JPS6283473A - Formation of glass film on grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To form a glass film having fine appearance and high adhesion on a grain-oriented silicon steel sheet by coating the steel sheet with MgO suspended in water as a protective coating material for annealing, removing water of hydration from hydrated MgO by heating in a nonoxidizing atmosphere and carrying out finish annealing. CONSTITUTION:A grain-oriented silicon steel sheet having scale contg. SiO2 formed on the surface by decarburization annealing is coated with a protective coating material for annealing contg. MgO suspended in water as the principal component. The steel sheet is passed through a nonoxidizing atmosphere, where it is dried by heating to remove nearly completely water from the slurry on the steel sheet and water of hydration from Mg(OH)2 formed by the hydration of MgO. The steel sheet is then coiled at one and subjected to final finish annealing. By this method, a glass film having a uniform color tone, superior adhesion and superior magnetic characteristics can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming a glass film on a grain-oriented silicon steel sheet, and more particularly, to a method for forming a glass film with excellent film properties such as appearance and adhesion.

[Conventional technology]

A method of forming a glass film on a grain-oriented silicon steel sheet is to cold-roll a hot-rolled steel sheet to a desired thickness, and then decarburize it in a humid atmosphere at a temperature range of 700 to 900°C, for example, to coat the surface of the steel sheet. Subscale containing 5iO7 is generated, and then a slurry prepared by dissolving an annealing separator mainly composed of MgO in water is applied to the surface of the steel plate on which subscale has been formed, and the steel sheet is wound into a coil to perform high-temperature finish annealing. A method of forming a glass film (commonly known as a forsterite film) by doing this is conventionally known. Generally, annealing separators mainly contain MgO, which is suspended in water and applied to the steel plate in the form of a slurry. 011) to z(
It changes as shown in equation 11.

MgO+lI20→ Mg (OH) z i
l) The magnesium hydroxide is treated with M during high-temperature annealing.
g (O) I) z → MgO + H □0 (2) Thermal decomposition occurs, gradually releasing water, excessively oxidizing the steel plate, degrading the magnetic properties of the product, and forming on the surface of the steel plate. It has the disadvantage of causing unevenness in the glass coating.

As a method for preventing such drawbacks associated with the decomposition of magnesium hydroxide, there is a method using a molten metal as shown in U.S. Pat. No. 2,796,364, and a method of using
In order to suppress the hydration reaction of MgO, a method has been proposed in which MgO fired at a relatively high temperature is suspended in low-temperature water and applied to the surface of a steel sheet.

[Problem that the invention seeks to solve]

None of these methods can sufficiently improve the defects caused by the decomposition of magnesium hydroxide, and there is still room for investigation in order to form a better glass film.

The present inventors have discovered that during high-temperature finishing annealing, hydrated magnesium hydroxide thermally decomposes and releases moisture, preventing excessive oxidation of the grain-oriented silicon steel sheet and creating a glass with good appearance and adhesion. We conducted experiments and studies to produce a grain-oriented silicon steel sheet that can form a film and also have good magnetic properties. As a result, after applying an annealing separator containing MgO as a main component dissolved in water to a isotropic silicon steel sheet that had been decarburized and annealed and had subscales containing SiO□ formed on the surface of the steel sheet, a plate-like The sheet is threaded and heated and dried in a non-oxidizing atmosphere to almost completely remove the moisture in the annealing separator on the grain-oriented silicon steel sheet and the hydration water of the hydrated magnesium, then it is wound into a coil and subjected to high-temperature finish annealing. It was discovered that a good glass film was formed by doing so.

[Failure to solve the problem]

The present invention has been made based on this knowledge, and will be explained in detail below.

The manufacturing conditions up to decarburization annealing include hot rolling a silicon steel slab and annealing it once or twice or more with intermediate annealing in between.
- Any material that is decarburized and annealed to a predetermined final thickness by cold rolling may be used. The grain-oriented silicon steel sheet is decarburized by this decarburization annealing, and subscales including 5 in 2 are formed on the surface of the steel sheet. next? An annealing separator containing 1 gQ as a main component is suspended in water to form a slurry, and the slurry is applied onto the above-mentioned steel plate using a coating means such as a roll coater.

Next, the silicon steel sheet is passed in the form of a plate in a drying oven and heated to a temperature of about 500°C in a non-oxidizing atmosphere such as N2, N2, A-, or a mixed atmosphere of these.
The moisture from the slurry on the steel plate and the water of hydration in the hydrated magnesium hydroxide are almost completely removed. Heating devices for removing crystal water include induction heating, resistance heating 1 current heating, far infrared heating, microwave heating, etc.
Either device may be used. However, on a line with many repeated bends, the annealing separator may peel off, so collodyl particles of SiO□, for example, may be added as a thickener to the suspension of the annealing separator whose main component is MgO. good. The solid matter on the steel plate after removing crystallization water is 6 to Log.
/♂ (one side). Next, the dry-treated grain-oriented silicon steel sheet is immediately wound into a coil, and the coil is subjected to final finish annealing.

In the conventional method, when the temperature of the steel plate reaches 350 to 450°C during final finish annealing, magnesium hydroxide, which is the main component of the annealing separator coated on the steel plate and partially hydrated, thermally decomposes. However, moisture is released and the grain-oriented silicon steel sheet is excessively oxidized, and at the same time, as the moisture is removed, a ventilation conductive portion is formed in the annealing separator applied to the steel sheet. Through this ventilation conduction section, the reducing atmospheric gas around the coil can freely diffuse and permeate between the laminated plates of the coil, and the iron oxide produced together with 5iOz during decarburization annealing becomes FeO+N.
2→Fe→-1 (as seen in 20, it was reduced and was one of the causes of film defects.However, in the present invention, drying that was heated to a predetermined temperature in a non-oxidizing atmosphere before high-temperature finish annealing) Since the plate is passed through the furnace to remove hydration water, there is no release of moisture due to thermal decomposition of hydrated magnesium hydroxide during high-temperature finish annealing, and the grain-oriented silicon steel sheet is not only protected from oxidation. Since there is no formation of a gas ventilation conduction section that accompanies water release, external reducing atmospheric gas does not diffuse into and enter between the laminated plates of the coil, and the above-mentioned iron oxide is not reduced.

In this final annealing process, when the steel plate temperature reaches 900 to 110 (1'C), the subscale mainly composed of Sing formed on the steel plate surface reacts with the above-mentioned annealing separator to form a glass film. The obtained glass film was different from that obtained by conventional methods, in that the color tone was uniform and the film adhesion was poor.The magnetic properties were also uneven.

〔Example〕

Next, examples of the present invention will be described.

Si3.2%, 30.02%, Mn0.07%, A
A slab of grain-oriented silicon steel sheet containing 11.028% and 0.009% NO was hot-rolled to a thickness of 311 mm, hot-rolled at 1120°C for 3 minutes, and then cold-rolled to form the final sheet. The thickness was set to 0.311. Then at 850℃ for 3 minutes with a dew point of 60℃
The grain-oriented silicon steel sheet was continuously annealed in an atmosphere of 70% Hz, and water was added to and suspended in an annealing separator containing MgO as a main component to form a slurry, which was coated using a roll coater. Next, the steel plate coated with the annealing separator was passed through a drying oven in a mixed atmosphere of N2 and N2, and the steel plate temperature reached 500.
The temperature is raised to ℃ to almost completely remove the water of hydration from the hydrated magnesium hydroxide.

The completely dried grain-oriented silicon steel sheet was immediately wound into a coil and placed in a high-temperature finishing annealing furnace for the next step, where it was annealed at 1150°C. The properties of the steel plate after annealing were investigated and the properties shown in Table 1 were obtained.

Table-1 Characteristics of grain-oriented silicon steel sheet Note) Adhesion: Bending diameter that does not peel off after 180° bending Film defect: A sparkling metallic luster is present in areas where there is no forsterite film in the form of spots.

Claims (1)

[Claims] 1. A grain-oriented silicon steel plate was cold rolled to a predetermined thickness, decarburized and annealed to form a subscale containing SiO_2 on the surface of the steel plate, and an annealing separator containing magnesia oxide as the main component was applied onto the scale. Later, in the method of forming a final annealed glass film, an annealing separator containing magnesia oxide as a main component is suspended in water and applied onto a grain-oriented silicon steel sheet, and then the steel sheet is passed through in the form of a plate and non-woven. Heating and drying in an oxidizing atmosphere,
A method for forming a glass film on a grain-oriented silicon steel sheet, characterized in that hydration water in hydrated magnesia hydroxide is almost completely removed in a strip state before final annealing.