JP6863310B2 - Manufacturing method of grain-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a manufacturing method capable of inexpensively obtaining a grain-oriented electrical steel sheet having excellent magnetic properties and excellent film properties.

The grain-oriented electrical steel sheet is a soft magnetic material used as an iron core material for transformers and generators, and has a crystal structure in which the <001> orientation, which is the easy axis of iron magnetization, is highly aligned in the rolling direction of the steel sheet. .. Such an texture preferentially enlarges the crystal grains in the (110) [001] orientation, which is the so-called Goss orientation, during the secondary recrystallization annealing during the manufacturing process of the directional electromagnetic steel plate. It is formed through secondary recrystallization to grow.

Conventionally, in such a directional electromagnetic steel plate, a slab containing Si of about 4.5 mass% or less and an inhibitor component such as MnS, MnSe and AlN is heated to 1300 ° C. or higher to temporarily dissolve the inhibitor component. After that, it is hot-rolled, hot-rolled and annealed as necessary, and then cold-rolled once or two or more times with intermediate annealing in between to obtain the final plate thickness, and then primary recrystallization in a moist hydrogen atmosphere. After annealing, primary recrystallization and decarburization are performed, and then an annealing separator containing magnesia (MgO) as the main component is applied, and then for secondary recrystallization and purification of the inhibitor component, about 5 hours at 1200 ° C. It has been manufactured by performing the final finish annealing of (for example, Patent Document 1, Patent Document 2, Patent Document 3).

As described above, in the production of the conventional grain-oriented electrical steel sheet, precipitates (inhibitor components) such as MnS, MnSe and AlN are contained in the slab step, and these inhibitor components are removed by slab heating at a high temperature exceeding 1300 ° C. A step has been adopted in which secondary recrystallization is expressed by once dissolving the solid solution and finely precipitating it in a subsequent step. That is, in the conventional manufacturing process of grain-oriented electrical steel sheets, slab heating at a high temperature exceeding 1300 ° C. is required, so that the manufacturing cost must be extremely high, and there is a demand for reduction in manufacturing cost in recent years. The problem was that he could not respond.

In order to solve such a problem, for example, in Patent Document 4, 0.010 to 0.060 mass% of acid-soluble Al (sol.Al) is contained, slab heating is suppressed to a low temperature, and an appropriate nitriding atmosphere is obtained in the decarburization annealing step. A method has been proposed in which (Al, Si) N is used as an inhibitor during secondary recrystallization by nitriding underneath.
According to this method, (Al, Si) N is finely dispersed in steel and functions as an effective inhibitor. However, since the inhibitor strength is determined by the Al content, if the accuracy of Al in steelmaking is not sufficient, a major problem is that secondary recrystallization becomes unstable due to insufficient grain growth inhibitory power. There was a point.

On the other hand, a technique for expressing secondary recrystallization without containing an inhibitor component in a slab has been studied, and Patent Document 5 discloses a technique (inhibitorless method) capable of secondary recrystallization without containing an inhibitor component. It was. This inhibitorless method is a technique for expressing secondary recrystallization by texture (control of texture) using higher purified steel. Further, the inhibitorless method does not require high-temperature slab heating, and can manufacture grain-oriented electrical steel sheets at low cost.
However, in a material that does not contain such an inhibitor-forming component, the oxide film formed during primary recrystallization annealing becomes dendrite-like, leaving the problem that the adhesion of the forsterite film deteriorates, which causes further magnetism. Problems such as deterioration and deterioration of the coating have occurred.

On the other hand, in Patent Document 6, the structure of the oxide film formed during the primary recrystallization annealing is appropriately changed by controlling the material component of the steel sheet, and the forsterite film having good adhesion after the secondary recrystallization annealing. The technology for forming is disclosed.

Further, in Patent Document 7, the texture is controlled by positively controlling the heating rate of the heating process of the primary recrystallization annealing with respect to the grain-oriented electrical steel sheet which does not use an inhibitor, and the iron loss characteristic thereof is improved. Technology is being developed.

U.S. Pat. No. 1965559 Tokukousho 40-15644 Special Publication No. 51-13469 Japanese Patent No. 2782086 Japanese Unexamined Patent Publication No. 2000-129356 Japanese Unexamined Patent Publication No. 2003-193134 Japanese Patent Application No. 2012-165519

However, particularly in the production of grain-oriented electrical steel sheets containing almost no Se and S as described in Patent Document 6, the oxide film formed during primary recrystallization annealing tends to be dendrite-like. Therefore, there remains a problem that the adhesion of the forsterite film after the secondary recrystallization tends to deteriorate. Further, when the heating rate in the heating process of the primary recrystallization annealing is changed, the structure of the oxide film formed during the primary recrystallization annealing changes, and the adhesion of the forsterite film after the secondary recrystallization deteriorates. I had something to do.

As described above, in the method for producing grain-oriented electrical steel sheets, which has been proposed so far, particularly in a component system containing almost no S or Se as an inhibitor, good forsterite film adhesion is maintained while ensuring good characteristics. It was difficult to achieve.
The present invention is a component system in which Al is suppressed to less than 100 ppm, S, Se and O are suppressed to 50 ppm or less, and N is suppressed to 80 mass ppm or less, and the rate of temperature rise in the heating process of primary recrystallization annealing accompanied by decarburization is increased. Therefore, it is an object of the present invention to provide a method for producing a grain-oriented electrical steel sheet capable of advantageously forming a forsterite film having high adhesion even when trying to obtain good iron loss characteristics.

The inventors have made extensive studies on how the heating process during primary recrystallization annealing affects the oxide film formed during primary recrystallization annealing. As a result, we have found the following new findings.
When the rate of temperature rise in the heating process of primary recrystallization annealing is increased, recrystallization of the structure starts in a shorter time. On the other hand, the formation of the oxide film proceeds with the decarburization of the steel sheet. Therefore, the formation of the oxide film does not proceed in a short time only by increasing the rate of temperature rise, unlike the recrystallization of the structure. That is, if the rate of temperature rise is high, the formation of the oxide film is delayed for the structure that has already been recrystallized. Then, it was found that when the formation of the oxide film is delayed in this way, oxygen diffusion occurs along the crystal plane that has already been recrystallized, so that a dendrite-like oxide film is likely to be formed.

This means that the formation of a dendrite-like oxide film, which tends to occur in a component system that does not use an inhibitor, is promoted by increasing the rate of temperature rise in the heating process of primary recrystallization annealing. That is, in a component system that does not use an inhibitor, the problem of deterioration of the adhesion of the forsterite film, which may occur when the heating rate is increased in the heating process of primary recrystallization annealing accompanied by decarburization, is such dendrite-like oxidation. It was found that this was because the formation of the film was promoted.

Therefore, the inventors have investigated a measure for suppressing the formation of a dendrite-like oxide film, that is, densification of the oxide film. Specifically, in the heat cycle of primary recrystallization annealing, attention was paid to a relatively low temperature range of 700 ° C. to 800 ° C. This is because, in general, the higher the temperature, the easier the oxidation reaction proceeds.
If the oxidation reaction is performed at a low temperature, the oxidation rate itself is slow even for the recrystallized structure, so that oxygen cannot be sufficiently supplied to the steel sheet. As a result, the diffusion of oxygen into the crystal grains is suppressed, and the formation of a dendrite-like oxide film can be suppressed. However, even in that case, since it is desirable to suppress the amount of oxygen supplied to the steel sheet, it is desirable to increase the hydrogen concentration in the decarburized atmosphere and to carry out the operation in a state where the dew point is reduced.

Here, from the viewpoint of densification of the oxide film, Patent Document 6 describes that the addition of Cr is effective. However, since Cr addition has an excessive promotion of oxidation that causes deterioration of magnetic properties, it is necessary to use Sb or Cu as an oxidation inhibitory component. In addition, as an adverse effect of increasing the rate of temperature rise in the heating process of primary recrystallization annealing to improve manufacturability, even when a dendrite-like oxide film is more likely to be formed, a component having such an effect should be effectively used. For example, it is considered that the manufacturability of the steel sheet can be significantly improved at the same time.

Therefore, regarding the influence of the material components that affect the oxide film formed during the primary recrystallization annealing, a sample in which the heating rate of the heating process from 500 ° C to 700 ° C of the primary recrystallization annealing was set to 150 ° C / s was tested. Various investigations were conducted as materials.
As a result, it was newly found that among the components required for densification of the oxide film or the components useful for improving the magnetic properties of the steel sheet, particularly Mn and P have an influence on the formation of the oxide film. That is, it was found that under the conditions of this experiment, Mn behaved similarly to Cr, and had both the effect of densifying the oxide film and the excessive promotion of oxidation of the steel sheet.
However, the effect of adding Mn is smaller than that of Cr, and it was found that it is necessary to add about three times as much in order to obtain the effect of densifying the oxide film equivalent to that of Cr. On the other hand, it was found that excessive oxidation promotion requires addition of about 5 times as much as Cr.

On the other hand, it was found that P has an effect of densifying the oxide film, and at the same time, has an effect of suppressing excessive promotion of oxidation of the steel sheet. It was also found that the effect of adding P was about the same as that of Cr for densification of the oxide film, and that the effect of suppressing excessive oxidation promotion was about the same as that of Cu.

The present invention has been obtained based on the above findings, and the gist structure of the present invention is as follows.
1. 1. C: 0.08 mass% or less, Si: 2.0 to 8.0 mass% and Mn: 0.005 to 0.5 mass%, Al is reduced to less than 100 mass ppm, and S, Se and O are each 50 mass ppm or less. In addition, a steel slab having a component composition in which N is further reduced to 80 mass ppm or less is hot-rolled and cold-rolled once or two or more times with intermediate annealing sandwiched between them, and then primary recrystallization annealing accompanied by decarburization is performed. In the method for manufacturing grain-oriented electrical steel sheets, which is performed, an annealing separator is applied, and then final finish annealing is performed.
The composition of the steel slab further contains at least one of Sb, Cu and P, and the balance is iron and unavoidable impurities.
The above Sb, Cu, P and Mn
1 ≦ (4 [Sb (mass%)] + [Cu (mass%)] + [P (mass%)]) / (1/5 [Mn (mass%)]) ≦ 7 ... Relationship of Equation 1 The filling,
In addition, the above Mn and P are added to the temperature rise rate between 500 ° C. and 700 ° C. of the primary recrystallization annealing: T ° C./s (1/3 [Mn (mass%)] + [P (mass%)]. )]) ≧ 0.0002 × T + 0.07 ・ ・ ・ Equation 2
To the extent that the relationship is satisfied,
Further, T is a method for manufacturing a grain-oriented electrical steel sheet, characterized in that T ≧ 80.

2. In the method for producing a grain-oriented electrical steel sheet according to 1 above, the steel slab further contains Cr.
Among the components of the steel slab, Sb, Cu, P, Mn and Cr are
1 ≦ (4 [Sb (mass%)] + [Cu (mass%)] + [P (mass%)]) / ([Cr (mass%)] + 1/5 [Mn (mass%)]) ≦ 7 ... Satisfying the relationship of Equation 3
And, in relation to the temperature rising rate: T ° C./s ([Cr (mass%)] + 1/3 [Mn (mass%)] + [P (mass%)]) ≧ 0.0002 × T + 0.07・ ・ ・ Equation 4
A method for manufacturing a grain-oriented electrical steel sheet, which comprises the above-mentioned relationship in a range that satisfies the above-mentioned relationship.

3. 3. The method of manufacturing a grain-oriented electrical steel sheet described in 1 or 2, a 800 ° C. from heating process in 700 ° C. of the primary recrystallization annealing, H ₂ concentration: 40%, dew point: 63 ° C. under the following atmosphere A method for manufacturing a grain-oriented electrical steel sheet, which comprises a residence time of 5 seconds or more.

4. In the method for manufacturing grain-oriented electrical steel sheets according to 1 to 3, the Sb, Cu and P are Sb: 0.005 to 0.50 mass%, Cu: 0.01 to 1.50 mass% and P: 0. A method for manufacturing a grain-oriented electrical steel sheet, which comprises a range of .005 to 0.50 mass%.

5. The method for manufacturing a grain-oriented electrical steel sheet according to the above 2, wherein the Cr is in the range of 0.01 to 1.50 mass%.

6. In the method for producing grain-oriented electrical steel sheets according to 1 to 5, the steel slabs further include Ni: 0.005 to 1.50 mass%, Sn: 0.01 to 0.50 mass%, and Nb: 0.0005 to 5. A method for producing a grain-oriented electrical steel sheet, which comprises at least one selected from 0.0100 mass%, Mo: 0.01 to 0.50 mass% and Bi: 0.0005 to 0.05 mass%.

According to the present invention, it is possible to manufacture a grain-oriented electrical steel sheet having good film adhesion while ensuring good magnetic properties by using a component system containing almost no inhibitor.

6 is a graph showing the relationship between the residence time (seconds) between 700 and 800 ° C. and the bending peel diameter (mm) during the temperature rise of the primary recrystallization annealing.

The reasons for limiting each constituent requirement of the present invention will be described below.
First, the reason why the component composition of the steel slab is limited to the above range in the present invention will be described. Unless otherwise specified, the following "%" and "ppm" indications mean mass% and massppm, respectively.
C: 0.08% or less C is an element useful for improving the primary recrystallization texture, but if the content exceeds 0.08%, it causes deterioration of the primary recrystallization texture. In the invention, it is limited to 0.08% or less. The desirable addition amount from the viewpoint of magnetic properties is in the range of 0.01 to 0.06%. Further, when the required level of magnetic properties is not so high, C may be set to 0.01% or less in order to omit or simplify decarburization in the primary recrystallization annealing. The lower limit at that time is about 0.001%.

Si: 2.0-8.0%
Si is a useful element that improves iron loss by increasing electrical resistance, but if the content exceeds 8.0%, the cold rollability deteriorates significantly, so Si is limited to 8.0% or less. .. On the other hand, Si needs to function as a nitride forming element, and therefore needs to be contained in an amount of 2.0% or more. The desirable amount of addition is in the range of 2.0 to 4.5% from the viewpoint of ensuring low iron loss.

Mn: 0.005-0.5%
Mn has the effect of improving hot workability during production, but if the content exceeds 0.5%, the primary recrystallization texture deteriorates and the magnetic properties deteriorate. Therefore, the Mn content is limited to 0.5% or less. Further, in the present invention, Mn is a particularly useful element from the viewpoint of densification of the oxide film at the time of primary recrystallization, and therefore it is necessary to satisfy the above range and the range described below.

S, Se and O: 50 ppm or less, respectively When the contents of S, Se and O are more than 50 ppm, secondary recrystallization becomes difficult. The reason for this is that the coarse oxide and MnS and MnSe coarsened by slab heating make the primary recrystallization structure non-uniform. Therefore, S, Se and O are all suppressed to 50 ppm or less. The lower limit of the contents of S, Se and O may be 0 ppm without any problem.

Al: Less than 100 ppm Since no AlN inhibitor is required in this technology, the amount of Al is suppressed. In addition, Al may form a dense oxide film on the surface and inhibit decarburization. Therefore, the amount of Al is suppressed to less than 100 ppm. However, Al, which has a high oxygen affinity, can be expected to reduce the amount of dissolved oxygen in the steel by adding a small amount at the stage of steelmaking, and reduce oxide-based inclusions leading to deterioration of various steel sheet characteristics. Therefore, magnetic deterioration can be suppressed by adding significantly in the range of less than 100 ppm. There is no problem even if the lower limit of the Al content is 0 ppm.

N: 80 ppm or less In the present invention, the method for producing an inhibitorless steel sheet is applied to create an texture, so N must be suppressed to 80 ppm or less. This is because if it exceeds 80 ppm, there is an adverse effect that the texture is deteriorated due to the influence of grain boundary segregation and the formation of trace nitrides. Further, it is necessary to suppress the amount to 80 ppm or less from the viewpoint of causing defects such as blisters during slab heating. It should be noted that it is preferably 60 ppm or less. On the other hand, there is no problem even if the lower limit of N is 0 ppm.

Further, the steel slab of the present invention needs to contain at least one of Sb, Cu and P. Further, in the present invention, Sb, Cu and P, like Mn, are elements that need to be controlled from the viewpoint of controlling the formation of an oxide film during primary recrystallization. Therefore, the range described below is desirable, and the following formulas 1 to 4 are further desired. It is necessary to meet the range specified in.
Sb: 0.005 to 0.50%
Sb is a useful element that has a function of suppressing excessive oxidation of the steel sheet and, at the time of secondary recrystallization, promotes secondary recrystallization of crystal grains having a good crystal orientation and effectively improves magnetic properties. Is. For that purpose, it is preferably contained in an amount of 0.005% or more. On the other hand, if it is contained in excess of 0.50%, the cold rollability may be deteriorated. Therefore, it is desirable that Sb is contained in the range of 0.005 to 0.50%.

Cu: 0.01 to 1.50%
Like Sb, Cu has a function of suppressing excessive oxidation of the steel sheet, and suppresses oxidation of the steel sheet during secondary recrystallization annealing to promote secondary recrystallization of crystal grains having a good crystal orientation. It has the function of effectively improving the magnetic properties. Therefore, it is preferable to contain 0.01% or more. On the other hand, if it is contained in excess of 1.50%, the hot rollability may be deteriorated. Therefore, it is desirable that Cu is contained in the range of 0.01 to 1.50%.

P: 0.005 to 0.50%
P has a function of stabilizing the formation of a forsterite film through the formation of subscales during decarburization annealing. Therefore, it is preferable to contain 0.0050% or more. On the other hand, if the content exceeds 0.50%, the cold rollability may deteriorate. Therefore, it is desirable that P be contained in the range of 0.005 to 0.50%.

Here, in the above slab, Sb, Cu and P are combined with the amount of Mn.
1 ≦ (4 [Sb (%)] + [Cu (%)] + [P (%)]) / (1/5 [Mn (%)]) ≦ 7 ... It is necessary to satisfy the relationship of Equation 1. is there.
This is because satisfying the formula 1 makes it possible to balance the excessive oxidation promotion of Mn and the oxidation suppression effect of Sb, Cu or P.

In addition, the Mn and P were added to the temperature rise rate between 500 ° C. and 700 ° C. during the primary recrystallization annealing: T ° C./s (1/3 [Mn (%)] + [P (%)). ]) ≧ 0.0002 × T + 0.07 ・ ・ ・ Equation 2
It is necessary to contain it in a range that satisfies the relationship.
This is because when the heating rate in the heating process of primary recrystallization annealing is increased, the oxide film formed after annealing tends to take a dendrite-like form, but the contents of Mn and P satisfy the above formula 2. This is because the effect of suppressing the formation of a dendrite-like oxide film can be obtained.

Further, it is important that the temperature rising rate: T ° C./s is 80 ° C./s or higher. Desirably, the temperature is 100 ° C./s or higher. Although there is a problem in forming an oxide film, if it is assumed that Mn and P are contained in the range of the above formula 2, the core of secondary recrystallization is {110} <001 by increasing the heating rate. > This is because the formation of a structure can be promoted and the iron loss characteristics can be improved. Although the upper limit of the heating rate is not particularly limited, the upper limit of the heating rate is preferably about 1000 ° C./s from the viewpoint of the capacity of the manufacturing equipment and the like.

Further, in the present invention, Cr can be contained as required. Like Mn, Cr is an element that needs to be controlled from the viewpoint of densification of the oxide film during primary recrystallization. Therefore, Cr is in the range of the content described below, and Sb, Cu, P, and Mn. In addition, it is preferable that the range is defined in the following formulas 3 and 4.
Cr: 0.01 to 1.50%
Cr has a function of stabilizing the formation of a forsterite film through the formation of subscales during decarburization annealing, and for that purpose, it is preferably contained in an amount of 0.01% or more. On the other hand, if the content exceeds 1.50%, secondary recrystallization becomes difficult and the magnetic characteristics deteriorate. Therefore, when Cr is added, it is desirable to contain it in the range of 0.01 to 1.50%.

When the steel slab contains Cr, add Cr to the above formula 1 and add Cr.
1 ≦ (4 [Sb (%)] + [Cu (%)] + [P (%)]) / ([Cr (%)] + 1/5 [Mn (%)]) ≦ 7 ... Equation 3 age,
Moreover, it is necessary to satisfy the above equation 2 as ([Cr (%)] + 1/3 [Mn (%)] + [P (%)]) ≧ 0.0002 × T + 0.07 ... Equation 4.
This is because satisfying the formula 3 makes it possible to balance the excessive oxidation promotion of Cr and Mn with the oxidation suppression effect of Sb, Cu or P.
Further, by satisfying the formula 4, the effect of suppressing the formation of a dendrite-like oxide film even when the heating rate in the heating process of the primary recrystallization annealing is increased, as in the case of satisfying the formula 2. Is obtained.

Although the important component composition in the steel slab in the present invention has been described above, the following elements can be appropriately contained as components for improving the magnetic properties of the steel sheet more stably industrially.
Ni: 0.005 to 1.50%
Ni has a function of improving the magnetic properties by increasing the uniformity of the hot-rolled plate structure, and for that purpose, it is necessary to contain it in an amount of 0.005% or more. On the other hand, if the content exceeds 1.50%, secondary recrystallization becomes difficult and the magnetic characteristics may deteriorate. Therefore, it is desirable that Ni is contained in the range of 0.005 to 1.50%.

Sn: 0.01 to 0.50%
Sn is a useful element that suppresses nitriding and oxidation of the steel sheet during secondary recrystallization annealing, promotes secondary recrystallization of crystal grains having a good crystal orientation, and improves the magnetic properties of the steel sheet. Needs to be contained in an amount of 0.01% or more. On the other hand, if it is contained in excess of 0.50%, the cold rollability may be deteriorated. Therefore, it is desirable that Sn is contained in the range of 0.01 to 0.50%.

Nb: 0.0005 to 0.0100%, Mo: 0.01 to 0.50%
Nb and Mo have the effect of suppressing the generation of heddle after heat spreading through the suppression of cracking due to the temperature change during slab heating. Such an effect is hardly exhibited unless each of them is contained above the above lower limit. On the other hand, if it is contained in excess of the above upper limit, it may remain in the final product due to the formation of carbides and nitrides. In this case, iron loss deterioration is caused. Therefore, it is desirable that Nb and Mo are in the above range.

Bi: 0.0005-0.05%
Since Bi is an element advantageous for improving magnetic properties, it can be contained as needed. However, in order to obtain the effect of improving the magnetic characteristics, it is necessary to add 0.0005% or more. On the other hand, when added in excess of 0.05%, it inhibits the formation of a forsterite film. Therefore, it is desirable that Bi is in the above range.

The steel slab adjusted to the composition range according to the present invention described above is subjected to hot rolling without reheating or after reheating. When reheating the slab, it is desirable that the reheating temperature is about 1000 ° C. or higher and 1300 ° C. or lower. This is because slab heating above 1300 ° C is meaningless in the present invention containing almost no inhibitor and only increases the cost, while if it is less than 1000 ° C, the rolling load becomes high and hot rolling is performed. Is difficult.

Then, after hot-rolling the hot-rolled plate, if necessary, the hot-rolled plate is annealed, and then one cold-rolling or two or more times of cold-rolling sandwiching the intermediate annealing is performed to make the final cold-rolled plate. And. This cold rolling may be performed at room temperature, or may be hot rolling in which the temperature of the steel sheet is raised to a temperature higher than room temperature, for example, about 250 ° C.

Further, the final cold-rolled plate is subjected to primary recrystallization annealing.
The purpose of this primary recrystallization annealing is to primary recrystallize a cold-rolled plate having a rolled structure and adjust it to the optimum primary recrystallization grain size for secondary recrystallization. Further, by setting the annealing atmosphere to wet hydrogen nitrogen or wet hydrogen argon atmosphere, carbon contained in the steel is decarburized, and at the same time, an oxide film is formed on the surface by the annealing atmosphere. Therefore, it is desirable that the annealing temperature (retention temperature) of the primary recrystallization annealing is in a temperature range of about 800 ° C. or higher and lower than 950 ° C.
The oxide film formed by the primary recrystallization annealing reacts with MgO applied on the steel sheet in the subsequent secondary recrystallization annealing to form a forsterite film. Therefore, the morphology of the oxide film after the primary recrystallization annealing greatly affects the formation of the surface layer film in the subsequent process.

Further, from the viewpoint of improving the magnetic properties, it is effective to increase the rate of temperature rise in the heating process in the primary recrystallization annealing. Specifically, assuming that the rate of temperature rise between 500 ° C. and 700 ° C. is T ° C./s, T ≧ 80 ° C./s, preferably T ≧ 100 ° C./s. This is because the texture after the primary recrystallization can be improved and the magnetic properties after the secondary recrystallization can be improved by setting such a temperature rising rate. As described above, the upper limit of T is preferably about 1000 ° C./s.

As described above, it is important to satisfy the above formulas 2 and 4 in order to suppress the dendrite-like oxide film with respect to the above-mentioned temperature rising rate: T ° C./s.

Further, in the formation of the oxide film, if a sparse oxide film is formed at the initial stage, a dendrite-like sparse internal oxide layer continues to grow in response to the supply of oxygen. Therefore, it is effective to form a dense oxide film at the initial stage by suppressing the supply of oxygen to the steel sheet.

Specifically, after the rapid heating during the primary recrystallization annealing, in a temperature range of 800 ° C. from 700 ° C. to form the oxide film proceeds, be 40 vol% or more and a dew point of 63 ° C. under a following atmosphere with H ₂ concentration It is effective. If concentration of H ₂ takes less than a specified, or if higher than the prescribed dew point takes are both thereby increasing the atmosphere oxidizing. As a result, the oxide film formed tends to have a sparse structure, and a dendrite-like sparse oxide film tends to be formed during the subsequent annealing.
Further, in order to make the initial oxide film a dense structure, it is desirable to hold it in the above atmosphere for about 5 seconds or longer. Since the formation of the oxide film proceeds at the same time as decarburization, in a time of less than 5 seconds, a dense oxide film is not formed on the entire surface but is partially formed. As a result, a dendrite-like oxide film can be partially formed.

When a dendrite-like oxide film is widely formed in a region that is more than a certain amount, it becomes a forsterite film having a different thickness after secondary recrystallization annealing, resulting in a film having low peel resistance. Therefore, in the present invention, an appropriate element is added to the steel sheet, and the conditions at the time of primary recrystallization annealing are controlled.

After the primary recrystallization annealing under the above conditions, an annealing separator is applied to the surface of the steel sheet. In order to form a forsterite film on the surface of the steel sheet after secondary recrystallization annealing, magnesia (MgO) is used as the main agent of the annealing separator. At this time, by adding an appropriate amount of Ti oxide, Sr compound, or the like to the separating agent, the formation of the forsterite film can be further advantageous.

Following this, finish annealing is performed for secondary recrystallization and formation of a forsterite film. The annealing atmosphere is _{suitable for N 2} , Ar, H ₂ or a mixed gas thereof. In order to carry out the secondary recrystallization more advantageously, it is preferable to maintain an isothermal temperature in the vicinity of the secondary recrystallization temperature. However, this does not necessarily have to be maintained at an isothermal temperature because it has the same effect even if the rate of temperature rise is slowed down. If trace components are precipitated in the final product, the magnetic properties will deteriorate. Therefore, the maximum temperature for annealing is preferably 1100 ° C. or higher for component purification.

After the finish annealing, an insulating film can be further applied to the surface of the steel sheet and baked. The type of the insulating coating is not particularly limited, and any conventionally known insulating coating is advantageous. Further, a coating liquid containing phosphate-chromate-colloidal silica described in JP-A-50-79442 and JP-A-48-39338 is applied to a steel sheet and baked at about 800 ° C. The method is a preferable example.

Further, the shape of the steel sheet can be adjusted by performing flattening annealing, and this flattening annealing can be combined with the baking treatment of the insulating film.

(Example 1)
Table 1 shows the component compositions of C: 0.04 to 0.06%, Si: 3.20 to 3.32%, Mn: 0.08 to 0.32%, and used in formulas 1 to 4. Further, Al was reduced to less than 100 ppm, O, S and Se were reduced to 50 ppm or less, N was reduced to 80 ppm or less, and the balance was Fe and steel slabs as unavoidable impurities, which were heated to 1230 ° C. and then hot-rolled to form a plate. The thickness was 2.0 mm. Then, the hot-rolled plate was annealed at 1000 ° C. for 60 seconds, pickled, and cold-rolled once to a plate thickness of 0.27 mm.
After that, the average temperature rise rate T between 500 ° C. and 700 ° C. is set to the conditions shown in Table 1, and the temperature rise between 700 and 800 ° C. is set to 8 seconds, and the subsequent soaking temperature is set to 830 ° C. for 2 minutes. Crystal annealing was performed. The primary recrystallization annealing was carried out in a moist atmosphere with 50 vol% hydrogen + 50 vol% nitrogen and a dew point of 55 ° C. in all steps, and decarburization was also performed at the same time.
After the primary recrystallization annealing, an annealing separator containing 2 parts by mass _{of TIO 2 was applied to 100 parts by mass of MgO, and final finish annealing was performed.} After the final finish annealing, the unreacted separating agent was removed, an insulating coating containing magnesium phosphate as a main component was applied, and the product was baked at 800 ° C. to obtain a product board.

With respect to the product plate thus obtained, the iron loss W _17/50 was measured and the film adhesion was evaluated. The film adhesion was evaluated by the bending peeling diameter (the minimum bending diameter at which the steel sheet was wound around a round bar and the film did not peel off). The obtained measured values and the results of the film adhesion evaluation are also shown in Table 1. From Table 1, according to the present invention, _{a good grain-} oriented electrical steel sheet having an iron loss W 17/50 of 0.9 W / kg or less and a bending diameter of 25 mm or less in terms of coating characteristics can be stably obtained. I understand.

(Example 2)
C: 0.04%, Si: 3.25%, Mn: 0.09%, Al: 0.006%, N: 0.004%, Cr: 0.06%, P: 0.015%, Sb : 0.02% and Cu: 0.1%, S, Se and O are all 20 ppm or less, and the balance is Fe and unavoidable impurities after heating the slab at 1100 ° C. for 30 minutes. It was hot-rolled to obtain a hot-rolled plate having a plate thickness of 2.2 mm, annealed at 1050 ° C. for 1 minute, and then cold-rolled to obtain a cold-rolled coil having a final plate thickness of 0.23 mm. A sample having a size of 100 mm × 400 mm was collected from the central portion of the obtained cold-rolled coil, and annealed in a laboratory for both primary recrystallization and decarburization. Conditions of such primary recrystallization annealing, the heating rate was fixed at 100 ° C. / s between 500 to 700 ° C., _{H 2} concentration 50 vol%, and the residence time of up to 700 ° C. to 800 ° C. under an atmosphere of a dew point of 55 ° C. Was changed from 3 seconds to 10 seconds. Further, under the condition that the residence time is 7 seconds to change the concentration of H ₂ and dew point as shown in Table 2.

_{An annealing separator containing MgO as a main component and 5% of TiO 2} is applied to the decarburized annealed plate after the primary recrystallization annealing in the form of a water slurry, dried, and then baked onto a steel sheet to reach the maximum temperature. Secondary recrystallization annealing was performed by soaking at 1200 ° C. for 5 hours, and then a phosphate-based insulating tension coating was applied and annealed. All of the steel sheets thus obtained showed good magnetic properties. Then, the film adhesion was evaluated by the bending peeling diameter (the minimum bending diameter at which the steel sheet was wound around a round bar and the film did not peel), and is shown in FIGS. 1 and 2.
The value of Equation 2 in this example is 2.5, which satisfies the present invention. Further, the value on the right side of Equation 4 of the present embodiment is 0.09, while the value on the left side is 0.11, which satisfies the present invention.
Under any of the conditions, as long as the present invention was followed, a good film having a bending peel diameter of 35 mm or less was obtained. In particular, 700 to 800 residence time between ° C. is 5 seconds or more, _{H 2} concentration of 40 vol% or more, when performing primary recrystallization annealing under the following conditions dew point 63 ° C., the following bending peel diameter 20mm very good It can be seen that the characteristics are obtained.

(Example 3)
Contains C: 0.03%, Si: 3.4%, Mn: 0.05%, Cr: 0.05%, P: 0.08%, Sb: 0.05% and Cu: 0.1% , Al was reduced to less than 100 ppm, O, S and Se were reduced to 50 ppm or less, N was reduced to 80 ppm or less, and the balance was a vacuum steel ingot containing the components shown in Table 3 and Fe and unavoidable impurities at 1150 ° C. After heating, hot rolling was performed to obtain a plate thickness of 2.0 mm. Then, hot-rolled sheet was annealed at 900 ° C., cold-rolled to a thickness of 1.4 mm, intermediate-annealed at 1030 ° C., and further cold-rolled to a sheet thickness of 0.22 mm from 500 ° C. Primary recrystallization annealing was performed with an average heating rate of 150 ° C./s between 700 ° C. Next, an annealing separator containing MgO as the main component was applied, and final finish annealing was performed. After final finish annealing, an insulating coating containing magnesium phosphate as a main component was applied and baked at 800 ° C.
The value of Equation 2 in this example is 6.33, which satisfies the present invention. Further, the value on the right side of Equation 4 of the present embodiment is 0.10, while the value on the left side is 0.15, which satisfies the present invention.

With respect to the steel sheet thus obtained, the iron loss W _17/50 was measured and the film adhesion was evaluated. The coating adhesion was evaluated by the bending peel diameter (the minimum bending diameter at which the steel plate was wound around a round bar and the coating did not peel). The results of the obtained magnetic properties and film adhesion evaluation are also shown in Table 3. According to the present invention, it can be seen that a grain-oriented electrical steel sheet having excellent iron loss characteristics and coating characteristics is stably obtained.

Claims (6)

C: 0.08 mass% or less, Si: 2.0 to 8.0 mass% and Mn: 0.005 to 0.5 mass%, Al is reduced to less than 100 mass ppm, and S, Se and O are each 50 mass ppm or less. In addition, a steel slab having a component composition in which N is further reduced to 80 mass ppm or less is hot-rolled and cold-rolled once or two or more times with intermediate annealing sandwiched between them, and then primary recrystallization annealing accompanied by decarburization is performed. In the method for manufacturing grain-oriented electrical steel sheets, which is performed, then an annealing separator containing magnesia (MgO) as a main component is applied, and then final finish annealing is performed.
The composition of the steel slab further contains at least one of Sb, Cu and P, and the balance is iron and unavoidable impurities.
The above Sb, Cu, P and Mn
1.03 ≤ (4 [Sb (mass%)] + [Cu (mass%)] + [P (mass%)]) / (1/5 [Mn (mass%)]) ≤ 6.75 ... Satisfy the relationship of Equation 1
In addition, the above Mn and P are added to the temperature rise rate between 500 ° C. and 700 ° C. of the primary recrystallization annealing: T ° C./s (1/3 [Mn (mass%)] + [P (mass%)]. )]) ≧ 0.0002 × T + 0.07 ・ ・ ・ Equation 2
To the extent that the relationship is satisfied,
Further, T is a method for manufacturing a grain-oriented electrical steel sheet, characterized in that T ≧ 80. In the method for producing a grain-oriented electrical steel sheet according to claim 1, the steel slab further contains Cr.
Among the components of the steel slab, Sb, Cu, P, Mn and Cr are
1.03 ≤ (4 [Sb (mass%)] + [Cu (mass%)] + [P (mass%)]) / ([Cr (mass%)] + 1/5 [Mn (mass%)]) ≤ 6.75 ... Satisfying the relationship of Equation 3
And, in relation to the temperature rising rate: T ° C./s ([Cr (mass%)] + 1/3 [Mn (mass%)] + [P (mass%)]) ≧ 0.0002 × T + 0.07・ ・ ・ Equation 4
Relationship incorporated within a range that satisfies, for an additional 800 ° C. from heating process in 700 ° C. of the primary recrystallization annealing, H ₂ concentration: 40%, dew point: 63 ° C. under the following ambient, and the residence time: A method for manufacturing a grain-oriented electrical steel sheet, which is characterized in that it takes 5 seconds or more. The method of manufacturing a grain-oriented electrical steel sheet according to claim 1, a 800 ° C. from heating process in 700 ° C. of the primary recrystallization annealing, H ₂ concentration: 40%, dew point: 63 ° C. under less atmosphere, A method for manufacturing a grain-oriented electrical steel sheet, which comprises a residence time of 5 seconds or more. In the method for manufacturing grain-oriented electrical steel sheets according to claims 1 to 3, the Sb, Cu and P are Sb: 0.005 to 0.50 mass%, Cu: 0.01 to 1.50 mass% and P :. A method for manufacturing a grain-oriented electrical steel sheet, which comprises a range of 0.005 to 0.50 mass%. The method for manufacturing a grain-oriented electrical steel sheet according to claim 2, wherein the Cr is in the range of 0.01 to 1.50 mass%. In the method for producing grain-oriented electrical steel sheets according to claims 1 to 5, the steel slab is further increased with Ni: 0.005 to 1.50 mass%, Sn: 0.01 to 0.50 mass%, Nb: 0.0005. A method for producing a grain-oriented electrical steel sheet, which comprises at least one selected from ~ 0.0100 mass%, Mo: 0.01 to 0.50 mass% and Bi: 0.0005 to 0.05 mass%. ..

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