JP5286872B2 - Oriented electrical steel sheet and manufacturing method thereof - Google Patents

Description

  The present invention relates to a grain-oriented electrical steel sheet and a method for manufacturing the grain-oriented electrical steel sheet, and in particular, intends to further improve the orientation integration degree of the grain-oriented electrical steel sheet.

  Reflecting increasing interest in preventing global warming and saving energy in recent years, demands for low iron loss and low noise are becoming increasingly stringent for grain-oriented electrical steel sheets, which are core materials.

The grain-oriented electrical steel sheet is a steel sheet in which the <001> orientation, which is the easy axis of iron, is highly integrated in the rolling direction of the steel sheet. Usually, this crystal structure is obtained through secondary recrystallization that preferentially grows grains of {110} <001> orientation called goth orientation during the manufacturing process of grain-oriented electrical steel sheet, particularly in the finish annealing process. It is formed. From the viewpoint of reducing iron loss and noise, the structure of grain-oriented electrical steel sheet is preferably as high as possible in the Goss direction.
Hereinafter, annealing for causing secondary recrystallization is referred to as “secondary recrystallization annealing”.

Since secondary recrystallization annealing of grain-oriented electrical steel sheets takes a long time to develop secondary recrystallization and form a film, it is generally performed by batch annealing in a state where a coil form, that is, a steel sheet is wound around a coil. .
By the way, the crystal orientation of the secondary recrystallized grains obtained by this coil form annealing continuously changes along the rolling direction when viewed from the material coordinate system. That is, the orientation of the secondary recrystallized grains in the flattened product plate is in a state where the orientation of the secondary recrystallized grains is inclined in the rolling direction within the same crystal grains and the β angle is continuously changed along the rolling direction. Here, the β angle means a deviation angle (°) from the ideal Goss direction around the perpendicular direction (TD) in the rolling plane of the secondary recrystallization direction.
And it is known by this that the orientation integration degree of a product board will deteriorate according to a coil diameter.

In high magnetic flux density grain-oriented electrical steel sheets, the secondary recrystallized grain size reaches several tens of millimeters, and this deterioration in geometric orientation accumulation is insignificant.
As a technique for suppressing the deterioration of the orientation integration degree, Patent Document 1 proposes a method of setting the coil inner diameter to 600 mm or more.
Japanese Patent Publication No. 50-37128

  However, as a matter of course, in the prior art, it is impossible to exceed the orientation integration degree obtained when the steel sheet is flattened and the secondary recrystallization annealing is performed. Actually, the orientation accumulation obtained by coil foam annealing around 1000 mm in coil diameter has reached almost the same range as the integration obtained by flat annealing. In industrial production of grain-oriented electrical steel sheets, 600 to outer diameter: Secondary recrystallization annealing is performed with a coil diameter of about 1200 mm.

  The present invention relates to an improvement of the above-described technique, and further improves the orientation integration degree obtained by coil foam annealing, thereby further improving the magnetic properties of the grain-oriented electrical steel sheet together with its advantageous manufacturing method. The purpose is to propose.

Now, as a result of intensive studies to achieve the above object, the inventors have conducted secondary recrystallization annealing with a coil diameter (2000-6200mm) that is even larger than the conventional coil diameter (600-1200mm). We gained knowledge that the intended purpose can be achieved advantageously by doing so.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. A grain-oriented electrical steel sheet characterized in that the average value of the rate of change in β angle along the rolling direction in the same secondary recrystallized grains is 0.018 to 0.06 ° / mm over the entire length of the coil .
Here, β angle: deviation angle (°) from the ideal Goss direction around the perpendicular direction (TD) in the rolling plane of the secondary recrystallization orientation.

2. The slab for grain-oriented electrical steel sheets is heated and then hot-rolled, then combined with annealing and rolling to obtain the final thickness, and then the grain-oriented electrical steel sheet is manufactured by performing primary recrystallization annealing and secondary recrystallization annealing. In doing so, secondary recrystallization annealing is performed under the condition that the radius of curvature of the steel sheet in the rolling direction satisfies the range of 1000 to 3100 mm over the entire length of the coil .

ADVANTAGE OF THE INVENTION According to this invention, the orientation integration degree of a grain-oriented electrical steel sheet can be improved with the new method which is not in the past.
This makes it possible to provide a grain-oriented electrical steel sheet having a high degree of orientation integration, which in turn contributes to prevention of global warming and energy saving.

Hereinafter, the present invention will be specifically described.
First, a general secondary recrystallization mechanism will be described.
In the production process of grain-oriented electrical steel sheets, the primary recrystallization texture (the texture before secondary recrystallization annealing) and the Goss orientation are in an orientation relationship shifted by about 30 °. In this state, the crystal grains having goth orientation (goss grains) are frequently formed with high mobility grain boundaries, so the goss grains grow preferentially and secondary recrystallization accumulated in the goss orientation. It is believed that a texture can be obtained.

Next, the elucidation process of the present invention will be described.
Now, the inventors have considered the following about secondary recrystallization in coil foam. First, when the steel plate is flat (curvature radius = ∞), when the secondary recrystallization nucleus grows by engulfing the primary recrystallization structure, even if the secondary grain boundary moves, the primary recrystallization structure and the secondary recrystallization structure The orientation relation of crystal nuclei does not change. However, in a state where the steel plate is curved, as the secondary recrystallization nuclei grow and the grain boundaries move, the orientation relationship between the primary recrystallization texture and the secondary recrystallization nuclei changes continuously. For example, when the radius of curvature is 1000 mm, the orientation difference between the secondary recrystallization nucleus and the primary recrystallization texture changes by about 0.6 ° every time the secondary recrystallization grain boundary advances 10 mm in the rolling direction. In this state, it is considered that the secondary recrystallized nuclei slightly deviated from the Goss orientation can be aligned with the <001> orientation of the crystal grains and the rolling direction by growing in an appropriate direction. Since the mobility of the secondary grain boundary is considered to increase as it grows closer to the Goss direction, it is considered that the growth in this direction is likely to occur preferentially.
In other words, the inventors have come up with the idea that secondary recrystallization in coil form may have a higher orientation integration degree than secondary recrystallization in a flat state.
Hereinafter, the effect of improving the degree of orientation accumulation resulting from the curvature of the steel sheet is referred to as “curving effect”.

Although it is considered that the above-described bending effect can be obtained even with the coil diameter (600 to 1200 mm) of the prior art, it is considered that the improvement of the orientation integration degree due to this is offset by geometrical orientation deterioration. In other words, after secondary recrystallization by coil foam annealing, the curved steel sheet is flattened by annealing, so the secondary recrystallized grains are bent in the opposite direction and orientation changes occur within the grains. Since the degree is large, it is considered that the degree of integration deteriorates.
The frequency of secondary recrystallization nucleation is highest in the Goss orientation, but secondary recrystallization nuclei that are perfectly aligned with the Goss orientation will not benefit from the curving effect and will only receive geometrical degradation. .
Accordingly, the inventors have come to the idea that unless the coil diameter is increased appropriately and the influence of geometrical deterioration is reduced, the degree of orientation integration cannot be improved by the bending effect.

Therefore, the inventors conducted an experiment based on the idea that increasing the radius of curvature of the steel sheet in the secondary recrystallization annealing is more effective than the conventional technique in improving the orientation accumulation degree. In addition, unless otherwise indicated, "%" display regarding a component shall mean "mass%".
C: 0.051%, Si: 3.2%, Mn: 0.08%, S: 0.015%, Al: 0.022%, Sb: 0.024%, Cr: 0.02% and N: 0.0065%, the balance being Fe and inevitable impurities The steel having the composition was melted in the laboratory, heated at 1460 ° C. for 10 minutes, hot rolled to a thickness of 2.4 mm, and then subjected to hot-rolled sheet annealing at 1170 ° C. for 2 minutes. Subsequently, it was rolled to 1.7 mm thickness by the first cold rolling, and after the intermediate annealing for 1 minute at 1070 ° C., the final cold rolled sheet having a thickness of 0.27 mm was obtained by the second cold rolling. Next, the obtained cold-rolled sheet was subjected to primary recrystallization annealing at 850 ° C. for 2 minutes in an atmosphere of H ₂ : N ₂ = 55 vol%: 45 vol% and dew point: 60 ° C., followed by MgO as the main component. An annealing separator was applied. Thereafter, this plate was sandwiched and fixed between stainless plates having various radii of curvature, and then subjected to final finish annealing at 1150 ° C. for 15 hours in an H ₂ atmosphere to obtain a secondary recrystallized plate. Next, the curved secondary recrystallized plate is fixed by sandwiching it between flat stainless steel plates, subjected to annealing at 900 ° C. for 2 hours in a dry N ₂ atmosphere, and then subjected to magnetic flux density B ₈ < Magnetic flux density at H _max = 800 A / m) was measured.

The obtained results are shown in FIG. 1 in relation to the magnetic flux density B ₈ in the rolling direction and the radius of curvature during secondary recrystallization annealing.
As shown in the figure, the orientation frequency is improved by performing secondary recrystallization annealing in the state where the radius of curvature of the steel sheet in the rolling direction is 1000 to 3100 mm, that is, 2000 to 6200 mm in terms of the coil diameter. It can be seen that B ₈ is improved.

Next, FIG. 2 shows the results of examining the rate of change of the β angle along the rolling direction in the same secondary recrystallized grains of each product plate obtained.
As shown in the figure, the change rate (absolute value) of the β angle along the rolling direction in the same secondary recrystallized grains is 0.018 to 0.06 as a reflection of the processing with the radius of curvature as described above. It was within the range of ° / mm.

  As described above, the orientation integration degree obtained by coil foam annealing under the conditions according to the present invention exceeds that of flat annealing, and the present invention is distinct from the conventional technical idea. I understand.

There is no restriction | limiting in particular about the component composition range of the grain-oriented electrical steel sheet made into object by this invention, All will be suitable if it is a conventionally well-known thing. In the production of grain-oriented electrical steel sheets, C, Al, N, etc. are removed from the steel slab as the raw material in decarburization annealing and final finish annealing, so the composition of the steel slab and the composition of the product plate are not necessarily the same. However, the representative composition of the steel slab is as follows.
C: 0.015-0.1%
C is not only an element useful for improving the hot-rolled structure by utilizing transformation, but also an element useful for the generation of goth-oriented grains, and at least 0.015% may be contained in the steel slab. On the other hand, if over 0.1%, decarburization failure occurs in decarburization annealing, so C is preferably in the range of 0.015-0.1%. In addition, this C is reduced to 0.005% or less by decarburization annealing.

Si: 2.0-7.0%
Si is an element necessary for increasing the electrical resistance of the product plate to reduce iron loss and stabilizing alpha iron to enable high-temperature heat treatment, and preferably contains at least 2.0%. If it exceeds 7.0%, cold rolling becomes difficult, so Si is preferably 2.0 to 7.0%.

Mn: 0.02 to 0.2%
Mn not only effectively contributes to the improvement of hot brittleness of steel, but when S and Se are mixed, precipitates such as MnS and MnSe are formed to exert a function as an inhibitor. However, if the amount of Mn is less than 0.02%, the above effect is insufficient. On the other hand, if the amount exceeds 0.2%, the particle size of precipitates such as MnSe becomes coarse and the effect as an inhibitor is lost. A range of 0.2% is preferable.

S and / or Se: 0.001 to 0.03% each
Se and S combine with Mn and Cu to form MnSe, MnS, Cu _2-X Se, Cu _2-X S, and are useful components that emit the inhibitor action as a dispersed second phase in steel. . When the content of Se and S is less than 0.001%, the effect of addition is poor. On the other hand, when the content exceeds 0.03%, not only the solid solution during slab heating becomes incomplete, but also the cause of defects on the product plate surface. Therefore, the steel slab is preferably contained in the range of 0.001 to 0.03%. These Se and S are reduced to Se: less than 0.001% and S: less than 0.001%, respectively, by final finish annealing.

sol.Al: 0.001 to 0.04%
Al is a useful element that forms AlN in steel and acts as an inhibitor as a dispersed second phase. However, if the content is less than 0.001%, the precipitation amount of AlN cannot be secured sufficiently. On the other hand, if added over 0.04%, AlN precipitates coarsely and the action as an inhibitor is lost. Is preferably contained in the steel slab in the range of 0.001 to 0.04% as sol.Al. In addition, this Al is reduced to less than 0.001% by the final finish annealing.

N: 0.003-0.013%
N is an element necessary for forming a precipitated dispersed phase of AlN, and 0.003 to 0.013% is preferably contained in the steel slab in order to allow AlN to function well as an inhibitor. This is because if the content is less than 0.003%, precipitation of AlN or BN becomes insufficient, while if it exceeds 0.013%, blistering or the like occurs during slab heating. This N is reduced to less than 0.003% by the final finish annealing.

In addition to the above components, adding Sb, Cu, Sn, Cr, Mo, P, Bi or the like alone or in combination in order to enhance the suppressive force is effective in further improving the magnetic properties. .
Sb has the effect of segregating at the grain boundaries and increasing the suppression force, and it is desirable to contain Sb in the range of 0.01 to 0.08%.
Cu, like Mn, is useful as an element that combines with Se and S to form precipitates and enhances the suppressive force, and this effect is remarkable in the range of 0.05 to 0.02%.
Sn is a component that effectively acts to reduce iron loss by increasing the frequency of secondary recrystallized grains, and is preferably contained in the range of 0.005 to 0.4%.
Cr, like Mn and Cu, is useful as an element that combines with Se and S to form precipitates and enhances the suppressive force, and this effect is remarkable in the range of 0.02 to 0.08%.
Mo has the effect of sharpening the nuclei of the secondary grains in the Goth orientation, and the effect is remarkable in the range of 0.01 to 0.1%.
P, like Sb, is an element that segregates at the grain boundary and enhances the suppressive force. However, if less than 0.01%, the effect of addition is poor, while if it exceeds 0.03%, the magnetic properties and surface properties are destabilized. It is preferable to set it to -0.03%.
Bi is preferentially concentrated at the grain boundaries of the primary recrystallized grains, and by reducing the mobility of the grain boundaries during the final finish annealing, it is effective for raising the secondary recrystallization temperature and improving the crystal orientation accumulation degree. It is thought that it acts on. However, if the amount of Bi added is less than 0.001%, the disappearance from the steel will occur early, so that a sufficient effect cannot be obtained. On the other hand, if the amount added exceeds 0.04%, the residual amount in the product plate steel will be excessive. Since deterioration of hysteresis loss is caused, Bi is preferably 0.001 to 0.04%.

Next, the manufacturing process of the present invention will be described.
In the present invention, a known process can be adopted except that the radius of curvature of the steel at the time of secondary recrystallization annealing is defined. The preferred production conditions are as follows.
The silicon steel slab adjusted to the above-mentioned preferred component composition is heated to a high temperature of 1350 ° C. or higher for the inhibitor component solid solution. However, when the inhibitor is reinforced in the subsequent process by nitriding or the like, the slab heating temperature can be 1280 ° C. or less.
Next, after hot rolling, annealing treatment and cold rolling are combined to obtain a final thickness, and after performing primary recrystallization annealing and secondary recrystallization annealing, an insulating tension coating is baked to obtain a product.

Here, as a method of combining the annealing treatment and cold rolling to make the final plate thickness
1) After hot rolling, after performing hot-rolled sheet annealing, a method for obtaining a final sheet thickness by two or more cold rolling processes including intermediate annealing,
2) After hot rolling, after performing hot-rolled sheet annealing, a method of making the final sheet thickness by one cold rolling,
3) After hot rolling, there are three types of processes, ie, a method of obtaining a final sheet thickness by two or more cold rolling processes including intermediate annealing without performing hot-rolled sheet annealing. It is also possible to adopt.
At that time, cold rolling is performed at a temperature of 100 to 200 ° C., and aging treatment between passes is also advantageous for improving magnetic properties.
Furthermore, providing a plurality of linear grooves in the direction intersecting with the rolling direction of the steel sheet for magnetic domain subdivision is useful for further reducing the iron loss.

Next, primary recrystallization annealing is performed. In this primary recrystallization annealing, it is preferable to perform decarburization together with an atmosphere that is an oxidizing atmosphere containing water vapor and H ₂ .
After the primary recrystallization annealing, an annealing separator is applied to the surface of the steel plate. Here, as the annealing separator, a magnesia-based material is usually used.

After applying such an annealing separator, the final finish annealing consisting of secondary recrystallization annealing and purification annealing is performed, and then a tension-imparting coating or insulating coating is baked on the steel sheet surface as necessary, followed by flattening annealing To make a product.
In the present invention, when the secondary recrystallization annealing is performed, annealing is performed so that the radius of curvature of the steel sheet satisfies the range of 1000 to 3100 mm, in other words, the coil diameter is in the range of inner diameter: 2000 mm to outer diameter: 6200 mm. This is very important. Such annealing does not necessarily need to be coil form annealing, and secondary recrystallization annealing may be performed in a continuous annealing line as long as the radius of curvature of the steel sheet can satisfy the condition of 1000 to 3100 mm.

  In addition, the component of the film finally coat | covered is not prescribed | regulated, For example, TiN, a ceramic, a phosphate, chromate, an organic resin etc. can be used as a film.

C: 0.042%, Si: 3.3%, Mn: 0.076%, S: 0.019%, Al: 0.021%, Sb: 0.025%, Cr: 0.02% and N: 0.0071%, the balance being Fe and inevitable impurities The steel slab having the composition was heated at 1460 ° C. for 10 minutes, hot rolled to a sheet thickness of 2.4 mm, and then subjected to hot-rolled sheet annealing at 1170 ° C. for 2 minutes. Subsequently, it was rolled to 1.8 mm thickness by the first cold rolling, and after the intermediate annealing at 1100 ° C. for 1 minute, a final cold rolled sheet having a thickness of 0.27 mm was obtained by the second cold rolling. The obtained cold-rolled sheet is subjected to primary recrystallization annealing at 840 ° C. for 2 minutes in an atmosphere of H ₂ : N ₂ = 60 vol%: 40 vol%, dew point: 60 ° C., and then mainly MgO. An annealing separator was applied. Then, after winding the steel plate with various coil diameters, it was subjected to final recrystallization at 1180 ° C for 15 hours in H ₂ atmosphere, followed by secondary recrystallization, and then shaped by flattening annealing at 830 ° C for 30 seconds. Was corrected into a product plate.
Table 1 shows the results of measuring the average value of the rate of change of the β angle in the rolling direction and the magnetic flux density B ₈ by cutting out a test piece from each product plate thus obtained.

As shown in the table, according to the present invention, when the secondary recrystallization annealing is performed under the condition that the radius of curvature of the steel sheet in the rolling direction satisfies the range of 1000 to 3100 mm, excellent B ₈ is obtained. I understand that.

C: 0.051%, Si: 3.1%, Mn: 0.071%, S: 0.020%, Al: 0.024%, Sb: 0.02%, Cr: 0.02% and N: 0.079%, the balance being Fe and inevitable impurities The steel slab having the composition was heated at 1380 ° C. for 20 minutes, hot rolled to a thickness of 1.8 mm, and then subjected to hot-rolled sheet annealing at 1150 ° C. for 1 minute. Then, a final cold-rolled sheet having a thickness of 0.23 mm was obtained by one cold rolling. The obtained cold-rolled sheet was subjected to primary recrystallization annealing at 830 ° C. for 2 minutes in an atmosphere of H ₂ : N ₂ = 60 vol%: 40 vol%, dew point: 55 ° C. Subsequently, an annealing separator mainly composed of MgO was applied. Then, after winding the steel plate with various coil diameters, it was subjected to final recrystallization at 1180 ° C for 15 hours in H ₂ atmosphere, followed by secondary recrystallization, and then shaped by flattening annealing at 830 ° C for 30 seconds. Was corrected into a product plate.
Table 2 shows the result of measuring the average value of the rate of change of the β angle in the rolling direction and the magnetic flux density B ₈ by cutting out a test piece from each product plate thus obtained.

As shown in the table, according to the present invention, when the secondary recrystallization annealing is performed under the condition that the radius of curvature of the steel sheet in the rolling direction satisfies the range of 1000 to 3100 mm, excellent B ₈ is obtained. I understand that.

Steel slabs having various components shown in Table 3 were heated at 1390 ° C. for 20 minutes, hot rolled to a sheet thickness of 2.3 mm, and then subjected to hot rolled sheet annealing at 1120 ° C. for 2 minutes. Then, a final cold-rolled sheet having a thickness of 0.27 mm was obtained by one cold rolling. The obtained cold-rolled sheet is subjected to primary recrystallization annealing at 830 ° C. for 2 minutes in an atmosphere of H ₂ : N ₂ = 55 vol%: 45 vol% and dew point: 63 ° C., followed by MgO as the main component. An annealing separator was applied. Thereafter, the steel sheet was wound up under the conditions of an inner diameter of 2000 mm and an outer diameter of 3000 mm (curvature radius of the steel sheet: 1000 to 1500 mm), and then subjected to final finishing annealing at 1170 ° C. for 13 hours in an H ₂ atmosphere. Next, it was recrystallized, and then the shape was corrected by flattening annealing at 820 ° C. for 20 seconds to obtain a product plate.
Table 3 shows the results of measuring the average value of the rate of change of the β angle in the rolling direction and the magnetic flux density B ₈ by cutting out a test piece from each product plate thus obtained.

As is clear from the table, regardless of the component composition of the steel sheet, when the secondary recrystallization annealing is performed under a condition where the radius of curvature of the steel sheet in the rolling direction satisfies the range of 1000 to 3100 mm, Excellent B ₈ is obtained.

It is a graph showing the relationship between the curvature radius and the magnetic flux density B ₈ in the rolling direction of the steel sheet during the secondary recrystallization annealing. It is a graph which shows the relationship between the curvature radius of the rolling direction of the steel plate at the time of secondary recrystallization annealing, and the change rate of (beta) angle along the rolling direction in the same secondary recrystallized grain.

Claims (2)

A grain-oriented electrical steel sheet characterized in that the average value of the rate of change in β angle along the rolling direction in the same secondary recrystallized grains is 0.018 to 0.06 ° / mm over the entire length of the coil .
Here, β angle: deviation angle (°) from the ideal Goss direction around the perpendicular direction (TD) in the rolling plane of the secondary recrystallization orientation. The slab for grain-oriented electrical steel sheets is heated and then hot-rolled, then combined with annealing and rolling to obtain the final thickness, and then the grain-oriented electrical steel sheet is manufactured by performing primary recrystallization annealing and secondary recrystallization annealing. In doing so, secondary recrystallization annealing is performed under the condition that the radius of curvature of the steel sheet in the rolling direction satisfies the range of 1000 to 3100 mm over the entire length of the coil .

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