JP3388119B2 - Method of manufacturing low-grade non-oriented electrical steel sheet with high magnetic flux density - 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 manufacturing a low-grade non-oriented electrical steel sheet having a high magnetic flux density, which is 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 rotary machines in which non-oriented electrical steel sheets are used, there is an increasing demand for higher magnetic flux density and smaller size. Among such applications of non-oriented electrical steel sheets, like motors for automobile power windows, the operating time is short and iron loss does not require very good characteristics. Some are stronger. In such applications,
By increasing the magnetic flux density of the iron core, it is possible to increase the torque at the time of starting and operating, thereby making it possible to downsize the rotating machine. Furthermore, the non-oriented electrical steel sheet used for such applications is strongly required to be low in cost.

In the prior art, in order to increase the magnetic flux density of the non-oriented electrical steel sheet, a method of coarsening the crystal grain size before cold rolling to improve the magnetic flux density has been used. For this purpose,
Generally, hot-rolled sheet annealing is performed by continuous annealing or box annealing to coarsen the grain size before cold rolling and improve the recrystallized texture to improve the magnetic flux density. However, in this method, the cost is remarkably increased due to the addition of the hot-rolled sheet annealing step, and it is the current situation that it cannot be accepted by the customers who are used for the above purposes.

Therefore, 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 to 1000 ° C. and held in a coil. A self-annealing method of annealing by heat is disclosed in JP-A-54-764.
No. 22 and Japanese Patent Publication No. 62-61644 set the hot rolling end temperature to a high temperature of 1000 ° C. or higher and set no water injection time to recrystallize the hot rolled structure before winding on a so-called run-out table. A method for grain growth is disclosed.

Further, Japanese Patent Application Laid-Open No. 58-37121 discloses a method for producing a lower non-oriented electrical steel sheet in which finish annealing after cold rolling is performed by applying tension at a temperature of 400 ° C. or higher and a recrystallization temperature or lower. There is.

However, even in these manufacturing methods, since it is necessary to carry out a cold rolling step after the hot rolled sheet is manufactured, it is equivalent to the manufacturing cost of the conventional non-oriented electrical steel sheet manufacturing technology, and the recent demand. It was not possible to meet the strict demand for reducing the cost of the house.

In order to find a measure to meet the demands of customers for such a non-oriented electrical steel sheet, the present inventors have made a hot-rolled sheet or a so-called hot final product obtained by skin-passing the hot-rolled sheet as a final product. I focused on the development of and examined. Among non-oriented electrical steel sheets, so-called cold-rolled electrical steel sheets are superior in magnetic properties to hot final products, and therefore, in the market, they have been switched to cold-rolled electrical steel sheets. However, the inventors of the present invention have made earnest studies for the purpose of improving the properties of a low-cost hot final electrical steel sheet.

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

[0009]

DISCLOSURE OF THE INVENTION The present invention meets the strong demand for low cost high magnetic flux density non-oriented electrical steel sheet of such a consumer and has a high magnetic flux density low non-oriented which enables high torque and downsizing. The present invention provides a low-cost method for manufacturing a magnetic electrical steel sheet.

[0010]

The gist of the present invention is as described above. (1) In weight%, Si ≦ 0.30%, Mn ≦ 0.30%, 0.0050 <
C ≦ 0.10%, N ≦ 0.010%, S ≦ 0.05
0%, Al ≦ 0.10%, P ≦ 0.10%,
In addition, a slab that satisfies Mn / S ≧ 20 and the balance is Fe and unavoidable impurities is hot-rolled to form a hot-rolled sheet. , In the 1 or more consecutive passes from the final pass side, only the final pass or the sequence including the final pass
The rolling reduction of each of two or more consecutive passes is 5% or more and 50% or less, and the friction coefficient between the steel sheet and the rolling roll is 0.25.
A plate thickness of 0.9 mm or less characterized by being subjected to the following rolling
Below is a method for manufacturing a low-grade non-oriented electrical steel sheet having a high magnetic flux density.

(2) As a lubricant used during finish hot rolling, 0.5 to 20% by volume of oil and fat is mixed in cooling water for hot rolling rolls, which has a high magnetic flux density as described in (1). Manufacturing method of low grade non-oriented electrical steel sheet.

(3) The sheet bar after rough rolling is joined to the preceding sheet bar before hot rolling for finishing, and the sheet bar is continuously subjected to 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 as described.

(4) After finishing hot rolling, the steel sheet is pickled,
The method for producing a low non-oriented electrical steel sheet having a high magnetic flux density according to (1), (2) or (3), characterized in that skin pass rolling having a rolling rate of 2% or more and 20% or less is performed. (5) Characterized by applying an insulating film to the hot rolled sheet
Of the magnetic flux density described in (1), (2), (3) or (4)
Manufacturing method of high grade non-oriented electrical steel sheet.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below. First, the components will be described. Si is added in order to increase the specific resistance of the steel sheet, reduce the eddy current loss, and improve the iron loss value. In order to provide, the Si content is 0.3
It should be 0% or less.

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

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

However, the amount of Mn added is extremely important in ensuring the strength of the high temperature sheet bar joint before finish hot rolling. This is because the value of Mn / S, which is the ratio of the weight concentration of Mn and S, is set to 2 in order to prevent hot embrittlement of the sheet bar joint due to the presence of sulfides having a low melting point at the 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 the content exceeds 0.10%, the magnetic flux density decreases, so 0.10% or less is added.

If the C content exceeds 0.10%, carbides precipitate in the steel sheet, the iron loss remarkably increases, and the workability deteriorates. 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, C> 0.0050% is sufficient. If the C content is set to 0.0050% or less, the steelmaking cost remarkably rises and the product price rises, which is not preferable, so the C content is set to more than 0.0050%.

S and N are partially re-dissolved during heating of the slab in the hot rolling process, and sulfides such as MnS and A during hot rolling.
Form a nitride such as 1N. The presence of these impedes the grain growth of the hot rolled structure and deteriorates the workability, so S must be 0.050% or less and N must be 0.010% or less.

Next, the process conditions of the present invention will be described. The steel slab comprising the above components is melted in a converter and manufactured by continuous casting or ingot-slab rolling. The steel slab is heated by a known method. This slab is hot-rolled 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 finish hot-rolling on the magnetic properties of the product. Steel with the components shown in Table 1 was melted and finish hot rolling was performed.

[0023]

[Table 1]

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

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

The effect of improving the magnetic flux density can be seen even if the friction coefficient is reduced in any of the stands during hot rolling for finish.
According to the results of studies by 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, low friction rolling is performed in one or more continuous passes from the final pass side of finish hot rolling. That is, low friction rolling may be performed only in the final pass or in two or more continuous passes including the final pass. Of course, low-friction rolling may be performed in all passes of finish hot rolling. Although the lower limit of the friction coefficient is not particularly set, if the value is excessively small, slippage occurs during rolling and stable striping cannot be performed.
It is preferably at least 05.

Further, 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 it is carried out under a high pressure of more than 50%, slip during rolling tends to occur due to insufficient friction coefficient. Therefore, the rolling reduction of the pass for low friction rolling is specified to be 5% or more and 50% or less.

When the finish hot rolling is carried out at a low coefficient of friction as in the present invention, when the sheet bar is caught in the finishing hot rolling machine, the sheet bar is not caught properly and the roll is not rolled during the finishing hot rolling. In some cases, slips occur between the steel sheets, which significantly shortens the life of the rolling roll and causes deep rolling flaws on the surface layer of the steel sheet. As a method of solving such problems in finishing hot rolling with a low friction coefficient and stably operating, a sheet bar after rough rolling is joined to a preceding sheet bar before finishing 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 portion of the preceding sheet bar and the leading end portion of the succeeding sheet bar are butted and the butted portion is welded, or the butted portion is pressed. There are a method of applying pressure and pressure welding, a method of laser welding the butt portion, a method of welding the butt portion by induction heating, or a combination thereof.

Mixing oils and fats into the roll cooling water is effective as a means for reducing the coefficient of friction between the steel plate and the rolling roll during hot rolling for finishing. The amount of fats and oils is 0.5% or more and 20% or less by volume ratio. A surfactant is added as necessary to prevent the oil and fat from being separated from the cooling water. If the amount of oil or fat in the roll cooling water is less than 0.5%, the effect of improving the magnetic flux density cannot be obtained, and if it exceeds 20%, the effect is saturated and it is uneconomical. Therefore, the amount of oil or fat is 0.5% or more and 20% or less. And

As the oil and fat mixed in the roll cooling water, a known hot rolling oil for finish rolling mill may be used. Examples of such hot rolling oil for finish rolling mill include, for example, Cudor 5149, Cudor 0B068,
Cudor 4B313 (both are trade names of Kyodo Yushi Co., Ltd.).

In the present invention, the hot rolling finish temperature is not particularly specified, but the finish hot rolling finish temperature is preferably 750 ° C. or higher from the viewpoint of improving workability. Further, for the purpose of ensuring the plate thickness accuracy of the steel sheet, it is preferable that the hot rolling end temperature is avoided in the two-phase region where ferrite and austenite phase coexist, and finishes in the ferrite single phase or austenite single phase region.

The hot-rolled sheet obtained by the above method may be used without being pickled, but in order to improve the workability in the subsequent step, pickling is carried out to remove the oxide on the surface. Is more preferable. Furthermore, an insulating film may be applied to the surface.

The pickled hot rolled sheet may be subjected to skin pass rolling of 2% or more and 20% or less and strain relief annealing to improve the iron loss characteristics before use. At that time, if the rolling rate is less than 2%, there is no effect of improving the magnetic properties, and if it exceeds 20%, the cost increases, so the rolling rate is set to 2% or more and 20% or less.
The strain relief annealing is 700 ° C for the purpose of simplifying the annealing equipment.
It is preferable to carry out at a temperature of from about 750 ° C.

[0035]

EXAMPLES Next, examples 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 and finished to a rough bar having a thickness of 30 mm by a rough rolling mill, and then finished by a finishing hot rolling machine. Finished to 8 mm. The hot rolling end temperature was 860 ° C., which is in the 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 plate and the roll in the final hot rolling final pass was determined by measuring the advanced rate of the final stand. The rolling reduction in the final pass was 25%.

[0036]

[Table 2]

In order to prevent slippage between the steel sheet and the work roll during finish hot rolling and formation of flaws on the surface of the steel sheet, the sheet bar after rough rolling is welded to the preceding sheet bar, Finishing hot rolling was continuously performed. The joining of the sheet bars was performed by abutting the leading end portion of the trailing sheet bar and the trailing end portion of the preceding sheet bar by pressure welding, and by laser welding the abutting portion.

After that, it was cut into Epstein samples and the magnetic properties were measured. Table 3 shows the magnetic measurement results of the present invention and the comparative example. In this way, by controlling the final friction coefficient during finish hot rolling to be 0.25 or less, it is possible to obtain a low-grade non-oriented electrical steel sheet having a high magnetic flux density value.

[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 by a rough rolling machine into a coarse bar having a thickness of 30 mm, followed by a finishing hot rolling machine. Finished with 0.8mm. The hot rolling end temperature was 860 ° C., which is in the 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 plate and the roll in the final hot rolling final pass was determined by measuring the advanced rate of the final stand. The rolling reduction in the final pass was 25%.

[0041]

[Table 4]

Further, in order to prevent slippage between the steel sheet and the work roll during finish hot rolling and formation of flaws on the surface of the steel sheet, the sheet bar after rough rolling is welded to the preceding sheet bar, Finishing hot rolling was continuously performed. The sheet bars were joined in the same manner as in Example 1.

After that, it 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. In this way, by controlling the final friction coefficient during finish hot rolling to be 0.25 or less, it is possible to obtain a low-grade non-oriented electrical steel sheet having a high magnetic flux density value.

[0044]

[Table 5]

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

[0046]

[Table 6]

Further, in order to prevent slippage between the steel sheet and the work roll during finish hot rolling and formation of flaws on the surface of the steel sheet, the sheet bar after rough rolling is welded to the preceding sheet bar, Finishing hot rolling was continuously performed. The sheet bars were joined in the same manner as in Example 1.

After hot rolling was finished, pickling was carried out, and skin pass rolling was performed to finish to 0.80 mm, followed by annealing at 750 ° C. for 2 hours corresponding to strain relief annealing at the consumer. Then, it cut | disconnected to the Epstein sample and measured the magnetic characteristic. Table 7 shows the magnetic measurement results of the present invention and the comparative example. In this way, by controlling the friction coefficient of the final stand during finish hot rolling to be 0.25 or less, it is possible to obtain a lower non-oriented electrical steel sheet having a high magnetic flux density value.

[0049]

[Table 7]

[Example 4] A slab for non-oriented electrical steel having the components shown in Table 8 was heated by a usual method and finished by a rough rolling machine into a coarse bar having a thickness of 30 mm, followed by a finishing hot rolling machine. Was finished to 0.80 mm. The hot rolling end temperature was 980 ° C., which is the 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 plate and the roll in the final hot rolling final pass was determined by measuring the advanced rate of the final stand. The rolling reduction in 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 during finish hot rolling to form a flaw on the surface of the steel sheet, the sheet bar after rough rolling is welded to the preceding sheet bar, Finishing hot rolling was continuously performed. The sheet bars were joined in the same manner as in Example 1.

After hot rolling was finished, pickling was carried out, and after skin pass rolling to finish to 0.65 mm, annealing corresponding to strain relief annealing at 750 ° C. for 2 hours by a consumer was carried out. Then, it cut | disconnected to the Epstein sample and measured the magnetic characteristic. Table 9 shows the magnetic measurement results of the present invention and the comparative example. In this way, by controlling the friction coefficient of the final stand during finish hot rolling to be 0.25 or less, it is possible to obtain a lower non-oriented electrical steel sheet having a high magnetic flux density value.

[0054]

[Table 9]

[0055]

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

[Brief description of drawings]

FIG. 1 shows a relationship between a product's magnetic flux density and a friction coefficient between a steel plate and a roll in a final stand during finish hot rolling.

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Claims (5)

(57) [Claims] 1. 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 satisfying Mn / S ≥ 20 and the balance being Fe and unavoidable impurities is hot-rolled into a hot-rolled sheet to obtain a final product. In the method for manufacturing a non-oriented electrical steel sheet, the continuous 1
Only the final pass, or the final pass
The rolling reduction of 5% or more and 50% or less in each of continuous two or more passes including the steel sheet, and the rolling coefficient of the friction coefficient between the steel plate and the rolling roll being 0.25 or less are
A method for producing a low-grade non-oriented electrical steel sheet having a high magnetic flux density of 0.9 mm or less . 2. As a lubricant used during finish hot rolling,
The method for producing a low non-oriented electrical steel sheet having a high magnetic flux density according to claim 1, wherein 0.5 to 20% by volume of fats and oils is mixed in the hot-rolled roll cooling water. 3. The magnetic flux density according to claim 1, wherein the shishibar after rough rolling is joined to a preceding sheet bar before hot rolling for finishing, and the sheet bar is continuously subjected to hot rolling for finishing. Of high quality low grade non-oriented electrical steel sheet. 4. The high magnetic flux density low grade according to claim 1, 2 or 3, wherein the steel sheet after hot rolling is subjected to pickling and skin pass rolling with a rolling ratio of 2% to 20%. Manufacturing method of non-oriented electrical steel sheet. 5. A hot rolled sheet is provided with an insulating film.
High magnetic flux density according to any one of claims 1 to 4.
Manufacturing method of low grade non-oriented electrical steel sheet.