JPH08199240A - Method for measuring primary recrystallized grain diameter of magnetic steel sheet - Google Patents

Abstract

PURPOSE: To improve the accuracy in a method for measuring a primary recrystallized grain diameter of a magnetic steel sheet by using the measured value of iron loss. CONSTITUTION: The iron loss of the remained part except the part of a steel sheet having large variation of nitriding is measured to calculate the primary recrystallized grain diameter. By the above method, the variating width of the measured primary recrystallized average grain diameter can be reduced to almost 40%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring an average primary recrystallization grain size in producing a unidirectional electrical steel sheet used for a transformer core or the like.

[0002]

2. Description of the Related Art The unidirectional electrical steel sheets that have been put into practical use at present have a sharp texture formed by secondary recrystallization without exception. The secondary recrystallization texture is controlled so that the crystal orientation exhibits the best performance and efficiency when the steel sheet is used as an electric device. Therefore, the higher the sharpness of the secondary recrystallization texture, the better the performance of the electric device. The sharpness of the secondary recrystallized texture generally strongly reflects on the magnetic flux density B8 (the magnetic flux density strength in a magnetic field of 800 AT / m). The magnetic flux density depends on the behavior of secondary recrystallization,
It changes extremely sensitively. Therefore, proper secondary recrystallization growth is beneficial to manufacturers and users.

The grain-oriented electrical steel sheet is a type of steel that is sensitive to manufacturing conditions, and even in a normal material under normal manufacturing conditions, the magnetic flux density varies. For example, although there is almost no difference in composition, there is some variation in magnetic flux density between molten lots, within the same molten lot, and between coils, even within the same coil, and there is some variation in magnetic flux density, which stabilizes the magnetic flux density at a high level. Becomes an obstacle. This is because the secondary recrystallization behavior very sensitively reflects subtle variations in various process conditions.

The cause of the secondary recrystallization failure and the variation of the magnetic flux density is considered to exist in the process before the finish annealing. Specifically, it is considered that the primary recrystallization average grain size is greatly involved. Therefore, accurately grasping the primary recrystallized grain size by on-line measurement is extremely effective for improving the above-mentioned variation in secondary recrystallization, and eventually variation in magnetic characteristics.

Then, by changing the primary recrystallization annealing conditions to control the primary recrystallization grain size within an appropriate range and eliminate the adverse effect thereof, it becomes possible to stabilize the magnetic characteristics at a high level.
In the production of a grain-oriented electrical steel sheet, a technique for measuring the primary recrystallized grain size online and ensuring an appropriate primary recrystallized structure formation based on this is already disclosed in JP-A-2-267223. . However, in this method, the variation in the magnetic characteristics is not sufficiently eliminated, and further improvement is desired.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a method for eliminating and improving the above problems and for accurately measuring the average primary recrystallization grain size in order to generate primary recrystallization having an appropriate grain size. It is a thing.

[0007]

Means for Solving the Problems The gist of the present invention is (1) Crystals of a primary recrystallized sheet of grain-oriented electrical steel sheet that has been subjected to a nitriding treatment after hot rolling and before the start of secondary recrystallization of final finish annealing. In measuring the grain size, the nitriding amount of the steel sheet is a primary recrystallization of the electromagnetic steel sheet, which is characterized by measuring the remaining portion, except for a portion that has fluctuated by a predetermined value or more with respect to the average nitriding amount of the steel sheet. Particle size measurement method. (2) The method for measuring the primary recrystallized grain size of an electromagnetic steel sheet according to (1), wherein the remaining portion is measured except for the portion where the nitriding amount of the steel sheet varies by 30% or more compared to the average nitriding amount of the steel sheet. (3) As a primary recrystallized plate, C: 0.021-by weight ratio
0.075%, Si: 2.5-4.5%, acid-soluble A
1: 0.010 to 0.060%, N: 0.0010
0.0130%, S + 0.405Se: 0.014% or less, Mn: 0.05 to 0.8%, the balance consisting of Fe and inevitable impurities is heated at a temperature of less than 1280 ° C., and then hot rolled. The primary of the electromagnetic steel sheet according to (1) or (2), characterized in that the steel sheet is cold-rolled at least once including a final cold-rolling with a rolling reduction of 80% or more, and then decarburized and annealed. It is in the method of measuring the recrystallized grain size.

The details will be described below based on the experimental results in the grain-oriented electrical steel sheet having a slab heating temperature of less than 1280 ° C.
As a result of various studies on the measurement method of the primary recrystallization average grain size, the present inventors have compared the conventional means for measuring the iron loss of a steel sheet with a steel sheet, for example, with a standard such as an average nitriding amount in a certain sheet thickness direction. Value, and remove the part outside this part,
It was concluded that the method of measuring the iron loss of the remaining steel plate and calculating the primary average particle size is extremely effective in improving the particle size measurement accuracy. This measurement condition is not limited to online measurement and offline measurement.

First, C: 0.053% by weight and Si:
After heating a slab containing 3.25%, Mn: 0.13%, S: 0.005%, acid-soluble Al: 0.019%, N: 0.0074% to a temperature of 1150 ° C., hot rolling was performed. Then
Cold rolling was performed to a final plate thickness at a reduction rate of about 85%, decarburization annealing was performed, and a primary recrystallized plate for a grain-oriented electrical steel sheet was prepared. NH
_The steel plate nitrided in ₃ was cut into strips in the width direction.

The nitriding amount of the steel sheet has a distribution in the sheet width direction (FIG. 1). In this figure, the nitrogen content at both ends of W ・ S (work side) and D ・ S (drive side) of the steel sheet nitrided with NH ₃ gas at the factory is approximately 80 ppm with the center of the sheet.
Is different. This difference causes variations in iron loss measurement. By removing this portion and measuring the iron loss, the accurate primary recrystallization average grain size can be measured.

Next, the reasons for limiting the constituent features of the present invention will be described. In the measurement of the primary recrystallized grain size, it is expected that the nitriding fluctuation of the steel sheet will cause a local variation in the grain growth, and it will be greatly influenced by the place where the iron loss is measured. Therefore, the measurement is performed excluding the portion where the nitriding fluctuation occurs. For the measurement of the particle size, it is acceptable to measure any parameter related to the secondary recrystallization phenomenon, such as the average particle size, the ratio of coarse particles, and the dispersion of the particle size.

Regarding the nitriding treatment, in the present invention, the influence of nitrogen on the primary recrystallized grain size of the steel sheet subjected to the nitriding treatment after the hot rolling is completed and before the secondary recrystallization of the final finish annealing is started. It is assumed that the measurement is made excluding. By this nitriding treatment, a nitride is formed in the steel sheet, and at the time of temperature increase during final annealing, the nitride becomes AlN, (Al, Si) N, and during secondary recrystallization, grain boundaries move. It functions as an inhibitor that emphasizes the personality dependence. The nitriding method is not particularly limited, and any method such as a method using NH ₃ gas, a method using plasma, a method of containing N ₂ in the annealing atmosphere may be used.

If the nitriding amount in the steel sheet nitrided with NH ₃ gas at the factory deviates from its average value, the average grain size estimation error becomes large (FIG. 2). Here, the average grain size is estimated at the portion where the nitriding amount matches the average value. When the amount of nitriding deviates from the average value by 30% or more, the error in the average particle diameter sharply increases and exceeds 5%. It is considered that this is because the eddy current and the magnetic flux are concentrated inside due to the distribution of the nitride inside the steel sheet, which increases the iron loss.
This 5% is about ± 1 μm of the estimation error of the primary recrystallization average grain size.
This is not a value that can be controlled to a sufficiently appropriate range with respect to secondary recrystallization failure and variations in magnetic flux density. To ensure accuracy, the deviation from the average nitriding amount is 30%
Below. If the deviation from the average value of the nitriding amount is 10% or less, the estimation error of the average primary recrystallization grain size becomes 2.5% (about ± 0.5 μm), which is a level obtained by image processing an optical microscope image. It is more preferable because it reaches.

On the other hand, when the nitriding condition deviates from the average value of the NH ₃ flow rate for obtaining the same nitriding amount in the factory, the average particle size estimation error increases (FIG. 3). Here, the estimation of the average particle diameter is performed by using the portion where the NH ₃ flow rate for obtaining the predetermined nitriding amount has the average value. Similarly to the above, if the deviation of the flow rate exceeds 40%, the average particle size estimation error exceeds 5%, so in this case, it is desirable that the deviation be 40% or less. If the deviation from the average value is 10% or less, the estimation error of the average primary recrystallization particle size becomes ± 0.5 μm, which is more preferable because it reaches the level obtained by image processing with an optical microscope image. With respect to other nitriding conditions (temperature, time, dew point, etc.), the desired accuracy can be obtained by setting the deviation of the average value of the processing conditions for obtaining the same nitriding amount to 40% or less.

The particle size estimation accuracy is determined by the variation of the nitriding amount and the variation of the processing conditions for obtaining the same nitriding amount because nitrogen affects the iron loss of the steel sheet. Iron loss increases when non-magnetic nitride is present in the steel sheet. Further, the iron loss also changes depending on the distribution of the nitride in the plate thickness direction. This fluctuation of nitrogen in the plate thickness direction is particularly remarkable in the case of the steel sheet subjected to the nitriding treatment which is the target material of the present invention, and should be particularly noted. As a result, variations in iron loss cause variations, which affects the estimation accuracy.

Next, this measuring method is effective for measuring the primary recrystallized grain size of the steel sheet manufactured by the following manufacturing method. First, regarding the components, when C is less than 0.021% by weight (hereinafter simply referred to as%), secondary recrystallization becomes unstable,
Moreover, even if secondary recrystallization is performed, it is difficult to obtain B8> 1.80 (T), so 0.021% or more is desirable. On the other hand, if the amount of C is too large, the decarburization annealing time becomes long and it is not economical, so 0.075% or less is desirable.

If Si exceeds 4.5%, cracking during cold rolling becomes significant, so Si is preferably 4.5% or less. 2.5% again
If less than 2.5%, the specific resistance of the material is too low, and the low iron loss required as a transformer core material cannot be obtained, so 2.5% or more is desirable. More preferably, it is 3.2% or more.

Al is AlN necessary for stabilizing secondary recrystallization.
Alternatively, in order to secure (Al, Si) nitrides, the acid-soluble Al is preferably 0.010% or more.
When acid-soluble Al exceeds 0.060%, AlN of hot rolled sheet
Becomes inappropriate and the secondary recrystallization becomes unstable, so 0.0
60% or less is desirable.

N is 0.00 in normal steelmaking work.
Since it is difficult to make it less than 10% and it is not economically preferable, it is set to 0.0010% or more, while 0.01
If it exceeds 30%, "steel plate surface blistering" called blister occurs, so 0.0130% or less is desirable.

Even if Mns and MnSe are present in the steel, it is possible to improve the magnetic characteristics by properly selecting the conditions of the manufacturing process. However, when S and Se are high, secondary recrystallization defective portions called linear fine grains tend to occur, and in order to prevent the generation of the secondary recrystallization defective portion, (S + 0.405Se) ≦ 0. It is preferably 014%. When S or Se exceeds the above value, the probability of occurrence of a secondary recrystallization defect portion increases even if the manufacturing conditions are changed, which is not preferable. Further, the time required for purification in the final finish annealing becomes too long, which is not preferable, and it is meaningless to increase S or Se unnecessarily from such a viewpoint.

The lower limit of Mn is preferably 0.05%.
If it is less than 0.05%, the shape (flatness) of the hot-rolled sheet obtained by hot rolling, in particular, the side edge portion of the strip becomes corrugated, which causes a problem of lowering the product yield. on the other hand,
If the Mn content exceeds 0.8%, the magnetic flux density of the product is lowered, which is not preferable. Therefore, the upper limit of the Mn content is preferably 0.8%.

In addition, Sn, Sb, Cr, Cu, Ni, B, Ti, B, which are known as inhibitor constituent elements,
It is safe to contain a small amount of i, Nb, etc.

Next, the slab heating temperature is set to 1280 in this case for the purpose of cost reduction by making it equal to that of ordinary steel.
The temperature is lower than 0 ° C, but preferably 1200 ° C or lower. The subsequent hot-rolling step usually consists of heating a slab having a thickness of 100 to 400 mm, and then performing rough rolling and finish hot-rolling in multiple passes. The methods of rough rolling and hot rolling for finish are not particularly limited, and ordinary methods are used. After hot rolling,
If necessary, hot-rolled sheet is annealed, and the rolling reduction is 80%.
Including the above final cold rolling, and sandwiching intermediate annealing as required 1
The final cold-rolled sheet is obtained by performing cold rolling more than once. This final cold rolled sheet is decarburized and annealed in an annealing atmosphere containing O ₂ .

The present invention is particularly effective for the primary recrystallized plate obtained by this manufacturing method. The reason for this is not clear, but it is considered that this process is particularly susceptible to the primary recrystallized grain size. By this method, it is possible to improve the accuracy of primary recrystallization average particle size measurement by iron loss measurement, which could not be accurately measured in the past.
This is because the nitriding amount of the steel sheet, which was the cause of the variation in iron loss, was defined and iron loss outside this range was excluded. For the above reasons, it has become possible to stably produce a grain-oriented electrical steel sheet having excellent magnetic properties by measuring the primary recrystallization average grain size and controlling it appropriately.

[0025]

【Example】

(Example 1) C: 0.051% by weight, Si: 3.30
%, Mn: 0.13%, S: 0.005%, acid-soluble A
A slab containing 1: 0.019% and N: 0.0074% was heated to a temperature of 1150 ° C., then hot rolled, cold rolled to a final plate thickness at a reduction rate of about 85%, and decarburized and annealed. , A primary recrystallized plate for unidirectional electrical steel sheet was prepared. The steel sheet nitrided with NH ₃ was cut into strips in the width direction, and the core loss and primary recrystallization average grain size of each strip are summarized in FIG. Frequency 50H
In the iron loss (W15 / 50) measurement at z and magnetic flux density of 1.5 T, the average primary recrystallization grain size has a width of about 2.4 μm.
Next, the measured value of a strip taken out from the end where the amount of nitriding deviated from the average value of the steel sheet by 30% or more was excluded (FIG. 5). This reduces the width to about 1 μm (± 0.5 μm),
Accuracy improved.

(Example 2) C: 0.056% by weight, S
i: 3.24%, Mn: 0.14%, S: 0.006
%, Acid-soluble Al: 0.025%, N: 0.0079%
The slab containing is heated to a temperature of 1150 ° C., then hot-rolled, cold-rolled at a reduction rate of about 85% to the final sheet thickness, decarburized and annealed, and a primary recrystallized sheet for unidirectional electrical steel sheet is prepared. did.
When the nitriding amount was measured in advance in the width direction of the steel sheet at the tip of the coil, the deviation from the average value of the nitriding amount from the end to the portion 100 mm inward was 30% or more. In order to remove this portion from the measurement range, the measurement portion was surrounded by the 1/2 coil method (probe method), and the iron loss was measured online (FIG. 6). This measuring method measures the magnetic flux density in the steel sheet between two points by measuring the induced voltage between two different points,
This is a method of measuring iron loss. A copper roller was used for the contact portion in order to maintain the conductivity of the coil and the steel sheet portion. As a result, the estimation accuracy is improved as shown in FIG. 7 as compared with the conventional method.

(Example 3) C: 0.052% by weight, S
i: 3.29%, Mn: 0.14%, S: 0.005
%, Acid-soluble Al: 0.018%, N: 0.0074%
After heating the slab containing slab to a temperature of 1150 ° C, it is hot-rolled, cold-rolled to a final sheet thickness at a reduction rate of about 87%, decarburized and annealed to prepare a primary recrystallized sheet for unidirectional electrical steel sheet. did.
Next, when the factory investigated the relationship between the deviation of the flow rate of NH ₃ from the average value and the average particle size estimation error after nitriding to make the amount of nitrogen 200 ppm, Table 1 was obtained. As shown in Table 1, when the error of the average value of the flow rate of NH ₃ is small, the average particle size estimation error is improved. Table 1 shows the deviation of the flow rate of NH ₃ from the average value and the average particle size estimation error.

[0028]

[Table 1]

[0029]

As described above, according to the present invention, the primary recrystallized grain size of the grain-oriented electrical steel sheet can be accurately measured. Since the primary recrystallized grain size has a great influence on the magnetic flux density through the secondary recrystallization behavior, by maintaining it in an appropriate range using the present invention, it is possible to prevent secondary recrystallization defects from occurring and to stabilize the magnetic flux density at a high level. There is a very remarkable effect on industrialization, and the industrial benefit is extremely large.

[Brief description of drawings]

FIG. 1 shows the amount of steel sheet nitrogen in the sheet width direction.

FIG. 2 is a deviation from an average value of a nitriding amount and an average particle size estimation error.

FIG. 3 is a deviation from an average value of a flow rate of NH ₃ for obtaining the same nitriding amount and an average particle size estimation error.

FIG. 4 shows the relationship between the average primary recrystallization grain size and iron loss.

FIG. 5 is an example of measurement to which the method obtained according to the present invention is applied.

FIG. 6 shows the measurement principle of the 1/2 coil method (probe method).

FIG. 7: The average particle size in the coil length direction is 1 compared with the conventional method.
This is an example of measurement by the / 2 coil method.

Claims (3)

[Claims] 1. When measuring the grain size of a primary recrystallized grain of a grain-oriented electrical steel sheet that has been subjected to nitriding treatment after hot rolling and before the start of secondary recrystallization in final finish annealing, the nitriding amount of the steel sheet is measured. ,
A method for measuring a primary recrystallized grain size of an electromagnetic steel sheet, which comprises measuring a remaining portion of a steel sheet except for a portion that has fluctuated by a predetermined value or more with respect to an average nitriding amount. 2. The primary recrystallized grain size measurement of an electromagnetic steel sheet according to claim 1, wherein the remaining portion is measured except for the portion where the nitriding amount of the steel sheet fluctuates by 30% or more as compared with the average nitriding amount of the steel sheet. Method. 3. The primary recrystallized plate as a weight ratio of C: 0.
021 to 0.075%, Si: 2.5 to 4.5%, acid-soluble Al: 0.010 to 0.060%, N: 0.001
0 to 0.0130%, S + 0.405Se: 0.014
% Or less, Mn: 0.05 to 0.8%, the balance consisting of Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C., then hot rolled, and then finally cold rolled at a rolling reduction of 80% or more. The method for measuring the primary recrystallized grain size of an electromagnetic steel sheet according to claim 1 or 2, wherein the cold rolling is performed at least once and then decarburization annealing is performed.