JPH02104621A - Heat treatment of grain-oriented silicon band steel and heat-treating furnace - Google Patents

Abstract

PURPOSE:To obtain a high-performance silicon band steel having a uniform magnetic characteristic without cutting due to melting by keeping the band steel, which has been heated at a high rate, at a high temp. while winding the band steel at the time of coldrolling the title band steel having specified composition and thickness, and then heat-treating the steel under specified conditions. CONSTITUTION:A grain-oriented silicon band steel having 0.3-0.4mm thickness and contg., by weight, 0.02-0.09% C, 2.5-6.5% Si, 0.005-0.05% S, and 0.01-0.20% Mn is cold-rolled. The band steel 1 is wound in the form of a coil in the part 2 for setting a material to be heated, then gradually rewound, led to a high-rate heating part 3, and then sent into high temp. keeping part 4 through the electrodes 9 and 10 provided with a roller. Electric power is supplied to the electrodes 9 and 10, and the band steel 1 is heated in a nonoxidizing atmosphere from ordinary temp. to 1000-1200 deg.C at a rate of >=3 deg.C/sec. Since a current needs not be applied for a long time, the band steel is not cut due to melting. The band steel 1 is wound in the high temp. keeping part 4, and kept at the above- mentioned temp. for 3-8hr by a radiation heater 17.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a heat treatment method and a heat treatment furnace for a grain-oriented silicon steel strip, and particularly to a grain-oriented silicon steel strip with a high magnetic flux density and a low iron content. The present invention relates to a suitable heat treatment method and a heat treatment furnace suitable for implementing the method.

[Prior art]

C: 0.02-0.09% by weight, Si: 2.5-6.5
Weight %, S: 0.05-0.05 weight %, Mn
: After cold rolling a grain-oriented silicon steel strip with a thickness of 0.3 to 0.4 mm containing 0.01 to 0.20% by weight and some trace components, it is rolled in a vacuum or in H2, Ar, N. ,
100 at a heating rate of 3°C/S or more from room temperature in an atmosphere of
A method has been proposed (Japanese Patent Application No. 62-3270) in which the magnetic properties of the grain-oriented silicon steel strip are improved by raising the temperature to 0 to 1200 DEG C. and maintaining the temperature for 3 to 8' hours.

Conventionally, the method of raising and maintaining a high temperature using infrared rays or heat conduction, as described below, involves heating a large amount of silicon steel strip from room temperature to 1,000 degrees Celsius at a heating rate of 3°C/S or more.
Raising the temperature to ~1200℃ increases the speed of heat conduction,
It is known that this method is not practical due to high power loss.

Therefore, as a method to achieve rapid temperature rise and high temperature maintenance without temperature uniformity as described above, current is passed directly to the grain-oriented silicon steel strip, and the grain-oriented silicon steel strip is heated by the Joule heat generated by the grain-oriented silicon steel strip itself. A method of heating and a heating furnace have been proposed. In this method, the resistivity of a silicon steel strip at room temperature is approximately 50 μΩ/m, and the resistivity of a general steel plate is approximately 20 μΩ/m.
In addition, the electrical resistance of the silicon steel strip after cold rolling is extremely uniform in each part, and therefore the heating rate and temperature distribution are also uniform, so the heat-treated silicon steel strip has uneven magnetic properties. It has the characteristic of being able to obtain high performance products without any problems.

[Problems to be Solved by the Invention] However, this method has the problem that temperature unevenness occurs in the silicon steel strip due to uneven heat retention, and the silicon steel strip melts and breaks after being energized for a long time. The causes of fusing are listed below.

When a silicon steel strip is heated to 1000 to 1200°C and held at that temperature for 3 to 8 hours, the melting point of the silicon steel strip is 1400°C.
Since the temperature is close to ℃, the silicon steel strip evaporates and thins in the thickness direction. For example, experiments have shown that when held at 1200° C. for 7 hours in a vacuum, the thickness decreases by approximately 10% to 30% in the thickness direction.

Furthermore, although the electrical resistance of the silicon steel strip is extremely uniform in each part, it is very difficult to install a heat insulator so that the temperature of the silicon steel strip is uniform, resulting in temperature unevenness of several degrees Celsius at 1200 degrees Celsius. If a location where the temperature is several degrees higher than 1200°C due to the installation of heat insulating material occurs, the plate thickness will be reduced more than other locations. This phenomenon causes unevenness in the thickness of the silicon steel strip, and the resistance increases in areas where the thickness is reduced compared to other areas. Since the current flowing through the silicon steel strip is constant, the local applied voltage increases in areas where the resistance increases due to the decrease in plate thickness, and the applied power increases locally, and as the power increases, the resistance increases compared to other areas. The temperature increases. These interactions create the following closed loop, which causes the silica band to melt.

Experiments have shown that the time it takes to melt the high temperature - reduced plate thickness -> high resistance - high power - high temperature silicon steel strip under the conditions of 1200° C. and vacuum is 3 to 7 hours.

Therefore, with the above-mentioned conventional technology, it is difficult to maintain high temperature for a long time, and there is a problem that it is very difficult to stably improve the targeted magnetic properties.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to be able to raise the temperature from room temperature to 1000-1200°C at a heating rate of 3°C/S or more without causing the grain-oriented silicon steel strip to be heat-treated to melt. Another object of the present invention is to provide a heat treatment method and a heat treatment furnace that can maintain the temperature for 3 to 8 hours without temperature unevenness.

[Means to solve the problem]

The above objectives are: a high-speed heating section that has the function of heating a plate-shaped silicon steel strip at high speed; This is realized by a heat treatment furnace consisting of a high-temperature holding section that has the function of holding a plate-shaped silicon steel strip at a high temperature while winding it up.

[Effect]

As a typical example of the present invention, an apparatus will be described in which an electrical heating method is used in the high-speed heating section and a heat-resistant method is used in the high-temperature holding section.

In the present invention, the temperature is increased to 1200°C from room temperature at a heating rate of 3°C/S.
To raise the temperature to ℃, the advantage of the electric heating method is that it can raise the temperature quickly and evenly over a period of about 6 to 7 minutes, and the advantage of the heating method is that it can stably maintain the temperature evenly for a long time. This is a method that incorporates

〔Example〕

Next, the present invention will be explained in more detail using the drawings.

FIG. 1 is a sectional view of a heating furnace for carrying out the present invention. This heating furnace consists of a heat treatment target installation part 2 in which a silicon steel strip 1, which is a heat treatment target, is installed in advance, a high-speed temperature raising part 3, which has both a high-speed temperature raising function and a steel strip movement function, and a high-speed temperature raising part 3, which maintains the heat treatment target at a high temperature. It is composed of a high temperature holding section 4.

The silicon steel strip 1, which is the object to be heated, is placed in the object installation section 2.
It is wound into a coil shape and attached to the shaft 5 inside. The heat-treated material installation section 2 also includes a vacuum pump 6 for reducing the pressure inside the furnace to a vacuum atmosphere, and a carry-in door 7 for carrying the heat-treated material into the furnace.

The silicon steel strip 1 that is wound into a coil and installed in the heat-treated object installation section 2 is gradually unwound and guided to the high-speed temperature raising section 3 through the fixed roller 8 . In the high-speed temperature raising section 3, the material is fed into the high temperature holding section 4 through electrodes 9 and 10 with rollers, which are current-carrying terminals for energizing heating, and press rollers 11 and 12. The inner walls of the high-speed heating section 3 and the high-temperature holding section 4 are covered with a heat-resistant material 13 that also has a heat-insulating function.

Within the high temperature holding section 4, the silicon steel strip l is again wound around the shaft 14, and its temperature is maintained by a heater 17 installed between electrodes 15 and 16.

In addition, temperature sensors 18 and 19 for temperature control are installed inside the furnace.

〔Concrete example〕

In the heating furnace configured as described above, power is supplied to the roller electrodes 9 and 10 from a separate power supply control section. When the silicon steel strip 1 is energized, it generates Joule heat and its temperature increases. Because heat dissipation is prevented by the heat insulating material 13 surrounding the silicon steel strip 1, and because the silicon steel strip 1 is fed at a constant speed on the rollers, the silicon steel strip 1 moves from the electrode 9 to the electrode 1O. The temperature rises rapidly during this period. Further, the temperature increase rate and the final temperature can be easily adjusted by changing the amount of power supplied and the conveyance speed of the silicon steel strip.

Electrode 9. The distance between the electrodes 10 is 1000 mm, and the silicon steel strip l
For a transport speed of 5 × 10 m/s, the electrode 9.10
The steel strip 1 passes through the gap in 195 seconds, and there is no need for long-term energization as described in the prior art, so no fusing phenomenon of the steel strip 1 occurs.

The resistance of a silicon steel strip with a width of 250 mm, a thickness of 0.1 mm, and a length of 1000 mm after cold rolling is 0.5 Ω, and the silicon steel plate 1 is heated from room temperature to 1200 mm at a heating rate of 6° C./S in a good heat-insulated state. To raise the temperature to ℃, the voltage is 97V and the current is 19V.
The inventors' experiments have shown that 4A and 18kW of electric power are required.

Therefore, under the above conditions, electrode 9. Voltage 97V between electrodes 10
By applying a current of 194 A, the desired temperature increase rate and target temperature can be achieved.

The temperature reached by the silicon steel strip 1 is measured by the radiation temperature sensor 18.

After the high-speed temperature rise, the silicon steel strip 1 is wound around a shaft 14 within the high temperature holding section 4 and its temperature is maintained by a heating heater 17. Since the silicon steel strip 1 has already reached the required temperature in the high-temperature holding section 4, the electric power required for high-temperature holding is very small because only heat loss occurs in the high-temperature holding section 4 (and Since the holding part 4 has a simple furnace structure, it is easy to attach a heat insulator, and therefore the furnace has little heat loss.

A comparison will be made with the conventional technology regarding the power supply required to heat a silicon steel strip (resistance: 10Ω) with a width of 250 mm, a thickness of 0.1 mm, and a length of 20 m. Note that the heat retention state is assumed to be the same.

In the prior art, all the steel strips are heated in a furnace at the same time. The voltage required to heat the copper strip is proportional to the length of the copper strip, and the current required is proportional to the cross-sectional area of the steel strip. Therefore, when a 20 m copper strip is installed and heated in a furnace as in the prior art, the required voltage is 20 times the voltage of the present invention.
It becomes 0V.

Further, the current is 194V and the power is 376kW.

Such a voltage of 100 OV or more causes vacuum discharge in a vacuum and is not practical. In addition, the power supply system requires 37
Since it is large at 6 kW, the power supply itself is very large and expensive. However, in the present invention, since the steel strip corresponding to the length between the electrodes is gradually heated, the required performance as a power source is the same regardless of whether the copper strip is long or short, with a voltage of 97V and a current of 1.
It is constant at 94Δ and electric power is 18kW.

This example also shows that the present invention is an easy method to raise the temperature of a larger silicon steel strip at a high speed and maintain it at a high temperature for a long period of time without being unreasonable in terms of equipment.

In the above embodiment, an energization method was used in the high-speed heating section, but it is also possible to use an induction heating method using high frequency. An example using induction heating will be explained with reference to FIG. Note that the same parts as in Figure 1 are indicated by the same numbers.

In FIG. 2, the apparatus uses an induction heating method in the high temperature heating section 4. The feature is that an induction heating coil 20 and an induction heating coil support material 21 are used in the high-speed temperature rising section 4. In this example, the coil is wound closely by changing the winding density of the induction heating coil 20. The heating rate is high because the induction energy is concentrated, and the heating rate is low when the coils are loosely wound.Using these properties, the heating rate can be precisely controlled.

FIG. 3 is another embodiment suitable for the present invention, which differs from the embodiment of FIG. 1 in that the number of electrodes 22 and 23 with rollers is increased. In this example, by finely controlling the current and voltage flowing between the electrodes, the temperature increase rate can be finely controlled as in FIG. 2 above. Note that 24 and 25 in the figure are presser rollers.

〔Effect of the invention〕

According to the method and apparatus of the present invention, it is possible to raise the temperature of a large silicon steel strip at a high speed and to maintain the temperature at a high temperature for a long period of time. Therefore, it is possible to stably produce large quantities of silicon steel strips with excellent magnetic properties.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 are cross-sectional views of heating furnaces according to embodiments of the present invention. 1...Silicon steel strip, 2...
Heat-treated material installation section, 3... High temperature raising section, 4
・・・・・・High temperature holding part, 9゜10.22.23
...... Electrode with roller, 17...
...Calf elbow heater, 20...Induction heating coil. Figure 1 Figure 2 Figure 3

Claims (6)

[Claims] (1) C: 0.02~0.09% by weight: Si: 2.5~
6.5% by weight, S: 0.005-0.05% by weight, Mn
: After cold rolling a grain-oriented silicon steel strip with a thickness of 0.3 to 0.4 mm containing 0.01 to 0.20% by weight and some trace components, it is subjected to vacuum or H_2-, Ar, N_2
100 at a heating rate of 3°C/S or more from room temperature in an atmosphere of
In the method of improving the magnetic properties of the grain-oriented silicon steel strip by raising the temperature to 0 to 1200 ° C. and holding it at that temperature for 3 to 8 hours, the silicon steel strip is heated at high speed while moving in a belt shape. A method for heat treating a grain-oriented silicon steel strip, which is then wound into a coil and held at a high temperature for a long period of time. (2) C: 0.02~0.09% by weight, Si: 2.5~
6.5% by weight, S: 0.005-0.05% by weight, Mn
: After cold rolling a grain-oriented silicon steel strip with a thickness of 0.3 to 0.4 mm containing 0.01 to 0.20% by weight and some trace components, it is subjected to vacuum or H_2-, Ar, N_2
100 at a heating rate of 3°C/S or more from room temperature in an atmosphere of
In the method of improving the magnetic properties of the grain-oriented silicon steel strip by raising the temperature to 0 to 1200°C and holding it at that temperature for 3 to 8 hours, the temperature raising and high temperature holding means is a material to be heat treated. After a silicon steel strip is cold-rolled as described above, a high-speed heating section has a function of rapidly raising the temperature of the plate-shaped silicon steel strip, and a steel that allows the silicon steel strip to move smoothly from the high-speed heating section to the high-temperature holding section. A heat treatment furnace comprising a band moving device and a high-temperature holding section that has a function of holding a high temperature while winding a plate-shaped silicon steel band heated at a high speed. (3) The heat treatment furnace according to claim (2), characterized in that an energized heating furnace is used in the rapid temperature increase section. (4) The heat treatment furnace according to claim (2), characterized in that an induction heating furnace is used in the high-speed heating section. (5) The heat treatment furnace according to claim (2), characterized in that a radiation heating furnace is used in the high temperature holding section. (6) In claim (3), an electrode with rollers is provided in the energized heating furnace used in the high-speed heating section, and a plate-shaped silicon steel strip, which is the object to be heated, is passed over the electrode with rollers. A heat treatment furnace that is characterized by its ability to conduct electrical heating.