JPH06207221A - Production of grain-oriented silicon steel sheet excellent in surface characteristic - Google Patents

Abstract

PURPOSE:To produce a grain-oriented silicon steel sheet excellent in surface characteristics by applying a C-containing material or the mixture of this material and a specific carburizing accelerator to the surface of a silicon-containing steel slab prior to hot rolling at the time of producing a silicon steel sheet by subjecting a silicon-containing steel slab to hot rolling, cold rolling, and annealing. CONSTITUTION:A C-containing material, such as graphite powder and petroleum coke powder, is applied to the surface of a high silicon steel slab, or the mixture prepared by further mixing, as carburizing accelerator, the powder of alkali metal carbonate or alkaline earth metal carbonate, such as Na2CO3 and CaCO3, with the C-containing material is applied to the surface of the steel slab. Then the slab is heated up to a hot rolling temp. Since the coarsening of crystalline grains due to decarburization by heating is prevented in the steel slab, the slab is formed to the final sheet thickness by means of subsequent hot rolling and cold rolling and successively subjected to decarburizing and primary recrystallization annealing, and, after the application of a separation agent at annealing, composed essentially of MgO, finish annealing is performed. Thus, the grain-oriented silicon steel sheet free from cracking at the time of rolling, due to the coarsening of crystalline grains, can be obtained.

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 silicon steel sheet, and in particular, a grain-oriented material having excellent surface properties and excellent magnetic properties by adding a device to a method for heating a silicon-steel-containing slab. It is intended to obtain a silicon steel sheet.

[0002]

2. Description of the Related Art Grain-oriented silicon steel sheets are mainly used as core materials for transformers and generators. In recent years, reflecting the strong demand for energy saving, inexpensive supply of grain-oriented silicon steel sheets having excellent magnetic properties has been desired. In particular, it is desired to stably obtain a steel sheet having a high magnetic flux density and a low iron loss, and more recently, it has become an important issue to secure reliability that can withstand long-term use.

In order to obtain a grain-oriented electrical steel sheet having excellent magnetic properties, it is basically necessary to obtain a secondary recrystallized structure highly integrated in the {110} <001> orientation, the so-called Goss orientation. In order to develop the above Goss orientation secondary recrystallized structure, the presence of a so-called inhibitor, which is a dispersed precipitation phase that moderately suppresses grain boundary migration, is required.MnSe, MnS, AlN, etc. are generally used as such inhibitors. Is being used for In order to fully exert the action of the inhibitor,
It is very important to dissociate MnSe, MnS, AlN, etc. sufficiently during slab heating prior to hot rolling, and then hot-roll under appropriate conditions and cool to disperse and precipitate the inhibitor finely and uniformly. It is important to take such MnSe, MnS, AlN
It is said that a high slab heating temperature is required for solid dissolution separation of the above.

Therefore, many improvement efforts have been conventionally made in order to secure a high slab heating temperature. Recently, a heating method using an induction heating method has been developed as a method capable of heating the high temperature slab. It has been confirmed that a heating furnace utilizing such an induction heating system can be heated to a sufficiently high temperature with high accuracy and is extremely effective for improving magnetic characteristics.

On the other hand, with the high temperature heating of the slab, some disadvantages have occurred. In particular, the deterioration of the surface properties due to high temperature heating is a problem, and several techniques have been proposed for the purpose of preventing such surface defects. For example, JP-A-60-
In 145318 publication, a large amount of slag is generated on the surface of the slab during high temperature heating, which not only impairs the operability of the heating furnace but also causes surface defects, so as a method of preventing it, the slab surface temperature is 1250 ° C. It has been proposed above that the O ₂ concentration in the heating atmosphere should be 1% or less, and that the upper limit of the heating temperature in the gas combustion furnace should be 1230 ° C.

Further, in Japanese Patent Laid-Open No. 61-69927, melting of the furnace wall and reduction of yield due to generation of large amount of slag, roughening of hot coil due to grain boundary oxidation of slab surface during high temperature heating, decarburization of slab surface For the purpose of preventing the deterioration of the magnetic properties of the final product due to it, and further the coarsening of the slab columnar crystals, the heating in the electric heating furnace, the temperature is 1310 ~ 1350 ℃, the atmosphere is limited to non-oxidizing, It has been proposed that the upper limit of the soaking temperature in the fuel combustion furnace should be 1250 ° C.

Further, in Japanese Patent Laid-Open No. 61-69924, when the slab is heated at a high temperature by the induction heating method, melting loss starts when the slab surface temperature exceeds 1235 ° C.
It is proposed that the O ₂ concentration should be controlled below 10%. In the examples, examples are shown in which the heating temperature is 1350 ° C. and the O ₂ concentration is 10% or less and the heating temperature is 1370 ° C. and the O ₂ concentration is 1% or less.

Further, in JP-A-62-130219, in order to prevent the generation of molten slag, which causes a decrease in yield and seriously hinders the operation of a heating furnace, the O ₂ concentration in the atmosphere is changed to the following formula O ₂ (%) = 36.4-5.0 lnT (° C) or less is proposed. Further, as specific values, a range of 0.36% or less at 1300 ° C and 0.18% or less at 1400 ° C is shown. However, the technique of this specification is simply a mathematical formula of thermodynamic common sense that molten slag is less likely to be generated when the O ₂ concentration is lowered according to temperature, and does not give any further knowledge.

[0009]

As described above, various studies have been continued on the improvement of the high temperature heating technique using an induction heating furnace or the like, but the common points to the conventionally proposed methods are as follows. The purpose is to prevent the generation of a large amount of slag due to high temperature heating. Certainly, the generation of a large amount of slag due to the high temperature heating is not preferable because it lowers the yield and the operation efficiency, but it is not a new problem caused by changing the heating method to induction heating. Since the reaction rate of oxidation was increased simply by raising the temperature, the amount of slag produced increased only.
Therefore, in order to prevent slag, it can be easily estimated that lowering the O ₂ concentration or lowering the upper limit of the heating temperature is effective.

By the way, recently, a flaw of about 1 mm generated on the surface of a hot rolled sheet has become a problem. Application of any of the above-mentioned techniques to this problem hardly contributed to the suppression of defects. These flaws became apparent as the slab heating temperature increased, but they were stretched by cold rolling and became about 20 mm on the surface of the product sheet. In recent years, the demands on the surface appearance have become more strict, and even a flaw of this degree is regarded as a defective product, which makes shipment difficult.

The present invention is a method for producing a grain-oriented silicon steel sheet having excellent surface properties, which can effectively prevent the generation of surface defects due to high temperature heating of the slab, and can stably obtain good magnetic characteristics. The purpose is to propose.

[0012]

Means for Solving the Problems That is, according to the present invention, after heating a silicon-containing steel slab, it is hot-rolled and then cold-rolled once or twice with intermediate annealing to obtain a final plate thickness. In the method for producing a grain-oriented silicon steel sheet by a series of steps of performing decarburization / primary recrystallization annealing, then applying an annealing separator on the steel sheet surface and then performing finish annealing, prior to the hot rolling. In the slab heating, a carbon-containing substance is applied on the surface of the slab in advance, and then the slab is heated, which is a method for producing a grain-oriented silicon steel sheet having excellent surface properties (first invention).

Further, according to the present invention, after heating the silicon steel slab, it is hot-rolled and then cold-rolled once or twice with intermediate annealing to obtain the final thickness, and then de-rolled. In the method for producing a grain-oriented silicon steel sheet by a series of steps of performing charcoal / primary recrystallization annealing, then applying an annealing separator to the steel sheet surface and then applying finish annealing, in advance of the slab heating prior to the hot rolling, A method for producing a grain-oriented silicon steel sheet having an excellent surface property, which comprises applying a carbon-containing substance and a carbonate of an alkali metal or an alkaline earth metal on the surface of a slab, and then heating. ).

The detailed investigations and experimental results by the inventors who arrived at the present invention will be described below. C: 0.07wt
%, Si: 3.3 wt%, Mn: 0.07 wt%, Se: 0.02 wt%, the balance is a steel slab with a substantial Fe composition, at an ultrahigh temperature of 1400 ° C or higher in an atmosphere with an oxygen concentration of 1%. After being heated to 0, it was subjected to hot rough rolling and then finish rolling to obtain a hot rolled sheet having a sheet thickness of 2.0 mm. Here, the surface of the slab after heating, the surface of the roughly rolled sheet bar, and the surface of the hot rolled sheet were observed in detail. As a result, it was found that there was a close relationship between the surface crack initiation site and the surface phase structure in the hot rolled sheet. That is, it was found that in the slab heating performed prior to the hot rolling, the crystal grains coarsened in the decarburized layer portion generated on the surface, which became the starting point of cracks in the finish rolling.

Therefore, in order to prevent surface decarburization during slab heating, carbon (average particle size 5
mm powder) and CaCO ₃ in the proportions of 90 wt% and 10 wt% respectively, and then this mixed powder is dispersed in water and spray-applied at a coating amount of 30 g / m ² and then a slab for 30 minutes at 1440 ° C. I tried heating. When the slab structure after heating was observed, it was found that decarburization was suppressed and further carburization was performed. Along with this, it was possible to secure the refinement of the surface structure. A slab cross section according to FIG. 1 is shown by a metallographic photograph.

Next, as described above, carbon and carbon and CaCO ₃ are applied to the surface of the slab in advance, the slab is heated, and then hot rolling is performed to a plate thickness of 2.0 mm according to a usual method, and then 950 After hot-rolled sheet annealing at 1 ° C for 1 minute, primary cold rolling was performed to a sheet thickness of 1.5 mm, and then intermediate annealing at 1050 ° C for 1 minute was sandwiched to obtain a final sheet thickness of 0.2 mm. After that, 840 ℃, 2 minutes primary recrystallization annealing, and then apply annealing separator,
A final product plate obtained by performing secondary recrystallization annealing for a time was obtained. The surface appearance and magnetic properties of this final product plate were investigated.
For comparison, we also examined the case where carbon and CaCO ₃ were not applied to the slab surface. These results are shown in Table 1.
Shown in.

[0017]

[Table 1]

From FIG. 1, it was found that by coating carbon and CaCO ₃ , surface defects were reduced and magnetic characteristics were equal to or higher than those of the comparative material which was not coated. Further, although it is not always necessary to use a carburizing accelerator, it was found that the coating of the accelerator requires less carbon. In addition, the carburizing accelerator is changed from CaCO ₃ to Na ₂ CO ₃ or K ₂ CO.
Similar experiments were conducted using ₃ or BaCO ₃ , SrCO ₃ or Li ₂ CO ₃ , and any of these could carburize the slab surface and suppress grain growth during slab heating.

[0019]

The silicon-containing steel which is the starting material of the present invention,
Although any of the conventionally known component compositions are suitable, the representative compositions are as follows. C: 0.01 to 0.10 wt% C is a component useful not only for making the structure uniform and fine during hot rolling and cold rolling but also for developing Goss-oriented crystal grains, and addition of at least 0.01 wt% is preferable. However 0.10 wt
%, The Goss orientation is rather disordered, so the upper limit is preferably about 0.10 wt%. Si: 2.0-4.5 wt% Si increases the resistivity of the steel sheet and effectively contributes to the reduction of iron loss, but if it exceeds 4.5 wt%, the cold ductility is impaired, while 2.0 wt%
If the content is less than%, not only the specific resistance decreases, but also the crystal orientation is randomized by α-γ transformation during the final high temperature annealing performed for secondary recrystallization and purification, and the iron loss improving effect is sufficient. Therefore, the Si content is preferably 2.0 to 4.5 wt%. Mn: 0.02 to 0.12wt% Mn requires at least about 0.02wt% to prevent hot embrittlement, but if it is too much, the magnetic properties deteriorate, so the upper limit should be set to about 0.12wt%. preferable.

As the inhibitor, so-called MnS, MnS
There are e type and AlN type. In case of MnS, MnSe system, S, Se
1 or 2 of the above: 0.005 to 0.06 wt% S and Se are both useful components as inhibitors for controlling the secondary recrystallization of grain-oriented silicon steel sheets. From the viewpoint of securing such suppression power, at least about 0.005 wt% is required, but if it exceeds 0.06 wt%, its effect will be impaired, so the lower and upper limits are 0.005 wt% and 0.06 wt%, respectively.
It is preferably about the same.

In the case of AlN system, Al: 0.005 to 0.10 wt%, N: 0.004 to 0.015 wt% Al and N are the secondary recrystallisation of grain-oriented silicon steel sheets as in the case of MnS and MnSe systems described above. It is a useful component as an inhibitor that regulates. From the viewpoint of securing such restraint power,
At least Al: 0.005 wt% and N: 0.004 wt% are required, but if Al: 0.10 wt% and N: 0.015 wt% are exceeded, the effect will be impaired, so the lower and upper limits are Al: 0.005.
.About.0.10 wt% and N: 0.004 to 0.015 wt% are preferable. The above-mentioned MnS, MnSe and AlN systems can be used together.

As the inhibitor component, S and S described above are used.
e, Al, Cu, Sn, Cr, Ge, Sb, Mo, Te, Bi and P
Etc. are advantageously suited, so that a small amount can be contained together. The preferred addition ranges of the above components are Cu, Sn, Cr: 0.01 to 0.15 wt%, Ge, Sb, Mo, T, respectively.
e, Bi: 0.005 to 0.1 wt%, P: 0.01 to 0.2 wt%, and each of these inhibitor components can be used alone or in combination.

The slab is intended to be continuously cast, or slab crushed from an ingot, but it goes without saying that slab re-pressed in lump after continuous casting is also included in the target. Nor.

In the present invention, prior to heating the slab, carbon or carbon and SrCO ₃ , L are added to the surface of the slab.
It is essential to apply one or more selected from i ₂ CO ₃ , K ₂ CO ₃ , CaCO ₃ , Na ₂ CO ₃ and BaCO ₃ .
These coatings suppress decarburization of the slab surface during heating, and further positively carburize the surface. These can prevent the occurrence of surface cracks, which in turn can prevent the occurrence of surface defects.

Examples of the carbon-containing substance include graphite, carbon black, graphite, coke, organic resin, petroleum coke, organic resin, and charcoal, and liquid or powdery particles having a particle size of about 1 μm to 0.5 mm are preferable. However, it may be a lump.

Further, the first application of only the carbon-containing substance
In one invention, the reaction rate between carbon and steel is slow, and it is
The amount of carbon lost is a little higher. Therefore, the second invention
Then, in addition to carbon, alkali metal as a carburizing accelerator
Alternatively, apply an alkaline earth metal carbonate. Carbonate
But CaCO₃， K₂CO₃, Li₂CO₃, SrCO₃, Na₂CO₃And BaCO
₃One or two or more selected from the above are preferable.
CaCO₃， K₂CO₃, Li₂CO ₃, SrCO₃, Na₂CO₃And BaCO₃Is
Both have catalytic action when carbon reacts with steel,
By applying these, carburization is promoted. Note that
Carbonates other than these do not accelerate the reaction too much.
However, it is expensive.

The coating amount of carbon is 10 to 10 per steel plate surface.
The amount of carbonate is preferably about 1000 g / m ^2, and the amount of carbonate applied is preferably about 1 to 100 g / m ² per steel plate surface. When one or more coating materials selected from the above-mentioned carbon and carbonates of alkali metals or alkaline earth metals are mixed and applied, the mixing ratio is such that the coating amount described above is satisfied. The ratio may be set, and specifically, it is preferably about 1 to 20 wt%.

Specific coating methods include spray coating and roll coating. When carbon, CaCO ₃ , NaCO ₃ and BaCO ₃ are in powder form, the dispersion medium is water, alcohol or the like. There is.

The application time of the carbon and the carburizing accelerator is before charging the slab into the induction heating furnace for heating. Further, when heating in an induction heating furnace after passing through a gas furnace, it is desirable to apply carbon and a carburizing accelerator before charging into the gas furnace, but it may be before charging into the induction heating furnace. . In addition, if it is applied before charging in a gas furnace, and if sufficient carburization is carried out in the gas furnace, the residual carbon that is no longer needed and the carburizing accelerator are used with high-pressure water before charging the induction heating furnace. It can also be removed.

After the coated slab is heated, it is hot-rolled, hot-rolled sheet is annealed if necessary, and then cold-rolled once or twice with an intermediate anneal to obtain the final sheet thickness. Obtain a cold rolled sheet. After the final cold rolling, decarburization annealing is performed, an annealing separator is applied to the surface of the steel sheet, and then finish annealing is performed. Thereafter, an insulating coating, preferably an insulating coating which also gives tension, is applied to obtain a product.

[0031]

【Example】

Example 1 A width of 1000 was obtained by continuous casting from molten steel having the components shown in Table 2.
A slab having a size of mm and a thickness of 230 mm was produced.

[0032]

[Table 2]

On the surface of this slab, carbon (charcoal grains)
After coating a mixture with Na ₂ CO ₃ (mixing ratio 1: 9) at 50 g / m ² by a roll coating method, use a normal gas heating furnace for 1200
After heating to ℃ and holding for 30 minutes, immediately put it in the electromagnetic induction heating furnace and raise the temperature to 1420 ℃ in 50 minutes,
Soaked for minutes. Next, the slab was extracted from the induction heating furnace and subjected to rough rolling to form a sheet bar having a thickness of 40 mm, and then a finishing tandem mill was used to form a hot rolled steel sheet having a thickness of 3.0 mm. After that, the hot rolled steel sheet was pickled, first cold rolled to a thickness of 1.8 mm, then subjected to intermediate annealing at 1150 ° C. for 2 minutes, and then secondary cold rolled to a product sheet thickness of 0.30 mm. Then 830
After decarburization annealing for 3 minutes at ℃, apply an annealing separator containing MgO as the main component, then finish annealing after finishing annealing at 1200 ℃ for 3.5 hours for the purpose of secondary recrystallization and purification. Made as a product. Table 3 shows the results of examining the surface defects and the magnetic properties of the product thus obtained. For comparison, Table 3 also shows an example in which the mixture of carbon and Na ₂ CO ₃ was not applied to the slab surface.

[0034]

[Table 3]

As is apparent from the table, the surface appearance is improved in the conforming example in which carbon and the carburizing accelerator are applied.

Example 2 From the molten steel having the components shown in Table 4, a width of 1200 m was obtained by the continuous casting method.
A slab with a size of m and a thickness of 200 mm was produced.

[0037]

[Table 4]

A mixture of carbon (petroleum coke) and BaCO ₃ (mixing ratio 2: 8) was coated on the surface of this slab at a rate of 300 g / m ² by a spray coating method and then heated to 1200 ° C. in a normal gas heating furnace. After heating and holding for 30 minutes, immediately put it in the electromagnetic induction heating furnace and raise the temperature to 1380 ° C in 30 minutes,
It was soaked at 80 ° C for 15 minutes. Next, the slab was extracted from the induction heating furnace and subjected to rough rolling to form a sheet bar having a thickness of 30 mm, and then a finishing tandem mill was used to form a hot rolled steel sheet having a thickness of 2.6 mm. After that, the hot rolled steel sheet is pickled and the thickness is reduced by primary cold rolling.
After it was made 1.6 mm, it was subjected to intermediate annealing at 950 ° C for 3 minutes, and was further cold-rolled to a product plate thickness of 0.27 mm. After decarburization annealing at 840 ° C for 3 minutes, apply an annealing separator containing MgO as the main component, and then perform a finishing annealing process of 5 hours at 1180 ° C for the purpose of secondary recrystallization and purification. After that, it became the final product. Table 5 shows the results of examining the surface defects and the magnetic properties of the product thus obtained. For comparison, Table 5 also shows an example in which the mixture of carbon and BaCO ₃ was not applied to the surface of the slab.

[0039]

[Table 5]

As is clear from the table, the surface appearance is improved in the examples in which carbon and the carburizing accelerator are applied.

Example 3 A molten steel having the components shown in Table 6 was used to obtain a width of 1000 by continuous casting.
A slab having a size of mm and a thickness of 230 mm was produced.

[0042]

[Table 6]

The surface of this slab is carbon (coke)
After coating the mixture of CaCO ₃ and CaCO ₃ (mixing ratio 1: 9) at 500 g / m ² by the roll coating method, in a normal gas heating furnace
After heating to 1200 ° C and holding for 30 minutes, immediately put it in an electromagnetic induction heating furnace and raise the temperature to 1440 ° C in 50 minutes.
Heat soaked for 15 minutes. Then, the slab was extracted from the induction heating furnace and subjected to rough rolling to obtain a sheet bar having a thickness of 40 mm,
A hot rolled steel sheet with a thickness of 2.0 mm was produced using a finishing tandem mill. After that, the hot-rolled steel sheet is pickled, and the thickness is 0.9 mm by primary cold rolling.
Then, intermediate annealing was performed at 1070 ° C. for 1 minute, and secondary cold rolling was performed to finish the product sheet thickness to 0.20 mm. Then 8
After performing decarburization annealing at 20 ℃ for 3 minutes, apply an annealing separator containing MgO as the main component, then finish annealing at 1210 ℃ for 3 hours for the purpose of secondary recrystallization and purification. Made as a product. Table 7 shows the results of examining the surface defects and the magnetic properties of the product thus obtained. For comparison, Table 7 also shows an example in which the mixture of carbon and CaCO ₃ was not applied to the slab surface.

[0044]

[Table 7]

As is clear from the table, the surface appearance is improved in the examples by applying carbon and the carburizing accelerator.

Example 4 A molten steel having the components shown in Table 8 was used to obtain a width of 1200 by continuous casting.
A slab having a size of mm and a thickness of 230 mm was produced.

[0047]

[Table 8]

A mixture of carbon (graphite) and an alkali metal carbonate (mixing ratio 1:
9) was applied at 300 g / m ² by the spray method, then heated to 1200 ° C in a normal gas heating furnace and held for 30 minutes, then immediately charged into an electromagnetic induction heating furnace and heated to 1440 ° C in 50 minutes. The temperature was raised and soaked at 1440 ° C. for 15 minutes. Then, the slab was extracted from the induction heating furnace and subjected to rough rolling to obtain a sheet bar having a thickness of 40 mm, and then a finishing tandem mill to obtain a hot rolled steel sheet having a thickness of 2.0 mm. After that, the hot rolled steel sheet was pickled, subjected to primary cold rolling to have a thickness of 1.0 mm, then subjected to intermediate annealing at 1000 ° C. for 1 minute, and further subjected to secondary cold rolling to a product sheet thickness of 0.20 mm. After decarburization annealing at 820 ℃ for 2 minutes,
After applying an annealing separator containing O 2 as a main component, a final annealing process was performed at 1180 ° C. for 4 hours for the purpose of secondary recrystallization and purification to obtain a final product. Table 9 shows the results of examining surface defects and magnetic properties of the thus obtained product.
For comparison, Table 9 also shows an example in which carbon was not applied to the slab surface.

[0049]

[Table 9]

As is apparent from the table, the surface appearance is improved in the examples by applying carbon or carbon and a carburizing accelerator.

[0051]

As described above, according to the present invention, it is possible to improve the surface appearance of the grain-oriented silicon steel sheet and manufacture a product having magnetic characteristics equal to or higher than those of conventional materials.

[Brief description of drawings]

FIG. 1 is a micrograph showing a metal structure of a cross section of a silicon steel plate.

Claims (2)

[Claims] 1. After heating a silicon steel slab, it is hot-rolled and then cold-rolled once or twice with intermediate annealing to obtain a final plate thickness, followed by decarburization and primary re-rolling. In the method for producing a grain-oriented silicon steel sheet by a series of steps of performing crystal annealing, then applying an annealing separator to the steel sheet surface and then applying finish annealing, during slab heating prior to the hot rolling, the surface of the slab is previously prepared. A method for manufacturing a grain-oriented silicon steel sheet having excellent surface properties, which comprises applying a substance containing carbon and then heating it. 2. After heating a silicon steel slab, it is hot-rolled and then cold-rolled once or twice with intermediate annealing to obtain a final plate thickness, followed by decarburization and primary re-rolling. In the method for producing a grain-oriented silicon steel sheet by a series of steps of performing crystal annealing, then applying an annealing separator to the steel sheet surface and then applying finish annealing, during slab heating prior to the hot rolling, the surface of the slab is previously prepared. A method for producing a grain-oriented silicon steel sheet having an excellent surface property, which comprises applying a carbon-containing substance and an alkali metal or alkaline earth metal carbonate and then heating.