JPH0243320A - Heat treatment of grain oriented silicon steel strip - Google Patents

Abstract

PURPOSE:To prevent the fusion cutting of the grain oriented silicon steel strip during the course of the heat treatment thereof by making combination use of a method of heating the silicon steel strip by direct energization to the steel strip itself and a method of external heating by radiation, etc. CONSTITUTION:The grain oriented silicon steel strip having 0.02-0.09% C, 2.5-6.5% Si, 0.005-0.05% Si, 0.01-0.2% 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 heating-up rate from ordinary temp. and is held at said temp. for >=3 hours to improve the magnetic characteristics of the steel strip. The silicon steel strip 2 is thereupon heated by direct energization through an electrode 2 to the steel strip itself as a heating element. The external heating such as radiation or conduction heating of a heater 5 is executed together with said heating. The combination or independent use of the direct electrical heating and the external heating is equally well. The fusion cutting of the grain oriented silicon steel strip during the course of the heat treatment thereof is prevented in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of heat treating grain-oriented silicon steel strips, and is particularly suitable for obtaining grain-oriented silicon mesh strips with high magnetic flux density and low iron loss. It relates to a heat treatment method.

[Conventional technology]

After cold rolling the grain-oriented silicon steel strip, it was rapidly heated to 1200°C at a heating rate of 3"C/s or more, and then rolled to 1200°C.
It has been proposed that a silicon steel strip with better directionality and lower iron loss can be obtained by holding the temperature at 0° C. for 3 hours or more. (Patent Application No. 62-3270).

As a heat treatment method, the present inventors have developed a silicon steel strip which is characterized by applying electricity directly to both ends of the silicon steel strip, which is the material to be heat treated, and using the silicon steel strip itself as a heating element to rapidly raise the temperature and maintain the high temperature. A heat treatment method was proposed.

[Problem to be solved by the invention]

However, heating using the direct energization method alone has the following problems.

+11 A difference in the distance between the object to be heat treated and the heat insulating material causes a temperature difference in the object to be heat treated.

(2) In heat treatment in a vacuum, the high-temperature area generated due to the temperature difference in (1) during high-temperature holding causes large transpiration, resulting in large thickness reduction.
As a result, the resistance increases and the temperature further increases, which may repeatedly cause the object to be heat-treated to melt.

FIG. 4 is a diagram showing the maximum temperature difference in the object to be heat treated and the time until fusing, and shows that fusing is likely to occur when the temperature difference is 40''C or more.

The purpose of the present invention is to mainly use an external heating method during temperature maintenance, so that the temperature difference in the object to be heat treated is kept small and heat treatment is performed without melting during temperature maintenance.
The objective is to sweep a grain-oriented silicon steel strip with excellent magnetic properties.

[Means to solve the problem]

The above object is achieved by using both the direct energization method and the external heating method during rapid heating and until the furnace atmosphere temperature reaches the heat treatment holding temperature of the silicon tone zone, and then by using the external heating method.

In other words, it is difficult to raise the temperature rapidly with the external heating method, but since radiation and transmission are used, there is no melting, and it is possible to maintain a uniform temperature inside the furnace, so the temperature inside the heated object can be controlled. The difference will also become smaller.

[Embodiments of the invention]

Next, the present invention will be explained in more detail based on the drawings. FIG. 1 is a sectional view of the heat treatment apparatus.

A silicon steel strip 1 after cold rolling, which is an object to be heat treated, is inserted between ceramic spiral insulators 4 for insulation. Both ends thereof are connected to the electrodes 2, and the whole is placed on a heat-resistant stand 7 and housed in a vacuum container 13. Further, inside the container 13, a heater 6 used for external heating and a heat insulating material 8 for heat insulation are attached.

A thermocouple 9 is attached to measure the temperature of the furnace atmosphere and the object to be heat treated. These electrodes 2, heater 6,
The thermocouple 9 is electrically insulated from the container 13 by the insulating seal 5. This insulating seal 5 also serves as an airtight material.

In the figure, 3 is an electrode protection cover, 12 is the bottom plate of the OIJ song 14, and 15 is a flange.

In the case of vacuum suction, suction is carried out from the suction and discharge port 11, and when gas is used, the gas is supplied from the gas supply port 10,
Gas is discharged from the suction and discharge port 11.

In the heat treatment furnace configured as above, power is supplied from a separate power supply control section to the silicon steel strip 1 through the electrode 2 for rapid temperature rise. At the same time, power is also supplied to the heater 5 to raise the temperature of the atmosphere in the furnace.

After the temperature of the silicon steel strip 1 increases rapidly to 1200° C. and the atmosphere in the furnace also reaches 1200° C., the direct current supply is stopped.

The materials to be heat treated were commercially available oriented silicon mesh strips with a thickness of 0.30 mm cold-rolled to 0.10 mm, widths of 50 mm and lengths of 1 m, and spiral insulators with a width of 75 mm and a thickness of 3 mm. It was rolled up between the two ends, connected to the electrode 2 at both ends, and housed in the container. Since the heat treatment was carried out in a vacuum atmosphere, the heat treatment was carried out by suctioning the heat treatment to a degree of vacuum of 2×10 −5 Torr using a vacuum pump from the vacuum suction port.

Under these conditions, power was supplied to the silicon steel strip 1 from the electrode 2, and the temperature was raised to 1200''C at a rate of 10°C/S.At the same time, power was also supplied to the graphite heater 6 for atmospheric heating. The power supply for direct energization is performed when the object to be heat treated is 1
When the temperature reached 200℃, the atmosphere inside the furnace became 1.
The heating was stopped when the temperature reached 200° C. (start of heating & 50 minutes), and thereafter heating was performed solely by the heater 6 as an external heating source.

Further, after 7 hours had passed since the temperature of the silicon steel strip 1 reached 1200° C., the power supply to the heater 6 was stopped, and the silicon steel strip 1 was cooled.

This operation was performed on 10 samples, and the heat treatment could be performed without melting during the process, and the magnetic properties were as shown in Figure 3, magnetic flux density Be = 1.95T, iron loss W + 315
0 = 0.3 W/kg (value with tension applied 1kg/Ryu 2) was satisfied.

Note that the silicon steel strip 1 used in the present invention has a C: 0.02~
0.09wt%, Si:2.5-6.5Wt%, S
: 0.005~0.05wt%, Mn: 0.01~
Including 0.2 Wt% etc., thickness 0.3-0.4 m
It is m.

〔Effect of the invention〕

According to the method of the present invention, there is no melting during the heat treatment unlike in conventional heat treatment methods, and the production capacity is increased by 30% as shown in FIG. In addition, this fusing test was conducted at 12
This test was conducted to determine whether there was any melting during heat treatment at 00°C for 7 hours.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a heat treatment apparatus according to an embodiment of the present invention;
Fig. 2 is a sectional view taken along the line T-I in Fig. 1, Fig. 3 is a magnetic characteristic diagram of the grain-oriented silicon steel strip obtained by the present invention, and Fig. 4 is a diagram showing the effects of fusing during heat treatment due to direct current conductivity alone. A characteristic diagram showing the occurrence situation, and FIG. 5 is a diagram showing the results of a fusing test. 1... Silicon steel strip, 2... Electrode, 4... Spiral insulator, 6...
...Heater, 13...Vacuum container.

Claims (3)

[Claims] (1) C: 0.02-0.09%, Si: 2.5-6.
5%, S: 0.005~0.05%, Mn: 0.01~
After cold rolling a grain-oriented silicon steel strip with a thickness of 0.3 mm to 0.4 mm containing 0.2%, etc., the temperature is raised from room temperature to 1000 to 1250 °C at a high heating rate of 3 °C/s or more. Warm,
In the method of improving the magnetic properties of the grain-oriented silicon steel strip by maintaining the temperature at that temperature for 3 hours or more, there are two methods: a direct current heating method in which the silicon steel strip itself is used as a heating element as a rapid temperature increase and temperature maintenance means, and a radiation or transmission heating method. A method for heat treatment of grain-oriented silicon steel strip, characterized by using an external heating method such as thermal heating in combination. (2) In the heat treatment method described in claim (1), a directionality characterized in that a direct current heating method and an external heating method are used together when the temperature is raised rapidly, and an external heating method is mainly used when the temperature is maintained. Heat treatment method for silicon steel strip. (3) In the heat treatment method described in claim (1), switching from a combination of a direct current heating method and an external heating method to a single external heating method is performed so that the heating furnace atmosphere temperature maintains the heat treatment of the silicon steel strip. A method for heat treating a grain-oriented silicon steel strip, characterized in that the heat treatment is carried out when the temperature reaches a certain temperature.