JPH0243321A - Heat treatment and heat treating furnace for grain oriented silicon steel strip - Google Patents

Abstract

PURPOSE:To make mass production of the grain oriented silicon steel strip having excellent magnetic characteristics at a low cost by directly energizing the silicon steel strip after cold rolling to heat up the silicon steel strip at a high rate and to hold the same at a high temp. with the strip itself as a heating element. CONSTITUTION:The grain oriented silicon steel strip contg., by weight %, 0.02-0.09% C, 2.5-6.5% Si, 0.005-0.05% S, 0.01-0.20% Mn, etc., and having 0.3-0.4mm thickness is cold rolled. The steel strip is thereafter heated up to 1000-1250 deg.C at >=3 deg.C/sec rate and is held at said temp. for 3-8 hours to improve the magnetic characteristics of this steel strip. The cold rolled silicon steel strip 2 is placed on a heat resistant base 11 and electric power is supplied to the steel strip 1 through energizing terminals 5, 6. The steel strip 1 itself as a heating element is heated up at the high rate and is held at the high temp. The grain oriented silicon steel strip having the excellent magnetic characteristics is mass-produced at the low cost in this way.

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 high magnetic flux density and low iron loss. The present invention relates to a heat treatment method suitable for and a heat treatment furnace suitable for realizing the method.

[Prior Art] C: 0.02 to 0.09% by weight, Si: 2.5 to 6.
5 weight%, S: 0.005-0.05% by weight, M
After cold rolling a grain-oriented silicon steel strip with a thickness of 0.3 to 0,4 + nn containing 0.20% by weight and some trace components, it is rolled in a vacuum or in H2, Ar.
, Raise the temperature from room temperature to 1000 to 1250 °C at a heating rate of 3 °C/sec or more in an N2 atmosphere, and keep at that temperature for 3 to 8 seconds.
A method has been proposed (Japanese Patent Application No. 62-3270) of improving the magnetic properties of the grain-oriented silicon steel strip by holding it for a period of time.

Conventionally, methods for rapidly increasing and maintaining high temperatures as described above include the infrared heating method (e.g., infrared gold image furnace manufactured by Shinku Riko Co., Ltd.) or the heating method using external heat conduction (e.g., Maeyama's Three Kimio fools, Rotary annealing furnace for silicon steel: Kawasaki Steel Technical Report, Volume 15, No. 4,
p., 296-300 (1983)) has been adopted. For example, in an infrared heating furnace, the above-mentioned grain-oriented silicon steel strip is placed in the center, and the infrared rays are reflected by a mirror surface and concentrated on the copper strip, thereby raising the temperature at a high speed and maintaining the high temperature.

[Problem to be solved by the invention] At a heating rate of 3°C/sec or higher, the higher the heating rate, the better the magnetic properties of the silicon steel strip to be heat treated. In the infrared heating method, it depends on the size of the object to be heat treated, but in the inventors' examples described below, the heating temperature was 6°C.
The temperature increase rate of 1/sec was the limit. Moreover, when the size of the object to be heated increases, the concentration of hot rays does not spread over the entire object to be heat-treated, resulting in non-uniform heating rate, and as a result, there is a problem that it becomes difficult to improve the magnetic properties.

Even in heating furnaces that mainly use heat conduction, as the object to be heat treated becomes larger, the heat conduction rate is slower than the temperature increase rate, making it difficult to increase the temperature at a faster rate and ensure uniform temperature distribution. There is a problem that it cannot be improved sufficiently.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to achieve a temperature increase of 6°C/second or more even when the size of the grain-oriented silicon steel strip that is the object to be heat treated becomes large, and even when the amount of heat treatment becomes large. It is an object of the present invention to provide a heat treatment method and a heat treatment furnace which can ensure a high heating rate and do not cause non-uniformity in the heating rate.

That is, it is an object of the present invention to provide a heat treatment method and a heat treatment furnace that can obtain a grain-oriented silicon steel strip with high magnetic flux density and low iron loss, and achieve rapid temperature rise and high temperature maintenance that can withstand scale-up.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a joule system that directly conducts electricity to a cold-rolled silicon steel strip, which is a heat-treated object, and uses the silicon steel strip itself as a heating element. It uses heat to quickly raise the temperature and maintain the high temperature.

[Function] According to a typical example of the present invention, the width 5 after cold rolling
The electrical resistance of a silicon steel strip with a thickness of 0 mm, a thickness of 0.1 nn, and a length of 5 m is 0.55 Ω, and the amount of heat generated by passing electricity through the silicon steel strip is, for example, 0.5 Ω per second at a voltage of 17 V.
13 kcal, which is approximately ℃ if heat loss is ignored.
The temperature of the silicon steel strip can be raised from room temperature to 1200° C. at a heating rate of /second. Although there is actually heat loss,
It is possible to compensate for this by increasing the power supply and using heat insulation means, and it is possible to sufficiently secure a temperature increase rate of 6° C./second or more, which is difficult to achieve with the conventional technology. This is due to the discovery that the resistivity of silicon steel strip is more than twice as high as that of ordinary steel sheets, so it can effectively generate Joule heat, making practical heating possible. This is the beginning of the invention. For example, the low efficiency of a silicon steel strip at room temperature is about 50 μΩ/m, while the resistivity of a general steel plate is about 20 μΩ/m.

Furthermore, the present invention is advantageous in that 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 regardless of each part. It is possible to obtain high performance with uniform magnetic properties.

[Example] Next, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a longitudinal cross-sectional view of a direct current type heat treatment furnace for carrying out the method of the present invention, and FIG. 2 is a plan cross-sectional view of FIG. 1.

A silicon steel strip 1 after cold rolling, which is a coiled material to be heat-treated, is placed on a heat-resistant table 11 with a strip-shaped heat-insulating/electrical insulator 2 wound into the gap, and both ends 3, 4 are connected to current-carrying terminals 5 and 6, respectively. The heat-insulating/electrical insulator 2 is made of, for example, a band-shaped alumina fiber.

They are housed in a container 10 formed by a bell-shaped top lid 12 and a bottom plate 13. The current carrying terminals 5 and 6 and the thermocouple terminal 7 are electrically insulated from the bottom plate 13 by insulators 14, 15 and 16, respectively. M border 14, 15
and 16 also serve as an airtight material. The airtightness of the flange portion 17 of the container 10 is ensured by the ring seal 18.18'
maintained by Reference numeral 19 denotes a hanging metal fitting for the upper lid 12.

Conduits and valves 21 and 22, 23 and 24, 25 and 26 are installed for evacuation, gas supply and gas discharge, respectively.

In the direct energization type heat treatment furnace configured as above, power is supplied to the silicon steel strip 1 through the energization terminals 5 and 6 from a separate power supply control section (not shown). The silicon steel strip 1 generates Joule heat when energized, and its temperature increases by itself. Since heat dissipation is prevented by the heat insulating/electric M frame 2 wrapped around the silicon steel strip 1, the temperature increase rate is adjusted according to changes in the amount of power supplied, and the temperature increases at a rate higher than that of the conventional technology. be able to. The temperature of the silicon steel strip 1 is measured by a platinum-platinum rhodium ring thermocouple 8 inserted through the thermocouple terminal 7. Temperature maintenance after rapid temperature rise is also achieved by adjusting the amount of power supplied.

When maintaining the inside of the container 10 in a vacuum atmosphere, the conduit and valves 21 and 22 are connected to a vacuum device to exhaust gas. Also, H2, N2. When maintaining an Ar gas atmosphere, it is supplied through conduits and valves 23 and 24, and discharged through conduits and valves 25 and 26.

[Specific Example] A direct current type heat treatment furnace according to the present invention having the same structure as shown in Fig. 1 has a capacity of 8 kW and is equipped with a temperature control device.
The power supply was connected. Thickness 0.35nw as heat treated object
A commercially available grain-oriented silicon steel strip with a diameter of 0.1 nm and a length of 5 m was cold-rolled to a thickness of 0.1 nm.
It was sandwiched between alumina fiber bands having a thickness of 0 an and about 3 nn and wound into a coil shape, both ends of which were connected to current-carrying terminals 5.6 and placed in a container 10. A vacuum pump is connected to the conduit 21 to exhaust the air inside the container, and the vacuum level is 2 x 10' Tor.
It was held at r.

Under the above conditions, the temperature rise curves when power is supplied at settings of 3.3 kW and 6.1 kW are shown in A and B in Figure 3.
are shown respectively. As shown in FIG. 3, when the supplied power was 3.3 kW and 6.1 kW, the average temperature increasing rates were 8.1°C/sec and 14°C/sec, respectively. This result shows that a temperature increase rate that cannot be achieved with the prior art can be obtained, and that the temperature increase rate can be controlled by the amount of power supplied.

[Comparative Example] Figure 3 shows the temperature rise curve when a silicon steel strip of @5 mm, thickness 0.1 mm, and length 100 nyn was heated and heated by an infrared heating furnace with an electric capacity of 12 kW, which is a conventional technology. C
It was shown to. The average temperature increase rate obtained was 6.1° C./sec, which was the highest value achieved by the above-mentioned infrared heating furnace.

The comparative example shows that the present invention is a method that can easily achieve larger silicon steel strips with less power supply and at a heating rate faster than the conventional 6°C/sec. .

Next, another embodiment of the present invention will be described with reference to FIGS. 4 to 7. The same parts as in FIGS. 1 and 2 are designated by the same reference numerals.

FIG. 4 is a plan sectional view of another embodiment suitable for the present invention. In this embodiment, electrical insulation between adjacent silicon steel strips 1 is performed by appropriately inserting ceramic spacer poles 43 at key points to form gaps, and silicon steel strips installed in a coil shape are used for insulation. 1 and an inner peripheral heat insulating wall 42 surrounding the current-carrying terminal 5. Alumina fiber or the like is used as the material for the heat insulating walls 41, 4.2. This eliminates the need to fill the central region with a heat insulating material, thereby reducing the heat capacity, which is effective in reducing the amount of power required for temperature rise and improving the temperature rise rate.

FIG. 5 is also a plan sectional view of another embodiment suitable for the present invention, and what is different from FIG. As a result, heat reflecting plates 51 and 52 are provided. Heat reflecting plate 51 on the outer periphery
The reflective surface of the heat reflecting plate 52 is directed toward the inner silicon steel strip 1, and the reflective surface of the heat reflecting plate 52 is directed outward. As a result, the heat radiation from the high-temperature silicon steel strip 1 is reflected by the clear reflection plate, and the silicon steel strip 1 is heated again and sealed at a higher speed. Furthermore, heat loss is reduced more effectively by the heat reflecting plate 51 on the outer periphery.

FIG. 6 is also a plan sectional view of another embodiment suitable for the present invention. The difference from Fig. 4 is that the silicon steel strip 1 is connected to the end pole 6.
1 and reciprocated to fill it.

This allows the current-carrying terminals 5 and 6 to be installed outside the heat insulating wall 41, reducing exposure to high temperatures and preventing deterioration and wear.

FIG. 7 is also a plan sectional view of another embodiment.

The difference from FIG. 2 is that a plurality of pairs of current-carrying terminals 5 and 6 are connected to the silicon steel strip 1.

[Effects of the Invention] According to the method and apparatus of the present invention, it is possible to heat up a large silicon-copper strip at a faster rate than in the past with a smaller amount of power supplied than in the past. Therefore, silicon steel strips with excellent magnetic properties can be produced in large quantities at low cost.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a heat treatment furnace for carrying out the method of the present invention, and FIG. 2 is a sectional view taken along line 1-1 in FIG. FIG. 3 is a temperature rise curve diagram of a silicon steel strip according to the heat treatment furnace of the present invention and the prior art, and FIGS. 4, 5, 6, and 7 are plan sectional views of other embodiments of the heat treatment furnace of the present invention. It is. 1. Silicon steel strip, 2. Heat insulation, insulating material, 5, 6 energizing terminal, 12. Upper cover, 13. Bottom plate, 41.4.2.
・Insulation wall, 43 ... Spacer pole, 51, 52
· ·a reflector.

Claims (4)

[Claims] (1) C: 0.02~0.09% by weight, Si: 2.5~
6.5% by weight, S: 0.005-0.05% by weight, Mn
: Thickness 0.3~ containing 0.01~0.20% by weight etc.
After cold-rolling a 0.4 mm grain-oriented silicon steel strip, the temperature is raised from room temperature to 1000 to 1250 °C at a heating rate of 3 °C/sec or more, and maintained at that temperature for 3 to 8 hours to achieve the above-mentioned directionality. In a method for improving the magnetic properties of a silicon steel strip, as a means for raising and maintaining a high temperature, electricity is applied directly to the cold-rolled silicon steel strip that is the object to be heat treated, and the silicon steel strip itself is used as a heating element to raise the temperature at high speed. A heat treatment method for a grain-oriented silicon steel strip characterized by maintaining a high temperature and a high temperature. (2) C: 0.02~0.09% by weight, Si: 2.5~
6.5% by weight, S: 0.005-0.05% by weight, Mn
: Thickness 0.3~ containing 0.01~0.20% by weight etc.
After cold rolling a 0.4 mm grain-oriented silicon steel strip, the temperature is raised from room temperature to 1000 to 1250 °C at a heating rate of 3 °C/s or more, and maintained at that temperature for 3 to 8 hours to achieve the above directionality. In a heat treatment furnace for improving the magnetic properties of silicon steel strip,
A silicon steel strip wound into a coil is housed in a vacuum container equipped with a thermocouple, a vacuum exhaust conduit, a gas supply conduit, and a gas exhaust conduit, and a heat insulating and electrical insulating strip is wrapped in the gap between the coils for insulation. Furthermore, this is a direct current type heat treatment furnace, which is made by connecting a current-carrying terminal to a silicon steel strip. (3) In claim (2), the direct energization method is characterized in that ceramic spacer poles are inserted into the gaps between the silicon bands wound into coils to electrically insulate the coils from each other. Heat treatment furnace. (4) Claim (2) is characterized in that a heat reflecting plate is provided as the outer peripheral insulation wall surrounding the coiled silicon steel strip and the inner peripheral insulation wall surrounding the current-carrying terminal. Direct current type heat treatment furnace.