KR20120008189A - Method for manufacturing grain-oriented electrical steel sheets with extremely low core-loss and high flux-density - Google Patents

Abstract

PURPOSE: A method for manufacturing a grain-oriented electrical steel sheet with low core loss and high magnetic flux density is provided to improve magnetic properties by improving the thermal stability of an inhibitor. CONSTITUTION: A method for manufacturing a grain-oriented electrical steel sheet with low core loss and high magnetic flux density is as follows. A silicon steel slab, comprising C 0.10-0.30 weight%, Si 2.0-4.5 weight%, Al 0.05-0.040 weight%, Mn less than 0.20 weight%, N less than 0.010 weight%, S less than 0.010 weight%, P 0.005-0.05 weight%, Sn 0.08-0.10 weight%, residual Fe, and inevitable impurities, is heated and hot-rolled. The hot-rolled slab is annealed and cold-rolled. The slab is decarburized and nitrified. The slab is secondly annealed.

Description

Method for manufacturing grain-oriented electrical steel sheets with extremely low core-loss and high flux-density

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of grain-oriented electrical steel sheets used as iron core materials for electronic devices such as generators and transformers. The present invention relates to a method for manufacturing a low iron loss high magnetic flux density oriented electrical steel sheet having an extremely good magnetic property due to an increase in nucleation of goth aggregate tissue.

A grain-oriented electrical steel sheet exhibits a Goss texture having a texture of {110} <001> with respect to the rolling direction, and is a soft magnetic material having excellent magnetic properties in one direction or in the rolling direction. To express this goth aggregate structure, various processes such as component control in steelmaking stage, slab reheating and hot rolling process factor control in hot rolling, hot plate annealing, primary recrystallization annealing, and secondary recrystallization annealing are very precise and stringent. Should be managed.

On the other hand, one of the factors expressing goth aggregates, the inhibitor (Inhibitor), that is, the control of grain growth inhibitors to suppress the indiscriminate growth of primary recrystallization and to allow only the goth aggregates to grow when secondary recrystallization occurs. It is important. After the second recrystallization annealing, to obtain a final steel sheet having good goth aggregate structure, the growth of all primary recrystallization grains should be suppressed until just before the second recrystallization occurs. In order to achieve sufficient restraining force, the amount of inhibitor must be large enough, and the distribution must be uniform. In addition, in order for secondary recrystallization to occur during the high temperature secondary recrystallization annealing (final annealing), the thermal stability of the inhibitor should be excellent and not easily decomposed. Secondary recrystallization occurs when the inhibitor decomposes or loses restraining power at the appropriate temperature range during final annealing. In this case, specific grains such as relatively goth grains grow rapidly in a relatively short time.

In general, the quality of oriented electrical steel sheet can be evaluated by the magnetic flux density and iron loss, which are typical magnetic properties. The higher the precision of the goth assembly, the better the magnetic properties. In addition, high-quality directional electrical steel sheet is capable of manufacturing high-efficiency power equipment due to its characteristics, and thus, miniaturization of power equipment and high efficiency can be obtained.

R & D for reducing iron loss of oriented electrical steel sheet was first made for R & D to increase magnetic flux density. Initially oriented electrical steel sheets were prepared by two cold rolling using MnS suggested by M. F. Littman as grain growth inhibitor. According to this, the secondary recrystallization was stable, but the magnetic flux density was not so high and iron loss was high.

Since, Taguchi (田 口), 板倉 by using a combination of AlN, MnS precipitates, the cold rolling rate of more than 80% once cold-rolling technology has been proposed. It is a technique of obtaining a high magnetic flux density by improving the orientation of {110} <001> azimuth in the rolling direction by a strong grain growth inhibitor and cold rolling, and it is possible to obtain low iron loss characteristics by greatly improving hysteresis loss. .

On the other hand, by increasing the silicon content of the electrical steel sheet to increase the specific resistance of the steel sheet, to suppress the eddy current flowing through the steel sheet to improve iron loss, and to improve the cleanliness of the steel sheet by performing a pure annealing to remove unnecessary impurities in the steel sheet after secondary recrystallization In order to reduce iron loss by controlling the size of secondary recrystallized grains,

The method of increasing the silicon content is to improve the iron loss by adding silicon with high resistivity, but as the addition amount is increased, the brittleness of the steel sheet is greatly increased, resulting in very poor workability, and the SiO ₂ oxide layer is densely formed during decarbonization annealing. Base coating is difficult to form.

In addition, the method of removing impurities is to reduce the content of impurities by performing pure annealing at 1200 ° C for 10 hours or more using 100% hydrogen gas, but the pure annealing acts as a factor to greatly increase the manufacturing cost.

In addition, the method of controlling the size of secondary recrystallized grain is a very complicated process to control the formation of secondary recrystallization through grain growth inhibitor, cold rolling, and primary recrystallization control. No significant manufacturing technology has yet been developed. .

On the other hand, research to improve the iron loss through the method of miniaturizing the magnetic domain of the secondary recrystallized grain has been made a considerable technological development. The method of miniaturizing magnetic domains is to irradiate the surface of the steel sheet with laser to give temporary stress to the surface of the steel sheet to refine the magnetic domain of {110} <001> orientation, and to give a constant deformation to the surface of the steel sheet and to perform annealing heat treatment. There is a method of miniaturizing magnetic domains by inducing structural changes. This method of finer micronization requires the additional finer micron treatment on the final product after the final secondary recrystallization annealing, thus increasing the manufacturing cost.

In general, the technique of reducing the thickness of the steel sheet is a method of reducing the eddy current loss, which is one of the representative components of iron loss by causing deformation during cold rolling. However, in this case, the crystal growth driving force is increased, and the original crystal growth inhibitor does not suppress the crystal growth driving force, and thus there is a problem that the secondary recrystallization becomes unstable.

To reduce the thickness while balancing the crystal growth and crystal growth inhibitory force, rolling must be performed at the appropriate cold rolling rate during final cold rolling. The appropriate cold rolling rate depends on the inhibition of the crystal growth inhibitor. When using the AlN and MnS composite precipitates proposed by Taguchi as crystal growth inhibitors, the appropriate cold rolling ratio is about 87%, and when using the MnS precipitates proposed by Littman as the crystal growth inhibitors, 50 to 70% cold rolling is used. The rate is fair.

Another reason is that the secondary recrystallization is unevenly formed, and the other is that the magnetic domain width is increased due to the decrease in thickness in terms of static magnetic energy, and thus the magnetic domain movement is not easy when an arbitrary alternating magnetic field is applied.

On the other hand, in the manufacture of thin grain oriented electrical steel sheet with a steel sheet thickness of 0.1 ~ 0.25mm in order to solve the limitation of the thickness of the hot rolled sheet and to optimize the final rolling rate, the hot rolled sheet is pre-rolled at a rolling reduction of 10 to 50%, and then hot-rolled sheet annealing and steel A technique for performing cold rolling has been proposed, but in this case, two cold rolling and two recrystallization annealing create a burden of increasing manufacturing cost.

Therefore, a technique of adding B and Ti has been proposed for the purpose of reducing the manufacturing cost burden and reinforcing the weakening of crystal growth inhibition by one cold rolling.

However, in the case of the technique of adding B, it is extremely difficult to control the steelmaking step for the addition of a small amount, and it is easy to form coarse BN in the steel after the addition. In addition, Ti forms TIN and TiC. TIN and TiC remain higher after the second recrystallization because the solid solution temperature is higher than 1300 ° C, which may act to increase iron loss.

Another proposal to improve grain growth inhibition is to add a combination of Sn and Sb, and hot-rolled by slab heating at a temperature of 1200 ℃ or less, characterized in that the nitriding treatment using ammonia gas after cold rolling of more than 80% and decarbonization annealing Has been proposed a method of manufacturing a thin grain oriented electrical steel sheet of 0.23mm or less. However, this suggests a very strict manufacturing standard for manufacturing thin grain oriented electrical steel sheet, which is accompanied by hot rolling burden by 1200 ℃ slab heating in actual production, and increases the manufacturing cost and separates the decarburization and annealing in order to secure excellent magnetic properties. There is a difficulty.

On the other hand, fine AlN and MnS precipitates are distributed to suppress the increased crystal growth driving force due to cold rolling in addition to the alloy composition adjustment and multi-stage cold rolling technology for producing oriented electrical steel sheets having a steel sheet thickness of 0.23 mm or less and low iron loss and high magnetic flux density. Hot-rolled sheet annealing method that can form a has been proposed. This technique requires controlling the hot plate heating temperature according to the acid-soluble aluminum content, but the range of the control temperature is very narrow, making it difficult to manufacture easily.

In addition, as a patent for a method of manufacturing a grain-oriented electrical steel sheet of 0.23mm or less, electrostatic coating of MgO, annealing separator, three cold rolling and three vacuum annealing techniques, and work roll diameter change according to rolling thickness It has been proposed for the ultra-thin material manufacturing method by. However, these technologies are very difficult technologies that must newly accumulate additional facility investment and operation know-how in preparation for commercially available manufacturing technology, which has a disadvantage in that it is inferior in economic efficiency to quality.

On the other hand, slab heating temperature in the manufacture of grain-oriented electrical steel sheet is closely related to the solid solution temperature of AlN, MnS precipitates mainly used as grain growth inhibitors.

For example, hot slab heating is a technique in which a slab is heated to a temperature above 1300 ° C. so that AlN and MnS precipitates are completely dissolved, which means that the fully-solubilized AlN and MnS precipitates are subjected to hot rolling and subsequent hot-rolled sheet annealing. It is designed to exert a strong crystal growth inhibitory effect by allowing it to be precipitated.

This assumes that the steel sheet containing purely 3% by weight of silicon is in the ferrite phase, and the AlN solid solution can be expressed by the following equation proposed by IWAYAMA.

According to this, assuming that the acid-soluble aluminum is 0.028% by weight and N is 0.0050% by weight, the theoretical solidus temperature is 1258 ° C according to the IWAYAMA solid solubility formula, and it must be heated to about 1300 ° C to heat the slab of the electrical steel sheet. do.

However, when the slab is heated to a temperature above 1280 ℃, iron olivine (Fe ₂ SiO ₄ ; fayalite), a compound of low melting point silicon and ferrous metal, is formed on the steel sheet, and the surface of the steel sheet melts to perform hot rolling. It becomes difficult, and the molten water causes the problem of repairing the furnace.

In order to solve this problem, research and development on the technology of heating the slab to a low temperature below 1250 ℃ was in progress. For example, the slab is heated to a temperature of 1270 ° C. or lower to hot roll the grain growth inhibitor AlN without fully employing it, then completely precipitated in the hot rolled sheet annealing and nitriding in the process after cold rolling to increase the grain growth suppression ability. A technique to secure is proposed.

The low-temperature slab heating method does not use the precipitates present in the slab and hot rolling stages as inhibitors, and only the newly precipitated AlN as a crystal growth inhibitor due to the reaction of nitrogen ions in the steel by nitriding in a later process with acid-soluble aluminum. Because of the use, there is a disadvantage in that the suppression force is lower than the crystal growth driving force.

In summary, the conventional techniques discussed so far include the development of crystal growth inhibitors to secure high magnetic flux density characteristics, the silicon up-flow to secure low iron loss and the removal of impurities to increase the cleanliness of steel sheets, and the fine-graining treatment of final products. Finally, B, Ti, Sn, Sb addition, slab heating temperature and hot-rolled sheet annealing control techniques for reducing the thickness of steel sheet and reinforcing the crystal growth inhibitor were proposed. Low cost slab heating method is a factor of the increase of manufacturing cost, and the low magnetic growth inhibition capacity is limited.

The present invention has been made to solve all the problems of the prior art as described above, the object of the present invention is to improve the goose structure of the grain-oriented electrical steel sheet using high carbon-containing silicon steel slab and to improve the thermal rolling stability and thermal stability of the inhibitor The purpose of the present invention is to provide a low iron loss and high magnetic flux density oriented electrical steel sheet having extremely excellent magnetic properties and a method of manufacturing the same.

Low iron loss high magnetic flux density oriented electrical steel sheet manufacturing method of the present invention for solving the above problems by weight, C: 0.10 ~ 0.30%, Si: 2.0 ~ 4.5%, Al: 0.005 ~ 0.040%, Mn: 0.20% or less , N: 0.010% or less, S: 0.010% or less, P: 0.005 ~ 0.05%, Sn: 0.08 ~ 0.10%, high carbon containing silicon steel slab consisting of remainder Fe and other unavoidable impurities After rolling, hot rolling is performed followed by cold rolling, followed by decarburization and nitride annealing, and then secondary recrystallization annealing, wherein the hot rolled sheet annealing is performed to perform decarburization.

It is preferable that the said silicon steel slab contains Sb: 0.01-0.03% further.

The silicon steel slab is preferably contained so that Sn and Sb satisfy the following formula (1).

0.08 ≤ Sn (wt.%) + 0.3 x Sb (wt.%) ≤ 0.11 ----------------------- (Equation 1)

The method for manufacturing a grain-oriented electrical steel sheet of the present invention is characterized in that the β-angle is controlled to be less than 2.5 ° as the area weighted average of the absolute value of the crystal orientation in the secondary recrystallized steel sheet. Here, β angle is the deviation angle between the [100] direction and the rolling direction with respect to the rolling right angle direction of the secondary recrystallized texture.

According to the present invention, by using a high carbon-containing silicon steel slab to enhance the thermal stability of the inhibitor to have a strong crystal growth inhibition and at the same time to perform decarburization during hot-rolled sheet annealing {110} <001> orientation of extremely high orientation By providing the secondary recrystallization nucleus, it is possible to produce a grain-oriented electrical steel sheet having extremely excellent magnetic properties.

In addition, by adding an appropriate amount of Sn increases the fraction of the {110} goth aggregates, and reduces the aggregates that help the goth aggregates such as {111} and {411} to grow easily {110 after the final secondary recrystallization } <001> An ultra-low iron loss high magnetic flux density oriented electrical steel sheet composed of a goth aggregate structure having a very high degree of integration and a very fine grain size can be manufactured.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present inventors have conducted a number of studies and experiments on the technology to ensure that the AlN or MnS precipitates, which are grain growth inhibitors on the silicon steel ferrite, in the production of grain-oriented electrical steel sheet, so as to stably solidify and precipitate, 3% silicon steel is pure As the amount of carbon added in the ferrite region increases, the fraction of the austenite phase in the predetermined temperature range increases, so that the AlN solid solubility in the austenite phase can be improved by at least twice as high as that in the ferrite phase. Got to know.

The present inventors have studied the role of carbon as an austenite forming element and the fact that AlN has a high solubility rate and solid solution in austenite, and thus, the slab has a higher carbon content than usual, that is, at least 0.10 weight. When added up to 0.30% by weight, the fraction of austenite phase in the slab in the slab heating temperature range is 60% or more, and nitrides such as (Al, Si, Mn) N or AlN are sufficiently dissolved during slab heating. It was found for the first time that oriented electrical steel sheets with extremely good magnetic properties could be produced by increasing the nucleation site of the goth assembly by allowing decarburization to take place during the annealing of the hot rolled sheet and controlling the subsequent cooling process. .

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

According to this, when the acid-soluble aluminum is 0.028% by weight and N is 0.0050% by weight, the slab solid solution temperature is 1112 ° C (Darken) and 1002 ° C (Leslie), respectively, which is much lower than the solid solution temperature of 1258 ° C on ferrite.

Thus, the more austenite phase in the slab, the lower the AlN solution temperature is. Therefore, when a large amount of carbon is added to the slab to increase the austenite fraction, the solid solution of AlN can be maximized to secure sufficient grain growth inhibition.

As a result, by promoting the formation of the austenite phase through slab heating and hot-rolled sheet annealing, it is possible to obtain a fine AlN precipitate distribution in the steel sheet after cold rolling, and to obtain a secondary recrystallized grain having a high magnetic flux density and an advantageous low iron loss.

In addition, the amount of austenite during hot-rolled sheet annealing increases due to carbon in the hot-rolled sheet of 0.10% by weight to 0.30% by weight, which results in a heterogeneous, long-rolled hot-rolled structure generated by the previous process of hot rolling. Because of sufficient recrystallization, the heterogeneous hot-rolled microstructure is completely extinguished and composed of fine grains in all directions, so that the precipitate is uniformly dispersed and precipitated in the fine matrix, and the cold rolling is also improved, so that it is cold rolled once. It also becomes possible to roll to plate | board thickness 0.20 mm or less by this.

In addition, the hot rolled sheet is annealed in a wet atmosphere at the same time as excess carbon is removed, and the goose aggregates present in the surface layer grow deeply, and the fraction of the goose aggregates is greatly increased. It is possible to preserve the matrix structure composed of fine and homogeneous austenite and the finely dispersed precipitates present in the austenite grains or at the grain boundaries to room temperature.

On the other hand, the austenite phase undergoes a mixed transformation of hard bainite or martensite phase or two phases with high strength during the quenching process. As the strain stress increases greatly, the shear deformation band increases in the steel sheet, and the carbon remaining by hot-rolled sheet annealing with decarbonization annealing activates dislocation fastening during cold rolling, thereby increasing shear deformation band. It shows the effect of inducing an increase in nucleation.

The inside of the shear deformation zone is easily recrystallized by the grains of the {110} <001> orientation, which is the nucleus of the secondary recrystallization, so that the {110} <001> orientation texture increases in the primary recrystallization aggregate structure, and thus the secondary recrystallized { 110} <001> It is possible to secure the high magnetic flux density by increasing the density of goth aggregates, and to secure the magnetic properties of ultra low iron loss by reducing the size of secondary recrystallized grains.

In the grain-oriented electrical steel sheet of the present invention, the beta angle of the final steel sheet is 2.5 ° or less due to an increase in the nucleation site of the goth assembly structure, thereby obtaining extremely excellent magnetic properties. Here, β angle is the deviation angle between the [100] direction and the rolling direction with respect to the rolling right angle direction of the secondary recrystallized texture.

Hereinafter, the reason for component limitation of this invention is demonstrated.

Si is a basic composition of electrical steel sheet to increase the specific resistance of the material serves to lower the core loss (core loss). 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. This becomes severe and the secondary recrystallization becomes unstable. Therefore, Si is limited to 2.0 to 4.5% by weight.

Al combines with Al, Si, and Mn in solid solution in the steel in which nitrogen ions introduced by ammonia gas in the annealing process after cold rolling, in addition to AlN precipitated finely during hot rolling and hot-rolled sheet annealing (Al, By forming nitride of Si, Mn) N type, it plays a role of strong crystal growth inhibitor. If the content is less than 0.005%, sufficient effect as an inhibitor cannot be expected, and if it exceeds 0.040%, coarse AlN As a result, the crystal growth inhibitory power is lowered. Therefore, the content of Al is limited to 0.005 ~ 0.040% by weight.

Mn also has the effect of reducing the iron loss by increasing the specific resistance similar to Si, and the growth of primary recrystallized grains by forming a precipitate of (Al, Si, Mn) N by reacting with nitrogen introduced by nitriding treatment with Si It is an important element for suppressing and causing secondary recrystallization. However, when added in excess of 0.20% on the surface of the steel sheet in addition to Fe ₂ SiO ₄ as formed with a Mn Oxide is tteurige off the surface quality by interfering with the base coat is formed which is formed during high-temperature annealing. Therefore, Mn is made into 0.20 weight% or less.

N is an important element that reacts with Al to form AlN and is preferably added at 0.010% by weight or less in the steelmaking step. When added in excess of 0.01% by weight, the surface defect called Blister by nitrogen diffusion in the process after hot rolling is caused. In order to form AlN, N additionally needs to be strengthened by nitriding in steel using ammonia gas in the annealing process after cold rolling.

C is a core element of the present invention by adding carbon of 0.10% by weight or more and 0.30% by weight or less to make the austenitic fraction in the steel sheet 60% or more through hot-rolled annealing, due to the high fraction of austenite transformation By actively inducing phase transformation and recrystallization of the heterogeneous and elongated rolled structure formed by hot rolling, which is a preliminary process, the structure of the hot-rolled annealing plate can be homogeneously and finely controlled. On the other hand, by conducting decarbonization annealing at the same time as the hot rolled sheet annealing, the goth aggregate structure of the surface layer of the steel sheet grows deeply, and the goose grain size of the primary recrystallized annealing plate is increased to increase the goose density of the final annealing plate and the grain size. It can be reduced to obtain high magnetic flux density and ultra low iron loss.

In addition, the austenite phase can be transformed into a high-strength bainite phase or martensite phase through a predetermined cooling rate control. The bainite or martensite phase transformed by quenching is the austenite phase nucleation site in the hot-rolled sheet annealing process. Providing to provide a uniform and homogeneous microstructure by promoting the homogenization of the tissue during the heat treatment of the hot-rolled sheet annealing, accordingly it can make the AlN precipitate fine, and after the hot-rolled sheet annealing is quenched bainite or martensite By promoting the formation, it is possible to form a goth texture having a very high degree of orientation in the {110} <001> direction due to the concentration of strain stress during cold rolling. On the other hand, after hot-rolled annealing heat treatment, residual carbon in the steel sheet activates potential fixation during cold rolling, increases shear deformation zone, increases the generation of goth nucleus, and increases the fraction of goth grains of primary recrystallized annealing plate. do. To achieve this effect, at least 0.10% by weight of carbon must be contained in the slab. However, insufficient decarburization in the decarbonization annealing process results in deterioration of magnetic properties due to magnetic aging when the final product is applied to power equipment, and annealing of the hot rolled sheet when the slab contains more than 0.30% of carbon. When the time consumed for sufficient decarburization increases, the annealing time increases, and a thick oxide layer is formed on the surface, and as a result, a decarburization delay occurs, thereby preventing sufficient decarburization. Therefore, the content of C is preferably limited to 0.10 to 0.30% by weight.

When S is contained in excess of 0.01%, precipitates of MnS are formed in the slab to suppress grain growth, and segregation at the center of the slab during casting makes it difficult to control the microstructure in subsequent processes. In addition, in the present invention, since MnS is not used as the main grain growth inhibitor, it is not preferable to add and precipitate more than the amount in which S is inevitably added.

Sn is a grain boundary segregation element that inhibits the movement of grain boundaries. Therefore, Sn is an inhibitor that assists in inhibiting grain growth and improves the grain growth inhibition of nitrides and sulfides as main inhibitors. In particular, Sn increases the fraction of goth grains in the {110} <001> azimuth in the primary recrystallized texture, thereby increasing the number of goth-bearing nuclei that grow into the secondary recrystallized texture. Therefore, the addition of an appropriate amount of Sn reduces the size of the secondary recrystallized microstructure than that obtained in the conventional oriented electrical steel sheet, resulting in a smaller grain size in the final product, thereby reducing the eddy current loss, resulting in a more directional orientation with better magnetic properties. Electrical steel sheet can be manufactured.

As such, Sn plays an important role in suppressing grain growth through segregation at grain boundaries. More specifically, Sn improves the inhibitory effect of inhibiting the grain growth driving force of the refined primary recrystallized microstructure and increases the Si content. It also plays a role of preventing the particle having the grain growth inhibitory effect from being reduced in number to weaken the grain growth inhibitory force. In addition, Sn coarsens particles causing grain growth inhibitory effects such as (Al, Si, Mn) N and AlN during the high temperature annealing process to form secondary recrystallized texture, thereby reducing the grain growth inhibitory ability.

As a result, in the case of using slabs made of low Si content as well as using slabs made of high Si content, it is possible to ensure successful expression of secondary recrystallized texture, and to reduce the thickness of the final product for thinning. In case of upward, it compensates for the thermal instability of the grain, which is pointed out as a problem of the thin grain oriented electrical steel sheet having the grain growth suppression effect by the grain, and compensates the successful growth of the secondary recrystallized texture. Therefore, the addition of an appropriate amount of Sn can increase the fraction of goth aggregates in the primary recrystallized texture and increase the grain growth inhibition, resulting in better texture, stable grain growth inhibition, and iron loss reduction due to thinning. As a result, it is possible to secure a secondary recrystallization aggregate composed of high density Goth grains.

When the Sn content is less than 0.08% by weight, the magnetic properties are improved, but the density of goth aggregates is less enhanced and the effect of compensating grain growth inhibition by the particles present in the matrix is less. The effect is only minimal. On the other hand, when Sn is contained in excess of 0.10% by weight, the grain growth inhibitory force is excessively increased, so that the grain size of the primary recrystallized microstructure must be reduced in order to increase the grain growth driving force. As a result, it is difficult to control a proper oxide layer and thus a good surface cannot be secured. In addition, brittleness is increased due to excessive segregation of grain boundary segregation elements in terms of mechanical properties, which can cause breakage during the manufacturing process. Therefore, it is preferable to contain Sn at 0.08 to 0.10 weight%.

Sb, like Sn, has the effect of suppressing crystal growth as a grain boundary segregation element, and also has an effect of improving the iron loss by improving the adhesion between the steel sheet and the oxide layer by suppressing the formation of an oxide layer on the surface of the steel sheet formed during secondary recrystallization. However, since Sb has a low melting point, diffusion behavior toward the surface occurs during primary recrystallization annealing, thereby suppressing the formation of surface oxide layers. Excess addition of Sb results in the surface oxide layer formed during primary recrystallization annealing, which is the basis of base coating. Rather, it exacerbates the grain growth inhibitory ability to grow to other aggregates irrelevant to the goth aggregate, resulting in a problem of damaging the secondary recrystallized aggregate and inhibiting its magnetic properties. Sb is an element that plays a role of assisting the grain growth inhibiting force of Sn, and is preferably added in combination with Sn rather than being added alone. When Sb is added in combination with Sn, it is preferable to contain Sb at 0.01 to 0.03% by weight, and Sb + 0.3 × Sb preferably has a range of 0.08 or more and 0.11 or less.

P is an element exhibiting a similar effect to Sn and Sb, and segregates in the grain boundary to prevent the movement of the grain boundary and at the same time play a secondary role in inhibiting grain growth, and improves the {110} <001> aggregate structure in terms of microstructure. It is effective. If the content of P is less than 0.005% by weight, there is no effect of addition, and if it is added in excess of 0.05% by weight, brittleness is increased and rollability is greatly deteriorated, so it is preferable to limit it to 0.005 to 0.05% by weight.

The grain-oriented electrical steel sheet manufactured by using the slab having the above composition is formed in an appropriate size of 10 to 30 mm in which crystal grains after secondary recrystallization annealing are advantageous for magnetism, and increase the nucleation site of the goth aggregated tissue in the goth aggregated structure and in the rolling direction. One of the azimuth relations, the beta direction (β angle; the angle between the [001] direction and the RD direction based on the TD direction) is secured to within 2.5 ° and has extremely excellent magnetic properties.

Hereinafter will be described a low iron loss high magnetic flux density oriented electrical steel sheet manufacturing method of the present invention.

Carbon content and slab heating conditions are very important in relieving the casting structure, which is the columnar structure at the steelmaking stage, and reusing the coarse precipitates deposited during solidification to room temperature after casting. In general, the higher the carbon content, the more active the phase transformation, thereby improving the effect of mitigating the columnar texture. In addition, the slab reheating temperature and hot rolling operation is advantageous in terms of productivity to be manufactured under similar temperature conditions as other steel grades, and therefore, the slab heating temperature is preferably set to 1050 to 1250 ° C.

On the other hand, the content of acid-soluble Al and small steel N is very important to secure the stability of grains of grain-oriented electrical steel sheet. Acid-soluble Al and mild steel N are important elements to precipitate (Al, Si, Mn) N or AlN during solidification, and are dissolved or precipitated inside the base according to the following content relationship. That is, acid-soluble Al and calcined nitrogen have an equilibrium constant Ks according to the content, and the precipitation becomes more active as it is shifted to the right side from the equilibrium constant, and is employed in the base as it is shifted to the left side. In addition, if the slab reheating temperature is lower than the equilibrium constant Ks, unstable (Al, Si, Mn) N or AlN precipitated during solidification cannot be reclaimed in the base.

On the other hand, if the slab reheating temperature is too low, too many precipitates are formed during solidification, which hinders rolling properties. Therefore, the acid-soluble Al and the steel sheet N must be controlled, where the acid-soluble Al should be 0.005 ~ 0.040%, the steel sheet N should be less than 0.010%.

The slab is heated to a predetermined temperature as described above, and then hot rolled, so that the thickness of the hot rolled hot rolled sheet is 1.5 to 2.5 mm. If the thickness of the hot rolled sheet exceeds 2.5mm, in the rapid cooling process after hot rolling, the cooling rate drops and coarse carbides are formed to deteriorate the magnetic properties. In addition, hot rolling to a thickness of less than 1.5mm is difficult to increase the rolling load and difficult to control the thickness. Therefore, the thickness of the hot rolled sheet is preferably formed to 1.5 ~ 2.5mm.

Subsequently, it is cooled at a cooling rate of 15 ° C. or more per second and wound up at a temperature of 600 ° C. or less. When wound at a cooling rate of less than 15 ° C per second, coarse carbides form during the cooling process, leading to deterioration of magnetism, as well as the formation of fragile cementite (Fe ₃ C) and ferrite layered structure, pearlite. In addition, the transformation of bainite (bainite) and the diffusion-free transformation of martensite (martensite) is delayed, and thus it is not easy to refine the austenite phase and secure the homogeneity of the tissue in the hot-rolled sheet annealing. Therefore, it is desirable that the cooling rate of the hot rolled sheet after hot rolling is 15 ℃ or more per second .

When the hot rolled steel sheet is wound at a temperature exceeding 600 ° C, coarse carbides are also formed, so the winding temperature is preferably limited to 600 ° C or less.

In the hot rolled hot rolled sheet, there is a strain structure drawn in the rolling direction by stress, and AlN, MnS, etc. precipitate during hot rolling. Therefore, in order to have a uniform recrystallized microstructure and fine AlN precipitate distribution before cold rolling, the hot rolled sheet is heated once again to below slab heating temperature to recrystallize the deformed structure, and also to secure sufficient austenite phase to obtain crystal grains such as AlN and MnS. It is important to promote the employment of growth inhibitors. Therefore, the hot-rolled sheet annealing temperature is preferably heated to 900 ~ 1200 ℃ in order to maximize the austenite fraction.

Thus, after heating the hot rolled sheet to 900 ~ 1200 ℃ it is preferable to perform the cracking treatment at a temperature of 900 ℃ 1100 ℃. If the cracking temperature is less than 900 ℃, the precipitated solution is not diffused finely precipitated, if the cracking temperature exceeds 1100 ℃ precipitates are not uniformized and the problem occurs in the subsequent cooling process. Therefore, the cracking treatment is performed at a temperature of 900 ° C or more and 1100 ° C or less to strengthen the growth driving of the precipitate.

The cracking treatment is preferably carried out in a wet atmosphere to simultaneously carry out decarburization. This is to induce an increase in nucleation of goth aggregates and to reduce the amount of carbon remaining in the steel sheet to prevent quality degradation due to self aging.

In the cooling after the annealing heat treatment of the hot rolled plate as described above, it is preferable to perform a quenching treatment. Slow cooling reduces the amount of acid-soluble aluminum due to the additional precipitation of grain growth inhibitors such as AlN and MnS, and reduces coarse layered structures of cementite and ferrite instead of phases such as relatively high strength bainite or martensite. Perlite, which is a mixed structure, is formed, so that the formation of shear deformation zone due to work hardening is weakened during subsequent cold rolling. In addition, not only carbon is present as cementite in perlite, but also as a plate-shaped or spherical carbide at grain boundaries, resulting in nonuniformity of tissue. However, if the cooling rate exceeds 500 ℃ per second, the austenite phase is transformed into a martensite phase having a high total strength, which puts a load on the cold rolling process and inferior the quality of the cold rolled sheet.

Therefore, hot-rolled sheet annealing is heated to a temperature of more than 900 ℃ 1200 ℃, then subjected to cracking treatment and decarbonized annealing heat treatment under a wet atmosphere at a temperature of 900 ℃ to 1100 ℃ and then cooling rate of 15 ℃ to 500 ℃ or less per second It is preferable to cool by. In this case, the cooling method may be performed by air cooling, water cooling, oil cooling, or the like, or a mixture of two or more thereof may be applied.

After annealing the hot rolled sheet, cold rolling is performed to a thickness of 0.10 mm or more and 0.50 mm or less by using a reverse rolling mill or a tandem rolling mill.

If the temperature is lower than 150 ℃ during cold rolling, the movement of carbon is slower than the movement of dislocation during cold rolling, and thus the effect of fixing the dislocation is inferior. As a result, the shear deformation zone is not uniformly formed, and the cold rolling is performed at a temperature exceeding 400 ℃. In this case, the movement speed of carbon becomes faster than the movement speed of dislocations, and the effect of fixing dislocations is also reduced. Indicates. Therefore, cold rolling is most preferably carried out at a temperature of more than 150 ℃ 400 ℃.

Cold rolling is most preferably performed once cold rolling, rolling from the initial hot rolling thickness directly to the thickness of the final product without annealing heat treatment (intermediate annealing) of the deformed structure in the middle. One cold-rolled orientation allows the low-density orientations of the {110} <001> orientation to rotate in the strain direction and increases the secondary recrystallization nucleation sites with high orientation towards the {110} <001> orientation, which favors magnetism. Only grains will be present in the cold rolled plate. In two or more rolling methods, orientations with low integration are also present in the cold rolled plate, and thus the magnetic flux density and iron loss deteriorate since the secondary recrystallization is performed at the time of the final high temperature annealing. Therefore, cold rolling is most preferably rolled at a cold rolling rate of 90% or more by one strong cold rolling.

The cold rolled plate is subjected to decarburization, recrystallization of deformed tissue, and nitriding using ammonia gas to react with acid-soluble aluminum and nitrogen dissolved in the substrate during hot-rolled sheet annealing to produce a fine and uniform distribution as a strong grain growth inhibitor. A large amount of nitrides such as (Al, Si, Mn) N and AlN having a precipitate are precipitated to further maximize the effect of suppressing grain growth of the primary recrystallized grains.

Although carbon plays a very large role in the manufacture of the grain-oriented electrical steel sheet of the present invention, when a large amount of carbon is present in the final product, the primary recrystallization occurs due to a self aging phenomenon in which fine carbides are formed over time, thereby greatly increasing iron loss. Decarburization should be carried out in the annealing process to remove carbon to a certain level.

In the nitriding treatment, the tin extract (Al, Si, Mn) N can be formed by introducing nitrogen ions into the steel sheet using ammonia gas. This nitriding treatment may be carried out after the decarburization and recrystallization, or may be carried out using ammonia gas simultaneously so as to carry out the nitriding treatment simultaneously with decarburization, either of which has no problem in achieving the effect of the present invention.

In the decarburization and nitriding treatment, the annealing temperature of the steel sheet is preferably heat treated within the range of 800 to 950 ° C. When the annealing temperature of the steel sheet is lower than 800 ℃, it takes a long time to decarburize, and the SiO ₂ oxide layer is densely formed on the surface of the steel sheet, causing a base coating defect. On the contrary, when the steel sheet is heated to a temperature exceeding 950 ° C., the recrystallized grains grow coarse, and the crystal growth driving force is lowered, so that a stable secondary recrystallization is not formed.

Finally, in the manufacture of a grain-oriented electrical steel sheet, the {110} plane of the steel sheet is parallel to the rolled surface by applying an annealing separator based on MgO to the steel sheet, followed by final annealing for a long time to cause secondary recrystallization. To form a grain-oriented electrical steel sheet having excellent magnetic properties by forming a {110} <001> texture in the direction parallel to the rolling direction. The purpose of the final annealing is largely to form the {110} <001> texture by secondary recrystallization, and to remove the impurities imparting insulation and damaging the magnetic properties by forming a glassy film formed by the reaction of the oxide layer formed with decarburization with MgO. In the final annealing method, in the temperature rise section before the secondary recrystallization occurs, the secondary recrystallization can be developed well by protecting the nitride, which is a particle growth inhibitor, by maintaining the mixture gas of nitrogen and hydrogen, and after the secondary recrystallization is completed. It is kept in 100% hydrogen atmosphere for a long time to remove impurities.

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

By weight% Si: 3.2%, C: 0.080-0.321%, Mn: 0.090%, S: 0.003%, N: 0.004%, Sol. Slabs containing Al: 0.030%, P: 0.028%, Sn: 0.08% and containing the remaining Fe and other inevitable impurities are vacuum-dissolved to form an ingot, and then heated to a temperature of 1200 ° C., and then 2.3 mm thick. It was hot rolled and cooled to 600 ° C. at a cooling rate of 50 ° C. per second. The hot rolled hot rolled plate was heated to a temperature of 1050 ° C and then maintained at 950 ° C for 180 seconds to anneal and then water cooled. During annealing of the hot rolled sheet, decarburization was performed in a wet atmosphere during heat treatment. The water-cooled hot-rolled annealing plate was pickled and then cold-rolled once to a thickness of 0.23 mm. The cold rolled plate was maintained at 850 ° C. for 180 seconds in a humid hydrogen, nitrogen, and ammonia mixed gas atmosphere to simultaneously denitrify and anneal so that the nitrogen content was 200 ppm. MgO, an annealing separator, was applied to the steel sheet, followed by final annealing onto a coil. The final annealing was performed at a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, the annealing was carried out in a 100% hydrogen atmosphere for 10 hours or more and then cooled. For each condition, the residual C content and magnetic properties of the final annealing plate were measured, and tin extracts were observed and shown in Table 1 below.

As shown in Table 1, Inventive Materials 1 to 6 in which the carbon content is controlled to 0.1 to 0.3% by weight, which is the range of the present invention, are excellent in magnetic properties. It can be seen that the magnetic properties of the comparative material 2 and the comparative material 3 in which the carbon content exceeds 0.3% by weight are very poor. This is because decarburization does not occur sufficiently due to excess carbon content, resulting in thermal deterioration of the magnetic properties of the final product.

By weight%, Si: 3.2%, C: 0.210-0.326%, Mn: 0.09%, S: 0.003%, N: 0.004%, Sol. Slabs containing Al: 0.030%, P: 0.028%, Sn: 0.08%, and residual Fe and other unavoidable impurities are vacuum-dissolved to form an ingot, and then heated to 1200 ° C and then 3.0 to 2.0 mm The furnace was hot rolled at different thicknesses. Subsequently, after cooling to 600 ° C. at a cooling rate of 50 ° C. per second, the hot rolled hot rolled plate was heated to 1050 ° C. and then maintained at 950 ° C. for 180 seconds to be annealed, followed by water cooling. During annealing of the hot rolled sheet, decarburization was performed in a wet atmosphere during heat treatment. The water-cooled hot-rolled annealing plate was cold rolled once after pickling to prepare various cold-rolled plates having a thickness of 0.30 to 0.20 mm. The cold rolled plate was maintained at 850 ° C. for 180 seconds in a humid hydrogen, nitrogen, and ammonia mixed gas atmosphere to simultaneously denitrify and anneal so that the nitrogen content was 200 ppm. MgO, an annealing separator, was applied to the steel sheet, followed by final annealing onto a coil. The final annealing was performed at a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, the annealing was carried out in a 100% hydrogen atmosphere for 10 hours or more and then cooled. Magnetic properties of each condition were measured and shown in Table 2 below.

As can be seen in Table 2, all of the invention materials 7 to 10 in which the slab carbon content was controlled in the range (0.1 to 0.3%) of the present invention are excellent in magnetic properties. In particular, Inventive Material 10 was able to manufacture ultra-thin cold rolled sheet having a thickness of 0.20 mm by one cold rolling, which increased the amount of austenite during hot-rolled sheet annealing due to the high carbon content, thereby transferring by sufficient recrystallization. This is due to the improvement of the cold rolling property as the heterogeneous and long stretched tissues generated in the hot rolling process disappeared and were composed of fine grains in all directions and the precipitates were uniformly dispersed and deposited in the fine matrix. I can think of it.

By weight%, Si: 3.2%, C: 0.20%, Mn: 0.099%, S: 0.0045%, N: 0.0043%, Sol. Ingots were made after vacuum melting of slabs containing Al: 0.028%, P: 0.028%, Sn and Sb, balance Fe and other inevitable impurities, and the contents of Sn and Sb were changed as shown in Table 3. I was. It was then heated to a temperature of 1200 ℃ and hot rolled to a thickness of 2.3mm, and cooled to 600 ℃ at a cooling rate of 50 ℃ per second. The hot rolled hot rolled plate was heated to a temperature of 1050 ° C and then maintained at 950 ° C for 180 seconds to anneal and then water cooled. During annealing of the hot rolled sheet, decarburization was performed in a wet atmosphere during heat treatment. The water-cooled hot-rolled annealing plate was pickled and then cold-rolled once to be 0.23 mm thick. The cold rolled plate was maintained at 850 ° C. for 180 seconds in a humid hydrogen, nitrogen, and ammonia mixed gas atmosphere to simultaneously denitrify and anneal so that the nitrogen content was 200 ppm. MgO, an annealing separator, was applied to the steel sheet, followed by final annealing onto a coil. The final annealing was performed at a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, the annealing was carried out in a 100% hydrogen atmosphere for 10 hours or more and then cooled. Magnetic properties (W _{17 / 5O} , B ₈ ) were measured for each condition and are shown in Table 3 below. In addition, after calculating the absolute value of the angle deviating from the {110} <001> abnormal orientation of the secondary recrystallized grains, the β angle was measured by weighted average of the area at all positions, and the results are shown in Table 3.

As shown in Table 3, Inventive Materials 11 to 14 containing Sn in the range of 0.08 to 0.10% by weight, the β angle of the final steel sheet showing the degree of deviation from the goth direction by the effect of increasing the nucleation site of the goth assembly tissue is 2.5 ° It can be confirmed that the orientation is significantly improved as below, and has more excellent magnetic properties than Comparative Materials 8-14.

In particular, Inventive Material 13 and Inventive Material 14 were added with Sn so that Sb was added in a range of 0.01 to 0.03% by weight and Sn (wt.%) + 0.3 x Sn (wt.%) Satisfies 0.08 to 0.11. As a result, magnetic properties superior to Invention 11 and Invention 12 to which Sn was added alone are exhibited.

Claims (4)

By weight%, C: 0.10 to 0.30%, Si: 2.0 to 4.5%, Al: 0.005 to 0.040%, Mn: 0.20% or less, N: 0.010% or less, S: 0.010% or less, P: 0.005 to 0.05%, Sn: High carbon-containing silicon steel slab containing 0.08 to 0.10% and consisting of the balance Fe and other unavoidable impurities is heated and hot rolled, followed by hot rolled sheet annealing followed by cold rolling, followed by decarburization and nitride annealing After performing the second recrystallization annealing, the hot-rolled sheet annealing is a method of manufacturing a low iron loss high magnetic flux density oriented electrical steel sheet is carried out so that decarburization. The method according to claim 1,
The silicon steel slab is Sb: manufacturing method of low iron loss high magnetic flux density oriented electrical steel sheet further containing 0.01 to 0.03%. The method according to claim 2,
The silicon steel slab is a method for producing a low iron loss high magnetic flux density oriented electrical steel sheet containing Sn and Sb to satisfy the following formula 1.
0.08 ≤ Sn (wt.%) + 0.3 × Sb (wt.%) ≤ 0.11 ---------------------- (Equation 1) The method according to any one of claims 1 to 3,
A method for manufacturing a low iron loss high magnetic flux density oriented electrical steel sheet in which secondary angle is recrystallized so that β angle is less than 2.5 ° as an area weighted average of absolute values of crystal orientations.
However, β angle is the deviation angle between the [100] direction and the rolling direction with respect to the rolling right angle direction of the secondary recrystallized texture.