JPH0811809B2 - Manufacturing method of non-oriented electrical steel sheet with excellent magnetic properties - Google Patents

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 non-oriented electrical steel sheet having a very high magnetic flux density and a low iron loss.

[0002]

2. Description of the Related Art In recent years, demands for quality improvement of non-oriented electrical steel sheets as magnetic core materials for small rotating machines have become stronger from the viewpoint of energy saving. In order to meet this demand, the manufacturers of electromagnetic steel sheets are also conducting research and development to improve the magnetic properties of non-oriented electrical steel sheets, and industrially, a number of them are specified in JIS. So-called low grade non-oriented electrical steel sheets are manufactured.

In the manufacturing process of this kind of low grade non-oriented electrical steel sheet, in order to obtain a product with a low iron loss value, steel is conventionally highly purified in its melting stage.
Measures have been taken such as increasing the i content and sufficiently adjusting the temperature and time in finish annealing.

However, when these technical means are used, the iron loss value of the product is low, but the magnetic flux density is low. Therefore, there has been a limit to the high efficiency (energy saving) demanded in recent years.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above problems in the prior art and provides a manufacturing method capable of supplying a non-oriented electrical steel sheet having a low iron loss and a high magnetic flux density. To aim.

[0006]

The feature of the present invention is that, in weight%, Si ≦ 2.5%, Al ≦ 1.0%, and
(Si + 2Al) ≦ 2.5% , the balance: the molten steel consisting of Fe and unavoidable impurities, and coagulate by a cooling surface which moves update the cast strip, then the person casting thin strip by cold rolling a predetermined In the manufacturing method of the non-oriented electrical steel sheet that is finish annealed after the thickness (final sheet thickness) is set, the molten steel is solidified by the moving and renewing surface of the cooling body to form a casting ribbon, Cooling rate of cast ribbon (A
Average cooling rate in the range from _r3 to _Ar1 ) is 50 ° C /
It is a method for producing a non-oriented electrical steel sheet having an extremely excellent magnetic property, which is characterized in that it is not more than a second .

Hereinafter, the present invention will be described in detail. The inventors, as a result of extensive studies to solve the technical problem in the present invention, in the non-oriented electrical steel having a phase transformation,
Appropriate cooling conditions of the ribbon when directly obtaining the cast ribbon from molten steel can control the texture in the product after finish annealing, which results in extremely high magnetic flux density and good iron loss. We succeeded in obtaining a non-oriented electrical steel sheet with a low iron loss value.

First, the component system will be explained. For the purpose of improving the mechanical properties, magnetic properties, rust resistance, etc. of the product, or for other purposes, Mn, P, B, Ni, Cr, S.
The effect of the present invention is not impaired even if one or more of b, Sn, and Cu are contained in the steel.

If C is 0.0500% or less, the object of the present invention can be achieved. Low grade non-oriented electrical steel sheets are mainly used in small rotating machines, and from the viewpoint of stable magnetic properties, it is required that magnetic properties do not deteriorate (magnetic aging) during the use of non-oriented electrical steel sheets. To be done.

In the present invention, when the molten steel is solidified by the moving and renewing surface of the cooling body to form a cast ribbon,
Since the cooling rate (average cooling rate in the range from A _r3 point to A _r1 point) of the cast ribbon during the γ → α transformation is controlled to 50 ° C./second or less (γ processing), the carbide is sufficiently contained. Analytical agglomeration and therefore magnetic aging phenomena are reduced. Therefore, it is not required that the carbon content be extremely low in order to prevent the magnetic aging from occurring, and C ≦ 0.0500% is sufficient.

S is an element that is unavoidably mixed in at the stage of steel melting. Conventionally, it should have been S ≦ 0.0100%, but in the present invention, since γ treatment is performed, S can be rendered harmless. Therefore, in the present invention, S ≦ 0.020.
%.

N may be 0.010% or less. According to the conventional method for producing a non-oriented electrical steel sheet, when the content of N is large as in the case of S, N is temporarily re-dissolved during heating of the slab in the hot rolling process and precipitates AlN or the like during hot rolling. When a product is formed, the growth of recrystallized grains is hindered during finish annealing, or when the product is magnetized, a so-called pinning effect that hinders the movement of the magnetic domain wall is exerted, which is a factor that prevents lower iron loss of the product. Therefore, N ≦ 0.0050% should be satisfied, but in the present invention, it is possible to render N harmless by performing γ treatment, so N ≦ 0.010% is sufficient.

Si and Al are added to increase the specific resistance of the steel sheet and reduce the eddy current loss. C ≦ 0.02%
Under the condition (1), if (Si + 2Al) exceeds 2.50%, no transformation occurs, so (Si + 2Al) ≦ 2.
Must be 50%.

If the content of Mn is less than 0.1%, the workability of the product deteriorates, and Mn is added to render S harmless. However, the addition amount of Mn is 2.
If it exceeds 0%, the magnetic flux density of the product is significantly deteriorated, so Mn ≦ 2.0% must be satisfied.

P is added within the range of up to 0.1% in order to improve the punchability of the product. P ≦ 0.
If it is 2%, there is no problem from the viewpoint of magnetic properties of the product.

B is added to render N harmless. Since the balance with the amount of N is necessary, the maximum content is set to 0.005%. In the present invention, since the γ treatment is performed, it is not necessary to add B.

Next, the manufacturing process conditions of the present invention will be described. Conventionally, when a hot-rolled sheet of non-oriented electrical steel with phase transformation (hereinafter abbreviated as transformation steel) is reheated and transformed, the crystal grain orientation becomes random, and the crystal grain size of the hot-rolled sheet is small. Therefore, it has been considered that it is not suitable for improving the magnetic characteristics of the product, and was neglected.

This was the same in the manufacturing process of the non-oriented electrical steel sheet including the process of solidifying the molten steel by the moving and renewing surface of the cooling body to form a cast ribbon.
However, as a result of the inventors' earnest research, the reason is still not clear by controlling the cooling rate during the cooling transformation (γ → α) of the cast ribbon, but
We have found that the texture in the final product is significantly improved.

Thus, according to the present invention, the magnetic flux density is low even if the finish annealing is performed at a higher temperature than that in the conventional annealing condition to prolong the time for grain growth to improve the iron loss of the product. It never happens.

Further, in the present invention, since the cooling rate when the molten steel is solidified by the moving and renewing surface of the cooling body to form a cast ribbon, the cooling rate is low, so that the precipitation of impurities having a small solubility in the α phase is sufficiently performed. It is possible to obtain a non-oriented electrical steel sheet having a low iron loss value and a high magnetic flux density even if finish annealing is performed under the conventional conditions without obstructing crystal grain growth during finish annealing (detoxifying impurities).

The manufacturing process conditions of the present invention will be described in more detail. The controlled cooling of the cast ribbon in the present invention controls the cooling rate when the molten steel is cast into a ribbon (thickness of 3.5 to 0.5 mm) directly.
As a means for cooling the cast ribbon from the A _r3 point to the A _r1 point at a cooling rate of 50 ° C./sec or less, it is preferable to provide a heat retaining device for the cast ribbon or a mild heating device.

Further, by winding the cast ribbon in a high temperature region of A _r3 point + 50 ° C. or more to keep the strip coil warm, 50 ° C./sec _<br/sec> from A _r3 point to A _r1 point > The casting ribbon may be cooled at the following cooling rate. Furthermore, the cast ribbon was once cooled to room temperature fairly quickly, heated again to the γ range, and then controlled to be cooled at a cooling rate of 50 ° C./sec or less from the _{Ar 3} point to the _{Ar 1} point. However, this is disadvantageous in terms of manufacturing cost.

[0023]

【Example】

[0024]

[Table 1]

A molten steel having the components shown in Table 1 (silicon slab consisting of the balance Fe and unavoidable impurities) was solidified on the surface of the moving cooling body to directly obtain a steel strip of 2.5 mm.
Cooling was carried out between A _r3 + 50 ° C. and A _r1 −50 ° C. under the following conditions. Average cooling rate is 500 ° C / sec (cooling with normal temperature water), 50 ° C / sec (air cooling), 10 ° C / sec (uses a heat insulating cover when cooling without winding), 1 ° C / sec (A _r3 +50)
( _Turn up at ℃ or more and cool as it is), 0.07 ℃ / sec ( _Ar3 + 50 ℃ or more, take up the heat insulation cover and cool). Then, it was pickled and cold-rolled to a thickness of 0.50 mm. The cold-rolled steel sheet was degreased and annealed at 800 ° C. for 30 seconds in a continuous annealing furnace. After that, the magnetic characteristics (L
The average of + C , L: rolling direction, and C: L 90 ° direction ) were measured. These values are compared with those of the so-called self-annealing (Japanese Patent Laid-Open No. 54-76422) and c) a) which are comparative methods a) without hot-rolled sheet annealing, b) hot-rolled at 800 ° C. and held for 2 hours. The results are shown in Table 2 in comparison with the material annealed at 925 ° C. for 150 seconds by continuous hot rolling.

[0026]

[Table 2]

Photographs of the metal phase after the final annealing are shown in FIGS. 1 and 2.

Despite the same heat treatment and the same final annealing conditions, the crystal grain size after the final annealing was large for the γ-treated material (in the figure, for material 4, the γ-treated (average cooling rate 5
FIG. 1 shows the temperature at 00 ° C./sec., And FIG. 2 shows the γ treatment (0.07 ° C./sec.). ).

As described above, by using the method of the present invention, it is possible to manufacture a non-oriented electrical steel sheet having excellent magnetic flux density and iron loss.

[0030]

According to the present invention, it is possible to stably produce a non-oriented electrical steel sheet having a low iron loss and a high magnetic flux density, which is very effective in terms of energy saving and miniaturization of electric equipment. .

[Brief description of drawings]

FIG. 1 is a photograph showing a crystal structure of a final product of a comparative material (average cooling rate: 500 ° C./second ).

FIG. 2 is a photograph showing a crystal structure of a final product of the material of the present invention (average cooling rate: 0.07 ° C./sec ).

Claims (1)

[Claims] 1. A cooling body for moving and renewing molten steel consisting of Si ≦ 2.5%, Al ≦ 1.0% and (Si + 2Al) ≦ 2.5% by weight, the balance: Fe and inevitable impurities. coagulate the surface as a cast strip, then, after a predetermined thickness by the skilled cast strip was cold-rolled, in the manufacturing method of the non-oriented electrical steel sheet to finish annealing, cooling body moving update molten steel When solidified by the surface to form a cast ribbon, the cooling rate of the cast ribbon during the γ → α transformation (average cooling rate in the range from A _r3 point to A _r1 point) should be 50 ° C / sec or less. A method for producing a non-oriented electrical steel sheet having extremely excellent magnetic characteristics.