JPH1096030A - Manufacturing method of grain-oriented electrical steel sheet with high magnetic flux density - Google Patents

Abstract

(57) [Problem] To provide a method for manufacturing a grain-oriented electrical steel sheet having a high magnetic flux density. SOLUTION: 0.035% ≦ C ≦ 0% by weight in steel.
10%, 2.5% ≦ Si ≦ 4.5%, 0.010% ≦ S
≦ 0.040%, 0.010% ≦ sol-Al ≦ 0.0
50%, 0.0030% ≦ N ≦ 0.0150%, 0.0
A slab containing 20% ≦ Mn ≦ 0.40%, the balance consisting of 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, Manufacture of grain-oriented electrical steel sheet in which rolling is performed once or twice or more with intermediate annealing to a final rolling reduction of 80% or more, followed by decarburizing annealing, applying an annealing separator, and performing secondary recrystallization and purification by finish annealing. In the method, during finish hot rolling,
In the final pass or the final two passes, the strain rate is 150 s ^-1 or more and the tension between the final two stands is 1.5 kgf / mm ^2.
The finishing hot rolling is performed as described above.

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, 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 such a grain-oriented electrical steel sheet on the magnetic properties of a product and stably producing a grain-oriented electrical steel sheet.
In order to meet the demanding demands of consumers for energy saving in recent years, in order to overcome the limitation of low iron loss attainment technology which is in a dead end with the improvement by the conventional technology, the study focused on the finish hot rolling technology.

In finishing hot rolling of grain-oriented electrical steel sheets, higher precision of the product thickness is required as compared with thin steel sheets which are subjected to press forming of outer plates of automobiles and deep drawing of cans and the like. This is because the grain-oriented electrical steel sheets are laminated and used as an iron core, so that a slight deviation in the thickness of the product greatly affects the dimensional accuracy of the iron core. For this reason, strict control is required for the thickness accuracy of the product. For this purpose, strict control of the thickness is performed not only for cold rolling but also for hot rolling. Therefore, in the vicinity of the final pass of the finish hot rolling, the rolling reduction is reduced to light shape reduction for shape adjustment, and the strain rate is usually small.Therefore, an attempt to examine the conditions of the finish hot rolling from the viewpoint of improving magnetic properties has been made. Traditionally hardly ever.

[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 the product in relation to the hot rolling conditions in the production of grain-oriented electrical steel sheets in the prior art. It is another object of the present invention to provide a method for producing a grain-oriented electrical steel sheet having a high magnetic flux density.

[0021]

SUMMARY OF THE INVENTION The present invention provides a method for producing steel by weight
0.035% ≦ C ≦ 0.10%, 2.5% ≦ Si ≦ 4.5%, 0.010% ≦ S ≦ 0.040%, 0.010% ≦ sol-Al ≦ 0.050% A slab containing 0.0030% ≦ N ≦ 0.0150%, 0.020% ≦ Mn ≦ 0.40%, the balance being Fe and unavoidable impurities is heated to a temperature of 1280 ° C. or higher, and then hot-rolled. And, before cold rolling, hot-rolled sheet annealing is applied and cooled, and a final rolling reduction of 80% or more is performed by rolling once or twice or more including intermediate annealing,
Next, in a method for producing a grain-oriented electrical steel sheet in which a decarburized annealing and annealing separator is applied and subjected to secondary recrystallization and purification by finish annealing, the final pass or final 2
A method for producing a grain ^- oriented electrical steel sheet having a high magnetic flux density, wherein finishing hot rolling is performed at a strain rate of 150 s ^-1 or more and a tension between two final stands of 1.5 kgf / mm ² or more. At this time, it is preferable that the rough-rolled sheet bar is joined to a preceding sheet bar before the finish hot rolling, and the sheet bar is continuously subjected to the finish hot rolling.

The inventor studied 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 subject to be studied in manufacturing other than the inhibitor control technique. As described above, strict thickness control is required for grain-oriented electrical steel sheets not only in cold-rolled but also hot-rolled sheets, so in the vicinity of the final pass of hot rolling, the rolling reduction is reduced for shape adjustment and light reduction is performed. Usually the strain rate was also low. As a result of reviewing such operating conditions of the prior art, the inventor has found that during finishing hot rolling, on the final side of the rolling pass, while carefully controlling the strain rate, and also controlling the tension between the stands. As a result, the present inventors have found that it is possible to produce a grain-oriented electrical steel sheet having a high magnetic flux density in a product and a low iron loss, and have led to the invention.

Further, from the viewpoint of operation, in order to stably perform high-speed rolling under tension load as in the present invention,
The sheet bar after rough rolling is joined to the preceding sheet bar,
It has also been found that it is effective to continuously provide two or more sheet bars for finish hot rolling.

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. Therefore, the Si content is set to be 2.5% or more and 4.5% or less.

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.

The relationship between the finish hot rolling conditions and the product magnetic flux density will be described based on experimental results.

Strain speed of final pass during finishing hot rolling and final 2
The following experiment was conducted to investigate the influence of the inter-stand tension of the pass on the magnetic properties of the product.

C: 0.079%, Si: 3.24%, M
n: 0.09%, S: 0.023%, sol-Al:
0.028%, N: 0.0088%, 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. The test was performed by changing the pass schedule in order to change the strain rate of the final pass during the finish hot rolling and the tension between stands in the final two passes.

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.

The tension between the last two stands is set to 3.1 kgf /
FIG. 1 shows the dependence of the product magnetic flux density on the strain rate of the final pass when hot rolling is performed while the thickness is kept at ² mm. FIG.
According to the above, at a strain rate of 150 s ^-1 or more, the product magnetic flux density B8
Is found to rise.

The calculation of the strain rate is performed by the following equation (1). Here, r is {Drop rate (%) / 100}, n
Is the number of rotations of the roll (rpm), and R is the radius of the rolling roll (m
m) and H0 are the thickness (mm) before rolling.

[0042]

## EQU1 ## Distortion rate = (2πn / (60r ^0.5 )) (R /
H0) ^0.5 ln (1 / (1-r))

FIG. 2 shows the relationship between the tension between the last two stands and the magnetic flux density of the product when the hot rolling is performed while maintaining the strain rate of the final pass at 320 s ^-1 . As shown in FIG. 2, the tension between the last two stands of the hot-rolled finish is 1.5 kgf.
/ Mm ² or more, the product magnetic flux density increases.

As described above, the inventor has succeeded in developing a means for improving the magnetic properties of the grain-oriented electrical steel sheet by setting the strain rate in the final pass and the tension between stands in the final two passes under appropriate conditions. did.

As shown in the above experiments, it is sufficient that the strain rate in the final pass of the finish hot rolling is 150 s ^-1 or more and the tension between stands in the last two passes is 1.5 kgf / mm ² or more. There is no particular upper limit for these values. This is because the upper limit of the strain rate is naturally determined from the equipment capacity of the hot rolling mill and the sheet passing property in the lower process. In other words, the strain rate is determined by the rolling speed, the diameter of the hot-rolled roll, and the amount of reduction. However, the rolling speed and the amount of reduction are naturally determined by the limitations of the capacity of the hot-rolling machine and the thickness of the hot-rolled sheet in the post-process line. The limit is about 400 s ^-1 .

On the other hand, with respect to the final tension between the two stands, the tension between the stands that can be passed through is naturally determined from the rolling reaction force and the friction coefficient required for rolling down the steel sheet.

When the finishing hot rolling is performed at a high speed and under a tension as in the present invention, a slip occurs between the roll and the steel sheet during the finishing hot rolling, so that the life of the rolling roll is remarkably shortened and the surface layer of the steel sheet is reduced. May cause a deep rolling flaw. As a method for solving such problems and stably operating, a sheet bar after rough rolling is joined to a preceding sheet bar before finish hot rolling, and the sheet bar is continuously subjected to finish hot rolling. Is particularly effective.

In the process after hot rolling, annealing of a hot rolled sheet may be performed for the purpose of controlling precipitates. High B after pickling
In order to obtain No. 8, it is preferable to make the final sheet thickness by cold rolling at a high rolling ratio of 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.

[0051]

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 this time, in order to easily control the tension between the stands, the sheet bar was joined to the preceding sheet bar, and the finish hot rolling was continuously performed. The tension between the final two stands of the hot-rolled finish is 2.8 kgf / mm ² to 3.1 kg.
Rolling was performed while maintaining f / mm ² .

[0052]

[Table 1]

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 2 shows the relationship between the strain rate at the final stand at the time of finish hot rolling and the magnetic properties after finish annealing. From Table 2,
If the strain rate of the final stand at the time of finish hot rolling is increased to 150 s ⁻¹ or more, it is possible to obtain a grain ^- oriented electrical steel sheet having a high magnetic flux density and a low iron loss value and excellent magnetic properties.

[0055]

[Table 2]

[0056]

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 speed of distortion of the finish hot rolling final pass is carefully rolling speed since biting so that 150s ^-1 or more, and controls the pass schedule was the strain rate of the final pass over the coils overall length 250～270S ^-1 . Further, in order to prevent a slip from being generated 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.

[0057]

[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, 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
FIG. 11 also shows the results of magnetic measurement of the present invention and the comparative example.

[0059]

[Table 4]

By increasing the tension between the last two stands during finishing hot rolling to 1.5 kgf / mm ² or more, a grain-oriented electrical steel sheet having a high magnetic flux density and a low iron loss value and excellent magnetic properties can be obtained. It is possible to get.

[0061]

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. Rolling was performed while maintaining the tension between the final two stands of the hot-rolled finish at 2.7 kgf / mm ² to 3.0 kgf / mm ² .

[0062]

[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 also shows the components of the present invention and comparative examples and the results of magnetic measurement.

[0064]

[Table 6]

By increasing the strain rate of the final stand during hot-rolling to 150 s ^-1 or more, it is possible to obtain a grain ^- oriented electrical steel sheet having a high magnetic flux density and a low iron loss value and excellent magnetic properties. It is.

[0066]

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 strain speed of a final stand and the product magnetic flux density during hot rolling in finishing.

FIG. 2 is a diagram showing the relationship between the tension between the last two stands and the product magnetic flux density during hot rolling.

Claims (2)

[Claims] 1. In steel, 0.035% ≦ C ≦ 0.10%, 2.5% ≦ Si ≦ 4.5%, 0.010% ≦ S ≦ 0.040%, 0.010% by weight in steel % ≦ sol-Al ≦ 0.050%, 0.0030% ≦ N ≦ 0.0150%, 0.020% ≦ Mn ≦ 0.40%, and a balance of 1280 consisting of Fe and unavoidable impurities. After hot-rolling after heating to a temperature of at least ℃, 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 an annealing separator is applied by decarburizing annealing and subjected to secondary recrystallization and purification by finish annealing, a final pass or a final two passes is subjected to a strain rate of 150 s ^-1 during finish hot rolling. A method for producing a grain-oriented electrical steel sheet having a high magnetic flux density, wherein the finishing hot rolling is performed with the tension between the two last stands being 1.5 kgf / mm ² or more. 2. The high magnetic flux density according to claim 1, wherein the rough-rolled sheet bar is joined to a preceding sheet bar before finishing hot rolling, and the sheet bar is continuously subjected to finishing hot rolling. Manufacturing method of grain-oriented electrical steel sheet.