JPH10330843A - Electrolytic degreasing method for grain-oriented electrical steel sheets with excellent film properties - Google Patents

Abstract

(57) [Problem] To provide an electrolytic cleaning condition in a manufacturing process of a grain-oriented electrical steel sheet in which occurrence of a glass film film defect is prevented. SOLUTION: A strip for grain-oriented electrical steel sheet containing Si ≦ 4.5% or less, which is cold-rolled to a final thickness, is electrolytically degreased with a silicate-free alkaline cleaning agent, preferably caustic soda, and then washed with water. An electrolytic degreasing method for grain-oriented electrical steel sheets having excellent film properties, in which the track time for decarburizing annealing after cold rolling and decarburizing annealing after cold rolling is within 14 days.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a degreasing cleaning after a final finish cold rolling and before a decarburizing annealing step in a manufacturing process of a grain-oriented electrical steel sheet. The present invention relates to a method for producing a grain-oriented electrical steel sheet having an excellent glass coating that simultaneously satisfies both stabilization of secondary recrystallization and improvement of glass coating characteristics by adjusting the degreasing process.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet has a (110)
[001] A sheet thickness of 0.1%, usually containing 4.5% or less of Si, which is composed of crystal grains having an orientation (Goth orientation grains).
A steel plate of 0 to 0.35 mm, mainly used for transformer cores. The surface of the grain-oriented electrical steel sheet is covered with a forsterite film (hereinafter, referred to as a glass film) mainly composed of an oxide film usually called a glass film for the purpose of securing insulation and the like. It is well known that the quality of the formation of the glass film greatly affects the secondary recrystallization structure in the final finish annealing process, and influences the magnetic properties of the grain-oriented electrical steel sheet as a product.

On the other hand, in the production of the above-mentioned grain-oriented electrical steel sheet, the conventional production method based on high-temperature slab heating of 1350 ° C. or higher has been replaced.
No. 27, slab heating at the ordinary steel level, that is, slab heating at a temperature of 1280 ° C. or lower, and an inhibitor of AlN, (Al.S
i) A production method has been developed in which finely dispersed precipitates such as N are formed in a nitriding treatment step performed after decarburizing annealing, but there is still a problem in forming a good glass film.

In order to improve the uniformity and adhesion of the glass film, the total amount of an oxide film containing silica and firelite as main components is required, as disclosed in, for example, Japanese Patent Publication No. 58-46547. A method for obtaining a good glass film by controlling a specific range is disclosed. Specifically, this method specifically includes a method in which a silicon compound, for example, a silicon compound essentially containing Si, O, H or a silicon compound essentially containing S, O, H is formed on the surface of a grain-oriented electrical steel sheet strip before decarburizing annealing.
i, generation of although FeO generation of fayalite is promoted by the adhesion of the Si compound by either one of the deposition 0.5~7.0mg per strip one side 1 m ² of Si by weight of silicon compounds containing O The electrolytic treatment is performed in an aqueous solution of sodium orthosilicate as a means for attaching the silicon compound.

[0005] As a usual method for electrolytic degreasing of cold rolled steel sheets, sodium orthosilicate or caustic soda is generally used as a detergent. One example is JP-A-63-24.
No. 022. This technology is used to continuously heat-treat ordinary cold-rolled thin steel sheets in a non-oxidizing atmosphere.
Iron and iron oxides, and Si, Mn, Ca, etc.
In particular, in order to prevent the Si-based foreign matter from being picked up by the rolls in the furnace of the continuous annealing furnace, the Si-based foreign matter adheres to the steel sheet surface by washing with a cleaning agent of sodium orthosilicate or caustic soda in the washing step before the continuous annealing. Is to avoid.

[0006]

However, in the technique disclosed in Japanese Patent Publication No. 58-46547, the surface roughness of the grain-oriented electrical steel sheet before decarburization annealing is varied, and the amount of oil remaining on the strip surface is reduced. Variation,
The amount of electrodeposition of the silicon compound fluctuates in actual operation due to the aging of the silicate solution such as a change in silicate concentration, or the inclusion of oil or iron brought into the strip, and the amount of subscale generated on the strip surface must be accurately controlled. It is difficult. Further, after the electrolytic cleaning, in a state without water washing, there is a problem that substances contained in or remaining in the electrolytic solution such as sodium and iron powder adhere to the strip surface and adversely affect the glass film formation.

Further, in the technique disclosed in Japanese Patent Application Laid-Open No. 63-22022, sodium orthosilicate is used to positively prevent the adhesion of Si-based foreign matter to the surface of a steel sheet and prevent pickup to a roll in a furnace. Alternatively, it is washed with caustic soda. In particular, when caustic soda is used as a cleaning agent, iron-based pickup can only be prevented.
Furthermore, the substance adhering to the strip surface is a lump and is different from the subscale generated on the strip surface of the grain-oriented electrical steel sheet, and the material to be processed is a grain-oriented electrical steel sheet containing a large amount of Si. In some cases, the cleaning ability is poor,
It cannot be used practically.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and overcomes the drawbacks of the conventional electrolytic treatment in an aqueous solution of sodium orthosilicate. Caustic soda is used as a cleaning agent for the purpose of degreasing and cleaning strips for grain-oriented electrical steel sheets containing Si ≦ 4.5% or less, which is a completely different type of steel from sodium orthosilicate or caustic soda used in the above.

The gist of the present invention is that S cold rolled to the final sheet thickness is used.
A strip for grain-oriented electrical steel sheets containing i ≦ 4.5% or less is electrolytically degreased with a silicate-free alkaline cleaner, preferably caustic soda, then washed with water, decarburized and annealed, and cold-rolled. This is a method for electrolytically degreasing a grain-oriented electrical steel sheet having excellent film properties with a track time of up to 14 days before performing carbon annealing.

[0010]

FIG. 1 is a diagram showing the amounts of Si and Na deposited on the surface of a grain-oriented electrical steel sheet (steel sheet) after electrolytic degreasing and washing with conventional sodium orthosilicate and caustic soda according to the present invention. , (A) shows the Na electrodeposition amount (kcp).
s) and the charge density (c / dm ² )
(B) shows the Si electrodeposition amount (kcps) and the electric quantity density (c / d).
m ² ). In the figure, the symbol プ ロ ッ ト plots the value of electrolytic cleaning with sodium orthosilicate, and the symbol ● plots the value of electrolytic degreasing and water washing with the caustic soda used in the present invention. The data shown in FIG. 1 shows the directionality containing C: 0.057%, Si: 3.25%, and Sol Al: 0.027% as an inhibitor cold-rolled to a final thickness of 0.23 mm. It is data when the electromagnetic steel sheet is electrolytically cleaned before decarburizing annealing.
Conditions for the electrolytic cleaning include a concentration of aqueous sodium hydroxide solution:
5%, liquid temperature: 60 ° C., charge density: 25 c / dm ² ,
The treatment was performed under the condition of an electrolytic cleaning time of 1.5 seconds.

As can be seen from FIG. 1, when electrolytic cleaning is performed with the caustic soda according to the present invention and then with water, the amount of electrodeposition of Na and Si depends on the electric charge density, as compared with the conventional electrolytic cleaning using sodium orthosilicate. It shows a much smaller value without any. FIG. 2 shows the variation in the oxygen addition amount of the grain-oriented electrical steel sheet strip (steel sheet) after the decarburizing annealing after the electrolytic degreasing and washing with the conventional sodium orthosilicate and the caustic soda according to the present invention, as the oxygen amount (g / m ² ) of the steel sheet. It shows the result of observation in relation to H ₂ O / H ₂ . In the figure, the broken line plots the value of electrolytic cleaning with sodium orthosilicate, and the solid line plots the value of electrolytic degreasing and water washing with the caustic soda used in the present invention. As can be seen from FIG. 2, when the electrolytic degreasing cleaning with the caustic soda of the present invention is followed by the water washing treatment, the variation in the oxygen amount of the steel sheet is very small and stable as compared with the conventional electrolytic cleaning treatment with sodium silicate.

FIG. 3 shows the results of observation of the occurrence rate of pattern defects after finish annealing by comparison between the conventional sodium orthosilicate and the electrolytic degreasing cleaning using caustic soda according to the present invention. It can be seen that the electrolytic cleaning with sodium silicate has a pattern defect generation rate about four times that of the electrolytic degreasing cleaning with caustic soda of the present invention. This pattern-like defect occurrence rate means that the glass film generated after the final finish annealing is not in a state where the glass film is generated in a uniform and smooth state, but that a patchy film defect is generated on the entire surface of the steel sheet. A steel sheet having a spotty film defect has a reduced commercial value and is a graded product, or has no commercial value.

[0013] As described above, when electrolytically degreasing and washing with caustic soda and then washing with water, no silicon compound is present in the solution. Na and the like do not adhere, and the surface quality can be stably built. Next, the present invention stipulates that the track time for performing decarburization annealing after cold rolling is set to be within 14 days. The steel sheet is left for a long time while adhering to the steel sheet with water and moisture, etc., which are altered and fixed, or rust is generated on the steel sheet surface. This is because it has a great effect on the stable formation of the oxide layer during annealing.

[0014]

Next, the present invention will be described with reference to examples. C: 0.057%, Si: 3.25%, Sol Al:
0.027%, N: 0.007%, Mn: 0.15%,
A slab or a steel ingot for grain-oriented electrical steel sheets containing S: 0.007% and P: 0.024% was heated at a temperature of 1150 ° C., and hot-rolled into a hot-rolled sheet having a thickness of 2.3 mm. This hot-rolled sheet was annealed at 1100 ° C. for 2 minutes to obtain a final sheet thickness of 0.2.
It was cold rolled to 25 mm. Next, after electrolytic degreasing and washing with caustic soda of the present invention and water washing and conventional electrolytic washing with sodium orthosilicate, PH ₂ O / PH ₂ : 0.35
% Decarburizing annealing in an atmosphere of
A final finish anneal for an hour was performed. Table 1 shows the electrolytic cleaning conditions before the decarburizing annealing and the state of glass film formation thereby.

[0015]

[Table 1]

As can be seen from Table 1, in the conventional electrolytic cleaning with sodium orthosilicate, spotted glass film defects are generated on the surface of the steel sheet, whereas the caustic soda according to the present invention is used. In the water washing treatment after the electrolytic degreasing and washing, a good glass film without a glass film defect was obtained. The above-mentioned cold rolled sheet having a final sheet thickness of 0.225 mm is further subjected to water washing after electrolytic degreasing and washing with caustic soda of the present invention.
Decarburizing annealing was performed in an atmosphere of PH ₂ O / PH ₂ : 0.35%, and then final finishing annealing was performed at 1200 ° C. for 20 hours. Table 2 shows the conditions of the elapsed time from the cold rolling to the electrolytic degreasing and washing and the state of glass film formation thereby.

[0017]

[Table 2]

As is clear from FIGS. 1 to 3 and Tables 1 and 2, the present invention uses an alkaline cleaning agent, preferably caustic soda, in the electrolytic degreasing step, and reduces the track time from cold rolling to decarburizing annealing. It can be seen that when the time is within 14 days, the adhesion of the silicic acid to the steel sheet surface is small, so that it is possible to prevent the variation in the adhesion amount of the oxide layer and the occurrence of the glass film defect due to the adhesion of foreign substances other than the silicic acid.

[0019]

As described above, according to the present invention, there is no variation in the amount of silicate compound adhered in the electrolytic cleaning step in the production process of grain-oriented electrical steel sheets, and the effect of foreign substances adhering during degreasing and cleaning can be eliminated. In addition, since the amount of oxygen attached after the subsequent decarburization annealing can be accurately controlled, a good glass film can be stably obtained, and a high-quality grain-oriented electrical steel sheet product can be supplied.

[Brief description of the drawings]

FIG. 1 shows Na on the surface of a grain-oriented electrical steel sheet after electrolytic degreasing and washing with conventional sodium orthosilicate and caustic soda according to the present invention.
3A and 3B are diagrams illustrating the amounts of deposited Si and Si, wherein FIG. 3A illustrates the amount of Na electrodeposition, and FIG. 3B illustrates the amount of Si electrodeposition.

[Figure 2] steel oxygen content variation of oxygen addition amount of by the conventional orthosilicate soda present invention the oriented electrical steel sheet after decarburization annealing after electrolytic degreasing washing with sodium hydroxide (g / m ²⁾
A diagram showing the results of observation in relation to the H ₂ O / H ₂ and.

FIG. 3 is a diagram showing the occurrence rate of pattern defects after finish annealing in comparison with the conventional electrolytic degreasing cleaning using sodium orthosilicate and the caustic soda according to the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsuyoshi Hamaya 1-1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Yawata Works

Claims (2)

[Claims] 1. A strip for a grain-oriented electrical steel sheet containing Si ≦ 4.5% or less cold-rolled to a final sheet thickness is electrolytically degreased with a silicate-free alkaline cleaning agent, and then subjected to a water-washing treatment, followed by decarburization. A method for electrolytically degreasing a grain-oriented electrical steel sheet having excellent film properties, wherein a track time from annealing and cold rolling to decarburizing annealing is within 14 days. 2. The method according to claim 1, wherein the alkaline cleaning agent is caustic soda.