JP2703468B2 - Stable manufacturing method of high magnetic flux density unidirectional electrical steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stably producing a unidirectional magnetic steel sheet having a high magnetic flux density, which is used as a soft magnetic material for an iron core of electric equipment, using a continuous cast piece as a starting material. .

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is used as an iron core of a transformer or a generator as a soft magnetic material, and must have good magnetizing properties and iron loss properties as magnetic properties. Quality of magnetic properties is determined by the magnitude of the magnetic flux density induced in the core at a constant magnetic field exerted (represented by B _8). A material having a high magnetic flux density is desirable because it can reduce the size of an electric device.

[0003] Iron loss (represented by _{W17 / 50} ) is a power loss consumed as heat when a predetermined alternating magnetic field is applied to an iron core. The quality of iron loss is influenced by the magnetic flux density, plate thickness, impurity amount, specific resistance, and crystal grain size. Recently, there has been an increasing demand for a grain-oriented electrical steel sheet with a small iron loss reflecting the trend of energy saving.

[0004] Unidirectional electrical steel sheets are prepared by subjecting a steel sheet having a final thickness obtained by hot rolling and cold rolling to finish high-temperature annealing to obtain a # 1 magnetic steel sheet.
Primary recrystallized grains having a 10｝ <001> orientation are obtained by so-called secondary recrystallization in which preferentially growing preferentially.
In order to cause secondary recrystallization, fine precipitates such as MnS and AlN are present in the steel sheet before finish high-temperature annealing, so that primary recrystallization other than the {110} <001> orientation during finish high-temperature annealing is performed. It is necessary to suppress grain growth (inhibitor effect).

[0005] As a metallographic condition for stably performing the secondary recrystallization, the steel sheet before the appearance of the secondary recrystallization has fine precipitates (inhibitors) uniformly and finely present, and the crystal grains are uniform. Having an appropriate primary recrystallization texture.

[0006] By controlling such secondary recrystallization behavior, the magnetic flux density can be increased by increasing the ratio of accurate {110} <001> orientation grains. Since products with high magnetic flux density can reduce the size of electrical equipment and improve iron loss at the same time, it is important to establish a manufacturing technology for high magnetic flux density unidirectional magnetic steel sheets. As representative technologies, Japanese Patent Publication No. 40-15644 by Satoru Taguchi et al.
There is a method described in JP-A-13469.

By the way, in the current production of steel products, the continuous casting method is applied almost 100%, and the same applies to the production of grain-oriented electrical steel sheets. However,
After the continuous cast slab is heated to a high temperature of 1280 ° C. or higher, a product obtained by using a steel sheet manufactured by hot rolling as a starting material often has a secondary recrystallization defect portion continuous in the rolling direction (a linear secondary recrystallization defect). Abbreviation), and the magnetism was sometimes poor.

As a countermeasure against these, M. F. Littlem
An in Japanese Patent Application Laid-Open No. 48-53919 proposes a technique for producing a hot rolled sheet from a continuously cast slab through two hot rolling steps. Further, Akira Itakura et al. In Japanese Patent Publication No. 50-37009 proposes a technique for producing a hot-rolled sheet from a continuously cast slab through two hot-rolling steps in the production of a high magnetic flux density unidirectional silicon steel sheet.

However, each of these prior arts is a technique for obtaining a hot rolled sheet through two hot rolling steps, and cannot be said to be a technique that makes full use of the advantages of continuous casting. After that, as a production method using a continuously cast slab, the techniques disclosed in JP-A-53-19913 by Morio Shiozaki and JP-A-54-120214 by Fumio Matsu were proposed. However, all of these technologies require new measures for equipment.

[0010] Even if these measures are taken, the occurrence of linear secondary recrystallization failure has not been completely solved. That is, recently, there has been an increasing demand for low iron loss unidirectional electrical steel sheets for the purpose of energy saving. To meet this demand, it is important to increase the magnetic flux density and the Si content.

In particular, the technique disclosed in Japanese Patent Publication No. 40-15644 is a single rolling method, so that the manufacturing cost is low and a unidirectional magnetic steel sheet with a high magnetic flux density can be obtained. Great improvement in loss. However, when the Si content is increased in this method, the occurrence of secondary recrystallization defects rapidly increases, and especially in the case of such high Si,
Since the linear secondary recrystallization failure generated when using the continuously cast slab further increases, if the Si content exceeds 3.0%, industrially stable production has been extremely difficult.

This is disclosed in JP-A-48-51 by Akira Itakura et al.
As described in Japanese Patent Publication No. 852, if the Si content is increased, it becomes difficult to secure AlN suitable for the occurrence of secondary recrystallization. In particular, when a continuous cast slab is used, the secondary It was thought that the recrystallization failure became more prominent.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a high magnetic flux density unidirectional magnetic steel sheet in which final cold rolling is performed at a high rolling reduction, and a method for producing a linear secondary reusable steel sheet generated when a continuous cast slab is used. Completely prevent crystal defects, especially for low iron loss
It is an object of the present invention to solve a linear secondary recrystallization defect which is further increased when the i content is increased.

[0014]

The cause of the linear secondary recrystallization defect which occurs in the method for producing a grain-oriented electrical steel sheet using a continuously cast slab has been pointed out in Japanese Patent Application Laid-Open No. 48-53919. As described above, it is said that crystal grains grow excessively by slab heating performed prior to hot rolling, and large stretched grains remain in the hot rolled sheet.

Measures following this concept have been applied to high magnetic flux density unidirectional electrical steel sheets.
No. 009 was proposed. The present inventors have found a new cause of occurrence in addition to the cause of the linear secondary recrystallization defect considered as described above, and have completed the following invention.

That is, the gist of the present invention is as follows.

Si: 3.05 to 4.60% by weight;
C: 0.023 to 0.095%, Mn: 0.03 to 0.
17%, S: 0.014-0.037%, acid soluble A
l: 0.018-0.048%, total N: 0.
Molten steel containing 0050 to 0.0095%, balance: Fe and unavoidable impurities is continuously cast, the slab is heated to 1320 ° C or higher, hot rolled, and annealed in a temperature range of 850 to 1150 ° C for a short time. The steel sheet is subjected to strong cold rolling at a rolling reduction of 80% or more, decarburization annealing, and application of an annealing separator for the purpose of preventing seizure at the time of high-temperature annealing for finishing, and high-temperature annealing for finishing mainly for secondary recrystallization. In the method for producing a grain-oriented electrical steel sheet to be performed, the concentrated segregated portion of 0.050% or more of S caused by bulging cracks during continuous casting is provided on at least one side of the slab.
A method for stably producing a high magnetic flux density unidirectional magnetic steel sheet, comprising using a continuous cast piece controlled inward from a position corresponding to 53 μm from a surface of a product sheet thickness.

When the continuous cast piece is heated prior to hot rolling, the S-rich segregated portion caused by bulging cracks is controlled inward from a position corresponding to 53 μm from the surface of the product plate, and the surface on the casting side is heated by a heating furnace. 2. The stable production method according to 1, wherein the stable production method is provided.

3. The method according to 1 or 2, wherein cold rolling is performed at a rolling reduction of 45% or less before hot-rolled sheet annealing, and the product thickness after final cold rolling is 0.23 mm or less. .

The stable production method according to claim 3, wherein the hot-rolled sheet is annealed at 850 to 1120 ° C.

Hereinafter, the present invention will be described in detail. The present inventors have investigated in detail the cause of linear secondary recrystallization defects that occur in the production of high magnetic flux density unidirectional magnetic steel sheets using a continuously cast slab.
7 (1981), S1201. As a result of further research since this report, the present inventors have obtained new findings and completed the present invention.

Hereinafter, the present invention will be described in detail. C: 0.06%, Si: 3.0%, Mn: 0.08%,
S: 0.025%, acid-soluble Al: 0.027%,
N: A 250 mm thick continuous cast slab containing 0.008% is heated to about 1400 ° C., then turned into a 2.3 mm thick hot rolled sheet, annealed at 1120 ° C. for 3 minutes, rapidly cooled to room temperature, and cooled to 0.3 mm. Cold rolled to a thickness of 8 mm in a wet hydrogen atmosphere.
Perform decarburization annealing at 50 ° C for 3 minutes, apply MgO,
A high-temperature finish annealing at 1200 ° C. for 20 hours was performed.

The linear secondary recrystallization defects occur continuously in the rolling direction as shown in FIG. Therefore, as a survey, the microstructure and texture of the decarburized annealed sheet adjacent to the normal part and the linear secondary recrystallization part in the rolling direction corresponding to the normal part and the linear recrystallization part were compared as shown in FIG. 2 shows the results.

Further, during the finish annealing, the sample is pulled out,
Observe the change in the metal structure during the secondary recrystallization process,
FIG. 3 shows the results. As shown in FIG. 3 and as is already known, secondary recrystallization occurs from the surface.

The generated secondary recrystallized grains grow quickly and smoothly in the plate thickness direction in the normal portion, but stop growing at a position near the plate thickness of 1/4 in the linear secondary recrystallization defective portion. . As the annealing proceeds further, in the normal part, the secondary recrystallized grains eat the entire area of the primary recrystallized grains, and the secondary recrystallization is completed.

While the growth of the secondary recrystallized grains is delayed in the linear secondary recrystallization defective portion, surface grains not necessarily Goss-oriented grains grow, and are eaten by the secondary recrystallized grains until the final stage. It is considered that secondary recrystallization failure occurs because it remains without being removed. As described above, the direct cause of the linear secondary recrystallization defect is that growth stops at a position near the plate thickness of 1/4. Therefore, a singular point in the decarburized annealed plate corresponding to the position was investigated.

As shown in FIG. 2, the portion corresponding to the linear secondary recrystallization defect has a larger primary recrystallized grain size in the vicinity of 1/4 thickness and a smaller number of {111} plane orientation grains than the normal portion. You can see that it is an organization. In general, when the {110} oriented secondary recrystallized grains grow, the eaten primary recrystallized grains are small, and the {111} plane oriented grains are advantageous for the rapid growth. Therefore, the sheet thickness 1 /
It can be understood that the growth of the secondary recrystallized grains is delayed in the linear secondary recrystallization defective portion where the primary recrystallized grain size is large near the position 4 and the {111} plane orientation grains are small.

The causes of the two characteristics of the metal grain structure in the vicinity of the plate thickness of 1/4 were investigated. As a result, as compared to the normal part, the linear secondary recrystallization corresponding part has a strong {100} plane orientation and a weak {111} plane orientation as a texture of the hot-rolled sheet. Is large and the dispersion is sparse.

In particular, the sparse dispersion state of MnS is also a cause of an increase in the size of primary recrystallized grains, and is extremely interesting, and is generated in the production of a high magnetic flux density unidirectional magnetic steel sheet using a continuously cast slab. This is a novel phenomenon related to the cause of linear secondary recrystallization failure.

This is shown below in the experimental results. FIG. 4 shows the results of electron microscopic observation of the state of dispersion of MnS in the thickness direction of the decarburized annealed sheet. FIG. 5 shows the texture of the hot-rolled sheet in the thickness direction.

FIG. 5 shows that the {100} plane orientation, which is the rolling orientation, is strong and the {111} plane orientation, which is the recrystallization orientation, is weak in the texture of the hot rolled sheet corresponding to the linear secondary recrystallization defect. In the decarburized annealed sheet processed in the process of hot-rolled sheet → hot-rolled sheet annealing → cold rolling → decarburizing annealing, recrystallization is difficult to occur, and the number of {111} plane orientation grains, which is the recrystallization orientation, is reduced. Can understand well.

Further, it is also understood that the primary recrystallized grains in the decarburized annealed sheet are large because the dispersion of MnS is sparse and large. From the above research, various investigations were made by paying attention to the cause of the sparse and large MnS in the vicinity of the hot-rolled sheet 1/4 newly found as the cause of the linear secondary recrystallization failure.

As a result, segregation of S occurs in the continuously cast slab due to cracking caused by so-called bulging, and the high S region does not become a solution by heating during hot rolling, so that MnS
It was found that uniformity and fineness could not be achieved.

FIG. 6 shows a cast slab structure and a distribution diagram of S obtained by performing image processing after measuring the abundance of S in the structure by EPMA.

As can be seen from the figure, no crack is observed in the cast slab, but there is a dense segregation zone of S in the vicinity of 1/4 of the total thickness. The S content in this portion exceeds 0.050%. It is extremely difficult to form a solution by heating during hot rolling. For example, even at the minimum Mn of 0.03% defined in the present invention, MnS does not form a solution, and the MnS of the hot rolled sheet becomes large and sparse.

According to the investigation by the present inventor, this S segregation is caused by the so-called bulging phenomenon during continuous casting (in the state where the slab surface is solidified and the molten steel remains in the central part, the solidified portion generated by the molten steel pressure is generated). This is semi-macro segregation caused by cracking (unconsolidated steel in the central part where S in the cracked portion is concentrated enters). In addition to the semi-macro segregation, there is general central segregation of S in the center.

As shown by the metal structure in FIG. 2 and the precipitate (MnS) in FIG. 4, the structure in the vicinity of 板 of the plate thickness is different between the normal part and the linear secondary recrystallized part. In order to eliminate linear secondary recrystallization defects, it was considered effective to appropriately control semi-macro-segregation in which the positional relationship with the product is consistent.

In particular, from the results of the grain growth behavior of the secondary recrystallization, it is considered that if the secondary recrystallized grains generated from the vicinity of the surface grow smoothly toward the center of the sheet thickness, linear secondary recrystallization failure does not occur. Therefore, continuous casting was performed under the condition that the concentrated segregation zone of S was moved toward the center of the sheet thickness.

Although there is an S-rich segregation zone in the center,
Since the crystal grains in the linear secondary recrystallization portion are not larger than the normal portion, and the {222} orientation is not small in texture, it is considered that this is the cause of the linear secondary recrystallization failure. Absent.

Based on the above idea, the position of the semi-macro segregation zone due to bulging can be changed in relation to the molten steel pressure by controlling the cooling rate after casting to adjust the solidification thickness on the surface side. . Therefore, in order to adjust the cooling rate, the following tests were performed while changing the most common casting rate.

C: 0.065%, Si: 3.37%, M
n: 0.075%, S: 0.025%, acid-soluble Al:
250 mm of molten steel containing 0.030%, total N: 0.00835%, and balance: Fe and inevitable impurities.
It was continuously cast into thick slabs. The drawing speed at the time of casting was changed between two types, 0.7 and 1.0 m / min.

After heating this slab to 1410 ° C., 2.3
mm thick hot rolled sheet and annealed at 1120 ° C for 60 seconds,
After quenching, it was pickled. Next, cold-rolled to a thickness of 0.30 mm,
Decarburization annealing was performed at 50 ° C. for 180 seconds, and high-temperature annealing was performed at 1200 ° C. for 20 hours mainly for secondary recrystallization.

In this test, by setting high Si, which is one of the major aims of the present invention, in order to achieve low iron loss, a high magnetic flux density unidirectional magnetic steel sheet manufacturing method is used.
3.37% which is i amount was contained. Table 1 shows the position of the semi-macro segregation zone of S in the cast slab and the occurrence state of the linear secondary recrystallization failure.

[0044]

[Table 1]

When the drawing speed was 0.7 m / min, good secondary recrystallization was obtained without linear secondary recrystallization failure, but when the drawing speed was 1.0 m / min, the linear secondary recrystallization was good. Recrystallization failure occurred and the magnetic properties were poor. S of the slab at this time
Is located at a position corresponding to approximately 37 to 65 μm from the surface having a product thickness of 0.30 mm, which seems to have inhibited the growth of secondary recrystallized grains generated from the surface.
On the other hand, in the case of 0.7 m / min, the position is 58 to 102 μm, and it is considered that the growth of secondary recrystallized grains was not largely suppressed.

The secondary recrystallization onset behavior near the surface is considered as follows. The crystal grain (decarburized annealed sheet) of the steel sheet before the onset of the secondary recrystallization is about 12 to 18 μm, but secondary recrystallized grains are generated from the grain one below the outermost surface grain on average. Assuming that one grain below the secondary recrystallized grain is eaten by the secondary recrystallized grain, the grain is caused by the segregation zone of S from the bottom to the inside (36 to 54 μm) of three grains from the surface. The study results can be well explained by considering that secondary recrystallization is stabilized by adjusting the primary recrystallized grain structure that suppresses the growth of secondary recrystallized grains.

The cause of the linear secondary recrystallization failure clarified as described above, and the occurrence of the secondary recrystallization failure can be controlled by controlling the cause.
The present invention has been made based on the results of experiments that created nothing. The embodiment is as follows.

First, the reasons for limiting the steel components of the present invention will be described. In the present invention, the molten steel is not limited to a smelting method such as a converter or an electric furnace, but the component content must be within the following range. C
Is less than 0.023%, the secondary recrystallization becomes unstable, and the magnetic flux density is poor even after the secondary recrystallization.
0.023% or more. On the other hand, if C is too large, the decarburization annealing time will be long, and it is not economical.
% Or less.

If the Si content exceeds 4.60%, cracking during cold rolling becomes remarkable, so the content is set to 4.60% or less. 3.05
%, W _17/50 is 1.0 at a product thickness of 0.30 mm.
Since the highest iron loss of 5 W / kg or less cannot be obtained, the range is set to 3.05% or more, which meets the purpose of obtaining the highest grade unidirectional electrical steel sheet in the present invention. Desirably, it is at least 3.20%.

In the present invention, MnS and AlN are used as precipitates required for secondary recrystallization. Therefore, the necessary minimum M
In order to secure nS, Mn is 0.03% or more and S is 0.1%.
014% or more, and acid-soluble Al must be 0.018% or more.

If N is less than 0.0050%, AlN as an inhibitor becomes insufficient and secondary recrystallization does not occur. Therefore, the lower limit is required to be 0.0050%.
If it exceeds 95%, blisters on the surface of the steel plate called blisters occur, so the content was made 0.0095% or less.

When Mn exceeds 0.17% and acid-soluble Al exceeds 0.048%, MnS and AlN of the hot-rolled sheet become inappropriate and secondary recrystallization becomes unstable.
17% or less, and acid-soluble Al was set to 0.048% or less.
The balance is Fe and inevitable impurities.

It should be noted that Sn, Sb, etc. may be added as an element which does not affect the position control of the S-rich segregation zone, which is the object of the present invention. Molten steel containing the components in the above-described ranges is formed into a slab by continuous casting. One object of the present invention is to apply the advantages of using continuous cast slabs, so that continuous cast slabs are of limited scope.

In this continuous casting slab, the position of the semi-macro segregation zone of S caused by bulging during casting is controlled at least on one side of the slab to be inward from a portion corresponding to 53 μm from the surface of the product sheet thickness. There is a need to. The amount of S limited to the thick segregation zone is 0.03%
0.050% was defined as the amount of solution hardening when the continuous cast slab containing Mn was heated at 1320 ° C. or higher.

Incidentally, casting factors affecting bulging are generally well known. In order to control the bulging position aimed at in the present invention to the center side of the slab, for example,
A method of reducing the drawing speed, a method of adjusting the solidified thickness of the surface by cooling, and a method of reducing the molten steel pressure in combination are adopted.

In the present invention, a continuous cast slab having a thickness of 250 mm was prepared by changing the position of the S-rich segregation zone caused by bulging by adjusting the molten steel substantially equal to the components used in Table 1 by the above method. After heating this slab at 1410 ° C., 2.
3mm, 2.0mm, 1.8mm thick hot rolled sheet, 11
Annealing was performed at 20 ° C. for 60 seconds, quenched, and then pickled.

Next, the 2.3 mm thick material is cold rolled to 0.30 mm thickness, the 2.0 mm thick material is cold rolled to 0.27 mm thickness, and the 1.8 mm thick material is cold rolled to 0.23 mm thickness. 30mm
180sec for thick material, 160sec for 0.27mm thick material
c, The 0.23 mm thick material was decarburized and annealed for 120 sec, and was subjected to high-temperature anneal at 1200 ° C. for 20 hours mainly for secondary recrystallization.

The degree of occurrence of linear secondary recrystallization failure of this product and the position of S-rich segregation due to bulging (the S-rich segregation zone has a width, but first interferes with the secondary recrystallized grains near the surface. The position on the surface side is indicated by the distance from the surface of the product.Even if the thickness of the product changes, three grains of the top surface grain, the secondary recrystallized grain, and the grain eaten by the secondary recrystallized grain are added. The combined distance is constant, and there is an S-rich segregation zone inside the distance,
Since the presence or absence affects the occurrence of linear secondary recrystallization failure, it is indicated as a position from the surface of the product. 7) is shown in FIG.

From this figure, the occurrence of linear secondary recrystallization defects increases as the thickness of the product sheet decreases, but if the position of the S-rich segregation zone is adjusted inward from the position of 53 μm from the surface, the linear secondary recrystallization will occur. Good secondary recrystallization can be obtained without occurrence of defects.

By the way, in the early stage of the secondary recrystallization, # 11
The growth behavior of 0｝ <001> grains is equivalent on the front and back of the plate thickness. Therefore, as a continuous casting slab, at least the S-rich segregation zone on either the front or the back is adjusted, and {110} <0
01> Smooth growth of grains may be measured.

Next, the continuous cast slab is heated and then hot-rolled into a hot-rolled sheet. If the slab heating temperature is too low,
Since the precipitated dispersed phase does not form a solid solution, the secondary recrystallization becomes unstable and the magnetic flux density becomes low.
° C. As for the upper limit, the higher the heating equipment is in a range that can be industrially endured, the more advantageous the secondary recrystallization is, but the upper limit is about 1420 ° C. in terms of equipment.

It should be noted, that the side to adjust the S concentrated segregation zone located higher becomes easy furnace top temperature upon heating, high B ₈ for a more complete solid solution can be a precipitate obtained, desired . The hot rolled sheet obtained as described above is 85
Short-time continuous annealing is performed in the range of 0 to 1150 ° C. If the annealing temperature is lower than 850 ° C., a high magnetic flux density cannot be obtained, and 115
If it exceeds 0 ° C., secondary recrystallization becomes incomplete.

If the annealing time exceeds 30 minutes, the production efficiency becomes extremely poor, and the secondary recrystallization failure occurs. If the time is less than 30 seconds, the effect of the heat treatment is hardly obtained. After continuous annealing of the hot rolled sheet, cold rolling is performed. The purpose of the present invention is to obtain a high magnetic flux density unidirectional magnetic steel sheet, so that a cold rolling reduction of 80% or more is required as a cold rolling reduction. About 90% is optimal for stably obtaining a high magnetic flux density, and when it exceeds about 93%, secondary recrystallization becomes unstable, and the magnetic flux density of the obtained secondary recrystallized plate becomes poor.

In making the product thickness by this cold rolling, if the thickness is reduced in order to obtain a product with good iron loss, the thickness of the hot rolled sheet must be reduced, and the shape of the hot rolled steel sheet has to be reduced. It becomes difficult to secure. In addition, in order to manufacture various product sheet thicknesses, it is necessary to store hot-rolled sheets having a large number of sheet thicknesses as inventory, which is uneconomical.

Therefore, as a pre-stage of the cold rolling to the final product sheet thickness, preliminary cold rolling is performed to a sheet thickness at which an optimal final cold rolling rate is obtained, and then the above-described continuous annealing is performed, and final cold rolling is performed. The method can be adopted. When the rolling reduction is increased in this preliminary cold rolling, the recrystallization completely proceeds in the subsequent continuous annealing, and the influence of the high-pressure reduction rate of the final cold rolling is reduced, and a high magnetic flux density cannot be obtained. % Must not be exceeded.

The hot rolled sheet has different temperature histories in the longitudinal direction of rolling, and has a difference in crystal structure. When such a hot-rolled sheet is rolled and further annealed, the difference in crystal structure remains in a rather enlarged state. Therefore, when performing preliminary cold rolling,
850 to 1120 to obtain a product with uniform properties
It is desirable to carry out continuous annealing at a low temperature for a short time to make the crystal structure uniform.

The steel sheet having the final thickness as described above is subjected to decarburizing annealing in a wet hydrogen atmosphere. An annealing separator is applied to the surface of the steel sheet after the decarburizing annealing to prevent seizure at the time of finishing high-temperature annealing. Successively, finish high-temperature annealing mainly for secondary recrystallization is performed to obtain a product.

As described in detail above, the present invention is generated when a continuous cast slab is used as a starting material, which can be manufactured at a low cost and can be industrially manufactured with uniform magnetic properties due to uniform components in the longitudinal direction of the product. It is possible to prevent linear secondary recrystallization defects (especially, when Si is increased to reduce iron loss, it is more likely to occur, which is a problem in producing high-grade grain-oriented electrical steel sheets). By achieving Si and high magnetic flux density, it has become possible to obtain a low iron loss unidirectional electrical steel sheet that matches the recent trend of energy saving.

[0069]

【Example】

(Example 1) C: 0.07%, Si: 3.20%, Mn: 0.07
%, S: 0.025%, acid-soluble Al: 0.025%,
Total N: 0.0082%, balance: Fe and 250% thick continuous cast slab containing unavoidable impurities, withdrawal speed of 0.50 m / min under controlled water cooling conditions.
After casting under the conditions of 0.90 m / min and heating at 1400 ° C., a total of four types of hot-rolled sheets having a thickness of 2.3 mm and 2.0 mm were obtained.

After annealing at 1120 ° C. for 3 minutes, the material was rapidly cooled to room temperature, and the thickness of the 2.3 mm thick material was reduced to 0.30 mm.
The 0 mm thick material was cold rolled to 0.27 mm and 0.23 mm. Further, decarburizing annealing was performed at 850 ° C. for 3 minutes in a wet hydrogen atmosphere, MgO was applied, and finishing high-temperature annealing was performed at 1200 ° C. for 20 hours to obtain a product.

The position of the S-rich segregation zone of these cast slabs,
The occurrence of B ₈ and the linear secondary recrystallization defect as finished product characteristics are shown in Table 2.

[0072]

[Table 2]

Under the condition (A) within the range of the present invention, good magnetism was obtained without occurrence of linear secondary recrystallization defects. Under the condition (B) of the comparative example, linear secondary recrystallization failure occurred, and the occurrence was particularly large as the product thickness was reduced.

(Example 2) As a component, C: 0.07
%, Si: 3.20%, Mn: 0.07%, S: 0.0
25%, acid-soluble Al: 0.025%, total
A continuous casting slab having a thickness of 250 mm containing N: 0.0082%, balance: Fe and inevitable impurities was cast by two types of continuous casting machines. At that time, the surface was cooled with water slowly, and the drawing speed was 0.65 m / min.

The continuous casting machine is (A) a vertical type, and both surfaces have the same casting conditions. (B) It is a curved type, and columnar crystals are generated on the inside of the bend as compared with the outside, and the dense segregation zone of S due to bulging is also closer to the center side.

Next, for (A) the slab as it is (B), for the slab, (1) the inner side of the bend is the upper side of the hot-rolling furnace, (2) the inner side of the bend is the lower side of the hot-rolling furnace, After heating, a hot-rolled sheet having a thickness of 2.3 mm was obtained.

Further, after annealing at 1120 ° C. for 3 minutes,
Cool rapidly to room temperature, cool to 0.27 mm thickness, perform decarburization annealing at 850 ° C. for 3 minutes in a wet hydrogen atmosphere,
gO was applied and subjected to a high-temperature finish annealing at 1200 ° C. for 20 hours to obtain a finished product.

The position of the S-rich segregation zone of these cast slabs,
The occurrence of B ₈ and the linear secondary recrystallization defect as finished product characteristics are shown in Table 3.

[0079]

[Table 3]

(A), in which the S-rich segregation zone was within the range of the present invention on both sides of the cast slab, had good product properties. On the other hand, in the case of (B) in which only one surface of the S-rich segregation zone is within the range of the present invention, when the surface was set on the upper surface of the slab heating furnace, good product characteristics were obtained. If so, the product characteristics are slightly poor.

Example 3 The hot-rolled sheet having a thickness of 2.3 mm at a drawing speed of 0.50 m / min used in Example 1 used in Example 1 was (1) no annealing, (2) 950 ° C. × 3 mi.
n) and further (1) no cold rolling, (2) 20% cold rolling, and (3) 45% cold rolling (in the case of (1), do not perform annealing at 950 ° C. × 3 min before). And then 1120
After annealing for 3 min at ℃, quenched to room temperature
The product was cold-rolled to a thickness of 3 mm, decarburized annealing at 850 ° C. for 2 minutes, coated with MgO, and subjected to finishing high-temperature annealing at 1200 ° C. for 20 hours to obtain a product. Table 4 shows the magnetic properties of this product.

[0082]

[Table 4]

In each case, no linear secondary recrystallization failure occurred. For B _8, the first cold-rolled 25%
The highest value was obtained when the rolling reduction was performed, because the final cold rolling reduction was optimal. Further, by performing the annealing in the first cold rolling before, B ₈ is improved.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) are photographs showing the macrostructures of a normal part and a defective linear secondary recrystallization part.

FIGS. 2A and 2B are a photograph showing a grain structure of a primary recrystallization structure and a chart of a texture in a plate thickness direction.

FIG. 3 is a photograph of a change in a grain structure showing a progress of secondary recrystallization.

FIG. 4 is a photograph of a precipitate (inhibitor) in a thickness direction of a decarburized annealed sheet.

FIG. 5 is a chart of a texture in a thickness direction of a hot-rolled sheet.

FIG. 6 (a) is a macrostructure of a cast slab, and FIGS. 6 (b) and (c) are crystal structures showing the distribution of S concentration (0.05% or more).
It is a photo of the structure

FIG. 7 is a chart showing the influence of the position of the S-rich segregation zone from the surface corresponding to the product on the degree of occurrence of linear secondary recrystallization defects.

Claims (4)

(57) [Claims] 1. Si: 3.05 to 4.60%, C: 0.023 to 0.095%, Mn: 0.03 to 0.17%, S: 0.014 to 0.037 by weight %, Acid-soluble Al: 0.018-0.048%, total N: 0.0050-0.0095%, balance: continuous casting of molten steel containing Fe and unavoidable impurities, and heating the slab to 1320 ° C. or more And hot rolled, 850-
Short-time annealing at a temperature range of 1150 ° C and reduction of 80%
% Cold rolling, decarburization annealing, applying an annealing separator to prevent seizure during high temperature annealing, and performing high temperature annealing mainly for secondary recrystallization In the method for manufacturing an electromagnetic steel sheet, the concentrated segregation portion of S of 0.050% or more due to bulging cracks during continuous casting is at least 53 μm from the surface of the product sheet thickness at least on one side of the slab.
A method for stably producing a high magnetic flux density unidirectional magnetic steel sheet, comprising using a continuous cast piece controlled inward from a position corresponding to m. 2. A method for heating a continuous cast piece prior to hot rolling, in which a surface on the casting side is controlled such that an S-rich segregated portion caused by bulging cracks is controlled inward from a position corresponding to 53 μm from the surface of the product sheet thickness. 2. The stable production method according to claim 1, wherein the method is placed on the upper surface side of the furnace. 3. The method according to claim 1, wherein before the hot-rolled sheet annealing, cold-rolling is performed at a rolling reduction of 45% or less, and the product sheet thickness after final cold-rolling is 0.23 mm or less. Stable production method. 4. The stable production method according to claim 3, wherein the hot-rolled sheet is annealed at 850 to 1120 ° C.