JPH02213483A - Production of grain oriented silicon steel sheet excellent in magnetic characteristic - Google Patents

Abstract

PURPOSE:To obtain a grain oriented silicon steel sheet having a surface state excellent in adhesive properties of a coated film not to mention magnetic characteristics by performing electrolytic treatment for the grain oriented silicon steel sheet wherein secondary recrystallization annealing has been finished in an aq. soln. contg. a water-soluble halide and thereafter performing hot-melt-spray-coating on the surface of this steel sheet. CONSTITUTION:An oxidative layer on the surface of a grain oriented silicon steel sheet wherein secondary recrystallization annealing has been finished is removed by a chemical method such as pickling. Thereafter this surface is anodically electrolyzed. Thereby the steplike or groove-like recessed parts are formed in which a magnetic smooth face, namely grain boundary is >=10.4mum Rmax. Then electrolytic treatment is performed on the surface of steel sheet for which the above-mentioned electrolytic treatment has been performed in an aq. soln. contg. one or more kinds of water-soluble halides preferably at ordinary temp.-about 90<=. Then hot-melt-spray-coating is performed on the surface of steel sheet after this electrolytic treatment by oxide such as Al2O3 and ZrO2 and nitride such as Si3N4 and AlN. Thereby the grain oriented silicon steel sheet having the above-mentioned characteristics is stably obtained at low cost. Further as the water-soluble halide, e.g. HCl, NaCl HBr, NaBr, HI and KI, etc., are shown.

Description

[Detailed Description of the Invention] (Industrial Application Field) After the energy crisis a few years ago, the trend for electrical equipment with lower power loss became even stronger. Electric steel sheets are requested.

The present invention advantageously meets the above requirements and relates to an advantageous method for manufacturing grain-oriented silicon steel sheets that have excellent not only magnetic properties but also film adhesion.

(Prior art) A conventional method for manufacturing a unidirectional silicon steel sheet includes, for example, Si
After hot rolling, a material containing 2.0 to 4,0 wt% (hereinafter simply expressed in %) of MgO After applying an annealing separator mainly composed of
Next, secondary recrystallization annealing and purification annealing are performed, and then, if necessary, a phosphate-based insulating coating is applied. Furthermore, by adding a tensioning function to this phosphate-based insulating coating, magnetostriction and iron loss are further improved.

In addition, during the above purification annealing, the oxide layer mainly composed of SiO□ generated on the surface of the steel sheet during decarburization annealing reacts with MgO in the annealing separator to form forsterite (MggSi0
4) A film is formed, and this forsterite film not only has insulating properties itself, but also serves as a binder to maintain adhesion with the overlying insulating coating.

Unidirectional silicon steel sheets are products in which secondary recrystallized grains are accumulated in the (110) (001) or Goss orientation through the above process, and are mainly used as iron cores for transformers and other electrical equipment. For this reason, the characteristics of unidirectional silicon steel sheets include magnetic flux density (B+).

) is high, as well as iron loss (WI?/
S. (represented by the value) is required to be low. Particularly recently, from the standpoint of energy conservation, further reduction of iron loss has been desired in order to reduce power loss in transformers and the like.

By the way, the iron loss of silicon steel sheets consists of eddy current loss and hysteresis loss. An effective means of reducing the iron loss of silicon steel sheets is to reduce the sheet thickness, and this method mainly reduces eddy current loss, which greatly contributes to the reduction of iron loss and thus to energy conservation. However, when the plate thickness becomes 11 mil or less, the ratio of hysteresis loss to the total iron loss increases rapidly. Factors that affect hysteresis loss include the orientation of crystal grains, the degree of impurities, the influence of surface coatings, and the roughness of the steel sheet surface. Among these factors, regarding surface roughness, it is well known that hysteresis loss can be reduced if the surface of the steel plate is mirror-finished.

As a method for improving the surface of a steel sheet and reducing hysteresis loss, for example, Japanese Patent Publication No. 52-24499 discloses that after final annealing, oxides on the surface of a grain-oriented silicon steel sheet are removed by pickling, and then the surface is chemically treated. A technique has been disclosed in which a mirror finish is achieved by polishing or electrolytic polishing, and then the mirror finish surface is thinned with metal.

Furthermore, Japanese Patent Publication No. 56-4150 discloses that after removing non-metallic substances from the surface of a grain-oriented silicon steel sheet, the surface is finished to a mirror-like state by chemical polishing or electrolytic polishing, and then a ceramic thin film is applied to the mirror-finished surface. A technique for producing the same is disclosed.

Furthermore, JP-A No. 60-89589 discloses that after removing surface oxides from a grain-oriented silicon steel sheet after secondary recrystallization using an annealing separator mainly composed of alumina, chemical polishing or electrolytic polishing is performed. A technique for applying this has been disclosed.

Furthermore, JP-A No. 60-39123 discloses a technology that uses an annealing separator containing alumina as a main component to control the amount of oxides on the surface of a steel sheet, and then directly applies chemical polishing or electrolytic polishing without pickling. Disclosed.

(Problem to be Solved by the Invention) However, although all of these techniques have a very clear effect of reducing iron loss, they have not yet been implemented industrially.

The first reason is that mirror-finished surfaces and surfaces plated with metal cannot maintain the adhesion with the insulation coating required for grain-oriented silicon steel sheets, and the insulation coating or tension coating may peel off. This is because Furthermore, when a ceramic thin film is formed as in Japanese Patent Publication No. 56-4150, not only is the adhesion between the ceramic thin film and the surface of the steel base poor, but also the ceramic film has no flexibility. It had a fatal flaw in that it would peel off.

The second reason is that in the case of chemical polishing, the polishing liquid used as up+ttgo□, H3PO4+HtO□, etc. is expensive, resulting in high costs. Similarly, in the case of electrolytic polishing, the phosphoric acid baths, sulfuric acid baths, phosphoric acid-sulfuric acid baths, and perchloric acid baths that are commonly used as polishing solutions all have high concentration acids as their main component, and they do not contain additives. The use of chromate, hydrofluoric acid, organic compounds, etc. increases costs, and in order to process large quantities of steel sheets, uniformity,
There are many unresolved issues such as productivity and early deterioration of the liquid.

The present invention advantageously solves the above-mentioned problem, and eliminates the need for mirror polishing by electrolytic polishing or chemical polishing, which is a magnetically smooth surface, which prevents the movement of domain walls that cause hysteresis loss. The object of the present invention is to propose an advantageous manufacturing method for grain-oriented silicon steel sheets that form a surface that is free from scratches and has a surface state that is excellent not only in magnetic properties but also in film adhesion.

(Means for solving problems) This invention is based on the following findings.

The first point is that it is mainly the surface oxide that has a large effect on the hysteresis loss, and that the surface irregularities do not necessarily have to be mirror-like. Here, the specular state is an optical concept, and although it is not quantitatively defined, it refers to a surface roughness of 0.4 μm or less, preferably 0.1 μm or less in center line average roughness.

Figure 3 shows a grain-oriented silicon steel sheet with oxides on its surface.
The graph shows a comparison of the iron losses of a grain-oriented silicon steel sheet that has been subjected to mirror polishing treatment and a grain-oriented silicon steel sheet that has been further pickled and has a rough surface. Even if the mirror surface is lost, the iron loss does not deteriorate much.

In order to obtain a silicon steel sheet with low hysteresis loss in this way, it is not necessarily necessary to make the surface of the steel sheet a mirror surface.In other words, it is necessary to make the surface of the steel sheet a magnetically smooth surface, that is, to prevent the movement of the domain walls that cause hysteresis loss. It is sufficient to use a surface with no surface. Therefore, electrolytic polishing and chemical polishing are not indispensable conditions, and surface treatment means can be selected more freely.

Therefore, the inventors investigated various surface treatments, including treatments that had not been previously applied to silicon steel sheets, and found that electrolytic treatment in a halide bath would achieve the intended purpose. We have obtained knowledge that this method is extremely effective.

In other words, when a grain-oriented silicon steel sheet is subjected to anodic electrolysis treatment in an aqueous halide solution, the surface exhibits a unique mesh pattern different from a mirror surface (very similar to the graining surface obtained during electrolytic etching). Therefore, they found that a steel sheet with such a graining-like surface (hereinafter referred to as a graining-like surface) has an extremely small hysteresis loss.

The second finding is that the thermal spraying method is particularly suitable as a means of applying an insulating coating, and it is possible to achieve good adhesion without impairing the magnetic smoothness of the base material surface, that is, without the disadvantage of increasing hysteresis loss. It is possible to form a coating rich in . The thermal spraying effect was particularly excellent on the graining-like surface, and the reason for this is thought to be that the mechanical adhesion of the coating was further improved by the unevenness of the graining-like surface.

Furthermore, in the case of a thermally sprayed coating, even when a phosphate-based insulating tension coating is formed on top of the thermally sprayed coating, an insulating coating with good adhesion can be obtained. Therefore, if the thermal spray coating is preferably made to have an extremely thin basis weight and a phosphate-based insulating tension coating is applied thereon, an insulating coating with good adhesion and excellent tension imparting effect can be obtained.

That is, this invention electrolytically treats a grain-oriented silicon steel sheet after secondary recrystallization annealing in an aqueous solution containing one or more water-soluble halides, and then thermally sprays the surface of the steel sheet with a highly adhesive coating. A method for manufacturing a grain-oriented silicon steel sheet with good magnetic properties (first invention).

The present invention also provides a method for producing a grain-oriented silicon steel sheet with good magnetic properties (Second Embodiment), which comprises, after forming the thermal spray coating described above, further coating the surface of the coating with a tension imparting coating that provides insulation. invention).

This invention will be specifically explained below.

In this invention, all secondary recrystallized grain-oriented silicon steels and plates are targeted. Such a material is obtained by hot rolling a slab for silicon steel according to a conventional method, then cold rolling with intermediate annealing to obtain the final thickness, decarburizing the slab, and final finish annealing. .

As an annealing separator during this final annealing, an annealing separator containing MgO as a main component, which has traditionally been used to simultaneously form a forsterite film, can of course be used, but it is not possible to form such a forsterite film. For example, the main component is AlKO3 etc.
Particularly advantageous are separation agents to which inert MgO, Ca, and Sr compounds are added.

Next, the surface oxidation layer of the final annealed plate is removed as necessary. Removal methods include chemical fishing methods such as pickling and mechanical methods such as emery polishing, but are not particularly limited.
When the surface oxide layer is removed by mechanical methods, distortion tends to occur inside the steel sheet, and such distortion cannot be completely released by the subsequent electrolytic treatment, so it is better to remove the surface oxide by pickling treatment. preferable.

Next, the surface from which the surface oxide layer has been removed is subjected to anodic electrolysis treatment to form a magnetically smooth surface, that is, a grain boundary with Rsm
Step-like or groove-like recesses with x of 0.4 μm or more are formed, and the surface of the crystal grains has a so-called graining-like surface in which the recesses are adjacent to each other via the boundaries of the protrusions.

A magnetically smooth grained surface can be easily obtained by an anodic electrolytic treatment using an aqueous solution containing one or more water-soluble halides as an electrolyte.

Here, water-soluble halides include HCl, NH, C
I and various metal chlorides or acids with F, Br, and I as anions, their alkali, alkaline earth, and other metal salts and ammonium salts, water-soluble ones, and also fluorides (BP, salts) ) and silica fluoride (S
(in, salt) refers to water-soluble ones. Typical examples are HCI, NaC1+ KC1+ N
H4Cl, MgCh+ CaC1z+ AlCl31
HFI NaF.

KFI NH4FI HBr, NaBr, KBr,
MgBrt, CaBrz, NH4Br+HI+N
aI, KI+ NH411Ca1z, MgIz+
H2SIF61 Mg5iFh.

(NI+4)zsiF61118F41 NH4BF4
and NaBFi etc. These are all (110
) has a magnetic smoothing effect on grain-oriented silicon steel sheets after finish annealing, but in actual operation, considering prevention of metal precipitation on the cathode, etc. It is desirable to select and use them. In addition, the concentration is 20 g /
It is desirable that it is 1 or more. Note that seawater can also be used in the present invention due to its composition and concentration described above.

The bath temperature can be arbitrarily selected from room temperature or higher, but if the temperature is too high, the water will evaporate significantly, so a temperature between room temperature and about 90°C is appropriate. The current density can be set in the range from about 5 A/dm2 to several hundred A/dm''. However, if the current density is set to a high current density exceeding 100 A/dm when the bath temperature is low, it is likely to cause uneven surface treatment. In order to widen the range of current density, it is preferable to set the bath temperature to 40°C or higher.

In addition, from the viewpoint of reducing iron loss, the amount of electricity in electrolysis and the amount of electrolytic removal in this invention are each 300 C/dm.
As mentioned above, it is preferable that the thickness be 1 μm or more per side.

As described above, in this invention, the magnetic smoothing effect can be obtained under a much wider range of conditions than in the conventional method, and this point is also advantageous for the industrial implementation of this invention. This is an important basis.

Here, the changes in the bath caused by the electrolytic reaction are shown below, taking an NaCl aqueous solution as an example.

Anode: Pe+2CI--+ FeC1z+2e-"(
1) Cathode: 2Na"+211zO+2e--2NaO
H+IIz↑ −(2) Bulk: FeC1z +
2NaOH→2NaC1+ Fe(OH) z ↓ ・
(3) That is, FeC1 produced by equation (1) and NaOH produced by equation (2) automatically regenerate NaCl by the reaction shown in (3) 2. Therefore, the bath composition is basically controlled by Fe(
All you need to do is remove the OH)z precipitate, replenish water, and replenish NaC1, which the steel plate carries out of the system, making it much easier and cheaper than conventional chemical polishing or electrolytic polishing. Become. This point is also one of the reasons why the method of this invention is industrially superior.

By carrying out the above-mentioned magnetic smoothing treatment, it is possible to effectively improve the magnetic properties, but since the base iron is exposed on the surface of the tone plate after the treatment, there is no glabellar resistance during lamination. Therefore, it is necessary to apply an insulating coating to the surface of the steel plate. At that time, if an insulating coating that can apply tensile stress to the surface of the steel plate is used, it can be expected to reduce iron loss due to a reduction in eddy current loss, and this effect is particularly effective in the case of graining-like surfaces as in this invention. Significant.

Phosphate-based coatings and ceramic coatings are conventionally known as such insulating coatings, but these coatings cannot ensure sufficient adhesion to mirror-finished surfaces. Although it was possible to improve adhesion in some respects, the effect could not be said to be sufficient.

Therefore, the inventors investigated various ways to obtain an insulating film that has good adhesion and does not increase hysteresis loss.
, Cr, Off, oxides such as MgO, Si3N,
It has been found that thermal spray coating with nitrides such as AIN is extremely effective in achieving the desired objectives.

Any conventionally known thermal spraying method such as plasma spraying or gas spraying is suitable here. The particle size of the powder used during thermal spraying is preferably as fine as possible so that it can be transported in the carrier gas, and is particularly preferably on the order of 10 μm or less.

By further applying a tension-applying phosphate coating on top of the above-mentioned thermal spray coating, a greater tension-applying effect and insulation effect can be obtained.

In this case, it is preferable to coat the thermal sprayed coating with a material with good adhesion such as AlzOs to a thickness of about 0.5 μm, and in this way, the tension imparting effect inherent to the tension imparting type insulation coating can be fully exerted. It has now become possible to perform.

It should be noted that thermal spraying materials other than those listed above can be used alone or in combination as long as they have a low coefficient of thermal expansion and good adhesion.

(Function) A silicon steel plate after secondary recrystallization annealing was heated with NaC1:200g.
/ When a graining-like surface is obtained by electrolytic treatment in a halide bath containing 1, and a mixed solution of phosphoric acid and chromic acid (chromic acid: 200 g)!・When electrolytically polished using phosphoric acid (phosphoric acid) to obtain a mirror surface, furthermore, after that, each
Figures 1a and b show the results of an investigation into improvements in iron loss and magnetic flux density when spraying a 5iJ4 film with a thickness of about I.
are shown respectively.

As is clear from the figure, further improvement in magnetic properties is achieved according to the method of this invention.

Next, A1□0 was applied to the above graining surface at various thicknesses.
．． After plasma spraying of
Shown in Figure 2.

As is clear from the figure, by thermally spraying an Ahos film with a thickness of 0.3 μI or more prior to the tension-applying phosphate coating, the occurrence of poor adhesion is completely prevented.

(Example) Contains Si: 3.2% and Mn as an inhibitor
S.

Directional grain after secondary recrystallization obtained by hot rolling, cold rolling, decarburization/first recrystallization annealing, and final finish annealing of a slab for silicon steel containing MnSe and sb according to conventional methods. Made of raw steel plate.

Table 1 also lists the results of investigating the effects of improving film adhesion, iron loss, and magnetic flux density when this material was subjected to electrolytic treatment, thermal spraying, and top insulating coating under the various conditions shown in Table 1. .

Compatible Examples 1 to 3 were subjected to electrolytic treatment using NaCl or MCI and then thermally sprayed with a 0.5 μm thick film, and Compatible Examples 4 to 6 were further coated with a top coat. In all of these Compatible Examples 1 to 6, coatings with good adhesion were obtained, and both core loss and magnetic flux density were significantly improved.

On the other hand, in Comparative Examples 1 and 2, in which phosphate coating was applied directly after electrolytic treatment with a halide, peeling of close to 40% occurred.

(Effects of the Invention) Thus, according to the present invention, it is possible to stably obtain a grain-oriented silicon steel sheet that not only has excellent magnetic properties but also excellent film adhesion at a low cost.

[Brief explanation of the drawing]

Figures 1a and b show silicon steel sheets after secondary recrystallization annealing, which are finished with a graining-like surface or a mirror surface.
A graph comparing the improvements in iron loss and magnetic flux density when thermally sprayed N and films. Figure 2 shows the results of thermally sprayed films obtained by plasma spraying AhOff at various thicknesses on grained surfaces. Figure 3, a graph showing the relationship between thickness and adhesion defect incidence rate, shows grain-oriented silicon steel sheets with oxides on the surface, grain-oriented silicon steel sheets that have been subjected to mirror polishing treatment, and grain-oriented silicon steel sheets that have been further pickled afterwards. It is a graph showing a comparison of various iron losses of grain-oriented silicon steel sheets with roughened surfaces. 11 pieces! g 翳ε4ku - 徊 - ri】zu red exposure autopsy i

Claims (1)

[Claims] 1. A grain-oriented silicon steel sheet after secondary recrystallization annealing is electrolytically treated in an aqueous solution containing one or more water-soluble halides, and then a highly adhesive coating is formed on the surface of the steel sheet. A method for producing a grain-oriented silicon steel sheet with good magnetic properties characterized by thermal spray coating. 2. After secondary recrystallization annealing, the grain-oriented silicon steel sheet is electrolytically treated in an aqueous solution containing one or more water-soluble halides, and then a highly adhesive coating is thermally sprayed on the surface of the steel sheet, and then further A method for producing a grain-oriented silicon steel sheet with good magnetic properties, which comprises forming a tension-applying film with insulation properties on the surface of the film.