JPH11106827A - Production of mirror finished grain oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an industrially and inexpensively producing a mirror finished grain oriented silicon steel sheet excellent in magnetic properties. SOLUTION: In the method for producing a mirror finished grain oriented silicon steel sheet in which the final cold rolled sheet of a grain-oriented silicon steel sheet contg., by weight, 0.03 to 0.10% C and 3.0 to 4.0% Si is subjected to decarburizing annealing in an atmospheric gas in which the oxidizing degree (PH2 -O/PH2 ) is regulated to 0.01 to 0.15, is coated with a separation agent for annealing essentially consisting of alumina and is subjected to finish annealing, the content of Si in a depth to 2 μm from the steel sheet surface of the cold rolled sheet is regulated to <3.0%, by which the effective reduction of the content of C is made possible even by decarburizing annealing in an atmosphere with a low oxidizing degree, and, by a low oxidized layer on the decarburized and annealed surface and the organic effect of the separation agent for annealing of alumina, the mirror finished grain oriented silicon steel sheet extremely excellent in magnetic properties can be obtd. at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of a grain-oriented electrical steel sheet mainly used as an iron core for transformers and other electric equipment. In particular, concerning the production of mirror-oriented unidirectional electrical steel sheet which achieves good iron loss characteristics at low cost by effectively introducing mirror finishing of the steel sheet surface and magnetic domain refining means, cold rolled steel sheet with good decarburization property And a method for producing the same.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is mainly used as a soft magnetic material for core materials of transformers and other electric equipment, and must have good magnetic properties such as excitation properties and iron loss properties. No. The magnetic flux density B8 (magnetic flux density at a magnetic field strength of 800 A / m) is usually used as an index indicating the excitation characteristics, and W17 / 50 (magnetized to 1.7 T at 50 Hz) as an index indicating the iron loss characteristics. (Iron loss per unit weight at the time).

[0003] The grain-oriented electrical steel sheet contains 0.8 to 4.
8%, secondary recrystallization occurs in the final annealing step at a temperature of 900 ° C. or more in the final stage of the manufacturing process. Obtained by developing tissue. Among them, those having a magnetic flux density B8 of 1.88 T or more and having excellent excitation characteristics are called high magnetic flux density unidirectional magnetic steel sheets. As a typical manufacturing method of high magnetic flux density electromagnetic steel sheet,
JP-B-40-15644, JP-B-51-1346
No. 9 and the like. High magnetic flux density unidirectional electrical steel sheets currently being produced on a worldwide scale are:
It can be said that it is produced based on the above two patents. In recent years, social demands for energy savings and resource savings have become increasingly severe, and demands for reduction of iron loss and improvement of magnetic properties of the grain-oriented electrical steel sheets have also become fierce.

In general, as the magnetic flux density B8 increases, the crystal grains of the Goss structure tend to increase. Even if B8 is increased by increasing the magnetic flux density, the 180 ° magnetic domain width increases, so that the eddy current loss increases. However, in metallurgy, expectations for further improvement in iron loss are not desired. From this viewpoint, a magnetic domain control technique such as laser irradiation is a technical technique for reducing iron loss, which is disclosed in JP-B-57-2252 and JP-B-58-596.
No. 8, JP-A-58-26405, and the like. Further, since the reduction in iron loss by the above-described method is caused by distortion introduced by laser irradiation, it cannot be used for a wound iron core transformer which requires strain relief annealing after forming into a transformer.
Thus, for example, in Japanese Patent Publication No. Sho 62-53579, Japanese Patent Publication No. Sho 63-44804, and Japanese Patent Publication No. Sho 04-48847, grooves are introduced by, for example, a gear-type roll after finish annealing, and fine grains are added by adding processing strain. A method of forming and subdividing magnetic domains is disclosed. However, the method of forming grooves on the surface of a steel sheet by machining a gear-type roll, etc., requires grinding the surface ceramic layer called the primary film (glass film) of the grain-oriented electrical steel sheet. Large, causing a problem in manufacturing cost.

On the other hand, when the movement of the domain wall of the steel sheet subjected to the domain refining treatment was observed in detail, it was found that some domain walls which did not move exist statically in the domain refined. In order to further reduce the iron loss value of grain-oriented electrical steel sheets, together with the domain refining technique according to the above method, a technique for eliminating factors that hinder the motion of the domain wall (technology for activating the domain wall)
Need to be introduced. In other words, removing the glass coating on the steel plate surface, which is a major factor that hinders the motion of the domain wall,
A method of mirroring the surface is effective. As a means,
Japanese Patent Application Laid-Open No. 64-83620 discloses a method in which a glass film is removed by acid washing or the like after finish annealing and then the surface is mirror-finished by chemical polishing or electrolytic polishing. However, methods such as chemical polishing and electrolytic polishing,
Although it is possible to process small sample materials at the laboratory level, there are significant problems in the industrial scale, such as the control of chemical solution concentration, temperature control, and the provision of pollution equipment. Since the production cost is increased due to the addition of the various steps, it has not yet been put to practical use.

On the other hand, the applicant of the present invention has disclosed, for example,
JP-A-03-0352 and JP-A-6-093335 have developed a method for producing a mirror-finished steel sheet surface on an industrial scale at low cost. After controlling the amount of oxygen by controlling the atmosphere of decarburizing annealing, apply alumina as an annealing separating agent to the surface of the steel sheet and perform finish annealing to make the surface of the steel sheet mirror-finished and form a secondary recrystallization with high magnetic flux density. Is to be compatible. These techniques are suitable mainly for reducing the cost of manufacturing a magnetic domain control material for a wound iron core transformer because abrasion of a gear roll or the like is small when machining is performed on a steel sheet surface for magnetic domain subdivision processing. For example, Japanese Patent Application No. 6-07
Japanese Patent No. 2718 discloses that the life of a gear roll is increased five times or more when a glass coating is not present on the steel sheet surface after finish annealing as in the related art.

[0007]

As regards the mirror finishing of a grain-oriented electrical steel sheet, the present inventors disclosed in Japanese Patent Application Laid-Open No. Hei 7-118750 that the annealing atmosphere of decarburizing annealing was controlled to a degree of oxidation that does not form Fe-based oxides. Then, disclosed is a method of achieving mirror finishing of the steel sheet surface at low cost by using alumina as an annealing separator. However, if the degree of oxidation is lowered, decarburization becomes difficult.Therefore, as a measure to simultaneously control the oxidized layer and decarburization in decarburization annealing, a method of limiting the temperature rise rate of decarburization annealing, annealing temperature, and atmosphere gas components is considered. This is disclosed in Japanese Patent Application Laid-Open No. 7-278668. However, the cold rolled sheet thickness is, for example, 0.23 m
For example, when it exceeds m, it is difficult to decarburize depending on conditions.

Accordingly, the present inventors have developed a decarburizing annealing atmosphere in a low oxidation region where no Fe-based oxide is formed.
The following experiment was performed to confirm the effect of metallurgical fluctuations before the cold rolling process on the decarburization property. A cold rolled sheet manufactured at a factory with a sheet thickness of 0.23 mm in which the tapping component and the manufacturing conditions up to the cold rolling step fluctuated was sampled and decarburized and annealed in a laboratory. The component of the cold rolled sheet has a C content of 0.048 to 0.054%,
The amount of Si varied from 3.15 to 3.24%. After the cold-rolled sheet was sheared to a predetermined size, the oil was washed with alternative Freon and decarburized and annealed. The conditions of the decarburizing annealing were as follows: a heating rate of 28 ° C./second, a soaking temperature of 840 ° C., a soaking time of 90 seconds, and an annealing atmosphere of N ₂ : 25% + H ₂ : 75% mixed humidified gas. The dew point was changed in the range of 30-75C at 5C intervals. Oxidation degree of annealing gas (PH ₂ O / PH ₂ )
FIG. 1 and FIG. 2 show the analysis results of the C content and the O content after decarburizing annealing. As shown in FIG. 1, when the degree of oxidation is 0.15 or more, all of the samples have a C content of about 10 ppm, which is good for decarburization.
As shown in FIG. 2, when the oxidation degree is 0.15 or more, the O content is 200 pp.
It can be seen that it greatly exceeds m. As described in JP-A-6-93335, such a material impairs the mirror smoothness of the product plate and deteriorates the magnetic properties. Therefore, the oxidation degree of the decarburizing annealing must be 0.15 or less. . Therefore, the present inventors have paid attention to the variation in the C content after decarburization annealing when the degree of oxidation of the annealing gas is 0.15 or less. First
In the figure, for example, when the oxidation degree is 0.105, the C amount is 1
It fluctuates to about 0 to 200 ppm. Considering that the experiment was performed under the same conditions after the oil washing, it is considered that this variation in the amount of C reflects the metallurgical variation of the cold rolled sheet. Therefore, the factors of this metallurgical change were investigated.

First, considering the effect of fluctuations in the content of components in steel on decarburization, C, Si, Mn, P, S, Al, N, S
The components of n, Cr, Ti, and O were selected, and the correlation between the steel content and the C content after decarburization (C content with an oxidation degree of 0.105) was investigated. The content of each component and the amount of C were linearly approximated by the method of least squares to obtain a correlation coefficient (R ² ). Table 1 shows the results.

[0010]

[Table 1]

Although the correlation coefficient with S is as high as 0.61,
The correlation with the content of other elements was small. That is, a high correlation was not recognized between the fluctuation of the element content in the steel and the decarburization amount. Next, in order to investigate the effect of the component content of the outermost surface of the final cold-rolled sheet on the decarburization property, the fluorescent X
Line analysis was performed. The X-ray tube uses a rhodium target. The applied voltage was 50 kV (50 mA). 20mm
The measurement time was 20 seconds × 2 times using a φ Zr mask. In the same manner as in Table 1, the correlation coefficient between the fluorescent X-ray intensity of each component and the C content after decarburization annealing (C content at an oxidation degree of 0.105) was determined. The analysis was performed on both front and back sides of the cold rolled sheet, and a low value was adopted. Table 2 shows the results.

[0012]

[Table 2]

Each element showed a positive correlation, and the lower the element strength, the easier the decarburization. Among them, the element having the strongest correlation was Si, and R ² was 0.95. FIG. 3 shows the relationship between the Si intensity and the C content. Therefore, a factor that affects the decarburizing property in the decarburizing annealing in the low-oxidation atmosphere region is the Si content of the outermost surface of the cold-rolled steel sheet. It was found that the content had to be reduced.

In order to investigate the cause of the Si concentration fluctuation on the outermost surface of the cold-rolled steel sheet, GDS analysis of a decarburized material (low fluorescent X-ray intensity) and a poor decarburized material (high fluorescent X-ray intensity) was conducted. Was done. Looking at the Si profile in the depth direction, a Si-deficient layer was observed at a depth of 1.5 to 2 μm from the steel sheet surface, and the decarburized good material had lower Si on the outermost surface of the steel sheet than the poorly decarbonized material. Further, in order to confirm whether the Si-deficient layer was present before the cold rolling step, the surface section of the steel sheet immediately before the cold rolling step was analyzed by CMA. Each of these steel sheets is a steel sheet having a thickness of 2.3 mm that has been subjected to descaling treatment by pickling subsequent to hot-rolled sheet annealing. FIG. 4 shows the Si concentration mapping of CMA, and FIG. 5 shows the Si line analysis profile from the surface to the depth direction. In each case, the depth from the outermost surface of the steel plate is 1
Although a Si-deficient layer of 5 to 20 μm was observed, the poorly decarbonized material had a shallow Si-deficient layer, and the Si concentration of the outermost surface was as high as 3.1%. It was deep and the Si concentration at the outermost surface was as low as 2.8%. Therefore, it is considered that the fluctuation of the Si concentration on the outermost surface of the cold-rolled steel sheet is caused by the fluctuation of the Si-depleted layer (de-Si layer) on the outermost surface of the steel sheet before the cold-rolling step. The present invention focuses on the Si content of the outermost surface of a steel sheet of a cold-rolled sheet, and manufactures a mirror-oriented unidirectional electrical steel sheet using a cold-rolled sheet with extremely good decarburization even when the atmosphere gas oxidation degree of decarburization annealing is low. It discloses a method.

[0015]

The features of the present invention are as follows. (1) By weight%, C: 0.03 to 0.10%, Si:
The degree of oxidation (PH ₂ O / PH ₂ ) of the final cold-rolled sheet of the grain-oriented electrical steel sheet containing 3.0 to 4.0% was set to 0.
A method for producing a mirror-oriented unidirectional magnetic steel sheet, comprising performing the annealing in an atmosphere gas of not less than 01 and not more than 0.15, applying an annealing separator containing alumina as a main component, and performing finish annealing. A method for producing a mirror-oriented unidirectional electrical steel sheet having excellent magnetic properties, characterized in that the Si content at a depth from the surface to 2 μm is lower than 3.0%.

(2) C: 0.03-0.10% by weight
%, Si: 3.0 to 4.0%, a hot-rolled magnetic steel sheet is subjected to one or more cold-rolling steps after the hot-rolling sheet annealing, or without performing the hot-rolling sheet annealing. Cold rolling is performed two or more times with intermediate annealing to obtain a final sheet thickness. Subsequently, decarburizing annealing is performed in an atmosphere gas having an oxidation degree (PH ₂ O / PH ₂ ) of 0.01 to 0.15, and alumina A method for producing a mirror-oriented unidirectional electrical steel sheet having excellent magnetic properties comprising a step of applying an annealing separating agent containing as a main component and performing a finish annealing,
The conditions of annealing performed from hot rolling to final cold rolling are as follows: the soaking temperature of annealing is T ° C., the soaking time is t seconds, and the rolling reduction from the sheet thickness to be annealed to the final cold-rolled sheet thickness is R%. , (0.00
23T-1.9) t (100-R) ≧ 200 and the degree of oxidation (PH ₂ O / P) in the annealing atmosphere gas
A method for producing a mirror-oriented unidirectional electrical steel sheet having excellent magnetic properties, wherein H ₂ ) is 0.15 or more.

(3) The method for producing a mirror-oriented unidirectional magnetic steel sheet having excellent magnetic properties according to (1) or (2), wherein a magnetic domain refining treatment is performed after the finish annealing.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
It is considered that the Si-deficient layer on the surface of the cold-rolled steel sheet for improving the decarburization property is formed by a heat treatment and a pickling step before cold rolling. Then, the influence of the atmosphere gas oxidation degree of hot rolled sheet annealing and the pickling conditions on the Si deficiency layer was investigated. Si: 2.
8 to 3.4%, C: 0.05 to 0.07%, other A
A hot-rolled steel sheet having a thickness of 2.3 mm containing an inhibitor component such as l, N, or the like is heated at 1120 ° C. for 30 minutes with a surface scale attached.
Subsequently, annealing was performed at 900 ° C. for 2 minutes. Annealing atmosphere is N ₂ :
An atmosphere of 90% + H ₂ : 10% was used, and two levels were humidified at a dry gas (dew point −20 ° C., oxidation degree = 0.01) and a dew point 55 ° C. (oxidation degree = 1.84). After annealing, pickling is performed in a range of 0 to 300 seconds with a pickling solution of 80% of sulfuric acid at a liquid temperature of 80 ° C., and the difference between the result of measuring the plate thickness with a micrometer and the plate thickness before pickling is the pickling plate thickness. Weight loss. Thereafter, the sheet was cold-rolled to a sheet thickness of 0.23 mm at a rolling reduction of 90%, and the Si concentration on the outermost surface of the sheet was measured by fluorescent X-ray analysis. The cold rolled sheet is 840
Decarburization annealing was performed at 90 ° C. for 90 seconds, and the amounts of C and O before and after the annealing were analyzed. The degree of oxidation (PH ₂ O / PH ₂ ) of the decarburizing annealing is 0.
105. FIG. 6 shows that the thickness reduction of the pickled plate and the Si concentration of the outermost surface of the cold-rolled sheet (fluorescent X-ray S
i intensity). The material having an atmospheric oxidation degree of 1.84 in the hot-rolled sheet annealing had a low Si concentration and increased with a decrease in the pickling plate thickness. On the other hand, a material having a degree of oxidation of 0.01 had a small change in Si concentration. As shown in FIG. 7, the C content after the decarburizing annealing is the highest for materials having an atmospheric oxidation degree of 1.84.
The amount was low and increased after the pickling due to the decrease in plate thickness. on the other hand,
The material having an oxidation degree of 0.01 had a high C content, and the change was small even when the thickness of the pickled plate was reduced. That is, it is considered that since Si is selectively oxidized during hot-rolled sheet annealing, Si on the surface of the steel sheet is depleted, and a concentration gradient (de-Si layer) is formed by diffusion of Si to the surface. Further, it is considered that the ground iron is dissolved by the pickling after the hot-rolled sheet annealing, so that the de-Si layer is lost. Therefore, removal of S by hot-rolled sheet annealing and pickling conditions
It is considered that the i-layer fluctuates and the Si concentration on the steel sheet surface fluctuates. Further, when the Si concentration on the surface of the steel sheet is low, the formation of the SiO ₂ film in the early stage of the decarburization annealing is suppressed, and the O ₂
It is considered that the supply of CO or the release of the CO gas of the decarburized product was performed smoothly, and the decarburization property was improved. According to such a method, even if a multilayer is not formed using a special casting facility as disclosed in Japanese Patent Application Laid-Open No. 8-269560, for example, a slight de-Si layer can be utilized by a normal electromagnetic steel sheet manufacturing facility. Mirroring is possible.

Next, the components necessary for the present invention and the reasons for limiting them will be described. In the present invention, the components contained in the material are, by weight, C: 0.03 to 0.10% and Si:
3.0 to 4.0% is an essential component, and the other components are not limited. C is an open type element in the γ region, and is important for forming a recrystallization structure and texture advantageous for secondary recrystallization due to α → γ transformation or the presence of solid solution C in the steps of hot rolling to decarburizing annealing. Element. If C is 0.03% or less, α → γ transformation does not occur, which is not preferable. Further, even if it exceeds 0.10, the effect of improving the texture cannot be obtained, and even if the technique of the present invention is used, the decarburization annealing time is prolonged and the cost is increased, which is not preferable.

Si is an important element for increasing electric resistance and reducing iron loss. If the content exceeds 4.0%, the material is easily cracked during cold rolling, and cannot be rolled. On the other hand, if the content is less than 3.0%, it becomes difficult to reduce iron loss, and the decarburization property is improved without reducing the Si content on the outermost surface of the cold-rolled sheet by the deSi layer of the present invention (see FIG. 8). As a basic manufacturing method, (Al, Si) N by Komatsu et al.
Manufacturing method using as a main inhibitor (for example,
2-45285) or a production method using AlN and MnS as main inhibitors by Taguchi and Sakakura (for example, Japanese Patent Publication No. 40-15644). Acid-soluble Al combines with N to form AlN and is a main inhibitor constituent element for producing a high magnetic flux density unidirectional magnetic steel sheet. By controlling the amounts of Al and N, it is possible to adjust the inhibitor strength and obtain a sharp secondary recrystallization.

As other inhibitor constituent elements, M
n, S, Se, V, N, B, Nb, Sn, Cu, Ti,
Zr, Ta, Mo, Sn, Bi and the like can be added in combination. Next, the manufacturing process conditions will be described. The material for an ultra-high magnetic flux density unidirectional electrical steel sheet whose components are adjusted as described above can be used as the material of the present invention regardless of any ordinary melting method or ingot making method.

Next, the magnetic steel sheet material is rolled into a hot-rolled coil by ordinary hot rolling. Komatsu et al. (A
In a production method using (1, Si) N as a main inhibitor (for example, Japanese Patent Publication No. 62-45285), at a temperature of 1100 ° C. or more from the viewpoint of securing the temperature during hot rolling, and a temperature of 1280 ° C. or less at which AlN is not completely dissolved. After the heating, hot rolling is performed. AlN and MnS by Taguchi, Sakakura, etc.
Manufacturing method using as a main inhibitor (for example,
In 0-15644), hot rolling may be performed after heating at a temperature of 1300 ° C. or more at which complete solution is formed.

Subsequently, the final sheet thickness is obtained by a single cold rolling or a plurality of cold rolling including intermediate annealing. However, since a unidirectional magnetic steel sheet having a high magnetic flux density is obtained, the rolling reduction of the final cold rolling (one time) In the case of cold rolling, the rolling reduction is preferably from 65 to 95%. The rolling reduction of stages other than the final rolling need not be particularly defined. The hot-rolled sheet or the cold-rolled steel sheet for adjusting the rolling reduction controls the inhibitor such as AlN.
Anneal before final cold rolling. Annealing is performed in a temperature range of 900 to 1200 ° C. for 30 seconds to 30 minutes, and after annealing, 20 ° C./s.
It is cooled at a cooling rate of ec or more. This annealing is effective to enhance the magnetic properties of the product. During this annealing, a de-Si layer on the surface of the steel sheet, which is a requirement of the present application, is formed. Since the de-Si layer affects the quality of decarburization in low-oxidation decarburization annealing, it is necessary to control the de-Si layer prior to the final cold rolling step. De-S of about tens of μm even in the heating process of hot rolling
Although an i-layer is formed, the thickness of the slab is usually 200 mm or more. Therefore, when cold-rolled to about 0.2 to 0.3 mm, a clear Si-free layer hardly remains. Therefore usually 2-3m
It is desirable to control the Si removal layer in the hot rolled sheet annealing of about m or the intermediate annealing step of usually 1 to 2 mm. As described above, since the de-Si layer is formed by selective oxidation of Si during annealing and diffusion to the surface of Si, if the de-Si layer is also controlled in the heat treatment step before cold rolling for inhibitor control, the cost burden will increase. Few. At this time, the heat treatment cycle and the degree of oxidation of the annealing atmosphere are important. From the viewpoint of the selective oxidation of Si, if the oxidation degree (PH ₂ O / PH ₂ ) in the annealing atmosphere is less than 0.15, the selective oxidation of Si is unlikely to occur.
5 or more, preferably 0.50 or more is desirable. Further, in order to obtain a de-Si layer from the outermost surface to a depth of 2 μm from the cold rolled sheet, it is necessary to diffuse a necessary amount of Si by the thickness of the sheet to be annealed. From this viewpoint, when the calculation is performed using the data of the Si self-diffusion coefficient in Fe, when the electromagnetic steel sheet is annealed in the process from hot rolling to final cold rolling, the soaking temperature of annealing is T ° C. When the time is t seconds, and the reduction from the sheet thickness to be annealed to the final cold-rolled sheet thickness is R%, (0.0023T-
1.9) It is concluded that it is necessary to anneal in the range of t (100−R) ≧ 200.

On the other hand, when annealed with a surface scale such as a hot-rolled steel strip, since scale flaws are generated during cold rolling, descaling is performed by a chemical method such as pickling or a mechanical method such as shot blasting. Is required. At this time, since the de-Si layer formed on the surface of the steel sheet also disappears, it is necessary to control the reduction of the sheet thickness and the Si intensity in the fluorescent X-ray analysis of the cold-rolled sheet described later so that the de-Si layer is not lost. . Conditions for management may be determined in consideration of the depth of the formed de-Si layer and the method of descaling. According to this method, the descaling process is controlled so that the dissolution of the base iron is minimized, and there is also a merit of improving the yield.

The cold rolled sheet rolled to the final product thickness is subjected to primary recrystallization annealing and decarburization annealing in wet hydrogen or a mixed atmosphere of hydrogen and nitrogen for the purpose of removing carbon contained in steel. In this decarburization annealing, Fe-based oxides (Fe ₂ S
The point is that annealing is performed at an atmosphere gas oxidation degree that does not form iO ₄ , FeO, etc., and alumina is applied as an annealing separator. For example, in a temperature range of 800 ° C. to 850 ° C. in which normal decarburization annealing is performed, the degree of oxidation of the atmospheric gas (PH ₂ O / PH ₂ ) is adjusted to 0.15 or less to produce Fe-based oxides. Can be suppressed. However, if the degree of oxidation is too low, the decarburization rate will be low, which is not desirable from an industrial viewpoint. Taking these both into consideration, the degree of oxidation of the atmosphere gas (PH ₂ O / PH ₂ ) in the temperature range of 750-900 ° C .: 0.01-0.
Annealing in the range of 15 is preferred. The annealing time usually requires about 60 to 300 seconds to perform sufficient decarburization.
The annealing temperature is appropriately determined mainly from the viewpoint of obtaining an optimum primary recrystallized grain size.

An object of the present invention is to supply a cold-rolled steel sheet which is advantageous for decarburization under such decarburization annealing conditions. In order to clarify the requirements of the cold-rolled steel sheet, the outermost surface S at the Si content (2.8 to 3.4%) in each steel obtained in the experiment of FIG.
FIG. 8 shows the relationship between the i content and the C content after decarburizing annealing. FIG.
The horizontal axis indicates the Si intensity obtained by X-ray fluorescence analysis of the surface of the cold rolled sheet and converted into the Si content by a calibration curve (standard sample comparison method). As can be seen from FIG. 8, when the outermost surface Si content is lower than 3.0%, preferably lower than 2.8%,
The C amount becomes 30 ppm or less. That is, it is a requirement of the cold-rolled steel sheet immediately before decarburizing annealing that the outermost surface Si content is lower than 3.0%, preferably lower than 2.8%.

Further, as a result of a detailed investigation of the relationship between the profile in the depth direction of Si and the decarburization property using secondary ion mass spectrometry, it was found that the Si content in the range of 2 μm in depth from the surface is important. Was. This is the decarburization annealing temperature of 750-9
Since the Si diffusion distance at 50 ° C. is about 0.1 μm / sec, about 20 seconds from the heating to the initial stage of annealing where SiO ₂ that inhibits decarburization is formed (Si diffusion distance = 0.1 × 20)
= 2 µm), it is estimated that it is meaningful to prevent the Si concentration at the interface of the base iron from increasing. Generally, the analysis value by fluorescent X-ray is about 2
This is information of a depth of ３3 μm. The Si content at a depth of 2 μm from the outermost surface of the cold rolled sheet proposed in the present invention is effective almost in the measurement range of the fluorescent X-ray analysis.

In producing the grain-oriented electrical steel sheet of the present invention in a factory, controlling the Si content in the surface layer by performing fluorescent X-ray analysis on the surface of the cold-rolled sheet is important in terms of speed and measurement accuracy. Very effective from. It is necessary to set a standard for the Si strength of the cold-rolled sheet (or a converted value based on a calibration curve) and control the hot-rolled sheet annealing conditions or the cold-rolling pickling conditions.
Furthermore, it is also possible to adjust the degree of oxidation of the atmosphere gas in the decarburization annealing according to the Si strength to control the amounts of C and O. However, even if the pickled plate before cold rolling is analyzed with fluorescent X-rays, the disturbance of the surface irregularities is large, and it is difficult to control it accurately. In addition to the methods other than the fluorescent X-ray analysis, GDS analysis, Auger spectroscopy, secondary ion mass spectrometry, emission spectroscopy, and the like are also effective.

When it is necessary to strengthen the (Al, Si) N inhibitor in the decarburized annealed sheet, or when N (Al, S
i) In a manufacturing method using N as a main inhibitor (for example, Japanese Patent Publication No. 62-45285), a nitriding treatment is performed.
The method of the nitriding treatment is not particularly limited, and there is a method of performing the nitriding treatment in an atmosphere gas having a nitriding ability such as ammonia.

When these decarburized annealed sheets are wound around a coil form, the annealing separator is dry-coated by a water slurry or an electrostatic coating method. When applying with a water slurry, for example, it is preferable to adopt the method disclosed in Japanese Patent Application No. 5-212602. As the annealing separator,
As described in JP-A-7-118749, alumina is industrially preferable from the viewpoint of cost and magnetic smoothness of the surface.

The coil is finish-annealed to perform secondary recrystallization and purification of nitride. Secondary recrystallization is disclosed in
Performing in a predetermined temperature range by means such as holding at a constant temperature as disclosed in Japanese Patent No. 929 is effective in improving the magnetic flux density. After secondary recrystallization, 100% to purify impurities such as nitrides and smoothen the surface
Anneal with hydrogen at a temperature of 1100 or more.

After the final annealing, the excess annealing separating agent is continuously removed, and then continuous tension annealing for correcting coil winding and the like is performed, and at the same time, an insulating film coating is applied and baked. At this time, if necessary, the steel sheet is subjected to magnetic domain refining treatment such as laser irradiation, mechanical groove formation, and tension film coating. The domain refining treatment is effective in improving iron loss characteristics. There is no particular limitation on the method of magnetic domain subdivision.

In the case of performing magnetic domain subdivision by introducing a local distortion, for example, a method of irradiating a laser beam described in Japanese Patent Publication No. 57-2252 or Japanese Patent Application Laid-Open No. Sho 62-15-15
For example, a method of performing plasma flame irradiation described in JP-A-1511 and JP-B-6-45824 may be used. In the case of performing magnetic domain subdivision by forming a local groove, mechanical plastic working such as a gear roll method (for example, Japanese Patent Publication No. 4-48847) and a die pressing method (for example, Japanese Patent Publication No. 6-63037). A method using chemical etching or electrolytic etching such as a photo-etching method (for example, Japanese Patent Publication No. 5-69284) and a resist ink etching method (for example, Japanese Patent Publication No. 2-46673, Japanese Patent Publication No. 3-69968) may be used. .

As the tension coating, for example, a coating liquid mainly comprising colloidal silica and aluminum phosphate according to JP-A-48-39338;
A method of baking a coating liquid mainly comprising colloidal silica and magnesium phosphate according to Japanese Patent Application No. 0-79442 or a coating liquid mainly comprising alumina sol and boric acid according to Japanese Patent Application No. 4-22849. Etc. may be adopted.

[0035]

【Example】

<Example 1> C: 0.05%, Si: 3.3%, Mn:
0.1%, S: 0.01%, acid-soluble Al: 0.03
%, N: 0.008%, after melting and casting electromagnetic steel,
It was heated to 50 ° C., immediately after the extraction, hot-rolled to a thickness of 2.3 mm and air-cooled. Thereafter, in nitrogen gas, the oxidation degree was set to 0.03, 0.87, and 3.68, and annealing was performed at a temperature of 1050 ° C. for 120 seconds (T = 1050, t = 120). Then, the pickling plate thickness reduction by sulfuric acid solution pickling was 10, 30, 60 μm.
m. The specimen was cold-rolled with aging treatment at 250 ° C. 5 times to 0.23 mm (rolling reduction R = 90%), and the outermost surface Si content was determined by fluorescent X-ray analysis of the cold-rolled sheet. Where (0.0023T-1.9) t (100-R) ≦ 20
0 is satisfied.

These cold rolled sheets were annealed at a temperature of 830 ° C. for 90 seconds at an oxidation degree of a mixed gas of nitrogen and hydrogen of 0.12 and 0.28, and decarburized and primarily recrystallized. O
Analysis was carried out. Then, by annealing in an ammonia atmosphere, the amount of nitrogen was increased to 0.02% to strengthen the inhibitor. Alumina water slurry was added to these steel sheets.
While applying and drying, the steel sheets were laminated and subjected to finish annealing. After checking the mirror surface condition of the finished annealed plate, the sample was rolled with gear rolls in a direction 10 degrees from the direction perpendicular to the rolling direction.
After forming a groove having a width of 50 μm and a depth of 15 μm, a coating liquid containing colloidal silica and phosphate as main components was applied and baked at 850 ° C. for 2 minutes. After measuring the magnetic properties of these samples, strain relief annealing was further performed at 800 ° C. for 4 hours. Table 3 shows the magnetic properties of the obtained products.

[0037]

[Table 3]

Example 2 Si: 3.5% by weight, M
n: 0.07%, C: 0.07%, Se: 0.025
%, Acid-soluble Al: 0.02%, N: 0.008%, S
b: 0.03% of electromagnetic steel was melted, each was cast into a slab, then heated at 1350 ° C., and 2.2 mm immediately after extraction.
, And immediately cooled with water to 550 ° C.
The hot rolled sheet was pickled and cold rolled to an intermediate thickness of 0.9 mm. Thereafter, the degree of oxidation is set to 0.02, 0.
After annealing at 950 ° C. for 30 seconds and 60 seconds, the sheet was cold-rolled to a final sheet thickness of 0.18 mm without pickling, and the cold-rolled sheet was subjected to fluorescent X-ray analysis to determine the outermost surface Si content (T = 95
0, t = 30 or 60, R = 80). (0.0
023T-1.9) t (100-R),
t = 30 was 200 or less, and t = 60 was 200 or more.

These cold-rolled sheets were prepared by setting the oxidation degree of the mixed gas of nitrogen and hydrogen to 0.11, 0.14 and 0.18 and setting them to 850.
C, O analysis of the annealed plate which was annealed at a temperature of ° C. for 70 seconds and decarburized and primary recrystallized was performed. While applying alumina powder to these steel sheets with an electrostatic device, the steel sheets were laminated and subjected to finish annealing. After checking the mirror surface state of the finished annealed plate, a groove having a width of 30 μm and a depth of 10 μm is formed in the sample in a direction perpendicular to the rolling direction by a photoetching method, and then a core mainly composed of alumina sol and boric acid is formed. 870 after applying coating solution
Bake at 2 ° C. for 2 minutes. After measuring the magnetic properties of these samples, strain relief annealing was further performed at 800 ° C. for 4 hours.
Table 4 shows the magnetic properties of the obtained products.

[0040]

[Table 4]

Example 3 C: 0.05%, Si: 3.
2%, Mn: 0.1%, S: 0.01%, P: 0.03
%, Acid-soluble Al: 0.03%, N: 0.007%, S
Silicon steel containing n: 0.005% and Cr: 0.1% is melted, cast into a slab, heated to 1150 ° C, hot-rolled to 2.0 mm thickness immediately after extraction, and hot-rolled. 550 with water cooling
Wound at ℃. Thereafter, the hot rolled sheet is heated at a temperature of 1120 ° C. for 3 hours.
Annealed at 900 ° C for 0 seconds for 90 seconds, air-cooled to 750 ° C,
Quenched in water at ℃. The annealing gas was nitrogen, and the oxidation degree was adjusted to (A) 0.12 and (B) 1.39. Next, the hydrochloric acid concentration at 80 ° C. was set to 3%, and the resultant was pickled for 10 seconds.
Rolling 5 passes to 3mm
The aging treatment was performed for more than one minute (a reduction ratio of 88.5%).
The calculated value of (0.0023T-1.9) t (100-R) was 446, which satisfied 200 or more.

The Si content of the surface layer was measured by X-ray fluorescence analysis of the cold-rolled sheet, and then decarburization and primary recrystallization annealing were performed in a mixed gas of nitrogen and hydrogen with an oxidation degree of 0.13.
This was carried out at a temperature of 850 ° C. for 100 seconds, followed by nitriding annealing in an NH ₃ atmosphere so that the N content became 200 ppm, and then the C and O contents of the annealed plate were analyzed. Then, a 10T coil wound and wound while drying and applying an annealing separator containing alumina as a main component by air-water spray was subjected to secondary recrystallization finish annealing in a box-type annealing furnace. While flowing nitrogen into the furnace, the temperature was raised to 1200 ° C at 15 ° C / hr,
Subsequently, purification annealing was performed at 1200 ° C. for 75 hours while flowing hydrogen. As a result of removing the alumina of the coil by light pickling, the steel plate surface had a mirror surface over the entire width and the entire length of the coil. A coating solution containing hydrotalcite + boric acid as a main component was applied to these steel strips and baked at 850 ° C. for 2 minutes. Thereafter, the surface of the steel sheet was irradiated with laser at intervals of 5 mm in a direction perpendicular to the rolling direction. The Si content of the outermost surface of the cold rolled sheet, the C and O contents after decarburizing annealing, and the magnetic properties of the product are shown below.

Surface Si content C content O content W17 / 50 B8 (A) 3.15% 148 ppm 232 ppm 1.29 W / kg 1.93 T (B) 2.87% 14 ppm 235 ppm 0.69 W / kg 1.95 T

[0044]

As described above, by lowering the Si content at a depth of 2 μm from the steel sheet surface to less than 3.0, the C content can be effectively reduced even in decarburizing annealing in a low oxidation atmosphere. And the organic effect of the low-oxidized layer on the decarburized annealing surface and the alumina annealing separator makes it possible to obtain a mirror-oriented unidirectional magnetic steel sheet having extremely good magnetic properties at low cost.

[Brief description of the drawings]

FIG. 1 Atmosphere oxidation degree (PH ₂ O / PH ₂ ) when a cold-rolled sheet with varied steel sheet components and process conditions was decarburized and annealed.
FIG. 4 is a graph showing the relationship between C and the amount of C after annealing.

FIG. 2 is a diagram showing the relationship between the degree of atmospheric oxidation and the amount of O after annealing in FIG. 1;

FIG. 3 is a graph showing the relationship between the fluorescent X-ray analysis Si intensity of the outermost surface of a cold rolled sheet and the C content after decarburizing annealing at an oxidation degree of 0.105.

Fig. 4 Surface section C of cold rolled steel sheet of good decarburized material and bad material
The figure which shows the Si mapping image by MA analysis.

FIG. 5 is a diagram showing a change in Si concentration in a depth direction obtained by linearly converting FIG. 4 into a Si content.

FIG. 6 shows the relationship between the thickness reduction of the pickled sheet and the fluorescent X-ray Si intensity on the outermost surface of the cold-rolled sheet when the steel sheet annealed at the oxidation degree of 0.01 and 1.84 is pickled. FIG.

FIG. 7 is a diagram showing the relationship between the thickness reduction of the pickled plate and the C content when the cold-rolled plate of FIG. 6 is decarburized and annealed at an oxidation degree of 0.105.

FIG. 8 shows a case where the Si content of the outermost surface of the cold-rolled sheet is changed by using a material having a Si content of 2.8 to 3.4% in steel.
Si content of the outermost surface of the cold rolled sheet and after decarburizing annealing (oxidation degree 0.1
FIG. 05) is a view showing the relationship between C amounts in FIG.

Claims (3)

[Claims] (1) C: 0.03 to 0.10% by weight,
Si: the final cold rolled sheet of grain-oriented electrical steel sheet containing 3.0 to 4.0%, the decarburization annealing oxidation degree (PH ₂ O / PH ₂₎
Is performed in an atmosphere gas of 0.01 to 0.15,
In a method for producing a mirror-oriented unidirectional electrical steel sheet comprising applying an annealing separator containing alumina as a main component and performing finish annealing, the Si content at a depth of 2 μm from the steel sheet surface of the final cold-rolled sheet is determined. A method for producing a mirror-oriented unidirectional electrical steel sheet having excellent magnetic properties, characterized by being lower than 3.0%. 2. C: 0.03 to 0.10% by weight,
The hot-rolled sheet of the grain-oriented electrical steel sheet containing Si: 3.0 to 4.0% is subjected to one or more cold rollings after the hot-rolled sheet annealing, or to intermediate annealing without performing the hot-rolled sheet annealing. The final thickness is obtained by performing cold rolling two or more times, and then decarburization annealing is performed in an atmosphere gas having an oxidation degree (PH ₂ O / PH ₂ ) of 0.01 to 0.15, and alumina is mainly used. In a method for producing a mirror-oriented unidirectional electrical steel sheet having excellent magnetic properties, comprising the steps of applying an annealing separator as a component and performing finish annealing, the annealing conditions performed from hot rolling to final cold rolling are as follows: When the heat temperature is T ° C., the soaking time is t seconds, and the rolling reduction from the sheet thickness to be annealed to the final cold-rolled sheet thickness is R%, (0.0023
T-1.9) Excellent magnetic characteristics characterized by being in the range of t (100-R) ≧ 200 and having the degree of oxidation (PH ₂ O / PH ₂ ) in the annealing atmosphere gas being 0.15 or more. Method for producing mirror-oriented unidirectional magnetic steel sheets. 3. The method according to claim 1, wherein a magnetic domain refining treatment is performed after the finish annealing.