JP3277039B2 - Method for producing grain-oriented silicon steel sheet having homogeneous forsterite coating - Google Patents

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 silicon steel sheet, and more particularly to a method for producing a grain-oriented silicon steel sheet having a forsterite insulating coating having a uniform and excellent adhesion.

[0002]

2. Description of the Related Art Grain-oriented silicon steel sheets are used for laminated cores of transformers,
Alternatively, it is used as a wound core, and has an insulating coating on the surface of the steel sheet in order to maintain insulation between the layers. This coating film must satisfy many properties such as adhesion to ground iron, uniform appearance, and high space factor, in addition to insulating properties. In order to form such a coating, the following method is generally employed.

First, a silicon steel strip cold-rolled to a predetermined final thickness is decarburized and annealed in wet hydrogen at a temperature in the range of 700 to 900 ° C. to form a subscale mainly composed of SiO _{2 on the} surface of the steel sheet. Further, an annealing separator mainly composed of MgO is applied on the oxide film and dried, and then the strip is wound up in a coil shape, and then subjected to finish annealing again in hydrogen at a high temperature of 1100 to 1200 ° C. At this time, MgO and SiO ₂ are reacted to form a forsterite film on the steel sheet surface.

[0004] Therefore, the quality of the forsterite coating is strongly affected by the subscale formed after decarburizing annealing. Therefore, to improve the quality of the subscale,
Several methods have been proposed so far. For example, in Japanese Unexamined Patent Publication No. 50-71526, the surface layer of the final cold-rolled sheet before decarburizing annealing is removed by pickling at least 3 g / m ^{2 to} remove deposits on the surface. Is described as being improved.

Further, in Japanese Patent Laid-Open Publication No. Sho 57-101673, a uniform film is formed by removing the surface of the final cold-rolled sheet before decarburizing annealing by grinding or pickling 0.025 to 0.5 g / m ² on one side. It is described that the adhesion is improved. However, even with these methods, the quality of the subscale formed after the decarburizing annealing is largely varied, and as a result, the quality of the forsterite film is often unstable.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to propose a method for stably producing a grain-oriented silicon steel sheet having a uniform forsterite film having excellent adhesion and few defects. .

[0007]

Means for Solving the Problems The present inventors have studied the quality of the subscale formed after decarburizing annealing, the quality of the forsterite film formed after finishing annealing, and the steel sheet in each step before decarburizing annealing. The surface condition was studied in detail. As a result, it was found that the Si concentration decreased in the surface layer of the ground iron after the intermediate annealing, and this decrease in Si concentration was found to be the main cause of the variation in subscale quality. In addition, they have found that the thickness of the lower Si concentration layer increases as the temperature of the intermediate annealing increases. Therefore, the present inventors thought that by removing the surface layer having a thickness corresponding to the Si concentration lowering layer according to the intermediate annealing temperature, it is possible to eliminate variations in subscale quality, and to complete the present invention. Reached.

That is, according to the present invention, a silicon steel slab is hot-rolled, subjected to two or more cold rolling steps including intermediate annealing to obtain a final cold-rolled sheet thickness, and then subjected to decarburization annealing to provide a steel sheet surface. Si
By forming a sub-scale mainly composed of O ₂ , further applying an annealing separator mainly composed of MgO, and then performing a final annealing, an intermediate annealing is performed to form an insulating coating made of forsterite on the surface of the steel sheet. A method for producing a grain-oriented silicon steel sheet having a uniform forsterite coating, comprising removing a surface layer having a weight represented by the following formula prior to decarburization annealing.

A ≧ (0.65 × B−543) × C where A: surface layer to be removed (g / m ² ), B: intermediate annealing temperature (° C.), C: thickness before removal of surface layer (mm) ).

[0010]

FIG. 1 shows the Si concentration distribution in the depth direction of a grain-oriented silicon steel sheet cold-rolled to a thickness of 0.23 mm at 900 ° C., 1000 ° C. and 1100 ° C., respectively. The polishing in the depth direction was performed using # 180 emery paper, and the Si concentration was determined from the Si count obtained by X-ray fluorescence analysis.

According to FIG. 1, it is clear that the Si concentration in the surface layer is extremely reduced. Further, the degree of the decrease in the Si concentration is remarkable when the intermediate annealing temperature is high. If the Si concentration is reduced in this way, it is considered that the amount of generated SiO ₂ , which is a main component of the subscale, is also reduced. Therefore, we conducted experiments to remove the surface by various methods for grain-oriented silicon steel sheets with various intermediate annealing temperatures. As a result, if the amount of the surface layer determined by the following equation was removed, the subscale quality was stable. Therefore, the forsterite coating quality was found to be stable.

A ≧ (0.65 × B−543) × C where A: surface layer to be removed (g / m ² ), B: intermediate annealing temperature (° C.), C: sheet thickness before removal of surface layer (mm) ). Appropriate removal methods include shot, brush roll, grinder, grinding, and pickling. The removal may be performed at any time after the intermediate annealing and before the decarburizing annealing. However, it is advantageous to reduce the thickness of the sheet because the load is lighter. By the way, if it is rolled,
The thickness of the low-concentration Si layer is also reduced.

[0013]

Example After intermediate cold rolling to a thickness of 1.25 mm, intermediate annealing was performed at 1000 ° C, and a grain-oriented silicon steel sheet cold-rolled to 0.23 mm was subjected to decarburizing annealing in wet hydrogen at 830 ° C for 3 minutes. And then
By applying MgO containing 1.5% TiO ₂ as an annealing separator, and performing high-temperature finish annealing in hydrogen at 1200 ° C for 10 hours,
A forsterite coating was formed. In performing this treatment, the surface layer was ground and removed by variously changing the amount of grinding with a grinding roll at each stage of the thickness of 1.25 to 0.23 mm during the final cold rolling.

FIG. 2 shows the evaluation results of the uniformity of appearance and the adhesion of the forsterite film thus obtained. The adhesion was evaluated by the minimum diameter at which the forsterite film did not peel off when the grain-oriented silicon steel sheet was wound around a cylinder. According to the figure, the forsterite film obtained according to the present invention has good appearance and adhesion, but in the comparative example, the film appearance is non-uniform and adhesion is poor.

[0015]

According to the present invention, it is possible to stably and surely obtain a uniform forsterite film having good adhesion and particularly having no uneven appearance.

[Brief description of the drawings]

FIG. 1 is a graph showing Si concentration distribution in the thickness direction of a sheet when intermediate annealing is performed at various temperatures.

FIG. 2 is a graph showing the results of evaluating the relationship between the plate thickness before grinding and removal after the intermediate annealing temperature and the amount of grinding in terms of appearance uniformity and adhesion.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-96770 (JP, A) JP-A-60-145382 (JP, A) JP-A-61-96082 (JP, A) JP-A-62 133021 (JP, A) JP-A-62-156221 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 22/00-22/86 C21D 9/46 501

Claims (1)

(57) [Claims] 1. A silicon steel slab is hot-rolled and subjected to two or more cold-rollings including an intermediate annealing to a final cold-rolled sheet thickness, and then a decarburizing annealing is performed, and SiO ₂ is mainly applied to the surface of the steel sheet. In addition, an annealing separator mainly composed of MgO is applied, followed by finish annealing to form an insulating coating made of forsterite on the surface of the steel sheet. A method for producing a grain-oriented silicon steel sheet having a uniform forsterite film, wherein a surface layer having a weight represented by the following formula is removed. A ≧ (0.65 × B−543) × C where A: surface layer to be removed (g / m ² ), B: intermediate annealing temperature (° C.), C: thickness before removal of surface layer (mm) .