JPH0663035B2 - Method for producing grain-oriented electrical steel sheet with extremely low iron loss - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) In order to obtain a grain-oriented electrical steel sheet with extremely low iron loss, a base steel surface of a magnetic steel strip that has been subjected to finish annealing must be coated with an insulating film prior to formation. It is a useful technique to smooth the surface to a center line average roughness (Ra) of 0.3 μm or less by polishing, and in this specification, the improvement of the polishing technique for smoothing such a surface, particularly mechanical polishing. The following is related to the development results of the efficient smoothing adaptation by the.

Needless to say, the grain-oriented electrical steel sheet is mainly used as an iron core for transformers and other electrical equipment, and has excellent magnetization characteristics, and particularly has a very low iron loss (represented by W _17/50 value). The demand for is increasing.

In response to this demand, secondary recrystallized grains <100> in the steel sheet
Recent development efforts such as highly aligning the grain orientation with the rolling direction and reducing impurities in the final product have recently _led to a W _17/50 value of _{0.23 mm.}
It has become possible to reduce iron loss to about 0.9 W / kg.

However, since the energy crisis of several years ago, the tendency to demand electric equipment with less power loss has become stronger, and as a core material for them, grain-oriented electrical steel sheets with even lower iron loss are required. It has become.

(Prior Art) By the way, as a basic method for reducing the iron loss of grain-oriented electrical steel sheets, increasing the Si content, reducing the product sheet thickness, making secondary recrystallized grains finer, and containing impurities Although metallurgical methods are generally known, such as reducing the amount and making secondary recrystallized grains in the (100) [001] orientation more highly aligned, these methods are The production method has reached its limit, and further improvement is extremely difficult, and even if some improvement is recognized, iron loss improvement will be ineffective in spite of the efforts. It was

On the other hand, as disclosed in Japanese Patent Publication No. 54-23647, there has been proposed a method of forming secondary recrystallization inhibiting regions on the surface of a steel sheet to make secondary recrystallization grains finer. The method is not practical because the control of the secondary recrystallized grain size is not stable.

In addition, in Japanese Patent Publication No. 58-5968, the width of the magnetic domain is reduced by introducing a microstrain into the surface layer of the steel sheet with a ball-point pen-shaped small ball on the surface of the steel sheet after secondary recrystallization to reduce iron loss In Japanese Patent Publication No. 57-2252, a laser beam is applied to the surface of the final product plate by a few mm at a right angle to the rolling direction.
A technique has been proposed in which the width of the magnetic domain is made fine and the iron loss is reduced by irradiating the gaps at intervals and introducing a high dislocation density region into the surface layer of the steel sheet. Further, Japanese Patent Application Laid-Open No. 57-188810 proposes a similar technique in which a minute strain is introduced into the surface layer of a steel sheet by electric discharge machining to make the magnetic domain width finer and reduce the iron loss.

These three types of methods all aim to reduce the magnetic domain width to reduce the iron loss by introducing a minute plastic strain into the surface layer of the base metal of the steel sheet after secondary recrystallization, and are equally practical. Although it is also excellent in iron loss reduction effect, by stress relief annealing after punching, shearing, winding, etc. of steel sheet, and heat treatment such as baking treatment of coating,
With the drawback that the effect of introducing plastic strain is destroyed. If a small amount of plastic strain is introduced after the coating process,
Insulation coating must be re-applied in order to maintain the insulating property, resulting in a large increase in the steps of strain application and re-application, resulting in cost increase.

Separately from these techniques, Japanese Patent Publication No. 52-24499 discloses that magnetic properties, particularly iron loss, are reduced by mirror-finishing the surface of a silicon steel sheet after finish annealing. .

However, in this case, since chemical polishing or electrolytic polishing is required for mirror finishing, the cost becomes very high, and it is still difficult to actually apply it to an industrial process, and it is not suitable for mass production process. I haven't arrived.

When trying to reduce the cost burden by replacing mechanical processes such as a grindstone with such a high-cost process, residual strain due to the polishing process is applied to the silicon steel plate, and iron loss is rather impaired, which makes it impractical. there were.

(Problems to be Solved by the Invention) A grain-oriented electrical steel sheet that is easy to industrialize and has extremely low iron loss when polishing the surface of a grain-oriented electrical steel strip that has been subjected to finish annealing prior to forming a coating of an insulating film. It is an object of the invention to enable the application of a particularly advantageous mechanical polishing system for the production of

(Means for Solving Problems) The present invention is to polish the base steel surface of the grain-oriented electrical steel strip that has been subjected to finish annealing to smooth the surface roughness to a center line average roughness (Ra) of 0.3 μm or less. In doing so, the method for producing a grain-oriented electrical steel sheet with extremely low iron loss is characterized by applying mechanical polishing with a roll or disk of synthetic resin using free abrasive grains as the polishing step.

The inventor has studied various polishing methods, noting that the degree of deterioration of magnetic properties is different depending on the method of mechanical polishing applied to the smoothing of the grain-oriented electrical steel strip surface after finish annealing. As a result, they have found that there is a polishing condition that provides good magnetic properties, and based on this finding, they have led to the above-described configuration of the present invention.

Here, "mechanical polishing with synthetic resin rolls or discs using loose abrasive grains" means abrasives such as conventional grinding wheels, polishing cloths, polishing papers, polishing discs or polishing rolls. Compared with the case where abrasive grains are previously fixed to a synthetic resin, a cloth or even a substrate such as paper with the aid of a binder, it is characterized by not holding and holding the abrasive grains. A mechanical polishing method in which a roll or disk brush or sponge is rotated at high speed on the surface of the electromagnetic steel strip to be ground and fine abrasive powder or its dispersion is supplied toward the surface to be ground. As a base material for rolls or disks of synthetic resin, brushes such as polyurethane and nylon, sponges such as sponge, and abrasive grains include silicon carbide, alumina, silica, carbon, etc. Such as grinding material is compatible.

(Function) In the present invention, polishing for obtaining a smooth surface having a center line average roughness (Ra) of 0.3 μm or less needs to be applied to the surface of the grain-oriented electrical steel strip that has undergone finish annealing. This is because even if a smoothing treatment is performed before finish annealing, the surface of the steel strip becomes a magnetically rough surface due to the oxide formed on the surface during finish annealing. Further, the above-mentioned polishing applied to the surface of the strip steel after finish annealing is performed regardless of the steps applied to the strip steel, that is, the Si amount, the inhibitor amount or the plate thickness, the type of the annealing separator, etc. It goes without saying that the desired effect is brought about by.

That is, the eye of the present invention is to utilize the phenomenon that the hysteresis loss is reduced due to the smoothing of the surface of the grain-oriented electrical steel strip, and therefore does not depend on the manufacturing process of the grain-oriented electrical steel sheet itself. .

Next, regarding the surface roughness, the center line average roughness (Ra) is limited to 0.3 μm or less. When (Ra) exceeds 0.3 μm, the smoothing effect that should contribute to the reduction of hysteresis loss is lost. Because.

In general, mechanical polishing is accompanied by the formation of a work-affected layer, which results in deterioration of magnetic properties, particularly hysteresis loss. According to the results of studies conducted by the inventors, this deterioration is caused by a vertical moment of the polishing base material and abrasive grains added to the surface of the base metal during processing, and the abrasive grains are peeled or crushed from the abrasive during processing to the surface layer to be polished. Distortion due to embedding was the main cause. FIG. 1 shows a comparison between mechanical polishing with loose abrasive grains according to the present invention and mechanical polishing with fixed abrasive grains.

In this test, the composition of the steel sheet tested was C: 0.002%, Si: 3.1%, and the difference from the iron loss W _17/50 value of the product with a general forsterite film as the insulating film is shown on the vertical axis. It was The insulating coating after chemical polishing was coated with phosphate.

In each case, a flexible polyurethane sponge roll having a compressive Young's modulus of 10 ⁴ kg / cm ² or less was used as a base material.

The use of such a base material is to reduce the vertical impact force applied to the plate surface. As the abrasive grains, # 1000 green silicon carbide abrasive (GC) was used.

In the mechanical polishing with loose abrasive grains, the abrasive grains were mixed and dispersed in the grinding liquid and supplied to the surface to be polished, and the abrasive grains were mixed in polyurethane as a roll containing abrasive grains.

The pressing force applied to the plate surface of the roll was 3 kg / cm ² . In either case, the grinding allowance is adjusted to 2 μm for polishing with abrasive grains, and thereafter,
Compared with the results in Fig. 1, the plate thickness was sequentially reduced by various grinding allowances up to 12 μm in total value of the grinding allowance by chemical polishing using 3% hydrofluoric acid (HF) + ethyl alcohol as a polishing liquid. Indicated. In both of the above cases, Ra after chemical polishing is 0.
It is on the order of 2 μm, and contributes evenly to the reduction of iron loss, but it is noted that mechanical polishing with free abrasive grains has a significantly greater improvement.

When the total grinding allowance reaches 12 μm per side, the iron loss is almost the same regardless of the mechanical polishing method, but the iron loss in the lesser grinding allowance is the same as when performing mechanical polishing with loose abrasive grains. Better, it means that the thickness of the work-affected layer produced by mechanical polishing is much thinner than that by the roll with abrasive grains, which means that the abrasive grains are not This is probably because there is little embedding.

This tendency was almost the same in the comparison between the case in which the abrasive grain-containing brush and the free abrasive grain were used together with the brush.

By the way, Fig. 2 shows iron loss W _17/50 when polishing with # 1000 rotating grindstone (vitrified grindstone), emery polishing, and chemical polishing only.
This is a comparison of the effects on the values. In this case, the test steel plate was the same as in the above-mentioned experiment.

As shown in the same figure, undesired deterioration of iron loss was observed in rotating grindstones and emery polishing, which add unnecessary strain to the ground iron surface during polishing, whereas iron loss is reduced in chemical polishing. is doing. Therefore, in the past, chemical polishing or electrolytic polishing had to be used instead of mechanical polishing, but these polishing methods were very expensive and unsuitable for industrial production.

According to the present invention, an insulating film is formed by a conventional method on the surface of a silicon steel thin plate obtained by a smoothing treatment by mechanical polishing with loose abrasive grains to obtain a product. It is considered to be improved, and it is considered that this is because the tension effect is large on the smoothed surface.

Example 1 Example 1 The following chemical composition C using an MnSe + MnS-based inhibitor:
0.20mm obtained by cold rolling a hot-rolled silicon steel sheet with 0.001% and Si 3.2% according to the general procedure for processing grain-oriented electrical steel sheets, and then applying MgO as an annealing separator on the sheet surface.
Material (A) of the grain-oriented electrical steel strip that has been subjected to finish annealing of the plate thickness and the material after the finish annealing that was obtained by the same procedure except that Al ₂ O ₃ was used as the annealing separating agent and the plate thickness was 0.18 mm. Along with (B), vitrified grindstone (Comparative Example 1), urethane # 80
No. 0 abrasive grain-containing roll (Comparative Example 2), simple urethane roll without abrasive grains (Comparative Example 3), and the same urethane roll as Comparative Example 3 were used with # 800 abrasive grain-containing grinding liquid. In each of the conforming examples, Ra was polished to 0.2 μm or less. However, for Comparative Example 3, Ra is 0.35 to
It was only 0.4 μm.

Table 1 shows the magnetic characteristics of the grain-oriented silicon steel sheet product obtained by subjecting the smoothed surface to phosphate coating as an insulating film.

Table 2 shows the results when ion-plating TiN (film thickness: 1 μm) as a smoothing surface tension imparting coat after each of the above polishing.

Example 2 The following chemical composition using an AlN-based inhibitor C: 0.002
%, Si: 3.1%, obtained by cold rolling a hot-rolled grain-oriented silicon steel sheet according to the general procedure for grain-oriented electrical steel sheet, and then applying MgO as an annealing separator to the sheet surface. m
Material (C) and MnSe of grain-oriented electrical steel sheet after finishing annealing of m thickness
+ Cn composition using MnS inhibitor C: 0.001%,
0.15 mm plate obtained by cold rolling a grain-oriented silicon steel hot-rolled sheet with Si: 3.2% according to the general procedure for processing grain-oriented electrical steel sheets, and then applying MgO as an annealing separator on the sheet surface. With the material (D) of grain-oriented electrical steel sheet that has undergone thick finish annealing,
000 abrasive-containing brush rolls (Comparative Example 4), abrasive-free brush rolls (Comparative Example 5), and # 1000 abrasive particles as a slurry, which were applied to the plate surface and then the same abrasive-free brush rolls as Comparative Example 5 (Compatible example) was used to polish Ra to 0.2 μm or less. Ra of Comparative Example 5 was only 0.35 to 0.4 μm.

Table 3 shows the magnetic characteristics of the grain-oriented silicon steel sheet product obtained by applying phosphate coating on the smoothed surface as an insulating coating.

In addition, as a tension applying coat on the material surface after polishing,
Table 4 shows the result of ion plating of ₃ N ₄ .

(Effects of the Invention) According to the present invention, in mechanical polishing, which is industrially inexpensive and can be mass-produced, for smooth surface finishing of the steel plate surface,
Applying mechanical polishing with loose grains can achieve significant improvement in iron loss at low cost.

[Brief description of drawings]

FIG. 1 is a graph showing a comparison between the case of roll polishing with abrasive grains and the case of polishing with free abrasive grains, and FIG. 2 is a graph showing magnetic properties when various types of surface polishing of the material are performed.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nariko Sueda 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Headquarters (56) References JP 62-1821 (JP, A)

Claims (1)

[Claims] Claims: 1. When polishing the surface of the base iron of the grain-oriented electrical steel strip that has undergone finish annealing to smooth it to a surface roughness of center line average roughness (Ra) of 0.3 μm or less A method for producing a grain-oriented electrical steel sheet having an extremely low iron loss, characterized by applying mechanical polishing using a roll or disc of synthetic resin using abrasive grains.