KR101408231B1 - Method for manufacturing the grain-oriented electrical steel sheets with excellent magnetic properties - Google Patents

Abstract

The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which comprises 2.0 to 7.0% by weight of Si, 0.005 to 0.040% by weight of Al, 0.005 to less than 0.005% 0.02 to 0.07%, S: 0.005% or less, the total of one or two of Sn and Sb: 0.01 to 0.3%, and the balance Fe and other unavoidable impurities are reheated and hot rolled, Annealing at a temperature of 800 to 950 占 폚 under a mixed gas atmosphere of hydrogen and nitrogen containing ammonia gas and performing secondary recrystallization annealing after performing plate annealing and cold rolling, In this method for producing a highly directional electrical steel sheet, the reheating is characterized by reheating to a temperature above the temperature at which both AlN and MnS are completely dissolved. According to the present invention, the primary recrystallized grains are homogeneously coarsened and the size of the precipitates is finely and uniformly formed. Thus, the degree of integration of the {110} < 001 > crystal grains is greatly improved after the secondary recrystallization, It is possible to produce a grain-oriented electrical steel sheet having a high magnetic flux density and a low iron loss by reducing the sizing size.

Directional electric steel sheet, reheating temperature, solution temperature, low temperature heating, simultaneous decarburization, inhibitor

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet having excellent magnetic properties,

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used as an iron core material for electronic equipment such as various transformers and generators, and more particularly to a method for manufacturing a grain- The present invention also relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties by uniformly and largely forming primary recrystallized grains.

Generally, the grain-oriented electrical steel sheet is composed of grains having a so-called goss texture in which the crystal orientation of the steel sheet face is {110} plane and the crystal orientation of the rolling direction is parallel to the <001> axis, Is an excellent soft magnetic material. Obtaining such a {110} <001> texture can be accomplished by a combination of various manufacturing processes. Generally, steelmaking components, slab heating, hot rolling, annealing of hot-rolled sheet, annealing of primary recrystallization, .

Such a grain-oriented electrical steel sheet is intended to suppress the growth of the primary recrystallized grains and to exhibit excellent magnetic properties by a secondary recrystallized structure obtained by selectively growing crystal grains in a {110} < 001 > (Hereinafter referred to as "inhibitor") is very important. (Hereinafter referred to as "secondary recrystallization") in crystal grains having an aggregate structure of {110} &lt; 001 &gt; orientation stably in the crystal grains whose growth has been suppressed in the final annealing step It is the core of technology.

Specifically, as the inhibitor, fine precipitates or segregated elements which are artificially formed are used. In order to suppress the growth of all the primary recrystallized grains until the second recrystallization occurs in the final annealing step, It must be uniformly distributed, and it must be thermally stable up to the high temperature immediately before the secondary recrystallization, so that it is not easily decomposed. Secondary recrystallization begins to occur in the final annealing process because these inhibitors lose their ability to inhibit the growth of the primary recrystallized grains as they grow or decompose as the temperature rises. In this case, abnormal grain growth occurs in a relatively short time do.

The inhibitors that are currently widely used commercially under the above-mentioned conditions include MnS, AlN and MnSe. Of these, a typical known technique for manufacturing an electric steel sheet using only MnS as an inhibitor is disclosed in Japanese Patent Publication No. 30-3651. The production method is a method in which a stable secondary recrystallized structure is formed by cold rolling two times including intermediate annealing . However, a method using only MnS as an inhibitor has a problem that a high magnetic flux density can not be obtained, and a manufacturing cost is increased by cold rolling two times. On the other hand, a high magnetic flux density is required in a directional electric steel sheet because the use of an iron core having a high magnetic flux density enables the miniaturization of electric devices. For this reason, efforts are continuously being made to increase magnetic flux density.

Alternatively, MnS and AlN can be simultaneously used as an inhibitor to produce a grain-oriented electrical steel sheet. A typical known technique is disclosed in Japanese Patent Publication No. 40-15644. In this method, a product having a high magnetic flux density is obtained by cold rolling one time at a high rolling rate of 80% or more. Specifically, this method includes a series of steps of high-temperature slab heating, hot rolling, hot-rolled sheet annealing, cold rolling, decarburization annealing, and final annealing. At this time, as mentioned above, the final annealing refers to the process of developing the aggregate structure of the {110} < 001 > orientation by causing secondary recrystallization in a coil-wound state. In this final annealing step, the annealing separator containing MgO as a main component is applied to the surface of the steel sheet before annealing to prevent the steel sheets from adhering to each other, and the oxide layer formed on the steel sheet surface during the decarburization annealing reacts with the annealing separator A vitreous coating is formed so as to impart insulation to the steel sheet. Finally, the steel sheet having the texture of {110} < 001 > orientation is finally subjected to an insulating coating by final annealing to obtain a final product.

Another method is to produce a grain-oriented electrical steel sheet using MnSe and Sb as an inhibitor. Typical known techniques are disclosed in Japanese Patent Publication No. 51-13469. This manufacturing method includes the steps of high-temperature slab heating, hot rolling, hot-rolled sheet annealing, primary cold rolling, intermediate annealing, secondary cold rolling, decarburization annealing, and final annealing. This method has an advantage that a high magnetic flux density can be obtained, but there is a problem in that productivity is decreased and manufacturing cost is increased by performing cold rolling two times.

In addition, these methods have serious problems that are more serious than the aforementioned disadvantages. That is, the MnS or AlN contained in the slab of the grain-oriented electrical steel sheet must be reheated at a high temperature for a long time to be solidified to form a precipitate having an appropriate size and distribution during the cooling process after the hot rolling, .

Specifically, it is known that a high magnetic flux density can be obtained only by reheating the slab at 1300 ° C for the MnS inhibitor, 1350 ° C for the MnS + AlN inhibitor, and 1320 ° C for the MnSe + Sb inhibitor have. In actual industrial production, in order to obtain a uniform temperature distribution to the inside in consideration of the size of the slab, etc., it is reheated to a temperature of approximately 1400 ° C.

When the slab is heated at a high temperature for a long time, the amount of heat to be used is increased, resulting in an increase in manufacturing cost. In addition, since the surface of the slab is melted and flows down, the maintenance cost of the heating furnace is increased and the service life of the heating furnace is shortened. Particularly, when the main phase structure of the slab grows to a great extent by heating at high temperature for a long time, cracks are generated in the width direction of the plate in a subsequent hot rolling step, thereby significantly reducing the slump failure rate.

Therefore, if a directional electric steel sheet can be manufactured by lowering the reheating temperature of the slab, it can bring about many beneficial effects in terms of manufacturing cost and error rate. Therefore, new methods for lowering the slab heating temperature by appropriately controlling the type of precipitate and the precipitation amount capable of effectively suppressing crystal grain growth have been studied. As a result of these efforts, instead of entirely restricting the inhibition of grain growth of the elements contained in the liquefied elements, nitride is formed in an arbitrary step in the process of manufacturing an electrical steel sheet by a method known as nitriding treatment to secure the inhibition of grain growth It is possible to lower the slab heating temperature. This method solves the above problems by lowering the reheating temperature of the slab, secures a part of the necessary suppressing force by adding a certain amount of the precipitate forming element in the steelmaking process, and replenishes all the restraining force necessary for inhibiting grain growth. It is called the directional electric steel sheet manufacturing technology by the low temperature heating method.

Such a nitriding treatment method includes nitriding a steel sheet in a gas atmosphere having a nitriding ability after the decarburization step, coating the steel sheet with a nitriding compound in an annealing separator, Various methods are known in which they are contained in the atmosphere gas and put into the center of the steel sheet. Among them, nitriding the steel sheet in a gas atmosphere having a nitriding ability after decarburization is most commonly used.

The decarburization is carried out at a temperature of 800 ° C or lower, and nitrides such as Si ₃ N ₄ and (Si, Mn) N are formed on the surface portion. Such precipitates are easily formed at low temperatures but are very unstable thermally. Therefore, these precipitates are easily decomposed at high temperatures and can not be used as an inhibitor of the oriented electrical steel sheet. In addition, since the annealing temperature is low, diffusion of nitrogen is not so active, and nitride is formed intensively on the surface of the steel sheet. Therefore, it is necessary to decompose them again in the final annealing process, which is a subsequent process, to bond with other elements present in the steel sheet and to re-precipitate them. In this case, the precipitate formed can be used as an inhibitor of the grain-oriented electrical steel sheet with a stable nitride such as AlN or (Al, Si) N.

A method of supplying nitrogen into the steel sheet in a separate nitriding process including ammonia gas after decarburization annealing with (Al, Si) N nitrides is disclosed in Japanese Patent Publication No. 1-230721 and Japanese Patent Publication No. 1-283324 .

On the other hand, a method of forming a precipitate through simultaneous decarburization and nitriding requires an annealing temperature of 800 ° C or higher. Considering the de-elasticity, the annealing time becomes too long at a temperature of 800 ° C or lower, which is not industrially useful and is a temperature set considering diffusion of nitrogen. In this temperature range, unstable precipitates such as Si ₃ N ₄ and (Si, Mn) N can not be formed, and a thermally highly stable precipitate such as AlN, (Al, Si, Mn) N is formed. Therefore, it is not necessary to re-precipitate in the subsequent final annealing step and it can be used as a grain growth inhibitor.

A method of economically performing the decarburization and nitriding treatment is disclosed in Korean Patent Publication No. 97-43184 and Korean Patent Application No. 97-28305 discloses a method of decarburizing and nitriding Are performed at the same time.

In regard to the point of time when nitriding treatment is performed, Japanese Patent Application Laid-Open No. 3-2324 proposes a method in which decarburization annealing is performed first and nitriding is performed using ammonia gas after the crystal grain size is grown to some extent or more.

The methods related to the low-temperature slab heating are performed in a temperature range in which the slab heating is partially solvated with the AlN serving as the growth inhibitor of the primary recrystallized grains. When the slab is heated only to such a partial solution temperature, there is a large difference in the size distribution between the precipitation in the casting process and the re-precipitation in hot rolling. These differences result in a difference in the grain size distribution of the primary re-crystallization plate and are a factor that adversely affects the magnetism of the final annealed product. In addition, MnS precipitation also affects the size of the primary recrystallized grains even when AlN is used as a main inhibitor. Therefore, the precipitation behavior of MnS depending on the slab heating temperature is also important because it affects the primary recrystallization size distribution.

Recently, in Japanese Unexamined Patent Publication (Kokai) No. 2003-201518, a directional electric steel sheet excellent in magnetic property is produced by using only the difference in grain boundary movement speed of primary crystal grains without inhibitor as a component system containing no grain growth inhibitor forming element, The importance of partial solution has been recognized.

In Korean Patent Application Nos. 2001-0031104 and 12-167963, the slab reheating temperature is 1200 占 폚 or higher and the nitriding treatment is performed between decarburization annealing and the start of secondary recrystallization of the final annealing, And an average grain size of the sizing is 7 占 퐉 to 18 占 퐉. According to these results, at the reheating temperature of 1200 ° C or below, the grain size is 26.2 μm under the complete solution condition of the precipitate, and secondary recrystallization does not occur. As a result, the grain size distribution becomes wider as the grain size becomes larger. There is a problem that it can adversely affect magnetism.

Japanese Patent Publication (Kokai) No. 2-294428 discloses a method for producing a grain-oriented electrical steel sheet by heating the slab to a temperature of 1200 ° C or lower and nitriding it simultaneously with decarburization to form an inhibitor whose main composition is (Al, Si) N . However, in this method, AlN is partially solvated at a slab reheating temperature of 1200 ° C or less. This is because if the content of N is 0.0030 to 0.010%, the AlN precipitate partially unmelted as the N content increases, .

On the other hand, the nitriding by ammonia gas in the nitriding method utilizes the property that ammonia is decomposed into hydrogen and nitrogen at about 500 ° C or higher, and nitrogen generated by decomposition is introduced into the steel sheet. This is because the nitrogen introduced into the steel sheet reacts with Al, Si, Mn and the like which have already existed in the steel to form a nitride and use it as an inhibitor. Among the nitrides formed, AlN and (Al, Si, Mn) N based nitrides of N are used as inhibitors.

All of the above methods provide a method for manufacturing a grain-oriented electrical steel sheet by heating a slab at a low temperature and nitriding the steel sheet with a material having a nitriding ability or a gas to form a new precipitate in the steel sheet. As mentioned above, the nitriding gas is represented by ammonia, and the action and problems when it is nitrided after decarburization annealing is completed are as follows. Nitridation by decomposition of ammonia gas is possible when the decomposition temperature of ammonia gas is 500 ° C or more. However, since the diffusion rate of nitrogen in the steel sheet is very slow at a temperature near 500 ° C, nitriding time is required for a long time. When the temperature is higher than 800 ° C, nitriding is easy. However, since primary recrystallized grains are easy to grow, And the development of secondary recrystallization becomes unstable. Therefore, the proper nitriding temperature range can be considered as 500 to 800 ° C.

However, if the nitriding temperature is low and the nitriding time is too long, there is a problem in productivity, and the actual nitriding temperature is in the range of 700 to 800 ° C. A method of nitriding based on such an idea is disclosed in Korean Patent Publication No. 95-4710. In this temperature range, ammonia decomposition reaction and nitrogen diffusion are active. Therefore, very strict control of nitridation conditions is required to add the desired amount of nitrogen in the steel. That is, the amount of nitriding is determined by the concentration of ammonia, the nitriding temperature, and the nitriding time, and the appropriate amount of nitriding should be determined by a combination of these conditions. Considering productivity, nitriding must be performed in a short time, so the concentration of ammonia and the nitriding temperature should be high.

In this case, the nitriding takes place in a short time, and the nitrogen concentration at the surface portion of the steel sheet is mainly increased. Therefore, the deviation of the steel sheet by each part becomes very large. In the center portion of the steel sheet, there is almost no nitriding, and even in the surface portion, a nonuniform phenomenon appears in many places. Also, the amount of nitriding is greatly influenced by the state of the steel sheet.

Typically, the surface roughness, grain size, chemical composition and the like can greatly affect the nitriding of the steel sheet. If the surface roughness is large, the contact area with the atmosphere gas is widened, which causes a variation in the amount of nitriding. When the grain size is small, grain boundaries per unit area are increased, and the diffusion of nitrogen through the grain boundaries occurs more rapidly than diffusion in the crystal grains, resulting in a variation in the nitriding amount.

The chemical composition may lead to a variation in the nitriding amount depending on the relative amount of the elements that easily make the nitride among the elements in the steel sheet. Such deviation of the nitriding amount ultimately causes defects in the coating film, which can be solved by a combination of the atmosphere of final annealing and the heat treatment temperature as disclosed in Korean Patent Application No. 97-65356.

On the other hand, the final annealing process is a very important step to obtain a secondary recrystallized structure having a {110} < 001 > orientation as mentioned above. In particular, according to the method disclosed in Korean Patent Publication No. 95-4710, which performs nitriding after decarburization, it includes a step of transforming a precipitate produced after nitriding annealing in a final annealing process. Specifically, the precipitates formed after nitridation are precipitates of Si ₃ N ₄ and (Si, Mn) N, which are thermally unstable and are easily decomposed.

Therefore, these precipitates can not be used because they are incompatible with the conditions that the above-mentioned inhibitors should have. Therefore, they must be converted into thermally stable precipitates such as AlN and (Al, Si, Mn) N to function as inhibitors.

In the case of forming a nitride by decarburization and nitriding annealing, the nitride is transformed into a precipitate which can be used as an inhibitor after being maintained at a temperature of 700 to 800 ° C for a final annealing process as a subsequent process for at least 4 hours. This means that the final annealing process is lengthened and must be controlled very strictly, which is very disadvantageous in manufacturing cost.

In order to solve this problem, a method of performing decarburization and nitriding at the same time is disclosed in Korean Patent Application No. 98-58313. However, since decarburization and nitriding are simultaneously performed in this method, compared to the step of nitriding after decarburization, There is a problem that the crystal grain size of the crystal plate becomes small.

In other words, when decarburization and nitriding are performed at the same time, growth of the primary recrystallized grains is fundamentally hindered due to the intercalation elements carbon and nitrogen. Such reduction in the primary recrystallization grain size causes the secondary recrystallization initiation It will affect the temperature. More specifically, when the primary recrystallization size is small, the secondary recrystallization starting temperature is lowered, so that not only the crystal grains having {110} < 001 > orientation are secondary recrystallized but also those having other orientations are secondary recrystallized There is a problem in that the {110} < 001 > density of secondary recrystallized grains is deteriorated after the completion of annealing, so that the magnetic properties of the final plate may deteriorate.

Therefore, it is important to strictly control the secondary recrystallization in order to produce a grain-oriented electrical steel sheet having excellent magnetic properties. This second recrystallization behavior is the easiest way to control the size of the primary recrystallized grains. The temperature at the temperature just below the temperature region where the precipitation of AlN, (Al, Si, Mn) N, the inhibitor, Secondary recrystallization is completed. For this purpose, in the manufacturing process of simultaneous decarburization and nitriding, a method of growing primary recrystallized grains more or a method of increasing the deterrent required for secondary recrystallization has been used. In particular, it has been proposed to add an element such as B or Cu in order to increase the inhibiting power required for secondary recrystallization.

However, when B is added, it is easy to form a complex compound of B and C so that it is difficult to obtain a homogeneous and stable inhibiting force. Even when Cu is added, Cu emulsion is precipitated but not precipitated uniformly and iron loss and magnetic flux density The quality of the product is deteriorated.

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a method for manufacturing a grain-oriented electrical steel sheet by slab low-temperature heating, in which the grain size of the primary re- The N content in the steelmaking process is controlled to be very low and the role as inhibitor in the secondary recrystallization is small. However, MnS, which affects the primary recrystallization size, is also completely dissolved to uniformize the size of the primary recrystallization and to make the size The size and distribution of the precipitates are uniformly formed by adding at least one of Sn and Sb while controlling the S content to a very low level in the liquefied components so as to be large, and the texture of the {110} < 001 & Which is excellent in magnetic properties through simultaneous decarburization and nitriding treatment.

In order to accomplish the above object, the present invention provides a method of manufacturing a semiconductor device, comprising: 2.0 to 7.0% by weight of Si, 0.005 to 0.040% of an acid soluble Al, 0.20% or less of Mn (excluding 0% , 0.01 to 0.3% of the total of one or both of C and C, 0.02 to 0.07%, S: 0.005% or less (excluding 0%), Sn and Sb, the balance Fe and other unavoidable impurities The slab of the electric steel sheet is reheated and hot rolled, hot rolled sheet annealing and cold rolling are performed, and simultaneous decarburization steep annealing is performed at a temperature of 800 to 950 캜 in a mixed gas atmosphere of hydrogen and nitrogen containing ammonia gas, The reheating is characterized in that the reheating is performed at a temperature higher than a temperature at which both of AlN and MnS are completely dissolved.

Preferably, the slab reheating temperature may be 1200 ° C or less.

Preferably, the primary recrystallized grain size after the simultaneous decarburization steep annealing may be 20 to 32 탆.

Preferably, the standard deviation of the average grain size / grain size ratio of the first recrystallized grains after the simultaneous decarburization annealing is 1.2 or more.

As described above, according to the method of the present invention, the N and S contents are controlled to be very low and the slab is heated to the full solution temperature or more to uniformly form the recrystallized grains, Particularly, it is possible to control the initial grain size before cold rolling by controlling the low-N content to be low.

Further, by adding at least one of Sn and Sb, the number of crystal grains having a {110} < 001 > orientation in the primary re-crystal plate increases and the sizes of AlN, (Al, Si, Mn) N precipitates are finely and uniformly formed It is possible to improve the degree of integration of the {110} < 001 > crystal grains after the second recrystallization and reduce the secondary recrystallized grain size, thereby producing a grain-oriented electrical steel sheet having high magnetic flux density and low iron loss.

The inventors of the present invention have found that a method of controlling low-level N and low-level S as a method for preventing the reduction of the primary recrystallized grain size in the step of simultaneously performing decarburization and nitriding is very effective. That is, the size of the primary recrystallized grains is mainly determined by the AlN and MnS precipitates existing after hot rolling, and if the N content and the S content, which form precipitates, are controlled to be very low, the amount of precipitates can be made small.

On the other hand, when the slab is heated by heating at a partial solution temperature, there is a large difference in the distribution of the AlN precipitates, which causes a large variation in the size distribution of the primary recrystallized grains, which causes the magnetism to become unstable. However, when the N content and the S content are very low, it is possible to obtain a homogeneous and large primary recrystallized grains since the amount of precipitate is very small when heated to the full solution temperature in the slab.

In addition, the present inventors have found that when the low-N content and the low-S content are low, the initial grain size before cold rolling becomes coarse, so that the number of grains having {110} < 001 & To improve the magnetic properties of the final product.

The present inventors have also found that the addition of grain boundary segregation elements such as Sn and Sb can achieve the same effect as the increase of the grain in the {110} < 001 > orientation due to the initial coarse grain before rolling, (Al, Si, Mn) N precipitates formed by AlN, AlN, Si, and Mn are distributed finely and uniformly, so that secondary recrystallization occurs stably and the magnetic properties are greatly improved.

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

Si is the basic composition of the electric steel sheet, and it plays the role of lowering the core loss, that is, the iron loss, by increasing the resistivity of the material. When the content of Si is less than 2.0%, the resistivity decreases and the iron loss characteristic deteriorates. When the Si content exceeds 7.0%, the brittleness of the steel increases, which makes the cold rolling extremely difficult and the formation of the secondary recrystallization becomes unstable.

Al is ultimately a nitride acting as an AlN, (Al, Si, Mn) N type nitride and acts as an inhibitor. When the content is 0.005% or less, sufficient effect as an inhibitor can not be expected. The temperature required for solution treatment is increased to adversely affect the hot rolling workability, so it is set to 0.005 to 0.040%.

Mn has an effect of increasing the specific resistance and decreasing the iron loss by the same way as Si. It reacts with nitrogen introduced by the nitriding treatment together with Si to form precipitates of N (Al, Si, Mn) , It is an important element to cause secondary recrystallization. However, when 0.20% or more is added, it accelerates the austenite phase transformation during hot rolling so that the size of the primary recrystallization decreases to make the secondary recrystallization unstable. ).

When N is contained in an amount of 0.005% or more, when the slab is heated to a temperature at which it is completely dissolved, the size of the primary recrystallization decreases to lower the secondary recrystallization initiation temperature. Therefore, the crystal grains other than the {110} Causing deterioration of magnetism. On the other hand, when the N content is as low as 0.005% or less, it is possible to obtain a homogeneous and large primary recrystallized grains by heating the slab to a temperature at which the slab is completely dissolved, have. In addition, when the N content is as low as 0.005% or less, since the initial grain size before cold rolling becomes coarse, the number of grains having a {110} < 001 > orientation increases in the primary re- To improve the magnetic properties of the final product, so that N is 0.005% or less (excluding 0%).

When C is added in an amount of 0.02% or more, austenite transformation of the steel is promoted to assist in forming a uniform microstructure by miniaturizing hot rolled steel during hot rolling. However, when the content is 0.07% or more, coarse carbides are precipitated and it is difficult to remove carbon during decarburization, so C is 0.02 to 0.07%.

When S is contained in an amount of 0.005% or more, when the slab is heated to a temperature at which the slab is completely dissolved, the size of the primary recrystallization decreases to lower the secondary recrystallization initiation temperature. Therefore, the crystal grains other than the {110} Which deteriorates magnetism. On the other hand, when the S content is as low as 0.005% or less, it is possible to obtain a homogeneous and large primary recrystallized grains by heating the slab to a temperature at which the slab is completely dissolved, have. In addition, when the low S content is as low as 0.005% or less, the initial grain size before cold rolling becomes coarse, so that the number of grains having a {110} < 001 > orientation in the primary re- To improve the magnetic properties of the final product, so that S is 0.005% or less (excluding 0%).

Since Sn is an element which interferes with the grain boundary movement as a grain boundary segregation element, it is known as a crystal growth inhibitor and facilitates the generation of Goss grain in the {110} < 001 > orientation to help the secondary recrystallization to develop well. And the Goss crystal grains having good orientation properties are the essential elements of the present invention for secondary recrystallization to give a high magnetic flux density characteristic. If Sn is less than 0.01%, the effect of addition is deteriorated. If 0.3% or more is added, grain boundary segregation occurs severely and the brittleness of the steel sheet becomes large, resulting in plate breakage during rolling.

Sb is an effect of inhibiting crystal growth as a grain boundary segregation element like Sn, and has an effect of improving the adhesion of the steel sheet and the oxide layer by suppressing the formation of the oxide layer on the surface of the steel sheet formed at the time of secondary recrystallization, thereby improving iron loss.

In the present invention, at least one of Sn and Sb is added to obtain a crystal growth inhibiting effect and more Goss crystal grains having a {110} < 001 > orientation can be formed, and the sum of one or two of Sn and Sb If it is added in an amount of 0.01% or less, the effect is insignificant. If it is added in an amount of 0.3% or more, the addition cost is increased compared with the effect.

The process conditions are described below.

The heating temperature of the slab before hot rolling is set at the temperature at which the precipitates used as inhibitors are completely dissolved. When the heating temperature is partially dissolved, the size of the precipitate formed during casting and the size of the precipitate formed during reheating are large, which makes the grain size of the primary re-crystal plate uneven. Because of this possibility, the slab heating temperature is set to the temperature range in which the precipitates are completely dissolved, as the magneticity may become uneven.

The electric steel slabs heated as above are hot-rolled by a conventional method. In the currently used method, the final thickness of the hot-rolled sheet is usually 2.0 to 3.5 mm. The hot-rolled sheet is annealed in hot-rolled sheet and then cold-rolled to a final thickness of 0.20 to 0.35 mm. There are various methods of annealing the hot-rolled sheet, but a method of cooling the material after heating at 1000 to 1200 ° C and cracking at 850 to 950 ° C is adopted.

The cold-rolled plate performs decarburization and annealing simultaneously in a mixed gas atmosphere of ammonia + hydrogen + nitrogen. The dew point of the mixed gas of hydrogen and nitrogen depends on the annealing temperature and the composition ratio of the mixed gas, and is set so as to maximize the decarburization capability.

When the soda temperature of the simultaneous decarburization annealing and the nitriding annealing is lower than 800 ° C, it takes a long time to decarburize and the size of the primary recrystallized grains is small so that stable secondary recrystallization is not stable during final annealing. When the temperature is higher than 950 ° C, It is difficult to control and the primary recrystallized grains excessively grow or become uneven, making it difficult to develop a stable secondary recrystallized structure at the time of final annealing, so that it is preferable to perform at 800 to 950 ° C.

The annealing time for the simultaneous decarburization and nitriding is determined by the annealing temperature and the concentration of the ammonia gas introduced, and the annealing time is usually 30 seconds or more. Here, when the size of the primary recrystallized grains is 20 탆 or less, the grain growth driving force is increased, the secondary recrystallization starting temperature is lowered, and the crystal grains grow in a direction other than the Goss orientation, . When the size of the first recrystallized grain is 32 탆 or more, the grain growth driving force is lowered and the secondary recrystallization does not occur and the magnetic properties are deteriorated. Therefore, the primary recrystallized grain size is preferably controlled within the range of 20 to 32 탆.

If the value of the standard deviation of the mean grain size / grain size is less than 1.2, the grain size of the primary redeposited sheet is not Goss orientation but coarsens and deteriorates the magnetic properties. Therefore, in order to prevent deterioration of the magnetic properties, / The standard deviation of the grain size is controlled to be 1.2 or more.

Generally, in the production of a grain-oriented electrical steel sheet, an annealing separator based on MgO is applied to a steel sheet, and the steel sheet is subjected to final annealing for a long time to cause secondary recrystallization, whereby the {110} plane of the steel sheet is parallel to the rolling surface, {110} < 001 > texture structure parallel to the rolling direction is formed to produce a directional electric steel sheet excellent in magnetic properties.

The objective of the final annealing is largely the formation of {110} < 001 > texture by secondary recrystallization, the formation of a vitreous film by the reaction of the oxide layer and MgO formed during decarburization, and the removal of impurities which impair magnetic properties. As a method of final annealing, a secondary recrystallization can be well developed by maintaining nitride as a particle growth inhibitor by maintaining a mixed gas of nitrogen and hydrogen at a temperature rising period before the secondary recrystallization, and after the secondary recrystallization is completed It is kept in a 100% hydrogen atmosphere for a long time to remove impurities.

The nitride formed by simultaneous decarburization annealing and nitriding annealing does not require transformation of the precipitate when final annealing is performed with AlN, (Al, Si, Mn) N, and is directly used as an inhibitor. The difference in the types of nitrides produced depending on the difference in the nitriding method is due to the difference in annealing temperature. That is, Si ₃ N ₄ and (Si, Mn) N can not be stably present at a temperature of 800 ° C. or higher, and nitrogen diffuses very quickly.

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

[Example 1]

Si: 3.18%, C: 0.056%, Mn: 0.062%, S: 0.0061%, N: 0.0020%, Sol. In the slab of the grain-oriented electrical steel sheet containing Al and 0.026% of Fe and other inevitable impurities, the complete solution-forming temperature of the AlN was 1164 ° C and the complete solution temperature of MnS was 1136 ° C. The solidification temperature of 1130 ° C and MnS were completely heated, and the temperature was 1150 ° C, which is the partial solution temperature of AlN, and 1175 ° C and 1190 ° C, Rolled to obtain a hot-rolled sheet having a thickness of 2.3 mm. The hot-rolled sheet was heated to a temperature of 1100 占 폚 or higher, maintained at 900 占 폚 for 90 seconds, quenched in water, pickled, and then cold-rolled to a thickness of 0.30 mm.

The cold-rolled steel sheet was subjected to a simultaneous decarburization and nitriding treatment by maintaining at a temperature of 875 DEG C in a furnace a mixed atmosphere of 75% hydrogen and 25% nitrogen at a dew point temperature of 65 DEG C and 1% Respectively. At this time, the nitrogen content of the nitrided steel sheet was controlled in the range of 170 to 200 ppm.

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. In the final annealing, a mixed atmosphere of 25% nitrogen and 75% hydrogen was set up to 1200 ° C., and after reaching 1200 ° C., it was maintained in a 100% hydrogen atmosphere for 10 hours or more. The magnetic properties measured for each condition are shown in Table 1.

Slab heating temperature (℃) Magnetic flux density (B ₁₀ , T) The iron loss _{(W 17/50, W /} kg) division 1130 1.901 1.03 Comparison 1 1150 1.908 1.02 Comparative material 2 1175 1.925 0.98 Inventory 1 1190 1.924 0.99 Inventory 2

As shown in Table 1, inventive materials 1 and 2 having a complete solution temperature higher than that of comparative materials 1 and 2, in which the slab heating temperature is the temperature range in which both AlN and MnS or only AlN are solubilized, have high magnetic flux density and low iron loss Can be seen.

[Example 2]

Si: 3.21%, C: 0.056%, Mn: 0.055%, S: 0.006%, Sol. Al (0.024%) and N were changed as shown in Table 2, and the slab of the oriented electrical steel sheet consisting of Fe and other unavoidable impurities constituting the remainder was completely melted at a temperature (total solution temperature of MnS: 1125, solution temperature of AlN: 2) for 210 minutes and then hot-rolled to produce a hot-rolled sheet having a thickness of 2.3 mm. The hot-rolled sheet was heated to a temperature of 1100 占 폚 or higher, maintained at 900 占 폚 for 90 seconds, quenched in water, pickled, and then cold-rolled to a thickness of 0.30 mm.

The cold-rolled steel sheet was subjected to a simultaneous decarburization and nitriding treatment by maintaining at a temperature of 875 DEG C in a furnace a mixed atmosphere of 75% hydrogen and 25% nitrogen at a dew point temperature of 65 DEG C and 1% Respectively.

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. In the final annealing, a mixed atmosphere of 25% nitrogen and 75% hydrogen was set up to 1200 ° C., and after reaching 1200 ° C., it was maintained in a 100% hydrogen atmosphere for 10 hours or more. The results of measuring the magnetic properties for each condition are shown in Table 2.

N content
(weight%) AlN
Solution temperature Slab
Heating temperature (℃) Magnetic flux density
(B ₁₀ , Tesla) Iron loss
_{(W 17/50, W /} kg)
division 0.0011 1106 1135 1.933 0.95 Inventory 3 0.0023 1169 1190 1.931 0.97 Invention 4 0.0060 1260 1285 1.905 1.03 Comparative material 3 0.0078 1288 1310 1.896 1.04 Comparison 4

As shown in Table 2, it can be seen that inventive materials 3 to 4 having an N content of 0.0050% or less have a higher magnetic flux density and lower iron loss than the comparative materials 3 to 4 when heated to a temperature range in which a precipitate is completely dissolved .

[Example 3]

Si: 3.27%, C: 0.045%, Mn: 0.074%, N: 0.0015%, Sol. Al: 0.024%, and S is changed as shown in Table 3, and in the slab of the oriented electrical steel sheet composed of Fe and other unavoidable impurities, the AlN is at a temperature higher than the fully-dissolved temperature (1132 ° C) And then hot rolled after heating for 210 minutes to prepare a hot rolled sheet having a thickness of 2.3 mm. The hot-rolled sheet was heated to a temperature of 1100 占 폚 or higher, maintained at 900 占 폚 for 90 seconds, quenched in water, pickled, and then cold-rolled to a thickness of 0.30 mm.

The cold-rolled steel sheet was subjected to a simultaneous decarburization and nitriding treatment by maintaining at a temperature of 875 DEG C in a furnace a mixed atmosphere of 75% hydrogen and 25% nitrogen at a dew point temperature of 65 DEG C and 1% Respectively.

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. In the final annealing, a mixed atmosphere of 25% nitrogen and 75% hydrogen was set up to 1200 ° C., and after reaching 1200 ° C., it was maintained in a 100% hydrogen atmosphere for 10 hours or more. Table 3 shows the results of measuring the magnetic properties for each condition.

S content
(weight%) MnS
Solution temperature Slab
Heating temperature (℃) Magnetic flux density (B ₁₀ , T) Iron loss
_{(W 17/50, W /} kg)
division 0.0020 1064 1100 1.902 0.99 Invention Article 5 0.0037 1110 1130 1.921 0.97 Inventions 6 0.0066 1157 1195 1.905 1.01 Invention 7 0.0094 1188 1200 1.901 1.02 Invention 8 0.0130 1217 1250 1.886 1.04 Comparative material 5

As shown in Table 3, it can be seen that inventive materials 5 to 8 having an S content of 0.0100% or less when heated to a temperature range in which a precipitate is completely dissolved have a higher magnetic flux density and lower iron loss than the comparative material 5.

[Example 4]

Si: 3.25%, C: 0.057%, Mn: 0.06%, S: 0.0061%, N: 0.0018%, Sol. Al: 0.024% and the remainder Fe and other unavoidable impurities was heated at a temperature of 1160 캜, which is a temperature higher than the full solution temperature (1147 캜), for 210 minutes, and then hot-rolled to obtain a hot- . The hot-rolled sheet was heated to a temperature of 1100 占 폚 or higher, maintained at 900 占 폚 for 90 seconds, quenched in water, pickled, and then cold-rolled to a thickness of 0.30 mm.

The cold-rolled steel sheet was subjected to a simultaneous decarburization, dipping and sintering in a furnace maintained at a constant temperature while a mixed atmosphere of 75% hydrogen and 25% nitrogen at a dew point temperature of 65 ° C and 1% And the final amount of nitrogen was set to 180 to 230 ppm. At this time, the simultaneous decarburization and nitriding temperature were changed to 780, 810, 865, 940, and 980 ° C., and the time was changed to 120 to 240 seconds to control the nitriding amount.

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. In the final annealing, a mixed atmosphere of 25% nitrogen and 75% hydrogen was set up to 1200 ° C., and after reaching 1200 ° C., it was maintained in a 100% hydrogen atmosphere for 10 hours or more. The magnetic properties measured for each condition are shown in Table 4.

Simultaneous decarburization, nitriding annealing conditions Magnetic flux density (B ₁₀ , T) _Iron loss ( _{W17 / 50} , W / kg) division 780 ℃ x195 sec 1.898 1.05 Comparative material 6 810 ° C x 160 sec 1.934 0.95 Invention 9 865 ℃ x150sec 1.939 0.95 Inventions 10 940 ℃ x140 sec 1.935 0.97 Invention invention 11 980 ℃ x130 sec 1.883 1.06 Comparison 7

As can be seen from Table 4, even when the annealing conditions under the simultaneous decarburization annealing and nitriding annealing were adjusted so as to obtain a proper nitriding amount, the comparative materials 6 to 7 having an annealing temperature of 800 ° C. or lower or 950 ° C. or higher can not obtain excellent magnetic properties have.

[Example 5]

Si: 3.27%, C: 0.045%, Mn: 0.074%, Sol. Al: 0.024% and N, S were changed as shown in Table 5, and the slab heating of the oriented electrical steel sheet composed of Fe and other unavoidable impurities constituting the remainder was heated at 1180 ° C for 210 minutes and hot rolled to produce a 2.3 mm thick hot- Respectively. The hot-rolled sheet was heated to a temperature of 1100 占 폚 or higher, maintained at 900 占 폚 for 90 seconds, quenched in water, pickled, and then cold-rolled to a thickness of 0.30 mm.

The cold-rolled steel sheet was subjected to a simultaneous decarburization and nitriding treatment by maintaining at a temperature of 875 DEG C in a furnace a mixed atmosphere of 75% hydrogen and 25% nitrogen at a dew point temperature of 65 DEG C and 1% Respectively.

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. In the final annealing, a mixed atmosphere of 25% nitrogen and 75% hydrogen was set up to 1200 ° C., and after reaching 1200 ° C., it was maintained in a 100% hydrogen atmosphere for 10 hours or more. An extraction test was conducted under such a heat treatment condition to investigate the secondary recrystallization start temperature. The results of measuring the secondary recrystallization start temperature for each condition are shown in Table 5.

N content
(weight%)
S content
(weight%) AlN
Solution
Temperature MnS
Solution
Temperature
Grain
Size (㎛) Second reorganization
Constant temperature
(° C)
Magnetic flux density
(B ₁₀ , T) Iron loss
(W _17/50,
W / kg)
division 0.0023 0.0016 1169 1047 28.44 1110 1.927 0.99 Invention 12 0.0048 0.0018 1238 1056 26.07 1095 1.921 1.01 COMPARISON 8 0.0049 0.0038 1240 1113 25.00 1090 1.922 1.01 Comparative material 9 0.0067 0.0063 1272 1154 22.18 1030 1.907 1.02 Comparative material 10

As shown in Table 5, when the precipitate is heated to a temperature range in which the precipitate is completely dissolved, the grain size increases to 28.44 占 퐉, but the magnetic properties are such that the inventive material 12 has a higher magnetic flux density and lower iron loss Able to know. The secondary recrystallization temperature is much higher than that of the comparative material 10, and thus the degree of integration of the GOSS orientation is increased and the magnetic property is improved.

[Example 6]

Si: 3.23%, C: 0.048%, Mn: 0.071%, Sol. Al: 0.024% and N, S were changed as shown in Table 6, and the slab heating of the oriented electrical steel sheet consisting of Fe and other unavoidable impurities constituting the remainder was heated at 1180 ° C for 210 minutes and hot rolled to produce a 2.3 mm thick hot- Respectively. The hot-rolled sheet was heated to a temperature of 1100 占 폚 or higher, maintained at 900 占 폚 for 90 seconds, quenched in water, pickled, and then cold-rolled to a thickness of 0.30 mm.

The cold-rolled plate was maintained at a temperature of 830 to 880 ° C in a furnace at a dew point temperature of 65 ° C for a period of 180 seconds by simultaneously supplying a mixed atmosphere of 75% of hydrogen and 25% of nitrogen and 1% of dry ammonia gas, Nitrided.

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. In the final annealing, a mixed atmosphere of 25% nitrogen and 75% hydrogen was set up to 1200 ° C., and after reaching 1200 ° C., it was maintained in a 100% hydrogen atmosphere for 10 hours or more. An extraction test was conducted under such a heat treatment condition to investigate the secondary recrystallization start temperature. Table 6 shows the results of measuring the standard deviation and the magnetic characteristics of the average size and size distribution of the first recrystallized grain for each condition. In particular, the standard deviation of the grain size distribution is shown to indicate the uniformity of grain size. The smaller the standard deviation, the more uniform the size.

S content
(weight%)
N content
(weight%)
Decarburization annealing
Temperature (℃) Average
Grain
Size (㎛) Grain
Of
Standard Deviation
Mean / standard deviation
Magnetic flux density
(B ₁₀ , T) Iron loss
(W _17/50,
W / kg)
division 0.0083 0.0077 860 21.49 18.35 1.17 1.892 1.038 Comparative material 11 0.0063 0.0067 860 22.13 18.77 1.18 1.909 1.020 Comparative material 12 0.0040 0.0044 830 17.44 13.22 1.32 1.856 1.329 Comparative material 13 0.0038 0.0049 840 16.41 12.72 1.29 1.900 1.171 Comparative material 14 0.0040 0.0048 870 23.49 20.32 1.16 1.905 1.065 Comparative material 15 0.0040 0.0043 880 28.05 23.49 1.19 1.841 1.264 Comparative material 16 0.0015 0.0021 845 26.38 18.61 1.42 1.939 0.980 Invention invention 13

As shown in Table 6, the grain size of the inventive material 13 is larger than that of the comparative materials 11 to 16, and the standard deviation is smaller than that of the comparative materials 11 to 16 in terms of the average size and the standard deviation of the grain size distribution. According to comparative materials 13 to 16, when the average grain size is adjusted only at the decarburization annealing temperature under the similar composition conditions, the larger the average crystal grain size, the larger the standard deviation also becomes, and the nonuniformity is increased.

As described above, when the grain size is large, the effect is advantageous to the magnetism. However, when the grain size is too large, the grain size irregularity appears to have a bad influence. However, when the grain size is increased by decreasing the content of N and S, the increase of the standard deviation is not large. As a parameter for expressing this relationship, "average grain / standard deviation of grain size" is used, which is convenient because the grain size is large and the standard deviation is small. In Table 6, it can be seen that the magnetic properties are excellent when the grain size is 20 μm or more and the standard deviation of the average grain size / grain size is 1.2 or more.

[Example 7]

And at least one of Sn and Sb is added in a weight percent based on Si, 3.5%, 0.040%, 0.08%, 0.003%, and 0.024% N, And heated to 1200 DEG C and hot-rolled to form a hot-rolled sheet having a thickness of 2.0 mm. The hot-rolled sheet was subjected to heat treatment at 900 ° C, followed by quenching and pickling, and then cold-rolled to a final thickness of 0.30 mm by one-time cold rolling.

The steel sheet subjected to cold-rolling at the final thickness was subjected to decarburization annealing in a wet atmosphere at 850 ° C, and at the same time nitrogen ions decomposed in ammonia gas were introduced into the steel sheet to nitridate the steel sheet to produce AlN, (Al, Si, Mn) N precipitates .

After the coating with the following annealing separator, the final high-temperature annealing was annealed in a mixed atmosphere of 10% nitrogen + 90% hydrogen throughout the whole area. The high-temperature annealing was performed by raising the temperature to 1200 ° C at a heating rate of 15 ° C / hr, and then performing a final high-temperature annealing for 10 hours or more so that the secondary recrystallization completely took place. The changes in magnetic flux density with Sn and Sb contents added in the steelmaking process are shown in Table 7 below.

Sn Sb Sn + Sb Magnetic flux density (T) Iron loss (W / kg) Remarks 0.005 0.00 0.005 1.855 1.066 Comparative material 17 0.01 0.01 0.02 1.905 0.990 Invention Article 14 0.05 0.05 0.10 1.921 0.981 Invention material 15 0.07 0.10 0.17 1.915 0.955 Invention material 16 0.20 0.15 0.35 1.830 1.126 Comparative material 18 0.15 0.05 0.20 1.936 0.983 Inventions 17 0.20 0.12 0.32 1.895 1.110 Comparative material 19 0.10 0.25 0.35 1.783 1.103 Comparative material 20 0.15 0.03 0.18 1.933 0.973 Inventions 18 0.25 0.20 0.45 1.831 1.093 Comparative material 21 0.00 0.03 0.03 1.908 0.993 Inventions 19 0.00 0.005 0.005 1.845 1.095 Comparative material 22

As shown in Table 7, inventive materials 14 to 19 having a content of Sn and Sb of 0.01 to 0.3% in total of one or two added sintered bodies exhibited a high magnetic flux density of 1.90 T or more, and 0.955 to 0.993 W / kg. &lt; / RTI &gt; On the other hand, the comparative materials 17 and 22, which contain less than 0.01% of Sn and Sb as a total of one or two species, did not exhibit the additive effect and thus had only a magnetic flux density of about 1.85 T, It can be seen that Re 28 ~ 21 did not secure more than 1.90 T.

Claims (4)

(Excluding 0%), N: not more than 0.005% (excluding 0%), C: 0.02 to 0.07%, C: A slab of a grain-oriented electrical steel sheet composed of 0.005% or less of S (excluding 0%), 0.01 to 0.3% of a total of one or two of Sn and Sb, and the balance of Fe and other unavoidable impurities is reheated and hot- Annealing at a temperature of 800 to 950 캜 under an atmosphere of a mixed gas of hydrogen and nitrogen containing ammonia gas and performing secondary recrystallization annealing after performing hot-rolled sheet annealing and cold- A method for producing a directional electrical steel sheet excellent in characteristics, Wherein the reheating is reheated to a temperature higher than a temperature at which both of AlN and MnS are completely dissolved. The method according to claim 1, Wherein the slab reheating temperature is 1200 DEG C or less. The method according to claim 1, Wherein the primary recrystallized grain size after the simultaneous decarburization steep annealing is 20 to 32 占 퐉. The method according to claim 1, Wherein the primary recrystallized grains after the simultaneous decarburization steep annealing have a standard deviation of an average grain size / grain size ratio of 1.2 or more.