JPH1096028A - Manufacture of grain-oriented silicon steel sheet having high magnetic flux density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacture method for grain-oriented silicon steel sheet having a high magnetic flux density and used for an iron core material for electrical equipment. SOLUTION: A slab, having a composition consisting of, by weight, 0.025-0.075% C, 2.5-4.5% Si, <=0.015% S, 0.010-0.050% sol-Al, 0.0010-0.0120% N, 0.050-0.45% Mn, and the balance Fe with inevitable impurities, is heated to <=1200 deg.C, hot-rolled, and subjected to hot rolled plate annealing, and the resultant plate is rolled once or is rolled two or more times while process- annealed between the rolling stages to >=80% final rolling rate, and then, nitriding treatment is applied to the resultant steel sheet in the course between the completion of decarburizing annealing and the initiation of secondary recrystallization at finish annealing, by which the grain oriented silicon steel sheet can be manufactured. At this time, the average coefficient of friction between a hot roll and a steel plate at the time of finish hot rolling is regulated to <=0.25. Moreover, at the time of finish hot rolling, 0.5-20% of fats and fatty oils, as a lubricant, are mixed, in an emulsified state, into hot roll cooling water.

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 grain-oriented electrical steel sheet having a high magnetic flux density, which is used as an iron core material of electric equipment.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is a product in which crystal grains of a steel sheet are highly oriented in a specific direction by secondary recrystallization and has a {110} plane on a rolling surface and a <100> axis in a rolling direction. It is composed of crystal grains having an orientation.

[0003] Grain-oriented electrical steel sheets are mainly used as soft magnetic materials for core materials of transformers and other electric equipment. In recent years, social demands for energy saving and resource saving have become more and more severe. Demands for reduction of iron loss and improvement of magnetization characteristics of grain-oriented electrical steel sheets have also become severe.
For this reason, magnetic characteristics, particularly good excitation characteristics and iron loss characteristics, have been required.

A magnetic flux density B8 (magnetic flux density at a magnetic field strength of 800 A / m) is usually used as an index indicating the excitation characteristics of a grain-oriented electrical steel sheet. As an index indicating the iron loss characteristics, W17 / 50 (iron loss per unit weight when magnetized to 1.7 T at 50 Hz) and the like are used.

Iron loss consists of eddy current loss and hysteresis loss. The eddy current loss is governed by factors such as the electrical resistivity of the steel sheet, the thickness of the steel sheet, the grain size, the form of magnetic domains, and the film tension on the steel sheet surface. On the other hand, the hysteresis loss is governed by the crystal orientation, purity, internal strain and the like of the steel sheet that governs the magnetic flux density.

As an attempt to reduce iron loss by controlling these factors, in order to increase the electric resistance of
Increasing the i content has been performed, but increasing the Si content is accompanied by the problem that the secondary recrystallization becomes unstable, and the processability in the manufacturing process and the product is degraded. Is the current situation.

On the other hand, the purity and internal strain of the steel sheet have been studied in the manufacturing process, and the reduction of iron loss due to these reductions has reached the limit. Attempts have been made to reduce the eddy current loss by reducing the plate thickness, but from the manufacturing standpoint, there is a problem in that secondary thinning becomes difficult to control as the thickness becomes thinner. Since the cost at the time of manufacturing increases, thick materials are preferably used if the iron loss values are equal.

JP-A-57-9419 describes that it is effective to reduce the secondary recrystallized grain size as a means of reducing iron loss. However, when the secondary recrystallized grain size is reduced, there is a problem that the degree of azimuthal integration is reduced and it is difficult to obtain a high magnetic flux density.

The relationship between the effect of the film tension and the magnetic flux density of the grain-oriented electrical steel sheet is described in J. Am. Appl. Phys. , Vol. 4
1. no. 7. As pointed out in p2981-2984 (1970), it is known that the higher the value of the magnetic flux density B8, the greater the effect of reducing iron loss. Further, a method for reducing iron loss by magnetic domain refining is disclosed in JP-A-58-5968,
As described in JP-A-58-26405, it is known that the higher the magnetic flux density of the plain material before the magnetic domain refining process, the greater the effect.

Attempts to reduce iron loss in this way include electrical resistivity, plate thickness, grain size,
Since the improvement of purity, internal strain, etc. is approaching the limit in the conventional technology, by improving the degree of integration of the secondary recrystallization orientation and increasing the magnetic flux density, the effect of the film tension and the effect of domain segmentation can be improved. It has become important to reduce iron loss by further improving.

The role of the inhibitor is important as a factor for stably expressing secondary recrystallization, increasing the degree of azimuth integration, and improving magnetic flux density. For this purpose, conventionally, MnS, AlN, MnSe, etc. have been used as inhibitors.

Conventional methods for manufacturing grain-oriented electrical steel sheets are roughly classified into three types depending on the type of inhibitor used for controlling the secondary recrystallization orientation.

First of all, M.I. F. The method disclosed by Littmann in Japanese Patent Publication No. 30-3651 is a method in which MnS is used as an inhibitor and is produced by a double cold rolling method. Next, by the manufacturing method disclosed in Japanese Patent Publication No. 40-15644 by Taguchi, Sakakura et al. Using AlN as an inhibitor in addition to MnS, the magnetic flux density of the grain-oriented electrical steel sheet is improved to about 1.92T, It made a great contribution to energy saving by improving magnetic properties. Third, there is a method in which MnS and Sb or MnS, or MnSe and Sb, disclosed in JP-B-51-13469, are manufactured by a double cold rolling method.

However, in these conventional manufacturing methods, high-temperature slab heating is required for controlling inhibitor precipitation in order to obtain a good magnetic flux density. That is, at the time of slab heating, the precipitate constituting the inhibitor is once turned into a solution, and this is subjected to a hot rolling process or a process disclosed in JP-B-46-2382.
As disclosed in Japanese Patent Publication No. 0, it is necessary to precipitate finely during annealing of a hot-rolled sheet. Slag occurs when this high-temperature slab is heated, and the treatment is a problem.Furthermore, component adjustment in the steel making stage and the characteristics of the product are almost determined in the hot rolling stage, and adjustment of the magnetic characteristics in the subsequent process And there remains a problem in the flexibility of the manufacturing process.

Japanese Patent Publication No. 6-86631 discloses a means for solving the problem of the production of grain-oriented electrical steel sheets by the conventional high-temperature slab heating method. A method is disclosed that includes the step of forming an inhibitor by nitridation until the onset of crystallization.

[0016] According to this method, the properties are determined substantially at the time of the component adjustment in the conventional steel making stage and the hot rolling stage, and it is possible to obtain the inhibitor which was difficult to adjust in the subsequent process, and to obtain the inhibitor at a high temperature. Not only did the problem of slab heating be solved, but the improvement of magnetic properties has brought a certain advance in the manufacturing method of grain-oriented electrical steel sheets.

However, the market demands for energy savings in recent years are even more stringent. In order to save energy consumption and contribute to environmental improvement, the magnetic steel sheet used as an iron core has an increased magnetic flux density. The demand for reduction of iron loss is increasing.

Unlike electromagnetic steel plates used for rotating machines,
Since the grain-oriented electrical steel sheets used in applications such as transformers are always used in an energized state, the importance of loss reduction is very important from the viewpoint of operation rate. For this reason, the energy saving effect by the improvement of the magnetic properties is very large,
In order to increase the efficiency of the iron core while reducing costs as much as possible, the supply of products with higher magnetic flux density was required.

[0019]

SUMMARY OF THE INVENTION The present invention meets the demands of the market in recent years and solves the problems in the prior art for manufacturing grain-oriented electrical steel sheets while producing grain-oriented electrical steel sheets having a higher magnetic flux density. It is intended to provide a method.

[0020]

According to the present invention, 0.025% ≦ C ≦ 0.075%, 2.5% ≦ Si ≦ 4.5%, S ≦ 0.015%, and 0.025% ≦ C ≦ 0.075% by weight. A slab containing 010% ≦ sol-Al ≦ 0.050%, 0.0010% ≦ N ≦ 0.0120%, 0.050% ≦ Mn ≦ 0.45%, and the balance being Fe and inevitable impurities, After being heated to a temperature of 1200 ° C. or less, hot rolling is performed, hot-rolled sheet annealing is performed, and a final rolling reduction of 80% or more is performed by one or two or more rollings including an intermediate annealing. In the method for producing a grain-oriented electrical steel sheet in which the steel sheet is subjected to nitriding treatment before the start of the secondary recrystallization of annealing, the average friction coefficient between the hot-rolled roll and the steel sheet during finish hot rolling is set to 0.
This is a method for producing a grain-oriented electrical steel sheet having a high magnetic flux density, characterized by being 25 or less. At this time, 0.5 to 20% of fats and oils are mixed in the form of an emulsion into the hot roll cooling water as a lubricant at the time of finishing hot rolling, and the sheet bar after rough rolling is joined to the preceding sheet bar before finishing hot rolling. Then, it is preferable that two or more of the sheet bars are continuously subjected to hot rolling for finishing.

The inventor of the present invention has another problem to be studied in manufacturing other than the inhibitor control technique, which has been the main focus of the conventional study, as a method of manufacturing a grain-oriented electrical steel sheet having a high magnetic flux density by forming a hot-rolled sheet for controlling hot-rolling conditions. As a result of studying, the lubrication conditions were controlled during the hot-rolling process, and the low-friction rolling with a friction coefficient of 0.25 or less between the work roll of the finishing hot-rolling machine and the steel sheet was performed. Have been found to be improved, leading to the invention.

Further, from the viewpoint of operation, in order to stably perform the low friction rolling 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 also found that it was effective to carry out.

Hereinafter, the present invention will be described in detail.

First, the components will be described.

The Si content greatly affects the iron loss characteristics through the specific resistance of the magnetic steel sheet, but if it is less than 2.5%, the specific resistance is small and the eddy current loss increases. On the other hand, if the content exceeds 4.5%, the workability deteriorates, so that production and product processing become difficult.

When the C content is less than 0.025%, the secondary recrystallization becomes unstable and the magnetic flux density is remarkably reduced. On the other hand, if it exceeds 0.075%, the time required for decarburization annealing becomes too long, which is uneconomical.

The regulation of the S content is one of the differences between the conventional technology for manufacturing grain-oriented electrical steel sheets and the present invention. Because
In the present invention, the inhibitor is mainly (Al, S
i) Since N is used, MnS is not particularly required and is rather detrimental to magnetic properties. Therefore, the S content is 0.01
5% or less, preferably 0.007% or less.

Sol. Although Al combines with N to form AlN, which is an inhibitor, in the present invention, nitriding is performed after decarburizing annealing until the start of secondary recrystallization (Al, S).
i) Since N is formed, a certain amount of free AlN is required. For this reason, 0.010% or more and 0.050% or less are added.

N needs to be 0.0120% or less. If it exceeds this, blisters called blisters are generated on the surface of the steel sheet, and it becomes difficult to adjust the primary recrystallization structure. On the other hand, if the N content is less than 0.0010%, it becomes difficult to develop secondary recrystallization, so the N content is set to 0.0010% or more.

If the Mn content exceeds 0.45%, the magnetic flux density of the product is reduced, while if it is less than 0.050%, the secondary recrystallization becomes unstable, so the Mn content is 0.050%
At least 0.45%.

It should be noted that the inclusion of trace amounts of Sn, Cu, Cr, P and Ti in steel for stabilization of secondary recrystallization and other purposes does not impair the effects of the present invention.

Next, the slab processing of the above components will be described.

The electromagnetic steel slab is obtained by melting steel in a melting furnace such as a converter or an electric furnace, subjecting the steel to vacuum degassing if necessary, and then performing continuous casting or slab rolling after ingot making. Can be

Thereafter, slab heating is performed prior to hot rolling. In the present invention, the heating temperature of the slab is 120
As a low temperature of 0 ° C. or less, the heat source unit is saved, and the AlN in the steel is not completely dissolved to form an incomplete solid solution state.

This slab is hot-rolled into a hot-rolled sheet having 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, or the fat or oil is added to the roll by a special nozzle. Spray. If necessary, a surfactant may be added 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 finish hot rolling is 0.5% to 20% by volume ratio. If the amount of fat or oil in the roll cooling water is less than 0.5%, the reduction of the friction coefficient due to lubrication is not sufficient, and if it exceeds 20%, the effect is saturated and uneconomical.

The relationship between the friction coefficient of the finished hot rolling and the product magnetic flux density will be described based on experimental results.

C: 0.056%, Si: 3.2%, M
n: 0.12%, S: 0.007%, sol-Al:
0.027%, N: 0.0080%, Cr: 0.12%
Is heated to 1150 ° C. and then 60 m by a rough rolling mill.
m-thick sheet bar. Thereafter, the sheet bar was formed into a hot-rolled sheet having a thickness of 2.3 mm by a finishing mill. At that time, the lubricating oil was mixed in the emulsion state into the cooling water of the finishing hot rolling machine to change the friction coefficient between the steel sheet and the finishing hot rolling roll. The friction coefficient was obtained by calculation from the actually measured advanced rate, and the average of the calculated values of the respective stands was used.

1120 ° C. × 2 minutes + 90
A hot rolled sheet is annealed at 0 ° C. × 2 minutes, cooled in hot water at 100 ° C., then pickled, cold rolled to 0.30 mm, and then
Decarburization annealing was performed at 0 ° C. for 120 seconds. Next, nitriding treatment is performed at 750 ° C. × 3 in a hydrogen or nitrogen gas containing 1% of ammonia.
Performed for 0 seconds. Thereafter, an annealing separator in which TiO ₂ was mixed with MgO was applied, and finish annealing was performed at 1200 ° C. for 20 hours. FIG. 1 shows the relationship between the coefficient of friction between the steel sheet and the hot rolling roll during finish hot rolling and the product magnetic flux density B8.

FIG. 1 shows that the magnetic flux density is improved when the average of the friction coefficients of all the stands between the steel sheet and the hot rolling roll at the time of finishing hot rolling is 0.25 or less.

It is not clear why performing the finishing hot rolling in a highly lubricated state has the effect of improving the magnetic flux density of the present invention. However, the texture of the surface layer of the hot rolled steel sheet changes due to the decrease in the coefficient of friction. The inventor speculates that the control of the orientation serving as the nucleus of the next recrystallized grain may be the cause.

The lower limit of the friction coefficient is not particularly defined. However, if the friction coefficient is excessively small, a slip occurs between the steel sheet and the roll and rolling cannot be performed. The coefficient of friction is preferably 0.05 or more.

In the case where the finishing hot rolling is performed at a low friction rate as in the present invention, the sheet bar does not bite properly when the sheet bar is bitten into the finishing hot rolling machine, or the roll during the finishing hot rolling is not rolled. Slip occurs between the steel sheets, which significantly shortens the life of the rolling rolls and may cause deep rolling flaws 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 stably operating, 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 subject the bars to finish hot rolling continuously.

[0044] In the process after hot rolling, hot rolled sheet annealing may be performed for the purpose of controlling precipitates. After pickling, cold rolling is performed once or twice or more with intermediate annealing to obtain a final sheet thickness. If the final rolling reduction is less than 80%, the value of the magnetic flux density B8 decreases. The rate should be 80% or more. Although the properties are slightly inferior, the hot rolled sheet annealing may be omitted for cost reduction. In order to reduce the crystal grain size of the final product and reduce iron loss, the final thickness may be obtained by performing rolling twice or more including intermediate annealing.

Next, decarburizing annealing is performed in wet hydrogen or a mixed gas of wet hydrogen and nitrogen. The temperature at this time is not particularly defined in the present invention, but is preferably from 800 ° C to 900 ° C.

Next, an annealing separator is applied and finish annealing is performed, and secondary recrystallization and subsequent purification are performed. For this reason, the annealing temperature is usually set to a high temperature of 1100 ° C to 1200 ° C. The purification annealing after the completion of the secondary recrystallization is performed in a hydrogen atmosphere.

In the present invention, after the completion of the decarburizing annealing, the steel sheet is subjected to a nitriding treatment until the start of the secondary recrystallization of the finish annealing to form fine (Al, Si) N in the steel sheet. As an embodiment thereof, nitriding is performed in a gas atmosphere having a nitriding ability after soaking during decarburizing annealing, or N 2 provided separately after decarburizing annealing.
Nitriding by passing through a heat treatment furnace having an atmosphere such as H ₃ or MnN, C
An appropriate amount of rN or the like may be blended, or a gas such as NH _{3 having} nitriding ability may be contained in the atmosphere during the temperature raising process of the finish annealing. Further, nitriding may be performed by a combination of the above methods.

[0048]

Example 1 An electromagnetic steel slab containing the components shown in Table 1 and consisting of the balance of Fe and unavoidable impurities was heated to 1150 ° C., and then formed into a sheet bar having a thickness of 60 mm by a rough rolling mill. Thereafter, the sheet bar was formed into a hot-rolled sheet having a thickness of 2.1 mm by a finishing mill. At that time, the lubricating oil was mixed in the emulsion state into the cooling water of the finishing hot rolling machine to change the friction coefficient between the steel sheet and the finishing hot rolling roll. The friction coefficient was obtained by calculation from the actually measured advanced rate, and the average of the calculated values of the respective stands was used.

[0049]

[Table 1]

The obtained hot rolled sheet was heated at 1120 ° C. × 2 minutes + 90
A hot rolled sheet is annealed at 0 ° C. × 2 minutes, cooled in hot water at 100 ° C., then pickled, cold rolled to 0.23 mm, and then
Decarburization annealing at 0 ° C. for 90 seconds was performed in a wet hydrogen and nitrogen atmosphere at a dew point of 58 ° C. Next, a nitriding treatment was performed at 750 ° C. for 30 seconds in a hydrogen or nitrogen gas containing 1% of ammonia. Then, an annealing separator mixed with TiO ₂ in MgO is applied, and 12
Finish annealing was performed at 00 ° C. × 20 hours.

Table 2 shows the relationship between the average coefficient of friction during hot rolling and the magnetic properties after finish annealing. From Table 2, it can be seen that the magnetic flux density is high when the average friction coefficient between the hot-rolled roll and the steel sheet at the time of finish hot rolling is 0.25 or less.

[0052]

[Table 2]

[0053]

Example 2 An electromagnetic steel slab containing the components shown in Table 3 and consisting of the balance Fe and unavoidable impurities was heated to 1150 ° C., and then formed into a sheet bar having a thickness of 65 mm by a rough rolling mill. Thereafter, the sheet bar was formed into a hot-rolled sheet having a thickness of 2.3 mm by a finishing mill. At that time, the lubricating oil was mixed in the emulsion state into the cooling water of the finishing hot rolling machine to change the friction coefficient between the steel sheet and the finishing hot rolling roll. The friction coefficient was obtained by calculation from the actually measured advanced rate, and the average of the calculated values of the respective stands was used.

[0054]

[Table 3]

The obtained hot rolled sheet was subjected to 1120 ° C. × 2 and a half minutes + 9
A hot rolled sheet is annealed at 00 ° C. for 2 minutes, cooled in hot water at 100 ° C., then pickled, cold rolled to 0.30 mm, and then
Decarburization annealing was performed at 30 ° C. for 120 seconds. Next, nitriding treatment is performed at 750 ° C. in hydrogen and nitrogen gas containing 1% of ammonia.
Performed for 30 seconds. Thereafter, an annealing separator in which TiO ₂ was mixed with MgO was applied, and finish annealing was performed at 1200 ° C. for 20 hours.

Table 4 shows the relationship between the average coefficient of friction during hot rolling and the magnetic properties after finish annealing. Table 4 shows that the magnetic flux density is high when 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.

[0057]

[Table 4]

[0058]

According to the present invention, it is possible to manufacture a grain-oriented electrical steel sheet having a high magnetic flux density and excellent magnetic properties.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the average friction coefficient of a steel sheet and a hot-rolled roll at the time of finish hot rolling and the magnetic flux density of a product.

Claims (3)

[Claims] 1. In% by weight, 0.025% ≦ C ≦ 0.075%, 2.5% ≦ Si ≦ 4.5%, S ≦ 0.015%, 0.010% ≦ sol-Al ≦ 0 A slab containing 0.050%, 0.0010% ≦ N ≦ 0.0120%, 0.050% ≦ Mn ≦ 0.45%, and the balance consisting of Fe and unavoidable impurities was heated to a temperature of 1200 ° C. or less. After hot-rolling, hot-rolled sheet annealing is applied, and the final rolling reduction is 80% or more by rolling once or twice or more including intermediate annealing. Then, after the completion of decarburizing annealing, until the start of secondary recrystallization of finish annealing A method for producing a grain-oriented electrical steel sheet, wherein a steel sheet is subjected to nitriding treatment during a hot rolling process, wherein an average coefficient of friction between the hot-rolled roll and the steel sheet at the time of finish hot rolling is set to 0.25 or less. Manufacturing method of grain-oriented electrical steel sheet. 2. A grain-oriented electrical steel sheet having a high magnetic flux density according to claim 1, wherein 0.5 to 20% of fats and oils are mixed in a hot-roll roll cooling water as a lubricant at the time of finishing hot rolling in an emulsion state. Manufacturing method. 3. The sheet bar after the rough rolling is joined to a preceding sheet bar before the hot rolling, and two or more sheet bars are continuously subjected to the hot rolling. A method for producing a grain-oriented electrical steel sheet having a high magnetic flux density as described.