JP2515449B2 - 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: Fe and unavoidable. Steel slab consisting of mechanical impurities is hot-rolled into a hot-rolled sheet, and as it is or after being annealed, is cold-rolled once or twice or more with an intermediate anneal to obtain a final sheet thickness. In the method for manufacturing a non-oriented electrical steel sheet to be subjected to finish annealing, the material is heated to the γ region and transformed into the γ phase in the heat treatment before the final cold rolling, and then between A _r3 → A _r1 . This is a method for producing a non-oriented electrical steel sheet having extremely excellent magnetic properties, characterized by cooling the material at an average cooling rate of 50 ° C./second or less and retransforming it into an α phase.

Hereinafter, the present invention will be described in detail. The inventors, as a result of intensive studies to solve the technical problem in the present invention, in the non-oriented electrical steel sheet having transformation,
By controlling the heat treatment conditions just before the final cold rolling, the texture of the product after finish annealing is controlled, and the non-oriented electrical steel sheet with high magnetic flux density and good iron loss (low iron loss value) is produced. I got it successfully.

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, in the heat treatment in the preceding stage of the final cold rolling step, the material is heated to the γ range, and then the cooling rate is specified to retransform it into the α phase (γ processing). Outcoagulation 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 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 magnetized, a so-called pinning effect is formed to prevent the growth of recrystallized grains during the finish annealing and to prevent the movement of the domain wall when the product is magnetized, which is a factor that prevents the reduction of 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 process conditions of the present invention will be described. Conventionally, when a hot-rolled sheet of a non-oriented electrical steel having phase transformation (hereinafter abbreviated as transformation steel) is reheated and transformed, the orientation of crystal grains becomes random and the cooling transformation (γ →
Since the crystal grain size becomes small at α), it is not suitable for improving the magnetic properties of the product and was not considered.

However, as a result of intensive research conducted by the present inventors, it is possible to improve the texture of the final product by controlling the cooling rate during the transformation, although the reason is not always clear. Found. As a result, the magnetic flux density does not decrease during finish annealing even if the temperature is higher than in the conventional finish annealing and the time is lengthened to cause grain growth to improve the iron loss of the product.

In addition, since the cooling rate of the material is low in the γ treatment, the impurities having a small solubility in the α phase are sufficiently deposited, and the grain growth during finish annealing is not hindered (detoxification of impurities). It is possible to obtain a non-oriented electrical steel sheet having a low iron loss and a high magnetic flux density even when finish annealing is performed under the conditions of.

Next, the γ processing of the present invention will be described in detail. The γ treatment of the present invention may be performed in a continuous annealing furnace or a box annealing furnace. In any case, in the heat treatment before the final cold rolling, it is necessary to heat the material to the γ region and then cool the material at an average cooling rate of 50 ° C./sec or less to retransform it into the α phase. .

Therefore, when the hot rolled sheet is made to have the final thickness by one cold rolling step, in the hot rolled sheet annealing step,
After heating the material to the γ range, it is necessary to cool the material at an average cooling rate of 50 ° C./sec or less to retransform it into the α phase.

On the other hand, when the final thickness of the hot-rolled sheet is obtained by two or more cold rolling steps sandwiching the intermediate annealing, after the material is heated to the γ region in the intermediate annealing before the final cold rolling, The material may be cooled at an average cooling rate of 50 ° C./second or less and retransformed into the α phase, so that the hot rolled sheet annealing step is not essential.

The means itself for cooling the material at an average cooling rate of 50 ° C./sec or less using a continuous annealing furnace is disclosed in, for example, Japanese Patent Laid-Open No. 57-198214.
A two-step soaking annealing method can be applied in the manufacturing process of the unidirectional electrical steel sheet. The soaking condition in the γ treatment of the present invention is to bring the material into the γ phase at a temperature (A _c3 point or higher), which varies depending on the steel composition. As for the annealing (heat treatment) condition in actual operation, it is sufficient to maintain the temperature range of A _c3 point + 50 ° C. or higher for 90 seconds. Further, it is sufficient to cool the material from the γ region to the α region at an average of 50 ° C./sec or less from the _{Ar 3} point to the _{Ar 1} point.

[0024]

【Example】

[0025]

[Table 1]

A slab (a silicon slab consisting of the balance Fe and inevitable impurities) having the components shown in Table 1 above was hot-rolled by a conventional method to a thickness of 2.5 mm, and the condition 1) was followed by continuous hot-rolled sheet annealing. Performed at 1100 ° C for 2 minutes, and conveniently 1000-8
The average cooling rate between 50 ° C. is 500 ° C./sec (quenching in normal temperature water), 50 ° C./sec (air cooling), 10 ° C./sec (two-stage soaking), 1 ° C./sec (two-stage soaking), Was cooled at each cooling rate. Condition 2) After annealing at 1100 ° C. for 10 minutes by box annealing, it was cooled in a furnace after being cut off. In this case, the cooling rate is 0.07 ° C /
It was seconds. 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, magnetic properties (average of L + C , L: rolling direction, C: 90 ° direction of L)
Direction ) was measured. These values compare method is that a) hot-rolled sheet without annealing, b) so-called self-annealing of 2 hours retention after hot rolling 800 ° C. winding (JP 54-76422) material,
Table 2 shows the comparison of c) a) material with the material obtained by continuous hot-rolled sheet annealing at 925 ° C. for 150 seconds.

[0027]

[Table 2]

Photographs of the metal phase after the final annealing are shown in FIGS. 1 and 2. Despite the same heat and final annealing conditions,
The crystal grain size after the final annealing is large for the γ-processed material (in the figure, for the material 4, the γ-processed (average cooling rate 500
Fig. 1 shows γ treatment (0.07 ° C / sec) and Fig. 2
It was shown to. ).

As described above, by using the method of the present invention, it is possible to produce a non-oriented electrical steel 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)

(57) [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. As a hot rolled sheet, and as it is or after being annealed, is subjected to cold rolling once or twice or more with intervening intermediate annealing to obtain a final sheet thickness, and then subjected to finish annealing. In the heat treatment before the final cold rolling, the material is heated to the γ region and transformed into the γ phase, and then the material is cooled by setting the average cooling rate between _{Ar 3} → A _r1 to 50 ° C / sec or less. A process for producing a non-oriented electrical steel sheet having extremely excellent magnetic properties, which comprises retransforming into an α phase.