US 4,543,300 AGranted

Iron-zinc alloy electro-galvanized steel sheet having a plurality of iron-zinc alloy coatings

AssigneeNippon Kokan Kabushiki Kaisha

InventorsTomihiro Hara, Takeshi Adaniya, Masaru Sagiyama, Tsutomu Watanabe, Takashi Shimoma, Masaru Nabatame

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Abstract

An iron-zinc alloy electro-galvanized steel sheet having a plurality of iron-zinc alloy coatings, which comprises: at least one iron-zinc alloy coating as the lower layer, formed on the surface of a steel sheet, and at least two iron-zinc alloy coatings as the upper layer, formed on the at least one iron-zinc alloy coating as the lower layer. The ratio of iron content to the coating weight of each of the at least one iron-zinc alloy coating as the lower layer is within the range of from 1 to 15 wt. %, and the total coating weight of the at least one iron-zinc alloy coating as the lower layer is within the range of from 1 to 50 g/m.sup.2 per side of the steel sheet. The ratio of iron content to the coating weight of each of the at least two iron-zinc alloy coatings as the upper layer is over 15 wt. %, the ratio of iron content to the coating weight gradually increases from the innermost coating toward the outermost coating of the at least two iron-zinc alloy coatings as the upper layer, the difference in the ratio or iron content to the coating weight between two adjacent coatings of the at least two iron-zinc alloy coatings as the upper layer is within the range of from 1 to 15 wt. %, and the total coating weight of the at least two iron-zinc alloy coatings as the upper layer is within the range of from 1 to 40 g/m.sup.2 per side of the steel sheet. The difference in the ratio of iron content to the coating weight between the uppermost coating of the at least one iron-zinc alloy coating as the lower layer and the lowermost coating of the at least two iron-zinc alloy coatings as the upper layer is within the range of from 1 to 15 wt. %. The sum of the total coating weight of the at least one iron-zinc alloy coating as the lower layer and the total coating weight of the at least two iron-zinc alloy coatings as the upper layer is within the range of from 10 to 75 wt. % per side of the steel sheet.

An iron-zinc alloy electro-galvanized steel sheet having a plurality of iron-zinc alloy coatings, which comprises:

at least one iron-zinc alloy coating as the lower layer, formed on at least one surface of a steel sheet;
and
at least two iron-zinc alloy coating as the upper layer, formed on said at least one iron-zinc alloy coating as the lower layer, the ratio of iron content to the coating weight of each of said at least one iron-zinc alloy coating as the upper layer being higher than the ratio of iron content to the coating weight of each of said at least one iron-zinc alloy coating as the lower layer;
the ratio of iron content to the coating weight of each of said at least one iron-zinc alloy coating as the lower layer being within the range of from 1 to 15 wt.%, and the total coating weight of said at least one iron-zinc alloy coating as the lower layer being within the range of from 1 to 50 g/m.sup.2 per side of said steel sheet;
the ratio of iron content to the coating weight of each of said at least two iron-zinc alloy coatings as the upper layer being over 15 wt.%, the ratio of iron content to the coating weight gradually increasing from the innermost coating toward the outermost coating of said at least two iron-zinc alloy coatings as the upper layer, the difference in the ratio of iron content to the coating weight between two adjacent coatings of said at least two iron-zinc alloy coatings as the upper layer being within the range of from 1 to 15 wt.%, and the total coating weight of said at least two iron-zinc alloy coatings as the upper layer being within the range of from 1 to 40 g/m.sup.2 per side of said steel sheet;
the difference in the ratio of iron content to the coating weight between the uppermost coating of said at least one iron-zinc alloy coating as the lower layer and the lowermost coating of said at least two iron-zinc alloy coatings as the upper layer being within the range of from 1 to 15 wt.%;
and
the sum of said total coating weight of said at least one iron-zinc alloy coating as the lower layer and said total coating weight of said at least two iron-zinc alloy coatings as the upper layer being within the range of from 10 to 75 g/m.sup.2 per side of said steel sheet.

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Abstract

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