Bethlehem Steel Corporation

Louis K Allegra

Herbert E Townsend

Angelo R Borzillo

James B Horton

This invention relates to an aluminum-zinc alloy coated ferrous base product which exhibits improved atmospheric corrosion resistance, and to the process whereby such improved corrosion resistance may be realized. The process is characterized by the steps of heating such coated product to a temperature within the single phase region for the composition corresponding to the aluminum and zinc of said coating, defined as .alpha. in the FIGURE in the accompanying drawing, preferably at a temperature between about 650.degree. F. (343.degree. C.) to 750.degree. F. (399.degree. C.), for a period of time to solution treat the aluminum-zinc alloy coating overlay, and cooling slowly to at least 350.degree. F. (177.degree. C.). The resulting product is characterized by improved atmospheric corrosion resistance as a result of the combination of an aluminum-zinc alloy coating overlay having a structure comprised of a fine dispersion of beta-zinc within a matrix of alpha-aluminum, and a thin intermetallic layer interposed between said overlay and said ferrous base.

Method of producing an aluminum-zinc alloy coated ferrous product to

This invention is directed to an improved zinc containing metallic coated ferrous product, particularly sheet and strip, which is resistant to intergranular penetration by zinc and embrittlement of the ferrous base. Use of such zinc containing metallic coated ferrous product in elevated-temperature service, such as found with certain appliances and automotive exhaust components, is enhanced by the coated products of this invention. The resistance to embrittlement of the zinc containing metallic coated ferrous base, when subjected to elevated service temperatures, is achieved by the use of a high-phosphorus containing steel base. For a plain content steel base, a phosphorus content of at least 0.020% by weight, preferably at least 0.030%, and more preferably at least 0.039% was found sufficient to render such zinc-alloy coated ferrous base resistant to embrittlement by zinc. By use of such high phosphorus ferrous base, for the reception of a zinc containing alloy coating, an improved metallic coated ferrous product has been found which resists intergranular penetration by zinc and embrittlement of the ferrous base. Such coated product has extended service life at temperatures above about 450.degree. F. (232.degree. C.) and when restored to room temperature possesses a high degree of ductility.

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Bethlehem, PA, United States of America

Louis K Allegra