JPH10251752A - Production of hot rolled silicon steel plate excellent in magnetic property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon steel sheet excellent in magnetic properties in an as-hot-rolled state while obviating the necessity of particular finish annealing treatment, by applying sufficient strain by hot rolling and improving a texture. SOLUTION: A steel slab, having a composition consisting of, by weight, <=0.005% C, 0.1-1.85% Si, <=1.0% Al, <=1.5% Mn, and the balance Fe with inevitable impurities, is heated and held to and at a temp. in the γ-single phase region or (α+γ) two phases region and hot rough-rolled. Successive hot finish rolling is performed under the condition of 30-80% draft at the final stand, and the resultant plate is coiled at >=600 deg.C and subjected to recrystallization self-annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a non-oriented hot-rolled electrical steel sheet having excellent magnetic properties, and more particularly, to simplifying the manufacturing process and improving the magnetic properties by modifying the hot rolling step. The goal is to improve it.

[0002]

2. Description of the Related Art Generally, a non-oriented electrical steel sheet is obtained by hot rolling a silicon steel slab, subjecting it to a hot rolled sheet annealing if necessary, then pickling it, and then cold rolling it once or twice. After rolling, finish annealing is performed, and an insulating film is formed.
Products. About such non-oriented electrical steel sheet,
It is not unprecedented to have a technology to make a product only by hot rolling, but the conventional technology is to make the final sheet thickness by reverse lap rolling,
After pickling, it is subjected to finish annealing, which not only has poor manufacturability, but also has extremely low magnetic properties, especially magnetic flux density.
Currently not implemented.

[0003]

As described above, a cold-rolled electrical steel sheet obtained by performing cold rolling after hot rolling has excellent magnetic properties, but the production process is complicated and the production cost tends to increase. . Further, the hot-rolled magnetic steel sheet has problems that the productivity is poor and the magnetic flux density is extremely low. In the production of conventional hot-rolled magnetic steel sheets, hot rolling is performed merely to reduce the sheet thickness, and has not been studied from the viewpoint of forming a texture suitable for magnetic steel sheets. In addition, there is a limit in the capacity of the hot rolling mill, and the conventional hot rolling cannot provide a sufficient strain as a driving force for recrystallization.

[0004] The present invention advantageously solves the above-mentioned problems. By imparting a sufficient strain by hot rolling to improve the texture, the magnetic properties can be improved without special finish annealing. It is an object of the present invention to propose an advantageous method for producing a hot-rolled electrical steel sheet that can obtain a good product of the above.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and have obtained the following findings. 1. Coarse slab cast ferrite microstructure remaining during hot rolling cannot be obtained only by hot rolling if sufficient recrystallization driving force is not obtained in hot rolling and recrystallization is not performed without special annealing treatment at high temperature. Then it becomes unrecrystallized extended grains,
Deteriorate magnetic properties. In order to solve this, it is effective to perform slab heating before rough rolling in a γ single phase region or (α + γ) two phase region.

[0006] 2. Even if the slab heating temperature is the above-mentioned appropriate condition, the ferrite rolled structure may remain at the center of the thickness of the sheet, but the cause is that after the rough rolling and before the finish rolling, the crystal was recrystallized by γ → α transformation. Ferrite grains are not given sufficient recrystallization driving force at the later stage of finishing,
This is due to the fact that it does not recrystallize after finishing hot rolling and remains as a rolled structure. In order to solve this problem, it is effective to make the latter stage of the finishing hot rolling strongly reduced.
Sufficient hot rolling strain can be given to the ferrite grains recrystallized by the γ → α transformation after the rough rolling and before the finish rolling, and the coil can be recrystallized by self-annealing after coiling after the hot rolling.

[0007] 3. In addition, the texture of the steel sheet hot-rolled by the above method is a structure advantageous for a non-oriented electrical steel sheet. The present invention is based on the above findings.

That is, the present invention relates to the following: C: 0.005 wt% or less, Si: 0.1 to 1.85 wt%, Al: 1.0 wt% or less, Mn: 1.5
wt% or less, the balance being the composition of Fe and unavoidable impurities, the steel slab is heated and held in the γ single phase region or (α + γ) two phase region, and after hot rough rolling, subsequent hot finishing rolling is performed. The reduction rate of the final stand: 30% or more and 80% or less, then the coil is wound at a temperature of 600 ° C or more and self-annealed for recrystallization.
This is a method (first invention) for producing a hot-rolled electrical steel sheet having excellent magnetic properties of 1.2 mm or less.

Further, the present invention provides a method for producing a steel sheet comprising: C: 0.005 wt% or less;
Si: 0.1-1.85 wt%, Al: 1.0 wt% or less, Mn: 1.5 wt%
A steel slab having the composition of Fe and unavoidable impurities is heated and held in a γ single-phase region or a (α + γ) two-phase region including the following, and after hot rough rolling, subsequent hot finishing rolling is performed. Implement under the condition that the total reduction rate of three passes is 50% or more and 90% or less and the reduction rate of the final stand is 10% or more, and then wind the coil at a temperature of 600 ° C or more and self-anneal recrystallization. A method for producing a hot-rolled electrical steel sheet having excellent magnetic properties with a sheet thickness of 1.2 mm or less (a second invention).

According to the first or second aspect of the present invention, in the recrystallization self-annealing after hot finish rolling, 500 to 900
It is preferable to perform a heat retaining treatment for 10 hours or less in a temperature range of ° C. (third invention).

According to the present invention, if hot rolling, particularly hot finishing rolling conditions, is controlled, sufficient strain is introduced into the steel sheet to effectively improve the rolling structure, and thereafter, no special finish annealing treatment is required. However, the intended purpose is advantageously achieved by self-annealing after coil winding.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. First, in the present invention, the reason why the component composition of the material is limited to the above range will be described. C: 0.005 wt% or less C is a harmful component from the viewpoint of magnetic properties.
%, Magnetic aging occurs and magnetic properties deteriorate, so the C content was limited to 0.005 wt% or less.

Si: 0.1-1.85 wt% Si is a useful component for reducing iron loss by increasing the specific resistance, and at least 0.1 wt% is required to sufficiently exert this effect. , 1.85 wt%, the steel becomes an α-single phase steel, and heating in a γ single phase region or (α + γ) two phase region, which is a main item in the present invention, becomes impossible. The content is 0.1-1.
Limited to the range of 85 wt%.

Al: 1.0 wt% or less Al not only contributes to deoxidation of steel and reduction of Al inclusions,
Like Si, it is an effective component for increasing the specific resistance and improving iron loss. However, like Si, it is a ferrite homer and also increases the cost, so the upper limit was set to 1.0 wt%.

Mn: 1.5 wt% or less Mn is a component useful for enhancing magnetic properties. However, if the content is more than 1.5 wt%, the cost is increased.
The upper limit was 1.5 wt%. Other harmful impurity elements
It is desirable to reduce as much as possible, especially S, N and O etc.
It is desirable to reduce it to 0.005 wt% or less.

The molten steel adjusted to the above-mentioned preferable composition range is preferably made into a slab by continuous casting, and then subjected to a heat treatment prior to hot rolling. This heat treatment is performed to eliminate coarse slab cast ferrite grains before hot rolling. Therefore, the slab heating temperature is equal to or higher than the temperature at which the γ phase emerges, that is, the γ single phase region or (α +
γ) It is necessary to have a two-phase region.

Next, after rough rolling, finish rolling is performed.
In order to sufficiently recrystallize and improve magnetic properties after this finishing hot rolling, the rolling reduction rate of the final rolling final stand must be 30.
% To 80% or less, or the total rolling reduction of the subsequent three passes must be 50% or more and 90% or less and the rolling reduction of the final stand must be 10% or more. Because, in the present invention, it is important to impart a sufficient amount of strain energy to the steel sheet in the latter stage of the hot finish rolling, and the rolling reduction of the final stand is less than 30%, or If the rolling reduction is 10% or more and less than 30%, the total rolling reduction of the latter three passes is less than 50%, or even if the total rolling reduction of the latter three passes is 50% or more, the rolling reduction of the final stand is If it is less than 10%, sufficient strain energy required for recrystallization is not provided, and improvement in magnetic properties cannot be expected. In addition, the upper limit of each rolling reduction was prescribed as described above in terms of the sheet passing property of the steel sheet and the manufacturing cost.

Then, after the above-mentioned finish rolling, the coil is subjected to winding recrystallization self-annealing. If the winding temperature is lower than 600 ° C., the coil is not sufficiently recrystallized, and improvement in magnetic properties cannot be expected. Therefore, the winding temperature was set to 600 ° C or higher. In the heat retaining treatment during self-annealing after finish rolling, if the temperature is less than 500 ° C, it is difficult to sufficiently recrystallize.
If the temperature is higher than 00 ° C. and longer than 10 hours, the manufacturing cost increases.
It is desirable to keep the heat treatment for 10 hours or less in the temperature range of 500 to 900 ° C.

Further, in the present invention, the reason why the plate thickness is limited to 1.2 mm or less is that if the thickness is further increased, eddy current loss increases and iron loss deteriorates.

[0020]

【Example】

Example 1 A steel slab having the composition shown in Table 1 was heated to 1100 ° C., subjected to hot rough rolling, and finished to a sheet thickness of 0.8 mm with a reduction ratio of a final stand of hot finish rolling of 32%, and then. 650 ° C
At a temperature of 5 ° C. for self-recrystallization annealing. As a conventional example, a slab of the same composition is heated to 1100 ° C., hot-rolled to form a hot-rolled sheet having a thickness of 2.0 mm, and then finished by one cold-rolling to a thickness of 0.8 mm. And finish annealing. Table 2 shows the results of an investigation on the magnetic properties of the non-oriented electrical steel sheet thus obtained.

[0021]

[Table 1]

[0022]

[Table 2]

As is clear from Table 2, the hot-rolled magnetic steel sheet according to the present invention is different from the conventional cold-rolled magnetic steel sheet.
It had the same or better magnetic properties.

Example 2 The components other than Si were as follows: C: 0.003 wt%, Al: 0.21 wt%
%, Mn: 0.25 wt%, S: 0.003 wt%, N: 0.004 wt%,
O: adjusted to 0.005 wt%, and the amount of Si from 0.1 wt% to 2.5 wt%
The various slabs changed to 1120 ° C., and after hot rough rolling, were finished to a thickness of 0.8 mm under the conditions of a final three-pass reduction ratio of 58% and a final stand reduction ratio of 16%. Later, 70
It was wound around a coil at a temperature of 0 ° C. and self-annealed. FIG. 1 shows the result of examining the magnetic properties of the obtained steel sheet.
As is clear from the figure, good magnetic properties are obtained when Si is in the range of 0.1 to 1.85 wt%.

Example 3 A steel slab having the composition shown in Table 3 was heated at the temperature shown in Table 4, subjected to hot rough rolling, and then subjected to finish rolling under the conditions shown in Table 4 to a sheet thickness of 0.8 mm. After finishing, it was wound on a coil. Table 4 shows the magnetic properties of the obtained steel sheets.

[0026]

[Table 3]

[0027]

[Table 4]

As is clear from Table 4, all of the conforming examples manufactured under the conditions according to the present invention have better magnetic properties than the comparative examples. In this regard, Nos. 2, 7, and 13 whose coil winding temperature was out of the proper range of the present invention, and Nos. 3 and 8 whose hot rolling reduction was out of the proper range of the present invention each had deteriorated magnetic properties. doing. Nos. 14 and 15 in which the component composition was out of the appropriate range were examples in which slab heating could not be performed in the γ single phase region or (α + γ) two phase region, and although the iron loss was good, the magnetic flux density was good. Is significantly inferior. Further, the components, the hot rolling reduction, and the coil winding temperature are all within the scope of the present invention, but the heating temperature was in the α single phase region No. 10
Shows that the magnetic properties are also deteriorated.

Example 4 C: 0.003 wt%, Si: 1.15 wt%, Al: 0.27 wt%, Mn: 0.
23 wt%, S: 0.002 wt%, N: 0.002 wt%, O: 0.0018
A steel slab (Ac: ₁ point: 996 ° C) containing wt% and the balance being substantially Fe is heated to 1130 ° C, and after hot rough rolling, hot finish rolling is performed in the final three passes. The rate was 53%, and the final step reduction rate was 13%. The sheet was finished to a thickness of 0.8 mm, wound around a coil at the temperature shown in Table 5, and then kept warm under various conditions. Table 5 also shows the results of the magnetic measurement of the obtained product plate.

[0030]

[Table 5]

As is clear from Table 5, all of the conforming examples according to the present invention have superior magnetic properties as compared with the comparative examples, and especially those subjected to suitable heat insulation have further improved magnetic properties. In addition, the yield can be improved without deterioration of the magnetic properties of the outer peripheral portion of the coil. Here, the outer peripheral portion of the coil means the outermost one or two layers wound up in a coil shape. Usually, the temperature drops immediately after winding the coil, and recrystallization due to coil winding self-annealing may become defective. This is the part that has the potential.

[0032]

As described above, according to the present invention, it is possible to obtain an electrical steel sheet having particularly excellent magnetic properties as it is during hot rolling without performing special finish annealing after hot rolling. By greatly reducing the number of steps, a large reduction in manufacturing cost and energy saving can be achieved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between Si content and magnetic properties.

Claims (3)

[Claims] 1. A steel slab containing C: 0.005% by weight or less, Si: 0.1 to 1.85% by weight, Al: 1.0% by weight or less, Mn: 1.5% by weight or less, with the balance being Fe and unavoidable impurities. , Γ single phase range or (α + γ)
After heating and holding in the two-phase region and performing hot rough rolling, the subsequent hot finish rolling is performed. The rolling reduction of the final stand: 30% or more and 80%
It is carried out under the following conditions, and then is wound around a coil at a temperature of 600 ° C. or more and self-annealed for recrystallization,
A method for producing hot-rolled electrical steel sheets with excellent magnetic properties with a thickness of 1.2 mm or less. 2. A steel slab containing C: 0.005% by weight or less, Si: 0.1 to 1.85% by weight, Al: 1.0% by weight or less, Mn: 1.5% by weight or less, with the balance being Fe and unavoidable impurities. , Γ single phase range or (α + γ)
After heating and holding in the two-phase region, hot rough rolling, and subsequent hot finishing rolling, the final three-pass total reduction rate is 50% or more and 90% or less, and the final stand reduction rate is 10% or more. Characterized in that it is wound around a coil at a temperature of 600 ° C or higher and self-annealed for recrystallization.
A method for manufacturing hot-rolled electrical steel sheets with excellent magnetic properties of 1.2 mm or less. 3. The recrystallization self-annealing after hot finish rolling, wherein a heat retention treatment is performed in a temperature range of 500 to 900 ° C. for 10 hours or less. A method for producing hot-rolled electrical steel sheets with excellent magnetic properties of less than mm.