Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-10-26
2003-08-26
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C148S533000, C427S398100, C427S398300, C427S406000, C427S432000, C427S433000, C427S436000, C428S457000, C428S939000
Reexamination Certificate
active
06610423
ABSTRACT:
TECHNICAL FIELD
This invention relates to a plated steel material having enhanced corrosion resistance and workability, as required for outdoor and exposed uses such as structures, revetments, fishing nets, fences, etc., and a method to produce the plated steel material. The plated steel material includes: plated steel wires such as steel wires for gauze, concrete reinforcing fibers, bridge cables, PWS wires, PC wires, ropes and the like; structural steels such as H sections, sheet pilings and the like; machine components such as screws, bolts, springs and the like; steel sheets and plates; and other steel materials.
BACKGROUND ART
Among plated steel materials, and among plated steel wires in particular, galvanized steel wires and zinc—aluminum alloy plated steel wires, superior to galvanized steel wires in corrosion resistance, are commonly used. The zinc—aluminum alloy plated steel wires are produced, generally, by subjecting a steel wire to the following sequential processes: washing, degreasing, or other means of cleaning; flux treatment; plating by either a two-step plating process consisting of a first step of hot dip plating in a plating bath mainly containing zinc and a second step of hot dip plating in a Zn—Al alloy bath containing 10% of Al or a one-step plating process in a Zn—Al alloy bath containing 10% of Al; then, after the wire vertically extracted from the plating bath, cooling it and winding it into coils.
The good corrosion resistance of a zinc—aluminum alloy plated steel wire is enhanced yet further by increasing the plating thickness. One of the methods to secure a desired plating thickness is to increase the speed of a steel wire (wire speed) at plating operation so that it comes out of a plating bath at a high speed and to increase the amount of the plated alloy adhering to the steel wire owing to the viscosity of the molten plating alloy. By this method, however, the plating thickness of a plated steel wire, in the cross section perpendicular to its longitudinal direction, is likely to become uneven because of the high speed, and therefore there is a limitation related to a plating apparatus. Consequently, galvanizing or hot dip plating of Zn—Al alloy using current plating apparatuses cannot provide sufficient corrosion resistance and there is a problem that today's strong demands for a longer service life of a plated steel wire are not satisfactorily fulfilled.
To cope with the problem, Japanese Unexamined Patent Publication No. H10-226865 proposes a plating composition of a Zn—Al—Mg alloy system, wherein corrosion resistance is enhanced by the addition of Mg to a plating bath. However, the plating method based on this plating composition is meant for a small plating thickness on steel sheets and when the method is applied to heavy plating steel wires represented by steel wires for outdoor exposed uses such as structures, revetments, fishing nets, fences, etc., there occurs a problem that cracks develop in the plated layers during the working of the plated steel wires. Japanese Unexamined Patent Publication No. H7-207421 discloses a method to apply Zn—Al—Mg alloy plating of a heavy plating thickness. When this method is applied to the plating of steel wires without modification, however, a thick Fe—Zn alloy layer forms and there is a problem that the Fe—Zn alloy layer cracks or peels off during the working of the plated steel wires.
DISCLOSURE OF THE INVENTION
The object of the present invention is, in view of the above problems, to provide a hot dip zinc alloy plated steel material, particularly a hot dip zinc alloy plated steel wire, excellent in corrosion resistance and workability which does not suffer cracks and exfoliation in a plated layer and/or a plated alloy layer during the working of the plated steel wire, and a method to produce the plated steel wire.
The present inventors established the present invention as a result of studying the means to solve the above problems and the gist of the present invention is as follows:
(1) A plated steel material excellent in corrosion resistance and workability, characterized by having an alloy layer 20 &mgr;m or less in thickness consisting of, in mass, 25% or less of Fe, 30% or less of Al, 5% or less of Mg and the balance consisting of Zn, at the interface of a plated layer and a base steel.
(2) A plated steel material excellent in corrosion resistance and workability, characterized by having: an alloy layer 20 &mgr;or less in thickness consisting of, in mass, 25% or less of Fe, 30% or less of Al, 5% or less of Mg and the balance consisting of Zn at the interface of a plated layer and a base steel; and the plated layer consisting of, as an average composition in mass, 4 to 20% of Al, 0.8 to 5% of Mg, 2% or less of Fe and the balance consisting of Zn, on top of the alloy layer.
(3) A plated steel material excellent in corrosion resistance and workability, characterized by having, at the interface of a plated layer and a base steel, an alloy layer composed of: an inner alloy layer 5 &mgr;m or less in thickness consisting of, in mass, 15% or more of Fe, 20% or more of Al, 2% or more of Si, 5% or less of Mg and the balance consisting of Zn; and an outer alloy layer 30 &mgr;or less in thickness consisting of, in mass, 25% or less of Fe, 30% or less of Al, 2% or more of Si, 5% or less of Mg and the balance consisting of Zn.
(4) A plated steel material excellent in corrosion resistance and workability, characterized by having: at the interface of a plated layer and a base steel, an alloy layer composed of an inner alloy layer 5 &mgr;m or less in thickness consisting of, in mass, 15% or more of Fe, 20% or more of Al, 2% or more of Si, 5% or less of Mg and the balance consisting of Zn and an outer alloy layer 30 &mgr;m or less in thickness consisting of, in mass, 25% or less of Fe, 30% or less of Al, 2% or more of Si, 5% or less of Mg and the balance consisting of Zn; and, on top of the outer alloy layer, the plated layer consisting of, as an average composition in mass, 4 to 20% of Al, 0.8 to 5% of Mg, 0.01 to 2% of Si, 2% or less of Fe and the balance consisting of Zn, and containing Mg
2
Si dispersively existing therein.
(5) A plated steel material excellent in corrosion resistance and workability according to the item (2), characterized in that the solidification structure of the plated layer is a granular crystal structure or a columnar crystal structure.
(6) A plated steel material excellent in corrosion resistance and workability according to the item (2) or (4), characterized in that each of an a phase mainly composed of Al—Zn, a &bgr; phase consisting of Zn only or an Mg—Zn alloy layer and a Zn—Al—Mg ternary eutectic phase exist in the structure of the plated layer.
(7) A plated steel material excellent in corrosion resistance and workability according to the item (6), characterized in that the volume percentage of the &bgr; phase existing in the structure of the plated layer is 20% or less.
(8) A plated steel material excellent in corrosion resistance and workability according to the item (2) or (4), characterized in that the plated layer further contains one or more of the elements selected from among one or more of the groups of a, b, c and d below;
a: one or more elements of Ti, Li, Be, Na, K, Ca, Cu, La and Hf in 0.01 to 1.0 mass % each,
b: one or more elements of Mo, W, Nb and Ta in 0.01 to 0.2 mass % each,
c: one or more elements of Pb and Bi in 0.01 to 0.2 mass % each,
d: one or more elements of Sr, V, Cr, Mn and Sn in 0.01 to 0.5 mass % each.
(9) A plated steel material excellent in corrosion resistance and workability according to any one of the items (1) to (8), characterized in that the plated steel material further has any one of a paint coating and a heavy anticorrosion coating.
(10) A plated steel material excellent in corrosion resistance and workability according to the item (9), characterized in that the heavy anticorrosion coating consists of one or more of the high molecular compounds selected from among vinyl chloride, polyethylene, polyurethane and fluororesin.
(11) A plated
Nishida Seiki
Nishimura Kazumi
Sugimaru Satoshi
Takahashi Akira
Tanaka Satoru
Kenyon & Kenyon
Koehler Robert R.
Nippon Steel Corporation
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