JPH05156359A - Manufacture of electric steel sheet for small-sized transformer - Google Patents

Abstract

PURPOSE:To economically manufacture an electric steel sheet for a small-sized transformer excellent in magnetic properties. CONSTITUTION:A slab contg. >=0.01% C, <=1.50% Si, >=1.00% Mn, <=1.00% sol.Al, <=0.01% N, <=0.01% S, <=0.16% P and the balance Fe with inevitable impurities is subjected to hot rolling, is coiled at 450 to 550 deg.C coiling temp., is subjected to pickling treatment, is thereafter subjected to batch annealing at 600 to 1000 deg.C in a pure hydrogen atmosphere, is subjected to cold rolling and finish annealing and is subsequently subjected to skin pass rolling at 3 to 20% draft. In this way, from the hot rolled steel sheet subjected to low temp. coiling in the hot rolling, the objective nonoriented electric steel sheet having excellent magnetic properties particularly in magnetic flux density in a low magnetic field can be manufactured at low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic steel sheet for a small transformer, which is excellent in iron loss and magnetic flux density.

[0002]

2. Description of the Related Art Small transformers are widely used as power supply transformers and transformers for household electric appliances, ballasts for fluorescent lamps and the like. In recent years, household electric appliances have been required to be lighter and smaller, and transformers have also been required to be smaller and lighter. On the other hand, these transformers must be manufactured at low cost and can be miniaturized by using unidirectional electrical steel sheet, etc., but this is disadvantageous in terms of cost. Steel sheets have been used. A non-oriented raw material steel sheet is a steel sheet produced by a steel manufacturer that is punched by a transformer manufacturer and then strain-relieved annealed to obtain the desired magnetic properties. Many have higher magnetic flux density than magnetic steel sheets. Although iron loss and magnetic flux density are mentioned as characteristic values showing the performance of the electromagnetic steel sheet, iron loss has been conventionally used as showing the grade. The conventional non-oriented material steel plate has only an iron loss of about 3.5 W / kg (plate thickness 0.5 mm). Therefore, the non-oriented electrical steel sheet manufactured from the non-oriented material steel sheet has a high magnetic flux density and thus is suitable for downsizing of the transformer. There were many.

A non-oriented electrical steel sheet is generally produced by hot rolling-pickling-cold rolling-continuous annealing-surface treatment of a silicon steel slab produced by an LD converter with extremely small amounts of impurities and inclusions. It is manufactured through processes. In the production of a non-oriented electrical steel sheet, Si is added to improve the magnetic characteristics, but a steel sheet having a Si content of less than 1.5% is intended to improve the magnetic characteristics, particularly the magnetic flux density. Content is 1.5
%, The hot rolled steel sheets were annealed for the purpose of preventing ridging that occurs during cold rolling and improving the magnetic properties. In the case of a non-oriented electrical steel sheet, this hot-rolled steel sheet is generally annealed by continuous annealing.
As disclosed in Japanese Unexamined Patent Publication No. 8-31367, Ar ₃
Soaking for 30 seconds to 15 minutes at a temperature below the transformation point is effective. In batch annealing, since it is exposed to an annealing atmosphere for a long time, it is annealed in a non-oxidizing atmosphere.

As the non-oxidizing atmosphere gas, ammonia decomposition gas and nitrogen gas are usually used. In an atmosphere containing these nitrogen gas, if Al is present in the steel, it is nitrided at a high temperature exceeding 750 ° C. Occurs, and a remarkable defect in magnetic characteristics occurs. Further, when the steel contains a large amount of Si or Mn, the oxygen carried into the steel sheet causes a slight oxidation (temper color) at the edge of the steel strip. Nitriding due to Al in the steel inhibits the grain growth in the annealing in the subsequent step, the temper color promotes roll wear during cold rolling, and further in the continuous annealing for finishing,
This causes a difference in heat absorption and causes poor flatness. Therefore, it was very difficult to anneal the hot rolled steel sheet in a nitrogen atmosphere at 750 ° C or higher.

As a method for solving the above problems, C ≦
0.05%, Si ≦ 4.0%, sol. Al ≦ 1.0
%, Mn ≦ 1.5%, and the balance being Fe and unavoidable impurities, the steel strip is subjected to normal hot rolling to form a hot rolled steel strip, and pickled to obtain pure hydrogen at 600 to 1000 ° C. After performing box annealing in the atmosphere, cold rolling is performed to a predetermined plate thickness, and finish continuous annealing is performed, followed by insulation coating, or C ≦ 0.05%, Si ≦ 4.0%, sol. Al
Steel strips containing ≦ 1.0% and Mn ≦ 1.5%, the balance of which is Fe and unavoidable impurities, are subjected to normal hot rolling to form hot-rolled steel strips, and pickled to 600-1000. After box annealing in a pure hydrogen atmosphere at ℃, cold rolling is performed, then box annealing is performed in a pure hydrogen atmosphere at 600 to 1000 ℃, and cold rolling is performed again to obtain a predetermined plate thickness and finish. A method of applying an insulating coating after continuous annealing (Japanese Patent Laid-Open No. 3-479)
No. 19) has been proposed.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method disclosed in Japanese Laid-Open Patent Publication No. 19 is excellent as a method for producing a non-oriented electrical steel sheet, but since it is a normal hot rolling, that is, a hot rolling is performed at a winding temperature of 550 to 700 ° C., the hot rolled steel is rolled at the time of winding. Since no strain is applied to the strip, it is difficult for grains to grow during strain relief annealing, and the magnetic properties are not sufficiently improved, so that recent demands from customers cannot be sufficiently satisfied.

The object of the present invention is to provide the above-mentioned Japanese Patent Laid-Open No. 3-479.
An object of the present invention is to provide a method for manufacturing an electromagnetic steel sheet which solves the drawbacks of JP-A No. 19 and has the best magnetic characteristics and economy for a small transformer having a low iron loss value and an excellent magnetic flux density.

[0008]

[Means for Solving the Problems] The inventors of the present invention have conducted earnest research to achieve the above object. As a result, it was clarified that by imparting strain by low-temperature winding at 450 to 550 ° C. in hot rolling, strain relief annealing promotes the growth of grains in the easy magnetization direction, and the magnetic properties are improved. The invention has been reached.

That is, according to the present invention, C ≦ 0.01%, S
i ≦ 1.50%, Mn ≦ 1.00%, sol. Al ≦
1.00%, N ≦ 0.01%, S ≦ 0.01%, P ≦
A steel slab containing 0.10% and the balance Fe and unavoidable impurities is hot-rolled to a coiling temperature of 450 to 55.
After winding at 0 ℃ and pickling, 600 ℃ in pure hydrogen atmosphere
Batch annealing at ~ 1000 ° C, cold rolling, finish annealing,
Skin pass rolling is performed at a reduction rate of 3 to 20%.

[0010]

In the present invention, the chemical composition of the raw steel billet is limited for the following reason. If C exceeds 0.01%, magnetic aging is caused and the magnetic properties are deteriorated.
% Or less. Si contributes to the improvement of iron loss and is an essential element for the improvement of magnetic properties. However, if it exceeds 1.5%, it becomes too large and the recrystallization temperature rises, so that stress relief annealing (usually in an inert gas, The improvement in the magnetic properties at 750 ° C. for 2 hours is lost, so the content is made 1.5% or less. Mn is an element effective in improving iron loss, but if it exceeds 1.0%, the iron loss is deteriorated, so the content is made 1.0% or less. sol. Al is effective for improving grain growth and is an essential element for improving magnetic properties.
If it exceeds 1.0%, there is a danger of ignition during hot rolling and the cold rolling property is poor, so the content is made 1.0% or less. N,
Since S produces inclusions harmful to the improvement of magnetic properties and hinders grain growth, the content of S is set to 0.01% or less. P is an element necessary to secure mechanical strength, but 0.1%
If it exceeds 0.1%, the cold rolling property deteriorates, so the content is made 0.1% or less.

In the present invention, the coiling temperature in hot rolling is set to 450 to 550 ° C. to impart strain to the steel sheet by low temperature coiling and promote the growth of crystal grains by the effect of strain annealing during subsequent annealing. This is because the magnetic properties are improved by this, and when the winding temperature is lower than 450 ° C., the winding cannot be performed smoothly, and when it exceeds 550 ° C., distortion cannot be applied during the winding. In the present invention, after the hot rolled steel strip is pickled, batch annealing is performed in a pure hydrogen atmosphere at 600 to 1000 ° C. The annealing in a pure hydrogen atmosphere causes oxidation, nitriding, etc. that deteriorate the magnetic properties. Without
Moreover, the magnetic properties are improved by the purifying action such as denitrification. If the annealing temperature is less than 600 ° C, sufficiently grown crystal grains cannot be obtained, and if it exceeds 1000 ° C, α-γ.
The temperature range is 600 to 1000 ° C. because it causes transformation and has no effect on the improvement of magnetic properties and causes high cost.
In the present invention, the rolling reduction in the skin pass rolling after cold rolling and finish annealing is set to 3 to 20% because the strain generated in the skin pass rolling is too small if it is less than 3% and the strain in the stress relief annealing after punching is reduced. Can't take
If it exceeds 20%, the strain becomes too large, and the strain cannot be removed even by strain relief annealing after punching.

In the present invention, the winding temperature is 450 to 5
The hot-rolled steel strip coiled at 50 ° C is given strain by low-temperature coiling, and as a result, crystal grains, especially crystal grains in the easy magnetization direction, grow in the strain relief annealing after punching, and the magnetic properties are good. Becomes Further, the magnetic steel sheet obtained by the method of the present invention is superior to the magnetic steel sheet by the conventional method in magnetic flux density in a low magnetic field as shown in FIG. 1, and is particularly suitable for a small transformer.

[0013]

EXAMPLE X, Y, Z thicknesses 22 of the chemical components shown in Table 1
7mm, 1000mm width steel billet is heated to 1180 ℃,
Hot rolling was performed under the hot rolling conditions shown in Table 2 to obtain a hot rolled steel strip having a plate thickness of 2.3 mm. This hot-rolled steel strip was pickled, then annealed under various conditions as shown in Table 2, cold-rolled, and then continuously annealed at 720 ° C. for 1 minute in a nitrogen atmosphere, followed by the rolling reduction shown in Table 2. 0.50mm by rate skin pass rolling
Finished. Epstein test pieces were cut out from each of the obtained steel strips, subjected to strain relief annealing at 720 ° C. for 2 hours in nitrogen gas, and magnetic properties were evaluated by the methods specified in JIS C2550 7.1 and 7.2. Further, in order to evaluate the performance as a transformer, it was punched into an EI transformer core (EI-66 type specified in Japanese Electronic Industry Standards EIAJ RC622 and RC627), subjected to strain relief annealing after processing, and a test coil (impedance 6Ω). The no-load current and no-load loss were measured. The results are shown in Table 3. In addition, AX in the atmosphere gas column of Table 2 shows ammonia decomposition gas.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

As shown in Tables 2 and 3, the test No. satisfying the conditions of the present invention. In the case of Nos. 1, 7, and 10, the test No. which does not satisfy the conditions of the present invention. 2, 3, 4, 5, 6,
Compared with 8, 9, 11 and 12, the magnetic characteristics are remarkably excellent, and the EI66 transformer core has no load loss,
All of the no-load currents satisfy the conditions of 1.3 W or less and 130 mA or less required by the customer.

[0018]

As described above, according to the method of the present invention, magnetic properties suitable for a small transformer, particularly a low magnetic field, can be obtained from a hot-rolled steel strip which is wound at a low temperature by lowering the winding temperature in hot rolling. A non-oriented electrical steel sheet excellent in magnetic flux density can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a magnetization curve (0 °) showing a relationship between a magnetizing force H and a magnetic flux density B when magnetizing a magnetic steel sheet material according to the method of the present invention and a conventional method.

Claims (1)

[Claims] 1. C ≦ 0.01%, Si ≦ 1.50%, M
n ≦ 1.00%, sol. Al ≦ 1.00%, N ≦ 0.
A steel slab containing 01%, S ≦ 0.01%, P ≦ 0.10% and the balance being Fe and unavoidable impurities was hot-rolled and wound at a winding temperature of 450 to 550 ° C. A method for producing a magnetic steel sheet for a small transformer, which is characterized in that after washing treatment, batch annealing is performed in a pure hydrogen atmosphere at 600 to 1000 ° C., cold rolling, finish annealing, and then skin pass rolling is performed at a reduction rate of 3 to 20%.