Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2003-01-16
2004-10-19
McNeil, Jennifer (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S621000, C428S632000, C428S684000, C428S685000, C428S681000, C428S660000, C205S238000, C205S228000, C205S255000
Reexamination Certificate
active
06805975
ABSTRACT:
TECHNICAL FIELD
The present invention relates to steel sheet for porcelain enameling, method for producing the same, porcelain enamel products and a method for producing the same. In further detail, the invention relates to steel sheet for porcelain enameling having excellent adhesion with enamel and a method for producing the same, as well as to a porcelain enamel product and a method for producing the same, which enables excellent enamel adhesion by “direct-on” enameling of cover coat enamel on Ti-added steel sheet.
BACKGROUND ART
Porcelain enamel products are widely used as kitchen and table-top articles, components of heating appliance and components of cooking appliance, bathtubs, interior and exterior materials of buildings, and the like. Enamel products are generally produced by firing twice; a ground coat enamel is first applied on the steel sheet and fired, a cover coat enamel is further applied thereon, and fired again. In order to reduce the production cost, however, a production method of direct enameling for only once, i.e., “direct-on enameling”, comprising providing the cover coat enamel directly on the steel sheet followed by firing is employed. However, in the production method of direct-on enameling, it is necessary to perform pretreatment oh the steel sheet before enameling, such as intense pickling and Ni dipping treatment. Further, as a steel sheet for obtaining favorable adhesion of the enamel product with the steel sheet, a rolled sheet of high oxygen steel containing oxygen at a high concentration, which is produced by reducing C content in the steel-making stage and produced by continuous casting without performing deoxidation treatment, is widely utilized. However, a high oxygen steel generally suffers poor workability, and its application to usages requiring severe processing is limited.
Japanese Patent Publication No. 24413/1979 discloses that, by coating the surface of a steel material with an alloy of one or two types of metals selected from Ni and Fe with one or two types of metals selected from Mo and W, excellent affinity with the cover coat enamel and adhesion with the cover coat enamel can be obtained. However, there is no description concerning the workability of the steel sheet.
On the other hand, in usages requiring severe workability such as kitchen wares or bathtubs, rolled sheets of Ti-added steel or B-added steel have been used. However, as is disclosed in Japanese Patent Laid-Open No. 140286/1998, although Ti-added steel sheet is superior in workability, black specks defects generate in the enamel layer in case direct-on enameling is performed. Accordingly, the enamel layer had to be formed by means of ground coat enamel finishing or by applying the cover coat and ground enameling in two times.
As described above, there is required a steel sheet for porcelain enameling by reduced production steps and energy consumption, thereby reduced in production cost, yet improved in workability and having an enamel layer with high adhesion even in case direct-on enameling is performed only once.
In the present invention, the objects are to provide steel sheet for porcelain enameling having excellent adhesion with the steel sheet by applying direct-on enameling of cover coat enamel only once and still free of black specks defects, to provide the method for producing the same, as well as to provide a porcelain enamel product and the method for producing the same, in which Ti-added steel sheet is used.
DISCLOSURE OF THE INVENTION
The steel sheet for porcelain enameling according to present invention that solves the problems above is characterized by that it comprises a Ti-added steel sheet containing 0.01% by weight (wherein, % represents “% by weight” hereinafter) or less of C, 0.5% or less of Mn, 0.04% or less of P, 0.04% or less of S, 0.01 to 0.50% of Ti, and balance Fe accompanied by unavoidable impurities, which is obtained by providing thereon a Ni—Mo alloy plating film, and which is then subjected to heat treatment.
The reason for confining each of the components in the steel sheet for porcelain enameling above according to the present invention is as follows.
[C]
From the viewpoint of suppressing the generation of pores and black specks on firing the enamel while assuring favorable workability, the content of C is set to 0.01% or less.
[Mn]
Manganese bonds with S to exhibit effects of suppressing cracking attributed to embrittlement from occurring during hot working; hence, Mn should be incorporated at a concentration of 0.5% or lower. In case the content of Mn exceeds 0.5%, the content of sulfides in the steel decreases as to reduce the degree of surface roughening of the steel sheet during pickling, and it results in a loss of anchoring effect. This leads to a drop in adhesion of enamel.
[P]
Although P improves adhesion, from the viewpoint of suppressing the generation of pores and black specks on firing the enamel, the content thereof is set to 0.04% or lower.
[S]
Sulfur accelerates surface roughening of the steel sheet on pickling as to improve the adhesion of the enamel by anchoring effect. However, S causes cracks due to embrittlement on hot working. Hence, the content of S is constrained to 0.04% or lower.
[Ti]
Titanium should be contained in a range of from 0.01 to 0.50%. In case the content falls outside this range, hardening occurs as to impair moldability.
The steel sheet for porcelain enameling according to the one embodiment of the present invention is characterized by that, in the steel sheet for porcelain enameling the content of elements present in the surface of the steel sheet as measured by an energy-dispersion type X-ray microanalyzer hereinafter referred to as “EDX” is 5 to 75% Ni, 3 to 40% Mo, and 5 to 82% Fe provided that Ni, Mo, and Fe in total is 100%.
Furthermore, the method for producing steel sheet for porcelain enameling according to the one embodiment of the present invention is characterized by that it comprises providing a Ni-Mo alloy plating on the steel sheet described above, followed by applying a heat treatment thereto. Further, the method for steel sheet for porcelain enameling according to one embodiment of the present invention is characterized by that, as the Ni—Mo alloy plating, the plating is performed in such a manner that the plating film contains Ni at a coverage of 1.5 to 20.0 g/m
2
and Mo at a coverage of 0.4 to 7.0 g/m
2
. Furthermore, the method for steel sheet for porcelain enameling according to one embodiment of the present invention is characterized by that the heat treatment is performed in a temperature range of from 500 to 900° C.
Moreover, the porcelain enameled product according to one embodiment of the present invention is characterized by that it comprises an enamel layer provided on one of the steel sheets for porcelain enameling as described above. Then, the method for producing a porcelain enameled product according to one embodiment of the present invention is characterized by that it comprises once applying a cover coat enamel on one of the steel sheets for porcelain enameling as described above, followed by applying firing thereto.
BEST MODE FOR CARRYING OUT THE INVENTION
The mode for carrying out the present invention is described below.
The present invention is based on the findings that, by applying a Ni—Mo alloy plating on a Ti-added steel sheet having a specified composition range and containing ultra-low carbon, and by applying heat treatment thereto in order to control the content of Ni, Mo, and Fe present in the surface of the steel sheet for porcelain enameling in a predetermined range, excellent enamel adhesion properties are obtained even on porcelain enameled products having the enamel provided by direct-on enameling for only once.
The Ti-added steel sheet containing low carbon for use in the present invention has its composition adjusted as such that it should contain 0.01% by weight or less of C, 0.5% or less of Mn, 0.04% or less of P, 0.04% or less of S, 0.01 to 0.50% of Ti, and balance Fe accompanied by unavoi
Fujimoto Junichi
Hamada Toshihira
Hayashida Takahiro
Jono Yoshihiro
Komai Masao
Browdy and Neimark , P.L.L.C.
Ferro Enamels (Japan) Limited
McNeil Jennifer
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