JPH10158738A - Manufacture of low grade nonoriented silicon steel sheet with high magnetic flux density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacture of a low grade nonoriented silicon steel sheet having high magnetic flux density, used for an iron core material for electrical equipment. SOLUTION: This low grade nonoriented silicon steel sheet with high magnetic flux density is produced by hot-rolling a slab having a composition consisting of, by weight, <=0.30% Si, <=0.30% Mn, >0.0050-0.10% C, <=0.010% N, <=0.050% S, <=0.10% Al, <=0.10% P, and the balance Fe with inevitable impurities and then forming the resultant hot rolled plate, with or without application of an insulating film, into a final product. At this time, at the time of finish hot rolling, rolling is carried out at 5-50% draft per pass at one or more successive passes from the final pass side and <=0.25 coefficient of friction between the steel plate and a rolling roll.

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 low-grade non-oriented electrical steel sheet having a high magnetic flux density and used as an iron core material for electric equipment.

[0002]

2. Description of the Related Art In recent years, in the field of electric machines, particularly rotating machines in which non-oriented electrical steel sheets are used, there has been a growing demand for miniaturization by increasing the magnetic flux density. Among the uses of such non-oriented electrical steel sheets, as in motors for power windows of automobiles, the operating time is short, and iron loss does not require very good characteristics. Something is stronger. In such applications,
It is possible to reduce the size of the rotating machine by increasing the torque at the time of startup and operation by increasing the magnetic flux density of the iron core. Further, non-oriented electrical steel sheets used in such applications are characterized by low costs.

In the prior art, in order to increase the magnetic flux density of a non-oriented electrical steel sheet, a method of improving the magnetic flux density by coarsening the crystal grain size before cold rolling has been performed. For this purpose,
Generally, it has been practiced to perform hot-rolled sheet annealing by continuous annealing or box annealing to increase the crystal grain size before cold rolling and improve the recrystallization texture to improve the magnetic flux density. However, in this method, the cost increase is remarkable due to the addition of the hot-rolled sheet annealing step, and at present, it is unacceptable to consumers used for the above-mentioned purposes.

As a technique for inexpensively coarsening the crystal structure of a non-oriented electrical steel sheet before cold rolling, a hot rolled sheet after finish hot rolling is wound at a high temperature of 700 ° C. to 1000 ° C. Japanese Patent Laid-Open No. 54-764 discloses a self-annealing method of annealing with heat.
No. 22 and Japanese Patent Publication No. 62-64444, the hot-rolling end temperature is set to a high temperature of 1000 ° C. or higher, and no water injection time is set. A method for achieving grain growth is disclosed.

Japanese Patent Application Laid-Open No. 58-37121 discloses a method for producing a low-grade non-oriented electrical steel sheet in which finish annealing after cold rolling is performed under tension at a temperature of 400 ° C. or more and a recrystallization temperature or less. I have.

However, even in these production methods, it is necessary to carry out a cold rolling step after the production of a hot rolled sheet, and thus the production cost is equivalent to the production cost of the conventional non-oriented electrical steel sheet production technology. The stringent demands for house cost reduction were not met.

[0007] In order to find a way to meet the demands of customers for such non-oriented electrical steel sheets, the present inventors have proposed a hot rolled sheet or a so-called hot final product which is subjected to a skin pass on the hot rolled sheet to be a final product. We focused on the development of and studied. Among non-oriented electrical steel sheets, so-called cold-rolled electrical steel sheets have better magnetic properties than hot-final products, and the fact is that they have been switched to cold-rolled electrical steel sheets in the market. However, the present inventors have conducted intensive studies for the purpose of improving the characteristics of a low-cost hot final magnetic steel sheet.

As a result, the inventors have found that a hot-final non-oriented electrical steel sheet having a high magnetic flux density can be stably manufactured by a method focusing on the following points, and have completed the invention. From the viewpoint of improving the magnetic flux density, at the time of finishing hot rolling, it is effective to secure a constant rolling reduction in at least one pass and to lower the friction coefficient between the steel sheet and the rolling roll in that pass, In order to stably perform hot rolling with such a low friction coefficient, the sheet bar after rough rolling is joined to a preceding sheet bar before finish hot rolling, and the sheet bar is continuously subjected to finish hot rolling. Etc. are the main contents.

[0009]

SUMMARY OF THE INVENTION The present invention meets the strong demand for low-cost, high-flux-density non-oriented electrical steel sheets by such customers, and provides a high-flux-density, low-grade, non-directional non-oriented electrical steel sheet capable of high torque and downsizing. It is intended to provide an inexpensive method for producing a conductive magnetic steel sheet.

[0010]

The gist of the present invention is as follows. (1) By weight%, Si ≦ 0.30%, Mn ≦ 0.30
%, 0.0050 <C ≦ 0.10%, N ≦ 0.010
%, S ≤ 0.050%, Al ≤ 0.10%, P ≤
Manufacture of non-oriented electrical steel sheet containing 0.10% with the balance being Fe and unavoidable impurities, hot-rolled to form a hot-rolled sheet, with or without insulation coating, and as a final product In the method, at the time of finishing hot rolling, in one or more passes continuous from the final pass side, the rolling reduction of one pass is 5% or more and 50% or less, and the friction coefficient between the steel sheet and the rolling roll is 0.25. A method for producing a low-grade non-oriented electrical steel sheet having a high magnetic flux density, characterized by performing the following rolling.

(2) As a lubricant used at the time of finishing hot rolling, 0.5 to 20% by volume of fat or oil is mixed into the cooling water of the hot-rolled roll, wherein the high magnetic flux density described in (1) is used. A method for manufacturing low-grade non-oriented electrical steel sheets.

(3) The sheet bar after the rough rolling is joined to a preceding sheet bar before the hot rolling for finishing, and the sheet bar is continuously subjected to the hot rolling for finishing (1) or (2). A method for producing a low-grade non-oriented electrical steel sheet having a high magnetic flux density.

(4) The steel sheet after finish hot rolling is subjected to pickling,
The method for producing a low-grade non-oriented electrical steel sheet having a high magnetic flux density according to (1), (2) or (3), wherein skin pass rolling is performed at a rolling rate of 2% or more and 20% or less.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. First, to explain the components, Si is added to increase the specific resistance of the steel sheet, reduce the eddy current loss, and improve the iron loss value. To provide, the Si content is 0.3
It must be 0% or less.

Al also has the effect of increasing the specific resistance of the steel sheet and reducing the eddy current loss similarly to Si, but in order to provide the low-grade non-oriented electrical steel sheet aimed at by the present invention at low cost, The Al content needs to be 0.10% or less.

Mn has the effect of increasing the specific resistance of the steel sheet and reducing the eddy current loss similarly to Al and Si. However, the present invention has an object to provide a low-grade non-oriented electrical steel sheet at low cost. For this purpose, the content of Mn is set to 0.30% or less.

However, the addition amount of Mn is extremely important from the viewpoint of securing the strength of the high temperature sheet bar joint before the hot rolling. This is because the value of Mn / S, which is the weight concentration ratio between Mn and S, is set to 2 in order to prevent hot embrittlement of the sheet bar joint due to the presence of the low-melting sulfide at the crystal grain boundaries.
This is because it is preferably 0 or more.

P is added to secure the hardness of the steel sheet and to improve the punching workability. If it exceeds 0.10%, the magnetic flux density decreases, so it is added in a range of 0.10% or less.

If the C content exceeds 0.10%, carbides precipitate in the steel sheet, which significantly increases iron loss and deteriorates workability. Therefore, it is necessary to control the content to 0.10% or less. Further, in order to manufacture an inexpensive low-grade non-oriented electrical steel sheet aimed at by the present invention, it is sufficient that C> 0.0050%. When the content of C is set to 0.0050% or less, the cost of steel making increases remarkably and the product price increases, which is not preferable.

S and N partially re-dissolve during the slab heating in the hot rolling step, and sulfides such as MnS and A
A nitride such as 1N is formed. Since the presence of these elements hinders the grain growth of the hot-rolled structure and deteriorates the workability, it is necessary that S be 0.050% or less and N be 0.010% or less.

Next, the process conditions of the present invention will be described. The steel slab composed of the above components is produced by melting in a converter and being manufactured by continuous casting or ingot-bulking rolling. The steel slab is heated by a known method. This slab is subjected to hot rolling to a predetermined thickness.

The following experiment was conducted in order to investigate the influence of the average friction coefficient between the hot-rolled roll and the steel sheet during the finish hot-rolling on the magnetic properties of the product. Steel having the components shown in Table 1 was melted and subjected to finish hot rolling.

[0023]

[Table 1]

During the finishing hot rolling, the coefficient of friction at the final stand was changed by changing the oil content of the roll cooling water. The coefficient of friction was calculated from the measured advanced rate. The finishing hot rolling end temperature was fixed at 865 ° C., the rolling reduction of the final stand was 20%, the thickness was finished to 0.80 mm, and the Epstein sample was cut off by pickling to measure the magnetic properties.

FIG. 1 shows the relationship between the coefficient of friction and the product magnetic flux density in the final stand of the finish hot rolling. The coefficient of friction is 0.
It is understood that the magnetic flux density increases when the ratio is 25 or less. As can be seen from the above experiment, when the friction coefficient between the roll of finish hot rolling and the steel sheet exceeds 0.25, the effect of improving the magnetic flux density cannot be obtained.

Although the effect of increasing the magnetic flux density can be seen in any of the stands during the hot rolling, the effect of reducing the friction coefficient can be seen.
According to the study results of the inventors, the effect of improving the magnetic flux density is greater when the friction coefficient is reduced near the final pass. Therefore, in the present invention, the low friction rolling is performed in one or more consecutive passes from the final pass side of the finish hot rolling. That is, low friction rolling may be performed only on the final pass, or may be performed on two or more consecutive passes including the final pass. Of course, the low friction rolling may be performed in all passes of the finish hot rolling. The lower limit of the friction coefficient is not particularly set, but if the value is excessively small, slippage occurs during rolling and the sheet cannot be passed stably.
It is preferably at least 05.

The rolling reduction in one pass of low friction rolling is 5%.
If it is less than 50%, the effect of improving the magnetic flux density does not appear, and if a high pressure of more than 50% is applied, slip during rolling due to an insufficient frictional factor is likely to occur. Therefore, the rolling reduction of the pass where low friction rolling is performed is specified to be 5% or more and 50% or less.

In the case where the finishing hot rolling is performed at a low friction rate as in the present invention, when the sheet bar is bitten into the finishing hot rolling machine, a biting failure of the sheet bar occurs or the roll is not rolled during the finishing hot rolling. In some cases, slip occurs between the steel sheets, which significantly shortens the life of the rolling rolls and causes deep rolling flaws on the surface layer of the steel sheets. As a method of solving such a problem in the finish hot rolling with a low friction coefficient and performing a stable operation, the sheet bar after the rough rolling is joined to a preceding sheet bar before the finish hot rolling. It is particularly effective to continuously subject the sheet bar to finish hot rolling.

As a method of joining the preceding sheet bar and the succeeding sheet bar, the rear end of the preceding sheet bar and the leading end of the succeeding sheet bar are abutted, and the butted portion is welded. There are a method of applying pressure and pressure welding, a method of laser welding a butt portion, a method of welding a butt portion by induction heating, and a combination thereof.

It is effective to mix fats and oils in the roll cooling water as a means for reducing the coefficient of friction between the steel sheet and the rolling roll during hot rolling. The amount of the fat is 0.5% or more and 20% or less by volume. A surfactant is added as necessary to prevent separation of the oil and fat from the cooling water. When the amount of fats and oils in the roll cooling water is less than 0.5%, the effect of improving the magnetic flux density cannot be obtained, and when it exceeds 20%, the effect is saturated and uneconomical, so the amount of fats and oils is 0.5% or more and 20% or less. And

As the oil or fat mixed in the roll cooling water, a known hot rolling oil for a finishing mill may be used. Examples of such hot rolling oils for finishing mills include, for example, Cudol 5149, Cudol 0B068,
Q-doll 4B313 (both trade names of Kyodo Yushi Co., Ltd.).

In the present invention, the hot rolling end temperature is not particularly specified, but from the viewpoint of improving workability, the finishing hot rolling end temperature is preferably 750 ° C. or higher. Further, in order to ensure the thickness accuracy of the steel sheet, it is preferable that the hot rolling end temperature is finished in a ferrite single phase region or an austenite single phase region while avoiding a temperature in a two-phase region where a ferrite and an austenite phase coexist.

The hot-rolled sheet obtained by the above method may be used without being subjected to pickling. However, in order to improve workability in a subsequent step, the hot-rolled sheet is subjected to pickling to remove oxides on the surface. It is more preferable to do so. Further, an insulating film may be provided on the surface.

The pickled hot rolled sheet may be subjected to skin pass rolling of 2% or more and 20% or less and subjected to strain relief annealing to improve iron loss characteristics. At this time, if the rolling reduction is less than 2%, there is no effect of improving the magnetic properties, and if it exceeds 20%, the cost increases, so the rolling reduction is set to 2% or more and 20% or less.
700 ° C. for the purpose of simplifying the annealing equipment
To 750 ° C.

[0035]

Next, an embodiment of the present invention will be described. [Example 1] A slab for non-oriented electrical steel having the components shown in Table 2 was heated by a usual method, finished to a coarse bar of 30 mm in thickness by a rough rolling mill, and then finished to a thickness of 30 mm by a finishing hot rolling mill. Finished to 8mm. The hot rolling end temperature was 860 ° C., which is a ferrite region. The friction coefficient was changed by adjusting the amount of oil and fat mixed in the roll cooling water during rolling, and the friction coefficient between the steel sheet and the roll in the final pass of the finishing hot rolling was obtained by actually measuring the advance rate of the final stand. The rolling reduction of the final pass was 25%.

[0036]

[Table 2]

Further, in order to prevent a slip from occurring between the steel sheet and the work roll at the time of finishing hot rolling and forming a flaw on the surface of the steel sheet, the sheet bar after the rough rolling is welded to the preceding sheet bar, Finish hot rolling was performed continuously. The joining of the sheet bars was performed by abutting and pressing the front end portion of the following sheet bar and the rear end portion of the preceding sheet bar, and laser welding the butted portion.

Thereafter, the sample was cut into Epstein samples, and the magnetic properties were measured. Table 3 shows the results of the magnetic measurement of the present invention and the comparative example. By controlling the final friction coefficient at the time of finishing hot rolling to 0.25 or less, a low-grade non-oriented electrical steel sheet having a high magnetic flux density can be obtained.

[0039]

[Table 3]

Example 2 A slab for non-oriented electrical steel having the components shown in Table 4 was heated by a usual method, and finished into a 30 mm-thick coarse bar by a rough rolling mill. To 0.8mm. The hot rolling end temperature was 860 ° C., which is a ferrite region. The friction coefficient was changed by adjusting the amount of oil and fat mixed in the roll cooling water during rolling, and the friction coefficient between the steel sheet and the roll in the final pass of the finishing hot rolling was obtained by actually measuring the advance rate of the final stand. The rolling reduction of the final pass was 25%.

[0041]

[Table 4]

Further, in order to prevent a slip from occurring between the steel sheet and the work roll at the time of finishing hot rolling and forming a flaw on the surface of the steel sheet, the sheet bar after the rough rolling is welded to the preceding sheet bar, Finish hot rolling was performed continuously. The joining of the sheet bars was performed in the same manner as in Example 1.

Thereafter, the sample was cut into Epstein samples, and the magnetic properties were measured. Table 5 shows the magnetic measurement results of the present invention and the comparative example. By controlling the final friction coefficient at the time of finishing hot rolling to 0.25 or less, a low-grade non-oriented electrical steel sheet having a high magnetic flux density can be obtained.

[0044]

[Table 5]

Example 3 A slab for non-oriented electromagnetic steel having the components shown in Table 6 was heated by a usual method, and finished into a coarse bar having a thickness of 30 mm by a rough rolling mill. To 0.90 mm. The hot rolling end temperature was 860 ° C., which is a ferrite region. By adjusting the friction coefficient by adjusting the amount of oil and fat mixed in the roll cooling water during rolling,
By measuring the advance rate of the final stand, the coefficient of friction between the steel plate and the roll in the final pass of finishing hot rolling was determined.
The rolling reduction of the final pass was 20%.

[0046]

[Table 6]

Further, in order to prevent a slip from occurring between the steel sheet and the work roll at the time of finishing hot rolling and forming a flaw on the surface of the steel sheet, the sheet bar after the rough rolling is welded to the preceding sheet bar, Finish hot rolling was performed continuously. The joining of the sheet bars was performed in the same manner as in Example 1.

After the completion of the hot rolling, the steel sheet was pickled, finished to 0.80 mm by skin pass rolling, and then subjected to annealing at 750 ° C. for 2 hours, which was equivalent to strain relief annealing at a customer. Thereafter, the sample was cut into Epstein samples, and the magnetic properties were measured. Table 7 shows the results of the magnetic measurement of the present invention and the comparative example. By controlling the friction coefficient of the final stand at the time of finishing hot rolling to 0.25 or less, a low-grade non-oriented electrical steel sheet having a high magnetic flux density can be obtained.

[0049]

[Table 7]

Example 4 A slab for non-oriented electromagnetic steel having the components shown in Table 8 was heated by a usual method, and finished into a 30 mm-thick coarse bar by a rough rolling mill. To 0.80 mm. The hot rolling end temperature was 980 ° C., which is an austenite range. The friction coefficient was changed by adjusting the amount of oil and fat mixed in the roll cooling water during rolling, and the friction coefficient between the steel sheet and the roll in the final pass of the finishing hot rolling was obtained by actually measuring the advance rate of the final stand. The rolling reduction of the final pass was 20%.

[0051]

[Table 8]

Further, in order to prevent a slip from occurring between the steel sheet and the work roll at the time of finishing hot rolling and forming a flaw on the surface of the steel sheet, the sheet bar after the rough rolling is welded to the preceding sheet bar, Finish hot rolling was performed continuously. The joining of the sheet bars was performed in the same manner as in Example 1.

After the completion of the hot rolling, the steel sheet was pickled, finished to 0.65 mm by skin pass rolling, and then subjected to annealing at 750 ° C. for 2 hours, which was equivalent to strain relief annealing at a customer. Thereafter, the sample was cut into Epstein samples, and the magnetic properties were measured. Table 9 shows the magnetic measurement results of the present invention and the comparative example. By controlling the friction coefficient of the final stand at the time of finishing hot rolling to 0.25 or less, a low-grade non-oriented electrical steel sheet having a high magnetic flux density can be obtained.

[0054]

[Table 9]

[0055]

As described above, according to the present invention, it is possible to manufacture a low-grade non-oriented electrical steel sheet having a high magnetic flux density.

[Brief description of the drawings]

FIG. 1 shows a relationship between a friction coefficient between a steel plate and a roll in a final stand at the time of finish hot rolling and a product magnetic flux density.

Claims (4)

[Claims] 1. In% by weight, Si ≦ 0.30%, Mn ≦ 0.30%, 0.0050 <C ≦ 0.10%, N ≦ 0.010%, S ≦ 0.050%, Al ≦ A slab containing 0.10%, P ≦ 0.10% and the balance being Fe and unavoidable impurities is hot-rolled into a hot-rolled sheet, with or without an insulating coating, and as a final product In the method for producing a non-oriented electrical steel sheet, at the time of finishing hot rolling, in one or more passes continuous from the final pass side, the rolling reduction of one pass is 5%.
A method for producing a low-grade non-oriented electrical steel sheet having a high magnetic flux density, characterized in that rolling is performed with a friction coefficient between the steel sheet and the rolling roll of 0.25 or less. 2. A lubricant used in finish hot rolling,
The method for producing a low-grade non-oriented electrical steel sheet having a high magnetic flux density according to claim 1, wherein 0.5 to 20% by volume of a fat or oil is mixed into the hot-rolled roll cooling water. 3. The magnetic flux according to claim 1, wherein the sheet bar after the rough rolling is joined to a preceding sheet bar before the hot rolling, and the sheet bar is continuously subjected to the hot rolling. A method for manufacturing high-density low-grade non-oriented electrical steel sheets. 4. The lower grade having a high magnetic flux density according to claim 1, wherein the steel sheet after the finish hot rolling is subjected to pickling and skin pass rolling at a rolling rate of 2% or more and 20% or less. Manufacturing method of non-oriented electrical steel sheet.