JP2002275534A - Method for manufacturing grain-oriented silicon steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably manufacture a grain-oriented silicon steel sheet which has a uniform forsterite film having superior adhesion and free from defects over the overall width and overall length of a coil and also has excellent magnetic properties. SOLUTION: In manufacturing the grain-oriented silicon steel sheet, the ambient oxidizability (P[H2 O]/P[H2 ]) in the course of temperature rise at decarburizing annealing is controlled, according to the amount of decrease of Si in the surface layer part of the steel sheet before final annealing and after decarburizing annealing, to a value within the range represented by y>=0.57x+0.158 (wherein, y is ambient oxidizability (P[H2 O]/P[H2 ]); and x is the amount of decrease of Si in the surface layer part of the steel sheet).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet suitable for use as an iron core of transformers and other electrical equipment, and more particularly to a method for reducing the amount of Si reduction in the surface layer of a steel sheet before decarburizing annealing. By appropriately controlling the atmosphere of the decarburizing annealing in accordance therewith, the magnetic properties and the coating properties are advantageously improved.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are mainly used as iron core materials for transformers or rotating equipment, and are required to have high magnetic flux density, small iron loss and small magnetostriction as magnetic characteristics. Particularly in recent years, there has been an increasing need for grain-oriented electrical steel sheets having excellent magnetic properties from the viewpoint of energy saving and resource saving.

In order to obtain a grain-oriented electrical steel sheet having excellent magnetic properties, it is important to obtain a secondary recrystallized structure highly integrated in the (110) [001] orientation, so-called Goss orientation.
Such a grain-oriented electrical steel sheet was prepared by heating a steel slab containing an inhibitor required for secondary recrystallization, for example, a slab containing MnS, MnSe, AlN, BN, etc., followed by hot rolling and, if necessary, hot-rolled sheet annealing. After that, the final thickness is obtained by cold rolling one time or two or more times with intermediate annealing, and after decarburizing annealing,
It is manufactured by applying an annealing separator containing O as a main component and then performing final finish annealing.

[0004] Then, on the surface of the grain-oriented electrical steel sheet,
Except for special cases, an insulating coating mainly composed of forsterite (Mg ₂ SiO ₄ ) (hereinafter simply referred to as forsterite coating) is generally formed. This coating contributes not only to the electrical insulation of the surface but also to the improvement of iron loss and magnetostriction by applying a tensile stress to the steel sheet due to its low thermal expansion property.

[0005] Generally, grain-oriented electrical steel sheets are coated with a vitreous coating on the forsterite film. This coating is very thin and transparent, so that the forsterite film gives the final appearance of the product. decide.
Therefore, the quality of the appearance greatly affects the product value. For example, a coating having a partially exposed base iron is unsuitable as a product, and the influence of the coating properties on the product yield is extremely large. Therefore, the formed forsterite film is required to have a uniform appearance and no defects, and to be excellent in adhesion so that the film does not peel off in shearing, punching, bending and the like. Furthermore, the surface is required to be smooth and have a high space factor when laminated as an iron core.

[0006] Such a forsterite film is formed in the final finish annealing, and since the film forming behavior affects the inhibitory effect of MnS, MnSe, AlN, etc. in steel, it is necessary to obtain excellent magnetic properties. It also affects secondary recrystallization itself, which is an essential process. In addition, the formed forsterite film contributes to the improvement of the magnetic properties of the steel sheet by purifying the steel by sucking up an inhibitor component unnecessary after the secondary recrystallization is completed into the film. . Therefore, it is extremely important to control the process of forming the forsterite film and to form the film uniformly to obtain a grain-oriented electrical steel sheet having excellent magnetic properties.

The forsterite film which greatly affects the product quality as described above is generally formed by the following steps. First, a final cold-rolled sheet for grain-oriented electrical steel sheet cold-rolled to a desired final sheet thickness is 700 to 900 in wet hydrogen.
Anneal continuously at a temperature of ° C. By performing this annealing (decarburizing annealing), the structure after cold rolling is primarily recrystallized so that appropriate secondary recrystallization occurs in the final finish annealing, and the magnetic properties of the product are prevented from being aged and deteriorated. 0 in steel.
Reduce the carbon content of about 01-0.10 mass% to about 0.003 mass% or less. At the same time, a sub-scale containing SiO ₂ is generated on the surface of the steel sheet by oxidation of Si in the steel.
Then, apply an annealing separator mainly composed of MgO onto the steel sheet, wind it up in a coil shape, and perform the final finish annealing that combines secondary recrystallization annealing and purification annealing in a reducing or non-oxidizing atmosphere. By performing at a temperature of about 1200 ° C., a forsterite film is formed mainly by a solid phase reaction represented by the following reaction formula. 2MgO + SiO ₂ → Mg ₂ SiO ₄

The forsterite film is a ceramic film in which fine crystals of about 1 μm are densely integrated.
As described above, it was formed on the steel sheet surface layer during decarburization annealing.
Since the subscale containing SiO ₂ is formed on the steel sheet as one raw material, the type, amount, distribution, etc. of this subscale contribute to the nucleation and grain growth behavior of forsterite, and It also affects the grain boundaries of the crystal grains and the strength of the grains themselves, and thus has a great effect on the coating quality after finish annealing.

Further, annealing separator consisting mainly of MgO which is the other raw materials, to be applied to the steel sheet as a slurry suspended in water, after drying was also physically adsorbed H ₂ O
In addition, some have hydrated and changed to Mg (OH) ₂ . Therefore, during the finish annealing, H ₂ O is continuously released in a small amount until around 800 ° C. This H ₂ O oxidizes the steel sheet surface during the finish annealing. This oxidation also affects the formation behavior of forsterite and also affects the inhibitor effect. If the amount of additional oxidation is large, this causes deterioration of magnetic properties. The easiness of oxidation by H ₂ O released from magnesia is also greatly affected by the physical properties of the sub-scale formed by decarburizing annealing. In particular, when the sheet thickness is reduced, the influence of the surface becomes relatively strong. Therefore, control of the quality of the sub-scale formed during decarburization annealing is extremely important for obtaining excellent magnetic properties.

As described above, controlling the quality of the subscale formed on the surface of the steel sheet in the decarburization annealing is necessary to uniformly form an excellent forsterite film at an appropriate temperature and to improve the quality of the secondary scale. This is an indispensable technology for the normal development of crystals and is one of the important control items when manufacturing grain-oriented electrical steel sheets.

A method of controlling the oxygen content of a steel sheet after decarburization annealing, as disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 59-185725, is disclosed in Japanese Patent Publication No. Sho 59-185725. As disclosed in No. 57-1575, the oxidation degree of the atmosphere is set to 0.15 or more in the front region of the decarburizing annealing,
A method in which the degree of oxidation in the subsequent rear region is 0.75 or less and lower than that in the front region, is disclosed in JP-A-2-240215 and
No. 54-24686, a method of performing a heat treatment at 850 to 50 ° C. in a non-oxidizing atmosphere after decarburizing annealing,
As disclosed in Japanese Patent Publication No. 3-57167, cooling after decarburization annealing is performed at a temperature range of 750 ° C or less by an oxidation degree of 0.008.
The cooling method is as follows, and the degree of atmospheric oxidation (P [H ₂ O] / P [H ₂ ]) in the soaking process is reduced to less than 0.70 and increased as disclosed in JP-A-6-336616. A method in which the degree of atmospheric oxidation (P [H ₂ O] / P [H ₂ ]) in the temperature process is set to a value lower than that in the soaking process, and further, as disclosed in JP-A-7-278668. Methods for defining the speed and the annealing atmosphere are known.

[0012] All of the above-mentioned techniques are methods for controlling the quality of the sub-scale by adjusting the decarburizing annealing conditions such as atmosphere and temperature. However, the sub-scale quality is controlled according to the surface condition of the steel sheet before the decarburizing annealing. As a method of controlling the
No. 547 states that Si, O or Si, O,
A technique for adhering a Si compound containing H is disclosed in Japanese Patent Application Laid-Open No. 7-188757.
A technique of applying a Si compound according to ΔSi to a material having a difference in Si concentration (ΔSi) exceeding 20% of the Si concentration in steel is disclosed. Further, as a technique developed from these, JP-A-10-195536 discloses a method of controlling the amounts of Si and O in a surface oxide layer of an intermediate annealed plate.
According to No. 46, according to the ratio between the Si concentration of the surface oxide of the intermediate annealed sheet and the Si concentration of the ground iron,
A method for controlling the amount of Si compound attached has been disclosed.

[0013]

Although all of the above-mentioned methods have a certain effect, they are not always sufficient, and the quality of the sub-scale formed during the decarburization annealing still varies. In some cases, the resulting magnetic properties were not stable. In other words, there is still room for improvement in order to stably produce products having excellent quality and further improve the yield. The present invention has been developed in view of the above-mentioned circumstances, and has a forelite coating film with no defects and excellent adhesion over the entire width and length of the coil, and a grain-oriented electrical steel sheet having excellent magnetic properties. It is intended to propose a method that can be manufactured by using the method.

[0014]

Means for Solving the Problems In order to achieve the above object, the present inventors have developed not only the quality of the subscale formed after decarburizing annealing and the quality of the forsterite film formed after finishing annealing, but also The surface condition of the steel sheet before the decarburizing annealing was carefully studied. As a result, when the amount of Si reduction in the surface layer of the steel sheet before decarburization annealing is large,
It was found that the subscale quality and, consequently, the quality of the forsterite coating deteriorated.

That is, the grain-oriented electrical steel sheet is usually 2 to 4
Although it contains mass% Si, the heat treatment before hot rolling and the annealing process in the middle process oxidize the Si near the surface of the steel sheet, so that the surface layer of the steel sheet has a higher Si concentration than the inside of the base steel. descend. And the Si in the surface layer of such steel sheet
When the steel sheet with a large decrease is decarburized and annealed, a Si-depleted layer is formed immediately below the surface layer of the steel sheet during initial oxidation during the temperature rise process, which causes poor growth of SiO ₂ just below the surface layer even during the soaking process, resulting in a subscale. It has been found that the quality of the film deteriorates, and as a result, the film properties and the magnetic properties deteriorate. Therefore, if the amount of Si reduction in the surface layer of the steel sheet before decarburization annealing is accurately grasped and the result is reflected in the decarburization annealing conditions to prevent poor growth of SiO ₂ directly under the surface layer, a good sub It is possible to obtain a scale and thus a forsterite coating. The present invention is based on the above findings.

That is, the gist of the present invention is as follows. 1. The silicon-containing steel slab is hot-rolled, and if necessary, hot-rolled sheet annealing is performed, and then cold rolling is performed once or two or more times with intermediate annealing. After applying the annealing separator to the production of grain-oriented electrical steel sheet by a series of steps of final finish annealing, after the final cold rolling, measured the amount of Si reduction in the surface layer of the steel sheet before decarburization annealing, A method for producing a grain-oriented electrical steel sheet, comprising adjusting an atmospheric oxidation degree (P [H ₂ O] / P [H ₂ ]) in a temperature rising process of decarburizing annealing according to the measured value.

2. In the above 1, when the amount of Si reduction in the surface layer portion of the steel sheet is x, and the degree of atmospheric oxidation (P [H ₂ O] / P [H ₂ ]) in the temperature rise process of decarburizing annealing is y, the above x value Wherein the value of y is controlled within a range satisfying the following equation: y ≧ 0.57x + 0.158.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the invention will be described below. By the way, the present inventors have conducted various investigations on the descaled annealed sheet subscale corresponding to the product with deteriorated magnetic properties. It was found that a SiO ₂ deficient layer was formed in the sample. The inventors of the present invention have examined the cause of the formation of the SiO ₂ deficient layer immediately below the surface layer, and as a result, have found that the cause is a decrease in the Si concentration in the surface layer of the steel sheet before decarburizing annealing.

That is, when the Si concentration in the surface layer portion of the steel sheet after the decarburizing annealing was examined by glow discharge spectroscopy (GDS), the Si concentration went from the inside of the steel sheet to the surface as shown in FIG. From the surface, especially from 0.5 to 1.
It decreases most at a depth of 5 μm (0.05
0.50.5 mass%). If the amount of decrease in Si is large, after decarburization annealing, the position corresponding to the position where the above-mentioned Si concentration is minimum, that is, as shown in FIG. 1 (b), a position 0.5 to 1.5 μm deep from the surface. It was found that a SiO ₂ deficient layer was formed in the steel, and as a result, the quality of the subscale and thus the quality of the forsterite film deteriorated.

Then, the present inventors next examined the decarburization annealing conditions that do not harm the final product even when the amount of Si reduction in the surface layer of the steel sheet before the decarburization annealing is large. went. As a result, if the degree of oxidation of the atmosphere (P [H ₂ O] / P [H ₂ ]) in the temperature rise process of decarburization annealing is appropriately controlled according to the amount of Si reduction in the surface layer of the steel sheet, the amount of Si reduction It has been found that even if is large, good sub-scale and thus good magnetic and coating properties can be obtained without the adverse effect.

FIG. 2 shows that the degree of oxidation of the atmosphere (P [H ₂ O] / P [H ₂ ]) during the heating process was varied when the steel sheets having different amounts of Si reduction in the surface layer were subjected to decarburizing annealing. The results obtained by examining the effect on the product quality after final finish annealing when changing to? In this experiment, the product quality shall be judged by the magnetic properties of the final product and the appearance of the coating. If the magnetic flux density is B ≧ 1.885 T and there is no coating defect exposing the base iron, then ○, When it was recognized, it was evaluated with x. As shown in FIG. 2, when the amount of Si reduction (ΔSi) in the surface layer exceeds 0.25 mass%,
The product quality starts to deteriorate, but at this time, the degree of oxidation of the atmosphere (P [H ₂ O] / P [H ₂ ]) during the temperature rise process is increased. , The degree of oxidation of the atmosphere during the heating process is y
By controlling the degree of oxidation of the atmosphere y to satisfy the following equation, y ≧ 0.57x + 0.158, it was possible to effectively prevent such deterioration of the product quality.

Next, a preferred component composition of the grain-oriented electrical steel sheet targeted in the present invention will be described. As the silicon-containing steel as a raw material, any of conventionally known component compositions is suitable, and typical compositions are as follows. C: 0.02 to 0.10 mass% C is a useful component for improving the crystal structure by utilizing the α-γ transformation at the time of hot rolling, but the content is 0.02 mass%.
%, A good primary recrystallized structure cannot be obtained.
If the content exceeds 0.10 mass%, decarburization becomes difficult, resulting in poor decarburization and deterioration of magnetic properties. Therefore, the C content is 0.02 to 0.10 mass%.
% Is preferable.

Si: 2.0 to 4.5 mass% Si is an important component for increasing the electric resistance of the product and reducing the eddy current loss. However, the content is 2.0 mass
%, The crystal orientation is impaired by the α-γ transformation during final finish annealing, whereas if it exceeds 4.5 mass%, there is a problem in cold rolling. Therefore, the Si content is preferably about 2.0 to 4.5 mass%. .

Mn: 0.05 to 0.2 mass%, Se and / or S: 0.01 to 0.04 mass% Mn and Se, S function as inhibitors MnSe and MnS, but the Mn content is less than 0.05 mass%. If the Se or S content is less than 0.01 mass%, the inhibitor function becomes insufficient, while the Mn content exceeds 0.2 mass%, and the Se or S content is 0.04%.
If it exceeds mass%, the temperature required for slab heating becomes too high and is not practical.
%, And Se and S, either alone or in combination, are preferably about 0.01 to 0.04 mass%.

Sb: 0.005 to 0.05 mass% Sb functions as an auxiliary inhibitor and is an element useful for improving magnetic properties. However, the content is 0.005ma
If less than ss%, the effect of the addition is poor, while 0.05 mass
%, The decarburization property deteriorates, so the Sb content is 0.005 to 0.
It is preferable to be about 05 mass%.

Although the basic components have been described above, the present invention may further include the following elements as appropriate. Cu: 0.05 to 0.20 mass% Cu is an element effective for improving and stabilizing magnetic properties. When Cu is added, the inhibitor changes from MnSe or MnS to CuSe or CuS. In the present invention, in order to control the amount of Mn near the steel sheet surface after the intermediate annealing, MnSe or MnS
It is more preferable to use CuSe or CuS as an inhibitor than to use as an inhibitor. However, if the content is less than 0.05 mass%, it will not function sufficiently as an inhibitor. On the other hand, if it exceeds 0.20 mass%, the pickling property and the brittleness during hot rolling will deteriorate, so that Cu is about 0.05 to 0.20 mass%. It is preferable that

Cr: 0.05 to 0.30 mass% Cr is less effective when its content is less than 0.05%.
On the other hand, if it exceeds 0.30 mass%, a good primary recrystallized structure cannot be obtained. Therefore, it is preferable to contain Cr in an amount of about 0.05 to 0.30 mass%. Sn: 0.03 to 0.30 mass%, Ge: 0.03 to 0.30 mass% Sn and Ge have a poor addition effect when the content is less than 0.03 mass%, while a good primary recrystallization structure is obtained when the content exceeds 0.30 mass%. Therefore, it is preferable to contain them at about 0.02 to 0.30 mass% of each. Ni: 0.03 to 0.50 mass% Ni is less effective when its content is less than 0.03 mass%, whereas the hot strength is reduced when it exceeds 0.50 mass%, so the Ni content is about 0.03 to 0.50 mass%. Is preferred. P: 0.002 to 0.30 mass% P has a poor addition effect when the content is less than 0.002 mass%, whereas a good primary recrystallized structure cannot be obtained when the content exceeds 0.30 mass%, so that the P content is 0.002 to 0.30 mass%. It is preferable to set the degree. Nb: 0.003 to 0.10% by mass, V: 0.003 to 0.10% by mass Both Nb and V have poor addition effects when the content is less than 0.003% by mass, while the decarburization property deteriorates when the content exceeds 0.10% by mass. Therefore, it is preferable that each of them is contained at about 0.003 to 0.10 mass%.

Mo: 0.005 to 0.10 mass% Mo can be added to improve the surface properties. However, if the content is less than 0.005 mass%, the effect of the addition is poor. On the other hand, if it exceeds 0.10 mass%, the decarburization property deteriorates. Therefore, the Mo content is preferably set to about 0.005 to 0.10 mass%.

Next, preferred production conditions of the present invention will be specifically described. Molten steel adjusted to the above preferred component composition by the conventionally used steelmaking method is cast by a continuous casting method or an ingot-making method, and if necessary, a slab with a lumping step, and then at 1250 to 1450 ° C. After performing slab heating in a temperature range, hot rolling is performed. Next, after performing hot-rolled sheet annealing as needed, a cold-rolled sheet having a final thickness is formed by cold rolling once or twice or more with intermediate annealing.

Next, decarburization annealing is performed. In the present invention, it is important to accurately grasp the amount of Si reduction in the surface layer of the steel sheet before the decarburization annealing. Here, as a method of measuring the amount of Si reduction in the surface layer of such a steel sheet,
Glow discharge spectroscopy is advantageous. According to the glow discharge spectroscopy, as shown in FIG. 1 described above, it is possible to measure the concentration of a predetermined component from the outermost surface of the steel sheet to the inside of the base iron in one measurement. Can be. Therefore, based on this measurement result, from the amount of Si inside the base iron (for example, at a position 40 μm deep from the surface),
The position where the Si concentration directly below the surface layer is the lowest (0.5 to
Subtracting the amount of Si (at a depth of 1.5 μm) allows the amount of Si reduction in the surface layer to be determined. The method of measuring the amount of Si reduction in the surface layer of the steel sheet is not limited to the above-described glow discharge spectroscopy, and a chemical analysis or a fluorescent X-ray analysis is performed by shaving the vicinity of the surface and the ground iron part. Other measurement methods may be employed.

In this decarburizing annealing, the temperature rise process
Atmosphere oxidation degree (P [H_TwoO] / P [H _Two]), Steel sheet surface
It is important to control accurately according to the amount of Si reduction.
That is, the amount of Si reduction in the surface layer of the steel sheet is x,
Assuming that the degree of vapor oxidation is y, it is important to control the degree of atmospheric oxidation y to a range that satisfies the following equation: y ≧ 0.57x + 0.158.

Further, it is preferable that the upper and lower limits of the degree of oxidation of the atmosphere (P [H ₂ O] / P [H ₂ ]) in the heating process be limited to the range of 0.30 to 0.60. That is, if the degree of atmospheric oxidation during the temperature rise process is less than 0.30, the oxide film will be formed unevenly, and the oxide film will have poor additional oxidation resistance during the final annealing, whereas if it exceeds 0.60, it will be the FeO generation region. This is because an inert oxide film is formed.

The subscale amount of the decarburized annealed sheet is 0.5 to 1.0 g / oxygen per unit area (per one side).
preferably with m ² approximately. Since, 0.5 is less than g / m ^2, good film is difficult to form to subscale as the raw material of forsterite is insufficient, whereas 1.0 g / m
^{If it} exceeds ² , the forsterite film is excessively formed and becomes thick, resulting in a decrease in the space factor.

An annealing separator containing magnesia as a main component is applied in a slurry state to the surface of the steel sheet subjected to the decarburizing annealing as described above, and then dried. Here, the magnesia used for the annealing separator has a hydration amount (after hydration at 20 ° C. for 6 minutes,
It is preferable to use one having a weight loss by ignition at 1000 ° C. for one hour in the range of 1 to 4 mass%. This is because if the hydration of magnesia is less than 1 mass%, the formation of a forsterite film is insufficient, while if it exceeds 4 mass%, the amount of water carried between the coil layers becomes too large and the additional oxidation of the steel sheet increases. Therefore, a good forsterite film may not be obtained. The citric acid activity (CAA40) at 30 ° C. is preferably 30 to 150 seconds. This is because if the citric acid activity is less than 30 seconds, the reactivity is too strong and forsterite is rapidly generated and easily peels off, while if it exceeds 150 seconds, the reactivity is too weak and forsterite generation does not progress It is. In addition, BET
(Specific surface area) is preferably about 10 to 40 m ² / g. If it is less than 10 m ² / g, the reactivity is too weak and forsterite formation does not proceed, while if it exceeds 40 m ² / g, the reactivity is too strong and forsterite is rapidly generated,
This is because it is easy to peel off. Further, it is preferable to apply the amount of the annealing separator in the range of 4 to 10 g / m ² per one side of the steel sheet. If the coating amount is less than 4 g / m ^2, the formation of forsterite is insufficient, while if it exceeds 10 g / m ² , the forsterite film is excessively formed and becomes thick, resulting in a decrease in the space factor. Because.

Further, in order to further improve the uniformity of the film properties and the magnetic properties, TiO ₂ , SnO ₂ ,
Oxides such as _{Fe 2 O 3, CaO, MgSO} 4 and sulfides such as SnSO ₄ or SrSO _4, Sr (OH) 1 or more kinds chosen from among the ₂ · 8H ₂ O Such Sr compound May be added alone or in combination.

Next, after subjecting to secondary recrystallization annealing and purification annealing (final finish annealing), a phosphate insulating coating, preferably an insulating coating having tension, is applied to obtain a product. Secondary recrystallization annealing during annealing 750-900
Either a method of performing holding annealing at a certain temperature of 20 ° C. for 20 to 70 hours and then raising the temperature or a method of performing annealing without holding is performed. Also, a known magnetic domain refining treatment can be performed after the final cold rolling, the final finish annealing, or the insulating coating, which is effective for further reducing iron loss.

[0037]

EXAMPLES Example 1 C: 0.042 mass%, Si: 3.25 mass%, Mn: 0.070 mass
%, Se: 0.019 mass%, Sb: 0.022 mass% and Mo: 0.0
A silicon steel slab containing 12 mass% and the remainder consisting of Fe and unavoidable impurities was heated at 1420 ° C. for 20 minutes, and then hot-rolled into a hot-rolled sheet having a thickness of 2.6 mm. Then, 950 ℃,
After the hot-rolled sheet was annealed for one minute, the sheet was finished to a final thickness of 0.30 mm by two cold rollings with an intermediate annealing at 1000 ° C. for one minute. Here, the degree of atmospheric oxidation (P [H ₂ O] / P [H
₂ ]) and the subsequent pickling and grinding conditions were changed to adjust the amount of Si in the surface layer. Then, prior to decarburizing annealing, the amount of Si reduction in the surface layer of the steel sheet was measured by glow discharge spectroscopy, and the value was about 0.42 mass%. Then, decarburizing annealing was performed at 830 ° C. for 1 minute in an atmosphere of H ₂ —H ₂ ON ₂ . At this time, the degree of oxidation of the atmosphere (P [H ₂ O] / P [H ₂ ]) during the heating process was changed as shown in Table 1.

Next, an annealing separator containing magnesia as a main component is made into a slurry and applied to a decarburized annealed plate coil.
After drying, it is subjected to secondary recrystallization annealing at 850 ° C for 50 hours in a nitrogen atmosphere, and then heated to 1180 ° C at a rate of 30 ° C / h in an atmosphere of 20% nitrogen and 80% hydrogen. After warming,
Purification annealing was performed at 1180 ° C. for 5 hours in a hydrogen atmosphere.
Thereafter, an insulating coating containing magnesium phosphate and colloidal silica as main components was applied.

Magnetic properties of each product coil thus obtained
(Magnetic flux density B ₈ , iron loss W _17/50 ), bending adhesion of the coating and appearance of the coating were examined. The coating has a bending adhesion of 5
The test pieces were wound around round bars having various diameters at mm intervals, and evaluated with the minimum diameter at which the coating did not peel. Table 1 shows the obtained results.
It is described together.

[0040]

[Table 1]

As is clear from the table, all of the inventive examples manufactured under the conditions according to the present invention show good film properties and magnetic properties.

[0042]

Thus, according to the present invention, the degree of atmospheric oxidation (P [H ₂ O] / P [H] in the temperature rising process of decarburizing annealing depends on the amount of Si reduction in the surface layer of the steel sheet before decarburizing annealing. By appropriately controlling ₂ ]), a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties can be stably obtained.

[Brief description of the drawings]

FIG. 1 (a) is a diagram showing a Si concentration profile of a steel sheet surface portion before decarburizing annealing obtained by glow discharge spectroscopy, and FIG. 1 (b) is a diagram showing a cross section of a sub-scale after decarburizing annealing. It is.

Fig. 2 shows the effect of the amount of Si reduction on the surface layer of the steel sheet and the degree of atmospheric oxidation (P [H ₂ O] / P [H ₂ ]) during the heating process of decarburization annealing on the product quality after final finish annealing. FIG.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K033 AA02 BA02 CA01 CA02 CA03 CA04 CA07 CA08 FA01 FA12 HA01 HA03 JA04 LA04 RA04 SA02 TA01 5E041 AA02 CA01 HB11 NN01 5E062 AA01 AC15

Claims (2)

[Claims] 1. A silicon-containing steel slab is hot-rolled, subjected to hot-rolled sheet annealing if necessary, and then subjected to one or two or more cold-rolling steps including intermediate annealing, and then decarburization. After annealing,
After manufacturing the grain-oriented electrical steel sheet through a series of steps of applying an annealing separator to the steel sheet surface and then performing final finish annealing, measure the amount of Si reduction in the surface layer of the steel sheet after final cold rolling and before decarburizing annealing. A method for producing a grain-oriented electrical steel sheet, comprising adjusting the degree of atmospheric oxidation (P [H ₂ O] / P [H ₂ ]) in the temperature rising process of decarburizing annealing according to the measured value. 2. The method according to claim 1, wherein the amount of Si reduction in the surface layer portion of the steel sheet is x, and the degree of oxidation of the atmosphere (P [H ₂ O] / P [H ₂ ]) in the temperature rising process of decarburizing annealing is y. In this case, the value of y is controlled in a range satisfying the following equation: y ≧ 0.57x + 0.158 in accordance with the x value.