JPH0617511B2 - Manufacturing method of grain-oriented electrical steel sheet with excellent actual machine characteristics - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent actual machine characteristics.

(Prior Art and Its Problems) The unidirectional electrical steel sheet is widely used mainly as an iron core of a transformer or a generator.

As a method of improving the iron loss of such a grain-oriented electrical steel sheet,
Recently, a method has been proposed in which a minute strain is applied to the surface of a steel sheet to reduce the magnetic domain width. For example, Japanese Patent Publication No. 57-5968 proposes a method of applying a linear microstrain to the surface of a steel sheet by pressing, and Japanese Patent Publication No. 57-2252 discloses a method of irradiating the surface of a grain-oriented electrical steel sheet after finish annealing with a laser beam. Then, a method of forming a high dislocation density region in the steel sheet by the impact force is proposed.

On the other hand, the present applicant has recently proposed, instead of the above method, a method of forming a thermal strain region by locally applying thermal energy to the surface of the grain-finished grain-oriented electrical steel sheet that has been subjected to finish annealing to improve iron loss characteristics. (Japanese Patent Application No. 58-104618). It is disclosed that as the heat energy in this case, for example, a heat ray such as a laser beam, an electron beam, an ion beam or an infrared ray can be used.

When applying microstrain to a grain-oriented electrical steel sheet to improve iron loss, apply a tension insulation film to the steel sheet in advance to put it in a tensioned state rather than directly applying a microstrain to the steel sheet. The fact that a slight strain is applied to the steel sheet from above the tension insulating film has a large margin for improving iron loss.
It is disclosed in the publication.

In the case where a micro-strain imparting treatment is performed on the tension insulation film, if the tension insulation film is damaged and the base iron is partially exposed, the corrosion resistance, insulation property and withstand voltage property are deteriorated. Japanese Unexamined Patent Publication No. 36051 proposes that a repair insulating film treatment is performed after a minute strain is applied. However,
This repair insulation coating process is expensive and uneconomical.

Therefore, as a result of the studies made by the present inventors in order to solve this difficulty, as a result of appropriately selecting the use conditions of the above-mentioned various means, that is, the pressing method, the laser irradiation method, and the heat wire method, it is possible to reduce Even if straining treatment is performed, the tensile insulation coating does not cause damage such that the base steel is exposed, which eliminates the need for repair insulation coating treatment, thus solving the above-mentioned difficulties, but on the other hand, due to the following reasons Was found to be susceptible to deterioration.
That is, a compressive force is applied to the steel sheet due to the application of a minute strain from the tension insulating film, and the residual compressive stress easily deteriorates the actual machine characteristics of the transformer or the like after assembly.

(Object of the Invention) The present invention provides a grain-oriented electrical steel sheet having a tensile insulating coating as described above, which is improved in damage by imparting microstrain to the steel sheet without damaging the coating to reduce the magnetic domain width. On the other hand, the purpose is to provide excellent actual machine characteristics.

(Structure / Operation of the Invention) When the magnetic domain is subdivided and iron loss is improved by applying minute strain to the grain-oriented electrical steel sheet having a tensile insulating film, compressive stress remains in the steel sheet due to this minute strain.

Although the material has good iron loss characteristics and magnetostriction characteristics without excessive compressive stress, it is unavoidable due to various unavoidable stresses due to shearing, lamination, bolting, etc. when assembling the actual machine transformer. In this case, the iron loss characteristics and the magnetostrictive characteristics in the above are likely to deteriorate. This tendency of deterioration becomes remarkable when the compressive force remaining in the steel sheet exceeds a certain value.

Therefore, the present inventors have studied a method of reducing the compressive stress remaining in the steel sheet when a minute strain is applied to the grain-oriented electrical steel sheet.
It has been found that by performing heat treatment in a temperature range not exceeding ℃, the residual compressive stress can be reduced and the deterioration of the actual machine characteristics can be reduced without impairing the iron loss improving effect by the magnetic domain refinement.

When the heating in this case is performed at a high plate temperature exceeding 500 ° C., the iron loss improving effect due to the magnetic domain refinement decreases and good iron loss cannot be obtained. Therefore, the upper limit of heating is limited to the plate temperature 500 ° C. It is a thing.

Regarding the lower limit of the heating temperature, heating at 200 ° C. or higher is preferable because it is difficult to obtain the intended effect if the temperature is too low.

The tension insulating film treatment used in the present invention withstands baking at 700 ° C. or more and gives tension to the steel sheet during cooling, for example, colloidal silica, aluminum phosphate, chromic acid type treatment liquid described in JP-B-53-28375. , JP-A-5
A treatment liquid such as colloidal silica described in JP-A No. 2-25296, a phosphate, a chromate-based treatment liquid, a treatment liquid containing magnesium ion, phosphoric acid, silica, and a chromium ion described in US Pat. No. 5,804,49 is used. However, the treatment liquid is not limited to the above treatment liquid as long as it is a treatment liquid that can give tension to the steel sheet.

Example 1 High magnetic flux density grain-oriented electrical steel sheet after finish annealing (sheet thickness 0.3
0 mm) with a chromic acid-aluminum phosphate-colloidal silica-based tension insulating film treatment liquid and applied at 850 ° C for 70
Flattening of the steel sheet was performed at the same time as sec baking. The coating amount was 5.0 g / m ² .

This surface was irradiated with a continuous linear laser beam on one side. Laser beam irradiation conditions are used laser: Nd-YAG laser,
The power was 2.0 W, the irradiation line width was 0.2 mm, the irradiation line L direction interval was 5 mm, and the irradiation speed was 200 mm / sec.

After the irradiation, the surface film was scarcely damaged, and the base iron was not exposed. A sample was cut out from this, and changes in iron loss and magnetostriction under compressive stress after heating were investigated.

The results are shown in Table 1.

As is clear from Table 1, the iron loss before W _17/50 before laser irradiation was 1.05 W / kg, but it improved to 0.93 W / kg by laser irradiation.

When the sample after laser irradiation was heated to 200 ° C to 700 ° C, it was 500 in the state where no compressive stress was applied.
The iron loss hardly changes up to ℃ (No.3,4,5,6), but the iron loss deteriorates as the temperature rises to 600 ℃ and 700 ℃ (No.7,8). I understand.

Furthermore, the iron loss of these samples was measured under compressive stress. After laser irradiation (No. 2) and at 200 ° C
After heating (No.3) in 0.3 kg / mm ^2, the laser irradiation before as 0.6 kg / mm ² and the compression stress increases (No.1)
It can be seen that the deterioration is significantly larger than that of. On the other hand, when heating at 300 to 500 ° C (No. 4, 5, 6), harmful strain due to laser irradiation is removed with almost the same deterioration rate as before laser irradiation (No. 1). .

Next, although not observed little difference before and after heating the front and rear laser irradiation in the case of compressive stress 0 kg / mm ² with respect to magnetostriction, after laser irradiation under compressive stress of 0.3kg / mm ² (No.2 ) And after heating at 200 ° C. (No. 3).

Example 2 Compared to Example 1, the laser power was changed to 46 W, the irradiation line width was changed to 0.3 mm, and the irradiation speed was changed to 2000 mm / sec.
Other conditions were the same as in Example 1.

After the irradiation, the surface film was scarcely damaged, and the base iron was not exposed.

This laser-irradiated steel plate is heated as it is at 500 ° C. for 7
Three-phase, three-legged, 150-degree heat-treated materials
Table 2 shows the results of investigating the iron loss characteristics when assembled in a 0 kVA transformer. The characteristics of those without laser irradiation are also shown.

As is clear from Table 2, the one () of the present invention which was heated at 500 ° C. after laser irradiation is the same as the one (2) which has been subjected to the laser irradiation treatment in the material core loss characteristics,
The iron loss characteristic of the present invention () after assembly in a transformer is superior. On the other hand, the one (4) heated to 700 ° C. after the laser irradiation loses the effect of the laser irradiation and the characteristics are not good.

From this, after laser irradiation, by heating at 500 ° C or less (over 200 ° C), the residual compressive stress can be effectively reduced, and deterioration due to the compressive stress added when assembling an actual machine transformer, etc. can be suppressed. Can be done.

As described in detail above, according to the present invention, it is possible to effectively suppress the deterioration of the actual machine characteristics of the high-grade grain-oriented electrical steel sheet in which the iron loss is greatly improved by the magnetic domain refinement, and its industrial value. Some are really big.

Claims (1)

[Claims] 1. A grain-oriented electrical steel sheet having a tensile insulating coating, which is strained without damaging the coating to reduce the magnetic domain width to improve iron loss. A method for producing a grain-oriented electrical steel sheet having excellent actual machine characteristics, which comprises heating to a temperature not exceeding the temperature to reduce the compressive stress.