A method for pickling a steel plate having a first steel plate portion and a second steel plate portion which is connected to a tail end of the first steel plate portion and which requires a longer time for pickling than the first steel plate portion when pickled under the same condition includes: a step of pickling the steel plate by immersing the steel plate in an acid solution in at least one pickling tank while conveying the steel plate; a step of circulating the acid solution, through a circulation line connected to any of the at least one pickling tank, between the pickling tank and an oxidizing device disposed in the circulation line; a step of oxidizing Fe.sup.2+ in the acid solution to Fe.sup.3+ by the oxidizing device using a gaseous oxidant; and a feeding start step of, upon switching from pickling of the first steel plate portion to pickling of the second steel plate portion, starting feeding of a liquid oxidant for oxidizing Fe.sup.2+ in the acid solution to Fe.sup.3+ to any of the at least one pickling tank or to the circulation line.

A method for producing a grain oriented electrical steel sheet includes a decarburization annealing process where an oxidation degree PH.sub.2O/PH.sub.2 is controlled, a final annealing process where hydrogen in mixed gas atmosphere is controlled to 50 volume % or more, an annealing separator removing process where water-washing is conducted using solution with inhibitor, a smoothing process where chemical-polished is conducted to control average roughness Ra, and an insulation coating forming process where insulation coating forming solution in which crystalline phosphide is included is applied.

A method for producing a grain oriented electrical steel sheet includes a decarburization annealing process where an oxidation degree PH.sub.2O/PH.sub.2 is controlled, an annealing separator applying process where a mass ratio of MgO and Al.sub.2O.sub.3 in an annealing separator is controlled, a final annealing process where an oxidation degree is controlled when atmosphere includes hydrogen or a dew point is controlled when atmosphere consists of inert gas, and an insulation coating forming process where a baking temperature and a heat treatment temperature are controlled.

A method for producing a grain oriented electrical steel sheet includes a decarburization annealing process where an oxidation degree PH.sub.2O/PH.sub.2 is controlled, an annealing separator applying process where a mass ratio of MgO and MCl in an annealing separator is controlled, a final annealing process where an oxidation degree is controlled when atmosphere includes hydrogen or a dew point is controlled when atmosphere consists of inert gas, and an insulation coating forming process where a mass ratio of phosphoric acid and metal compound in insulation coating forming solution is controlled.

A grain-oriented electrical steel sheet according to an aspect of the present invention includes an underlying steel sheet and a tension-insulation coating arranged on the surface of the underlying steel sheet, and a ten-point average roughness RzL in an L direction obtained when the tension-insulation coating is removed from the grain-oriented electrical steel sheet with an alkaline solution, and then the surface of the underlying steel sheet is measured in a rolling direction is 6.0 μm or less.

The grain-oriented electrical steel sheet is a grain-oriented electrical steel sheet which does not have an inorganic coating containing forsterite as a main component, including a base steel sheet having a predetermined chemical component, a silicon-containing oxide layer provided on the base steel sheet, an iron-based oxide layer provided on the silicon-containing oxide layer, and a tension-insulation coating provided on the iron-based oxide layer, having a thickness of 1 to 3 μm, and containing phosphate and colloidal silica as main components. When elemental analysis is performed from a surface of the tension-insulation coating in a sheet thickness direction by glow discharge optical emission spectrometry, predetermined requirements are satisfied.

A grain oriented electrical steel sheet includes a base steel sheet, an oxide layer, and a tension-insulation coating. When the iron oxide layer is analyzed by a fourier transform infrared spectroscopy, an absorbance A.sub.650 at 650 cm.sup.−1 and an absorbance A.sub.1250 at 1250 cm.sup.−1 satisfy 0.2≤A.sub.650/A.sub.1250≤5.0. Moreover, a magnetic flux density B8 in a rolling direction of the grain oriented electrical steel sheet is 1.90 T or more.

A method for producing a grain oriented electrical steel sheet includes a decarburization annealing process where an oxidation degree PH.sub.2O/PH.sub.2 is controlled, a final annealing process where hydrogen in mixed gas atmosphere is controlled to 50 volume % or more, an annealing separator removing process where water-washing is conducted using solution with inhibitor, a smoothing process where mixed gas and temperature are controlled for annealing, and an insulation coating forming process where a baking temperature and a heat treatment temperature are controlled.

A grain-oriented electrical steel sheet is a grain-oriented electrical steel sheet which does not have an inorganic coating containing forsterite as a main component and which includes: a base steel sheet containing a prescribed chemical component; a silicon-containing oxide layer provided on the base steel sheet; an iron-based oxide layer provided on the silicon-containing oxide layer; and a tension-insulation coating provided on the iron-based oxide layer, having a thickness of 1 to 3 μm, and containing phosphate and colloidal silica as main components. When the tension-insulation coating undergoes elemental analysis using a glow discharge optical emission spectrometry in a sheet thickness direction from a surface of the tension-insulation coating, a peak Si emission intensity satisfies a prescribed requirement.

A grain oriented electrical steel sheet includes a base steel sheet, an oxide layer, and a tension-insulation coating. When a glow discharge spectroscopy is conducted in a region from a surface of the tension-insulation coating to an inside of the base steel sheet, a sputtering time Fe.sub.0.5 at which a Fe emission intensity becomes 0.5 times as compared with a saturation value thereof and a sputtering time Fe.sub.0.05 at which a Fe emission intensity becomes 0.05 times as compared with the saturation value satisfy (Fe.sub.0.5−Fe.sub.0.05)/Fe.sub.0.5≥0.35. A maximal point of a Cr emission intensity is included between the Fe.sub.0.05 and the Fe.sub.sat. Moreover, a magnetic flux density B8 in a rolling direction of the grain oriented electrical steel sheet is 1.90 T or more.