JP2005120452A - Method for producing oriented magnetic steel sheet excellent in magnetic properties and film coated properties - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oriented magnetic steel sheet excellent in a film coated properties and a magnetic properties, even in the component system containing Bi as a sub-inhibitor. <P>SOLUTION: When the oriented magnetic steel sheet is produced by using, as a blank, a silicon steel slab having a composition containing 0.005-1.5 mass% Bi as the sub-inhibitor composition, a relation between a secondary recrystallization starting temperature T<SB>1</SB>and the sheet thickness t, is regulated so that an α value shown in an expression (1): α=5.8×10<SP>-4</SP>×(T<SB>1</SB>-940)/(t-0.07)<SP>1.4</SP>falls within in the range of 0≤α<1. Further, in an annealing separating agent mainly containing magnesia, a metallic lithium compound is incorporated in an amount of 0.01-1.5 pts. mass in terms of metallic lithium to 100 pts. mass of the magnesia. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties.

A grain-oriented electrical steel sheet used as a core material for transformers and generators is required to have high magnetic flux density and low iron loss as the most important characteristics.
To date, various means have been taken to achieve low iron loss in grain-oriented electrical steel sheets. Among them, the crystal orientation of the steel sheet after final finish annealing is referred to as the Goss orientation {110} <001> Accumulation in the direction is one of the development goals that has been regarded as most important. This is because, by highly accumulating the crystal orientation <001>, which is the easy axis direction of the iron crystal, in the rolling direction, the magnetizing force required for magnetization in the rolling direction is reduced, and the coercive force is reduced. This is because the hysteresis loss and thus the iron loss can be reduced.

In addition, an important required characteristic of grain-oriented electrical steel sheets is that noise when magnetized is small. This problem is also greatly improved by aligning the crystal orientation to the Goth orientation.
That is, it is known that the main cause of noise generated in the transformer is magnetostrictive vibration and electromagnetic vibration of the iron core material, but if the degree of integration of the crystal orientation in the Goth orientation is improved, This is because the generation of the 90 ° magnetic domain is suppressed, and at the same time, the excitation current is reduced and the electromagnetic vibration is suppressed. As a result, noise is reduced.

Thus, it can be said that it is the most important issue for the grain-oriented electrical steel sheet to accumulate the crystal orientation <001> in the rolling direction.
Here, B ₈ (T), which is a magnetic flux density at a magnetic force of 800 A / m 2, is often used as an index of the degree of integration of crystal orientation, and the development of grain-oriented electrical steel sheets has improved this B ₈ . Promoted as a major goal.
As a typical value of iron loss, W _17/50 (W / kg), which is an energy loss when excitation magnetic flux density is 1.7 T and excitation frequency is 50 Hz, is mainly used.

The secondary recrystallization structure of such grain-oriented electrical steel sheets is formed through a phenomenon called secondary recrystallization during the final finish annealing, and this secondary recrystallization preferentially grows goss-oriented crystal grains. To obtain a product with the desired magnetic properties.
In order to effectively promote the accumulation of secondary recrystallized grains as described above, it is necessary to form a precipitated dispersed phase called an inhibitor that selectively suppresses the growth of primary recrystallized grains with a uniform and appropriate size. is important. Due to the presence of this inhibitor, normal grain growth of primary recrystallized grains is suppressed, fine primary recrystallization state is maintained up to high temperature during final finish annealing, and selectivity for growth of grains with good orientation is enhanced. Therefore, a high magnetic flux density is realized. In general, it is considered that a higher degree of orientation accumulation is obtained as the inhibitor is stronger and the normal grain growth inhibitory power is higher.

Such _{inhibitors, MnS, MnSe, Cu 2-} X S, etc. AlN Oyopi BN, less material solubility in steel used. For example, in Patent Document 1 and Patent Document 2, AlN is included in the material, and the final cold rolling reduction ratio is 81 to 95% under high pressure, and AlN is a powerful inhibitor that is annealed before final cold rolling. A technique for precipitating is disclosed.

Further, in addition to the above inhibitor components, additional inhibitor components such as Ni, Sb, P, Cr, Te, Bi and Pb, especially Bi, may be added to increase the degree of orientation of secondary recrystallization. It is known that it is effective for improvement.
In other words, it is known that additional secondary inhibitor components such as Bi segregate on the grain boundaries and on the surface of the steel sheet, thereby strengthening the suppression of normal grain growth and enhancing the magnetic properties in cooperation with the main inhibitor. It has been.
However, when a steel sheet containing Bi is used as a secondary inhibitor component, the formation of forsterite film on the steel sheet surface during final finish annealing becomes poor, and the film appearance of the product and the adhesion of the insulating coating deteriorate. It is known to do.

For this reason, for such poor formation of the forsterite film, a method of adjusting the moisture content of the annealing separator used in the final finish annealing to a range of 0.3 to 3% (for example, Patent Document 3), decarburization. A method of adjusting the oxygen basis weight of the annealed plate to a range of 550 to 850 ppm (for example, Patent Document 4), a method of adjusting the Ig-Loss value of MgO used for the annealing separator to 0.4 to 1.5% (for example, Patent Document 5) Although many improvement measures such as a method of appropriately adjusting the atmospheric gas flow rate in the final finish annealing (for example, Patent Document 6) have been proposed, none of them can provide a satisfactory coating improvement effect.
That is, by using the above-described conventional technology, although some coating improvement effect can be expected, deterioration of the coating due to the secondary inhibitor component such as Bi cannot be completely prevented, and the product has a good appearance. Has not yet been manufactured.

Furthermore, in many of the above-mentioned measures for improving the film, there has also been a problem that secondary recrystallization defects such as primary recrystallized structure not yet recrystallized are likely to occur in the secondary recrystallized structure after final finish annealing. .
Compared to slow magnetic deterioration due to slowing of the secondary recrystallization orientation, secondary recrystallization failure in which primary recrystallized structure is mixed is unacceptable as a product because the degree of magnetic deterioration is significant and should be avoided. There must be.

  The above-mentioned secondary recrystallization failure is performed by using a component system such as Bi addition for the purpose of sharpening the secondary recrystallization orientation, and annealing performed before cold rolling or between two or more cold rollings. This is likely to occur when performed at high temperatures. That is, aiming for sharpening of the secondary recrystallization orientation involves a risk of secondary recrystallization failure.

Japanese Patent Publication No.33-4710 Japanese Patent Publication No. 40-15644 Japanese Patent Laid-Open No. 11-229036 JP-A-10-152725 Japanese Patent Laid-Open No. 10-25516 JP-A-9-3542

  The present invention effectively prevents the film defects and secondary recrystallization defects that occur in the final finish annealing when Bi is added as a secondary inhibitor, as described above, thereby improving the appearance and adhesion. An object of the present invention is to propose an advantageous method for producing a grain-oriented electrical steel sheet having a stellite film and having excellent magnetic properties.

Now, when the inventors investigated the cause of deterioration of the forsterite film in the material containing Bi as a secondary inhibitor, the concentration of Bi occurs in the surface layer during the final finish annealing, and the concentration of such a surface layer occurs. As a result, it was found that the film deteriorates as a result of inhibiting the forsterite film formation reaction.
And in order to prevent the deterioration of the coating film due to the above-mentioned causes, it was found that it is effective to contain a very small amount of the lithium metal compound in the annealing separator.

In addition, the secondary recrystallization start temperature T ₁ rises due to the action of Bi as a secondary inhibitor, but the primary recrystallization grains in the surface layer until the temperature during the temperature rise reaches the secondary recrystallization start temperature T _1. When the sheet is thin, especially when the plate thickness is thin, even after secondary recrystallization occurs in the final finish annealing, the primary recrystallized grains coarsened to the secondary recrystallized grains are not eroded and the final finish is completed. It has been found that it is easy to remain after annealing, that is, the risk of secondary recrystallization failure is increased.
Then, in the order to prevent this, pre Bi or by adjusting the content of the other components while suppressing excessive increase of the secondary recrystallization starting temperature T ₁ of, the secondary recrystallization starting temperature T ₁ of the plate thickness t It has been found that it is extremely effective to control the relationship between and the above in an appropriate range.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. C: 0.01 to 0.10 mass% and Si: 1.0 to 5.0 mass%, and as an inhibitor component, it contains a component that forms at least one of nitride, sulfide, and selenide, and as a secondary inhibitor component Bi: A silicon steel slab having a composition containing 0.003 to 1.5 mass% is hot-rolled and then subjected to primary recrystallization annealing after the final thickness is obtained by one or more cold rolling processes including annealing. Then, after applying the annealing separator to the steel sheet surface, in the method for producing a grain-oriented electrical steel sheet consisting of a series of steps for final finishing annealing,
(1)
α = 5.8 × 10 ⁻⁴ × (T ₁ −940) / (t−0.07) ^1.4 --- (1)
Where T ₁ : secondary recrystallization start temperature (° C.)
t: Thickness (mm)
The relationship between the secondary recrystallization start temperature T ₁ and the plate thickness t is determined so that the α value represented by the formula 0 falls within the range of 0 ≦ α <1, and in the annealing separator mainly containing magnesia, , Magnesia: 0.01 to 1.5 parts by mass in terms of metallic lithium with respect to 100 parts by mass, A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties.

2. 2. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties as described in 1 above, wherein the amount of Bi in the silicon steel slab is 0.01 to 0.35 mass%.

3. In the annealing separation agent mainly composed of magnesia, an alkali metal compound other than the lithium metal compound is further added. At that time, the magnesia: 100 parts by mass of the lithium metal compound and the other alkali metal compound in the metal conversion total. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties according to the above 1 or 2, characterized by containing 0.01 to 1.5 parts by mass.

Here, the secondary recrystallization start temperature T ₁ is defined as the lowest temperature at which the area ratio of secondary recrystallized grains generated in the final finish annealing exceeds 30% of the total.

  According to the present invention, even when Bi is contained as a secondary inhibitor component in steel, a grain-oriented electrical steel sheet having excellent coating properties and excellent magnetic properties can be stably obtained.

Hereinafter, the background to the present invention will be described.
C: 0.06 mass%, Si: 3.3 mass%, Mn: 0.07 mass%, Se: 0.02 mass%, Al: 0.022 mass%, N: 0.0082 mass% and Cu: 0.15 mass%, and as a secondary inhibitor component Bi: 0.035 mass%, with the balance being Fe and unavoidable impurities, silicon steel slabs processed according to conventional methods. Plate thickness: 0.23mm decarburized annealed plate An annealing separator having lithium hydroxide added at various ratios with respect to 100 parts by mass of magnesia as a main agent was applied to the surface of the steel sheet and then dried. The coating conditions at this time were such that hydration was at 20 ° C. for 30 minutes and the basis weight was 12 g / m ^{2 on} both sides. Then, as final finish annealing, the temperature was raised to 800 ° C over 46 hours, held at 800 ° C for 20 hours, then heated to 800-1150 ° C at an average rate of 25 ° C / h, and 1150-1200 ° C. Annealing with a residence time of 20 hours was performed.

Further, the steels of the secondary recrystallization starting temperature T ₁ of the result of measurement for, was 1035 ° C.. Here, the secondary recrystallization start temperature T ₁ is defined as the lowest temperature at which the area ratio of secondary recrystallized grains generated in the final finish annealing exceeds 30% of the entire steel sheet. After that, annealing is performed separately using a test piece coated with an annealing separator, and the test piece is taken out at several temperatures in the temperature rising process, and the initial oxide film on the surface layer and the film being formed are removed to visualize the grain boundaries. After processing accordingly, the area ratio of secondary recrystallized grains in the test piece was measured. It is desirable to anneal the test piece for T ₁ measurement under the same conditions as the actual final finish annealing. However, the annealing process and soaking process in the lower temperature range than T ₁ that is normally performed when annealing the product coil ( (Retaining) is usually intended to eliminate temperature non-uniformity in the coil, and may be omitted in annealing the test piece for measuring T _1, which is a small amount compared to that.

Table 1 and FIG. 1 show the results of examining the film adhesion and the magnetic flux density after the final finish annealing in relation to the amount of Li in the annealing separator. In addition, the amount of Li in Table 1 and FIG. 1 is obtained by converting Li in the added lithium hydroxide into mass parts.
The film adhesion was evaluated based on the minimum diameter at which the coating film was not peeled off after a test piece was wound around a round bar having various diameters of 5 mm after applying an insulating coating mainly composed of magnesium phosphate and colloidal silica.

  As is apparent from Table 1 and FIG. 1, good values were obtained for both the magnetic properties and the coating properties by incorporating Li in an amount of 0.01 to 1.5 parts by mass.

The reason why the above film characteristics were obtained has not yet been clearly clarified, but the inventor thinks as follows.
Bi, a secondary inhibitor of the present invention, concentrates preferentially at grain boundaries and surfaces of crystal grains, lowers the mobility of grain boundaries during annealing, increases secondary recrystallization temperature, and improves magnetic flux density. There is a work to make. However, at the time of final finish annealing, the dew point is increased by the hydration water of magnesia and annealing is performed in a highly oxidizing atmosphere, so Bi is oxidized in the steel sheet surface layer, and this oxide forms a liquid phase and is removed. The SiO ₂ in the internal oxide film produced during the carbon annealing is aggregated at the base metal-coating interface, thereby eliminating the irregularities between the base metal and the coating film. Therefore, after the secondary recrystallization is completed, it is necessary to release such elements out of the system and eliminate the adverse effect on the coating.

According to the present invention, the coating film improving effect is remarkably increased by adding a very small amount of the lithium metal compound to the annealing separator. Conventionally, alkali metals are considered to be harmful to the coating. For example, as shown in Japanese Patent Publication No. 54-14556, it has been necessary to reduce alkali metal elements as much as possible. Otherwise, it was recognized that SiO ₂ in the internal oxide film formed during the decarburization annealing floats on the surface of the steel plate during the final finish annealing, and film defects and partial film peeling easily occur.
However, when Bi is used as a secondary inhibitor as in the present invention, the presence of trace amounts of alkali metals, particularly Li, promotes the concentration of SiO _{2 on} the steel sheet surface, and this concentrated SiO 2 _It is considered that ₂ becomes a barrier and hardly affected by the oxygen content in the atmosphere, and as a result, the adverse effect of Bi on the coating is avoided.

JP-A-49-29305 discloses a method of forming an oxide film containing magnesium silicate and Li by adding a compound containing Li, but includes Bi as in the present invention. Even if this technique was simply applied to a steel sheet, good film properties and magnetic properties were not necessarily obtained. This is because the method disclosed in this publication is intended to form a MgO—SiO ₂ —LiO ₂ -based film by increasing the amount of Li added. This is because the film is damaged by the movement of Bi to the surface layer because it is less stable than the SiO ₂ film.

In this regard, in the present invention, since only a very small amount of a lithium metal compound is included in order to promote film formation, an MgO—SiO ₂ based film containing almost no Li is formed, and this MgO—SiO ₂ based film is It is considered that a good film can be maintained because it is chemically stable and is not easily damaged by Bi.

As an auxiliary agent for the annealing separator, in addition to the lithium metal compound, other alkali metal compounds such as sodium metal compound and potassium metal compound can be used, but the lithium metal compound is particularly excellent in the coating improving effect. .
Therefore, in the present invention, when these alkali metal compounds are used, the lithium metal compound is used as an essential component.

Next, it contains C: 0.06 mass%, Si: 3.3 mass%, Mn: 0.07 mass%, Se: 0.02 mass%, Al: 0.022 mass%, N: 0.0082 mass% and Cu: 0.15 mass%, A silicon steel slab containing 0.005, 0.02, 0.03, 0.06, 0.10, 0.20, 0.30, 1.00, and 1.50 mass% of Bi as a secondary inhibitor component, with the balance being Fe and inevitable impurities, is treated according to a conventional method. Thickness: 0.15, 0.20, 0.23, 0.27, 0.30, 0.35mm decarburized and annealed plates, magnesia was the main agent, and lithium hydroxide was converted to Li for 0.1 parts by mass of magnesia: 100 parts by mass. The annealing separator added with parts by mass was applied to the surface of the steel sheet and then dried. The coating conditions at this time were such that hydration was at 20 ° C. for 30 minutes and the basis weight was 12 g / m ^{2 on} both sides. Then, as final finish annealing, the temperature was raised to 800 ° C over 46 hours, held at 800 ° C for 20 hours, then heated to 800-1150 ° C at an average rate of 25 ° C / h, and 1150-1200 ° C. Annealing with a residence time of 20 hours was performed. Further, by using a final annealing prior to the test piece described above was separately measured secondary recrystallization starting temperature T _1.

FIG. 2 and Table 2 show the results of examining the effects of the secondary recrystallization start temperature T ₁ and the plate thickness t on the magnetic flux density B ₈ after the final finish annealing.
In the figure, when the magnetic flux density satisfies B ₈ ≧ 1.94T, it is indicated by ○, and when B ₈ <1.94T, it is indicated by x.

As shown in FIG. 2 and Table 2, in order to obtain a good magnetic property of B ₈ ≧ 1.94T, the following equation (1) which is a relational expression between the secondary recrystallization start temperature T ₁ and the plate thickness t
α = 5.8 × 10 ⁻⁴ × (T ₁ −940) / (t−0.07) ^1.4 --- (1)
It was found that it is effective to control the α value represented by the formula in the range of 0 or more and less than 1, that is, 0 ≦ α <1.

FIG. 3 shows the result of the above experiment in relation to the α value and the magnetic flux density B _8. As shown in FIG. 3, when the α value satisfies the range of 0 ≦ α <1, Good magnetic properties are obtained. However, out of this range, especially when α ≧ 1, the magnetic flux density B ₈ rapidly deteriorated.

This phenomenon is considered to be the next mechanism.
First, the secondary recrystallization start temperature T ₁ rises due to the action of Bi as a secondary inhibitor. This is because Bi concentrates preferentially on the grain boundaries and surfaces of the crystal grains and lowers the mobility of the grain boundaries during annealing. In this investigation experiment, the secondary recrystallization start temperature T ₁ was changed by adjusting the Bi content. However, it may be changed depending on the contents of other components and the manufacturing conditions.
When the secondary recrystallization start temperature T ₁ deviates from an appropriate range at a predetermined plate thickness to the high temperature side, a matrix in which the secondary recrystallization grains are eroded before reaching the secondary recrystallization start temperature T ₁ is formed. Although the growth of primary recrystallized grains is suppressed near the center of the plate thickness, the coarsening of the crystal grains gradually proceeds on the surface layer. If the ratio of the size of the coarsened surface layer grains to the plate thickness increases, even if the plate thickness is relatively thin, the coarse primary layer recrystallized grains will not grow even after secondary recrystallization occurs at the center of the plate thickness. It remains after the final finish annealing without being phagocytosed by the next recrystallized grains. The remaining primary recrystallized grains are very fine compared to the secondary recrystallized grains even though they are coarsened, and the crystal orientation is greatly deviated from the Goth orientation. Incurs significant deterioration.

On the other hand, when the secondary recrystallization start temperature T ₁ deviates from the appropriate range to the low temperature side, that is, when α <0, the secondary recrystallization temperature does not occur, but the secondary recrystallization temperature does not occur. And the effect of sharpening the secondary recrystallization orientation to the Goth orientation is not exhibited, and the magnetic properties are insufficient.

Next, the reason why the component composition of the present invention is limited to the above range will be described.
C: 0.01-0.10mass%
C is not only useful for improving the hot-rolled structure by utilizing the α-γ transformation, but is also an element advantageous for the generation of goth-oriented crystal grains. In order to obtain such an effect, it is necessary to contain at least 0.01 mass%, but if it exceeds 0.10 mass%, decarburization failure occurs in decarburization annealing, so C is limited to a range of 0.01 to 0.10 mass%. .

Si: 1.0-5.0 mass%
Si is an element necessary not only to increase electrical resistance and reduce iron loss, but also to stabilize the α phase of iron and enable high-temperature heat treatment, and it must contain at least 1.0 mass%. However, if it exceeds 5.0 mass%, cold rolling becomes difficult, so Si is limited to the range of 1.0 to 5.0 mass%.

In addition to the above-described C and Si, an element that forms a main inhibitor is added. As the main inhibitor, AlN, BN, MnS, MnSe, and the like are well known, but any of these may be used, or two or more of these may be used in combination.
When MnS and / or MnSe is used as the main inhibitor, it is preferable to contain Mn: 0.03 to 0.10 mass% and a total amount of S and Se: 0.01 to 0.03 mass%.
On the other hand, when AlN is used as the main inhibitor, Al: 0.01 to 0.04 mass% and N: 30 to 120 ppm, and when BN is used as the main inhibitor, B: 0.0010 to 0.015 mass% and N: 30 to 120 It is preferable to contain ppm. In either case, if the content is less than the lower limit, the effect as an inhibitor is poor, whereas if the content exceeds the upper limit, secondary recrystallization becomes unstable.

Furthermore, in the present invention, it is necessary to contain Bi: 0.003 to 1.50 mass% as a secondary inhibitor component. Bi preferentially concentrates at the grain boundaries of the primary recrystallized grains and lowers the mobility of the grain boundaries during annealing, thereby raising the secondary recrystallization start temperature and improving the magnetic flux density. _{Moreover, MnS, MnSe, Cu 2-} x S, Cu 2-X Se, by the presence at the same time in the steel and precipitation distributed main inhibitor such as AlN and BN, effectively act by improving the magnetic properties. Here, if the Bi content is less than 0.003 mass%, the above-described effect of suppressing normal grain growth due to concentration at the grain boundary is not exhibited, while if it exceeds 1.50 mass%, the present invention has the technology. However, since deterioration of the coating appearance cannot be prevented, the appropriate range is limited to 0.003 to 1.50 mass%. More preferably, it is the range of 0.01-0.35 mass%.

In addition to Bi addition, as a component having a secondary inhibitory effect similar to Bi, Ni: 0.01 to 1.50 mass%, Sb: 0.005 to 0.50 mass%, P: 0.005 to 0.50 mass%, Cr: 0.02 to 1.50 mass %, Te: 0.003 to 1.50 mass%, and Pb: 0.003 to 1.50 mass%, or one or two or more kinds selected from them.
Here, if the content of each element described above is less than the lower limit, the effect of supplementing the secondary inhibitor effect of Bi will not be exhibited, and if added beyond the upper limit, even with this technique, the appearance of the coating deteriorates. Therefore, when it is added, it is preferably performed within the above range.

In addition to the above-described inhibitor elements, Mo, V, Nb, etc. can be added to improve the magnetic characteristics, and Cu, B, etc. can be added to improve both the film characteristics and the magnetic characteristics.
In any case, if the amount is less than 0.005 mass%, the above-mentioned improvement effect is small. On the other hand, if it exceeds 0.5 mass%, the magnetic properties and film properties of the product are deteriorated, so both are in the range of 0.005 to 0.50 mass%. It is preferable to contain.

Next, the manufacturing process of the present invention will be described.
The silicon steel slab adjusted to the above preferred component composition is heated to a high temperature of 1350 ° C. or higher for the inhibitor component solid solution. However, when the inhibitor is reinforced in the subsequent process by nitriding or the like, the slab heating temperature can be 1280 ° C. or less.
Next, after hot rolling, annealing treatment and cold rolling are combined to obtain a final thickness, and after decarburization annealing and final finish annealing, an insulating tension coating is baked to obtain a product.

Here, as a method of combining the annealing treatment and cold rolling to make the final plate thickness,
1) After hot rolling, after performing hot-rolled sheet annealing, a method for obtaining a final sheet thickness by two or more cold rolling processes including intermediate annealing,
2) After hot rolling, after performing hot-rolled sheet annealing, a method of making the final sheet thickness by one cold rolling,
3) After hot rolling, there are three types of processes, ie, a method of obtaining a final sheet thickness by two or more cold rolling processes including intermediate annealing without performing hot-rolled sheet annealing. It is also possible to adopt.
In this case, the annealing atmosphere is made oxidizing by hot-rolled sheet annealing or intermediate annealing, the surface layer is weakly decarburized, or the annealing cooling process is rapidly cooled to increase the solid solution C in the steel. Subsequently, a low temperature holding treatment for precipitating fine carbides in the steel is effective in improving the magnetic properties of the product.
Further, cold rolling is performed at a temperature of 100 to 200 ° C., and aging treatment between passes is also advantageous for improving magnetic properties.

Furthermore, providing a plurality of linear grooves in the direction intersecting with the rolling direction of the steel sheet for magnetic domain subdivision is useful for further reducing the iron loss.
In addition, as is well known, a technique for performing nitriding that contains N within a range of 300 ppm or less after decarburization and primary recrystallization and before the start of the secondary recrystallization temperature is also effective for enhancing restraint. In combination with the present invention, it is possible to produce a product having excellent coating properties and magnetic properties.

Decarburization annealing is performed in an atmosphere containing water vapor and H ₂ , soaking temperature is about 700-900 ° C, heating rate is about 5-80 ° C / s between room temperature and 700 ° C, soaking time is 20-240 It is preferable to carry out secondary recrystallization and film formation which are good for about seconds. Further, it is preferable from the same point of view that the atmospheric oxidation property (P [H ₂ 0] / P [H ₂ ]) in the soaking region is preferably 0.3 to 0.85, and the soaking region is further divided into two stages. It is also possible to further enhance the effect of improving the coating by changing the heat temperature and atmospheric oxidizability between the former stage and the latter stage.
Moreover, it is preferable that the atmospheric oxidation property (P [H ₂ 0] / P [H ₂ ]) in the heating region of decarburization annealing is set to 0.25 to 0.70. That is, by setting the atmospheric oxidation property in the heating region to 0.25 or more, the oxide film at the initial stage of decarburization annealing becomes dense, and the dense oxide film is maintained even in the soaking region. On the other hand, by setting the atmospheric oxidizability to 0.70 or less, it becomes possible to suppress the formation of a complex-shaped film due to peroxidation mainly composed of iron oxide. Therefore, by setting the atmospheric oxidation property of the heating region in the above range, the oxide film after decarburization annealing becomes a more preferable state, and the effect of adding the lithium metal compound to the annealing separator to be described later can be further exhibited.

After performing decarburization annealing as described above, an annealing separator is applied. Here, the annealing separator mainly contains magnesia. And it is one of the most important requirements of the present invention that a small amount of a lithium metal compound is contained in such magnesia.
The amount of lithium metal compound added should be 0.01 to 1.5 parts by mass in terms of Li with respect to 100 parts by mass of magnesia. By adding in this range, a film mainly composed of dense forsterite is formed. Is done. In this respect, if the addition amount is less than 0.01 parts by mass, it is too small to obtain a sufficient effect, while if it exceeds 1.5 parts by mass, a film containing Li is formed during the final finish annealing, and the secondary inhibitor component As a result of the Bi being damaged by certain Bi, film defects such as point-like film defects and a decrease in film adhesion occur. In addition, as for magnetic properties, as a result of forming a rough coating during the final finish annealing, the steel sheet is easily affected by the atmosphere, and the magnetic improvement effect due to Bi addition is lost.

The reason why good film properties were obtained by including an appropriate amount of Li metal compound in magnesia has not been clearly clarified, but is considered as follows.
In the present invention, Bi is added as a secondary inhibitor, but the dew point rises due to the release of magnesia hydration water during final finish annealing, and the steel sheet is exposed to a highly oxidizing atmosphere, so it is concentrated on the surface layer. Bi is oxidized. Would be permitted to aggregate in the coating interface - The Bi oxide to form a liquid phase, the Si0 ₂ in the internal oxide film formed during decarburization annealing the steel matrix. Thus, gone irregularities between the base steel one coating from a proper dispersion of Si0 _2, coating flaked off, the coating defects.
However, the presence of a small amount of alkali metal, particularly Li, promotes the concentration of SiO _{2 on} the steel sheet surface. The thickened the Si0 ₂ is hardly affected by the high oxidizing atmosphere becomes a barrier. As a result, it is considered that the oxidation of Bi on the surface layer of the steel sheet was suppressed, and thereby the unevenness between the ground iron and the coating was normally formed.
In addition, Bi and its oxide existing on the surface layer of the steel sheet have a low melting point and boiling point, so that steam is violently generated at higher temperatures. Therefore, if the formation of irregularities between the forsterite coating and the ground iron-coating is delayed during the final finish annealing, the coating in the middle of formation is etched by this vapor and peeled off. At this time, if there is a trace amount of alkali metal, especially Li, the formation of unevenness between the forsterite film and the ground iron-coating is promoted, and the unevenness between the base iron-coating is formed before Bi vapor generation becomes intense. The Once the strong irregularities between the base metal and the coating are formed, it becomes difficult to be etched by Bi vapor, so that a normal forsterite coating can be formed.

  Moreover, it is also possible to contain the alkali metal compound which has the effect similar to this in combination with said lithium metal compound in an annealing separation agent. For example, in the case of a sodium metal compound, magnesia: 0.005 to 1 part by mass in terms of Na with respect to 100 parts by mass, and in the case of a potassium metal compound, 0.001 to 0.5 part by mass in terms of K is suitable. The total amount of Li and Li must be 0.01 to 1.5 parts by mass. As described above, since the lower limit value of the addition amount of the lithium metal compound is 0.01 parts by mass, the total amount with the other alkali metal compounds is not less than 0.01 parts by mass. In addition, when the total amount of the lithium metal compound and other alkali metal compound exceeds 1.5 parts by mass, the film containing these alkali metals forms a point-like film defect or film adhesion caused by the final finish annealing. Defects such as deterioration of coating properties occur.

In addition, compounds such as Ti, Mn, Fe, Zn, Si, and S for the purpose of promoting film formation, and compounds such as Mg, Ca, Sr, and Cu for the purpose of suppressing additional oxidation are further re-primary. Compounds such as Sn, Sb and Al can be added to the annealing separator for the purpose of strengthening the suppression of crystal grain growth. At that time, the addition amount is preferably about 0.5 to 15 parts by mass with respect to 100 parts by mass of magnesia.
Further, the application amount and the hydration amount of the annealing separator may be about 5 to 15 g / m ² and about 0.5 to 5% as usual.

After applying such an annealing separator, after final finishing annealing by a known method, if necessary, baked a tension-imparting coating or insulating coating on the surface of the steel sheet and then flattened annealing to make a product .
In addition, for the purpose of reducing iron loss due to magnetic domain subdivision, it is advantageous to subject the steel plate after flattening annealing to a plasma jet or laser irradiation in a linear manner or a treatment to provide a linear recess by a protruding roll. In addition, as a magnetic domain subdivision process, the process which forms the groove | channel substantially orthogonal to a rolling method by etching etc. after final cold rolling can also be employ | adopted.
Furthermore, it is also effective for reducing iron loss to combine techniques for forming a tension coating by a known method such as a sol-gel method or TiN deposition after the final finish annealing.

C: 0.06 mass%, Si: 3.3 mass%, Mn: 0.07 mass%, P: 0.003 mass%, S: 0.003 mass%, Se: 0.02 mass%, Al: 0.023 mass%, N: 0.0082 mass% and Cu: A steel steel slab containing 0.05 mass% and containing Bi: 0.050 mass% as a secondary inhibitor component, with the balance being Fe and inevitable impurities, heated at 1420 ° C., and then hot rolled to obtain a thickness: A 2.6 mm hot-rolled sheet was used. Subsequently, after hot-rolled sheet annealing was performed at 1000 ° C., cold rolling was performed twice with intermediate annealing at 1000 ° C. to finish a final cold-rolled sheet having a thickness of 0.23 mm or 0.27 mm. Next, decarburization annealing was performed at 820 ° C. for 120 seconds.
With respect to the decarburized and annealed sheet having a thickness of 0.23 mm or 0.27 mm, magnesia is the main agent. As shown in Table 3, lithium hydroxide, lithium sulfate or carbonate is used for 100 parts by mass of magnesia. Lithium was added at a rate of 0 to 2.0 parts by mass in terms of Li, and an annealing separator added with titanium oxide at a rate of 4 parts by mass was applied to the surface of the steel sheet, dried, and wound around a coil. The coating conditions at this time were such that hydration was at 20 ° C. for 30 minutes and the basis weight was 12 g / m ^{2 on} both sides.
A test piece was taken from this coil, and the secondary recrystallization start temperature T ₁ was measured separately.

Thereafter, the coil was heated to 800 ° C. over 46 hours as final finish annealing, held at 800 ° C. for 20 hours, and then heated to 800 to 1150 ° C. at an average rate of 25 ° C./h. Annealing was performed with a residence time at ˜1200 ° C. of 20 hours. Next, an insulating tension coating mainly composed of magnesium phosphate and colloidal silica was applied, and after flattening annealing, a product plate was obtained.
From the product plate thus obtained, a test piece having a length in the rolling direction of 500 mm and a length in the direction perpendicular to the rolling direction of 500 mm was sampled and subjected to magnetic measurement using an SST (single plate magnetometer).
The film appearance and film adhesion were also investigated.
The obtained results are shown in Table 3.

As shown in the table, according to the present invention, an appropriate amount of a lithium metal compound is added to magnesia as an annealing separator, and the α value determined by the relationship between the thickness t and the secondary recrystallization start temperature T ₁ is 0 ≦ When it was in the range of α <1, it was possible to obtain a product plate having excellent coating appearance and coating adhesion and excellent magnetic properties.

C: 0.06 mass%, Si: 3.3 mass%, Mn: 0.07 mass%, P: 0.002 mass%, S: 0.002 mass%, Se: 0.02 mass%, Al: 0.025 mass%, N: 0.0082 mass% and Cu: A silicon mesh slab containing 0.10 mass% and containing 0.01, 0.04, 0.08, 0.12, 0.20, 1.0 mass% Bi as a secondary inhibitor component, and the balance is heated at 1410 ° C with a composition of Fe and inevitable impurities Thereafter, hot rolling was performed to form a hot-rolled sheet having a thickness of 2.4 mm. Next, after final cold-rolled sheets with thicknesses of 0.23, 0.27, 0.30, and 0.35 mm were obtained by two cold rollings including intermediate annealing at 1050 ° C, decarburization annealing was performed at 850 ° C for 100 seconds. .
Thickness: 0.23, 0.27, 0.30, 0.35mm decarburized and annealed plates, magnesia as the main agent, and 0.1 parts by mass of lithium hydroxide in terms of Li metal is added to 100 parts by mass of magnesia. The applied annealing separator was applied to the surface of the steel sheet, dried, and wound on a coil. The coating conditions at this time were such that hydration was at 20 ° C. for 30 minutes and the basis weight was 12 g / m ^{2 on} both sides.
A test piece was taken from this coil, and the secondary recrystallization start temperature T ₁ was measured separately.

Thereafter, the coil was heated to 800 ° C. over 46 hours as final finish annealing, held at 800 ° C. for 20 hours, and then heated to 800 to 1150 ° C. at an average rate of 25 ° C./h. Annealing was performed with a residence time at ˜1200 ° C. of 20 hours. Next, an insulating tension coating mainly composed of magnesium phosphate and colloidal silica was applied, and after flattening annealing, a product plate was obtained.
From the product plate thus obtained, a test piece having a length in the rolling direction of 500 mm and a length in the direction perpendicular to the rolling direction of 500 mm was sampled and subjected to magnetic measurement using an SST (single plate magnetometer).
The film appearance and film adhesion were also investigated.
Table 4 shows the obtained results.

As shown in the table, according to the present invention, an appropriate amount of a lithium metal compound is added to magnesia as an annealing separation, and the α value determined by the relationship between the plate thickness t and the secondary recrystallization start temperature T ₁ is 0 ≦ When it was in the range of α <1, it was possible to obtain a product plate having excellent coating appearance and magnetic properties.

It is the figure which showed the relationship between the amount of lithium hydroxide (Li conversion value) added in the annealing separation agent, and the bending peeling diameter after final finishing annealing. Illustrates the effects of final finish secondary recrystallization starting on the magnetic flux density B ₈ after annealing temperatures T ₁ and the plate thickness t. It is a diagram showing the relationship between the magnetic flux density B ₈ of α values and final finish after annealing.

Claims (3)

C: 0.01 to 0.10 mass% and Si: 1.0 to 5.0 mass%, and as an inhibitor component, it contains a component that forms at least one of nitride, sulfide, and selenide, and as a secondary inhibitor component Bi: A silicon steel slab having a composition containing 0.003 to 1.5 mass% is hot-rolled and then subjected to primary recrystallization annealing after the final thickness is obtained by one or more cold rolling processes including annealing. Then, after applying the annealing separator to the steel sheet surface, in the method for producing a grain-oriented electrical steel sheet consisting of a series of steps for final finishing annealing,
(1)
α = 5.8 × 10 ⁻⁴ × (T ₁ −940) / (t−0.07) ^1.4 --- (1)
Where T ₁ : secondary recrystallization start temperature (° C.)
t: Thickness (mm)
The relationship between the secondary recrystallization start temperature T ₁ and the plate thickness t is determined so that the α value represented by the formula 0 falls within the range of 0 ≦ α <1, and in the annealing separator mainly containing magnesia, , Magnesia: 0.01 to 1.5 parts by mass in terms of metallic lithium with respect to 100 parts by mass, A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties.   The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties according to claim 1, wherein the Bi content in the silicon steel slab is 0.01 to 0.35 mass%.   In the annealing separation agent mainly composed of magnesia, an alkali metal compound other than the lithium metal compound is further added. At that time, the magnesia: 100 parts by mass of the lithium metal compound and the other alkali metal compound in the metal conversion total. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and coating properties according to claim 1 or 2, wherein 0.01 to 1.5 parts by mass are contained.

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