JPS624881A - Formation of glass film of grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To form a glass film having fine appearance and superior adhesion on a grain-oriented silicon steel sheet by adding silicon nitride to an MgO-base protective coating material for annealing, applying the coating material to the steel sheet having sub-scale contg. SiO2 formed on the surface by decarburization annealing and subjecting the steel sheet to finish annealing. CONSTITUTION:A grain-oriented silicon steel sheet is cold rolled to a prescribed thickness and subjected to decarburization annealing to form sub-scale contg. SiO2 on the surface of the steel sheet. Silicon nitride is added to a magnesium oxide-base protective coating material for annealing, the coating material is applied to the subscale and the steel sheet is subjected to finish annealing at 900-1,100 deg.C to form a forsterite-base glass film.

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.

(Prior art) As a method for forming a glass film on a grain-oriented silicon steel sheet, the sheet is cold-rolled to a desired thickness and then rolled to a temperature of, for example, 700 to
Decarburized in a temperature range of 900℃, the surface of the steel plate K 5I
Subscale containing O2'e is generated, and then an annealing separator mainly composed of MgO is dissolved in water to form a slurry, applied to the surface of the steel plate on which subscale has been formed, and wound into a coil to heat the slurry at high temperature. A method is known in which a diglas film (also referred to as a forsterite film) is formed by final annealing. Generally, the annealing separator is mainly M
MgO, which is the main component of gO'i, is suspended in water and applied to a steel plate in the form of a slurry, but the coating film shows sufficient adhesion to prevent peeling when dry. is produced and changes to magnesium hydroxide as shown in the following formula (1).

MgO+ H20→Mg(OH)2... (1) Then, the magnesium hydroxide undergoes the following (2) during high-temperature finish annealing.
A thermal decomposition reaction as shown in formula % (2) occurs, gradually releasing moisture, excessively oxidizing the steel plate, deteriorating its magnetic properties, and causing unevenness in the glass film formed on the surface of the steel plate. There are drawbacks.

Conventionally, various methods for forming glass films have been proposed. For example, JP-A No. 55-58331 uses an annealing separator mainly composed of low-activity MgO, and JP-A No. 56-75577 uses S.

It has been proposed to use an annealing separator to which an S compound, Sr, or Sr compound is added. JP-A-58-9985 proposes to use an annealing separator to which sulfuric acid and sulfate are added to non-hydrated Mgo.

(Problems to be Solved by the Invention) All of these have their own effects, but the improvement of the defects caused by the decomposition of magnesium hydroxide is not yet sufficient and there is still room for further investigation. In high-temperature finish annealing, a reducing gas containing hydrogen gas is used to prevent oxidation of the coil at high temperatures or to remove impurities from the steel sheet. This reducing gas penetrates and diffuses between the laminated layers of the coil during high-temperature finishing annealing, reduces iron oxide (fayalite) produced together with 810□ during decarburization annealing, and becomes one of the causes of glass film defects.

The present inventors have discovered that hydrated magnesium hydroxide during high-temperature finish annealing thermally decomposes, releases moisture, and excessively oxidizes grain-oriented silicon steel sheets, and that iron oxide produced during decarburization annealing is caused by reducing gas. Experiments and studies were conducted in order to simultaneously resolve defects in the glass coating caused by reduction of silica, to form a glass coating with good appearance and adhesion, and to produce a grain-oriented silicon steel sheet with good magnetic properties. As a result, silicon nitride was added to an annealing separator mainly composed of MgOl, and this was applied to a grain-oriented silicon steel sheet that had been decarburized and annealed to form subscales containing 5i02ft on the surface of the steel sheet. It was found that a glass film was formed.

(Means for Solving the Problems) The present invention has been made based on this knowledge, and will be explained in detail below.

The method of the present invention is widely applied to the formation of a glass film on grain-oriented silicon steel sheets, and includes the steel composition of grain-oriented silicon steel sheets, which is cold-rolled to a predetermined thickness, and then decarburized and annealed.
There is no need to specify the manufacturing conditions until the annealing separator is applied.For example, the starting steel component is AtN as an inhibitor to prevent secondary recrystallization from occurring during finish annealing.
, MnS.

It is prepared so that Mn5s, BN, etc. are produced, and Cu, Sn, Cr, Ni,
It contains elements such as Mo, Sb, and P. As for manufacturing conditions, for example, a slab is hot rolled, annealed and cold rolled once or twice or more with intermediate annealing ft to a predetermined final thickness, and then decarburized and annealed.

The grain-oriented silicon steel sheet is decarburized by this decarburization annealing, and a subscale (oxide layer) containing 5iO7 is formed on the surface of the steel sheet. Next, according to the present invention, silicon nitride, such as 513N4, is added to an annealing separator mainly composed of MgO, and water is suspended to form a slurry.
etc., to coat the steel plate. The silicon nitride added to the annealing separator is in the form of fine powder, and the amount added does not necessarily have to be specified, but it is 2 to 1 part by weight per 100 parts by weight of Mg0.
5 parts by weight is preferred.

Next, water is removed from the slurry on the steel plate by raising the temperature of the steel plate to, for example, about 150° C. in a drying oven. The solid matter on the steel plate after moisture removal is approximately 5 to 1497
m2 (one side). However, in this temperature range, the water of crystallization of magnesium hydroxide in which MgO is hydrated is not removed.

After drying, the steel plate is immediately wound into a coil, and final annealing is performed in the coil. When the steel plate temperature reaches 350 to 450° C. in final finish annealing, magnesium hydroxide is thermally decomposed and releases moisture, as shown in equation (2) above. This thermal decomposition is at the steel plate temperature.

The process is completed when the temperature reaches about 500°C.

On the other hand, 513N4 has the property of starting to decompose even at a low temperature of 200°C in a non-oxidizing atmosphere where moisture is present, so the moisture released by magnesium hydroxide can be removed by S
It is inferred that the reaction 3) proceeds as l3N4 is absorbed.

SiN+6HO→3810+4NH,・・・・・・
・(3) Due to the action of the added 513N4, as mentioned above, the moisture released as a result of the thermal separation by the hydrated magnesium hydroxide of MgO is removed. Moisture generated inside the coil diffuses into the coil esso, which is heated to a higher temperature than the inside, significantly oxidizes the steel plate, and does not cause defects in the glass coating on the surface of the steel plate, which deteriorates magnetic properties.

In addition, as a result of the 513N4 separation, SlO□ is supplied to the steel plate from the outside, so it protects the subscale mainly composed of SiO2 formed on the surface of the steel plate during decarburization annealing, and creates a reducing atmosphere. In the final annealing process below, the subscale is maintained at high temperatures without being reduced. These subscales on the surface of the steel sheet react with the above-mentioned annealing separator at a steel sheet temperature of 900 to 1100 DEG C. during the final annealing process of the coiled steel sheet to form a glass film containing forsteritetra as a main component.

Unlike those obtained by conventional methods, the glass coating obtained according to the present invention not only has a uniform color tone and a beautiful appearance, but also has excellent coating adhesion and magnetic properties.

(Example) Next, examples of the present invention will be described.

Si 3.2%, 80.02%, Mn 0.07%,
A silicon steel slab containing A40,028CH, NO,009% was hot rolled to a thickness of 3cm, hot-rolled at 1120°C for 3 minutes, and then cold rolled to a final thickness of 0°. It was set as 3■. Next, after continuous annealing at 850°C for 3 minutes in a gas atmosphere with a dew point of 60°C and 70% H2, water was added to the annealing separator containing 5 parts by weight of 5113N4 per 100 parts by weight of Mg0 to this grain-oriented silicon steel sheet. The slurry was suspended and coated with a roll coater, and then heated in a drying oven until the steel sheet temperature reached 150° C. to remove moisture, and then wound into a coil. Next, the coil was placed in a high-temperature finishing annealing furnace and annealed at 1150°C.

The properties of the steel plate after annealing were investigated, and the properties shown in Table 1 were obtained.

(Effects of the Invention) According to the present invention, it is possible to produce a grain-oriented silicon steel sheet having a glass film having excellent appearance and adhesion and having excellent magnetic properties, which is extremely useful industrially.

Claims (1)

[Claims] Grain-oriented silicon steel was cold rolled to a predetermined thickness, then decarburized and annealed to form a subscale containing SiO_2 on the steel plate surface, and an annealing separator containing magnesium oxide as the main component was applied onto the subscale. A method for forming a glass film on a grain-oriented silicon steel sheet, characterized in that, in the method of forming a glass film after finishing annealing, an annealing separator whose main component is magnesium oxide to which silicon nitride is added is used.