JPH10183248A - Semiprocess nonoriented silicon steel sheet excellent in magnetic property and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a semiprocess nonoriented silicon steel sheet having highly stable magnetic properties with small variation in magnetism and to provide a method for producing the same. SOLUTION: A steel sheet having electrically insulated coating is composed of the one contg., by weight. <=0.005% C, <=2% Si, <=0.007% Al, <=1.5% Mn, <=0.2% P, <=0.02% S and <=0.006% N, furthermore contg., at need one or >=two kinds among B, Cu, Ni, Cr, Sn, Sb and Bi by <=0.1%, satisfying the compositional ratio of inclusions of Al2 O3 /(Si2 O+Al2 O3 +MnO)<=0.25, and the balance iron with inevitable impurities. In this case, the average grain size is regulated to 5 to 15μm, it has rolling strain equal to that by skinpass at a draft of 2 to 15%, and its surface roughness measured from the one above the electrically insulated coating is regulated to 0.05 to 0.6μmRa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a semi-process non-oriented electrical steel sheet which is mainly a small transformer material.

[0002]

2. Description of the Related Art Small transformers are used in fluorescent lamps and microwave ovens as electric appliances, and non-oriented electrical steel sheets are often used. This small transformer is sometimes referred to as EI core or LT core due to its shape. Since it is used for a transformer, magnetic properties in a specific direction are required unlike a motor, and this direction is usually designed in the rolling direction (longitudinal direction of the coil). For small transformers, so-called semi-process non-oriented electrical steel sheets and full-process non-oriented electrical steel sheets that do not perform annealing are used, assuming magnetic annealing performed at a temperature of about 750 ° C by customers. The invention is limited to semi-processes.

As a conventional technique, for example, Japanese Patent Application Laid-Open No.
JP 09815 discloses a method for obtaining excellent magnetic properties in the rolling direction by a combination of Si deoxidation and skin pass rolling roughness control. However, in this method, the obtained magnetic properties were not satisfactory. In addition, Japanese Unexamined Patent Publication
Japanese Patent Application Laid-Open No. 1-119618 also discloses a method similar to that of the above-mentioned Japanese Patent Application Laid-Open No. SHO 63-131, but similarly failed in satisfactory magnetic properties.

[0004]

SUMMARY OF THE INVENTION In view of the above, the present invention provides a semi-processed non-oriented electrical steel sheet having unprecedented excellent rolling direction magnetic properties and a method for producing the same.

[0005]

In order to solve the above-mentioned problems, the present invention provides (1) a steel sheet having an electric insulating film, wherein, by weight%, C ≦ 0.005%, Si ≦ 2%, Al ≦
0.007%, Mn ≦ 1.5%, P ≦ 0.2%,
Including S ≦ 0.02%, N ≦ 0.006%,
Inclusion composition ratio Al ₂ O ₃ / (Si ₂ O + Al ₂ O ₃ +
MnO) ≦ 0.25, the balance being iron and unavoidable impurities, the average crystal grain size is 5 to 15 μm,
It has a rolling strain corresponding to a skin pass with a rolling reduction of 2 to 15%, and a surface roughness measured from above the electric insulating film of 0.1%.
It is a semi-processed non-oriented electrical steel sheet having excellent magnetic properties, characterized in that the magnetic steel sheet has a magnetic property of 0.5 to 0.6 µm Ra. (2) The steel sheet of (1) further includes B, Cu, Ni, Cr, Sn,
0.1% by weight of one or more of Sb and Bi
A semi-process non-oriented electrical steel sheet having excellent magnetic properties, comprising:

(3) The present invention relates to a method of the present invention wherein C ≤
0.005%, Si ≦ 2%, Al ≦ 0.007%,
Mn ≦ 1.5%, P ≦ 0.2%, S ≦
0.02%, N ≦ 0.006%, and the composition ratio of inclusions Al ₂ O ₃ / (Si ₂ O + Al ₂ O ₃ + MnO) ≦ 0.
25, the balance being iron and unavoidable impurities, a steel pass having an average crystal grain size of 5 to 15 μm after cold rolling annealing, after applying an electric insulating film to the skin pass with a rolling reduction of 2 to 15%. Rolling to make the surface roughness 0.05-0.6μ
a method for producing a semi-processed non-oriented electrical steel sheet characterized by having a mRa of (4) one or more of B, Cu, Ni, Cr, Sn, Sb, and Bi added to the steel sheet of (3). A semi-process non-oriented electrical steel sheet having excellent magnetic properties, characterized by containing 0.1% or less by weight of at least one kind.

The points of the present invention are as follows. That is, in order to improve the magnetic properties in the rolling direction, it is necessary to cause selective crystal orientation growth by magnetic annealing. For this purpose, the balance between the amount of Al ₂ O ₃ and other inclusions, It has been discovered that the crystal grain size before magnetic annealing, the rolling reduction of skin pass rolling, and the roughness of the product surface can be achieved only when they are combined. By controlling these four, a steel sheet having excellent magnetic properties in the rolling direction can be obtained.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the present invention will be described below. C content is limited to 0.005% or less. The smaller the C content is, the better from the viewpoint of magnetic aging.
05%.

The amount of Si is set to 2% or less. Si is effective in reducing iron loss by increasing the specific resistance of the steel sheet, but when it increases, the magnetic flux density decreases. In the field of small transformers, the magnetic flux density tends to be regarded as important, so the amount of Si is set to 2% or less.

The amount of Al is limited to 0.007% or less.
When Al increases, Al ₂ O ₃ also increases, and the magnetism in the rolling direction deteriorates.

The amount of Mn is 1. 5% or less. Mn has the effect of increasing the specific resistance and at the same time improving the texture, but if it is too much, there is a problem of addition cost, so Mn must be 1.5% or less.

The amount of P is limited to 0.2% or less. P is effective in reducing drooling and burrs of the steel sheet in the punching step, but if it is too large, a problem of cracking in the slab occurs. Since this upper limit is 0.2%, it is restricted.

[0013] The amount of S is limited to 0.02% or less. Since S forms fine sulfides such as MnS and Cu _x S (x = 1.6) and deteriorates iron loss, it is better to use a small amount of S.
If it exceeds 02%, the amount of deterioration of magnetism increases, so it must be avoided.

The amount of N is limited to 0.006% or less. N
If the amount is large, blisters due to nitrogen gas called blisters are generated on the surface of the steel sheet after annealing, so it is preferable that the amount is small. However, in order to prevent this surface defect, it must be 0.006% or less.

Inclusion composition ratio Al ₂ O ₃ / (Si ₂ O)
+ Al ₂ O ₃ + MnO) is limited to 0.25 or less.
The ratio of Al ₂ O ₃ plays a large role in forming a texture after magnetic annealing, and Al ₂ O ₃ / (Si ₂ O + Al ₂ O ₃ +
When the MnO) is 0.25 or less, the easy axis <
Although there are many orientation grains with 100> aligned, if it exceeds 0.25, the orientation selectivity is lost and the magnetic flux density in the rolling direction deteriorates due to randomization, so it is limited to 0.25 or less. Al ₂ O ₃
Is controlled at the steel making stage. For example, as a means for reducing free oxygen performed during the vacuum degassing process, the added amount of Si or Mn is increased, the added amount of Al is reduced, and Al ₂ O ₃
It is effective to reduce the Al ₂ O ₃ ratio by relatively decreasing the ratio. Further, a conventional method of not adding Al at all, or a method of adding Al after deoxidizing Si before deoxidizing is also effective. The addition of elements during the vacuum degassing process is usually performed in the form of ferrosilicon, ferromanganese, or an aluminum rod.

As other elements, B, Cu, Ni, Cr, Sn, Sb, B known as effective elements for magnetic properties
Even if a small amount of i or the like is added, the effect of the present invention is not impaired, so there is no limitation. However, from the viewpoint of cost, the addition amount of each is preferably 0.1% or less.

In hot rolling, a slab is heated at a normal temperature of 900 to 1300 ° C., and hot rolling is performed to obtain a hot rolled sheet. At this time,
Conventionally known technology for increasing the crystal grain size of a hot-rolled sheet, a higher winding temperature, for example, 650 to 900 ° C.
It is also possible to wind at a temperature of. Subsequently, it is generally known that the magnetic flux density is improved by annealing the hot-rolled sheet, but it is desirable to omit it from the viewpoint of production cost.

The cold rolling after pickling of the hot rolled sheet is not particularly limited. Although the rolling is carried out at a conventional reduction rate of 50 to 95%, as the rolling roll, a normal smooth roll is preferable from the viewpoint of controlling the crystal orientation of the final magnetic annealing and the roll cost. The steel sheet roughness after the strong cold rolling is preferably set to 0.05 to 0.7 μm Ra from the viewpoint of controlling the crystal orientation in the final magnetic annealing. As a rolling mill, conventional tandem rolling or reversing rolling is possible, and reversing rolling provides a slightly higher magnetic flux density, but tandem is advantageous from the viewpoint of productivity.

The crystal grain size after recrystallization by annealing is 5 to 5.
Limit to 15 μm. This crystal grain size is defined by the average crystal grain size of the sectional structure. If the crystal grain size is not in the range of 5 to 15 μm, a crystal orientation in which easy axes are accumulated in a stable rolling direction cannot be obtained after magnetic annealing. Although the cause is not yet clear, it is presumed that the orientation selection mechanism works in conjunction with the Al ₂ O ₃ composition ratio in the strain-induced grain growth during magnetic annealing. The crystal grain size can be easily controlled by the annealing temperature and time. However, in this case, care must be taken that the recrystallization temperature and the grain growth property differ depending on the component system. For example, when the amount of Si increases, the recrystallization temperature increases. When the amount of MnO-based inclusions or impurities such as Ti and Nb increases, crystal grain growth deteriorates. For this reason, the temperature × time cannot be generally specified, but if continuous annealing is performed,
８850 ° C. × 5 to 300 seconds is appropriate.

For the control of the crystal grain size, it is preferable to directly observe the microscopic structure. For example, the relationship between the iron loss and the coercive force and the crystal grain size is examined in advance, and the indirect measurement is performed using the iron loss and the coercive force. Control method is simple. As in the conventional case, the crystal grain size cannot be controlled even if the temperature × time is specified, so that the crystal grain size must be strictly controlled. In addition,
Due to the need to control the crystal grain size, annealing is performed inside, inside,
Continuous annealing is preferable to batch annealing in which variation in the outer crystal grain size tends to occur.

After the recrystallization annealing of the steel sheet, an insulating film is applied and baked. The insulating film is formed by applying and baking a known inorganic / organic mixed coating having improved both ordinary insulating properties and punching properties. If necessary, the entire surface of the insulating film may be an inorganic or organic film. The thickness of the insulating film is usually 0.5 to 3 μm. It is also possible to apply and bake this insulating film after skin pass rolling, instead of before skin pass.However, the annealing line is usually equipped with a coating device, so the same timing as recrystallization annealing is used. It is easy to implement in terms of cost.

In the skin pass rolling, the conventional rolling reduction is 2 to 15%. If it is less than 2% or more than 15%, crystal grain growth by magnetic annealing is not sufficient, and iron loss is unsatisfactory. The skin pass roll improves the texture and the space factor by the conventional smooth roll. For this reason, both the front and back of the steel plate of the product are limited to 0.05 to 0.6 μm Ra. Production of a steel sheet having a roughness of less than 0.05 μm Ra is avoided in an industrial sense because polishing of a roll is difficult.
On the other hand, if the Ra exceeds 0.6 μm Ra, the magnetic properties in the rolling direction are deteriorated, so that it is limited. The control of the steel plate roughness is, of course, controlled by the roll roughness of the skin pass, but the roll roughness is not the same value depending on the hardness of the steel plate, the amount of reduction, the amount of the electric insulating film, and the like. Roll roughness is 0.05 to 1.2 μm
Ra is preferred. A preferable texture can be obtained by controlling the roughness of the steel sheet. The roughness is an average value in the rolling direction and the width direction perpendicular to the rolling direction, and Ra is an amount defined by the center line average roughness.

[0023]

Embodiments will be described below with reference to embodiments. [Example 1] The components were adjusted to the values shown in Table 1, melted, and slabs were cast. The control of the Al ₂ O ₃ ratio is based on the Fe-
This was performed by changing the timing of adding Al before and after the addition of Fe-Si. Predeoxidation with Fe-Si leads to Al
_{The 2} O ₃ ratio tends to decrease. 1000 slabs
Heating at 870 ° C and winding temperature of 650 ° C.
It was a hot-rolled sheet of 5 mm. The hot-rolled sheet was pickled and then tandem cold-rolled to obtain a cold-rolled steel sheet having an average surface roughness of 0.25 μmRa. Subsequently, after degreasing, the annealing temperature was adjusted in hydrogen, and soaking was performed for 30 seconds to obtain the average crystal grain size shown in Table 2. In addition, an insulating film of an inorganic / organic mixture was applied and baked to a thickness of 1 μm on one side. Next, 5% skin pass rolling was performed to produce a steel sheet having a roughness of 0.38 μmRa on the front and back sides (steel plate thickness 0.5 mm). After punching out the Epstein sample, annealing was performed in nitrogen at 750 ° C. for 2 hours, and the magnetic properties in the rolling direction were measured.

As shown in the examples, component elements and Al ₂ O ₃
When the ratio and crystal grain size were strictly controlled within the range of the present invention, excellent magnetic properties in the rolling direction were obtained.

[0025]

[Table 1]

[0026]

[Table 2]

[Embodiment 2] The material No. Tandem cold rolling using the hot rolled sheet No. 2 and average surface roughness 0.35μ
An mRa cold rolled steel sheet was obtained. Subsequent continuous annealing reduces the grain size to 10
After coating and drying the insulating film, adjust the rolling reduction and the roughness of the skin pass, measure the product with a thickness of 0.5 mm, measure the roughness, and perform annealing at 750 ° C for 2 hours. The results of measuring the magnetism in the rolling direction are shown below.

[0028]

[Table 3]

As shown in the examples, when the rolling reduction of the skin pass and the steel plate roughness were controlled within the range of the present invention, excellent magnetic properties in the rolling direction were obtained.

[0030]

According to the present invention, a semi-process non-oriented electrical steel sheet having excellent magnetic properties in the rolling direction was obtained.

Claims (4)

[Claims] Claims: 1. A steel sheet having an electric insulating film, wherein the weight%
Including C ≦ 0.005%, Si ≦ 2%, Al ≦ 0.007%, Mn ≦ 1.5%, P ≦ 0.2%, S ≦ 0.02%, N ≦ 0.006% , Inclusion composition ratio Al ₂ O ₃ / (Si ₂ O + Al
₂ O ₃ + MnO) ≦ 0.25, the balance consisting of iron and unavoidable impurities, average grain size of 5 to 15 μm
Having a rolling strain corresponding to a skin pass with a rolling reduction of 2 to 15%, and a surface roughness measured from above the electric insulating film of 0.05 to 0.6 μm Ra. Excellent semi-process non-oriented electrical steel sheet. 2. The steel sheet according to claim 1, further comprising B, Cu, N
A semi-process non-oriented electrical steel sheet having excellent magnetic properties, characterized in that one or more of i, Cr, Sn, Sb, and Bi are contained in 0.1% by weight or less. 3. Weight%, C ≦ 0.005%, Si ≦ 2%, Al ≦ 0.007%, Mn ≦ 1.5%, P ≦ 0.2%, S ≦ 0.02%, N ≦ 0.006%, the composition ratio of inclusions Al ₂ O ₃ / (Si ₂ O + Al
₂ O ₃ + MnO) ≦ 0.25, the balance being iron and unavoidable impurities, and after applying an electrical insulating film to a steel sheet having an average crystal grain size of 5 to 15 μm after cold rolling annealing.
A method for producing a semi-process non-oriented electrical steel sheet, comprising: performing skin pass rolling at a rolling reduction of 2 to 15% to a surface roughness of 0.05 to 0.6 μmRa. 4. The steel sheet according to claim 3, further comprising B, Cu, N
A method for producing a semi-processed non-oriented electrical steel sheet having excellent magnetic properties, comprising one or more of i, Cr, Sn, Sb, and Bi in an amount of 0.1% by weight or less.