Kawasaki Steel Corporation

Dai Nippon Toryo Co., Ltd.

Hajime Kimura

Toshio Ichida

Toshio Irie

Chiaki Kato

Nobuyuki Morito

Koji Yamato

Kazuaki Kyono

Shigeru Umino

Shigeo Kurokawa

Akira Yasuda

Kazuo Mochizuki

Kenji Takao

Shinobu Okano

Takahisa Yoshihara

Yasuji Uesugi

Akira Matsuda

Ryoichi Muko

Kouichi Yasuda

Yuko Takeuchi

Yuki Nakahara

Yoichi Tobiyama

Shigeru Kobayashi

Shunichi Harada

Shuichi Sakaguchi

Hideo Ogishi

Hideo Ohgishi

A method of manufacturing a galvanized steel sheet with high press formability, the sheet having an inorganic compound on a metallic galvanized-layer thereof. The method includes the step of effecting a galvanization on a steel sheet followed by an alloying treatment. The sheet of galvanized steel is immersed in a bath of an aqueous solution containing 0.1 wt % or more of borate of an alkali metal, and then taking the steel sheet out of the bath and effecting such control as to make the amount of deposition of the water-containing borate film on the steel sheet surface to range from 10 to 1,000 mg/m.sup.2, and then heating the steel sheet at a temperature ranging from 60.degree. to 400.degree. C. Thereafter, the steel sheet is cooled to a normal temperature.

Method of manufacturing of galvanized steel sheet having high press

A zinc or zinc-alloy plated steel sheet having an improved weldability and plating properties, as well as a method for making the same is provided. Even when the substrate steel sheet is the one which is difficult to deposit a zinc or zinc-alloy layer by conventional methods, such as an extra low carbon steel sheet, the present invention enables a reliable production of a galvanized steel sheet suffering from no plating failure of insufficient adhesion as well as a reliable production of a galvanized steel sheet suffering from no plating failure or streaking of the alloyed layer. The zinc or zinc-alloy plated steel sheet having improved weldability comprises an extra low carbon steel sheet, an iron-carbon plated layer or a carbon-rich layer generated by diffusion of the iron-carbon plated layer on at least one major surface of the extra low carbon steel sheet, and a zinc or zinc-alloy plated layer on the iron-carbon plated layer or the carbon-rich layer. The zinc or zinc-alloy plated steel sheet having improved weldability and/or plating properties is produced by depositing on the steel sheet an iron-carbon plated layer having a carbon content of from 0.01% by weight to 10% by weight to a coating weight of from 0.01 g/m.sup.2 to 10 g/m.sup.2, optionally annealing the iron-carbon plated steel sheet, and depositing a zinc or zinc-alloy plated layer, preferably by galvanizing or galvannealing, on the annealed steel sheet.

Surface-treated steel sheet having improved weldability and plating

A zinc or zinc-alloy plated steel sheet having an improved weldability and plating properties, as well as a method for making the same is provided. Even when the substrate steel sheet is the one which is difficult to deposit a zinc or zinc-alloy layer by conventional methods, such as an extra low carbon steel sheet, the present invention enable a reliable production of a galvanized steel sheet suffering from no plating failure or insufficient adhesion as well as a reliable production of a galvannealed steel sheet suffering from no plating failure or streaking of the alloyed layer. The zinc or zinc-alloy plated steel sheet having improved weldability comprises an extra low carbon steel sheet, an iron-carbon plated layer or a carbon-rich layer generated by diffusion of the iron-carbon plated layer on at least one major surface of the extra low carbon steel sheet, and a zinc or zinc-alloy plated layer on the iron-carbon plated layer or the carbon-rich layer. The zinc or zinc-alloy plated steel sheet having improved weldability and/or plating properties is produced by depositing on the steel sheet an iron-carbon plated layer having a carbon content of from 0.01% by weight to 10% by weight to a coating weight of from 0 01 g/m.sup.2 to 10 g/m.sup.2, optionally annealing the iron-carbon plated steel sheet, and depositing a zinc or zinc-alloy plated layer, preferably by galvanizing or galvannealing, on the annealed steel sheet.

Organic composite coated steel strips having improved corrosion resistance, weldability and coating adherence are obtained when an organic composite layer is applied to a chromate layer on a zinc or zinc base alloy plated steel substrate. The chromate layer containing up to 70% of Cr.sup.6+ based on the total chromium weight is coated in a weight of 5 to 500 mg/m.sup.2 of Cr. The organic composite layer is formed to a dry weight of 0.2 to 3.0 g/m.sup.2 from a coating composition comprising (A) a silica sol having silica dispersed in an organic solvent with a water content of up to 3.0%, the silica having an organic deposit on its surface in an amount of up to 5.0% of C based on the total silica weight, the silica having an average particle size of 0.05 to 3.0 .mu.m and a specific surface area of 50 to 800 m.sup.2 /g, and (B) an organic resin binder having a number average molecular weight of at least 2,000. The coated strips are suitable for use as automobile bodies by press forming.

Organic composite coated steel strip having improved corrosion

A Zn-Ni alloy plated steel plate having stable formability may be obtained by subjecting the plated surface of a Zn-Ni alloy plated steel plate having Ni contents of 10 to 17 wt. % to a dipping treatment, a spraying treatment or to an anodic treatment, using a solution containing one or both H.sub.2 PO.sub.4.sup.- and HPO.sub.4.sup.2-.

Method for producing Zn-Ni alloy plated steel plate having superior

The improved corrosion-resistant steel plate with an organic coating comprises a steel plate having a zinc or zinc alloy plate layer which is overlaid with a chromate film which in turn is coated with an organic resin paint film. The organic resin coat comprises an epoxy resin having a dialkanolamine incorporated into its bisphenol A skeleton, an amino resin, and silica. The dialkanolamine combines with the amino resin to provide satisfactory curability at low temperatures; at the same time, it combines with the silica to provide a satisfactory film reinforcing effect. The organic coat formed of this composition can be effectively cured at low temperatures and yet it will neither dissolve nor soften upon swelling under the action of the alkali that is generated during cationic electrodeposition at the interface between the electrodeposited film and the organic coat. Thus, the organic coat has good paint adhesion, high corrosion resistance, as well as good workability and weldability and makes the steel plate suitable for use as an automotive part after painting. If the proportion of trivalent chromium in the chromate film and the amounts of zinc oxide and silica sol to be incorporated as additives are properly adjusted, the organic coating will exhibit satisfactory resistance to chromium dissolution and hence its paint adhesion and corrosion resistance are further improved to make the steel plate more suitable for use as an automotive part after painting.

Steel plate with organic coating having improved corrosion resistance

A chromate-treated steel strip comprising a chromate film on a zinc plated steel strip is improved in corrosion resistance and coating adherence by forming the chromate film of three layer structure consisting of a metallic Cr layer, a Cr.sup.3+ oxide layer, and an outermost surface layer of SiO.sub.2, and Cr.sup.3+ oxide plus Cr.sup.6+ oxide. The three layered chromate film is deposited on a zinc plated steel strip by effecting cathodic electrolysis in a bath containing hexavalent chromium, colloidal silica, optional alumina sol, and a fluoride, by supplying electricity at a specific current density to a controlled quantity.

Chromate-treated zinc-plated steel strip and method for making

A zinc-nickel alloy is electrodeposited on a steel strip by passing the steel strip through a stream of sulfuric acid-containing plating solution which contains 2-3 mol/liter in total of Zn.sup.2+, Ni.sup.2+, H.sup.+, and SO.sub.4.sup.2- ions and at least 0.1 mol/liter of Na.sup.+, K.sup.+, or NH.sub.4.sup.+ ion at pH 1 to 2.5, feeding the solution at a flow speed of at least 1 m/sec., and applying electricity between the strip and an anode in the solution such that the current density between the strip and the anode at the outlet of the solution is lower than that at the inlet of the solution. The anode may preferably be divided into a plurality of segments. This process may be carried out by use of a radial or horizontal cell.

Preparation of Zn-Ni alloy plated steel strip

A chromate-treated steel strip comprising a chromate film on a zinc plated steel strip is improved in corrosion resistance and coating adherence by forming the chromate film of three layer structure consisting of a metallic Cr layer, a Cr.sup.3+ oxide layer, and an outermost surface layer of SiO.sub.2 and Cr.sup.3+ oxide plus Cr.sup.6+ oxide plus Cr.sup.6+ oxide. The three layered chromate film is deposited on a zinc plated steel strip by effecting cathodic electrolysis in a bath containing hexavalent chromium, colloidal silica, optional alumina sol, and a fluoride, by supplying electricity at a specific current density to a controlled quantity.

A method of producing both-side electrolytically zinc plated steel strips utilizing a chloride bath including the steps of plating one side of the steel strip in a first plating cell, wetting the thus one-side plated steel strip in a wetting tank, and then plating the other nonplated side of the steel strip in a second plating cell. The method provides for limiting the concentration of zinc in the wetting solution to a range of 0.1-50 g/l so as to improve the zinc coating coverage, glossiness and corrosion resistance.

Method of producing a both-side electrogalvanized steel strip in a

Composite plated steel strips comprising a zinc base layer electrodeposited on at least one surface of a steel strip exhibit excellent corrosion resistance with or without painting provided that the zinc base layer contains 0.1 to 10% by weight of cobalt, 0.05 to 5% by weight of chromium, 0.05 to 8% by weight of aluminum, and optionally, 0.05 to 5% by weight of Si, the balance being zinc. Such composite plated steel strips are prepared by subjecting a steel strip to composite electroplating in an acidic zinc plating bath which contains at least one water-soluble compound of Co.sup.2+ in an amount of 0.3 to 60 g/l of metallic cobalt, at least one water-soluble compound of Cr.sup.3+ in an amount of 0.2 to 2.5 g/l of metallic chromium, a pseudo-boehmite like alumina sol in an amount of 0.5 to 20 g/l of alumina, and optionally, colloidal silica in an amount of 0.5 to 20 g/l of silica at pH 1 or higher and a current density of at least 40 A/dm.sup.2.

Method for making high corrosion resistance composite plated steel strip

Composite plated steel strips comprising a zinc base layer electrodeposited on at least one surface of a steel strip exhibit excellent corrosion resistance with or without painting provided that the zinc base layer contains 0.1 to 10% by weight of cobalt, 0.05 to 5% by weight of chromium, 0.05 to 8% by weight of aluminum, and optionally, 0.05 to 5% by weight of Si, the balance being zinc. Such composite plated steel strips are prepared by subjecting a steel strip to composite electroplating in an acidic zinc plating bath which contains at least one water-soluble compound of Co.sup.2+ in an amount of 0.3 to 60 g/l of metallic cobalt, at least one water-soluble compound of Cr.sup.3+ in an amount of 0.2 to 2.5 g/l of metallic chromium, a pseudo-boehmite like alumina sol in an amount of 0.5 to 20 g/l of alumina, and optionally, colloidal silica in an amount of 0.5 to 20 g/l of silica of pH 1 or higher and a current density of at least 40 A/dm.sup.2.

High corrosion resistance composite plated steel strip

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.

Corrosion-resistant steel strip having Zn-Fe-P alloy electroplated

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. A lower layer of zinc or a zinc alloy can also be electrodeposited on at least one surface of the steel strip, prior to formation of the Fe-P layer. A surface film can be formed by chemically treating the Fe-P plating layer with a phosphate.

Corrosion resistant surface-treated steel strip and process for making

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.

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Chiba, Japan

Hajime Kimura