JPH1096029A - 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, 0.035-0.10% C, 2.5-4.5% Si, 0.010-0.040% S, 0.010-0.050% sol-Al, 0.0030-0.0150% N, 0.020-0.40% Mn, and the balance Fe with inevitable impurities, is heated to >=1280 deg.C, hot-rolled, and subjected, before cold rolling, to hot rolled plate annealing and to cooling, and the resultant steel plate is rolled once or rolled two or more times while process-annealed between the rolling stages to >=80% final rolling rate, and, after decarburizing annealing and application of a separation agent at annealing, secondary recrystallization and purification are carried out by means of 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 tie 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 workability of the manufacturing process and products 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, 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, the magnetic flux density of the grain-oriented electrical steel sheet is improved to 1.870 T or more by a manufacturing method disclosed in Taguchi and Sakakura et al. In Japanese Patent Publication No. 40-15644 using AlN as an inhibitor in addition to MnS. It made a great contribution to energy saving by improving characteristics. Third,
Japanese Patent Publication No. 51-13469 discloses a method in which MnS and Sb or MnS or MnSe and Sb are used and are produced by a double cold rolling method.

In these conventional manufacturing methods, in order to obtain a good magnetic flux density, for the purpose of controlling the precipitation of the inhibitor, the precipitate constituting the inhibitor is once dissolved in solution by high-temperature slab heating, and this is subjected to a hot rolling process. Alternatively, as disclosed in JP-B-46-23820, it is necessary to precipitate finely during hot-rolled sheet annealing. As described above, in the conventional method, the properties of the product are almost determined at the stage of the component adjustment at the steel making stage and at the stage of hot rolling. Therefore, it is an important issue to establish the stability of the material building in the upper process.

For this purpose, in the hot rolling process of a grain-oriented electrical steel sheet, from the viewpoint of more stably controlling precipitates, use of a heat retaining cover for a sheet bar after rough rolling, cooling on a run-out table. A great deal of effort has been put into controlling the precipitates in the longitudinal direction of the coil by measures such as control. However, the variation of the hot rolling conditions of the grain-oriented electrical steel sheet still has a large effect on the magnetic properties of the product, and there remains a problem in the stability of the hot rolling conditions.

Further, there is a severe demand in the market for energy saving these days, and in order to save energy consumption and contribute to environmental improvement, an electromagnetic steel sheet used as an iron core has an increased magnetic flux density and an increased iron loss. There is an increasing demand for reduction.

Unlike electromagnetic steel sheets 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.

The present inventor has developed a technique for reducing the influence of the hot rolling conditions of the grain-oriented electrical steel sheet by the high-temperature slab heating on the magnetic properties of the product and stably producing the grain-oriented electrical steel sheet. For the purpose, the hot rolling process was studied.

Furthermore, the inventor of the present invention has been trying to meet the severe demands of consumers for energy saving in recent years, and to overcome the limitations of the technology for achieving low iron loss which is in a deadlock state by the improvement of the prior art. The study was repeated to develop a method.

[0020]

SUMMARY OF THE INVENTION The present invention meets the demands of the market in recent years and solves the problem of the stability of the magnetic properties of a product to the hot rolling conditions in the production of grain-oriented electrical steel sheets by high-temperature slab heating in the prior art. It is an object of the present invention to provide a method for manufacturing a grain-oriented electrical steel sheet having a higher magnetic flux density while solving the problems.

[0021]

According to the present invention, 0.035% ≦ C ≦ 0.10%, 2.5% ≦ Si ≦ 4.5%, 0.010% ≦ S ≦ 0% by weight. 040%, 0.010% ≦ sol-Al ≦ 0.050%, 0.0030% ≦ N ≦ 0.0150%, 0.020% ≦ Mn ≦ 0.40%, with the balance being Fe and unavoidable impurities Is heated to a temperature of 1280 ° C. or more, hot rolled, subjected to hot rolled sheet annealing and cooled before cold rolling, and subjected to one or two or more rollings including an intermediate annealing to a final rolling reduction of 80%. Above
Next, in a method for producing a grain-oriented electrical steel sheet in which a decarburizing annealing and annealing separator is applied and secondary recrystallization and purification are performed by finish annealing, the average friction coefficient between the hot-rolled roll and the steel sheet during the finish hot rolling is set to 0. .25 or less, which is a method for producing a grain-oriented electrical steel sheet having a high magnetic flux density. At this time, 0.5 to 2 times as much
It is preferable to mix 0% of fats and oils in an emulsion state, to join the sheet bar after rough rolling to the preceding sheet bar before finish hot rolling, and to continuously apply two or more sheet bars to finish hot rolling. .

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. Was found to be improved, and the present invention was achieved.

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 two or more sheet bars are joined. It has been found that it is effective to continuously provide hot rolling for finishing.

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 0.035%, secondary recrystallization becomes unstable and the magnetic flux density is remarkably reduced. On the other hand, if it exceeds 0.10%, the time required for decarburization annealing becomes too long, which is uneconomical.

If the S content is less than 0.010%, the amount of inhibitor deposited becomes insufficient, and secondary recrystallization becomes unstable. On the other hand, if the content exceeds 0.040%, the precipitate is excessively coarsened, the inhibitor effect is impaired, and the magnetic flux density is reduced.

Sol. Al combines with N to form AlN, an inhibitor. If the content is less than 0.010%, the amount of inhibitor precipitation becomes insufficient, and secondary recrystallization becomes unstable. Therefore, the content is set to 0.010% or more. On the other hand, 0.05
If the content exceeds 0%, the precipitation state becomes coarse, the inhibitor effect is impaired, and the magnetic flux density is reduced.

N needs to be not less than 0.0030% and not more than 0.0150%. If it exceeds 0.0150%, blisters called “blisters” occur on the steel sheet surface, and it becomes difficult to adjust the primary recrystallization structure. On the other hand, if it is less than 0.0030%, it becomes difficult to develop secondary recrystallization, so the N content is 0.0030%.
Above.

When the Mn content exceeds 0.40%, the magnetic flux density of the product is reduced, while when it is less than 0.020%, the secondary recrystallization becomes unstable.
At least 0.40%.

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

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

The electromagnetic steel slab is obtained by smelting 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 128.
Main inhibitor MnS, AlN at 0 ° C or higher
It is important to re-dissolve in steel. 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: 0.075%, Si: 3.25%, M
n: 0.08%, S: 0.024%, sol-Al:
0.027%, N: 0.0090%, balance Fe
And 1340 electromagnetic steel slabs consisting of unavoidable impurities
After heating to ° C., a roughing mill was used to form a 75 mm thick sheet bar. Thereafter, the sheet bar is subjected to 2.
It was a hot-rolled sheet having a thickness of 3 mm. 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.

The obtained hot-rolled sheet was subjected to hot-rolled sheet annealing at 1100 ° C. × 2.5 minutes, cooled in hot water at 100 ° C., then pickled, cold-rolled to 0.30 mm, and then at 830 ° C. for 120 seconds. Was subjected to decarburization annealing. Thereafter, an annealing separator containing MgO as a main component was applied, and finish annealing was performed at 1200 ° C. for 20 hours. FIG. 1 shows the relationship between the average coefficient of friction between the steel sheet and the hot-rolled roll at the time of 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.

Although the detailed reason why performing the finish hot rolling in a highly lubricated state brings about the effect of improving the magnetic flux density of the present invention is not clear, Met. Sci. vol. 1
8, No. 2, page 57-65 (1984), since the deformation structure of the surface layer of the steel sheet plays an important role in the nucleation of secondary recrystallization, the crystal structure of the surface layer of the hot-rolled steel sheet is reduced due to the decrease in the coefficient of friction. The inventors presume that the cause is that the texture changes and, as a result, the orientation of the nuclei of the secondary recrystallized grains can be controlled.

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 the pickling, the final thickness is obtained by cold rolling once or twice or more including intermediate annealing. If the final cold rolling reduction is less than 80%, a high magnetic flux density B8 cannot be obtained, so the final cold rolling reduction is 80%.
Above. 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.

[0047]

EXAMPLE 1 An electromagnetic steel slab containing the components shown in Table 1 and consisting of the balance Fe and unavoidable impurities was heated to 1320 ° C. and formed into a 70 mm-thick sheet bar 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.

[0048]

[Table 1]

The obtained hot rolled sheet was annealed at 1100 ° C. for 2 minutes, cooled in hot water at 100 ° C., then pickled, cold rolled to 0.23 mm, and then heated at 830 ° C. for 90 seconds. The decarburization annealing was performed in a wet hydrogen and nitrogen atmosphere at a dew point of 50 ° C.
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 2 shows the relationship between the average friction coefficient at the time of finish 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.

[0051]

[Table 2]

[0052]

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 1330 ° C., and then formed into a 75 mm-thick sheet bar 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.

[0053]

[Table 3]

The obtained hot-rolled sheet was subjected to hot-rolled sheet annealing at 1100 ° C. × 2 and a half minutes, cooled in hot water at 100 ° C., then pickled and cold-rolled to 0.30 mm, and then at 830 ° C. for 120 seconds. Was carried out in a wet hydrogen and nitrogen atmosphere at a dew point of 50 ° C. 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.

[0056]

[Table 4]

[0057]

Example 3 An electromagnetic steel slab containing the components shown in Table 5 and consisting of the balance Fe and unavoidable impurities was heated to 1340 ° C., and then formed into a 70 mm-thick sheet bar 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.

[0058]

[Table 5]

The obtained hot-rolled sheet was subjected to hot-rolled sheet annealing at 1100 ° C. × 2 minutes, cooled in hot water at 100 ° C., then pickled, cold-rolled to 0.23 mm, and then heated at 830 ° C. for 90 seconds. The decarburization annealing was performed in a wet hydrogen and nitrogen atmosphere at a dew point of 50 ° C.
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 6 shows the relationship between the average friction coefficient at the time of finish hot rolling and the magnetic properties after finish annealing. Table 6 shows that the magnetic flux density is high when the average friction coefficient between the hot-rolled roll and the steel sheet during the finish hot-rolling is 0.25 or less.

[0061]

[Table 6]

[0062]

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 view showing a relationship between an average coefficient of friction between a steel sheet and a hot rolling roll during finish hot rolling and a magnetic flux density of a product.

Claims (3)

[Claims] 1. In% by weight, 0.035% ≦ C ≦ 0.10%, 2.5% ≦ Si ≦ 4.5%, 0.010% ≦ S ≦ 0.040%, 0.010% ≦ A slab containing sol-Al ≦ 0.050%, 0.0030% ≦ N ≦ 0.0150%, 0.020% ≦ Mn ≦ 0.40%, the balance being Fe and unavoidable impurities is 1280 ° C. or more. After hot-rolling after heating to a temperature of not more than 1, hot-rolled sheet annealing is performed before cold rolling and cooled, and a final rolling reduction of 80% or more is achieved by rolling once or twice or more with intermediate annealing,
Next, in a method for producing a grain-oriented electrical steel sheet in which a decarburizing annealing and annealing separator is applied and subjected to secondary recrystallization and purification by finish annealing, the average friction coefficient between the hot-rolled roll and the steel sheet during the finish hot rolling is reduced to 0. 25. A method for producing a grain-oriented electrical steel sheet having a high magnetic flux density, characterized by being at most 25. 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.