JPH05247529A - Continuous decarburization annealing method of grain-oriented silicon sheet - Google Patents

Abstract

PURPOSE:To obtain the decarburized annealed sheet having the desired medium quality by stabilizing the partial pressure of the moisture in the atmosphere in the continuous decarburization annealing of the grain-oriented silicon sheet, and by controlling the reaction of decarburization and oxidation. CONSTITUTION:The continuous decarburization annealing method of the grain- oriented silicon sheet is characterized in that the amount of the moistened gas to be supplied to the respective zones and the partial pressure of the moisture of the gas to be supplied are controlled so that the partial pressure of the water content of the in-furnace atmospheric gas of the respective zones may be constant in the continuous decarburization annealing of the cold-rolled grain-oriented silicon sheet 2 which has been divided into a plurality of pieces in the longitudinal direction of the furnace in the annealing furnace 1 to supply the atmospheric gas to the respective zones.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous decarburizing and annealing method for grain-oriented electrical steel sheets which enables an in-furnace reaction to be carried out efficiently and stably.

[0002]

2. Description of the Related Art Strips, such as grain-oriented electrical steel sheets cold-rolled to a predetermined thickness, are decarburized and annealed. In the decarburization annealing, carbon in the steel is removed, an oxide layer is formed on the surface of the steel sheet, and the annealing separator applied to the steel sheet and the oxide layer react in the finish annealing process to form a glass film.

These decarburization and oxygen addition reactions in the decarburization annealing process are performed by supplying moist hydrogen gas into the furnace and continuously heating and stripping the strip, and each reaction is carried out as follows. As shown in Fig. 5, it is caused by the contact between the water in the furnace atmosphere and the steel sheet. C + H ₂ O → CO + H ₂ Si + H ₂ O → SiO ₂ + 2H ₂ Due to the reaction, the carbon in the steel needs to be lowered to a predetermined value or less, and in order to obtain a glass film of a good product, the oxygen addition amount is set to a predetermined value. It is necessary to set a value, but in order to produce the reaction in a targeted and stable manner in this way, the water partial pressure in the atmosphere required for the reaction must be kept stable at a possible target value. is important.

Various methods have heretofore been proposed as methods for controlling and stabilizing moisture in the atmosphere near the steel sheet. For example, Japanese Utility Model Laid-Open No. 62-3381 discloses that it is possible to stabilize the reaction by providing a pipe for directly blowing an atmospheric gas in the vicinity of the strip in the furnace.

[0005]

However, even such a current decarburization annealing method is insufficient for controlling and stabilizing the water content in the atmosphere.
In particular, compared to the amount of water in the atmosphere in the furnace consumed by the reaction in the furnace, it cannot be said that the water in the supply gas is sufficiently large, and the partial pressure of the water in the atmosphere gas in the furnace is The actual situation is that the pressure decreases compared to the partial pressure, and when the reactivity of the steel sheet changes, the dew point in the furnace also changes, which is an unstable reaction state. Furthermore, the reaction state of the steel sheet changes in the furnace length direction, whereas the atmospheric gas and moisture contained in the furnace are currently uniformly supplied to each zone. The partial pressure of water has a distribution in the furnace length direction, and tends to further promote the instability of the reaction described above.

[0006]

According to the present invention, the instability of the decarburization and oxidative addition reactions occurring in the furnace, especially the reaction state of the steel sheet changes as the annealing progresses, whereas the present situation is Eliminates the distribution of water partial pressure in the longitudinal direction of the furnace caused by the constant supply of atmospheric gas and water,
It is intended to provide a decarburizing annealing method capable of further stabilizing the reaction and controlling the reaction.

That is, the gist of the present invention is that the humidifying gas is uniformly supplied to each zone divided into a plurality in the furnace length direction, whereas the moisture content in the atmosphere accompanying the progress of decarburization and oxidation reaction of the steel sheet. A method of adjusting the supply amount of gas humidified to a constant water partial pressure for each zone in response to changes in the consumption amount of
Alternatively, it is a method of adjusting the moisturizing water content of the gas being supplied at a fixed amount for each zone, and using any of these methods, control the water partial pressure in the longitudinal direction in the annealing furnace to be almost constant. It is in.

The present invention will be described in detail with reference to the drawings. 1 and 2 schematically show a method for supplying an atmospheric gas to a decarburization annealing furnace according to the present invention. Annealing furnace 1
Humidifier to each zone divided into multiple in the furnace length direction
Gas humidified by 7, 8 is supplied. The gas in the furnace flows against the steel plate 2 toward the front of the furnace and is discharged from the exhaust bladder 3. At the same time as the steel sheet 2 enters the furnace, it is heated to a predetermined temperature, and when it comes into contact with moisture in the atmosphere, decarburization and oxidation reactions start. These reactions react in a large amount at the start of the reaction and consume a large amount of water, but the reaction amount gradually decreases as the reaction progresses, and the water consumption also decreases.

The amount of water in the atmosphere gas currently being supplied is not sufficiently large as described above with respect to the amount of water consumed by these reactions. The water partial pressure in the internal atmosphere will decrease. FIG. 3 shows the distribution of water partial pressure in the furnace atmosphere in the furnace length direction in comparison between the current operating method B and the present invention A. In the current method of uniformly supplying the atmospheric gas and the amount of water to each zone in the furnace length direction, due to the nonuniformity of the reaction in the furnace length direction as described above, the water content in the front part of the furnace as shown by the dotted line B A distribution of water partial pressure is generated such that the partial pressure is low and the partial pressure is high in the rear part. A steel sheet treated through such a distribution of water partial pressure exhibits complicated reaction behavior particularly in an oxidation reaction, and it is very difficult to estimate and control this.

In order to control the reaction in the furnace, particularly the oxidation reaction, the present inventors make it important to keep the water partial pressure in the atmosphere of the furnace as constant as possible in the furnace length direction to simplify the reaction. I realized it in two ways. 4 in Figures 1 and 2
Is a dew point meter that measures the water partial pressure in the furnace, which allows the distribution state of the water partial pressure to be grasped and controlled in the furnace length direction. That is, FIG. 1 shows that the humidifier 6 humidifies the gas to a constant water partial pressure, and multiple gases are properly distributed by the valve 5 according to the reaction state in the furnace as grasped by the dew point meter 4 (a large amount in the front part of the furnace, a large amount in the rear part of the furnace). This is a method of making the distribution of the water partial pressure in the furnace length direction constant by supplying a small amount to the furnace. Furthermore, FIG.
As an example, using 7, 8 and 2 humidifiers, the moisture humidification amount of each humidifier is properly adjusted according to the reaction state in the furnace as grasped by the dew point meter 4, and the distribution of moisture partial pressure in the furnace length direction is calculated. This is a method of making the value constant.

By using any of these methods of distributing the supply gas amount and adjusting the humidification amount of the supply gas, FIG.
Medium, as shown by the solid line A, a constant water partial pressure in the furnace length direction,
It is possible to obtain a distribution, which is very effective in stabilizing and controlling the reaction.

[0012]

As described above, according to the present invention, the partial pressure of the water partial pressure in the furnace length direction in the decarburization annealing furnace can be made constant, which is very effective in stabilizing the atmosphere. . Decarburization in the furnace, based on the atmosphere of this constant moisture partial pressure,
It is possible to control the oxidation reaction with higher precision, and it is possible to obtain a decarburized annealed plate with the desired intermediate quality, which is a major improvement in the magnetic properties and coatings of grain-oriented electrical steel products. effective.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an atmospheric gas supply method according to the present invention.

FIG. 2 is a schematic diagram showing another atmospheric gas supply method according to the present invention.

FIG. 3 is a diagram showing a distribution state of water partial pressure in an annealing furnace in comparison between a conventional method and the present invention.

[Explanation of symbols]

 1: Annealing furnace 2: Steel plate 3: Exhaust bleeder 4: Dew point meter 5: Flow control valve 6, 7, 8: Gas humidifier

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hide Miyamoto 1-1, Toibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Co., Ltd. Yawata Works

Claims (1)

[Claims] 1. A continuous decarburizing annealing of a grain-oriented electrical steel sheet after cold rolling in a furnace having a plurality of zones in the furnace length direction and supplying an atmospheric gas to each zone. The directionality characterized by controlling the amount of humidified gas supplied to each zone and the humidified water partial pressure of the supplied gas to each zone so that the partial pressure of water in the furnace atmosphere gas is almost constant. Continuous decarburization annealing method for electrical steel sheets.