the metal oxide layer positioned on the bottom portion and the side portion exceed 0.5 μm, and a defective groove in which thicknesses of the metal oxide layer positioned on the bottom portion and the side portion are 0.5 μm or less, the insulating layer positioned on the normal groove has a thickness of 0.5 μm to 1.5 μm, and the insulating layer positioned on the defective groove has a thickness of 1.5 to 10 μm.

A manufacturing method of a grain-oriented electrical steel sheet according to an embodiment of the present invention includes: manufacturing a cold-rolled sheet; forming a groove in the cold-rolled sheet; removing an Fe—O oxide formed on a surface of the cold-rolled sheet; primary recrystallization annealing the cold-rolled sheet; and applying an annealing separating agent to the primary recrystallized cold-rolled sheet, and secondary recrystallization annealing it, wherein a close contacting property coefficient calculated by Formula 1 below is 0.016 to 1.13.

close contacting property coefficient (S.sub.ad)=(0.8×R)/H.sub.hill-up  [Formula 1] (In Formula 1, R represents the average roughness (μm) of the surface of the cold-rolled sheet after the removing of the oxide, and H.sub.hill-up represents the average height (μm) of the hill-up present on the surface of the cold-rolled sheet after the removing of the oxide.)

A manufacturing method of a grain-oriented electrical steel sheet according to an embodiment of the present invention, includes: manufacturing a cold-rolled sheet; forming a groove by irradiating a laser beam on the cold-rolled sheet; and partially removing an oxide layer formed on a surface of the cold-rolled sheet so that a thickness of the oxide layer remains at 1 to 5 nm, wherein the grain-oriented electrical steel sheet has islands of 0.25 or less having sphericity of 0.5 to 0.9 under the oxide layer under the groove.

Provided is a manufacturing method of a grain-oriented electrical steel sheet including preparing a hot-rolled sheet by hot-rolling a slab; removing some of scales formed on the hot-rolled sheet and leaving a scale layer having a thickness of 10 nm or more to prepare a hot-rolled sheet on which the scale layer remains; preparing a cold-rolled sheet by cold-rolling the hot-rolled sheet on which the scale layer remains; preparing the decarburization annealed cold-rolled sheet by decarburization annealing the cold-rolled sheet; coating an annealing separator on the decarburization annealed cold-rolled sheet to form a metal oxide layer; and final annealing the steel sheet on which the metal oxide layer is formed, wherein the annealing separator includes magnesium oxide (MgO) or magnesium hydroxide (MgOH) and fluoride.

A double oriented electrical steel sheet according to an embodiment of the present invention includes: in wt %, Si at 2.0 to 4.0 wt %, Al at 0.01 to 0.04 wt %, S at 0.0004 to 0.002 at %, Mn at 0.05 to 0.3 wt %, N at 0.008 wt % or less (excluding 0 wt %), C at 0.005 wt % or less (excluding 0 wt %), P at 0.005 to 0.15 wt %, Ca at 0.0001 to 0.005 wt %, Mg at 0.0001 to 0.005 wt %, and the balance including Fe and other impurities unavoidably added thereto.