JPH07166240A - Production of ultrahigh magnetic flux density grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To stably obtain a product high in magnetic flux density, at the time of producing a grain oriented silicon steel sheet from molten steel having a specified componental compsn., by regulating the cooling rate after the completion of hot rolling to a one slower than that in the conventional method. CONSTITUTION:Molten steel having a compsn. contg., as fundamental components, by weight, 0.03 to 0.15% C, 2.5 to 4.0% Si, 0.02 to 0.30% Mn, 0.05 to 0.040% S, 0.010 to 0.065% acid soluble Al, 0.0030 to 0.0150% N and 0.0005 to 0.05% Bi, and the balance Fe with inevitable impurities is prepd. This molten steel is cast and is successively subjected to hot rolling, annealing, cold rolling, decarburizing annealing, application of a separation agent and secondary recrystallization finish annealing to produce a grain-oriented silicon steel sheet. At that time, in the hot rolling stage, the cooling rate after the completion of the hot rolling is regulated to a one slower by 70 deg.C than that in water cooling and is subjected to cooling treatment milder than the conventional one. Thus, the grain-oriented silicon steel sheet extremely high in magnetic flux density even if the range of the hot rolled sheet annealing temp. is widely taken can stably be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrahigh magnetic flux density unidirectional electrical steel sheet having a highly developed {110} <001> orientation, that is, Goss orientation, which is used for an iron core of a transformer or the like.

[0002]

2. Description of the Related Art Unidirectional magnetic steel sheets are mainly used as a soft magnetic material for iron core materials of transformers and other electric equipment. The magnetic characteristics are not good in excitation characteristics and iron loss characteristics. Don't The magnetic flux density B ₈ (the magnetic flux density at a magnetic field strength of 800 A / m) is usually used as an index showing this excitation characteristic, and as an index showing the iron loss characteristic,
W _17/50 (iron loss per unit weight when magnetized to 1.7 T at 50 Hz) is used. The unidirectional electrical steel sheet undergoes secondary recrystallization in the final annealing step at a temperature of 900 ° C. or higher in the final stage of the manufacturing process, and the steel sheet surface has {11
0} plane, so-called Go having a <001> axis in the rolling direction
It has been obtained by developing ss tissue. Among them, a magnetic flux density B ₈ having an excellent excitation characteristic of 1.88 T or more is called a high magnetic flux density unidirectional electrical steel sheet.

As a typical method for producing a high magnetic flux density grain-oriented electrical steel sheet, Japanese Patent Publication No. 40-15644 and Japanese Patent Publication No. 51-13469 can be cited. It can be said that the high magnetic flux density unidirectional electrical steel sheets currently produced on a global scale are produced based on the above two patents. However, the magnetic flux density B _{8 of the} product based on the above-mentioned patent is about 1.88T to at most 1.95T, which is only about 95% of the saturation magnetic flux density 2.03T of 3% Si steel.
However, in recent years, social demands for energy saving and resource saving have become more and more severe, and demands for reducing iron loss and improving magnetization characteristics of unidirectional electrical steel sheets have also become fierce.

On the other hand, technically, as a technique for reducing iron loss, a magnetic domain control technique such as laser irradiation is disclosed in JP-B-58-5968.
This method is established by Japanese Patent Publication No. 57-2252 and Japanese Patent Publication No. 57-2252. In this method, the requirement for further higher magnetic flux density is becoming stronger as a condition for reducing iron loss. That is, the magnetic flux density B _{8 of} the conventional high magnetic flux density unidirectional electrical steel sheet
It is the current situation that the appearance of a means to bring the object closer to the ideal azimuth is awaited.

As a means for achieving this goal, the present inventors have disclosed a method of adding a carbonate-containing material to the molten steel of a conventional Al-containing high magnetic flux density unidirectional electrical steel sheet in Japanese Patent Publication No. 57-1565. Proposed. However, although this method is feasible in the laboratory, it is not practiced on an industrial scale. Further, the present applicant has proposed a temperature gradient annealing method in Japanese Patent Publication No. 58-50295. With this method, a product having a magnetic flux density B ₈ of 1.95 T or more can be stably obtained for the first time. However, when this method is carried out with a factory-sized coil foam, heating from one end of the coil and cooling at the other end to create a temperature gradient entails a very high thermal energy loss, which is a major problem for industrial production. It was full of.

Therefore, the inventors of the present invention have proposed a method of increasing the magnetic flux density by industrial means to a very high level from the conventional high magnetic flux density unidirectional electrical steel sheet level to the ultrahigh magnetic flux density unidirectional electrical steel sheet level. -240702, Japanese Patent Application No. 4-2
No. 40701, etc. By this method, the super high magnetic flux density unidirectional electrical steel sheet became relatively stable for the first time, but when the present inventors examined the manufacturing conditions thereafter, it was found that there was a problem in some cases. . For example, it has been found that secondary recrystallization failure may occur unless the hot-rolled sheet annealing temperature is strictly controlled. Therefore, there has been a demand for establishment of a method for extremely stably manufacturing this ultra-high magnetic flux density grain-oriented electrical steel sheet.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to avoid such problems and to manufacture an ultrahigh magnetic flux density grain-oriented electrical steel sheet having an extremely high magnetic flux density in an extremely stable manner. .

[0008]

The features of the present invention are as follows. 1) By weight, C: 0.03 to 0.15%, Si: 2.5
~ 4.0%, Mn: 0.02-0.30%, S: 0.0
05-0.040%, acid-soluble Al: 0.010-0.
065%, N: 0.0030 to 0.0150%, Bi:
A step of casting a molten steel containing 0.0005 to 0.05% as a basic component and containing unavoidable impurities and the balance being substantially Fe, a step of hot rolling, a step of high temperature annealing before the final cold rolling, A step of performing cold rolling once or more including a final strong cold rolling with a rolling reduction of 65 to 95%, or two or more times of intermediate rolling, followed by decarburization annealing, a step of applying an annealing separator, and further secondary re-rolling. In the method for producing a unidirectional electrical steel sheet comprising a step of performing crystal finish annealing, the cooling rate of the steel sheet after hot rolling in the hot rolling step is slower than that of water cooling at 70 ° C. Manufacturing method of density unidirectional electrical steel sheet. 2) The method for producing an ultrahigh magnetic flux density grain-oriented electrical steel sheet according to 1), characterized in that Sn: 0.05 to 0.50% is contained. 3) Cu: 0.01-0.10% is contained, The manufacturing method of the ultra high magnetic flux density grain-oriented electrical steel sheet of 2) characterized by the above-mentioned.

The details of the present invention will be described below. The present inventor has conducted various studies to stably produce a so-called ultra-high magnetic flux density unidirectional electrical steel sheet having a magnetic flux density B ₈ of 1.95 T or more, but aluminum nitride is the main inhibitor. By adding Bi to the material for the grain-oriented electrical steel sheet, the magnetic flux density B8 of the currently marketed high-oriented grain-oriented electrical steel sheet is significantly higher than B ₈ = 1.93T or more than 1.95T or 2T. To obtain an ultra-high magnetic flux density unidirectional electrical steel sheet having a high magnetic flux density and to carry out a steel sheet coiling temperature of 550 to 650 ° C at 500 ° C after completion of hot rolling, which is carried out in the production of ordinary high magnetic flux density unidirectional electrical steel sheet. By controlling the following, we succeeded in obtaining a more stable ultrahigh magnetic flux density grain-oriented electrical steel sheet.

The reasons for limiting the component composition of the present invention will be described.
If C is less than 0.03%, abnormal grain growth occurs during slab reheating prior to hot rolling, and secondary recrystallization defects called linear fine grains occur in the product, which is not preferable. On the other hand, 0.15%
If it exceeds the above range, decarburization in the decarburization annealing process is likely to be incomplete, which causes magnetic aging in the product, which is not preferable. Si
If less than 2.5%, the eddy current loss of the product increases, and if it exceeds 4.0%, cold rolling at room temperature becomes difficult, and both are not preferable. The above range is required for Mn and S to act as auxiliary inhibitors by forming manganese sulfide.

Acid-soluble Al is a main inhibitor constituent element for the production of high magnetic flux density unidirectional electrical steel sheet,
If it is less than 0.010%, the amount is insufficient and the inhibitor strength is insufficient. On the other hand, if it exceeds 0.065%, the precipitated aluminum nitride becomes coarse and, as a result, the inhibitor strength is lowered, which is not preferable. N, like the acid-soluble Al, is a main inhibitor constituent element, and if it deviates from the above range, it destroys the optimum state of the inhibitor, which is not preferable. Bi is
It is an essential element for the production of ultra-high magnetic flux density unidirectional electrical steel sheet, and the addition content is effectively in the range of 0.0005 to 0.05%. If it is less than 0.0005%, the improvement of the magnetic flux density is slight, and if it exceeds 0.05%, the effect of improving the magnetic flux density saturates and cracks occur at the edges of the hot-rolled sheet. limit.

Further, Sn is an element that stabilizes the secondary recrystallization of a thin product, and also has an effect of reducing the secondary recrystallization grain size. Therefore, it is necessary to add 0.05% or more. be able to. In that case, even if it exceeds 0.50%, its action and effect are saturated, so from the viewpoint of cost increase, it is limited to 0.50% or less. Cu is effective as a film-improving element of the Sn-added material, and if it is less than 0.01%, the effect is small, and if it exceeds 0.10%, the magnetic flux density of the product decreases, so the range of 0.01 to 0.10% Can be added at.

Next, the manufacturing process conditions will be described.
The raw material for ultra-high magnetic flux density unidirectional electrical steel sheet having the components adjusted as described above can be used as the raw material of the present invention even when any ordinary melting method or casting method is used.

Next, this raw material for electromagnetic steel sheets is rolled into a hot rolled coil by ordinary hot rolling. This hot rolling step is a feature of the present invention. In a high magnetic flux density unidirectional electrical steel sheet manufacturing method using AlN or MnS, which is a commonly known inhibitor, as a main inhibitor, it is general to cool the steel sheet after hot rolling as fast as possible mainly to suppress precipitation of AlN. Japanese Patent Publication No. 51-2290 discloses a process of quenching in water immediately after the hot rolling is completed.

However, when Bi is contained as the inhibitor of the present invention, a secondary recrystallization defect may occur depending on the conditions when the hot-rolled sheet subjected to such quenching is subjected to a post-process. It has been found. Therefore, as a result of studying the optimum hot rolling conditions in the hot rolled sheet, it was found that the defects due to the hot rolled sheet annealing conditions are completely alleviated by performing the cooling rate after the hot rolling at a rate slower than 70 ° C water cooling. Invented

Although the mechanism by which the problem due to the annealing conditions of the hot rolled sheet could be solved by making the cooling rate after the hot rolling of the present invention slower than that of water cooling at 70 ° C. is not necessarily clear, the present inventors presume as follows. ing. One is that Bi has a very low solubility at temperatures such as 1200 ° C or lower, so its dispersion state cannot be controlled by hot-rolled sheet annealing, and the heat for controlling the dispersion state of known inhibitors such as AlN and MnS cannot be controlled. It is considered that this is because the rolled sheet annealing conditions cannot always be taken. One reason is that when Bi is contained, Bi also affects the precipitation of AlN and MnS, and it is thought that the quenching treatment after the hot rolling cannot maintain the optimum state of the inhibitor in the subsequent hot rolled sheet annealing.

Subsequently, final sheet thickness is obtained by one-stage cold rolling or multiple-stage cold rolling including intermediate annealing. However, since a high magnetic flux density unidirectional electrical steel sheet is obtained, the final cold rolling reduction rate (1 In the case of cold rolling of the stage, the rolling reduction) requires a strong reduction of 65 to 95%. The rolling ratio of the stages other than the final rolling need not be specified.

Before the final cold rolling, annealing is performed to control the inhibitor for suppressing grain growth. The cold-rolled sheet rolled to the final product sheet thickness is subsequently decarburized and annealed by a usual method. The conditions of decarburization annealing are not particularly specified, but preferably 700 to 90.
It is advisable to carry out in the temperature range of 0 ° C. for 30 seconds to 30 minutes in wet hydrogen or a mixed atmosphere of hydrogen and nitrogen.

On the surface of the steel sheet after decarburization annealing, in order to prevent seizure and glass film formation in the secondary recrystallization annealing,
An annealing separator having a usual composition is applied by a usual method. The secondary recrystallization annealing is performed at a temperature of 1000 ° C. or higher for 5 hours or longer in hydrogen or nitrogen or a mixed atmosphere thereof. Subsequently, after removing the excess annealing separator, continuous annealing for straightening the coil winding is performed, and at the same time, an insulating coating is applied and baked. Further, magnetic domain subdivision processing such as laser irradiation is performed if necessary. The method of subdividing the magnetic domains is not particularly limited.

[0020]

【Example】

(Example 1) C: 0.09%, Si: 3.05%, M
n: 0.07%, S: 0.023%, acid-soluble Al:
0.026%, N: 0.008%, Bi: 0.007%
The silicon steel containing was melted. After casting into billet 1350
Immediately after extraction, the product was hot-rolled to a plate thickness of 2.3 mm and the cooling conditions after hot-rolling were changed to three levels of 20 ° C. water cooling, 100 ° C. water cooling, and air cooling. Hot rolled sheet at 1050 ℃, 1150
It was annealed at two temperature levels of 0 ° C and immediately quenched in water at 100 ° C. Then, after pickling, the aging treatment at 250 ° C. was repeated 5 times to cool it to 0.30 mm. 850 ℃ continuously
Then, decarburization annealing was performed, and an annealing separator having MgO as a main component was applied, and then secondary recrystallization finish annealing at 1200 ° C. was performed. Two
Table 1 shows the next recrystallization state and the magnetic measurement results of the obtained products.
Shown in.

[0021]

[Table 1]

As is clear from Table 1, in the water cooling of 20 ° C. of the comparative example, the secondary recrystallization rate is as low as 30% and the magnetic flux density B ₈ is also extremely low as 1.67 T under the hot rolled sheet annealing temperature of 1150 ° C. On the other hand, in the case of slow cooling such as water cooling with a cooling rate of 100 ° C., the secondary recrystallization rate is 100% even when the hot-rolled sheet annealing temperature is 1050 ° C. or even at a high temperature of 1150 ° C.
Then, the magnetic flux density B ₈ of the obtained product is 1.98 to 2.01.
T is extremely high.

(Example 2) C: 0.09%, Si: 3.
25%, Mn: 0.07%, S: 0.025%, acid-soluble Al: 0.026%, N: 0.008%, Bi: 0.
Silicon steel containing 007% and Sn: 0.12% was melted. After casting into a steel slab, it was heated to 1350 ° C, hot rolled to a thickness of 2.3mm immediately after extraction, and the cooling conditions after hot rolling were changed to three levels: 20 ° C water cooling, 100 ° C water cooling, and air cooling. .
The hot-rolled sheet was annealed at two levels of temperature of 1050 ° C and 1150 ° C and immediately quenched in water of 100 ° C. Next, after pickling, the aging treatment at 250 ° C. was repeated 5 times while cooling to 0.23 mm. Then, decarburization annealing is performed at 850 ° C, and M
After applying the annealing separating agent containing gO as a main component, the temperature is kept at 1200 ° C for 2
Next, recrystallization finish annealing was performed. Table 2 shows the secondary recrystallization state and the magnetic measurement result of the obtained product.

[0024]

[Table 2]

As is clear from Table 2, the secondary recrystallization rate is as low as 20% and the magnetic flux density B ₈ is also extremely low as 1.58 T under the processing conditions of the hot-rolled sheet annealing temperature of 1150 ° C. in the comparative example of 20 ° C. water cooling. On the other hand, in the case of slow cooling such as water cooling with a cooling rate of 100 ° C., the secondary recrystallization rate is 100% even when the hot-rolled sheet annealing temperature is 1050 ° C. or even at a high temperature of 1150 ° C.
Then, the magnetic flux density B ₈ of the obtained product is also 1.98 to 2.00.
T is extremely high.

(Example 3) C: 0.08%, Si: 3.
30%, Mn: 0.08%, S: 0.026%, acid-soluble Al: 0.026%, N: 0.008%, Bi: 0.
Silicon steel containing 010%, Sn: 0.12%, Cu: 0.05% was melted. After casting into a steel slab, it was heated to 1350 ° C., hot rolled immediately after extraction to a thickness of 2.0 mm, and the cooling conditions after hot rolling were changed to 3 levels: 20 ° C. water cooling, 100 ° C. water cooling, and air cooling. . Hot-rolled sheet at 1050 ℃ and 1150 ℃ 2
It was annealed at a standard temperature and immediately quenched in water at 100 ° C. Next, after pickling, the aging treatment at 250 ° C. was repeated 5 times while cooling to 0.23 mm. Subsequently, decarburization annealing was performed at 850 ° C., an annealing separator containing MgO as a main component was applied, and then secondary recrystallization finish annealing was performed at 1200 ° C. Table 3 shows the secondary recrystallization state and the magnetic measurement result of the obtained product.

[0027]

[Table 3]

As is clear from Table 3, in the comparative example of 20 ° C. water cooling, the secondary recrystallization rate was as low as 30% and the magnetic flux density B ₈ was also extremely low as 1.63 T under the treatment conditions of the hot rolled sheet annealing temperature of 1150 ° C. On the other hand, in the case of slow cooling such as water cooling with a cooling rate of 100 ° C., the secondary recrystallization rate is 100% even when the hot-rolled sheet annealing temperature is 1050 ° C. or even at a high temperature of 1150 ° C.
Then, the magnetic flux density B ₈ of the obtained product is 1.98 to 2.01.
T is extremely high.

[0029]

The method of slow cooling the hot rolling cooling rate according to the present invention as compared with the conventional method can stably obtain a product having extremely high magnetic flux density even if the hot rolling sheet annealing temperature is wide, and is industrially very valuable. Highly beneficial.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C22C 38/06 38/16

Claims (3)

[Claims] 1. By weight, C: 0.03 to 0.15%, Si: 2.5 to 4.0%, Mn: 0.02 to 0.30%, S: 0.005 to 0.040. %, Acid-soluble Al: 0.010 to 0.065%, N: 0.0030 to 0.0150%, Bi: 0.0005 to 0.05% as a basic component, including unavoidable impurities, and the balance being substantially F
Step of casting molten steel consisting of e, step of hot rolling, step of high temperature annealing before final cold rolling, reduction ratio 65 to 95
% Cold-rolling at least once including the final strong cold rolling or at least two times through intermediate annealing, followed by decarburizing annealing, applying an annealing separator, and further performing secondary recrystallization finishing annealing. In the method for producing a unidirectional electrical steel sheet comprising the steps, an ultrahigh magnetic flux density unidirectional electromagnetic field is characterized in that in the hot rolling step, the cooling rate of the steel sheet after the hot rolling is slower than that of water cooling at 70 ° C. Steel plate manufacturing method. 2. The method for producing an ultrahigh magnetic flux density grain-oriented electrical steel sheet according to claim 1, wherein Sn: 0.05 to 0.50% is contained. 3. The method for producing an ultra-high magnetic flux density grain-oriented electrical steel sheet according to claim 2, wherein Cu: 0.01 to 0.10% is contained.