KR20120074025A - Grain-oriented electrical steel sheets with extremely low core-loss and high flux-density and method for manufacturing the same - Google Patents

Abstract

PURPOSE: An oriented electrical steel sheet with low core loss and high magnetic flux density and a manufacturing method thereof are provided to improve agglomeration degree of a goss texture in a firstly recrystallized structure by controlling the quantity of Sn(Stannum) used as a main inhibitor in proper range. CONSTITUTION: An oriented electrical steel sheet with low core loss and high magnetic flux density manufacturing method is as follows. A slab is composed of Si 2.0 to 4.5wt.%, Al(Aluminum) 0.005 to 0.040wt.%, Mn(Manganese) lower than 0.20wt.%, N(Nitrogen) lower than 0.006wt.%, S(Sulfur) lower than 0.006wt.%, P(Phosphorus) 0.005 to 0.05wt.%, C(Carbon) 0.04 to 0.10wt.%, Sn 0.08 to 0.10wt.%, As(Arsenic) 0.005 to 1.0wt.%, residual Fe(Iron), and inevitable impurities. The slab is heated in 1200 to 1300°C and hot-rolled and the hot-rolled sheet is annealed and cold-rolled, and decarbonization and nitride annealing are applied, and secondary recrystallization and annealing are applied to the sheet.

Description

Grain-oriented electrical steel sheets with extremely low core-loss and high flux-density and method for manufacturing the same

The present invention relates to the manufacture of oriented electrical steel sheet used in iron core materials of electronic devices such as generators and transformers, to increase the fraction of goth aggregate structure of the primary recrystallized grain and to optimize the secondary recrystallized grain size after the final high temperature annealing, Low iron loss high magnetic flux density oriented electrical steel sheet and its manufacture to perform stable slab reheating under relatively low temperature and complete precipitation of precipitates such as nitrides and sulfides to uniformly obtain primary magnetism It is about a method.

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 process conditions 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 It must be strictly controlled.

Inhibitor, one of the factors expressing goth aggregates, has a very important function as a grain growth inhibitor that suppresses indiscriminate growth of primary recrystallized grains and allows only goth aggregates to grow when secondary recrystallization occurs. To do. After the second recrystallization annealing, in order to obtain a final steel sheet having a good goth aggregate structure, the growth of all primary recrystallization grains must be suppressed until the second recrystallization occurs, and the amount of inhibitor must be large enough to obtain sufficient restraining force. The distribution should also be uniform. In addition, in order for secondary recrystallization to occur simultaneously during high temperature secondary recrystallization annealing (final high temperature annealing), the thermal stability of the inhibitor should be excellent and not easily decomposed. Secondary recrystallization occurs when the inhibitor decomposes or loses restraining force at the appropriate temperature range during the final high temperature annealing. In this case, specific grains such as 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. The initial grain-oriented electrical steel sheet was MnS proposed by M. F. Littman as a grain growth inhibitor, and was produced by two cold rolling methods. According to this, secondary recrystallization was relatively stable, but the magnetic flux density was not so high and iron loss was high.

Since, Taguchi (田 口), Al by using a combination of AlN, MnS precipitates as grain growth inhibitor, a technique for producing a grain-oriented electrical steel sheet by cold-rolling once at a cold rolling rate of more than 80%. 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. .

In general, reducing the thickness of the steel sheet is effective to reduce the iron loss by reducing the eddy current loss. This method can be obtained by adding deformation during cold rolling. In this case, since the driving force of grain growth is increased, there is a problem that secondary recrystallization is unstable because the original grain growth inhibitor is not sufficiently suppressed.

In order to reduce the thickness while balancing the grain growth driving force and the inhibitory force, rolling must be performed at an appropriate cold rolling rate during final cold rolling, and the appropriate cold rolling rate depends on the inhibitory power of the grain growth inhibitor.

When using the AlN and MnS composite precipitates proposed by Taguchi as grain growth inhibitors, a cold rolling rate of about 87% is appropriate, and when using MnS precipitates proposed by Littman as grain growth inhibitors, about 50 to 70% of cold The rolling rate is appropriate. However, these strict cold rolling conditions place a burden on the production process.

In addition to the above-described techniques, techniques for adding alloying elements capable of obtaining a level of suppression similar to the precipitates have been proposed, as opposed to techniques through grain growth suppression by precipitates, as part of improving magnetic properties of oriented electrical steel sheets.

In this regard, a technique of adding B and Ti has been proposed to reinforce the weakening of grain growth inhibition by one cold rolling. However, the technique of adding B is difficult to control in the steelmaking step by adding a small amount, and the added B is likely to form coarse BN in steel. In addition, the technique of adding Ti also acts as a factor to increase the iron loss as the TiN or TiC having a solid solution temperature of 1300 ° C or higher is present after the secondary recrystallization.

Another method for improving grain growth inhibition is a technique for producing a grain-oriented electrical steel sheet using MnSe as a grain growth inhibitor. However, this method has the advantage of obtaining high magnetic flux density due to high grain growth suppression ability, but the material itself is considerably hardened, so it cannot be manufactured by one cold rolling, and thus two colds which are essentially passed through intermediate annealing. Since rolling must be performed and toxic and expensive Se is used, a separate facility for handling toxic substances is essential, which increases manufacturing costs.

On the other hand, a technique for producing a grain-oriented electrical steel sheet by adding alloying elements such as Sb, P, Sn, B, etc. has been introduced, but the range of alloying elements is generally described too broadly, and each alloying element is added alone. Most of the effects of the present invention are mainly described, but are described only to include at least one of two or more alloying elements.

Moreover, no specific technique for utilizing the alloying elements as a major grain growth inhibitor has been introduced until now. That is, according to the current techniques, only the degree to which magnetism can be improved by adding at least one of alloy elements such as Sb, P, Sn, and B is known, and each element is used as a major grain growth inhibitor. The detailed contents of the proper content and process conditions or the causal relations for this were not made at all, and although the behavior of the primary recrystallization and the secondary recrystallization of the grain-oriented electrical steel sheet were different, no solution was provided. There is a situation.

The present invention has been made to solve all the problems of the prior art as described above, the purpose is to add Sn in the step of steel, but control in an appropriate range that can be utilized as a major grain growth inhibitor goth in the primary recrystallized structure The purpose of the present invention is to provide a method for manufacturing a low iron loss high magnetic flux density oriented electrical steel sheet having improved magnetic properties by increasing the aggregate fraction and optimizing the size of secondary recrystallized grains.

In addition, the present invention is to adjust the content of N and S in the steelmaking step so that the precipitates such as nitride and sulfide completely dissolved during slab reheating, and then reheating the slab under the appropriate temperature conditions, and the effect of Sn as a major grain growth inhibitor In order to maximize the temperature control of decarburization and nitride annealing, and control the decarbonization annealing temperature conditions appropriately to maintain the balance between the grain growth driving force and the restraining force to form the primary recrystallized grain of the appropriate size, without reducing the productivity An object of the present invention is to provide a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties.

Low iron loss high magnetic flux density oriented electrical steel sheet manufacturing method of the present invention for solving the above problems by weight, Si: 2.0 ~ 4.5%, Al: 0.005 ~ 0.040%, Mn: 0.20% or less, N: 0.006% or less, S: 0.006% or less, P: 0.005 to 0.05%, C: 0.04 to 0.10%, Sn: 0.08 to 0.10%, As: 0.005 to 1.0%, and a slab made of remaining Fe and other unavoidable impurities Heating to a temperature in the range of ˜1300 ° C., followed by hot rolling, hot rolled sheet annealing, cold rolling, decarburization and nitride annealing, and then secondary recrystallization annealing. Sn is used as a major grain growth inhibitor.

The decarburization and nitride annealing is preferably carried out at a temperature range of 800 ~ 950 ℃ to control the size of the primary recrystallized grain to 18 ~ 25㎛.

In addition, the method for manufacturing a grain-oriented electrical steel sheet of the present invention is controlled so that the β angle is less than 3 ° as the area weighted average of the absolute value of the crystal orientation in the secondary recrystallized steel sheet, the average grain size of the secondary recrystallized steel sheet 1 ~ 2cm It characterized in that the control to be.

The oriented electrical steel sheet of the present invention for solving the above problems by weight, Si: 2.0 ~ 4.5%, Al: 0.005 ~ 0.040%, Mn: 0.20% or less, N: 0.006% or less, S: 0.006% or less, P : 0.005% to 0.05%, Sn: 0.08% to 0.10%, As: 0.005% to 1.0%, and it is characterized by consisting of remaining Fe and other unavoidable impurities.

The grain-oriented electrical steel sheet of the present invention is characterized in that the β-angle is less than 3 ° as the area weighted average of the absolute values of the crystal orientation in the secondary recrystallized steel sheet, and the average grain size of the secondary recrystallized steel sheet is 1 to 2 cm.

According to the present invention, the Sn added in an appropriate amount acts as a major grain growth inhibitor, thereby increasing the fraction of Goth-bearing grains in the primary recrystallized texture, thereby increasing the degree of integration in the {110} <001> orientation after the final secondary recrystallization. It is possible to manufacture ultra-low iron loss high magnetic flux density oriented electrical steel sheet composed of goth aggregate structure having high grain size and fine grain size.

In addition, according to the present invention, after adjusting the content of N and S in the steelmaking step so that precipitates such as nitrides and sulfides are completely dissolved during slab reheating, slab reheating is performed at an appropriate temperature condition. Maximizes the effect of Sn as a major grain growth inhibitor by controlling it, and decarburization and nitride annealing are carried out in a temperature range slightly higher than normal conditions so that primary recrystallized grains are formed in an appropriate size, thereby appropriately balancing the grain growth driving force and the inhibitory force. By holding and stabilizing the secondary recrystallization, a grain-oriented electrical steel sheet having extremely excellent magnetism can be produced.

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

The present inventors have studied and studied the effects of various alloying elements on the magnetism in the production of grain-oriented electrical steel sheet, and the effects of the processing conditions such as slab heating and decarburization annealing on the component system containing each alloying element. As a result, when Sn was added as 0.08 ~ 0.10% by weight and used as the main grain growth inhibitor, the fraction of Goth-bearing grains in the primary recrystallized texture increased and the {110} <001> orientation after the final secondary recrystallization. It was found that secondary recrystallized structure composed of goth aggregated structure with very high integration density and fine grain size can be manufactured to produce oriented electrical steel sheet with extremely low iron loss and high magnetic flux density.

Furthermore, the inventors of the present invention suggest that in order to stably produce secondary recrystallization using the slab of the component system in which Sn is added in the above-described composition range, decarburization and nitride annealing are carried out at a temperature range slightly higher than normal conditions so that the balance between the grain growth driving force and the inhibitory force is maintained. (800 ~ 950 ℃), the primary recrystallized grain should be formed into 18 ~ 25㎛ size, and the slab reheating is completely dissolved in precipitates such as nitride and sulfide in order to secure stable magnetic properties. The present invention was completed by paying attention to the fact that the size of the primary recrystallized grains should be uniformly formed by performing the above conditions.

In the present invention, by weight%, Si: 2.0 to 4.5%, Al: 0.005 to 0.040%, Mn: 0.20% or less, N: 0.006% or less, S: 0.006% or less, P: 0.005 to 0.05%, C: 0.04 to A slab containing 0.10%, Sn: 0.08 ~ 0.10%, As: 0.005 ~ 1.0%, balance Fe and other unavoidable impurities, is heated to 1200 ~ 1300 ℃ to completely solidify AlN and MnS precipitates, and After rolling, hot rolled sheet annealing at 900 ~ 1200 ℃, cold rolling, decarburization and nitride annealing at 800 ~ 950 ℃ to control the size of primary recrystallized grain to 18 ~ 25㎛ Then, by performing secondary recrystallization annealing to control the average grain size of the secondary recrystallized steel sheet to 1 ~ 2cm to produce a grain-oriented electrical steel sheet excellent in magnetism, characterized in that Sn is used as a major grain growth inhibitor It is.

In the present invention, Sn acts as a major grain growth inhibitor, which segregates at grain boundaries other than Goth grains and hinders the movement of grain boundaries. In order to generate stable secondary recrystallization, Sn should be added in an appropriate amount of 0.08 to 0.10%. When the appropriate amount of Sn is added, the {110} <001> azimuth goose grain fraction of the primary recrystallized texture is increased to increase the degree of integration, and the nucleus of the goth defense grown to the secondary recrystallized texture is increased.

The present invention uses a component-based slab to which the appropriate amount of Sn is added as described above, and when reheating the slab, AlN and MnS precipitates are completely dissolved at a relatively low temperature so that primary recrystallized grains are formed in a uniform size. Decarbonized annealing temperature is controlled to maintain the balance between the crystal growth driving force and the inhibitory force to form primary recrystallized grains with an appropriate size of 18 to 25 μm, and the size of the secondary recrystallized grains to 1 to 2 cm in the final product. As a result, the nucleation site of the goth-assembly structure is increased, and the β angle of the final steel sheet is 3 ° or less, so that it is possible to manufacture a grain-oriented electrical steel sheet having 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.

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

[Si: 2.0 ~ 4.5 wt%]

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, which leads to deterioration of iron loss characteristics and phase transformation between ferrite and austenite at high temperature annealing, resulting in not only unstable secondary recrystallization but also severely damaged texture. When the Si content exceeds 4.5%, the brittleness, which is the mechanical property of the electrical steel sheet, increases, and the toughness decreases, causing the occurrence of plate breakage during the rolling process, and unstable secondary recrystallization. Therefore, Si is preferably limited to 2.0 to 4.5% by weight.

[Al: 0.005-0.04 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, The formation of nitrides in the Si, Mn) N form serves as a powerful grain growth inhibitor. When Al is less than 0.005%, since the number and volume of formation are considerably low, sufficient effect as an inhibitor cannot be expected. When the content is more than 0.040%, Al forms coarse nitrides, thereby suppressing grain growth. Will fall. Therefore, the content of Al is limited to 0.005 ~ 0.040% by weight.

[Mn: 0.02% by weight or less]

Mn also has the effect of reducing the iron loss by increasing the specific resistance and reducing the eddy current loss, like Si, by reacting with the nitrogen introduced by the nitriding treatment with Si to form a precipitate of (Al, Si, Mn) N 1 It is an important element for causing secondary recrystallization by suppressing growth of secondary recrystallized grains. However, when added in excess of 0.20%, a large amount of (Fe, Mn) and Mn oxides are formed on the surface of the steel sheet in addition to Fe ₂ SiO ₄ , which hinders the formation of the base coating formed during high temperature annealing, thereby deteriorating the surface quality. Due to the phase transformation between ferrite and austenite in the process, the texture is severely damaged and the magnetic properties are greatly deteriorated. Therefore, Mn is made into 0.20 weight% or less.

[N: 0.006% by weight or less]

N is an important element that reacts with Al to form AlN and is preferably added at 0.006% by weight or less in the steelmaking step. If it is added in excess of 0.006% by weight, the heating furnace must be maintained at 1300 ° C. or higher to completely solidify the AlN described above. Has a fatal weakness that makes it very uneconomical. Therefore, N should be 0.006% by weight or less, preferably 0.004% by weight or less. On the other hand, N needed to form nitrides such as (Al, Si, Mn) N and AlN is strengthened by nitriding in steel using ammonia gas in the annealing process after cold rolling.

[C: 0.04-0.10 wt%]

C is an element that causes phase transformation between ferrite and austenite. It is brittle and is an essential element for improving the rollability of electrical steel sheets with poor rolling properties, but when it remains in the final product, carbides formed due to magnetic aging effects Since it is an element which worsens magnetic properties, it is preferable to be controlled to an appropriate content. When the C content is less than 0.04% in the above-described Si content, the phase transformation between ferrite and austenite does not work properly, causing unevenness of the slab and the hot rolled microstructure. Therefore, the minimum content of C is preferably made 0.04% or more. On the other hand, after the hot-rolled annealing heat treatment, residual carbon in the steel sheet activates dislocation fixation during cold rolling to increase shear deformation zone, thereby increasing the generation site of goose nucleus, thereby increasing the goth grain fraction of the primary recrystallized microstructure. It may be considered to increase the C content, but if C contains more than 0.10% in the above Si content range, sufficient decarburization cannot be obtained in the decarburization and nitriding annealing process unless additional process or equipment is added. In addition, the secondary transformation crystal structure is severely damaged by the phase transformation phenomenon caused by this, and furthermore, when the final product is applied to the power equipment, the deterioration of the magnetic properties by the magnetic aging. Therefore, it is preferable to contain C at 0.10% at maximum. When the C content is more than 0.07%, decarburization is not easy, so it is more preferable that C is contained at 0.07% or less.

[S: 0.006% by weight or less]

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 this invention, since MnS is not used as a main grain growth inhibitor, it is unpreferable to precipitate more than content which S inevitably mixes.

On the other hand, if S exceeds 0.006% by weight, the heating furnace must be maintained so that the slab temperature is 1300 ° C. or more in order to uniformly heat the temperature at which the precipitate is completely dissolved. This is very uneconomical because the oxidation scale of the slab surface melts and flows down. If the slab is heated above the complete solution temperature when S is contained in excess of 0.006% by weight, the size of the primary recrystallized grains is too small to lower the secondary recrystallization initiation temperature. This causes recrystallization and degrades magnetism. Therefore, S is limited to 0.006% by weight or less, preferably 0.004% by weight or less.

[Sn: 0.08-0.10 wt%]

Sn is an alloy element, which is the core of the present invention, and acts as an inhibitor that segregates in the grain boundary and inhibits grain growth by preventing movement of the grain boundary. In addition, by increasing the fraction of Goth grains in the {110} <001> azimuth in the primary recrystallization aggregates and monitoring the aggregates that facilitate the growth of goth aggregates such as {111} and {411}, secondary recrystallization aggregates The nucleus of the Goth defense which grows to a lot increases. Therefore, when an appropriate amount of Sn is added, the size of the secondary recrystallized microstructure is reduced, and thus the grain size is reduced in the final product, so that the eddy current loss is reduced, thereby making it possible to manufacture a directional electrical steel sheet having excellent magnetic properties.

As such, Sn plays an important role in suppressing grain growth through segregation at the grain boundary, which not only enhances the effect of suppressing the grain growth driving force of the refined primary recrystallized microstructure, but also for forming secondary recrystallized texture. Coarse particles causing grain growth inhibition (Al, Si, Mn) N and AlN during the high temperature annealing process to reduce grain growth inhibition, and the number of particles with grain growth inhibitory effect decreases numerically by increasing Si content This prevents the grain growth inhibition from weakening. This in turn guarantees successful expression of secondary recrystallized texture at high Si content as well as low Si content.

Sn also compensates for the thermal instability of particles, which is pointed out as a problem of thin grain oriented electrical steel sheets having grain growth inhibition by grains in order to increase the rolling rate in order to reduce the thickness of the final product for thinning. Compensate for successful growth of the vehicular decision-making organization. Therefore, the addition of an appropriate amount of Sn increases the fraction of goth aggregates in the primary recrystallized texture, and increases the grain growth inhibitory ability, so that better texture, stable grain growth inhibition, and iron loss reduction due to thinning can be simultaneously obtained. As a result, it is possible to secure a secondary recrystallization aggregate structure composed of goth grains having a very high density.

When the Sn content is less than 0.08% by weight, the results of the present inventors confirmed that the magnetic properties are improved, but the effect of improving the density of the Goth aggregate tissue is small, but rather to the particles present in the matrix. Due to the small effect of compensating for grain growth inhibition, the effect of improving magnetism was only minimal.

Conversely, if Sn is contained in excess of 0.10% by weight, the grain growth inhibitory force is excessively increased, and 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 the proper oxide layer and a good surface cannot be secured. In addition, since the brittleness is increased due to excessive segregation of the grain boundary segregation element in terms of mechanical properties, it may cause plate breakage during the manufacturing process, and therefore, Sn is preferably contained in an amount of 0.08 to 0.10% by weight.

[As: 0.005-1.0 wt%]

As acts as a ferrite stabilization and grain boundary segregation element, and stabilizes primary recrystallized grains, which are ferrite single phases, thereby preventing deterioration of the texture due to phase transformation. In addition, by acting as a grain boundary segregation element, there is an effect of inhibiting the growth of grains other than the goose texture to induce stable secondary recrystallization of the goth texture. As a result, the secondary recrystallization nucleus increases after the high temperature annealing due to the quantitative increase of the goth texture, thereby reducing the iron loss by reducing the size of the secondary recrystallized grains. In order to achieve the above effect, As must be contained in at least 0.005%. If As is contained in excess of 1.0%, surface oxide layer formation becomes unstable, so that the quality of the surface and the sedimentation reaction from the outside to the inside of the steel become difficult, and both the magnetic properties and the surface properties become worse. Therefore, As is preferably contained in 0.005 ~ 1.0%.

[P: 0.005-0.05 wt%]

P is an element exhibiting a similar effect to Sn, and may have a secondary role of segregating in the grain boundary to hinder the movement of the grain boundary and at the same time inhibiting grain growth, and improving the {110} <001> aggregate structure in terms of microstructure. There is. 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 composition has a beta orientation (β angle; TD orientation based on the TD orientation as one of azimuth relationship between the goth assembly structure and the rolling direction by increasing the nucleation site of the goth assembly structure). Azimuth between the azimuth and the RD azimuth) is secured to within 3 ° and has extremely good magnetic properties.

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

First, the slab is reheated prior to hot rolling, and the slab reheating is carried out in a temperature range in which the solid solution N and S are completely dissolved. In the steelmaking step, carbon content and slab reheating conditions are very important in relieving the casting structure, which is the columnar structure, and retreating the coarse precipitates that precipitated during solidification to room temperature after casting. In the present invention, the steel slab reheating temperature before hot rolling is Precipitates used as grain growth inhibitors are heated to 1200 ~ 1300 ℃, which is the temperature at which they are completely dissolved.

If the slab reheating is performed under the condition that the precipitates are partially solidified, there is a large difference in the size of precipitates produced during casting and precipitates that are reconsidered during heating and produced, resulting in non-uniform grain size of the primary recrystallization plate. Since it may be obtained unevenly, the heating temperature of the steel slab is limited to the temperature range in which the precipitates are completely dissolved, that is, 1200 to 1300 ° C or less.

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 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 in the base according to the content relationship shown in the following formula.

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 T (K) is low, 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 mild steel N must be controlled, in the present invention, the content of the acid-soluble Al to 0.005 ~ 0.040%, limit the content of the small steel N to 0.006% or less.

After reheating the slab, hot rolling is performed. In the hot rolled hot rolled sheet, there is a strain structure drawn in the rolling direction due to stress, and AlN or MnS is precipitated 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 once again heated to below the slab heating temperature to recrystallize the deformed structure and to secure sufficient austenite phase such as AlN and MnS. It is desirable to promote the employment of grain growth inhibitors. It is preferable to take such a method that the hot-rolled sheet annealing is heated to a temperature of 900 to 1200 ° C, subjected to a crack heat treatment, and then cooled in order to maximize the austenite fraction. The average size of precipitates in the steel sheet annealed hot-rolled is formed to have a range of 200 ~ 3000Å.

After annealing the hot rolled sheet, cold rolling is performed using a reverse rolling mill or a tandem rolling mill to produce a cold rolled sheet of 0.10 mm to 0.50 mm. In cold rolling, it is most preferable to use one-time cold rolling which rolls from the initial hot rolling thickness to the thickness of the final product without performing annealing heat treatment (intermediate annealing) of the deformed structure in the middle. With one cold rolling, the low-density orientations of the {110} <001> orientation are rotated in the deflection direction, and only the best aligned goth grains in the {110} <001> orientation exist on the cold rolled plate. Therefore, 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 so that the cold rolling rate is 87% or more by one cold rolling.

This cold rolled plate is subjected to decarburization and annealing. This removes carbon below a certain level to prevent self aging, allows the deformed tissue to recrystallize, and nitriding with ammonia gas. In the nitriding treatment, nitrides such as (Al, Si, Mn) N and AlN, which are tin extracts, 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.

According to the researches and experiments of the present inventors, when manufacturing a grain-oriented electrical steel sheet using a slab added with Sn, the balance between the grain growth inhibiting force and the grain growth driving force acts differently, which needs to be strictly considered. As a result of research on this point, in order to secure extremely excellent magnetism in the component system proposed in the present invention, the balance between the grain growth driving force and the grain growth inhibiting force must be properly adjusted. It was found that the size of the grain should be controlled from 18um to 25um.

In order to control the primary recrystallized grain size from 18 μm to 25 μm as described above, decarburization and annealing are at least 10 ° C. and at most 30 ° C., compared to the case of using a slab composed of a conventional component system containing a lower Sn content than the present invention. This should be done in the high temperature range.

Hereinafter, the above knowledge will be described in more detail. In order to manufacture a grain-oriented electrical steel sheet using a slab having a composition range of the present invention, the effect of making the fine grains of the primary recrystallized grains and the segregation of the grains at the grain boundaries are enhanced at the same time. do. In other words, when manufacturing a grain-oriented electrical steel sheet using a slab having a composition range of the present invention, the size of the recrystallized grains is miniaturized, so that secondary recrystallization occurs well. Since the secondary recrystallization is less likely to occur, it is necessary to examine the decarbonized annealing temperature condition by closely examining which factor is more predominant among the grain growth driving force and the grain growth suppression force. The present inventors have found that the increase factor of the grain growth driving force acts more strongly than the increase factor of grain growth inhibition in the component composition range of the present invention, so that secondary recrystallization tends to occur quickly. .

That is, in the case where the grain boundary segregation element Sn is added in the same content as in the present invention, when the decarbonization annealing is carried out in the normal temperature range, the primary recrystallized structure becomes finer, and the grain growth driving force becomes stronger than when using the general component system. Therefore, decarbonization annealing needs to be performed at a temperature range higher than a normal temperature range to stabilize the primary recrystallized microstructure.

Therefore, in the present invention, it is necessary to set the decarbonized annealing temperature range to 800 to 950 ° C., more preferably 850 to 950 ° C., at least 10 ° C. or more and 30 ° C. or more as compared with the conventional case. If the decarbonization annealing temperature is lower than 800 ° C, the size of the primary recrystallized grain becomes too small to increase the driving force for grain growth, and decarburization takes a long time due to annealing heat treatment at a low temperature, thereby lowering production. In addition, Fe ₂ SiO ₄ is formed on the surface of the steel sheet is very dense, the decarburization and internal oxide layer formation is delayed, the SiO ₂ oxide layer is formed densely in a narrow area, the base coating defects occur. On the contrary, when the decarbonization temperature exceeds 950 ° C, recrystallized grains and nitrides grow coarsely, so that the crystal growth driving force is excessively lowered so that a stable secondary recrystallization is not formed.

Therefore, in the present invention, by adjusting the balance of the grain growth driving force and the grain growth inhibiting force as described above, the primary recrystallized grains are formed to have an appropriate size of 18 to 25㎛ to obtain a suitable secondary recrystallization made of goth aggregate structure. .

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 high temperature annealing, 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 high temperature annealing is to form the {110} <001> texture by secondary recrystallization, and to remove the impurities imparting insulation and damaging magnetic properties by forming a glassy film formed by the reaction of the oxide layer formed by decarburization with MgO. In the method of final high temperature annealing, in the temperature rising section before the secondary recrystallization occurs, the secondary recrystallization is well developed by maintaining the mixed gas of nitrogen and hydrogen to protect the nitride which is a particle growth inhibitor, and after the secondary recrystallization is completed. Is kept in 100% hydrogen atmosphere for a long time to remove impurities.

The grain-oriented electrical steel sheet manufactured by the above-described method using the slab having the composition range of the present invention is a beta orientation (β angle), which is one of the orientation relations of the goth-assembly structure and the rolling direction by increasing the nucleation site of the goth-assembly structure. The angle between the [001] direction and the RD direction) is secured within 3 °, and the average grain size of the secondary recrystallized steel sheet is formed in a range of 1 to 2 cm, with extremely excellent magnetic properties.

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

By weight%, Si: 3.2%, C: 0.055%, Mn: 0.099%, S: 0.0045%, N: 0.0043%, Sol. An ingot was prepared after vacuum melting of a slab containing Al: 0.028%, P: 0.028%, Sn, balance Fe, and other inevitable impurities. The content of Sn was changed as shown in Table 1 below. Then it was heated to a temperature of 1200 ℃ and hot rolled to a thickness of 2.3mm. 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. The hot-rolled annealing plate was cold rolled once to be 0.23mm thick after pickling, and the cold-rolled plate was maintained at a temperature of 870 ° C. for 180 seconds in a humid hydrogen, nitrogen, and ammonia mixed gas atmosphere so that the nitrogen content was 200 ppm. Simultaneous decarburization and nitriding annealing. 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 were measured for each condition and are shown in Table 1 below.

Sn (% by weight) _Iron loss (W _17/50 , W / kg) Magnetic flux density (B ₁₀ , Tesla) division 0.000 0.948 1.882 Comparative Material 1 0.012 0.942 1.881 Comparative Material 2 0.025 0.913 1.885 Comparative Material 3 0.033 0.919 1.884 Comparative Material 4 0.041 0.884 1.902 Comparative Material 5 0.052 0.882 1.903 Comparative Material 6 0.060 0.864 1.906 Comparative Material7 0.071 0.860 1.905 Comparative Material 8 0.080 0.783 1.942 Invention 1 0.083 0.791 1.941 Invention 2 0.085 0.784 1.947 Invention 3 0.089 0.783 1.946 Invention 4 0.092 0.790 1.945 Invention 5 0.095 0.787 1.948 Invention 6 0.097 0.792 1.942 Invention Material7 0.105 0.953 1.872 Comparative Material 9 0.113 0.961 1.870 Comparative Material 10 0.122 1.010 1.851 Comparative Material 11

As can be seen from Table 1, Inventive Materials 1 to 7 containing Sn in the range of 0.08 to 0.10% by weight are lower in iron loss and higher magnetic flux density than Comparative Materials 1 to 11.

In Comparative Materials 1 to 11, the tendency of lowering iron loss and increasing magnetic flux density in proportion to the amount of Sn added is recognized to some extent. have. This is because Sn must be added at 0.08% or more and 0.10% or less to act as a major grain growth inhibitor.

By weight%, Si: 3.2%, C: 0.055%, Mn: 0.099%, S: 0.0045%, N: 0.0043%, Sol. An ingot was prepared after vacuum melting of a slab containing Al: 0.028%, P: 0.028%, Sn, balance Fe, and other inevitable impurities. The content of Sn was changed as shown in Table 2 below. Then it was heated to a temperature of 1200 ℃ and hot rolled to a thickness of 2.3mm. 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. The hot-rolled annealing plate was pickled and cold-rolled once so as to have various thicknesses as shown in Table 2 below, and the cold-rolled plate was maintained at 870 ° C. for 180 seconds in a humid hydrogen, nitrogen, and ammonia mixed gas atmosphere. The decarburization and nitriding were carried out simultaneously 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 _17/50 and B ₈ ) were measured for each condition and are shown in Table 2 below.

Cold Rolled Sheet Thickness
(mm) Sn (% by weight) Iron loss (W / kg) Magnetic flux density (Tesla) division 0.30 0.011 1.051 1.882 Comparative Material 12 0.30 0.032 1.043 1.884 Comparative Material 13 0.30 0.080 0.923 1.943 Invention Material 8 0.27 0.012 0.974 1.895 Comparative Material14 0.27 0.032 0.951 1.899 Comparative Material 15 0.27 0.081 0.901 1.945 Invention Material 9 0.23 0.009 0.949 1.881 Comparative Material 16 0.23 0.031 0.921 1.883 Comparative Material17 0.23 0.081 0.783 1.946 Invention 10 0.20 0.013 0.882 1.891 Comparative Material 18 0.20 0.030 0.895 1.903 Comparative Material 19 0.20 0.084 0.748 1.945 Invention Material 11

As can be seen in Table 2, the invention materials 8 to 11 containing Sn in the range of 0.08 to 0.10% by weight, regardless of the thickness of the final product, iron loss compared to the comparative materials 12 to 19 all manufactured with the same thickness The lower the magnetic flux density, the thinner the final product tends to be.

By weight%, Si: 3.2%, C: 0.055%, Mn: 0.099%, S: 0.0045%, N: 0.0043%, Sol. Al: 0.028%, P: 0.028%, Sn, the balance Fe and other unavoidable slabs containing impurities are vacuum dissolved after the ingot was made, the content of Sn was changed as shown in Table 3 below. Then it was heated to a temperature of 1200 ℃ and hot rolled to a thickness of 2.3mm. 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 a temperature of 870 ° C. for 180 seconds in a humid atmosphere of mixed hydrogen, nitrogen, and ammonia, and simultaneously decarburized and nitrified to a nitrogen content of 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. Also, after calculating the absolute value of the angle deviating from the {110} <001> ideal orientation of the secondary recrystallized grains, the weight-averaged area is measured at all positions, and the β angle is measured. Together. The secondary recrystallized grain size is calculated by dividing the maximum length and the shortest length of the secondary recrystallized microstructures observed on the surface of the secondary recrystallized steel plate in half and calculating the size of each secondary recrystallized grain, The size of the vehicle recrystallized grains was calculated as an average value.

Sn (% by weight) Iron loss (W / kg) Magnetic flux density (Tesla) β angle (°) Secondary recrystallized grain size (cm) division 0.012 0.942 1.881 4.8 6.2 Comparative Material 2 0.025 0.913 1.885 4.5 5.9 Comparative Material 3 0.033 0.919 1.884 4.1 5.9 Comparative Material 4 0.041 0.884 1.902 3.4 5.2 Comparative Material 5 0.052 0.882 1.903 3.6 5.0 Comparative Material 6 0.060 0.864 1.906 3.5 4.8 Comparative Material7 0.071 0.860 1.905 3.4 4.8 Comparative Material 8 0.083 0.791 1.941 2.1 1.8 Invention 2 0.089 0.783 1.946 2.3 1.9 Invention 4 0.095 0.787 1.948 2.3 1.4 Invention 6 0.097 0.792 1.942 2.2 1.3 Invention Material7 0.122 1.010 1.851 3.4 0.7 Comparative Material 11

As can be seen in Table 3, Inventive Materials 2, 4, 6, and 7 containing Sn in the range of 0.08 to 0.10% by weight are the final steel sheets showing the degree of deviation from the goth bearing due to the effect of increasing the nucleation site of the goth assembly tissue. Although the beta angle of is less than 3 °, the orientation is greatly improved, and the secondary recrystallized grains are formed to an appropriate size of 1 to 2 cm, which is excellent in magnetism, but Comparative materials 2 to 8 and 11, in which Sn is out of the scope of the present invention, are final The beta angle of the steel sheet exceeded 3 ° and the magnetic inferiority.

By weight%, Si: 3.2%, C: 0.055%, Mn: 0.099%, Sol. Ingots were prepared after vacuum dissolving slabs containing Al: 0.028%, P: 0.028%, Sn: 0.085%, balance Fe and other inevitable impurities. The contents of N and S were changed as shown in Table 4 below. The slabs were then heated to various temperatures as shown in Table 4 and then hot rolled to a thickness of 2.3 mm. 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 cooled. The hot-rolled annealing plate was cold rolled once to be 0.23mm thick after pickling, and the cold-rolled plate was maintained at a temperature of 870 ° C. for 180 seconds in a humid hydrogen, nitrogen, and ammonia mixed gas atmosphere so that the nitrogen content was 200 ppm. Simultaneous decarburization and nitriding annealing. 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 _17/50 and B ₈ ) were measured for each condition and are shown in Table 4 below.

Slab heating
Temperature (℃) Small Steel N
(weight%) S steel amount
(weight%) Iron loss
(W17 / 50; W / Kg) Magnetic flux density
(B8; Tesla) division 1150 0.0043 0.0045 0.889 1.907 Comparative Material 20 1150 0.010 0.0098 0.909 1.902 Comparative Material21 1200 0.0043 0.0045 0.784 1.947 Invention Material12 1200 0.010 0.0098 0.868 1.915 Comparative Material 22 1250 0.0043 0.0045 0.792 1.943 Invention Material 13 1250 0.010 0.0098 0.887 1.905 Comparative Material 23 1300 0.0043 0.0045 0.790 1.944 Invention 14 1300 0.010 0.0098 0.887 1.905 Comparative Material 24 1350 0.0043 0.0045 0.925 1.899 Comparative Material 25 1350 0.010 0.0098 0.933 1.898 Comparative Material 26

As can be seen in Table 4, the contents of the steels N and S is 0.006% or less, and the inventive materials 12 to 14 that control the slab heating temperature to 1200 ° C or more and 1300 ° C or less are significantly different from the comparative materials 20 to 26. It can be seen that there is an improvement in magnetic properties. Comparative materials 22 to 24 were heated at 1200 to 1300 ℃ of the slab, but the inferior magnetic properties because the content of the small steel N and S exceeds 0.006%. Comparative materials 20 and 25 are inferior in magnetism, although the content of steel N and S is in the range of the present invention, but the slab heating temperature is out of the range of the present invention.

By weight%, Si: 3.2%, C: 0.055%, Mn: 0.099%, Sol. Ingots were prepared after vacuum dissolving slabs containing Al: 0.028%, P: 0.028%, Sn: 0.085%, N: 0.043%, S: 0.045%, As, balance Fe and other inevitable impurities. As content was changed to various values as shown in Table 5. Subsequently, the ingot was heated at 1250 ° C. for 200 minutes and hot rolled to a thickness of 2.3 mm. The hot rolled hot rolled plate was heated to a temperature of 1050 ° C and then maintained at 950 ° C for 180 seconds and then cooled. The hot-rolled annealing plate was pickled and then cold-rolled once so as to be 0.23 mm thick at a predetermined temperature. The cold rolled plate was maintained at a temperature of 870 ° C. for 180 seconds in a humid atmosphere of mixed hydrogen, nitrogen, and ammonia, and simultaneously decarburized and nitrified to a nitrogen content of 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 the As content were measured and shown in Table 5.

As content (wt%) Iron loss (W17 / 50; W / Kg) Magnetic flux density (B8; Tesla) division 0.001 0.929 1.892 Comparative material 27 0.012 0.795 1.938 Invention 15 0.135 0.810 1.924 Invention 16 0.547 0.826 1.922 Invention 17 1.384 1.101 1.873 Comparative Material 28

As can be seen in Table 5, it can be seen that there is a significant improvement in magnetic properties when Inventions 15 to 17 containing 0.005 to 1.0% of As are compared with the comparative materials. The comparative material 27 contained less than 0.005% of As, and the comparative material 28 contained more than 1.0% of As, resulting in inferior magnetic properties.

Claims (8)

By weight%, Si: 2.0-4.5%, Al: 0.005-0.040%, Mn: 0.20% or less, N: 0.006% or less, S: 0.006% or less, P: 0.005-0.05%, C: 0.04-0.10%, A slab containing 0.08 to 0.10% of Sn and 0.005 to 1.0% of As and consisting of the remaining Fe and other unavoidable impurities is heated to a temperature in the range of 1200 to 1300 ° C, hot rolled, and then hot rolled annealing is performed. Next, after cold rolling, decarburization and nitriding annealing, and then secondary recrystallization annealing, the method of manufacturing a low iron loss high magnetic flux density oriented electrical steel sheet Sn is used as the main grain growth inhibitor . The method according to claim 1,
The decarburization and nitride annealing method for producing a low iron loss high magnetic flux density oriented electrical steel sheet carried out at a temperature range of 800 ~ 950 ℃. The method according to claim 1 or 2,
A method of manufacturing a low iron loss high magnetic flux density oriented electrical steel sheet to control the size of the primary recrystallized grain to 18 ~ 25㎛. The method according to claim 1 or 2,
A method for manufacturing a low iron loss high magnetic flux density oriented electrical steel sheet in which secondary angle is recrystallized so that the β angle is less than 3 ° as the area weighted average of the absolute values of the 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. The method according to claim 1 or 2,
A method of manufacturing a low iron loss high magnetic flux density oriented electrical steel sheet to control the average grain size of the secondary recrystallized steel sheet to 1 ~ 2cm. By weight%, Si: 2.0 to 4.5%, Al: 0.005 to 0.040%, Mn: 0.20% or less, N: 0.006% or less, S: 0.006% or less, P: 0.005 to 0.05%, Sn: 0.08 to 0.10%, As: Low iron loss high magnetic flux density oriented electrical steel sheet containing 0.005 to 1.0% and consisting of the balance Fe and other inevitable impurities. The method of claim 6,
A low iron loss high magnetic flux density oriented electrical steel sheet whose β angle is less than 3 ° as the area weighted average of the absolute values of crystal orientations in secondary recrystallized steel sheets.
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. The method according to claim 6 or 7,
A low iron loss high magnetic flux density oriented electrical steel sheet having an average grain size of 1 ~ 2 cm of secondary recrystallized steel sheet.