JPH0680175B2 - Method for producing grain-oriented silicon steel sheet having good magnetic properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) Regarding a method for producing a grain-oriented silicon steel sheet having an extremely low iron loss by smoothing the surface of a steel sheet, this specification describes a polishing method for smoothing the surface. The improvement is also described.

Needless to say, grain-oriented silicon steel sheets are mainly used as iron cores for transformers and other electrical equipment, and have excellent magnetization characteristics, especially iron loss (represented by W _17/50 value).
The demand for very low is becoming increasingly stronger.

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 seek electrical equipment with less power loss has become stronger, and as a core material for them, grain-oriented silicon steel sheets with even lower iron loss are required. It is like this.

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

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 fine crystal 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, the 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, JP-B-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 is very high, and it is still difficult to apply it to an industrial 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) Therefore, smoothing of the surface of the grain-oriented silicon steel sheet which has undergone finish annealing is achieved by industrially feasible mechanical polishing and subsequent electrolytic treatment, resulting in a significant reduction in iron loss. It is an object of the invention to realize

(Means for Solving Problems) As a result of various studies on the method applied to smoothing the surface of the grain-oriented silicon steel sheet after finish annealing, the inventors have found that the steel sheet surface after finish annealing is By mechanically polishing with fine abrasive grains under pressure and then electrolytically treating the steel plate after mechanical polishing as an anode in a bath of a water-soluble chloride solution, it is industrially easier and more stable than chemical polishing or electrolytic polishing. It has been found that smoothing can be performed, and the structure of the present invention has been derived based on this finding.

That is, the present invention performs mechanical polishing using an elastic abrasive on the surface of a grain-finished grain-oriented silicon steel sheet, and then performs electrolytic treatment with a water-soluble chloride solution to obtain good magnetic properties. Manufacturing method of grain-oriented silicon steel sheet and mechanical annealing using elastic abrasives on the surface of grain-finished grain-oriented silicon steel sheet, followed by electrolytic treatment with water-soluble chloride solution, and then surface tension A method for producing a grain-oriented silicon steel sheet having good magnetic properties, which is characterized by forming a film.

(Function) In this invention, mechanical polishing and then electrolytic treatment with a water-soluble chloride solution must be applied to the grain-finished grain-oriented silicon steel sheet. This is because the surface of the steel strip becomes a magnetically rough surface due to the oxide formed on the surface during the finish annealing even if the smoothing treatment is performed before the finish annealing.

On the surface of finish-annealed grain-oriented silicon steel sheet, the separating agent usually applied during finish-annealing reacts with the base iron or the oxides of silicon and iron present on the surface of the base iron to form an oxide layer. Are generated, and the oxide needs to be removed prior to electrolytic treatment. This oxide layer is usually used as an annealing separator.
Since M ₉ O is used, it is generally a reaction product with silica, that is, forsterite. Of course, even when alumina or the like is used without using M ₉ O, it is the same that an oxide layer such as silica or iron oxide is formed.

When an electrolytic treatment is applied to the surface of a steel sheet, the presence of such an oxide layer is extremely harmful and the electrolytic reaction does not proceed, so that the intended purpose cannot be achieved. Although pickling can be considered as a method for removing the oxide layer, when the pickling treatment is performed, the oxide layer can be removed, but the unevenness increases and is further smoothed to smooth these unevenness. It is industrially unfavorable because the thickness of the base metal to be removed must be several times redundant because it must be treated. Other than pickling, smoothing by mechanical polishing can be considered, but removal of the oxide layer by mechanical grinding such as grinding rolls or brushes or jot blasting, which is conventionally done, removes the magnetic layer of silicon steel. This is also not preferable because it significantly deteriorates the characteristics.

Therefore, the present invention applies mechanical polishing using an elastic abrasive that does not cause deterioration of magnetic properties, which is a drawback of mechanical polishing.

Here, the elastic abrasive means that the base material holding the abrasive grains is made of an elastic material having a compressive Young's modulus of 10 ⁴ kg / cm ² or less. Needless to say, a grinding brush can be used as long as it has the same elasticity.

Note that the abrasive grains used for elastic abrasives should have a grain size of # 100 or more (JIS R
(According to 6001) is preferable, and it is advantageous that the vertical pressure applied to the surface of the steel sheet is 3 kg / cm ² or less. This pressure can usually be achieved only by polishing with an elastic abrasive.

Further, the abrasive grains do not necessarily have to be fixed to the elastic polishing material, and so-called free abrasive grains may be mixed in the grinding fluid.

Fig. 1 shows the grain sizes of the surface of the grain-finished grain-oriented silicon steel sheet with different polishing pressures, that is, with a non-woven fabric roll with a vertical pressure of ² kg / cm ² or less and a belt polishing method with a vertical pressure of 6 kg / cm ^2. Polished by mechanical polishing using the above-mentioned abrasive grains, and then electrolytically treated in NaCl solution (removal amount 4 μm; concentration 100 g / l;
The current loss is 300 A / dm ² ) and the surface is subjected to a TiN tension coating (1 μm thick), and the iron loss at each stage is compared and shown.

From the figure, there is a large difference in iron loss after electrolytic treatment between the case of using the nonwoven fabric roll (elastic abrasive) according to the present invention and the case of using the comparative belt polishing (inelastic abrasive). I understand.

By the way, Fig. 2 shows the iron loss W _17/50 values for the case of polishing with a # 1000 rotating grindstone (vitrified grindstone: inelastic abrasive), emery polishing, and chemical polishing only. It is a comparison of the effect on. 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.

When the above-mentioned mechanical polishing desirably completes the polishing of 0.5 μm or more on one side, the steel sheet surface is then subjected to electrolytic treatment with a water-soluble chloride solution.

The surface of the finished annealed silicon steel sheet is composed of crystal grains with a (110) plane orientation, and electrolytic treatment using a water-soluble chloride solution smoothes only this silicon steel sheet with a (110) plane orientation. Show the effect of the other, (111), (21
1) For crystal grains with plane orientation, the surface roughness is increased by electrolytic treatment.

Figure 3 is a photograph showing the metallographic structure of the (110) and (111) planes subjected to electrolytic treatment (electrolyte solution Nal, 60 ° C current density 1000 A / dm ² ). Also indicates that surfaces exhibiting different smoothness can be obtained. The (110) plane shows a smooth surface divided into fine mesh-like regions (not crystal grain boundaries), and the (111) plane is a rough textured surface that is black due to light. .

Further, in the electrolytic treatment, if the surface to be smoothed is a cathode, a smooth surface cannot be obtained, so it is necessary to use it as an anode. As the water-soluble chloride used in the electrolytic bath, NaCl gives the best results, and even if an acidic electrolytic bath such as hydrochloric acid or sulfuric acid is used, a good smooth surface cannot be obtained. Further, even when using an electrolytic bath for so-called electrolytic polishing such as conventionally known chromic acid and phosphoric acid,
Although similar iron loss reducing effects can be obtained, these electrolytic polishing bath solutions are very costly and not practical for industrial use.

Further, by coating the surface of the grain-oriented silicon steel sheet that has been subjected to the above treatment with a tension film, it is possible to obtain a further iron loss reducing effect.

As a magnetic steel sheet material, the tension film is effective in imparting electrical insulation to the surface and at the same time imparting tension to the plate surface to improve magnetostriction characteristics and magnetic characteristics (magnetic flux density, iron loss). When the tension film is formed on the smooth surface obtained according to the present invention, the iron loss reduction effect by the coating of the tension film is greater than that of the conventional silicon steel sheet covered with the forsterite oxide film. The tension film may be a conventionally known one consisting of colloidal silica and phosphate, or an intermetallic compound, oxide, nitride or the like formed by plating or dry plating, as long as it gives tension, And does not depend on the film quality.

Example 1 A hot-rolled silicon steel sheet containing C: 0.032 wt% and Si: 3.3 wt% and containing MnSe and Sb as inhibitors was prepared according to a general procedure for processing grain-oriented silicon steel sheets. After cold working to a thickness of 0.23 mm, finish annealing was performed using alumina as an annealing separating agent.
The grain size in the grain-oriented silicon steel sheet after this finish annealing was 50
When the grains were examined, the crystal grains in the (110) [001] orientation (deviation angle within 5 °) were 94%.

Next, the grain-oriented silicon steel sheet was mechanically polished (vertical pressure: 1 kg / cm ² ) by a non-woven fabric roll with alumina as abrasive grains and pickled (10% H ₂ SO ₄ 80 ° C), respectively, and the surface oxide Was removed.

Using the surface of each steel plate as an anode, electrolytic treatment (current density: 100 A / dm ² ) using 100 g / l NaCl aqueous solution was performed for 10 seconds or 20 seconds, and the surface of the steel sheet that had been electrolytically treated for 20 seconds Formed a tension film of TiN. Table 1 shows the results of examining the iron loss after each treatment.

From the above table, it can be seen that the steel sheet that has undergone the treatment according to the present invention exhibits good properties both after the electrolytic treatment and after the tension coating. On the other hand, in the case where the pickling is carried out as the oxide removing treatment, the same characteristics can be obtained if the electrolytic treatment is carried out for a long time, but the removing thickness of the steel sheet becomes very large, which is not preferable.

Example 2 A hot-rolled silicon steel sheet containing C: 0.31 wt% and Si: 3.2 wt% and having AlN and MnS as inhibitors was cooled to a thickness of 0.23 mm according to a general procedure for processing a grain-oriented silicon steel sheet. After interworking, finish annealing was performed using MgO as an annealing separator. When 50 grains were examined in the grain-oriented silicon steel sheet after the finish annealing, the grains of (110) [001] orientation (deviation angle of 5 °
Within) was 100%.

Then, the grain-oriented silicon steel plate was mechanically polished by a non-woven fabric roll using # 1500 abrasive grains (vertical pressure: 1 kg / cm ² ),
The oxide on the surface was removed.

Using the surface of each steel plate as an anode, electrolytic treatment (current density: 80 A / dm ² ) using 100 g / l NaCl aqueous solution and 50 g / l NH ₄ Cl aqueous solution was performed for 10 seconds, and the ₃ N
₄ tension film was coated.

As a comparison, the same finish-annealed steel sheet was subjected to mechanical polishing with a non-woven fabric roll containing abrasive grains of # 60 and a belt roll having abrasive grains of # 1000, and then with respect to the steel plate subjected to these treatments. Subsequent processing was similarly performed.

Table 2 shows the results of examining the iron loss after each treatment.

From the above table, it can be seen that the steel sheet that has undergone the treatment according to the present invention shows good properties after the electrolytic treatment and after the formation of the tension film.

(Effects of the Invention) According to the present invention, an elastic abrasive is applied to mechanical polishing, which can be industrially manufactured at low cost and in mass production, and is subsequently industrially manufactured at low cost with water-soluble chloride. By applying the solution to smooth the surface of the steel sheet, a significant improvement in iron loss can be achieved at low cost.

[Brief description of drawings]

Fig. 1 is a graph showing a comparison of iron loss after polishing when applying a non-woven fabric roll and belt polishing to mechanical polishing, after electrolytic treatment and after TiN coating. A graph showing characteristics, and FIG. 3 are photographs showing metal structures of the (110) plane and the (111) plane after electrolytic treatment.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Superiority of the inventor 1st Kawasaki-cho, Chiba-shi, Chiba Technical Research Division, Kawasaki Steel Co., Ltd. (72) Hiroi Ishihii 1st Kawasaki-cho, Chiba-shi Technical Research Division

Claims (2)

[Claims] Claims: 1. A surface of a grain-finished grain-oriented silicon steel sheet is mechanically polished using an elastic abrasive, and then electrolytically treated with a water-soluble chloride solution to obtain good magnetic properties. Method for producing grain-oriented silicon steel sheet 2. A surface of a grain-finished grain-oriented silicon steel sheet is mechanically polished using an elastic abrasive, and then electrolytically treated with a water-soluble chloride solution to form a tension film on the surface. A method for producing a grain-oriented silicon steel sheet having good magnetic properties, which is characterized by the above.