KR20140131496A - Manufacturing method for grain-oriented electrical steel sheet - Google Patents

Abstract

A method to manufacture a grain-oriented electrical steel sheet is disclosed. According to an embodiment of the present invention, provided is a method to manufacture a grain-oriented electrical steel sheet which comprises heating in wt%: 2.0% or greater or smaller than 3.05% of Si; 0 and no more than 0.085% of C; 0.015-0.04% of acid-soluble Al; 0 and no more than 0.20% of Mn; 0 and no more than 0.010% of N; 0 and no more than 0.010% of S; and the remainder consisting of Fe and inevitable impurities; hot-rolling the mixture, performing a hot band annealing process of the same, cold-rolling the same at least two times which an intermediate annealing process is performed therebetween; annealing first recrystallization of the same; and performing a final annealing process of the same.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for manufacturing a directional electric steel sheet,

More particularly, the present invention relates to a method for manufacturing a grain-oriented electrical steel sheet, and more particularly, to a method for manufacturing a grain-oriented electrical steel sheet by increasing the strain energy accumulated during cold rolling through the downward direction of the cooling rate and the coiling temperature during hot rolling, To a method of manufacturing a low iron loss and high specific gravity directional electrical steel sheet in which magnetic properties are improved by applying a three-stage heating heating pattern comprising heating, rapid heating and general heating.

The directional electrical steel sheet is composed of crystal grains having a so-called Goss orientation in which the crystal orientation of the steel sheet face is {110} plane and the crystal orientation in the rolling direction is parallel to the <001> axis, It is a soft magnetic material.

This directional electric steel sheet is superior in the secondary recrystallization texture obtained by selectively growing the crystal grains in {110} < 001 > orientations among the crystal grains suppressed in growth and inhibited the growth of the primary recrystallized grains in the final annealing process after the primary recrystallization (Hereinafter referred to as &quot; inhibitor &quot;) is very important because it exhibits magnetic properties. Therefore, it is desirable that the crystal grains having a group structure stably oriented in the {110} < 001 > orientation in the crystal grains whose growth is suppressed are preferentially grown in the final annealing process (hereinafter referred to as secondary recrystallization) It is the core of manufacturing technology.

Secondary recrystallization begins to occur in the final annealing process because these inhibitors lose their ability to inhibit the growth of the primary recrystallized grains as they grow or decompose as the temperature rises, resulting in a relatively short period of grain growth . It is necessary that the growth of all primary recrystallized grains be suppressed until the second recrystallization occurs in the final annealing process. For this purpose, the precipitates should be uniformly distributed in a sufficient amount and a proper size, and thermally stable until the high temperature immediately before the secondary recrystallization It should not be easily broken down.

In order to obtain such a {110} < 001 > texture, it is possible to use a combination of various manufacturing processes. Generally, the slab composition is controlled strictly by heating the slab, hot rolling, annealing hot- A series of process conditions such as annealing and final annealing (secondary recrystallization annealing) must be strictly controlled.

Primary recrystallization refers to recrystallization commonly referred to as the recrystallization of a crystal, where new crystals with no strain at a certain temperature or higher are nucleated and grain growth is achieved. The primary recrystallization is usually carried out after decarburization annealing performed after cold rolling or immediately after decarburization annealing is performed. The primary recrystallization results in the formation of uniform and granular grains of uniform grain size. In general, the orientations of the recrystallized grains in the directional electrical steel sheet have an aggregate structure in which the orientations of the recrystallized grains are dispersed in various directions or orientations other than the Goss orientation are arranged in parallel with the surface orientation, and the ratio of the Goss orientation finally obtained in the grain- Very low.

As a technique for improving the magnetic properties by controlling the heating and heating conditions during the first recrystallization annealing, Japanese Patent Application Laid-Open No. 2003-3213, 2008-1978, 2008-1979, 2008-1980, 2008-1981, 2008-1982, 2008-1983 Techniques have been reported for introducing rapid heating in the temperature raising process of the decarburization annealing process.

In the above-described Japanese Patent Application Laid-Open No. 2003-3213, a technique for producing a mirror-surface directional electric steel sheet having a high magnetic flux density by controlling the ratio of I [111] / I [411] in the amount of nitriding treatment and the texture after annealing to 2.5 or less , And it is shown that the heating rate of the heating process of aluminum and nitrogen and the decarburization annealing process must be controlled in order to control the texture.

In the above-described Japanese Patent Laid-Open Publication Nos. 2008-1978, 2008-1979, 2008-1980, 2008-1981, 2008-1982, 2008-1983, the lamellar spacing is controlled by decarburizing the annealed hot- A rapid heating at a heating rate of 40 ° C / sec or more, preferably 75 to 125 ° C / sec in a temperature range of 550 to 720 ° C during decarburization annealing to improve the magnetic flux density is proposed. These patents report that the crystal grains in the {411} orientation in the first recrystallization affect the first growth of the second recrystallized grains in the {110} orientation, and the {111} / { 411} ratio is adjusted to 3.0 or less, nitriding treatment is performed, and the inhibitor is strengthened, thereby producing a directional electric steel sheet having a high magnetic flux density.

However, in the above-mentioned patents, only a method of improving magnetic flux density through rapid heating is proposed in a temperature range of 700 to 720 ° C where a large tissue change occurs during the temperature increase of the decarburization annealing process and a temperature range of 550 ° C to 720 ° C including the temperature range In addition, the upper limit of the heating rate is limited to 125 ° C / sec or less even if rapid heating is applied. These patents are not intended to directly increase the ratio of grains having Goss orientation even in the aspect of the idea, There is a limitation in that it is an attempt to increase the ratio of crystal grains having a {411} orientation that indirectly affects the abnormal grain growth (secondary recrystallization) of the Goss orientation during the second recrystallization annealing

In order to solve the above problem, the present inventors have proposed a method of controlling the heating rate at different temperature intervals during the primary recrystallization annealing in Korean Patent Publication No. 10-2012-0009755, A method of manufacturing a grain-oriented electrical steel sheet capable of improving the magnetic properties by controlling the fraction and the degree of integration of the Goss orientation in the plate has been proposed.

The nucleation of the Goss orientation takes place in the shear band where the deformation energy is concentrated during the first recrystallization after the strong deformation. The strain energy accumulated in the shear deformation zone is the temperature of the first recrystallization annealing It can be deduced that energy recovery is caused by partial recovery and thus the nucleation site of Goss is reduced. Thus, it is possible to maintain the magnetism without decreasing the strain energy accumulated in the shear deformation band due to the three stage heating pattern including the rapid heating .

However, in this patent, the hot rolling conditions except slab heating have not been studied. Further, when the accumulation energy of the shear deformation band before the application of the heating pattern is lowered, there is a problem that the effect of improving the magnetic properties may not be large. In addition, when induction heating is used, the heating efficiency is increased at the same output when the resistivity of the sample is high due to the joule effect. It is necessary to examine a method of maximizing such efficiency.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems,

During the hot rolling, the deformation energy of the shear deformation zone of the primary material is increased through the upward movement of the cooling rate and the coiling temperature. The temperature rise of the primary recrystallization anneal introduces the three-stage heating pattern consisting of rapid heating and rapid heating To increase the volume fraction of the Goss orientation, particularly the Exact Goss orientation crystal grains, and to improve the crystal orientation integration degree after the second recrystallization, thereby improving the magnetic properties.

An embodiment of the present invention is a steel sheet comprising, by weight percent (wt%), at least 2.0% Si and less than 3.05% of C, more than 0.085% of C, less than 0.015% of an acid soluble Al, , N: more than 0 and not more than 0.010%, S: more than 0 and not more than 0.010%, and the balance of Fe and other inevitably incorporated impurities are heated, hot rolled, hot rolled sheet annealed, A method for producing a grain-oriented electrical steel sheet, which comprises performing cold rolling at least two times while annealing is performed, performing primary recrystallization annealing, and final annealing, characterized in that a hot- The hot-rolled sheet is quenched at a temperature of 600 to 700 占 폚 at which the carbide is formed at a rate of 10 to 25 占 폚 / sec and rolled at a low temperature of 520 占 폚 or less to inhibit the formation of the coarse carbide, The annealing is carried out at a temperature range of 200 DEG C to 250 DEG C for at least 5 minutes, The first primary recrystallization annealing is a rapid reheating step of raising the temperature of the cold-rolled sheet at an average heating rate of 300 ° C / sec or higher, and an average temperature increasing rate of 100 ° C / sec or more while being lower than the average rate of temperature rise in the super- (B10, Tesla) or higher, and a temperature increase step of increasing the temperature by an average heating rate lower than the average temperature increasing rate in the rapid heating step after the rapid heating step. (W17 / 50, W / kg) or less of the grain size of the oriented electrical steel sheet is 0.85 (W17 / 50, W / kg) or less.

The heating temperature of the slab may be 1,280 ° C or less.

The reduction ratio in the cold rolling may be 80% or more.

The initial superclass temperature raising process is performed at a temperature ranging from room temperature to Ts (占 폚) to 300 占 폚 / sec or more, Ts (占 폚) to 700 占 폚 The rapid heating step is rapidly heated at an average heating rate of 100 to 250 DEG C / sec in a period from Ts (DEG C) to 700 DEG C, and the normal temperature raising process is performed at 700 DEG C The temperature can be raised at an average heating rate of 40 deg. C / sec or less in the section from the annealing temperature to the decarburization annealing temperature.

A treatment for increasing the nitrogen content in the steel sheet between the cold rolling and the final annealing can be performed.

The treatment for increasing the nitrogen content can be accomplished by simultaneous decarboxylation.

The method for manufacturing a grain-oriented electrical steel sheet according to the present invention has the following effects.

In the first recrystallization annealing step, a three-step heating pattern (super rapid heating + rapid heating + normal temperature elevation) is introduced to introduce a Goss orientation, especially a volume fraction of the Exact Goss orientation crystal grain in the primary recrystallized steel sheet To increase the crystal orientation integration degree after the second recrystallization and to improve the magnetic properties. Also, when the heating pattern is applied, the method of increasing the shearing capacity of the cold-rolled sheet and increasing the deformation energy of the shear band, By increasing the fraction of the hard phase existing in the steel through temperature downward and adjusting the distribution of carbide to increase the strain energy accumulated in the cold rolling, this energy is maintained at a rapid temperature rise, and the volume fraction of the Exact Goss orientation grains The directional electric steel sheet having a high magnetic flux density and low iron loss can be manufactured. In addition, the increase of the accumulation energy leads to the increase of the resistivity of the sample, and when the induction heating is used, the input power can be reduced to reduce the cost.

1 is a process diagram of a method for manufacturing a directional electrical steel sheet according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

In addition, since the sizes and thicknesses of the respective components shown in the drawings are arbitrarily shown for convenience of explanation, the present invention is not necessarily limited to those shown in the drawings.

Also, throughout the specification, when an element is referred to as "including" an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

Hereinafter, a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention will be described.

The inventors of the present invention found that since the crystal grains of the Goss orientation, which becomes the nucleus of the secondary recrystallization, are formed in the shear band of the primary recrystallized grains, the formation of the shear strain band in the cold rolling state before the primary recrystallization, It is possible to maximize the effect of the invention disclosed in Korean Patent Publication No. 2012-0009755, and by adjusting the reduction rate, the cooling rate, and the coiling temperature for hot rolling, it is possible to reduce the accumulation energy in the cold state before decarburization annealing And the like.

It is possible to have a high accumulation energy even at the same cold rolling rate when an element capable of applying friction force is included in cold rolling. Among them, the amount of solid carbon can greatly affect the accumulated energy in cold rolling. The amount of solid carbon can be increased by controlling the hot rolling rate or the cooling pattern.

Since coarse carbides are usually produced at 600 to 700 ° C, the cooling rate is increased and the coiling temperature is lowered to suppress the formation of carbides, thereby preventing the formation of coarse carbides during cold rolling, increasing the amount of solid carbon, .

In addition, when the hard phase fraction is increased before the cold rolling, the accumulation energy in cold rolling can be increased. This can also be achieved by rapid cooling after hot rolling. The rapid cooling rate during the cooling process inhibits the formation of coarse carbides and reduces the formation of perlite, a layered structure of cementite (Fe ₃ C) and ferrite, which is in the form of hard bainite, Martensite transformation occurs, so that it becomes easy to miniaturize the osteine or more homogeneity in the plate annealing and to secure homogeneity of the structure.

1 is a process diagram of a method for manufacturing a directional electrical steel sheet according to an embodiment of the present invention.

1, a method of manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes: 2.0 to 4.0% of Si, more than 0% and less than 0.085% of Si, 0.015 to 0.04%, Mn: more than 0% and not more than 0.20%, N: more than 0% and less than 0.010%, S: more than 0% and less than 0.010%, and the balance Fe and other inevitably incorporated impurities Producing; Subjecting the slab to reheating, hot rolling and annealing the hot-rolled steel sheet; Cold-rolling the annealed hot-rolled sheet; A rapid heating step of raising the temperature of the cold-rolled sheet at an average heating rate of 300 ° C / sec or more, and an average temperature increasing rate of 100 ° C / sec or more while being lower than the average heating rate in the super- And a normal temperature raising step of raising the temperature at an average raising rate lower than an average raising rate in the rapid raising step after the rapid raising step; And finally annealing the primary recrystallized annealed cold rolled sheet, and cooling the rolled sheet at a rate of 10 DEG C / sec or more after the hot rolling and winding the sheet at a temperature of 550 DEG C or less.

First, a slab having the above composition range is prepared (S10). The reason for limiting the composition range of the slab of one embodiment of the present invention is as follows. Each component content is percent by weight (wt%).

Si: 2.0 to 4.0 wt%

Silicon (Si) plays a role in lowering the core loss, that is, the iron loss, by increasing the resistivity of the oriented electrical steel sheet. When the Si content is less than 2.0%, the resistivity is decreased and the iron loss is deteriorated. When the Si content is more than 4.0%, the brittleness of the steel becomes large and cold rolling becomes difficult and the formation of the secondary recrystallization becomes unstable. Therefore, Si is limited to 2.0 to 4.0%.

C: more than 0% and not more than 0.085%

Carbon (C), when added in an appropriate amount, promotes the austenite transformation of steel and helps to form uniform microstructure by miniaturizing the hot rolled structure during hot rolling. However, if the content is too large, coarse carbides are precipitated and it becomes difficult to remove carbon during decarburization. Therefore, it is limited to 0.085% or less.

Acid soluble Al: 0.015 to 0.04%

Aluminum (Al) ultimately becomes an N-type nitride of AlN, (Al, Si, Mn) and acts as an inhibitor. When the content is less than 0.015%, sufficient effect as an inhibitor can not be expected. The hot rolling workability is adversely affected. Therefore, Al is limited to 0.015 to 0.04%.

Mn: more than 0% and not more than 0.20%

Manganese (Mn) also has the effect of reducing the iron loss by increasing the resistivity as Si. It reacts with the nitrogen introduced by the nitriding treatment together with Si to form precipitates of N (Al, Si, Mn) It is an important element for suppressing the growth of sizing and causing secondary recrystallization. However, when it is added in excess of 0.20%, the austenite phase transformation is accelerated during hot rolling, and the size of the primary recrystallized grains is reduced, resulting in unstable secondary recrystallization. Therefore, Mn is limited to 0.20% or less.

N: more than 0% and not more than 0.010%

Nitrogen (N) is an element that reacts with Al or the like to refine the crystal grains. If these elements are appropriately distributed, it may be helpful to appropriately fine-graze the structure after cold rolling to ensure proper primary recrystallization, but if the content is excessive, the primary recrystallized grains become excessively fine and as a result, There is a problem that the driving force that causes crystal grain growth during the secondary recrystallization increases due to the crystal grains, so that the crystal grain can grow to an undesired orientation other than the Goss orientation. Also, when the content exceeds 0.010%, the secondary recrystallization starting temperature rises and the magnetic properties deteriorate. Therefore, the content of N is limited to 0.010% or less. On the other hand, when the treatment for increasing the nitrogen amount is performed between the cold rolling and the secondary recrystallization annealing, it is sufficient that the content of N in the slab is 0.006% or less.

S: more than 0% and less than 0.010%

Sulfur (S) is one of the inevitable impurities contained in steelmaking, although it is desirable that it is not contained as an element having a high solid solution temperature during hot rolling and segregation. S forms MnS and affects the primary recrystallized grain size, so the content of S is preferably limited to 0.010% or less, more preferably 0.006% or less.

In addition to the above-mentioned components, various components included in the grain-oriented electrical steel sheet may be included as an alloy component of the electrical steel sheet according to an embodiment of the present invention. Any person skilled in the art can understand will be. The combination of the commonly known components and their application are naturally within the scope of the present invention.

The slab having the above composition is reheated (S20). At this time, the reheating temperature of the slab is preferably 1,280 DEG C or less, and the precipitate is partially dissolved. If the reheating temperature of the slab is increased, the manufacturing cost of the steel sheet is increased, and the melting of the surface of the slab can repair the heating furnace and shorten the life of the heating furnace. If the reheating temperature of the slab is set to 1,280 캜, the columnar structure of the slab is prevented from being grown to a great extent, thereby preventing the occurrence of cracks in the width direction of the plate in the subsequent hot rolling process, thereby improving the yield rate.

After the slab is reheated, it is rolled at a rate of 10 DEG C / sec or more after hot rolling, and then wound at 600 DEG C or less (S30).

A hot rolled sheet having a thickness of 2.0 to 3.5 mm can be produced by hot rolling. By adjusting the hot rolling reduction ratio, the cooling rate and the coiling temperature in the hot rolling, it is possible to influence the accumulated energy in the cold state before the decarburization annealing. When containing an element capable of imparting frictional force in cold rolling, it is possible to have a high accumulation energy even at the same cold rolling rate.

If the cooling rate after hot rolling is increased and the coiling temperature is lowered, the amount of solid carbon can be increased and the carbide can be made finer. Generally, coarse carbides are produced at 600 to 700 ° C. Therefore, it is possible to increase the cooling rate in such a temperature range and lower the coiling temperature by suppressing the formation of carbides, thereby preventing formation of coarse carbides during cold rolling, The carbide can be stretched. Therefore, the coiling temperature is preferably 600 占 폚 or lower, and more preferably 550 占 폚 or lower.

In addition, as a factor affecting the accumulation energy in cold rolling, it is possible to increase the accumulation energy when the fraction of the hard phase before cold rolling is increased. The rapid cooling rate during the cooling process hinders the formation of coarse carbides and reduces the formation of pearlite, a layered structure of weak cementite (Fe ₃ C) and ferrite, and the formation of hard bainite martensite Martensite transformation occurs, and it becomes easy to make the austenite phase fine in the hot-rolled sheet annealing and secure homogeneity of the structure. Therefore, it is preferable that the cooling rate of the hot-rolled sheet after hot rolling is 10 ° C / sec or more . If the cooling rate is less than 10 ° C / sec, the formation of pearlite increases during cooling and the formation of hard phase is reduced, and the effect of securing homogeneity of the structure is insufficient. The higher the cooling rate, the more the transformation of the hard phase may occur, so the upper limit is not particularly limited.

When the hot-rolled sheet is produced, the hot-rolled sheet is annealed and cold-rolled (S40). The hot-rolled sheet annealing may be a decarburization annealing in an oxidizing atmosphere. The cold-rolling may be performed through a single pressure rolling to a final thickness of 0.1 to 0.5 mm, preferably 0.18 to 0.35 mm. The cold rolling may be performed through a single pressure rolling or may be performed through two or more rolling operations with intermediate annealing interposed therebetween.

At this time, when the hot rolled steel sheet is cooled down at a temperature of 150 to 300 ° C. for 5 minutes or more at the intermediate thickness during cold rolling, the accumulation energy due to interaction between the solid carbon and the dislocations called cottrell atomosphere can be increased. If the coiling temperature after hot rolling is less than 150 캜, the intrusion elements such as C and N hardly move to the electric potential. If the coiling temperature exceeds 300 캜, the accumulated strain energy is lowered due to the high temperature, .

In addition, when the cold reduction ratio is high, formation of a shear band in the tissue increases. The shear deformation zone is a place where crystal grains in the Goss orientation, which becomes the nuclei in the secondary recrystallization in the subsequent annealing process, are generated at the time of primary recrystallization. That is, when the cold reduction ratio is increased, the formation of the shear deformation zone is increased, and Goss nuclei are increased in the first recrystallization. Therefore, the cold rolling reduction is preferably 80% or more, and the effect is reduced when the cold rolling reduction is less than 80%.

The cold-rolled steel sheet is heated at an average temperature raising rate of 100 ° C / sec or more while being lower than the average temperature raising rate in the ultra-rapid temperature raising process after the ultra-rapid temperature raising process, A first step of performing a first recrystallization annealing step by a three step heating pattern including a rapid heating step and a normal heating step of raising the temperature by an average heating rate lower than the average heating rate in the rapid heating step after the rapid heating step S50).

In the super-rapid heating step of the three-step heating pattern, an average heating rate of 300 ° C / sec or more at a certain temperature between 500 ° C and 600 ° C, preferably between 550 ° C and 600 ° C, At a temperature raising rate of 100 to 250 DEG C / sec in the section from the specific temperature (Ts) to 700 DEG C in the rapid heating step, and at 40 DEG C / sec or more, and the magnetic property of the grain-oriented electrical steel sheet can be improved.

Rapid rise of the temperature up to a temperature before recrystallization (500 to 600 ° C) at a heating rate of 300 ° C / sec or more, and rapid temperature rise at a temperature raising rate of 100 to 250 ° C / sec in the recrystallization section, Energy recovery, that is, recovery is minimized so as to maximize nucleation of the Goss orientation and grow to good recrystallized grains. The Ts (° C) is a temperature at which the rapid heating process is initiated in the ultra-rapid temperature raising process. Normally, the recrystallization is started at a temperature in the range of about 550 to 600 ° C., so Ts is 500 to 600 ° C., Lt; RTI ID = 0.0 &gt; C, &lt; / RTI &gt;

The normal temperature refers to the temperature of the steel sheet at the time when the temperature raising process is started in the first recrystallization annealing.

In one embodiment of the present invention, the fraction of the Exact Goss bearing as a seed capable of causing secondary recrystallization by the rapid-temperature raising process under the recrystallization temperature during the primary recrystallization annealing is increased, Nucleation of the orientation is induced, thereby maximizing the magnetic property improving effect.

In the case of introducing a typical heating-up pattern that raises the temperature after the rapid heating in the first recrystallization annealing process, the volume fraction of the orientation deviated by 15 ° from the orientation higher than {110} <001> is only about 1%. In contrast, in an embodiment of the present invention, the annealing temperature in the first recrystallization anneal is 300 ° C / sec or more (more preferably 400 ° C / sec or more, more preferably, 500 ° C / sec or higher), and at a temperature rising rate of 570 ° C or lower to 700 ° C or higher, a rapid heating rate of 100-250 ° C / sec or higher (more preferably 120-180 ° C / sec or higher) The volume fraction of the crystal grains having a bearing orientation of 15 degrees from the orientation of {110} < 001 > or more from the orientation at a temperature elevation rate of 40 DEG C / sec or less in the section from the temperature of 700 DEG C or more to the decarburization annealing temperature is 2% . In particular, it is possible to control the volume fraction of the exact Goss crystal grains having a 5-degree orientation from the orientation of {110} < 001 > or more to 0.09% or more.

In the sample which has been heated in the first recrystallization annealing and has undergone more than 95% recrystallization immediately after rapid temperature rise, it is within 1/5 of the total thickness from the surface and within the range of 5 °, 10 °, 15 ° from {110} As a result of measurement of the volume fraction of the crystal grains, it was found that not only the whole goss orientation was increased at the rapid temperature rise, but also in the recrystallization formed by the ultra-rapid heating + rapid heating + (Goss) orientation, that is, the fraction of the Exact Goss orientation is maximized.

As described above, when the rate of increase in the orientation closer to {110} < 001 > or more in the primary recrystallization texture, that is, the rate of increase in the Exact Goss orientation is higher than the rate of increase in the orientation deviating much from {110} < It acts directly as a nucleus of the secondary recrystallization and directly affects the improvement of the degree of integration of the GOS orientation growing into the secondary recrystallized grains, thereby greatly improving the magnetic flux density and iron loss.

However, when the temperature raising rate is too high at rapid heating after rapid raising, the magnetism is deteriorated. The reason can be estimated as follows. That is, when the two-stage rapid heating (super-rapid heating + rapid heating) is applied in the first recrystallization annealing, the crystal grain size distribution is uniform up to a specific heating rate, ° C / sec, the non-uniformity of crystal grains is increased, and a fraction having a crystal grain size of 35 μm or more becomes excessively large, and crystal grains having bad orientation grow due to grain growth, resulting in deterioration of magnetism.

The orientation of {111} <112> and {411} <148> orientations are recrystallized first, because the Goss orientation has the highest strain energy. {111} <112>, {411} <148> and the like can decrease the Goss orientation during the first recrystallization as the orientation fraction such as {411} It is not necessary to increase the heating rate, and it is more preferable to heat at a heating rate of 40 DEG C / sec or less in a temperature range of 680 DEG C or more.

Therefore, in the temperature raising process during the primary recrystallization annealing, the temperature is increased from the room temperature to the Ts temperature at an average heating rate of 300 ° C / sec or more, and then rapidly increased to an average heating rate of 100 to 250 ° C / Heating at an average heating rate of 40 DEG C / sec or less in the temperature range of 700 DEG C or higher is effective in increasing the magnetic fraction by raising the fraction of the Goss orientation.

Further, the present inventors measured the area weighted average of angles deviating from {110} < 001 > orientations of the secondary recrystallization grains with respect to the specimen obtained by raising the temperature in the three-stage heating pattern in the first recrystallization annealing.

The main features of this measuring device are as follows. Based on the X-ray Laue method and measured with a fixed X-ray CCD detector, the position at which the X-ray diffraction occurs in the CCD detector and the specimen, and the tilt angle of the detector are set to 1 The measurement accuracy was improved by minimizing the strain of the single crystal which was not deformed by controlling it in ㎛ unit. The specimens were measured for each orientation at each position and the absolute values of the deviations from the ideal Goss orientation were calculated from the orientations measured at each position, and then the area weighted average at all positions was used to calculate the area weight The average was measured.

The off angle was measured for four kinds of angle α, β angle, γ angle, and δ angle, and α angle was the direction of {110} <001> direction around the normal direction (ND) And the? Angle are the average deviation angle from the {110} < 001 > or more orientation in the vicinity of the rolling perpendicular direction (TD) of the secondary recrystallized texture, the? Angle is the rolling direction of the secondary recrystallization texture The average deviation angle and the? Angle from {110} < 001 > or more orientation in the vicinity of the <001> crystal orientation and the rolling direction RD in the secondary recrystallization texture are defined as an average deviation angle between the <001> crystal orientation and the rolling direction RD.

As a result of the measurement, it was confirmed that all of the off-angles were reduced when the two-stage rapid heating condition of the first-order recrystallization temperature and the first-order recrystallization temperature were applied as in the present invention. In particular, it was confirmed that the area weighted average β angle was as low as 2 ° and the δ angle was also drastically lowered. If β angle is close to 2 °, it means not only the magnetic domain width is minimized to minimize the electromagnetic energy but also the magnetic property is improved by minimizing the dislosure magnetic field which is harmful to the magnetism.

According to the method for producing a grain-oriented electrical steel sheet according to the present invention, when the value measured for a steel sheet subjected to secondary recrystallization annealing is used as a reference, an area weighted average of an absolute value of the crystal orientation is set to a range of 1.5 to 2.6 degrees , More preferably within the range of 1.5 to 2.4 °, and the angle? Can be controlled to be within 5 °, more preferably within 4.5 °.

The steel sheet heated by primary recrystallization annealing undergoes decarburization and annealing. After the decarburization is completed, the annealing may be performed in a separate process, but nitriding annealing may be performed simultaneously with decarburization.

When nitriding annealing is performed simultaneously with decarburization, it can be carried out in a mixed gas atmosphere of ammonia, hydrogen and nitrogen. According to the method in which the decarburization is first carried out after the temperature elevating process in the first recrystallization annealing and then the nitriding annealing is performed, precipitates such as Si ₃ N ₄ and (Si, Mn) N are generated in the surface layer portion of the steel sheet. (Al, Si, Mn) N, which is thermally stable in the final annealing process, which is a subsequent process, since the annealing temperature is controlled to 700 to 800 ° C. It is possible to perform a role as an inhibitor by re-precipitation. On the contrary, when the decarburization and the nitriding annealing are performed at the same time, AlN or (Al, Si, Mn) N precipitates are formed at the same time, so that the precipitates can be used as an inhibitor without being transformed during the final annealing. Therefore, It is more preferable to carry out decarburization and nitriding annealing at the same time.

However, the method for producing the grain-oriented electrical steel sheet of the present invention is not limited to the simultaneous decarburization and nitriding treatment during the primary recrystallization annealing, and the conventional nitriding annealing method after the decarburization annealing is also an advantageous method Which is effective in producing a directional electrical steel sheet.

Final annealing is performed after primary recrystallization annealing (S60). The steel sheet subjected to the primary recrystallization annealing is subjected to the secondary recrystallization after the annealing separator is applied for a long period of time after the annealing separator is applied so that the {110} plane of the steel sheet is parallel to the rolling plane and the < 001 > direction is parallel to the rolling direction } &Lt; 001 > The annealing separator may be preferably one produced based on MgO, but is not particularly limited thereto.

The purpose of the final annealing is largely in the formation of {110} < 001 > texture by secondary recrystallization, the formation of a vitreous coating by the reaction of the oxide layer and MgO formed during decarburization, and the removal of impurities that impair magnetic properties. As the final annealing method, the nitride is inhibited by keeping the mixed gas of nitrogen and hydrogen at the temperature rising period before the secondary recrystallization, and the secondary recrystallization is well developed. After completion of the secondary recrystallization, 100% hydrogen It is kept in the atmosphere for a long time to remove impurities.

Hereinafter, a method for manufacturing a grain-oriented electrical steel sheet according to the present invention will be described in more detail with reference to examples. However, the following examples are only illustrative of the present invention and are not intended to limit the scope of the present invention.

Example

Example  One

Si: 2.95%, C: 0.052%, Mn: 0.105%, S: 0.0090%, N: 0.0079%, Sol. A slab of a grain-oriented electrical steel sheet containing 0.030% of Al and the balance of Fe and other inevitably incorporated impurities was heated at a temperature of 1150 ° C for 210 minutes and then hot-rolled to produce a hot-rolled steel sheet having a thickness of 2.2 mm. Adjust the cooling rate as shown in Table 1. The hot-rolled sheet was annealed at a temperature of 900 ° C or higher, pickled, and decarburized in an oxidizing atmosphere at the same time as annealing of the hot-rolled sheet. At this time, the degree of decarburization was adjusted by adjusting the degree of oxidation. Followed by cold rolling to a thickness of 0.27 mm. In the middle of cold rolling, heat treatment was performed for 10 minutes at the temperature shown in Table 1 or not.

The cold-rolled steel sheet was heated in the furnace at a temperature of 850 ° C for 120 seconds in a mixed atmosphere of a dew point temperature of 63 ° C formed by simultaneously charging 50% of hydrogen, 50% of nitrogen and 1% of dry ammonia gas, Respectively. The nitrogen content of the nitrided steel sheet was controlled in the range of 200 to 250 ppm. At this time, when the temperature was elevated, it was heated at various temperature raising rates shown in Table 1 at a room temperature to 570 ° C, and at a temperature raising rate of 140 ° C / sec at a temperature range of 570 ° C to 700 ° C. Was heated at a heating rate of 20 DEG C / sec.

This steel sheet was coated with MgO as an annealing separator, and finally annealed in a coiled state. In the final annealing, a mixed atmosphere of 25% nitrogen and 75% hydrogen was set up to 1,200 ° C. After the temperature reached 1,200 ° C., the furnace was maintained in a 100% hydrogen atmosphere for 20 hours or more. The magnetic properties measured for each condition are shown in Table 1.

Hot-rolled cooling rate
(° C / sec) Low temperature heat treatment temperature in cold rolling (℃ / sec) Temperature rise rate in the range of room temperature ~ 570 ℃
(° C / sec) Magnetic flux density
(B10, Tesla) Iron loss
(W17 / 50, W / kg) division 5 250 580 1.94 0.90 Comparative Example 1 25 250 580 1.96 0.85 Inventory 1 25 No aging 580 1.91 0.88 Comparative Example 2 5 200 420 1.94 0.89 Comparative Example 3 25 200 420 1.95 0.86 Inventory 2

As shown in Table 1, the hot-rolled cooling rate is fast, and the inventive method falling within the scope of the present invention has a very high iron loss and magnetic flux density, and the magnetic improvement effect is somewhat lowered when the cooling rate is low. In addition, when hot rolling is performed at a high cooling rate and pass aging at the time of cold rolling, the magnetism is excellent even though the temperature rising rate in a range of room temperature to 570 ° C is somewhat lowered.

Example  2

2.99%, C: 0.045%, Mn: 0.112%, S: 0.0088%, N: 0.0074%, Sol. A slab of a grain-oriented electrical steel sheet containing 0.032% of Al and the balance of Fe and other inevitably incorporated impurities was heated at a temperature of 1150 ° C for 210 minutes and hot-rolled to produce a hot-rolled steel sheet having a thickness of 2.3 mm. The hot-rolled sheet was heated to a temperature of 1,050 占 폚 or higher and held at 910 占 폚 for 90 seconds. After cooling, the coiling temperature was changed as shown in Table 2. The steel sheet was then pickled, hot rolled sheet annealed, and then cold rolled to a thickness of 0.27 mm.

The cold-rolled steel sheet was heated in the furnace at a temperature of 855 DEG C for 120 seconds in a mixed atmosphere of a dew point temperature of 63 DEG C formed by simultaneous introduction of 50% hydrogen, 50% nitrogen and 1% dry ammonia gas and subjected to simultaneous decarburization and nitriding Respectively. The nitrogen content of the nitrided steel sheet was controlled in the range of 180 to 230 ppm. At this time, the temperature was raised at various temperature raising rates of 580 ° C / sec in the temperature range from room temperature to 570 ° C at the time of elevating the temperature, at a temperature raising rate of 140 ° C / sec in the temperature range of 570 ° C to 700 ° C, And heated up to 850 DEG C at a heating rate of 20 DEG C / sec.

This steel sheet was coated with MgO as an annealing separator, and finally annealed in a coiled state. In the final annealing, a mixed atmosphere of 25% nitrogen and 75% hydrogen was set up to 1,200 ° C. After the temperature reached 1,200 ° C., the furnace was maintained in a 100% hydrogen atmosphere for 20 hours or more. The magnetic properties measured for each condition are shown in Table 2.

Hot rolled coiling temperature
(° C) Magnetic flux density
(B10, Tesla) Iron loss
(W17 / 50, W / kg) division 800 1.88 0.96 Comparative Example 4 650 1.92 0.91 Comparative Example 5 520 1.96 0.85 Inventory 3

As shown in Table 2, it can be seen that the magnetization was improved downward at the coiling temperature during hot rolling.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (6)

Si: not less than 2.0% and not more than 3.05%, C: more than 0 and not more than 0.085%, acid soluble Al: 0.015 to 0.04%, Mn: more than 0 and not more than 0.20%, N: more than 0 and not more than 0.010% , S: more than 0 and not more than 0.010%, and the balance of Fe and other inevitably incorporated impurities are heated, hot-rolled, hot-rolled sheet annealed, and subjected to intermediate annealing at least two times 1. A method for producing a grain-oriented electrical steel sheet which is subjected to cold rolling, primary recrystallization annealing, and final annealing,
The hot rolled sheet is quenched at a temperature of 600 to 700 占 폚 at which a coarse carbide is formed on the hot rolled sheet between the hot rolling and the hot rolled sheet annealing at a rate of 10 to 25 占 폚 / sec, Temperature coiling to inhibit the formation of the coarse carbides,
The intermediate annealing is performed at a temperature range of 200 DEG C to 250 DEG C for 5 minutes or more,
The primary recrystallization annealing may be performed by a super rapid temperature raising process of raising the cold rolled sheet at an average temperature raising rate of 300 ° C / sec or higher and an average temperature raising rate of 100 ° C / sec or more while being lower than the average raising rate in the ultra- And a normal temperature raising step of raising the temperature by an average temperature raising rate lower than the average temperature raising rate in the rapid raising step after the rapid raising step,
A method for producing a grain-oriented electrical steel sheet having a magnetic flux density of 1.95 (B10, Tesla) or more and an iron loss of 0.85 (W17 / 50, W / kg) or less.
The method according to claim 1,
Wherein the heating temperature of the slab is 1,280 占 폚 or less.
The method according to claim 1,
Wherein the reduction ratio in the cold rolling is 80% or more.
The method according to claim 1,
The initial superclass temperature raising process is performed at a temperature ranging from room temperature to Ts (占 폚) to 300 占 폚 / sec or more, Ts (占 폚) to 700 占 폚 The superheated temperature was raised at an average heating rate which was more than twice the rate,
In the rapid heating step, the temperature is rapidly raised at an average heating rate of 100 to 250 DEG C / sec in a period from Ts (DEG C) to 700 DEG C,
Wherein the normal temperature raising step raises the temperature at an average heating rate of 40 DEG C / sec or less in a range from 700 DEG C to decarburization annealing temperature.
The method according to claim 1,
And performing a treatment for increasing the nitrogen content in the steel sheet between the cold rolling and the final annealing.
6. The method of claim 5,
Wherein the treatment for increasing the nitrogen content is performed by simultaneous decarburization and nitridation.

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