KR101149792B1 - Grain-oriented electrical steel sheets with extremely low core loss and high flux density, and Method for manufacturing the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented electrical steel sheet, wherein a high carbon-containing silicon steel slab is heated and hot rolled, followed by hot rolled sheet annealing and cold rolling, followed by decarburization and nitride annealing, followed by secondary recrystallization annealing. In the method for manufacturing an electrical steel sheet, there is provided a low iron loss high magnetic flux density oriented electrical steel sheet production method characterized in that the decarburization is performed simultaneously with the hot rolled sheet annealing.

Grain-oriented electrical steel sheets, ferrosilicon slabs, hot rolled sheet annealing, grains

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 as a core material such as generator or transformer iron core, which is manufactured from a high carbon-containing silicon steel slab to ensure solid solution stability of the inhibitor and by the decarburization performed at the same time as the hot-rolled sheet annealing The present invention relates to a low iron loss high magnetic flux density oriented electrical steel sheet having an extremely good magnetic property due to increased nucleation of goth aggregate tissue and a method of manufacturing the same.

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 that suppress the indiscriminate growth of primary recrystallized grains so that only the goth aggregates can 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, cold rolling was proposed a technique of cold rolling once 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. .

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 a pure annealing at 1200 ° C for 10 hours or more using 100% water extraction, but the 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 order to solve the limitation of the thickness of hot rolled sheet and to optimize the final rolling rate in the production of thin grain oriented electrical steel sheet having a thickness of 0.1 to 0.25 mm, the hot rolled sheet is subjected to pre-rolling of 10 to 50%, followed by hot rolled sheet annealing and cold rolling. A method of manufacturing oriented electrical steel sheet is 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 for improving grain growth inhibition is to add Sn and Sb in combination, hot-rolled by slab heating at a temperature below 1200 ℃, and nitriding by using ammonia gas after cold rolling over 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, by using a high carbon-containing silicon steel slab to improve the goth aggregate structure of the grain-oriented electrical steel sheet and to improve the ultra-thin rolling properties and thermal stability of the inhibitor An object of the present invention is to provide a low iron loss and high magnetic flux density oriented electrical steel sheet having excellent magnetic properties and a method of manufacturing the same.

The low iron loss high magnetic flux density oriented electrical steel sheet manufacturing method of the present invention for solving the above problems is heated and hot rolled high-carbon-containing silicon steel slab, subjected to hot rolled sheet annealing and cold rolling, subjected to decarburization and nitride annealing Thereafter, the secondary recrystallization annealing is performed to produce a grain-oriented electrical steel sheet, characterized in that the decarburization is performed simultaneously with the hot rolled sheet annealing.

The silicon steel slab is in 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: It is preferred to contain 0.005 to 0.05% and consist of the balance Fe and other unavoidable impurities.

Moreover, it is more preferable that the said silicon steel slab further contains 0.01 to 0.3% of Sn and Sb alone or in combination.

The heating temperature of the slab is preferably set to 1050 ~ 1250 ℃.

The hot rolling process preferably includes a process of cooling the hot rolled slab to 15 ° C. or more per second and winding it at a temperature of 580 ° C. or less, and the annealing temperature of the hot rolled plate is preferably 900 to 1200 ° C.

In addition, the hot rolled sheet annealing is particularly preferably carried out by heating the hot rolled sheet to 900 ~ 1200 ℃ in a wet atmosphere at 900 ~ 1100 ℃.

The hot rolled sheet annealing is more preferably included a step of cooling the hot rolled sheet annealing at a rate of 15 ~ 500 ℃ per second.

In the cold rolling, the steel sheet after the hot rolled sheet annealing is preferably rolled to a plate thickness of 0.20 mm or less by one-time cold rolling without performing intermediate annealing.

The low iron loss high magnetic flux density oriented electrical steel sheet of the present invention for solving the above problems is a oriented electrical steel sheet manufactured by heating and hot rolling annealing high carbon-containing silicon steel slab, secondary recrystallization annealing After the average grain size is characterized in that 10 ~ 30mm.

The silicon steel slab is by weight, C: 0.10 to 0.30%, Si: 2.0 to 4.5%, acid soluble Al: 0.005 to 0.040%, Mn: 0.20% or less, N: 0.010% or less, S: 0.010% or less, It is preferable to contain P: 0.005-0.05% and consist of remainder Fe and other unavoidable impurities.

Moreover, it is more preferable that the said silicon steel slab further contains 0.01 to 0.3% of Sn and Sb alone or in combination.

Β angle of the steel sheet is characterized in that less than 3 °.

The steel sheet is preferably produced by performing decarburization at the same time as the hot rolled sheet annealing.

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 inhibiting force and at the same time performing a decarburization at the same time hot rolled sheet annealing {110} <001> orientation By providing the secondary recrystallization nuclei of the oriented electrical steel sheet having extremely excellent magnetic properties can be produced.

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 aggregate by performing decarburization and controlling the cooling process during annealing of the hot rolled sheet.

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. As a result of sufficient recrystallization, the heterogeneous hot-rolled microstructure is completely extinguished and composed of fine grains in all directions, so that precipitates are uniformly dispersed and precipitated in the fine matrix, and cold rolling is also improved, so that once cold rolled 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.

The grain-oriented electrical steel sheet of the present invention is formed with a suitable size of 10 ~ 30mm, the crystal grains after the secondary recrystallization annealing is advantageous for magnetic, and the β angle of the final steel sheet is less than 3 ° due to the increase in the nucleation site of the goth aggregate structure is extremely excellent Magnetic properties are gained.

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 that are finely precipitated during hot rolling and hot-rolled sheet annealing 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 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 to suppress the 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 key element in the present invention, by adding carbon of 0.10% or more and 0.30% or less so as to contain 60% or more of the austenite fraction in the steel sheet. Due to this high fraction of austenite transformation, the phase transformation and recrystallization of the heterogeneous and elongated rolled tissue formed by hot rolling, which is a preliminary process, can be induced actively, thereby homogeneous and finely controlling the structure of the hot-rolled annealing plate. Can be. On the other hand, by performing decarbonization annealing at the same time as the hot-rolled sheet annealing, the goth aggregation structure of the steel plate surface layer grows to the deep part, increasing the fraction of goth grains of the primary recrystallization annealing plate, increasing 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. By promoting the homogenization of the tissue during hot-rolled sheet annealing heat treatment, it is possible to secure a fine and homogeneous microstructure, thereby making the AlN precipitate fine, and when the quenched after hot-rolled sheet annealing or bainite or By promoting martensite formation, it is possible to form a goth texture having a very high degree of orientation in the {110} <001> direction due to 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 known as a grain growth inhibitor because it is a grain boundary segregation element and is an element that hinders the movement of grain boundaries. It also promotes the formation of goth grains in the {110} <001> azimuth, helping secondary recrystallization to develop well. Therefore, as in the present invention, the role of Sn in producing grain-oriented electrical steel sheet is an important element for reinforcing inhibition in addition to AlN, (Al, Si, Mn) N as grain growth inhibitor.

Sb, like Sn, has the effect of suppressing crystal growth as a grain boundary segregation element, and 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. In the present invention, by adding Sn and Sb alone or in combination to obtain a crystal growth inhibitory effect and adding 0.01% to 0.3% of Sn and Sb alone or in combination to form more Goth grains of the {110} <001> orientation It is preferable.

If Sn and Sb are added alone or in combination less than 0.01% by weight, it is difficult to obtain the effect, and when it is added in excess of 0.3% by weight, the effect on additional input cost is insignificant, and grain boundary segregation is severe, resulting in high brittleness of the steel sheet. You lose. Therefore, Sn and Sb is preferably added 0.01 to 0.3% by weight alone or in combination.

P is an element having a similar effect to Sn and Sb, and segregates in the grain boundary to hinder the movement of the grain boundary and at the same time have a secondary role of inhibiting grain growth. There is an effect of improving the {110} <001> aggregate tissue in terms of microstructure. If the content of P is less than 0.005% by weight, there is no addition effect, and when it is added in excess of 0.05% by weight, brittleness is increased and the rolling property is deteriorated, so it is preferable to limit it to 0.005 to 0.05% by weight.

Hereinafter will be described for the 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 580 ° 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 580 ° C, coarse carbides are also formed, so the winding temperature is preferably limited to 580 ° 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, or oil cooling, or two or more of them may be mixed.

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. At this time, it is preferable to perform a one-time cold rolling to roll the thickness of the final product directly from the initial hot rolled thickness without performing annealing heat treatment 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 preferably rolled at a cold rolling rate of 90% or more by one cold rolling.

The cold rolled plate is subjected to decarburization, recrystallization of deformed tissue, and nitriding using ammonia gas to react the acid-soluble aluminum dissolved in the substrate with nitrogen in the hot rolled sheet annealing to obtain 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, tin oxide (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 at the same time as the 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. By forming a {110} <001> texture in which the direction is parallel to the rolling direction, a grain-oriented electrical steel sheet having excellent magnetic properties is produced. 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 heating zone before the secondary recrystallization occurs, the mixed gas of nitrogen and hydrogen is maintained to protect the nitride, which is a particle growth inhibitor, so that the secondary recrystallization is well developed, 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.

Example 1

Si: 3.3%, C: 0.15%, Mn: 0.090%, S: 0.003%, N: 0.004% by weight, Sol. Slabs containing Al: 0.028%, P: 0.030% and Sb: 0.10% 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., followed by thickness 2.0mm It was hot-rolled and cooled to a winding temperature of 580 ° C at a cooling rate of 50 ° C per second. The hot rolled sheet thus obtained was annealed and decarburized in a wet atmosphere. At this time, the hot rolled sheet annealing was carried out by heating to 1050 ℃ and maintained at 950 ℃ for 180 seconds, the hot rolled sheet annealing was quenched at a cooling rate of 50 ℃ per second. The quenched hot-rolled annealing plate was pickled and cold-rolled once to a thickness of 0.20 mm, and then maintained at 850 ° C. for 180 seconds in a humid hydrogen, nitrogen, and ammonia mixed gas atmosphere to denitrify and nitrify the nitrogen to 200 ppm. Was carried out. MgO, an annealing separator, was applied to the steel sheet and finally annealed into a coil. The final annealing was a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ℃, and after reaching at 1200 ℃ for 10 hours at 100% hydrogen atmosphere, it was quenched to obtain a final steel sheet.

On the other hand, for comparison, some of the steel sheets were annealed without annealing during the annealing of the hot rolled sheet, except that the hot rolled sheet was annealed in a nitrogen atmosphere instead of a wet atmosphere. This was used as a comparative material.

In addition, the slab contained 0.05% of C, and only the hot-rolled sheet annealing was carried out in a nitrogen atmosphere, and the other conditions were the same as in the production of the test material to obtain a final steel sheet, which was used as a conventional material.

The magnetic properties of each condition were measured and shown in Table 1.

[Table 1]

As shown in Table 1, the test material using 0.15% high carbon containing slab and decarburizing during hot-rolled sheet annealing, compared to the conventional material using C: 0.05% -containing slab and not performing decarburization during hot-rolled sheet annealing Iron loss and magnetic flux density were very good.

In the case of the comparative material, 0.15% high carbon containing slab was used, but decarburization was not performed during annealing of the hot rolled sheet, resulting in high residual annealed sheet C and deterioration of magnetic flux density and iron loss.

[Example 2]

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% and Sn + Sb: 0.10%, containing the remaining Fe and other inevitable impurities, are vacuum-dissolved to form an ingot, and then heated to a temperature of 1200 ° C., followed by thickness Hot rolled at 2.0 mm, and then wound at a temperature of 580 ℃ after cooling at a cooling rate of 50 ℃ per second. The hot rolled hot rolled sheet was heated at a temperature of 1050 ° C. and maintained at 950 ° C. for 180 seconds to perform hot rolled sheet annealing. At the same time, the hot rolled sheet was annealed in a wet atmosphere. The hot rolled sheet was quenched at a cooling rate of 50 ° C. per second, and the quenched hot rolled sheet was pickled and cold rolled once to a thickness of 0.20 mm. The cold rolled plate was annealed simultaneously for 180 seconds in a humid atmosphere of mixed hydrogen, nitrogen, and ammonia at a temperature of 850 ° C. to a nitrogen content of 200 ppm. MgO, an annealing separator, was applied to the steel sheet and finally annealed into 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 magnetic properties, the average grain size of the final steel plate, and the β angle of the final steel plate were measured and shown in Table 2 below.

TABLE 2

As shown in Table 2, the inventive material which controlled the carbon content to 0.1 to 0.3% by weight belonging to the scope of the present invention has an iron loss of 0.90 (W17 / 50) or less, and a magnetic flux density of 1.92 (B10) or more. The magnetic properties are very good in comparison with the comparable materials. In particular, it can be seen that in the case of the comparative material in which the carbon content exceeds 0.3% by weight, the magnetic properties are considerably thermally deteriorated. This is because decarburization does not occur sufficiently due to excess carbon content, inferior to the magnetic properties of the final product.

Thus, the steel sheet manufactured by using slab containing 0.1 to 0.3% by weight of carbon and decarburized simultaneously with hot-rolled sheet annealing was formed in an appropriate size of 10 to 30 mm in which the average grain after secondary recrystallization was favorable for magnetism. When the average grain size after the secondary recrystallization was less than 10 mm, the magnetic flux density was extremely low and the iron loss was very high. The magnetic flux density and the iron loss were deteriorated even when the average grain size exceeded 30 mm.

In addition, in the case of the invention material which is manufactured by using slab containing 0.1 to 0.3% by weight of carbon and decarburized at the same time as hot-rolled sheet annealing, and the average grain after secondary recrystallization is 10 ~ 30 mm, the nucleation site of goth assembly tissue is increased. As a result, the β angle of the final steel sheet showing the degree of deviation from the goth direction is less than 3 °, and the orientation is significantly improved compared to the conventional oriented electrical steel sheet, and thus it is confirmed that the oriented electrical steel sheet having extremely excellent magnetic properties can be manufactured. It became.

Example 3

Si: 3.1%, C: 0.25%, Mn: 0.10%, S: 0.003%, N: 0.004% by weight, Sol. Slabs containing Al: 0.028%, P: 0.027% and Sn: 0.10%, containing the remaining Fe and other unavoidable impurities, are vacuum-dissolved, ingots are formed, and then heated to various temperatures, and then heated to a thickness of 2.0 mm. It was rolled, cooled at various cooling rates, and wound up at different winding temperatures. The hot rolled hot rolled sheet was heated to annealing at various conditions and the cooling rate was changed. The quenched hot-rolled annealing plate was pickled and then cold-rolled once to a thickness of 0.20 mm. The cold rolled plate was decarburized and nitrided and annealed at a temperature of 850 ° C. for 180 seconds in a humid atmosphere of mixed hydrogen, nitrogen, and ammonia to achieve a nitrogen content of 200 ppm. MgO, an annealing separator, was applied to the steel sheet and finally annealed into 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 2 below.

[Table 3]

As shown in Table 3, Test Sample K, which heated the slab to a temperature higher than 1250 ° C., was difficult to perform hot rolling, and in the case of Test Material H heated to a temperature lower than 1050 ° C., the solid solution of the inhibitor was insufficient. Inferior.

Test sample G, which cooled the hot-rolled slab to less than 15 ° C per second, was inferior in magnetism due to the formation of coarse carbides and reduced homogeneity of the structure, and test sample C, which wound the hot-rolled steel sheet at a temperature above 580 ° C, Again, the inferior magnetism was due to the formation of coarse carbides.

In addition, Test Material A having a hot-rolled sheet annealing temperature of less than 900 ° C. was inferior in magnetic properties because sufficient austenite phase was not secured and the grain growth inhibitor had low solubility. Test specimen K having a hot-rolled sheet annealing temperature exceeding 1200 ° C. was inferior in cold rolling property and inferior in magnetic properties.

In Test F, the hot-rolled steel sheet was cooled at a rate of less than 15 ° C per second, and coarse lamellar structure of cementite and ferrite was formed, resulting in weak formation of shear strain, and carbon in cementite was cemented. In addition to being present in the grain boundary alone as a plate-shaped or spherical carbides caused a nonuniformity of the tissue was inferior to the magnetic. In the case of Test Material H in which the hot rolled sheet was cooled at a rate exceeding 500 ° C. per second, cold rolling was not easy, and the quality of the cold rolled sheet was inferior.

On the other hand, as in the scope of the present invention, the slab is heated to 1050 ~ 1250 ℃, the hot rolled slab is cooled to 15 ℃ or more per second and wound up at a temperature of 580 ℃ or less, annealing hot rolled plate at a temperature of 900 ~ 1200 ℃ In case of test materials B, D, E, I, J, the hot-rolled steel sheet was cooled at a rate of 15 ~ 500 ℃ per second, the iron loss was 0.90 (W17 / 50) or less, and the magnetic flux density was 1.92 (B10) or more. Magnetic properties were very good.

Claims (19)

In the method of manufacturing a grain-oriented electrical steel sheet by heating and hot rolling a silicon steel slab, performing hot rolled sheet annealing and cold rolling, decarburizing and nitride annealing, and then performing secondary recrystallization annealing. The silicon steel slab contains C: 0.10 to 0.30% by weight, and a low iron loss high magnetic flux density oriented electrical steel sheet characterized in that the hot rolled sheet annealing at the same time as the hot rolled sheet annealing. delete The method according to claim 1, The silicon steel slab is by weight, in the state containing C: 0.10 to 0.30%, Si: 2.0 to 4.5%, Al: 0.005 to 0.040%, Mn: more than 0 to 0.20% or less, N: more than 0 to 0.010 A method for producing a low iron loss high magnetic flux density oriented electrical steel sheet, which comprises% or less, S: greater than 0 to 0.010%, P: 0.005 to 0.05%, and is made of residual Fe and other unavoidable impurities. The method of claim 3, The silicon steel slab is a low iron loss high magnetic flux density oriented electrical steel sheet manufacturing method characterized in that it further contains 0.01 ~ 0.3% of Sn and Sb alone or in combination. The method according to any one of claims 1, 3, 4, The heating temperature of the slab is a low iron loss high magnetic flux density oriented electrical steel sheet manufacturing method characterized in that 1050 ~ 1250 ℃. The method according to any one of claims 1, 3, 4, The hot rolling process is a method for producing a low iron loss high magnetic flux density oriented electrical steel sheet comprising the step of cooling the hot-rolled slab to 15 ℃ or more per second and wound at a temperature of 580 ℃ or less. The method according to any one of claims 1, 3, 4, The annealing temperature of the hot rolled sheet is a low iron loss high magnetic flux density oriented electrical steel sheet, characterized in that 900 ~ 1200 ℃. The method according to any one of claims 1, 3, 4, The hot rolled sheet annealing is a low iron loss high magnetic flux density oriented electrical steel sheet manufacturing method characterized in that carried out by heating the hot rolled sheet to 900 ~ 1200 ℃ in a wet atmosphere. The method according to claim 8, The hot rolled sheet annealing is a low iron loss high magnetic flux density oriented electrical steel sheet manufacturing method comprising the step of cooling the hot rolled sheet annealing at a rate of 15 ~ 500 ℃ per second. The method according to any one of claims 1, 3, 4, The cold rolling is a low iron loss high magnetic flux density oriented electrical steel sheet manufacturing method characterized in that the one-time cold cold rolling without intermediate annealing. The method of claim 10, The cold rolling is a method for producing a low iron loss high magnetic flux density oriented electrical steel sheet, characterized in that the hot rolled sheet annealing the steel sheet to a thickness of 0.20mm or less. In the grain-oriented electrical steel sheet produced by heating a silicon steel slab, annealing a hot rolled sheet, followed by hot rolling and cold rolling, The silicon steel slab contains C: 0.10 to 0.30% by weight, the average grain size after secondary recrystallization annealing is 10 ~ 30mm, and the steel sheet is produced by performing hot-rolled sheet decarburization at the same time as the hot-rolled sheet annealing Low iron loss high magnetic flux density oriented electrical steel sheet. delete The method according to claim 12, The silicon steel slab is in weight percent, in a state containing C: 0.10 to 0.30%, Si: 2.0 to 4.5%, acid soluble Al: 0.005 to 0.040%, Mn: greater than 0 to 0.20%, N: greater than 0 A low iron loss high magnetic flux density oriented electrical steel sheet containing less than ~ 0.010%, S: over 0 to 0.010%, P: 0.005 to 0.05%, and consisting of the balance Fe and other unavoidable impurities. The method according to claim 14, The silicon steel slab is a low iron loss high magnetic flux density oriented electrical steel sheet, characterized in that it further contains 0.01 to 0.3% of Sn and Sb alone or in combination. The method according to any one of claims 12,14,15, Β angle of the steel sheet is low iron loss high magnetic flux density oriented electrical steel sheet, characterized in that less than 3 °. However, β angle represents the degree of deviation from the goth direction, and is the angle between the [100] direction and the rolling direction about the axis of the rolling perpendicular direction of the secondary recrystallized texture. delete The method according to any one of claims 12,14,15, The sheet thickness of the steel sheet is 0.20mm or less low iron loss high magnetic flux density oriented electrical steel sheet. The method according to any one of claims 12,14,15, The iron loss (W17 / 50) of the steel sheet is 0.90W / Kg or less, the magnetic flux density (B10) is low iron loss high magnetic flux density oriented electrical steel sheet, characterized in that more than 1.92T.