JP5564571B2 - Low iron loss high magnetic flux density grain-oriented electrical steel sheet and manufacturing method thereof - Google Patents

Description

The present invention relates to the production of grain-oriented electrical steel sheets used as core materials such as iron cores of generators or transformers, and is manufactured from a high carbon content silicon steel slab to ensure the solid solution safety of inhibitors, and hot rolled sheet annealing. The present invention relates to a low iron loss high magnetic flux density grain-oriented electrical steel sheet having extremely excellent magnetic properties, and a manufacturing method thereof.

The grain-oriented electrical steel sheet exhibits a Goss texture where the aggregate structure of the slabs is {110} <001> with respect to the rolling direction, and thus has excellent magnetic properties in one direction or the rolling direction. Soft magnetic material. In order to form such goth assembly, component control in the steelmaking stage, slab reheating in hot rolling and factor control in hot rolling process, hot rolled sheet annealing, primary recrystallization annealing, Various processes, such as the next recrystallization annealing, must be controlled very precisely and strictly.

  On the other hand, the inhibitor (Inhibitor), one of the factors forming the Goth aggregate organization, suppresses the indiscriminate growth of primary recrystallized grains, and only the Goth aggregate organization grows when secondary recrystallization occurs. It is also very important to control the grain growth inhibitor. In order to obtain a final steel sheet having an excellent goth aggregate structure after secondary recrystallization annealing, the growth of all primary recrystallized grains must be suppressed until just before secondary recrystallization occurs. For this reason, in order to obtain sufficient inhibitory power, the amount of inhibitor must be sufficiently large and its distribution must be uniform. Moreover, in order for secondary recrystallization to occur together in high-temperature secondary recrystallization annealing (final annealing), the inhibitor must be easily decomposed with excellent thermal safety. Secondary recrystallization is a phenomenon that occurs when the inhibitor is decomposed in an appropriate temperature interval or loses its inhibitory power during the final annealing. In this case, specific crystal grains such as goth crystal grains are relatively short. It will grow rapidly in time.

Usually, the quality of grain- oriented electrical steel sheets can be evaluated by the magnetic flux density and iron loss, which are typical magnetic characteristics, and the higher the accuracy of goth assembly, the better the magnetic characteristics. Moreover, the grain-oriented electrical steel sheet having excellent quality can produce a highly efficient electric power device with various characteristics, and can provide high efficiency as well as downsizing of the electric power device.

Research and development for reducing the iron loss of grain- oriented electrical steel sheets has been done from research and development for increasing the magnetic flux density. The initial grain-oriented electrical steel sheet is M.M. F. Manufactured by a cold rolling method twice using MitS proposed by Littman as a grain growth inhibitor. According to this, secondary recrystallization was formed stably, but the magnetic flux density was not so high and the iron loss was also high.

  Subsequently, Taguchi (Taguchi) and Itakura have proposed a technique of using AlN and MnS precipitates in combination and performing a cold rolling at a cold rolling rate of 80% or more once. According to this, it is a technique for obtaining a high magnetic flux density by improving the {110} <001> orientation degree in the rolling direction by a strong grain growth inhibitor and cold rolling, and the history loss is greatly improved. Low iron loss characteristics can be obtained.

On the other hand, by increasing the silicon content of the electromagnetic steel sheet, the specific resistance of the steel sheet is increased, the eddy current flowing in the steel sheet is suppressed and iron loss is improved, and the purification is performed to remove unnecessary impurities in the steel sheet after secondary recrystallization. Research has been conducted on a method of increasing the cleanliness of a steel sheet by performing annealing and a method of reducing iron loss by controlling the size of secondary recrystallized grains to an appropriate size.

The method of increasing the silicon content is to obtain iron loss improvement effect by adding silicon with high specific resistance. However, as the addition amount increases, the brittleness of the steel sheet greatly increases and the workability becomes very high. At the time of falling and decarburizing annealing, the SiO ₂ oxide layer is formed densely, making it difficult to form the base coating.

  Moreover, the method for removing impurities is to reduce the impurity content by carrying out purification annealing at 1200 ° for 10 hours or more using 100% hydrogen gas. However, purification annealing significantly increases the manufacturing cost. It acts as a factor.

The method for controlling the grain size of the secondary recrystallized grains is a very complicated process in which the secondary recrystallization formation process must be controlled by a grain growth inhibitor, cold rolling and primary recrystallization control. Thus, there has been a situation where innovative manufacturing technology could not be developed so far.

  On the other hand, considerable technological development has been made with progress in research to improve iron loss by a method of refining the magnetic domains of secondary recrystallized grains. The method of refining the magnetic domain includes irradiating the surface of the steel sheet with a laser to apply a temporary stress to the surface of the steel sheet, thereby refining the magnetic domain in the {110} <001> orientation, There is a method of refining the magnetic domain by inducing structural change of the magnetic domain by performing an annealing heat treatment by applying a certain deformation. Such a magnetic domain refining method involves the burden of increasing the manufacturing cost because the magnetic domain refining process must be performed on the final product after the final secondary recrystallization annealing.

  In general, a technique for reducing the thickness of a steel sheet is a method for reducing one eddy current loss in a typical component of iron loss by causing deformation during cold rolling. However, in this case, the crystal growth driving force increases, and there is a problem that the secondary recrystallization becomes unstable because the crystal growth driving force cannot be suppressed depending on the original crystal growth inhibitor.

  In order to reduce the thickness while balancing the crystal growth and the crystal growth inhibiting force, the final cold rolling must be rolled at an appropriate cold rolling rate. The cold rolling rate varies depending on the restraining force of the crystal growth inhibitor. When the AlN and MnS composite precipitate proposed by Taguchi is used as a crystal growth inhibitor, the appropriate cold rolling ratio is about 87%. When the MnS precipitate proposed by Littman is used as a crystal growth inhibitor A cold rolling rate of 50 to 70% is appropriate.

  One reason is that secondary recrystallization is formed non-uniformly, and the other is that the magnetic domain width is widened due to the thickness reduction on the side of magnetostatic energy, and an arbitrary AC magnetic field is generated. This is because magnetic domain movement is not easy during application.

On the other hand, the thickness 0.1~0.25mm of the steel sheet in the production of thin grain oriented electrical steel sheet, in order to solve the constraints and final rolling rate optimization of hot-rolled sheet thickness, the hot rolled sheet of 10-50% A method of manufacturing a grain-oriented electrical steel sheet that performs hot-rolled sheet annealing and cold rolling after pre-cold rolling is proposed. In this case, the production cost is reduced by two cold rollings and two recrystallization annealings. The burden of rising will arise.

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

  However, in the case of the technique of adding B, it is extremely difficult to control at the steelmaking stage for addition of a minute amount, and coarse BN is easily formed in the steel after the addition. Further, Ti forms TIN and TiC, and TIN and TiC have a solid solution temperature higher than 1300 ° C. and remain after the secondary recrystallization and may act as a factor to increase iron loss.

As another proposal for improving the crystal grain growth inhibiting power, Sn and Sb are added in combination, slab heated at a temperature of 1200 ° C. or less, hot rolled, and cold rolling and decarburization of 80% or more. There has been proposed a method of manufacturing a thin grain-oriented electrical steel sheet having a thickness of 0.23 mm or less, in which nitriding is performed using ammonia gas after annealing. However, by proposing a very strict manufacturing standard for manufacturing thin grain-oriented electrical steel sheets, there is a burden of hot rolling by 1200 ° C slab heating in actual production, separating decarburization and nitrification annealing. As a result, the manufacturing cost increases, and it is difficult to secure excellent magnetic properties.

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

In addition, as a patent document on a method for producing a grain-oriented electrical steel sheet of 0.23 mm or less, a method of electrostatically applying MgO as an annealing separator, three cold rollings, and three vacuum annealings A technique and a method for producing an ultrathin material by changing the diameter of a work roll depending on the rolling thickness have been proposed. However, this technology is very difficult because it requires additional capital investment and operation know-how to be accumulated compared to the currently commercialized manufacturing technology. is there.

On the other hand, in the manufacture of grain-oriented electrical steel sheets, the slab heating temperature has a very close relationship with the solid solution temperature of AlN and MnS precipitates mainly used as a crystal grain growth inhibitor.

  For example, the high-temperature slab heating method is a technique in which the slab is heated to a temperature of 1300 ° C. or higher so that all of the AlN and MnS precipitates are solid-dissolved. It is designed to exert a strong crystal growth suppressing effect by being finely precipitated in the hot rolling and subsequent annealing process of the hot rolled sheet.

This is based on the assumption that a steel sheet containing pure 3 % by mass of silicon is a ferrite phase, and the AlN solid solubility at this time can be expressed by the following formula proposed by IWAYAMA.

According to this, when it is assumed that the acid-soluble aluminum is 0.028 mass% and N is 0.0050 mass% , the theoretical solid solution temperature according to the IWAYAMA solid solubility equation is 1258 ° C., In order to heat the slab of the electrical steel sheet, it must be heated to about 1300 ° C.

However, if the slab is heated to a temperature of 1280 ° C. or higher, the surface of the steel sheet is melted while iron olivine (Fe ₂ SiO ₄ ; faylite), which is a low melting point silicon and a base metal iron compound, is generated on the steel sheet. It becomes very difficult to perform hot rolling, and the problem arises that the furnace must be repaired due to molten molten iron.

  In order to solve such a problem, research and development on a technique for heating a slab at a low temperature of 1250 ° C. or lower is in progress. For example, the slab is heated to a temperature of 1270 ° C. or lower and hot-rolled to a state where the grain growth inhibitor AlN is not completely dissolved, and then completely precipitated by annealing of the hot-rolled sheet. There has been proposed a technique for performing a nitriding treatment in a process to ensure a crystal grain growth suppressing power.

  Such a low temperature slab heating method does not use precipitates present in the slab and hot rolling stages as inhibitors, and nitrogen ions that enter the steel by nitriding treatment in the subsequent process react with acid-soluble aluminum to newly Since only precipitated AlN is used as a crystal growth inhibitor, there is a drawback that the suppressive force is inferior to the crystal growth driving force.

  To summarize the conventional technologies discussed so far, the development of a crystal growth inhibitor to ensure high magnetic flux density characteristics, the silicon content to ensure low iron loss, and the impurity removal purification to enhance the cleanliness of the steel sheet. Annealing and domain refinement treatment for the final product, final steel sheet thickness reduction, addition of B, Ti, Sn, Sb to reinforce the crystal growth inhibitor, slab heating temperature, and hot rolled sheet annealing Although control technology has been proposed, the actual proposed conditions are strict production conditions that act as a burden on the production process, leading to an increase in manufacturing costs. In the case of the low-temperature slab heating method, the crystal growth inhibition power is low. Therefore, there is a limit to the improvement of magnetism.

The present invention was made in order to solve the various problems of the prior art as described above, and improved goth assembly of grain-oriented electrical steel sheets using a high carbon content silicon steel slab, ultrathin rolling It is an object of the present invention to provide a low iron loss high magnetic flux density grain-oriented electrical steel sheet having extremely excellent magnetic properties and a method for producing the same, by improving the property and the thermal safety of the inhibitor.

The manufacturing method of the low iron loss high magnetic flux density directional electrical steel sheet according to the present invention for solving the above-mentioned problems is as follows: a high-carbon silicon steel slab is heated and hot-rolled, and then hot-rolled sheet is annealed and cold-rolled. After performing decarburization and nitrification annealing, secondary recrystallization annealing is performed to produce a grain-oriented electrical steel sheet, which is decarburized simultaneously with the annealing of the hot-rolled sheet.

The silicon steel slab is, by mass , 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: comprises from 0.005 to 0.05%, it is preferable that the balance of Fe and other inevitable impurities.

More preferably, the silicon steel slab further contains 0.01 to 0.3 % by mass of Sn and Sb alone or in combination.

  The heating temperature of the silicon steel slab is preferably 1050 to 1250 ° C.

  The hot rolling step preferably includes a step of cooling the hot-rolled slab at 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 sheet is 900 to 1200 ° C. It is preferable that

  Moreover, it is particularly preferable that the hot-rolled sheet is annealed after the hot-rolled sheet is heated to 900 to 1200 ° C and then maintained at 900 to 1100 ° C in a humid atmosphere.

  More preferably, the annealing of the hot-rolled sheet includes a step of cooling the hot-rolled sheet-annealed steel sheet at a rate of 15 to 500 ° C. per second.

  In the cold rolling, it is preferable that the steel sheet after annealing of the hot-rolled sheet is rolled to a thickness of 0.20 mm or less by one strong cold rolling without intermediate annealing.

The low iron loss high magnetic flux density directional electrical steel sheet according to the present invention for solving the above problems is manufactured by heating and hot rolling a high carbon content silicon steel slab and then annealing and cold rolling the hot rolled sheet. In the grain- oriented electrical steel sheet, the average grain size after secondary recrystallization annealing is 10 to 30 mm .

The silicon steel slab is, by mass , C: 0.10 to 0.30%, Si: 2.0 to 4.5%, acid-soluble Al: 0.005 to 0.040%, Mn: 0.20 %: N: 0.010% or less, S: 0.010% or less, P: 0.005 to 0.05%, and the balance is preferably composed of Fe and other inevitable impurities.

More preferably, the silicon steel slab further contains 0.01 to 0.3 % by mass of Sn and Sb alone or in combination.

  The β angle of the steel sheet is preferably 3 ° or less.

  It is preferable that the steel plate is manufactured by decarburization simultaneously with the annealing of the hot-rolled plate.

According to the present invention, a high carbon content silicon steel slab is used to strengthen the thermal safety of the inhibitor so that it has a strong crystal growth inhibiting force and simultaneously decarburizes while annealing the hot-rolled sheet. By providing secondary recrystallized nuclei with {110} <001> orientation having a very high degree of orientation, a grain-oriented electrical steel sheet having extremely excellent magnetic properties can be produced.

  Hereinafter, the present invention will be described in detail.

The inventors of the present invention have made many researches on techniques for stably producing solid solution and precipitation of AlN or MnS precipitates as grain growth inhibitors on silicon steel ferrite in the production of grain-oriented electrical steel sheets. As a result, 3% silicon steel is a pure ferrite region, but as the amount of carbon added increases, the fraction of austenite phase increases in a predetermined temperature region. It has been found that the AlN solid solubility in the austenite phase can be improved by at least twice as much as the solid solubility on ferrite.

Accordingly, the present inventors have studied the role of carbon as an austenite-forming element and the point that AlN is an austenite phase and has a high solid solution rate and a high solid solution amount. When added in a higher range, that is, from a minimum of 0.10 % by mass to a maximum of 0.30 % by mass , a fraction of the austenite phase in the slab in the slab heating temperature region will be 60% or more (Al, Si, The core of Goss collective organization by nitrides such as (Mn) N or AlN being sufficiently dissolved during the heating of the slab and by decarburizing and controlling the cooling process during annealing of the hot-rolled sheet It was first found that a grain-oriented electrical steel sheet having extremely excellent magnetic properties can be produced by increasing the number of generation sites.

  The formula of AlN solid solubility in the austenite phase can be obtained by 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 mass and N is 0.0050 % by mass , the slab solid solution temperatures are 1112 ° C. (Darken) and 1002 ° C. (Leslie), respectively. Melting temperature is much lower than 1258 ° C.

  Thus, the more the austenite phase in the slab, the lower the solid solution temperature of AlN. Therefore, if a large amount of carbon is added to the slab to increase the austenite fraction, the solid solution of AlN is maximized and sufficient crystal grains are obtained. Growth restraint power can be secured.

  Eventually, by promoting the formation of the austenite phase by slab heating and hot-rolled sheet annealing, a fine AlN precipitate distribution can be obtained inside the cold-rolled steel sheet, resulting in high magnetic flux density and iron loss. Secondary recrystallized grains advantageous for lowering can be obtained.

In addition, the amount of austenite during hot-rolled sheet annealing is increased by 0.10 % by mass or more and 0.30 % by mass or less of carbon in the hot-rolled sheet. Since sufficient recrystallization of the hot rolled structure stretched long in the rolling direction is possible, all the non-homogeneous hot rolled fine structures disappear, and the fine base structure is composed of fine crystal grains in all directions. Precipitates are uniformly dispersed and deposited in the job, the cold rolling property is improved, and the sheet thickness can be reduced to 0.20 mm or less by one strong cold rolling.

  At the same time as hot-rolled sheet annealing, excess carbon is removed by decarburization in a humid atmosphere, and the Goss collective organization existing in the surface layer grows deeply, greatly increasing the percentage of Goss collective organization. By rapidly cooling the hot-rolled annealed sheet, the base structure composed of fine and homogeneous austenite and the finely dispersed precipitates present in the austenite crystal grains or at the grain boundaries are stored up to room temperature. Can do.

  On the other hand, the austenite phase undergoes a hard bainite or martensite phase or a mixed transformation of both phases during the rapid cooling process. At this time, during one strong cold rolling, the deformation stress is greatly increased around bainite or martensite, which is several times as strong as ferrite, which is the base organization, and the shear deformation band is increased inside the steel sheet. Furthermore, the carbon remaining by annealing of the hot-rolled sheet accompanied with decarburization annealing further activates dislocation fixation during cold rolling and increases the shear deformation zone. It has the effect of inducing increased nucleation.

  Inside the shear deformation zone, grains of {110} <001> orientation, which are the nuclei of secondary recrystallization, easily recrystallize, so in the primary recrystallization set organization, the set of {110} <001> orientation The number of jobs increases, thereby increasing the degree of integration of {110} <001> goth aggregates that have been secondary recrystallized to ensure a high magnetic flux density, and the size of secondary recrystallized grains The magnetic characteristics of extremely low iron loss can be secured.

Such a grain-oriented electrical steel sheet according to the present invention has a grain size after secondary recrystallization annealing formed to an appropriate size of 10 to 30 mm, which is advantageous for magnetism. The β angle of the final steel sheet is 3 ° or less, and extremely excellent magnetic properties can be obtained.

  Hereinafter, the reason for limiting the components of the present invention will be described.

Si is a basic composition of an electromagnetic steel sheet, and serves to increase the specific resistance of the material and lower the core loss. When the Si content is less than 2.0%, the specific resistance decreases and the iron loss characteristics deteriorate, and during high-temperature annealing, there is a phase transformation section and the secondary recrystallization becomes unstable. If the content exceeds V, the brittleness of the magnetic steel sheet increases, and the sheet breakage becomes severe during rolling, and the formation of secondary recrystallization becomes unstable. Therefore, Si is limited to 2.0 to 4.5 mass% .

In addition to the finely precipitated AlN during the hot rolling and annealing of the hot rolled sheet, Al is present in the steel in the form of a solid solution in which nitrogen ions introduced by ammonia gas in the annealing process after the cold rolling are present. By combining with Al, Si, Mn to form (Al, Si, Mn) N form nitride, it will act as a powerful crystal growth inhibitor, its content is less than 0.005% In this case, it is not possible to expect a sufficient effect by the inhibitor, and when it exceeds 0.040%, the crystal growth inhibiting power is reduced by forming coarse AlN. Therefore, the Al content is limited to 0.005 to 0.040 mass% .

Similar to Si, Mn also has the effect of increasing the specific resistance and decreasing the iron loss, and reacts with nitrogen introduced by nitriding with Si to form (Al, Si, Mn) N precipitates. It is an important element for causing secondary recrystallization by suppressing the growth of secondary recrystallized grains. However, if added in excess of 0.20%, Mn Oxide is formed on the surface of the steel plate in addition to Fe ₂ SiO ₄ , which interferes with the formation of the base coating formed during high-temperature annealing and improves the surface quality. Will be reduced. Therefore, Mn is 0.20 % by mass or less.

N is an important element that reacts with Al to form AlN, and is preferably added at 0.010 % by mass or less in the steelmaking stage. If it is added in excess of 0.01 % by mass, it will cause a surface defect called Blister due to nitrogen diffusion in the process after hot rolling. Further, N necessary for forming AlN is reinforced by performing nitriding treatment in steel using ammonia gas in an annealing process after cold rolling.

C is an important element in the present invention, and 0.10% or more and 0.30% or less of carbon can be added to include 60% or more of the austenite fraction in the steel sheet. Such a high fraction austenite transformation can actively induce phase transformation and recrystallization of the inhomogeneous and long stretched roll formed by the hot rolling, which is the previous process. The composition of the spread annealed sheet can be controlled uniformly and finely. On the other hand, by carrying out decarburization annealing at the same time as annealing of hot-rolled sheet, the goth aggregate structure of the steel sheet surface layer part will grow deeper, increasing the fraction of goth crystal grains in the primary recrystallization annealed sheet Thus, the goth accumulation degree of the final annealing plate can be increased, and the grain size of the crystal grains can be decreased to obtain a high magnetic flux density and an extremely low iron loss.

In addition, the austenite phase can be transformed into a high-strength bainite phase or martensite phase by a predetermined cooling rate control, and the bainite or martensite transformed by rapid cooling is the nucleation site of the austenite phase during the annealing process of the hot-rolled sheet. To provide a uniform and fine structure in the annealing process of the hot-rolled sheet, thereby ensuring a fine and uniform fine structure, thereby making the AlN precipitate fine. When the steel sheet is rapidly cooled after the annealing of the hot-rolled sheet, the formation of bainite or martensite is promoted, and the degree of orientation in the {110} <001> direction due to deformation stress concentration during cold rolling is very high. A high Goss collective organization can be formed. On the other hand, after annealing heat treatment of the hot-rolled sheet, the residual carbon present in the steel sheet activates dislocation fixation during cold rolling, increases the shear deformation band, increases the generation site of goth nuclei, The fraction of goth crystal grains in the next recrystallization annealed plate will be increased. In order to obtain such an effect, 0.10 % by mass or more of carbon must be included in the slab. However, if decarburization is not sufficiently performed in the decarburization annealing process, when the final product is applied to an electric machine, it will cause a deterioration phenomenon of magnetic characteristics due to self-aging, and 0.30% of carbon is added to the slab. If it is included in excess of the above, when the hot-rolled sheet is annealed, the time consumed for sufficient decarburization increases, and a thick oxide layer is formed on the surface as the annealing time increases. Not only this, but a decarburization delay phenomenon occurs, so that sufficient decarburization cannot be performed. Therefore, the C content is preferably limited to 0.10 to 0.30 mass% .

  If S is contained in an amount exceeding 0.01%, MnS precipitates are formed in the slab to suppress grain growth, and segregate at the center of the slab during casting. It is difficult to control the fine organization. Further, in the present invention, since MnS is not used as a main crystal grain growth inhibitor, it is not preferable that S is added and precipitated in an amount that is inevitably added.

Sn is a grain boundary segregation element and is an element that hinders the movement of crystal grain boundaries, and is therefore known as a crystal growth inhibitor. In addition, it promotes the formation of goth crystal grains with {110} <001> orientation to help the secondary recrystallization develop well. Therefore, in the production of grain-oriented electrical steel sheets as in the present invention, the role of Sn is an important element for reinforcing the inhibitory force in addition to AlN and (Al, Si, Mn) N as the crystal grain growth inhibitor. .

Sb is a grain boundary segregation element like Sn, and has the effect of suppressing crystal growth, and improves the adhesion between the steel sheet and the oxide layer by suppressing the formation of the surface oxide layer of the steel sheet formed during secondary recrystallization. This also has the effect of improving iron loss. In the present invention, Sn and Sb are added singly or in combination to obtain a crystal growth suppressing effect, and Sn and Sb are singly formed so that more goth crystal grains of {110} <001> orientation are formed. Alternatively, it is preferable to add 0.01% to 0.3 % by mass in combination.

If Sn and Sb are added alone or in combination in an amount of less than 0.01 % by mass , it is difficult to obtain the effect, and if added in excess of 0.3 % by mass , the effect of additional input cost is low. However, the grain boundary segregation is severely generated and the brittleness of the steel sheet becomes high. Therefore, it is preferable to add 0.01 to 0.3 % by mass of Sn and Sb alone or in combination.

P is an element having an effect similar to that of Sn and Sb. It can segregate at the grain boundary to obstruct the movement of the grain boundary, and at the same time can serve as an auxiliary role for suppressing the growth of the crystal grain. From the side, {110} <001> has the effect of improving the collective organization. P is no effect of addition is less than 0.005 mass% content of, if it is added more than 0.05 mass%, the rolling property brittleness increases is deteriorated, 0.005 It is preferable to limit to mass% .

Hereinafter, the manufacturing method of the low iron loss high magnetic flux density grain-oriented electrical steel sheet of this invention is demonstrated.

  The carbon content and slab reheating conditions are very important in refining the coarse precipitates that have been solidified to room temperature after casting after relaxing the casting structure, which is a columnar crystal structure in the steelmaking stage. It is. In general, the higher the carbon content, the more active the phase transformation and the more effective the relaxation of the columnar crystal structure that is the casting structure. Moreover, it is advantageous in terms of productivity that the slab reheating temperature and the hot rolling operation are manufactured under temperature conditions similar to those of other steel types, and therefore, the slab heating temperature is preferably determined to be 1050 to 1250 ° C.

On the other hand, the contents of acid-soluble Al and steel nitrogen are very important for ensuring the safety of crystal grains of grain-oriented electrical steel sheets. Acid-soluble Al and steel nitrogen are important elements that cause (Al, Si, Mn) N and AlN to precipitate during solidification. Become. That is, acid-soluble Al and steel nitrogen have an equilibrium constant Ks depending on their contents, and precipitation becomes more active as they move to the right in the equilibrium constant, and are dissolved in the base as they move toward the left. If the slab reheating temperature is lower than the equilibrium constant Ks, unstable (Al, Si, Mn) N and AlN precipitated during solidification cannot be re-dissolved in the matrix.

  On the other hand, if the slab reheating temperature is too low, the amount of precipitates produced during solidification is too much and hinders the rollability. Therefore, acid-soluble Al and steel nitrogen must be controlled. Here, the acid-soluble Al must be 0.005 to 0.040%, and the steel nitrogen must be 0.010% or less.

  After the slab is heated to the predetermined temperature as described above, hot rolling is performed. The hot-rolled sheet that has been hot-rolled is formed to have a thickness of 1.5 to 2.5 mm. If the thickness of the hot-rolled sheet exceeds 2.5 mm, the cooling rate decreases during the rapid cooling process after hot rolling, coarse carbide is formed, and magnetism deteriorates. Moreover, hot rolling to a thickness of less than 1.5 mm has difficulty in increasing the rolling load, and the thickness is difficult to control. Therefore, it is preferable that the thickness of the hot-rolled plate is formed to be 1.5 to 2.5 mm.

Subsequently, it cools with the cooling rate of 15 degreeC or more per second, and winds up at the temperature of 580 degrees C or less. When it is wound at a cooling rate of less than 15 ° C. per second, coarse carbides are formed in the cooling process and the magnetism is deteriorated. At the same time, pearlite that is a layered structure of brittle cementite (Fe ₃ C) and ferrite is formed. Further, since the bainite of the diffusion transformation and the martensitic transformation of the non-diffusion transformation are delayed, it becomes difficult to refine the austenite phase and ensure the homogeneity of the composition in the annealing of the hot rolled sheet. Therefore, after hot rolling, the cooling rate of the hot-rolled sheet is preferably 15 ° C. or more per second.

  If the hot-rolled steel sheet is wound at a temperature exceeding 580 ° C., coarse carbides are also formed. Therefore, the winding temperature is preferably limited to 580 ° C. or less.

  In the hot-rolled sheet that has been hot-rolled, there is a deformed structure stretched in the rolling direction by stress, and AlN, MnS, and the like are precipitated during hot-rolling. Therefore, in order to have a uniform recrystallized fine structure and fine AlN precipitate distribution before cold rolling, the deformed composition is recrystallized by heating the hot-rolled sheet once again below the slab heating temperature, and It is important to secure a solid austenite phase and promote solid solution of crystal grain growth inhibitors such as AlN and MnS. Therefore, the annealing temperature of the hot-rolled sheet is preferably heated to 900 to 1200 ° C. in order to have the maximum austenite fraction.

  Thus, after heating a hot-rolled sheet to 900-1200 degreeC, it is preferable to perform a soaking process at the temperature of 900 degreeC or more and 1100 degrees C or less. If the soaking temperature is less than 900 ° C., the solid-dissolved precipitates cannot be diffused and are finely precipitated. If the soaking temperature exceeds 1100 ° C., the precipitates are not homogenized. The problem of precipitation during the cooling process will occur. Accordingly, the soaking process is performed at a temperature of 900 ° C. or higher and 1100 ° C. or lower to enhance the growth driving of the precipitate.

  It is preferable that the soaking is performed in a humid atmosphere and decarburization is performed simultaneously. This is to prevent the deterioration of quality due to self-aging by inducing an increase in nucleation of Goss collective organization and at the same time reducing the amount of residual carbon in the steel sheet.

  As described above, when the hot-rolled sheet is cooled after being annealed, it is preferably subjected to a rapid cooling treatment. When slowly cooled, the amount of acid-soluble aluminum decreases due to the additional precipitation of grain growth inhibitors such as AlN and MnS, and instead of a relatively strong phase such as bainite or martensite, Pearlite, which is a mixed structure of cementite and ferrite having a structure, is formed, and the formation of shear deformation bands due to work hardening is weakened during subsequent cold rolling. Further, not only carbon is present as cementite in pearlite, but also plate-like or spherical carbides are present alone at the crystal grain boundaries, resulting in uneven organization. However, if the cooling rate exceeds 500 ° C. per second, the austenite phase is transformed into a high-strength martensite phase, which places a burden on the cold rolling process and reduces the quality of the cold rolled sheet. Become.

  Therefore, the annealing of the hot-rolled sheet is performed at a temperature of 900 ° C. or higher and 1200 ° C. or lower, followed by a soaking treatment at a temperature of 900 ° C. or higher and 1100 ° C. or lower and a decarburizing annealing heat treatment in a humid atmosphere, and then 15 It is preferable to cool at a cooling rate of not less than 500C and not more than 500C. At this time, the cooling method can be performed by air cooling, water cooling, or oil cooling, or two or more of them can be combined.

  After the hot-rolled sheet is annealed, cold rolling is performed to a thickness of 0.10 mm or more and 0.50 mm or less using a reverse rolling mill or a tandem rolling mill. At this time, it is preferable to perform one strong cold rolling that performs rolling from the initial hot rolled thickness to the thickness of the final product immediately without performing the annealing heat treatment of the structure deformed in the middle. An orientation with a low accumulation degree of {110} <001> orientation is rotated to a deformation orientation in one strong cold rolling, and secondary recrystallization nucleation with a high orientation degree to {110} <001> orientation By increasing the number of locations, only goth crystal grains advantageous to magnetism are present in the cold-rolled sheet. In the rolling method of two or more times, the orientation with a low degree of integration also exists in the cold-rolled sheet and is recrystallized together during the final high-temperature annealing, so that the magnetic flux density and the iron loss are deteriorated. . Therefore, it is preferable that the cold rolling is performed at a cold rolling rate of 90% or more by one strong cold rolling.

  The cold-rolled plate is subjected to decarburization, recrystallization of the deformed composition and nitriding treatment with ammonia gas, and the acid-soluble aluminum dissolved in the base material during annealing of the hot-rolled plate and Nitrogen is reacted to deposit a large amount of nitrides such as (Al, Si, Mn) N and AlN, which are powerful grain growth inhibitors and have a fine and uniform distribution. Increase the effect of suppressing the growth of.

The role of carbon in the production of the grain-oriented electrical steel sheet of the present invention is very large, but if there is a lot of carbon in the final product, the self-aging phenomenon that forms fine carbides and increases iron loss greatly over time will occur. As a result, decarburization must be performed in the primary recrystallization annealing step to remove carbon to a certain level.

  The nitriding treatment can form (Al, Si, Mn) N, which is the main precipitate, by introducing nitrogen ions into the steel sheet with ammonia gas. Such nitriding treatment can be performed after decarburization and recrystallization, or can be performed using ammonia gas at the same time as it is performed simultaneously with decarburization, and any of them has a problem in exerting the effect of the present invention. Absent.

In the decarburization and nitriding treatment, it is preferable that the annealing temperature of the steel plate is heat-treated within a range of 800 to 950 ° C. If the annealing temperature of the steel plate is lower than 800 ° C., it takes a long time for decarburization, and a SiO ₂ oxide layer is densely formed on the surface of the steel plate, thereby causing a base coating defect. On the contrary, if the steel sheet is heated to a temperature exceeding 950 ° C., the recrystallized grains grow coarsely and the crystal growth driving force decreases, so that stable secondary recrystallization is not formed.

Finally, in the production of a normal grain-oriented electrical steel sheet, after applying an annealing separator based on MgO to the steel sheet, it is finally annealed over a long period of time to cause secondary recrystallization, thereby {110} of the steel sheet. A {110} <001> aggregate is formed in which the surface is parallel to the rolling surface and the <001> direction is parallel to the rolling direction to produce a grain-oriented electrical steel sheet having excellent magnetic properties. The purpose of the final annealing can be broadly seen as {110} <001> aggregate formation by secondary recrystallization, imparting insulation by forming a vitreous film by reaction of the oxide layer formed during decarburization and MgO, It is the removal of impurities that impair the magnetic properties. As a method of final annealing, secondary recrystallization is well developed by maintaining a mixed gas of nitrogen and hydrogen in the temperature rising period before secondary recrystallization occurs to protect the nitride which is a particle growth inhibitor. By doing so, after the secondary recrystallization is completed, impurities are removed by maintaining in a 100% hydrogen atmosphere for a long period of time.

  Hereinafter, based on an Example, this invention is demonstrated more concretely.

[Example 1]
In mass% , Si: 3.3%, C: 0.15%, Mn: 0.090%, S: 0.003%, N: 0.004%, Sol. A slab containing Al: 0.028%, P: 0.030%, Sb: 0.10% and the balance Fe and other inevitable impurities contained therein was vacuum-melted, and then an ingot was manufactured. After heating at a temperature of ° C., it was hot-rolled to a thickness of 2.0 mm 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, annealing of the hot-rolled sheet was performed by heating to 1050 ° C. and then maintaining at 950 ° C. for 180 seconds, and the hot-rolled sheet annealed steel sheet was rapidly cooled at a cooling rate of 50 ° C. per second. The rapidly cooled hot-rolled annealed plate is pickled and then subjected to one cold rolling to a thickness of 0.20 mm, and then at a temperature of 850 ° C. in a humidified hydrogen, nitrogen and ammonia mixed gas atmosphere for 180 seconds. Maintaining, decarburization and nitridation annealing were performed so that the nitrogen content was 200 ppm. The steel sheet was coated with MgO, which is an annealing separator, and finally annealed into a coil shape. The final annealing is performed in a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C., it is maintained in a 100% hydrogen atmosphere for 10 hours or more, then cooled in a furnace to obtain a final steel plate, and a test material It was.

  On the other hand, for the sake of comparison, in the case of annealing the hot-rolled sheet, only the difference was that the annealing of the hot-rolled sheet was performed in a nitrogen atmosphere that was not a wet atmosphere without decarburization. The conditions were the same as in the production of the test material, and a final steel plate was obtained and used as a comparative material.

  Also, the difference between the slab containing 0.05% C and that the annealing of the hot-rolled sheet was carried out in a nitrogen atmosphere, and the other conditions were the same as in the production of the above test material to obtain the final steel sheet. Conventional materials were used.

  The magnetic characteristics were measured for each condition and are shown in Table 1.

  As shown in Table 1, in the case of a test material that was decarburized during annealing of a hot-rolled sheet using a 0.15% high-carbon-containing slab, C: 0.05% -containing slab was used and hot-rolled Compared to the conventional material that was not decarburized during annealing of the plate, the iron loss and magnetic flux density were very excellent.

  In the case of the comparative material, a slab having a high carbon content of 0.15% was used, but since decarburization was not performed during the annealing of the hot-rolled sheet, the residual C of the final annealed sheet was high, and the magnetic flux density and the iron loss were deteriorated. did.

[Example 2]
In terms of mass% , Si: 3.2%, C: 0.080 to 0.321%, Mn: 0.090%, S: 0.003%, N: 0.004%, Sol. A slab containing Al: 0.030%, P: 0.028%, Sn + Sb: 0.10% and the balance Fe and other inevitable impurities contained therein was vacuum-melted, and then an ingot was manufactured. After heating to a temperature of ° C., it was hot-rolled to a thickness of 2.0 mm, cooled at a cooling rate of 50 ° C. per second, and wound up at a temperature of 580 ° C. The hot-rolled hot-rolled sheet was heated to a temperature of 1050 ° C., then maintained at 950 ° C. for 180 seconds to anneal the hot-rolled sheet, and decarburized in a humid atmosphere simultaneously with the annealing of the hot-rolled sheet. The annealed steel sheet was rapidly cooled at a cooling rate of 50 ° C. per second, and the rapidly cooled hot-rolled annealed sheet was pickled and then subjected to strong cold rolling once to a thickness of 0.20 mm. The cold-rolled sheet was maintained in a humid hydrogen, nitrogen and ammonia mixed gas atmosphere at a temperature of 850 ° C. for 180 seconds so that the nitrogen content became 200 ppm, and at the same time, decarbonitizing and annealing were performed. The steel sheet was coated with MgO, which is an annealing separator, and finally annealed into a coil shape. The final annealing was performed in a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C., the furnace was cooled after being maintained in a 100% hydrogen atmosphere for 10 hours or more. The magnetic characteristics, the average grain size of the final steel sheet, and the β angle of the final steel sheet were measured for each condition and are shown in Table 2 below.

As shown in Table 2, the inventive material in which the carbon content is controlled to 0.1 to 0.3 % by mass 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 characteristics are very excellent as compared with a comparative material that is out of the scope of the present invention. In particular, it can be seen that in the case of a comparative material having a carbon content exceeding 0.3 % by mass , the magnetic properties are considerably deteriorated. This is because the excess carbon content does not cause sufficient decarburization and deteriorates the magnetic properties of the final product.

As described above, the steel sheet manufactured by decarburizing simultaneously with the annealing of the hot-rolled sheet using the slab containing 0.1 to 0.3 % by mass of carbon is advantageous in that the average crystal grain after the secondary recrystallization is magnetic. It was formed in a proper size of 10 to 30 mm. If the average crystal grains having a grain size after the secondary recrystallization is less than 10 mm, the iron loss is very high magnetic flux density is very low, the magnetic flux density and core loss even when the particle size of the average crystal grain exceeds 30mm Deteriorated.

Furthermore, it is manufactured by decarburizing simultaneously with annealing of hot-rolled sheet using a slab containing 0.1 to 0.3 % by mass of carbon, and the average grain size after secondary recrystallization is 10 to 30 mm. In the case of the formed invention material, the β angle of the final steel sheet showing the degree of deviation from the Goth orientation due to the effect of increasing the nucleation location of Goss collective organization is less than 3 °, which is several compared to the conventional grain-oriented electrical steel sheet It was confirmed that a grain-oriented electrical steel sheet having improved orientation and extremely excellent magnetic properties can be produced.

[Example 3]
In mass% , Si: 3.1%, C: 0.25%, Mn: 0.10%, S: 0.003%, N: 0.004%, Sol. A slab containing Al: 0.028%, P: 0.027%, Sn: 0.10%, and the balance Fe and other inevitable impurities contained therein was vacuum-melted, and then ingots were manufactured. After heating to a certain temperature, it was hot-rolled to a thickness of 2.0 mm, cooled at various cooling rates, and wound at different winding temperatures. The hot-rolled hot-rolled sheet was heated and annealed at temperatures of many conditions, and the cooling rate was changed. The rapidly cooled hot-rolled annealed sheet was pickled and then subjected to strong cold rolling once to a thickness of 0.20 mm. The cold-rolled plate was decarburized and nitrided and annealed at a temperature of 850 ° C. in a humidified hydrogen, nitrogen and ammonia mixed gas atmosphere for 180 seconds so that the nitrogen content was 200 ppm. The steel sheet was coated with MgO, which is an annealing separator, and finally annealed into a coil shape. The final annealing was performed in a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C., it was maintained in a 100% hydrogen atmosphere for 10 hours or more and then cooled in the furnace. The magnetic characteristics were measured for each condition and are shown in Table 3 below.

  As shown in Table 3, the test material K in which the slab was heated to a temperature higher than 1250 ° C. was difficult to hot-roll, and in the case of the test material H heated to a temperature lower than 1050 ° C., the inhibitor was not sufficiently dissolved. The magnetism has deteriorated.

  The test material G, in which the hot-rolled slab was cooled at less than 15 ° C per second, deteriorated in magnetism due to the formation of coarse carbides and a decrease in the homogeneity of the structure, and the hot-rolled steel sheet was wound at a temperature exceeding 580 ° C. The taken test material C also deteriorated in magnetism due to the formation of coarse carbides.

  In addition, the test material A having an annealing temperature of the hot-rolled sheet of less than 900 ° C. did not secure a sufficient austenite phase, and the solid solubility of the crystal grain growth inhibitor was lowered and the magnetism was deteriorated. The test material K in which the annealing temperature of the hot-rolled sheet exceeded 1200 ° C. deteriorated the cold rolling property and deteriorated the magnetism.

  In the test material F obtained by cooling the hot-rolled steel sheet at a rate of less than 15 ° C. per second, pearlite, which is a mixed structure of cementite and ferrite, which is a coarse layered structure, is formed and a shear deformation band is formed. The formation became weak, and not only carbon was present as cementite in the pearlite, but was also present alone as a plate-like or spherical carbide at the grain boundary, resulting in non-uniform organization and magnetism deterioration. In the case of the test material H in which the hot-rolled sheet annealed steel 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 deteriorated.

  On the other hand, as in the scope of the present invention, the slab is heated to 1050 to 1250 ° C., the hot-rolled slab is cooled at 15 ° C. or more per second, and wound at a temperature of 580 ° C. or less, In the case of test materials B, D, E, I, and J, which were annealed at 900 to 1200 ° C. and cooled at a rate of 15 to 500 ° C. per second, the iron loss was 0.90 (W17 / 50) or less, the magnetic flux density was 1.92 (B10) or more, and the magnetic characteristics were very excellent.

Claims (9)

After the silicon steel slab is heated and hot-rolled, the hot-rolled sheet is annealed and cold-rolled, decarburized and nitrided, and then subjected to secondary recrystallization annealing to obtain a grain-oriented electrical steel sheet. A method of manufacturing comprising:
The silicon steel slab is in mass%, C: 0.10 to 0.30%, Si: 2.0 to 4.5%, Al: 0.005 to 0.040%, Mn: 0.20% or less, N: 0.010% or less, S: 0.010% or less, P: 0.005-0.05%, balance Fe and other inevitable impurities,
The silicon steel slab is heated to 1050 to 1250 ° C. and hot-rolled,
The hot rolling step includes a step of cooling the hot-rolled slab at 15 ° C. or more per second and winding it at a temperature of 580 ° C. or less.
Annealing of the hot-rolled sheet is performed at a temperature of 900 to 1200 ° C., and includes a step of cooling the annealed steel sheet at a rate of 15 to 500 ° C. per second,
Low iron loss high magnetic flux density directional electromagnetic wave, in which decarburization is performed simultaneously with annealing of hot-rolled sheet, average grain size after secondary recrystallization annealing is 10 to 30 mm, and β angle is 3 ° or less A method of manufacturing a steel sheet.   The method for producing a low iron loss high magnetic flux density grain-oriented electrical steel sheet according to claim 1, wherein the silicon steel slab further contains 0.01 to 0.3 mass% of Sn and Sb alone or in combination.   The annealing of the hot-rolled plate is performed by heating the hot-rolled plate to 900 to 1200 ° C, and then maintaining the hot-rolled plate at 900 to 1100 ° C in a wet atmosphere. Method for producing an electrical steel sheet.   The said cold rolling is a manufacturing method of the low iron loss high magnetic flux density directionality electrical steel plate as described in any one of Claim 1 to 3 which is one strong cold rolling which does not implement intermediate annealing.   The said cold rolling is a manufacturing method of the low iron loss high magnetic flux density directionality electrical steel plate of Claim 4 which rolls the annealed steel plate to plate | board thickness 0.20 mm or less. The direction in which the high-carbon silicon steel slab is heated and hot-rolled, then hot-rolled sheet is annealed and cold-rolled, decarburized and nitrided, and then subjected to secondary recrystallization annealing. Electrical steel sheet,
The silicon steel slab is in mass%, C: 0.10 to 0.30%, Si: 2.0 to 4.5%, Al: 0.005 to 0.040%, Mn: 0.20% or less, N: 0.010% or less, S: 0.010% or less, P: 0.005-0.05%, balance Fe and other inevitable impurities,
The silicon steel slab is heated to 1050 to 1250 ° C. and hot-rolled,
The hot rolling step includes a step of cooling the hot-rolled slab at 15 ° C. or more per second and winding it at a temperature of 580 ° C. or less.
Annealing of the hot-rolled sheet is performed at a temperature of 900 to 1200 ° C., and includes a step of cooling the annealed steel sheet at a rate of 15 to 500 ° C. per second,
The decarburization is performed simultaneously with the annealing of the hot-rolled sheet,
The average crystal grain diameter 10~30mm der after the secondary recrystallization annealing Ri, beta angle is 3 ° or less, low core loss and high magnetic flux density oriented electrical steel sheet.   The low iron loss high magnetic flux density grain-oriented electrical steel sheet according to claim 6, wherein the silicon steel slab further contains 0.01 to 0.3 mass% of Sn and Sb alone or in combination. The low iron loss high magnetic flux density grain-oriented electrical steel sheet according to claim 6 or 7 , wherein a thickness of the steel sheet is 0.20 mm or less.   The low iron loss high magnetic flux density directional electrical steel sheet according to claim 6 or 7, wherein the steel sheet has an iron loss (W17 / 50) of 0.90 W / Kg or less and a magnetic flux density (B10) of 1.92 T or more.