Hot dip aluminum coated chromium alloy steel
AssigneeArmco Steel Corporation
InventorsSteven L. Boston, William R. Seay, Richard A. Coleman
Life of this patent
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Abstract
Continuous hot dip aluminum coated ferritic chromium alloy steel strip. Strip is cleaned by heating to a temperature no greater than about 650.degree. C. in a direct fired furnace. The cleaned strip is further heated in a protective atmosphere containing at least 95% by volume hydrogen, cooled in the protective hydrogen atmosphere to near or slightly above the melting point of an aluminum coating metal, and passed into a bath of the aluminum coating metal. The low direct fired furnace cleaning temperature and hydrogen protective atmosphere provides good wetting of a chromium alloy steel surface to prevent uncoated areas or pin holes in the aluminum coated layer.
Claims8
A method of continuous hot dip coating a steel strip with aluminum, comprising the steps of:
- heating a ferritic chromium alloy steel strip to a temperature no greater than about 650.degree. C. by direct combustion of fuel and air wherein the gaseous products of said combustion have no free oxygen,
- further heating said strip to a temperature of at least about 830.degree. C., cooling said strip to a temperature near or slightly above the melting point of an aluminum coating metal,
- passing said strip through a protective atmosphere having at least about 95% by volume hydrogen,
- dipping said strip into a molten bath of said coating metal to deposit a coating layer on said strip,
- said coating layer being substantially free of uncoated areas and tightly adherent to said strip.
A method of continuous hot dip coating a steel strip with aluminum, comprising the steps of:
- heating a ferritic chromium alloy steel strip in a first furnace portion of the direct fired type to a temperature no greater than about 650.degree. C.,
- further heating said strip to a temperature at least about 830.degree. C. in a second furnace portion containing a protective atmosphere of at least about 95% by volume hydrogen having a dew point no greater than -18.degree. C.,
- cooling said strip in said atmosphere to near or slightly above the melting point of an aluminum coating metal,
- passing said strip through an enclosed snout containing said atmosphere and into a molten bath of said coating metal to deposit a coating layer on said strip,
- said atmosphere in said snout having at least about 97% by volume hydrogen having a dew point no greater than -29.degree. C.,
- said coating layer being substantially free of uncoated areas and tightly adherent to said strip.
Dependencies are inferred from the claim text.