KR101263851B1 - Method for manufacturing grain-oriented electrical steel sheets with extremely low core-loss and high flux-density - Google Patents

Abstract

The present invention relates to a grain-oriented electrical steel sheet, in weight percent, C: 0.10 to 0.30%, Si: 2.0 to 4.5%, Al: 0.005 to 0.040%, Mn: 0.20% or less, N: 0.006% or less, S: 0.006 High carbon-containing silicon steel slab containing less than or equal to% and P: 0.005 to 0.05% and consisting of remainder Fe and other unavoidable impurities, is heated to a temperature of 1200 ° C or more and 1300 ° C or less, followed by hot rolling After cold rolling, followed by decarburization and nitriding annealing, secondary recrystallization annealing was performed, and the hot rolled sheet annealing was performed using a low temperature loss high magnetic flux density oriented electrical steel sheet using a medium temperature slab heating method. It provides a manufacturing method.
Therefore, by using a high carbon-containing silicon steel slab to enhance the thermal stability of the inhibitor to have a strong crystal growth suppression, while performing hot-rolled sheet annealing and decarburization at the same time, the highly oriented {110} <001> azimuth secondary By providing the recrystallized nucleus, it is possible to produce a grain-oriented electrical steel sheet having extremely excellent magnetic properties.

Description

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

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of oriented electrical steel sheets used as iron core materials for electronic devices such as generators and transformers, and is manufactured from high carbon-containing silicon steel slabs to ensure solid solution stability of the inhibitor and to be carried out simultaneously with hot rolled sheet annealing. The present invention relates to a method for manufacturing a low iron loss high magnetic flux density oriented electrical steel sheet having an extremely good magnetic property by increasing nucleation of a goth aggregated tissue by a medium temperature slab heating 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.

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

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

The research and development to improve the magnetism of oriented electrical steel sheet first started from the attempt to increase the magnetic flux density. Initially oriented electrical steel sheets were prepared by two cold rolling methods using MnS as grain growth inhibitors as suggested by MF Littman. According to this, secondary recrystallization was formed stably, but the magnetic flux density was not high and iron loss was high. It was.

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

In addition, there is a technology for producing a grain-oriented electrical steel sheet using MnSe and Sb as inhibitors, but not MnS and AlN, but it is subjected to two cold rolling including intermediate annealing heat treatment and grain growth of expensive grains such as Sb and Se Since it is used as an inhibitor, there is a problem that the manufacturing cost is increased and these elements are toxic and workability is bad.

The above technologies are designed to exert a strong crystal growth inhibitory effect by allowing the fully employed AlN and MnS precipitates to be finely precipitated during hot rolling and subsequent hot-rolled sheet annealing, and MnS or AlN contained in the slab of the grain-oriented electrical steel sheet. Stable solid solution can be used as a grain growth inhibitor by controlling the precipitate to have the proper size and distribution during cooling after hot rolling. Therefore, the slab must be reheated at a high temperature for a long time.

Assuming that the steel sheet containing 3% silicon is in the ferrite phase, the solubility of AlN 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.

In addition, the technology of using MnS as a grain growth inhibitor, the technology of using MnS and AlN as a grain growth inhibitor, and the technology of using MnSe and Sb as grain growth inhibitors, respectively, have a slab reheating temperature of 1300 ° C or higher, 1350 ° C or higher and 1320 ° C or higher. It is known to be raised. In practice, however, considering the steel slab weight of about 20 tons for commercial production, in order to obtain a uniform temperature distribution to the inside of the slab it is reheated to almost 1400 ℃.

As described above, when the steel slab is heated for a long time at a high temperature of about 1400 ° C., various problems may occur commercially. That is, the production cost increases due to the large amount of heat used, and the oxidized scale existing on the surface of the steel slab melts and flows into the furnace near 1300 ° C, so that the refractory to the furnace needs to be repaired frequently. There is a problem of this being shortened. Even more serious problem is the fact that due to the long time slab heating at high temperature, the columnar structure, which is the cast structure of steel slab, grows quite coarsely, and the hot rolling plate breaks in the width direction due to the coarse columnar structure in the hot rolling process. This can be significantly lowered.

In order to solve the above serious problems, it is possible to produce a high magnetic flux density oriented electrical steel sheet by controlling the appropriate size and distribution of grain growth inhibitor while lowering the reheating temperature of the steel slab, which will have a significant effect in terms of manufacturing cost and error rate. Can be. As the above demands rise, new technologies have been studied that do not use MnS, which has a relatively high solidus temperature, as the primary grain growth inhibitor.

That is, the slab is heated to a low temperature to hot roll the AlN, which is a grain growth inhibitor, without fully employing it, and when the hot rolled sheet is annealed, the AlN is completely precipitated and nitrided in the process after cold rolling to form nitride. These are techniques that aim to suppress grain growth of grains. The above-mentioned techniques are generally known as low temperature slab heating.

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.

To summarize the conventional techniques discussed so far, the development of crystal growth inhibitors and the slab heating temperature and hot-rolled sheet annealing control techniques to secure high magnetic flux density characteristics have been proposed, but the actual conditions presented are strict production conditions that act as a burden on the production process. In addition, the high temperature slab heating method has problems such as an increase in manufacturing cost and a decrease in the error rate of the hot rolled plate, and the low temperature slab heating method has a low crystal growth inhibitory ability, which leads to a limit in magnetic enhancement.

The present invention has been made to solve all the problems of the prior art as described above, the object of the present invention is to improve the goose structure of the grain-oriented electrical steel sheet using high carbon-containing silicon steel slab and to improve the thermal rolling stability and thermal stability of the inhibitor The present invention aims to provide a method for producing low iron loss and high magnetic flux density oriented electrical steel sheet having a medium magnetic slab heating method by improving the temperature of the slab.

Method for producing a low iron loss high magnetic flux density oriented electrical steel sheet of the present invention for solving the above problems in weight%, C: 0.10 ~ 0.30%, Si: 2.0 ~ 4.5%, Al: 0.005 ~ 0.040%, Mn: 0.20% Hereafter, a high carbon-containing silicon steel slab containing N: 0.006% or less, S: 0.006% or less, P: 0.005% to 0.05%, balance Fe and other unavoidable impurities, at a temperature of 1200 ° C or more and 1300 ° C or less After heating and hot rolling, hot rolling followed by annealing, followed by decarburization and nitriding annealing, and then secondary recrystallization annealing, wherein the hot rolled sheet annealing is performed such that decarburization is performed. .

The silicon steel slab preferably further contains 0.01 to 0.3% of Sn and Sb alone or in combination.

The method for producing a low iron loss high magnetic flux density oriented electrical steel sheet of the present invention is characterized in that the primary recrystallized grain size is controlled to 19 µm or less when decarburization and annealing are performed at a temperature in the range of 820 to 880 ° C.

According to the present invention, by using a high carbon-containing silicon steel slab to enhance the thermal stability of the inhibitor to have a strong crystal growth inhibition and at the same time to make the decarburization during hot-rolled sheet annealing {110} <001> azimuth By providing the secondary recrystallization nuclei of the oriented electrical steel sheet having excellent magnetic properties, it can be produced by the medium temperature slab heating method.

In addition, by using a component-based slab containing less than 0.006% by weight of N and S and heating the slab to a medium temperature of 1200 to 1300 ° C. to completely solidify the grain growth inhibitor, the primary recrystallized grains in a wide range of decarburization and annealing temperature By forming it in an appropriate size, it is possible to stably manufacture a grain-oriented electrical steel sheet having extremely excellent magnetic properties.

Hereinafter, the present invention will be described in detail.

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

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

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

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

As the austenite phase in the slab increases, the temperature of AlN is lowered. Therefore, when a large amount of carbon is added to the slab and the austenite fraction is increased, the solubility of AlN is maximized to secure sufficient grain growth restraining ability.

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

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

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

On the other hand, the carbon present in the hot rolled plate not only participates in the austenite phase control as described above, but also acts on the secondary recrystallization nucleation site generated during cold rolling. In general, when cold rolled steel sheet, the blade potential and screw potential are generated by the interaction between the main stress and the shear stress. In terms of crystallography, such dislocations are more likely to occur on austenite having a face-centered cubic structure than a ferrite having a body-centered cubic structure, and form a shear deformation zone serving as a secondary recrystallization nucleation site.

However, since cold rolling is performed in the ferrite single-phase temperature range, the generation of dislocations is relatively small, which makes it difficult to form many shear deformation zones. Even though the shear deformation zones are formed, they are formed as uneven distribution in the microstructure. The shift of dislocation is proportional to the rolling reduction acting upon rolling and the temperature of rolling.The higher the rolling reduction, the higher the dislocation generation, but the dislocation is difficult to move, so that the shear deformation in the steel sheet is unevenly formed. On the other hand, the amount of shear deformation is reduced by the disappearance or the formation of sublattices or subgrains due to the incorporation of positive and negative potentials. Nevertheless, invasive elements such as carbon increase the Peierls-Nabarro force required for dislocation movement and form a Cottrell-Lomer atmosphere at the tip of the dislocation. It shows the effect of fixing. In general, as the temperature rises, the diffusion speed of invasive elements such as carbon becomes faster than the movement speed of the potential, so that not only the movement of the potential is active but also the temperature at which the adhesion of the potential by carbon can be efficiently controlled. Cold rolling in the zone causes a large amount of shear deformation within the steel sheet, and within this shear deformation zone, the grains in the {110} <001> direction, the nucleus of secondary recrystallization, are easily recrystallized. The aggregate structure of the {110} <001> bearing is increased, which increases the density of the secondary recrystallized {110} <001> goth aggregate, thereby securing high magnetic flux density and magnetic properties of low iron loss. .

As described above, the role of carbon in the grain-oriented electrical steel sheet is very large. However, when a large amount of carbon is present in the final product, the first recrystallization annealing process occurs as a result of self-ageing which greatly increases iron loss by forming fine carbides over time. Carbon must be removed from

If a lot of carbon is added to the slab, it is common to require a lot of time for decarburization. However, decarburization takes place as a result of diffusion of carbon atoms, so the time required for decarburization is inversely proportional to the decarburization temperature and proportional to the movement distance of the carbon atoms, and the higher the decarburization temperature, the faster the decarburization proceeds, and the thinner the steel sheet the carbon is. The time to move to the surface and remove is shortened. This means that the thinner the steel sheet thickness, the less time required for decarburization and the higher the carbon content under a given decarbonization annealing condition.

In conclusion, the present invention adds 0.10 to 0.30% by weight of carbon to the silicon steel slab to induce fine homogeneous dispersion of the inhibitor in hot rolled and hot rolled sheet annealing plate, and performs hot-rolled sheet annealing heat treatment in a wet atmosphere. To increase the fraction of the Goss texture, and then to increase the shear deformation by one cold-rolling after hot-rolled sheet annealing, and to increase the orientation of the {110} <001> -oriented Goth secondary recrystallized nucleus. You can get it.

In line with the above findings, the inventors of the present invention provide a method for stably obtaining primary recrystallized grains of suitable size in a wide range of decarburization and annealing temperature, and in the component system containing low steel N and S, the grain growth inhibitor is completely used when the slab is heated. It was found that the reheating method in the range of 1200 ~ 1300 ° C, which is the temperature to be embodied, is very effective.

The size of the primary recrystallized grain is mainly determined by the AlN and MnS precipitates which exist after hot rolling. The effect of the grain growth inhibition of these precipitates is a fine precipitate and dispersion after the complete solidification of the precipitates in the reheating of the steel slab. Since it depends on the precipitate, the larger the number of fine precipitates, the slower growth of the primary recrystallized grains occurs. In the present invention, it is stable in a wide range of decarburization and annealing temperature by using a slab of a component system containing N and S of 0.006% by weight or less and heating the slab to a medium temperature of 1200 to 1300 ° C. so that the AlN and MnS inhibitors are completely dissolved. As a result, the size of the primary recrystallized grains is 19 μm or less, and when the size of the primary recrystallized grains is smaller than 19 μm, the secondary recrystallization cannot be formed in a subsequent process, and the magnetic properties are not deteriorated. This is because the nitrides such as AlN in the present invention can act as an inhibitor because the thermal stability is maintained up to 1100 ℃ temperature described above.

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

Si is a basic composition of an electric steel sheet and plays a role of lowering the core loss by increasing the resistivity of the material. If the Si content is less than 2.0%, the resistivity decreases, the iron loss characteristics deteriorate, and there is a phase transformation section at high temperature annealing, so the secondary recrystallization becomes unstable. This becomes severe and the secondary recrystallization becomes unstable. Therefore, Si is limited to 2.0 to 4.5% by weight.

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

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

N is an important element that reacts with Al to form AlN and is preferably contained at 0.006% by weight or less in the steelmaking step.

If it contains more than 0.006% by weight, the heating furnace should be maintained at 1300 ℃ or higher in order to uniformly heat the steel slab to the complete solution temperature. This causes the oxidation scale of the steel slab surface to melt and flow down. It has a fatal weakness which high temperature heating method has and becomes uneconomical. Therefore, N is made into 0.006 weight% or less, More preferably, you may be 0.004 weight% or less.

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

In addition, the austenite phase may be transformed into a hard bainite phase or martensite phase having a very high intensity or a mixture transformation of the two phases through a quenching process by controlling a predetermined cooling rate. The bainite phase or martensite phase transformed by quenching provides an austenitic nucleation site in the hot-rolled sheet annealing process to promote homogenization of the tissue during the hot-rolled sheet annealing process, thereby securing a fine and homogeneous microstructure. The precipitate can be made fine, and when the quenching is completed after hot-rolled sheet annealing, it promotes the formation of bainite or martensite phase, so that the Goth texture has a very high orientation in the {110} <001> direction due to the concentration of strain stress during cold rolling. Is formed. Subsequently, during one cold-rolling, the strain stress is increased around the bainite or martensite, which is much stronger than the ferrite, which is the base structure, and the shear deformation band increases in the steel sheet. The remaining carbon increases the shear strain by activating the dislocation fixation during cold rolling, so that the grains of the {110} <001> orientation, which is the nucleus of the secondary recrystallization, are easily recrystallized and {110} <001 in the primary recrystallization texture. > The fraction of Goth grains is increased by showing the effect of inducing the increase of nucleation of the texture of the defense.

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.

If S is contained in excess of 0.006%, the heating furnace must be maintained at 1300 ° C or higher in order to uniformly heat the slab to a temperature at which the solution is completely dissolved. It is economical. In addition, if the slab is heated to a temperature higher than the total solution when S is contained in an amount exceeding 0.006% by weight, the size of the primary recrystallized grains becomes too small, which lowers the secondary recrystallization initiation temperature. Oriented grains also cause secondary recrystallization, degrading magnetism. Therefore, S is limited to 0.006% by weight or less, more preferably 0.004% by weight or less.

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

The grain-oriented electrical steel sheet manufactured by using the slab having the above composition is formed in an appropriate size of 10 to 30 mm in which crystal grains after secondary recrystallization annealing are advantageous for magnetism, and increase the nucleation site of the goth aggregated tissue in the goth aggregated structure and in the rolling direction. Beta orientation (β angle; angle between [001] orientation and RD orientation based on TD orientation), which is one of the defense relations, is secured to within 3 ° and at a medium temperature of 1200 to 1300 ° C. in which the grain growth inhibitor is completely dissolved. By heating the slab, the primary recrystallized grains are stably formed in a range of 20 μm or less in a wide range of decarburization and annealing temperature, thereby having extremely excellent magnetic properties.

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

Carbon content and slab heating conditions are very important in relieving the casting structure, which is the columnar structure at the steelmaking stage, and reusing the coarse precipitates deposited during solidification to room temperature after casting. In the present invention, the steel slab reheating temperature before hot rolling is heated at 1200 to 1300 ° C., which is a temperature at which precipitates used as grain growth inhibitors are completely dissolved. For the component system exceeding the component limit range of N and S presented in the present invention, when the steel slab reheating temperature is partially solutioned, a large difference occurs in the precipitates produced during casting and the precipitates produced during re-heating. Since the grain size of the secondary recrystallization plate may become uneven and the magnetism may become uneven, the heating temperature of the silicon steel slab is limited to 1200 ° C. to 1300 ° C., which is a temperature range in which the precipitates are completely dissolved.

In order to secure the stability of grains of grain-oriented electrical steel sheet, the contents of acid-soluble Al and small steel N are very important. 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 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, acid-soluble Al and calcined steel N must be controlled, where acid-soluble Al should be 0.005 ~ 0.040%, and calcined steel N should be less than 0.006%.

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.

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

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

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

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

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

In the cooling after the annealing heat treatment of the hot rolled plate as described above, it is preferable to perform a quenching treatment. Slow cooling reduces the amount of acid-soluble aluminum due to the additional precipitation of grain growth inhibitors such as AlN and MnS, and reduces coarse layered structures of cementite and ferrite instead of phases such as relatively high strength bainite or martensite. Perlite, which is a mixed structure, is formed, so that the formation of shear deformation zone due to work hardening is weakened during subsequent cold rolling. In addition, not only carbon is present as cementite in perlite, but also as a plate-shaped or spherical carbide at grain boundaries, resulting in nonuniformity of tissue. However, if the cooling rate exceeds 600 ℃ per second, the austenite phase is transformed into a martensite phase with a high total strength, which puts a load on the cold rolling process and the quality of the cold rolled sheet is inferior.

Therefore, hot-rolled sheet annealing is heated to a temperature of 900 ℃ or more than 1200 ℃, then subjected to crack treatment and decarbonization annealing in a wet atmosphere at a temperature of 900 ℃ or more than 1100 ℃ and then cooling rate of 15 ℃ or more and 600 ℃ or less per second It is preferable to cool by. In this case, the cooling method may be performed by air cooling, water cooling, oil cooling, or the like, or a mixture of two or more thereof may be applied.

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

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

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

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

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

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

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

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

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

By weight%, Si: 3.2%, C: 0.080-0.321%, Mn: 0.090%, S: 0.003%, N: 0.004%, Sol. Slabs containing Al: 0.030%, P: 0.028%, Sn + Sb: 0.10% and containing the remaining Fe and other unavoidable 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 to a temperature of 1050 ° C. and maintained at 950 ° C. for 180 seconds to perform hot rolled sheet annealing, and the hot rolled sheet was annealed in a wet atmosphere to simultaneously perform decarburization. The hot rolled sheet was quenched at a cooling rate of 50 ° C. per second, and the quenched hot rolled annealing plate was pickled and then cold rolled once to a thickness of 0.20 mm at a temperature of 200 ° C. The cold rolled plate was maintained at 850 ° C. for 180 seconds in a humid hydrogen, nitrogen, and ammonia mixed gas atmosphere to simultaneously denitrify and anneal so that the nitrogen content was 200 ppm. This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. 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 1 below.

As shown in Table 1, 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 having a carbon content of more than 0.3% by weight, the magnetic properties are very poor. 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.

By weight%, Si: 3.2%, C: 0.225-0.233%, Mn: 0.090%, S: 0.003%, N: 0.004%, Sol. The grain-oriented electrical steel slab containing Al: 0.028% and consisting of the remaining Fe and other inevitable impurities was heated. In the above-described grain-oriented electrical steel slab, the complete solution temperature of AlN is 1217 ° C, and the complete solution temperature of MnS is 1173 ° C. The slab was heated to 1250 ° C., which was higher than 1150 ° C., the temperature at which both AlN and MnS were partially solvated, and higher than 1217 ° C., which was the temperature at which both AlN and MnS were completely dissolved. For comparison with the inventive material, the slab heating temperature was set to 1150 ° C for some of them.

After slab heating, hot rolling was made by hot rolling to prepare a hot rolled sheet having a thickness of 2.3 mm. The hot rolled sheet was heated to 1050 ° C. and then maintained at 900 ° C. for 180 seconds to anneal the hot rolled sheet, followed by water cooling at a cooling rate of 50 ° C. per second, and the winding temperature. It cooled to 600 degreeC which is phosphorus. Hot-rolled sheet annealing heat treatment was carried out in a wet atmosphere to decarburize. Subsequently, the hot-rolled annealing plate was pickled and then cold-rolled once so as to be 0.23 mm thick. Cold rolled plate is maintained for 180 seconds in the atmosphere of mixed hydrogen and nitrogen and ammonia gas, and the temperature is changed to 820 ℃, 840 ℃, 860 ℃, and 880 ℃ so that nitrogen content is 180 ~ 200ppm. It was.

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. 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. The primary recrystallized grain size and magnetic properties for each condition are shown in Table 2 below.

As shown in Table 2, Inventive Materials 1 to 4, which were slab heated to a temperature where both AlN and MnS were completely dissolved, had a primary recrystallized grain size in all cases where the decarburization and annealing temperatures were varied from 820 to 880 ° C. 20 µm or less, and it was found that the magnetic properties were superior to those of Comparative Materials 1-4, which were heated at a temperature where both AlN and MnS were partially dissolved.

On the other hand, when the decarburization and nitride annealing temperature is 880 ℃, the comparative material 4 is quite inferior in magnetic properties, while the magnetic properties of the invention material 4 controlled by the complete solution temperature is confirmed to be good.

By weight%, Si: 3.2%, C: 0.225-0.233%, Mn: 0.090%, S: 0.003%, N: 0.004%, Sol. The grain-oriented electrical steel slab containing Al: 0.028% and consisting of the remaining Fe and other inevitable impurities was heated. In the above-described grain-oriented electrical steel slab, the complete solution temperature of AlN is 1217 ° C, and the complete solution temperature of MnS is 1173 ° C. The slab was heated to 1250 ° C., which was higher than 1150 ° C., the temperature at which both AlN and MnS were partially solvated, and higher than 1217 ° C., which was the temperature at which both AlN and MnS were completely dissolved. For comparison with the inventive material, the slab heating temperature was set to 1150 ° C for some of them.

After slab heating, hot rolling was performed to prepare a hot rolled sheet having a thickness of 2.3 mm. The hot rolled sheet was heated to a temperature of 1050 ° C., and then maintained at 950 ° C. for 180 seconds to be annealed, followed by water cooling at a cooling rate of 50 ° C. per second, followed by a coiling temperature. It cooled to 600 degreeC which is phosphorus. Hot-rolled sheet annealing heat treatment was carried out in a wet atmosphere to decarburize. Subsequently, the hot rolled annealing plate was pickled and then cold rolled once to prepare a cold rolled plate having various thicknesses of 0.30 to 0.20 mm. The cold rolled plate was maintained at 860 ° C. for 180 seconds in a humid atmosphere of mixed hydrogen, nitrogen, and ammonia gas, and subjected to simultaneous decarburization and annealing to achieve nitrogen content of 180 to 200 ppm.

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. 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 primary recrystallized grain size and magnetic properties were measured and shown in Table 3 below.

As shown in Table 3, Invention 3 and Inventive Materials 5 to 7 which were slab heated to a temperature where both AlN and MnS were completely dissolved were dissolved, and the slab heating temperature was less than 20 µm. It can be seen that the magnetic properties are superior to those of Comparative Materials 3 and 5 to 7, which all belong to the partial solution temperature range.

In particular, it is confirmed that the inventive material 7 can obtain excellent magnetic properties despite the fact that the thickness of the cold rolled sheet is 0.20 mm, which is an ultra-thin material in which the grain growth inhibition is weakened.

Claims (3)

By weight%, C: 0.10 to 0.30%, Si: 2.0 to 4.5%, Al: 0.005 to 0.040%, Mn: 0.20% or less, N: 0.006% or less, S: 0.006% or less, P: 0.005 to 0.05% And a high carbon-containing silicon steel slab composed of residual Fe and other inevitably mixed impurities, heated to a temperature of 1200 ° C. or higher and 1300 ° C. or lower, followed by hot rolling, followed by cold rolling, followed by decarburization and After performing nitride annealing, secondary recrystallization annealing, wherein the hot rolled sheet annealing is carried out so that decarburization is carried out. The method according to claim 1,
The silicon steel slab is a method for producing a low iron loss high magnetic flux density oriented electrical steel sheet, characterized in that it further contains 0.01 ~ 0.3% of Sn and Sb alone or in combination. The method according to claim 1 or 2,
A method for producing a low iron loss high magnetic flux density oriented electrical steel sheet characterized by controlling the primary recrystallized grain size to be 19 µm or less when decarburization and annealing are performed at a temperature in the range of 820 to 880 ° C.