JP6292146B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for producing a so-called grain-oriented electrical steel sheet in which crystal grains are Miller indices and {110} planes are accumulated on the plate surface and <001> orientation is accumulated in the rolling direction. The grain-oriented electrical steel sheet is a soft magnetic material and is mainly used as an iron core of electrical equipment such as a transformer.

  It is known that grain-oriented electrical steel sheets exhibit excellent magnetic properties by accumulating crystal grains in {110} <001> orientation (hereinafter referred to as Goss orientation) by secondary recrystallization annealing (for example, , See Patent Document 1).

And as an index of magnetic characteristics, magnetic field strength: magnetic flux density B _{8 at} 800 A / m and excitation frequency: iron loss W _17/50 per 1 kg of steel sheet when magnetized to 1.7 T with an alternating magnetic field of 50 Hz. Mainly used.

  One means for reducing the iron loss of grain-oriented electrical steel sheets is to highly accumulate the crystal grains after secondary recrystallization annealing in the Goss orientation. A difference in grain boundary mobility so that only Goss-oriented grains grow preferentially, that is, by forming a texture of the primary recrystallized plate into a predetermined structure, and using precipitates called inhibitors It is important to suppress the growth of recrystallized grains other than the Goss orientation.

  As a technique using this inhibitor, for example, Patent Document 1 discloses a method using AlN and MnS, and Patent Document 2 discloses a method using MnS and MnSe, both of which are industrially used. It has been put into practical use. In the method using these inhibitors, uniform fine dispersion of the inhibitor is an ideal state, but in order to achieve this, slab heating before hot rolling must be performed at a high temperature of 1300 ° C. or higher. The conventional method for producing grain-oriented electrical steel sheets using an inhibitor has a problem in that the production cost is high because a large amount of energy is required for high-temperature slab heating.

In Patent Document 3, a technique for developing secondary recrystallization without including an inhibitor component in the slab has been studied, and a technique capable of causing secondary recrystallization without including an inhibitor component (inhibitorless). Law) is disclosed.
This inhibitorless method is a technology that uses secondary steel with higher purity and develops secondary recrystallization by texture (control of texture). Further, the inhibitorless method does not require slab heating at a high temperature, and can produce a grain-oriented electrical steel sheet at low cost.

  In this technique, since control of the primary recrystallization texture is an important factor, many techniques such as warm rolling for texture control have been proposed, but this texture control cannot be performed sufficiently. In some cases, the degree of integration in the Goth orientation after secondary recrystallization was low and the magnetic flux density tended to be low as compared with the technique using an inhibitor.

  Here, as a predetermined primary recrystallization structure in which only sharp Goss orientation grains can be preferentially grown, {554} <225> orientation grains, {411] <148> orientation grains, and the like are known. By accumulating these oriented grains in a well balanced and highly integrated manner in the matrix of the primary recrystallized plate, Goss oriented grains can be highly accumulated after the secondary recrystallization annealing (see, for example, Patent Document 4).

Furthermore, in Patent Document 5, rolling at a reduction ratio of 85% or more is performed by one cold rolling, or rolling reduction of the final cold rolling is performed by 80% or more by two or more cold rolling sandwiching intermediate annealing. In the method for producing a grain-oriented electrical steel sheet, which is subjected to rolling as described above to obtain a cold-rolled sheet having a final thickness, and then subjected to primary recrystallization annealing and secondary recrystallization annealing, the total rolling reduction in the cold rolling is 50% or less. In this stage, the strain rate: 150 s ⁻¹ or less of low strain rate cold rolling is applied for one pass or more, so that the {001} <110> strength of the steel sheet structure after cold rolling at the low strain rate is 10 or less. It is disclosed that a secondary recrystallized plate exhibiting excellent magnetic properties can be obtained.

  Moreover, in patent document 6, in the manufacturing method of the grain-oriented electrical steel sheet which performs the cold rolling of 2 times or more sandwiching intermediate annealing, it cools between 750 degreeC and 200-300 degreeC after hot-rolled sheet annealing at 800 degreeC or more. Cool to the stop temperature at a cooling rate of 45 ° C./s or higher, then let cool, and perform the first cold rolling at 1 pass or more with a total rolling reduction of 25 to 50%, and all passes Using a roll having a diameter of 200 mmφ or more, setting the biting temperature to the first roll to 100 ° C. or less, and performing the second cold rolling with 2 passes or more and a total rolling reduction of 80 to 95%, and It is disclosed that a secondary recrystallized plate exhibiting excellent magnetic properties can be obtained by performing inter-pass aging at a temperature of 200 to 300 ° C. in at least one pass.

Japanese Patent Publication No. 40-15644 Japanese Patent Publication No. 51-13469 JP 2000-129356 A JP 2001-60505 A JP 2012-184497 A JP 2013-139629 A

However, the technique described in Patent Document 5 has a problem that productivity is inferior because it is manufactured at a low strain rate in the initial cold rolling.
In addition, in the technique described in Patent Document 6, good magnetic properties cannot be obtained unless aging between several minutes to several tens of minutes is applied in the second cold rolling, so productivity is still high. There was a problem of being inferior.

  The present invention has been made in view of the above-described problems of the prior art, and its purpose is superior to the prior art in the method of manufacturing grain-oriented electrical steel sheets, which is a low-cost process that does not perform high-temperature slab heating. Another object of the present invention is to propose a method of manufacturing a grain-oriented electrical steel sheet that exhibits high magnetic properties and high productivity.

  The inventors have intensively studied to solve the above problems. As a result, it is particularly important to improve the magnetic properties of the steel sheet to increase the cooling rate at the time of cooling after annealing immediately before the final cold rolling, and then start the final cold rolling within 72 hours. I found out. In addition, in the stage where the total rolling reduction of the final cold rolling is 50% or less, the strain rate during cold rolling is increased or the critical strain rate is calculated by using the material C amount, Si amount and rolling temperature. By controlling, it became possible to build a good primary recrystallization texture without imparting aging between passes for a long time, and found that a steel sheet having a high magnetic flux density appears after secondary recrystallization annealing, The present invention has been developed.

The present invention is based on the above-described knowledge, and the gist configuration is as follows.
1. C: 0.002 to 0.100 mass%, Si: 2.00 to 4.50 mass%, Mn: 0.03 to 1.00 mass%, sol. Al: 0.003 mass% or more and less than 0.010 mass% and N: (14.00 / 26.98) × [% sol. Al] or more and 0.008 mass% or less, and S: 0.002 to 0.005 mass% and / or Se: 0.002 to 0.005 mass% (one or two selected from S and Se) The seed contains 0.002 to 0.005 mass% in total amount, and the slab consisting of Fe and inevitable impurities as the remainder is hot-rolled into a hot-rolled sheet, and the hot-rolled sheet is subjected to hot-rolled sheet annealing Cold-rolled sheet with a final thickness by performing cold rolling two or more times without intermediate annealing, or after subjecting the hot-rolled sheet to hot-rolled sheet annealing, sandwiching once or intermediate annealing A grain-oriented electrical steel sheet comprising a series of processes in which cold rolling is performed twice or more to obtain a cold-rolled sheet having a final thickness, primary recrystallization annealing is performed, an annealing separator is applied to the surface of the steel sheet, and finish annealing is performed. In the manufacturing method of
The average cooling rate between 800 and 300 ° C. after annealing immediately before the final cold rolling is set to 40 ° C./s or more, then the final cold rolling is started within 72 hours, and the total rolling reduction of the final cold rolling is 50 % At a critical strain rate calculated from the following equation (1): a strain rate equal to or higher than X (s ⁻¹ ) and a cold rolling with a rolling reduction rate of 10% or higher per pass at least once. A method for producing a grain-oriented electrical steel sheet, comprising:
X (s ⁻¹ ) = f ([% C], [% Si]) · g (T) (1)
However, f ([% C], [% Si]) = 1 / ([% C] + [% Si] / 150)
g (T) = exp (-100 / T)
[% M] represents the content (% by mass) of the element M in the steel sheet.

2. 2. The method for producing a grain-oriented electrical steel sheet according to 1 above, wherein deformation twins are introduced into the recrystallized grains immediately before the final cold rolling by the final cold rolling.

3. In addition to the slab, Ni: 0.01-1.50 mass%, Cr: 0.03-0.50 mass%, Cu: 0.03-0.50 mass%, P: 0.005-0.500 mass%, Sb: 0.005-0.500 mass%, Sn: 0.005-0.50 mass%, Bi: 0.005-0.500 mass%, Mo: 0.005-0.100 mass%, B: 0.0002- 0.0025 mass%, Te: 0.0005 to 0.0100 mass%, Nb: 0.001 to 0.010 mass%, V: 0.001 to 0.010 mass%, and Ta: 0.001 to 0.010 mass% The method for producing a grain-oriented electrical steel sheet according to 1 or 2 above, comprising one or more component compositions selected from the group consisting of:

4). 4. The method for producing a grain-oriented electrical steel sheet according to any one of 1 to 3, wherein a rate of temperature increase between 200 and 700 ° C. in the temperature increasing process of the primary recrystallization annealing is 50 ° C./s or more. .

5. The heating rate between 200 and 700 ° C. in the temperature raising process of the primary recrystallization annealing is 50 ° C./s or more, and further between 1 and 10 s at any temperature between 250 and 600 ° C. in the temperature raising process. The method for producing a grain-oriented electrical steel sheet according to any one of the above 1 to 3, wherein the retaining is performed.

6). The rate of temperature increase between 200 and 700 ° C. in the temperature raising process of the primary recrystallization annealing is set to 50 ° C./s or more, and at any temperature between 250 ° C. and less than 500 ° C. in the temperature raising process, 0.5 1 to 4 times for 10 seconds, and 1 to 2 times for 0.5 to 3 seconds at any temperature of 500 ° C. to 700 ° C. A method for producing a grain-oriented electrical steel sheet having low iron loss according to claim 1.

7). 7. The method for producing a grain-oriented electrical steel sheet according to any one of 1 to 6, wherein nitriding treatment is performed at any stage from the primary recrystallization annealing to the secondary recrystallization annealing.

  According to the present invention, the cooling rate after annealing immediately before the final cold rolling is increased, and then the final cold rolling is started within 72 hours, and the total rolling reduction of the final cold rolling is 50% or less. In the stage, the primary recrystallization texture can be effectively improved by increasing the strain rate according to the amount of C and Si of the material, so that excellent magnetic properties compared to the prior art are expressed, and A grain-oriented electrical steel sheet with high productivity can be obtained.

It is a figure which shows the influence of the strain rate of the 1st pass of the last cold rolling on the random strength ratio of {411} <148> orientation of the thickness center layer of a primary recrystallization annealing board. It is a diagram showing the effect of the product sheet final cold rolling the first pass of the strain rate on the magnetic flux density B ₈ of. It is a figure which shows the influence of the temperature increase rate (20 degreeC / s) of 200-700 degreeC of the primary recrystallization annealing which influences the iron loss _{W17 / 50} of a product board, and the holding temperature and holding time in the middle of temperature rising. It is a figure which shows the influence of the temperature increase rate (50 degreeC / s) of 200-700 degreeC of the primary recrystallization annealing which influences the iron loss _W17 / 50 of a product board, and the retention temperature and retention time in the middle of temperature increase. It is a figure which shows the influence of the temperature increase rate (100 degrees C / s) of 200-700 degreeC of the primary recrystallization annealing which influences the iron loss _{W17 / 50} of a product plate, and the retention temperature and retention time in the middle of temperature increase. It is a figure which shows the influence of the temperature increase rate between 200-700 degreeC (200 degreeC / s) of the primary recrystallization annealing which influences the iron loss _{W17 / 50} of a product board, and the retention temperature and retention time in the middle of temperature increase. It is a figure which shows how to obtain | require the heating rate of this invention. It is a figure which shows the relationship between the core temperature _{W17 / 50} of a product board, and the temperature increase rate between 200-700 degreeC of primary recrystallization annealing.

Hereinafter, the present invention will be specifically described.
First, an experiment that triggered the development of the present invention will be described.
<Experiment 1>
Three types of steel consisting of Fe and unavoidable impurities, Steel A (C: 0.021 mass%, Si: 3.05 mass%, Mn: 0.064 mass%, sol.Al: 0.007 mass%, N: 0 .004 mass%, S: 0.003 mass%), Steel B (C: 0.040 mass%, Si: 3.36 mass%, Mn: 0.062 mass%, sol.Al: 0.007 mass%, N: 0.004 mass) %, S: 0.002 mass%) and steel C (C: 0.078 mass%, Si: 3.77 mass%, Mn: 0.068 mass%, sol. Al: 0.007 mass%, N: 0.004 mass%, S: 0.002 mass%), and a steel slab is obtained by a continuous casting method, and then reheated to a temperature of 1200 ° C. and hot-rolled to obtain a plate thickness of 2 After 5mm hot-rolled sheet and subjected to hot-rolled sheet annealing at 1020 ° C x 60s, first cold rolled to an intermediate sheet thickness of 1.8mm, and further subjected to intermediate annealing at 1120 ° C x 80s, The cooling between 800-300 degreeC of annealing was cooled by the average cooling rate: 60 degreeC / s. After that, 4 stands of tandem rolling was started after 18 hours to obtain a cold-rolled sheet having a final thickness of 0.26 mm.

また、最終冷間圧延の総圧下率が５０％以下の段階における臨界ひずみ速度：Ｘ（ｓ^−１）は、鋼Ａ、ＢおよびＣで、それぞれ、１９．５（ｓ^−１）、１２．０（ｓ^−１）、７．２（ｓ^−１）であった。 Here, the rolling speed in the first pass carried out at an inlet temperature of 25 ° C. was changed, and samples were produced at various strain rates shown in FIG. Here, the strain rate (ε _m ) during rolling was calculated using the following Ekelund equation.

Further, critical strain rates X (s ⁻¹ ) at the stage where the total rolling reduction of the final cold rolling is 50% or less are steels A, B, and C, respectively, 19.5 (s ⁻¹ ), 12. It was 0 (s ⁻¹ ) and 7.2 (s ⁻¹ ).

Next, the cold-rolled sheet was subjected to primary recrystallization annealing with decarburization annealing at 840 ° C. × 100 s in a humid atmosphere of 50 vol% H ₂ -50 vol% N ₂ , dew point: 60 ° C. In addition, the said primary recrystallization annealing set the temperature increase rate between 200-700 degreeC in the temperature increase process to 840 degreeC to 20 degrees C / s.

  After that, after applying an annealing separator mainly composed of MgO to the steel sheet surface, secondary recrystallization annealing is performed at 1200 ° C. for 10 hours, followed by application of a phosphate-based insulation tension coating. Then, flattening annealing for the purpose of baking and flattening of the steel strip was performed to obtain a product, and a test piece under each condition was obtained.

FIG. 1 shows the results of investigating the influence of the strain rate of the first cold rolling first pass on the {411} <148> orientation versus random strength ratio of the thickness center layer of the primary recrystallization annealed plate. Regarding the crystal orientation of the primary recrystallized annealed plate, the thinned sample polished to the thickness center layer was etched with 10% nitric acid for 30 s, and (110), (200), (211) by X-ray Schulz method The surface was measured, ODF (Orientation Distribution Function) analysis was performed from the data, and the intensity of each crystal orientation was calculated. The analysis was performed by the ADC (Arbitrary Defined Cell) method using the Resmat software Texttools. The intensity ratio of the {411} <148> orientation relative to the random intensity was set to (φ ₁ , Φ, φ ₂ ) = (20, 20, 45) in Bunge's Euler angle display.
As shown in FIG. 1, in the condition where the strain rate of the first cold rolling first pass exceeds the critical strain rate: X (s ⁻¹ ), {411} <148 of the thickness center layer of the primary recrystallization annealed plate. > The orientation to random intensity ratio increased.
In the present invention, the plate thickness center layer of the primary recrystallization annealed plate indicates a range of plate thickness of 0.5 t ± 0.1 t, where t is the total plate thickness.

Next, FIG. 2 shows the results of examining the effect of the final cold rolling the first pass on the magnetic flux density B ₈ of the product plate strain rate.
As shown in FIG. 2, the magnetic flux density B ₈ of the product plate was increased under the condition that the strain rate in the first cold rolling first pass exceeded the critical strain rate: X (s ⁻¹ ).
By rolling under the condition that the strain rate of the first pass of the final cold rolling exceeds the critical strain rate: X (s ⁻¹ ), {411} <148> of the center thickness layer of the primary recrystallization annealed plate Although the reason why the azimuth-to-random intensity ratio has increased has not yet been fully clarified, the inventors consider as follows.

As a result of crystal orientation analysis of various samples after one pass of final cold rolling using backscattered electron diffraction (Electron Back Scattering Diffraction Pattern: EBSD), critical strain rate: exceeding X (s ⁻¹ ) In the samples, linear regions having a width of about several hundred nm to several μm, which differed in orientation from the parent phase, were confirmed in various initial grains.
In this region, the continuity of orientation is interrupted when it hits the initial grain boundary, and there is a crystal orientation relationship that forms a large misorientation angle around the <111> axis with the parent phase, and on both sides of the linear region Since the orientation relationship is the same, it can be identified as a deformation twin. Here, it is known that the deformation twins of the BCC crystal structure have an orientation relationship of 60 ° around the <111> axis with the parent phase. However, even after the deformation twins having the above-mentioned crystal orientation relationship are formed in one pass of the final cold rolling, the crystal orientation rotation by rolling further occurs, so in the sample after one pass, as described above The exact twin orientation relationship is not maintained.
Therefore, the deformation twin in the present invention is a width of 100 nm or more and 20 μm or less in the linear region existing in the sample after the final cold rolling 1 pass, and <111> It means a region having an orientation relationship of 40 ° or more around the axis.
In general, in a tensile test, it is known that deformation twins increase as the amount of raw material Si increases.

  In this case, in the electrical steel sheet to which 2.5 mass% or more of Si was added, no deformation twins were formed with the C-free material. This is considered to be because the deformation mode is different between the tensile process and the rolling process. On the other hand, it was confirmed that deformation twins were formed by rolling by increasing the amount of material C. For this reason, the addition of Si suppresses slip deformation as a base, that is, in addition to being in a stress state that induces twin deformation, the addition of C further suppresses the slip deformation, It is presumed that twin deformation was relatively activated. From the above, it is considered that adding Si and C together has the effect of increasing the deformation twins of the steel sheet.

  In addition, the present invention provides an average cooling rate between 800 ° C. and 300 ° C. after annealing immediately before the final cold rolling at 40 ° C./s or more, and then starts the final cold rolling within 72 hours. It has been clarified that the product plate exhibits the effect of increasing the magnetic flux density. Although the reason for this has not been fully clarified yet, the inventors consider as follows.

  Increasing the cooling rate between 800 to 300 ° C. after annealing, and starting the final cold rolling in a short time after that, does not precipitate carbide in the final cold rolled base metal, leaving sufficient solid solution C It means that the final cold rolling is performed in a state of being made to occur. That is, leaving sufficient solid solution C in the final cold-rolled steel sheet induces twin deformation, resulting in an increase in primary recrystallized {411} <148> grains, and the product according to the present invention. We think that the effect of increasing the magnetic flux density of the plate may be demonstrated.

Furthermore, the reason why the induction of twin deformation becomes more conspicuous by increasing the strain rate in the first cold rolling first pass is considered as follows.
Among metal deformations, slip deformation is a thermal activation process, so the critical resolved shear stress (CRSS) of slip deformation is temperature-dependent, and CRSS may increase as the temperature decreases. Are known. Further, it is known that the CRSS of slip deformation is also dependent on the strain rate, and it is known that the CRSS of slip deformation increases as the strain rate increases. On the other hand, among metal deformations, twin deformation CRSS is known to have extremely low temperature dependence compared to slip deformation CRSS. That is, it is presumed that twin deformation is not a thermal activation process or its influence is extremely small.
Therefore, when the processing temperature is lowered or the strain rate is increased, the CRSS of the slip deformation increases, whereas the CRSS of the twin deformation does not increase or only slightly increases. Since the twin deformation CRSS is lower than the deformation CRSS, twin deformation is likely to occur, and it is presumed that the deformation twin was formed preferentially.

Since the twin plane of the BCC structure is {112} and the Burgers vector is <111>, the twin region formed at the initial stage of cold rolling has a specific crystal orientation, and the latter stage of cold rolling When slip deformation occurs, a crystal orientation different from the conventional one is formed.
In the present invention, it is presumed that the primary recrystallization {411} <148> grains are increased by subjecting the final cold rolled sheet as described above to the primary recrystallization annealing.
As the primary recrystallized {411} <148> grains increase, the deviation angle of the secondary recrystallized Goss orientation grains decreases, and the magnetic flux density of the product plate is increased. Furthermore, as mentioned above, the thickness center layer of the primary recrystallization annealed sheet is obtained by rolling with the strain rate in the first cold rolling first pass exceeding the critical strain rate: X (s ⁻¹ ). It is presumed that the {411} <148> orientation to random intensity ratio increased and consequently the product plate achieved a higher magnetic flux density.

<Experiment 2>
Next, the influence of the temperature increase rate of primary recrystallization annealing was investigated. C: 0.052 mass%, Si: 3.31 mass%, Mn: 0.066 mass%, sol. It contains Al: 0.008 mass%, N: 0.005 mass%, S: 0.003 mass%, and the remainder melts steel having a component composition consisting of Fe and unavoidable impurities, and is made into a steel slab by a continuous casting method. Then, after reheating to a temperature of 1240 ° C. and hot rolling to obtain a hot rolled sheet having a thickness of 2.2 mm, the hot rolled sheet is annealed at 1050 ° C. × 30 s, and then 800 to 300 of this hot rolled sheet is annealed. The average cooling rate during cooling between 0 ° C. was 45 ° C./s, and after 70 hours, 4 stands of tandem rolling was started to obtain a cold rolled sheet having a final thickness of 0.26 mm. Each stand entry side temperature was 50 ° C., 60 ° C., 70 ° C., 80 ° C., and each stand exit side plate thickness was 1.2 mm, 0.68 mm, 0.40 mm, and 0.26 mm, respectively. Moreover, the strain rate in each stand was 31.2 s ⁻¹ , 71.9 s ⁻¹ , 156.1 s ⁻¹ and 277.9 s ⁻¹ , respectively. Note that the critical strain rate: X is 9.7 s ^{−1 when} the total rolling reduction of the final cold rolling is 50% or less.
Next, the cold-rolled sheet was subjected to primary recrystallization annealing with decarburization annealing at 840 ° C. × 120 s in a humid atmosphere of 60 vol% H ₂ -40 vol% N ₂ with a dew point of 58 ° C. In the primary recrystallization annealing, various heating rates between 200 and 700 ° C. in the temperature rising process up to 840 ° C. were examined, and further, a treatment for holding at various temperatures for 5 s during the temperature rising was also performed. In addition, holding temperature is 100, 250, 400, 600, and 700 degreeC as shown to FIGS.

Further, in the present invention, as shown in FIG. 7, the rate of temperature increase is the average rise in t ₁ , t ₃ , t ₅ excluding the holding time t ₂ , t ₄ from the time from 200 ° C. to 700 ° C. It refers to the temperature rate ((700-200) / (t ₁ + t ₃ + t ₅ )).
After that, after applying an annealing separator mainly composed of MgO to the steel sheet surface, secondary recrystallization annealing is performed at 1180 ° C. for 10 hours, followed by application of a phosphate-based insulating tension coating. Then, flattening annealing for the purpose of baking and flattening of the steel strip was performed to obtain a product, and a test piece under each condition was obtained.

FIGS. 3 to 6 show the heating rate in the heating (heating) process between 200 and 700 ° C. of the primary recrystallization annealing on the iron loss W _17/50 of the product plate, and the holding temperature and holding time during the heating. The result of investigating the influence was shown.
As shown in FIGS. 3-6, 200-700 in the temperature rising process of the primary recrystallization annealing under the condition that the strain rate of the first cold rolling first pass exceeds the critical strain rate: X (s ⁻¹ ). It can be seen that the iron loss W _17/50 of the product plate is reduced by _{performing the} rapid heat treatment at a temperature of 50 ° _C./s or more. Moreover, while heating between 200-700 degreeC in the temperature rising process of primary recrystallization annealing with the temperature increase rate of 50 degrees C / s or more, it is 1 at any temperature selected from between 250-600 degreeC of temperature rising process. It can be seen that the iron loss W _17/50 of the product plate is further reduced by performing the holding process of holding for 10 seconds.

The result shown in the above _<< Experiment 2 >>, that is, the reason why the iron loss W _17/50 of the product plate is reduced by rapidly heating the temperature _raising process of the primary recrystallization annealing is not yet sufficiently clear. However, the inventors consider as follows.
By raising the temperature to the vicinity of the recrystallization temperature of the steel sheet in a short time, the development of the γ fiber (<111> // ND orientation) formed preferentially at a normal heating rate is suppressed. It is presumed that the generation of {110} <001> structure which becomes the nucleus of the next recrystallization is promoted, and sharp {110} <001> is increased. Furthermore, as a result, it is presumed that the crystal grains (Goss-oriented grains) after the secondary recrystallization are refined and the iron loss characteristics of the steel sheet are improved.

In the temperature rising process, increasing the temperature rising rate suppresses the development of the <111> // ND orientation in the recrystallization texture as described above, and the Goss orientation grains ({110 } <001>) is considered to be effective. This is because, in general, in cold rolling, the <111> // ND orientation introduces more strain than other orientations, and the accumulated strain energy is high. In the primary recrystallization annealing that is heated at a speed, recrystallization occurs preferentially from a rolled structure having a <111> // ND orientation in which the accumulated strain energy is high. As a result, in recrystallization, <111> // ND orientation grains usually appear preferentially from a rolled structure with <111> // ND orientation, and the structure after recrystallization has <111> // ND orientation as the main orientation. Become.
On the other hand, by increasing the heating rate, more thermal energy than that released by recrystallization is supplied to the steel sheet, so that recrystallization occurs even in a Goss orientation with a relatively low accumulated strain energy. Thus, the <111> // ND orientation after recrystallization relatively decreases, and the Goss orientation ({110} <001>) increases. This is because when the Goss orientation is increased, many Goss orientation grains appear in the secondary recrystallization, so that the secondary recrystallization grains become finer and the iron loss is reduced.

In the middle of the temperature increase, when a holding process is performed to hold for a predetermined time at a temperature at which recovery occurs, the <111> // ND orientation with high strain energy recovers preferentially. Therefore, the driving force causing recrystallization of <111> // ND orientation generated from the rolled structure of <111> // ND orientation is selectively reduced, and other orientations cause recrystallization. As a result, the <111> // ND orientation after recrystallization is relatively reduced.
On the other hand, if the holding temperature of the holding process is too high or the holding time exceeds 10 s, recovery occurs in a wide range of the steel sheet, so that the recovery structure remains as it is, and the structure is different from the primary recrystallization structure described above. turn into. As a result, the secondary recrystallization is greatly adversely affected and the iron loss characteristics are deteriorated.

  In addition, the effect of improving the magnetic properties by performing a short-term holding treatment at a temperature at which recovery during the temperature rise occurs can be obtained from the temperature rise rate (10 to 30 ° C./s) using a conventional radiant tube or the like. However, it is limited to a case where the heating rate is high, specifically, the heating rate is 50 ° C./s or more. Therefore, in the present invention, the rate of temperature increase in the temperature range of 200 to 700 ° C. during primary recrystallization annealing is preferably 50 ° C./s or more. In addition, although there is no restriction | limiting in the upper limit of this temperature increase rate, it is about 500 degreeC / s on an installation.

Here, as a demerit when performing the rapid heating as described above during the primary recrystallization annealing, the time spent for the initial oxidation during the temperature increase is shortened, so the subscale structure after the primary recrystallization annealing changes, and the finish It is conceivable that a film defect occurs during annealing and a secondary recrystallization defect occurs, resulting in deterioration of magnetic properties. However, it is considered that by performing the retention treatment during the temperature rise, proper initial oxidation is performed even during rapid heating, preventing deterioration of the film and improving the magnetic characteristics.
And in order to obtain the further magnetic improvement effect by the above-mentioned film improvement, it is preferable to hold at least twice during the temperature rise, once in the temperature range where the recovery occurs at 250 ° C. or more and less than 500 ° C., once again the initial oxidation It is considered preferable that the temperature is maintained in a temperature range of 500 ° C. or higher and 700 ° C. or lower. At least 0.5 s is required for recovery, but it is considered necessary to suppress it to 10 s at the longest. Keeping the holding time to 10 s or less is because there is a possibility that subsequent recrystallized grains will not be generated if recovered too much.

  Further, the holding may be performed a plurality of times, but if the number of holdings is large, it may be recovered too much to stop recrystallization, so that it is desirable to keep it within 4 times. More preferably, even when held at 250 to 500 ° C. a plurality of times, the total holding time is preferably within 10 s from the viewpoint of preventing recrystallization failure.

  Furthermore, it is considered that the retention in the temperature range where the initial oxidation is active is preferably 0.5 s or more. However, this temperature range is also a temperature range where recrystallization of the steel sheet occurs. However, since recrystallization at this point needs to be avoided as much as possible, it is preferably within 3 s. In addition, although holding in this temperature range may be performed a plurality of times, it is desirable to suppress it within two times from the viewpoint of preventing recrystallization failure.

Next, the component composition of the steel material (slab) used for the material of the grain-oriented electrical steel sheet of the present invention will be described.
C: 0.002 to 0.100 mass%
If C is less than 0.002 mass%, the grain boundary strengthening effect due to C is lost, and cracks occur in the slab, which causes problems in production. Further, the formation of deformation twins, which is a feature of the present invention, is also suppressed. On the other hand, when it exceeds 0.100 mass%, it becomes difficult to reduce C to 0.005 mass% or less at which no magnetic aging occurs by decarburization annealing. Therefore, C is set to a range of 0.002 to 0.100 mass%. Preferably it is the range of 0.010-0.080 mass%.

Si: 2.00 to 4.50 mass%
Si is an element necessary for increasing the specific resistance of a steel sheet and reducing iron loss. When the addition is less than 2.00 mass%, not only these effects cannot be sufficiently exhibited, but also the formation of deformation twins, which is a feature of the present invention, is suppressed. On the other hand, when it exceeds 4.50 mass%, the workability of the steel sheet is lowered, and it becomes difficult to perform rolling. Therefore, Si is set to a range of 2.00 to 4.50 mass%. Preferably it is the range of 2.50-4.50 mass%.

Mn: 0.03-1.00 mass%
Mn is an element necessary for improving the hot workability of steel. If the effect is less than 0.03 mass%, it is not sufficient. On the other hand, if it exceeds 1.00 mass%, the magnetic flux density of the product plate decreases. Therefore, Mn is set to a range of 0.03 to 1.00 mass%. Preferably it is the range of 0.05-0.20 mass%.

Acid-soluble Al (Sol.Al): 0.003 mass% or more and less than 0.010 mass% Al forms a dense oxide film on the surface, making it difficult to control the amount of nitridation during nitridation or inhibiting decarburization Sol. It suppresses to less than 0.01 mass% with Al. However, since Al having high oxygen affinity can be added in a small amount in steelmaking, the amount of dissolved oxygen in the steel can be reduced and oxide inclusions leading to property deterioration can be expected. It is necessary to contain Al in an amount of 0.003 mass% or more, which can suppress deterioration of magnetic characteristics.

N: (14.00 / 26.98) × [% sol. Al] or more and 0.008 mass% or less The present invention is characterized in that silicon nitride is precipitated by nitriding. Therefore, N or more of N that precipitates as AlN can be included in advance with respect to the amount of Al contained. It is essential. Since AlN is bonded at a ratio of 1: 1, N of 1 or more in atomic weight ratio, that is, Sol. Mass% content of Al: [% Sol. By containing N of (14.00 / 26.98) or more with respect to Al], a trace amount of N contained in the steel can be precipitated as silicon nitride. On the other hand, since N may cause defects such as blisters during slab heating, it is necessary to suppress N to 0.008 mass% or less. Desirably, it is 0.006 mass% or less.

S and / or Se: 0.002 to 0.005 mass%
S and Se combine with Mn to form an inhibitor. However, when the content of one or two selected from S and Se is less than 0.002 mass%, the absolute amount of the inhibitor is insufficient, and normal grains Insufficient growth control. On the other hand, if the content of one or two selected from S and Se exceeds 0.005 mass%, since the de-S and de-Se are incomplete in the secondary recrystallization annealing, the iron loss is deteriorated. cause. Therefore, 1 type or 2 types selected from S and Se were set in the range of 0.002 to 0.005 mass%, respectively.

In the steel material used for the grain-oriented electrical steel sheet of the present invention, the balance other than the above components is Fe and inevitable impurities.
In the present invention, for the purpose of improving magnetic properties, Ni: 0.01-1.50 mass%, Cr: 0.03-0.50 mass%, Cu: 0.03-0.50 mass%, P : 0.005-0.500 mass%, Sb: 0.005-0.500 mass%, Sn: 0.005-0.50 mass%, Bi: 0.005-0.500 mass%, Mo: 0.005-0 100 mass%, B: 0.0002 to 0.0025 mass%, Te: 0.0005 to 0.0100 mass%, Nb: 0.001 to 0.010 mass%, V: 0.001 to 0.010 mass%, and Ta: You may contain suitably 1 type or 2 types chosen from 0.001-0.010mass%.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
A steel material (slab) may be produced by a conventional ingot-bundling rolling method or continuous casting method after melting the steel having the above-described component composition by a conventional refining process, or A thin cast piece having a thickness of 100 mm or less may be manufactured by a direct casting method. The slab is reheated to a temperature of about 1250 ° C. or less and subjected to hot rolling according to a conventional method. In addition, when not containing an inhibitor component, you may use for hot rolling immediately after casting, without reheating a slab. In the case of a thin slab, the hot rolling may be omitted and the process may proceed as it is.

  Next, the hot-rolled sheet obtained by hot rolling is subjected to hot-rolled sheet annealing as necessary. The temperature of this hot rolled sheet annealing is preferably in the range of 800 to 1150 ° C. in order to obtain good magnetic properties. If it is less than 800 degreeC, the band structure formed by hot rolling will remain, it will become difficult to obtain the primary recrystallized structure of a sized grain, and the growth of a secondary recrystallized grain will be inhibited. On the other hand, when the temperature exceeds 1150 ° C., the grain size after the hot-rolled sheet annealing is excessively coarsened, so that it becomes difficult to obtain a primary recrystallized structure of sized particles.

  The steel sheet after hot rolling or after hot-rolled sheet annealing is made into a cold-rolled sheet having a final thickness by one or more cold rollings or two or more cold rollings sandwiching intermediate annealing. The annealing temperature of the intermediate annealing is preferably in the range of 900 to 1200 ° C. When the temperature is lower than 900 ° C., the recrystallized grains after the intermediate annealing become finer, and the Goss nuclei in the primary recrystallized structure are reduced to deteriorate the magnetic properties of the product plate. On the other hand, when the temperature exceeds 1200 ° C., the crystal grains become too coarse as in the hot-rolled sheet annealing, and it becomes difficult to obtain a primary recrystallized structure of the sized grains.

  Furthermore, the present invention sets the average cooling rate at the time of cooling between 800 and 300 ° C. after annealing immediately before the final cold rolling to 40 ° C./s or more, and then starts the final cold rolling within 72 hours. It is an indispensable condition. When the final cold rolling is started after the cooling rate between 800 and 300 ° C. after annealing immediately before the final cold rolling is less than 40 ° C./s and / or after 72 hours, the final cold rolling base material This is because a sufficient amount of dissolved C cannot be secured due to the precipitation of carbides, and the effect of increasing the magnetic flux density of the product plate of the present invention cannot be sufficiently exhibited. In the present invention, the annealing immediately before the final cold rolling refers to after hot-rolled sheet annealing when only one cold rolling is performed, and performs two or more cold rolling sandwiching the intermediate annealing. In the case, it refers to the intermediate annealing immediately before the final cold rolling.

Further, the present invention provides a one-pass reduction at a strain rate equal to or higher than the critical strain rate: X (s ⁻¹ ) calculated from the following equation (1) in a stage where the total rolling reduction of the final cold rolling is 50% or less. It is necessary to perform rolling at a rate of 10% or more at least once.
X (s ⁻¹ ) = f ([% C], [% Si]) · g (T) (1)
F ([% C], [% Si]) = 1 / ([% C] + [% Si] / 150),
g (T) = exp (-100 / T)
Here, [% M] is mass% of the element M in the steel sheet, and T is the rolling stand entry side temperature (K).

  Further, the present invention is characterized in that deformed twins are introduced into recrystallized grains before cold rolling by performing the cold rolling, and the ratio of recrystallized grains introduced with deformed twins is 10%. If it is at least%, the effect of the present invention will remarkably appear. On the other hand, if the deformation twins increase excessively, the risk of fracture occurring during rolling increases, so the ratio of recrystallized grains in which the deformation twins are introduced is preferably 90% or less. The ratio of recrystallized grains introduced with deformation twins is specified as deformation twins by the above-mentioned EBSP orientation analysis among all recrystallized grains before cold rolling in the 1/5 layer region of the plate thickness center. Refers to the ratio of the number of recrystallized grains introduced.

  As described above, the cold rolling (final cold rolling) with the final plate thickness can sufficiently obtain the magnetic improvement effect of the product plate even by tandem rolling (unidirectional rolling). In addition, further improvement in characteristics can be obtained by using a conventionally known warm rolling technique or pass aging technique. In that case, it is preferable to employ reverse rolling rather than tandem rolling (unidirectional rolling).

  The cold-rolled sheet having the final thickness is then subjected to primary recrystallization annealing. The annealing temperature in the primary recrystallization annealing is preferably in the range of 800 to 900 ° C. from the viewpoint of promptly proceeding with the decarburization reaction when serving also as decarburization annealing, and the atmosphere is a humid atmosphere. Is preferred. On the other hand, when using a steel material with C: 0.005 mass% or less that does not require decarburization, the temperature is preferably in the range of 800 to 1000 ° C. In addition, you may perform a primary recrystallization annealing and a decarburization annealing separately.

  Furthermore, in the present invention, a nitriding treatment can be applied as an additional inhibitor treatment at any stage from the primary recrystallization annealing to the secondary recrystallization annealing. This nitriding treatment includes gas nitriding in which heat treatment is performed in an ammonia atmosphere after primary recrystallization annealing, salt bath nitriding in which heat treatment is performed in a salt bath, plasma nitriding, and nitride containing an annealing separator. Any known nitriding technique such as changing the secondary recrystallization annealing atmosphere to a nitriding atmosphere can be applied.

  When the steel sheet subjected to primary recrystallization annealing places importance on iron loss characteristics and transformer noise, an annealing separator mainly composed of MgO is applied to the steel sheet surface, dried, and then subjected to finish annealing. It is preferable to develop a secondary recrystallized structure highly accumulated in the orientation and to form a forsterite film. On the other hand, when emphasizing the punching processability and not forming the forsterite film, it is not necessary to apply an annealing separator or to perform a final annealing using an annealing separator mainly composed of silica, alumina or the like. preferable. In addition, when a forsterite film is not formed, it is also effective to perform electrostatic coating without bringing moisture into the coating of the annealing separator. Further, a heat resistant inorganic material sheet (silica, alumina, mica) may be used in place of the annealing separator.

  As a condition for the finish annealing, when forming a forsterite film, it is maintained at around 800 to 1050 ° C. for 20 hours or more to develop and complete secondary recrystallization, and then the temperature is raised to a temperature of 1100 ° C. or more. In the case where the iron loss characteristic is emphasized and the purification process is performed, it is more preferable to raise the temperature to about 1200 ° C. On the other hand, when the forsterite film is not formed, the secondary recrystallization may be completed, so that the annealing can be completed by raising the temperature to 800 to 1050 ° C.

  In addition, the steel sheet after finish annealing can be iron loss by removing the unreacted annealing separator adhering to the steel sheet surface by water washing, brushing, pickling, etc., and then performing flattening annealing to correct the shape. It is effective in reducing the above. This is because the finish annealing is usually performed in a coil state, so that the coil has wrinkles, and this may cause deterioration of characteristics when measuring iron loss.

  Furthermore, in the case where the steel plates are laminated and used, it is effective to form an insulating film on the steel plate surface in the above-described flattening annealing or before and after that. In particular, in order to reduce iron loss, it is preferable to apply a tension-imparting film that imparts tension to the steel sheet as the insulating film. For the formation of a tension-imparting coating, it is possible to apply a method of applying a tension coating via a binder or a method of depositing an inorganic substance on the surface of a steel sheet by physical vapor deposition or chemical vapor deposition. Since an insulating film having a large loss reducing effect can be formed, it is more preferable.

  Moreover, in order to further reduce the iron loss, it is preferable to perform a magnetic domain fragmentation process. As a processing method, a method of generally forming a groove in the final product plate, introducing a thermal strain or an impact strain in a linear or dotted manner by electron beam irradiation, laser irradiation, plasma irradiation, or the like, A publicly known and publicly-known magnetic domain subdividing method can be used, such as forming a groove by etching a steel sheet that has been cold-rolled to a final thickness or a steel sheet surface in an intermediate process.

[Example 1]
C: 0.046 mass%, Si: 3.45 mass%, Mn: 0.069 mass%, sol. Al: 0.006 mass%, S: 0.004 mass%, Se: 0.003 mass% and N: 0.003 mass% Steel, the balance of which is composed of Fe and inevitable impurities, and is made into a steel slab by a continuous casting method, and then reheated to a temperature of 1180 ° C. and hot-rolled to obtain a plate thickness of 2. The hot-rolled sheet of 5 mm was subjected to hot-rolled sheet annealing at 1000 ° C. × 50 s, the thickness of the intermediate sheet was 1.8 mm by primary cold rolling, and the intermediate annealing was performed at 1020 ° C. × 20 s. The average cooling rate during cooling between ˜300 ° C. was 40 ° C./s, and after 18 hours, final cold rolling was started under the conditions shown in Table 1-1 and Table 1-2. In Table 1-1 and Table 1-2, symbols 1 to 3 were tandem mills, and symbols 4 and 5 were finally cold-rolled by a reverse mill to finish a cold-rolled sheet having a final sheet thickness of 0.26 mm. Moreover, the critical strain rate: X (s ⁻¹ ) at the stage where the total rolling reduction of the final cold rolling of this sample is 50% or less is 10.6.
Subsequently, the cold-rolled sheet was subjected to primary recrystallization annealing with decarburization annealing at 840 ° C. × 100 s in a wet atmosphere of 50 vol% H ₂ -50 vol% N ₂ , dew point: 56 ° C. At this time, the temperature was raised between 200 and 700 ° C. at 25 ° C./s.
Furthermore, after applying an annealing separator mainly composed of MgO to the surface of the steel sheet, secondary recrystallization annealing is performed at 1180 ° C. for 50 hours, followed by application of a phosphate-based insulating tension coating. The product was subjected to flattening annealing for the purpose of baking and flattening of the steel strip.
Table 1-1 and Table 1-2 show the strain rate between each pass of the final cold rolling, and Table 1-3 shows the {411} <148> orientation of the center thickness layer of the primary recrystallization annealed plate The measurement results of the to-random strength ratio, the magnetic flux density B _{8 of} the product plate, and the iron loss W _17/50 are shown.

With respect to the material finally cold-rolled by the tandem mill, in symbol 1, the average cooling rate between 800 and 300 ° C. after annealing immediately before the final cold rolling is set to 40 ° C./s or higher, and then the final cold rolling is performed within 72 hours. Even when rolling was started, the strain rate in the first pass was 5.7, which is equal to or less than the critical strain rate: X (s ⁻¹ ), so that good magnetic properties of the product plate could not be obtained. Regarding symbols 2 and 3, since the critical strain rate or higher was achieved in the first pass, the first pass, and the second pass, respectively, good magnetic properties of the product plate were obtained. Symbols 4 and 5 rolled with a reverse mill set the average cooling rate between 800 to 300 ° C. after annealing immediately before the final cold rolling to 40 ° C./s or more, and then start the final cold rolling within 72 hours. Furthermore, in the first pass, extremely good magnetic properties were obtained in combination with the achievement of cold rolling at a critical strain rate or higher and a rolling reduction rate of 10% or higher in one pass and the effect of aging between passes.

[Example 2]
C: 0.036 mass%, Si: 3.37 mass%, Mn: 0.088 mass%, sol. A steel having a component composition containing Al: 0.007 mass%, S: 0.005 mass%, and N: 0.004 mass%, the balance being Fe and inevitable impurities, was melted, and a steel slab was obtained by a continuous casting method. Thereafter, it was reheated to a temperature of 1240 ° C., hot-rolled to obtain a hot-rolled sheet having a thickness of 2.2 mm, and subjected to hot-rolled sheet annealing of 1120 ° C. × 60 s. The average cooling rate at the time of cooling between 800 and 300 ° C. during the hot-rolled sheet annealing is set to various values shown in Table 2, and reverse rolling is started after various times shown in Table 2 to obtain a final sheet thickness of 0.22 mm. Finished in cold rolled sheet. Each stand entry side temperature is 40 ° C., 100 ° C., 140 ° C., 170 ° C., 190 ° C., 100 ° C., and each stand exit side plate thickness is 1.4 mm, 0.90 mm, 0.60 mm, 0.42 mm, They were 0.30 mm and 0.22 mm. Moreover, the strain rate in each stand was 234.2 s ⁻¹ , 289.9 s ⁻¹ , 344.3 s ⁻¹ , 392.2 s ⁻¹ , 453.6 s ⁻¹ , and 512.8 s ⁻¹ , respectively. It should be noted that the critical strain rate X (s ⁻¹ ) = 11.9 at the stage where the total rolling reduction of the final cold rolling of the steel is 50% or less.
Subsequently, the cold-rolled sheet was subjected to primary recrystallization annealing with decarburization annealing at 840 ° C. × 100 s in a humid atmosphere of 55 vol% H ₂ -45 vol% N ₂ , dew point: 55 ° C. At this time, the temperature was raised between 200 and 700 ° C. at 25 ° C./s.
Furthermore, after applying an annealing separator mainly composed of MgO to the surface of the steel sheet, secondary recrystallization annealing is performed at 1180 ° C. for 50 hours, followed by application of a phosphate-based insulating tension coating. The product was subjected to flattening annealing for the purpose of baking and flattening of the steel strip.
Table 2 shows the measurement results of the {411} <148> orientation-to-random strength ratio of the primary recrystallization annealed plate, the magnetic flux density B _{8 of} the product plate, and the iron loss W _17/50 .

From Table 2, in the stage where the total rolling reduction of the final cold rolling is 50% or less, the cold rolling is performed at a strain rate of critical strain rate: X (s ⁻¹ ) or more and a rolling reduction rate of 1% or more in one pass. And the average cooling rate between 800-300 ° C. after hot-rolled sheet annealing (immediately before the final cold rolling) is 40 ° C./s or more, and then the final cold rolling is started within 72 hours. It can be seen that good magnetic properties of the product plate can be obtained.

[Example 3]
Steels of symbols A to L having the composition shown in Table 3 were melted, made into a steel slab by a continuous casting method, reheated to 1230 ° C., and hot-rolled to a hot-rolled sheet having a thickness of 1.8 mm After performing 1050 ° C. × 30 s hot-rolled sheet annealing, the average cooling rate during cooling between 800-300 ° C. of this hot-rolled sheet annealing was set to 70 ° C./s, and after 14 hours, 4-stand tandem rolling And finished into a cold-rolled sheet having a final sheet thickness of 0.22 mm.
Each stand entry side temperature was 40 ° C., 50 ° C., 60 ° C., 70 ° C., and each stand exit side plate thickness was 1.3 mm, 0.71 mm, 0.40 mm, and 0.22 mm, respectively. Moreover, the strain rate in each stand was 54.6 s ⁻¹ , 167.5 s ⁻¹ , 390.2 s ⁻¹ , and 967.7 s ⁻¹ , respectively.
Thereafter, the cold-rolled sheet was subjected to primary recrystallization annealing with decarburization annealing at 850 ° C. × 120 s in a humid atmosphere of 60 vol% H ₂ -40 vol% N ₂ , dew point: 58 ° C. During the primary recrystallization annealing, the temperature was raised between 200 and 700 ° C. at a rate of temperature rise of 15 ° C./s.
Next, after applying an annealing separator mainly composed of MgO to the steel sheet surface, secondary recrystallization annealing is performed at 1180 ° C. for 10 hours, followed by application of a phosphate-based insulation tension coating. The product was subjected to flattening annealing for the purpose of baking and flattening of the steel strip.
Table 3 shows the critical strain rate at the stage where the total rolling reduction of the final cold rolling is 50% or less: X (s ⁻¹ ), a pair of {411} <148> orientations of the center thickness layer of the primary recrystallization annealed sheet The random strength ratio, the magnetic flux density B _{8 of} the product plate, and the iron loss W _17/50 are also shown.

As shown in Table 3, the average cooling rate between 800 and 300 ° C. after annealing immediately before the final cold rolling is set to 40 ° C./s or more, then the final cold rolling is started within 72 hours, and further the total reduction In a stage where the rate is 50% or less, the final recrystallization annealing plate is subjected to final cold rolling with a critical strain rate of each sample: X (s ⁻¹ ) or more and a one-pass reduction rate of 10% or more. The {411} <148> orientation to random strength ratio of the plate thickness center layer increased, and good product plate magnetic properties were obtained.

[Example 4]
The steel of the symbol J shown in Table 3 is melted and made into a steel slab by a continuous casting method, reheated to 1230 ° C., and then hot-rolled into a hot-rolled sheet having a thickness of 2.2 mm, 1020 ° C. × 30 s. After performing the hot-rolled sheet annealing, the intermediate sheet thickness is set to 1.8 mm by primary cold rolling, and after performing the intermediate annealing of 1020 ° C. × 60 s, the average of this intermediate annealing during cooling between 800 to 300 ° C. The cooling rate was set to 40 ° C./s, and after 18 hours, 4 stands of tandem rolling was started to finish a cold rolled sheet having a final thickness of 0.22 mm. Each stand entry side temperature was 50 ° C., and each stand exit side plate thickness was 1.0 mm, 0.58 mm, 0.35 mm, and 0.22 mm, respectively. Moreover, the strain rate in each stand was 86.1 s ⁻¹ , 190.6 s ⁻¹ , 397.2 s ⁻¹ and 775.1 s ⁻¹ , respectively. Note that. The critical strain rate: X (s ⁻¹ ) = 12.9 at the stage where the total rolling reduction of the steel of symbol J is 50% or less.
Subsequently, the cold-rolled sheet was subjected to primary recrystallization annealing with decarburization annealing at 840 ° C. × 120 s in a humid atmosphere of 60 vol% H ₂ -40 vol% N ₂ , dew point: 55 ° C.
During the primary recrystallization annealing, the temperature is increased between 200 and 700 ° C. at a temperature increase rate of 120 ° C./s in the temperature increasing process up to 840 ° C., and various temperatures, times, A retaining process was performed to retain the number of times. The conditions are also shown in Table 3.
Furthermore, after applying an annealing separator mainly composed of MgO to the steel sheet surface, secondary recrystallization annealing is performed at 1180 ° C. for 10 hours, followed by application of a phosphate-based insulation tension coating. The product was subjected to flattening annealing for the purpose of baking and flattening of the steel strip.
Table 3 _shows the measurement results of the magnetic flux density B ₈ and the iron loss W _17/50 of the product plate.

As shown in Table 4, the average cooling rate between 800 and 300 ° C. after annealing immediately before the final cold rolling is set to 40 ° C./s or more, then the final cold rolling is started within 72 hours, and the total reduction rate When the final cold rolling is performed with the critical strain rate of each sample: X (s ⁻¹ ) or more and the one-pass reduction ratio of 10% or more at a stage of 50% or less, good product sheet magnetic properties can be obtained. Obtained.

[Example 5]
The steel of symbol B shown in Table 3 is melted and made into a steel slab by a continuous casting method, reheated to 1230 ° C., and then hot-rolled to obtain a hot-rolled sheet having a thickness of 2.2 mm, 1120 ° C. × 30 s. After performing the hot-rolled sheet annealing, the average cooling rate at the time of cooling between 800 to 300 ° C. of this hot-rolled sheet annealing was set to 55 ° C./s, and reverse rolling was started after 24 hours, and the final sheet thickness was 0 Finished in a cold-rolled plate of 26 mm. Each stand entry side temperature is 40 ° C., 100 ° C., 140 ° C., 160 ° C., 180 ° C., 180 ° C., and each stand exit side plate thickness is 1.4 mm, 0.90 mm, 0.63 mm, 0.45 mm, They were 0.34 mm and 0.26 mm. Moreover, the strain rate in each stand was 234.2 s ⁻¹ , 289.9 s ⁻¹ , 320.2 s ⁻¹ , 370.4 s ⁻¹ , 395.8 s ⁻¹ , 444.4 s ⁻¹ , respectively. Note that the critical strain rate at the stage where the total rolling reduction of the final cold rolling of the steel of symbol B is 50% or less: X (s ⁻¹ ) = 9.8.
Subsequently, the cold-rolled sheet was subjected to primary recrystallization annealing with decarburization annealing at 820 ° C. × 120 s in a humid atmosphere of 60 vol% H ₂ -40 vol% N ₂ , dew point: 58 ° C.
During the primary recrystallization annealing, the temperature was raised between 200 and 700 ° C. at various heating rates shown in FIG. Next, after performing gas nitriding treatment at 750 ° C. for 30 s in a mixed atmosphere of ammonia, nitrogen, and hydrogen, an annealing separator containing MgO as a main component was applied to the steel sheet surface, and then purified at 1200 ° C. for 50 hours. Secondary recrystallization annealing that also serves as annealing was performed, and then the product was subjected to flattening annealing for the purpose of applying a phosphate-based insulating tension coating, baking, and flattening the steel strip.

FIG. 8 shows the iron loss W _17/50 of the product plate.
As shown in FIG. 8, the average cooling rate between 800 and 300 ° C. after annealing immediately before the final cold rolling is set to 40 ° C./s or more, then the final cold rolling is started within 72 hours, and further the total reduction In a stage where the rate is 50% or less, a final cold rolling with a critical strain rate of X (s ⁻¹ ) or more and a one-pass reduction rate of 10% or more is performed, and the temperature is increased from 200 to 200 in the temperature increase process of primary recrystallization annealing. It can be seen that by applying the rapid heat treatment between 700 ° C., even better product plate magnetic properties are obtained.

  Since the technology of the present invention is suitable for control of the texture of cold-rolled steel sheets, it can be applied to automobile steel sheets that require workability and ferritic stainless steels that require ridging suppression. it can.

Claims (7)

C: 0.002 to 0.100 mass%, Si: 2.00 to 4.50 mass%, Mn: 0.03 to 1.00 mass%, sol. Al: 0.003 mass% or more and less than 0.010 mass% and N: (14.00 / 26.98) × [% sol. Al] or more and 0.008 mass% or less, and further contains S: 0.002 to 0.005 mass% and / or Se: 0.002 to 0.005 mass%, with the balance being Fe and inevitable impurities. The slab is reheated to a temperature of 1250 ° C. or lower , hot-rolled to form a hot-rolled sheet, and subjected to cold rolling at least twice with intermediate annealing without subjecting the hot-rolled sheet to hot-rolled sheet. It is a cold-rolled sheet having a thickness, or after subjecting the hot-rolled sheet to hot-rolled sheet annealing, it is subjected to cold rolling twice or more sandwiching one or intermediate annealing, to obtain a cold-rolled sheet having a final sheet thickness, In the method for producing a grain-oriented electrical steel sheet comprising a series of steps of applying an annealing separator to the steel sheet surface and performing final annealing after the primary recrystallization annealing,
The average cooling rate between 800 and 300 ° C. after annealing immediately before the final cold rolling is set to 40 ° C./s or more, then the final cold rolling is started within 72 hours, and the total rolling reduction of the final cold rolling is 50 % At a critical strain rate calculated from the following formula (1): S ( ¹ ) or more, and at least one cold rolling with a reduction rate of 10% or more in one pass. A method for producing a grain-oriented electrical steel sheet, comprising:
X (s ⁻¹ ) = f ([% C], [% Si]) · g (T) (1)
However, f ([% C], [% Si]) = 1 / ([% C] + [% Si] / 150)
g (T) = exp (-100 / T)
[% M] represents the content (mass%) of the element M in the steel sheet , and T represents the rolling stand entry side temperature (K) .   The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein deformation twinning is introduced into the recrystallized grains immediately before the final cold rolling by the final cold rolling.   In addition to the slab, Ni: 0.01-1.50 mass%, Cr: 0.03-0.50 mass%, Cu: 0.03-0.50 mass%, P: 0.005-0.500 mass%, Sb: 0.005-0.500 mass%, Sn: 0.005-0.50 mass%, Bi: 0.005-0.500 mass%, Mo: 0.005-0.100 mass%, B: 0.0002- 0.0025 mass%, Te: 0.0005 to 0.0100 mass%, Nb: 0.001 to 0.010 mass%, V: 0.001 to 0.010 mass%, and Ta: 0.001 to 0.010 mass% The manufacturing method of the grain-oriented electrical steel sheet according to claim 1 or 2, comprising one or more component compositions selected from the group consisting of:   The grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein a heating rate between 200 and 700 ° C in the heating process of the primary recrystallization annealing is 50 ° C / s or more. Manufacturing method.   The heating rate between 200 and 700 ° C. in the temperature raising process of the primary recrystallization annealing is 50 ° C./s or more, and further between 1 and 10 s at any temperature between 250 and 600 ° C. in the temperature raising process. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the retaining is performed.   The rate of temperature increase between 200 and 700 ° C. in the temperature raising process of the primary recrystallization annealing is set to 50 ° C./s or more, and at any temperature between 250 ° C. and less than 500 ° C. in the temperature raising process, 0.5 10 to 10 s, held 1 to 4 times, and held at a temperature of 500 ° C. to 700 ° C. for 0.5 to 3 s, 1 to 2 times. A method for producing a grain-oriented electrical steel sheet having low iron loss according to claim 1. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 6, wherein nitriding is performed at any stage from the primary recrystallization annealing to the finish annealing .

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