JP2000017335A - Production of grain oriented silicon steel sheet free from edge crack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain a steel sheet free from edge crack and good in magnetic properties by controlling the contents of acid soluble Al, N, Se and S in steel contg. specified ratio of C, Si and Mn, the size of the grains in the slab columnar crystal parts after casting and the heating temp. SOLUTION: Steel contg., by weight, 0.005 to 0.08% C, 1.0 to 7.0% Si and 0.03 to 2.5% Mn is melted to cast to form into a silicon steel slab, which is successively subjected to heating, hot rolling and hot rolled sheet annealing and is thereafter subjected to cold rolling to control its sheet thickness into the final one, and, finish annealing is executed to produce a grain oriented silicon steel sheet. At this time, the contents of acid soluble Al, N, Se and S in the steel are controlled to the ranges of, by weight, 0.001 to 0.030% acid soluble Al, 0.003 to 0.010% N and <=0.035% Se+2.47S, the size of the grains in the columnar crystal parts in the slab after the casting is controlled to <=10 mm on the average by the size equivalent to a circle in the cross section vertical to the elongating direction of the columnar crystals, and the slab heating temp. is controlled to <=1300 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet, and more particularly to a method for stably producing a grain-oriented electrical steel sheet having no cracks and good magnetic properties. It is.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are mainly used as iron core materials for transformers and other electric equipment, and are basically required to have excellent magnetic properties such as magnetic flux density and iron loss value. For this reason, a silicon steel slab having a thickness of 100 to 300 mm is heated to a high temperature and then hot-rolled, and then the hot-rolled sheet is subjected to one or two or more cold-rollings with intermediate annealing to obtain a final thickness, Next, a complicated process of performing primary recrystallization annealing also serving as decarburization, applying an annealing separator, and then performing final finish annealing for the purpose of secondary recrystallization and purification is employed. In order to enhance the magnetic properties of such a grain-oriented electrical steel sheet, the <001> axis, which is the axis of easy magnetization, is aligned in the rolling direction by secondary recrystallization in the finish annealing step {110} <001>.
It is fundamentally important to grow crystal grains of the orientation.

[0003] In order to effectively promote such secondary recrystallization, it is important to first disperse a dispersed phase called an inhibitor which suppresses the growth of primary recrystallized grains into a uniform and appropriate size. As such an inhibitor
There are sulfides such as MnS, MnSe, AlN and VN, selenium compounds and nitrides, and Sb, Nb, Ge, Sn, Cr
And the like are appropriately added.

[0004] As a method of proper control for dispersing the above-mentioned inhibitors mainly composed of sulfides, selenium compounds and nitrides in steel in a uniform and appropriate size, in a conventional process, the inhibitors are temporarily removed during slab heating before hot rolling. A method has been employed in which the solid solution is completely dissolved and then finely precipitated after the hot rolling step. In order for this inhibitor to form a solid solution,
It is necessary to heat to a temperature of about 1400 ° C., and therefore, the slab heating of grain-oriented electrical steel sheets is generally performed at about 200 ° C. higher than the slab heating of ordinary steel.

[0005] In addition to the above-described appropriate control of the inhibitor,
In order to effectively cause secondary recrystallization, it is necessary to appropriately control the crystal grain size and texture after primary recrystallization. That is, the larger the primary recrystallized grain size, the smaller the driving force for grain growth during final finish annealing. Therefore, by appropriately controlling the balance between the driving force for the growth of primary recrystallized grains and the inhibitory force of the inhibitor, secondary recrystallization can be effectively generated. Also, {110} <00
1) In order for only the grains accumulated in the orientation to undergo secondary recrystallization,
At the stage after primary recrystallization, {110} <001> orientation grains serving as nuclei for secondary recrystallization are scattered in a matrix having a texture in which the {110} <001> orientation is likely to grow. This is very important. By controlling these inhibitors, primary recrystallized grains, texture, etc., {110} <00
1> It becomes possible to obtain secondary recrystallization which is integrated as much as possible in the orientation, and products with high magnetic flux density and low iron loss have been obtained.

[0006] Recently, in grain-oriented electrical steel sheets, not only magnetic properties but also inexpensive supply has been strongly desired. Therefore, it is an important issue for the manufacturer to manufacture high-quality products having excellent magnetic properties with high yield. From the viewpoint of improving the yield, in hot rolling at the time of manufacturing a grain-oriented electrical steel sheet, it is an important issue how to prevent the shape defect of the end of the hot-rolled sheet. This is because at the end (edge) of the hot-rolled sheet, the ears of the coil are shaved off, or saw-like cracks are easily generated in the ears, which is a major factor in lowering the yield. . Such cracks in the edge of the hot-rolled sheet are defined by the Japanese Iron and Steel Institute
In IJ TR006), it is also referred to as "ear cracks", but in this specification it will be referred to as "ear cracks".

[0007] There have already been many disclosures of techniques for preventing edge cracks in the hot rolling step in the production of grain-oriented electrical steel sheets. For example, Japanese Patent Application Laid-Open No. 55-62124 discloses a method in which the temperature drop during finish hot rolling is kept within 220 ° C., and Japanese Patent Application Laid-Open No. 61-96032 controls a reduction rate after finish rolling. Although methods have been disclosed, these techniques have not been able to obtain the effect of preventing ear cracks occurring at the time of rough rolling or before finish rolling. Also, Japanese Patent Application Laid-Open
JP-A-145204, JP-A-61-71104, JP-A-60-200916, and JP-A-62-1
JP-A-96328 and JP-A-5-138207 disclose methods of preventing edge cracks by adjusting the shape of the side surface of a sheet bar during hot rolling. However, these techniques are also used for rough rolling and finishing. There is a disadvantage that there is almost no effect of preventing ear cracks generated at the previous stage of rolling.

In Japanese Patent Application Laid-Open No. 9-70602, it is ascertained that ear cracks mainly occur at the stage before hot finishing, and regarding the shape of the sheet bar after the rough rolling, the thickness te (mm) of the side edge portion of the sheet bar is determined. ) And the thickness tc at the center of the sheet bar in the width direction.
(Mm) discloses a technique for forming a shape that satisfies te-tc ≥ 1 (mm). In particular,
This is a technique of performing appropriate width reduction during rough rolling. This makes it possible to considerably reduce the frequency of occurrence of ear cracks and the depth of the ear cracks (the length of the crack measured in the width direction from the edge of the steel plate). Did not reach.

[0009]

The problem to be solved by the present invention is to develop a method of manufacturing a grain-oriented electrical steel sheet which completely prevents edge cracks during hot rolling and maintains good magnetic properties. It is.

[0010]

Means for Solving the Problems As a result of intensive studies, the present inventors have developed a method for manufacturing a grain-oriented electrical steel sheet which completely prevents edge cracks during hot rolling and maintains good magnetic properties. Newly found. That is, the present invention provides C: 0.005 to 0.
08 wt% (hereinafter simply referred to as%), Si: 1.0 to 7.0%,
Mn: A steel containing 0.03 to 2.5% is melted and cast to form a silicon steel slab. After heating the silicon steel slab, hot-rolling, and then subjecting the hot-rolled sheet to annealing, once or once. In the method for producing a grain-oriented electrical steel sheet that is subjected to finish annealing by applying a decarburizing annealing and an annealing separating agent, by applying a cold rolling of two or more times of cold rolling sandwiching intermediate annealing, the acid-soluble Al in the steel, N,
When the content of Se and S is acid-soluble Al: 0.001 to 0.030%,
N: controlled within the range of 0.003 to 0.010%, Se + 2.47S ≦ 0.035%, and the grain size of the columnar crystal part of the slab after casting is 10 mm or less on average in a circle equivalent diameter of a cross section perpendicular to the elongation direction of the columnar crystal. And a slab heating temperature of 1300 ° C. or lower.

According to the present invention, in controlling the slab structure as described above, the time during which a portion within 10 mm from the slab surface stays in the temperature range of 1300 ° C. from the solidification temperature during casting is set to 5 times.
It is effective to keep the time within minutes or to perform electromagnetic stirring. In addition, if necessary, after the end of hot rolling and before the start of secondary recrystallization, performing a nitriding treatment on the steel sheet enhances the inhibitory power of the inhibitor and produces a good secondary recrystallization. It is valid.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below. We believe that the biggest cause of edge cracking in hot-rolled steel sheets is that the slab heating temperature of grain-oriented electrical steel sheets is much higher than that of general steel. An experiment was performed in which the temperature was changed up to 1400 ° C.

(Condition A) C: 0.048 by the continuous casting method
%, Si: 3.16%, Mn: 0.08%, sol.Al: 0.035%, S:
Eight 200 mm thick slabs containing 0.019%, Se: 0.021% and N: 0.0088%, with the balance consisting of iron and unavoidable impurities, were cast and heated to eight different temperatures from 1150 ° C to 1400 ° C. And hot-rolled into a 2.5 mm hot-rolled coil. Thereafter, hot-rolled sheet annealing maintained at 1000 ° C. for 60 seconds was performed, pickled, and then cold-rolled to a thickness of 0.34 mm. Thereafter, after degreasing, decarburizing annealing was performed at 850 ° C. for 120 seconds. After decarburizing annealing, a final finish annealing was performed by applying an annealing separator. After the final finish annealing, the unreacted annealing separating agent was removed, an insulating coating agent containing magnesium phosphate containing colloidal silica as a main component was applied, and baked at 800 ° C. to obtain a product. From each product, was cut out Epstein size along the rolling direction in the vicinity of the center of the plate width direction, the magnetic flux density was measured B _8. After hot rolling,
The occurrence of ear cracks was investigated. The relationship between the edge cracking incidence of slab heating temperature and the hot-rolled sheet in FIG. 1, showing the relationship between the magnetic flux density B ₈ of the slab heating temperature and the product is shown in Figure 2 (symbol ○)
The frequency of occurrence of cracks in ears was determined by examining the frequency of cracks with a depth of 3 mm or more (the same applies hereinafter). From the results shown in FIGS. 1 and 2, under the condition A, lowering the slab heating temperature certainly reduced the frequency of occurrence of ear cracks, but also caused deterioration of the magnetic properties of the product.

(Condition B) Under the condition A, the magnetic properties of the product deteriorated with the decrease in the slab heating temperature because Al and N contained as inhibitors cannot be completely dissolved in the slab during heating. It was found that coarse precipitates were formed after hot rolling. Al, N in hot rolled sheet
When coarse precipitates are formed, it becomes difficult to precipitate finely in a later step, leading to a decrease in the ability to suppress grain growth and leading to secondary recrystallization failure.

Therefore, even if the slab heating temperature is low, in order to prevent coarse precipitation of Al and N on the hot-rolled sheet, the A
l, to reduce the N content to complete solid solution and to reduce Se compounds and S compounds which are likely to be nuclei for precipitation, C: 0.053%, Si: 3.14%, Mn: 0.08%, sol.Al:
0.015%, S: 0.003%, Se: 0.004% and N: 0.0079
%, With the balance being iron and unavoidable impurities. Slab casting conditions,
The conditions after the hot rolling are the same as the conditions A. The relationship between the edge cracking incidence of slab heating temperature and the hot-rolled sheet in FIG. 1, showing the relationship between the magnetic flux density B ₈ of the slab heating temperature and the product is shown in Figure 2 (symbol ●). Note that when measuring the magnetic flux density, was cut out Epstein size along the vicinity of the center in the plate width direction to the rolling direction, were measured B _8.

From the results shown in FIGS. 1 and 2, deterioration of the magnetic properties of the product due to the decrease in the slab heating temperature was eliminated by setting the component composition under the condition B. In addition, the frequency of occurrence of ear cracks was also reduced, and cracks with a depth of 3 mm or more did not occur at a slab heating temperature of 1300 ° C or less. As for the cause, S,
It is considered that the generation of cracks originating from the precipitated S and the precipitated Se was suppressed by reducing the content of Se.

However, when the macrostructure of the product was observed, it was found that when the slab heating temperature was 1300 ° C. or less, secondary recrystallization failure occurred at the end in the width direction. Therefore, the slab heating temperature 1200 ° C., for 1300 ° C., 1400 ° C. Conditions product was investigated sheet width direction change of the magnetic flux density B ₈ in detail. The result is shown in FIG. From FIG. 3, it was found that the magnetic properties were good at the center in the sheet width direction irrespective of the slab heating temperature, but the magnetic properties were degraded at the ends in the sheet width direction with a decrease in the slab heating temperature. Observation of the cross-sectional structure of the slab revealed that the columnar crystal region at the end in the width direction of the slab corresponded to the region where the magnetic flux density decreased due to secondary recrystallization failure in the product, as schematically shown in FIG. all right.

(Condition C) It was considered that the secondary recrystallization defect at the end in the width direction might be caused by the slab structure, and an experiment was performed to change the casting speed of the slab. The component composition was the same as the condition B, and a slab b1 having a higher casting speed and a slab b2 having a lower casting speed than the condition B (slab b) were produced. In each case, the slab thickness was 200 mm. After heating these slabs b1 and b2 to 1200 ° C., hot rolling and subsequent steps were performed to obtain products. The conditions after hot rolling are the same as conditions A and B. The obtained each product were investigated the sheet width direction change of the magnetic flux density B _8. The results are shown in FIG. When the slab b1 with a higher casting speed was used, the magnetic flux density was good over the entire width direction. On the other hand, when the slab b2 with a lower casting speed was used, the magnetic characteristics deteriorated at the end in the width direction. Became more intense.

The slab cross-sectional structures of b1 and b2 were observed and compared with the slab of condition B (slab b). As a result, there was no significant difference in the abundance of columnar crystals, but the thickness of the columnar crystals was significantly different. Was. When evaluated by the average value of the circle equivalent diameter of the cross section perpendicular to the elongation direction of the columnar crystal, slab b1: 3.5 mm,
The slab b was 11.2 mm and the slab b2 was 14.6 mm.

The effect of the columnar portion of the slab on the secondary recrystallization is considered as follows. Columnar grains close to the surface of the slab tend to be oriented in the <001> direction, whereas equiaxed grains inside the slab have no particular orientation. As the rolling and recrystallization are repeated in the steps after hot rolling, the difference in the structure and texture between the originally columnar and equiaxed parts becomes smaller. It does not completely disappear even after annealing. In particular, the end portion in the width direction originally had a columnar crystal throughout the thickness direction, so that there was a difference in texture from the inside in the width direction. When the slab heating temperature is high, the inhibitor is sufficiently dissolved and secondary inhibitor recrystallization occurs stably due to the strong inhibitory power of the inhibitor, but when the slab heating temperature is low, the texture of the decarburized annealed plate is increased. Slight change in the temperature tends to lead to secondary recrystallization failure.

By the way, the place where recrystallization nuclei are generated is as follows.
There are intragranular and near grain boundaries, but when the grain size is small, the latter is the main. In addition, in intragranular nucleation, the recrystallization orientation strongly depends on the orientation before processing, whereas in near-grain nucleation,
The recrystallization orientation does not depend much on the orientation before processing. Therefore, when the thickness of the columnar crystals is small even in the vicinity of the columnar crystals of the slab, in the rolling recrystallization process after hot rolling, recrystallization nucleation from the vicinity of the grain boundaries becomes mainstream, and the nucleus with the inside of the slab becomes The difference from the texture disappears relatively easily. Therefore, it is considered that good secondary recrystallization occurs in the entire width direction even under the condition that the slab heating temperature is low and the inhibitor is relatively weak.

Under conditions C (and B), it is considered that the change in the casting speed of the slab led to the change in the thickness of the columnar crystals. The main factors that determine the thickness of the columnar crystals are as follows.
The cooling rate near the slab surface is mentioned. Slab b1,
Estimating the time for the part 10 mm from the surface of b and b2 to stay in the temperature range of 1300 ° C. from the solidification temperature, slab b1: 1 minute
15 seconds, slab b: 5 minutes and 50 seconds, slab b2: 8 minutes and 0 seconds.

Hereinafter, the constituent features of the present invention will be described more specifically. (Regarding components) C: 0.005% or more and 0.08% or less C is a component necessary for improving the structure and stabilizing the secondary recrystallization. For that purpose, 0.005% or more is required. However, if the content exceeds 0.08%, the fracture during cold rolling increases, and the time required for decarburization during decarburization annealing increases and the productivity decreases, so the content is set to 0.08% or less.

Si: 1.0% or more and 7.0% or less Si is an essential component for increasing electric resistance and reducing iron loss. For this purpose, it is necessary to contain 1.0% or more. %, The workability deteriorates and the production and processing of the product become extremely difficult. Therefore, 1.0% or more and 7.0%
The range is as follows.

Mn: 0.03% or more and 2.5% or less Mn is also a necessary component because it also increases electric resistance and improves hot workability during manufacturing. For this purpose, a content of 0.03% or more is necessary. However, if the content exceeds 2.5%, γ transformation is induced and magnetic properties are deteriorated. Therefore, a range of 0.03% or more and 2.5% or less is set. I do.

Acid-soluble Al: 0.001% or more and 0.030% or less Al must be contained as an inhibitor component in an amount of 0.001% or more and 0.030% or less. Al is combined with N and Al
Although N serves as an inhibitor, the effect of suppressing the growth of primary recrystallized grains is enhanced by dissolving AlN during slab heating and finely precipitating it during the heating process of hot-rolled sheet annealing. However, when the Al content is less than 0.001% in sol.Al, the amount of AlN precipitated during the heating process of hot-rolled sheet annealing becomes insufficient. Conversely, when the Al content exceeds 0.030%, the Since the solid solution of AlN becomes difficult during slab heating, the amount of AlN that precipitates finely during the heating process of hot-rolled sheet annealing is insufficient. Therefore, in order to effectively exhibit the effect as an inhibitor, the content of Al should be 0.001% or more and 0.030% or more.
% Or less.

N: not less than 0.0030% and not more than 0.0100% Since N forms AlN and functions as an inhibitor, it is necessary to contain 0.030% or more. However, if it exceeds 0.0100%, it will gasify in the steel,
0.0030% or more, 0.01 due to defects such as blisters
Must be in the range of 00% or less.

Se and S: Se + S ≦ 0.035% Se and S are combined with Mn or Cu to function as an inhibitor. In the technique of the present invention, as described in Experiment 1, when Se and S are excessively contained. , MnSe or MnS as a nucleus tends to cause coarse precipitation of AlN, and the inhibitory power of the inhibitor is rather weakened. The amount of Se and S is as follows: under conditions where the slab heating temperature is 1300 ° C. or less, 0.035% of Se + 2.47S
It is necessary to:

Other inhibitor components Sb, Sn, Cr, Ge, Nb, Ti, B, etc. can function as inhibitors, and can be added as necessary. In particular, Sb or Sn tends to segregate at the grain boundaries,
It has a remarkable effect on reinforcing the grain growth suppressing power. The contents of these components to function as inhibitors are as follows: Sb: 0.001% or more, Sn: 0.001% or more,
Cr: 0.001% or more, Ge: 0.001% or more, Nb: 0.001% or more, Ti: 0.0005% or more, B: 0.0001% or more are required. However, Sb: more than 0.080%, Sn: more than 0.30%, C
r: Over 0.30%, Ge: Over 0.30%, Nb: Over 0.30%, T
If i: 0.0020% or more, B: 0.0020% or more, mechanical properties such as vent properties of the product are deteriorated. Therefore, when these components are used as inhibitors, the contents of Sb are in the range of 0.001 to 0.080%, Sn is in the range of 0.001 to 0.30%, Cr is in the range of 0.001 to 0.30%, and Ge is 0.001 to 0.30%. % Range, Nb 0.001 to 0.30%
, Ti is in the range of 0.0005 to 0.0020%, B is 0.0001 to 0.
0020%.

(Casting of Slab) The molten steel adjusted to the above components is cast by a continuous casting method or an ingot making method, and if necessary, a slab is formed with a lumping step. As described in the previous experiment, the slab structure is controlled so that the equivalent circle diameter of the cross section perpendicular to the elongation direction of the columnar crystal is 10 mm or less on average with respect to the grain size of the columnar crystal part of the slab. Average circle equivalent diameter is 10
If it is larger than mm, the magnetic properties will be degraded at the widthwise end of the steel sheet. In controlling the slab organization in this way,
It is effective to make the time within 10mm from the slab surface stay in the temperature range of 1300 ° C from the solidification temperature within 5 minutes or to perform electromagnetic stirring. In addition, the casting speed can be increased as performed in the previous experiment.

(Hot rolling) The coil adjusted as described above is subjected to slab heating according to a usual method,
A hot-rolled coil is formed by hot rolling. The slab heating temperature is set to 1300 ° C. or less to prevent edge cracks during hot rolling. A low slab heating temperature is also preferable for reducing energy costs. In recent years, a method has been disclosed in which hot rolling is performed directly after continuous casting without performing slab heating. However, the present invention can be suitably implemented in the present invention because the slab heating temperature can be lowered.

(Hot Rolled Sheet Annealing)
Subsequently, hot-rolled sheet annealing is performed. The purpose of hot rolled sheet annealing is
This is the fine precipitation of the inhibitor AlN and the homogenization of the structure during the heating process, but in the present invention, the slab heating temperature is low,
Since the hot-rolled sheet structure is relatively uniform, hot-rolled sheet annealing is performed with emphasis on fine precipitation of the inhibitor. The temperature and time of the hot-rolled sheet annealing are not particularly limited, but it is effective to perform the hot-rolled sheet annealing under conditions optimized to enhance the inhibitory force of the inhibitor in combination with other process conditions. .

(Cold rolling) After hot-rolled sheet annealing, 1
The final thickness is obtained by cold rolling two or more times, with or without intermediate annealing. Cold rolling may be performed by a Sendzimir rolling mill or a tandem rolling mill. A method in which the rolling temperature is set higher than the normal temperature and the texture is controlled by dynamic strain aging during rolling or static strain aging between passes is also effective in improving the magnetic properties of the product in the present invention.

(Decarburizing annealing, final finishing annealing, coating) After cold rolling, decarburizing annealing is performed according to a conventional method, and then an annealing separator is applied, followed by final finishing annealing. After final finishing annealing, apply and bake an insulation coating as necessary.
Further, it is flattened or annealed to obtain a product.

[0035]

EXAMPLES (Example 1) The composition of the components a to i shown in Table 1
One 200 mm thick slab was cast by a continuous casting method. During this casting, electromagnetic stirring was applied, and the time during which the portion 10 mm from the surface stayed in the temperature range from the solidification temperature to 1300 ° C. during the slab cooling process was controlled to be 60 seconds to 120 seconds. Next, each slab was heated to a temperature of 1200 ° C., and then hot-rolled into a hot-rolled coil of 2.5 mm.
Hot rolled sheet annealing was performed for 30 seconds. Then, after pickling, it was cold-rolled to a thickness of 0.34 mm, degreased, and then decarburized at 850 ° C. for 120 seconds. After decarburizing annealing, a final finish annealing was performed by applying an annealing separator. After the final finish annealing, the unreacted annealing separating agent was removed, an insulating coating mainly composed of magnesium phosphate containing colloidal silica was applied, and the product was baked at 800 ° C. From each product, cut out Epstein size test pieces along the rolling direction from near the center and the end in the sheet width direction,
The magnetic flux density B ₈ and iron loss W _{1 7/50} were measured (magnetic flux density 1.7 T, the iron loss in 50 Hz). After the completion of hot rolling, the occurrence of ear cracks having a depth of 3 mm or more was investigated. Table 2 shows the results.
As shown in Table 2, when the component composition of the slab satisfied the requirements of the present invention, ear cracks did not occur in hot rolling and the magnetic properties of the product were good.

[0036]

[Table 1]

[0037]

[Table 2]

Example 2 20% of the component composition of f shown in Table 1
Nine slabs having a thickness of 0 mm were cast by a continuous casting method. During the cooling process, the part 10 mm from the surface
Three slabs were controlled to stay in the 1300 ° C temperature range at 60 seconds (± 10 seconds), three slabs were controlled to 240 seconds (± 20 seconds), and 480 seconds (± 30 seconds). There were three slabs. Next, for three slabs under the same conditions, 1150 ° C, 1250
After being heated to each temperature of 1350 ° C. and 1350 ° C., it was hot-rolled into a hot-rolled coil having a thickness of 2.5 mm, and subsequently subjected to hot-rolled sheet annealing maintained at 900 ° C. for 50 seconds. Then, after pickling, it was cold-rolled to a thickness of 0.34 mm, degreased, and then decarburized at 850 ° C. for 120 seconds. After decarburizing annealing, a final finish annealing was performed by applying an annealing separator. The final finish annealing, the unreacted annealing separating agent was removed, an insulating coating mainly composed of magnesium phosphate containing colloidal silica was applied and baked at 800 ° C. to obtain a product. From each product, test specimens of Epstein size were cut out from the vicinity of the center and the end in the strip width direction along the rolling direction, and the magnetic flux density B ₈ and iron loss value W
_17/50 (magnetic flux density 1.7 T, iron loss at 50 Hz) was measured. After the completion of hot rolling, the occurrence of ear cracks having a depth of 3 mm or more was investigated. Table 3 shows the results. As shown in Table 3, with respect to the size of the columnar crystal grains of the slab, the equivalent circle diameter of the cross section perpendicular to the direction of extension of the columnar crystal is 10 mm or less on average, and the slab heating temperature is 1300 ° C or less. In addition, ear cracks did not occur in the hot rolling, and the magnetic properties of the product were good.

[0039]

[Table 3]

Example 3 Two slabs each having a component composition of c and f shown in Table 1 and having a thickness of 250 mm were cast by a continuous casting method. During casting, electromagnetic stirring was applied, and the time required for the part 10 mm from the surface to stay in the temperature range from the solidification temperature to 1300 ° C during the slab cooling process was controlled from 60 seconds to 120 seconds. Next, the slab of each component was heated to a temperature of 1200 ° C. and 1400 ° C., then hot-rolled into a hot-rolled coil having a thickness of 2.8 mm, and subsequently subjected to hot-rolled sheet annealing at 950 ° C. for 50 seconds. did. Thereafter, it is pickled, subjected to a first cold rolling to a thickness of 1.7 mm, subjected to an intermediate annealing at 950 ° C., and then pickled again to obtain a 0.22
A second cold rolling to a thickness of mm was performed. afterwards,
After the degreasing treatment, decarburization annealing was performed at 850 ° C. for 120 seconds. After decarburizing annealing, a final finish annealing was performed by applying an annealing separator. After the final finish annealing, the unreacted annealing separating agent was removed, an insulating coating mainly composed of magnesium phosphate containing colloidal silica was applied, and the product was baked at 800 ° C. From each product, test specimens of Epstein size were cut out from the vicinity of the center and the end in the sheet width direction along the rolling direction, and the magnetic flux density B ₈ and _iron loss value W _17/50 (magnetic flux density 1.7
T, iron loss at 50 Hz) was measured. After the completion of hot rolling, the occurrence of ear cracks having a depth of 3 mm or more was investigated.
Table 4 shows the results. As shown in Table 4, when the component composition of the slab satisfies the requirements of the present invention and the slab heating temperature is 1300 ° C. or lower, the ear cracks do not occur in hot rolling and the magnetic properties of the product Was good.

[0041]

[Table 4]

Example 4 Two 250 mm thick slabs each having the component compositions d and i shown in Table 1 were cast by a continuous casting method. During casting, the time required for the part 10 mm from the surface to stay in the temperature range from the solidification temperature to 1300 ° C during the slab cooling process from 60 seconds
Controlled to 120 seconds. Next, the slab of each component was heated to a temperature of 1150 ° C. and 1350 ° C., and then hot-rolled to 2.4.
A hot-rolled coil having a thickness of mm was formed, and subsequently a hot-rolled sheet was held at 1000 ° C. for 50 seconds. Then, it was pickled and cold rolled to a thickness of 0.34 mm. Then, after performing degreasing, decarburization annealing was performed at 850 ° C. for 120 seconds. After the decarburizing annealing, while the strip was running, nitriding treatment was performed at 750 ° C for 30 seconds in a mixed gas of 75% hydrogen, 25% nitrogen and a small amount of ammonia, and the nitrogen content of the steel sheet was reduced to 220 ppm. did.
Next, an annealing separator was applied to perform a final finish annealing.
After the final finish annealing, the unreacted annealing separating agent was removed, an insulating coating mainly composed of magnesium phosphate containing colloidal silica was applied, and the product was baked at 800 ° C. From each product, test specimens of Epstein size were cut out from the vicinity of the center and the end in the sheet width direction along the rolling direction, and the magnetic flux density B ₈ and _iron loss value W _17/50 (magnetic flux density 1.7 T, 50 Hz
Was measured. After hot rolling,
The occurrence of ear cracks with a depth of 3 mm or more was investigated. Table 5 shows the results. As shown in Table 5, the component composition of the slab satisfies the requirements of the present invention, and the slab heating temperature is
When the temperature is 1300 ° C or less, edge cracking does not occur in hot rolling,
In addition, the magnetic properties of the product were good.

[0043]

[Table 5]

[0044]

As described above, according to the present invention, it is possible to produce a grain-oriented electrical steel sheet having no cracks and good magnetic properties.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a slab heating temperature and a frequency of edge cracks of a hot-rolled sheet.

Fig. 2 Slab heating temperature and product magnetic properties (magnetic flux density)
B ₈ ) is a diagram showing the relationship.

3 is a diagram showing a change in the plate width direction of the product of the magnetic flux density B ₈ each slab heating temperature.

FIG. 4 is a schematic diagram showing a relationship between a slab cross-sectional structure and a secondary recrystallization defect generation region of a product.

5 is a diagram showing a change in magnetic flux density B ₈ in the plate width direction of the product in the case of using slabs different casting conditions.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01F 1/16 H01F 1/16 B (72) Inventor Tadashi Tadashi Nakanishi 1-chome Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture No) Kawasaki Steel Corporation Mizushima Works F-term (reference) 4K033 AA02 BA01 CA02 CA03 CA05 CA06 CA07 CA09 DA01 FA01 FA12 GA00 HA01 HA03 JA04 LA00 MA00 5E041 AA02 AA11 AA19 BC01 CA02 HB05 HB07 HB11 HB14 NN18NN

Claims (4)

[Claims] 1. C: 0.005 to 0.08 wt%, Si: 1.0 to 7.0
wt%, Mn: 0.03 to 2.5 wt% of steel is melted and cast to form a silicon steel slab. After heating this silicon steel slab,
After hot rolling, and then subjected to hot-rolled sheet annealing, the final thickness by cold rolling one or two or more times sandwiching the intermediate annealing,
Further, in a method for producing a grain-oriented electrical steel sheet in which decarburizing annealing and an annealing separator are applied and finish annealing is performed, the content of acid-soluble Al, N, Se and S in the steel is determined by adjusting the content of acid-soluble Al: 0.001 to 0.030. wt%, N: 0.003 to 0.010
wt%, Se + 2.47S ≦ 0.035 wt%, and control the grain size of the columnar crystal part of the slab after casting to an average of 10 mm or less in terms of the equivalent circle diameter of the cross section perpendicular to the elongation direction of the columnar crystal. A method for producing a grain-oriented electrical steel sheet without edge cracks, wherein the slab heating temperature is 1300 ° C or lower. 2. The method for producing a grain-oriented electrical steel sheet without edge cracks according to claim 1, wherein the time during which the portion within 10 mm from the slab surface stays in the temperature range of 1300 ° C. from the solidification temperature during casting is within 5 minutes. 3. The method according to claim 1, wherein electromagnetic stirring is performed during casting. 4. The grain-oriented electrical steel sheet according to claim 1, wherein the steel sheet is subjected to nitriding treatment after completion of hot rolling and before the start of secondary recrystallization. Production method.