Abstract: A coated steel sheet having a coated layer on surfaces of a steel sheet of a composition containing not less than 0.1 mass % and under 3 mass % of Al, wherein a following condition A or B is met: A: An AlN precipitate layer exists on a matrix side near an interface between said steel sheet and said coated layer B: Oxide of Al exists in said matrix right under said surfaces of said steel sheet.

Abstract: The present invention provides a galvannealed steel sheet excellent in the adhesion with a base steel sheet and a manufacturing method thereof. The galvannealed steel sheet according to the invention has, in an interface between a galvannealed layer and the base steel sheet thereon the galvannealed layer is formed, an irregularity that has a depth of 10 nm or more at a pitch of 0.5 ?m or less at least one per 5 ?m of a length of the interface.

Abstract: A galvannealed steel sheet having excellent surface appearance and press formability, characterized in that a steel sheet comprises a galvannealed layer at least one surface of the steel sheet, the steel sheet comprising 0.001 to 0.005% by mass of C, 0.010 to 0.040% by mass of Si, 0.05 to 0.25% by mass of Mn, and 0.010 to 0.030% by mass of P, wherein the Si, Mn, and P satisfy the relation 0.030%?Si+P+Mn/20?0.070%, and its production method.

Abstract: The present invention provides a coating that includes a thermoplastic resin having a glass transition point of more than 100° C. and an acid value of from 20 to 350 mg-KOH/g, a metallic soap of metal stearate, an anti-galling agent, and a surface-treated metal sheet having a film of this coating. The coating according to the present invention has the superior durability of the film, in particular, wear resistance and peel resistance. The surface-treated metal sheet having the film of this coating has superior press formability, in particular, galling resistance and lubricity, and further, a temporary antirust property and alkaline solubility of the film even in a high temperature environment caused by severe ironing.

Abstract: A coated steel sheet having a coated layer on surfaces of a steel sheet of a composition containing not less than 0.

Abstract: A method for determining a quantity of each of alloy phases in the plating layer includes subjecting each alloy phase in the plating layer to constant potential electrolysis in each of a plurality of ranges of potentials obtained on the basis of the immersion potential of each alloy phase and the immersion potential of a basis metal, by using a plated metal material having different kinds of alloy phases in the plating layer as the anode, to determine the quantity of each alloy phase in the plating layer on the basis of the quantity of electricity consumed in each range of the potentials during the electrolysis.

Abstract: A steel composition, in which, Si content is regulated to a given range and Nb and Cu or Ni, Mo are compositively added, and a recrystallization annealing is carried out to form an internal oxide layer just beneath a surface of a steel sheet and a surface oxide simultaneously formed on the surface of the steel sheet is removed by pickling. As a result, the formation of oxides of Si, Mn and the like is considerably decreased on the surface of the steel sheet in a subsequent heating before plating because the above internal oxide layer acts as a diffusion barrier. Thus, there can be obtained high tensile strength hot-dipped steel sheets having a considerably excellent plating property.

Abstract: A method for determining a quantity of each of alloy phases in the plating layer includes subjecting each alloy phase in the plating layer to constant potential electrolysis in each of a plurality of ranges of potentials obtained on the basis of the immersion potential of each alloy phase and the immersion potential of a basis metal, by using a plated metal material having different kinds of alloy phases in the plating layer as the anode, to determine the quantity of each alloy phase in the plating layer on the basis of the quantity of electricity consumed in each range of the potentials during the electrolysis.

Abstract: A galvannealed steel sheet having excellent surface appearance and press formability, characterized in that a steel sheet comprises a galvannealed layer at least one surface of the steel sheet, the steel sheet comprising 0.001 to 0.005% by mass of C, 0.010 to 0.040% by mass of Si, 0.05 to 0.25% by mass of Mn, and 0.010 to 0.030% by mass of P, wherein the Si, Mn, and P satisfy the relation 0.030%≦Si+P+Mn/20≦0.070%, and its production method.

Abstract: As to a steel composition, in this invention, Si content is regulated to a given range and Nb and Cu or Ni, Mo are compositively added, and a recrystallization annealing is carried out to form an internal oxide layer just beneath a surface of a steel sheet and a surface oxide simultaneously formed on the surface of the steel sheet is removed by pickling. As a result, the formation of oxides of Si, Mn and the like is considerably decreased on the surface of the steel sheet in a subsequent heating before plating because the above internal oxide layer acts as a diffusion barrier.

Abstract: The high tension steel sheet includes 0.1 wt % or more of silicon and has a zinc-plating layer thereon. When sputtering analysis is performed in the depth direction from the surface of the high tension steel sheet after the zinc-comprising-plating layer is removed by dissolution, a surface-concentrated Si index X defined by the formula, X=(the maximum intensity A of Si on the surface of the high tension steel sheet/the average intensity B of Si in the steel)×the content of Si in the steel sheet on a wt % basis, is 12 or less.

Abstract: The high tension steel sheet includes 0.1 wt. % or more of silicon and has a zinc-plating layer thereon.

Abstract: This invention can form a sufficiently internal oxide layer in a surface layer portion of an iron matrix of a steel sheet by hot rolling a base steel and subjecting to a heat treatment at a temperature range of 650-950° C. in an atmosphere substantially not causing reduction while being adhered with a black skin scale irrespectively of a chemical steel composition or production history, or even when a radiation type heating of a radial tube or the like is used in a recrystallization annealing before a hot dipping treatment, and hence excellent hot-dipping property and conversion treating property can be given to a steel sheet for hot dipping.

Abstract: A zinc and zinc-alloy hot-dip-coated steel sheet and an alloyed zinc and zinc-alloy hot-dip-coated steel sheet, and a method for manufacturing these steel sheets, which steel sheets are used for automobiles. A zinc and zinc-alloy hot-dip-coated steel sheet which has oxides of readily oxidizable elements just under a coated layer and which shows a decreased number of bare spots and excellent coating adhesion. According to the method, the temperature for coiling during hot rolling is set to not less than 600.degree. C. and the cooling is conducted at a slow-cooling rate so that the-oxides remain after the following steps.

Abstract: In connection with the manufacture of zinc hot dip galvanized or galvannealed steel strip using a high strength, high tensile steel strip containing Si, Mn or Cr as a starting steel strip, the invention provides a method for hot dip galvanizing a high tensile steel strip with minimal bare spots which can manufacture a bare spot-free steel strip of quality in an inexpensive manner while minimizing process complications and lowered productivity. The invention is achieved by subjecting a cold rolled steel strip containing at least one component of 0.1 to 2.0% of Si, 0.5 to 2.0% of Mn, and 0.1 to 2.0% of Cr and optionally further containing up to 0.2% of P, in % by weight, to recrystallization annealing in a continuous annealing line, cooling the steel strip, removing a steel component concentrated layer at the surface of the steel strip by polishing and/or pickling, subjecting the steel strip again to heat reduction at a temperature from 650.degree. C.

Abstract: Steel strips having a Zn-Fe-P alloy electroplated thereon exhibit improved corrosion resistance, particularly perforation corrosion resistance, as long as the plating contains 5 to 30% by weight of iron and 0.0003 to 0.5% by weight of phosphorus.

Abstract: Highly corrosion resistant plated steel strips or sheets adapted for phosphate treatment and cathodic electrodeposition and intended for use in automobiles, are produced by electroplating at least one surface of a steel strip with an alloy consisting essentially of 0.0003 to 15% by weight of phosphorous, balance essentially iron, in a plating bath containing Fe.sup.2+ ions in an amount of from 0.3 mol/liter to the solubility limit and hypophosphorous acid and/or a hypophosphite in an amount of 0.001 to 25 g/liter expressed as NaH.sub.2 PO.sub.2.H.sub.2 O at a pH of 1.0 to 5.0, a temperature of 30.degree. to 60.degree. C., and a current density of from more than 20 to 200 A/dm.sup.2, preferably 40 to 150 A/dm.sup.2. A top coat can be applied thereover, of one element selected from the group consisting of Ni, Zn, Mn, and Ti, deposited on the Fe-P plating layer to a build-up of 5 to 50 mg/m.sup.2.

Abstract: Steel strips are electroplated with a Zn-Fe base alloy containing 10 to 30% by weight of iron in a chloride bath which contains zinc and ferrous chlorides to give a total concentration of zinc and ferrous ions of from 1.0 mol/l to the solubility limit with a weight ratio of Fe.sup.2+ /Zn.sup.2+ between 0.10 and 0.35, and chloride ions in a total concentration of at least 6.0 mol/l under electrolytic conditions: pH 1.0-6.0, current density 80-200 A/dm.sup.2, and relative flow velocity 30-200 m/min. The bath may further contain a polycarboxylic acid such as citric acid and a Zn-Fe-P alloy plating may be deposited when the bath further contains hypophosphorous acid.

Abstract: One-side zinc hot dipped steel sheets are produced by coating one surface of a steel sheet with an aqueous slurry of an anti-plating agent based on MgO, alkali metal silicates, boric acid, MOH (M is an alkali metal) and the like and containing such additives as TiO.sub.2 and Al.sub.2 O.sub.3, heating the coated sheet for drying and baking, immersing the steel sheet with an anti-plating film in a molten zinc bath to zinc plate the other surface of the sheet, wetting the anti-plating film, and bending the steel sheet to cause the anti-plating film to peel off, thereby removing the anti-plating film from the steel sheet. This invention carries out the coating and baking of the anti-plating agent such that it is baked to a film having a thickness of 20 to 60 microns at a temperature of 750.degree. C. to about 930.degree. C.