JP2002266027A - Method for manufacturing grain-oriented silicon steel sheet with excellent coating quality of forsterite film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of dot defects in a forsterite insulating film on the furnace-top side of a coil which is liable to occur in the case that rapid heating is performed in a box annealing furnace and a forsterite film is abruptly formed. SOLUTION: In manufacturing a grain-oriented silicon steel sheet, oxygen coating weight over the direction of sheet width after decarburizing annealing is controlled in such a way that the oxygen coating weight in the region between the edge of the steel sheet and a position at a distance of at least 100 mm from the edge becomes -10% to +5% of that in the central part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent forsterite coating quality,
In particular, it is intended to effectively prevent the occurrence of point-like defects in the forsterite coating after the final finish annealing.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are mainly used as core materials for transformers and other electrical equipment, and have excellent electromagnetic properties such as magnetic flux density and iron loss, and excellent film properties such as insulation and adhesion. It is basically important.

In such a grain-oriented electrical steel sheet, a steel slab containing an inhibitor required for secondary recrystallization, for example, a slab containing MnS, MnSe, AlN or the like is hot-rolled, and if necessary, hot-rolled sheet annealing is performed. After the final thickness is obtained by cold rolling once or twice or more with intermediate annealing, decarburizing annealing is performed.
Next, an annealing separator such as MgO is applied to the surface of the steel sheet, followed by final finish annealing to produce the steel sheet. Except for special cases, a forsterite (Mg ₂ SiO ₄ ) -based insulating coating is generally formed on the surface of the grain-oriented electrical steel sheet.

This forsterite film, when used in a laminated steel sheet, electrically insulates between the layers and effectively contributes to reducing eddy current, but the insulating film on the steel sheet surface is uneven. In addition, if film peeling occurs during winding core production, not only does the commercial value decrease, but also the space factor decreases, and furthermore, the insulation property decreases due to tightening during core assembly, causing local heat generation. It can cause accidents in transformers.

The forsterite coating not only provides electrical insulation on the surface of the steel sheet but also contributes to improvement of iron loss and magnetostriction by applying tensile stress to the steel sheet by utilizing its low thermal expansion property. ing. Further, the forsterite film also contributes to the improvement of the magnetic properties by purifying the steel by sucking up the unnecessary inhibitor component after the completion of the secondary recrystallization and purifying the steel. Therefore, obtaining a uniform and smooth forsterite film is one of the important points that affect the product quality of grain-oriented electrical steel sheets.

In general, if the amount of forsterite film is too large, a point defect in which the forsterite film is locally peeled tends to occur, while if the amount of forsterite film is too small, the adhesion of the film deteriorates. Therefore, conventionally,
Various measures have been taken to obtain a good forsterite coating.

[0007] For example, there is known a method of reducing the oxygen basis weight of a steel sheet after decarburization annealing by reducing the oxygen basis weight of the steel sheet before decarburization annealing (Japanese Patent Laid-Open No. 9-3154).
No. 5). Further, a method of controlling the oxygen weight of a steel sheet after decarburizing annealing by controlling the degree of atmospheric oxidation during decarburizing annealing is also known (Japanese Patent No. 25797).
No. 17).

[0008]

As described above, the amount of forsterite film formed during box annealing can be controlled by adjusting the basis weight of oxygen after decarburizing annealing. However, even when the oxygen basis weight after decarburizing annealing is controlled according to the above-mentioned technology, the forsterite film is rapidly heated due to the large heat receiving area in the box-type annealing furnace at the time of final finish annealing, and the forsterite film is rapidly On the furnace top side of the coil formed in the above, spot-like defects were sometimes generated in the forsterite film.

The present invention advantageously solves the above-mentioned problems, and effectively prevents the generation of point-like defects in the forsterite film on the furnace top side of a coil subjected to rapid heating in a box type annealing furnace. It is an object of the present invention to propose a method for improving the quality of a forsterite film on a grain-oriented electrical steel sheet, which can prevent the quality of the forsterite film.

[0010]

That is, the gist of the present invention is as follows. 1. After the silicon-containing steel slab is hot-rolled, it is subjected to one or two or more cold-rollings sandwiching intermediate annealing, and then, after decarburizing annealing, after applying an annealing separator containing MgO as a main component, In producing a grain-oriented electrical steel sheet by a series of steps of performing final finish annealing, the oxygen basis weight in the sheet width direction after decarburizing annealing should be at least 100 mm from the steel sheet edge.
Over the range of -10% of that of the central part
A method for producing a grain-oriented electrical steel sheet having excellent forsterite coating quality, characterized in that the grain size is controlled within the range of + 5%.

2. After hot rolling the silicon steel slab, it is subjected to cold rolling once or twice or more with intermediate annealing, then electrolytic degreasing, decarburizing annealing, and then Mg.
After applying an annealing separator containing O as a main component, when manufacturing a grain-oriented electrical steel sheet by a series of steps of performing a final finish annealing, during the electrolytic degreasing treatment, an electrode mask is provided on an edge portion of the steel sheet. A method for producing a grain-oriented electrical steel sheet having excellent forsterite coating quality, wherein the amount of electrodeposited Si in a region extending at least 100 mm from the edge of the steel sheet is smaller than that in the central part.

3. 2. The method for producing a grain-oriented electrical steel sheet having excellent forsterite coating quality according to the above item 2, wherein the amount of electrodeposited Si in a region extending at least 100 mm from the edge of the steel sheet is 0.5 to 0.8 times that of the central portion.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. First, the details of the invention will be described. By the way, the inventors reexamined the manufacturing history of the coil in which point-like defects frequently occurred in the forsterite film after box-shaped annealing. As a result, it was found that, in such a coil, in the decarburization annealing plate stage, the oxygen basis weight at the edge portion in the plate width direction was about 20% higher than that at the center portion in the plate width. It was also found that such a coil had a large amount of electrodeposited Si adhered at the edge portion during electrolytic degreasing.

FIGS. 1 (a) and 1 (b) show the amount of electrodeposited Si and the amount of electrodeposition during the electrolytic degreasing treatment of the coil in which point-like defects of the forsterite film finally occurred frequently and the coil in which almost no point defects occurred. The results of examining the basis weight of oxygen after charcoal annealing are arranged and shown. As shown in the figure, in all of the coils in which point-like defects of the forsterite film occurred frequently, the amount of electrodeposited Si during electrolytic degreasing and the basis weight of oxygen after decarburization annealing were higher at the edge than at the center of the plate width. It was found to be increasing in some parts. On the other hand, in the coil where point-like defects of the forsterite film hardly occurred, the amount of electrodeposited Si during electrolytic degreasing and the amount of oxygen per unit area after decarburizing annealing were almost the same at the center and edge of the plate width. There was no.

Then, next, what is the difference in the basis weight of oxygen after decarburization annealing between the center part and the edge part of the sheet width?
Finally, it was examined whether point-like defects were generated in the forsterite film. As a result, it was found that an excellent forsterite film free of point-like defects could be obtained if the oxygen basis weight in a region extending at least 100 mm from the steel sheet edge was in the range of -10% to + 5% of that of the central portion. .

Therefore, even if the weight per unit area of the edge portion after decarburizing annealing is increased by about 20% as compared with that at the central portion of the sheet width by manufacturing according to the conventional method, it is necessary to carry out the same before the next step. If the basis weight of oxygen at the edge portion is controlled in the range of −10% to + 5% of that at the center portion by grinding, pickling, or the like, generation of point defects can be effectively prevented.

As means for controlling the oxygen basis weight,
Although there is a method of newly providing a process such as grinding and pickling as described above, a more preferable means in terms of productivity was examined below. The inventors found that the oxygen basis weight of the steel plate edge was
In view of the strong correlation with the amount of electrodeposited Si adhered during electrolytic degreasing, we attempted to adjust the basis weight of oxygen at the edge by devising this electrolytic degreasing treatment.

First, the amount of electrodeposited Si in the width direction of the sheet during the normal electrolytic degreasing treatment was examined. As shown in FIG. 2, the amount of electrodeposited Si at the edge of the steel sheet was larger than that at the center. confirmed. In addition, the amount of electrodeposited Si was evaluated by intensity measured by fluorescent X-ray: kcps (kiro count per second).

Then, as a result of various studies on means for preventing an increase in the amount of electrodeposited Si at the edge of the steel sheet, as shown in FIG. It has been found that it is effective to insert an electrode mask 3 between the electrodes 2 and 2 to reduce the electrolytic force at the edge. FIG. 4 shows the results of examining the amount of electrodeposited Si in the width direction of the sheet when an electrode mask is placed in a region extending 100 mm from the steel sheet edge and electrolytic degreasing is performed. As shown in the figure, by installing such an electrode mask, the amount of electrodeposited Si at the edge of the steel sheet could be effectively reduced.

The edge region of the steel sheet to be covered with the electrode mask is at least 100 mm from the edge. However, if the coating area is too wide, there is a disadvantage that the amount of electrodeposited Si at the edge portion is too small, so the upper limit of the coating area is preferably about 200 mm from the edge. A more preferred range is 10 from the edge
It is in the range of 0-150 mm. Furthermore, the electrodeposited Si at the steel sheet edge to be reduced by masking as described above
The amount is preferably 0.5 to 0.8 times that of the central part. This is because the above range is optimal in order to finally obtain a uniform and excellent forsterite coating with good oxygen basis weight after decarburizing annealing.

The composition of the grain-oriented electrical steel sheet targeted in the present invention is not particularly limited, and any conventionally known one can be used. There are no particular restrictions on the manufacturing conditions for the grain-oriented electrical steel sheet, and any conventionally known method may be used. However, in the present invention, it is important to adjust the basis weight of oxygen after decarburization annealing. That is, after the decarburization annealing, the weight per unit area of the steel sheet is examined in the width direction of the steel sheet, and if the oxygen weight per unit area at the edge is larger than that at the center of the width of the sheet, before being subjected to the next step, Oxygen weight at edge is reduced by -10% of that at center by grinding or pickling.
It is important to control within the range of + 5%.

When electrolytic degreasing is performed prior to the above decarburizing annealing, an electrode mask is inserted between the electrolytic electrode and the steel sheet in an area extending at least 100 mm from the steel sheet edge during the electrolytic degreasing. It is important to reduce the electrolytic force at the edge and to make the amount of electrodeposited Si at the edge of the steel sheet 0.5 to 0.8 times that at the center.

The amount of electricity during the electrolytic degreasing treatment is preferably about 0.1 to 100 A / dm ² , and the bath composition is preferably an alkaline aqueous solution containing sodium silicate. Potassium silicate is used instead of soda. An alkali metal silicate such as lithium silicate may be used. Also,
The concentration is preferably about 0.5 to 15 mass%, and more preferably about 1 to 8 mass%.

[0024]

[Example] C: 0.040 mass%, Si: 3.2 mass%, Mn: 0.
067 mass%, Se: 0.020 mass% and Sb: 0.021 mass%
, The balance being Fe and unavoidable impurities, a silicon steel slab is hot-rolled and then cold-rolled twice with intermediate annealing to obtain a sheet thickness: 0.23 mm and a sheet width: 1200 mm
Cold rolled sheet. Then, sodium orthosilicate (Na ₄ SiO
_In a electrolytic bath containing 1) to 10% by mass of ₄ ) and 0.5% by mass of a surfactant, electrolytic degreasing treatment was performed under various conditions, and Si was electrodeposited on the surface of the steel sheet. The above-mentioned electrolytic degreasing treatment was performed in two cases, as before, without an electrode mask, and in a region 100 mm from the steel plate edge according to the present invention, when an electrode mask was inserted between the electrolytic electrode and the steel plate.

After the above electrolytic degreasing treatment, the degree of oxidation in the atmosphere [P
(H ₂ 0) / P (H ₂ )] was subjected to decarburizing annealing at 800 ° C. for 3 minutes in an atmosphere of 0.4. FIGS. 5 (a) and 5 (b) show comparisons of the results of the examination of the basis weight of oxygen in the width direction of the steel sheet after the decarburization annealing in the case without and with the electrode mask.
As shown in the figure, in each case without the electrode mask as in the conventional case, the oxygen basis weight at the edge portion was larger than that at the center portion, whereas when the electrode mask was provided according to the present invention. In each case, the basis weight of oxygen at the edge was smaller than that at the center.

Thereafter, an annealing separator containing MgO as a main component is applied, wound around a coil, and then placed in a nitrogen atmosphere.
Secondary recrystallization annealing at 50 ° C for 70 hours and in a hydrogen atmosphere
Purification annealing was performed at 1180 ° C for 7 hours.

FIG. 6 shows the results obtained by examining the state of occurrence of point defects on the product plate thus obtained. The point-like defects were evaluated based on the rate of occurrence of the point-like defect length, that is, the ratio of the length of the point-like defect occurrence to the entire length of the coil. As shown in the figure, when an electrode mask was installed on the edge of a steel sheet during electrolytic degreasing according to the present invention, the occurrence of point-like defects was much more noticeable than in the conventional method without such an electrode mask. Has been reduced.

[0028]

As described above, according to the present invention, it is possible to effectively prevent point-like defects of a forsterite film, which has been a concern in the past, on the furnace top side of a coil subjected to rapid heating in a box type annealing furnace. Thus, it is possible to obtain a grain-oriented electrical steel sheet having an excellent forsterite coating that is uniform and free from defects.

[Brief description of the drawings]

[FIG. 1] The amount of electrodeposited Si during electrolytic degreasing treatment of coils where point-like defects of the forsterite film frequently occurred and coils where almost no point defects occurred, and the basis weight of oxygen after decarburization annealing (b) FIG.

FIG. 2 is a graph showing the amount of electrodeposited Si over the width direction of a sheet during a normal electrolytic degreasing process.

FIG. 3 is an explanatory view of how to insert an electrode mask between an electrolytic electrode and a steel plate.

FIG. 4 is a graph showing the amount of electrodeposited Si in the sheet width direction when an electrode mask is installed in a region extending 100 mm from the steel sheet edge and electrolytic degreasing is performed.

FIG. 5 is a graph showing the basis weight of oxygen in the width direction of the steel sheet when the electrolytic degreasing treatment is performed in the case where the electrode mask is not provided (a) and the case where the electrode mask is provided (b).

FIG. 6 is a diagram showing a comparison of the state of occurrence of a point defect in the case where the basis weight of oxygen is controlled and the case where the basis weight is not controlled.

[Explanation of symbols]

 1 Electrolytic electrode 2 Steel plate 3 Electrode mask

Claims (3)

[Claims] 1. A silicon steel slab is hot-rolled, subjected to one or two or more cold-rolling steps with intermediate annealing, then decarburized and then an annealing separator containing MgO as a main component. After manufacturing the grain-oriented electrical steel sheet through a series of steps of applying final finish annealing after coating, the oxygen weight per unit area in the width direction at least 100 mm from the edge of the steel sheet after the decarburizing annealing is calculated. A method for producing a grain-oriented electrical steel sheet having excellent forsterite coating quality, wherein the grain size is controlled in a range of -10% to + 5% of that of the central part. 2. The silicon-containing slab is hot-rolled, subjected to one or two or more cold-rolling steps including intermediate annealing, and then subjected to electrolytic degreasing treatment, followed by decarburizing annealing, and then to Mg.
After applying an annealing separator containing O as a main component, when manufacturing a grain-oriented electrical steel sheet by a series of steps of performing final finish annealing, installing an electrode mask on an edge portion of the steel sheet during the electrolytic degreasing treatment. At least 100mm from steel plate edge
A method for producing a grain-oriented electrical steel sheet having excellent forsterite coating quality, characterized in that the amount of electrodeposited Si in the region extending over the region is smaller than that in the central portion. 3. The directional electromagnetic field with excellent forsterite coating quality according to claim 2, wherein the amount of electrodeposited Si in a region extending at least 100 mm from the edge of the steel sheet is 0.5 to 0.8 times that of the central portion. Steel plate manufacturing method.