KR100825306B1 - Method for manufacturing the grain-oriented electrical steel sheets with excellent magnetic properties - Google Patents

Abstract

A method for manufacturing a grain-oriented electrical steel sheet is provided to improve magnetic properties of the grain-oriented electrical steel sheet by adding arsenic to molten steel while lowering the content of sulfur. A method for manufacturing a grain-oriented electrical steel sheet comprises the step of reheating and hot-rolling a slab while adjusting contents of nitrogen and sulfur such that the slab is completely mixed with AlN and MnS, which are produced during the reheating process. Then, the slab is subject to the cold rolling process after performing an annealing process or without performing the annealing process. The primary annealing process is performed relative to the slab such that the slab is subject to decarburization and nitrification, then the secondary annealing process is performed relative to the slab.

Description

Method for manufacturing the grain-oriented electrical steel sheets with 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 devices such as large rotary machines such as various transformers and generators, and more particularly, by adding Sb to make recrystallized grains uniform and large. The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, so that the grain-oriented electrical steel sheet can be produced.

In the grain-oriented electrical steel sheet, the grain orientation of the steel sheet is {110} and the grain orientation in the rolling direction is composed of grains having a so-called Goss texture, which is parallel to the <001> axis. Very good soft magnetic material. It is possible to obtain the {110} <001> texture by a combination of various manufacturing processes, and in general, the components, slab heating, hot rolling, hot roll annealing, primary recrystallization annealing, final annealing, etc. are very tightly controlled. It is important to be.

The grain-oriented electrical steel sheet suppresses the growth of primary recrystallized grains, and exhibits excellent magnetic properties by the secondary recrystallized structure obtained by selectively growing grains of {110} <001> orientation among the grains in which growth is suppressed. Therefore, the growth inhibitory agent (hereinafter referred to as "inhibitor") of the primary recrystallized grain is very important. In addition, in the final annealing process, it is possible to stably produce grains having a collective structure of {110} <001> orientation among the grains suppressed in growth, hereinafter, referred to as "secondary recrystallization". It is the core of technology.

Specifically, as an inhibitor, fine precipitates or segregation elements formed artificially are used, and in order to suppress the growth of all primary recrystallized grains until the second recrystallization occurs in the final annealing process, these precipitates have a sufficient amount and an appropriate size. It should be uniformly distributed and thermally stable up to the high temperature just before secondary recrystallization occurs and should not be easily degraded. Secondary recrystallization starts in the final annealing process because these inhibitors grow or decompose as the temperature increases and they lose their ability to inhibit the growth of the primary recrystallized grains. .

MnS, AlN, MnSe, and the like, which are currently commercially widely used as the above-mentioned conditions are satisfied. Among them, a representative known technique for manufacturing an electrical steel sheet using only MnS as an inhibitor is presented in Japanese Patent Publication No. 30-3651. The manufacturing method is a stable secondary recrystallization structure by two cold rolling including intermediate annealing. To get. However, the method using only MnS as an inhibitor cannot obtain a high magnetic flux density, and there is a problem in that the manufacturing cost is increased by two cold rolling. High magnetic flux density is required in oriented electrical steel sheet because the use of a product with high magnetic flux density as an iron core enables the miniaturization of electric equipment, and for this reason, efforts are being made to increase the magnetic flux density. On the other hand, there is a method for producing a grain-oriented electrical steel sheet using both MnS and AlN as an inhibitor at the same time, a typical known technique is that disclosed in Japanese Patent Publication No. 40-15644. In this method, cold rolling is performed once at a high rolling rate of 80% or more to obtain a product having a high magnetic flux density. Specifically, this method consists of a series of processes of hot slab heating, hot rolling, hot rolled sheet annealing, cold rolling, decarbonization annealing, and final annealing. In this case, as mentioned above, the final annealing refers to a process of developing a collective structure of the {110} <001> orientation by causing secondary recrystallization in a coil wound state. In this final annealing process, no matter what inhibitor is used, an annealing separator composed mainly of MgO before annealing is applied to the surface of the steel sheet to prevent the steel sheets from sticking to each other, and the oxide layer formed on the surface of the steel sheet during the decarbonization annealing reacts with the annealing separator. In order to form a glassy film, insulation is provided to a steel plate. In this way, the final annealing is applied to the steel sheet having the aggregate structure of the {110} <001> orientation by the final annealing to make a final product. Another method is to prepare a grain-oriented electrical steel sheet using MnSe and Sb as inhibitors, and a representative known technique is described in Japanese Patent Publication No. 51-13469. The production method consists of hot slab heating, hot rolling, hot rolled sheet annealing, primary cold rolling, intermediate annealing, secondary cold rolling, decarbonization annealing, and final annealing. Although this method has the advantage of obtaining a high magnetic flux density, it is subjected to two cold rollings and uses expensive Sb or Se as an inhibitor, resulting in high manufacturing costs, and these elements are toxic and have poor workability. The methods also present a more fundamental problem than the above mentioned disadvantages. In other words, MnS or AlN contained in the slab of oriented electrical steel sheet should be reheated and employed for a long time at high temperature to make precipitates having appropriate size and distribution in the cooling process after hot rolling to be used as an inhibitor. Should be heated. Specifically, the method using MnS as an inhibitor is known to be able to obtain high magnetic flux density only by reheating the slab to 1300 ° C., using MnS + AlN as an inhibitor, 1350 ° C., and using MnSe + Sb as an inhibitor. have. In actual industrial production, considering the size of the slab, etc., in order to obtain a uniform temperature distribution to the inside, it is reheated to a temperature of almost 1400 ℃. As such, when the slab is heated at a high temperature for a long time, there is a problem in that a large amount of heat is used and a manufacturing cost is increased, and since the surface portion of the slab flows down to a molten state, the maintenance cost of the furnace is high and the life of the furnace is shortened. In particular, when the columnar structure of the slab grows coarsely by high temperature heating for a long time, there is a problem in that a crack is generated in the width direction of the plate in the subsequent hot rolling process, thereby significantly lowering the error rate.

Therefore, if the slab reheating temperature can be manufactured to produce oriented electrical steel sheet, it can bring many beneficial effects in terms of manufacturing cost and error rate. Therefore, new methods have been studied that do not use MnS with high employment temperature as an inhibitor. This has been made possible by techniques that form nitrides in the proper processes of the manufacturing process, in a manner known as nitriding, rather than depending solely on the inhibitors of the elements contained in the steel components. This method solves the above problems by lowering the reheating temperature of the slab, and the necessary inhibitor is made by nitriding at the final thickness of the steel sheet.

The nitriding treatment includes nitriding a steel sheet in a gas atmosphere having nitriding capability after decarburization, applying a nitriding compound to the steel sheet by applying an annealing separator, and applying a nitriding gas to the atmosphere during the elevated temperature of the high temperature annealing process. Various methods are known, such as including them in gas and putting them in the center of the steel sheet. Among these, nitriding steel sheets in a gas atmosphere having nitriding ability after decarburization is most commonly used. Currently, a method of supplying nitrogen to the inside of a steel sheet in a separate nitriding process including ammonia gas after decarburization using Al-based nitride is described in Japanese Patent Application Laid-Open No. Hei 1-230721 and Japanese Patent Laid-Open No. 1-283324. Presented. Meanwhile, a method of economically performing decarbonization and nitride annealing at the same time is presented in Korean Patent Application Publication No. 97-43184, and Korean Patent Application No. 97-28305 discloses a method of simultaneously performing decarburization and nitriding using a component system different from the previous patent. Is presented. As for the time point of nitriding treatment, Japanese Patent Laid-Open No. 3-2324 proposes a method of preferentially performing decarbonization annealing, growing the crystal grain to a certain extent or more, and nitriding with ammonia gas.

In all of the above-mentioned patents, slab heating is carried out at a temperature range in which AlN partially solvates, which acts as an inhibitor of secondary recrystallization. If the slab is heated only to a temperature that is partially solutioned, there is a large difference in the size distribution between the precipitated in the casting process and the re-precipitated during hot rolling. This difference eventually causes a difference in the grain size distribution of the primary recrystallization plate and is a factor that adversely affects the magnetization of the finished annealing product. In addition, even when AlN is used as a major inhibitor, it is important that MnS affects the size of primary recrystallized grains. In fact, Japanese Laid-Open Patent Publication No. 2003-201518 has a component system containing no inhibitor-forming element, and manufactures a grain-oriented electrical steel sheet having excellent magnetic properties by using only the difference in the grain boundary moving speed of primary grains without an inhibitor. It reminds me of the meaning of embodiment.

In Korean Patent Application No. 2001-0031104 and Japanese Patent Application Laid-Open No. 12-167963, the average particle diameter of primary recrystallized grains was subjected to nitriding treatment between slab reheating temperature of 1200 ° C or higher and decarburization annealing until the start of secondary recrystallization of finish annealing. 7 micrometers-18 micrometers are proposed the electronic steel plate manufacturing method as a claim. In this patent, when the reheating temperature is lower than 1200 ℃, it was reported that the second recrystallization does not occur in the complete solution conditions and the second recrystallization does not secure the magnetism. If the grain size is large, the distribution of grain size is also widened, which may cause non-uniform secondary recrystallization, which may have a weak effect on the magnetism. However, in the present invention, the secondary recrystallization is performed even at a large grain size because the crystal is uniform due to the simultaneous decarbonation process and the small amount of inhibitor. It can be easily produced to produce an excellent electrical steel sheet magnetic. Unlike in Korean Patent Application No. 2001-0031104 and Japanese Patent Application Laid-Open No. 12-167963, in the present invention, the slab reheating temperature is maintained at 1200 ° C. or lower, and the solution is completely dissolved. Simultaneous decarbonation treatment is performed and the average primary recrystallization is performed. It is characterized by having a grain size of 20-32 micrometers. In addition, Japanese Patent Publication No. Hei 2-294428 proposes a method of manufacturing a grain-oriented electrical steel sheet by heating the slab to a temperature below 1200 ° C, nitriding simultaneously with decarburization, and forming an inhibitor having (Al, Si) N as castability. have. However, this patent suggests that Al is incomplete solution at slab reheating temperature. This leaves the inhibitor containing Al which is incomplete solution by increasing the N content by setting the content of N to 0.0030 ~ 0.010%.

In the above method, nitriding with ammonia gas utilizes a property in which ammonia is decomposed into hydrogen and nitrogen at about 500 ° C. or higher to inject nitrogen generated by decomposition into the steel sheet. This is because the nitrogen that enters the steel sheet reacts with Al, Si, Mn, etc. already present in the steel to form nitride, and uses it as an inhibitor. At this time, among the nitrides formed as the inhibitor are Al-based nitrides of AlN and (Al, Si, Mn) N. All of the above methods provide a method of manufacturing a grain-oriented electrical steel sheet by heating the slab to a low temperature and nitriding the material with a nitriding material or 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 nitriding it after decarbonization is completed are as follows. Nitriding by decomposition of ammonia gas can be carried out if it is 500 degreeC or more which is the decomposition temperature of ammonia gas. However, at temperatures around 500 ℃, the diffusion rate of nitrogen in the steel sheet is very slow, so that nitriding time is required for a long time, and if it is above 800 ℃, nitriding is easy, but primary recrystallized grains are easy to grow, and the grain distribution in the steel sheet Inhomogeneous, the development of secondary recrystallization becomes unstable. Therefore, the proper nitriding temperature range can be seen as 500 ~ 800 ℃. However, if the nitriding temperature is low and the nitriding treatment time is too long, there is a problem in productivity, and the actual nitriding temperature is performed in the range of 700 to 800 ° C. Nitriding method based on this idea is described in Korean Patent Publication No. 95-4710. In such a temperature range, the decomposition reaction of ammonia and the diffusion of nitrogen are active, so very precise control of the nitriding conditions is necessary to put the amount of nitrogen in the river as desired. 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 the combination of these conditions. In consideration of productivity, since nitriding should be performed in a short time, the concentration of ammonia and nitriding temperature should be high. In this case, nitriding is performed in a short time, and the nitrogen concentration at the surface portion of the steel sheet is mainly increased. Therefore, the deviation of each part of the steel sheet becomes very large. Almost no nitriding occurs at the center of the steel sheet, and unevenness is severely observed at each surface portion. In addition, the amount of nitride is greatly affected by the state of the steel sheet. Typical examples include surface roughness, grain size, and chemical composition. If the surface roughness is large, the contact area with the atmospheric gas is widened, which causes a variation in the amount of nitride. If the grain size is small, the grain boundary per unit area increases, and the diffusion of nitrogen through the grain boundary occurs faster than the diffusion in the grain, causing variation in the amount of nitride. In chemical composition, the amount of nitride can be varied depending on the relative amount of the element in the steel sheet to facilitate the nitride. This variation in the amount of nitride ultimately causes film defects, which can be solved by a combination of the atmosphere and heat treatment temperature of the final annealing, as shown in Korean Patent Application No. 97-65356.

The final annealing process, as mentioned above, is a very important process to obtain the secondary recrystallization structure with the {110} <001> orientation. In particular, according to the method disclosed in Korean Patent Publication No. 95-4710 for nitriding after decarburization, the method includes transforming the precipitate produced after nitriding annealing in the final annealing process. Specifically, precipitates formed after nitriding are Si ₃ N ₄ or (Si, Mn) N precipitates, which are thermally unstable and easily decomposed. Therefore, these precipitates cannot be used because they do not meet the conditions mentioned above. Therefore, it is necessary to replace them with thermally stable precipitates such as AlN and (Al, Si, Mn) N to function as inhibitors. When nitride is formed by denitrification after nitriding, at least 4 hours must be maintained at a temperature of 700-800 ° C. in the subsequent annealing process to transform into a precipitate that can be used as an inhibitor. This means that the final annealing process is long and must be very tightly controlled, which is also very disadvantageous in terms of manufacturing cost. In order to solve this problem, a method of simultaneously performing decarburization and nitriding is described in Korean Patent Application No. 98-58313. However, in this method, decarburization and nitriding are performed simultaneously. There is a problem that the grain size of is small. Therefore, since the temperature at which secondary recrystallization is started during the final annealing is lowered, grains having orientations other than {110} <001> also increase the probability that secondary recrystallization occurs, and after the final annealing is completed, the { 110} <001> has a problem that the degree of integration deteriorates, the magnetic properties can be degraded.

Accordingly, the present invention is to solve the above-mentioned problems of the prior art, in the manufacture of a low-temperature heating oriented electrical steel sheet using ammonia gas, even if AlN acting as an inhibitor completely melted during slab heating primary recrystallized plate In order to increase the grain size, the low content of nitrogen is controlled very low, and the role of inhibitor in the second recrystallization is small, but MnS, which affects the size of the primary recrystallization, is also completely dissolved so that the size of the primary recrystallized grain is reduced. High-strength grain-oriented electrical steel sheet that enables the manufacture of oriented electrical steel sheets with excellent magnetic properties by simultaneously controlling decarburization and nitriding by adding Sb to the steel components while controlling the sulfur content in the steel components very low so that they can be made uniform and large in size. It aims to provide a manufacturing method.

 In the present invention, by managing the amount of steel N less than 0.0030% by fully solidifying the precipitate containing Al and Mn that is incompletely dissolved during slab reheating can improve the magnetization by grain uniformity and grain size increase as described above. In the present invention, it is possible to further improve the magnetism by adding Sb while maintaining a uniform crystal size by managing the N, S content extremely low. Sb is a grain boundary segregation element, and it is an alloying element that hinders the growth of grain boundaries by interfering with the movement of grain boundaries. Therefore, Sb effectively prevents the growth of grains without being present in the form of precipitates such as (Al, Si, Mn) N. It helps to recrystallize. In addition, Sb is known to promote the growth of goth grains, thereby helping to improve the magnetic flux density and iron loss by participating more secondary goth grains.

Method for producing a grain-oriented electrical steel sheet having the above-described characteristics and excellent magnetic properties of the present invention for achieving the object of the present invention, Si: 2.0 ~ 7.0%, acid soluble Al: 0.015 ~ 0.035%, Mn: 0.20% or less , Sb: 0.01% ~ 0.10% of the slab of the grain-oriented electrical steel sheet containing the remaining Fe and other unavoidable impurities, the content of N and S contained in the other unavoidable impurities is completely used AlN and MnS produced in the slab reheating step After reheating to adjust to a very small amount that can be embodied, hot rolling, omit or conduct the hot rolled sheet annealing, cold rolling, followed by annealing to simultaneously carry out decarburization and sedimentation, and then perform secondary recrystallization annealing. It is characterized by consisting of.

In addition, the simultaneous decarbonation annealing is characterized in that a mixed gas atmosphere of ammonia, hydrogen and nitrogen is formed at a temperature of 800 to 950 ° C.

In addition, the slab reheating temperature is characterized in that 1100 ~ 1200 ℃.

In addition, N and S contained in the slab is characterized in that each 30ppm or less.

The mole fraction of the amount of precipitates including N in the coil after the hot rolling is 0.015% or less, and the mole fraction of the amount of precipitates including S is 0.007% or less.

In addition, the start temperature of the secondary recrystallization annealing is characterized in that it is determined by controlling the simultaneous decarbonation annealing temperature to adjust the primary recrystallized grain size.

In addition, the primary recrystallized grain size is controlled in the range of 20 ~ 32㎛, the secondary recrystallization start temperature is characterized in that carried out at 1030 ~ 1150 ℃.

In addition, the primary recrystallized plate is characterized in that the standard deviation of the average grain size / grain size is 1.2 or more.

Hereinafter, the operation of the present invention will be described in detail.

Nitriding is carried out simultaneously with a separate nitriding process or decarburization after decarburization, and nitrogen generated by decomposition of ammonia gas enters the inside of the steel sheet to form nitride. The method of nitriding after decarburization is carried out in an ammonia + hydrogen + nitrogen atmosphere at 700 to 800 占 폚 and the method of simultaneously performing decarburization and nitriding at 800 to 950 占 폚. However, these two methods are based on metallurgical different ideologies beyond just nitriding or annealing temperatures.

After the decarburization, a method of forming a precipitate through a separate nitriding process is performed at an annealing temperature of 800 ° C. or lower, and nitrides such as Si ₃ N ₄ and (Si, Mn) N are formed on the surface. Such precipitates are easily formed at low temperatures but are very unstable thermally. Therefore, these precipitates are easily decomposed at high temperature and cannot be used as inhibitors of the grain-oriented electrical steel sheet. In addition, since the annealing temperature is low because the diffusion of nitrogen is not very active, nitride is concentrated in the surface portion of the steel sheet. Therefore, in the subsequent annealing process, they must be decomposed again to combine with other elements existing in the steel sheet to be reprecipitated. At this time, the produced precipitate is a stable nitride such as AlN or (Al, Si) N can be used as an inhibitor of the grain-oriented electrical steel sheet.

The method of forming a precipitate through simultaneous decarburization and nitriding requires an annealing temperature of 800 ° C. or higher. In view of the decarburizing property, the annealing time is too long at temperatures below 800 ° C., so there is no industrial value, and the temperature is set in consideration of the diffusion of nitrogen. In this temperature region, unstable precipitates such as Si ₃ N ₄ and (Si, Mn) N are not formed, and thermally very stable precipitates such as AlN and (Al, Si, Mn) N are formed. Therefore, it can be used as an inhibitor without the need for reprecipitation in subsequent final annealing process.

However, in the case of simultaneously performing decarburization and nitriding, the growth of primary recrystallized grains is fundamentally hampered by the invasive elements carbon and nitrogen. This reduction in primary recrystallized grain size will affect the secondary recrystallization start temperature in the subsequent final annealing process. In other words, if the size of the primary recrystallized grain is small, the secondary recrystallization start temperature is lowered, and not only the grains having the {110} <001> orientation are secondary recrystallized, but also the grains having different orientations are secondary recrystallized and thus the magnetic properties of the final plate are reduced. This is deteriorated. Therefore, it is important to strictly control the secondary recrystallization in order to manufacture a grain-oriented electrical steel sheet having excellent magnetic properties. This secondary recrystallization behavior is the easiest way to control the size of the primary recrystallization grains, at the temperature just below the temperature range where the precipitates of the inhibitors AlN, (Al, Si, Mn) N begin to become unstable rapidly. To complete the second recrystallization. Therefore, in the simultaneous decarburization and nitriding, the primary recrystallized grains are grown more and the method for increasing the repressive force required for secondary recrystallization has been mainly used. Although the addition of elements such as B and Cu has been considered to increase the inhibitory force required for secondary recrystallization, the addition of B tends to form very coarse B and C complex compounds, making it difficult to obtain uniform and stable inhibitory forces. On the other hand, the addition of Cu, although forming a Cu emulsion, precipitates unevenly, thereby increasing the variation of iron loss and magnetic flux density, which causes a problem of degrading product quality.

The inventors have found that the method of controlling the low calcined nitrogen and sulfur is very effective as a method for preventing the reduction of the primary recrystallized grain size in the process of simultaneously performing decarburization and nitriding. The size of the primary recrystallized grain is mainly determined by the AlN and MnS precipitates which are present after hot rolling, and the amount of precipitates can be reduced by controlling the N content and the S content that form the precipitates very low.

In the case of containing Sb with low control of N and S, Sb is a grain boundary segregation element and it is an alloying element that hinders the growth of grains by hindering the movement of grain boundaries and does not exist in the form of precipitates such as (Al, Si, Mn) N. Effectively inhibits grain growth, helping Goss grains to recrystallize second. Sb is also known to promote the growth of goth grains, thereby helping to improve magnetic flux density and iron loss by allowing more Goss grains to participate in secondary recrystallization.

At this time, the primary recrystallized grain size is controlled within the range of 20 ~ 32㎛. Sb is a grain boundary segregation element that inhibits the movement of grain boundaries, thereby inhibiting the crystal growth of primary recrystallized grains, thereby suppressing excessive growth of grains and forming a more suitable primary recrystallized grain size. If the size of the primary recrystallized grain is 20 µm or less, the grain growth driving force is increased, and thus the secondary recrystallization start temperature is lowered, and the grain growth of the orientation is not detrimental to the orientation of the grain. . In addition, when the size of the primary recrystallized grain is 32 µm or more, the grain growth driving force is lowered, so that the secondary recrystallization does not occur, and thus the magnetic properties are deteriorated.

On the other hand, when heating at the partial solution temperature during slab heating, there is a big difference in the distribution of AlN precipitates, which causes a large deviation in the size distribution of the primary recrystallized grains, which is a factor that causes the magnetism to become unstable. However, even when the N content and the S content are very low, even when the slab is heated to the complete solution temperature, the amount of precipitates generated is very small, thus making it possible to obtain uniform and large primary recrystallized grains. In addition, when the N content and the S content are low, the initial grain size before cold rolling is coarsened, so the number of grains having the {110} <001> orientation in the primary recrystallization plate increases, thereby reducing the size of the secondary recrystallized grain. To improve the magnetism of the final product. At this time, in the primary recrystallized sheet, when the standard deviation value of the average grain size / crystal grain size is 1.2 or less, the grains other than the Goss orientation are coarsened to deteriorate the magnetic properties, so that the average grain size is prevented to deteriorate the magnetic properties. The standard deviation of the size / grain size should not be less than 1.2.

Hereinafter, the reason for component limitation of the present invention will be described in more detail.

Si is the basic composition of electrical steel sheet to increase the specific resistance of the material serves to lower the core loss (core loss). If the Si content is less than 2.0%, the resistivity decreases and the iron loss characteristics deteriorate. If the content is over 4.0%, the brittleness of the steel increases, making the cold rolling extremely difficult and unstable secondary recrystallization. Therefore, Si is set at 2.0 to 4.0%.

Al is finally made of AlN, (Al, Si, Mn) N type nitride and acts as an inhibitor. If the content is 0.015% or less, sufficient effect as an inhibitor cannot be expected. The temperature required for the sieving becomes high, which adversely affects hot rolling workability. Therefore, the Al content is set at 0.015 to 0.035%.

Mn also has the effect of reducing the iron loss by increasing the specific resistance similar to Si, and the growth of the primary recrystallized grains by forming a precipitate of (Al, Si, Mn) N by reacting with nitrogen introduced by nitriding treatment with Si It is an important element for suppressing and causing secondary recrystallization. However, when 0.20% or more is added, the austenite phase transformation is promoted during hot rolling, so the size of the primary recrystallized grains is reduced to make the secondary recrystallization unstable. Therefore, Mn is made into 0.20% or less.

When N is contained at 0.003% or more, the slab is heated to a temperature that completely solidifies, and thus, the size of the primary recrystallized grains decreases, thereby lowering the temperature of the secondary recrystallized grains. It causes deterioration of magnetism. On the other hand, if the N content is lower than 0.003%, even though the slab is heated to the temperature where it is completely dissolved, the amount of precipitates generated is very small. Therefore, it is possible to obtain a uniform and large primary recrystallized product, which has excellent magnetic properties. You can get it. In addition, when the steel content N is lower than 0.003%, the initial grain size before cold rolling is coarsened, so the number of grains having the {110} <001> orientation in the primary recrystallization plate increases, thereby reducing the size of the secondary recrystallized grains. Reduce the magnetic properties of the final product. Therefore, N is set to 0.003% or less.

When C is added more than 0.04%, it promotes the austenite transformation of the steel to refine the hot rolled structure during hot rolling to help form a uniform microstructure. However, if the content is too high, coarse carbides precipitate and carbon removal becomes difficult during decarburization. Therefore, C is set at 0.04 to 0.07%.

When the S is heated to a temperature that completely melts when it contains more than 0.003%, the size of the primary recrystallized grains decreases, thereby lowering the temperature of the secondary recrystallization grains. It causes deterioration of magnetism. On the other hand, if the S content is lower than 0.0030%, even though the slab is heated to the temperature where it is completely dissolved, the amount of precipitates generated is very small. Therefore, it is possible to obtain a uniform and large primary recrystallized product, which has excellent magnetic properties. You can get it. In addition, when the S content is less than 0.003%, the initial grain size before cold rolling is coarsened, so the number of grains having the {110} <001> orientation in the primary recrystallization plate increases, thereby reducing the size of the secondary recrystallized grain. Reduce the magnetic properties of the final product. Therefore, S is set to 0.003% or less.

Sb is not normally contained in the low-temperature heating oriented electrical steel sheet.

In the case of containing Sb with low control of N and S, Sb is a grain boundary segregation element and it is an alloying element that hinders the growth of grains by hindering the movement of grain boundaries and does not exist in the form of precipitates such as (Al, Si, Mn) N. Effectively inhibits grain growth, helping Goss grains to recrystallize second. Sb is also known to promote the growth of goth grains, thereby helping to improve magnetic flux density and iron loss by allowing more Goss grains to participate in secondary recrystallization.

Sb is a grain boundary segregation element that inhibits the movement of grain boundaries, thereby inhibiting the crystal growth of primary recrystallized grains, thereby suppressing excessive growth of grains and forming a more suitable primary recrystallized grain size. If excessively contained Sb, the primary recrystallization size is too small, the density of Goss orientation in the secondary recrystallization is lowered, and the magnetism is worsened. Therefore, Sb is set at 0.01% to 0.10% or less.

The following process conditions are demonstrated.

The slab heating temperature before hot rolling is defined as the temperature at which the precipitates used as inhibitors are completely dissolved. When the heating temperature is partially solutionized, a large difference occurs in the size of precipitates produced during casting and precipitates re-used during heating, resulting in uneven grain size of the primary recrystallized sheet. Because of this, there is a possibility of magnetic nonuniformity, so the slab heating temperature is a temperature range in which the precipitates are completely dissolved.

The heated steel sheet slabs are hot rolled in a conventional manner. In the current commonly used method, the final thickness of the hot rolled sheet is usually 2.0 ~ 3.5mm. Hot rolled plate is hot rolled and then cold rolled to make final thickness 0.23 ~ 0.35mm. Hot-rolled sheet annealing can be done in various ways, but it is heated to 1000 ~ 1200 ℃, cracked at 800 ~ 950 ℃, and cooled.

The cold rolled plate simultaneously performs decarburization and annealing 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 to maximize the decarburization capacity. Moreover, it is preferable to perform annealing temperature of simultaneous decarburization and annealing at 800-950 degreeC. If the annealing temperature is lower than 800 ° C., decarburization takes a long time, and the size of the primary recrystallized grain is also small, so that stable secondary recrystallization cannot be expected during final annealing. If the annealing temperature is higher than 950 ° C, it is difficult to control the rate of the nitriding reaction, and the primary recrystallized grains grow excessively or unevenly, making it difficult to develop a stable secondary recrystallized tissue during final annealing. The annealing time of simultaneous decarburization and nitriding is determined by the annealing temperature and the concentration of the injected ammonia gas, and the annealing time usually requires 30 seconds or more.

In general, during the production of grain-oriented electrical steel sheet, the annealing separator based on MgO is applied to the steel sheet, followed by final annealing for a long time to cause secondary recrystallization, so that the {110} plane of the steel sheet is parallel to the rolled surface, and the <001> direction is {110} <001> texture is formed parallel to the rolling direction to produce a grain-oriented electrical steel sheet having excellent magnetic properties. The purpose of the final annealing is largely to form the {110} <001> texture by secondary recrystallization, and to remove the impurities imparting insulation and damaging the magnetic properties by forming a glassy film formed by the reaction of the oxide layer formed with decarburization with MgO. In the final annealing method, in the temperature rise section before the secondary recrystallization occurs, the secondary recrystallization can be developed well by protecting the nitride, which is a particle growth inhibitor, by maintaining the mixture gas of nitrogen and hydrogen, and after the secondary recrystallization is completed. It is kept in 100% hydrogen atmosphere for a long time to remove impurities. In the method of nitriding after decarburization, the transformation of precipitates occurs in the final annealing process. In this method, the annealing temperature is 700 to 800 ° C. After nitriding, Si ₃ N ₄ and (Si, Mn) N are formed in the surface layer of the steel sheet, and they are thermally stable AlN or (Al It must be reprecipitated with a nitride such as Si) N to be used as an inhibitor of oriented electrical steel sheet. On the other hand, nitrides produced during simultaneous decarburization and nitride annealing are AlN, (Al, Si, Mn) N and do not require transformation of precipitates during final annealing and are used as direct inhibitors. The different kinds of nitrides produced by different nitriding methods are due to differences in annealing temperatures. In other words, Si ₃ N ₄ or (Si, Mn) N can not be stably present at a temperature higher than 800 ℃, nitrogen diffusion also occurs very quickly.

The present invention will be described in more detail with reference to the following Examples.

Example 1

Si: 3.25%, C: 0.056%, Mn: 0.062%, S: 0.0028%, N: 0.0020%, Sol. AlN in slabs of oriented electrical steel sheet containing Al: 0.026% and containing Sb 0.000%, 0.006%, 0.017%, 0.025%, 0.050%, 0.092%, 0.12% and the balance of Fe and other inevitable The complete solution temperature is 1164 ° C and the complete solution temperature of MnS is 1075 ° C. Both AlN and MnS were heated for 210 minutes at 1170 ° C., which was the partial solution temperature, and hot rolled to prepare 2.3 mm thick hot rolled plates. The hot rolled sheet was heated to a temperature of 1100 ° C. or higher, held at 900 ° C. for 90 seconds, quenched with water, pickled, and cold rolled to a thickness of 0.30 mm.

(A) The cold rolled plate was kept at 875 ° C for 180 seconds by adding 75% of hydrogen and 25% of nitrogen with a dew point temperature and 1% of dry ammonia gas at the same time. And nitriding.

(B) The cold rolled plate was decarbonized for 150 seconds in a mixed atmosphere of 75% hydrogen and 25% nitrogen with a dew point temperature of 65 ° C in a furnace maintained at 845 ° C for 30 seconds in a furnace maintained at 770 ° C. Nitrided by adding a dry ammonia gas for a while.

Nitrogen content of the steel plate nitrided by each method (A) and (B) was the same in the range between 190-210 ppm.

MgO, an annealing separator, was applied to the steel sheet and finally annealed into a coil. The final annealing was performed at a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, the annealing was maintained at 100% hydrogen atmosphere for at least 10 hours. Magnetic properties measured for each condition are shown in Table 1.

As shown in Table 1, in the case of the simultaneous method of decarburization and sedimentation, the inventors of the present invention containing 0.01 to 0.10% of P in the range of the present invention had higher magnetic flux density and lower iron loss than the comparative materials. have. On the other hand, when the same P is contained, the A method subjected to simultaneous decarburization and sedimentation treatment has superior magnetic properties as compared to the B method subjected to decarburization and sedimentation treatment.

Example 2

Si: 3.27%, C: 0.045%, Mn: 0.074%, N: 0.0015% by weight, Sol. Al: 0.024%, S 0.0020% and Sb are changed as shown in Table 2, and the balance of Fe and other unavoidable oriented electrical steel slabs, AlN is above the complete solution temperature (1132 ℃) and MnS is also the complete solution ( 1064 ° C.) was heated at 1150 ° C. for 210 minutes, followed by hot rolling to prepare a hot rolled plate having a thickness of 2.3 mm. The hot rolled sheet was heated to 1100 ° C., held at 900 ° C. for 90 seconds, quenched with water, pickled, and cold rolled to a thickness of 0.23 mm and 0.27 mm. The cold rolled plate is treated with simultaneous decarburization and nitriding for 180 seconds by adding 75% hydrogen and 25% nitrogen and 1% dry ammonia gas at a dew point temperature of 875 ° C. It was.

MgO, an annealing separator, was applied to the steel sheet and finally annealed into a coil. The final annealing was performed at a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, the annealing was maintained at 100% hydrogen atmosphere for at least 10 hours. The results of measuring the magnetic properties for each condition are shown in Table 2.

As shown in Table 2, regardless of the thickness of the product, it can be seen that the inventive materials 5 and 6 belonging to the scope of the present invention have better magnetic properties than the comparative materials 4 and 5.

Example 3

Si: 3.17%, C: 0.056%, Mn: 0.055%, S: 0.006% by weight, Sol. Al: 0.024% N0.0022%, Sb: 0.033% and the temperature at which complete balance of Fe and other inevitably slabs of oriented electrical steel sheets (complete solution temperature of MnS: 1125 ℃, AlN solution temperature: 1165 It was heated for 210 minutes at 1170 ℃ or more and hot rolled to prepare a hot rolled plate of 2.3mm thickness. The hot rolled sheet was heated to 1100 ° C., held at 900 ° C. for 90 seconds, quenched with water, pickled, and cold rolled to a thickness of 0.30 mm. Cold rolled plate is kept at a constant temperature by adding 75% hydrogen and 25% nitrogen mixed atmosphere and 1% dry ammonia gas at a dew point temperature of 65 ℃ to maintain definite period of time. The treatment gave a final nitrogen amount of 200 to 230 ppm. At this time, the simultaneous decarburization and nitriding temperature were changed to 740, 770, 795, 810, 865, 940, 975 ° C, and the time was changed to 120 to 240 seconds to control the nitriding amount.

MgO, an annealing separator, was applied to the steel sheet and finally annealed into a coil. The final annealing was performed at a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, the annealing was maintained at 100% hydrogen atmosphere for at least 10 hours. The magnetic properties measured for each condition are shown in Table 3.

As shown in Table 3, even when the annealing conditions during simultaneous decarburization and nitride annealing were adjusted to an appropriate amount of nitride, comparative materials having an annealing temperature of 800 ° C. or lower or 950 ° C. or higher did not obtain excellent magnetic properties.

Example 4

Si: 3.18%, C: 0.056%, Mn: 0.062%, S: 0.0061%, N: 0.0020%, Sol. In slabs of oriented electrical steel sheets containing Al: 0.026% and remaining Fe and other inevitably, AlN complete solution temperature is 1164 ° C and MnS complete solution temperature is 1136 ° C. Both AlN and MnS are partially solutionized at 1130 ° C and MnS are fully dissolved, AlN is partially dissolved at 1150 ° C and both AlN and MnS are at 1175 ° C and 1190 ° C, which are above the complete solution (1164 ° C). After hot rolling, a hot rolled plate having a thickness of 2.3 mm was manufactured. The hot rolled sheet was heated to a temperature of 1100 ° C. or higher, held at 900 ° C. for 90 seconds, quenched with water, pickled, and cold rolled to a thickness of 0.30 mm.

The cold rolled plate is treated with simultaneous decarburization and nitriding for 180 seconds by simultaneously adding 75% hydrogen and 25% nitrogen and 1% dry ammonia gas to the furnace at 875 ° C. It was. At this time, the nitrogen content of the nitrided steel sheet was managed in the range of 170 ~ 200 ppm.

MgO, an annealing separator, was applied to the steel sheet and finally annealed into a coil. The final annealing was performed at a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, the annealing was maintained at 100% hydrogen atmosphere for at least 10 hours. Magnetic properties measured for each condition are shown in Table 4.

As shown in Table 4, it can be seen that the magnetic flux density is high and the iron loss is low in the inventive material having a slab heating temperature higher than the complete solution temperature compared to the comparative material in which both AlN and MnS or only AlN are partial solution temperature ranges.

Example 5

Si: 3.27%, C: 0.045%, Mn: 0.074% by weight, Sol. Al: 0.024% and N, S are changed as shown in Table 5, and the slab heating of the oriented electrical steel sheet containing Fe and other unavoidable constituents is heated for 210 minutes at 1180 ° C., followed by hot rolling to prepare a hot rolled sheet having a thickness of 2.3 mm. It was. The hot rolled sheet was heated to a temperature of 1100 ° C. or higher, held at 900 ° C. for 90 seconds, quenched with water, pickled, and cold rolled to a thickness of 0.30 mm. The cold rolled plate is treated with simultaneous decarburization and nitriding for 180 seconds by simultaneously adding 75% hydrogen and 25% nitrogen and 1% dry ammonia gas to the furnace at 875 ° C. It was.

MgO, an annealing separator, was applied to the steel sheet and finally annealed into a coil. The final annealing was performed at a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, the annealing was carried out in a 100% hydrogen atmosphere for at least 10 hours and then annealed. An extraction test was performed under these heat treatment conditions to investigate the secondary recrystallization start temperature. The result of measuring the secondary recrystallization start temperature for each condition is shown in Table 5.

As shown in Table 5, when the precipitates were heated to a temperature range in which the precipitates were completely dissolved, the grain size increased to 28.44 µm, but the magnetic properties showed that the inventive material had higher magnetic flux density and lower iron loss than the comparative material. The secondary recrystallization temperature is much higher than that of Comparative Material 3, which increases the degree of integration of GOSS azimuth and thus improves the magnetism.

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 containing Fe and other unavoidable constituents was heated for 210 minutes at 1180 ° C., followed by hot rolling to prepare a hot rolled sheet having a thickness of 2.3 mm. It was. The hot rolled sheet was heated to a temperature of 1100 ° C. or higher, held at 900 ° C. for 90 seconds, quenched with water, pickled, and cold rolled to a thickness of 0.30 mm. The cold rolled plate is maintained at 830 ~ 880 ℃ for 180 seconds by simultaneously adding 75% hydrogen and 25% nitrogen and 1% dry ammonia gas with dew point temperature of 65 ℃. Nitriding.

MgO, an annealing separator, was applied to the steel sheet and finally annealed into a coil. The final annealing was performed at a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, the final annealing was performed at 100% hydrogen atmosphere for 10 hours or more, followed by quenching. An extraction test was performed under these heat treatment conditions to investigate the secondary recrystallization start temperature. Table 6 shows the results of measuring the average size of the primary recrystallized grains and the standard deviation of the size distribution for each condition.

The standard deviation of grain size distribution is shown to show the uniformity of grain size. Lower standard deviations indicate a uniform size. As shown in Table 6, in the standard deviation of the average size and distribution of grains according to the process conditions, the invention material has a larger grain size and a smaller standard deviation than the comparative material. According to Comparative Materials 4-9, when the average grain size was controlled only by the decarbonization temperature under similar composition conditions, as the average grain size increased, the standard deviation also increased in proportion to increase the nonuniformity. As described above, when the grain size is large, it shows a favorable effect on the magnetism, but when the grain size is too large, it can be seen that non-uniformity of grain size appears, which adversely affects the grain size. However, if the grain size is increased by decreasing the N and S content, the increase of the standard deviation is not large. Using the "standard deviation of average grain size / grain size" as a parameter to express this relationship, this value is convenient because it is large when the grain size is large and the standard deviation is small. In Table 6, when the grain size is 20 µm or more and the average grain size / standard deviation of grain size is 1.2 or more, the magnetic properties are excellent.

As described above, the method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to the present invention is controlled by adding a Sb content while controlling the N and S content very low, and heating the slab above the complete solution temperature to uniform recrystallized grains. In addition, when the N, S content is low, the initial grain size before cold rolling is coarsened, so the number of grains having the {110} <001> orientation in the primary recrystallization plate increases, resulting in secondary recrystallization. It reduces the size of the grains, and because Sb is an alloy element that prevents grain growth by interfering with the movement of grain boundaries as a grain boundary segregation element, grain growth without being present in the form of precipitates such as (Al, Si, Mn) N Effectively prevents Goss grains from secondary recrystallization, while Sb promotes the growth of Goth grains, resulting in more Goss grains. Participating in the secondary recrystallization provides an effect of producing a grain-oriented electrical steel sheet having low iron loss and high magnetic flux density.

Claims (8)

The slab of a grain-oriented electrical steel sheet containing 2.0% by weight of Si: 2.0% to 7.0%, acid solubility Al: 0.015% to 0.035%, Mn: 0.20% or less, Sb: 0.01% to 0.10%, and the balance of Fe and other unavoidable impurities After reheating to adjust the content of N and S contained in the other unavoidable impurities so that the AlN and MnS produced in the slab reheating step can be completely solvated, and after hot rolling, the hot rolled sheet annealing may be omitted or performed, followed by cold rolling. And then performing annealing to simultaneously perform decarburization and immersion, followed by secondary recrystallization annealing. The method of manufacturing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein the simultaneous decarbonation annealing is performed at a temperature of 800 to 950 ° C by forming a mixed gas atmosphere of ammonia, hydrogen, and nitrogen. The method of claim 1, wherein the slab reheating temperature is 1100 to 1200 ° C. 6. The method of manufacturing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein N and S contained in the slab are each 30 ppm or less. The magnetic composition as set forth in claim 1, wherein a mole fraction of the amount of precipitates including N in the coil after the hot rolling is 0.015% or less, and a mole fraction of the amount of precipitates including S is 0.007% or less. Method for producing this excellent grain-oriented electrical steel sheet. The method of claim 1, wherein the starting temperature of the secondary recrystallization annealing is determined by controlling the simultaneous decarburization annealing temperature to adjust the size of the primary recrystallization grain. The method of claim 1, wherein the primary recrystallized grain size is controlled within a range of 20 to 32 μm, and the secondary recrystallization start temperature is performed at 1030 to 1150 ° C. 3. The method of claim 1, wherein the primary recrystallized sheet has a standard deviation of an average grain size / crystal grain size of 1.2 or more.