JP2001107147A - Method for producing grain-oriented silicons steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an advantageous method for producing a grain-oriented silicon steel sheet in which various problems incidental to high temperature slab heating before hot rolling and high temperature purification annealing after secondary recrystallization which have been apprehended in the case of using inhibitors are advantageously evaded. SOLUTION: At the time of producing a grain-oriented silicon steel sheet, the content of Al as impurities in the steel is reduced to <100 ppm, moreover, the contents of Se, S, O and N are respectively reduced to <=30 ppm, and furthermore, after the completion of primary recrystallization, in the meanwhile, till the steel sheet temperature reaches 850 deg.C at the time of final finish annealing, the content of nitrogen in the steel is increased to >=30 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet mainly used for a core material of a power transformer.

[0002]

2. Description of the Related Art In the production of grain-oriented electrical steel sheets, it is a general technique to utilize precipitates called inhibitors to perform secondary recrystallization during final finish annealing. For example, AlN, described in Japanese Patent Publication No. 40-15644,
The method using MnS and the method using MnS and MnSe described in JP-B-51-13469 are typical ones, and all of them are industrially practically used. In addition, regarding the use of such inhibitors, CuSe and B
Technology for adding N (Japanese Patent Publication No. 58-42244), Ti,
Many techniques are known, such as a method using a nitride of Zr, V (Japanese Patent Publication No. 46-40855).

[0003] The method using these inhibitors is a useful method for stably developing secondary recrystallized grains, but it is necessary to disperse precipitates finely. It must be performed at a high temperature of 1300 ° C or higher. However, the high-temperature heating of the slab increases the equipment cost for realizing the heating, and also increases the amount of scale generated during hot rolling, so that not only the yield decreases, but also problems such as equipment maintenance are caused. More.

Further, from the viewpoint of the crystal structure, there is a problem that such high-temperature heating of the slab causes excessively coarsening of the slab crystal structure. That is, the crystal structure of the slab has a stable hot rolling orientation and is hard to recrystallize.
Since the slab structure is accumulated in the 00 ° <011> direction, such a coarsening of the slab structure results in a large hindrance to secondary recrystallization and a large deterioration in magnetic characteristics.

[0005] As a method for solving the above-mentioned problems, a method for reducing
Although Al is contained, by reducing the amount of N,
A method of omitting high-temperature heating of the slab, forming (Si, Al) N by nitriding treatment before secondary recrystallization, and functioning as an inhibitor to perform secondary recrystallization is disclosed in
-45285. In order to obtain good iron loss by this method, it worked as an inhibitor (S
In order to remove i, Al) N from the steel, it is necessary to carry out several hours of purification annealing in a hydrogen atmosphere at 1100 ° C. or higher following completion of the secondary recrystallization. However, due to such high-temperature annealing, there is a problem that the mechanical strength of the steel sheet is reduced, the lower part of the coil buckles, and the yield of the product is significantly reduced. Further, the (Si, Al) N precipitate is removed from the steel by the purification annealing, but is not completely removed from the surface oxide film, and thus remains on the surface (Si, Al). Even a small amount of N precipitates significantly hinders the movement of the domain wall, so that the core loss must be deteriorated.

In order to solve the above-mentioned problems, a method for producing a grain-oriented electrical steel sheet without using an inhibitor is disclosed in JP-A-64-55339, JP-A-2-57635, and JP-A-7-76.
732 and JP-A-7-197126. What is common to these techniques is that the {110} plane is preferentially grown using surface energy as a driving force. Here, in order to effectively use the surface energy difference, it is inevitably required to reduce the plate thickness in order to increase the contribution of the surface.

For example, in the technique disclosed in JP-A-64-55339, the thickness is limited to 0.2 mm or less, and in the technique disclosed in JP-A-2-57635, the thickness is limited to 0.15 mm or less. . According to the technique disclosed in Japanese Patent Application Laid-Open No. 7-76732, the thickness is not limited, but according to Example 1, the thickness is 0.30.
The magnetic flux density in the case of mm is 1.700 T or less at B ₈ , and the azimuth integration degree is extremely low. The thicknesses of the examples in which good magnetic flux density is obtained are all limited to 0.10 mm. Even in the technique disclosed in Japanese Patent Application Laid-Open No. 7-197126, the sheet thickness is not limited, but since this technique is a technique of performing 50 to 75% tertiary cold rolling, the sheet thickness is inevitably reduced. In the embodiment, the thickness is 0.10 mm. Since the thickness of 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 surface energy as described above.

In order to use surface energy, high-temperature final finish annealing must be performed in a state where formation of surface oxides is suppressed. For example, JP-A-64-55339
In the technology disclosed in Japanese Patent Application Laid-Open Publication No. H11-260, it is described that the annealing is performed at a temperature of 1180 ° C. or more, in a vacuum, an inert gas, a hydrogen gas, or a mixed gas of a hydrogen gas and a nitrogen gas, as the annealing atmosphere. . According to the technique disclosed in Japanese Patent Application Laid-Open No. 2-57635, at a temperature of 950 to 1100 ° C., in an inert gas atmosphere, a hydrogen gas atmosphere, or a mixed atmosphere of hydrogen gas and an inert gas,
Moreover, it is recommended to reduce the pressure. In the technique disclosed in Japanese Patent Application Laid-Open No. 7-197126, the final finish annealing is performed at a temperature of 1000 to 1300 ° C. in a non-oxidizing atmosphere or a vacuum with an oxygen partial pressure of 0.5 Pa or less.

As described above, in order to obtain good magnetic properties by utilizing surface energy, an inert gas or hydrogen is used as an atmosphere for the final finish annealing, and further, a recommended condition is a vacuum or the like. However, it is extremely difficult to achieve both high temperature and vacuum in terms of equipment, resulting in high costs.
Also, when surface energy is used, in principle, ｛1
Only the 10 ° plane can be selected, and the growth of only goth grains whose <001> direction is aligned with the rolling direction is not necessarily selected. The grain-oriented electrical steel sheet has an easy axis <001 in the rolling direction.
>, The improvement of the magnetic properties can be expected. Therefore, good magnetic properties cannot be obtained in principle only by selecting the {110} plane. Therefore, the rolling conditions and annealing conditions under which good magnetic properties can be obtained by a method using surface energy are limited, and as a result, the magnetic properties have to be unstable.

[0010]

SUMMARY OF THE INVENTION The present invention has been developed in view of the above-mentioned circumstances, and does not contain an inhibitor component in a material, so that the heat generated during the production of a grain-oriented electrical steel sheet containing an inhibitor is eliminated. An object of the present invention is to propose an advantageous method for manufacturing a grain-oriented electrical steel sheet, which advantageously avoids various problems associated with high-temperature slab heating before elongation and high-temperature purification annealing after secondary recrystallization. Also, the present invention
The present invention has also effectively solved the limitations on the thickness of the steel sheet and the deterioration of the degree of secondary recrystallization orientation integration, which are inevitably involved when surface energy is used without using an inhibitor.

[0011]

The details of the present invention will be described below. By the way, the present inventors have conducted intensive studies on the mechanism of secondary recrystallization of Goss-oriented grains. As a result, the present inventors have found that the misorientation angle in the primary recrystallized structure (the minimum rotation required for overlapping the lattices of adjacent crystals). Acta) found that grain boundaries with an angle of 20-45 ° played an important role.
Material 45 (1997) Reported on page 85.

FIG. 1 shows an analysis of a primary recrystallized structure, which is a state immediately before the primary recrystallization of a grain-oriented electrical steel sheet. The result which investigated the ratio (%) with respect to the whole of the grain boundary which is 20-45 degrees is shown. In FIG. 1, the crystal orientation space is displayed using a section of Φ ₂ = 45 ° at Euler angles (Φ ₁ , Φ, Φ ₂ ), and the main directions such as Goss direction are schematically displayed. According to the figure, the frequency of the presence of the grain boundary having the misorientation angle of 20 to 45 ° around the Goss grain is the highest (about 80 degrees).
%).

A misorientation angle: a grain boundary of 20 to 45 ° is obtained from experimental data by CGDunn et al. (AIME Transaction vol. 188 (1949) p.
According to 368), it is a high energy grain boundary. The high energy grain boundary has a large free space in the grain boundary and has a random structure. Since the grain boundary diffusion is a process in which atoms move through the grain boundary, the high energy grain boundary having a large free space in the grain boundary has a faster grain boundary diffusion. It is known that secondary recrystallization develops with the growth of a precipitate called an inhibitor by diffusion control. The precipitate on the high energy grain boundary is
It is considered that the coarsening preferentially proceeds during the finish annealing, so that the pinning is preferentially released, the grain boundary starts to move, and the goth grains grow.

The present inventors have further developed this research, and the essential factor for the appearance of secondary recrystallization is the distribution of high-energy grain boundaries in the primary recrystallized structure, and the role of the inhibitor is as follows. It has been found that a difference in the moving speed between a high energy grain boundary and another grain boundary is caused. Therefore,
According to this theory, secondary recrystallization can be performed without using an inhibitor if a difference in the moving speed of the grain boundary can be generated.

[0015] Since impurity elements existing in steel tend to segregate at grain boundaries, especially at high energy grain boundaries, 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 it is. Therefore, if the influence of such an impurity element is eliminated by purifying the material, a difference in the original moving speed depending on the structure of the high-energy grain boundary becomes apparent, and the secondary recrystallization of the Goss-oriented grains is performed. It is expected to be possible.

As a result of further research based on the above considerations, the present inventors have found that, in a component system containing no inhibitor component, the inventors purify the material, and after completing the primary recrystallization, complete the steel plate during final finish annealing. By completely increasing the amount of nitrogen in the steel until the temperature reaches 850 ° C, the inventors have found out completely that secondary recrystallization effectively occurs, and have completed the present invention. .

That is, the gist configuration of the present invention is as follows. 1. C: 0.12 wt% or less, Si: 2.0 to 8.0 wt% and Mn:
Contains 0.005 to 1.0 wt%, Al is less than 100 ppm, S
e, S, O, and N are each reduced to 30 ppm or less. A steel slab having a component composition of 30 ppm or less is hot-rolled and, if necessary, subjected to hot-rolled sheet annealing. Cold rolling, followed by primary recrystallization annealing, then applying an annealing separator if necessary, and then producing a secondary recrystallization by final finish annealing. In the steel sheet manufacturing method, after the primary recrystallization is completed, the steel sheet temperature is 850 ° C in the final finish annealing process.
A method for producing a grain-oriented electrical steel sheet, wherein the nitrogen content in the steel is increased to 30 ppm or more before the steel reaches the temperature.

2. The means for increasing the amount of nitrogen in the steel is to increase the nitrogen partial pressure during the final finish annealing, to add a compound having a nitriding ability to the annealing separator, and after the primary recrystallization is completed, perform annealing in an atmosphere having a nitriding ability. 2. The method for producing a grain-oriented electrical steel sheet according to the above item 1, wherein the method is any one of the steps or a combination thereof.

3. 3. The method for producing a grain-oriented electrical steel sheet according to 1 or 2, wherein the basis weight of oxygen on the steel sheet surface after the primary recrystallization annealing is 1.0 g / m ² or less per one side.

4. 150μm average grain size before final cold rolling
Below, and the final cold rolling reduction is 70% or more and 91% or less,
The method for producing a grain-oriented electrical steel sheet according to the above 1, 2, or 3, wherein a {110} <001> structure is grown.

5. 200μm average grain size before final cold rolling
And the final cold rolling reduction is 60% or more and 90% or less,
4. The method for producing a grain-oriented electrical steel sheet according to the above 1, 2, or 3, wherein a {100} <001> structure is grown.

6. In steel, Ni: 0.01-1.50 wt%,
Sn: 0.01 to 0.50 wt%, Sb: 0.005 to 0.50 wt%, Cu: 0.01
~ 0.50wt%, Mo: 0.005 ~ 0.50wt% and Cr: 0.01 ~ 1.
6. The method for producing a grain-oriented electrical steel sheet according to any one of the above items 1 to 5, wherein at least one selected from 50 wt% is contained.

The present invention uses a material that does not contain an inhibitor component, is a concept completely opposite to the conventional secondary recrystallization technique in that precipitates and impurities at crystal grain boundaries are eliminated, and has a low surface energy. Since the technology used is also different, it is possible to cause secondary recrystallization even if an oxide is present on the steel sheet surface.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the results of experiments which led to the success of the present invention will be described. Experiment 1 C: 0.007 wt%, Si: 3.44 wt% and Mn: 0.054 wt%, and N: 5 ppm, Al: 15 ppm, Se:
Steels A and C reduced to 3 ppm, S: 18 ppm, O: 10 ppm A and C: 0.005 wt%, Si: 3.33 wt%, Mn: 0.062 wt%,
N: 0.0090wt%, impurity element: Al: 15ppm, Se:
Slabs of steel B reduced to 3 ppm, S: 18 ppm, and O: 10 ppm were each manufactured by continuous casting. Then 1120
After heating to ° C., a hot-rolled sheet having a thickness of 2.7 mm was formed by hot rolling, and then soaked in a nitrogen atmosphere at 1020 ° C. for 30 seconds, followed by rapid cooling. Then, after performing cold rolling to finish to a final thickness of 0.35 mm, the atmosphere dew point is 920 ° C. in a dry Ar atmosphere at −20 ° C.
Primary recrystallization annealing was performed at ℃ for 15 seconds.

Next, the final finish annealing is performed at a rate of 20 ° C./h.
The test was performed by raising the temperature to 1050 ° C. At this time, experiments were conducted in which the nitrogen partial pressure during the finish annealing was varied. As a result, in steel A, secondary recrystallization occurred on the entire surface of the steel sheet when the nitrogen partial pressure was about 10% or more, but in steel B,
No secondary recrystallization occurred at any nitrogen partial pressure.

Based on this finding, as a result of further research, it was found that primary elements using impurity elements other than Si and Mn, in particular, high-purity materials with a reduced amount of O and inhibitor-forming elements such as N, Al, Se, and S were used. After recrystallization is completed, the steel sheet temperature during final finish annealing
It was newly determined that secondary recrystallization was effectively developed by appropriately increasing the amount of nitrogen in steel before reaching 850 ° C.

FIG. 2 shows that the temperature of the steel sheet was 8 at the time of final finish annealing.
The results obtained by examining the relationship between the amount of nitrogen in the steel, which was taken out and examined when the temperature reached 50 ° C., and the secondary recrystallization completion area ratio of the steel sheet after the final finish annealing, are shown. As shown in the figure, in steel A, the secondary recrystallization completion area ratio is 100% when the nitrogen content in the steel is 30 ppm or more. In contrast,
In steel B containing N from the material stage, the secondary recrystallization is not completed even if nitrogen is present in the steel.

Next, the present inventors have made intensive studies on the primary recrystallization annealing conditions in order to find more stable secondary recrystallization conditions. Experiment 2 That is, using the slab of steel A in Experiment 1 described above, after finishing up to cold rolling in the same process, an experiment was conducted in which the atmosphere oxidizability of the primary recrystallization annealing was variously changed.
The final finish annealing is performed in a nitrogen atmosphere at a dew point of -20 ° C.
The heating was completed at a rate of 10 ° C./h up to 1050 ° C. Through this experiment, it was newly found that secondary recrystallization was particularly favorably performed by reducing the basis weight of oxygen after primary recrystallization annealing.

FIG. 3 shows the results of a study on the relationship between the basis weight of oxygen after primary recrystallization annealing, the secondary recrystallization completion area ratio, and the secondary recrystallization particle size. As shown in the figure, the secondary recrystallization completion rate becomes 100% when the oxygen basis weight is 1.0 g / m ² or less, and the secondary recrystallized grains become larger as the oxygen basis weight decreases, and the secondary recrystallization is favorably performed. It was found to crystallize.

Further, the inventors conducted the following experiment to clarify the relationship between the texture obtained by secondary recrystallization and the cold rolling step using a high-purity material containing no inhibitor. Was. Experiment 3 C: 0.022 wt%, Si: 3.32 wt% and Mn: 0.050 wt%, and the impurity elements are Al: 39 ppm, Se: 6 ppm, S:
Steel slabs reduced to 13 ppm, O: 10 ppm and N: 5 ppm were produced by continuous casting. Then, after heating to 1050 ° C,
After a hot-rolled sheet having a thickness of 2.8 mm was formed by hot rolling, the hot-rolled sheet was annealed in a hydrogen atmosphere at various temperatures and soaking conditions. Then, after finishing to a final thickness of 0.30 mm by cold rolling at a temperature of 200 ° C, the dew point is set to 30 ° C in a hydrogen atmosphere.
Primary recrystallization annealing was performed at 50 ° C for 20 seconds. At this time, the basis weight of oxygen after primary recrystallization annealing was 0.4 g / m ² . Thereafter, final finish annealing was performed in nitrogen at 10 ° C./h at a rate of 1020 ° C. In this experiment, when the steel plate temperature during final annealing reached 850 ° C, the nitrogen content in the steel was 40-60 ppm.
, And 100% secondary recrystallization could be completed under all hot-rolled sheet annealing conditions.

When the secondary recrystallized structure obtained in this experiment was examined, it was found that there was a close relationship between the particle size before final cold rolling and the secondary recrystallized structure. FIG.
In addition, Goss structure {110} <0 in secondary recrystallization orientation
01> and the cube organization {100} <001>. In each case, the azimuth difference angle from the ideal azimuth is 15
It was indicated by the area ratio of secondary recrystallized grains within °. According to the figure, it is completely newly found that the goss structure develops when the grain size before cold rolling is as small as 150 μm or less, while the cube structure develops when the grain size before cold rolling is as large as 200 μm or more. Was.

The Goss structure is a unidirectional magnetic steel sheet mainly used as an iron core material for transformers, while the cube structure is a bidirectional electromagnetic steel sheet mainly used as a core material for large generators and motors. The fact that these differently oriented magnetic steel sheets can be manufactured by using the same material and adjusting the grain size before cold rolling, which can be easily controlled, can be said to be a completely new technology that has not been available before.

Further, FIGS. 5 and 6 show the results of investigations on the cold rolling reduction in order to obtain a highly integrated Goss structure and cube structure. FIG. 5 shows that the particle size before cold rolling was 98 μm.
6 shows the relationship between the reduction ratio of the cold rolling and the magnetic flux density in the rolling direction of the product sheet for the steel sheet having a grain size of 222 μm before cold rolling. 2 shows the relationship between the rolling direction and the average magnetic flux density in the direction perpendicular to the rolling direction. According to FIG. 5, when the grain size before cold rolling is 98 μm, a goss structure is suitably developed when the rolling reduction is 70% or more and 91% or less, and the magnetic flux density B ₈ in the rolling direction is 1.80 T or more. That is, a good characteristic value. On the other hand, according to FIG. 6, when the grain size before cold rolling is 222 μm, the rolling reduction of the cold rolling is 60%.
More than 90% or less of the cube structure develops favorably,
The average magnetic flux density B ₅₀ in the rolling direction and the direction perpendicular to the rolling direction is 1.825T
Good characteristic values as described above are obtained.

[0034]

[Action] In a component system containing no inhibitor component,
By purifying the material and increasing the nitrogen content in the steel to 30 ppm or more by the time the temperature of the steel plate during final annealing reaches 850 ° C, favorable secondary recrystallization occurs.
Although the reason why a high magnetic flux density can be obtained has not yet been clearly elucidated, the inventors consider as follows. In the high-purity material containing no inhibitor according to the present invention, it is considered that the easiness of movement of the grain boundaries reflects the grain boundary structure. In this regard, the impurity element is likely to segregate preferentially at the grain boundary, especially at the high energy grain boundary, so that when the impurity element is contained in a large amount, there is no difference in the moving speed between the high energy grain boundary and another grain boundary. it is conceivable that. It is presumed that if the influence of such impurity elements is eliminated by purifying the material, the superiority of the moving speed of the high-energy grain boundaries will occur, and the secondary recrystallization of Goss-oriented grains will be possible. .

The influence of the trace N is considered as follows. After the completion of the primary recrystallization in the present invention, the presence form of nitrogen increased until the steel sheet temperature at the time of final finish annealing reaches 850 ° C. does not contain inhibitor-forming elements such as Al, B, Nb, and V; Considering that silicon nitride, which is considered to be the only nitride-forming element, cannot stably exist at high temperatures of 800 ° C or higher, it is thought that it acts almost as a solid solution in the temperature range of 850 ° C or higher. Can be Since the grain boundary movement is promoted by the purification of the material, the particle size after the primary recrystallization is about 30 to 100 μm, which is 5 to 10 times as large as that in the case where the inhibitor is present. If the amount of N is not increased after the completion of recrystallization until the steel sheet temperature during final finish annealing reaches 850 ° C, grain growth is not suppressed in the temperature range where grain boundary movement of 850 ° C or more is possible, It is considered that secondary recrystallization does not occur because the grain boundary energy as a driving force for secondary recrystallization tends to be insufficient. It is presumed that the effect of solute nitrogen is an effect of suppressing grain growth and securing a driving force for secondary recrystallization. The reason why it is important to increase the amount of nitrogen before reaching 850 ° C at the time of final finish annealing is because the grain boundaries are selectively nitrided by rapid grain boundary diffusion below the temperature range where grain boundary migration starts. It is presumed that it is necessary to suppress grain boundary movement.

The technique of the present invention is disclosed in JP-B-62-45285.
The method differs from the method disclosed in Japanese Patent Application Publication No. JP-A-2003-175572 in which Al is contained in a material component and nitriding treatment is performed before secondary recrystallization to perform secondary recrystallization. That is, in the case of the technique disclosed in Japanese Patent Publication No. Sho 62-45285, the existence form of nitrogen after nitriding exists in a precipitated state of (Si, Al) N, and the distribution of nitride in steel is almost uniform. And the difference between the grain boundaries and within the grains is small. Further, in order to make the (Si, Al) N precipitate formed in the method of secondary recrystallization by containing Al in the material component and performing a nitriding treatment before the secondary recrystallization function as an inhibitor, There is a need for an amount of N that is greater than the 60 to 100 ppm N required in the prior art where MnS or MnSe is used in combination with AlN as an inhibitor at the stage. For example, in the example of Japanese Patent Publication No. 62-45285, the nitriding amount at 850 ° C. is 148 ppm and 145 ppm.
(P. 7, left column, line 13).
No. 631 stipulates that the N content be 0.01 wt% (100 ppm) or more.

On the other hand, in the present invention, since the solid solution nitrogen is mainly used, the necessary amount of N is about 30 ppm is sufficient. In the present technology, when N is contained in the material in advance, secondary recrystallization does not occur, so that the incorporation of N in the material must be reduced as much as possible. When N was present at 30 ppm or more before the primary recrystallization annealing, a precipitate of silicon nitride was formed in the steel, and after the primary recrystallization was completed, the N content was increased during the final finish annealing. In this case, it is presumed that silicon nitride newly precipitates with the precipitate of silicon nitride existing before recrystallization annealing as a nucleus, and selective nitridation at the grain boundary does not occur. If selective nitridation at the grain boundaries does not occur, the effect of suppressing the grain growth will not be sufficient with a nitrogen amount of about 30 ppm, and silicon nitride will be unstable at high temperatures compared to (Si, Al) N precipitates. Therefore, it is estimated that secondary recrystallization does not occur even if about 80 ppm of nitrogen is present.

Further, even if the solid solution nitrogen remains in the product plate, it does not hinder the domain wall movement unlike the nitride precipitate, so that it is not particularly necessary to remove the solid solution nitrogen by performing high-temperature purification annealing. Therefore, in the present invention, at the time of completion of the secondary recrystallization or the formation of the forsterite film, the final finish annealing can be completed, and it goes without saying that the productivity is improved.
This is far superior to the prior art in that the equipment can be simplified and the lower part of the coil can be prevented from buckling during high-temperature annealing.

The technology of the present invention is superior to the technology utilizing surface energy in the following points. First, since the secondary recrystallization is performed using the grain boundary energy as a driving force, there is no restriction on the thickness of the sheet. For example, secondary recrystallization is possible even for a plate with a thickness of 1 mm or more, and such a thick product can be used as a magnetic shielding material because its iron loss value is deteriorated but its magnetic permeability is high. . In addition, secondary recrystallization can be performed at a temperature of 850 to 950 ° C. where a general heat treatment is performed while the surface oxide is generated. Furthermore, the atmosphere for the final finish annealing does not need to use vacuum or expensive inert gas, and can be performed mainly using inexpensive nitrogen, which is most commonly used.

Next, the reason why the composition of the material slab is limited to the above range in the present invention will be described. C: 0.12 wt% or less C does not affect the appearance of secondary recrystallization itself,
If the content exceeds 0.12 wt%, the generation amount of the γ phase in the hot-rolled sheet increases, and as a result, it adversely affects the development of the texture during recrystallization annealing and decreases the degree of integration of the secondary recrystallization orientation. In addition, since it becomes difficult to reduce the magnetic aging during primary recrystallization annealing to 50 ppm or less, which is a range that does not cause magnetic aging, the C content is limited to 0.12 wt% or less.

Si: 2.0 to 8.0 wt% Si is a useful element for increasing electric resistance and improving iron loss, but its effect is poor if the content is less than 2.0 wt%.
In addition, γ transformation occurs and the hot-rolled structure changes significantly, and it transforms in the final finish annealing, so that good magnetic properties cannot be obtained. On the other hand, if the Si content exceeds 8.0 wt%, the secondary workability of the product deteriorates and the saturation magnetic flux density also decreases, so the Si content was limited to the range of 2.0 to 8.0 wt%.

Mn: 0.005 to 1.0 wt% Mn is an element necessary for improving hot workability, but if it is less than 0.005 wt%, the effect of its addition is poor.
If it exceeds 1.0 wt%, the magnetic flux density will decrease, so the Mn content will be
It was limited to the range of 005 to 1.0 wt%.

Al: less than 100 ppm, Se, S, O and N:
30 ppm or less All of these elements inhibit the appearance of secondary recrystallization,
Moreover, it is a harmful element that remains in the base iron and deteriorates iron loss. Therefore, Al is less than 100 ppm, Se, S, O and N
Were reduced to 30 ppm or less (preferably 20 ppm or less).

Although the essential components and the suppressing components have been described above, the present invention may contain other elements as described below. First, Ni can be added to improve the magnetic flux density. However, if the addition amount is less than 0.01 wt%, the improvement amount of the magnetic properties is small,
On the other hand, if the content exceeds 1.50 wt%, secondary recrystallized grains are insufficiently developed and satisfactory magnetic properties cannot be obtained.
50 wt%. In addition, in order to improve iron loss, Sn: 0.01
~ 0.50wt%, Sb: 0.005 ~ 0.50wt%, Cu: 0.01 ~ 0.50wt
%, Mo: 0.005 to 0.50 wt%, and Cr: 0.01 to 1.50 wt%. Any of these elements has no effect of improving iron loss when the added amount is less than the above range, while when the added amount is large, secondary recrystallized grains do not develop and lead to deterioration of iron loss.

Next, the manufacturing conditions of the present invention will be described. The molten steel adjusted to the above preferable component composition is usually made into a slab by an ingot-making method or a continuous casting method. Further, a thin slab having a thickness of 100 mm or less may be directly manufactured using a direct casting method. The slab is heated and hot rolled in the usual way,
After casting, it may be subjected to hot rolling immediately without heating. Also,
In the case of a thin slab, hot rolling may be performed, or the hot rolling may be omitted and the process may proceed to the subsequent steps. Since the slab heating temperature does not include the inhibitor component in the raw material component, a minimum temperature of about 1100 ° C. at which hot rolling is possible is sufficient.

Next, after hot-rolled sheet annealing is performed as necessary, one or more cold-rolling steps including intermediate annealing are performed as necessary, and then primary recrystallization annealing is performed. Hot rolled sheet annealing
It is useful for improving magnetic properties. Similarly, sandwiching intermediate annealing between cold rollings is useful for stabilizing magnetic properties. However, since both increase the production cost, the selection of hot-rolled sheet annealing and intermediate annealing, and the annealing temperature and time are determined from the economical viewpoint and the necessity of setting the primary recrystallized grain size to an appropriate range. . After the final cold rolling or primary recrystallization annealing, the silicon
Techniques for increasing the amount may be used in combination.

Then, after the completion of the primary recrystallization, an annealing separator is applied as required, and then subjected to final finish annealing.
In the present invention, in the final finish annealing step, until the steel sheet temperature reaches 850 ℃, the nitrogen content in the steel 30 ppm
It is particularly important to increase the above. Methods for increasing the amount of nitrogen in steel include: a) increasing the partial pressure of nitrogen during the final finish annealing; b) adding a compound capable of nitriding into the annealing separator; c) after completion of the primary recrystallization. Performing annealing in an atmosphere having a nitriding ability or a combination thereof is preferable.

Here, in order to increase the nitrogen content in the steel by increasing the nitrogen content during the final finish annealing, the nitrogen partial pressure in the atmosphere until the steel plate temperature reaches 850 ° C. is increased by 10%.
It is preferable to make the above. The compound having nitriding ability to be added to the annealing separator is not particularly limited, but ferromanganese nitride, manganese nitride, titanium nitride, molybdenum nitride, and the like are advantageously suitable. Further, the atmosphere having a nitriding ability is not particularly limited, but ammonia or the like is advantageously suitable.

In the above-mentioned final finish annealing, the upper limit of the steel sheet temperature for increasing the nitrogen content in the steel to 30 ppm or more is 850 ° C.
The reason is that if the temperature of the steel sheet exceeds 850 ° C., the movement of the grain boundary starts, the grain growth of the matrix occurs, the secondary recrystallization becomes unstable, and the magnetic properties deteriorate. If the nitrogen content at this temperature is less than 30 ppm, the effect of suppressing the grain boundary movement by solid solution nitrogen is insufficient and secondary recrystallization becomes unstable, so the nitrogen content should be increased to 30 ppm or more. It is necessary.

In the final finish annealing, since the secondary recrystallization completion temperature is in a range of approximately 850 to 1,050 ° C., the temperature can be raised to this temperature at an arbitrary rate and kept at this temperature range for at least 20 hours. desirable. At this time, the annealing atmosphere may be any non-oxidizing atmosphere necessary to increase or maintain the N content in the steel, and may be nitrogen, hydrogen, Ar, or a mixed atmosphere thereof.

The atmosphere for the primary recrystallization annealing may be any non-oxidizing atmosphere, such as nitrogen, hydrogen, Ar or a mixed atmosphere thereof. However, in order to obtain a good secondary recrystallization structure, the primary recrystallization It is preferable that the oxygen basis weight of the steel sheet surface after the crystal annealing is 1.0 g / m ² or less per one side. By reducing the oxygen basis weight after the primary recrystallization annealing, the reason why secondary recrystallization is particularly favorably brought about is to reduce the oxide layer on the surface layer, after the completion of the primary recrystallization, during the final finish annealing. In addition to the effect of easily increasing the amount of N in steel, the surface oxide promotes internal oxidation as a supply source of oxygen, thereby forming secondary recrystallization nuclei that are considered to be generated from the surface layer of the plate. It is thought that it is affecting.

Further, in the present invention, in order to obtain a Goss structure developed by secondary recrystallization, the average crystal grain size before final cold rolling is set to 150 μm or less, and the final cold rolling reduction is reduced.
It is preferable to be 70% or more and 91% or less, and outside this range, the degree of integration of the Goss structure in the secondary recrystallized structure decreases, and the magnetic flux density in the rolling direction decreases. In order to obtain a cube structure developed by secondary recrystallization, it is preferable that the average crystal grain size before final cold rolling is 200 μm or more, and the final cold rolling reduction is 60% or more and 90% or less. Outside this range, the degree of integration of the cube structure in the secondary recrystallized structure decreases, and the average magnetic flux density in the rolling direction and the direction perpendicular to the rolling decreases.

As described above, the particle size before final cold rolling was 150 μm.
m or less and a final cold rolling reduction of 70 to 91%, the reason why a Goss structure is obtained by secondary recrystallization is that the grain diameter before final cold rolling is kept small and the cold rolling reduction is reduced. By increasing the height, recrystallization nucleation from the grain boundary during recrystallization annealing is promoted, and the azimuth difference angle from the Goss orientation is 20 to
The {111} recrystallized grains in the range of 45 ° increase, and the Goss oriented grains undergo secondary recrystallization due to preferential movement of high-energy grain boundaries in which the misorientation angle is 20 to 45 ° during final finish annealing. It is considered that a texture advantageous to the above is formed. The reason why the cube structure ({100} <001> structure) can be obtained by secondary recrystallization by setting the particle size before final cold rolling to 200 μm or more and the final rolling reduction to 60 to 90%. Is to reduce the recrystallization nucleation from grain boundaries during recrystallization annealing by increasing the grain size before final cold rolling and making the cold rolling reduction slightly lower, and recrystallizing from the deformation zone in the grains. It promotes nucleation, increases {411} <148> recrystallized grains and goss oriented recrystallized grains whose misorientation angle with the cube orientation is in the range of 20 to 45 °, and has a misorientation angle of 20 during the final finish annealing. It is considered that the preferential movement of the high-energy grain boundary of about 45 ° forms a texture advantageous for secondary recrystallization of the cube-oriented grains.

When the steel sheets are laminated and used,
After the above-mentioned final finish annealing, it is effective to apply an insulating coating to the steel sheet surface in order to improve iron loss. For this purpose, a multilayer film composed of two or more kinds of films may be used, or a coating mixed with a resin or the like may be applied according to the application.

[0055]

EXAMPLES Example 1 C: 40 ppm, Si: 3.45 wt%, Mn: 0.25 wt%, Al: 30 pp
m, Se: 4 ppm, S: 5 ppm, N: 7 ppm and O: 7
A steel slab containing ppm and the balance substantially consisting of Fe was manufactured by continuous casting. Then, after slab heating at 1150 ° C for 300 minutes, a hot-rolled sheet with a thickness of 2.5 mm was formed by hot rolling, followed by annealing at 950 ° C for 60 seconds, and then a 0.35 mm final sheet by cold rolling. Finished thick. The average particle size before cold rolling was 70 μm. Then, after performing primary recrystallization annealing at 900 ° C. for 30 seconds in an Ar atmosphere with variously changed dew points, final finish annealing was performed at a rate of 15 ° C./h in various atmospheres shown in Table 1. The test was performed by raising the temperature to 1050 ° C. During the final annealing, a sample was taken when the temperature of the steel sheet reached 850 ° C., and the amount of nitrogen in the steel was investigated. After that, apply a coating liquid mixed with aluminum dichromate, emulsion resin and ethylene glycol,
The product was baked at 300 ° C. Table 1 shows the dew point of the atmosphere during the primary recrystallization annealing, the oxygen basis weight on the steel sheet surface after the primary recrystallization annealing, and the atmosphere of the final finish annealing.
The result of having investigated about the amount of nitrogen in steel at the time of reaching ° C and the magnetic properties of the obtained product is shown.

[0056]

[Table 1]

As shown in Table 1, during the final finish annealing, when the steel sheet temperature was 850 ° C. and the nitrogen content in the steel was 30 ppm or more, good magnetic properties were obtained. In particular, when the oxygen basis weight after the primary recrystallization annealing is low, more excellent magnetic properties are obtained.

Example 2 A steel slab having the composition shown in Table 2 was produced by continuous casting. Then, without heating the slab, it was finished by direct hot rolling to 3.8 mm, hot rolled sheet annealing at 900 ° C for 30 seconds, the first cold rolling to 2.0 mm intermediate sheet thickness,
Then, after intermediate annealing at 950 ° C. for 60 seconds, a final sheet thickness of 0.23 mm was obtained by final cold rolling. Particle size before final cold rolling is 80
It was in the range of 120120 μm. Then, in a mixed atmosphere of hydrogen: 98% and ammonia: 2% with a dew point of −20 ° C., 950 ° C.
After primary recrystallization annealing at 30 ° C for 30 seconds, MgO was applied as an annealing separator on the steel sheet surface, and then final finish annealing was performed.
The method was carried out in a dry hydrogen atmosphere by increasing the temperature to 1120 ° C. at a rate of 5 ° C./h. During the final finish annealing, when the temperature of the steel plate reached 850 ° C, a sample was taken to investigate the nitrogen content. Thereafter, an inorganic coating solution mainly composed of phosphate was applied, and flattening annealing was performed at 800 ° C. to obtain a product.
Table 3 shows the results of examining the nitrogen content in steel when the temperature reached 850 ° C. and the magnetic properties of the obtained product.

[0059]

[Table 2]

[0060]

[Table 3]

As shown in Table 3, as a material, Al was 1
Less than 00 ppm, and each of Se, S, N and O is 30 ppm
Following the case of using a steel slab, the magnetic flux density B ₈ in the rolling direction is able to obtain a product of more excellent magnetic properties 1.85 T.

Example 3 C: 230 ppm, Si: 3.20 wt%, Mn: 0.35 wt%, Al: 70 pp
m, Se: 2 ppm, S: 6 ppm, N: 5 ppm and O: 9
Containing ppm, the balance is substantially Fe composition.
m thin slabs were produced by direct casting. Then 1100 ° C
After hot rolling for 300 minutes, a hot-rolled sheet having a thickness of 3.0 mm was formed by hot rolling. Then, after hot-rolled sheet annealing under the conditions shown in Table 4,
Cold rolling was performed at a temperature of 250 ° C. to finish to a final thickness of 0.50 mm. The cold rolling reduction at this time is 83%. Next, primary recrystallization annealing was performed at 950 ° C. for 30 seconds in a hydrogen atmosphere with a dew point of 35 ° C. At this time, the basis weight of oxygen on the steel sheet surface after the primary recrystallization annealing was 0.4 g / m ² . Then, after applying a separating agent containing 5 wt% of ferromanganese nitride in MgO as an annealing separating agent to the surface of the steel sheet, the final finish annealing is performed at -30 ° C in a dry hydrogen atmosphere at 15 ° C / h. At a speed of 1050
The method was carried out by raising the temperature to ° C. During the final finish annealing, when the steel sheet temperature reached 850 ° C, a sample was taken to examine the nitrogen content, which was in the range of 40 to 60 ppm. Table 4
Table 2 shows the results of investigations on the hot-rolled sheet annealing conditions, the average particle size before final cold rolling, and the magnetic properties of the obtained product.

[0063]

[Table 4]

As shown in Table 4, the particle size before final cold rolling was
When the particle size is 150 μm or less, the product has good magnetic flux density in the rolling direction.On the other hand, when the particle size before final cold rolling is 200 μm or more, good magnetic properties are obtained on average in the rolling direction and the direction perpendicular to the rolling direction. ing.

[0065]

Thus, according to the present invention, using a high-purity material that does not contain an inhibitor component, after the completion of the primary recrystallization, the amount of nitrogen in the steel during the final finish annealing until the steel plate temperature reaches 850 ° C. Is increased to 30 ppm or more, secondary recrystallization can be effectively generated at the time of final finish annealing.Accordingly, according to the present invention, a grain-oriented electrical steel sheet having excellent magnetic properties can be obtained by a simplified process. Obtainable.

[Brief description of the drawings]

FIG. 1 is a diagram showing the frequency of the presence of grain boundaries having a misorientation angle of 20 to 45 ° in a primary recrystallized structure of a grain-oriented electrical steel sheet.

FIG. 2 is a graph showing the relationship between the amount of nitrogen in steel and the area ratio of completed secondary recrystallization when the temperature of a steel sheet reaches 850 ° C.

FIG. 3 is a graph showing the relationship between the basis weight of oxygen after primary recrystallization annealing, the secondary recrystallization completion area ratio, and the secondary recrystallization particle size.

FIG. 4 is a graph showing the relationship between the particle size before final cold rolling and the area ratio of secondary recrystallized grains of a Goss structure and a cube structure.

FIG. 5 is a graph showing the relationship between the reduction ratio of cold rolling and the magnetic flux density in the rolling direction of a product sheet when the particle size before cold rolling is 98 μm.

FIG. 6 is a graph showing the relationship between the reduction ratio of cold rolling and the average magnetic flux density in the rolling direction and the direction perpendicular to the rolling direction of a product sheet for a particle size before cold rolling of 222 μm.

Continuation of the front page F term (reference) 4K033 AA02 CA01 CA02 CA03 CA04 CA07 CA09 HA06 JA07 LA01 MA03 RA04 SA03 TA02

Claims (6)

[Claims] 1. C: 0.12% by weight or less, Si: 2.0 to 8.0% by weight
And Mn: 0.005 to 1.0 wt%, and 100 pp of Al
A steel slab having a composition of less than 30 m and Se, S, O and N each reduced to 30 ppm or less is hot-rolled, subjected to hot-rolled sheet annealing if necessary, and then sandwiched once or intermediately. A series of steps of performing cold rolling two or more times, then performing primary recrystallization annealing, applying an annealing separator as needed, and then performing secondary recrystallization by final finish annealing. In the method for producing grain-oriented electrical steel sheets, the nitrogen content in the steel is increased to 30 ppm or more after the primary recrystallization is completed and before the steel sheet temperature reaches 850 ° C in the final finish annealing step. Manufacturing method of electrical steel sheet. 2. The means for increasing the amount of nitrogen in steel includes increasing the partial pressure of nitrogen during final finish annealing, adding a compound having a nitriding ability to the annealing separator, and reducing the nitriding ability after the completion of the primary recrystallization. 2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the annealing is performed in any atmosphere or a combination thereof. 3. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the basis weight of oxygen on the surface of the steel sheet after the primary recrystallization annealing is 1.0 g / m ² or less per one side. 4. An average crystal grain size before final cold rolling is 150 μm or less, and a final cold rolling reduction is 70% or more and 91% or less.
4. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the {110} <001> structure is grown. 5. An average crystal grain size before final cold rolling is 200 μm or more, and a final cold rolling reduction is 60% or more and 90% or less,
4. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the {100} <001> structure is grown. 6. The steel further contains Ni: 0.01-1.50 wt%, S
n: 0.01 to 0.50 wt%, Sb: 0.005 to 0.50 wt%, Cu: 0.01
~ 0.50wt%, Mo: 0.005 ~ 0.50wt% and Cr: 0.01 ~ 1.
The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein at least one selected from 50 wt% is contained.