Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-12-22
2002-10-15
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C148S264000, C148S267000, C427S433000, C428S626000, C428S679000, C428S680000, C428S334000, C428S335000, C428S341000, C428S450000, C428S926000
Reexamination Certificate
active
06465114
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a Zn coated steel material, a Zn coated steel sheet and a painted steel sheet, more particularly to a Zn coated steel material, a Zn coated steel sheet and a painted steel sheet that are excellent in corrosion resistance and can be applied to various purposes, such as for home electrical appliances and building materials. The present invention further relates to a Zn coated steel sheet for construction materials and home electrical appliances that is excellent in corrosion resistance of machined portions and is planet-friendly since it does not contain chromium which is believed to put a heavy load on the environment.
BACKGROUND TECHNOLOGY
Zinc-system coated steel sheet is among those most often used as a Zn coated steel material excellent in corrosion resistance. Zinc-system coated steel sheet is used in various manufacturing industries, including the automotive, home electrical appliance and building material sectors. In the building material sector particularly, Zn coated steel sheet is used without further processing for prepreg components and the like and after coating for roofing, wall materials and the like.
The need for improvement of the corrosion resistance of galvanized steel sheet used in these building material sectors is further intensifying and conventional Zn coated steel sheet is incapable of fully meeting the needs of consumers.
Galvano-aluminum steel sheet, which usually called “Galvalume”®, (55%Al—1.6%Si—Zn-alloy coated steel sheet) is therefore used as high-corrosion-resistance coated steel sheet for building materials. As peripheral patents of U.S. Pat. No. 3,026,606, that relates to this “Galvalume®” steel sheet, Japanese Patent Publication No. Hei 3-21627 proposes a Zn coated steel sheet having 3-20% Mg, 3-15% of Si, Al/Zn=1-1.5, and as intermetallic compound Mg
2
Si, MgZn
2
, SiO
2
, Mg
32
(Al, Zn)
49
, and discloses that the corrosion resistance is good. However, owing to the fact that, similarly to “Galvalume”® steel sheet, the Al content of the bulk coating layer is high relative to Zn, the sacrificial corrosion prevention capability is low and the corrosivity of portions where the underlying metal is exposed, such as the end faces of coated materials, remains a problem.
On the other hand, in comparison with the method of applying a paint after first forming the steel sheet into a complex shape, painted steel sheet (precoated steel sheet) is advantageous in such points as that the painting process can be streamlined, the quality is uniform and painting material consumption is reduced, and, therefore, much has been used up to now and the amount used is expected to increase in the future. Painted steel sheet is generally formed into the desired shape after the cold-rolled steel sheet or zinc-coated steel sheet has been coated, and is then submitted to the final use. It is used in, for example, home electrical appliances (refrigerators, washing machines, microwave ovens etc.), automatic vending machines, office equipment, automobiles, the outdoor units of airconditioners, and the like.
In these various applications, the painted steel sheet is required to have an attractive appearance while also possessing machinability and corrosion resistance. In the case of products for home electrical appliances and building materials used outdoors, occurrence of corrosion at machined portions and scratched portions tends to be particularly objectionable as degrading product value, because the painted steel sheet is used after machining.
Various ways for improving the corrosion resistance of painted steel sheet have therefore been proposed. Japanese Unexamined Patent Publication No. Sho 61-152444, for instance, teaches improving fabricated-portion corrosion resistance by forming a chromate layer and a zinc-rich painting material on a Zn—Ni coated steel sheet.
However, the foregoing and other coated steel materials, coated steel sheets and painted steel sheets disclosed up to now cannot be said to achieve sufficient corrosion resistance.
Japanese Unexamined Patent Publication No. Hei 8-168723 teaches a technology for obtaining a painted steel sheet, excellent in machinability, anticontamination property and hardness, by defining a film structure, and Japanese Unexamined Patent Publication No. Hei 3-100180 discloses a painted steel sheet improved in end face corrosion resistance by using a specific chromate treatment solution.
Such film structures are formed by subjecting a coated steel sheet of excellent corrosion resistance to a base metal treatment, called chromate treatment, that provides excellent corrosion resistance and adherence, providing an undercoating containing a chromium-system anti-rust pigment that is excellent in corrosion resistance thereon, and providing a colored overcoating on the undercoating.
The hexavalent chromium contained in the chromate-treated portion and the chromium-system anti-rust pigment is water soluble and acts to suppress corrosion of the zinc-coated steel sheet by dissolving out. If the coating should crack under harsh machining, for example, the chromium suppresses corrosion at this portion. Owing to such outstanding features, chromate treatments and chromium-system anti-rust pigments have been widely used on painted steel sheet.
However, hexavalent chromium, which may dissolve out of the chromate-treated portion and the chromium-system anti-rust pigment, is a substance that puts a heavy load on the environment. Calls for chromium-free base metal treatments and chromium-free anti-rust pigments have recently intensified.
Highly corrosion-resistant coated steel materials (steel sheet, steel wire etc.) are very likely to be used in large amounts with a view to extending service life in building material applications as well as civil engineering applications such as guardrails, sound-insulting walls, basket mats and the like. Particularly in applications such as guardrail posts and the like, whose fabrication involves roll forming, grinding with a cutting tool etc., the ordinary hot-dip galvanized steel sheet is easily scratched by the rolls and the chip from the cutting tool. On the other hand, the coating layer of Zn coated wire for basket mats is likely to develop scratches or cracks during coiling or net fabrication. As these often become a cause for degradation of corrosion resistance and the like, product improvement has been desired.
PCT/J97/04594 teaches a hot-dip Zn—Al—Mg alloy galvanized steel sheet, and a method of producing the same, that is a hot-dip Zn—Al—Mg alloy galvanized steel sheet good in corrosion resistance and surface appearance obtained by forming, on a surface of a steel sheet, a hot-dip Zn—Al—Mg alloy galvanized layer composed of 4.0-10 wt % of Al, 1.0-4.0 wt % of Mg, Ti and B as required, and the balance of Zn and unavoidable impurities, the coating layer having a metallic structure including a primary crystal Al phase interspersed in a matrix of Al/Zn/MgZn
2
ternary eutectic structure. Although this invention aims at the ternary eutectic point in the ternary state diagram and provides a steel sheet excellent in corrosion resistance, it still has room for improvement regarding the corrosion resistance of the end faces and fabricated portions.
Earlier, in Japanese Unexamined Patent Publication No. Hei 4-147955, the present inventors proposed a method of producing a Zn—Mg—Al alloy galvanized steel sheet whose resistance to red rust after fabrication is markedly superior to an ordinary hot-dip galvanized steel sheet. In the present invention, the inventors have developed a Zn coated steel material, a Zn coated steel sheet and a painted steel sheet that have improved corrosion resistance of end faces and fabricated portions, and a method of producing the same. Specifically, in a Zn—Al—Mg—Si quaternary system, the present invention achieves high sacrificial corrosion prevention performance and enhances end-face corrosion resistance by defining a Zn-based coating layer containing 2-19% of Al, 1-10% of Mg, and 0.01-2% of Si. Sacrificial corrosion preventio
Furukawa Hiroyasu
Honda Kazuhiko
Kanai Hiroshi
Kurosaki Masao
Maki Jun
Kenyon & Kenyon
Koehler Robert R.
Nippon Steel Corporation
LandOfFree
-Zn coated steel material, ZN coated steel sheet and painted... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with -Zn coated steel material, ZN coated steel sheet and painted..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and -Zn coated steel material, ZN coated steel sheet and painted... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2996840