JP2002194445A - Method for manufacturing grain-oriented electrical steel sheet having high magnetic flux density and excellent film characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a grain-oriented electrical steel sheet which has a forsterite film having excellent film appearance and adhesion and also has excellent magnetic properties by effectively prevent the occurrence of film defects in a stock containing Bi. SOLUTION: In manufacturing the grain-oriented electrical steel sheet by using a stock containing Bi, TiO2 is added in an amount of >=3 pts.wt. per 100 pts.wt. of MgO into a separation agent for annealing composed essentially of MgO, water content in the separation agent for annealing after application and drying is regulated to <=0.5 g/m2 per side of the steel sheet, and further the length of residence time of a coil in the temperature region of 700 to 900 deg.C in the course of temperature raise at final finish annealing is regulated to <=60 h.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high magnetic flux density grain-oriented electrical steel sheet having excellent coating characteristics, and more particularly to a method for manufacturing a magnetic steel sheet having a high magnetic flux density.
An object of the present invention is to effectively prevent forsterite coating defects that may be caused in a high magnetic flux density grain-oriented electrical steel sheet manufactured from a slab containing slab.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets used as core materials for transformers and generators are required to have high magnetic flux density and low iron loss as the most important characteristics. Until today, various measures have been taken to reduce the iron loss of grain-oriented electrical steel sheets. Among them, the crystal orientation of the steel sheet after final finish annealing is referred to as Goss orientation {110} <001.
> High integration in azimuth is one of the most important development goals. This is because, by highly accumulating the crystal orientation <001>, which is the direction of the easy axis of magnetization of the iron crystal, in the rolling direction, the magnetizing force required for magnetization in the rolling direction is reduced, and the coercive force is reduced. This is because loss is reduced and iron loss is reduced.

Another important characteristic of grain-oriented electrical steel sheets is that noise when magnetized is small. This problem can be greatly improved by aligning the crystal orientation with the Goss orientation. That is, as a cause of noise generated from the transformer, it is known that there is a magnetostrictive vibration or an electromagnetic vibration of the iron core material. However, by improving the degree of integration of the crystal orientation in the Goss orientation, it becomes a cause of the magnetostrictive vibration. At the same time as the generation of 90 ° magnetic domains is suppressed, the exciting current is reduced to suppress the electromagnetic vibration, and as a result, noise is reduced.

As described above, it can be said that accumulation of crystal orientation <001> in the rolling direction is the most important issue for grain-oriented electrical steel sheets. Note that B ₈ (magnetizing force: magnetic flux density at 800 A / m) is often used as an index of the degree of integration of crystal orientation, and the development of grain-oriented electrical steel sheets has been promoted with the aim of improving B ₈ as a major goal. ing. As a typical value of iron loss, W _17/50, which is an energy loss when the excitation magnetic flux density is 1.7 T and the excitation frequency is 50 Hz, is used.

[0005] The secondary recrystallized grain structure of such a grain-oriented electrical steel sheet is formed through a phenomenon called secondary recrystallization during final finish annealing. Giant growth to obtain a product with the desired magnetic properties. In order to effectively promote the accumulation of the above-mentioned secondary recrystallized grains, it is important to form a uniform and appropriate size of a dispersed dispersed phase called an inhibitor which selectively suppresses the growth of the primary recrystallized grains. is there. The presence of this inhibitor suppresses the normal growth of primary recrystallized grains.
During the final annealing, the state of fine primary recrystallized grains is maintained up to a high temperature, and at the same time, the selectivity for the growth of crystal grains with good orientation is increased, so that a high magnetic flux density is realized. In general, it is considered that the stronger the inhibitor and the stronger the ability to suppress normal grain growth, the higher the degree of azimuth accumulation.

[0006] Such inhibitors include MnS,
Materials having low solubility in steel, such as MnSe, Cu _2-X S, Cu _2-X Se, AlN, and BN, are used. For example, JP-B-33-4710 and JP-B-40-15644 disclose that Al is contained in the material, the final cold rolling reduction is 81-95%, and the annealing is performed before the final cold rolling. A technique for precipitating AlN which is a strong inhibitor is disclosed. In addition to the above inhibitor components, Sn, As, Bi, Sb, B, Pb, Mo, Te,
It is known that the addition of V, Ge, or the like is effective for improving the degree of orientation of secondary recrystallized grains.

[0007] Among these additional inhibitor elements, P, As, Sb, and Pb which are classified into Group 5B elements in the periodic table.
Bi is that segregates on grain boundaries, which is the main inhibitor _{MnS, MnSe, Cu 2-X} S, Cu 2-X Se, jointly with AlN or the like to enhance the normal grain growth inhibiting force, the magnetic characteristics Among these elements, Bi is particularly attracting attention as an element for enhancing normal grain growth suppressing power due to a grain boundary segregation effect because of its low solubility in iron.

However, when a material containing Bi is used, it is known that the formation of forsterite on the steel sheet surface during the final finish annealing becomes poor, and the appearance of the coating of the product and the adhesion of the insulating coating are deteriorated. Have been.
For such poor formation of forsterite film,
The water content of the annealing separator used for final finish annealing is 0.3
A method of adjusting the oxygen basis weight of the decarburized annealed sheet to a range of 550 to 850 ppm (Japanese Patent Application Laid-Open No. 10-152725), A method for adjusting the Ig-Loss value of MgO used as a separating agent to 0.4 to 1.5% (Japanese Patent Application Laid-Open No. 10-25516), and a method for appropriately adjusting the atmosphere gas flow rate in the final finish annealing (Japanese Patent Application Laid-Open No. 9-1997).
Although many improvement measures have been proposed, such as the method disclosed in Japanese Patent No. 3542, they are all methods within the range of the current manufacturing conditions of grain-oriented electrical steel sheets, and the effect of improving the coating is not necessarily high. Therefore, although some improvement of the coating can be achieved by using the conventional technique as described above, the harmful effects of Bi cannot be completely prevented.
At present, it is not possible to obtain products having good appearance with respect to the contained materials.

As a method of appropriately controlling the rate of temperature rise in the final annealing, Japanese Patent Application Laid-Open No. 8-269552 discloses a method.
A method is disclosed in which the rate of temperature rise in the 900 to 1150 ° C. range is increased to 15 to 50 ° C./h, which is higher than in the past, in order to obtain an appropriate inhibitor strength. However, this technique is a technique for appropriately controlling the rate of temperature rise in a high temperature region near the secondary recrystallization start temperature in order to stably obtain a high magnetic flux density, and does not mention the effect of improving the film formation. .

Further, Japanese Patent Application Laid-Open No. 7-258802 discloses a method in which an antimony compound or the like is added to an annealing separating agent, and a temperature rising rate from 800 ° C. to a maximum attained temperature is 0.1 to 80 ° C./h.
Alternatively, a boron-based, strontium-based, barium-based, carbon / nitride-based, sulfide-based, or chloride-based material is added to increase the heating rate by 5%.
Techniques of up to 400 ° C./h are disclosed. This method
Although it relates to the technology for improving the coating of the final finish annealed sheet, the rate of temperature rise here depends on the additive to the annealing separator.
This technique aims at accelerating the melting of MgO and maximizing the effect of improving the film formation by these additives. In addition, since the rate of temperature increase in a high temperature range from 800 ° C. to the maximum temperature is taken up, it is not possible to effectively prevent the concentration of Bi on the steel sheet surface as described later.

[0011] Furthermore, Japanese Patent Application Laid-Open No. 4-187721 discloses that in a material containing Al and Se, the temperature rise rate of the final finish annealing is set to 20 ° C./h or more up to a predetermined temperature between 700 and 875 ° C. Then, from the temperature up to the temperature range of 1100 to 1300 ° C, 5
℃ / h, less than 15 ℃ / h technology is disclosed,
This technique does not relate to the improvement of a forsterite coating of a material containing Bi as an inhibitor element as intended by the present invention.

[0012]

SUMMARY OF THE INVENTION The present invention is to provide a forsterite film having excellent film appearance and adhesion by effectively preventing film defects occurring in a Bi-containing material as described above. An object of the present invention is to propose a novel manufacturing method capable of obtaining a grain-oriented electrical steel sheet having excellent characteristics.

[0013]

Means for Solving the Problems The inventors of the present invention have investigated the cause of deterioration of the forsterite film when using Bi-containing steel as a raw material. It was found that Bi enrichment occurred in the surface layer portion of the steel sheet in such a region, and that such Bi in the surface layer slowed down the film formation reaction in the low-temperature region, thereby deteriorating the film. Then, the inventors conducted various studies on measures to prevent the deterioration of the coating due to the above-mentioned causes, and as a result, (1) 700-90 during final finish annealing
By shortening the residence time in the 0 ° C region, the concentration of Bi to the surface layer is suppressed. (2) In addition, a predetermined amount or more of TiO ₂ is added to the annealing separator, It was found that by controlling the water content as the basis weight of the steel sheet, it was possible to suppress the adverse effect of some Bi concentrated on the surface layer. The present invention is based on the above findings.

That is, the gist of the present invention is as follows. 1. C: 0.01 to 0.10 mass%, Si: 1.0 to 5.0 mass%, M
n: 0.03 to 0.20 mass% and N: 0.0015 to 0.0130 mass%
And sol.Al: 0.015 to 0.035 mass% and B:
A steel slab containing one or two selected from 0.0010 to 0.0150 mass% and further containing Bi: 0.001 to 0.10 mass% is heated, hot-rolled, and then, if necessary. After hot-rolled sheet annealing, the final thickness is obtained by two cold rollings including intermediate annealing, or after the hot-rolled sheet annealing, the final thickness is obtained by one cold rolling, followed by decarburization. Annealing, then applying an annealing separating agent, winding the coil, and then performing the final finish annealing In a method of manufacturing a grain-oriented electrical steel sheet, the main process is to apply MgO to the steel sheet before final finish annealing. In the annealing separator as a component, 3 parts by weight or more of TiO ₂ is added to 100 parts by weight of MgO, and the amount of water in the annealing separator after coating and drying is 0.5 g / m ² or less per one side of the steel sheet, In addition, during the temperature rise process of final finish annealing, the coil Process for producing a high magnetic flux density oriented electrical steel sheet excellent in coating properties, characterized by a residence time in the range within 60 hours.

2. In the above item 1, the steel slab further comprises one or two selected from S and Se: 0.010 to
A method for producing a high magnetic flux density grain-oriented electrical steel sheet having excellent coating properties, characterized by having a composition containing 0.030 mass%.

3. The method for producing a high magnetic flux density grain-oriented electrical steel sheet according to 1 or 2, wherein the steel slab has a composition further containing Cr: 0.05 to 0.50 mass%.

4. In the above 1, 2 or 3, the steel slab further comprises one or more selected from Cu, Sb and Sn.
Species or more: A method for producing a high magnetic flux density grain-oriented electrical steel sheet having excellent coating properties, which has a composition containing 0.05 to 0.50 mass%.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the invention will be described below. The inventors investigated the cause of deterioration of the forsterite film when using a Bi-containing steel as a raw material, focusing on the concentration of Bi in the surface layer of the steel sheet during final finish annealing. FIG. 1 shows an investigation of the concentration of Bi in the surface layer during the final annealing of a 0.23 mm thick material containing 0.010 mass% of Bi. That is, in the final finishing annealing in the laboratory, the temperature range from 600 to 1100 ° C is raised at a constant rate of 2.5 ° C / h or 5.0 ° C / h,
After reaching the respective temperatures, the temperature was lowered to remove the annealing separator, and then the Bi amount (total Bi amount) and the surface film (3 μm in the surface layer) with the surface film being formed still attached were removed. (Bi content) was measured. In addition,
In FIG. 1, the total thickness Bi is used as an index of the degree of enrichment of Bi in the surface layer.
The value obtained by subtracting the amount of ground iron Bi from the amount is shown.

As shown in FIG. 1, during the final finish annealing,
It can be seen that Bi is remarkably concentrated on the surface in a temperature range of about 700 to 900 ° C., and that the concentration of Bi on the surface can be suppressed by increasing the heating rate. In addition, the appearance of the coating after the final annealing was better when the heating rate was increased rapidly to 5.0 ° C / h. From these results, it was found that, by increasing the heating rate in the final finish annealing, the concentration of Bi in the surface layer portion was suppressed, and the appearance of the coating film was improved.
In addition, the improvement in the appearance of the film is 700 to 90 times faster than the rate of temperature increase in the high temperature region, which has been conventionally regarded as important from the viewpoint of secondary recrystallization.
The residence time in the low temperature range of 0 ° C. was found to be important.

Subsequently, an experiment was conducted to determine an appropriate range of the temperature rising rate in the range of 700 to 900 ° C. from the viewpoint of improving the forsterite film. C: 0.06 mass%, Si: 3.3 mass%, Mn: 0.07 mass%, S
e: 0.02 mass%, sol.Al: 0.022 mass%, N: 0.0082mas
s%, Cu: 0.15mass% and Bi: 0.010mass%, the balance being from a steel ingot having a substantially Fe composition to a decarburized annealed sheet having a thickness of 0.23mm obtained by a conventional method. After applying an annealing separator mainly composed of MgO, final finishing annealing was performed in a laboratory annealing furnace. At this time, the residence time in the 700-900 ° C range and 900-1100 ° C range was variously changed by changing the heating rate. Table 1 shows the results of the visual judgment of the appearance of the coating film after the final annealing and the evaluation results of the bending adhesion.
In addition, bending adhesion, after applying an insulating coating mainly composed of magnesium phosphate and colloidal silica,
The test pieces were wound around round bars of various diameters at 5 mm intervals, and evaluated by the minimum diameter at which the coating did not peel.

[0021]

[Table 1]

As shown in Table 1, the film appearance and film adhesion are dominated by the rate of temperature rise in the range of 700 to 900 ° C., and the rate of temperature rise in the range of 900 to 1100 ° C. almost entirely affects the appearance. It turns out that you haven't. Therefore, as expected above, 7
It is considered that formation of the forsterite film was improved by suppressing the concentration of Bi in the surface layer of the steel sheet in the range of 00 to 900 ° C.

By the way, according to the results shown in Table 1, 700 to 900 ° C.
Although the appearance of the coating is improved by setting the residence time in the above temperature range to 60 hours or less, it cannot be said that a sufficiently good appearance of the coating is always obtained. Then, the further coating improvement method was examined. With respect to the material, the amount of Ti0 ₂ to be added to the annealing separator,, Sr (O
Amount of H) ₂ · 8H ₂ 0, the MgO hydration amount, annealing basis weight of the separating agent (when varying the weight) of the annealing separator applied to the steel sheet one side 1 m ² per final finish after annealing Table 2 shows the results of examining the coating appearance and the bending adhesion of the coating. Here, the MgO hydration amount was adjusted by changing the temperature and time of the MgO hydration treatment. Also, after applying the annealed separating agent to the steel sheet in a slurry state and drying, the annealed separating agent is peeled off from the steel sheet, and the amount of moisture contained in the annealed separating agent is measured. (Weight of water in the annealing separator applied per 1 m ^{2 of} one side of the steel sheet) was calculated.

[0024]

[Table 2]

As shown in Table 2, the final finish annealing
By setting the residence time in the 700-900 ° C range to 60 hours and adding TiO ₂ to the annealing separator in an amount of 3 parts by weight or more based on 100 parts by weight of MgO, a good coating appearance and adhesion can be obtained. The moisture content in the annealing separator is 0.3 g / m ²
Hereinafter, when the amount of TiO ₂ added is 6 parts by weight or more, a good coating film having a bending adhesion of 25 mm or less is obtained. Also, Sr
(OH) ₂ · 8H ₂ 0 amount or MgO hydration amount, if the baked net separating agent basis weight was varied, the amount of water contained in the annealing separator per unit area of the steel sheet is changed, the table In the result of No. 2, when the basis weight of water was 0.5 g / m ² or less per one side of the steel sheet, a good coating appearance was obtained. Therefore, it can be said that the quality of the coating appearance is in accordance with the amount of water per unit area in the annealing separator (the basis weight of water). Even if the amount of TiO ₂ added and the basis weight of water are optimized, a good film cannot be obtained unless the residence time in the 700-900 ° C. range is appropriate.

Although the reason why the above results are obtained is not necessarily clear, the mechanism for improving the appearance of the coating film by optimizing the amount of TiO ₂ added and the basis weight of water by the annealing separator is as follows. Can be considered. TiO ₂ is known as an additive in an annealing separator useful for improving the coating appearance of grain-oriented electrical steel sheets. At around 800 to 850 ° C, a compound with MgO (Mg
TiO ₃ ), which is thought to have the effect of promoting the forsterite formation reaction between MgO and SiO ₂ in a high temperature range. For materials containing Bi, if the residence time in the 700-900 ° C region is long in the final finish annealing,
It is estimated that not only the concentration of Bi on the steel sheet surface occurs, but also the concentration of Bi in the annealing separator increases, and the reaction between TiO ₂ and MgO is delayed, and the film formation reaction in the high temperature region will not be performed normally. Is done. Considered effective to suppress the increase in the Bi concentration in the baked net separating agent is sufficiently short residence time at 700 to 900 ° C. zone in order to make a good film formation promoting effect Therefore TiO ₂ .

In manufacturing a grain-oriented electrical steel sheet, MgO and SiO ₂ (silica) react near the steel sheet surface during the final annealing to form forsterite. Silica is formed during the decarburization annealing on a portion of about 2 μm near the surface of the steel sheet,
During the final annealing, it reacts with MgO while moving (floating) toward the surface of the steel sheet to form a forsterite film.
At this time, if the silica floats excessively, anchors (projections of the forsterite film to the ground iron) are not formed inside, and the adhesion of the film is impaired, resulting in deterioration of the film after final annealing. On the other hand, when the floating of the silica is excessively suppressed, a concentrated zone of the silica is formed inside the steel sheet, and peels off from this portion at a high temperature to impair the appearance of the coating. Therefore, in order to obtain a forsterite film having a good appearance, it is important to appropriately control the floating of silica during final finish annealing.

It is considered that the deterioration of the appearance of the coating in the Bi-added material is caused by the fact that the floating of the silica near the surface layer is inhibited by the Bi concentrated in the coating. Therefore, Bi
The concentration of Bi on the surface layer is reduced by shortening the temperature range in which the surface layer is concentrated, and the oxidizing property of the interlayer atmosphere of the steel strip is reduced by reducing the amount of water in the annealing separator to raise the floating of silica. It is thought that the film can be effectively improved by accelerating. Here, in order to suppress the increase in the oxidizing property of the interlayer atmosphere of the steel strip and obtain a good forsterite film, the moisture per unit area of the steel sheet is required rather than controlling the basis weight and the moisture amount of the annealing separator separately. It is important to optimize the amount.

Next, the added elements in the steel and 700 to 900 ° C.
A survey was conducted to clarify the appropriate range of residence time in the region. C: 0.06 mass%, Si: 3.3 mass%, Mn: 0.07 mass%, S
e: 0.02 mass%, sol.Al: 0.02 mass%, N: 0.008 mass
%, Cu: 0.15 mass% and Bi: 0.010 mass%
Furthermore, (a) Cr: 0.03 mass%, (b) Cr: 0.05 mass%, (c)
Cr: 0.15mass% is contained, and the balance is made of three types of steel ingots having substantially the composition of Fe. The final annealing was performed by changing the residence time in the range of 700 to 900 ° C. in various ways.
At this time, the amount of TiO ₂ added in the annealing separator was 8 mass%, and the amount of water in the annealing separator was 0.25 g per 1 m ^{2 of} one surface of the steel sheet. Table 3 shows the results obtained by examining the appearance of the coating film and the bending adhesion of the coating film of the product plate thus obtained.

[0030]

[Table 3]

As shown in Table 3, if the residence time in the 700-900 ° C. range is 60 hours or less, good coating appearance and coating adhesion can be obtained. 30
By setting the time to not more than the time, a film having particularly excellent appearance and bending adhesion can be obtained. Furthermore, by adding 0.05 mass% or more of Cr to steel, the bending adhesion is improved, and the conditions of final finish annealing for obtaining a particularly good appearance are expanding.

Next, using the decarburized annealed plate obtained from the steel ingot of (b) above, the basis weight of water per one side of the steel plate in the annealing separator after coating and drying was set to 0.3 g / m ² , During the temperature rise process of finish annealing, the residence time in the
Final finish annealing was performed with various amounts of TiO ₂ added. FIG. 2 shows the results of determination of the appearance of the forsterite film at this time. Further, using the same decarburization annealed sheet, the TiO ₂ was added 8 parts by weight annealing separator, 700-90 in the final finish annealing
FIG. 3 shows the results of determination of the appearance of the forsterite film when the residence time in the 0 ° C. region and the basis weight of the water per side of the steel sheet in the annealing separator after coating and drying were variously changed. In both FIGS. 2 and 3, the coating appearance was evaluated according to the following criteria. ◎: very good, ○: good, Δ: slightly poor, ×: bad.

As is apparent from these results, the residence time in the temperature range of 700 to 900 ° C. during the temperature raising step of the final finish annealing was 60 hours.
It is preferable that the amount of TiO ₂ in the annealing separator is 3 parts by weight or more, and the basis weight of moisture per one side of the steel sheet in the annealing separator after coating and drying is 0.5 g / m ² or less. It turns out that a coating appearance is obtained. Furthermore, the residence time at 700 to 900 ° C. range in the final finish annealing is 30 hours or less, annealing amount of Ti0 ₂ in the separation agent is 6 parts by weight or more, per steel sheet one side in the annealing separator after application and drying Under conditions where the basis weight of water is 0.3 g / m ² or less, it is possible to produce a product having particularly excellent appearance of the coating.

Next, with respect to the component composition and the production method of the grain-oriented electrical steel sheet of the present invention, requirements for obtaining the effects of the present invention, the range thereof, and the operation will be described. First, the reasons for limiting the component composition of the material will be described. C: 0.01 to 0.10 mass% C is not only an element useful for improving the hot-rolled structure by utilizing transformation, but also an element useful for generating Goss-oriented crystal grains, and 0.01 mass% or more. Is required, but 0.
C is limited to the range of 0.01 to 0.10 mass%, because if it exceeds 10 mass%, decarburization failure occurs in decarburization annealing.

Si: 1.0 to 5.0 mass% Si not only increases the electrical resistance to reduce iron loss, but also
It is an element necessary to stabilize the α phase of iron and enable high-temperature heat treatment. It must contain at least 1.0 mass%, but if it exceeds 5.0 mass%, cold rolling becomes difficult. And Si were limited to the range of 1.0 to 5.0 mass%.

Mn: 0.03 to 0.20 mass% Mn not only effectively contributes to improving hot brittleness of steel, but also forms precipitates such as MnS and MnSe when S and Se are mixed. It functions as an inhibitor. When the content of Mn is less than 0.03 mass%, the above effect is insufficient. On the other hand, when the content of Mn exceeds 0.20 mass%, the particle size of precipitates such as MnSe becomes coarse and the effect as an inhibitor is lost. Was limited to the range of 0.03 to 0.20 mass%.

N: 0.0015 to 0.0130 mass% N is added to steel at the same time as Al and B to form AlN.
And BN are necessary elements to form BN. However, when the content is less than 0.0015 mass%, the precipitation of AlN and BN becomes insufficient, and a sufficient inhibitor effect cannot be obtained.
On the other hand, if the content exceeds 0.0130 mass%, swelling or the like occurs during slab heating, so N was limited to the range of 0.0015 to 0.0130 mass%.

Sol.Al: 0.015 to 0.035 mass% Al is a useful element that forms AlN in steel and acts as an inhibitor as a dispersed second phase, but has a content of 0.015 ma.
If it is less than ss%, a sufficient amount of precipitation cannot be secured.
If it exceeds 35 mass%, AlN precipitates coarsely and loses its effect as an inhibitor.
It was made to be contained in the range of 035 mass%.

B: 0.0010 to 0.0150 mass% B is a useful element that forms BN in steel and acts as an inhibitor as a dispersed second phase. BN is a precipitate having a strong inhibitory effect comparable to AlN, and it is possible to obtain a product with a high magnetic flux density by adding it to steel simultaneously with Bi. However, the content of B is 0.
If the content is less than 0010 mass%, the amount of BN deposited cannot be sufficiently ensured. On the other hand, if the content exceeds 0.0150 mass%, BN is coarsely deposited and the action as an inhibitor is lost.
It was limited to the range of ~ 0.0150 mass%. In addition, sol.Al and B may be contained alone or in combination.

Bi: 0.001 to 0.10 mass% Bi concentrates preferentially at the grain boundaries of the primary recrystallized grains, suppresses the movement of the grain boundaries during annealing, raises the secondary recrystallization onset temperature, and increases the magnetic flux. It has the effect of increasing the density.
This effect is similar to that of Sb, As, etc., but Bi has a particularly low solubility in iron and a very low melting point of 271 ° C. Since the steel escapes from the steel in the high temperature range of annealing, it is possible to provide a stronger inhibitory force than a normal inhibitor component. Further, Bi is a grain boundary segregation-type inhibitory strengthening element, like Sb, etc., so that MnSe, MnS, Cu _2-X Se, Cu _2-X
The presence of a precipitation-dispersed inhibitor such as S, AlN, or BN in steel together with the precipitation-dispersed inhibitor has the effect of improving the magnetic properties of any of them. Here, if the content of Bi is less than 0.001 mass%, the effect of suppressing the normal grain growth due to the above-mentioned enrichment at the grain boundary is not exhibited, while the content of Bi is 0.10 mass%.
%, Bi cannot be prevented from deteriorating the appearance of the film even with the technique of the present invention. Therefore, Bi is contained in the range of 0.001 to 0.10 mass%.

The essential components have been described above. In the present invention, the following elements can be appropriately contained as needed. S and / or Se: 0.010 to 0.030 mass% Se and S combine with Mn and Cu to form MnSe, MnS, Cu _2-X S
e, Cu _2-X is a useful component that forms S and acts as an inhibitor as a second dispersed phase in steel. However, if the content of Se and S is less than 0.010 mass%, the effect of the addition is poor. On the other hand, if the content exceeds 0.030 mass%, not only the solid solution at the time of slab heating becomes incomplete, but also defects on the product surface are reduced. Therefore, it is preferable that the content be in the range of 0.010 to 0.030 mass% in either case of single addition or composite addition.

Cr: 0.05 to 0.50 mass% Cr has the effect of preventing the deterioration of the coating film produced from the material to which Bi is added, and the residence time in the final finish annealing at 700 to 900 ° C. and the TiO in the separating agent. _{(2) By} combining the addition amount and the moisture content, it is possible to obtain a product having a better film appearance. The reason for this is that the addition of Cr in steel promotes the development of forsterite anchors and prevents exfoliation during final annealing.
Here, if the Cr content in the material is less than 0.05 mass%, the effect of improving such a coating is small, while if the Cr content exceeds 0.50 mass%, the magnetic properties of the product are deteriorated.
It is preferable to contain it in the range of 05 to 0.50 mass%.

One or two selected from Cu, Sb and Sn
Species or more: 0.05 to 0.50 mass% Cu is a useful element that forms Cu _2-x Se and Cu _2-x S in steel and exhibits an inhibitory action as a dispersed second phase in steel. It contributes to stabilization of the next recrystallization. Also, Sb, Sn
Has the function of secondaryly strengthening the inhibitory effect by segregating at the crystal grain boundaries, and has the effect of stabilizing secondary recrystallization. When the formation of the forsterite film proceeds according to the present invention, the surface inhibitors (AlN, MnS
e, MnS, Cu _2-X Se, Cu _2-X S) may be excessively decomposed to cause magnetic deterioration. However, Cu,
If Sb or Sn is added as an inhibitor-enhancing element, such secondary recrystallization failure can be prevented, and a product having good magnetic properties can be obtained _. Here, the total amount of these elements is 0.05 mass
%, The effect of the inhibitor is not sufficient, while if it exceeds 0.50 mass%, problems such as cracking of the hot-rolled sheet and deterioration of the surface properties of the product will occur. 0.05 ~ 0.50
It is preferable to contain it in the range of mass%.

Further, in addition to the above-mentioned components, Ni or Ge can be contained in the steel alone or in combination as an inhibitor element. Here, the content for Ni or Ge to have an inhibitory function is 0.0010 to 1.30 mass%. That is, if it is less than this range, sufficient restraining force cannot be provided, while if it exceeds the above range, cracks are easily formed by hot rolling or cold rolling, and the product yield is reduced. descend. In addition to the above elements, Te, P, Zn,
A known inhibitor element such as In can be added.

Next, the manufacturing method of the present invention will be described. The steel slab adjusted to the above-mentioned preferable component composition is heated to a high temperature of 1350 ° C. or more to form a solid solution of the inhibitor component. In this regard, when the inhibitor is reinforced in a later step by nitriding or the like, the heating temperature can be set to 1280 ° C. or lower. Then, after hot rolling, annealing treatment and cold rolling are combined to obtain a final sheet thickness, decarburizing annealing and final finishing annealing are performed, and an insulating tension coating is baked to obtain a product.

Here, the method of combining the annealing treatment and the cold rolling to obtain the final sheet thickness is as follows: 1) After hot rolling, performing hot rolling sheet annealing, and then performing two cold rolling operations including intermediate annealing 2) A method in which after hot rolling, hot-rolled sheet annealing is performed, and then a single cold rolling is performed to obtain a final sheet thickness. 3) After hot rolling, hot-rolled sheet annealing is performed. There is a method in which the final sheet thickness is obtained by performing cold rolling twice including intermediate annealing without performing the above-described steps, but any of these steps can be adopted in the present invention. In addition, the annealing atmosphere is oxidized by hot-rolled sheet annealing or intermediate annealing to perform a process of weakly decarburizing the surface layer, or a process of increasing the solid solution C in steel by rapidly cooling the annealing cooling process. The subsequent low-temperature holding treatment for precipitating fine carbides in the steel is effective for improving the magnetic properties of the product. In addition, cold rolling is
Performing at a temperature of up to 300 ° C. or aging between passes also advantageously works to improve magnetic properties. Further, providing a plurality of linear grooves substantially perpendicular to the rolling direction of the steel sheet for subdividing magnetic domains is also effective for further improving iron loss.

Further, as is well known, a technique of performing nitriding treatment in which N is contained in steel in a range of 300 ppm or less after decarburization and primary recrystallization annealing until the start of secondary recrystallization is also known. Therefore, in combination with the present invention, it is possible to further improve the film characteristics and the magnetic characteristics.

Next, after decarburizing annealing, an annealing separator is applied, and then final finishing annealing is performed. Then, an insulating coating is applied, and annealing for both baking and flattening is performed to obtain a product. It is the gist of the present invention to properly combine the separating agent with the method of final finish annealing. Hereinafter, the conditions of the annealing separator and the final finish annealing will be described. In the temperature rise process of final finish annealing
Residence time As mentioned earlier, Bi becomes significantly concentrated on the surface layer in the temperature range of 700-900 ° C. Therefore, in order to improve the appearance of the film after final annealing, 700-900
It is necessary to shorten the residence time in the ° C range. 700-900
When the residence time at ℃ exceeds 60 hours, the concentration of Bi in the surface layer of the steel sheet becomes remarkable, and the appearance of the coating deteriorates.
Limited to the above range. Here, 700-90 for film formation
The residence time is more important than the heating rate in the 0 ° C range,
If the residence time in this temperature range is within 60 hours, this temperature range may be heated at a constant rate, or the rate of temperature rise may be changed, or even maintained at a constant temperature. ,
Either is acceptable. As shown in Table 3 and FIGS. 2 and 3, when the residence time at 700 to 900 ° C. is within 30 hours, the appearance and bending adhesion of the coating can be further improved. Therefore, it is more desirable that the residence time in the 700-900 ° C. range be within 30 hours.

The amount of TiO ₂ added in the separating agent The experimental results shown in FIG.
The residence time in the 00-900 ° C range should be within 60 hours,
By setting the amount of TiO ₂ in the annealing separator to 3 parts by weight (MgO: 100 parts by weight) or more, a good film appearance can be obtained. Has been obtained. 800 ° C for TiO ₂
In the vicinity of the temperature range, it reacts with MgO, which is the main component of the annealing separator, to form MgTiO ₃ , which has the effect of promoting the forsterite formation reaction in the higher temperature range.
It is considered that, when is moved into the annealing separator, the reaction between MgO and TiO ₂ is suppressed and the effect of TiO ₂ addition does not appear.
It is also expected that the concentration of Bi on the steel sheet surface will increase in the 700-900 ° C range _. Therefore, it is considered that by shortening the residence time in the 700 to 900 ° C. region and suppressing the increase in the concentration of Bi in the annealing separator, the reaction between MgO and TiO ₂ is sufficiently caused to improve the film formation. However, TiO ₂ in the incinerated separating agent
Is less than 3 parts by weight, the reaction with MgO does not proceed even if the Bi concentration is sufficiently reduced, and a good forsterite film cannot be obtained after the final annealing. Therefore, the amount of TiO ₂ added is 3 parts by weight. Parts or more.

The concentration of water in the surface layer of the steel sheet in the range of 700 to 900 ° C. in the moisture content of the annealing separator after coating and drying suppresses the floating of silica particles generated near the surface of the decarburized annealed sheet. It is considered that this causes peeling of the coating during the finish annealing and deterioration of the adhesion of the coating of the product. On the other hand, even when the atmosphere during the final finish annealing has a high oxidizing property, the floating of silica is suppressed. Therefore, when Bi is concentrated on the surface, the deterioration of the coating becomes more remarkable. H ₂ O contained as water of hydration in the annealing separator oxidizes iron on the steel sheet surface in a low temperature range to form iron oxides such as FeO, and furthermore, by introducing hydrogen in a high temperature range of final finish annealing. The iron oxide is reduced to generate H ₂ O again, which causes an increase in the oxidizing property near the steel sheet. Therefore, in the final finish annealing of the Bi-containing material, it is necessary to limit the amount of water per unit area of the steel strip brought into the annealing separator to a certain level or less. Since, H ₂ O contained in the annealing separator is, after forming the temporarily iron oxides the strip surface as mentioned above, the oxidizing near the surface to form again H ₂ O by the introduction of hydrogen To enhance
This is because the water content of the applied annealing separating agent as a whole intensively contributes to an increase in oxidizing properties near the steel strip surface. Therefore, even with an annealing separator having a low water content, an excessive amount of coating results in deterioration of the coating.

The moisture contained in the annealing separator is MgO
Or the water of hydration of additives, and calculate the amount of water contained from the composition of the annealing separator, or collect the annealing separator after coating and drying, and calculate the amount of weight loss by heating at 1000 ° C for 1 hour. Can be measured. The moisture content of such an annealing separator is obtained, and the weight of the annealing separator is multiplied by the basis weight of the annealing separator (applied amount per unit area of one surface of a steel sheet) to obtain the basis weight of moisture. When basis weight of the water obtained in this way is more than 0.5 g / m ^2, in the final finish annealing
Even when the residence time at 700 to 900 ° C is shortened to suppress the surface enrichment of Bi, a good film cannot be obtained.Therefore, the basis weight of moisture of the annealing separator after application and drying is 0.5 g / m ²
Limited to the following.

After the above-mentioned final finish annealing, if necessary, a tension imparting coating or an insulating coating is baked on the surface of the steel sheet, and then flattening annealing is performed to obtain a product. Also,
In order to reduce iron loss by subdividing magnetic domains, plasma-jet or laser irradiation is applied linearly to the steel sheet after flattening and annealing, or a linear concave is formed by a projection roll, and etching is performed after final cold rolling. For example, a process of forming a linear groove in a direction substantially perpendicular to the rolling direction can also be performed. It is also effective to reduce the iron loss by combining a technique of forming a tension film by a known method such as a sol-gel method or TiN vapor deposition after removing the oxide on the surface as necessary after the final annealing. is there.

[0053]

EXAMPLES Example 1 C: 0.06 mass%, Si: 3.25 mass%, Mn: 0.07 mass%,
P: 0.003 mass%, S: 0.003 mass%, sol.Al: 0.023
mass%, Se: 0.020 mass%, Sb: 0.030 mass%, Cu: 0.0
A steel slab containing 5 mass%, N: 0.0082 mass% and Bi: 0.020 mass%, with the balance being substantially Fe, was charged into a gas heating furnace, heated to 1230 ° C, and retained for 60 minutes. After heating at 1400 ° C. for 30 minutes by induction heating, a hot-rolled sheet having a thickness of 2.5 mm was formed by hot rolling. Then, after hot-rolled sheet annealing at 1000 ° C for 1 minute, pickling and primary cold rolling are applied to make the thickness: 1.
After 6 mm, intermediate annealing at 1000 ° C for 1 minute, pickling, and secondary cold rolling at the maximum temperature of 220 ° C to a final thickness of 0.23 mm after the pickling, followed by oxidation in the soaking process Sex is P
(H ₂ 0) / P (H ₂ ): After decarburizing annealing at 850 ° C. for 100 seconds in an atmosphere of 0.45, apply an annealing separator in an amount of 7 g / m ² per one side of the steel sheet. , And wound up in a coil. Here, by adjusting the hydration amount of MgO, the basis weight of the moisture per one side of the steel sheet in the annealing separator after coating and drying was adjusted as shown in Table 4.
Was changed as shown in FIG. In addition, TiO ₂ is used for the annealing separator.
10 parts by weight were added. Final finish annealing from room temperature to 700 ℃
The temperature was raised over a period of 70 hours, and the temperature was raised between 700 and 900 ° C. at a constant rate, or when the temperature reached 850 ° C., the temperature was kept constant for a certain period of time, and then the temperature was raised. The residence time of the material at 700-900 ° C was varied as shown in Table 4. Atmosphere in final finish annealing, and up to 900 ° C. and N _2, 900
11150 ° C. was H ₂ : 75 vol%, N ₂ : 25 vol%, and then the atmosphere was switched to H ₂ to perform a purification treatment at 1200 ° C. for 10 hours.

Thereafter, the unreacted separating agent was removed by washing with water, followed by applying an insulating tension coating mainly containing magnesium phosphate containing colloidal silica, followed by flattening annealing to obtain a product. Then, a linear strain was introduced by irradiation with a plasma flame under the conditions that the distance between the rolling directions was 10 mm and the angle between the rolling directions was 80 °, and the magnetic domain was subdivided. Thus resulting specimen of 500mm was taken from the product, SST (single plate magneto tester) magnetometry by (magnetic flux density B ₈ and iron loss W _17/15 by Epstein test method)
Was done. In addition, the appearance of the coating film after the final annealing was visually determined, and the bending adhesion was investigated. The bending adhesion was measured after applying an insulating coating mainly composed of magnesium phosphate and colloidal silica.
The test pieces were wound around round rods of various diameters at mm intervals, and evaluated at the minimum diameter at which the coating did not peel. Table 4 shows the obtained results.

[0055]

[Table 4]

As shown in the table, all of the product sheets manufactured according to the present invention exhibited excellent film appearance and bending adhesion, and also had excellent magnetic properties.

Example 2 Twenty-one steel slabs having the composition shown in Table 5 were heated at 1200 ° C. for 60 minutes by gas heating, and then heated at 1400 ° C. by induction heating.
After heating for 30 minutes, a hot-rolled sheet having a thickness of 2.2 mm was formed by hot rolling. Then, after annealing the hot rolled sheet at 950 ° C for 1 minute,
After the thickness is reduced to 1.5 mm by primary cold rolling, 1050 ° C, 1
Intermediate annealing for minutes, and after pickling, maximum sheet temperature: 220
Finished to a final thickness of 0.18 mm by secondary cold rolling at ℃. Then, by resist etching, the angle to the rolling direction: 75 °, the distance between the rolling directions: 3.5 mm, the depth: 12 μm
After forming a linear groove having a width of 70 μm, the oxidizing property P (H ₂₀ ) / P (H ₂ ) of the atmosphere during the soaking process is 0.42, and the soaking temperature is 820.
Decarburization annealing was performed under the conditions of ° C. and soaking time: 150 seconds. Thereafter, an annealing separator containing 4 parts by weight of TiO ₂ with respect to 100 parts by weight of MgO was applied at 7 g / m ² per one surface of the steel sheet. The moisture content of the annealing separator after coating and drying was 4.0 mass%, and the basis weight was 0.28 g / m ² .

[0058] The final finish annealing, the temperature range of 700-850 ° C. The temperature was raised at a rate of 20 ° C. / h C. in N _2, 17.5 hours N ₂ at 850 ° C.
Kept in the temperature range of from 850 to 1,150 ° C. The H _2: 50 vol%,
N ₂ : Heated at a rate of 10 ° C./h in an atmosphere of 50 vol%, and
A purification treatment was performed at 1200 ° C. for 12 hours in an H ₂ atmosphere at 0 ° C. or higher. At this time, the residence time at 700 to 900 ° C. was 30 hours. Next, after performing an insulating tension coating treatment mainly containing magnesium phosphate and colloidal silica, flattening annealing was performed to obtain a product. From the product thus obtained, a sample having a length of 500 mm in the rolling direction and a length of 500 mm in the direction perpendicular to the rolling direction was sampled and subjected to magnetic measurement by SST. In addition, the appearance of the film after the final annealing and the adhesion of the film after the insulating coating were investigated. Table 6 shows the obtained results.

[0059]

[Table 5]

[0060]

[Table 6]

As shown in Table 6, all of the steel sheets obtained according to the present invention were excellent in appearance, adhesion and magnetic properties of the coating.

Embodiment 3 C: 0.06 mass%, Si: 3.25 mass%, Mn: 0.07 mass%,
P: 0.003 mass%, S: 0.003 mass%, sol.Al: 0.023
mass%, Se: 0.020 mass%, Cr: 0.15mass%, Sb: 0.03
0 mass%, Cu: 0.05 mass%, N: 0.0082 mass% and B
i: 0.020 mass% is contained, and the balance is substantially Fe composition
Steel slab is heated at 1400 ° C for 30 minutes by induction heating.
Thereafter, a hot-rolled sheet having a thickness of 2.2 mm was formed by hot rolling. About
After hot-rolled sheet annealing at 1050 ° C for 1 minute, pickling
Degree: Cold rolled at 200 ° C and thickness: 0.27mm final thickness
Finished. Next, the oxidizing P (H
_Two0) / P (H _Two): 0.45, soaking temperature: 820 ° C, soaking time: 150
The decarburization annealing was performed under the condition of seconds. Then, MgO: 100 weight
9 parts by weight of Ti0_TwoAnd 1 to 10 parts by weight of MgSO_Four・
7H _Two0 to 2 to 4 parts by weight of Sr (OH)_Two・ 8H_TwoBaking with 0 added
7g / m per side of steel sheet^TwoApplied. this
Hydration of MgO after coating and drying on steel sheet in slurry state
The amount was 2.6 mass%.

Next, as final annealing, 700 to 90
After raising the temperature in N ₂ to a temperature range of 0 ℃ 20 hours, 1200
Purification treatment was performed at 12 ° C for 12 hours. Then, after performing an insulating tension coating treatment mainly containing magnesium phosphate and colloidal silica, flattening annealing was performed to obtain a product. From the product thus obtained, the length in the rolling direction: 50
0 mm, sample perpendicular to the rolling direction: 500 mm in length, SS
Magnetic measurements with T were performed. In addition, the appearance of the film after the final annealing and the adhesion of the film after the insulating coating were investigated. Table 7 shows the obtained results.

[0064]

[Table 7]

As shown in the table, when manufactured according to the present invention, it was possible to obtain a product having excellent coating appearance, adhesion and magnetic properties.

Example 4 C: 0.07 mass%, Si: 3.30 mass%, Mn: 0.15 mass%,
P: 0.003 mass%, sol. Al: 0.025 mass%, S: 0.005
mass%, Cr: 0.15mass%, Sn: 0.05mass%, Cu: 0.15ma
ss%, N: 0.0035 mass% and Bi: 0.015 mass%, the balance being 1150
After heating at 60 ° C for 60 minutes, hot rolling was performed to obtain a hot-rolled sheet having a thickness of 2.5 mm. After annealing the hot-rolled sheet at 950 ° C for 1 minute, it was pickled and then subjected to primary cold rolling. 1.6 mm, then 10
Intermediate annealing was performed at 50 ° C for 1 minute, and after pickling, the sheet was finished to a final sheet thickness of 0.23 mm by secondary cold rolling at a maximum sheet temperature of 250 ° C. Thereafter, decarburizing annealing was performed, and subsequently, nitriding annealing was performed in an NH ₃ atmosphere so that the N content in the steel was 0.020 mass%.

Then, an annealing separator containing 10 parts by weight of TiO ₂ with respect to 100 parts by weight of MgO was added in an amount of 5 g / side per one side of the steel sheet.
and m ² is applied, the temperature was raised over a period of up to 700 ° C. 45 hours, 700
The temperature is raised at a constant rate so that 900 ° C stays for the time shown in Table 8, 900-1150 ° C is raised at an average rate of 15 ° C / h, and the residence time at 1150-1200 ° C is 20 hours. Final finish annealing was performed. Atmosphere during final annealing is to up to 850 ° C. and N _2, from 850 to 1,150 ° C. The _{H 2: 80 vol%, N} 2: 20 vol
% And the atmosphere, the above 1150 ° C. was an H ₂ atmosphere. After the final annealing, the product was subjected to an insulating tension coating treatment containing magnesium phosphate and colloidal silica as main components, followed by a flattening annealing, and a magnetic domain refining treatment by laser irradiation to obtain a product. From the product thus obtained,
Length in the rolling direction: 500 mm, length perpendicular to the rolling direction: 500 mm
Specimens were collected and subjected to magnetic measurement by SST. Also,
The appearance of the coating after the final annealing and the adhesion of the coating after the insulating coating were investigated. Table 8 shows the obtained results.

[0068]

[Table 8]

As shown in the table, when manufactured in accordance with the present invention, products having excellent coating film appearance, adhesion and magnetic properties were obtained.

[0070]

As described above, according to the present invention, it is possible to effectively prevent the occurrence of forsterite coating defects, which were a concern when using a Bi-containing steel as a material, and as a result, the coating characteristics are excellent and A grain-oriented electrical steel sheet having a high magnetic flux density can be stably manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing the behavior of the surface enrichment of Bi during final finish annealing.

[Fig. 2] Effect of final finish annealing on coating appearance
FIG. 3 is a graph showing the influence of the residence time in the 900 ° C. region and the amount of TiO ₂ in the annealing separator.

[Fig. 3] Effect of final finish annealing on coating appearance 700-
FIG. 3 is a graph showing the influence of the residence time in the 900 ° C. region and the amount of water in the purified separator after coating and drying.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C22C 38/60 C22C 38/60 (72) Inventor Tadashi Nakanishi 1-chome Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture Mizushima Steel Works, Kawasaki Steel Corporation (72) Inventor Mitsumasa Kurosawa 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture LA01 LA02 RA04 SA02 TA01 TA02 5E041 AA02 AA19 BC01 CA02 HB11 HB14 NN01 NN18

Claims (1)

[Claim 1] C: 0.01 to 0.10 mass%, Si: 1.0 to 5.0 mass%, Mn: 0.03 to 0.20 mass% and N: 0.0015 to 0.0130 mass%, and sol. After heating a steel slab containing one or two selected from 0.015 to 0.035 mass% and B: 0.0010 to 0.0150 mass%, and further containing Bi: 0.001 to 0.10 mass%, After rolling, and then subject to hot-rolled sheet annealing if necessary, the final sheet thickness by two cold rolling including intermediate annealing,
Alternatively, after hot-rolled sheet annealing, a series of steps in which the final sheet thickness is obtained by one cold rolling, followed by decarburizing annealing, then applying an annealing separating agent, winding the coil, and then performing final finishing annealing. In a method for producing a grain-oriented electrical steel sheet comprising: an annealing separator containing MgO as a main component, which is applied to the steel sheet before final finish annealing, wherein at least 3 parts by weight of TiO ₂ is added to 100 parts by weight of MgO; the amount of moisture in the annealing separator after applying dry than steel per side 0.5 g / m ^2, and within more finishing 60 hours of time which the coil is retained in the temperature range of 700 to 900 ° C. in the Atsushi Nobori process of the annealing A method for producing a high magnetic flux density grain-oriented electrical steel sheet having excellent coating characteristics. 2. The steel slab according to claim 1, wherein the steel slab further comprises one or two selected from S and Se: 0.010 or more.
A method for producing a high magnetic flux density grain-oriented electrical steel sheet having excellent coating properties, characterized by having a composition containing 0.030 mass%. 3. The method for producing a high magnetic flux density grain-oriented electrical steel sheet according to claim 1 or 2, wherein the steel slab has a composition further containing Cr: 0.05 to 0.50 mass%. . 4. The steel slab according to claim 1, 2 or 3, further comprising one or more selected from Cu, Sb, and Sn.
Species or more: A method for producing a high magnetic flux density grain-oriented electrical steel sheet having excellent coating properties, which has a composition containing 0.05 to 0.50 mass%.