Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-01-22
2001-04-10
Lorin, Francis J. (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S699000, C428S702000, C428S704000
Reexamination Certificate
active
06214483
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a member for a molten metal bath such as a roll to be used in a molten zinc plating line and the like for a steel member such as a steel strip.
BACKGROUND ART
As rolls and the like to be used in a plating bath of a molten zinc plating line or a molten zinc-aluminum plating line, there have been used members obtained by spraying various cermet materials or oxide ceramic materials on a surface of a thermal resistant steel roll.
Cermet sprayed coatings applied on the surfaces of the steel member have, however, such disadvantages that corrosion resistance against a molten metal is poor and that the ceramic sprayed coatings may be easily peeled off.
As means to solve the above-mentioned problems, there has been proposed in JP-A-5-209259 a method for spraying a cermet material containing 5-60% of metal boride, 5-30% of one or more member(s) selected from the group consisting of Co, Cr, Mo and W, as well as the balance comprising carbide and unavoidable impurities on a surface of a steel member and spraying thereon an oxide ceramic. Cr
2
O
3
is mentioned therein as an example of the oxide ceramics. Although properties thereof have been improved in use and good results have been attained, more absolute means have been required for further improvement.
On the other hand, there has been proposed in JP-A-4-350154 a sprayed coating having two-layer constitution in which an oxide ceramic sprayed layer containing SiO
2
and the balance consisting of at least one member selected from the group consisting of MgO, CaO, ZrO
2
, Al
2
O
3
, Y
2
O
3
and TiO
2
is arranged on a lower layer of a carbide cermet sprayed layer containing one or more carbide(s) and one or more metal(s) selected from the group consisting of Co, Ni, Cr and Mo.
That is, in the case that the lower layer is a carbide cermet, fine cracks for absorbing thermal stress can be produced in the upper ceramic layer by containing 10-40% by weight of SiO
2
in the upper ceramic layer. It is explained therein that the sprayed coating is effective as a member for a molten metal bath.
It is, however, required to produce fine cracks in the ceramic layer (the upper layer), since the method has a prerequisite of using the carbide cermet as the lower layer. Furthermore, thermal impact resistance is improved but stability in quality against a molten metal becomes poor, since corrosion resistance and wetting resistance against a molten metal are influenced by an extent of fine longitudinal cracks.
DISCLOSURE OF THE INVENTION
An object of the present invention is to solve the problems in the above-mentioned prior art and to provide a member for a molten metal bath provided with a composite sprayed coating having excellent corrosion resistance and peeling resistance against a molten metal.
We, inventors, have studied eagerly for accomplishing the above-mentioned object and found that a combination of an upper sprayed layer (a top coat) of oxide ceramics containing two or more oxides with a lower cermet sprayed layer (a bond coat) containing boride(s) and carbide(s) has excellent corrosion resistance and peeling resistance against a molten metal. Thus, we completed the present invention.
It is an essential aspect of the present invention based on the above-mentioned finding that a member for a molten metal bath provided with a composite sprayed coating having excellent corrosion resistance and peeling resistance against molten metal comprises a cermet sprayed coating lower layer formed on a surface of a substrate and a ceramic sprayed coating surface layer formed on a surface of the coating lower layer, wherein the lower layer comprises 5-60% by weight of a metal boride and 5-30% by weight of at least one member selected from the group consisting of Co, Cr, Mo, and W with the balance consisting of a metal carbide and unavoidable impurities, and the surface layer comprises A-B type oxides in which at least one member (component A) selected from the group consisting of MgO and CaO and at least one member (component B) selected from the group consisting of Al
2
O
3
, SiO
2
, ZrO
2
and Ta
2
O
5
are combined.
Furthermore, it is also another essential aspect of the present invention to adopt a ceramic sprayed coating layer comprising C-D type oxides comprising a calcined composite member or mixed member composed of an oxide ceramic (component C) in which at least two members selected from the group consisting of MgO, CaO, Al
2
O
3
, SiO
2
and Ta
2
O
5
are combined and ZrO
2
—Y
2
O
3
type or ZrO
2
—CeO
2
type oxide (component D), to adopt a ceramic sprayed coating layer comprising Cr
2
O
3
—E type oxides in which Cr
2
O
3
and at least one member (component E) selected from the group consisting of Al
2
O
3
, SiO
2
, ZrO
2
, TiO
2
, Ta
2
O
5
, Y
2
O
3
and CeO
2
are combined, or to adopt a ceramic sprayed coating layer comprising A-B-F type oxides in which at least one member (component F) selected from the group consisting of Y
2
O
3
and CeO
2
is added to A-B type oxides that is a combination of at least one member (component A) selected from the group consisting of MgO and CaO and at least one member (component B) selected from the group consisting of Al
2
O
3
, SiO
2
, ZrO
2
and Ta
2
O
5
.
Furthermore, it is also another essential aspect of the present invention to provide a member for a molten metal bath provided with a composite strayed coating having excellent corrosion resistance and peeling resistance against molten metal which is obtained by sealing a composite sprayed coating comprising the above-mentioned oxide ceramic sprayed coating surface layer and a cermet sprayed coating lower layer formed on a surface of a substrate and comprising 5-60% by weight of a metal boride and 5-30% by weight of at least one member selected from the group consisting of Co, Cr, Mo, and W with the balance consisting of a metal carbide and unavoidable impurities by means of an inorganic sealing agent.
It is still another essential aspect of the present invention that the sealing agent to be used is a solution of chromic acid (a solution of H
2
CrO
4
and H
2
Cr
2
O
7
), a solution of colloidal silica, a solution of a metallic alcohol compound in alcohol, a solution of a metallic salt in water or alcohol, a solution of metallic phosphate in water, a suspension of metallic hydroxide, a suspension of metallic oxide fine powders in alcohol or water, or a mixed solution of two or more of these solutions.
It is further another essential aspect of the present invention that a thickness of the above-mentioned lower layer is 20-500 &mgr;m and a thickness of the surface layer is 5-500 &mgr;m.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is explained as follows about constitution and effects thereof.
It was confirmed that the cermet coating used in the present invention containing metallic borides such as tungsten boride is superior in corrosion resistance against molten metal.
Furthermore, it was found that a fitting property of the metallic boride with the ceramic surface layer is good since the boride forms B
2
O
3
partly when sprayed and produces a flux action. Therefore, the coating has the following characteristics. The oxide ceramic sprayed coating surface layer formed on the cermet sprayed coating lower layer containing the metallic boride has a high fitting property with the lower layer and has superior corrosion resistance. The molten metal is hardly adhered on the coating. The surface of the layer is hardly peeled off from the lower layer. In the present invention, a spraying member containing a metallic borides such as tungsten boride WB and metallic carbides such as tungsten carbide WC is used as a cermet material for a bond coat. However, if the metallic boride is much used, the fitting property with a substrate is lowered, thus the upper limit thereof is 60% by weight. Furthermore, in the case of less than 5% by weight, an additional effect of the metallic boride is hardly obtained. Thus, a content of the metallic boride is limited to 5-60% by weight.
The metallic carbide has
Hiroshige Munetoshi
Sato Takao
Tarumi Kiyohiro
Kanesaka & Takeuchi
Lorin Francis J.
Nippon Steel Hardfacing Co. Ltd.
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