JP2014173103A - Method of producing grain-oriented magnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a grain-oriented magnetic steel sheet excellent in magnetic properties and having little variation in magnetic properties in a coil longitudinal direction.SOLUTION: The method of producing a grain-oriented magnetic steel sheet is provided in which an a steel raw material containing, by mass%, C:0.002 to 0.10%, Si:2.0 to 8.0% and Mn:0.005 to 1.0% is hot rolled, cold rolled after subjected to hot rolled sheet annealing as needed, and the resulting cold rolled sheet is subjected to primary recrystallization annealing acting also as decarbonization annealing, then final annealing. In the method, each aging treatment conducted between path in the final cold rolling satisfies the following expression: (Dt/T)≤2.0×10, where D=0.394exp(-(8.02×10)/8.31T), T:aging temperature (K), t:aging time (second), and the cold rolled steel sheet is subjected to a soaking treatment for holding the cold rolled steel sheet at any temperature between 250 to 600°C for 1 to 10 seconds when the cold rolled steel sheet is rapidly heated at 50°C/s or more between 200 to 700°C in a heating process of the primary recrystallization annealing.

Description

  The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet, and specifically relates to a method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics and small variations in the coil longitudinal direction.

  Electrical steel sheets are soft magnetic materials that are widely used as core materials for transformers and motors. Among them, grain oriented electrical steel sheets are highly integrated in the {110} <001> orientation, which is called the Goss orientation. Because of its excellent magnetic properties, it is mainly used for iron cores of large transformers. In order to reduce the no-load loss (energy loss) in the transformer, it is necessary that the iron loss is low.

  Iron loss reduction method for grain-oriented electrical steel sheets includes increasing Si content, reducing plate thickness, improving crystal orientation orientation, imparting tension to the steel sheet surface, smoothing the steel sheet surface, secondary recrystallization texture It is known that fine graining is effective.

Among these methods, the technology for refining secondary recrystallized grains includes rapid heating at the time of decarburization annealing, or heat treatment to be rapidly heated immediately before decarburization annealing, thereby providing a primary recrystallization texture. A method for improving the above has been proposed. For example, in Patent Document 1, when decarburizing and annealing a cold-rolled sheet rolled to the final sheet thickness, in a non-oxidizing atmosphere where P _H2O / _PH2 is 0.2 or less, the temperature is 100 ° C./s or more and 700 ° C. A technique for obtaining a grain-oriented electrical steel sheet with low iron loss by rapid heating to the above temperature is disclosed. Patent Document 2 discloses that the oxygen concentration in the atmosphere is set to 500 ppm or less, and is rapidly heated to 800 to 950 ° C. at a heating rate of 100 ° C./s or higher, and subsequently 775 to 840 ° C. lower than the temperature after the rapid heating. A technique for obtaining a grain-oriented electrical steel sheet with low iron loss by holding at a temperature of 815 ° C. and further holding at a temperature of 815 to 875 ° C. is disclosed. Patent Document 3 discloses that the film characteristics and the film characteristics are obtained by heating a temperature range of 600 ° C. or higher to 800 ° C. or higher at a rate of temperature increase of 95 ° C./s or more and appropriately controlling the atmosphere in this temperature range. A technique for obtaining an electrical steel sheet having excellent magnetic properties is disclosed. Furthermore, in Patent Document 4, the amount of N as AlN in the hot-rolled sheet is limited to 25 ppm or less, and heating at a heating rate of 80 ° C./s to 700 ° C. or more during decarburization annealing reduces low iron loss. A technique for obtaining a grain-oriented electrical steel sheet is disclosed.

  In these techniques for improving the primary recrystallization texture by rapid heating, the temperature range for rapid heating is from room temperature to 700 ° C. or higher, and the rate of temperature rise is uniquely defined. This technical idea suppresses the development of γ fibers (<111> // ND orientation) that are preferentially formed at a normal heating rate by raising the temperature to near the recrystallization temperature in a short time, The primary recrystallization texture is intended to be improved by promoting the generation of a {110} <001> structure that becomes the nucleus of secondary recrystallization. By applying this technique, the crystal grains (Goss-oriented grains) after the secondary recrystallization are refined, and the iron loss characteristics are improved.

  Further, as another technique for improving the primary recrystallization texture, a method of applying an aging treatment during cold rolling has been proposed. For example, Patent Document 5 proposes a technique for improving magnetic properties by holding at a temperature of 50 to 350 ° C. for 1 minute or longer during cold rolling. In Patent Document 6, a heat treatment is performed in the course of cold rolling at a temperature of 100 ° C. or higher for 1 minute or longer, and 700 ° C. at a heating rate of 50 ° C./s or more immediately before decarburization annealing. There has been proposed a technique for improving magnetic properties by rapid heating to the above temperature. These aging treatments during cold rolling are such that interstitial elements such as C and N are fixed to dislocations introduced by cold rolling, change the deformation mechanism, and cold rolling texture and primary recrystallization texture. It is considered that the magnetic properties will be improved and eventually the magnetic properties will be improved.

Japanese Patent Laid-Open No. 07-062436 Japanese Patent Laid-Open No. 10-298653 JP 2003-027194 A Japanese Patent Laid-Open No. 10-130729 Japanese Patent Publication No. 54-013846 Japanese Patent Application Laid-Open No. 07-062437

  However, according to the knowledge of the inventors, when the heating rate of decarburization annealing is increased, the secondary recrystallized grains become finer, but the degree of orientation accumulation after the secondary recrystallization tends to decrease, and iron There is a problem that the loss improvement effect cannot be obtained stably.

In addition, when performing aging treatment during cold rolling, especially when aging treatment is performed using heat generated by rolling, the effect of improving magnetic properties is not sufficient, and the aging conditions are constant in the longitudinal direction of the coil. Therefore, there is a problem that the magnetic characteristics tend to fluctuate in the coil longitudinal direction. For example, when an aging treatment is performed at the time of winding in reverse rolling, the temperature tends to decrease at both ends in the coil longitudinal direction, so that the magnetic characteristics are deteriorated. In the case of tandem rolling, it can be considered that aging treatment is performed for a very short time between each stand, but the steel plate temperature between each pass is strongly influenced by the rolling speed, so the steel plate temperature Is high at the center of the coil where the rolling speed is high, and low at both ends of the coil where the rolling speed is low, so that the magnetic properties are likely to deteriorate at both ends of the coil.
The above problem can be solved by adopting a method in which the coil is once moved to another line and subjected to an aging treatment during the cold rolling, but there is a problem that the cost increases.

  The present invention has been made in view of the above-described problems of the prior art, and its purpose is to provide a method for producing a grain-oriented electrical steel sheet that is excellent in magnetic characteristics and has small fluctuations in magnetic characteristics in the longitudinal direction of the coil. It is to propose.

  The inventors have intensively studied to solve the above problems. As a result, the aging treatment at the time of cold rolling is processed at a low temperature and in a short time, and when it is rapidly heated in the heating process of the primary recrystallization annealing, the holding treatment is held for a predetermined time in the temperature range where the recovery occurs. The inventors have found that excellent magnetic properties can be obtained over the entire length of the coil, and have developed the present invention.

That is, the present invention hot-rolls a steel material containing C: 0.002 to 0.10 mass%, Si: 2.0 to 8.0 mass%, and Mn: 0.005 to 1.0 mass%. After rolling and hot-rolling sheet annealing as necessary, cold rolling is performed once or two times with intermediate annealing in between to make a cold-rolled sheet with the final thickness, which is also used for decarburization annealing. In the method for producing a grain-oriented electrical steel sheet, after applying crystal annealing, applying an annealing separator to the steel sheet surface and performing final annealing,
Each aging treatment performed between passes in the final cold rolling is expressed by the following formula (1):
(Dt / T) ^2/3 ≦ 2.0 × 10 ⁻⁷ (1)
Here, D = 0.394exp (− (8.02 × 10 ⁴ ) /8.31T)
T: Aging temperature (K)
t: Aging time (seconds)
And when the 200-700 ° C. section of the heating process of the primary recrystallization annealing is rapidly heated at 50 ° C./s or more, it is held for 1-10 seconds at any temperature between 250-600 ° C. It is a manufacturing method of the grain-oriented electrical steel sheet characterized by performing a process.

  The steel material used in the method for producing a grain-oriented electrical steel sheet according to the present invention further includes, as an inhibitor forming element, Al: 0.010-0.050 mass% and N: 0.003-0.020 mass in addition to the above component composition. %, Or Al: 0.010-0.050 mass%, N: 0.003-0.020 mass%, Se: 0.003-0.030 mass% and / or S: 0.002-0.03 mass% And the balance is made of Fe and inevitable impurities.

  Further, the steel material used in the method for producing a grain-oriented electrical steel sheet according to the present invention includes Se: 0.003 to 0.030 mass% and S: 0.002 to 0 as an inhibitor forming element in addition to the above component composition. It contains one or two kinds selected from 0.03 mass%, and the balance consists of Fe and inevitable impurities.

  In addition to the above component composition, the steel material used in the method for producing a grain-oriented electrical steel sheet according to the present invention further includes Al: less than 0.01 mass%, N: less than 0.0050 mass%, Se: less than 0.0030 mass%. And S: less than 0.0050 mass%, with the balance being Fe and inevitable impurities.

  In the steel material used in the method for producing a grain-oriented electrical steel sheet according to the present invention, the steel material further includes Ni: 0.010 to 1.50 mass%, Cr: 0.01 to 0.50 mass in addition to the component composition. %, Cu: 0.01 to 0.50 mass%, P: 0.005 to 0.50 mass%, Sb: 0.005 to 0.50 mass%, Sn; 0.005 to 0.50 mass%, Bi: 0.00. 005 to 0.50 mass%, Mo: 0.005 to 0.10 mass%, B: 0.0002 to 0.0025 mass%, Te: 0.0005 to 0.010 mass%, Nb: 0.0010 to 0.010 mass% V: 0.001 to 0.010 mass% and Ta: 0.001 to 0.010 mass%, or one or more selected from the group consisting of 0.001 to 0.010 mass%.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the grain-oriented electrical steel sheet with a low iron loss and small dispersion | variation over the full length of a coil longitudinal direction stably and cheaply.

It is a figure explaining the temperature rising pattern in the heating process of primary recrystallization annealing. It is a graph which shows the influence which the holding time in the middle of heating of primary recrystallization annealing has on iron loss _{W17 / 50} . It is a graph which shows the influence which the aging conditions in cold rolling exert on iron loss _{W17 / 50} .

First, an experiment that triggered the development of the present invention will be described.
C: 0.065 mass%, Si: 3.44 mass%, Mn: 0.08 mass%, Al: 0.022 mass%, N: 0.008 mass%, and Se: 0.020 mass% After making the steel slab by the continuous casting method, it is reheated to 1410 ° C., hot-rolled to obtain a hot-rolled sheet having a thickness of 2.1 mm, and subjected to hot-rolled sheet annealing at 1050 ° C. × 60 seconds, followed by primary cooling The sheet was rolled to an intermediate thickness of 1.6 mm, subjected to intermediate annealing at 1150 ° C. for 60 seconds, and then cold-rolled with a reverse rolling mill to obtain a cold-rolled sheet having a final thickness of 0.23 mm.

The reverse rolling was performed under the following two conditions.
Condition I: The following always 100 ° C. coiling temperature after each rolling pass was adjusted so that the waiting time is 20 minutes or less, the following (1) the value of the left side of the expression is 4.0 × 10 ^-8 or less Control to be.
Conditions II: and at the coiling temperature after each rolling pass is always 0.99 ° C. or higher, and adjusted so that the waiting time is 20 minutes or more, the following (1) the value of the left side of the expression is 2.0 × 10 ^-7 or more Control to be.
(Dt / T) ^2/3 ≦ 2.0 × 10 ⁻⁷ (1)
Here, D = 0.394exp (− (8.02 × 10 ⁴ ) /8.31T)
T: Aging temperature (K)
t: Aging time (seconds)
In the calculation of the value on the left side of the above equation (1), it is assumed that the coiling temperature and the aging temperature are equal. It is considered that the effect of aging is weakened at both ends of the coil of Condition II.

Next, primary recrystallization annealing was performed which also served as decarburization annealing in which decarburization was performed at 840 ° C. for 80 seconds in a wet atmosphere of 50 vol% H ₂ -50 vol% N ₂ . The primary recrystallization annealing is performed at a heating rate of 200 to 700 ° C. in the heating process up to 840 ° C. at 100 ° C./s, and further maintained at a temperature of 450 ° C. during the heating for 0 to 30 seconds. A retaining treatment was applied. Here, the temperature increase rate of 100 ° C./s is the average temperature increase rate at t ₁ and t ₃ excluding the holding time t ₂ from the time from 200 ° C. to 700 ° C. as shown in FIG. ((700-200) / (t ₁ + t ₃ )) (hereinafter the same). The temperature increase rate between 700 ° C. and 840 ° C. was 5 ° C./s. Thereafter, an annealing separator mainly composed of MgO was applied to the steel sheet surface and dried, followed by secondary recrystallization annealing and finishing annealing including purification at 1200 ° C. for 7 hours in a hydrogen atmosphere to obtain a product plate. .

A test piece was collected from the product plate thus obtained, and the iron loss W _17/50 was measured by the method described in JIS C2556. Here, the said test piece was extract | collected from the both ends and center part of the coil longitudinal direction, and the highest iron loss value was employ | adopted as the representative value of the coil. The results are shown in FIG. 2 as the relationship between the holding time and the iron loss. From this figure, it can be seen that the iron loss can be reduced by setting the holding time at 450 ° C. during heating in the range of 1 to 10 seconds. In addition, under condition I where the aging treatment during cold rolling is performed at a low temperature and in a short time, iron loss was reduced over the entire length of the coil, but under condition II where the aging treatment during cold rolling was performed at a high temperature and for a long time, The iron loss at both ends of the coil was high, and the iron loss at the coil representative value tended to be high.

  Furthermore, the inventors have C: 0.071 mass%, Si: 3.20 mass%, Mn: 0.06 mass%, Al: 0.024 mass%, N: 0.009 mass%, Se: 0.018 mass%, and Sb. : Steel containing 0.01 mass% was melted and made into a steel slab by a continuous casting method, then reheated to 1430 ° C, hot-rolled to obtain a hot-rolled sheet having a thickness of 2.3 mm, 1080 ° C x After hot-rolled sheet annealing for 60 seconds, primary cold rolling was performed to obtain an intermediate sheet thickness of 1.5 mm, and after intermediate annealing at 1100 ° C. for 60 seconds, cold rolling was performed to obtain a final sheet thickness of 0. A 23 mm cold-rolled plate was used. Here, in the cold rolling, a reverse rolling mill or a tandem rolling mill was used, and the rolling aging and the coolant amount were adjusted to perform aging between passes under various aging conditions (temperature, time).

Next, primary recrystallization annealing was performed which also served as decarburization annealing in which decarburization was performed at 840 ° C. for 80 seconds in a wet atmosphere of 50 vol% H ₂ -50 vol% N ₂ . In the primary recrystallization annealing, the temperature increasing rate between 200 to 700 ° C. in the heating process up to 840 ° C. is set to 100 ° C./s, and the holding treatment is held for 5 seconds at a temperature of 350 ° C. during the temperature increasing. Was given. The temperature increase rate between 700 ° C. and 840 ° C. was 5 ° C./s. Thereafter, an annealing separator mainly composed of MgO was applied to the steel sheet surface and dried, followed by secondary recrystallization annealing and finishing annealing including purification at 1200 ° C. for 7 hours in a hydrogen atmosphere to obtain a product plate. .

A test piece was collected from the product plate thus obtained, and the iron loss W _17/50 was measured by the method described in JIS C2556. Here, the said test piece was extract | collected from the both ends and center part of the coil longitudinal direction, and the highest iron loss value was employ | adopted as the representative value of the coil. The result is shown in FIG. 3 as the relationship between the parameter ((Dt / T) ^2/3 ) and the iron loss W _17/50 represented by the left side of the equation (1). From this figure, it is understood that an excellent iron loss characteristic can be obtained by setting the parameter ((Dt / T) ^2/3 ) to 2.0 × 10 ⁻⁷ or less.

  As described above, the rapid heat treatment has an effect of suppressing the development of γ fiber (<111> // ND orientation) and promoting the generation of {110} <001> structure that becomes the nucleus of secondary recrystallization. . Generally, since a lot of strain is introduced into the <111> // ND orientation during cold rolling, the strain energy accumulated is higher than other orientations. For this reason, in primary recrystallization annealing in which heating is performed at a normal temperature increase rate, recrystallization occurs preferentially from a <111> // ND-oriented rolling structure in which accumulated strain energy is high. In recrystallization, <111> // ND oriented grains usually appear from a rolled structure with <111> // ND orientation. For this reason, the <111> // ND orientation is the main orientation of the recrystallized structure.

  However, rapid heating gives more thermal energy than that released by recrystallization, so that recrystallization can occur even in orientations with relatively low strain energy. {110} <001> after recrystallization increases, <111> // ND orientation decreases, and magnetic properties improve. This is the reason for the rapid heating of the prior art. However, since the <111> // ND orientation is an orientation necessary for sharpening the secondary recrystallization orientation, the <111> // ND orientation is lowered by rapid heating, and the degree of orientation integration is likely to be lowered. It is considered to be.

  Therefore, the inventors investigated the primary recrystallization texture of the steel sheet of Condition I exhibiting excellent magnetic properties in the above experiment, and found that the {111} <112> orientation is particularly necessary for sharpening the secondary recrystallization orientation. It was found that the other <111> // ND orientations were greatly reduced. Although the detailed mechanism is not clear, first, the degree of integration of <111> // ND orientation can be increased by performing an aging treatment during rolling at a low temperature for a short time. When the heating process of the subsequent primary recrystallization annealing is raised at a high speed and the holding process is performed during the heating, the recovery of the rolling structure proceeds by the holding process during the heating, but {111} <112> <111> // ND orientation other than that causes recovery preferentially, strain energy decreases, and loss of recrystallization driving force. As a result, {111} <112> does not decrease in the primary recrystallization texture. The other <111> // ND orientations are considered to have decreased.

  In addition, the effect of improving the magnetic properties due to the decrease in <111> // ND orientation other than the above {111} <112> includes the aging conditions during cold rolling, the heating rate during the heating process of primary recrystallization annealing, and the retention treatment. It can be obtained only when all the conditions are optimized, and if any one of the conditions is off, the effect cannot be obtained.

  The effect of improving the magnetic characteristics described above has the effect of reducing variations in the magnetic characteristics in the coil longitudinal direction. This is because, for example, when using an aging treatment utilizing the heat generated by cold rolling, the magnetic properties of both ends of the coil are likely to deteriorate. This is because fluctuations in the coil longitudinal direction are less likely to occur. Moreover, since the aging treatment time can be shortened, an effect of improving productivity can be expected.

Next, the component composition of the steel material (slab) used as the material of the grain-oriented electrical steel sheet of the present invention will be described.
C: 0.002-0.10 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. On the other hand, when it exceeds 0.10 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 in the range of 0.002 to 0.10 mass%. Preferably it is the range of 0.010-0.080 mass%.

Si: 2.0 to 8.0 mass%
Si is an element necessary for increasing the specific resistance of steel and reducing iron loss. If the effect is less than 2.0 mass%, it is not sufficient. On the other hand, if it exceeds 8.0 mass%, the workability deteriorates and it is difficult to roll and manufacture. Therefore, Si is set to a range of 2.0 to 8.0 mass%. Preferably it is the range of 2.5-4.5 mass%.

Mn: 0.005 to 1.0 mass%
Mn is an element necessary for improving the hot workability of steel. If the effect is less than 0.005 mass%, it is not sufficient. On the other hand, if it exceeds 1.0 mass%, the magnetic flux density of the product plate is lowered. Therefore, Mn is set to a range of 0.005 to 1.0 mass%. Preferably it is the range of 0.02-0.20 mass%.

Components other than C, Si and Mn are classified into cases where an inhibitor is used and cases where no inhibitor is used in order to cause secondary recrystallization.
First, when an inhibitor is used to cause secondary recrystallization, for example, when an AlN-based inhibitor is used, Al and N are changed to Al: 0.010 to 0.050 mass%, N: 0.003, respectively. It is preferable to make it contain in the range of -0.020 mass%. Moreover, when utilizing a MnS * MnSe type | system | group inhibitor, it is preferable to contain Mn of the quantity mentioned above, and S: 0.002-0.030 mass% and / or Se: 0.003-0.030 mass%. When the addition amount is less than the above lower limit value, the inhibitor effect is not sufficiently obtained. On the other hand, when the upper limit value is exceeded, the inhibitor component remains undissolved during slab heating, and the inhibitor effect is reduced. Magnetic properties cannot be obtained. Of course, an AlN-based and MnS / MnSe-based inhibitor may be used in combination.

  On the other hand, when an inhibitor is not used to cause secondary recrystallization, the content of Al, N, S and Se, which are the above-described inhibitor forming components, is reduced as much as possible, Al: less than 0.01 mass%, N : It is preferable to use a steel material reduced to less than 0.0050 mass%, S: less than 0.0050 mass%, and Se: less than 0.0030 mass%.

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.
However, for the purpose of improving magnetic properties, Ni: 0.010 to 1.50 mass%, Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, P: 0.005 to 0 .50 mass%, Sb: 0.005-0.50 mass%, Sn: 0.005-0.50 mass%, Bi: 0.005-0.50 mass%, Mo: 0.005-0.10 mass%, B: 0.0002-0.0025 mass%, Te: 0.0005-0.0100 mass%, Nb: 0.0010-0.010 mass%, V: 0.001-0.010 mass%, and Ta: 0.001-0. One or more selected from 010 mass% may be added as appropriate.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
A steel material (slab) may be manufactured by a conventional ingot-bundling rolling method or a continuous casting method after melting the steel having the above-described component composition by a conventional refining process, or directly. A thin slab having a thickness of 100 mm or less may be manufactured by a casting method. The slab is reheated to a temperature of about 1400 ° C. according to a conventional method, for example, when an inhibitor component is contained, and after reheating to a temperature of 1250 ° C. or less when no inhibitor component is contained. Used for hot rolling. 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 sheet thickness by one or more cold rolling 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, and the magnetic properties of the product plate tend to be lowered. 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.

Of the cold rolling, the final cold rolling with the final plate thickness needs to be subjected to an aging treatment satisfying the following (1) between the rolling passes.
(Dt / T) ^2/3 ≦ 2.0 × 10 ⁻⁷ (1)
Here, D = 0.394exp (− (8.02 × 10 ⁴ ) /8.31T)
T: Aging temperature (K)
t: Aging time (seconds)

D in the formula (1) is a diffusion coefficient of C, D ₀ = 0.394 (mm ² / sec), activation energy Q = 80.2 (kJ / mol), gas constant R = 8.31 (J / mol · K). According to Cottelell et al. (A. H. Cotrel and B. A. Bilby: Proc. Phys. Soc., 62A (1949), 49), the left side of equation (1) is an aging treatment at temperature T and time t. This is a parameter that is proportional to the amount of solute atoms that reach dislocations in, and represents the progress of aging. Therefore, a small value on the left side of the above equation (1) means that an interstitial element such as C is not sufficiently fixed to the dislocation. In such a case, the primary recrystallization texture <111> // ND orientation increases. However, an increase in the <111> // ND orientation is not preferable for the magnetic characteristics, and the effect of improving the magnetic characteristics cannot be obtained unless the rapid heating described later and the holding treatment in the middle thereof are combined.

According to the experimental results of the inventors, in order to obtain the above effect of increasing the <111> // ND orientation of the primary recrystallization texture, the value on the left side of the above equation (1) is 2.0 × 10 ⁻ It must be ⁷ or less. When it exceeds 2.0 × 10 ⁻⁷ , the <111> // ND orientation in the primary recrystallization texture decreases, and the orientation integration degree after secondary recrystallization decreases. In order to further increase the <111> // ND orientation, it is preferable to control the value of the left side of the above equation (1) to 5.0 × 10 ⁻⁸ or less.

  From the viewpoint of ensuring productivity, the aging treatment at the time of cold rolling satisfying the above formula (1) is such that the aging temperature T is 50 to 400 ° C. and the aging time t is 0.1 to 3600 seconds. Is preferred. When the aging temperature T is less than 50 ° C. and the aging time t is less than 0.1 second, strong cooling equipment and ultra-high speed rolling are required, which increases the manufacturing cost. On the other hand, when the aging temperature T exceeds 400 ° C. and the aging time t exceeds 3600 seconds, not only the above equation (1) is not satisfied, but also productivity is lowered and manufacturing costs are increased. In addition, when performing cold rolling with a reverse rolling mill, the aging temperature T may be a winding temperature after rolling. In addition, the coil temperature after winding on the coil gradually decreases, especially at both ends of the coil, but the aging conditions of the present invention do not require high temperature and long time treatment, and thus affect the magnetic properties. The impact is small.

  The relationship of the above formula (1) can be easily satisfied by adjusting the rolling speed and the amount of coolant regardless of whether the rolling mill is a reverse type or a tandem type, but obtains stable magnetic characteristics in the longitudinal direction of the coil. For this purpose, it is preferable to control so as to satisfy the above expression (1) over the entire length of the coil.

  Further, the rolling reduction of the final cold rolling is preferably in the range of 80 to 95% in order to sufficiently develop the <111> // ND orientation. However, when the yield of the product is regarded as important and the stability of the secondary recrystallization is to be improved even if some deterioration of the magnetic properties is allowed, the reduction ratio of the final cold rolling is preferably 50 to 80%.

  The cold-rolled sheet having the final thickness is then subjected to primary recrystallization annealing that also serves as decarburization annealing. The annealing temperature in the primary recrystallization annealing is preferably in the range of 800 to 900 ° C. from the viewpoint of ensuring decarburization, and the atmosphere is preferably a wet atmosphere. However, this is not the case when a steel material with C: 0.005 mass% or less that does not require decarburization is used. In addition, you may perform a primary recrystallization annealing and a decarburization annealing separately.

  Here, what is important in the present invention is that in the heating process of the primary recrystallization annealing, the section of 200 to 700 ° C. is rapidly heated at 50 ° C./s or more, and at any temperature between 250 to 600 ° C. It is to perform a holding process for 1 to 10 seconds. In addition, the temperature increase rate (50 degreeC / s or more) in the said 200-700 degreeC area is an average temperature increase rate in the time except the time to hold | maintain, as mentioned above. The temperature elevation rate is preferably in the range of 100 to 300 ° C./s.

  The reason why the rapid heating is required is to promote the generation of a {110} <001> structure that becomes the nucleus of secondary recrystallization. However, since the <111> // ND orientation is lowered only by rapid heating, the sharpness of the secondary recrystallization orientation is likely to be lowered, and the effect of improving the magnetic properties is not stable.

  In addition, the reason why the holding process is necessary is that when the recovery of the rolling structure proceeds during the holding process, the strain energy in the <111> // ND direction other than {111} <112> is preferentially reduced and restarted. This is because the strength of <111> // ND orientation other than {111} <112> in the primary recrystallization texture is reduced by losing the driving force of the crystal. The temperature for the retention treatment is limited to 250 to 600 ° C., and the time is limited to a range of 1 to 10 seconds. If the temperature of the retention treatment is less than 250 ° C. and the time is less than 1 second, the desired effect cannot be obtained because the recovery does not occur. On the other hand, if the temperature exceeds 600 ° C. and the time exceeds 10 seconds, the recovery proceeds too much. This is because the primary recrystallization structure deteriorates. Note that the retention treatment does not necessarily have to be a constant temperature, and a similar effect can be obtained as long as the temperature change is ± 10 ° C./s or less.

  For steel sheets that have undergone primary recrystallization annealing, when stressing iron loss characteristics or reducing the noise of transformers, 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 that is highly accumulated in the Goss 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 for the annealing temperature in the finish annealing, it is desirable that the highest temperature be in the range of 1100 to 1300 ° C. when forsterite film formation or purification treatment is performed. On the other hand, when the forsterite film is not formed, it is only necessary to complete the secondary recrystallization. Therefore, it is preferable to perform the finish annealing with the maximum temperature reached in the range of 800 to 1100 ° C.

  After the finish annealing, the steel sheet can be smoothed by brushing, brushing, pickling, etc. to remove unreacted annealing separator adhering to the steel sheet surface and then flattening annealing to reduce the iron loss. Is valid. This is because the finish annealing is usually performed in a coil state, so that the coil has wrinkles and this may cause deterioration in characteristics when measuring iron loss.

  Further, in the case of using steel plates in a stacked manner, it is effective to deposit an insulating film on the surface of the steel plate in the 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 tension-imparting coatings, it is excellent in coating adhesion and significantly reduces iron loss when 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 is adopted. Since an insulating film having a large 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 forming a groove in a final product plate or introducing thermal strain or impact strain in a linear or dotted manner by electron beam irradiation, laser irradiation, plasma irradiation or the like is generally performed. For example, a method of forming a groove by etching a steel sheet cold-rolled to a final thickness or a steel sheet surface in an intermediate process can be used.

  C: 0.060 mass%, Si: 3.32 mass%, Mn: 0.09 mass%, Al: 0.023 mass%, Se: 0.022 mass% and N: 0.009 mass%, the balance being Fe and inevitable A steel slab made of mechanical impurities is manufactured by a continuous casting method, reheated to a temperature of 1420 ° C., and then hot-rolled to form a hot-rolled sheet having a thickness of 2.3 mm, which is 1000 ° C. × 30 seconds. After annealing, the first cold rolling to an intermediate sheet thickness of 1.7 mm, after an intermediate annealing of 1100 ° C. × 30 seconds, the final cold rolling into a cold rolled sheet with a sheet thickness of 0.23 mm Finished. In the final cold rolling, the plate temperature (aging temperature T) and the waiting time (aging time t) between the passes are changed, the value on the left side of the equation (1) is calculated, and the maximum value of the values is shown. It was shown in 1. In addition, when rolling with a reverse rolling mill, winding temperature was made into aging temperature.

Next, primary recrystallization annealing was performed which also served as decarburization annealing in which decarburization was performed at 840 ° C. for 100 seconds in a wet atmosphere of 50 vol% H ₂ -50 vol% N ₂ . In the primary recrystallization annealing, the heating rate between 200 and 700 ° C. in the heating process up to 840 ° C. is changed as shown in Table 1, and in some cold-rolled plates, 400 ° C. during the heating. The holding treatment was performed at the same temperature and time as described in Table 1. The temperature increase rate between 700 ° C. and 840 ° C. was 6 ° C./s. Thereafter, an annealing separator mainly composed of MgO was applied to the steel sheet surface and dried, followed by secondary recrystallization annealing and finish annealing including purification at 1200 ° C. for 10 hours in a hydrogen atmosphere to obtain a product plate. . The atmosphere of the finish annealing was H ₂ when maintaining at 1200 ° C. for the purification treatment, and N ₂ when raising and lowering the temperature.

A test piece was collected from the product plate thus obtained, and the iron loss W _17/50 was measured by the method described in JIS C2556. Here, the said test piece was extract | collected from the both ends and center part of the coil longitudinal direction, and the highest iron loss value was employ | adopted as the representative value of the coil. The results are also shown in Table 1. From this table, it can be seen that, by applying the present invention, a grain-oriented electrical steel sheet having a low iron loss can be obtained stably.

No. having various component compositions shown in Table 2. 1 to 15 steel was melted and made into a steel slab by a continuous casting method, then reheated to a temperature of 1400 ° C., hot-rolled to obtain a hot-rolled sheet having a thickness of 2.1 mm, 1050 ° C. × 10 seconds After performing the hot-rolled sheet annealing, it was cold-rolled to finish a cold-rolled sheet having a final plate thickness of 0.23 mm. In addition, a reverse rolling mill is used for cold rolling, and the winding temperature (aging temperature T) is adjusted to 100 ° C. or less and the waiting time (aging time t) is set to 20 minutes or less. The value was set to 4.0 × 10 ⁻⁸ or less.

Next, primary recrystallization annealing was performed which also served as decarburization annealing in which decarburization was performed at 840 ° C. for 60 seconds in a wet atmosphere of 50 vol% H ₂ -50 vol% N ₂ . The primary recrystallization annealing is a holding treatment in which the temperature rising rate between 200 to 700 ° C. in the heating process up to 840 ° C. is 75 ° C./s, and the temperature is maintained at 450 ° C. during the temperature rising for 2 seconds. Was given. Moreover, the average temperature increase rate from 700 degreeC to 840 degreeC was 6 degreeC / s. Thereafter, an annealing separator mainly composed of MgO was applied to the steel sheet surface, dried, and then subjected to secondary recrystallization annealing and finish annealing with a purification treatment at 1220 ° C. for 4 hours in a hydrogen atmosphere to obtain a product plate. . The atmosphere of the finish annealing was H _{2 at} the time of 1220 ° C. for the purification treatment, and Ar at the time of temperature increase and temperature decrease.

A test piece was collected from the product plate thus obtained, and the iron loss W _17/50 was measured by the method described in JIS C2556. Here, the said test piece was extract | collected from the coil both ends and the center part, and the highest iron loss value was employ | adopted as the representative value of the coil. The results are also shown in Table 2. From the table, it can be seen that by applying the present invention, a grain-oriented electrical steel sheet with low iron loss can be obtained stably.

Claims (5)

A steel material containing C: 0.002-0.10 mass%, Si: 2.0-8.0 mass% and Mn: 0.005-1.0 mass% is hot-rolled to form a hot-rolled sheet. After performing hot-rolled sheet annealing according to the above, after cold rolling at least once with intermediate or intermediate annealing, to obtain a cold-rolled sheet with the final thickness, and after performing primary recrystallization annealing that also serves as decarburization annealing In the method for producing a grain-oriented electrical steel sheet, by applying an annealing separator to the steel sheet surface and performing final annealing,
Each aging treatment performed between passes in the final cold rolling satisfies the following formula (1), and
When the 200-700 ° C. section of the heating process of the primary recrystallization annealing is rapidly heated at 50 ° C./s or higher, a holding treatment is performed in which the temperature is maintained at any temperature between 250-600 ° C. for 1-10 seconds. A method for producing a grain-oriented electrical steel sheet.
(Dt / T) ^2/3 ≦ 2.0 × 10 ⁻⁷ (1)
Here, D = 0.394exp (− (8.02 × 10 ⁴ ) /8.31T)
T: Aging temperature (K)
t: Aging time (seconds) In addition to the above component composition, the steel material further includes Al: 0.010-0.050 mass% and N: 0.003-0.020 mass%, or Al: 0.010-0. 050 mass%, N: 0.003-0.020 mass%, Se: 0.003-0.030 mass% and / or S: 0.002-0.03 mass%, with the balance being Fe and inevitable impurities The method for producing a grain-oriented electrical steel sheet according to claim 1. In addition to the component composition, the steel material further includes one or two selected from Se: 0.003-0.030 mass% and S: 0.002-0.03 mass% as an inhibitor-forming element. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the grain-containing electrical steel sheet is contained and the balance is made of Fe and inevitable impurities. In addition to the component composition, the steel material further contains Al: less than 0.01 mass%, N: less than 0.0050 mass%, Se: less than 0.0030 mass%, and S: less than 0.0050 mass%, the balance being It consists of Fe and an unavoidable impurity, The manufacturing method of the grain-oriented electrical steel sheet of Claim 1 characterized by the above-mentioned. In addition to the component composition, the steel material further includes Ni: 0.010 to 1.50 mass%, Cr: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, P: 0.00. 005 to 0.50 mass%, Sb: 0.005 to 0.50 mass%, Sn; 0.005 to 0.50 mass%, Bi: 0.005 to 0.50 mass%, Mo: 0.005 to 0.10 mass% , B: 0.0002 to 0.0025 mass%, Te: 0.0005 to 0.010 mass%, Nb: 0.0010 to 0.010 mass%, V: 0.001 to 0.010 mass%, and Ta: 0.001. The method for producing a grain-oriented electrical steel sheet according to any one of claims 2 to 4, comprising one or more selected from -0.010 mass%.

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