Abstract: There is disclosed a method of manufacturing a plated steel sheet with a Zn--Cr composite plating, wherein a total of 0.01 to 300 g/l of at least one type of salt having a pH buffering action in a pH range of 2 to 6 in a bath containing only zinc are added to an acidic Zn--Cr composite plating bath containing zinc ions and trivalent chromium ions to prepare a plating bath, and plating film is formed on a steel sheet using the resultant plating bath.

Abstract: A zinciferous plated steel sheet excellent in press-formability and corrosion resistance, which comprises: a steel sheet, a zinciferous plating layer formed on at least one surface of the steel sheet, a chromate film formed on the zinciferous plating layer, and a resin film formed on the chromate film. The resin film comprises a solvent-base thermosetting resin, a solid internal lubricant and a rust-preventive pigment. The solvent-base thermosetting resin comprises: (A) urethane prepolymer containing a hydroxyl group, and (B) at least one of a block polyisocyanate compound and an amino resin as a curing agent. The urethane prepolymer containing a hydroxyl group comprises: (a) at least one of polyether polyol, polyester polyol and polyether-polyester polyol, (b) an isocyanate compound, and (c) dihydric alcohol.

Abstract: A method for continuously tin-electroplating a metal strip, which comprises the steps of: causing a DC electric current to flow between a metal strip and an anode arranged adjacent to the metal strip while passing the metal strip at a travelling speed of at least 1 m/minute through an acidic tin-electroplating solution containing tin ions and an organic acid within a range of from 4.8 to 98 g/l as converted into sulfuric acid, to form a tin-electroplating layer on at least one surface of the metal strip; and applying an ultrasonic vibration, emitted from at least one ultrasonic vibrator and having an intensity within a range of from 0.01 to 1,000 W/100 cm.sup.2 and a frequency within a range of from 25 to 55 kHz, to the acidic tin-electroplating solution between the metal strip and the anode, thereby removing a diffusion layer of tin ions existing in the acidic tin-electroplating solution adjacent to the surface of the metal strip.

Abstract: A steel sheet plated with zinc or a zinc alloy carries a chromate film formed on each side thereof and having a coating weight of 1 to 200 mg/m.sup.2 in terms of metallic chromium, and a black film formed at least on the chromate film on one side thereof. The black film contains 100 parts by weight of a thermosetting resin which is soluble in an organic solvent, 1 to 200 parts by weight of a black dye which is also soluble in an organic solvent, and 1 to 100 parts by weight of organic resin particles. It may further contain 1 to 100 parts by weight of fine inorganic particles, or a solid lubricant, or both. The black film has a thickness of 0.3 to 5.0 microns which is sufficiently small to permit the welding of the sheet, and yet has an excellently black surface. The organic resin particles, etc., which are used as a matting agent, give the film a surface of low gloss which resists visible staining by fingerprints.

Abstract: A nickel alloy electroplated cold-rolled steel sheet excellent in press-formability and phosphating-treatability, which comprises: (a) a cold-rolled steel sheet consisting essentially of: carbon (C): up to 0.06 wt. %, silicon (Si): up to 0.5 wt. %, manganese (Mn): up to 2.5 wt. %, phosphorus (P): up to 0.1 wt. %, sulfur (S): up to 0.025 wt. %, soluble aluminum (Sol.Al): up to 0.10 wt. %, nitrogen (N): up to 0.005 wt. %, and the balance being iron (Fe) and incidental impurities; (b) a nickel alloy electroplating layer, formed on at least one surface of the cold-rolled steel sheet, the nickel alloy electroplating layer consisting of nickel alloy particles precipitated at a distribution density of at least 1.times.10.sup.12 /m.sup.2, the nickel alloy particles containing at least one of phosphorus (P), boron (B) and sulfur (S) in an amount of 1 to 15 wt. %, the plating weight of the nickel alloy electroplating layer being 5 to 60 mg/m.sup.

Abstract: A method for manufacturing a tin-electroplated cold-rolled steel strip, which comprises the steps of: continuously annealing a degreased cold-rolled steel strip; then, subjecting, following the continuous annealing treatment, the continuously annealed cold-rolled steel strip to a continuous tin-electroplating treatment in a tin-electroplating bath to form, on at least one surface of the cold-rolled steel strip, a tin-electroplating layer having a plating weight within a range of from 0.1 to 2.8 g/m.sup.2 per surface of the cold-rolled steel strip; and then, temper-rolling, following the continuous tin-electroplating treatment, the cold-rolled steel strip having the tin-electroplating layer on at least one surface thereof, at a reduction ratio within a range of from 1 to 5%.

Abstract: A method for manufacturing an electrolytically chromated steel sheet, comprising the steps of: subjecting a steel sheet intermittently to a plurality of runs of cathodic electrolytic chromate treatment in an acidic electrolytic chromating solution. At least one of these plurality of runs of cathodic electrolytic chromate treatment is carried out at a high electric current density within the range of from 90 to 200 A/dm.sup.2, to form on at least one surface of the steel sheet a chromating film comprising a metallic chromium layer as a lower layer having numerous granular projections over the entire surface thereof, and a hydrated chromium oxide layer as an upper layer. The electrolytically chromated steel sheet manufactured in accordance with the method of the present invention is excellent in a secondary paint adhesion and a weldability, and has a satisfactory surface hue.

Abstract: A method for manufacturing an electrolytically chromated steel sheet, comprising the steps of: subjecting a steel sheet to an anodic electrolytic treatment with a quantity of electricity of from 0.3 to 30 coulomb/dm.sup.2 in an acidic electrolyte containing at least one of chromic anhydride, chromate and bichromate, to form a hydrated chromium oxide film having numerous holes and numerous thin portions over the entire area of at least one surface of the steel sheet; and then subjecting the anodically treated steel sheet to a cathodic electrolytic chromate treatment in an acidic electrolytic chromating solution to form on the at least one surface of the steel sheet a chromate film comprising a metallic chromium layer as a lower layer having thereon numerous granular projections, and a hydrated chromium oxide layer as an upper layer.