KR20140084897A - Oriented electrical steel steet and method for manufacturing the same - Google Patents

Abstract

The present invention relates to an oriented electrical steel sheet and a method to manufacture the same. The oriented electrical steel sheet includes: 2.0-4.5 wt% of silicon (Si), 0.001-0.10 wt% of carbon (C), 0.001-0.010 wt% of aluminum (Al), 0.001-0.08 wt% of manganese (Mn), 0.0005-0.005 wt% of nitrogen (N), 0.001-0.050 wt% of sulfur (S), 0.005-0.2 wt% of copper (Cu), and the remainder consisting of iron (Fe) and inevitable impurities. The sulfur (S) is separately segregated in a grain boundary of the steel sheet, or at least one among FeS or Cu_2S precipitate is applied as a secondary grain growth restrainer.

Description

TECHNICAL FIELD [0001] The present invention relates to a directional electric steel sheet and a method of manufacturing the same. BACKGROUND ART < RTI ID = 0.0 &

The present invention relates to a directional electrical steel sheet and a method of manufacturing the same, and more particularly, to a method of manufacturing a grain oriented electrical steel sheet using a secondary recrystallization of {110} < 001 > orientation by utilizing the effect of inhibiting primary recrystallization growth of grain boundaries of S and FeS precipitates. To a directional electric steel sheet having excellent magnetic properties and a method of manufacturing the same.

The oriented electrical steel sheet has a so-called goss texture in which the orientation of all the grains on the steel sheet face is {110} plane and the crystal orientation in the rolling direction is parallel to the <001> axis, It is an excellent soft magnetic material. In general, the magnetic properties can be expressed by the magnetic flux density and the iron loss, and the high magnetic flux density can be obtained by precisely aligning the orientation of the crystal grains in the {110} < 001 > orientation.

The electric steel sheet having a high magnetic flux density not only makes it possible to reduce the size of the iron core material of the electric equipment, but also reduces the hysteresis loss, thereby making it possible to miniaturize the electric equipment and increase the efficiency at the same time. Iron loss is a power loss consumed by thermal energy when an arbitrary alternating magnetic field is applied to the steel sheet. It is largely changed depending on the magnetic flux density and plate thickness of the steel sheet, the amount of impurities in the steel sheet, resistivity and secondary recrystallization size, The higher the specific resistivity and the lower the plate thickness and the impurity content in the steel sheet, the lower the iron loss and the higher the efficiency of the electric equipment.

Generally, a directional electric steel sheet having excellent magnetic properties is required to strongly develop a goss texture in the {110} < 001 > orientation in the rolling direction of the steel sheet. In order to form such a texture, It is necessary to perform an abnormal crystal growth called recrystallization. Unusual crystal growth occurs when normal crystal growth is inhibited from migration of grains which normally grow by precipitates, inclusions, or elements that are dissolved or segregated in the grain boundaries, unlike ordinary grain growth. As described above, precipitates and inclusions that inhibit grain growth are specifically referred to as crystal grain growth inhibitors. Studies on the production of grain oriented electrical steel sheets by secondary recrystallization in the {110} < 001 & Has been focused on securing good magnetic properties by forming secondary recrystallization with high degree of integration in the {110} < 001 > orientation.

MnS was used as a grain growth inhibitor in the directional electric steel sheet which was initially developed and was manufactured by cold rolling two times. Thereafter, a method of producing a grain-oriented electrical steel sheet by using a combination of AlN and MnS precipitates and then performing cold rolling once at a cold rolling rate of 80% or more.

In recent years, nitriding has been carried out after one strong cold rolling without using MnS, and then nitrogen is supplied to the inside of the steel sheet through a separate nitriding process using ammonia gas. A method of producing a grain-oriented electrical steel sheet for causing recrystallization of tea has been proposed in Japanese Patent Publication No. 1-230721 and Japanese Patent Publication No. 1-283324.

The directional electric steel sheet manufacturing method using such AlN and MnS precipitates as crystal grain growth inhibitors has an advantage of stably inducing secondary recrystallization. However, in order to exhibit a strong grain growth inhibiting effect, the precipitates are distributed finely and uniformly on the steel sheet . In order to uniformly distribute the fine precipitates in this manner, the slab is heated at a high temperature of 1300 DEG C or more for a long time before the hot rolling to solidify coarse precipitates present in the steel and then hot rolled in a very short time, The hot rolling must be completed.

This requires a large amount of slab heating equipment. In order to minimize precipitation, it is necessary to control the hot rolling and winding process very strictly and to control the precipitation of dissolved precipitates in the hot- . In addition, when the slab is heated at a high temperature, the slab washing phenomenon occurs due to the formation of Fe ₂ SiO ₄ having a low melting point, thereby reducing the water content.

Along with the above-mentioned problems, a method of producing a directional electric steel sheet in which secondary recrystallization is caused by using AlN or MnS precipitates as a crystal grain growth inhibitor, requires a long period of 30 hours or more at a high temperature of 1200 ° C in order to remove precipitate components after completion of secondary recrystallization The complexity and the cost burden of the manufacturing process which requires annealing should follow.

By this refinement annealing, MnS precipitates are separated into Mn and S, Mn is dissolved in the steel, S diffuses to the surface and reacts with hydrogen gas in the atmosphere to form H ₂ S and is discharged.

Recently developed cold rolling, after the decarburization annealing, the secondary recrystallization is formed by the AlN-based nitride precipitate through the nitriding treatment. The slab low temperature heating technique is used to produce slab heating temperature of 1200 ° C or less, And problems such as a decrease in the error rate at the hot rolling stage have been greatly improved. However, this method also fails to overcome the problem of complexity and cost burden of the manufacturing process, which requires the annealing annealing for a long time at a high temperature of 1200 ° C for 20 hours or more in order to remove constituents of the AlN precipitate after completion of the second recrystallization.

After AlN-based precipitates are decomposed into Al and N in the refining annealing process, Al is moved to the surface of the steel sheet and reacted with oxygen in the surface oxidation layer to form Al ₂ O ₃ oxides. The Al- AlN precipitates not decomposed during the annealing process interfere with the movement of the magnetic domains in the steel sheet or near the surface, thereby deteriorating the iron loss.

Therefore, in order to further improve the magnetic properties of the grain-oriented electrical steel sheet and reduce the burden of the annealing annealing to improve the productivity, a technique for manufacturing a new grain-oriented electrical steel sheet which does not use a precipitate such as AlN or MnS as a grain growth inhibitor was required.

In order to solve the above-mentioned problems, the present invention uses S and FeS precipitates segregated in the grain boundaries alone as a main grain growth inhibitor, and enhances the magnetic properties by reinforcing the suppression ability of S and FeS by using Cu ₂ S precipitates And the deformation is added to the steel sheet through temper rolling after decarburization annealing to accelerate the secondary recrystallization so as to shorten the time for performing the high temperature annealing, and to provide a method for producing the same.

In one or more embodiments of the present invention, it is preferable that Si: 2.0-4.5%, C: 0.001-0.10%, Al: 0.001-0.010%, Mn: 0.001-0.08%, N: 0.0005-0.005% : 0.001 to 0.050%, and Cu: 0.005 to 0.2%, and the slab comprising the remainder Fe and other impurities is heated, hot-rolled, hot-rolled sheet annealed or omitted, and then cold- The steel sheet is subjected to two or more cold rolling steps including annealing and then to decarburization and primary recrystallization annealing and then subjected to temper rolling to impart a deformation of 10% or less to the steel sheet through temper rolling, followed by secondary recrystallization annealing A steel plate manufacturing method can be provided.

Wherein at least one of S segregated at grain boundaries of the steel sheet during the secondary recrystallization annealing and FeS and Cu2S precipitates is used as a grain growth inhibitor.

The secondary recrystallization annealing is performed at a temperature of 1000 占 폚 or less within one hour, and at least one of Ti, Mg, and Ca is contained in an amount of 0.005% by weight or less.

After the secondary recrystallization annealing, the annealing is further performed within a period of one hour at a temperature of 1000 to 1200 ° C, and the deformation amount is 1 to 5%.

In one or more embodiments of the present invention, it is preferable that the steel sheet contains 2.0 to 4.5% of Si, 0.001 to 0.10% of C, 0.001 to 0.010% of Al, 0.001 to 0.08% of Mn, 0.0005 to 0.005% of N, , 0.001 to 0.050% of S, 0.005 to 0.2% of Cu, and the balance of Fe and other impurities, wherein at least one of Ti, Mg and Ca is contained in an amount of 0.005% A steel sheet may be provided.

Wherein the number of inclusions and precipitates containing Al, Si, Mg, Ca and Ti in the steel sheet is 0.01 to 500 pieces / mm 2, the magnetic flux density B 10 of the steel sheet is 1.90 or more, (W17 / 50) is 0.95 or less.

The B10 is a magnitude (Tesla) of the magnetic flux density induced when a magnetic field of 1000 A / m is added, and the iron loss (W17 / 50) is the rolling direction when magnetic flux density of 1.7 Tesla is induced at 50 Hz frequency, (W / kg) in the vertical direction.

Further, the steel sheet is characterized in that S is contained in an amount of 0.005% or more.

According to the embodiment of the present invention, as the crystal grain growth inhibitor necessary for the formation of the secondary recrystallization, while the content of Mn forming the Al-based oxide or the precipitate and the Mn forming the MnS precipitate are positively minimized, Secondary recrystallization can be stably formed by suppressing strong crystal growth by using single grain boundary segregation, FeS and Cu ₂ S precipitates.

In addition, the steel sheet is subjected to temper rolling prior to the secondary recrystallization annealing to impart deformation of less than 10% to the steel sheet, thereby accelerating the secondary recrystallization, thereby shortening the high temperature annealing step for forming the secondary recrystallization, .

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below. 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.

In order to solve the above-described problems, an embodiment according to the present invention is characterized in that, in weight%, 2.0 to 4.5% of Si, 0.001 to 0.10% of C, 0.001 to 0.010% of Al, 0.001 to 0.08% of Mn, 0.005 to 0.0050%, S: 0.001 to 0.050%, and Cu: 0.005 to 0.2%, and the balance Fe and other inevitably incorporated impurities is heated, hot rolled, then hot rolled sheet annealed or omitted And then performing cold rolling twice or more including cold rolling or intermediate annealing, and then performing decarburization and primary recrystallization annealing, followed by temper rolling. The present invention also provides a method for producing a directional electrical steel sheet.

Further, by applying a deformation of 10% or less through the temper rolling to the steel sheet and performing secondary recrystallization annealing within 1 hour, a low iron loss directional electrical steel sheet having excellent productivity can be produced.

In addition to the above-mentioned composition, the grain-oriented electrical steel sheet after completion of the high-temperature annealing has an inclusions such as oxides including Al, Si, Mg, Ca and Ti and the number of precipitates of 0.01 to 500 pieces / mm ² , A directional electrical steel sheet exhibiting magnetic properties is provided.

Hereinafter, embodiments according to the present invention will be described in more detail.

In the conventional directional electrical steel sheet production technology, precipitates such as AlN and MnS are used as crystal grain growth inhibitors. In all processes, the distribution of the above precipitates is strictly controlled and the precipitates remaining in the secondary recrystallized steel sheet are removed Process conditions are extremely constrained by the conditions.

However, in the embodiment of the present invention, various alloying elements, impurities, and precipitates thereof are used as a grain growth inhibitor so as to stably induce secondary recrystallization without using AlN or MnS precipitates as a grain growth inhibitor, A method for manufacturing a directional electrical steel sheet is disclosed.

For this purpose, in the embodiment of the present invention, S, which is a grain boundary grain source, is segregated in grain boundaries alone, and the second grain recrystallization in {110} < 001} orientation is stably caused by suppressing grain growth by using FeS precipitates A directional electrical steel sheet having extremely low iron loss by minimizing Al precipitates and oxides in a steel sheet after final high temperature annealing.

That is, in order to investigate the influence of the grain boundary segregation element on the grain growth in the embodiment according to the present invention, the ingot of the component system in which the elements forming the precipitate are added and the grain boundary segregation element S is added in various amounts, As a result of investigation of the possibility of secondary recrystallization by dissolution, secondary recrystallization of {110} <001> direction was stably formed when S was added in an appropriate amount while Mn addition was restricted and magnetic flux density (B ₁₀₎ together with it was confirmed the fact that securing the excellent iron loss (W _17/50), the following properties 0.95 (W / kg). Wherein B ₁₀ is a magnitude (Tesla) of magnetic flux density induced when a magnetic field of 1000 A / m is added, and the iron loss (W 17/50) is a rolling direction and a rolling direction when magnetic flux density of 1.7 Tesla is induced at ₅₀ Hz frequency (W / kg) in the vertical direction.

Further, in the embodiment according to the present invention, when a component system excluding elements forming AlN and MnS precipitates is used, in the case where the frequency of occurrence of Al-containing precipitates and oxides in the secondary recrystallized steel sheet is usually in the case of using a component system using AlN- It is confirmed that the generation rate of the Al-containing precipitates and the oxides is significantly lower than that of the conventional AlN-based precipitates, which is superior to the conventional case of using the AlN-based precipitates as the crystal grain growth inhibitors.

It has already been known that S is an element segregating in the grain boundary, and segregation occurs at the grain boundaries due to center segregation during the solidification process, thereby promoting cracking during high temperature deformation, thereby causing difficulty in hot rolling. In addition, S reacts with about 0.08 ~ 0.2% of Mn in the general directional steel sheet manufacturing process to form MnS precipitates, and the formed MnS precipitates act as crystal grain growth inhibitors and are used to miniaturize the grain size.

However, in order to distribute the MnS precipitates finely and uniformly, the slab must be heated to a high temperature of 1300 DEG C or higher and annealed at a high temperature of 1200 DEG C for a long time so that coarse MnS can be decomposed after the secondary recrystallization annealing at high temperature.

Therefore, in order to solve the above problems, a large amount of carbon is used in the steelmaking step in order to induce the S to be uniformly distributed without being segregated at the center during production of the slab of the grain-oriented electrical steel sheet, By suppressing the fracture and minimizing the content of Mn so that MnS precipitate is hardly formed, S is segregated in the grain boundary alone or in the state of not reacting with Mn to form FeS precipitate, thereby positively suppressing the growth of crystal grains, The second recrystallization in the {110} < 001 > orientation is caused to occur.

That is, it is not necessary to heat the slab for a long time at a high temperature in order to solidify the AlN and MnS precipitates by exerting the effect of inhibiting the grain growth by the grain boundary segregation and the FeS precipitate of S alone without using the AlN and MnS precipitates, It is possible to lower the {110} < 001 > secondary recrystallization start temperature to 1000 DEG C or less by using a low melting point FeS at 1194 DEG C, A method of manufacturing a grain-oriented electrical steel sheet which does not require a long-term annealing annealing at a temperature of 100 占 폚 is established.

In addition, in the embodiment according to the present invention, when Cu is added to the S-component system, Cu ₂ S is precipitated, and the segregation effect of S is further enhanced, and the crystal growth inhibiting power of the FeS precipitate is further strengthened, And at the same time excellent magnetic properties can be ensured.

On the basis of the above results, when the deformation within 10% is added to the steel sheet through temper rolling before the secondary recrystallization high-temperature annealing, the secondary recrystallization forming temperature is lowered, and the secondary recrystallization high- It can be shortened to within one hour.

Hereinafter, the reason for limiting the components according to the embodiment of the present invention will be described.

Unless otherwise stated, the unit of component content is% by weight.

Si: 2.0 to 4.5%

Si is a basic composition of an electric steel sheet, and plays a role of lowering the core loss, that is, the iron loss, by increasing the resistivity of the material. When the Si content is less than 2.0%, the resistivity decreases and the iron loss characteristic deteriorates. In the high temperature annealing, the second phase recrystallization becomes unstable due to the presence of the phase transformation section. When the Si content exceeds 4.5%, the brittleness of the steel becomes excessively large. The content of C for containing an austenite fraction of 40% or more is greatly increased, and the formation of secondary recrystallization becomes unstable. Therefore, Si in the embodiment according to the present invention is limited to 2.0 to 4.5%.

Al: 0.001 to 0.010%

Al bonds with nitrogen in the steel to form AlN precipitates. Therefore, in the embodiment according to the present invention, the Al content is positively suppressed to avoid formation of Al-based nitride or oxide. If the content of acid soluble Al exceeds 0.010%, the formation of AlN and Al ₂ O ₃ is promoted, and the annealing annealing time for removing the AlN and Al ₂ O ₃ is increased. The inclusions such as AlN precipitates and Al ₂ O ₃ , It will remain in the product and increase the coercive force to increase the iron loss. Therefore, the content of acid soluble Al in the low-temperature step is positively suppressed to 0.010% or less. Therefore, the content of Al in the examples according to the present invention is limited to 0.001 to 0.010%.

Mn: 0.001 to 0.08%

Although Mn has an effect of increasing specific resistance and decreasing iron loss by the same as that of Si, the main object of the additive claimed in the conventional patent was to react with S in the steel to form MnS precipitates to suppress grain growth. However, in the embodiment according to the present invention, since the MnS precipitate is not used as the crystal grain growth inhibitor, it is preferable to positively suppress the Mn content. A very ideal method is to limit the addition amount to 0.08% or less if Mn is not added or inevitably added in the steelmaking process. When Mn is added in an amount exceeding 0.08%, MnS is precipitated, so that the effect of S segregation by grain boundaries is deteriorated and FeS precipitation becomes difficult. Further, even if the secondary recrystallization is formed by using MnS precipitates, it takes a long time to decompose MnS in the subsequent annealing step, and it may remain as a precipitate in the final product to increase iron loss. Therefore, the content of Mn is 0.08% or less . Therefore, the content of Mn in the examples according to the present invention is limited to 0.001 to 0.08%.

N: 0.0005 to 0.005%

N is an element which reacts with Al to form AlN and Si ₃ N ₄ precipitates. Therefore, the formation of AlN should be positively suppressed by positively suppressing the content of acid soluble Al. In the case of Si ₃ N ₄ , the precipitate decomposition temperature is around 800 ° C., which has no effect of suppressing the crystal growth of the primary recrystallized grains and does not greatly affect the formation of secondary recrystallization due to grain boundary segregation of S. However, when the content of N is large, AlN is formed by reaction with Al, which is unavoidably present in the steel, or when segregation occurs at the grain boundaries alone, it affects the grain boundary segregation of S. Therefore, the content of N is 0.005% or less . Therefore, in the embodiment of the present invention, the content of N is limited to 0.0005 to 0.005%.

C: 0.001 to 0.10%

C is an austenite stabilizing element, which causes phase transformation at a temperature of 900 ° C or higher, and thereby suppresses the slab center segregation of S in addition to the effect of refining the coarse columnar structure occurring during the performance. In addition, it promotes work hardening of the steel sheet during cold rolling, thereby promoting generation of secondary recrystallization nuclei in the {110} < 001 > orientation in the steel sheet. However, when the content is less than 0.001%, the effect of phase transformation and work hardening can not be obtained. When the content is more than 0.1%, occurrence of hot-edge-crack occurs, The amount of C added in the embodiment according to the present invention is limited to 0.001 to 0.10%.

S: 0.001 to 0.050%

S is a core element of the present invention, which enables the secondary recrystallization of the {110} < 001 > orientation by suppressing the movement of the grain boundaries by forming FeS or Cu ₂ S precipitates in the grain boundaries at the grain boundaries. Ideally, S should be added in an amount of 0.002 to 0.05% as a pure S content alone or in order to form FeS and Cu ₂ S. Inevitably, however, when S is incorporated by incorporation, MnS is formed And S is added in an amount of 0.005% or more in the steelmaking step so that the content of remaining S is at least 0.002% or more. Therefore, S is added in the range of 0.002 to 0.05%, and more preferably 0.005 to 0.05%. If S is added in an amount less than 0.002% or S does not react with MnS and the amount of S present alone is less than 0.002%, the effect of grain boundary segregation or precipitate is insufficient. If it is added in excess of 0.05% The hot-rolling operation becomes difficult due to occurrence of edge-crack due to the hot-rolling.

In addition, when S is added in the range of 0.005 to 0.05% in the steelmaking step, S remains in the final product, and the residual S content in the final product is 0.0005% by weight or more. S reacts with H ₂ atmosphere gas after forming secondary recrystallization in the final annealing step and is naturally removed from the steel sheet by H ₂ S gas, but is not removed in large amounts as in the case of the conventional long-time annealing at 1200 ° C., Depending on the method.

The residual S is mainly present in the grain boundary and does not adversely affect the magnetic properties of the final product. The S characteristic is one of the important reasons for enabling the present invention. In the final product, S remains at least 0.0005 wt% or more, and the maximum S residual amount differs depending on the high temperature annealing method.

Therefore, the content of S in the examples according to the present invention is limited to 0.001 to 0.050%.

Cu: 0.005 to 0.2%

Cu, together with S, is a key element of the present invention, and plays an important role in stably forming secondary recrystallization by reacting with S to form Cu ₂ S, thereby suppressing crystal growth together with FeS. It is also an extremely effective additive element from the viewpoint of maximizing the effect of adding S by forming Cu ₂ S before the Mn reacts with S in the steel to form MnS. If Cu is added in an amount of at least 0.005% or more, fine Cu ₂ S precipitation can be caused. If it is added in an amount exceeding 0.2%, all of the S added in the steel reacts, The grain growth inhibiting power is rather weakened and the desired secondary recrystallization can not be obtained.

Further, excessive Cu addition prevents an decarburization reaction by forming an oxide layer on the surface layer during decarburization to prevent secondary recrystallization itself. Therefore, the content of Cu in the examples according to the present invention is limited to 0.005 to 0.2%.

In the embodiment according to the present invention, other alloying elements may be added as long as they do not inhibit the effect of inhibiting grain growth of grain boundary segregation of S or FeS and Cu ₂ S precipitates in addition to the alloying elements.

 That is, Se, P, Sn, Sb, Bi, and B are added to form precipitates together with the grain boundaries, thereby exhibiting crystal grain growth restraining ability.

In addition, components such as Ti, Mg, and Ca react with oxygen in the steel to form oxides. Therefore, it is necessary to strongly inhibit the components. Therefore, the content of these components is limited to 0.005% or less in the examples of the present invention.

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

In order to achieve the object according to the embodiment of the present invention, it is necessary to control the content of AlN precipitate and Al, which is an oxide forming element, to be as low as possible in the steelmaking step. In order to form a large amount of Cu ₂ S, the precipitation of MnS should be suppressed as much as possible. For this purpose, it is necessary to control the content of Mn as low as possible. Moreover, precipitation of MnS should be suppressed as much as possible by forming Cu ₂ S prior to MnS by Cu addition.

Pb, Sn, and Sb, which are advantageous for {110} <001> texture formation as needed, in addition to the addition of C for enhancing the resistivity and the addition of C for grain uniformity, , Bi and B may be added. The molten steel whose composition is adjusted in the steelmaking process is made into a slab through continuous casting. The subsequent heating of the slab may be performed by setting the heating temperature of the slab so as not to interfere with the heating conditions of the slab of the other steel type. In the embodiment of the present invention, the heating of the slab is performed at a temperature range of 1050 to 1300 ° C.

First, in terms of% by weight, Si: 2.0 to 4.5%, C: 0.001 to 0.10%, Al: 0.001 to 0.010%, Mn: 0.001 to 0.08%, N: 0.0005 to 0.005% 0.005 to 0.2% of the remainder Fe and other inevitably mixed impurities are heated to a predetermined temperature and then subjected to hot rolling and subjected to final cold rolling at a final rolling thickness of 50 to 95% Hot-rolled steel sheets are manufactured from 1.5 to 4.0 mm thick hot-rolled sheets.

The hot-rolled hot-rolled sheet is subjected to hot-rolled sheet annealing as required or cold-rolled without hot-rolled sheet annealing. In the case of annealing the hot-rolled sheet, the hot-rolled sheet is heated to a temperature of 900 ° C or more to uniform the hot-rolled structure, and is then cooled for a predetermined time and cooled.

Thereafter, the cold rolling is carried out by using a reverse mill or a tandem mill so as to produce a cold rolled sheet having a final product thickness by two or more cold rolling processes including one cold rolling or intermediate annealing. At this time, warm rolling in which the temperature of the steel sheet is maintained at 100 占 폚 or higher during cold rolling is advantageous for improving the magnetic properties.

After cold rolling, decarburization annealing is performed. The carbon decontamination can be reduced to about 0.0030% or less by maintaining the steel at a temperature of 750 ° C or more for 30 seconds or longer so that decarburization can be easily caused. At the same time, an appropriate amount of oxide layer is formed on the surface of the steel sheet. In addition to the decarburization annealing, the deformed cold-rolled structure is recrystallized and the crystal grains are grown to a proper size. At this time, the decarburization annealing temperature and the cracking time are adjusted so that the size of the primary recrystallized grain grows by 5 μm or more.

After decarburization and primary recrystallization annealing, MgO, which is an annealing separator, is usually applied and secondary recrystallization annealing is performed. However, in the embodiment of the present invention, after the secondary recrystallization annealing, 10% To the steel sheet, thereby promoting the formation of the secondary recrystallization, and significantly shortening the high temperature annealing time of the secondary recrystallization from 30 hours to 1 hour.

Generally, when the steel sheet subjected to the first recrystallization is subjected to temper rolling within 10%, the crystal grains of the cube and the Goss bearing having the lowest strain energy encroach upon the grains of the other bearing having high strain energy, Organic crystal growth occurs. Using this phenomenon, a strain of less than 10% is added in order to accelerate the crystal grains of Goss orientation to cause secondary recrystallization more quickly.

If a deformation greater than 10% is added, the crystal grains are largely deformed in the original orientation, so that they can not maintain the original crystal orientation and cause recrystallization, which adversely affects the secondary recrystallization of the Goss orientation. In addition, deformation of less than 1% is insufficient to maximize the strain energy difference of the crystal grains, and does not affect the secondary recrystallization promotion, but it is not difficult to form secondary recrystallization securing good magnetic properties. Therefore, in the embodiment according to the present invention, the amount of deformation applied to the steel sheet by temper rolling is limited to 10% or less, more preferably 1 to 5%, in order to promote secondary recrystallization.

As described above, when the steel sheet is subjected to temper rolling with a strain of less than 10% through the temper rolling before the secondary recrystallization annealing, the secondary recrystallization becomes lower by about 50 캜 than the normal temperature and the secondary recrystallization occurs very quickly. According to this phenomenon, it is possible to shorten the annealing time within one hour in the heat treatment method in which the secondary recrystallization annealing is cracked in the conventional batch type annealing furnace for 30 hours or more, It is possible to perform recrystallization.

The second recrystallization high-temperature annealing in the embodiment according to the present invention raises the temperature at a temperature increase rate of 10 ° C / hr or more to cause secondary recrystallization in the {110} <001> Goss orientation. After that, Rough and then cooled. Since the precipitates such as AlN and MnS are not used as the crystal grain growth inhibitors in the embodiment of the present invention, the conventional annealing annealing time of about 30 hours is not necessary. S reacts with hydrogen gas, which is an annealing atmosphere gas, and is easily removed by H ₂ S, so that it does not remain in the vicinity of the shortening annealing time to affect the magnetic properties. Therefore, it is sufficient to set the annealing temperature to 1000 deg. C or higher. The time required for the annealing annealing depends on the annealing annealing temperature. However, the annealing annealing can be performed at a temperature of about 1000 to 1200 deg. A directional electrical steel sheet can be produced.

Hereinafter, the present invention will be described in more detail with reference to examples.

[Example 1]

The ingot was prepared by vacuum melting a component system consisting of C, Si, Mn, S, and Cu and the balance Fe or other inevitably incorporated impurities of the contents shown in the following Table 1 and then heating the ingot to a temperature of 1250 캜 And then hot rolled to a thickness of 2.8 mm. The hot-rolled hot-rolled sheet was heated to a temperature of 900 ° C and then cracked for 180 seconds to anneal the hot-rolled sheet. The hot-rolled steel sheet was then cooled, pickled, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 0.30 mm. The cold-rolled steel sheet was subjected to decarburization and recrystallization heat treatment at a temperature of 810 ° C for 180 seconds in a mixed gas atmosphere of wet hydrogen and nitrogen. The decarburized and primary recrystallized steel sheet was subjected to temper rolling to impart a 2% deformation amount to the steel sheet, and then MgO as the annealing separator was applied and finally annealed in a coiled state. The final annealing was performed under a mixed atmosphere of 25% nitrogen and 75% hydrogen until 1200 ° C. After reaching 1200 ° C, it was cracked in a 100% hydrogen gas atmosphere for 1 hour and then cooled. The magnetic properties of the oriented electrical steel sheet according to the change of the Cu content were measured and are shown in Table 1 below.

As can be seen in Table 1, inventive materials 1 to 9, in which the Cu content was added in the range of 0.005 to 0.2% in the range of the examples according to the present invention, were excellent in magnetic flux density and iron loss. However, the comparative material 1 could not obtain the effect of suppressing the growth of grains due to Cu ₂ S precipitates due to low Cu content, and the magnetism was weakened.

When the Cu content exceeds the range of the present invention as in comparative material 2, the S content added to the steel reacts with Cu to form Cu ₂ S, thereby interfering with the segregation of S and FeS precipitation, The recrystallization itself was difficult and the magnetism was weakened.

                   Variation of Magnetic Properties of Orientated Electrical Sheets with Variation of Cu Content C Si Mn S Cu Al N Magnetic flux density
(B ₁₀ ) Iron loss
(W _17/50) division 0.052 3.3 0.0050 0.015 0.001 0.0030 0.0020 1.895 1.08 Comparison 1 0.054 3.3 0.0103 0.012 0.007 0.0015 0.0029 1.921 0.98 Inventory 1 0.060 3.3 0.0160 0.020 0.012 0.0028 0.0029 1.933 0.93 Inventory 2 0.041 3.3 0.0095 0.015 0.028 0.0041 0.0035 1.923 0.94 Inventory 3 0.055 3.3 0.0180 0.025 0.058 0.0018 0.0044 1.942 0.91 Invention 4 0.058 3.3 0.0210 0.010 0.070 0.0032 0.0029 1.953 0.90 Invention Article 5 0.050 3.3 0.0430 0.018 0.082 0.0028 0.0033 1.938 0.91 Inventions 6 0.065 3.3 0.0393 0.028 0.103 0.0015 0.0038 1.929 0.93 Invention 7 0.056 3.3 0.0559 0.035 0.128 0.0023 0.0027 1.921 0.94 Invention 8 0.071 3.3 0.0630 0.030 0.151 0.0035 0.0043 1.938 0.92 Invention 9 0.050 3.3 0.0760 0.023 0.225 0.0033 0.0042 1.818 1.39 Comparative material 2

[Example 2]

And the balance Fe, and other inevitably incorporated impurities, containing 0.056% of C, 3.25% of Si, 0.005% of Al, 0.003% of N, 0.003% of Mn, 0.030% of S and 0.05% The ingot was heated to a temperature of 1250 캜, and hot-rolled to a thickness of 2.3 mm.

The hot-rolled hot-rolled sheet was heated to a temperature of 1100 ° C, cracked for 180 seconds, and annealed in hot-rolled sheet. The cold-rolled steel sheet was then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 0.23 mm. The cold-rolled steel sheet was then held at a temperature of 830 ° C for 180 seconds in a mixed gas atmosphere of wet hydrogen and nitrogen, followed by decarburization and recrystallization heat treatment Respectively. The decarburized and primary recrystallized steel sheet was subjected to tempering at a maximum of 30% using temper rolling, followed by secondary recrystallization and high temperature annealing. In the second recrystallization high temperature annealing, the mixed atmosphere of 50% nitrogen + 50% hydrogen was set to 1200 ° C at a heating rate of 100 ° C / hr. After reaching 1200 ° C, the furnace was kept in a 100% . Table 2 shows the magnetic properties of the oriented electrical steel sheet subjected to high temperature annealing for one hour according to the deformation amount by the temper rolling.

As shown in Table 2, when the amount of deformation due to temper rolling is within 10%, excellent magnetic properties can be secured through the one-hour high-temperature annealing process. However, when a deformation amount of 10% or more is added, the crystal grains of other orientations besides the secondary recrystallization of the Goss orientation are also subjected to secondary recrystallization, and the magnetic properties are greatly deteriorated.

 Change of magnetic properties of oriented electrical steel sheet by deformation amount by temper rolling Deformation due to temper rolling Magnetic flux density (B ₁₀ ) _Iron loss (W _17/50 ) division 0 % 1.912 0.99 Inventions 10 1.0% 1.924 0.97 Invention invention 11 2.1% 1.941 0.96 Invention 12 3.0% 1.938 0.95 Invention invention 13 5.0% 1.927 0.94 Invention Article 14 7.0% 1.914 0.97 Invention material 15 9.0% 1.919 0.98 Invention material 16 12% 1.878 1.19 Comparative material 3 15% 1.846 1.22 Comparison 4 20% 1.806 1.35 Comparative material 5

As described above, according to the embodiment of the present invention, it is possible to secure excellent magnetic properties by forming secondary recrystallization of stable Goss orientation based on strong segregation of Fe due to precipitation of FeS and Cu ₂ S along with segregation of S At the same time, the secondary recrystallization is promoted by adding a deformation amount within 10% to the steel sheet prior to the secondary recrystallization annealing, and secondary recrystallization annealing can be performed within 1 hour, thereby maximizing the productivity.

While the present invention has been described in connection with certain exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. 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)

0.001 to 0.00% of Al, 0.001 to 0.08% of Mn, 0.0005 to 0.005% of N, 0.001 to 0.050% of S, 0.001 to 0.050% of Cu, 0.2%, and the remaining slab comprising Fe and other impurities is heated, followed by hot rolling, hot rolling annealing, or omission, followed by two or more cold rolling steps including cold rolling or intermediate annealing once After performing decarburization and primary recrystallization annealing,
A method for producing a directional electric steel sheet in which a steel sheet is subjected to tempering with a deformation of less than 10% through temper rolling, followed by secondary recrystallization annealing. The method according to claim 1,
Wherein at least one of S segregated at grain boundaries of the steel sheet during the secondary recrystallization annealing and FeS and Cu ₂ S precipitates is used as a grain growth inhibitor. 3. The method according to claim 1 or 2,
Wherein the secondary recrystallization annealing is performed at a temperature of 1000 占 폚 or less within 1 hour. The method of claim 3,
Ti, Mg, or Ca is contained in an amount of 0.005 wt% or less, respectively. The method according to claim 1,
Wherein after the secondary recrystallization annealing, the annealing is further carried out at a temperature of 1000 to 1200 占 폚 within one hour. The method according to claim 1,
Wherein the deformation amount is 1 to 5%. 0.001 to 0.00% of Al, 0.001 to 0.08% of Mn, 0.0005 to 0.005% of N, 0.001 to 0.050% of S, 0.001 to 0.050% of Cu, 0.2%, and the balance Fe and other impurities,
Ti, Mg, or Ca in an amount of 0.005 wt% or less, respectively. 8. The method of claim 7,
Wherein the number of inclusions and precipitates containing Al, Si, Mg, Ca and Ti in the steel sheet is 0.01 to 500 pieces / mm ² . 9. The method according to claim 7 or 8,
And the magnetic flux density (B ₁₀ ) of the steel sheet is 1.90 or more.
Here, B ₁₀ is the magnitude of the magnetic flux density (Tesla) induced when a magnetic field of 1000 A / m is added. 9. The method according to claim 7 or 8,
_Wherein an iron loss (W _17/50 ) of the steel sheet is 0.95 or less.
However, it is the iron loss (W _17/50) is the average loss (W / kg) in the rolling direction and the direction perpendicular to the rolling direction when the magnetic flux density in 1.7Tesla at 50Hz frequency organic. 8. The method of claim 7,
Wherein the steel sheet contains S in an amount of 0.005% or more.