JPH0811810B2 - 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
A silicon steel slab consisting of (Si + 2Al) ≦ 2.5%, balance: Fe and unavoidable impurities is hot-rolled into a hot-rolled sheet to a final sheet thickness in one cold rolling step, and then finish annealing. In the method for producing a non-oriented electrical steel sheet, the strip winding temperature in the hot rolling step is set to a temperature range of A _r3 point or higher, and then the average cooling rate from A _r3 point to A _r1 point is 50 ° C / sec or less. Is a method for producing a non-oriented electrical steel sheet having extremely excellent magnetic properties, characterized by cooling a strip coil and transforming it into an α phase.

Hereinafter, the present invention will be described in detail. As a result of intensive studies to solve the technical problem in the present invention, the inventors appropriately adopt the so-called self-annealing condition and cooling condition during hot rolling in a non-oriented electrical steel having a transformation. As a result, we have succeeded in obtaining a non-oriented electrical steel sheet that controls the texture in the product after finish annealing and has extremely high magnetic flux density and good iron loss (low iron loss value).

That is, by defining the hot rolling conditions (high temperature finishing, high temperature winding and subsequent slow cooling),
The texture of the product after finish annealing is controlled to produce a non-oriented electrical steel sheet having extremely high magnetic flux density and good iron loss (low iron loss value). High-temperature finishing and high-temperature winding itself in the non-oriented electrical steel sheet manufacturing process are called self-annealing, and are disclosed in, for example, JP-A-54-7.
It is known as disclosed in Japanese Patent No. 6422.

As a result of intensive studies conducted by the inventors to obtain a non-oriented electrical steel sheet having a low iron loss value and a high magnetic flux density, a hot rolling process for the non-oriented electrical steel sheet having α to γ transformation is carried out. In the above, the winding temperature is set sufficiently high at A _r3 point or higher and the cooling rate is decreased to control the texture in the product after finish annealing, and the magnetic flux density is extremely high and the iron loss is good (the iron loss value is It has been found that (low) non-oriented electrical steel sheets can be produced.

First, the component system will be explained. In order to improve 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.

[0012] In the present invention, the strip winding temperature in the hot rolling step and a high temperature range of not lower than A _r3 point A _r3
Since the range from the point to A _r1 point is cooled (γ treatment) at an average cooling rate of 50 ° C./sec or less, the carbide is sufficiently precipitated and agglomerated, and therefore the magnetic aging phenomenon is 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 inevitably 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, by controlling the hot rolling conditions of a non-oriented electrical steel sheet having a phase transformation (hereinafter, abbreviated as transformation steel), it is possible to individually heat the rolled steel sheet with or without hot-rolled sheet annealing after hot rolling. The grain size of the rolled sheet was controlled. However, it has not been considered until now to take up the γ → α transformation at high temperature after hot rolling finish.

The reason is that the material is cooled and transformed (γ → α).
This is because the orientation of the crystal grains becomes random and the crystal grain size of the hot-rolled sheet becomes small, which is considered to be unsuitable for improving the magnetic properties of the product.

However, as a result of earnest studies by the inventors, the reason for this is not always clear by winding the strip at a high temperature in the hot rolling process and controlling the cooling rate of the material when passing through the transformation. Found that the texture in the product was improved.

According to the present invention, the magnetic flux density is low even if the iron loss of the product is improved even if the finish annealing is performed at a higher temperature than the conventional annealing condition for a longer period of time to grow the grains and grow the grains. It never happens.

In the present invention, since the cooling rate in the self-annealing after winding in the hot rolling step is low, the impurities having a small solubility in the α phase are sufficiently precipitated, and therefore the crystals during the finish annealing. Grain growth is not hindered (detoxification of impurities), and it is possible to obtain a product with low iron loss and high magnetic flux density even when treated under conventional finish annealing conditions.

The γ processing of the present invention will be described in more detail. The high temperature winding and slow cooling treatments in the present invention are carried out in the hot rolling process, so that the transformation point (A _r3 point)
However, if the material has a high transformation point (A _r3 point), by installing a winding machine (reel) immediately after the final stand of the hot rolling mill train, A _r3 point or more can be obtained. Can be wound in the temperature range of. However, in order to reduce the average cooling rate of the material (strip coil) to 50 ° C./sec or less, it may be necessary to attach a heat insulating cover to the strip coil after winding or provide a mild heating means. is there.

At this time, in order to improve the pickling property of the material in the subsequent pickling step, the inside of the heat insulating cover is filled with an inert gas atmosphere such as N ₂ . The holding temperature of the material is γ
The temperature is a phase (A _r3 point or higher), but this temperature varies depending on the steel composition. In actual operation, A _r3 points +50
90 seconds or more at 90 ° C. is sufficient. Regarding the cooling rate, it is sufficient to cool the material in the range of A _r3 point to A _r1 point at an average cooling rate of 50 ° C./sec or less .

[0026]

【Example】

[0027]

[Table 1]

A slab of the above components (a silicon slab consisting of the balance Fe and unavoidable impurities) is heated by a usual method,
The thickness is 2.5 mm, the hot rolling is completed at 1050 to 950 ° C, and the film is wound at 1000 to 900 ° C for convenience.
Average cooling rate between 850 ° C is 500 ° C / sec (quenched in normal temperature water), 50 ° C / sec (forced air cooling), 10 ° C / sec (air cooling), 1 ° C / sec (uses heat insulating cover), 0.07.
It cooled at each cooling rate of ° C / sec (weakly heated in the heat insulation cover). 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, without a comparison method a) hot-rolled sheet annealing, b) self-annealing of 2 hours retention after hot rolling 800 ° C. winding (JP 54-76422) material, c) a) material 925
Table 2 compares the material with the continuous hot-rolled sheet annealed at 150 ° C for 150 seconds.
Shown in

[0029]

[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 large number of materials had a large grain size after high temperature self-annealing after the final annealing (for the material 4, after high temperature self-annealing (average cooling rate 500 ° C./sec. ) Is shown in FIG. 1, and γ treatment (0.07 ° C./sec) is shown in FIG. 2).

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.

[0033]

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 silicon steel slab consisting of Si ≦ 2.5%, Al ≦ 1.0% and (Si + 2Al) ≦ 2.5% by weight, the balance: Fe and inevitable impurities, is hot-rolled. In the manufacturing method of the non-oriented electrical steel sheet in which the final sheet thickness is obtained by one cold rolling step and then finish annealing is performed, the strip winding temperature in the hot rolling step is A _r3 point or more. The non-directional electromagnetic field with excellent magnetic characteristics, characterized in that the strip coil is cooled and transformed into the α phase at an average cooling rate from A _r3 point to A _r1 point of 50 ° C./sec or less. Steel plate manufacturing method.