JPH02107722A - Production of grain-oriented electrical steel easy to punch and having metallic luster - Google Patents

Abstract

PURPOSE:To stably obtain the title electrical steel sheet by removing an oxide film contg. SiO2 on the surface of a decarburization-annealed steel sheet, then applying a annealing and separation agent, and finish-annealing the steel sheet. CONSTITUTION:The grain-oriented steel sheet cold-rolled to final thickness is decarburization-annealed, coated with an annealing and separation agent, an then finish-annealed to produce a grain-oriented electrical steel sheet. In this case, an oxide film contg. SiO2 is formed on the steel sheet surface by the decarburization annealing. Accordingly, the oxide film is removed by pickling, chemical polishing, electrolytic polishing, etc. An annealing and separation agent is then applied on the steel sheet, and the steel sheet is finish-annealed. Since the oxide film contg. SiO2 on the steel sheet surface is removed in this case, the effect of each process condition on the oxide film formation such as delicate variations in the decarburization annealing is eliminated, hence a glass coating film is not formed on the steel sheet, and a steel sheet having metallic luster is stably obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing grain-oriented electrical steel sheets with excellent punchability and metallic luster.

(Prior Art) A directional electric E'tl tA plate is generally manufactured as follows. A magnetic steel slab containing 4.0% or less of Si is hot-rolled, and after being hot-rolled or annealed, cold-rolled once or twice or more with intermediate annealing in between to obtain the final thickness. Then, decarburization annealing is performed to generate an oxide film containing SiO In addition to developing secondary recrystallized grains with Goss orientation, the 5i
A glass film is formed by the reaction between 02 and MgO. Then, if necessary, an insulating coating liquid is applied and a baking heat treatment is performed to form an insulating coating film.

Grain-oriented electrical steel sheets are used as core materials for electrical equipment such as generators and transformers. The core is usually manufactured by stacking a large number of core single plates that are punched out using a die or cut into a predetermined shape by shearing. For example, manufacturing the core of a turbine generator requires 100,000 to 200,000 core veneers, depending on its capacity.

These iron core veneers have a small punching return, for example 30 μm.
It is important that the thickness be less than m in order to prevent an abnormal increase in iron loss due to a short circuit at the end face of the iron core when the core veneers are laminated. In addition, it is desired that the punching return be small in order to facilitate the manufacturing process of the core.

A grain-oriented electrical steel sheet is provided with a glass coating or a double insulation coating consisting of the glass coating and an insulating coating. These insulating coatings have the effect of applying tension to 1[Ji and reducing iron loss, but on the other hand, since glass coatings are hard, they cause abrasion of the mold during punching. For this reason, for example, when punching is performed several thousand times, punching returns exceeding a predetermined value may occur.
The mold must be reground or replaced with a new one. This significantly reduces workability and increases costs.

In order to improve punchability, a method for producing grain-oriented electrical steel sheets has been proposed that suppresses the formation of glass coatings. For example, in Japanese Patent Application Laid-Open No. 53-22113, the thickness of the oxide film on the surface of the electromagnetic saw plate formed by decarburization annealing is set to 3 μm or less, fine-particle alumina mixed with hydrated silicate mineral powder is used as an annealing separator, and finish annealing is performed. are doing. In this way, an easily peelable glass coating is formed on the steel plate by the thin oxide film and the annealing separator mainly composed of alumina, thereby improving the punching property.

Furthermore, in JP-A No. 59-96278, fine particle alumina with a particle size of 10 μm or less and 13
By using inert MgO fired at a high temperature of 00°C or higher, the reaction with the oxide film on the surface of the steel plate is suppressed to prevent the formation of a glass film or make it easy to peel off, thereby improving punching properties.

(Problems to be Solved by the Invention) These methods have certain effects, suppress the formation of a glass film on the surface of grain-oriented electrical steel sheets, and improve punchability.

However, an oxide film is inevitably formed on the surface of the Si-containing directional external electric current f (f 1m plate) during decarburization annealing performed in a humid atmosphere to remove carbon, and the oxide film naturally contains SiO This 5i02 reacts with the annealing separator MgO to form a glass film, but in decarburization annealing, glass film is formed on the steel sheet surface due to subtle differences in the atmosphere and temperature deviation at the position in the furnace. During oxidation, differences in thickness and composition occur depending on the location of the steel plate.

Under the influence of such differences in the thickness and composition of the oxide film, there may be local differences in the suppression of the formation of the glass film or in the releasability, and the punching performance may not necessarily be good.

The object of the present invention is to stably obtain a grain-oriented electrical steel sheet with excellent punchability, regardless of subtle differences in conditions such as decarburization annealing atmosphere.

(Means for Solving the Problems) The gist of the present invention is to decarburize a grain-oriented electrical steel sheet that has been cold-rolled to the final thickness, apply an annealing separator, and finish annealing the grain-oriented electrical steel sheet. In the manufacturing method, after decarburization annealing, an oxide film containing SiO2 on the surface of the steel sheet generated by the decarburization annealing is removed, and then an annealing separator is applied and finish annealing is performed. The present invention provides a method for producing a grain-oriented electrical steel sheet having a metallic luster.

Next, the present invention will be explained in detail.

In the present invention, the steel composition and decarburization annealing are not particularly required and can be done arbitrarily. Decarburization annealing is carried out at 700 to 1000'C in a humid atmosphere such as lh, II□mon N2 gas, etc. to raise the dew point so as to sufficiently remove carbon in the steel sheet. In the decarburization annealing, an oxide film containing SiO□ is formed on the surface of the steel sheet.

In the present invention, after decarburization annealing, the oxide film on the surface of the steel sheet is removed by pickling, chemical polishing, electrolytic polishing, or the like. for example,
Pickling is performed with a solution containing one or both of sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid, and the oxide film containing SiO2 is removed from the steel plate surface to form a metal surface.

After removing the oxide film and prior to final annealing, an annealing separator is applied.
Sulfides, polysulfides, hydroxides, chlorides, nitrates, phosphates of alkaline earth metals such as Ba, Mg, Sr, etc.
One or a combination of two or more carbonates, or low hydration magnesia is used.

After applying an annealing separator to the steel plate, finish annealing is performed. At this time, the oxide film containing SiO□ on the surface of the steel sheet is removed, so
The influence of various process conditions that affect oxide film formation, such as subtle variations in decarburization annealing conditions, is eliminated, no glass coating is formed on the steel sheet, and steel sheets with a metallic luster can be stably obtained.

When performing flattening annealing after final annealing, inorganic coating agents such as phosphoric acid, phosphates such as aluminum phosphate, and magnesium phosphate, chromic acid such as chromic acid, aluminum chromate, and magnesium chromate are applied to the surface of the metallic gloss steel sheet. Flattening annealing may be performed by applying one or more of salt, dichromate, and colloidal silica.

In addition, organic coating agents such as acrylic, styrene, polyvinyl, melamine, phenol, vinyl acetate, epoxy coating agents, etc., or mixtures of organic coating agents and inorganic coating agents,
Semi-organic coating agents can also be used. In either case, the punching properties are even better.

Next, examples will be described.

<Example 1> c, o, oso%, St; 3.13%, Mn;
A grain-oriented electrical steel sheet material containing 0.062%, S, and 0.024%, with the remainder consisting of Fe and unavoidable impurities, was hot rolled to a thickness of 2.3 mm. Next, cold rolling was performed twice with intermediate annealing at 980°C for 13 minutes to achieve a final thickness of 0.
．． It was made into a 35 mm cold rolled sheet. Next, decarburization annealing was performed in a humid atmosphere of N2+H2. 10% of this steel plate by weight
After pickling with 11□SO4 solution (80°C) to remove the oxide film generated during decarburization annealing, MgO was applied as an annealing separation agent, and final finish annealing was performed at 1200°C for 20 hours. After this, in continuous heat flattening, a coating based on phosphate + colloidal silica was applied and baked at a rate of 2 g/n (weight after baking).

Table 1 also shows the results of investigating the appearance, punchability, and magnetic properties of the obtained steel plate.

<Example 2> A 0.35 mm O decarburized annealed plate obtained in the same manner as in Example 1 was used as a test material. This decarburized annealed plate was treated with H2SO,
After pickling in a mixed acid solution to remove the oxide film generated during decarburization annealing, annealing separators with different hydration moisture levels as shown in Table 2 were applied, and final finish annealing was performed at 1200°CX20+. Ta. Thereafter, in continuous heat flantoning, a phosphate + colloidal silica coating solution was applied and baked at a rate of 2.5 g/n (weight after baking).

Table 2 also shows the results of investigating the appearance, punchability, and magnetic properties of the obtained steel plate.

(Effects of the Invention) As described above, according to the present invention, a grain-oriented electrical steel sheet that does not form a glass film, exhibits metallic luster over the entire surface, and has excellent punchability can be produced in a decarburizing annealing atmosphere, dew point, etc. It can be obtained without being affected by slight fluctuations in conditions.

Claims (1)

[Claims] In a method for manufacturing a grain-oriented electrical steel sheet, in which a grain-oriented electrical steel sheet cold-rolled to the final thickness is decarburized, an annealing separator is applied, and finish annealed.
1. A method for producing a grain-oriented electrical steel sheet having a metallic luster and excellent punchability, the method comprising: removing an oxide film containing an oxide film, then applying an annealing separator and final annealing.