JP3707268B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

【００５３】
【表２】

【００５４】
表２から明らかなように、本発明に従い、インヒビター成分を含まず、かつ鋼中Ｏ量を30 ppm以下に抑制した鋼スラブを用いて、最終仕上焼鈍前の酸化被膜付きの鋼板におけるAlの含有量を 100 ppm以下、Ｂ，Ｖ，Nb，Se，Ｓ，Ｐ，Ｎ量を各々50 ppm以下に低減すると共に、最終仕上焼鈍中、 850〜950 ℃の温度範囲における窒素量を６〜80ppm の範囲に制御した場合には、いずれも良好な磁気特性の製品を得ることができた。
【００５５】
実施例２
Ｃ：７ppm 、Si：3.4 wt％、Mn：0.15wt％、Ｎ：29ppm 、Ｏ：10ppm 、Al：19ppm 、Ｂ：３ppm 、Ｖ：10ppm 、Nb：20ppm 、Se：10ppm 、Ｓ：10ppm 、Ｐ：30ppm を含み、残部は実質的にFeの組成になる板厚：4.5 mmの薄鋳片を、直接鋳造で製造した。その後、冷間圧延で0.90mmの最終板厚に仕上げた。
最終仕上焼鈍前の冷延板におけるAl，Ｂ，Ｖ，Nb，Se，Ｓ，Ｐ，Ｎ量を分析したところ、各元素とも50ppm 以下に低減されていた。
ついで、MgO を主成分とする焼鈍分離剤を塗布してから、最終仕上焼鈍を行った。最終仕上焼鈍は、表３に示す雰囲気中にて15℃/hの速度で 950℃まで加熱して終了した。
【００５６】
かくして得られた方向性電磁鋼板の磁束密度Ｂ₈ と最大透磁率μ_max を測定した。
また、最終仕上焼鈍中、 850, 900 ，950 ℃の温度において、コイル外巻部から試料を取り出し、鋼中窒素量を分析した。
【００５７】
【表３】

【００５８】
表３に示したとおり、Ｃを低減し、かつインヒビター成分を含有しない高純度成分系の薄鋳片を素材として用いた場合には、脱炭焼鈍を省略しても、最終仕上焼鈍前の酸化被膜付きの鋼板におけるAl，Ｂ，Ｖ，Nb，Se，Ｓ，Ｐ，Ｎ量を各々50 ppm以下に低減すると共に、最終仕上焼鈍中、 850〜950 ℃の温度範囲における窒素量を６〜80ppm の範朗に制御することにより、透磁率が良好な製品を得ることができた。
【００５９】
【発明の効果】
かくして、本発明によれば、インヒビター成分を含有しない高純度成分系の鋼スラブを用い、最終仕上焼鈍前の酸化被膜付きの鋼板におけるAl含有量を100ppm以下、Ｂ，Ｖ，Nb，Se，Ｓ，Ｐ, Ｎ量を各々50 ppm以下に低減すると共に、最終仕上焼鈍中、 850〜950 ℃の温度範囲における窒素量を６〜80ppm の範囲に制御することにより、良好な磁気特性の製品を得ることができる。
また、本発明によれば、スラブの高温加熱、不純物除去のための高温純化焼鈍が不要となるので、経済的効果も極めて大きい。
さらに、本発明では、フォルステライト被膜を必要としない用途の場合にはＣを含まない素材を用いて、脱炭焼鈍を省略することも可能である。
【図面の簡単な説明】
【図１】仕上焼鈍前における方位差角が20〜45°である粒界の各方位粒に対する存在頻度（％）を示す図である。
【図２】仕上焼鈍中の鋼中窒素量と仕上焼鈍後の磁束密度との関係を示したグラフである。
【図３】各不純物元素の含有量と磁束密度との関係を示したグラフである。
【図４】各元素の添加量と鉄損との関係を示したグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet mainly used as a main material of an iron core of a power transformer.
[0002]
[Prior art]
In the production of grain-oriented electrical steel sheets, it is a common method to cause secondary recrystallization during final finish annealing using precipitates called inhibitors. For example, as a typical technique, Japanese Patent Publication No. 40-15644 discloses a method using AlN and MnS, and Japanese Patent Publication No. 51-13469 discloses a method using MnS and MnSe. It is practically used industrially.
Apart from these, a technique for adding CuSe and BN is proposed in Japanese Patent Publication No. 58-42244, and a method using a nitride such as Ti, Zr, V, etc. is proposed in Japanese Patent Publication No. 46-40855, etc. Many other techniques are known.
[0003]
Although the method using these inhibitors is a useful method for developing secondary recrystallized grains stably, it is necessary to finely disperse precipitates, so the slab heating temperature before hot rolling is 1300 ° C. It is necessary to set it as the above high temperature.
However, high-temperature heating of the slab not only increases the equipment cost, but also increases the amount of scale generated during hot rolling, so that not only the yield is lowered, but there are many problems such as complicated maintenance of the equipment.
[0004]
Another problem of the technique using an inhibitor is that if these components remain after final finish annealing, the magnetic properties are deteriorated. Therefore, for the purpose of removing the inhibitor components such as Al, B, Se, and S from the steel, it is necessary to carry out purification annealing for several hours in a hydrogen atmosphere at 1100 ° C. or higher following the completion of the secondary recrystallization.
However, due to such high-temperature purification annealing, there is a problem that the mechanical strength of the steel sheet is reduced, the lower part of the coil is buckled, and the yield of the product is significantly reduced.
[0005]
In addition, although the contents of Al, B, Se, S, etc. in the steel are each reduced to 50 ppm or less by the high temperature purification annealing described above, it is difficult to remove Nb, Ti, V, etc. It causes damage deterioration. In addition, Al, B, Se, S and the like, which are components removed from the steel, are rather concentrated in the forsterite film. Therefore, Al, B, Se, S, etc. inevitably remain as a single substance or a compound at the interface between the coating and the ground iron. The presence of such a substance prevents the domain wall from moving and causes an increase in iron loss.
In addition, there are often fine grains that are not completely engulfed by secondary recrystallized grains directly under the surface layer, and this is also the result of the grain boundary movement under the coating being suppressed by the substances present at the coating base iron interface. The presence of such fine grains also causes deterioration of magnetic properties.
Therefore, a technique that does not use an inhibitor as described above is a means for solving such a problem.
[0006]
Examples of methods for producing grain-oriented electrical steel sheets without using an inhibitor include those disclosed in JP-A Nos. 64-55339, 2-57635, 7-76732 and 7-197126. Technology is known.
What is common to these techniques is that the {110} plane is intended to grow preferentially using surface energy as the driving force. In order to effectively use the surface energy difference, it is necessary to reduce the plate thickness in order to increase the contribution of the surface. For example, in the technique disclosed in Japanese Patent Application Laid-Open No. 64-55339, the plate thickness is In the technique disclosed in Japanese Patent Laid-Open No. 2-57635, the plate thickness is limited to 0.15 mm or less.
In this regard, the plate thickness is not particularly limited in the technique disclosed in Japanese Patent Laid-Open No. 7-76732, but according to Example 1, when the plate thickness is 0.30 mm, the magnetic flux density is B.₈At 1.700T or less, the degree of orientation accumulation is extremely bad. Further, in the examples, the plate thickness at which a good magnetic flux density can be obtained is limited to 0.10 mm.
Similarly, even with the technique disclosed in Japanese Patent Application Laid-Open No. 7-197126, the sheet thickness is not limited. However, since this technique is a technique for performing the third cold rolling of 50 to 75%, the sheet thickness is inevitably thin. In the embodiment, the thickness is 0.10 mm.
Since the thickness of the grain-oriented electrical steel sheet currently used is almost 0.20 mm or more, it is difficult to obtain a normal product by the method using the surface energy as described above.
[0007]
Furthermore, in order to utilize the surface energy, it is necessary to perform high-temperature final finish annealing in a state in which the generation of surface oxides is suppressed. For example, in the technique disclosed in Japanese Patent Application Laid-Open No. 64-55339, a vacuum or an inert gas or hydrogen gas or a mixed gas of hydrogen gas and nitrogen gas is used as an annealing atmosphere at a temperature of 1180 ° C. or higher. Is described.
In the technique disclosed in Japanese Patent Application Laid-Open No. 2-57635, it is recommended to reduce the pressure in an inert gas atmosphere or hydrogen gas or a mixed atmosphere of hydrogen gas and inert gas at a temperature of 950 to 1100 ° C. Has been.
Furthermore, the technique disclosed in Japanese Patent Application Laid-Open No. 7-197126 describes that the final finish annealing is performed in a non-oxidizing atmosphere or a vacuum at a temperature of 1000 to 1300 ° C. and an oxygen partial pressure of 0.5 Pa or less. .
[0008]
Thus, when trying to obtain good magnetic properties using surface energy, the atmosphere of the final finish annealing requires an inert gas or hydrogen, and a vacuum is required as a recommended condition. However, coexistence of high temperature and vacuum is extremely difficult in terms of equipment, and the cost is high.
[0009]
Furthermore, when surface energy is used, in principle, only the {110} plane can be selected, and the growth of goth grains with the <001> direction aligned in the rolling direction is not selected. Absent.
The grain-oriented electrical steel sheet is improved in magnetic properties only when the easy magnetization axis <001> is aligned in the rolling direction, so that in principle, good magnetic properties cannot be obtained only by selecting the {110} plane. Therefore, the rolling conditions and annealing conditions that can obtain good magnetic properties by a method using surface energy are extremely limited, and as a result, the obtained magnetic properties must be unstable.
[0010]
Furthermore, in the method using the surface energy, the final finish annealing must be performed while suppressing the formation of the surface oxide layer. For example, an annealing separator such as MgO cannot be applied and annealed. An oxide film similar to that of a normal grain-oriented electrical steel sheet cannot be formed. For example, a forsterite film is a film formed when MgO is applied as a main component as an annealing separator. This film not only applies tension to the steel sheet surface, but also applies a coating and baking onto the forsterite film. It is responsible for ensuring the adhesion of insulating tension coatings composed mainly of acid salts. Therefore, when there is no forsterite film, the iron loss is greatly deteriorated.
[0011]
[Problems to be solved by the invention]
The present invention is a manufacturing technique that does not use an inhibitor, avoiding problems associated with high-temperature slab heating before hot rolling and high-temperature purification annealing after secondary recrystallization when using an inhibitor.
And, the present invention is inevitably associated with a method using surface energy without using an inhibitor, because the steel plate thickness is limited, secondary recrystallization orientation is inferior, and there is no surface oxide film. This is an advantageous solution to various problems that iron loss is inferior.
[0012]
[Means for Solving the Problems]
The elucidation process of the present invention will be described below.
Now, as a result of extensive research on the mechanism of secondary recrystallization of goth-oriented grains, the inventors of the present invention have played an important role in the grain boundaries having an orientation difference angle of 20 to 45 ° in the primary recrystallized structure. And reported on Acta Material 45 (1997) 85.
FIG. 1 shows the existence frequency (%) of each grain at a grain boundary having an orientation difference angle of 20 to 45 ° in the primary recrystallized structure of the grain-oriented electrical steel sheet, and the Goss orientation has the highest frequency. And a grain boundary with a misorientation angle of 20 to 45 ° is a high energy grain boundary according to experimental data (AIME Transaction 188 (1949) 368) by C. G. Dunn et al. This high energy grain boundary has a messy structure with a large free space within the grain boundary. Grain boundary diffusion is a process in which atoms move through the grain boundary. Therefore, grain boundary diffusion is faster in a high energy grain boundary with a large free space in the grain boundary.
It is known that secondary recrystallization occurs with the growth of precipitates called inhibitors, which is controlled by diffusion rate. Precipitation on the high-energy grain boundaries preferentially progresses during the finish annealing, so that the pinning is preferentially released, and the grain boundary migration starts and the goss grains grow.
[0013]
The inventors further developed this research, and the essential factor of secondary recrystallization of Goss-oriented grains is the distribution state of high energy grain boundaries in the primary recrystallization structure, and the role of inhibitors is high energy. It has been found that there is a difference in moving speed between the grain boundary and other grain boundaries.
Therefore, according to this theory, secondary recrystallization can be performed if a difference in the moving speed of the grain boundary can be generated without using an inhibitor.
[0014]
Now, the impurity elements present in steel are easy to segregate at the grain boundaries, especially at high energy grain boundaries, so when there are many impurity elements, there is no difference in the moving speed between the high energy grain boundaries and other grain boundaries. It is thought that there is.
In this regard, if the influence of the impurity elements as described above can be eliminated by increasing the purity of the material, the inherent difference in the moving speed depending on the structure of the high energy grain boundary becomes obvious, and the two goss-oriented grains are It is considered that next recrystallization is possible.
[0015]
As a result of intensive research based on the above-mentioned idea, the inventors have newly found that secondary recrystallization proceeds in a component system that does not contain an inhibitor component due to the high purity of the material and the action of a small amount of nitrogen. Based on this knowledge, the present invention has been completed.
This technique is completely opposite to the conventional secondary recrystallization technique in that it eliminates precipitates and impurities at the grain boundaries, and is different from the technique that uses surface energy. Even if it exists, secondary recrystallization can be satisfactorily performed.
[0016]
  That is, the gist configuration of the present invention is as follows.
1. C: 0.12 wt% or less,
    Si: 1.0-8.0 wt%
    Mn: 0.005 to 3.0 wt%
ContainingThe rest Fe And the composition of inevitable impuritiesThe steel slab is hot-rolled, then hot-rolled sheet annealed as necessary, and then cold-rolled once or twice with intermediate annealing, and finished to the final thickness, then as required In the method for producing a grain-oriented electrical steel sheet comprising a series of steps of applying a final finishing annealing after applying a decarburizing annealing and further applying an annealing separator as required.
(1) To suppress the O content in the steel slab to 30 ppm or less,
(2) At least the Al content in impurities is 100 ppm or less, and the contents of B, V, Nb, Se, S, P and N are each 50 ppm or less in the whole steel sheet including the oxide film before final finish annealing. To suppress,
(3) During final finish annealing, control the amount of N in steel in the temperature range of at least 850 to 950 ° C within the range of 6 to 80 ppm.
A method for producing a grain-oriented electrical steel sheet characterized by the above.
[0017]
2. In the above 1, in the final finish annealing, means for controlling the N content in the steel is:
(a) during the final finish annealing, increasing the nitrogen partial pressure in the atmosphere up to a temperature range of at least 850-950 ° C;
(b) Inclusion of a nitriding accelerator in the annealing separator
A method for producing a grain-oriented electrical steel sheet, characterized in that any one of or two or more treatments are performed.
[0018]
3. 3. A method for producing a grain-oriented electrical steel sheet according to 1 or 2, wherein the steel slab is directly subjected to hot rolling without heating.
[0019]
4). In the above 1, 2, or 3, hot rolling using a thin slab having a thickness of 100 mm or less obtained by direct casting from molten steel, or using the thin slab as a hot-rolled sheet material as it is A method for producing a grain-oriented electrical steel sheet characterized by the above.
[0020]
5. In the above 1, 2, 3 or 4, the steel slab is further
Ni: 0.005 to 1.50 wt%
      Sn: 0.02-0.50wt%
      Sb: 0.01 to 0.50 wt%,
      Cu: 0.01 to 0.50 wt% and
      Mo: 0.01-0.50wt%
A method for producing a grain-oriented electrical steel sheet, comprising a composition containing one or more selected from among the above.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the experimental results that led to the success of the present invention will be described.
C: 0.070 wt%, Si: 3.22 wt%, Mn: 0.070 wt%, Al is reduced to 10 ppm, N is 30 ppm, O is reduced to 15 ppm, and other impurities are 50 ppm each. Steel A containing the following slabs, C: 0.065 wt%, Si: 3.32 wt%, Mn: 0.070 wt%, Al: 0.025 wt%, N: 30 ppm, and other impurities of 50 ppm or less. B slab, and C: 0.055 wt%, Si: 3.25 wt%, Mn: 0.070 wt%, Al is reduced to 10 ppm, N is reduced to 30 ppm, O is reduced to 60 ppm. Steel C slabs each reduced to 50 ppm or less were produced by continuous casting. Subsequently, in any case, after heating to 1100 ° C., a hot-rolled sheet having a thickness of 2.6 mm was finished by hot rolling. Each hot-rolled sheet was soaked in a nitrogen atmosphere at 1000 ° C. for 1 minute and then rapidly cooled. Thereafter, cold rolling was performed to obtain a final thickness of 0.34 mm. Subsequently, decarburization annealing was performed at 840 ° C. for 120 seconds in an atmosphere having a dew point of 65 ° C. with hydrogen: 75% and nitrogen: 25% to reduce C to 0.0020 wt%. Further, when component analysis was performed on the other components before finish annealing, the amounts of components other than C were hardly changed in Steel A, Steel B, and Steel C. In addition, no impurity element contained more than 50 ppm.
Thereafter, an annealing separator mainly composed of MgO was applied, and then final finish annealing was performed. The final finish annealing was completed by heating to 1050 ° C. at a rate of 20 ° C./h in a nitrogen atmosphere.
For comparison, the same final finish annealing was performed in an Ar atmosphere.
[0022]
As a result, in Steel A, secondary recrystallization occurred in a nitrogen atmosphere, but not in an Ar atmosphere. On the other hand, secondary recrystallization did not occur in Steel B and Steel C in either atmosphere. Further, the magnetic flux density of the product obtained in the nitrogen atmosphere of steel A was 1.87 T, which was a satisfactory level as a grain-oriented electrical steel sheet.
In this experiment, it was revealed that secondary recrystallization occurs in a specific annealing atmosphere with respect to steel A having a high purity component that does not contain any inhibitor component and Al and O are reduced.
The amount of nitrogen in steel A after annealing at 1050 ° C. was 35 ppm in the nitrogen atmosphere and 3 ppm in the Ar atmosphere, and a correlation was observed between the annealing atmosphere and the nitrogen amount.
[0023]
As a result of diligent research based on the above findings, it became clear that the amount of nitrogen in steel between 850 ° C and above until the end of secondary recrystallization has an effect on the appearance of secondary recrystallization. Here, the amount of nitrogen in the steel was adjusted by changing the amount of nitrogen in the slab material and the nitrogen partial pressure in the annealing atmosphere. The amount of nitrogen was measured by a method in which a sample was taken and analyzed during the final finish annealing performed at a temperature elevation rate of 20 ° C./h.
The final finish annealing was terminated at 1050 ° C., and the magnetic flux density was measured.
The obtained results are organized and shown in FIG.
[0024]
As shown in the figure, if the amount of N before finish annealing is small and the amount of nitrogen in the steel between 850 ° C and 950 ° C where secondary recrystallization starts is in the range of 6 to 80 ppm, it is satisfactory. It was found that subsequent recrystallization occurred.
On the other hand, when the amount of N before finish annealing was large and when the amount of nitrogen during finish annealing was low, secondary recrystallization did not occur and the magnetic flux density was lowered.
[0025]
Next, investigation was made on the influence of trace components (Al, B, V, Nb, Se, S, P, Ni, O, N) contained in the material before final finish annealing. As the basic components of the molten steel, the C content was fixed to 0.06 wt%, the Mn content was fixed to 0.06 wt%, the Si content was fixed to 3.3 wt%, and the magnetic properties were investigated by processing in the same process as the above experiment. However, nitrogen was used as the final finish annealing atmosphere.
FIG. 3 summarizes the influence of each impurity element on the magnetic flux density.
[0026]
As shown in the figure, the expression state of secondary recrystallization was deteriorated by increasing the content of almost all elements regardless of precipitation type or solid solution type. In particular, the nitride-forming element Al exceeds 100 ppm, and the content of B, V, Nb, and N exceeds 30 ppm. Magnetic properties begin to deteriorate, and when it exceeds 50 ppm, secondary recrystallization occurs. It was found that development is significantly inhibited. This tendency is the same for Se, S, and P. In particular, when O exceeds 30 ppm, abrupt magnetic deterioration occurs.
In exceptional cases, it was confirmed that the magnetic flux density of Ni was improved by adding Ni.
[0027]
[Action]
In a component system that does not contain an inhibitor component, the reason why secondary recrystallization occurs due to the high purity of the material and the action of a small amount of nitrogen, and a high magnetic flux density is not necessarily clearly elucidated. Thinks as follows.
In the high-purity material containing no inhibitor in the present invention, it is considered that the ease of movement of grain boundaries reflects the grain boundary structure. Impurity elements are likely to segregate preferentially at grain boundaries, particularly high energy grain boundaries, so it is considered that there is no difference in the moving speed between high energy grain boundaries and other grain boundaries when they contain a large amount of impurity elements. . In this regard, if the influence of such impurity elements is eliminated by increasing the purity of the material, the advantage of the moving speed of the high energy grain boundary will occur, and secondary recrystallization of Goss-oriented grains will be possible. Inferred.
[0028]
The influence of nitrogen is considered as follows.
That is, in the present invention, the nitrogen is present in such a manner that when it contains a nitride-forming element such as Al, B, or Nb, secondary recrystallization does not occur, and the amount of nitrogen effective for secondary recrystallization is solid solution. Since it is less than the possible amount, it is considered that it acts as solute nitrogen. Grain boundary migration is promoted by the high purity of the material, so the particle size after the primary recrystallization is about 10 times that of the presence of an inhibitor, about 100 μm. When solute nitrogen is not included, further grain growth occurs during finish annealing, so that the grain boundary energy as a driving force for secondary recrystallization tends to be insufficient, and secondary recrystallization does not occur.
On the other hand, it is estimated that the effect of solute nitrogen will be the effect of suppressing the grain growth and securing the driving force of secondary recrystallization.
[0029]
Further, the grain growth suppressing effect of solute nitrogen differs from the nitride effect in the following points.
That is, solute nitrogen has an effect of segregating at the grain boundary and resisting grain boundary movement, the so-called Dragging effect, unlike the grain boundary pinning effect by the inhibitor. In the case where a nitride-forming element is present, if nitrogen is mixed during the final finish annealing, the nitride penetrates from the atmosphere to the fast-diffusing crystal grain boundary, and the precipitation of nitride on the grain boundary preferentially proceeds. Moreover, the diffusion speed is higher on the high energy grain boundaries with more free space in the grain boundaries, and the precipitation proceeds preferentially, so that the movement of the high energy grain boundaries is preferentially suppressed. It is considered that secondary recrystallization of orientation grains does not occur.
Secondary recrystallization is also inhibited when nitrogen is present in an amount of 50 ppm or more before the finish annealing. The reason for this is not clear, but it is considered that coarse silicon nitride is formed and the amount of dissolved nitrogen is reduced.
[0030]
In addition, when solid solution type impurity elements such as P, S, and Se are present, they are preferentially segregated to a high energy grain boundary having a lot of free space in the grain boundary, and the moving speed of the high energy grain boundary is increased. It stagnates greatly and as a result, secondary recrystallization does not occur. Therefore, in general, a solid solution element is not used alone, but is used in combination with an inhibitor.
[0031]
In contrast, nitrogen has a sufficiently high diffusion rate in the secondary recrystallization temperature region, and solute nitrogen can follow the grain boundary movement. Therefore, the Draging effect is weak compared to other impurity elements. However, it is considered to have an effect of reducing the grain boundary moving speed almost uniformly regardless of the grain boundary structure. Because of the action of this solute nitrogen, it is possible to suppress grain growth while maintaining the superiority of grain boundary migration over other grain boundaries with high energy, so that the driving force necessary for secondary recrystallization is ensured. I guess that.
[0032]
Moreover, even if solute nitrogen remains in the product plate, unlike the nitride precipitate, it does not become an obstacle to the domain wall movement, so it is not necessary to remove it by performing high temperature purification annealing. Therefore, in the present invention, the final finish annealing can be finished when the secondary recrystallization is completed or the forsterite film is formed. As a result, the productivity is improved and the equipment is simplified. It is possible to prevent buckling of the lower part of the coil.
[0033]
The magnetic flux density is improved by adding Ni. The reason for this is presumed that the addition of Ni promotes the α → γ transformation and improves the crystal structure. Further, since Ni does not form precipitates such as nitride and is not a grain boundary segregation element, it is considered that there is little harm to the occurrence of secondary recrystallization.
Furthermore, Ni is also considered to be a ferromagnetic element that contributes to the improvement of magnetic flux density.
[0034]
In addition, FIG. 4 shows the results of examining the influence of the addition of Sn, Sb, Cu, and Mo on the iron loss of the product plate in the previous experiment.
As shown in the figure, it can be seen that iron loss is reduced by adding appropriate amounts of these elements. The reason for this is considered to be that the secondary recrystallized grains are refined by the addition of these elements.
Here, in order to improve iron loss, it is necessary to add Sn in the range of 0.02 to 0.50 wt%, Sb in the range of 0.01 to 0.50 wt%, Cu in the range of 0.01 to 0.50 wt%, and Mo in the range of 0.01 to 0.50 wt%. If the amount added is increased, secondary recrystallization does not occur and the iron loss is rather deteriorated.
[0035]
This technology has an advantage over technology that uses surface energy in the following respects.
First, since it is secondary recrystallization using the grain boundary energy as the driving force, there is no limitation on the plate thickness. For example, secondary recrystallization is possible even when the plate thickness is 1 mm or more, and such a thick product can be used as a magnetic shielding material because it has a high magnetic permeability although the iron loss value is deteriorated.
Further, secondary recrystallization at a general heat treatment temperature of 850 to 950 ° C. is possible in a state where a surface oxide is formed. The annealing atmosphere does not need to use a vacuum or an expensive inert gas, and can be mainly composed of inexpensive nitrogen that is most commonly used.
However, when the raw material component contains a relatively large amount of nitrogen, in order to maintain an appropriate amount of nitrogen, hydrogen, Ar, or the like may be mixed, or these atmospheres may be used alone.
[0036]
Next, the reason why the component composition of the material is limited to the above range in the present invention will be described.
C: 0.12wt% or less
C is a useful element that improves magnetic properties by improving the structure, but if the content exceeds 0.12 wt%, it becomes difficult to remove by decarburization annealing, so the upper limit is made 0.12 wt%. The lower limit is not particularly provided because a secondary recrystallization is possible even for a material not containing C. In particular, if C is reduced to 30 ppm or less from the material stage, decarburization annealing can be omitted, which is advantageous in terms of production cost. Therefore, in the production of low-grade products, use a material with reduced C. Is possible. In addition, when applying the grain-oriented electrical steel sheet according to the present invention as a magnetic shield material that requires only the magnetic permeability, a forsterite film is not particularly necessary. Finish annealing can be performed immediately without charcoal annealing.
[0037]
Si: 1.0 to 8.0 wt%
  Si increases the electrical resistance and contributes effectively to the reduction of iron loss, but this requires at least 1.0 wt%, while exceeding 8.0 wt% not only reduces the magnetic east density, Since the next workability deteriorated remarkably, it was limited to the range of 1.0 to 8.0 wt%. It is particularly preferably in the range of 2.0 to 4.5 wt%.
[0038]
Mn: 0.005 to 3.0 wt%
Mn is an element necessary for improving the hot workability, but if it is less than 0.005 wt%, the effect of addition is poor, while if it exceeds 3.0 wt%, secondary recrystallization becomes difficult, so 0.005 to Limited to a range of 3.0 wt%.
[0039]
O: 30 ppm or less
In the present invention, it is important to reduce O to 30 ppm or less in the slab stage. This is because O greatly inhibits the occurrence of secondary recrystallization in the present invention and is difficult to remove in the subsequent step.
[0040]
Moreover, in this invention, the following elements can be contained suitably for a magnetic characteristic improvement.
Ni: 0.005 to 1.50wt%
  Ni is a useful element that improves the magnetic properties by improving the structure, and can be added as necessary. If the content is less than 0.005 wt%, the improvement in magnetic properties is small. On the other hand, if it exceeds 1.50 wt%, secondary recrystallization becomes unstable and the magnetic properties deteriorate, so the Ni content is 0.005 to 1.50 wt%.
[0041]
Sn: 0.02 to 0.50 wt%, Sb: 0.01 to 0.50 wt%, Cu: 0.01 to 0.50 wt%, Mo: 0.01 to 0.50 wt%
All of the above elements are iron loss improving components, and can be added alone or in combination as required. Here, if the content is less than the lower limit, the effect of improving the iron loss is poor. On the other hand, if the content exceeds the upper limit, secondary recrystallization does not occur. Therefore, the addition amount of each element is limited to the above range.
[0042]
Furthermore, in the present invention, it is necessary to reduce impurity elements as much as possible. In particular, Al is a nitride-forming element that is not only harmful to the occurrence of secondary recrystallized grains but also remains in the ground iron and degrades iron loss. It is less than 100 ppm, B, V, Nb, About each element of S, Se, P, and N, it is necessary to reduce to 50 ppm or less, preferably 30 ppm or less.
Note that these elements do not necessarily have to be reduced to the above range at the material stage, and may be reduced to 50 ppm or less before the final finish annealing. However, since removal is difficult in subsequent processes, it goes without saying that it is desirable to reduce as much as possible at the material stage.
In addition, the above-described content limit is a value not only for the base iron but also for the entire steel sheet including the oxide film on the surface. Here, the surface oxide film means a subscale or an oxide film.
[0043]
Next, the manufacturing process according to the present invention will be specifically described.
First, a slab is manufactured from the molten steel adjusted to the above-mentioned preferred component composition. Such a slab may be manufactured by a normal ingot-bundling method, a continuous casting method, or a thickness of 100 mm or less. Thin cast slabs may be produced by a direct casting method.
The slab is usually heated and hot-rolled, but may be hot-rolled immediately after casting without being heated. In the case of a thin slab, the hot rolling may be omitted and the raw slab may be supplied as it is to the subsequent processes.
[0044]
Next, after performing hot-rolled sheet annealing as necessary, cold rolling is performed once or two or more times with intermediate annealing, followed by decarburization annealing as necessary, and further MgO as necessary. The final annealing is performed after applying the main annealing separator.
Here, it is possible to improve the magnetic properties by performing hot-rolled sheet annealing. It is also useful for stabilizing the magnetic properties to sandwich the intermediate annealing between cold rolling. However, since both increase production costs, the selection of hot-rolled sheet annealing or intermediate annealing is determined from an economic viewpoint.
The preferred temperature range for hot-rolled sheet annealing and intermediate annealing is 700 ° C or higher and 1200 ° C or lower. This is because if the annealing temperature is less than 700 ° C, the recrystallization does not proceed during annealing, so the effect is weak. On the other hand, if it exceeds 1200 ° C, the mechanical strength of the steel sheet decreases and it becomes difficult to pass through the line. .
[0045]
Decarburization annealing is not particularly necessary when a material that does not contain C is used. Further, since the oxidation of the steel sheet surface is performed by the oxide and hydroxide in the annealing separator during the final finish annealing, the oxidation before the final finish annealing is not necessarily required.
Furthermore, prior to the final finish annealing, a technique for increasing the amount of Si after the end of cold rolling by a siliconization method may be used in combination.
[0046]
Now, in the present invention, in the entire steel sheet including the oxide film before final finish annealing, the Al content is 100 ppm or less, and the amount of each element such as B, V, Nb, Se, S, P, N is 50 ppm or less. However, it is an essential condition for causing secondary recrystallization to be limited to 30 ppm or less.
In the present invention, it is important to control the N content in the steel in the temperature range of at least 850 to 950 ° C. within the range of 6 to 80 ppm during the final finish annealing.
This is because if the amount of nitrogen is less than 6 ppm, secondary recrystallization will not occur, so the magnetic properties cannot be improved. On the other hand, if it exceeds 80 ppm, grains with poor orientation will secondary recrystallize. This is because the characteristics are deteriorated. A particularly preferable N content in this temperature range is 20 to 50 ppm.
[0047]
Here, the amount of N in steel can be controlled by the following means.
(a) During the final finish annealing, increase the nitrogen partial pressure in the atmosphere in the temperature range of at least 850-950 ° C. In this case, the nitrogen partial pressure in the atmosphere is changed according to the material component.
(b) A nitriding accelerator is included in the annealing separator. Here, the nitriding agent is TiN, FeN, MnN, etc., which decomposes during the final finish annealing and nitrides the steel sheet. These nitriding agents can be contained in the annealing separator in an amount of about 0.1 to 10 wt%. It ’s fine.
[0048]
Even after the final finish annealing as described above, the Al content in the entire steel sheet including the oxide coating is 100 ppm or less, and the contents of B, V, Nb, Se, S, P, N, etc. are each 50 ppm. In the following, it is desirable to reduce it to 30 ppm or less, and thus good iron loss characteristics can be obtained. For that purpose, it is important to sufficiently reduce such elements in the raw material stage, but it is also important not to include such elements in the annealing separator.
[0049]
Furthermore, in order to further improve the iron loss, it is effective to generate a tension coating on the steel sheet surface. For this purpose, a multilayer film structure composed of two or more kinds of coatings may be used.
Moreover, you may give the coating which mixed resin etc. according to a use.
Furthermore, magnetic domain refinement techniques can be used to obtain good iron loss. Here, as the magnetic domain subdividing method, a method of irradiating a product plate with a pulse laser described in JP-B-57-2252, a method of irradiating a product plate described in JP-A-62-96617, a method of A method of providing grooves by etching before decarburization annealing disclosed in Japanese Patent Publication No. 3-69968 is effective.
[0050]
【Example】
Example 1
Steel slabs having the composition shown in Table 1 were manufactured by continuous casting, and then each slab was heated at 1050 ° C. for 20 minutes, and then hot rolled into 2.5 mm thick hot rolled sheets. Next, hot-rolled sheet annealing was performed at 1000 ° C. for 60 seconds, and then finished to a final sheet thickness of 0.34 mm by cold rolling.
Next, decarburization annealing was performed at 830 ° C for 120 seconds in an atmosphere with hydrogen: 75%, nitrogen: 25%, and dew point: 60 ° C, and after reducing C in the steel to 0.0020wt%, MgO was mainly used. After applying an annealing separator as a component, final finish annealing was performed. For comparison, borax was used as a partial annealing separator.
The final finish annealing was completed by heating to 1050 ° C. at a rate of 15 ° C./h in the atmosphere shown in Table 2.
[0051]
In the above manufacturing process, the steel sheet before final finish annealing was analyzed with the film on and the amounts of Al, B, V, Nb, Se, S, and P were investigated.
Also, the magnetic flux density B of the steel plate after final finish annealing₈And iron loss W_17/50Was measured.
Further, during the final finish annealing, samples were taken out from the coil outer winding portions at temperatures of 850, 900, and 950 ° C., and the nitrogen content in the steel was analyzed.
Further, the steel sheet after the final finish annealing was analyzed with an oxide film, and the amounts of Al, B, V, Nb, Se, S, and P were investigated.
Table 2 summarizes the results obtained.
[0052]
[Table 1]

[0053]
[Table 2]

[0054]
As is apparent from Table 2, the inclusion of Al in the steel sheet with an oxide film before final finish annealing using a steel slab that does not contain an inhibitor component and suppresses the amount of O in steel to 30 ppm or less according to the present invention. The amount of B, V, Nb, Se, S, P, and N is reduced to 50 ppm or less respectively, and the amount of nitrogen in the temperature range of 850 to 950 ° C. is 6 to 80 ppm during final finish annealing. When controlled within the range, products with good magnetic properties could be obtained.
[0055]
Example 2
C: 7 ppm, Si: 3.4 wt%, Mn: 0.15 wt%, N: 29 ppm, O: 10 ppm, Al: 19 ppm, B: 3 ppm, V: 10 ppm, Nb: 20 ppm, Se: 10 ppm, S: 10 ppm, P: A thin slab with a thickness of 4.5 mm containing 30 ppm and the balance being substantially Fe composition was produced by direct casting. Thereafter, it was cold rolled to a final thickness of 0.90 mm.
When the amounts of Al, B, V, Nb, Se, S, P, and N in the cold-rolled sheet before final finishing annealing were analyzed, each element was reduced to 50 ppm or less.
Next, after applying an annealing separator mainly composed of MgO, final finishing annealing was performed. The final finish annealing was completed by heating to 950 ° C. at a rate of 15 ° C./h in the atmosphere shown in Table 3.
[0056]
Magnetic flux density B of the grain-oriented electrical steel sheet thus obtained₈And maximum permeability μ_maxWas measured.
In addition, during the final finish annealing, samples were taken out from the coil outer winding at temperatures of 850, 900 and 950 ° C., and the amount of nitrogen in the steel was analyzed.
[0057]
[Table 3]

[0058]
As shown in Table 3, when a high-purity component thin cast slab that reduces C and does not contain an inhibitor component is used as a material, oxidation before final finish annealing is possible even if decarburization annealing is omitted. The amount of Al, B, V, Nb, Se, S, P and N in the coated steel sheet is reduced to 50 ppm or less respectively, and the nitrogen amount in the temperature range of 850 to 950 ° C. is 6 to 80 ppm during final finish annealing. By controlling in the above manner, a product with good permeability could be obtained.
[0059]
【The invention's effect】
Thus, according to the present invention, a steel slab of a high purity component system that does not contain an inhibitor component is used, and the Al content in a steel plate with an oxide film before final finish annealing is 100 ppm or less, B, V, Nb, Se, S , P and N are reduced to 50 ppm or less, respectively, and during final finish annealing, the amount of nitrogen in the temperature range of 850 to 950 ° C. is controlled to a range of 6 to 80 ppm, thereby obtaining a product with good magnetic properties. be able to.
In addition, according to the present invention, high temperature heating and high temperature purification annealing for removing impurities are not required, so that the economic effect is extremely large.
Furthermore, in the present invention, it is possible to omit the decarburization annealing by using a material that does not contain C in the case of an application that does not require a forsterite coating.
[Brief description of the drawings]
FIG. 1 is a graph showing the existence frequency (%) for each orientation grain at a grain boundary having an orientation difference angle of 20 to 45 ° before finish annealing.
FIG. 2 is a graph showing the relationship between the amount of nitrogen in steel during finish annealing and the magnetic flux density after finish annealing.
FIG. 3 is a graph showing the relationship between the content of each impurity element and the magnetic flux density.
FIG. 4 is a graph showing the relationship between the amount of each element added and iron loss.

Claims (5)

C: 0.12 wt% or less,
Si: 1.0-8.0 wt%
Mn: 0.005 to 3.0 wt%
The steel slab with a balance of Fe and inevitable impurities is hot-rolled and then subjected to hot-rolled sheet annealing as necessary, and then cold-cooled twice or more sandwiching one or intermediate annealing. A directional electrical steel sheet consisting of a series of processes that are finished to the final sheet thickness by performing hot rolling, then decarburized and annealed as necessary, and further applied with an annealing separator as necessary, followed by final finish annealing. In the manufacturing method of
(1) To suppress the O content in the steel slab to 30 ppm or less,
(2) At least the Al content in impurities is 100 ppm or less, and the contents of B, V, Nb, Se, S, P and N are each 50 ppm or less in the whole steel sheet including the oxide film before final finish annealing. To suppress,
(3) A method for producing a grain-oriented electrical steel sheet characterized by controlling the amount of N in steel in a temperature range of at least 850 to 950 ° C. to a range of 6 to 80 ppm during final finish annealing. In claim 1, the means for controlling the amount of N in steel during the final finish annealing,
(a) increasing the nitrogen partial pressure in the atmosphere up to a temperature range of at least 850 to 950 ° C. during final finish annealing;
(b) A method for producing a grain-oriented electrical steel sheet, characterized in that any one or two or more treatments of containing a nitriding accelerator in the annealing separator. 3. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the steel slab is directly subjected to hot rolling without heating. In Claim 1, 2, or 3, the thickness obtained by direct casting from molten steel: hot rolling using a thin slab of 100 mm or less, or using the thin slab as a hot-rolled sheet material as it is A method for producing a grain-oriented electrical steel sheet, comprising: The steel slab according to claim 1, 2, 3, or 4, further comprising:
Ni: 0.005 to 1.50 wt%
Sn: 0.02-0.50wt%
Sb: 0.01 to 0.50 wt%,
Cu: 0.01 to 0.50 wt% and
Mo: 0.01-0.50wt%
A method for producing a grain-oriented electrical steel sheet, comprising a composition containing one or more selected from among the above.

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