The prior art enameling of cold rolled steel sheet comprises the following steps: material.fwdarw. shaping the sheet.fwdarw.degreasing.fwdarw.pickling.fwdarw.Ni-dipping, if necessary.fwdarw.neutralization.fwdarw.drying.fwdarw.application of enamel.fwdarw.drying.fwdarw.baking. When one coat of enamel is to be applied to the material sheet consisting of an enameling steel sheet produced by decarburization-annealing, vacuum degassing, etc., the above-mentioned steps are all those required for producing a product enameled steel sheet. When two or more coats of enamel are to be applied to the material sheet, the steps of application of enamel, drying and baking are further repeated to produce a product enameled steel sheet.
In such enameling processes, the pickling step is indispensable for a good enamel adherence to the steel sheet, and it is said that pickling with a pickling steel loss of 20 g/m.sup.2 or more is required for obtaining a high enamel adhesive property. For this reason, the following methods have been proposed to obtain a high enamel adhesive property.
1. When a sufficient pickling steel loss to obtain a high enamel adhesive property cannot be obtained by using an existing pickling facility or a conventional pickling method: a method of adjusting the chemical composition of steel sheet by adding phosphorus or limiting the Cu content to achieve a desired pickling steel loss (e.g., U.S. Pat. Nos. 3,436,808, 3,282,685).
2. A method of pickling in combination with Ni-dipping, i.e., Ni-flashing, comprising dipping a pickled steel sheet in a several percent nickel sulfate aqueous solution and causing nickel to be precipitated on the steel surface, in order to make up for the insufficient enamel adhesive property obtained by pickling.
3. A method of improving the kind of acids and the composition of pickling baths used for pickling.
The above-mentioned methods all require a pickling step, thus presenting the following problems:
A. Since the concentration and temperature of a pickling bath have substantial effect on the enamel adhesive property of a steel sheet, strict control of the pickling bath is necessary for obtaining a desired enamel adhesive property. This control is however very difficult.
B. The need of the pickling step leads to an increase in cost of enameling operation and is an obstacle to the improvement in the efficiency of enameling operation. Further, the pickling bath is a source of environmental pollution and worsens the work environment.
c. Pickling tends to cause defects such as blister formed on the enameled products.
In consideration of the foregoing, cold rolled steel sheets capable of giving a high enamel adhesive property even with total omission of the pickling step or with pickling performed only to the slightest degree. Such cold rolled steel sheets have not however as yet been proposed.
USPTO Backgrounds
USPTO Backgrounds