JP2001107145A - Method for producing grain-oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the defect of secondary recrystallization easy to be caused in a Bi-added grain-oriented silicon steel sheet, to stably improve its magnetic properties and to realize good film deposition as well. SOLUTION: In the method for producing a grain-oriented silicon steel sheet containing 0.0005 to 0.070 wt.% Bi, as the main agent as a separation agent for annealing, MgO in which pore volume is 0.03 to 0.20 ml/g is used, and moreover, the ratio between the coating weight of oxygen in the surface of the final finish-annealed sheet σf and the coating weight of oxygen in the surface of the decarburized and annealed sheet σd is controlled to the range in the following inequality (1): σf/σd<=3.5...(1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for manufacturing a grain-oriented electrical steel sheet used for an iron core of a transformer or other electric equipment.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets used as core materials for transformers, generators and rotating machines 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, and among them, to highly integrate the crystal orientation in the {110} <001> orientation called Goss orientation, This is one of the most important development goals. This is because the easy axis of magnetization of the iron crystal is <001.
> Is highly integrated in the rolling direction, the magnetizing force required for the magnetization in the rolling direction is reduced, and the coercive force is reduced. As a result, the hysteresis loss is reduced and the iron loss is advantageously reduced. is there.

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

[0004] 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. Here, B ₈ (magnetizing force: magnetic flux density at 800 A / m) is often used as an index of the degree of integration of the crystal orientation, and the development of grain-oriented electrical steel sheets has been promoted with a major goal of improving B _8. ing. Typical values of iron loss include an excitation magnetic flux density: 1.7 T, an excitation frequency:
W _17/50 , the energy loss at 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 necessary to form a uniform and appropriate size of a dispersed dispersed phase called an inhibitor which selectively inhibits the growth of the primary recrystallized grains. is important. The presence of this inhibitor suppresses the normal grain growth of the primary recrystallized grains, maintains the state of fine primary grains up to high temperatures during final annealing, and increases the selectivity for the growth of crystal grains with good orientation. , 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 orientation accumulation.

[0007] Such inhibitors include MnS,
Materials having low solubility in steel, such as MnSe, Cu _2-X S, Cu _2-X Se, and AlN, are used. For example, JP-B-33-4710 and JP-B-40-15644 contain Al in the material,
A technique is disclosed in which a final cold rolling reduction is set to a high pressure of 81 to 95%, and AlN which is a strong inhibitor is precipitated by annealing before final cold rolling. Further, in addition to the above inhibitor components, the addition of Sn, As, Bi, Sb, B, Pb, Mo, Te, V, Ge, and the like additionally improves the degree of orientation accumulation of secondary grains. And is known to be effective.

[0008] Among these additional inhibitor elements,
P, As, Sb and Bi classified as group 5B elements in the periodic table
Segregates on the grain boundaries, strengthens the ability to suppress normal grain growth in cooperation with the main inhibitors MnS, MnSe, Cu _2-X S, Cu _2-X Se, AlN, etc. It is known that Bi has a low solubility in iron. Therefore, Bi has been regarded as a promising element as an element for enhancing the normal grain growth suppressing power by the grain boundary segregation effect.

As a technique for improving magnetic properties by adding Bi, Japanese Patent Publication No. Sho 51-29496 and Japanese Patent Publication No. Sho 54-32412 are known. In addition, Japanese Patent No. 2872404 and Japanese Patent Publication No. 7-62176 describe a method in which AlN, MnSe, MnS, etc. and Bi are added to steel in a complex manner. Although these technologies certainly utilize the strengthening effect of Bi on the suppression force, they have not yet established appropriate manufacturing conditions for Bi-added materials, and to obtain stable and high magnetic properties It was not enough.

Similarly, in JP-A-6-88171, JP-A-6-88172, JP-A-6-88173 and JP-A-6-88174, Bi is added to an Al-based inhibitor. It is described that the magnetic flux density can be greatly improved, but the effect itself of adding Bi is not only conventionally known, but also a method for stably extracting the effect of improving magnetic properties is proposed. Not.

As described above, although Bi is an extremely promising method for improving the magnetic properties of grain-oriented electrical steel sheets, secondary recrystallization defects are liable to occur due to various factors, and high magnetic properties are stable. The problem was that it was hard to get.

Other prior arts relating to the coating amount of the final finish annealed sheet of a material in which Bi is added to steel include Japanese Patent Publication No. 2-58324, Japanese Patent Publication No. 2-58325, and Japanese Patent Publication No. 2-58325.
No.-58326, for example, specifies the forsterite coating amount on one side of the final annealed plate to be 1 to 4 g / m ² . However, in these techniques, only the amount of forsterite is specified for the purpose of reducing the iron loss by applying an appropriate tension to the final finish annealed sheet, which is advantageous for the stability of the secondary recrystallization. Is not shown.

Japanese Patent Application Laid-Open No. Hei 8-232019 discloses a method of performing nitridation during the manufacturing process with respect to an oxygen basis weight of a decarburized annealed sheet made of a material in which Bi is added to steel. A method is disclosed in which the specific weight of oxygen is set to 600 to 900 ppm and a predetermined substance is added to the annealing separator. The purpose of this method is to improve the forsterite film, which tends to occur in the nitriding step, and cannot sufficiently stabilize the secondary recrystallization of the Bi-added material. Also,
Japanese Patent Application Laid-Open No. 10-152725 discloses a technique for controlling the basis weight of oxygen on the surface of a decarburized annealed sheet of a material in which Bi is added to steel to 550 to 850 ppm. Since it is intended to stabilize it, there is no regulation on the physical properties of MgO as shown in the present invention, which is insufficient for stabilizing magnetic properties. Furthermore, the present inventors previously described in Japanese Patent Application No. 10-133487, the cooling rate during hot rolling, the atmosphere for decarburizing annealing, and the surface oxygen content of the final finish annealed sheet to improve the magnetic properties. Although a technique for stabilization has been proposed, this technique has a problem that it is difficult to obtain a good coating because the surface oxygen content of the final finish annealing plate is limited to a low level.

[0014]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the above-mentioned problems, and eliminates secondary recrystallization defects which tend to occur in grain-oriented electrical steel sheets to which Bi is added, and at the same time, forms a good film. It is another object of the present invention to propose a method for manufacturing a grain-oriented electrical steel sheet having excellent magnetic properties, which is also realized.

[0015]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, in the case of Bi-added material, the base material of the annealing separating agent used in the final finish annealing is used. By appropriately controlling the pore volume of a certain MgO and optimizing the ratio of the oxygen basis weight of the final finishing annealed plate to the oxygen basis weight of the decarburized annealed plate, a film having a sufficient film thickness is formed. It has been found that secondary recrystallization is stable and stable production of grain-oriented electrical steel sheets having a high magnetic flux density is possible. The present invention is based on the above findings.

Here, the pore volume referred to in the present invention is a value measured by a quantitative gas adsorption method.
After treating O 2 in vacuum at 400 ° C. for 2 hours, the adsorption gas was measured by the BET multipoint method with N _{2 at} an adsorption temperature of 77 K, and the adsorption data was evaluated by analysis by the DH method. . The DH method is an abbreviation of the Dollimore-Heal method, and is a method of obtaining the distribution of pores from the relative pressure of the adsorbed gas and the increment of the amount of adsorption, assuming that the pores are cylindrical.

That is, the gist configuration of the present invention is as follows. 1. C: 0.01 to 0.10 wt%, Si: 1.0 to 5.0 wt%, Mn: 0.
A steel slab containing 03-0.20 wt%, Bi: 0.0005-0.070 wt% and an inhibitor element is hot-rolled, and then subjected to one or more cold rollings including an annealing treatment to obtain a final sheet thickness. After that, decarburizing annealing, then apply an annealing separator on the surface of the steel sheet, then, in a method for manufacturing a grain-oriented electrical steel sheet comprising a series of steps of performing a final finish annealing, the pore volume as a main component of the annealing separator 0.03 to 0.20 ml / g of MgO is used, and the oxygen basis weight σ _f per side of the surface of the finally finished annealed plate and the oxygen basis weight σ _d per side of the surface of the decarburized annealed plate are expressed by the following formula (1) σ _f / σ _d ≤ 3.5 --- A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, satisfying the range of (1).

2. As an inhibitor element of steel slab,
One or more selected from Al, S, Se, Sb, Sn, Cu, Cr, Ni, Ge, B and N are added, and Al, S, Se
0.010 to 0.060 wt% for Sb alone or 0.0010 to 0.080 wt% for Sb, 0.0010 to 1.30 wt% for Sn, Cu, Cr, Ni, Ge, 5 to 50 ppm for B, N
3. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties as described in 1 above, wherein the content is added in the range of 30 to 100 ppm.

3. Oxidation potential P in decarburized annealing atmosphere
(H ₂ 0) / P 1 above (H ₂₎ was in the range of 0.45 to 0.65, and characterized by the coating amount of the annealing separator composed mainly the steel sheet per side 9 g / m ² or less of MgO Or the method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to 2.

4. 4. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to the above 1, 2, or 3, wherein the average rate of temperature rise in the 850 to 1100 ° C. range in the final finish annealing step is 10 to 60 ° C./h.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the above-mentioned Japanese Patent Application No. 10-133687, there is proposed a method of stabilizing secondary recrystallization by limiting the amount of oxygen on the surface of a finally finished annealed sheet to a low level. In this case, however, there is a problem that the appearance of the product is easily deteriorated due to the shortage of the film formation amount. On the other hand, the present inventors have found that even when the oxygen content on the surface of the final finish annealing plate is increased, MgO as the main component of the annealing separator is used.
It has been found that the secondary recrystallization is stabilized by properly controlling the physical properties, that is, the pore volume, and completed the present invention.

Hereinafter, an experiment on which the present invention is based will be described. As main components, C: 0.06wt%, Si: 3.3wt
%, Mn: 0.07 wt%, Se: 0.02 wt%, S: 0.005 wt%, A
l: 0.022 wt% and N: 0.0082 wt%.
Of silicon steel slabs with and without 0.010 wt%
After heating to 00 ° C and holding for 30 minutes, hot rolling
The thickness was 2.4 mm. Subsequently, the hot-rolled sheet was annealed at 1000 ° C. for 30 seconds, pickled, and then subjected to primary cold rolling to a thickness of 1.5 mm. Subsequently, intermediate annealing was performed at 1050 ° C. for 1 minute, and this was pickled, and then subjected to secondary cold rolling to a final thickness of 0.23 mm. In the subsequent decarburization annealing process, P (H ₂ 0) /
P (H ₂ ) was set to 0.45, and the soaking time was set to 100 seconds. Subsequently, these materials were added to MgO: 10 with different pore volumes.
0 parts by weight of TiO ₂ and 5 parts by weight of annealed separating agent mixed with water to form a slurry, 7.5 g per side of steel sheet
/ m ² was applied. Where the hydration of MgO is
Adjusted to 3.0%. Then, final finishing annealing was performed at a maximum temperature of 1200 ° C. for 5 hours at an average temperature rising rate of 20 ° C./h in the range of 800 to 1000 ° C. Then, an insulating coating mainly composed of magnesium phosphate containing colloidal silica was applied and baked on the obtained final finish annealed plate to obtain a product.

From the thus obtained product plate, 16 test pieces (width: 30 mm, length: 280 mm) were sampled, and the magnetic flux density B ₈ was measured by the Epstein test method. Also, when the oxygen basis weight σ _d per one side of the steel sheet of the decarburized annealed sheet and the oxygen basis weight σ _f per one side of the steel sheet of the final finish annealed sheet were measured, they were 0.7 g / m ² and 1.9 g / m ² , respectively. Was. They are,
The surface oxide film was removed from the amount of oxygen analyzed with the oxide film attached, the amount of oxygen analyzed only with the base iron was subtracted, and the oxygen content per one side of the steel sheet was converted into the weight per unit area.

FIG. 1 shows the pore volume and the magnetic flux density B _{8 of} MgO.
(Magnetizing force: magnetic flux density at 800 A / m) is shown. As is clear from the figure, the material with Bi added to steel has a pore volume of 0.03-0.20 ml / g.
It was found that when O 2 was used, both the film properties and the magnetic properties were good. On the other hand, in the material to which Bi is not added, B ₈ hardly depends on the pore volume.

Based on the above results, a more detailed investigation was conducted. As a result, it is not enough to stably control the MgO 2 pore volume in order to stabilize the secondary recrystallization of the Bi-containing material. It is important to control the ratio of the oxygen basis weight of the final finish annealed plate to the oxygen basis weight of the decarburized annealed plate within an appropriate range, and by satisfying these conditions, the oxygen basis weight of the surface of the final finish annealed plate is reduced. It has been found that a grain-oriented electrical steel sheet having a high magnetic flux density can be stably obtained even when it exceeds 1.5 g / m ² .

FIGS. 2, 3 and 4 show the relationship between the oxygen basis weight σ _f per one side of the surface of the final finish annealing plate and B _8, and the oxygen basis weight σ _d and B per side of the decarburized annealed plate surface, respectively.
Shows the results of examining the relationship between the relationship and both ratios σ _f / σ _d and B ₈ and _8. The experimental method for obtaining these results is based on the experimental method described above,
The pore volume of O 2 was 0.100 ml / g. Further, σ _d was adjusted by the oxidation potential P (H ₂ 0) / P (H ₂ ) in the decarburizing annealing atmosphere, and σ _f was adjusted by the hydration amount and the basis weight of the pure separator.

FIG. 2 shows that when the pore volume of MgO used as the annealing separator is 0.10 ml / g, when the surface oxygen content σ _{f of} one surface of the finally finished annealed plate exceeds 1.75 g / m ² , B ₈ becomes A falling case occurred. However, even if σ _f exceeds 1.75 g / m ² , good magnetic properties may be obtained, and the dispersion is large. Also, large variation in the relationship between the decarburization annealed sheet oxygen basis weight sigma _d and B ₈ of the surface shown in FIG. 3, sigma
Magnetic degradation cannot be accurately explained by _f and σ _d alone. In contrast, in FIG. 4, B ₈ changes according to σ _f / σ _d with almost no variation, and σ _f / σ _d
By a 3.5 or less, B ₈ is seen to be able to stably manufactured products high magnetic flux density exceeding 1.960T.

FIG. 5 shows the results of examining the effects of σ _f / σ _d and pore volume on B ₈ for grain-oriented electrical steel sheets manufactured from billets containing 0.010 wt% Bi. . As shown in the figure, when σ _f / σ _d and the pore volume satisfy the range of the present invention, the product yield of B ₈ ≧ 1.97T is 100%, and the magnetic flux density is extremely high. It can be seen that excellent products can be obtained stably.

Next, FIG. 6 shows the Bi content in the raw steel slab and the B content.
_This shows the relationship with ₈ . Of these, in condition 1, the pore volume of MgO was 0.10 ml / g and σ _f / σ _d was 2.0, while in condition 2, the pore volume of MgO was 0.30 ml / g, σ
_f / σ _d was set to 3.7. The atmosphere of the decarburizing annealing was set to P (H ₂ 0) / P (H ₂ ) = 0.50. From the results shown in the figure, it was found that according to the production method of the present invention, excellent magnetic properties of B ₈ ≧ 1.96T were obtained when the Bi content was 0.0005 to 0.070 wt%.

Next, the influence of the decarburizing annealing atmosphere and the amount of the applied annealing separator was examined, and it was examined whether further improvement of the magnetic properties was possible. FIG. 7 shows the relationship between P (H ₂ 0) / P (H ₂ ) and B ₈ in a decarburizing annealing atmosphere investigated by the same experiment as described above. Here, σ _d also changes in accordance with the change in the decarburizing annealing atmosphere, so in this experiment, σ _d was maintained in the range of 0.60 to 0.65 g / m ² by adjusting the soaking time. Also, Mg
O should be designed pore volume 0.180 ml / g, and the coating amount of the annealing separator and the steel plate per one surface 8 g / m ² or 10 g / m ^2.
As shown in the figure, when the applied amount of the annealing separating agent is 8 g / m ² per one surface of the steel sheet, the P (H ₂₀ ) / P (H ₂ ) of the decarburizing annealing atmosphere is
By the 0.45 to 0.65, B ₈ are products obtained with excellent magnetic properties exceeds 1.97T. On the other hand, when the coating amount of the separating agent was 10 g / m ² , sufficient characteristics were not obtained even when P (H ₂₀ ) / P (H ₂ ) was changed.

Subsequently, the temperature rise rate of the final finish annealing and the MgO
The effect of pore volume on the film appearance and magnetic properties was investigated. FIG. 8 shows that the pore volume of MgO used as the annealing separator was 0.10 ml / g or 0.25 ml / g, and the rate of temperature rise in the 850 to 1100 ° C. range of the final finish annealing was 4 to 90 ° C./h. The results of examining the appearance of the coating at a constant speed are shown. As shown in the figure, the pore volume was 0.10 ml / g,
The final heating rate in the 850-1100 ° C range was 10
By setting the temperature to 6060 ° C./h, a good coating appearance and magnetic properties are obtained.

As described above, the cause of stabilizing the secondary recrystallization of the Bi additive by properly controlling the pore volume of MgO 2 has not been clearly elucidated so far. Have estimated as follows. That is,
When the annealing separator is slurried and applied to a steel sheet, moisture adsorbs on the MgO surface, but if MgO has pores, water preferentially adsorbs on the pores. Such water of hydration of MgO 2 is released during the final annealing to serve as an oxygen source and has an action of oxidizing the surface of the steel sheet. The water adsorbed in the pores is stronger than the water adsorbed on the outside of MgO, and is considered to be released at high temperatures. Here, Bi is considered to increase the degree of crystal orientation accumulation after secondary recrystallization by increasing the ability to suppress normal grain growth on the surface layer of the base iron, so that when moisture is released from MgO in the high-temperature region, It is presumed that the oxidation of Bi progresses and the Bi concentration near the surface of the base iron decreases, so that the ability to suppress normal grain growth near the surface layer decreases and the magnetic properties deteriorate.

Further, the cause if the ratio of oxygen basis weight sigma _d of the final finishing oxygen basis weight of the annealed sheet surface sigma _f and decarburization annealed sheet surface is increased to B ₈ is degraded is considered as follows. That is, when σ _d is reduced, the protection against the external atmosphere is reduced due to the incomplete development of the oxide layer on the surface of the decarburized annealed sheet, and the magnetic properties are deteriorated to promote the deterioration of Bi and other surface inhibitors. On the other hand, by increasing the oxygen basis weight sigma _f of final annealing plate surface for the decomposition of the base steel surface layer of Bi is promoted, it believed to cause deterioration of magnetic properties. Therefore, all of these factors are correlated with the decomposition and disappearance of Bi on the surface of the base iron during final annealing.
These must be controlled simultaneously to obtain good magnetic properties. Therefore, the ratio σ _f / σ _{d of the two} is Bi
It can be said that this is an excellent index regarding the degree of disappearance of the surface layer inhibitory effect due to.

Here, the pore volume of MgO mainly determines the amount of surface oxidation in a high temperature region near the secondary recrystallization temperature, and has a strong effect in a short time on deterioration of the inhibitory force of the surface layer of the steel sheet. Exert. On the other hand, σ _f / σ _d can be considered as an amount that controls the long-term deterioration of the suppressing force from the beginning to the end of the final annealing. Therefore, it is considered that it is difficult to stably obtain a product having excellent magnetic characteristics unless these two factors are simultaneously optimized.

Further, as shown in FIG. 7, the secondary recrystallization is further stabilized by the increase in the oxidizing atmosphere in the decarburizing annealing because the internal structure of the oxide layer on the surface of the decarburized annealing plate changes. It can be assumed that the loss of Bi in the steel was suppressed.
However, if the atmospheric oxidation degree is excessively increased so that P (H ₂ 0) / P (H ₂ ) exceeds 0.65, a non-uniform film is formed on the decarburized annealed sheet to cause magnetic deterioration. It is estimated to be.

The requirements for obtaining the effects of the present invention, the range thereof, and the effects thereof will be described below with respect to the component composition and the production method of the grain-oriented electrical steel sheet of the present invention. First, the reason why the component composition of the material is limited to the above range will be described. C: 0.01 to 0.10 wt% 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. Need to be included,
If the content exceeds 0.10 wt%, decarburization failure occurs during decarburization annealing, so C was limited to the range of 0.01 to 0.10 wt%.

Si: 1.0 to 5.0 wt% Si is an element necessary for increasing electric resistance to reduce iron loss and stabilizing the α phase of iron to enable heat treatment at a high temperature. 1.0 wt% is required,
If the content exceeds 5.0 wt%, cold rolling becomes difficult.
Limited to 5.0 wt%.

Mn: 0.03 to 0.20 wt% Mn not only effectively contributes to the improvement of hot brittleness of steel, but also forms an inhibitor such as MnS or MnSe when S and Se are mixed. Exhibits a function as an inhibitor. However, if the content is less than 0.03 wt%, the above effect is insufficient. On the other hand, if the content exceeds 0.20 wt%, precipitates such as MnSe are coarsened and the effect as an inhibitor is lost. The range was limited to 0.20.20 wt%.

Bi: 0.0005 to 0.070 wt% Bi concentrates preferentially at the grain boundaries of the primary recrystallized grains, lowers the mobility of the grain boundaries during annealing, raises the secondary recrystallization temperature, and increases the magnetic flux. It has the effect of increasing the density. Although this effect is similar to that of Sb, As, etc., Bi has a particularly low solubility in iron and a very low melting point of 271 ° C, so it tends to be unevenly distributed on the grain boundaries. In order to escape from the steel in the region, it is possible to provide a strong inhibitory force as compared with a normal inhibitor component. Also Bi
Are MnSe, MnS, Cu _x S, Cu _x Se, AlN and BN
The presence of such a precipitation-dispersion type inhibitor in steel at the same time as the above has an effect of improving the magnetic properties of any of them. However, if the Bi content is less than 0.0005 wt%, the effect of suppressing the normal grain growth due to the above-mentioned enrichment at the grain boundaries is not exhibited. On the other hand, if the Bi content exceeds 0.070 wt%, the film deteriorates and cracks due to hot rolling. Increases, so Bi is 0.0005
It was made to contain in the range of -0.070 wt%.

In the steel, in addition to these components, Al, S, Se, Sb, Sn, Cu, Cr, Ni, Ge,
One or more of B and N may be selected and added alone or in combination. Here, the addition range for each element to exhibit the function as an inhibitor is 0.010 to 0.060 wt% for Al, S, Se alone or in total, and 0.0010 to 0.080 wt% for Sb.
%, For Sn, Cu, Cr, Ni, Ge 0.0010-1.30 wt%,
B is 5 to 50 ppm, and N is 30 to 100 ppm. If the amount is less than the above range, a sufficient suppressing force cannot be imparted. On the other hand, if the amount exceeds the above range, cracks are easily formed in hot rolling or cold rolling, and the product yield is reduced. In addition to the above elements, known inhibitor elements such as Te, P, Zn, In, and P can be added.

Next, the manufacturing method of the present invention will be described.
The silicon steel slab adjusted to the above preferable component composition is heated to a high temperature in order to form a solid solution of the inhibitor component. However, when the inhibitor is reinforced in a later step by nitriding or the like, heating is performed at a relatively low temperature of 1280 ° C. or less. 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, as a method of obtaining the final sheet thickness, 1) a method of obtaining a final sheet thickness by performing two cold rollings including intermediate annealing after hot rolling and then performing a norma annealing, 2) after a hot rolling, After performing the quota annealing, a method of making the final thickness by one cold rolling,
3) After the hot rolling, there is a method in which the final thickness is obtained by performing two cold rollings including the intermediate annealing without performing the norma annealing. In the present invention, any of these steps can be adopted.

In addition, the surface of the steel surface is weakly decarburized by oxidizing the annealing atmosphere by norma annealing or intermediate annealing, or the process of increasing the solid solution C in steel by rapidly cooling the cooling process of the annealing. Subsequent to that, a low-temperature holding treatment for precipitating fine carbides in the steel is effective for improving the magnetic properties of the product. Performing cold rolling in a warm state or performing aging treatment between passes also advantageously acts to improve magnetic properties. Providing a plurality of linear grooves substantially perpendicular to the rolling direction of the steel sheet for subdividing the magnetic domains is also applicable since it has the effect of further improving iron loss.

Further, a technique of nitriding, in which the steel contains N in a range of 50 ppm or less after the decarburization / primary recrystallization annealing and before the start of the secondary recrystallization, is also known as a technique for reinforcing the suppression force. In combination with the present invention, it effectively contributes to improvement of magnetic characteristics.

In the present invention, when producing a grain-oriented electrical steel sheet by the above-described steps, the pore volume of MgO used in the final finish annealing is set to 0.03 to 0.20 ml / g, and the oxygen content of the final finish annealed plate is adjusted. The ratio σ _f / σ _d between the basis weight and the oxygen basis weight of the decarburized annealed plate is set to 3.5 or less. Here, if the pore volume is less than 0.03 ml / g, the magnetic properties will be slightly deteriorated and the coating properties will be degraded due to the insufficient amount of water carried. On the other hand, if it exceeds 0.20 ml / g, the magnetic properties deteriorate due to rapid surface oxidation progressing in a high temperature region (near the secondary recrystallization start temperature). Further, when σ _f / σ _d exceeds 3.5, the effect of suppressing normal grain growth of Bi decreases due to the progress of surface oxidation during final finish annealing, and secondary recrystallization failure becomes remarkable. Therefore, it is important that the pore volume is 0.03 to 0.20 ml / g, and the ratio σ _f / σ _d of the oxygen basis weight of the final finish annealing plate to the oxygen basis weight of the decarburized annealing plate is 3.5 or less. .

As the value of the oxygen basis weight σ _d of the decarburized annealed sheet,
A range of 0.3 to 1.2 g / m ² is recommended. In the final finish annealing, the equation (1) is obtained according to the oxygen basis weight σ _d of the decarburized annealed plate.
By adjusting σ _f so as to satisfy the following condition, the magnetic properties after the secondary recrystallization can be stabilized. In order to obtain a good forsterite coating after final annealing, σ _f must be at least 0.6 g / m ² , but even when σ _f is less than 0.6 g / m ² , equation (1) is satisfied. Thus, an excellent high B ₈ can be obtained, and a grain-oriented electrical steel sheet with low iron loss can be obtained by forming an artificial tension / insulating coating after the final annealing.

Further, in the present invention, the decarburization annealing atmosphere
Atmosphere oxidation degree P (H_Two0) / P (H_Two) In the range of 0.45-0.65
It is advantageous to do so. Oxidation of decarburized annealing atmosphere is above
The structure of the internal oxide layer of the decarburized annealed sheet
Changes, the loss of Bi in the steel is suppressed, and the secondary recrystallization is stable
It is thought that. On the other hand, P (H_Two0) / P (H_Two) Is 0.45
Below, the Bi in the steel due to the oxide film on the surface of the decarburized annealed sheet
The loss cannot be prevented, and the magnetic properties deteriorate. on the other hand,
P (H_Two0) / P (H _TwoIs greater than 0.65
The disappearance of Bi in the steel is promoted by the film formation, and the magnetic properties deteriorate.
Occurs.

In order to make σ _f / σ _d 3.5 or less, it is important to limit the oxygen basis weight of the final finish annealing plate. It is known that an increase in the basis weight of the annealing separator increases the basis weight of oxygen after the final annealing, and in order to limit this and stabilize the magnetic properties, the basis weight of the annealing separator is 9 g / unit. It is preferable to limit it to m ² or less. Furthermore, the oxygen basis weight σ _d of the decarburized annealed plate increases due to an increase in the degree of atmospheric oxidation P (H ₂₀ ) / P (H ₂ ) during the decarburization annealing, and the oxygen basis weight σ _f of the final finish annealed plate is It is known that σ _f / σ _d can be controlled to a predetermined range by appropriately controlling these influential factors, since it is known that the hydration amount of the annealing separator increases with an increase in the hydration amount.

Further, as shown in FIG. 8, in order to improve the appearance of the coating of the final finish annealed plate, the pore volume of MgO used as the annealing separator was limited to the range of 0.03 to 0.20 ml / g. In the final finishing annealing, it is preferable to set the average heating rate in the 800 to 1100 ° C. range to 10 to 60 ° C./h. Heating rate
When the temperature is lower than 10 ° C./h, Bi is considered to be concentrated on the surface of the steel sheet and inhibit the film formation. On the other hand, when the temperature exceeds 60 ° C./h, the growth of secondary recrystallized grains is not sufficient, and the magnetic properties are deteriorated. In this regard, if the rate of temperature rise satisfies the above conditions and the pore volume of MgO is within an appropriate range, the amount of water released during the final annealing will be appropriate and a good film will be formed. Conceivable.

After the final finishing 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,
To reduce iron loss, the steel sheet after flattening annealing is subjected to plasma jet or laser irradiation linearly as a well-known domain refining process, or to a process of providing a linear recess by a projection roll. Can also. Furthermore, after the final finish annealing, after removing the oxide on the surface as necessary, the sol-gel method, a known method such as TiN vapor deposition, may be combined with a technique of forming a tension film, to reduce iron loss. It is valid.

[0050]

EXAMPLES Example 1 Continuously cast silicon steel slabs (thickness: 220 mm) having various component compositions (steel symbols A to Z) shown in Table 1 were kept at 1180 ° C. for 3 hours and then reduced to 200 mm. And put it into an induction heating furnace and reach 1430 ° C in 30 minutes
Temperature, and soaked for 20 minutes, hot-rolled to 2.4
A hot-rolled sheet having a thickness of mm was used. Next, apply 1050 ° C, 30
After performing a hot-rolled sheet annealing for 2 seconds, it was cooled at a rate of 30 ° C./s by mist water cooling (cooling by sprayed water). Next, after pickling, the sheet is subjected to primary cold rolling to have a thickness of 1.5 mm, and then has a dew point of 1100 ° C. in an atmosphere of 35 ° C. (50% N ₂ −50% H ₂ ).
Intermediate annealing for 30 seconds, then 900 mist water cooling
The temperature range of 400400 ° C. was cooled at a rate of 40 ° C./s. afterwards,
Each coil is pickled and the exit temperature of each rolling pass is 200-250 ° C in a Sendzimer rolling mill.
, And after degreasing, decarburizing annealing was performed at 850 ° C. for 2 minutes at an oxidation potential of P (H ₂ 0) / P (H ₂ ) = 0.52 in an annealing atmosphere.

Next, TiO was added to 100 parts by weight of MgO._Two5 weight
After addition, mix with water to form a slurry and after drying
Weight per side of steel plate is 6g / m^TwoCoating so that
After drying, it was wound on a coil. Where MgO
Has different pore volumes of 0.02 ml / g, 0.15 ml / g and 0.30 ml / g
Three types were used. Also, the water of the annealing separator after coating and drying
The sum was adjusted to 2.0%. After the final finishing annealing
Is 100% N up to 850 ℃ _Two Atmosphere, 850 ~ 1150 ℃ (7
5% H_Two−25% N_Two) Atmosphere, 850 ~ 1100 ℃ temperature range is 15 ℃
/ h at a constant rate of 100% H_Two atmosphere
At 1200 ° C. for 8 hours. After final finishing annealing,
After washing off the unreacted separating agent with water, colloidal silica is removed.
Insulation coating mainly containing magnesium phosphate
Baking and rolling on the steel plate surface at 5mm intervals
Irradiates a plasma jet in a line perpendicular to the
Product. Cut out 500g Epstein coupons from each product
And the iron loss W by the Epstein test method._17/50 And magnetic flux density
B₈ Was measured. Table 2 shows the obtained results.

[0052]

[Table 1]

[0053]

[Table 2]

As shown in Table 2, the component composition range and
When the pore volume of MgO satisfies the requirements of the present invention,
Products having excellent magnetic properties with an iron loss W _{17/50 of less} than 0.70 W / kg have been obtained.

Example 2 A silicon steel continuous cast slab (thickness: 220 mm) having various component compositions (steel symbols A to Z) shown in Table 1 was kept at 1180 ° C. for 3 hours, and then reduced to 200 mm. 1430 ℃ in 30 minutes after charging in induction heating furnace
Temperature, and soaked for 20 minutes.
A hot-rolled sheet having a thickness of mm was used. Next, apply 1050 ° C, 30
After performing hot-rolled sheet annealing for 20 seconds, mist water cooling is performed at 20 ° C / s.
Cooled at the speed. Next, after pickling, the sheet is subjected to primary cold rolling to a thickness of 1.5 mm, and then has a dew point of 35 ° C (50% N ₂ -50% H ₂ ).
Intermediate annealing was performed at 1100 ° C for 30 seconds in an atmosphere of, and then the temperature range of 900 to 400 ° C was cooled at a rate of 30 ° C / s by mist water cooling. Thereafter, each coil was pickled and rolled to a final thickness of 0.23 mm by a four-pass warm rolling process in which the exit temperature of each rolling pass was 200 to 250 ° C. in a Sendzimer rolling mill. afterwards,
Angle made with the rolling direction by local etching: 85
°, interval in the rolling direction: 3 mm, depth: 15 μm, width: 100 μ
m grooves were formed. Next, after degreasing, at an oxidation potential of P (H ₂ 0) / P (H ₂ ) = 0.48 in an annealing atmosphere, the temperature was set to 840 ° C.
A 2-minute decarburization annealing was performed.

Then, after adding 7 parts by weight of TiO ₂ to 100 parts by weight of MgO, the mixture was mixed with water to form a slurry, and dried and coated at a basis weight of 6 g / m ² per one side of the steel sheet. Rolled up. Here, MgO has a pore volume of 0.15 ml
/ g was used. The hydration amount of the annealing separator after application and drying was adjusted to 1.5% or 3.5% by adjusting the hydration time and hydration temperature. 850 ° C for subsequent final annealing
Below a 100% N ₂ atmosphere, 850 ° C. After retaining the 20 hours constant temperature reaches point _{(80% H 2 -20% N} 2) switched to an atmosphere, and 1150 ° C. over a period of 24 hours at a constant heating rate, A temperature of 1150 ° C. or higher was maintained at 1200 ° C. for 8 hours in a 100% H ₂ atmosphere. After the final finishing annealing, the unreacted separating agent was washed off with water. Further, an insulating coating mainly composed of magnesium phosphate containing colloidal silica was baked to obtain a baked product. 500 g of Epstein test _pieces were cut out from each product, and the iron loss W _17/50 and the magnetic flux density B ₈ were measured by the Epstein test method.
Table 3 shows the obtained results.

[0057]

[Table 3]

As shown in Table 3, when the composition range of the components and the hydration amount of the annealing separating agent were appropriately adjusted according to the present invention, the excellent magnetic loss W _17/50 was _less than 0.70 W / kg. The product of the characteristic is obtained.

Example 3 Continuously cast silicon steel slabs (thickness: 220 mm) having various component compositions (steel symbols A to I) shown in Table 1 were kept at 1180 ° C. for 3 hours and then reduced to 200 mm. 1430 ℃ in 30 minutes after charging in induction heating furnace
Temperature, and soaked for 20 minutes, then hot-rolled to 2.6
A hot-rolled sheet having a thickness of mm was used. Next, apply 1100 ° C, 60
After subjecting the hot-rolled sheet to annealing for 20 seconds, mist water cooling to 20 ° C
Cooled at a rate of / s. Then, after pickling, it is rolled to a final thickness of 0.30 mm by cold rolling using a tandem rolling mill, and after degreasing, the oxidation potential of the annealing atmosphere P (H ₂ 0) / P (H ₂ ) = 0.
Decarburization annealing was performed at 830 ° C for 2 minutes at 55 ° C.

Next, after adding 5 parts by weight of TiO ₂ to 100 parts by weight of MgO, the mixture was mixed with water to form a slurry, and the basis weight per one side of the steel sheet after drying was 7 g / m ² or 10 g / m ² . After coating and drying, the film was wound around a coil. Here, two types of MgO having different pore volumes of 0.10 ml / g and 0.25 ml / g were used. The hydration amount of the annealing separator after application and drying was adjusted to 2.0%. In the subsequent final annealing, up to 900 ° C, 100% N ₂ atmosphere, 900-1150 ° C
(90% H ₂ -10% N ₂ ) atmosphere and a temperature range of 850 to 1100 ° C for 25
° C. / heated by h, 12 more than 1150 ° C. as 100% H ₂ atmosphere
It was kept at 00 ° C. for 8 hours. After the final annealing, the unreacted separating agent was washed away with water, and then an insulating coating mainly composed of magnesium phosphate containing colloidal silica was baked to obtain a product. 50 Epstein coupons from each product
0g was cut out and iron loss W _{17/50 was determined} by Epstein test.
And the magnetic flux density B ₈ were measured. Table 4 shows the obtained results.

[0061]

[Table 4]

As shown in Table 4, the component composition range and
When the pore volume of MgO satisfies the requirements of the present invention,
B ₈ exceeds 1.96T, iron loss W _17/50 is the product were obtained with excellent magnetic properties below 0.95 W / kg.

Example 4 C: 0.072 wt%, Si: 3.20 wt%, Mn: 0.069 wt%, Al:
0.023 wt%, N: 0.0020 wt%, S: 0.005 wt%, Sn: 0.
07 wt%, Cr: 0.10 wt%, Cu: 0.12 wt% and Bi: 0.022
A continuous cast slab of silicon steel (thickness: 220 mm) containing wt%, with the balance being Fe and unavoidable impurities, kept at 1180 ° C for 3 hours, reduced to 200 mm, and charged into an induction heating furnace 30
The temperature was raised to 1430 ° C. in 20 minutes, and after soaking for 20 minutes, hot rolling was performed to obtain a hot-rolled sheet having a thickness of 2.4 mm. Then 1050 for each coil
After hot-rolled sheet annealing for 30 seconds at ℃, mist water cooling
It was cooled at a rate of 20 ° C./s. Next, after pickling, the sheet is subjected to primary cold rolling to a sheet thickness of 1.7 mm, and then has a dew point of 35 ° C (50%
Intermediate annealing was performed at 1100 ° C. for 30 seconds in an atmosphere of N ₂ -50% H ₂ ). After that, each coil is pickled, the exit temperature of each rolling pass is 200 to 250 ° C. in a Sendzimer rolling mill, and is rolled to a final thickness of 0.23 mm by warm rolling in four passes, and after degreasing, oxidizing the annealing atmosphere. At potential P (H ₂ 0) / P (H ₂ ) = 0.35 to 0.60
Decarburization annealing was performed at 820 ° C for 2 minutes. Thereafter, nitriding treatment was performed in an NH ₃ atmosphere to increase the N content in the steel to 0.0100 wt%.

Then, 4 parts by weight of TiO ₂ was added to 100 parts by weight of MgO, mixed with water to form a slurry, and coated so that the basis weight per one side of the steel sheet after drying was 6 g / m ² . After drying, it was wound on a coil. Here, MgO 2 having a pore volume of 0.15 ml / g was used. The hydration amount of the annealing separator after application and drying was adjusted to 2.0%. In the subsequent final annealing, the atmosphere up to 850 ° C was a 100% N ₂ atmosphere, and the atmosphere at 850 to 1150 ° C was a (75% H ₂ -25% N ₂ ) atmosphere. At this time, the temperature was raised from 100 to 850 ° C at a constant rate of 25 ° C / h,
The temperature was raised from 50 to 1100 ° C at a constant rate in the range of 5 to 70 ° C / h.
Subsequently, a temperature of 1150 ° C. or higher was set as a 100% H ₂ atmosphere and maintained at 1200 ° C. for 8 hours. After the final finish annealing, the unreacted separating agent is washed away with water, and then an insulating coating containing magnesium phosphate containing colloidal silica as a main component is baked. The product was subjected to magnetic domain refining treatment by laser light to obtain a product. 500 g of Epstein test _pieces were cut out from each product, and the iron loss W _17/50 and the magnetic flux density B ₈ were measured by the Epstein test method. Table 5 shows the obtained results.

[0065]

[Table 5]

Under conditions compatible with the present invention, iron loss W
_Products with excellent magnetic properties, with 17/50 below 0.7 W / kg, have been obtained. Among them, P (H ₂ 0) / P
C, d, e, f, g, with (H ₂ ) in the range of 0.45 to 0.65
In h and k, low iron loss with W _17/50 below 0.70 W / kg is obtained,
Furthermore, the temperature rise rate (850-1100 ° C) of final
For d, e, f, g and h at ~ 60 ° C / h, W _17/50 is 0.65
Products with extremely low iron loss of less than W / kg have been obtained.

[0067]

As described above, according to the method for manufacturing a grain-oriented electrical steel sheet of the present invention, the grain-oriented electrical steel sheet has excellent magnetic properties with a high magnetic flux density and low iron loss, and also has excellent coating properties. Can be obtained stably.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the pore volume of MgO used as a main component of an annealing separator and B ₈ and coating properties of a product.

FIG. 2 is a graph showing a relationship between an oxygen basis weight σ _f per one surface of a final annealed plate and B ₈ of a product.

FIG. 3 is a graph showing a relationship between an oxygen basis weight σ _d per one surface of a decarburized annealed plate and B ₈ of a product.

FIG. 4 is a graph showing a relationship between σ _f / σ _d and B ₈ of a product.

FIG. 5 is a graph showing the effect of σ _f / σ _d and the pore volume of MgO on B ₈ of a product.

FIG. 6 is a graph showing the relationship between the Bi content in the material and B ₈ of the product.

[FIG. 7] Oxidation potential P (H ₂ 0) /
It is a graph showing the relationship between P and (H ₂₎ and product B _8.

FIG. 8 is a graph showing the relationship between the rate of temperature rise in the final finish annealing in a temperature range of 850 to 1100 ° C. and the appearance of a coating film on a product.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/04 C22C 38/04 (72) Inventor Tadashi Tadashi Nakanishi 1-chome Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture Mizushima Steel Works, Kawasaki Steel Co., Ltd. (72) Inventor Mitsumasa Kurosawa 1-chome, Mizushima Kawasaki-dori, Kurashiki City, Okayama Pref. CA07 CA09 JA04 LA01 LA04 NA04 RA04 SA02 SA03 TA02

Claims (4)

[Claims] 1. C: 0.01-0.10 wt%, Si: 1.0-5.0 wt%
%, Mn: 0.03 to 0.20 wt%, Bi: 0.0005 to 0.070 wt%, and a steel slab containing an inhibitor element are hot-rolled, and then subjected to one or more cold rollings including an annealing treatment. After the final sheet thickness, decarburizing annealing, then apply an annealing separator on the steel sheet surface, then a final finishing annealing in a manufacturing method of grain-oriented electrical steel sheet consisting of a series of steps, as the main agent of the annealing separator With a pore volume of 0.03-0.20 ml / g
With use of MgO, final finish annealing plate following equation for the oxygen basis weight sigma _d per surface oxygen basis weight sigma _f and decarburization annealed steel sheet surface per one surface of the surface _{(1) σ f / σ d} ≦ 3.5 --- A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which satisfies the range of (1). 2. As an inhibitor element of steel slab, A
One or more selected from l, S, Se, Sb, Sn, Cu, Cr, Ni, Ge, B and N are added, and Al, S, Se are used alone or in total of 0.010 to 0.060. wt%, 0.0010 to 0.080 wt% for Sb, 0.0010 to 1.30 wt% for Sn, Cu, Cr, Ni, Ge, 5 to 50 ppm for B, and 30 to 100 ppm for N. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1. 3. An oxidation potential P (H) in a decarburizing annealing atmosphere.
₂₀ ) / P (H ₂ ) is in the range of 0.45 to 0.65, and the application amount of the annealing separator containing MgO as a main component is 9 g / m ² or less per one side of the steel sheet. 2. A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to 2. 4. The directionality excellent in magnetic properties according to claim 1, wherein the average temperature rising rate in the 850 to 1100 ° C. range in the final annealing step is 10 to 60 ° C./h. Manufacturing method of electrical steel sheet.