JPH05255889A - Electrolytic treatment of cold rolled steel strip - Google Patents

Abstract

PURPOSE:To provide the method for electrodeposition of an Si compd. in an adequate amt. on the surface of a cold rolled steel strip. CONSTITUTION:The electrodeposition quantity of the Si compd. is exactly controlled in a wide range by effecting an electrolysis in a range where the potential of the steel strip subjected to cold rolling with respect to an aq. soln. essentially consisting of silicate is higher than the potential to induce hydrogen generation and is lower than the potential to induce the reduction reaction of the silicate at the time of subjecting the steel strip to an electrolytic treatment in the aq. soln.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic treatment of a steel strip after cold rolling, and more particularly to a method for electrodepositing an appropriate amount of a Si compound on the surface of a cold rolled steel strip.

[0002]

2. Description of the Related Art A steel strip wound as a coil after cold rolling is usually contaminated with rolling oil or the like. If such a soiled steel strip is annealed as it is, these deposits will seize on the surface of the steel sheet due to heating during annealing, or the steel sheet surfaces will seize, resulting in flaws when rewinding in the next step, and The appearance of the surface may be impaired, and defects may be further generated, which significantly reduces the product value. To solve these problems, the surface of the steel strip was cleaned by performing electrolytic treatment in an aqueous solution containing silicate as a main component before box annealing, and at the same time, a Si compound was electrodeposited on the surface. It is known that a technique for preventing image sticking is effective.

However, in this method for preventing seizure,
If too much Si compound is electrodeposited on the surface of the steel strip, a milky white temper color is produced during annealing, while if the amount of electrodeposited Si compound is too small, the effect of preventing seizure cannot be expected. Therefore, in order to prevent both the seizure and the temper color from occurring at the same time, it is necessary to control the electrodeposition amount of the Si compound within a predetermined appropriate range.

As a method of controlling the electrodeposition amount of Si compound,
Japanese Patent Publication No. 62-21078 proposes a method for switching the polarity of a steel strip, and Japanese Patent Application Laid-Open No. 62-235500 proposes a method for varying the amount of current or the strip running speed. However, since the appropriate range of the electrodeposition amount of the Si compound is narrow, it is difficult to stably electrodeposit the appropriate amount of the Si compound even by these methods.

As an example in which it is particularly necessary to stably electrodeposit a proper amount of Si compound, an insulating coating of grain-oriented silicon steel sheet can be cited. That is, the grain-oriented silicon steel sheet has an insulating coating on the surface, and the following method is generally employed to form this coating. First,
To a silicon steel strip with a predetermined final thickness by cold rolling,
Continuous decarburization annealing is performed in a hydrogen atmosphere in the temperature range of 700 to 900 ° C, and at the same time, a subscale mainly composed of SiO ₂ is formed on the surface of the steel strip. Next, apply an annealing separator containing MgO as a main component on the oxide film, dry it, wind the steel strip on a coil, and anneal it again at a high temperature within a temperature range of 1100 to 1250 ° C in hydrogen. I do. At this time, MgO and SiO ₂ are reacted with each other to form a forsterite coating on the surface of the steel sheet.

Here, before decarburization annealing, a compound of Si, O and H is added in an amount of 0.5 to 7.0 mg by weight of Si per 1 m ^{2 of} one side of the steel sheet.
It is known that a uniform and good forsterite coating can be obtained by making it adhere (see Japanese Patent Publication No. 58-46547). And, as a method of attaching this Si compound, electrolytic treatment in an aqueous solution containing silicate as a main component is performed, but it is difficult to control the electrodeposition amount of the Si compound in the electrolytic treatment step, and conventionally Due to the small amount of this, defects in the forsterite coating often occurred.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to propose a method capable of advantageously realizing the control of the amount of Si compound deposition in the electrolytic treatment step, which was difficult in the past.

[0008]

[Means for Solving the Problems] The inventors have conducted various studies on the influence of electrolysis conditions in electrolysis on the electrodeposition amount of Si compounds. As a result, they have found that the electrodeposition amount of the Si compound can be controlled in a wide range by controlling the electrolytic potential, and completed the present invention.

That is, according to the present invention, when a steel strip subjected to cold rolling is subjected to electrolytic treatment in an aqueous solution containing silicate as a main component, the potential of the steel strip with respect to the aqueous solution is higher than the potential at which hydrogen generation occurs. It is an electrolytic treatment method for a cold-rolled steel strip, which is characterized in that electrolysis is performed at a high temperature and lower than a potential at which a reduction reaction of caustic acid salt occurs.

[0010]

Next, the experimental results which are the basis of the present invention will be described. The cold-rolled steel sheet was subjected to electrolytic treatment in an aqueous solution of sodium orthosilicate while changing the electrolytic potential to -0.6 to -2.0 V, and then infrared absorption spectrum analysis of the steel sheet surface was performed.
As shown in FIG. 1 as an example of the reflection infrared absorption spectrum of the surface of the steel sheet after electrolytic treatment, the absorption around 1040 cm ⁻¹ corresponds to the electrodeposited Si compound.

Therefore, FIG. 2 shows the relationship between the absorbance and the current density at the absorption around 1040 cm ^-1 in the infrared absorption spectrum and the electrolytic potential. The electrolytic potential is a value for a saturated calomel electrode. From FIG. 2, when the electrolysis potential exceeds -0.9V, the electrodeposition of the Si compound does not occur, and the electrolysis potential is -0.9 to-.
It can be seen that the absorbance increases remarkably when it decreases to the range of 1.2 V, and when the electrolysis potential becomes −1.3 V or less, electrolysis of water begins to occur, the current density increases, hydrogen gas is generated, and the absorbance decreases. .. In the figure, no clear correlation was found between the electrolytic potential and the absorbance in the potential region where hydrogen generation occurred, and it was found that it was difficult to control the electrodeposition amount of the Si compound. Therefore, in order to control the electrodeposition amount of the Si compound, it is higher than the potential range of −1.3 V, that is, higher than the potential of hydrogen generation, rather than electrolysis in the potential range of hydrogen generation. It is advantageous to carry out the electrolytic treatment in a potential region lower than the potential at which the reduction reaction occurs.

It can also be seen that the electrolytic treatment in this potential region requires a low current density required for electrodeposition, and that the amount of electrodeposition can be expected to increase.

The reasons for limitation of the present invention will be described below. The electrolytic treatment for electrodepositing the Si compound according to the present invention is first performed in an aqueous solution containing silicate as a main component. By using this aqueous solution, it is possible to attach the Si compound and degrease the surface of the steel sheet. Here, as the silicate, sodium orthosilicate, sodium metasilicate, sodium disilicate, sodium pyrosilicate, water glass, etc. are advantageously suitable. Although the concentration of the aqueous solution is not particularly limited, it is sufficient to select the conditions under which degreasing and Si can adhere to a desired amount.

As described above, the electrolysis potential is higher than the potential at which hydrogen is generated and lower than the potential at which the reduction reaction of oxalate starts to occur. That is, in the potential region where hydrogen generation occurs, it is difficult to control the electrodeposition amount of the Si compound, while the upper limit of the electrolysis potential is the potential at which the reduction reaction of the silicate starts in order to electrodeposit the Si compound. ..

In practice, after degreasing treatment in the above-mentioned aqueous solution, when using a plurality of electrodes, electrolytic treatment is carried out so that the potential at the final electrode falls within the above range, and the Si compound is electrodeposited. That is, as shown in FIG. 3, the electrodes 1 and 2 on the inlet side of the steel strip S are electrolyzed at a potential at which water is electrolyzed, and defoaming treatment is performed by the generated bubbles. Then the electrodes 3,
In No. 4, according to the required amount of electrodeposited Si compound and plate passing speed, electrolytic treatment was performed at an arbitrary electrolysis potential in a potential range higher than the hydrogen generation potential and lower than the potential at which the reduction reaction of the oxalic acid salt occurred. The compound is electrodeposited. In the figure, 5 and 6 are power supplies. With the device shown in FIG. 3,
It is possible to perform electrolytic treatment that combines degreasing of the steel strip surface and control of the electrodeposition amount of Si compound.

When electrolytic treatment is performed using a plurality of electrodes,
In order to electrodeposit the Si compound, at least the potential at the final electrode may be kept at a potential between the potential at which the silicate reduction reaction begins and the potential at which hydrogen generation begins,
The other electrodes can be expected to have a degreasing effect due to bubbles generated by setting the potential to generate hydrogen, for example.

[0017]

【Example】

Example 1 A 0.23 mm thick grain-oriented silicon steel sheet was electrolyzed for 2, 5 and 10 seconds in an aqueous solution containing sodium orthosilicate as a main component. At this time, the electric potential of the steel sheet with respect to the aqueous solution is from -0.9 V to -1.2 V on the saturated calomel electrode basis.
The amount of electrodeposited Si compounds when changing to V was investigated.

The result is shown in FIG.
In the range of −1.2 V, as time increased and the potential decreased, the amount of electrodeposited Si compounds increased. That is, by appropriately selecting the potential and time, Si
It is understood that the electrodeposition amount of the compound can be easily controlled.

Further, since the amount of electrodeposited Si compound is larger than that in the conventional electrolytic treatment in which bubbles are generated, the required amount of Si compound can be electrodeposited in a shorter time than in the conventional case. And is industrially very advantageous.

Comparative Example 1 The same grain-oriented silicon steel sheet as in Example 1 was electrolyzed for 2, 5 and 10 seconds in an aqueous solution containing sodium orthosilicate as a main component. At this time, the potential of the steel sheet with respect to the aqueous solution was changed from -1.3 V to -2.0 V based on the saturated calomel electrode. This potential region corresponds to the conventional electrolytic treatment condition where hydrogen is generated from the surface of the steel sheet.

As shown in the results of FIG. 5, there is no clear correlation between time and potential and the amount of Si compound electrodeposited. Therefore, in the conventional electrolytic treatment in which bubbles are generated, it is very difficult to control the electrodeposition amount of the Si compound, and the electrodeposition amount is small.

Example 2 A grain-oriented silicon steel sheet cold-rolled to 0.30 mm was subjected to 3 ° C. at 90 ° C.
% Electrolytic solution in sodium orthosilicate aqueous solution, followed by decarburizing annealing, applying an annealing separator mainly composed of MgO, and then performing high temperature finish annealing to form a forsterite coating.

At this time, the potential of the steel sheet with respect to the aqueous solution was -1.0 V, -1.1 V and -1.
Table 1 shows the results of evaluating the appearance uniformity of each forsterite coating, the adhesion of forsterite, and the iron loss at 2 V.

Comparative Example 2 The same grain-oriented silicon steel sheet as in Example 2 was electrolytically treated in a 3% sodium orthosilicate aqueous solution at 90 ° C. for 2 seconds, then decarburized and annealed and separated mainly from MgO. Apply the agent,
A forsterite coating was formed by high temperature finish annealing.

At this time, the potential of the steel sheet with respect to the aqueous solution was set to -1.5 V and -1.7 V on the basis of saturated calomel electrode, and the results of evaluating the appearance uniformity of each forsterite coating, the adhesion of forsterite and the iron loss were shown. , Table 1 together.

[0026]

[Table 1]

From Table 1, it can be seen that in the examples, the coating appearance and adhesion are good, and the iron loss is small.
On the other hand, in the comparative example, the outer appearance of the coating film has many irregularities, and the adhesiveness is inferior to the examples.

Example 3 A cold rolled steel plate of ordinary steel was electrolyzed for 0.5, 1, 2 and 5 seconds in an aqueous solution containing sodium orthosilicate as a main component. At this time, the potential of the steel sheet with respect to the aqueous solution was set to -1.2 V based on the saturated calomel electrode. Table 2 shows the occurrence of seizure when box annealing was performed after the electrolytic treatment.

Comparative Example 3 In the same aqueous solution as in Example 3, 0.5% of cold rolled steel of ordinary steel was used,
It was electrolyzed for 1, 2 and 5 seconds. At this time, the potential of the steel sheet with respect to the aqueous solution was set to -1.5 V based on the saturated calomel electrode. Since hydrogen is generated from the surface of the steel sheet in the potential region, it corresponds to the conventional electrolytic treatment condition that also serves as degreasing. Table 2 shows the occurrence of seizure when box annealing was performed after the electrolytic treatment.

[0030]

[Table 2]

According to Table 2, in the examples, the seizure prevention effect can be seen by the electrolytic treatment for 0.5 seconds or more. In the comparative example, electrolysis for 5 seconds or more is required to prevent seizure. Therefore, according to the present invention, the speed of the electrolytic treatment line can be increased.

[0032]

According to the present invention, it is possible to control the electrodeposition amount of Si compounds in a wide range and to electrodeposit more Si compounds than in the conventional electrolytic treatment. It is possible to increase the electrodeposition amount of Si compounds. Moreover, since the current density required for electrodeposition of the Si compound is small, it is possible to significantly reduce power consumption. Furthermore Si
The compound can be evenly attached, and seizure during steel box box annealing can be prevented.

In particular, the forsterite coating of grain-oriented silicon steel sheet formed from the Si compound electrodeposited by the method of the present invention is superior in appearance, adhesion and iron loss to the coating by the conventional method. There is.

[Brief description of drawings]

FIG. 1 is a graph showing an infrared absorption spectrum of an electrodeposited Si compound.

FIG. 2 is a graph showing the absorbance of infrared absorption of Si compounds and the dependence of the current density on the electrolytic potential.

FIG. 3 is a schematic diagram showing an example of implementing the present invention.

FIG. 4 is a graph showing a relationship between an electrolytic potential and an electrodeposition amount of a Si compound.

FIG. 5 is a graph showing the relationship between the electrolytic potential and the electrodeposition amount of Si compound.

[Explanation of symbols]

 1 electrode 2 electrode 3 electrode 4 electrode 5 power supply 6 power supply

Claims (1)

[Claims] 1. When subjecting a steel strip that has been cold-rolled to electrolytic treatment in an aqueous solution containing silicate as a main component, the potential of the steel strip with respect to the aqueous solution is higher than the potential at which hydrogen is generated, and A method for electrolytically treating a cold-rolled steel strip, which comprises performing electrolysis in a range lower than a potential at which a reduction reaction of silicate occurs.