JPH02243770A - Production of grain-oriented silicon steel sheet having small iron loss - Google Patents

Abstract

PURPOSE:To industrially produce a grain-oriented silicon steel sheet having a very small iron loss by forming an oxide coating film by a sol-gel process on the surface of a grain-oriented silicon steel sheet after finish annealing. CONSTITUTION:A silicon steel sheet is finish-annealed to grow secondary recrystallized grains and an oxide coating film is directly formed by a sol-gel process on a forsterite coating film formed on the surface of the steel sheet. The oxide coating film may be formed by the sol-gel process on the base iron exposed to the surface of the steel sheet and smoothened. A grain-oriented silicon steel sheet having a small iron loss can be produced at a low cost with high productivity. When a sol of alkoxide of a metal having a lower coefft. of thermal expansion than the steel, e.g., Si, Al, Zr or Ti or a sol of spodumene (Li2O-Al2O3-SiO2 mixture) having a negative coefft. of thermal expansion is used, the formed oxide coating film has a remarkable iron loss reducing effect.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a grain-oriented silicon steel sheet having an extremely low core loss value.

(Prior Art) Unidirectional silicon steel sheets are often used as magnetic iron cores, and are required to reduce iron loss in order to reduce energy loss. Therefore, as a means to reduce iron loss in unidirectional silicon steel sheets, a laser beam is irradiated onto the material surface after final annealing to give local strain, thereby subdividing the magnetic domains and reducing iron loss. A method is disclosed, for example, in Japanese Patent Application Laid-Open No. 58-26405. Furthermore, as a magnetic domain refining means in which the magnetic domain refining effect does not disappear even if a unidirectional silicon steel plate is processed into an iron core and then subjected to stress relief annealing, it is disclosed in, for example, JP-A-62-86175. There is a way it has been done. These technical measures can reduce the iron loss value of unidirectional silicon steel sheets, but when attempting to further reduce the iron loss value, it is necessary to remove the glass film that exists on the material surface after final annealing. However, it is important to remove irregularities on the surface of the steel plate that inhibit the movement of magnetic domains near the surface of the steel plate. As a means for this purpose, there is a method of mirror-finishing the bare surface of the material after finish annealing, or applying metal plating to the mirror-finished material surface. Furthermore, Japanese Patent Publication No. 52-24499 proposes a method of obtaining an ultra-low core loss unidirectional silicon steel plate by applying and baking an insulating film on the surface of the mirror-finished and metal-plated material. Furthermore, for example, in Japanese Patent Application Laid-Open No. 6i201732, a unidirectional silicon steel plate finished in a mirror-like state with an average surface roughness of 0.4 μm or less is heated for 500 minutes in an atmosphere consisting of a Ti-containing gas and a non-oxidizing gas. Heat treated in the temperature range of ~1000°C and TiN on the surface.

A method is disclosed in which a unidirectional silicon steel sheet with a low core loss value is obtained by forming an ultra-thin tensile film made of TiC, Ti (C, N) and further covering with an insulating film.

(Problem to be solved by the invention) The base surface of the unidirectional silicon steel plate is mirror-finished, CVD,
Recently, many proposals have been made to form a film by means such as PVD or ion blating. Although these methods are recognized to be effective to some extent, 10
It requires a vacuum of -5 Torr or less and takes a long time to form a thick film, resulting in extremely low productivity and high cost.

The present invention has been made with the object of solving these problems in the prior art and providing a manufacturing process that can industrially produce unidirectional silicon steel sheets with extremely low iron loss values at low cost.

(Means for solving problems) The gist of the present invention is as follows.

(1) A method for producing a low core loss unidirectional silicon steel sheet, which comprises forming an oxide film on the surface of the unidirectional silicon steel sheet after final annealing by a sol-gel method.

(2) A method for producing a low core loss unidirectional silicon steel sheet, which comprises forming an oxide film on the metal (substrate) surface of the unidirectional silicon steel sheet after final annealing by a sol-gel method.

The present invention will be explained in detail below.

In order to solve the problems in the prior art described above, the inventors focused on forming an oxide film on the surface of a unidirectional silicon steel plate by a sol-gel method.

The inventors repeated various experiments to form a high-tension film with few defects and good adhesion on the surface of a silicon steel plate using the sol-gel method.
．． It has been found that by repeating drying and coating at about 500°C with a thickness of 5 μm or less, it is possible to form a defect-free and good oxide film with a thickness of 11 m or more on the surface of a silicon steel sheet. - If the coating is applied to a thickness exceeding 0.5 μm, the coating will crack due to shrinkage and will not be a good coating. The oxide film formed on the surface of the silicon steel sheet in this way is
It can withstand high temperatures of around 1000°C, and can withstand stress relief annealing after processing silicon steel plates into transformers and the like.

The inventors' method of forming an oxide film using the sol-gel method is as follows:
The glass film on the surface of the material after final annealing is removed to expose the surface of the base metal, and it can be applied to form an oxide film on the surface of the base metal to make it smooth. Also,
When this oxide film forming means is applied to a conventional glass film-coated finish annealed material, it is possible to obtain an iron loss value lower than that of a product formed with a conventional phosphoric acid tension film, depending on the type of sol. Of course, it is possible to apply magnetic domain control technology to the product thus obtained to further reduce the iron loss value.

The present invention will be explained in more detail below.

A steel slab containing 4 ivt% or less of Si is heated and hot rolled into a hot rolled sheet, annealed at this stage if necessary, and then annealed once or twice with intermediate annealing. After cold rolling to the final thickness, decarburizing annealing and applying an annealing separator to form a strip coil, followed by finishing annealing at high temperature for a long period of time to create a secondary recycle with (110) <001> orientation. An oxide film is formed directly on the forsterite film formed on the surface of a steel sheet with developed crystal grains by a sol-gel method, or the forsterite film is removed by chemical or mechanical means. Alternatively, the base iron on the surface of the steel plate after finish annealing is exposed by using a material that does not form a forsterite film, such as alumina, as the annealing separator, and immersing it in a solution containing hydrofluoric acid and hydrogen peroxide, or by electrolytic polishing. After smoothing the surface of the base metal, an oxide film is formed using the sol-gel method.

Figure 1 shows how Si alkoxide is applied to the surface of a silicon steel sheet metal (substrate) to a thickness of approximately 3 μm by varying the amount of Sing applied per time and heating to 500°C after each application. This figure shows what happens when a thin film is formed.

As is clear from Figure 1, the coating thickness per coat was 0.
If it exceeds 5μ, the film cracks due to shrinkage, and as a result, a good film cannot be formed.

Figure 2 shows the film adhesion (
The results are shown below. As is clear from FIG. 2, by reducing the coating thickness per coating, the adhesion of the oxide film is significantly improved.

Next, the sol used in the sol-gel method of the present invention will be explained.

The sol used in the sol-gel method in the present invention is Si, AI, ZrTi, which has a smaller coefficient of thermal expansion than the substrate (substrate).
When using not only metal alkoxides such as, but also sol of spodumene system (mixed system of 1-+zO+ Al2O:II SiO□) which has a negative coefficient of thermal expansion (thermal contraction occurs as temperature rises), this phenomenon is extremely noticeable. The effect of reducing iron loss was observed.

Single-component sols (sols of St, Tt, /1+j, Zr, etc.) and multi-component sols (multi-component mixed sols such as the above-mentioned spodumene) are produced by removing the forsterite film on the silicon steel plate to expose the base steel. This multi-component sol, which has a negative thermal expansion coefficient, is effective when applied to a material with a smooth surface, but when applied to a material with a forsterite film, it is more effective than the conventional phosphoric acid-based sol. It was found that greater tension can be obtained than with a tension coating, and the iron loss value of the product is improved (decreased) by about 6%.

(Example) Example I A high magnetic flux density unidirectional silicon steel plate containing 3.3 wt% Si and having a thickness of 0.2 mm after final annealing was immersed in a mixed solution of sulfuric acid and hydrofluoric acid. After removing the forsterite film on the surface to expose the steel base, the surface of the steel base was smoothed into a mirror-like finish in a solution containing hydrofluoric acid and hydrogen peroxide.

After that, the amount of ethyl silicate applied per time was 0.4 μm.
A silica film was formed on the front and back surfaces of the silicon steel plate by applying and baking four times, repeating baking at 500° C. for 30 seconds for each coating.

After the silica film was formed, baking was performed at 750° CXI minutes in order to improve film adhesion.

The iron loss values of the products thus obtained are shown in Table 1 in comparison with those obtained by the conventional method.

First: The iron surface is smoothed and finished to a mirror finish. After that, eucryptite (LiO□-IVz (ternary system of L+-5iO2)
Immersed in a solution consisting of sol, and the amount applied per time is 0.
．． Coating and baking were repeated five times to obtain a thickness of 2 μm. Baking for each application was performed at 400° C. for 30 seconds. After film formation, further heat treatment at 800°C x 5
I baked it for a minute. The iron loss values of the products thus obtained are shown in Table 2 in comparison with those obtained by the conventional method.

Table 2 As shown, when the present invention is used, the iron loss value is significantly improved compared to when the conventional technology is used.

Example 2 A silicon steel plate containing 3.2 wt% Si and having a thickness of 0.2 mm was decarburized and annealed, then alumina was applied as an annealing separator and finish annealing was performed to create a high magnetic flux density unidirectional film with no forsterite film. It was made of silicon steel sheet. This finish annealed material is
As described above, the present invention results in a product having significantly lower core loss values than the prior art.

Example 3 St: Plate thickness containing 3.2wtχ: 0.175m
Spodumene (LiO□-A
The amount of 12O3SiO□)-based sol applied per coat is 0.3 I! on a smooth surface. The coating was applied to a thickness equivalent to m, and the coating and baking were performed four times, with a baking treatment of 500°CXI minutes interposed between each coating. After film formation, further 8
00''CX 4 minute baking process was performed.

The iron loss values of the products thus obtained are shown in Table 3 in comparison with those obtained by the conventional method.

Table 3 shows that by using the spodumene-based sol, even higher tension can be applied than with the conventional phosphoric acid-based tension coating, and as a result, the iron loss of the product is significantly improved (decreased).

(Effects of the Invention) The present invention reduces the iron loss of book products by forming an oxide film by a sol-gel method on the base iron surface of a silicon steel plate after finish annealing or on the surface with a forsterite film. According to the present invention, it is possible to significantly reduce iron loss at a lower cost and with higher productivity than when using conventional film formation technology, and its industrial effects are extremely large. be.

[Brief explanation of drawings]

Figure 1 shows the results when a film with a thickness of approximately 3 pm was formed on the surface of a silicon steel sheet metal (substrate) by varying the amount of 5iOz applied per application and repeating heating to 500°C after each application. Figure 2 shows the state of the film. The same sample as in Figure 1 is wound around a 20++ nnφ round rod and rotated 180°.
It is a figure which shows the result of investigating film adhesion by a bending test. Everyone ￥a＠-

Claims (2)

[Claims] (1) A method for producing a low core loss unidirectional silicon steel sheet, which comprises forming an oxide film on the surface of the unidirectional silicon steel sheet after final annealing by a sol-gel method. (2) A method for producing a low core loss unidirectional silicon steel sheet, which comprises forming an oxide film on the metal (substrate) surface of the unidirectional silicon steel sheet after final annealing by a sol-gel method.