US 4,064,320 A · Chromated electro-galvanized steel sheet excellent in corrosion resistance and process for manufacturing same

Abstract

A chromated electro-galvanized steel sheet is manufactured by electro-galvanizing a steel sheet in an acidic galvanizing bath containing zinc with or without specified amounts of cobalt, or with specified amounts of cobalt and with at least one of chromium (Cr.sup.+3, Cr.sup.+6 or Cr.sup.+3 and Cr.sup.+6) and zirconium; then electro-galvanizing in a zinc-based galvanizing bath containing specified amounts of at least one of chromium (Cr.sup.+3, Cr.sup.+6 or Cr.sup.+3 and Cr.sup.+6), tin and indium; and chromating the resulting steel sheet.

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Claims21

Dependent claims

A process for manufacturing a chromated electrogalvanized steel sheet which comprises subjecting a steel sheet to an electro-galvanizing treatment, and then subjecting said electro-galvanized steel sheet to a chromate treatment, characterized by:

subjecting a steel sheet to a first electro-galvanizing treatment under galvanizing conditions in an acidic galvanizing bath selected from the group consisting of:
A. an acidic galvanizing bath in which zinc is the sole galvanizing metal;
B. galvanizing bath (A) containing an additive capable of improving the bare corrosion resistance of a galvanizing layer formed on the surface of said steel sheet, said additive consisting essentially of 50 - 10,000 ppm Co;
and
C. galvanizing bath (B) containing at least one additive having said capability and being selected from the group consisting of:
i. Cr.sup.3+ 50 - 700 ppm,
ii. Cr.sup.6+ 50 - 500 ppm,
iii. Cr.sup.3+ and Cr.sup.6+ 50 - 700 ppm, in which the maximum of Cr.sup.6+ is 500 ppm,
and
iv. Zr 10 - 2,500 ppm,
to form on the surface of said steel sheet a first galvanized layer which is excellent in bare corrosion resistance;
then, subjecting said electro-galvanized steel sheet with said first galvanized layer formed thereon to a second electro-galvanizing treatment under galvanizing conditions in an additive-containing Zn-based acidic galvanizing bath the additive thereof being capable of improving the adaptability of a galvanized layer to chromating and consisting essentially of at least one selected from the group consisting of:
a. Cr.sup.3+ 50 - 700 ppm,
b. Cr.sup.6+ 50 - 500 ppm,
c. Cr.sup.3+ and Cr.sup.6+ 50 - 700 ppm, in which the maximum of Cr.sup.6+ is 500 ppm,
d. Sn 10 - 5,000 ppm, and
e. In 10 - 3,000 ppm,
to form on said first galvanized layer a second galvanized layer in an amount of at least 0.2 g/m.sup.2, said second galvanized layer being excellent in adaptability to chromating;
and then, subjecting said electro-galvanized steel sheet with said first and said second galvanized layers formed thereon to a chromate treatment to form a chromate film on said second galvanized layer.

16 more elements

Dependencies are inferred from the claim text.

Description10,842 words

Summary7,420 words

#The present invention relates to a chromated electro-galvanized steel sheet excellent in the bare corrosion resistance and the corrosion resistance after chromating, hardly susceptible of secular degradation of the deep-drawing formability, and having a first galvanizing layer (lower layer) excellent in the bare corrosion resistance and a second galvanizing layer (upper layer) excellent in the adaptability to chromating, and the process for manufacturing same.

#It is in general inevitable that impurities from a galvanizing apparatus, an electrode, galvanizing bath materials and a steel sheet to be electro-galvanized are entangled into a galvanizing bath during electrogalvanizing operations of the steel sheet. Impurities thus mixed into the galvanizing bath not only causes degradation of the surface quality of the produced galvanizing layer, but also exerts adverse effects on a chromate treatment to be applied thereafter. If, for example, a galvanizing bath contains Fe.sup.2+ mixed in it as impurities, formation of a chromate film on the galvanizing layer of an electro-galvanized steel sheet is seriously impaired in applying a chromate treatment as the next step, and hence, the amount of deposited chromate is largely reduced. If, furthermore, impurities such as Cu.sup.2+ and Ni.sup.2+ are contained in a galvanizing bath, the amount of chromate deposited onto the galvanizing layer of an electro-galvanized steel sheet is small in applying a chromate treatment. Consequently, an intensification of chromate treatment conditions, as described later, cannot increase at all the amount of deposited chromate. As a result, it is impossible to obtain a chromated electro-galvanized steel sheet having a satisfactory corrosion resistance after chromating.

#For the purpose of preventing impurities from coming into a galvanizing bath, or removing impurities from a galvanizing bath, it has been usual practice to apply a closer control over impurities in a galvanizing bath, to employ a corrosion resistant material for the construction of a galvanizing apparatus, to remove such impurities as cadmium, lead and copper dissolved in a galvanizing bath by substituting zinc for such impurities through a treatment of the galvanizing bath with zinc powder, or, to cause precipitation of such impurities as copper by suspending an iron plate in a galvanizing bath.

Detailed description3,422 words

#Example A is an embodiment of the first process of the present invention.

#A steel sheet was subjected to the first electro-galvanizing treatment under the following conditions:

#a. Chemical composition of acidic galvanizing bath:

Facts

Application

05/662,618Filed 1 Mar 1976

Priority

JA 50-3528926 Mar 1975

Granted

20 Dec 1977

Term ended

20 Dec 1994

Estimated · how

Pre-1995 term; greater of 17 years from grant or 20 years from filing when eligible. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.

Classification6 codes

C25D 3/22
From solutions: of zinc
C25D 9/00
Electrolytic coating other than with metals
Y10T 428/12611
With additional, spatially distinct nonmetal component: oxide-containing component
Y10T 428/12799
Zn-base component: next to Fe-base component [e.g., galvanized]

Description10,842 words

Summary7,420 words

Detailed description3,422 words

#Example A is an embodiment of the first process of the present invention.

#A steel sheet was subjected to the first electro-galvanizing treatment under the following conditions:

#a. Chemical composition of acidic galvanizing bath:

Chromated electro-galvanized steel sheet excellent in corrosion resistance and process for manufacturing same

Life of this patent

Chromated electro-galvanized steel sheet excellent in corrosion resistance and process for manufacturing same

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims21

Description10,842 words

Drawings

Classification6 codes

Life of this patent

Description10,842 words