JPH10324922A - Method for decarburize-annealing grain oriented electrical steel sheet and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely raise the temp. without overshooting or insufficient heating at the time of heating in a decarburize-annealing process by controlling temp. deviation from the targeted heating transition to a value within a specific range while the heating temp. of a strip for grain oriented electrical steel sheet containing a specific ratio or lower of Si is in a specific range and decarburizing. SOLUTION: The strip for grain oriented electrical steel sheet cold-rolled to a finish strip thickness and containing <=4.5% Si, is decarburized. At this time, while the steel strip at the heating step of the strip is at 600-800 deg.C, the temp. deviation from the targeted heating transition is controlled to within ±15 deg.C, the decarburize-annealing is executed. Desirably, the strip is heated by a gas heating system with a radiant tube until the steel strip temp. at the heating step of the strip is 550-650 deg.C, and successively, the strip is heated by an electric heating system with a tubular heater till reaching a soaking temp. higher than the above temp. and at the soaking step, the soaking is executed by an element heater system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a decarburizing annealing method and a decarburizing annealing method for accurately raising the temperature without overshoot or underheating during heating in a decarburizing annealing step in a process of manufacturing a grain-oriented electrical steel sheet. Things.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is (110) [0
01] It is composed of crystal grains having an orientation (Goth orientation grains), usually contains 4.5% or less of Si, and has a thickness of 0.10.
0.35mm steel plate, mainly used for transformer cores. For this purpose, recently, in the production of the grain-oriented electrical steel sheet, a conventional production method based on high-temperature slab heating of 1350 ° C. or more has been replaced by Japanese Patent Laid-Open No. 3-12222.
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 method for producing a grain-oriented electrical steel sheet in which a finely dispersed precipitate such as N is formed in a nitriding step performed after decarburizing annealing has been developed.

However, in the technology based on the slab heating at a temperature of 1280 ° C. or lower, the quality of decarburizing annealing (primary recrystallization annealing) depends on the formation of glass film and secondary A number of improvement proposals have been made in the decarburizing annealing step, particularly in the heating step, since this step is an important step in determining the quality of recrystallization.

Usually, in this technical field, a gas heating system using a radiant tube by gas heating having a large heating capacity is used in a heating zone for decarburizing annealing, and a heating system using an element heater system is used in a soaking zone. However, the gas heating by the radiant tube has a large heating capacity as described above, but has a disadvantage in that the heating temperature varies and sometimes the temperature reaches the soaking temperature is delayed. When the above-mentioned delay in reaching the soaking temperature occurs, the time required for decarburization is reduced by that amount, which causes a problem that the decarburization property is deteriorated. In order to cope with this, recently, as disclosed in JP-A-1-290716 and JP-A-6-128646, an object is to reduce the secondary recrystallized grain size and improve the final magnetic properties. From ultra-rapid heating technology of 100 ° C / sec or more by means of electromagnetic induction heating, resistance heating, and direct energy heating means, and the relationship between the target temperature and the heating rate at a heating rate of 50 ° C / sec or more by the direct current heating means There is a balanced heating technique.

[0005]

However, if overshoot due to rapid heating occurs in the above-described decarburization annealing step, the oxide layer formed at an early stage is removed if the target soaking temperature exceeds the target soaking temperature for a very short time. There is a problem that the decarburization property is deteriorated because the carbon is inhibited. In particular, in the gas heating method with a large input heat amount in the above-mentioned heating zone, or in the rapid heating method such as the electric heating method, a wide range of throughput change is required for grain-oriented electrical steel sheets requiring complicated processes and advanced technology. When a small amount of input heat is required in such equipment, high-precision heating control is difficult with the above-described equipment.

[0006] In particular, in a production line for grain-oriented electrical steel sheets,
When products of various thicknesses and widths in a wide range are decarburized and annealed in one furnace, high-precision heating control over a wide range of input heat is required. This is noticeable when the heating stage of the decarburizing annealing shifts from the heating stage to the soaking stage, and in the gas heating method described above, the combustion may exceed the stable combustion range of the combustion burner, causing soot clogging and the like, resulting in unstable combustion. In the case of manufacturing a grain-oriented electrical steel sheet which is required to have a temperature rising stability in the transition region, it is necessary to stabilize the quality by operating with a marginal output.

In order to solve the above-mentioned problems, the present invention provides a decarburizing annealing method for accurately raising the temperature without overshoot or underheating during heating in the decarburizing annealing step in the production process of grain-oriented electrical steel sheets. The device is provided.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method for decarburizing annealing a grain-oriented electrical steel sheet containing Si ≦ 4.5% or less, which is cold-rolled to a final sheet thickness, in a heating step of the strip. A decarburizing annealing method for grain-oriented electrical steel sheets, characterized in that the temperature deviation with respect to the target heating transition is controlled within ± 15 ° C while the steel sheet temperature is between 600 and 800 ° C, and the decarburizing annealing is performed. In the heating step of the strip, the steel sheet is heated by a gas heating method using a radiant tube until the temperature of the steel sheet reaches 550 to 650 ° C., and then heated by an electric heating method using a tubular heater until the temperature reaches the soaking temperature. This is a method for decarburizing and annealing a grain-oriented electrical steel sheet, in which a uniform heating is performed by an element heater method in a heat stage.

In order to realize the above decarburizing annealing method, in a decarburizing annealing apparatus for a grain-oriented electrical steel sheet strip containing Si ≦ 4.5% or less, which is cold-rolled to a final sheet thickness, A decarburizing annealing apparatus for grain-oriented electrical steel sheets, comprising a combination means of a gas heating method using a radiant tube and an electric heating method using a tubular heater and a soaking means using an element heater method.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a burner capacity and stability in each zone of a heating zone in a decarburizing annealing furnace by a conventional 10-radiant tube gas heating system (divided into seven zones for convenience). It is the figure which showed the combustion range typically. In FIG. 1, the burner capacity of each of the zones 1 to 4 has 120,000 kcal / Hr, and
The zone was operated at a burner capacity of 80,000 kcal / Hr, and the burner capacity of the 7 zones was operated at 60,000 kcal / Hr. In the above embodiment, all of the zones 1 to 5 are within the stable combustion range and satisfy the target heating condition.
Zones 7 to 7 exceeded the stable combustion range, soot clogging occurred and an unstable combustion state occurred. 6-7
The zone is an area corresponding to the transition zone to the solitary tropics, and how strictly the temperature is controlled in this transition zone is the key to determining the quality of the glass film by decarburization. Therefore, instead of the conventional radiant tube gas heating system for the transition zone heating, the decarburization is achieved by using a tubular heater that is a wide-ranging and electrically controllable electric heater capable of strict temperature control. Decarburization annealing became possible without loss.

FIG. 2 shows a temperature rise curve based on FIG.
In FIG. 2, the target heating curve of the decarburization annealing cycle is shown by a solid line. In the case of the heating operation in the conventional gas heating method using a radiant tube, the target heating curve is changed from the vicinity of 600 ° C. with the passage of time. If it deviates and moves to the + side (deviation higher than the target heating curve; dashed line curve), as described above, the oxide film precedes and the decarburization property deteriorates, while the-side (from the target heating curve) If the temperature changes to a lower value, the effective soaking time becomes shorter, and the decarburization property deteriorates. In particular, this tendency is more likely to occur in a transition zone from a heating zone at 600 ° C. to 800 ° C. to a solitary zone. Therefore, according to the present invention, this temperature zone is heated in a temperature range (dotted line curve) within ± 15 ° C. at the maximum with respect to the target temperature rising curve by a heating means capable of obtaining a strict temperature rising curve with a small temperature fluctuation according to the present invention. Decarburization can be kept within an allowable range.

Table 1 shows the evaluation results of the decarburization properties of the method according to the present invention and the conventional method using a gas heating method using a radiant tube. The data shown in Table 1 is actual data for 100 coils.

[0013]

[Table 1]

In practicing the method of the present invention, in the arrangement of the heating zone means in the decarburizing annealing apparatus, about 3/4 of the length of the apparatus is used as a gas heating means using a radiant tube, and in the latter half of the heating zone, almost the remaining one is used. This is achieved by configuring the / 4 portion with 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 adequately supported by commercially available equipment specifications.

[0015]

As described above, in the present invention, the overshoot and undershoot of heating are eliminated by defining the temperature rise transition in the latter half of the heating zone of decarburization annealing, and stable decarburization annealing is possible. In addition, the heating method in the latter half of the heating zone of decarburization annealing uses a tubular heater with a large heat generation density and a heating resistor arranged in a nectar to enable a wide range of steel plate size changes despite a furnace with a large processing capacity. In this case, it is possible to flexibly cope with the problem and to adopt a stable heating / heating curve.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an arrangement of a heating means in a conventional decarburizing annealing apparatus.

FIG. 2 is a diagram showing a target heating curve, a curve of a conventional method, and a curve of the present invention in a decarburizing annealing apparatus.

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Shigenobu Koga 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division

Claims (3)

[Claims] When a strip for a grain-oriented electrical steel sheet containing Si ≦ 4.5% or less cold-rolled to a final sheet thickness is decarburized and annealed, the steel sheet temperature in a heating step of the strip is raised to 600 to 800 ° C. A decarburizing annealing method for grain-oriented electrical steel sheets, characterized in that a temperature deviation with respect to a target heating transition is controlled within ± 15 ° C. during a certain period to perform decarburizing annealing. 2. When the strip for grain-oriented electrical steel sheet containing Si ≦ 4.5% or less cold-rolled to the final sheet thickness is decarburized and annealed, the steel sheet temperature in the heating step of the strip is 550 to 650 ° C. Is heated by a gas heating method using a radiant tube, and then heated by an electric heating method using a tubular heater until the temperature reaches the soaking temperature above the temperature, and in the soaking stage, the element is heated by an element heater method. Decarburization annealing method for grain-oriented electrical steel sheets. 3. A decarburizing annealing apparatus for a strip for a grain-oriented electrical steel sheet containing Si ≦ 4.5% or less cold-rolled to a final sheet thickness, wherein a heating means is a gas heating system using a radiant tube and a tube heater. A decarburizing annealing apparatus for grain-oriented electrical steel sheets, comprising a combination means of an electric heating method and a soaking means by an element heater method.