KR20140010477A - Oriented electrical steel sheets and method for manufacturing the same - Google Patents

Abstract

The present invention relates to an oriented electrical steel sheet and a method for manufacturing the same. The oriented electrical steel sheet consists of 2.0 to 4.5 wt% of silicone (Si), 0.001 to 0.10 wt% of carbon (C), 0.010 wt% or less of aluminum (Al), 0.08 wt% or less of manganese (Mn), 0.005 wt% or less of nitrogen (N), 0.002 to 0.050 wt% of sulfur (S), 0.001 to 0.15 wt% of niobium (Nb), remainder iron (Fe), and other inevitable impurities.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a directional electric steel sheet,

The present invention relates to a grain-oriented electrical steel sheet and a method of manufacturing the same, and more particularly grain-oriented segregation of sulfur (S) and FeA precipitate and NbN precipitate by using the primary recrystallized grain growth inhibited grain-oriented electrical steel sheet and its It relates to a manufacturing method.

Generally, the grain 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, Is a soft magnetic material having excellent magnetic properties.

In general, a oriented electrical steel sheet having excellent magnetic properties has a strongly developed Goss texture of {110} <001> orientation in the rolling direction of the steel sheet. There should be abnormal grain growth by subsequent recrystallization. This abnormal grain growth occurs when normal grain growth, unlike normal grain growth, is inhibited by the movement of grain boundaries that normally grow by precipitates, inclusions, or elements that are dissolved or segregated at grain boundaries. As such, precipitates and inclusions that inhibit grain growth are specifically referred to as "crystal growth inhibitors" (inhibitors), and research on the production of grain-oriented electrical steel sheet by secondary recrystallization of {110} <001> azimuth is a powerful grain growth inhibitor. We focused on securing excellent magnetic properties by forming secondary densities with high density for the {110} <001> direction.

In the past, almost all steel companies that manufacture grain-oriented electrical steel sheets mainly used AlN, MnS [Se], etc., as a grain growth inhibitor, and used a manufacturing method of causing secondary recrystallization.

The method for producing a grain-oriented electrical steel sheet using AlN and MnS precipitates as a grain growth inhibitor has the advantage of stably causing secondary recrystallization, but in order to exhibit a strong grain growth inhibitory effect, the precipitates are distributed very finely and uniformly on the steel sheet. You have to. In order to uniformly distribute the fine precipitates, the slab is heated to a high temperature of 1300 ° C. or more for a long time before hot rolling, so that coarse precipitates existing in the steel are dissolved, and then hot rolling is performed in a very fast time to prevent precipitation. Hot rolling must be completed at. To this end, a large-scale slab heating facility is required, and in order to suppress precipitation as much as possible, the hot rolling and winding processes are strictly controlled, and the precipitates employed in the hot rolled sheet annealing process after hot rolling are managed to be finely deposited. This follows. In addition, when the slab is heated to a high temperature, as the Fe ₂ SiO ₄ having a low melting point is formed, a slab washing phenomenon occurs, thereby lowering the error rate.

Along with the above problems, the method for producing a grain-oriented electrical steel sheet using AlN or MnS precipitate as a grain growth inhibitor for secondary recrystallization is followed by purifying annealing for 20 hours or longer at a high temperature of 1200 ° C. to remove the constituents of the precipitate after completion of the secondary recrystallization. This is accompanied by the complexity and cost burden of the manufacturing process.

In addition, attempts were made to utilize various precipitates such as TiN and VN as grain growth inhibitors, but failed to form stable secondary recrystallization due to thermal instability and excessively high precipitate decomposition temperature.

In order to solve the above problems, the present invention effectively suppresses the growth of primary grains due to grain boundary segregation and precipitates, thereby stably forming secondary recrystallization in the {110} <001> azimuth. To provide a manufacturing method.

In one or more embodiments of the present invention, in weight percent (wt%), Si: 2.0-4.5%, C: 0.001-0.10%, Al: 0.010% or less, Mn: 0.08% or less, N: 0.005% or less, S: 0.002-0.050%, Nb: 0.001-0.15%, the balance may be provided with a grain-oriented electrical steel sheet made of Fe and other unavoidable impurities.

In one or more embodiments of the present invention, the electrical steel sheet may include NbN precipitates and FeS precipitates.

In one or more embodiments of the present invention, in weight percent (wt%), Si: 2.0-4.5%, C: 0.001-0.10%, Al: 0.010% or less, Mn: 0.08% or less, N: 0.005% or less, S: 0.002-0.050%, Nb: 0.001-0.15%, balance reheating the slab made of Fe and other unavoidable impurities; Hot rolling the reheated slab; Subjecting the hot rolled sheet produced by hot rolling to two or more cold rollings including one cold rolling or intermediate annealing; Decarbonization and nitride annealing of the cold rolled cold rolled plate; And a second recrystallization annealing of the decarburized and nitrided annealed steel sheet may be provided.

In one or more embodiments of the present invention, the method may further include performing a hot rolled sheet annealing after the hot rolling step. The hot rolled sheet annealing step may include heating at a temperature of 900 ° C. or higher. In the step, characterized in that the decarburized steel sheet is carried out in a mixed gas atmosphere of ammonia and hydrogen.

In addition, in one or more embodiments of the present invention, the decarbonization annealing step is performed at a temperature of 750 ° C. or more, characterized in that the carbon content in the steel sheet is reduced to 0.005% by weight or less, and the annealing step is , Made in the range of 700 ~ 950 ℃ and characterized in that the nitrogen content in the steel sheet to satisfy the 0.005 ~ 0.03 weight percent, the decarbonized annealing and nitride annealing, either decarbonized annealing and nitride annealing independently or at the same time And nitriding annealing.

In one or more embodiments of the present invention, the second recrystallization annealing step may include performing a pure annealing in a range of 1000 to 1200 ° C., and the cold rolling step is performed at a temperature of 100 ° C. or more. do.

According to an embodiment of the present invention, grain boundary segregation of S and Nb occurs and stably secondary recrystallization using FeS and NbN precipitates reduces the amount of Al-based precipitates and oxides on the secondary recrystallized steel sheet, thereby preventing magnetic migration. By minimizing the directional electrical steel sheet having an extremely low iron loss can be manufactured at low cost and efficiently.

1 is a TEM photograph of the NbN observed in the specimen of the embodiment according to the present invention.
2 is an EDS photograph of the specimen of FIG. 1.

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

Example according to the present invention is a weight percent (wt%), Si: 2.0 ~ 4.5%, C: 0.001 ~ 0.10%, Al: 0.010% or less, Mn: 0.08% or less, N: 0.005% or less, S: 0.002 0.050%, Nb: 0.001-0.15%, the balance relates to a grain-oriented electrical steel sheet made of Fe and other inevitable impurities.

In the embodiment according to the present invention, the slab having the composition is heated to produce the grain-oriented electrical steel sheet, followed by hot rolling, followed by annealing or omitting a hot rolled sheet, followed by one cold rolling or intermediate annealing. After two or more cold rollings, decarburization is followed by annealing after nitridation or by nitridation for decarburization and NbN formation through simultaneous denitrification, followed by secondary recrystallization annealing.

The slab contains Nb of 0.001% or more, S of 0.001% or more, and the secondary recrystallization annealing is carried out by denitrification and then nitrification or co-denitrification treatment to raise the temperature to a temperature of 1000 ° C. or higher, thereby causing secondary recrystallization. Cracking is done within 10 hours in the temperature range of 1000 ~ 1200 ℃.

In the embodiment according to the present invention, without using AlN and MnS precipitates as grain growth inhibitors, grain growth is suppressed by using FeS precipitates produced by reacting with Fe while S is segregated at grain boundaries. The secondary recrystallization of the {110} <001> direction was stably generated, and at the same time, Al precipitates and oxides were minimized in the steel sheet after the final high temperature annealing, thereby making it possible to manufacture a grain-oriented electrical steel sheet having low iron loss.

In addition, Nb is added to solid solution in the steel sheet to hinder the movement of the grain boundary to promote secondary recrystallization of grains having a Goss orientation, and at the same time react with the nitrogen present in the steel or the nitrogen ions introduced into the steel sheet to form NbN. By forming, the growth of primary recrystallized grains was suppressed to facilitate formation of secondary recrystallized grains in the Goss orientation.

As described above, when the elements forming AlN and MnS precipitates are excluded and the grain boundary segregation elements S and Nb are added, when Al-containing precipitates and oxides are commonly used in steel sheets on which secondary recrystallization is completed, Significantly less than the occurrence frequency of Al-containing precipitates and oxides can improve the iron loss characteristics compared to the case of using a conventional AlN-based precipitates as grain growth inhibitors.

The S is known as an element segregating at the grain boundary, which induces central segregation during casting and promotes cracking during hot rolling deformation, thereby inducing S to be uniformly distributed without segregation in the center of the general grain-oriented electrical steel sheet. In order to add a certain amount of carbon (C) is used. In addition, S reacts with Mn to form MnS precipitate in the general grain-oriented electrical steel sheet manufacturing process, and the formed MnS precipitate acts as a grain growth inhibitor and is used to refine the grain size.

However, in order to distribute the MnS precipitate finely and uniformly, the slab must be heated to a high temperature of 1300 ° C. or higher, and annealing must be performed at a high temperature of 1200 ° C. for a long time to decompose coarsely grown MnS after secondary recrystallization high temperature annealing.

The present invention minimizes the amount of Mn so that MnS precipitates are hardly formed in order to compensate for the above problems. As a result, S is segregated at grain boundaries alone in a state in which S does not react with Mn, and FeS precipitates are formed to form primary recrystallized grains. By actively inhibiting growth, secondary recrystallization in the {110} <001> orientation was caused.

In addition, in the embodiment according to the present invention, Fe precipitates and grain boundaries made by adding only S by suppressing the growth of primary recrystallized grains by forming NbN by reacting with nitrogen ions introduced into the steel sheet in the process after cold rolling by adding Nb It is possible to obtain a greater inhibitory force than the grain growth inhibitory force due to segregation, and to obtain better magnetic properties through stable secondary recrystallization.

When Nb is added as described above, NbC is formed by reacting with carbon in the steelmaking step, but the residual carbon content remains below 0.01% during the decarbonization annealing process after cold rolling. At this time, the remaining carbon is present in the form of NbC, but when nitrogen ions are introduced into the steel sheet using a method of adding nitrogen simultaneously with decarbonization, for example, NH 3 gas, NbN is precipitated. The amount of NbN precipitation increases as the added nitrogen content increases and plays an important role in inhibiting primary recrystallization.

In the embodiment according to the present invention, the steelmaking step refers to the slab manufacturing step up to the step before the heat treatment. That is, the steps before hot rolling.

Although the solid solution temperature of the NbN varies depending on the content of the added nitrogen ions, all of them may be decomposed during secondary recrystallization hot annealing by inducing coupling with the nitrogen ions within the solid solution at 1200 ° C. or lower. Nitrogen (gas) in the NbN is removed into the hydrogen gas atmosphere in the high temperature annealing process for secondary recrystallization, Nb is in a solid solution state does not significantly affect the magnetic properties.

On the other hand, Nb remaining after reacting with nitrogen exists in the grains and grain boundaries, and finally exhibits the same effect as S by suppressing the movement of the primary recrystallized grain boundary.

In the embodiment according to the present invention by the principle as described above it is possible to improve the magnetic properties of the grain-oriented electrical steel sheet.

Hereinafter, the reason for component limitation of the component system in the Example which concerns on this invention is demonstrated.

Hereinafter, unless otherwise indicated, the content means weight percent (wt%).

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. If the Si content is less than 2.0%, the resistivity decreases, the iron loss characteristics deteriorate, and there is a phase transformation section at high temperature annealing, so the secondary recrystallization becomes unstable. If the content exceeds 4.5%, cold rolling becomes extremely difficult due to the brittleness of the steel. The content of C for containing 40% or more of the austenite fraction is greatly increased, and secondary recrystallization is unstable. Therefore, in the embodiment according to the present invention, Si is limited to 2.0 to 4.5%.

Al: 0.010% or less

Since Al combines with nitrogen in steel to form AlN precipitates, in the embodiment according to the present invention, Al content is suppressed to avoid Al-based nitride or oxide formation. When the content of acid-soluble Al exceeds 0.010%, AlN and Al ₂ O ₃ formation is promoted, thereby increasing the annealing time to remove it, and oxides such as Al ₂ O ₃ remain in the final product to increase the coercivity. Therefore, in order to increase the iron loss, according to the embodiment of the present invention, the content of acid-soluble Al in the steelmaking step is limited to 0.010% or less.

Mn: 0.08% or less

Mn has the effect of reducing the iron loss by increasing the specific resistance similar to Si. Conventionally, the main purpose of the addition of Mn was to suppress grain growth by forming MnS precipitates by reacting with S in steel, but in the embodiment of the present invention, grain growth segregation and FeS precipitation suppression effect are obtained. It is desirable to actively suppress the content of Mn. Therefore, the ideal method is to not add Mn, but if it is inevitably added during the steelmaking process, the addition amount is preferably limited to 0.08% or less.

If Mn is added in excess of 0.08%, MnS is coarse precipitated, so only S has a poor effect of grain boundary segregation, and FeS is difficult to precipitate, and even though secondary recrystallization is formed using MnS precipitate in subsequent purifying annealing process. Since MnS takes a long time to decompose and may remain as a precipitate in the final product, which may cause an increase in iron loss, the content of Mn in the embodiment according to the present invention is limited to 0.08% or less.

N: 0.005% or less

N reacts with Al, Si, and Nb to form precipitates such as AlN, Si ₃ N ₄ , NbN, and the like. By controlling the acid-soluble Al content low, formation of AlN is actively suppressed. In the case of Si ₃ N ₄ , it is possible to affect grain growth, but Si ₃ N ₄ precipitates have a decomposition temperature of about 800 ° C. and do not significantly affect secondary recrystallization due to grain boundary segregation of S. However, when a large amount of N is added in the steelmaking step, NbN precipitates are formed coarsely, and thus it is difficult to use as a primary recrystallization growth inhibitor. In the embodiment according to the present invention, the content of N is less than 0.005% in the steelmaking step. It is limited.

C: 0.001-0.1%

C is an austenite stabilizing element, which induces phase transformation at a temperature of 900 ° C. or higher, thereby miniaturizing the coarse columnar tissue generated in the process of playing, and suppressing Slab slab segregation. 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. Therefore, there is no big restriction on the amount of addition, but if it is contained less than 0.001%, the effect of phase transformation and hardening cannot be obtained, and when it is added more than 0.1%, hot rolled edge-crack occurs, and decarburization is performed during decarbonization after cold rolling. Since the process load occurs, the amount of C added in the embodiment according to the present invention is limited to 0.001 ~ 0.1%.

S: 0.002-0.05%

S is a key element of the present invention, which does not react with other elements alone, segregates at grain boundaries, and simultaneously reacts with Fe at grain boundaries to form FeS precipitates, thereby strongly inhibiting the movement of grain boundaries, thereby increasing the strength of the {110} <001> azimuth. Enable re-determination. Ideally, pure S is present at grain boundaries and S is required to form FeS as 0.002 ~ 0.05%. However, if Mn is mixed and contained, MnS is formed and remaining S S is added in an amount of 0.005% or more in the steelmaking step so that the content is at least 0.002% or more.

Therefore, S is added in 0.002 to 0.05%, and more preferably in the range of 0.005 to 0.05%. If S is added less than 0.002% or does not react with MnS and S alone is less than 0.002%, grain boundary segregation or precipitate effect is insufficient, and if it is added more than 0.05%, hot brittleness is applied in hot rolling step. Hot-rolling becomes difficult due to edge-cracking caused by the cracks.

In addition, when S is added in a range of 0.005 to 0.05% in the steelmaking step, S remains in the final product, and the content of S remaining in the final product is more than 0.0005wt%. S is naturally removed from the steel plate by H ₂ S gas after reacting with hydrogen atmosphere gas after forming the secondary recrystallization in the final annealing process, but it is not removed in a large amount as in the case of long annealing at 1200 ° C. Therefore, some remain. The remaining S is mainly present at the grain boundaries and does not adversely affect the magnetic properties of the final product.

The characteristic of the S is one of the important reasons to enable the present invention, S is at least 0.0005wt% remaining in the final product, the maximum S residual content is not particularly limited because it depends on the hot annealing method.

Nb: 0.001-0.15%

Nb is a representative solid solution strengthening element and is an effective element for delaying recrystallization from phase transformation and strain structure, and it is an element that significantly lowers the movement of grain boundaries in the solid solution state or when it segregates at grain boundaries. In addition, it is an element that is very effective in forming NbC or NbN precipitates to suppress the movement of grain boundaries. In the present invention, in order to suppress the growth of grains by segregating alone or generating precipitates as in S, crystal growth inhibition effect may be obtained only by adding 0.001% or more. In addition, NbC reacted with carbon present in the steelmaking process with 0.15% added is very coarse, making it difficult to effectively remove carbon in the decarbonization annealing process. The effect of inhibiting primary recrystallized grain growth by NbN precipitates is reduced so that NbC is present in the steel sheet. Therefore, the amount of Nb added in the embodiment according to the present invention is limited to 0.001 ~ 0.15%.

In addition to the alloying elements described above, other alloying elements may be added as long as they do not inhibit grain boundary segregation of Nb and S or grain growth inhibiting effect of FeS and NbN precipitates.

Hereinafter will be described a method for producing a grain-oriented electrical steel sheet excellent in the magnetic properties of the embodiment according to the present invention.

In the embodiment according to the present invention, it is necessary to manage the content of Al, which is an AlN precipitate and an oxide forming element, as low as possible in the steelmaking step, and in order to form a lot of grain boundary segregation and FeS precipitates of S, the precipitation of MnS should be suppressed as much as possible. do. To this end, it is necessary to control the Mn content as low as possible, and in addition to the addition of Si to increase the specific resistance, the addition of C for the tissue homogenization, and the addition of S necessary to obtain crystal growth inhibitory ability, if necessary, {110} <001> It is also possible to add an alloying element which is advantageous for forming the texture.

In the embodiment according to the present invention, Si: 2.0 to 4.5%, C: 0.001 to 0.10%, Al: 0.010% or less, Mn: 0.08% or less, N: 0.005% or less, S: 0.002 to 0.050%, Nb : 0.001 ~ 0.15%, balance is made of slab using molten steel composed of Fe and other inevitable impurities.

Then, the slab is heated, the heating of the slab in the embodiment according to the invention is made in a temperature range of 1050 ~ 1280 ℃. The slab is heated within the above temperature range and then hot rolled. In the final cold rolling step, a hot rolling of 1.5 to 4.0 mm thickness is performed by hot rolling to apply a rolling rate of 50 to 95% to produce a final product thickness. Manufacture into plates.

The hot rolled hot rolled sheet is subjected to cold rolling without performing hot rolled sheet annealing or hot rolled sheet annealing as necessary. In the case of performing hot-rolled sheet annealing, in order to make the hot-rolled structure uniform, it is heated to a temperature of 900 ° C or higher, cracked for a suitable time, and then cooled. At this time, the hot rolled sheet annealing is preferably not higher than the hot rolling temperature.

The cold rolling is then cold rolled two or more times including one cold rolling or intermediate annealing using a reverse mill or tandem rolling mill to produce a cold rolled sheet having a final product thickness. It is advantageous to improve the magnetic properties by performing warm rolling to maintain the temperature of the steel sheet at 100 ° C. or higher during cold rolling.

After cold rolling, decarbonization annealing is carried out. The decarbonization annealing is maintained at a temperature of at least 750 ° C. for at least 30 seconds in a mixed gas atmosphere of hydrogen and nitrogen gas containing moisture so that carbon content of the steel sheet is approximately 0.005. Decreases below%. If the carbon content is not reduced below 0.005%, NbN formation by nitrogen ions added in the subsequent process becomes unstable, and thus does not serve as a desired primary recrystallization growth inhibitor in the present invention.

Therefore, the decarburization process is preferably carried out for 30 seconds or more in a mixed gas atmosphere of hydrogen and nitrogen containing water at a temperature of 750 ℃ or more capable of decarburization.

In an embodiment according to the present invention, in order to form NbN together with decarbonization annealing, a nitriding annealing process of adding nitrogen ions to the steel sheet is required. By holding at least 700 seconds at a temperature of at least 700 ° C. under a mixed hydrogen and nitrogen atmosphere, NbN is formed by nitrogen ions added to the steel sheet.

At this time, in the annealing process, the nitrogen content in the steel sheet is 0.005 to 0.03 weight percent. If the nitrogen content is less than 0.005 weight percent, the effect of adding nitrogen is negligible, and if the nitrogen content exceeds 0.03 weight percent, it causes problems in surface quality. In other words, if the nitrogen content exceeds 0.03% by weight, some of the nitrogen must be removed, and the base coating is destroyed during the release of nitrogen, which causes surface defects. In addition, the brittleness is increased to easily break the steel sheet in the embodiment according to the invention in the decarbonization annealing process so that the content of nitrogen to 0.005 ~ 0.03 weight percent.

The annealing temperature, the gas ratio of the hydrogen, nitrogen and NH mixed gas and the nitriding time are controlled so that the nitrogen content of the steel sheet is 0.005 to 0.03 weight percent.

Nitride annealing temperature using NH gas in the embodiment according to the present invention is controlled in the range of 700 ~ 950 ℃. If the annealing temperature is lower than 700 ℃, NH ₃ gas is not decomposed may cause work environment problems, on the contrary, if it exceeds 950 ℃ NH ₃ gas does not react with the steel sheet is degraded to reduce the nitriding effect.

Such annealing may be performed separately from the decarbonization annealing, or decarburization and nitride annealing may be simultaneously performed in the same annealing furnace.

After decarburization and nitride annealing, MgO, an annealing separator, is applied and secondary recrystallization annealing is performed. Secondary recrystallization high temperature annealing may be performed by raising the temperature at an appropriate temperature increase rate to cause secondary recrystallization of the {110} <001> Goss orientation, followed by purifying annealing, which is a process of removing impurities, and then cooling. In the decarburization and nitride annealing process, the annealing atmosphere gas may be heat-treated using a mixture of hydrogen and nitrogen in an elevated temperature process as in a normal case, and a method of removing impurities using 100% hydrogen gas in a pure annealing process may be applied. have.

In the present invention, since AlN and MnS precipitates are not used as the main grain growth inhibitor, the burden of purifying annealing for decomposing and removing AlN and MnS is alleviated, and it is sufficient that the purifying annealing temperature is about 1000 ° C or more. This is because FeS and NbN start to decompose at about 1000 ° C. In addition, when the annealing exceeds 1200 ° C., the steel sheet becomes soft and the shape deformation may occur due to its own weight. Therefore, in the embodiment of the present invention, the temperature during the annealing is limited to the range of 1000 to 1200 ° C.

The time required for the annealing depends on the annealing temperature, but it is possible to produce a grain-oriented electrical steel sheet having extremely excellent magnetic properties only by cracking within 20 hours, more preferably within 1 hour at a temperature of about 1000 to 1200 ℃. have.

According to the embodiment according to the present invention, the slab is not more than 1300 ℃ in order to solidify the AlN and MnS precipitates by the strong grain growth inhibitory effect by grain boundary segregation of S and Nb and NbN and FeS precipitates without using AlN, MnS precipitates It does not need to be heated at high temperature for a long time, and after the cold rolling process, by adding additional nitrogen to the steel sheet to form NbN, S and Nb and FeS and NbN complexly inhibit the growth of primary recrystallized grains, thereby maintaining a stable Goss orientation. Secondary recrystallization can be formed. In addition, FeS has a very low melting point of 1194 ° C, which makes it possible to reduce the {110} <001> secondary recrystallization initiation temperature to about 1000 ° C. At temperatures above 1000 ° C, FeS and NbN are easily decomposed during purifying annealing. The discharge of can be made very easily.

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

Electricity containing different amounts of Nb to the basic composition of C: 0.055%, Si: 3.35%, Mn: 0.03%, S: 0.014%, N: 0.003% by weight, and other Fe and other unavoidable impurities The steel sheet was vacuum melted to make an ingot, heated to a temperature of 1250 ° C., and hot rolled to a thickness of 2.3 mm. The hot rolled hot rolled plate was heated to a temperature of 1100 ° C., cracked for 180 seconds, cooled, pickled, and cold rolled to a thickness of 0.30 mm. The cold rolled plate was maintained at a temperature of 830 ° C. for 180 seconds in a humid hydrogen and nitrogen mixed gas atmosphere to perform decarburization and nitriding annealing.

The decarburized and nitrided steel sheet was finally annealed onto a coil by applying MgO, an annealing separator. The final annealing was performed in a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, the annealing was carried out at 100% hydrogen atmosphere for 5 hours and then the furnace was cooled.

Table 1 shows the change in magnetic properties according to the Nb content in the composition and the total nitrogen of the steel sheet by nitriding treatment.

Changes in Magnetic Properties of Oriented Electrical Steels According to Nb and N Contents [Unit wt%] C Si Mn S Nb Total N Magnetic flux density
(B10) Iron loss
(W17 / 50) division 0.055 3.35 0.03 0.014 0.0007 0.0098 1.891 1.09 Comparison 1 0.055 3.34 0.03 0.015 0.005 0.0165 1.921 0.91 Inventory 1 0.055 3.35 0.03 0.014 0.015 0.0135 1.935 0.92 Inventory 2 0.055 3.31 0.03 0.015 0.022 0.0218 1.947 0.90 Inventory 3 0.055 3.32 0.03 0.015 0.055 0.0152 1.930 0.95 Invention 4 0.055 3.32 0.03 0.013 0.081 0.0324 1.842 1.18 Comparative material 2 0.055 3.35 0.03 0.014 0.150 0.0195 1.918 0.94 Invention Article 5 0.055 3.33 0.03 0.014 0.250 0.0051 1.839 1.21 Comparative material 3 0.055 3.31 0.03 0.015 0.320 0.0042 1.644 1.92 Comparison 4

As can be seen in Table 1, both the magnetic flux density and the iron loss were excellent in the case of the invention material in which the Nb content was controlled to 0.001 to 0.15% of the range of the embodiment according to the present invention.

Comparative material 1 used the grain boundary segregation effect of S and FeS precipitates in the state in which Nb was added 0.0007%, and the effect of Nb was almost insignificant. Inventive materials 1 to 5 show improved magnetic properties than that of comparative material 1. 1 is a TEM photograph of the NbN observed in the specimen of Inventive Material 1 and FIG. 2 is an EDS photograph of the Inventive Material 1, referring to FIGS. 1 and 2, it can be seen that NbN is finely and uniformly distributed. .

On the other hand, when the Nb content of 0.15% or more is added, the decarburization process causes a load, and thus, more than 0.005% of the desired nitrogen cannot be added to the steel sheet, resulting in unstable secondary recrystallization and deterioration of magnetic properties. Therefore, it is preferable to control the Nb content to 0.15% or less and the total nitride content to 0.03% or less.

In the embodiment according to the present invention in order to find out the effect of the grain boundary segregation element on the grain growth as described above by vacuum melting the ingot of the component system to exclude the elements forming the precipitate and to add the grain boundary segregation element S in various contents We investigated the possibility of secondary recrystallization. As a result, secondary recrystallization of {110} <001> azimuth was stably formed when S was added in an appropriate amount with Mn limited, and 0.94 (W / kg) or less with a magnetic flux density of 1.90 (Tesla) or more. It was confirmed that excellent iron loss characteristics of.

In addition, NbN, which is added to the core component system and precipitated by nitrogen ions through nitriding treatment, was able to improve magnetic flux density and iron loss by more strongly inhibiting crystal growth of primary recrystallized grains together with FeS precipitates.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand.

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 (13)

By weight percent (wt%), Si: 2.0 to 4.5%, C: 0.001 to 0.10%, Al: 0.010% or less, Mn: 0.08% or less, N: 0.005% or less, S: 0.002 to 0.050%, Nb: 0.001 -0.15%, the balance is a grain-oriented electrical steel sheet composed of Fe and other inevitable impurities. The method of claim 1,
The electrical steel sheet is a grain-oriented electrical steel, characterized in that it comprises NbN precipitates and FeS precipitates. By weight percent (wt%), Si: 2.0 to 4.5%, C: 0.001 to 0.10%, Al: 0.010% or less, Mn: 0.08% or less, N: 0.005% or less, S: 0.002 to 0.050%, Nb: 0.001 ~ 0.15%, balance reheating the slab made of Fe and other unavoidable impurities;
Hot rolling the reheated slab;
Subjecting the hot rolled sheet produced by hot rolling to two or more cold rollings including one cold rolling or intermediate annealing;
Decarbonization and nitride annealing of the cold rolled cold rolled plate; And
Performing a second recrystallization annealing of the decarburized and nitrided steel sheet;
Wherein the method comprises the steps of: The method of claim 3,
The method of claim 1, further comprising performing a hot rolled sheet annealing after the hot rolling. The method according to claim 3 or 4,
In the annealing step,
Method for producing a grain-oriented electrical steel sheet characterized in that the decarburized steel sheet is carried out in a mixed gas atmosphere of ammonia and hydrogen. The method of claim 5,
The nitride annealing step,
Method for producing a grain-oriented electrical steel sheet, characterized in that made in the range of 700 ~ 950 ℃. The method according to claim 6,
The annealing step, the method for producing a grain-oriented electrical steel sheet characterized in that the nitrogen content in the steel sheet to satisfy 0.005 ~ 0.03 weight percent. The method of claim 3,
The decarbonization step,
Method for producing a grain-oriented electrical steel sheet characterized in that carried out at a temperature of 750 ℃ or more. 9. The method of claim 8,
The decarbonization step,
A method for producing a grain-oriented electrical steel sheet, characterized in that the carbon content in the steel sheet is reduced to 0.005 weight percent or less. The method of claim 3,
The decarburization and nitride annealing step,
Method for producing a grain-oriented electrical steel sheet characterized in that the de-carbon annealing and nitride annealing is carried out independently or the de-carbon annealing and nitride annealing at the same time. The method of claim 3,
The second recrystallization annealing step,
Method for producing a grain-oriented electrical steel sheet comprising the step of performing a pure annealing in the range of 1000 ~ 1200 ℃. The method of claim 3,
The cold rolling step is a grain-oriented electrical steel sheet manufacturing method characterized in that carried out at a temperature of 100 ℃ or more. 5. The method of claim 4,
The hot rolled sheet annealing step,
Method for producing a grain-oriented electrical steel sheet comprising the step of heating at a temperature of 900 ℃ or more.

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