JP4105780B2 - Decarburization annealing method and apparatus for grain-oriented electrical steel sheet - Google Patents

Description

【００１４】
また、本発明方法を実施するに当たっては、脱炭焼鈍装置内の加熱帯の手段の配列において装置長の約３／４をラジアントチューブによるガス加熱手段とし、加熱帯後半、ほぼ残り１／４の部位をチューブ状ヒーターによる電気加熱手段とで構成することにより達成させる。なお、前記ラジアントチューブによるガス加熱手段およびチューブ状ヒーターによる電気加熱手段は、何ら特別の仕様である必要はなく市販の設備仕様で十分対応可能である。
【００１５】
【発明の効果】
以上説明したように、本発明においては、脱炭焼鈍の加熱帯後半の昇温推移を規定することで加熱のオーバーシュートやアンダーシュートが解消され、安定した脱炭焼鈍が可能であると共に、脱炭焼鈍の加熱帯後半の加熱方法を発熱密度の大きい、発熱抵抗体を密に配置したチューブ状ヒーターを用いることで処理能力の大きい炉にもかかわらず広範囲の鋼板サイズ変更に対しても柔軟な対応ができ、しかも安定した加熱昇温カーブを採用することが可能である。
【図面の簡単な説明】
【図１】従来の脱炭焼鈍装置内における加熱手段の配置を示す模式図である。
【図２】脱炭焼鈍装置における目標昇温カーブ、従来方法のカーブおよび本発明カーブを示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a decarburization annealing method and apparatus for accurately raising the temperature without causing overshoot or heating failure during heating in a decarburization annealing process in the production process of a grain-oriented electrical steel sheet.
[0002]
[Prior art]
The grain-oriented electrical steel sheet is composed of crystal grains having a (110) [001] orientation in the rolling direction (Goss orientation grains) and usually contains 4.5% or less of Si and has a thickness of 0.10 to 0.00. It is a 35mm steel plate and is mainly used for transformer iron cores.
For this purpose, recently, in the production of the grain-oriented electrical steel sheet, instead of the conventional manufacturing method based on high-temperature slab heating of 1350 ° C. or higher, the level of ordinary steel as disclosed in JP-A-3-122227 is disclosed. Directional slab heating based on slab heating, ie, slab heating at a temperature of 1280 ° C. or less, and forming finely dispersed precipitates such as AlN and (Al · Si) N as inhibitors in a nitriding process performed after decarburization annealing Steel plate manufacturing methods have been developed.
[0003]
However, in the technology based on the slab heating at a temperature of 1280 ° C. or less, the quality of decarburization annealing (primary recrystallization annealing) is determined by the glass film formation and secondary recrystallization in the subsequent nitriding treatment and final finish annealing steps. Since it is a process that holds an important key that determines success or failure, many improvements have been proposed for the decarburization annealing process, particularly the heating process.
[0004]
Usually, in this technical field, a gas heating method using a radiant tube by gas heating with a large heating capacity is used for a heating zone for decarburization annealing, and a heating method using an element heater method for soaking. However, the gas heating by the radiant tube has a large heating capacity as described above, but has a disadvantage that the heating temperature varies and sometimes the arrival at the soaking temperature is delayed. When the arrival delay to the soaking temperature described above occurs, there is a problem that the time required for decarburization is reduced by that amount, and the decarburization property is deteriorated. In order to cope with this, recently, as disclosed in JP-A-1-290716 and JP-A-6-128646, the secondary recrystallized grain size is refined and the final magnetic characteristics are improved. From electromagnetic induction heating, resistance heating, ultra-rapid heating technology of 100 ° C / sec or more by direct energy heating means, or direct heating heating means at a heating rate of 50 ° C / sec or more, the relationship between target temperature and temperature rise rate There is a balanced heating technique.
[0005]
[Problems to be solved by the invention]
However, if overshoot occurs due to rapid heating in the decarburization annealing process described above, the oxide layer formed at an early stage inhibits decarburization when the target soaking temperature is exceeded even in a very short time. There is a problem of deterioration. In particular, the gas heating method with a large amount of input heat in the heating zone described above and the rapid heating method such as the energization heating method require a wide range of throughput changes in grain oriented electrical steel sheets that require complicated processes and advanced technology. When a small amount of input heat is required in the equipment, it is difficult to perform highly accurate heating control with the equipment described above.
[0006]
In particular, in the production line for grain-oriented electrical steel sheets, when decarburizing and annealing products of various thicknesses and widths in a single furnace in a wide range, high-precision heating control is required over a wide range of input heat amounts. . This appears prominently during the transition from the heating stage of decarburization annealing to the soaking stage, and the above-mentioned gas heating system can cause clogging beyond the stable combustion range of the combustion burner, resulting in unstable combustion. In the production of grain-oriented electrical steel sheets that require stability in temperature rise in the transition region, it is necessary to stabilize the quality by operating with sufficient output.
[0007]
In order to solve the above problems, the present invention provides a decarburization annealing method and apparatus for accurately raising the temperature without causing overshoot or heating failure during heating in the decarburization annealing process in the production process of grain-oriented electrical steel sheets. It is to provide.
[0008]
[Means for Solving the Problems]
In the present invention, when decarburizing and annealing a strip for grain-oriented electrical steel sheet containing Si ≦ 4.5% or less cold-rolled to the final sheet thickness, the steel sheet temperature in the heating stage of the strip is 600 to 800 ° C. In the meantime, the temperature deviation with respect to the target heating transition is controlled within ± 15 ° C. , and the preceding stage of the heating zone where the steel plate temperature in the heating stage of the strip is 550 to 650 ° C. is heated by a gas heating method using a radiant tube, Next, the latter stage of the heating zone above the temperature until the soaking temperature is reached is heated by an electric heating method using a tube heater, and the soaking is performed using an element heater in the soaking stage, and the decarburization of the grain-oriented electrical steel sheet, An annealing method.
[0009]
Further, in order to realize the above decarburization annealing method, in the decarburization annealing apparatus for grain-oriented electrical steel strips containing Si ≦ 4.5% or less cold-rolled to the final sheet thickness, the heating means is a heating zone. A decarburization annealing apparatus for grain-oriented electrical steel sheets, characterized in that the first stage is composed of a combination means of a gas heating method using a radiant tube and the second stage of the heating zone is an electric heating system using a tube heater and a soaking means using an element heater. It is.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 schematically shows a burner capacity and a stable combustion range for each zone of heating zone by gas heating method using 10 radiant tubes in the decarburization annealing furnace (divided into 7 zones for convenience). It is a figure. In FIG. 1, each burner capacity up to 1 to 4 zones has 12 million kcal / Hr, burner capacity in 5 to 6 zones is 8 million kcal / Hr, and burner capacity in 7 zones is 6. Operation was performed at 0,000 kcal / Hr. In the above embodiment, all of the zones 1 to 5 are within the stable combustion range and satisfy the target heating conditions, but the zones 6 to 7 exceed the stable combustion range, so they become clogged and become unstable combustion. A condition has occurred. The zones 6 to 7 are just equivalent to the transition zone to the soaking zone, and how strictly the temperature of the transition zone is controlled is the key to determining the quality of the glass coating in terms of decarburization. Therefore, instead of the conventional gas heating method using a radiant tube, this transition zone is heated by using an electric heating method using a tube heater, which is a wide and strict temperature control. Decarburization annealing is now possible without loss.
[0011]
FIG. 2 shows a temperature rise curve based on FIG. In FIG. 2, the target temperature rise curve of the decarburization annealing cycle is shown by a solid line, but in the case of the heating operation in the gas heating method using the conventional radiant tube, from the target temperature rise curve with the passage of time from around 600 ° C. When it is off and changes to the + side (higher than the target temperature rise curve, one-dot chain line curve), the oxide film precedes and decarburization deteriorates as described above, while the-side (from the target temperature rise curve). When it changes to a one-dot chain curve), the effective soaking time is shortened and the decarburization property deteriorates. In particular, this tendency tends to occur in the transition zone from the heating zone of 600 ° C. to 800 ° C. to the soaking zone. Therefore, by heating this temperature zone in a temperature range (dotted line curve) within ± 15 ° C. at the maximum with respect to the target temperature rise curve, the temperature range is a heating means which has a small temperature fluctuation and can take a strict temperature rise curve according to the present invention. Decarburization can be kept within an allowable range.
[0012]
Table 1 shows the evaluation results of decarburization by the method according to the present invention and the conventional gas heating method using a radiant tube. The data shown in Table 1 is actual data for 100 coils.
[0013]
[Table 1]

[0014]
Further, in carrying out the method of the present invention, in the arrangement of means for heating zones in the decarburization annealing apparatus, about 3/4 of the apparatus length is used as gas heating means by the radiant tube, and the latter half of the heating zone, almost the remaining 1/4. This is achieved by configuring the part with an electric heating means using a tubular heater. The gas heating means using the radiant tube and the electric heating means using the tubular heater do not need to have any special specifications, and can be sufficiently handled by commercially available equipment specifications.
[0015]
【The invention's effect】
As described above, in the present invention, by defining the temperature rise transition in the latter half of the heating zone of decarburization annealing, heating overshoot and undershoot are eliminated, and stable decarburization annealing is possible. The heating method in the second half of the heating zone for carbon annealing uses a tube heater with a large heat generation density and densely arranged heating resistors, making it flexible for a wide range of steel plate size changes despite a furnace with a high processing capacity. It is possible to adopt a stable heating temperature rising curve.
[Brief description of the drawings]
FIG. 1 is a schematic view showing the arrangement of heating means in a conventional decarburization annealing apparatus.
FIG. 2 is a diagram showing a target temperature increase curve, a conventional method curve, and a curve of the present invention in a decarburization annealing apparatus.

Claims (2)

When decarburizing and annealing the strip for grain-oriented electrical steel sheet containing Si ≦ 4.5% or less, which is cold-rolled to the final sheet thickness, while the steel sheet temperature in the heating stage of the strip is 600 to 800 ° C., The temperature deviation with respect to the heating transition to be controlled is controlled within ± 15 ° C. , and the preceding stage of the heating zone where the steel plate temperature in the heating stage of the strip is 550 to 650 ° C. is heated by a gas heating method using a radiant tube, and then the above temperature or more A decarburization annealing method for grain-oriented electrical steel sheets, characterized in that the latter stage of the heating zone until reaching the soaking temperature is heated by an electric heating method using a tube heater, and soaking is performed by an element heater in the soaking stage. In the decarburization annealing apparatus for strips for grain-oriented electrical steel sheets containing Si ≦ 4.5% or less cold-rolled to the final thickness, the heating means is preceded by a gas heating method using a radiant tube and the latter stage of the heating zone. Is a decarburization annealing apparatus for grain-oriented electrical steel sheets, characterized by comprising a combination means of an electric heating system using a tube heater and a soaking means using an element heater.

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