A grain-oriented electrical steel sheet includes: a steel sheet; and an amorphous oxide layer that is formed on the steel sheet, in which a glossiness of a surface is 150% or higher.

Grain-oriented electrical steel sheet excellent in coating adhesion and magnetic properties is provided. The method for manufacturing grain-oriented electrical steel sheet excellent in coating adhesion and magnetic properties includes a process of heating to 1280° C. or more and hot rolling a slab containing, by mass %, Bi and a predetermined composition of constituents and having a balance of Fe and impurities so as to obtain hot rolled steel sheet, a process, after hot rolling annealing the hot rolled steel sheet, of cold rolling it one time or cold rolling it two times or more with process annealing performed interposed so as to obtain cold rolled steel sheet, a process of rapidly heating then decarburization annealing the steel sheet, a process of coating the surface of the cold rolled steel sheet after decarburization annealing with an annealing separator containing predetermined compounds including sulfates or sulfides and having MgO as its main constituent, then performing finish annealing, a process of performing strictly controlled finish annealing, and a process of coating an insulating coating, then performing flattening annealing.

An electrical steel sheet provided with an insulating coating is disclosed. Therefore, a pre-treatment liquid used on an electrical steel sheet having a forsterite coating on a surface thereof is provided before applying an insulating coating treatment liquid containing at least one salt selected from the group consisting of phosphate, borate, and silicate, the pre-treatment liquid. The pre-treatment liquid includes: at least one inorganic acid selected from the group consisting of hydrochloric acid, sulfuric acid, and phosphoric acid; and acetic acid, wherein a content of the acetic acid is not less than 1 mass ppm and not more than 3000 mass ppm.

A grain-oriented magnetic steel sheet with chromium-free insulating tension coating includes a grain-oriented magnetic steel sheet and an insulating tension coating containing a phosphate salt and silica on a surface of the grain-oriented magnetic steel sheet, the coating further including a crystalline compound represented by the general formula (1): M.sup.II.sub.3M.sup.III.sub.4(X.sup.VO.sub.4).sub.6 . . . (1). A method for producing a grain-oriented magnetic steel sheet with chromium-free insulating tension coating includes applying an insulating tension coating liquid to a surface of a finish annealed grain-oriented magnetic steel sheet, the coating liquid including colloidal silica, a phosphate salt and a metal element M-containing compound in a specific ratio, and heat treating the steel sheet at least one time at a temperature of not less than 900° C. in an atmosphere including a non-oxidizing gas and having a dew point of not more than 0° C.

A grain-oriented magnetic steel sheet with chromium-free insulating tension coating includes a grain-oriented magnetic steel sheet and an insulating tension coating containing a phosphate salt and silica on a surface of the grain-oriented magnetic steel sheet, the coating further including a crystalline compound represented by the general formula (1): M.sup.II.sub.3M.sup.III.sub.4(X.sup.VO.sub.4).sub.6 . . . (1). A method for producing a grain-oriented magnetic steel sheet with chromium-free insulating tension coating includes applying an insulating tension coating liquid to a surface of a finish annealed grain-oriented magnetic steel sheet, the coating liquid including colloidal silica, a phosphate salt and a metal element M-containing compound in a specific ratio, and heat treating the steel sheet at least one time at a temperature of not less than 900° C. in an atmosphere including a non-oxidizing gas and having a dew point of not more than 0° C.

A grain-oriented electrical steel sheet according to the present invention includes a silicon steel sheet as a base steel sheet, and when an average value of amplitudes in a wavelength range of 20 to 100 μm among wavelength components obtained by performing Fourier analysis on a measured cross-sectional curve parallel to a sheet width direction of the silicon steel sheet is set as ave-AMP.sub.C100, ave-AMP.sub.C100 is 0.0001 to 0.050 μm.

Disclosed is a heat exchange tube of waste heat boiler, which includes a tube body. The outer surface of the tube body is sprayed with a layer of anti-corrosion coating. The components of the anti-corrosion coating are Al.sub.2O.sub.3, CaAl.sub.2O.sub.4 and Ca.sub.3(PO.sub.4).sub.2. On the surface of nano anti-corrosion coating, HF reacts with Al.sub.2O.sub.3, CaAl.sub.2O.sub.4 and Ca.sub.3(PO.sub.4).sub.2 to form AlF.sub.3 and Ca.sub.5(PO.sub.4).sub.3F, which are tightly wrapped on the surface of the coating, thereby effectively preventing HF from corroding the interior of the coating and the heat exchange tube. Meanwhile, due to the anti-corrosion coating with the specific composition of the present disclosure, the heat exchange tube of the present disclosure can be resistant to fluorine corrosion at a high temperature of 600° C. or more, and can be used at a rather high temperature of 1000° C. or more.

A solution for forming an insulation coating of grain-oriented electrical steel sheet includes an aqueous solution prepared by mixing a phosphate solution and colloidal silica. Chromium is not added to the aqueous solution. The colloidal silica includes silica particles surface-modified by an aluminate or is prepared by adding an aluminate to colloidal silica such as conventional colloidal silica.

A solution for forming an insulation coating of grain-oriented electrical steel sheet includes an aqueous solution prepared by mixing a phosphate solution and colloidal silica. Chromium is not added to the aqueous solution. The colloidal silica includes silica particles surface-modified by an aluminate or is prepared by adding an aluminate to colloidal silica such as conventional colloidal silica.

An electrical steel sheet (10) is provided with a base iron (1) and an insulating film (2) formed on a surface of the base iron (1). The insulating film (2) contains: a first component: 100 parts by mass, the first component containing: a metal phosphate: 100 parts by mass; and one kind selected from a group consisting of an acrylic resin, an epoxy resin and a polyester resin which have an average particle size of 0.05 μm to 0.50 μm, or a mixture or copolymer of two or three kinds selected from the group: 1 part by mass to 50 parts by mass; and a second component composed of dispersion or powder of a fluorine resin having an average particle size of 0.05 μm to 0.35 μm: 0.5 parts by mass to 10 parts by mass.