JPH03294466A - 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 very small iron loss at a low cost by plating the matrix iron surface of a finish annealed grain-oriented silicon steel sheet with a metal and forming an oxide film by low pressure plasma spraying. CONSTITUTION:The matrix iron surface of a finish-annealed grain-oriented silicon steel sheet contg. about <=4wt.% Si is plated with a metal. This matrix iron surface is formed by chemically or mechanically removing a forsterite film formed by annealing so that the matrix iron in the surface of the steel sheet is exposed. By the metal plating, a plating layer of Zn, Sn, Cu or Ni is preferably formed in about >=1mum thickness. An oxide film is formed on the plating layer by low pressure plasma spraying. Alumina or silica may be used as the oxide. A tension applying film is further formed by coating and baking as required. The iron loss of the silicon steel sheet can remarkably be reduced with high productivity at a low cost.

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 the unidirectional silicon mesh plate, but when trying to further reduce the iron loss value, it is necessary to reduce the glass film that exists on the surface of the material after final annealing. It is important to remove the irregularities on the surface of the steel substrate 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, JP-A-61-201732
In the publication, a unidirectional silicon steel plate finished to a mirror finish with an average surface roughness of 0.4n or less is heated in a temperature range of 500 to 1000°C in an atmosphere consisting of a Ti-containing gas and a non-oxidizing gas. The surface was heat treated with TiN, TiC, Ti (
A method of obtaining a unidirectional silicon steel sheet with a low core loss value by forming an ultra-thin tensile film consisting of C, N) and further covering with an insulating film is disclosed.

(Problem B 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 -'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) Production of a low iron loss unidirectional silicon steel sheet, which is characterized by applying metal plating to the base surface of the unidirectional silicon steel sheet after final annealing, and then forming an oxide film by low-pressure plasma spraying. Method.

(2) After applying metal plating to the base surface of the unidirectional silicon steel sheet after finish annealing, an oxide film is formed by low-pressure plasma spraying, and a tension-imparting film is further applied and baked. A method for producing a silicon steel plate with unidirectional iron loss.

The present invention will be explained in detail below.

In order to solve the problems in the prior art described above, the inventors considered forming an oxide film on the surface of a unidirectional silicon steel plate using a low-pressure plasma spraying method. In conventional low-pressure plasma spraying, the particle size of the sprayed oxide is as large as 50 to 100 mm, resulting in an extremely thick oxide film of 100 mm or more. The inventors reduced the particle size of the oxide to 15 μm or less and raised the temperature of the substrate to 400°.
It has been found that by setting the temperature to C or higher, a film with a thickness of 15 mm or less with extremely excellent adhesion can be formed in a short time.

The film thus formed has a tension of 1 to 3 kg/-
This is significantly larger than that of the forsterite film. However, if thermal spraying is performed directly on the underlying surface, the underlying surface will be roughened due to the collision of the sprayed particles, causing pinning of the magnetic domains and deterioration of the magnetic properties. As a result of various studies, we have found that a low-pressure plasma sprayed coating can be applied without impairing magnetic properties by applying metal plating to the underlying surface, preferably to a thickness of lItm or more, and then thermal spraying.

The method of forming an oxide film by low-pressure plasma spraying described above is applied to form an oxide film on the surface after removing the glass film on the surface of the material after final annealing and applying metal plating to the surface of the base steel. This method can also be applied to the process of secondary recrystallization of a unidirectional silicon steel sheet under the condition of running a strip.Furthermore,
Special Publication No. 63-44804, Special Publication No. 63-6611
Of course, as disclosed in the above publication, it can be used in combination with magnetic domain control technology 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 strain relief annealing. .

The present invention will be explained in more detail below.

A steel slab containing 4 svt% or less of Si is heated and hot-rolled to form a hot-rolled plate, and if necessary, annealed at this stage and then cold-rolled once or twice with intermediate annealing interposed. After rolling to the final thickness, decarburization annealing and application of an annealing separator to form a strip coil, followed by finishing annealing at high temperature and long time to develop secondary recrystallized grains with 110) <001> orientation. The forsterite film of the steel plate that has been annealed is removed chemically or mechanically, or the annealing separator is used with a material that does not form a forsterite film, such as alumina, to expose the base iron on the surface of the steel plate after finish annealing. After that, metal plating is performed and an oxide film is formed in a low-pressure plasma spraying device.

The purpose of applying metal plating is to prevent damage to the underlying surface due to particle collision during plasma spraying. The metal plating is not particularly limited in terms of the plating metal or the plating method, but it is most practical to perform metal plating such as Zn+Sn and Cu+Ni. Under normal plasma spraying conditions, irregularities of about 1% occur in the base, which pinning the movement of magnetic domains in an alternating magnetic field, impairing iron loss. To prevent this, it is effective to perform low-pressure plasma spraying after plating to a thickness of preferably 1% or more. It is an object of the present invention to obtain a product with extremely good magnetic properties by protecting the underlying surface with metal plating and applying a large tension to the underlying surface with a low-pressure plasma spray coating.

Below, an example of the low pressure plasma spraying conditions used in carrying out the present invention is shown.

Working gas: Ar 1Hz Input: 90kK Thermal spraying atmospheric pressure 52Torr Thermal spraying distance: 500mm Powder feed rate: 46g 7'win Note that the present invention is not limited to the above thermal spraying conditions.

FIG. 1 shows the relationship between the average particle diameter of alumina and the spray thickness when alumina is used as the spray powder. As can be seen from this figure, the smaller the particle size of the sprayed oxide (spray powder), the thinner the coating can be formed in the same spraying time.

Next, FIG. 2 shows the results of investigating the temperature of the silicon steel plate (substrate) during thermal spraying and the adhesion of the thermal sprayed coating after thermal spraying. As is clear from FIG. 2, as the temperature of the substrate is gradually raised from room temperature, the adhesion of the sprayed coating improves. This is achieved by keeping the substrate temperature high during thermal spraying.
This is thought to be due to both the effects of improved wettability between the molten thermal spray material droplets and the substrate and diffusion.

The adhesion of the thermal sprayed coating was evaluated by the peeling rate of the thermal sprayed coating when the silicon steel plate after thermal spraying was wound around a round bar with a diameter of 20 mm. As is clear from FIG. 2, when the temperature of the substrate is 400° C. or higher, the adhesion of the sprayed coating becomes better (the peeling rate decreases). At substrate temperatures of 400°C or higher, it exhibits adhesion comparable to that of ordinary forsterite films.

Powders used for thermal spraying include alumina, silica, zirconia,
Single oxides such as magnesia and titania, or mixtures thereof, as well as mullite and spinel.

Any composite oxide such as chromium silicate or molybdenum silicate may be used, but when considering improving the steel structure of the product,
Using an oxide with a large difference in thermal expansion coefficient from the underlying silicon steel plate (substrate) provides greater tension to the underlying material and improves iron loss. After forming the oxide film, heat the substrate to 800℃
Iron loss is improved by heating to a certain degree to relax the strain on the base and oxide film. After the oxide film is formed, if a tension film is applied to the steel plate and baked, the baking is so
Since it is done in a temperature range of 800°C or higher, the strain on the base and oxide film is relaxed.When the product is processed into a rolled iron core, etc., and then subjected to strain relief annealing in a temperature range of 800°C or higher. Also, the strain on the base and oxide film is relaxed.

(Example) Example I A high magnetic flux density unidirectional silicon steel plate containing 3.2% Si and having a thickness of 0.3 mm after final annealing was immersed in a mixed solution of sulfuric acid and hydrofluoric acid to form forsterite. After removing the film, a 2p Cu coating was applied, and the steel plate was introduced into a low-pressure plasma spraying device, and alumina with an average grain size of 12-under was sprayed at a substrate temperature of 500°C to form an oxide film with a thickness of 1On. Formed. Thereafter, the strain was relaxed by heating to 800°C in a hydrogen atmosphere. Table 1 shows the iron loss values of the products thus obtained.

Table 1 As shown, the method of the present invention has a significantly improved iron loss value compared to the conventional method.

(Example 2) Si: 0.3 mm plate thickness containing 3.2% (7),
After mechanically removing the forsterite film on the high magnetic flux density unidirectional silicon mesh plate after final annealing using a grindstone,
After applying Ni plating of n, this steel plate was introduced into a low pressure plasma device, and the average grain size was set to 600"C and an average grain size of 10".
- Under thermal spraying of molybdenum silicate powder 1
An oxide film of zero thickness was formed.

After that, apply a phosphoric acid-based tension coating solution and
Burning for 0 seconds was processed. The magnetic properties of the product thus obtained are shown in Table 2.

Table 2 It can be seen that the iron loss further improves (the iron loss value decreases) when the tension imparting film formation treatment is performed after the oxide film is formed on the steel plate surface by the low-pressure plasma of the present invention.

(Effects of the Invention) The present invention removes the forsterite film of a silicon steel plate after final annealing, then metal plating it, and then spraying oxide powder using a low-pressure plasma spraying method to form an oxide film. This reduces the iron loss of the product, and when using the present invention, compared to when using conventional film forming technology,
It can significantly reduce iron loss at low cost and with high productivity.
Its industrial effects are enormous.

[Brief explanation of drawings]

Figure 1 shows the relationship between the particle size of the oxide powder to be sprayed and the thickness of the oxide film formed, and Figure 2 shows the relationship between the temperature of the substrate during spraying and the adhesion of the sprayed film after spraying. FIG.

Claims (2)

[Claims] (1) Production of a low iron loss unidirectional silicon steel sheet, which is characterized by applying metal plating to the base surface of the unidirectional silicon steel sheet after final annealing, and then forming an oxide film by low-pressure plasma spraying. Method. (2) After applying metal plating to the base surface of the unidirectional silicon steel sheet after finish annealing, an oxide film is formed by low-pressure plasma spraying, and a tension-imparting film is further applied and baked. A method for producing a silicon steel plate with unidirectional iron loss.