# US 5,344,550 A · Process for producing surface-treated steel sheet superior in weldability and paint-adhesion

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- Number: US 5,344,550 A
- Document ID: US5344550A
- Status: Granted
- Kind: A
- Application number: 08/073,665
- Filed: 1993-06-08
- Granted: 1994-09-06
- Earliest claimed: 1991-01-24
- Assignees: Nippon Steel Corporation
- Inventors: Yoshihiro Kaneda; Ryoichi Yoshihara; Ryousuke Wake
- Web page: https://patentgrep.com/patent/US5344550A

## CPC

- C25D 11/38: Chromatising
- Y10T 428/12722: Next to Group VIII metal-base component
- Y10T 428/12854: Next to Co-, Fe-, or Ni-base component
- Y10T 428/12993: Surface feature [e.g., rough, mirror]
- C25D: PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

A surface-treated steel sheet is provided, at a low cost, which has high weldability and is useful for a material of containers of foods and beverages. The surface treatment is conducted by applying flattened granular tin coating deposits having a specified diameter and high adhesion on a steel sheet surface at a specified plated area ratio, and applying thereon a metallic chromium coating and a chromium hydrate oxide coating. In the surface treatment, firstly, the surface of a steel sheet is subjected to tin-plating in an acidic tin plating bath containing a conventionally used brightener in an amount of from 0,001 to 0.05 g/l so as to form flattened granular tin coating deposits having a diameter of 0.4-2.4 .mu. at a plated area ratio of 5 to 30% and to improve the adhesion to the steel sheet and decrease falling-off of the granular tin coating deposits until completion of chrome-plating, thereby the variation of the amount of tin coating being decreased. Subsequently, the sheet is plated with metallic chromium in an amount of 50-150 mg/m.sup.2, and further chromium hydrate oxide layer is formed in an amount of 2-40 mg/m.sup.2 as chromium. Thus a surface-treated steel sheet, which has satisfactory surface appearance, paint adhesiveness, under-paint-coating corrosion resistance of conventional tin-free steel sheets, and stable weldability, is producible at a low cost.

## Claims

### Claim 1

A steel sheet having deposited a the surface thereof a flattened granular tin coating having a diameter in a range of from 0.4 to 2.4 .mu.m at a plated area ratio a the range of from 5 to 30%, said steel sheet being produced by a process which comprises degreasing and acid-pickling a steel sheet surface and tin-plating the steel sheet surface in an acidic tin-plating bath containing a conventional brightener in an amount of from 0.001 to 0.05 g/l.

### Claim 2

A surface-treated steel sheet superior in weldability and paint adhesion produced in accordance with a process comprising the steps of degreasing and acid-pickling a steel sheet surface; tin-plating the steel sheet surface in an acidic tin-plating bath containing a conventional brightener in an amount of from 0,001 to 0.05 g/l so as to deposit flattened granular tin coating having a diameter in a range of from 0.4 to 2.4 .mu.m at a plated area ratio in the range of from 5 to 30%; and subsequently coating the tin-plated steel sheet with metallic chromium in an amount of from 50 to 150 mg/m.sup.2 and chromium oxide in an amount of from 2 to 40 mg/m.sup.2 in terms of chromium by a conventional chrome plating process, or a conventional chrome plating and chromate treatment process.

### Claim 3 (depends on 2)

A surface-treated steel sheet according to claim 2, wherein the tin-plating in the acidic tin-plating bath is performed under the conditions of a bivalent tin ion concentration M (g/l), a plating current density D (A/dm.sup.2), and a tin-coating amount W (mg/m.sup.2), satisfying the formulas (1) and (2) below: ##EQU3##