JPH0623410B2 - Method for manufacturing non-oriented electric iron plate with high magnetic flux density - Google Patents

Description

The present invention relates to a method for manufacturing a non-oriented electric iron sheet, and more particularly to a method for manufacturing a non-oriented electric iron sheet with low iron loss and high magnetic flux density.

Non-directional electric iron plates are used as iron cores in rotating machines such as motors and stationary units such as small transformers and ballasts. Recently, in order to improve the efficiency and reduce the size and weight of these devices, There has been a demand for a non-oriented electric iron plate with low iron loss and high magnetic flux density.

Generally, a non-oriented electrical iron sheet is produced by hot rolling a steel slab having a predetermined chemical composition, pickling, cold rolling, refining, and subjecting it to the required surface treatment. It is already well known that in order to reduce the grain size, it is necessary to increase the crystal grain size in the final refining step. As described above, in order to increase the grain size in the final annealing step, conventionally, as a first method, hot rolling is finished in the ferrite-austenite region and then rolled at a high temperature, and as a second method, hot rolling is performed. A method of annealing a plate and a third method of applying a slight strain to a hot rolled sheet at room temperature and then annealing the hot rolled sheet have been proposed. However, according to the first method, since the crystal grain size is still small, the magnetic characteristics are not sufficient, and the second and third
According to the method (1), since annealing is performed after hot rolling, the number of steps is increased and the manufacturing cost is inevitably high.

The present inventors have conducted extensive studies to solve the above-mentioned problems in the production of non-oriented electrical iron sheets, for steel slabs having a predetermined chemical composition, while controlling the hot rolling conditions and winding temperature, After hot rolling, a predetermined amount of plastic strain is applied to the hot rolled plate during winding, and a coarse crystal grain size is obtained by a method different from the conventional method of performing cold rolling and annealing after winding, thus, The present invention has been accomplished by finding that it is possible to obtain a non-oriented electric iron plate having a low iron loss and a high magnetic flux density.

The manufacturing method of the non-oriented electrical iron sheet according to the present invention is as follows: C 0.03% or less by weight%, total amount of Si or Si and Al 2.0% or less, Mn 1.0% or less, P 0.1% Hereinafter, when hot-rolling a copper piece composed of the balance iron and unavoidable impurities, after hot-rolling at a temperature higher than the Ar ₃ transformation temperature and before winding, the temperature of the Ar ₁ transformation temperature is not higher than 3 ~
It is characterized by introducing a plastic strain of 30%, winding at a temperature of 700 ° C. or higher, then cold rolling, and then refining.

First, the chemical composition of the steel material used in the method according to the present invention will be described.

C is an element that greatly affects the magnetic properties, and when the steel material contains a large amount of it, the magnetic properties such as iron loss and magnetic flux density are greatly deteriorated, so the content is 0.
It should be 03% or less. Particularly preferably, the C content is 0.015% or less in order to further improve the magnetic properties.

Si is an important element for increasing the specific resistance of steel and obtaining a low iron loss, and Al is an element which has the same effect as Si and at the same time has the effect of improving the crystal grain growth. However, both Si and Al have the property of raising the ferrite-austenite transformation temperature, and when the total amount of Si or Si and Al exceeds 2.0%, the austenite region does not exist, so in the present invention. To finish hot rolling in the austenite region, Si or S
The total amount of i and Al is 2.0% or less. Note that Si is preferably added in an amount of 0.2% or more in order to reduce the eddy current loss of the obtained electric iron plate.

Mn is contained to suppress hot embrittlement, but 1.
If it exceeds 0%, the magnetic properties are adversely affected, and in the case of the ultra low C steel by the method according to the present invention, the steelmaking work becomes difficult. Therefore, the Mn content is 1.0% or less.
The lower limit is preferably 0.1% in terms of workability in steelmaking.

P is an element that improves punchability by increasing steel hardness, and is preferably added in an amount of 0.015% or more. However, when it is contained in excess, it causes cracking during welding after core material lamination. Therefore, the upper limit of the P content is 0.1
%.

Next, the method of the present invention will be described.

The method for producing a non-oriented electrical iron sheet according to the present invention uses a steel piece having the above-described chemical composition as a material, and when hot rolling this, finish the hot rolling at a temperature of Ar ₃ transformation temperature or higher, 3 to 30 below the Ar ₁ transformation temperature before winding
% Plastic strain, and winding at a temperature of 700 ° C. or higher, thus coarsening the crystal grains of the hot-rolled sheet, thereby providing magnetic properties superior to conventional ones, in particular, non-direction having a high magnetic flux density. This is to obtain a sex electric iron plate.

That is, in the method of the present invention, in order to obtain a fine ferrite fine grain structure in the intermediate stage of hot rolling, it is necessary to finish the hot rolling at a temperature of Ar ₃ transformation temperature or higher, and thus, the structure is fine grain fine grain. A so-called strain grain growth is completed by introducing a plastic strain into the hot-rolled sheet which is a structure in a hot state and using this strain as a driving force by the self-annealing effect at the time of high-temperature winding. In detail, after completing the hot rolling in the austenite region, by completing the austenite-ferrite transformation,
In addition to obtaining a uniform and fine transformed ferrite structure, plastic strain is introduced immediately after this, and strain grain growth is completed by performing high temperature winding, so the magnetic properties of the final product differ from the conventional method. It is possible to obtain coarse grains that form an advantageous texture.

The amount of strain introduced into the hot rolled sheet after completion of hot rolling is 3 to 30%.
Is the range. If the strain amount is less than 3%, it is difficult to coarsen the crystal grains after high-temperature winding, while if it exceeds 30%,
This is because the crystal grains obtained are rather fine. In particular,
From the viewpoint of magnetic properties, it is preferably 5 to 15%.

To introduce the above plastic strain, any method such as rolling method, leveler method, and tensile tension method can be adopted and is not particularly limited.

After introducing the compositional strain to the hot-rolled sheet in this manner, the self-annealing effect is sufficiently exerted during winding, and in order to complete the strained grain growth, the winding temperature is preferably as high as possible. In the invention, this is 700 ° C. or higher. This is because if the winding temperature is lower than 700 ° C., the coarsening of crystal grains is insufficient.

Cold rolling and annealing after high-temperature winding as described above can be performed by a conventional ordinary method, and for cold rolling,
It may be done only once, or two cold-rolls with intermediate annealing in between.
It may be repeated. If necessary, steps such as continuous forging, direct feed rolling, and low temperature heating of the slab can be adopted. The final annealing may be either box annealing or continuous annealing, but rapid heating by continuous annealing is preferable to obtain a high magnetic flux density.

As described above, according to the method of the present invention, for a steel slab having a predetermined chemical composition, the hot rolling conditions and the winding temperature are regulated, and after hot rolling, the hot rolled sheet is hot-rolled. A certain amount of plastic strain is applied to the alloy to complete the strained grain growth by the self-annealing effect, so that a coarse grained grain and an advantageous texture for the magnetic property are obtained, and the non-directional electrical property excellent for the magnetic property is obtained. You can get an iron plate.

Example 1 A steel slab having the chemical composition of 0.01% C, 0.25% Si, 0.25% Mn, 0.025% P and 0.002% Al was prepared in the austenite region as shown in the table. After finishing hot rolling, 3 in the ferrite area
Rolled to a hot rolled sheet of 2.0 mm with a rolling reduction of -60% and 740
It was wound up at ℃. Also, for comparison, after hot rolling,
It was wound at 740 ° C. without rolling in the ferrite region to obtain a hot rolled sheet having a sheet thickness of 2.0 mm. FIG. 1 shows the relationship between the grain size of these hot-rolled sheets and the reduction ratio.

As is clear from FIG. 1, when the reduction ratio in the ferrite region is less than 3%, the coarsening of the crystal grains is not completed,
It has a mixed grain structure. However, according to the present invention, when the rolling reduction in the ferrite region is in the range of 3 to 30%, coarse coarse particles are obtained, and particularly when the rolling reduction is in the range of 3 to 15%, an extremely coarse grain is obtained. Grains are obtained.

Example 2 A steel slab having the same chemical composition as in Example 1 was treated under the conditions shown in the table to obtain a material before cold rolling having a plate thickness of 2.0 mm.

Comparative method a is a hot rolled sheet finished in the austenite region, and comparative method b is a hot rolled sheet finished in the austenite / ferrite region. Comparative method c is 7% cold rolling at room temperature and then 2 ° C. at 750 ° C. in order to perform strain grain growth treatment according to a conventionally known method after hot rolling is completed. It was annealed for a period of time to obtain a material before cold rolling. On the other hand, in the method d of the present invention, after the hot rolling was completed, 10% rolling was performed in the ferrite region and wound at 740 ° C. to obtain a material before cold rolling. The structures of these materials before cold rolling are shown in FIG. 2 under an optical microscope (100 times).

Each pre-cold-rolling material thus obtained was pickled, cold-rolled to a plate thickness of 0.5 mm, and annealed at a temperature of 850 ° C. for 1.5 minutes to obtain a non-oriented electric iron plate. These magnetic properties are shown in the table. According to the comparative methods a and b, the obtained non-oriented electric iron plate has a large iron loss and a small magnetic flux density. The inferior magnetic properties of the non-oriented electrical iron sheets produced by the comparative methods a and b correspond to the small crystal grain size in the microstructure before cold rolling, as shown in FIG. .

According to the comparative method c in which the conventional strained grain growth process is performed, as shown in FIG. 1, an electric iron plate having relatively good magnetic properties is associated with the large grain size before cold rolling. Although obtained, according to the method d of the present invention, the crystal grain size before cold rolling is remarkably coarsened, and a non-oriented electric iron plate having further improved magnetic properties can be obtained. This seems to be the way to use the coarse crystal grain structure due to the strain introduced hot after the end of hot rolling more favorably for the magnetic properties than the structure due to the strain grain growth treatment.

Example 3 A steel slab having a chemical composition of 0.01% C, 1.5% Si, 0.20% Mn, 0.01% P and 0.001% Al was prepared under the conditions shown in the table and the plate thickness was 2.
A 0 mm hot rolled sheet was pickled, cold rolled to a sheet thickness of 0.5 mm, and then annealed at a temperature of 850 ° C. for 1.5 minutes to obtain a non-oriented electric iron sheet. these The magnetic properties of are shown in the table.

The hot-rolled sheet according to the comparative method e had an austenite finish, and the hot-rolled sheet according to the comparative method f had a ferrite-austenite finish. The coiling temperature was 800 ° C in both cases. The hot-rolled sheet according to the method g of the present invention is obtained by rolling at a reduction rate of 10% in the ferrite region after completion of hot rolling and winding at 800 ° C.

It is clear that the non-oriented electric iron plate produced by the method of the present invention has excellent core loss and magnetic flux density.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the rolling reduction of plastic strain in the ferrite region after the hot rolling and the grain size number, and FIG. 2 is a micrograph showing the structure before cold rolling in Example 2 (100
(A), (b) and (c) show the comparative method, and (d) shows the method of the present invention.

Claims (1)

[Claims] 1. A weight percentage of C 0.03% or less, a total amount of Si or Si and Al 2.0% or less, Mn 1.0% or less, P 0.1% or less, balance iron and unavoidable impurities. When hot rolling a steel slab consisting of _{3 to 3 at a} temperature not higher than the Ar ₁ transformation temperature after the hot rolling is finished at a temperature exceeding the Ar ₃ transformation temperature and before winding.
A method for producing a non-oriented electrical iron sheet having a high magnetic flux density, which comprises introducing a plastic strain of 30%, winding at a temperature of 700 ° C. or higher, followed by cold rolling and then refining.