JPH02243754A - Production of grain-oriented silicon steel sheet reduced in iron loss - Google Patents

Abstract

PURPOSE:To industrially produce a grain-oriented silicon steel sheet minimal in iron loss value at a low cost by forming an oxide film on the smoothed ferrite surface of a finish-annealed grain-oriented silicon steel sheet by means of low pressure plasma spraying. CONSTITUTION:A steel slab containing <=4wt.% Si is heated and hot-rolled into a hot rolled plate. This plate is subjected to decarburizing annealing and to the application of a separation agent at annealing so as to be formed into a strip coil. Subsequently, finish annealing is applied to the above at high temp. for a long time, and a forsterite film on a steel sheet in which secondary recrystallized grains are developed is chemically or mechanically removed, or, as the separation agent at annealing, those forming no forsterite film, such as alumina, are used, by which the ferrite on the surface of the finish-annealed steel sheet is allowed to appear. Then, the ferrite surface is smoothed by immersion into a solution containing hydrofluoric acid or hydrogen peroxide or by electropolishing. An oxide film is then formed in a low-pressure plasma spraying apparatus.

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. 5224499 proposes a method of obtaining an ultra-low core loss unidirectional silicon steel plate by coating 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. 61-201732, a unidirectional silicon steel plate finished in a mirror-like state with an average surface roughness of 0.4 μm or less is exposed to an atmosphere containing a Ti-containing gas and a non-oxidizing gas. was heat-treated at a temperature range of 500 to 1000°C, and the surface was coated 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 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 iron loss unidirectional silicon steel sheet, which comprises forming an oxide film by low-pressure plasma spraying on the smoothed base surface of the unidirectional silicon copper sheet after final annealing.

(2) Low core loss unidirectional, characterized by forming an oxide film by low-pressure plasma spraying on the smoothed base steel surface of the unidirectional silicon steel plate after finish annealing, and then applying and baking a tension imparting film. manufacturing method of silicon steel sheet.

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 between 50 and 100 pI1.
1, the formed oxide film is also extremely thick, 100 μm or more. The inventors have discovered that by reducing the particle size of the oxide to 15 μm or less and increasing the temperature of the substrate to 400°C or higher, it is possible to form a film of 15p or less with extremely excellent adhesion in a short period of time. .

The particle size of the sprayed oxide used in the low-pressure plasma spraying of the present invention is 1 to 44 pn+, preferably 1 to 257/I11. If coarse particles with a particle size exceeding 44 μm are used, it becomes difficult to form a dense film with excellent adhesion.

On the other hand, if the particle size is less than 111 m, the feeding of the particles becomes unstable and thermal spraying becomes difficult. The present invention is characterized by setting the particle size of the thermally sprayed oxide to 1 to 44n, and setting the temperature of the substrate to be thermally sprayed to 400°C or higher.
By doing so, a film having a thickness of 15 μm or less with extremely excellent adhesion can be formed in a short time.

A unidirectional silicon steel sheet having a film formed in this manner has extremely excellent magnetic properties.

The above-described means for forming an oxide film by low-pressure plasma spraying can be applied to remove the glass film on the surface of the material after final annealing, smooth the surface of the steel base, and form an oxide film on the surface. This method can also be applied to a process in which a grain-oriented silicon steel sheet is subjected to secondary recrystallization under the condition of running a strip. In addition, the Tokuko Sho 6
As disclosed in Japanese Patent Publication No. 344804 and Japanese Patent Publication No. 63-6611, it is combined 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. Of course, it can be used.

The present invention will be explained in more detail below.

A steel slab containing 4 wt% 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. 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. chemically or mechanically removing the forsterite film of the steel plate that has been annealed, or using a material that does not form a forsterite film, such as alumina, as the annealing separator to expose the base iron on the surface of the steel plate after finish annealing; After smoothing the surface of the base metal by immersion in a solution containing hydrofluoric acid and hydrogen peroxide or by electrolytic polishing, an oxide film is formed in a low-pressure plasma spraying device.

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

Working gas: Ar+Hz Input: 87 kW Thermal spraying atmospheric pressure 50 Torr Thermal spraying distance: 4BOn+m Powder feeding rate: 46 g/min 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 and the substrate is passed through the plasma jet at a speed of 85 mm/s under the spray conditions described above. 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 recesses. 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, and 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 iron loss of the product,
It is better to use an oxide that has a large difference in coefficient of thermal expansion from the underlying silicon steel plate (substrate).

After forming the oxide film, the core loss is improved by heating the base to about 800°C to relax the strain between the base and the oxide film. When a tension coating is applied to a steel plate and baked after the oxide film is formed, the baking is done at a temperature of 800° C. or higher, so that the strain on the base and the oxide film is relaxed. When a product is processed into a wound iron core or the like and then subjected to strain relief annealing at a temperature of 800°C or higher, the strain on the base and oxide film is also relaxed.

(Example) Example I A high magnetic flux density unidirectional silicon steel plate having a thickness of 0.2 mm and containing St: 3.2% after finish annealing was immersed in a mixed solution of sulfuric acid and hydrofluoric acid to form a forsterite film. After removing this, the surface of the steel base was smoothed and finished to a mirror finish in a solution containing hydrofluoric acid and hydrogen peroxide. After mirror finishing, this steel plate was introduced into a low-pressure plasma spraying device, and the substrate temperature was set at 500°C, and the average grain size was 12.
An oxide film with a thickness of 10 mm was formed by thermal spraying alumina under I1 m.

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 Table 2 As described above, the method of the present invention significantly improves the iron loss value compared to the conventional technology.

(Example 2) The forsterite film of a high magnetic flux density unidirectional silicon steel plate containing 3.2% Si and having a thickness of 0.2 mm after final annealing was mechanically removed using a grindstone, and then treated with hydrofluoric acid. The surface of the bare iron was smoothed and finished to a mirror surface in a solution containing hydrogen peroxide. After mirror finishing, this steel plate was introduced into a low-pressure plasma device, the substrate temperature was set at 600°C, and molybdenum silicate powder with an average particle size of less than 10 μm was sprayed to form an oxide film with a thickness of 10 μm. Thereafter, a phosphoric acid-based tension coating solution was applied, and the coating was baked at 850'CX for 60 seconds. The magnetic properties of the product thus obtained are shown in 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 surface of the steel sheet 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 finish annealing and smoothes the surface of the base steel, and then sprays oxide powder using a low-pressure plasma spraying method to form an oxide film. By this, the iron loss of the product is lowered, and when the present invention is used, the iron loss can be significantly lowered at lower cost and with higher productivity than when using conventional film forming technology, and the industrial The effect is 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) A method for producing a low iron loss unidirectional silicon steel sheet, which comprises forming an oxide film on the smoothed base surface of the unidirectional silicon steel sheet after final annealing by low-pressure plasma spraying. (2) Low core loss unidirectional, characterized by forming an oxide film by low-pressure plasma spraying on the smoothed base steel surface of the unidirectional silicon steel plate after finish annealing, and then applying and baking a tension imparting film. manufacturing method of silicon steel sheet.