JP2006253555A - Super-low iron loss grain-oriented magnetic steel sheet excellent in coat adhesion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a super-low iron loss grain-oriented magnetic steel sheet which is excellent in coat adhesion and hardly generates peeling of an insulation film, even if stress relief annealing is applied while bending process is carried out and a stress is applied to the bending processing part thereafter. <P>SOLUTION: In a grain-oriented magnetic steel sheet, a ceramics film consisting of metallic nitride, metallic carbide or metallic carbonitride is formed in a copper plate surface without a forsterite film. Chlorine of 0.001 to 1 mass% is incorporated in the ceramics film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultra-low iron loss grain-oriented electrical steel sheet having excellent film adhesion, and particularly intends to improve the iron loss characteristics by improving the adhesion of a ceramic film formed on the surface thereof. is there.

Oriented electrical steel sheets are mainly used as iron core materials for transformers and other electrical equipment, and materials with lower iron loss are required to reduce power loss.
In order to reduce the iron loss of grain-oriented electrical steel sheets, there are methods such as reducing the sheet thickness, increasing the Si content, and increasing the orientation of the crystal orientation, but in addition to that, tension can be applied to the steel sheet. It is an effective method.

  As a method for imparting tension to a steel plate, it is common to form a film made of a material having a smaller thermal expansion coefficient than that of the steel plate on the surface. That is, in the final finish annealing process that serves as both secondary recrystallization to align the crystal orientation and purification of the steel sheet, the oxide on the steel sheet surface reacts with the annealing separator applied to the steel sheet surface, and the main component is forsterite. Although a film is formed, this film gives tension to the steel sheet and is effective in reducing iron loss. Furthermore, in order to increase the tension effect, it is also common to produce a product by applying a low thermal expansion coating on the forsterite film.

However, in recent years, a method for magnetically smoothing the surface of steel sheets has been developed, and the surface of the steel sheet is smoothed after intentionally blocking the forsterite film formation or removing the formed forsterite film in the final annealing process. It has become clear that finishing to be effective in reducing iron loss.
For example, Patent Document 1 discloses a method in which a surface product is removed by pickling after finish annealing, and then the steel plate surface is finished in a mirror state by chemical polishing or electrolytic polishing.
Patent Document 2 discloses a method of performing thermal etching in H ₂ at 1000 to 1200 ° C. after removing the forsterite film.
The reason why the iron loss is reduced by such surface treatment is that, in the magnetization process, unevenness having a pinning action that hinders the domain wall movement in the vicinity of the steel sheet surface is reduced.

  The magnetically smooth surface that reduces the hysteresis loss is not only expressed by Ra (arithmetic mean roughness), which is generally expressed by so-called surface roughness, but for example, as described in Patent Document 3 In addition, those obtained by so-called crystal orientation emphasizing treatment, in which surface products are removed and then electrolyzed in an aqueous halide solution, are also known.

In addition, since an insulating coating is required on the surface of the electrical steel sheet, it is customary to apply an insulating coating, and the tension-added type currently applied to grain-oriented electrical steel sheets having a forsterite coating Insulating coating is formed by applying and baking a treatment liquid mainly composed of Al and alkaline earth metal phosphates and colloidal silica, chromic anhydride or chromate onto a steel plate. There are many. The tension-added insulation coating is a steel sheet at room temperature that uses the difference in thermal expansion between the ground iron and the insulation coating by forming an inorganic coating typified by colloidal silica with a smaller coefficient of thermal expansion than that of the steel sheet. The tension is applied to the.
The insulating coating formed by the above method has a great effect of imparting tension to the steel sheet and is effective in reducing iron loss. For example, Patent Document 4 and Patent Document 5 disclose typical forming methods.

However, a film having a greater effect of applying a tension to a steel plate is peeled off if the adhesion to the substrate is not strong. The tension imparting coating as described above is not a problem when a forsterite-based final finish annealing coating exists on the surface of the steel sheet, but the forsterite coating is applied after the final finishing annealing by performing a surface smoothening treatment such as mirror finishing. In the absence of the film, the coating could not be suitably deposited.
For this reason, it has been difficult to achieve both the technique of reducing the iron loss by magnetically smoothing the surface and the technique of reducing the iron loss by the tension-imparting coating.

Conventionally, several methods have been proposed as a method for forming a tension-added coating on a surface without a forsterite film, and further on a smoothed surface. For example, Patent Document 6 discloses a method of applying and baking a tension-added coating solution after metal plating and Patent Document 7 after forming a SiO ₂ thin film, respectively. Further, Patent Document 8 discloses a method of forming a ceramic thin film by vapor deposition, sputtering, or thermal spraying, and Patent Document 9 discloses a method of forming a nitride or carbide film by ion plating or ion plantation. It is disclosed. Further, Patent Document 10 discloses a method of directly forming a high tension imparting type oxide film on the surface of a steel sheet by a so-called sol-gel method.

These methods have been developed as methods for applying tension to a steel plate having a smooth surface, but have not yet been put into practical use because some problems remain.
That is, the method of applying a coating treatment on a thin metal plating as a base is not sufficient in the adhesion of the film due to the smoothness of the uniform plating surface, and the method of forming the SiO ₂ thin film is inferior in the effect of imparting tension. The effect of improving iron loss was not sufficient. In addition, since the thermal expansion coefficient of any coating made of nitride, carbide, or a combination thereof is considerably lower than that of the base iron, the effect of imparting tension due to the difference in thermal expansion coefficient is large, therefore, the bending process Problems often occurred in the adhesion between the base iron and the coating.

  On the other hand, the chemical vapor deposition method (CVD method) disclosed in Patent Document 11 is a powerful method capable of forming a uniform ceramic film over a large area without requiring a vacuum chamber with many restrictions. It is. That is, due to the high temperature reaction, the adhesion between the ceramic coating and the steel plate is good, and compared with the physical vapor deposition method (PVD method) such as sputtering, thermal spraying, ion plating, ion plantation, etc., the product steel plate Ceramic coatings can be formed due to weak impact on the surface or without compromising the extremely low hysteresis loss achieved with a smoothed surface. In particular, this method is suitable for forming nitrides and carbides having a large Young's modulus and a small thermal expansion coefficient on the steel sheet surface.

  Furthermore, in Patent Document 12, in the formation of the ceramic coating by such a CVD method, by reducing the chlorine (Cl) component in the surface layer portion of the steel sheet, the interface between the ground iron and the coating and the ceramic coating as much as possible, A method for preventing deterioration of the coating appearance, corrosion resistance, and magnetic properties with time has been proposed.

Japanese Patent Publication No.52-24499 JP-A-5-43943 Japanese Examined Patent Publication No. 4-72920 Japanese Patent Publication No.53-28375 Japanese Patent Publication No.56-52117 Japanese Patent Publication No.52-24499 JP-A-6-184762 Japanese Patent Publication No.56-4150 Japanese Patent Publication No. 63-54767 JP-A-2-243770 JP 61-201732 A JP 2004-197154 A

  However, even with a grain-oriented electrical steel sheet with a ceramic film formed using the CVD method as described above, strain-relief annealing is performed in a bent state, particularly as seen during the processing of a wound core transformer. When the stress is applied to the bent portion after application, it has been found that the adhesion of the coating is deteriorated and the insulating coating is easily peeled off.

  The present invention advantageously solves the above-mentioned problem, and even if the stress relief is applied to the bent portion after the bending treatment is performed, the insulating coating is peeled off. The object is to propose an ultra-low iron loss directional electrical steel sheet that does not occur and has excellent coating adhesion.

Now, the inventors have intensively studied to improve the adhesion after heat treatment such as strain relief annealing of the film formed by the CVD method or the PVD method.
As a result, when the TiN film is formed by changing the atmospheric temperature, the atmospheric gas mixture ratio, and the steel plate temperature, it becomes clear that there is a difference in the adhesion of the insulating coating after strain relief annealing even if the film thickness is the same. It was.

Then, when the cause was investigated, it turned out that the difference has arisen in adhesiveness by the chlorine concentration contained in trace amount in the TiN film.
That is, regarding the film adhesion, it has been found that better results can be obtained if a certain amount of chlorine is contained in the TiN film.
The present invention is based on the above findings.

  That is, the present invention is a grain-oriented electrical steel sheet in which a ceramic film made of metal nitride, metal carbide or metal carbonitride is formed on the surface of a steel sheet not having a forsterite film, and 0.001 to 1 mass in the ceramic film % Grain-oriented electrical steel sheet characterized by containing chlorine

  According to the present invention, the adhesion of a ceramic coating formed on a smooth steel plate surface without a forsterite coating can be remarkably improved after strain relief annealing, and as a result, a grain-oriented electrical steel plate having excellent iron loss characteristics can be stabilized. Can be obtained.

The present invention will be specifically described below.
As the grain-oriented electrical steel sheet to be used in the present invention, any conventionally known grain-oriented electrical steel sheet can be used, and particularly preferred component compositions are as follows. Unless otherwise specified, “%” in relation to ingredients means mass%.
In this invention, it is desirable to contain Si in 1.5 to 7.0% of range. That is, Si is an effective component for increasing the electrical resistance of the product and reducing the iron loss. However, if the content exceeds 7.0%, the hardness becomes high and it becomes difficult to manufacture and process. On the other hand, if it is less than 1.5%, transformation occurs during final finish annealing, and a stable secondary recrystallized structure cannot be obtained.

  In addition to the above-mentioned elements, B, Bi, Sb, Mo, Te, Sn, P, Ge, As, Nb, Cr, as inhibitor components suitable for the manufacture of known grain-oriented electrical steel sheets are contained in steel. Ti, Cu, Pb, Zn and In can be contained alone or in combination. Furthermore, the present invention can also be applied to grain-oriented electrical steel sheets manufactured by such a method that does not use an inhibitor.

  On the other hand, C, S, Se, N and the like are harmful elements in terms of magnetic properties as impurities. Particularly, in order to deteriorate the iron loss, C: 0.003% or less, S and Se: 0.002 respectively in the final product. % Or less and N: 0.002% or less are preferable.

Moreover, the grain-oriented electrical steel sheet adjusted to the above component composition needs to be in a state in which there is no forsterite film on the surface after finish annealing.
As a method for that, the method of removing the forsterite film formed by the conventional method by pickling or polishing, or adjusting the composition of the annealing separator, to suppress the production of forsterite film on the steel sheet surface, Alternatively, it is possible to apply a method of substantially having a metal appearance by a method of forming the film so as to be easily peeled off and then cleaning and removing.
Furthermore, it is effective to reduce the iron loss value by subjecting the surface to a smoothing treatment. For example, the surface roughness is made as small as possible by pickling, thermal etching, chemical polishing, etc., and the surface is mirror finished, and the graining surface obtained by crystal orientation enhancement treatment by electrolysis in an aqueous halide solution It is done.
In addition, the state without a forsterite film includes a case where a film is not substantially formed, such as a small amount of forsterite being discrete or partly in the form of islands.

Subsequently, a film made of a metal nitride, carbide or carbonitride such as Ti or Si is formed by CVD or PVD.
The CVD method includes a metal chloride gas such as TiC1 ₄ and the other source gas, N ₂ , NH ₃ , (CH ₃ ) ₃ N, (CH ₃ ) ₂ NH gas, etc. Then, heating the steel sheet in an atmosphere containing CH ₄ , CO, C ₂ H ₄ , C ₃ H ₆ , C ₃ H ₈ , C ₂ H ₆ , iC ₅ H _12, etc. obtain. Of course, there is no problem even if both are mixed to form carbonitride. In addition, Ar gas or the like is used as a balance gas.
In addition, a so-called MO-CVD method, plasma, laser, photo induction, or the like using an organometallic gas as a metal source may be employed.

As the PVD method, for example, a hollow cathode method, a magnetron sputtering method, a multi-arc discharge method, or the like can be applied. In these methods, the metal source is supplied from an evaporation target, while nitrogen and carbon can utilize gas.
The coating materials obtained by these methods are nitrides, carbides, carbonitrides such as Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Co, Ni, Al, B and Si, Two or more of these may be laminated. Further, an oxide may be mixed.

  The thickness of such a ceramic coating is preferably about 0.01 μm or more and 5 μm or less. When the film thickness is less than 0.01 μm, sufficient tension imparting effect and film adhesion cannot be obtained. On the other hand, when the film thickness exceeds 5 μm, the film adhesion deteriorates, and the occupancy rate of the electromagnetic steel sheet is disadvantageous.

Now, in the present invention, the film after strain relief annealing is formed by adding 0.001 to 1 mass% of chlorine in the ceramic film made of metal nitride, metal carbide or metal carbonitride formed as described above. Improve adhesion. If the chlorine content is less than 0.001%, the adhesion after strain relief annealing deteriorates, while if it exceeds 1%, the corrosion resistance is impaired and the long-term reliability of the insulation is lowered. More preferably, it is 0.005 to 1% of range.
As a method of containing an appropriate amount of chlorine in the coating, a method of adjusting the balance of the amount of chloride, which is one of the coating raw materials, and the other nitrogen-containing gas or carbon-containing gas in CVD, etc., and PVD There is a method of introducing a small amount of chlorine-containing gas into the atmosphere during vapor deposition.
The mechanism by which the adhesion of the film after strain relief annealing is improved by adding chlorine in this way has not yet been clarified yet, but the deformability of the film during strain relief annealing is improved. I guess that.

Furthermore, when an insulating film is formed on the above-described ceramic film, an inorganic coat used for the grain-oriented electrical steel sheet can be used as such an insulating film. In particular, a coating having a tension imparting effect is extremely effective when combined with a grain-oriented electrical steel sheet having a smooth surface in order to achieve ultra-low iron loss.
As the tension-applying coating, a coating containing silica that reduces the thermal expansion coefficient is recommended. For example, a phosphate-colloidal silica-chromic acid type coating conventionally used for grain-oriented electrical steel sheets having a forsterite film is suitable in terms of its effect, cost, and uniform processability. .
The thickness of such an insulating film is preferably about 0.3 μm or more and 10 μm or less in consideration of the tension application effect, space factor, film adhesion, and the like.
In addition to the above-described tension coating, boric acid-alumina and the like proposed in JP-A-6-65754, JP-A-6-65755, JP-A-6-299366, etc. It is also possible to apply an oxide coating.

  Even if the steel plate obtained as described above is irradiated with a laser or a plasma flame to further subdivide the magnetic domain for the purpose of further reducing iron loss, there is no problem with the adhesion of the insulating coating. In addition, at any stage of the manufacturing process of the grain-oriented electrical steel sheet according to the present invention, it is possible to further reduce iron loss by forming grooves at regular intervals on the steel sheet surface by etching, pressing, etc. for magnetic domain subdivision. It is effective as a means.

Example 1
A directional electrical steel sheet containing 3% Si and having a thickness of 0.23 mm was prepared, and the forsterite film formed on the surface thereof was removed by mechanical polishing, followed by surface smoothing by electrolytic etching. Subsequently, a TiN film having a thickness of 1.2 μm was formed on both surfaces of the steel sheet by a CVD method in which the steel sheet was heated in an atmosphere composed of a mixed gas of TiCl ₄ , H ₂ and N ₄ . At this time, the Cl concentration remaining in the formed TiN coating was changed by variously changing the mixing ratio and concentration of each gas and the steel plate temperature. Further, a part of the obtained steel sheet was heat-treated at 920 ° C. in a vacuum to volatilize and remove Cl, thereby forming a film containing almost no Cl.
Next, a coating liquid composed of colloidal silica, magnesium phosphate, and chromic acid was applied to the surface of the obtained steel sheet and baked at 810 ° C. to form a silica-phosphate-based tension coating.
Thereafter, the obtained steel plate was subjected to strain relief annealing at 820 ° C. for 3 hours in a nitrogen atmosphere in a state of 90 ° bending around a stainless steel round bar having a diameter of 20 mm.
Table 1 shows the results of examining the coating adhesion, corrosion resistance, and iron loss characteristics of the grain-oriented electrical steel sheet with ceramic coating thus obtained. Table 1 also shows the results of examining the chlorine content in the ceramic coating.

The evaluation method of each characteristic is as follows.
Film adhesion After performing strain relief annealing in a 90 ° bent state as described above, this steel sheet is further bent 180 ° along a round bar with a diameter of 20 mm, and when the insulating film is stretched flatly. Evaluation was performed in a peeled state. When peeling did not occur at all, ◯, when peeling occurred even on one side of 180 ° bending or flattening, Δ, and when further peeling was observed, X.
Corrosion Resistance Corrosion resistance was evaluated by exposing the steel sheet after strain relief annealing to an atmosphere of temperature: 40 ° C. and relative humidity: 98% for 10 days. The case where there was no rust and discoloration after exposure for 10 days was marked with ◯, the case where there was no rust but discoloration was marked with Δ, and the case where rust occurred was marked with ×.
Iron loss characteristics Evaluation was made _using iron loss W _17/50 at a frequency of 50 Hz and an excitation force of 1.7 T.
Chlorine Concentration A steel sheet with a coating was dissolved in sulfuric acid, and the residue obtained by filtration was alkali-melted and extracted by warm water and analyzed by absorptiometry.

  As is apparent from the table, when an appropriate amount of chlorine is contained in the ceramic coating according to the present invention, both good coating adhesion, corrosion resistance, and iron loss characteristics are obtained.

Example 2
In the same manner as in Example 1, on the surface of a directional electrical steel sheet having a thickness of 0.23 mm containing 3% Si subjected to surface smoothing treatment, various nitrides and carbides shown in Table 2 were formed by CVD. The resulting ceramic coating was formed on both sides of the steel sheet. Next, the same treatment as in Example 1 was performed to produce a grain-oriented electrical steel sheet with a ceramic coating.
Table 2 shows the results of examining the coating adhesion, corrosion resistance, iron loss characteristics, and chlorine content in the ceramic coating of the grain-oriented electrical steel sheet with the ceramic coating thus obtained.

  As shown in the table, it was confirmed that good film adhesion, corrosion resistance, and iron loss characteristics can be obtained even when various films containing chlorine are formed within the scope of the present invention.

Claims (1)

  A grain-oriented electrical steel sheet in which a ceramic film made of metal nitride, metal carbide or metal carbonitride is formed on the surface of a steel sheet not having a forsterite film, and 0.001 to 1 mass% of chlorine is contained in the ceramic film. A grain-oriented electrical steel sheet characterized by that.