JPH1036912A - Production of nonoriented silicon steel sheet having high magnetic flux density and low iron loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of production of a nonoriented silicon steel sheet having high magnetic flux density and low iron loss at a low cost. SOLUTION: The nonoriented silicon steel sheet can be produced by using a slab having a composition consisting of, by weight, >0.1-4.0% Si, 0.1-1.0% Mn, <=0.005% C, <=0.005% N, <=0.005% S, and the balance Fe with inevitable impurities, hot-rolling the slab, subjecting the resultant hot rolled plate to acid pickling and to a single cold rolling stage, and applying finish annealing or applying skin pass rolling after finish annealing. At this time, the average coefficient of friction between the finish hot rolling roll and the steel plate is <=0.25 and coiling temp. is 750-1000 deg.C, and self-annealing is performed by means of the retained heat of a coil. Further, it is preferable to mix 0.5-20% fats and oils as lubricant with hot rolling roll cooling water at the time of hot rolling or to join a roughed sheet bar to a preceding sheet bar before finish hot rolling and carry out finish hot rolling continuously.

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 excellent magnetic properties with high magnetic flux density and low iron loss, which is used as an iron core material of electric equipment.

[0002]

2. Description of the Related Art In recent years, in the fields of electric machines, especially rotating machines and medium-sized and small-sized transformers in which non-oriented electrical steel sheets are used as iron core materials, worldwide electric power and energy savings, as well as chlorofluorocarbon gas regulations. Among the movements for global environmental conservation, such as the above, the movement for higher efficiency is rapidly spreading.

In non-oriented electrical steel sheets, as a means of reducing iron loss, a method of increasing the content of Si, Al, or the like has been generally adopted from the viewpoint of reducing eddy current loss due to an increase in electric resistance. However, this method has a problem that the magnetic flux density decreases. In order to overcome such problems, a method of improving both the magnetic flux density and the iron loss by increasing the crystal grain size of the hot-rolled sheet has been performed.

[0004] In order to provide a material having a high magnetic flux density and a low iron loss, after the finish hot rolling, a hot rolled sheet is subjected to box annealing or continuous annealing to increase the crystal structure. . However, these methods inevitably increase the cost due to hot-rolled sheet annealing or box annealing, and cannot simultaneously satisfy the strict demands of the functions and prices of recent customers at the same time, resulting in low cost, high magnetic flux density and low iron loss. Development of a method capable of manufacturing non-oriented electrical steel sheets is required.

As a method for solving such a problem,
Japanese Patent Application Laid-Open No. 54-76422 discloses that a coil is heated at 750 ° C.
And a method of self-annealing with the heat held by the coil itself. However, even for the low-cost, high-flux-density non-oriented electrical steel sheets provided by the earlier application, there are even more stringent demands on customer prices and magnetic properties, and it is necessary to develop a manufacturing process that satisfies these requirements. I was

[0006]

SUMMARY OF THE INVENTION The present invention has been made to provide a manufacturing method which achieves a high magnetic flux density and a low iron loss at a low cost, which has been difficult in the past, in response to such demands of the market. It is the purpose.

[0007]

The gist of the present invention is as follows. (1) 0.10% ≦ Si ≦ 4.00% by weight in steel
%, 0.10% ≦ Mn ≦ 1.00%, C ≦ 0.0050
%, N ≦ 0.0050%, and S ≦ 0.0050%, and the remainder is made of a slab containing Fe and inevitable impurities, hot-rolled into a hot-rolled sheet, pickled, and washed once. In the method for producing a non-oriented electrical steel sheet which is subjected to cold rolling and then subjected to finish annealing, the average coefficient of friction between the hot-rolled roll and the steel sheet at the time of finishing hot rolling is 0.25 or less, and after finishing the hot rolling. A method for producing a non-oriented electrical steel sheet, comprising: winding a coil at a temperature of 750 ° C. or more and 1000 ° C. or less and self-annealing with the heat of the coil itself for 5 minutes or more and 5 hours or less. (2) After the first cold rolling, finish annealing is performed, and further 2
The method for producing a non-oriented electrical steel sheet according to the above (1), wherein skin pass rolling of up to 20% is performed. (3) The above item (1) or (2), wherein the steel further contains 0.10% ≦ Al ≦ 2.00% by weight.
The method for producing a non-oriented electrical steel sheet according to the above. (4) Any one of (1), (2) and (3) above, wherein 0.5 to 20% of fats and oils is mixed in an emulsion state in hot roll cooling water as a lubricant at the time of finishing hot rolling. A method for producing a non-oriented electrical steel sheet according to one aspect. (5) The preceding paragraphs (1), (2), and (2), wherein the sheet bar after the rough rolling is joined to a preceding sheet bar before the hot rolling for finish, and the sheet bar is continuously subjected to the hot rolling for finish. 3)
Alternatively, the method for producing a non-oriented electrical steel sheet according to any one of (4).

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The present inventors have conducted intensive studies on the problems in the prior art in order to simultaneously achieve a low iron loss and a high magnetic flux density. As a result, the weight percentage of Si exceeds 0.1% and is 4.0% or less, and Mn is 0% or less. 0.1% or more and 1.0% or less, Al is 0.1% or more and 2.0% or less.
% Or less, and the average friction coefficient between the hot-rolled roll and the steel sheet at the time of finishing hot rolling is set to 0.25 or less, and hot-rolled. The inventors have found that it is possible to manufacture a non-oriented electrical steel sheet having a high magnetic flux density and a low iron loss by performing self-annealing with own heat, and have completed the invention.

The magnetic properties of the non-oriented electrical steel sheet can be improved by increasing the crystal structure before cold rolling. In the prior art, in order to further coarsen the crystal structure before cold rolling,
Hot-rolled sheet annealing by a continuous annealing furnace or box annealing has been performed. However, in these prior arts,
Although the magnetic flux density of the product has been improved, the cost increase due to the addition of the hot-rolled sheet annealing process has been large, and it has been difficult for consumers to accept the cost increase.

On the other hand, as a method for solving such a problem, Japanese Patent Laid-Open Publication No.
A method of winding at a temperature of 0 ° C. to 1000 ° C. and self-annealing with the heat retained by the coil itself is disclosed. However, even with the low-cost non-oriented electrical steel sheet with improved magnetic flux density according to the prior application, more and more stringent demands have been placed on the price and magnetic properties from recent consumers.

The present inventors have conducted intensive studies to overcome the limitations of the magnetic properties of such non-oriented electrical steel sheets in a low-cost process, and as a result, the content of Si exceeded 0.1% and was 4.0.
% Or less, Mn is 0.1% or more and 1.0% or less, and Al is 0.1% or less.
In a steel containing 1% or more and 2.0% or less, hot rolling is performed by setting the average friction coefficient between a hot-rolled roll and a steel sheet at the time of finish hot rolling to 0.25 or less, and further increasing the temperature to 750 ° C or more and 10% or less.
By winding the coil at a temperature of 00 ° C or less and applying self-annealing with the heat held by the coil itself, the magnetic flux density in the product after finish annealing is higher than that of the conventional self-annealing method, and the iron loss is low. Succeeded in producing steel sheets. In addition, from the viewpoint of stably performing the finish hot rolling with a low friction coefficient as in the present invention, the sheet bar after the rough rolling is joined to the preceding sheet bar, and the finish hot rolling is continuously performed. It was found to be effective.

First, the components will be described. Si is added to increase the specific resistance of the steel sheet, reduce eddy current loss, and improve the iron loss value. If the Si content is less than 0.10%, sufficient resistivity cannot be obtained, so it is necessary to add Si in an amount of 0.10% or more. On the other hand, when the Si content is 4.0
%, Ear cracks at the time of rolling increase remarkably, and rolling becomes difficult. Therefore, it is necessary to be 4.0% or less.

Al, like Si, has the effect of increasing the specific resistance of the steel sheet and reducing eddy current loss. In order to obtain a low iron loss high magnetic flux density non-oriented electrical steel sheet aimed at by the present invention, it is necessary to add 0.10% or more. On the other hand, A
If the 1 content exceeds 2.0%, the magnetic flux density decreases and the cost increases, so the content is set to 2.00% or less.

Mn, like Al and Si, has the effect of increasing the specific resistance of a steel sheet and reducing eddy current loss. For this purpose, the Mn content needs to be 0.10% or more. On the other hand, if the Mn content exceeds 1.00%, the deformation resistance during hot rolling increases, and hot rolling becomes difficult, and the crystal structure after hot rolling tends to become finer, and the magnetic properties of the product deteriorate. , Mn content must be 1.00% or less. Further, the amount of Mn addition is extremely important from the viewpoint of ensuring the strength of the high temperature sheet bar joint before hot rolling. This is because Mn is used 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 necessary to set the value of Mn / S, which is the ratio of the weight concentration of S and S, to 20 or more. In the component range of the present invention, since the Mn content is 0.10% or more and the S content is 0.0050% or less, the value of Mn / S is maintained at 20 or more. Absent.

In order to improve the mechanical properties, magnetic properties, and rust resistance of the product or for other purposes, P,
Even if one or more of B, Ni, Cr, Sb, Sn, and Cu are contained in steel, the effect of the present invention is not impaired.

If the C content exceeds 0.0050%, iron loss is deteriorated by magnetic aging during use and energy loss during use is increased. Therefore, it is necessary to control the content to 0.0050% or less. In order to improve the magnetic properties of the product by promoting the growth of crystal grains during hot-rolled sheet annealing, and to promote the growth of crystal grains during finish annealing and further improve (reduce) iron loss.
In order to measure the C content is preferably 0.0020
%, More preferably 0.0010% or less.

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. The presence of S prevents the grain growth of the hot-rolled structure, and also impairs the growth of crystal grains during finish annealing, resulting in an increase in iron loss.
% And N must be 0.0050% or less. In addition,
In order to promote crystal grain growth during hot-rolled sheet annealing to improve the magnetic properties of the product, and to promote crystal grain growth during finish annealing and further improve (reduce) iron loss, Both S and N are preferably 0.0020% or less, more preferably 0.0010% 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.

In the finishing hot rolling, in order to reduce the friction coefficient between the work roll of the finishing hot rolling machine and the steel sheet, fat or oil is mixed into the roll cooling water as a lubricant. A surfactant is added as necessary to prevent separation of the oil and fat from the cooling water. The amount of fats and oils mixed into the roll cooling water at the time of finishing hot rolling is 0.5% or more and 20% or less by volume ratio. If the amount of fats and oils in the roll cooling water is less than 0.5%, the effect cannot be obtained,
If it exceeds 20%, the effect saturates and is uneconomical.
% Or less.

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 product magnetic properties. Steels having the components shown in Table 1 were melted and finish hot rolling was performed. The friction coefficient at the time of hot rolling was changed from 0.1 or less to 0.3 or more by changing the oil content and the oil component in the roll cooling water. The average coefficient of friction was calculated from the measured advanced rate at each stand, and the average value was determined. The finishing hot rolling end temperature was fixed at 1000 ° C., finished to a thickness of 2.5 mm, wound up at 900 ° C., immediately charged with a coil in a heat retaining furnace, and self-annealed at 860 ° C. for 1 hour. This was pickled, cold rolled to a thickness of 0.50 mm, and degreased.
The sample was annealed at 45 ° C. for 45 seconds, and the Epstein sample was cut to measure magnetic properties.

[0021]

[Table 1]

FIG. 1 shows the dependency of the product magnetic flux density on the average friction coefficient during hot rolling. The average of the actually measured values of each stand of the finishing hot rolling mill was used as the average friction coefficient. It can be seen that when the average coefficient of friction during hot rolling is 0.25 or less, the product magnetic flux density increases. As shown in the above experiment, the value of the coefficient of friction between the rolling roll and the steel plate of the hot-rolled finish may be such that the average value of all the stands of the hot-rolled finish is 0.25 or less. If it exceeds 0.25, the effect is insufficient, and the product magnetic flux density decreases.

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, the sheet bar biting failure occurs, and 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 rolls and causes deep rolling defects on the surface layer of the steel sheets. As a method of solving such problems 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 the preceding sheet bar before the finish hot rolling, and It is particularly effective to continuously subject the sheet bar to finish hot rolling.

The coil winding temperature during self-annealing is 7
If the temperature is lower than 50 ° C., the magnetic properties are not sufficiently improved.
50 ° C. or higher. On the other hand, if the temperature is higher than 1000 ° C., the coil is likely to be displaced, and the surface layer of the steel sheet is oxidized too much. The time for self-annealing is
If the time is less than 5 minutes, the improvement of the magnetic properties is insufficient, so that it is performed for 5 minutes or more. If the time exceeds 5 hours, oxidation of the steel sheet becomes severe, and poor pickling tends to occur. The preferable self-annealing time is 30 to 90 minutes in view of the effect of the annealing and the economic efficiency. In the present invention, in order to prevent oxidation of the coil during self-annealing, self-annealing may be performed in a reducing atmosphere containing hydrogen, in an inert gas atmosphere such as nitrogen or argon, or under reduced pressure. The hot-rolled sheet thus subjected to self-annealing may be subjected to one cold rolling step and then to finish annealing, or may be further subjected to a skin pass rolling step to obtain a product.

The finish annealing is performed by continuous annealing. At that time, as disclosed in Japanese Patent Application Laid-Open No. 61-231120, the former stage is performed at a temperature range of 950 ° C. to 1100 ° C. for 5 seconds to 5 hours.
Anneal for a short time of 1 minute, and at a later stage at 800 to 950 ° C for 1 minute.
Finish annealing may be performed by a method such as holding for 0 seconds to 2 minutes.

Further, a skin pass rolling step may be added after the continuous annealing to obtain a product. Skin pass rolling rate is 2
If it is less than 20%, the effect cannot be obtained, and if it exceeds 20%, the magnetic properties are deteriorated.

[0027]

Next, an embodiment of the present invention will be described. (Example 1) A slab for non-oriented electromagnetic steel having the components shown in Table 2 was heated by a usual method, finished to a rough bar with a thickness of 50 mm by a rough rolling machine, and then finished by a finishing hot rolling machine. Finished to 5mm. Oil and fat were mixed in an emulsion state into the cooling water of the roll of the finishing hot rolling machine, and the friction coefficient was adjusted by changing the mixing amount. The average coefficient of friction was calculated from the measured advanced rate at each stand, and the average value was determined. At this time, the finish hot rolling end temperature was 1000 ° C.
Winding at 0 ° C, charging the coil into a heat retention furnace,
Time self-annealing was applied.

After that, it is pickled and then cold-rolled to a thickness of 0.1 mm.
Finished to 50mm. This was heated at 900 ° C in a continuous annealing furnace for 4 hours.
Anneal for 5 seconds. Then, cut into Epstein samples,
The magnetic properties were measured. Table 3 also shows the components of the present invention and comparative examples and the results of magnetic measurement. If the average friction coefficient at the time of finishing hot rolling is reduced to 0.25 or less, it is possible to obtain a non-oriented electrical steel sheet having a high magnetic flux density and a low iron loss value and excellent magnetic properties.

[0029]

[Table 2]

[0030]

[Table 3]

(Example 2) A slab for non-oriented electromagnetic steel having the components shown in Table 4 was heated by a usual method, and was finished into a rough bar having a thickness of 55 mm by a rough rolling mill. To 2.5 mm. Oils and fats were mixed in an emulsion state into the cooling water of the roll of the finishing hot rolling machine, and the average friction coefficient was changed by adjusting the mixing amount. The average coefficient of friction was calculated from the measured advanced rate at each stand, and the average value was determined. Further, in order to prevent a slip from occurring between the steel sheet and the work roll during the finish 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, and the finish heat is applied. Cold rolling was performed continuously. The hot-rolling finishing temperature was 950 ° C., the coil was wound at 860 ° C., the coil was immediately charged into a heat retaining furnace, and self-annealed at 860 ° C. for 1 hour.

Thereafter, pickling is carried out and cold rolling is carried out to obtain 0.1%.
Finished to 35mm. This was annealed in a continuous annealing furnace at 1050 ° C. for 10 seconds in the first stage and 900 ° C. for 30 seconds in the second stage. Thereafter, the sample was cut into Epstein samples, and the magnetic properties were measured. Table 5 also shows the components of the present invention and comparative examples and the results of magnetic measurement. As shown in Table 5, if the average friction coefficient at the time of finishing hot rolling is reduced to 0.25 or less, a non-oriented electrical steel sheet having a high magnetic flux density and a low iron loss value and excellent magnetic properties can be obtained. Is possible.

[0033]

[Table 4]

[0034]

[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 50 mm-thick coarse bar by a rough rolling mill. To 2.5 mm. Oils and fats were mixed in an emulsion state into the roll cooling water of the finishing hot rolling mill, and the average friction coefficient was adjusted to 0.21 by adjusting the mixing amount. The average coefficient of friction was calculated from the measured advanced rate at each stand, and the average value was determined. After the completion of hot rolling, the coil was subjected to self-annealing under the conditions shown in Table 7. Then, it was pickled and finished to 0.35 mm by cold rolling. This was annealed at 980 ° C. for 45 seconds in a continuous annealing furnace. Thereafter, the sample was cut into Epstein samples, and the magnetic properties were measured. Table 7 also shows the self-annealing conditions and the results of the magnetic measurement.

As shown in Table 7, the self-annealing temperature was 7
When it is 50 ° C. or more and 1000 ° C. or less, it is possible to obtain a non-oriented electrical steel sheet having excellent characteristics. If the temperature is lower than 850 ° C., the improvement of the magnetic properties is insufficient, and if the winding temperature of the coil is raised to 1000 ° C. or higher, a winding deviation occurs, so that self-annealing was impossible. Further, it can be seen that excellent magnetic properties are obtained when the self-annealing time is 5 minutes or more and 5 hours or less. If the annealing time of the hot-rolled sheet by continuous annealing is 5 hours or more, poor pickling occurs, and iron loss is rather deteriorated. As described above, by reducing the average friction coefficient at the time of finishing hot rolling and appropriately controlling the annealing conditions of the hot rolled sheet, the value of the magnetic flux density is high, and the iron loss value is low. It is possible to obtain

[0037]

[Table 6]

[0038]

[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 was finished into a rough bar having a thickness of 50 mm by a rough rolling mill. To 2.5 mm. Oil and fat were mixed in an emulsion state into the cooling water of the roll of the finishing hot rolling machine, and the friction coefficient was adjusted by changing the mixing amount. The average coefficient of friction was calculated from the measured advanced rate at each stand, and the average value was determined. At this time, the finish hot rolling end temperature was 950 ° C., the film was wound at 850 ° C., the coil was immediately charged into a heat retaining furnace, and self-annealing was performed at 850 ° C. for 1 hour.

After that, it is pickled and then cold-rolled to a thickness of 0.1 mm.
Finished to 50mm. This is heated at 850 ° C in a continuous annealing furnace for 3 hours.
Annealed for 0 seconds. Then, cut into Epstein samples,
The magnetic properties were measured. Table 9 also shows the components of the present invention and comparative examples and the results of magnetic measurement. If the average friction coefficient at the time of finishing hot rolling is reduced to 0.25 or less, it is possible to obtain a non-oriented electrical steel sheet having a high magnetic flux density and a low iron loss value and excellent magnetic properties.

[0041]

[Table 8]

[0042]

[Table 9]

[0043]

As described above, according to the present invention, the cost is lower than that of the conventional hot-rolled sheet annealing method, the magnetic flux density is higher than the conventional self-annealing method, the iron loss is lower, and the magnetic properties are excellent. It is possible to manufacture a non-oriented electrical steel sheet.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between an average coefficient of friction during finished hot rolling and a product magnetic flux density.

Continuing on the front page (72) Inventor Seichi Senoo 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works (72) Inventor Kazufumi Hanzawa 1 Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka No. 1 New Nippon Steel Corporation Yawata Works

Claims (5)

[Claims] 1% by weight in steel 0.10% ≦ Si ≦ 4.00%, 0.10% ≦ Mn ≦ 1.00%, C ≦ 0.0050%, N ≦ 0.0050%, Using a slab containing S ≦ 0.0050% and the balance being Fe and unavoidable impurities, hot-rolled into a hot-rolled sheet, pickled,
In the method for producing a non-oriented electrical steel sheet that is subjected to cold rolling twice and then subjected to finish annealing, the average coefficient of friction between the hot-rolled roll and the steel sheet at the time of finish hot rolling is 0.25 or less; A method for producing a non-oriented electrical steel sheet, comprising: winding a coil at a temperature of 750 ° C. or more and 1000 ° C. or less, and performing self-annealing with heat held by the coil itself for 5 minutes or more and 5 hours or less. 2. After the first cold rolling, a finish annealing is performed,
2. The method for producing a non-oriented electrical steel sheet according to claim 1, further comprising subjecting skin pass rolling to 2 to 20%. 3. The method for producing a non-oriented electrical steel sheet according to claim 1, wherein the steel further contains 0.10% ≦ Al ≦ 2.00% by weight in the steel. 4. The method according to claim 1, wherein 0.5 to 20% of fats and oils is mixed in a hot-roll roll cooling water in the form of an emulsion as a lubricant during hot-rolling for finishing. The method for producing a non-oriented electrical steel sheet according to the above. 5. The method 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. 5. The method for producing a non-oriented electrical steel according to any one of the above items 4.