Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Patent
1996-10-23
2000-01-25
Thibodeau, Paul
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
428654, 428684, 427 8, 427 9, 427431, 427436, 118674, 118712, 118407, 118419, 374124, 374137, B32B 1510, B05D 314, B05C 1100
Patent
active
060176431
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a hot-dip aluminized steel sheet with high resistance to heat and corrosion which is useful as a member of auto exhaust systems and heat appliances. The present invention also relates to a method of manufacturing the aluminized steel sheet and an alloy-layer control apparatus which is used in the method. More particularly, the present invention relates to the control of the thickness and section pattern of an Fe--Al--Si alloy layer which is inevitably produced at the interface between a coating-metal layer and a base-metal steel sheet within an aluminized layer.
DESCRIPTION OF THE BACKGROUND ART
When a hot-dip aluminized steel sheet is manufactured with a continuous hot-dip aluminizing plant (line), as illustrated in FIG. 17, a base-metal steel sheet 4 is guided into a hot-dip Al--Si plating (aluminizing) bath 1 which has been adjusted to a specific bath composition and bath temperature and guided out of the bath 1 after having rounded a sink roll 2 in the bath 1. Next, the amount of the coating (the thickness of the coating layer) is adjusted by a gas-wiping unit 3 placed immediately above the bath 1. Here, the plant is generally provided with a cooling unit 5 above the bath 1 which forcedly cools the coating-metal layer (with jets of a gas, gas/liquid, etc.) so as to completely solidify the coating-metal layer before the coated steel sheet 6 reaches an upward top roll 9.
With hot-dip aluminized steel sheets manufactured in this way, diffusion of Fe atoms across the interface between the base metal steel sheet and the coating-metal layer (infiltration of Fe atoms in the base metal steel sheet into the coating-metal layer through diffusion) results in the inevitable formation of an Fe--Al--Si alloy layer at the interface. The alloy layer, being hard and fragile, promotes peeling of the coating layer from the coated steel sheet during press working. Particularly in cases where the steel sheet is subjected to strong working such as drawing or squeezing, the alloy-layer thickness must be controlled to approximately 5 .mu.m or smaller in order to ensure the press workability (e.g., Japanese Examined Patent Application Publication SHO 51-46739).
A variety of proposals have been suggested for coating conditions to control the production and the growth of the alloy-layer including: composition (Si content: 3-13%), and limiting the bath-immersion temperature of the base metal steel sheet (the sheet temperature immediately before its immersion into the bath) to a range between the melting point of the metal in the aluminizing bath and the melting point plus 40.degree. C. (Japanese Unexamined Patent Application Disclosure HEI 4-176854); spraying a coolant (a liquid, gas plus liquid, etc.) from a cooling unit placed above the bath (Japanese Unexamined Patent Application Disclosure SHO 5260239); metal having a lower melting point than the coating (i.e. plating) metal to maintain the steel sheet temperature at 500.degree. C. or lower until the coating is accomplished (Japanese Unexamined Patent Application Disclosure HEI 1-104752); a temperature 50-100.degree. C. lower than the coating bath temperature (Japanese Unexamined Patent Application Disclosure HEI 5-287488); etc.
However, it has proven difficult to satisfactorily control the alloy-layer thickness only through control of the operation conditions as suggested by the prior art, in other words through the adjustment of the coating bath composition and temperature, the control of the bath-immersion temperature of the base metal steel sheet and the high-level forced-cooling of the coated metal layer, etc. While precoating the surface of the base-metal steel sheet with a special metal layer results in an increased number of steps and an increased cost. In addition, all the processes of the prior art fail to precisely control the alloy-layer thickness, since no quantitative relationship is elucidated to exist between the production and the growth rate of the alloy layer, and the operational conditions.
After
REFERENCES:
patent: 3632453 (1972-01-01), Patterson
patent: 3664293 (1972-05-01), Hozumi et al.
patent: 4751957 (1988-06-01), Vaught
patent: 4891274 (1990-01-01), Higuchi et al.
patent: 5518772 (1996-05-01), Andachi et al.
patent: 5529816 (1996-06-01), Sartini et al.
Kobayashi Masayuki
Okano Masaki
Saori Takashi
Nisshin Steel Co. Ltd.
Rickman Holly C
Thibodeau Paul
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