JPS6156314B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an enameled steel plate, and particularly to an enameled steel plate having excellent adhesion and surface texture. Conventionally, as a method to improve the adhesion between the steel plate and the base enamel product, after pickling the base steel plate, Ni flushing treatment is performed, or adhesion improving elements such as Co and Ni are included in the glaze. Methods such as these have been adopted. However, as the use of enamel products has expanded in recent years, the conditions in which enamel steel plates are used have become harsher, and the conventional methods for improving adhesion are often insufficient. Especially for enameled steel plates that are repeatedly heated and cooled,
Products coated with enamel by the conventional method have had the problem that the enamel adhesion deteriorates during use, and the enamel layer eventually peels off. Furthermore, when pretreating a base steel sheet, the pickling speed and the amount of Ni precipitated by Ni immersion vary depending on the composition of the steel sheet, resulting in variations in enamel adhesion. Furthermore, when an adhesion-improving element such as Co or Ni is included in the glaze or the amount thereof is increased, there is a drawback that large variations in adhesion occur due to changes in firing temperature. SUMMARY OF THE INVENTION In view of the above-mentioned shortcomings of the prior art regarding improvement of enamel adhesion, the object of the present invention is to fundamentally improve this and provide an enameled steel plate with significantly superior adhesion. The gist of the present invention is as follows.
That is, it is an enameled steel plate characterized by comprising a forsterite (2MgO, SiO ₂ ) coating layer coated on a steel plate and an enamel layer coated on the forsterite coating layer. The present inventors conducted numerous experiments on a method for improving the adhesion of the enamel layer coated on a steel plate. As a result, the inventors formed a thin forsterite (2MgO, SiO ₂ ) base film on the surface of the steel plate, and then It has been found that by forming an enamel layer, the adhesive force between the enamel layer and the steel plate can be significantly strengthened.
In this case, there is no need for pre-treatment such as pickling or Ni immersion on the base steel plate, and as a glaze,
It was found that there was no need to include conventional adhesion-improving elements such as Co and Ni. Next, a forsterite coating according to the present invention was formed on a steel plate of the same composition and enameled thereon, and a steel plate pretreated by a conventional method in which the steel plate was first pickled with sulfuric acid and then immersed in Ni. Table 1 shows the results of a comparative test of adhesion and surface properties when enameled. The adhesion properties in Table 1 are based on the DIN51156 enamel adhesion test method. Results in Table 1

[Table] As is clearer, test materials No. 1 and 2 according to the present invention, in which a forsterite film was first coated on a steel plate and then enameled without any pretreatment, were not subjected to any pretreatment as described above. It was found that the adhesion was superior to that of the conventional sample material No. 3, which was then enameled. The adhesive according to the present invention also had particularly excellent adhesion, especially when the forsterite layer had a thickness of several micrometers, and the surface quality was very good with no microscopic flaws present at all. The forsterite film is conventionally formed on the surface of the steel sheet by a solid phase reaction during the secondary recrystallization annealing of a unidirectional silicon steel sheet containing 3 to 4% Si and the subsequent purification annealing process (2MgO,
It is a ceramic material called SiO ₂ ) and is known as a heat-resistant insulating coating that is dense, has excellent adhesion, and is uniform. That is, a unidirectional silicon steel material is heated at a high temperature to dissociate and solidify MnS, and then hot rolled to uniformly and finely disperse MnS precipitates. After that, intermediate annealing is performed and cold rolling is performed twice to obtain the final cold rolled sheet, followed by primary recrystallization annealing that also serves as decarburization in wet hydrogen to form subscales containing SiO ₂ on the steel sheet surface. After that, an annealing separator mainly composed of MgO is applied to the surface of the steel sheet and final annealing is performed (110).
It is manufactured through a series of steps in which secondary recrystallized grains in the [001] orientation are developed, harmful impurities are removed at the same time, and a forsterite-based insulating film is formed. Therefore, in order to form a forsterite film, it is essential to form subscales containing SiO ₂ on the surface of the steel sheet. For this purpose, a silicon steel plate is suitable as the enameled base steel plate, and it is also possible to use a grain-oriented silicon steel plate as the base steel plate of the present invention. However, unidirectional silicon steel sheets are extremely expensive due to limited material composition and various rigorous process treatments, and therefore are not suitable as base steel sheets for the present invention. Therefore, the present inventors investigated what composition of steel sheet is suitable for obtaining a forsterite coating with excellent adhesion equivalent to or better than that of unidirectional silicon steel sheet, and in particular, the relationship between the adhesion of the enamel coating and the Si content. We conducted a number of experiments regarding this relationship using the following materials. Steel ingot composition used: C: 0.003% Mn: 0.30% Si: 0.003 to 6.0% P: 0.015% S: 0.015% O: 0.0300% N: 0.0015% In other words, only Si was varied from 0.003% to 6.0%, and the other compositions were Each sample steel ingot with the same properties was hot-rolled into a 2.0mm thick hot-rolled steel plate, then cold-rolled by about 75% to make a 0.5mm-thick cold-rolled plate, and then heated in wet hydrogen at 850°C. Annealing was performed for 3 minutes. Then on the steel plate surface
After applying MgO annealing separator, in _N2 gas
Annealing was performed at 1150°C for 1 hour to form a forsterite film on the surface of the steel plate. The thickness of the forsterite coating was the same for each sample material, and enameling was performed on it under the same conditions to form an enamel coating. Adhesion of each sample material with different Si
When the relationship with the Si content was determined using the enamel adhesion test method according to DIN51156, the results shown in FIG. 1 were obtained. As is clear from Figure 1, the adhesion of the enamel film formed on the forsterite base film is closely related to the Si content in the steel plate used, and is excellent within the range of 1.0 to 4.5% Si. It shows adhesion, especially in the range of Si: 2 to 4%.
It shows strong adhesion of 6.5 to 7.2 kg. The reason why such an optimum value of Si content exists for adhesion is considered to be as follows. In other words, 1 which also serves as decarburization of the final cold-rolled silicon steel sheet in wet hydrogen at 800℃
During the next recrystallization annealing process, the amount of Si increases, which is closely related to the formation of subscales containing _SiO2 on the steel sheet surface.
If it is less than 1.0%, the amount of subscale produced containing SiO ₂ will be small, and if the amount of Si is more than 4.5%,
This is because the amount of subscales containing SiO ₂ becomes too large, and an appropriate forsterite film is not formed in the final annealing after applying an annealing separator mainly composed of MgO to the steel plate surface in the next process. it is conceivable that. Therefore, a silicon steel plate containing 1.0 to 4.5% Si is most suitable as the material to be used for the enamel product according to the present invention. Example 1

[Table] After hot-rolling a silicon steel material having 2.95% Si as shown in Table 2 to a thickness of 1.8mm, it is cold-rolled to approximately 70% to form a cold-rolled sheet of 0.5mm thickness. After that, 850
Annealing was performed for 3 minutes in wet hydrogen at .degree. After that, after applying MgO annealing separator to the steel plate surface, it was placed in Ar gas.
The steel plate was annealed for 1 hour at 1150°C to form a forsterite coating on the surface of the steel plate. Enameling was carried out on the steel plate having this forsterite base coating in a conventional manner. The enamel product thus obtained has a beautiful enamel surface with excellent surface gloss.
As a result of the enamel adhesion test according to DIN51156, the adhesion reached 7.2 kg, indicating excellent adhesion. Example 2

[Table] A silicon steel ingot with Si: 3.35% as shown in Table 3 was hot rolled and finished to a thickness of 2.4mm, and then cold rolled to a thickness of approximately 75% to form a cold rolled steel plate of 0.6mm thickness. After that, 800
Annealing was performed in wet hydrogen at ℃ for 5 minutes. Thereafter, a slurry of MgO annealing separator was applied to the surface of the steel sheet, and annealing was performed in N ₂ at 1200° C. for 30 minutes to form a forsterite film on the surface of the steel sheet. Enameling was performed on the steel plate having this forsterite undercoating in a conventional manner. The enamel product thus obtained had a beautiful enamel surface with excellent surface gloss, and the adhesion was 7.0 kg according to the enamel adhesion test method according to DIN51156, indicating excellent adhesion. As is clear from the above examples, the enameled steel plate according to the present invention has a forsterite base coating layer formed on a steel plate and an enameled layer formed on the forsterite coating, and is particularly suitable for use as a steel plate. A silicon steel plate containing Si: 1.0 to 4.5% is suitable, and has the following excellent effects. (a) Excellent adhesion of enamel coating, DIN51156
The adhesion according to the enamel adhesion test method is 5
It reaches ~7.2Kg. (b) The formed enamel surface has a beautiful enamel surface with excellent surface gloss. (c) There is no need for any pretreatment of the base steel plate before enameling, and there is no need to add adhesion-improving elements to the glaze as in the past. (d) It is of great value in the chemical industry because it can withstand harsh use with repeated heating and cooling.

[Brief explanation of the drawing]

FIG. 1 is a correlation diagram showing the relationship between the adhesion according to DIN51156 of the enamel product according to the present invention and the Si content in the base steel plate used, which was obtained from the experimental results for obtaining the present invention.

Claims (1)

[Claims] 1. Enamel comprising a forsterite (2MgO, SiO ₂ ) coating layer coated on a steel plate and an enamel layer coated on the forsterite coating layer. steel plate. 2. The enameled steel plate according to claim 1, wherein the steel plate is a silicon steel plate containing 1.0 to 4.5% by weight of Si.