JPH11158645A - Production of grain-oriented silicon steel sheet low in strain sensitivity and excellent in magnetic property and grain-oriented silicon steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the strain sensitivity of a grain-oriented silicon steel sheet excellent in magnetic properties. SOLUTION: For a grain-oriented silicon steel sheet after finish annealing having forsterite coating, coating and baking treatment in which a coating soln. contg. phosphate, chromic anhydride or chromate and a coloidal silica is applied in the range of 3 to 6 g/m<2> per side by dry weight in the temp. range of 750 to 900 deg.C for 30 sec is repeatedly executed two times, a brittle part is formed on the boundary between the primary and secondary tensile coating, and the total coating weight for two times is regulated to the range of 7 to 12 g/m<2> per side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented electrical steel sheet which is advantageously used for an iron core such as a transformer, and more particularly, to a tension coating having a large effect of reducing strain sensitivity and improving magnetic properties on a silicon steel sheet. An object of the present invention is to propose a method for manufacturing a grain-oriented electrical steel sheet on which a tension (insulation) film is formed and a grain-oriented electrical steel sheet obtained by this method.

[0002]

2. Description of the Related Art As one of the methods for reducing iron loss of a grain-oriented electrical steel sheet, means for imparting tension to a steel sheet by a difference in thermal expansion coefficient between an insulating coating and a steel sheet is known. Of iron loss when strain is applied to steel (strain sensitivity)
It also has the effect of reducing

As a method for coating such a coating, Japanese Patent Publication No. 175-1521 (a method for forming a heat-resistant overcoating insulating film on a directional silicon steel sheet) and Japanese Patent Application Laid-Open No.
No. 28043 (a method for forming an insulating film on a grain-oriented silicon steel sheet) and the like each propose and disclose a technique using a coating solution composed of colloidal silica, phosphate and anhydrous chromate.

Further, Japanese Patent Application Laid-Open No. Sho 59-197520 (a method for producing a unidirectional magnetic steel sheet having a low iron loss) and Japanese Patent Application Laid-Open No. 63-42332 (a method for producing a magnetic iron sheet having a low iron loss) have been disclosed. Discloses a technique for introducing a linear flaw or the like into a steel sheet. A grain-oriented electrical steel sheet with a low iron loss, in which the iron loss does not deteriorate even when the strain is removed by the linear flaw and annealing is performed, is obtained. This reduction in iron loss is considered to be a so-called domain refining effect due to a decrease in the domain width.

However, in the case of a grain-oriented electrical steel sheet in which linear flaws or the like are introduced on the surface of a steel sheet, the strain introduced from the outside of the steel sheet tends to concentrate around the flaw, and iron loss and magnetostriction characteristics may deteriorate. is there. For example, when a pinch roll for transporting a steel sheet or a measuring roll for measuring the length of the steel sheet is pressed, there is a case where low iron loss cannot be maintained. Therefore, even if the iron loss is reduced by the effect of linear flaws or the like, the iron loss after processing the transformer may not be as low as expected. Since removal annealing is not performed, there is a concern that problems such as deterioration of iron loss and increase in noise may occur.

[0006] The tension of the steel sheet by the tension coating, which is effective to reduce the influence of such external strain, increases as the coating becomes thicker. However, if the coating is too thick, the water vapor generated inside the coating during baking is transferred to the outside. Discharge is hindered, and bulge-like defects and hole defects called blisters are easily formed in the coating. In such a case, there is a problem that, for example, powder is generated when the measuring roll is pressed down, causing idle rotation.

Japanese Patent Application Laid-Open No. Hei 5-1387 (a method for forming an insulating coat on a grain-oriented silicon steel sheet) discloses a technique for preventing blistering by controlling the rate of temperature rise during baking. Even when the technique is used, there is a problem that a large amount of blisters are generated when the coating is thick.

[0008] On the other hand, in a method in which the sensitivity to strain is alleviated simply by excessively increasing the thickness of the coating, there is also a problem that the space factor is reduced.

[0009]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems, and provides a directional material having low iron loss and low strain sensitivity by forming a suitable tension coating. An object of the present invention is to propose a method of manufacturing an electrical steel sheet and a grain-oriented electrical steel sheet.

[0010]

In order to solve the above-mentioned problems, a detailed investigation was made on the relationship between the coating method and the core loss and strain susceptibility. As a result, a weak portion was formed in the middle of the tensile coating in the thickness direction. The inventors have obtained a new finding that the provision thereof is extremely effective in reducing strain sensitivity, and have achieved the present invention. That is, the gist of the present invention is as follows.

In producing a grain-oriented electrical steel sheet by forming a tension coating on a grain-oriented silicon steel sheet having a forsterite film on the surface after finish annealing, phosphate, anhydrous chromium is added to the surface of the silicon steel sheet. A coating solution containing an acid or a chromate and colloidal silica is applied in a range of 3 g / m ² or more and 6 g / m ² or less per side on a dry weight basis.
The coating and baking process is repeated twice, at a temperature range of ℃ to 900 ° C, for at least 30 seconds, to create a fragile portion at the boundary between the first and second tension coatings, and the total of two coatings A method for producing a grain-oriented electrical steel sheet having low strain sensitivity and excellent magnetic properties, characterized in that the amount is adjusted to a range of 7 g / m ² or more and 12 g / m ² or less per one side by dry weight (first invention).

A grain-oriented electrical steel sheet obtained by repeatedly forming a tension coating twice on a grain-oriented silicon steel sheet having a forsterite coating on its surface, wherein a fragile portion is formed at the boundary between the repeatedly formed tension coatings. A grain-oriented electrical steel sheet having low strain sensitivity and excellent magnetic properties, characterized in that the coating amount per side of the tension coating is in the range of 7 g / m ² or more and 12 g / m ² or less (No. 2) invention).

A second invention according to the second invention, wherein the surface of the silicon steel sheet has a number of linear grooves having a depth of 10 to 50 μm, a width of 50 to 300 μm, and an interval of 1 mm or more in a direction intersecting the rolling direction. A grain-oriented electrical steel sheet having low strain sensitivity and excellent magnetic properties (third invention).

Here, the fragile portion of the tension coating is a portion where a minute crack is generated to such an extent that the coating does not peel off due to the action of local stress about the pressure of the pinch roll or measuring roll in the amount of adhesion of the present invention. Means

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The function and effect of the present invention will be described below. This invention applies a solution containing phosphate, chromic anhydride or chromate, and colloidal silica to a silicon steel sheet having a forsterite coating after final finish annealing obtained through a usual process, and baking, applying tension. The purpose of the present invention is to produce a grain-oriented electrical steel sheet by forming a coating, and in particular, the gist of the present invention is to perform an operation of baking and drying in a temperature range of 750 to 900 ° C. for 30 seconds or more after applying a coating solution. It is repeated twice, and the total of the two times of the application amount per one side by dry weight (same as the adhesion amount, hereinafter simply referred to as the application amount or the adhesion amount) is set in the range of 7 to 12 g / m ² , and A brittle portion is intentionally provided at the boundary between the first and second coating films. Thus, as a grain-oriented electrical steel sheet, it is possible to reduce iron loss and reduce strain sensitivity without adversely affecting other properties.

The above-mentioned coating solution is disclosed, for example, in Japanese Patent Publication No. Sho 56-52117 (a method for forming an insulating film on a grain-oriented silicon steel sheet). This provides a more effective coating that applies greater tension to the steel sheet and reduces strain sensitivity.

The operation and effect of the present invention will be described in more detail below. When a stress such as a roll pressure is locally applied from the outside to the grain-oriented electrical steel sheet on which the tensile coating is formed by repeating the above twice, the boundary surface between the first and second coatings is applied. In the fragile portion, fine cracks are generated to such an extent that the coating does not peel off, so that the applied stress is relieved. Therefore, the strain applied to the steel sheet is reduced, and the strain sensitivity is reduced.

At this time, even if a thick coating having an adhesion amount of 7 g / m ² or more is formed by one application, since a fragile portion does not exist, a fine crack is generated due to the external stress as described above. In addition, the effect of reducing the sensitivity to strain is not only inferior, but also, when such a thick tension coating is formed by a single application and baking, problems such as blistering and powdering and surface roughness increase. This causes problems such as a decrease in space factor. In addition, these problems similarly occur when the tension film is formed on the forsterite film for the first time and when the tension film is formed again on the tension film for the second time.

Further, if the application amount of each application is less than 3 g / m ² in each of the first application and the second application, the tension applied to the steel sheet becomes small, and the effect of reducing iron loss and reducing strain sensitivity is reduced. If the total amount of the ^two coatings is not more than 7 g / m ^{2, the} effect of reducing the strain sensitivity is insufficient, and if it exceeds 12 g / m ² , the effect of reducing the strain sensitivity does not improve so much and the space factor decreases. It is not preferable.

Therefore, the application amount of the tension film is to be 3 g / m ² or more and 6 g / m ² or less for the first and second times, and the total of the two times is 7 g / m ² or more and 12 g / m ² or less. is necessary.

In the case where the same coating solution is applied and baked three times, the fragile portions are not the first and the second.
The second and third and second coatings are formed at two places on the boundary surface of each coating, and external stresses cause fine cracks to be generated at those two places, respectively.
The peeling of the coating increases rapidly. As a result, dusting occurs, and the amount of deposits on the measuring roll or the like increases, causing troubles. Therefore, the number of application and baking needs to be limited to two. Further, increasing the number of times of application and baking more than two times impairs productivity accordingly, which is not preferable from this point.

Next, the baking temperature after application of the coating solution needs to be 750 ° C. or more in both the first and second times. As disclosed in JP-A-5-279864 (a method of forming an insulating film on a grain-oriented silicon steel sheet), when the first baking temperature is 600 ° C or lower, the glass transition temperature of the coating solution is not reached. Since the tension introduced into the steel sheet is small, and the first coating and the second coating formed thereafter are integrated and a brittle portion is not generated at the boundary surface, the external coating causes Since fine cracks for relaxing stress do not occur, the effect of reducing strain sensitivity is insufficient.

Therefore, when the baking temperature is set to 750 ° C. or higher, the tension introduced into the steel sheet becomes larger and a brittle portion is formed at the boundary between the first coating and the second coating. High adhesion can be obtained. The upper limit of the temperature is preferably 900 ° C, and 900 ° C
If the temperature is higher, oxidation of the steel sheet and deterioration of iron loss characteristics occur, which is not preferable.

It is necessary that the baking time is 30 seconds or longer. If the baking time is shorter than 30 seconds, the dehydration-condensation reaction of the coating solution does not sufficiently proceed, which is not preferable.

When such a tension coating is formed on a steel sheet without a forsterite coating, a large crack is generated between the tension coating and the steel sheet due to external stress, and the tension coating is peeled off. Therefore, in order to ensure the adhesion of the tension film, it is necessary to apply a tension to the steel sheet via the forsterite film, and in addition, the adhesion to prevent the tension film from peeling due to crack generation. In order to obtain the above, it is preferable that the surface roughness of the forsterite film is 0.5 μm or more.

In the case where the tension coating is formed by applying and baking two times repeatedly, in order to make the appearance of the final second tension coating beautiful, phosphoric acid pickling is performed immediately before the formation of the second tension coating. And drying.

Further, the above-mentioned tension coating conforming to the present invention may contain a small amount of silica or alumina powder for the purpose of preventing seizure between steel sheets during strain relief annealing.

Further, the present invention can be advantageously applied to a case where a linear groove for subdividing magnetic domains is provided on the surface of a steel sheet, and a more effective reduction in strain sensitivity can be obtained.

Next, a preferred component composition and a preferred manufacturing process of the material for a grain-oriented electrical steel sheet of the present invention will be described.

Component Composition This is intended for a silicon steel slab for producing a grain-oriented electrical steel sheet having excellent magnetic properties. The preferred component composition is as follows.

C: 0.10 wt% or less (hereinafter simply expressed as%) C is reduced in the tapping stage to prevent decarburizing annealing, and to secure a certain amount of C to improve the structure. There is a method of removing by decarburization and primary recrystallization annealing, and both methods are applicable in the present invention. In the case of the former method, the content of C is set to avoid the adverse effect of C.
It is preferably less than 0.01%, and in the case of the latter method, a preferable range for tissue improvement is 0.01% or more and 0.10% or less.

Si: 2.0 to 4.5% Si effectively increases the specific resistance of steel and effectively contributes to the reduction of iron loss. If the content is less than 2%, the effect of reducing iron loss is not sufficient, and the content exceeds 4.5%. In this case, the cold rolling property is impaired.

[0033] In addition to these components, it is important to include an inhibitor component. When MnS and / or MnSe is used for this inhibitor, Mn: 0.03
0.10% and S + Se: 0.01-0.03%. When AlN is used, Al: 0.01-0.04% and N: 0.005-0.012%. When the content is lower than the above ranges, the effect as an inhibitor is insufficient, and when the content is high, secondary recrystallization becomes unstable. In addition to the above, Cu, Sn, Sb, Ge, Mo, Te, Bi,
P, V and Nb may be used. Each of the above inhibitors can be used alone or in combination.

Manufacturing process The molten steel adjusted to the above-mentioned composition obtained by the conventional steelmaking method is cast by a continuous casting method or an ingot-making method, and if necessary, a slab is formed by interposing a baking process. Rolled, and if necessary, hot-rolled sheet annealing, and cold rolling is performed once or multiple times with intermediate annealing to obtain the final cold-rolled sheet thickness. After crystal annealing, a grain-oriented silicon steel sheet may be formed by a series of ordinary steps of applying an annealing separator and then performing final finish annealing.

The directional silicon steel sheet thus obtained after the final finish annealing is coated with a tension coating in which the coating solution is repeatedly applied and baked twice, as described above, to obtain a directional magnetic steel sheet product.

The introduction of the linear grooves on the surface of the steel sheet may be carried out in any step before the final finish annealing.

[0037]

EXAMPLE A silicon steel slab containing C: 0.069%, Si: 3.34%, Mn: 0.073%, sol. Al: 0.026%, N: 0.0083% and Sb: 0.024% is obtained through a normal process. After removing the unreacted annealing separating agent on the forsterite film using the final finished annealed plate (thickness: 0.23 mm),
After the strain relief annealing, perform phosphoric acid pickling and drying,
The operation of applying the coating solution and baking and drying in an electric furnace under a nitrogen atmosphere was repeated once, twice or three times to form a tension film.

Here, a steel plate has a depth of 20 μm on one surface.
m, width: 200 μm, spacing: 3 mm, with a linear groove introduced in a direction substantially perpendicular to the rolling direction. The coating solution was magnesium phosphate: 50.5%, chromic anhydride: 7%, colloid. Silica: 42% and silica powder:
What consisted of 0.5% was used.

In the case where the tension coating was formed once, and the case where the tension coating was formed once and the second tension coating was further formed, the application amount and the tension coating were determined. The relationship between surface properties and dust resistance was investigated.

Here, the baking conditions of the tension film are all 800
° C for 60 seconds. The measuring roll is a combination of two steel rolls having a diameter of 100 mm and a width of 50 mm, and the upper roll is pressed against the lower roll by an air cylinder. This pressing load is 150k with respect to the roll width.
It was adjusted to gf / cm 2 and passed through the plate. Table 1 summarizes the results of these investigations.

[0041]

[Table 1]

As is evident from Table 1, when the amount of the first application exceeds 6 g / m ² in both the first and second applications, the surface properties are poor and there is a problem of powdering.

Part 2 The relationship between the amount of the tension coating and the tension applied to the steel sheet was investigated.

At this time, the adhesion amount of the tension film was 4 g / m^TwoNomo
Is a single application and baking, 6kg / m ^TwoThe above is once
4g / m in eyes^TwoAfter applying, apply and bake for the second time
These baking conditions were 800 ° C for 60 seconds.
Between. Also, cut the tension into 30mm width and 280mm length.
The tensile coating on one side of the steel plate of the specimen
The amount of warpage of the steel sheet when removed with a solution
The greater the tension).

FIG. 1 is a graph showing the relationship between the warpage of the steel sheet and the amount of the tension coating based on the results of these investigations.

As is clear from FIG. 1, the warpage, ie, the tension, of the steel sheet increases as the amount of adhesion of the tension coating increases, and the degree of the tension increases greatly when the amount of adhesion is between 4 and 7 g / m ^2. .

Part 3 The strain susceptibility of each steel sheet was examined in the case where the tension coating was formed by changing the amount of application and the number of application and baking was once, and in the case where the tension coating was formed by repeating twice.

At this time, the amount of adhesion in the application of the tension film is in the range of 6 to 12 g / m ² for one application and baking, and the first and second applications for the two coating and baking. Were made in approximately the same amount to a total of 4 to 15 g / m ² . The baking conditions were all 800 ° C. for 60 seconds.

The strain sensitivity is as follows: width: 100 mm, length: 400 mm
The steel sheet cut into pieces was evaluated by the iron loss difference between before and after the passing of the steel sheet when passed between two rolls having a diameter of 60 mm and a width of 30 mm at a roll reduction pressure of 15 kgf / cm. This reproduces the effect of the measuring roll when the rolling force is relatively large. In the above results, the smaller the iron loss difference, the lower the strain sensitivity.

FIG. 2 is a graph showing the relationship between the adhesion amount of the tension coating and the strain sensitivity using the number of coating and baking as a parameter based on the results of these investigations.

As is clear from FIG. 2, when the number of times of application and baking is compared with the number of times of application and baking, the iron loss difference is smaller when the number of times of coating and baking is two with the same amount of the tension film. Small, ie, low strain sensitivity. In addition, when the number of coating and baking is two, when the amount of adhesion is 7 g / m ² or more, the strain sensitivity is extremely low, and the effect of reducing the strain sensitivity is not significant when the amount of adhesion exceeds 12 g / m ^2. . Therefore, since the space factor decreases as the amount of adhesion increases, the upper limit of the amount of adhesion of the tension film is preferably set to 12 g / m ² .

Part 4 The number of coating and baking is changed to 2 by changing the amount of coating and the baking conditions.
The iron loss difference as an index of strain sensitivity is investigated by the same method as in the above-mentioned item 3 for each steel sheet coated with the tension coating as the third or third times, and the powdering after the roll passing similar to the above-mentioned third item is performed. The situation was investigated. Table 2 summarizes the results of these investigations.

[0053]

[Table 2]

As is clear from Table 2, the iron loss difference is small and the powdering problem does not occur in the conforming example of the present invention of sample No. 1, whereas in the comparative examples of sample nos. If the loss difference is large, or the first baking temperature is too high, as in sample No. 3, the iron loss before applying strain is already high, or if coating and baking are performed three times as in sample No. 5, Flouring has occurred.

Part 5 First application amount: 4 g / m ² , baking conditions: 800 ° C./60 seconds, second application amount: 4 g / m ² , baking conditions: 800 ° C./60
A tension coating is applied for 2 seconds, and the total adhesion amount of 2 times is 8 g /
and m ² and the directional electromagnetic steel plates (adaptations), one coating and baking in (baking conditions: 800 ° C., 60 sec) deposition amount of 4g / m ²
With respect to the grain-oriented electrical steel sheet (Comparative Example), the iron loss in the steel sheet was measured, and test transformers were manufactured using these steel sheets, and the characteristics of those transformers were investigated.

The test transformer was a three-phase three-legged iron core transformer. The leg and yoke width: 150 mm, external dimensions: 750 m
mx 750mm, steel plate usage: 100kg. Also,
When cutting the steel plate, a measuring roll having a diameter of 100 mm and a width of 50 mm was pressed at 15 kgf / cm. Table 3 summarizes the results of these investigations.

[0057]

[Table 3]

As is evident from Table 3, the iron loss in the steel sheet is the same in both the conforming example and the comparative example, while the iron loss and noise in the transformer show superior values in the conforming example. .

Further, after examining the characteristics of the transformer, the transformer was dismantled and the steel plate used was examined. As a result, the steel plate of the comparative example showed iron loss deterioration in the portion reduced by the measuring roll, and the lancet was observed in the magnetic domain observation. However, such a phenomenon was not observed in the example of adaptation of the present invention.

Part 6: A silicon steel sheet similar to the above was used except that no linear grooves were introduced on the steel sheet surface, and a tension coating was formed by changing the amount of adhesion by twice coating and baking, and then forming Iron loss was measured for the grain-oriented electrical steel sheet passed through the measuring roll under the same conditions as in Example 3, and the relationship between the amount of adhesion and the iron loss was investigated. At this time, the application condition of the tension film is such that the first and second adhesion amounts are the same, and the total adhesion amount is 4 to
The range was 15 g / m ² . This was baked at 800 ° C. for 60 seconds.
FIG. 3 is a graph showing the relationship between the adhesion amount of the tension coating and the iron loss based on the results of these investigations.

As is apparent from FIG. 3, even when a steel sheet having no linear grooves on the surface is used, when the coating and baking are performed twice, the iron loss decreases with an increase in the adhesion amount of the tension film, that is, the strain is reduced. Sensitivity is reduced, and good iron loss is shown at a coating weight of 7 g / m ² or more.

[0062]

According to the present invention, a tensile coating is formed on a grain-oriented electrical steel sheet having a forsterite coating after finish annealing by repeatedly performing application and baking twice specifying the amount of coating and baking conditions. Thus, the grain-oriented electrical steel sheet according to the present invention can reduce distortion sensitivity and produce a more efficient transformer, and can advantageously contribute to reducing power loss.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the warpage of a steel sheet and the amount of adhesion of a tension film.

FIG. 2 is a graph showing the relationship between the adhesion amount of a tension film and the sensitivity to strain using the number of times of application and baking as a parameter.

FIG. 3 is a graph showing the relationship between the adhesion amount of a tension coating and iron loss.

Claims (3)

[Claims] When producing a grain-oriented electrical steel sheet by applying a tension coating to a grain-oriented silicon steel sheet after a finish annealing having a forsterite film on its surface, a phosphate, A coating solution containing chromic anhydride or chromate salt and colloidal silica is applied at a dry weight of 3 g / m ² or more and 6 g / m ² or less per side, and applied at a temperature of 750 ° C. or more and 900 ° C. or less. The coating and baking treatment for 30 seconds or more is repeated twice to obtain 1
A brittle portion is formed at the boundary surface between the second and the second tension coatings, and the total application amount of the two applications is adjusted to a range of 7 g / m ² or more and 12 g / m ² or less per one side by dry weight. Method for producing grain-oriented electrical steel sheet with low strain sensitivity and excellent magnetic properties. 2. A grain-oriented electrical steel sheet formed by repeatedly applying a tension coating to a grain-oriented silicon steel sheet having a forsterite coating on its surface, wherein the grain coating is fragile at an interface between the repeatedly formed tension coatings. Part, the adhesion amount per one side of the tension coating is 7 g / m ² or more,
A grain-oriented electrical steel sheet having low strain sensitivity and excellent magnetic properties, characterized by being in the range of 12 g / m ² or less. 3. The silicon steel sheet according to claim 2, wherein the surface thereof has a large number of linear grooves having a depth of 10 to 50 μm, a width of 50 to 300 μm, and an interval of 1 mm or more in a direction intersecting the rolling direction. A grain-oriented electrical steel sheet having a low strain sensitivity and excellent magnetic properties.