KR20140058942A - Grain-oriented electrical steel sheet and manufacturing method for the same - Google Patents

Abstract

Disclosed is a method for manufacturing an oriented electrical steel plate According to the present invention, a method for manufacturing the oriented electrical steel plate comprises a step of: 1) manufacturing a slab consisting of 2.0 ~ 4.0 wt% of Si; 0.085 ~ 0.30 wt% of acid-soluble Al; less than 0.20 wt% of Mn; less than 0.010 wt% of N; less than 0.010 wt% of S; residual Fe and impurities; 2) reheating the slab; 3) annealing a hot-rolled steel plate including a decarbonizing process in oxidative environment after hot-rolling the reheated slab; 4) first recrystallizing and annealing the hot-rolled steel plate by three temperature increasing patters, which are: (1) super rapidly increasing temperature of the cold-rolled steel plate at more than 300°C/sec; (2) rapidly increasing the temperature of the cold-rolled steel plate at more than 100°C/sec lower than a temperature increase speed in the step of super rapidly increasing the temperature of the cold-rolled steel plate after the step of super rapidly increasing the temperature of the cold-rolled steel plate; (3) generally increasing the temperature of the cold-rolled plate at an average temperature increasing speed lower than the temperature increasing speed in the step of rapidly increasing the temperature of the cold-rolled steel plate after the step of rapidly increasing the temperature of the cold-rolled steel plate; and 5) finally annealing the first recrystallized and annealed cold-rolled steel plate.

Description

TECHNICAL FIELD [0001] The present invention relates to a grain-oriented electrical steel sheet and a method of manufacturing the same. BACKGROUND ART [0002]

The present invention relates to a grain-oriented electrical steel sheet and a method of manufacturing the same, and more particularly, to a grain-oriented electrical steel sheet and a method of manufacturing the same. More particularly, the present invention relates to a grain- The present invention relates to a low iron loss and high specific gravity directional electrical steel sheet having improved magnetic properties by applying three stages of heating at elevated temperatures including a temperature rise, a rapid temperature rise and a normal temperature rise, and a method for manufacturing the same.

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 step of the aluminum and nitrogen amount and the decarburization annealing process should 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 by differently controlling the heating rate for each temperature interval 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 steel sheet is proposed.

The first order recrystallization texture is controlled and the first order recrystallization size is equalized by the reduction of the heating rate at 700 ° C or more. When induction heating is used at such a rapid temperature rise, the so-called skin effect causes the heating of the surface portion to be faster than in the middle.

Induction heating is applied based on Lenz's law and Joule effect. If a metal sample is present in the induction coil and the magnetic field due to the alternating current changes in the induction coil, a current is induced in the metal sample. This induced current is called a vortex. In the Joule effect, this current heats the metal sample. This heating is done regardless of the magnetic properties. Factors influencing induction heating include electrical conductivity, resistivity, magnetic properties, and thickness. In induction heating, the vortex flow is concentrated on the surface, so the surface is heated quickly. This is called a skin effect. When induction heating is used, the texture of the surface and the center can be different. Therefore, although the improvement of the texture of the surface area has improved considerably, the improvement of the magnetic property can be maximized by reducing the difference between the surface and the center.

When the heating rate is increased in the primary recrystallization, the primary recrystallized grains become smaller. When the decarburization annealing temperature is increased, the grain size distribution becomes uneven, so that the magnetism improving effect is not maximized. In other words, the effect of maximizing the fraction of Exact Goss due to the improvement of the temperature is that when the primary recrystallized grain distribution is nonuniform, the angle deviating from the Goss orientation is slightly larger than the scattered Goss orientation or the grain size is relatively larger The magnetic properties of the final electrical steel sheet may deteriorate due to growth of secondary recrystallized grains. Therefore, in order to maximize the effect of temperature change, it is necessary to make the primary recrystallization size distribution extremely uniform.

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

In the first recrystallization annealing step, the three-stage temperature elevation consisting of rapid heating, rapid heating and normal temperature elevation is introduced to increase the volume fraction of the Goss orientation, particularly the Exact Goss orientation crystal grain, and to increase the crystal orientation density after the second recrystallization And improving the magnetic properties by improving the first recrystallization heating method to make the recrystallized grain size distribution as homogeneous as possible, thereby providing a method of manufacturing a grain-oriented electrical steel sheet.

In addition, the decarburization annealing is carried out in the hot-rolled steel sheet annealing after hot rolling by the low-temperature slab heating method while the austenite fraction is increased by the high carbon content in the slab, thereby adjusting the solubility of the precipitate to uniformize the primary recrystallized grain size distribution as much as possible And to provide a method of manufacturing a grain-oriented electrical steel sheet that maximizes the effect of improving magnetic properties by improving the temperature recrystallization method.

In order to achieve the above object, a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises: 2.0 to 4.0% of Si, 0.085 to 0.30% of C, 0.015 to 0.04 %, Mn: not more than 0.20%, N: not more than 0.010%, S: not more than 0.010%, and the balance of Fe and other inevitably incorporated impurities; reheating the slab; Subjecting the cold rolled steel sheet to a cold rolling process; subjecting the cold rolled steel sheet to a rapid heating step of heating the cold rolled steel sheet at an average heating rate of 300 DEG C / sec or more; And a rapid heating step of raising the temperature at an average heating rate of 100 ° C / sec or more while being lower than an average temperature raising rate of the rapid heating step after the rapid heating step, The method comprising annealing, primary recrystallization by a three-stage temperature elevation, including normal temperature raising process of raising the temperature to degrees lower average temperature rising rate and a step of final annealing the primary recrystallization annealing the cold-rolled sheet.

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.

The hot-rolled sheet annealing may be performed by heating the hot-rolled sheet at 900 to 1200 ° C and then maintaining the temperature at 850 to 1100 ° C in an oxidizing atmosphere.

The three-stage heating can be performed by an induction heating method.

The amount of decarburization in the hot-rolled sheet annealing may be 0.02 to 0.25 wt%.

The amount of residual carbon in the steel sheet after annealing the hot-rolled steel sheet may be 0.04 wt%.

The cold rolling step may be performed by cold-rolling the hot-rolled and annealed sheet once or twice or more while performing the intermediate annealing.

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 size of the average primary recrystallized grains of the steel sheet before the final annealing after the primary recrystallization annealing may be 18 to 30 탆 and the ratio of the standard deviation of the grain size distribution to the average grain size of the primary recrystallized grains may be 0.8 or less.

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, three stages of temperature elevation (super rapid temperature rise + rapid temperature rise + normal temperature elevation) are introduced to introduce the Goss orientation, especially the volume fraction of the Exact Goss orientation crystal grain to the primary recrystallized steel sheet The magnetic orientation can be improved by improving the crystal orientation density after the secondary recrystallization. In addition, even when the temperature is elevated, the carbon content of the slab can be increased to increase the austenite fraction , The decarburization annealing is performed at the time of annealing the hot-rolled sheet after the hot-rolling by the low-temperature slab heating method, and the degree of solidification of the primary recrystallized grain is made as uniform as possible by adjusting the solidification degree of the precipitate.

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

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims. Like reference numerals refer to like elements throughout the specification.

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

The present inventors focused their attention on the fact that the effect of the method of manufacturing a directional electrical steel sheet of Korean Patent Publication No. 10-2012-0009755 can be maximized if the primary recrystallized grain distribution can be more uniformized.

If the precipitates can be precipitated so as to have a similar size and uniform distribution in the low-temperature slab heating method, it can contribute to the homogenization in the primary recrystallization and is closely related to the employment of precipitates such as Al-based nitride and Mn-based sulfide And the research on the control method of these exhalations was repeated.

In addition, we studied on the method that can reduce the difference between the surface and the center part by the skin effect when induction heating is used.

3% silicon steel is a pure ferrite region, but as the amount of carbon added increases, the fraction of austenite phase increases at a predetermined temperature region, and thus the solubility of the precipitate in austenite is at least 2 Can be improved more than twice. In addition, the increase of carbon improves the texture of the middle part in the thickness direction, thereby improving the difference in the temperature of the first recrystallization annealing by induction heating.

Carbon is an austenite-forming element. As the carbon content increases, the austenite fraction increases and the solubility and solubility of the precipitates in the high austenite fraction increases. In the low temperature slab heating method, the precipitate is maximally solidified (Al, Si, Mn) The Al-based nitride such as AlN is sufficiently solidified during the heating of the slab, which affects the distribution of the primary recrystallized grains in the future.

In addition, such high amount of carbon lowers productivity during decarburization annealing after cold rolling, and residual carbon in steel sheet becomes high, resulting in carbon being present in more than 30 ppm in the final product, which causes magnetic aging phenomenon during use as a transformer component.

In addition, when the decarburization annealing is performed, the grain size is made very small and the magnetic property is deteriorated. In order to solve this problem, it is possible to control the size of the primary recrystallized grains without deteriorating the productivity of the annealing after cold rolling by wetting the atmosphere in the annealing of the hot-rolled sheet or decarburizing it by using a decarburization accelerator or the like, Thereby making it possible to maximize the magnetic improvement effect.

Here, the employment of the precipitates will be described in detail.

The solubility of AlN on ferrite can be represented by the following formula proposed by Iwayama.

Iwayama equation: log [% Al] [% N] = - 10062 * 1 / T (K) +2.72 (References: K. Iwayama, T Haratani, Journal of Magnetism and Magetic Materials, 19 )

The solubility of MnS in the ferrite phase can be represented by the following formula proposed by Wriedt.

Wriedt equation: log [% Mn] [% S] = - 10590 * 1 / T (K) + 4.092 (References: HA Wriedt and H. Hu, Matall. Nakashima, K. Takasihma and J. Harase, Iron and Steel vol 77 (1991) p1717)

The solubility equation of AlN on austenite can be obtained by Darken (Fe-0.1C-0.4Mn-0.01S) and Leslie (Al-killed steel) as follows.

Darken equation; log [% Al] [% N] = - 7400 * 1 / T (K) + 1.95

Leslie equation; log [% Al] [% N] = - 6700 * 1 / T (K) + 1.033

(References: K. Iwayama, T Haratani, Journal of Magnetism and Magetic Materials, 19 (1980) pp 15-17)

According to this, when the content of the acid soluble aluminum is 0.029 wt% and the content of N is 0.0060 wt%, the slab full-solidification temperature is 1028 째 C (darken) and 11141 째 C (Leslie) respectively and is much lower than the solidus temperature (Iwayama) 1280 째 C in the ferrite phase.

In the case of 0.029% by weight and 0.0060% by weight of N in the above formula, when the hot rolling reheating temperature is reheated to 1190 ° C, the maximum amount of solid solution Al can be completely employed as austenite at 0.0485% ° C (Darken) and 0.0337 ° C (Leslie) But in ferrite phase, it is 0.0232%, and it is difficult to complete solidification and 0.0058% of Al is precipitated. When the reheating temperature is 1190 ° C, the maximum solid solution N can be completely employed as 0.0161% ° C (Darken) and 0.0084 ° C (Leslie) in the case of austenite phase, but 0.0030% in the ferrite phase is difficult to complete solidification and 0.0030% N precipitates do. As the austenite phase in the slab increases, the temperature of AlN is lowered. Therefore, when a large amount of carbon is added to the slab and the austenite fraction is increased, the solubility of AlN is maximized to secure sufficient grain growth restraining ability.

This effect seems to be similar to S. As a result, the formation of the austenite phase is promoted through the slab heating and the annealing of the hot-rolled steel sheet to obtain the distribution of the AlN precipitates uniformly distributed in the steel sheet after cold rolling, and the secondary recrystallized grains having a high magnetic flux density and low iron loss You can.

In addition, the amount of austenite in the hot-rolled steel sheet is increased due to the presence of 0.085 wt% or more and 0.30 wt% or less of carbon in the hot-rolled steel sheet. This causes an increase in the amount of austenite during the hot- The heterogeneous hot-rolled microstructure is entirely extinguished and composed of fine grains in all directions, and precipitates are uniformly dispersed and precipitated in a fine matrix.

That is, it is possible to obtain a uniform distribution of precipitates due to an increase of the austenite fraction using the high carbon component system and the increase of the precipitate solubility, and thus the primary recrystallized grain distribution becomes uniform and the magnetic property can be improved. It is also possible to improve the difference in heating effect of the center part in the thickness direction by the skin effect in the induction heating by the change of the middle partial texture when annealing the hot and hot rolled sheets by the formation of austenite according to the increase of the carbon content.

In order to prevent deterioration of the decarburization effect when the primary recrystallization annealing is performed when the amount of carbon is increased, decarburization through heat treatment in an oxidizing atmosphere is performed to anneal the hot rolled steel sheet, thereby lowering the productivity. In the case of applying decarburization in annealing a hot-rolled sheet with such a high carbon content system, when the temperature of the decarburization annealing proposed in Korean Patent Publication No. 10-2012-0009755 is applied, the effect of improving the magnetic property by raising the fraction of Exact Goss You can maximize.

1 is a process diagram of a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention. The grain-oriented electrical steel sheet according to an embodiment of the present invention comprises 2.0 to 4.0% of Si, 0.085 to 0.30% of C, 0.015 to 0.04% of an acid soluble Al, , Mn: not more than 0.20%, N: not more than 0.010%, S: not more than 0.010%, and the balance of Fe and other inevitably incorporated impurities; reheating the slab; Subjecting the cold-rolled sheet to a cold-rolling step of heating the cold-rolled sheet at an average heating rate of 300 ° C / sec or more, and A rapid heating step of raising the temperature at an average heating rate of 100 ° C / sec or more while being lower than an average temperature raising rate of the super-basic temperature raising step after the rapid heating step; day Comprises a first recrystallization annealing step by raising the temperature by three stages including a normal temperature raising step of raising the temperature at an average heating rate and final annealing of the recrystallized annealed cold rolled steel sheet.

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%

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 material. 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: 0.085 to 0.30%

Carbon (C) can increase the content of austenite in the slab by increasing the addition amount as described above. The higher the austenite phase in the slab, the lower the solubilization temperature of AlN. Therefore, when a large amount of carbon is added to the slab to increase the austenite fraction, the solubility of AlN is maximized and sufficient grain growth restraining force can be ensured.

This effect can also appear to be similar to S. As a result, the formation of the austenite phase is promoted through the slab heating and the annealing of the hot-rolled steel sheet, whereby the distribution of the AlN precipitates uniformly distributed in the steel sheet after the cold rolling can be obtained, and the secondary recrystallized grains having high magnetic flux density and low iron loss Can be obtained.

In addition, the amount of austenite during the annealing of the hot-rolled steel sheet due to carbon in the hot-rolled steel sheet is increased, which makes it possible to sufficiently recrystallize the hot rolled steel sheet which is inhomogeneous and long- A hot rolled microstructure is entirely extinguished and composed of fine grains in front, and precipitates are uniformly dispersed and precipitated in a fine matrix.

On the other hand, by performing decarbon annealing at the same time as the hot-rolled sheet annealing, the goss texture of the surface layer of the steel sheet grows into the deep portion, and the fraction of the Goss grain of the primary recrystallized annealed sheet is increased to increase the degree of Goss integration of the final annealed sheet, To obtain a high magnetic flux density and an extremely low iron loss.

This makes it possible to compensate for the reduction of the iron loss improvement effect due to the thickness direction deviation during induction heating. In order to achieve this effect, the carbon content in the slab should be 0.085% or more. However, if decarburization is not carried out sufficiently in the decarburization annealing process, the magnetic properties will deteriorate due to magnetic aging when the final product is applied to electric power equipment. If the carbon content in the slab exceeds 0.30%, sufficient The time consumed for decarburization is increased and a thick oxide layer is formed on the surface due to an increase in annealing time and a decarburization delay phenomenon occurs and sufficient decarburization can not be performed. Therefore, the content of C is limited to 0.085 ~ 0.30%.

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: 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: 0.010% or less

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 adequate grain size. However, if the content is excessive, the first-order 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 carried out 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: not more 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. Since S forms MnS and affects the size of the primary recrystallized grain, 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.

After the slab having the above composition is reheated, hot rolling is performed. (S20)

At this time, the heating of the slab is preferably carried out at 1,280 DEG C or lower, and it is preferable to partially refine the precipitate. If the heating temperature of the slab is increased, the manufacturing cost of the steel sheet is increased, and the heating furnace can be repaired by melting the surface portion of the slab and the lifetime of the heating furnace can be shortened. In addition, if the slab is heated to a temperature of 1,280 ° C or lower, the slab can be prevented from being grown in a large size, thereby preventing cracks from being generated in the width direction of the slab in the subsequent hot rolling process, thereby improving the slump rate.

After the slab is reheated, hot rolling is performed. A hot rolled sheet having a thickness of 2.0 to 3.5 mm can be produced by hot rolling.

When the hot-rolled sheet is produced, hot-rolled sheet annealing is performed. (S30) At this time, it is preferable to include decarburization annealing in an oxidizing atmosphere. In order to obtain a homogeneous recrystallized microstructure and a fine AlN precipitate distribution before cold rolling, the hot rolled sheet is again heated to a temperature not higher than the slab heating temperature to recrystallize the deformed structure, and sufficient austenite phase is secured and grain growth such as AlN and MnS It is important to promote the employment of inhibitors. Therefore, it is preferable to heat the hot-rolled sheet annealing to 900 to 1,200 DEG C in order to maximize the austenite fraction.

After the hot-rolled sheet is heated to 900 to 1,200 占 폚, it is preferable to perform the cracking treatment at a temperature of 900 to 1,100 占 폚. When the cracking temperature is less than 900 캜, the precipitated solid does not diffuse and is precipitated finely. When the cracking temperature exceeds 1,100 캜, precipitates are not uniformized and precipitate in a subsequent cooling process. Therefore, the cracking treatment is performed at 900 to 1,100 ° C to strengthen the growth drive of the precipitate.

The cracking treatment is performed in an oxidizing atmosphere to simultaneously perform decarburization. This is to induce an increase of nucleation of the Goss texture and to reduce the amount of carbon remaining in the steel sheet to prevent quality deterioration due to magnetic aging.

In addition, when the amount of carbon black is excessive during annealing of hot-rolled steel sheet, formation of shear band due to carbon during cold rolling is weakened, and strain energy accumulation is reduced, and thus the fraction of Exact Goss due to 3- And the decarburization amount at the time of annealing the hot-rolled steel sheet is too small, the decarburization becomes insufficient at the time of the first recrystallization, and the magnetism is extremely weakened. Therefore, the amount of decarburization during annealing of the hot-rolled sheet is limited to 0.02 to 0.25 wt% or less.

The cold-rolled steel sheet is subjected to cold rolling (S40)

The cold-rolling can be performed through a one-time rolling to a final thickness of 0.1 to 0.5 mm, more preferably 0.18 to 0.35 mm. The cold rolling may be carried out through a single depressurization, or it may be carried out through two or more rolling operations with intermediate annealing interposed therebetween.

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 recrystallization annealing step is carried out by raising the temperature by three steps 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 rapid-rise heating process during the three-stage heating, the average heating rate is 300 ° C / sec or more at a certain specific temperature between 500 ° C and 600 ° C, preferably between 550 ° C and 600 ° C, In the rapid heating step, rapid heating is performed at an average heating rate of 100 to 250 ° C / sec in the section from the specific temperature (Ts) to 700 ° C, and then 40 ° C / sec or less It is possible to improve the magnetic properties of the grain-oriented electrical steel sheet.

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 first recrystallization annealing, when the normal temperature rise which is a general temperature increase after the rapid heating is introduced in the heating process, the volume fraction of the 15 ° orientation in the orientation of {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 recrystallized by the first recrystallization annealing and has been recrystallized by 95% or more immediately after the rapid temperature rise, the crystal grains belonging to 5 10 0 15 ° in the orientation higher than {110} <001> As a result of measurement of the volume fraction, it was found that not only the total goss orientation was increased at rapid temperature rise, but also in the recrystallization formed by ultra-rapid heating + rapid heating + ) Bearing fraction, that is, the fraction of the Exact Goss bearing, 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 by three stages 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 °.

There is no particular limitation on the heating method during the heating process in the primary recrystallization annealing. An induction heating furnace can be used, and it is possible to raise the temperature by three stages of elevation by a plurality of induction heating furnaces. For example, in the first induction heating furnace, the temperature is raised at a rapid heating rate of 300 DEG C / s or more, preferably 400 DEG C / s, in the second induction heating furnace at 100 to 250 DEG C / s, The temperature can be rapidly increased at a heating rate of 180 DEG C / s, and the temperature can be generally raised at a rate of 40 DEG C / sec or less in the third induction heating furnace.

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.

When the cross-section of the steel sheet before secondary recrystallization after the primary recrystallization annealing is observed, it is preferable that the grain size is 18 to 35 mu m. It is also preferable that the ratio of the standard deviation of the grain size distribution to the average grain size of the primary recrystallized grain divided by the average grain size of the primary recrystallized grain is 0.80 or less. When the grain size is 18 mu m or more, the effect of improving the magnetic property by uniformizing the grain size is exhibited. However, in the case of exceeding 35 탆, the crystal grains of the orientation which adversely affects the magnetic properties due to the large crystal grains are grown by the size advantage, and the crystal grains deviating from the {110} < 001 > . When the value obtained by dividing the standard deviation by the average grain size of the primary recrystallized grains is 0.80 or less, the grain size distribution is uniform even when the grain size is increased, so that the magnetic improvement effect can be further improved.

Final annealing is performed after primary recrystallization annealing. 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 the following examples.

Si: 3.45%, Mn: 0.089%, S: 0.0045%, N: 0.0061%, Sol. Al: 0.026% and C as shown in Table 1 and the balance Fe and other inevitably mixed impurities was heated at a temperature of 1190 캜 for 210 minutes and hot-rolled to obtain a hot-rolled steel sheet having a thickness of 2.3 mm . The hot-rolled sheet was heated to a temperature of 1,050 ° C or higher, then held at 910 ° C for 90 seconds, quenched in water and pickled, and decarburized in an oxidizing atmosphere at the same time as annealing 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.

The cold-rolled steel sheet was heated in the furnace at a temperature of 855 DEG C for 150 seconds in a mixed atmosphere of a dew point temperature of 63 DEG C formed by simultaneously charging 50% hydrogen, 50% nitrogen and 1% dry ammonia gas, 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 1.

C content
(weight%) Residual carbon amount in annealing of hot rolled sheet
(weight %) Amount of residual carbon after first recrystallization annealing [ppm] Magnetic flux density (B10, Tesla) Iron loss
(W17 / 50, W / kg) division 0.065 0.035 5 1.95 0.88 Comparative Example 1 0.095 0.051 8 1.96 0.84 Inventory 1 0.15 0.054 11 1.96 0.83 Inventory 2 0.22 0.063 10 1.96 0.85 Inventory 3 0.35 0.106 59 1.85 1.17 Comparative Example 2

As shown in Table 1, the inventive example in which the carbon content was controlled to 0.85 to 0.3 wt.%, Which falls within the range of the present invention, has a very high iron loss and magnetic flux density and has a very high magnetic property compared with the comparative example great. In particular, the comparative material having a carbon content exceeding 0.3 wt% can be seen to have a considerable heat loss. This is because the decarburization is not sufficiently caused by the excess carbon content.

3.38%, C: 0.14%, Mn: 0.105%, S: 0.0051%, N: 0.0057%, Sol. A slab of a grain-oriented electrical steel sheet containing 0.026% of Al and the balance of Fe and other inevitably incorporated impurities was heated at a temperature of 1190 캜 for 210 minutes and then 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 ° C or higher, then held at 910 ° C for 90 seconds, quenched in water and pickled, and decarburized in an oxidizing atmosphere at the same time as annealing 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.

The cold-rolled steel sheet was heated in the furnace at a temperature of 855 DEG C for 150 seconds in a mixed atmosphere of a dew point temperature of 63 DEG C formed by simultaneously charging 50% hydrogen, 50% nitrogen and 1% dry ammonia gas, 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.

Annealing of hot rolled sheet
Residual carbon content
(weight %) Amount of residual carbon after first recrystallization annealing [ppm] Magnetic flux density (B10, Tesla) Iron loss
(W17 / 50, W / kg) division 0.0012 5 1.92 0.93 Comparative Example 3 0.051 8 1.96 0.84 Honorable 4 0.012 261 1.81 1.02 Comparative Example 4 0.14 600 1.65 1.51 Comparative Example 5

In Table 2, as in Comparative Example 3, when the amount of decarburization during annealing of the hot-rolled steel sheet is excessively excessive, the formation of shear band due to carbon during cold rolling is weakened and the accumulation of strain energy is decreased. Thus, the exact goss fraction The effect of increasing the magnetic properties is reduced. Therefore, when the amount of decarburization is too small when the hot-rolled steel sheet is annealed, the decarburization becomes insufficient at the time of the first recrystallization, and the magnetism becomes extremely dull.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the exemplary embodiments or constructions. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. will be.

It is therefore to be understood that the above-described embodiments are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (11)

(% By weight), Si: 0.0 to 0.30%, C: 0.085 to 0.30%, acid-soluble Al: 0.015 to 0.04%, Mn: not more than 0.20%, N: not more than 0.010%, and S: not more than 0.010% And a balance Fe and other inevitably incorporated impurities;
Reheating the slab;
Subjecting the reheated slab to hot rolling and then annealing the hot rolled sheet including decarburization in an oxidizing atmosphere;
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 heating step of raising the temperature at an average heating rate lower than the average heating rate in the rapid heating step after the rapid heating step; And
A step of final annealing the primary recrystallized annealed cold rolled steel sheet
Wherein the method comprises the steps of: The method of 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 the decarburization annealing temperature. 3. The method of claim 2,
Wherein the hot-rolled sheet annealing is performed by heating the hot-rolled sheet at 900 to 1200 占 폚 and maintaining the hot-rolled sheet at 850 to 1100 占 폚 in an oxidizing atmosphere. 3. The method of claim 2,
Wherein the three-step heating is performed by an induction heating method. 5. The method according to any one of claims 1 to 4,
The decarburization amount in the hot-rolled sheet annealing is 0.02 to 0.25 wt%. The method of claim 5,
Wherein the amount of carbon remaining in the steel sheet after annealing the hot-rolled steel sheet is 0.04 wt% or more. 5. The method according to any one of claims 1 to 4,
Wherein the cold rolling step comprises cold rolling the hot rolled annealed sheet twice or more while cold rolling or intermediate annealing is performed one time 5. The method according to any one of claims 1 to 4,
And performing a treatment for increasing the nitrogen content in the steel sheet between the cold rolling and the final annealing. 9. The method of claim 8,
Wherein the treatment for increasing the nitrogen content is performed by simultaneous decarboxylation. The method of claim 9,
Wherein the average primary recrystallized grain size of the steel sheet before the final annealing after the primary recrystallization annealing is 18 to 30 占 퐉 and the ratio of the standard deviation of the grain size distribution to the average grain size of the primary recrystallized grains is 0.80 or less. Steel plate manufacturing method. A directional electrical steel sheet produced by any one of claims 1 to 4.

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