JP5417936B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet, and in particular, to stably obtain a grain-oriented electrical steel sheet having extremely low iron loss by maximizing the effect of reducing iron loss by rapid heating during primary recrystallization annealing. It is what.

  Electrical steel sheets are widely used as iron core materials for transformers and generators. In particular, grain oriented electrical steel sheets are highly integrated in the {110} <001> orientation, called the Goss orientation, and have good iron loss that directly leads to reduction of energy loss in transformers and generators. It has characteristics. Effective means for improving the iron loss characteristics include reducing the plate thickness, increasing the Si content, improving the orientation of the crystal orientation, applying tension to the steel sheet, smoothing the surface of the steel sheet, and refining the secondary grains. It is.

  As a technique for refining secondary grains, Patent Document 1, Patent Document 2, Patent Document 3 and Patent Document 4, etc., include a method of rapid heating during decarburization annealing or rapid heating treatment immediately before decarburization annealing, A method for improving the recrystallization texture has been proposed. Although the iron loss characteristics are improved by applying this technique, it has been found that the secondary grains do not become finer in some cases, and the expected iron loss reduction effect cannot be obtained.

In addition, Patent Document 5 and Patent Document 6 disclose a technique for improving the magnetic properties by performing rapid heat treatment in the temperature raising process of decarburization annealing and controlling the atmospheric oxidation degree in the temperature range where decarburization annealing is performed. Has been proposed.
However, although this technique can be expected to improve the magnetic characteristics to some extent, there are still problems in terms of stability, such as variations in the magnetic characteristics in the longitudinal direction of the coil and, in some cases, a small margin for improving the magnetic characteristics. .

JP-A-8-295937 JP 2003-96520 A Japanese Patent Laid-Open No. 10-280040 JP-A-6-49543 JP 2002-60843 A JP 2008-1980

  The present invention advantageously solves the above-mentioned problems, and achieves the expected iron loss reduction effect stably by maximizing the iron loss reduction effect due to rapid heating during primary recrystallization annealing. It aims at proposing the manufacturing method of the grain-oriented electrical steel sheet which can do.

The elucidation process of the present invention will be described below.
The inventors conducted a thorough investigation on the factors affecting secondary grain refinement by rapid heating, and reflected changes in primary recrystallization texture due to rapid heating in secondary recrystallization behavior. In order to achieve this, it is important to control the nitriding behavior during secondary recrystallization annealing. As this nitriding behavior control means, secondary recrystallization annealing can be performed without forming a subscale on the steel sheet surface. It became clear that it was important.
Hereinafter, the experimental results that led to obtaining the above knowledge will be described.

<Experiment 1>
Contains C: 0.07 mass%, Si: 3.05 mass%, Mn: 0.075 mass%, P: 0.008 mass%, Al: 250 ppm, N: 80 ppm, S: 200 ppm and Se: 5 ppm, the balance being Fe and inevitable impurities A steel slab with the following composition is produced by continuous casting, heated to 1400 ° C, hot rolled to a thickness of 2.3 mm, and then hot-rolled at 1100 ° C for 80 seconds. did. Next, after the first cold rolling, the intermediate sheet thickness was set to 0.50 mm, and then the atmospheric oxidation degree (P [H ₂ O] / P [H ₂ ]): 0.30, temperature: 850 ° C., time: 300 seconds Intermediate annealing was performed. Then, after removing the subscale on the surface by hydrochloric acid pickling, the second cold rolling is performed to obtain a cold rolled sheet having a final thickness of 0.23 mm, followed by primary recrystallization annealing at 840 ° C. for 200 seconds. gave. During this primary recrystallization annealing, the degree of atmospheric oxidation in the temperature raising process and the soaking process and the temperature raising rate between 500-700 ° C. were variously changed. Then, colloidal silica is electrostatically applied as an annealing separator, and as secondary recrystallization annealing, first annealing is performed at 850 ° C. for 100 hours in an N ₂ atmosphere, and then 1200 ° C., 10% in an H ₂ atmosphere. Time annealing was performed. Thereafter, TiC was formed on both surfaces of the steel sheet in an atmosphere composed of a mixed gas of TiCl ₄ , H ₂ and CH ₄ , and finally an insulating coating made of 50% colloidal silica and magnesium phosphate was applied to obtain a product.

In the above experiment, the primary recrystallization texture and the magnetic properties of the product plate were investigated. The primary recrystallization texture is evaluated by the two-dimensional intensity distribution in the Euler space φ2 = 45 ° section in the thickness center layer, and the magnetic properties are subjected to strain relief annealing at 800 ° C for 3 hours. After JIS C Evaluation according to 2550.

FIG. 1 shows the relationship between the heating rate between 500-700 ° C. and the Goss orientation strength (φ = 90 °, φ1 = 90 °, φ2 = 45 °) of the primary recrystallized plate.
As is clear from the figure, in order to change the primary recrystallization texture by rapid heating (to increase the Goss azimuth strength), it is understood that the heating rate needs to be 150 ° C./s or more.

FIG. 2 shows the relationship between the degree of atmospheric oxidation during the primary recrystallization annealing and the iron loss characteristics of the product.
From the figure, it can be seen that the iron loss improvement allowance increases when rapid heating is performed under the condition where the atmospheric oxidation degree is P [H ₂ O] / P [H ₂ ] ≦ 0.05.

From the above results, in order to maximize the iron loss improvement effect by rapid heating, not only the rate of temperature increase but also the primary recrystallization annealing should be performed with the atmospheric oxidation degree (P [H ₂ O] / P [H ₂ ]) It can be seen that it is extremely important to perform at ≦ 0.05.

<Experiment 2>
Contains C: 0.025 mass%, Si: 3.05 mass%, Mn: 0.075 mass%, P: 0.005 mass%, Al: 30 ppm, N: 20 ppm, S: 10 ppm and Se: 5 ppm, the balance being Fe and inevitable impurities A steel slab with the following composition is manufactured by continuous casting, heated to 1100 ° C, hot-rolled to a thickness of 2.0 mm, and then hot-rolled for 120 seconds at 950 ° C. gave. Next, after cold rolling to obtain a cold rolled sheet having a final thickness of 0.23 mm, primary recrystallization annealing was performed at 835 ° C. for 600 seconds. During this primary recrystallization annealing, the degree of atmospheric oxidation in the temperature raising process and the soaking process and the temperature raising rate between 500-700 ° C. were variously changed. Thereafter, alumina powder is applied as a slurry as an annealing separator, and annealing is first performed at 900 ° C. for 200 hours in an atmosphere of N ₂ : Ar = 40%: 60%, and then 1250 ° C. in an H ₂ atmosphere. Annealing was performed for 10 hours. Thereafter, TiN was formed on both surfaces of the steel plate in an atmosphere consisting of a mixed gas of TiCl ₄ , H ₂ and N ₂ , and finally an insulating coating consisting of 50% colloidal silica and magnesium phosphate was applied to obtain a product. Here, the magnetic properties were evaluated.

FIG. 3 shows the relationship between the degree of atmospheric oxidation during the primary recrystallization annealing and the iron loss characteristics of the product.
As shown in the figure, in the component system that does not contain an inhibitor, if the atmospheric oxidation degree is not controlled to P [H ₂ O] / P [H ₂ ] ≦ 0.05, the effect of reducing iron loss by rapid heating can be obtained at all. I found that there was no.
From the above, in order to obtain an iron loss improvement effect by rapid heating in a component system that does not contain an inhibitor, it was found that it is indispensable not only to perform rapid heat treatment but also to control the degree of atmospheric oxidation during primary recrystallization annealing. did.

<Experiment 3>
From Experiments 1 and 2, in order to obtain the maximum iron loss improvement effect by rapid heating, the atmospheric oxidation degree during rapid heating treatment and primary recrystallization annealing is P [H ₂ O] / P [H ₂ ] ≦ 0.05. It became clear that it was very important. Next, the reason for this was investigated.
Contains C: 0.003 mass%, Si: 2.55 mass%, Mn: 0.22 mass%, P: 0.005 mass%, Al: 25 ppm, N: 35 ppm, S: 5 ppm and Se: 3 ppm, the balance being Fe and inevitable impurities A steel slab with the following composition is manufactured by continuous casting, heated to 1150 ° C, hot rolled to a hot rolled sheet with a thickness of 1.8mm, and then subjected to hot rolled sheet annealing at 1030 ° C for 120 seconds. did. Next, after finishing to a final plate thickness of 0.23 mm by cold rolling, etching grooves of 5 mm intervals are formed on this cold rolled plate for magnetic domain subdivision treatment, and then primary recrystallization is performed at 880 ° C. for 10 seconds. Annealed. During the primary recrystallization annealing, the degree of atmospheric oxidation during the heating process and the soaking process was changed. Moreover, about the temperature increase rate between 500 degreeC-700 degreeC, it carried out at 500 degreeC / s. Thereafter, annealing was performed at 900 ° C. for 100 hours in an N ₂ atmosphere. After cleaning the surface by hydrochloric acid pickling, TiC is formed on both sides of the steel plate in an atmosphere consisting of a mixed gas of TiCl ₄ , H ₂ and CH ₄ , and finally insulation consisting of 50% colloidal silica and magnesium phosphate The product was coated.

Fig. 4 shows the results of investigating the nitrogen content in the base iron (hereinafter referred to as the amount of iron N) in the outer, middle and inner windings of the coil for the sample at the end of secondary recrystallization annealing. This is shown in relation to the degree of atmospheric oxidation during annealing.
As shown in the figure, when the degree of atmospheric oxidation at the time of primary recrystallization annealing is P [H ₂ O] / P [H ₂ ] ≦ 0.05, the amount of steel N after secondary recrystallization annealing is small. It can be seen that the difference between the outer part of the coil, the middle part and the inner part is also reduced.
On the other hand, when P [H ₂ O] / P [H ₂ ]> 0.05, the amount of steel N after secondary recrystallization annealing is large, and the difference between the outer, middle, and inner coil portions is also large. It has become.

In addition, FIG. 5 shows the results of examining the relationship between the amount of ground iron N and iron loss.
As is clear from the figure, there is a correlation between the amount of iron in the ground and iron loss, and it is important to obtain good iron loss to suppress nitriding fluctuations in secondary recrystallization annealing. I understand.

The reason why rapid heating and atmospheric oxidation during primary recrystallization annealing influence the nitriding behavior during secondary recrystallization annealing is considered as follows.
The reason for the increase in the amount of iron in the atmosphere when the degree of atmospheric oxidation is high is that the porous subscale formed on the surface of the steel sheet facilitates the penetration of N. Rather, it is better not to form the subscale. It is thought that the invasion of is suppressed. In addition, when the amount of ground iron N is high, the iron loss did not improve because the state of precipitates formed by impurities or inhibitor components changes due to nitridation / denitrification during secondary recrystallization annealing, This is considered to have caused an adverse effect on the secondary recrystallization behavior. Therefore, in order to reflect the improvement of the primary recrystallization texture in the secondary recrystallization behavior, the nitriding / denitrification during the secondary recrystallization annealing is suppressed by not forming the subscale as much as possible, and impurities or inhibitors are used. We believe that it is a very important point not to change the state of the formed precipitate.

The subscale that facilitates the penetration of N into the ground iron includes not only Fe-based oxides but also Si-based oxides. Since the Si-based oxide is formed at a relatively low temperature, not only the soaking process of the primary recrystallization annealing but also the atmosphere control in the heating process is important. Although the nitriding behavior during secondary recrystallization annealing can be accurately controlled by making the atmosphere of this temperature rising process appropriate, conventionally, no consideration has been given to the control of the degree of atmospheric oxidation during this temperature rising process. It was.
For this reason, Si-based oxides were formed on the steel sheet surface, and the nitriding behavior was not sufficiently controlled, and it was thought that the effect of improving iron loss by rapid heating treatment, especially the effect of increasing Goss azimuth strength, was not evident. It is done. Note that when the rapid heating process is performed separately from the primary recrystallization annealing, not only the temperature raising process during the primary recrystallization annealing but also the atmosphere control of the rapid heating process is essential.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. When using at least one selected from AlN, MnS, and MnSe as an inhibitor, and containing AlN, by mass%, C: 0.08% or less, Si: 2.0-8.0% and Mn: 0.005-1.0% Contains Al: 0.010 to 0.065% and N: 0.005 to 0.012%, S: 0.005 to 0.03% when MnS is used, Se: 0.005 to 0.03% when MnSe is used, and the balance is Fe. And steel slab consisting of unavoidable impurities, hot-rolled, subjected to hot-rolled sheet annealing as necessary, then subjected to one or more cold rolling sandwiching intermediate annealing to the final sheet thickness, Next, in the method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing primary recrystallization annealing and then performing secondary recrystallization annealing,
Before the primary recrystallization annealing, atmosphere oxidation degree (P [H2O] / P [ H2]) is in a non-oxidizing atmosphere of 0.05 or less, at least for 500 to 700 temperature range of ° C. 0.99 ° C. / s or more It is characterized by a rapid heat treatment that heats at a rate of temperature rise, followed by primary recrystallization annealing in a non-oxidizing atmosphere with an atmospheric oxidation degree (P [H2O] / P [H2]) of 0.05 or less. A method for producing grain-oriented electrical steel sheets.

2. In mass%, C: 0.08% or less, Si: 2.0-8.0% and Mn: 0.005-1.0%, and the inhibitor component Al is reduced to 100 ppm or less, and N, S, Se are reduced to 50 ppm or less, The remainder is a steel slab composed of Fe and inevitable impurities, hot-rolled, and subjected to hot-rolled sheet annealing as necessary, followed by one or more cold rollings sandwiching intermediate annealing, and the final plate In the manufacturing method of the grain-oriented electrical steel sheet consisting of a series of steps that are thick and then subjected to primary recrystallization annealing and then secondary recrystallization annealing,
Before the primary recrystallization annealing, atmosphere oxidation degree (P [H2O] / P [ H2]) is in a non-oxidizing atmosphere of 0.05 or less, at least for 500 to 700 temperature range of ° C. 0.99 ° C. / s or more It is characterized by a rapid heat treatment that heats at a rate of temperature rise, followed by primary recrystallization annealing in a non-oxidizing atmosphere with an atmospheric oxidation degree (P [H2O] / P [H2]) of 0.05 or less. A method for producing grain-oriented electrical steel sheets.

3. When using at least one selected from AlN, MnS, and MnSe as an inhibitor, and containing AlN, by mass%, C: 0.08% or less, Si: 2.0-8.0% and Mn: 0.005-1.0% Contains Al: 0.010 to 0.065% and N: 0.005 to 0.012%, S: 0.005 to 0.03% when MnS is used, Se: 0.005 to 0.03% when MnSe is used, and the balance is Fe. And steel slab consisting of unavoidable impurities, hot-rolled, subjected to hot-rolled sheet annealing as necessary, then subjected to one or more cold rolling sandwiching intermediate annealing to the final sheet thickness, Next, in the method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing primary recrystallization annealing and then performing secondary recrystallization annealing,
The primary recrystallization annealing is performed in a non-oxidizing atmosphere having an atmospheric oxidation degree (P [H ₂ O] / P [H ₂ ]) of 0.05 or less, and at that time, a temperature of 500 to 700 ° C., which is a temperature rising process A method for producing a grain-oriented electrical steel sheet, characterized by rapidly heating the zone at a rate of 150 ° C / s or more.

4). In mass%, C: 0.08% or less, Si: 2.0-8.0% and Mn: 0.005-1.0%, and the inhibitor component Al is reduced to 100 ppm or less, and N, S, Se are reduced to 50 ppm or less, The remainder is a steel slab composed of Fe and inevitable impurities, hot-rolled, and subjected to hot-rolled sheet annealing as necessary, followed by one or more cold rollings sandwiching intermediate annealing, and the final plate In the manufacturing method of the grain-oriented electrical steel sheet consisting of a series of steps that are thick and then subjected to primary recrystallization annealing and then secondary recrystallization annealing,
The primary recrystallization annealing is performed in a non-oxidizing atmosphere having an atmospheric oxidation degree (P [H ₂ O] / P [H ₂ ]) of 0.05 or less, and at that time, a temperature of 500 to 700 ° C., which is a temperature rising process A method for producing a grain-oriented electrical steel sheet, characterized by rapidly heating the zone at a rate of 150 ° C / s or more.

5. 5. The grain-oriented electrical steel sheet according to any one of 1 to 4 above, wherein in the secondary recrystallization annealing step, the ratio of N ₂ in the atmosphere in the temperature rising process of 750 ° C. or higher is suppressed to 60% or less. Manufacturing method.

6). The steel slab is further in mass%, Ni: 0.03-1.50%, Sn: 0.01-1.50%, Sb: 0.005-1.50%, Cu: 0.03-3.0%, P: 0.03-0.50%, Mo: 0.005-0.1 % And Cr: A method for producing a grain-oriented electrical steel sheet according to any one of 1 to 5 above, wherein the composition contains one or more selected from 0.03 to 1.50%.

  According to the present invention, a grain-oriented electrical steel sheet with extremely low iron loss can be stably obtained by maximizing the effect of reducing iron loss by rapid heating during primary recrystallization annealing.

It is the figure which showed the relationship between the temperature increase rate between 500-700 degreeC, and the goth orientation strength ((phi) = 90 degree, (phi) 1 = 90 degree, (phi) 2 = 45 degree) of a primary recrystallization board. It is the figure which showed the relationship between the atmospheric oxidation degree at the time of primary recrystallization annealing in the component system containing an inhibitor, and the iron loss characteristic of a product. It is the figure which showed the relationship between the atmospheric oxidation degree at the time of primary recrystallization annealing in the component system which does not contain an inhibitor, and the iron loss characteristic of a product. It is the figure which showed the amount of base iron N in the outer / middle / inner winding part of the coil at the time of completion | finish of secondary recrystallization annealing in relation to the atmospheric oxidation degree at the time of primary recrystallization annealing. It is the figure which showed the relationship between the amount of ground iron N and an iron loss.

Hereinafter, the present invention will be specifically described.
First, the reason why the component composition of the steel slab is limited to the above range in the present invention will be described. In addition, hereinafter, “%” and “ppm” relating to ingredients mean “mass%” and “mass ppm” unless otherwise specified.
The present invention may be either a component system containing an inhibitor or a component system not containing an inhibitor, and the amounts of C, Si and Mn as basic components are common to both.

C: 0.08% or less When the amount of C exceeds 0.08%, it becomes difficult to reduce C to 50 ppm or less at which no magnetic aging occurs during the manufacturing process. Therefore, the amount of C is limited to 0.08% or less. Note that the lower limit of the amount of C is not particularly provided because secondary recrystallization is possible even for materials not containing C.

Si: 2.0-8.0%
Si is an element effective in increasing the electrical resistance of steel and improving iron loss. However, if the content is less than 2.0%, the effect of addition is poor, while if it exceeds 8.0%, the workability is significantly reduced. In addition, since the magnetic flux density also decreases, the Si content is limited to the range of 2.0 to 8.0%.

Mn: 0.005 to 1.0%
Mn is an element necessary for improving the hot workability, but if it is less than 0.005%, the effect of addition is poor, while if it exceeds 1.0%, the magnetic flux density of the product plate decreases, so the amount of Mn is 0.005. Limited to -1.0% range.

Next, when an inhibitor is used for secondary recrystallization, conventionally known Al, S, N, Se and the like are contained as an inhibitor component.
When using AlN as an inhibitor, Al: 0.010 to 0.065% and N: 0.005 to 0.012%, when using MnS, S: 0.005 to 0.03%, when using MnSe, Se: 0.005 to 0.03%
When AlN, MnS, or MnSe is used as an inhibitor, the desired inhibitor effect cannot be obtained unless each component is lower than the lower limit. On the other hand, if the upper limit is exceeded, the dispersed state of precipitates becomes uneven, and the desired inhibitor is obtained. Since the effect could not be obtained, each inhibitor component was included in the above range.

When the inhibitor is not used, Al: 100 ppm or less, and N, S, Se: 50 ppm or less respectively When the inhibitor is not used, the Al amount is 100 ppm or less, and the N, S, and Se amounts are each 50 ppm or less. This is essential for good secondary recrystallization of the steel sheet. Although it is desirable to reduce these components as much as possible from the viewpoint of magnetic characteristics, since the reduction of these components increases the cost, there is no problem even if they are left within the above range.

As described above, the essential element and the suppressing element have been described. In the present invention, at least one selected from Ni, Sn, Sb, Cu, P, Mo, and Cr as other magnetic property improving elements is within the following range. It can be contained as appropriate.
Ni: 0.03-1.50%
Ni is a useful element for improving the magnetic properties by improving the hot-rolled sheet structure. However, if the added amount is less than 0.03%, the effect of improving the magnetic properties is small, while if it exceeds 1.50%, secondary recrystallization is achieved. Since Ni becomes unstable and the magnetic properties deteriorate, Ni is included in the range of 0.03 to 1.50%.

Sn: 0.01-1.50%, Sb: 0.005-1.50%, Cu: 0.03-3.0%, P: 0.03-0.50%, Mo: 0.005-0.10% and Cr: 0.03-1.50%
All of these elements are useful elements for improving the magnetic properties. However, when the lower limit is not reached, the effect of addition is poor.On the other hand, when the upper limit is exceeded, the development of secondary recrystallized grains is suppressed. In this case, each of the above-mentioned ranges is used.

Next, the manufacturing process of the present invention will be described.
The molten steel adjusted to the above preferred component composition is made into a slab by a normal ingot-making method or a continuous casting method. Further, a thin cast piece having a thickness of 100 mm or less may be manufactured by a direct casting method. In the case of a slab, it is heated and rolled by a normal method, but may be immediately subjected to hot rolling without heating after casting. In the case of a thin slab, hot rolling may be performed, or the hot rolling may be omitted and the process may proceed as it is. The slab heating temperature before hot rolling is a low temperature of 1250 ° C. or lower because there is no need to dissolve the inhibitor in the case of a component system that does not contain an inhibitor component with reduced Al, N, S, and Se. This is desirable in terms of cost.

  Next, hot-rolled sheet annealing is performed as necessary. In order to highly develop a goth structure in the product plate, it is preferable that the hot-rolled sheet annealing temperature is about 800 ° C. or higher and 1100 ° C. or lower. If the hot-rolled sheet annealing temperature is less than 800 ° C., a band structure in hot rolling remains, and it becomes difficult to realize a sized primary recrystallized structure, which hinders the development of secondary recrystallization. On the other hand, when the hot-rolled sheet annealing temperature exceeds 1100 ° C., the grain size after the hot-rolled sheet annealing is excessively coarsened, which is extremely disadvantageous for realizing a sized primary recrystallized structure.

  After hot-rolled sheet annealing, re-annealing is performed after performing cold rolling twice or more sandwiching once or intermediate annealing. Cold rolling is performed by raising the temperature to 100 to 250 ° C., or performing aging treatment at 100 to 250 ° C. one or more times during the cold rolling to develop the goth structure. It is valid. In addition, even if it forms an etching groove | channel in order to subdivide a magnetic domain after cold rolling, there will be no trouble in this invention.

After the cold rolling is completed, rapid heat treatment is performed. This rapid heating treatment is performed in order to improve the Goss orientation strength of the primary recrystallization texture, and in order to achieve this purpose, the heating rate in the temperature range of at least 500 to 700 ° C. is set to 150 ° C./s. It is necessary to do it above. This rapid heating step may be performed before the primary recrystallization annealing step separately from the conventional primary recrystallization annealing step, or may be applied to the temperature raising process of the primary recrystallization annealing step. The rapid heating method is not particularly limited, and may be performed by a known method such as induction heating or direct current heating.
The degree of atmospheric oxidation in the rapid heating step and the primary recrystallization annealing step is P [H ₂ O] / P [H ₂ ] ≦ 0.05, preferably P [H ₂ O] in order to suppress the formation of subscales as much as possible. / P [H ₂ ] ≦ 0.01 is required. This atmosphere control is an indispensable condition for effectively controlling the nitriding behavior during secondary recrystallization annealing, and it is important to control this atmosphere not only in the primary recrystallization annealing process but also in the rapid heating process. It is.
In particular, since the temperature range in which the subscale is easily formed is 500 ° C. or higher, the above atmosphere control is necessary at 500 ° C. or higher.

After the primary recrystallization annealing, secondary recrystallization annealing is performed. At this time, if there is a concern about the adhesion between the steel plates, a known annealing separator that does not react with the steel plates (does not form a subscale on the steel plate surface) may be applied.
Here, in order to control the nitriding / denitrifying behavior in the secondary recrystallization annealing, it is also effective to reduce the ratio of N ₂ in the atmosphere during the secondary recrystallization annealing. However, nitriding and denitrifying are sufficiently suppressed by controlling the atmospheric oxidation degree in the rapid heat treatment and primary recrystallization annealing to P [H ₂ O] / P [H ₂ ] ≦ 0.05. Control of the N ₂ ratio is not always essential.

In order to reduce the secondary particle size, it is necessary to generate many secondary recrystallization nuclei. Since secondary recrystallization nuclei are generated in the early stage of secondary recrystallization annealing, when controlling the atmospheric N ₂ partial pressure during secondary recrystallization annealing, the ratio of N ₂ in the atmosphere during the temperature rise process above 750 ° C Is preferably 60% or less. Here, the reason why the atmosphere control start temperature is set to 750 ° C. or more is that nitriding / denitrifying tends to occur from around 750 ° C.

Next, a tension coating is formed on the surface of the obtained steel plate. This forming method may be a known method and is not particularly limited. For example, a method of forming a ceramic film made of nitride, carbide, carbonitride using a vapor deposition method such as CVD or PVD is effective.
After the tension film is formed, an insulating coating is applied. As an insulating coating, an inorganic coating conventionally used for grain-oriented electrical steel sheets is promising.
It is also possible to subdivide the magnetic domains by irradiating the steel plate thus obtained with a laser or a plasma flame for the purpose of further reducing iron loss.

Example 1
Steel slabs with the composition shown in Table 1 were manufactured by continuous casting, heated to 1450 ° C, hot rolled into a hot rolled sheet with a thickness of 2.0 mm, and then hot rolled at 950 ° C for 180 seconds. Plate annealing was performed. Next, after the first cold rolling, the intermediate plate thickness was set to 0.75 mm, and the atmosphere oxidation degree (P [H ₂ O] / P [H ₂ ]) = 0.30, temperature: 830 ° C., time: 300 seconds Intermediate annealing was performed. Then, after removing the sub-scale on the surface by hydrochloric acid pickling, the second cold rolling is performed to form a cold rolled sheet having a final thickness of 0.23 mm, and then etching grooves at intervals of 5 mm are formed for magnetic domain subdivision processing. After the formation, rapid heating treatment was performed before the primary recrystallization annealing. In this rapid heating treatment, as shown in Table 2, the temperature increase rate in the temperature range of 350 to 800 ° C. is changed in the range of 50 to 300 ° C./s, and the atmospheric oxidation degree is also P [H ₂ O ] / P [H ₂ ] = 0.001 to 0.5. Next, primary recrystallization annealing was performed under the conditions of atmospheric oxidation degree (P [H ₂ O] / P [H ₂ ]) = 0.001 to 0.5, temperature: 840 ° C., time: 200 seconds. Thereafter, colloidal silica was electrostatically applied, and then batch annealing for the purpose of secondary recrystallization and purification was performed in an H ₂ atmosphere at 1250 ° C. for 30 hours. During the secondary recrystallization annealing, the N ₂ ratio in the atmosphere was changed as shown in Table 2 in the temperature rising process of 750 ° C. or higher. For the other atmospheres, the temperature rising process at 750 ° C. or lower was an N ₂ atmosphere, the holding process was an H ₂ atmosphere, and the cooling process was an Ar atmosphere.
TiC is formed on both sides of the steel plate in an atmosphere consisting of a mixed gas of TiCl ₄ , H ₂ and CH ₄ for the steel plate having a smooth surface without the forsterite film obtained as described above, and finally 50% An insulating coating made of colloidal silica and magnesium phosphate was applied to make a product.
The results of examining the magnetic properties of the grain-oriented electrical steel sheet thus obtained are also shown in Table 2.

As shown in Table 2, all the grain-oriented electrical steel sheets obtained according to the present invention have extremely good iron loss characteristics.
On the other hand, even if one manufacturing condition is out of the scope of the present invention, the iron loss characteristics as good as expected in the present invention are not obtained.

Example 2
Steel slabs with the composition shown in Table 3 were manufactured by continuous casting, heated to 1140 ° C, hot rolled into a hot rolled sheet with a thickness of 1.6 mm, and then hot rolled at 980 ° C for 100 seconds. Plate annealing was performed. Next, after cold rolling to finish a cold rolled sheet having a thickness of 0.23 mm, primary recrystallization annealing was performed under a soaking condition of 850 ° C. for 100 seconds. In this primary recrystallization annealing, in the temperature rising process leading to the soaking process, as shown in Table 4, the temperature rising rate between 400 and 750 ° C. is changed in the range of 40 to 300 ° C./s, and the atmospheric oxidation is performed. The temperature was changed in the range of P [H ₂ O] / P [H ₂ ] = 0.001 to 0.5 in both the temperature raising process and the soaking process. Thereafter, batch annealing for the purpose of secondary recrystallization was performed at 900 ° C. for 120 hours. At the time of the secondary recrystallization annealing, the N ₂ ratio in the atmosphere in the temperature rising process of 750 ° C. or higher was changed as shown in Table 4. The other atmosphere was N ₂ : 100%.
TiN is formed on both sides of the steel plate in an atmosphere consisting of a mixed gas of TiCl ₄ , H ₂ and N ₂ for the steel plate having a smooth surface without the forsterite film obtained as described above, and finally 50% An insulating coating made of colloidal silica and magnesium phosphate was applied to make a product.
The results of examining the magnetic properties of the grain-oriented electrical steel sheet thus obtained are also shown in Table 4.

As is apparent from Table 4, any grain-oriented electrical steel sheet obtained according to the present invention can obtain extremely good iron loss characteristics.
On the other hand, even if one production condition was not within the scope of the present invention, the iron loss characteristics as good as expected in the present invention could not be obtained.

  According to the present invention, the effect of reducing iron loss due to rapid heating can be exerted to the maximum. Therefore, it becomes possible to stably manufacture a grain-oriented electrical steel sheet having a lower iron loss than before.

Claims (6)

When using at least one selected from AlN, MnS, and MnSe as an inhibitor, and containing AlN, by mass%, C: 0.08% or less, Si: 2.0-8.0% and Mn: 0.005-1.0% Contains Al: 0.010 to 0.065% and N: 0.005 to 0.012%, S: 0.005 to 0.03% when MnS is used, Se: 0.005 to 0.03% when MnSe is used, and the balance is Fe. And steel slab consisting of unavoidable impurities, hot-rolled, subjected to hot-rolled sheet annealing as necessary, then subjected to one or more cold rolling sandwiching intermediate annealing to the final sheet thickness, Next, in the method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing primary recrystallization annealing and then performing secondary recrystallization annealing,
Before the primary recrystallization annealing, atmosphere oxidation degree (P [H2O] / P [ H2]) is in a non-oxidizing atmosphere of 0.05 or less, at least for 500 to 700 temperature range of ° C. 0.99 ° C. / s or more It is characterized by a rapid heat treatment that heats at a rate of temperature rise, followed by primary recrystallization annealing in a non-oxidizing atmosphere with an atmospheric oxidation degree (P [H2O] / P [H2]) of 0.05 or less. A method for producing grain-oriented electrical steel sheets. In mass%, C: 0.08% or less, Si: 2.0-8.0% and Mn: 0.005-1.0%, and the inhibitor component Al is reduced to 100 ppm or less, and N, S, Se are reduced to 50 ppm or less, The remainder is a steel slab composed of Fe and inevitable impurities, hot-rolled, and subjected to hot-rolled sheet annealing as necessary, followed by one or more cold rollings sandwiching intermediate annealing, and the final plate In the manufacturing method of the grain-oriented electrical steel sheet consisting of a series of steps that are thick and then subjected to primary recrystallization annealing and then secondary recrystallization annealing,
Before the primary recrystallization annealing, atmosphere oxidation degree (P [H2O] / P [ H2]) is in a non-oxidizing atmosphere of 0.05 or less, at least for 500 to 700 temperature range of ° C. 0.99 ° C. / s or more It is characterized by a rapid heat treatment that heats at a rate of temperature rise, followed by primary recrystallization annealing in a non-oxidizing atmosphere with an atmospheric oxidation degree (P [H2O] / P [H2]) of 0.05 or less. A method for producing grain-oriented electrical steel sheets. When using at least one selected from AlN, MnS, and MnSe as an inhibitor, and containing AlN, by mass%, C: 0.08% or less, Si: 2.0-8.0% and Mn: 0.005-1.0% Contains Al: 0.010 to 0.065% and N: 0.005 to 0.012%, S: 0.005 to 0.03% when MnS is used, Se: 0.005 to 0.03% when MnSe is used, and the balance is Fe. And steel slab consisting of unavoidable impurities, hot-rolled, subjected to hot-rolled sheet annealing as necessary, then subjected to one or more cold rolling sandwiching intermediate annealing to the final sheet thickness, Next, in the method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing primary recrystallization annealing and then performing secondary recrystallization annealing,
The primary recrystallization annealing is performed in a non-oxidizing atmosphere having an atmospheric oxidation degree (P [H2O] / P [H2]) of 0.05 or less. A method for producing a grain-oriented electrical steel sheet, characterized by rapid heating at a rate of at least ° C / s. In mass%, C: 0.08% or less, Si: 2.0-8.0% and Mn: 0.005-1.0%, and the inhibitor component Al is reduced to 100 ppm or less, and N, S, Se are reduced to 50 ppm or less, The remainder is a steel slab composed of Fe and inevitable impurities, hot-rolled, and subjected to hot-rolled sheet annealing as necessary, followed by one or more cold rollings sandwiching intermediate annealing, and the final plate In the manufacturing method of the grain-oriented electrical steel sheet consisting of a series of steps that are thick and then subjected to primary recrystallization annealing and then secondary recrystallization annealing,
The primary recrystallization annealing is performed in a non-oxidizing atmosphere having an atmospheric oxidation degree (P [H2O] / P [H2]) of 0.05 or less. A method for producing a grain-oriented electrical steel sheet, characterized by rapid heating at a rate of at least ° C / s.   5. The grain-oriented electrical steel sheet according to claim 1, wherein, in the secondary recrystallization annealing step, a ratio of N 2 in the atmosphere in a temperature rising process of 750 ° C. or more is suppressed to 60% or less. Manufacturing method.   The steel slab is further in mass%, Ni: 0.03-1.50%, Sn: 0.01-1.50%, Sb: 0.005-1.50%, Cu: 0.03-3.0%, P: 0.03-0.50%, Mo: 0.005-0.1 % And Cr: It becomes a composition containing 1 type, or 2 or more types selected from 0.03 to 1.50%, The manufacturing method of the grain-oriented electrical steel sheet in any one of Claims 1-5 characterized by the above-mentioned.

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