KR20020044243A - A method for manufacturing grain oriented electrical steel sheet with superior magnetic property - Google Patents

Abstract

PURPOSE: A method for manufacturing grain oriented electrical steel sheet with superior magnetic property is provided, in which with the addition of REM, slab reheating temperature is lowered, and moreover nitriding treatment in sequent processes can be omitted. CONSTITUTION: The method includes the steps of reheating a steel slab comprising C 0.02-0.1 wt.%, Si 1.0-4.8 wt.%, Mn 0.2 wt.% or less, S 0.035 wt.% or less, Al 0.005-0.02 wt.%, N 0.005 wt.% or less, Cu 0.1-0.25 wt.%, 0.04 wt.%<=REM<=0.13 wt.%, a balance of Fe and other inevitable impurities in the temperature range of 1200 to 130 0°C followed by hot rolling; annealing the hot rolled steel sheet in the temperature range of 900 to 1150°C; and then cold rolling, decarburizing annealing, and hot annealing.

Description

A method for manufacturing oriented electrical steel sheets with excellent magnetic properties {A METHOD FOR MANUFACTURING GRAIN ORIENTED ELECTRICAL STEEL SHEET WITH SUPERIOR MAGNETIC PROPERTY}

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used as an iron core material of an electric device such as a transformer, and more particularly, by adding REM (rare earth element) in a small steel component to easily form an inhibitor, thereby providing excellent magnetic properties. It relates to a method for producing a grain-oriented electrical steel sheet.

A grain-oriented electrical steel sheet has developed a {110} <001> agglomerate structure in the rolling direction. Since the manufacturing method was first presented in US Patent No. 1,965,559, a new manufacturing method has been proposed with many improvements. Common in the production of such grain-oriented electrical steel sheet is the use of precipitates and grain boundary segregation elements that inhibit the growth of primary recrystallized crystal grains called inhibitors. In other words, such inhibitors inhibit the growth of primary recrystallized grains, and play a role of preferentially growing grains of the {110} <001> orientation among the grains whose growth is suppressed. This is called secondary recrystallization, and the development of secondary recrystallized grains in the {110} <001> orientation in the rolling direction using an appropriate inhibitor is the core of the oriented electrical steel sheet manufacturing technology.

The conditions for the precipitates to function as inhibitors are as follows. That is, the precipitates should be evenly distributed in sufficient quantity and in an appropriate size so that the growth of the primary recrystallization is prevented until just before the secondary recrystallization occurs, and it is thermally stable to the high temperature just before the secondary recrystallization occurs and is not easily decomposed. do. Such conditions include MnS, AlN, MnSe, and the like.

In the production of the grain-oriented electrical steel sheet currently produced industrially, precipitates such as MnS, AlN, and MnSe are used alone or in combination as inhibitors. Representatively, MnS + AlN is a method of using only MnS as an inhibitor. And MnS (Se) + Sb as an inhibitor. These methods include one rolling-1 annealing and two rolling-2 annealing before annealing (called secondary recrystallization annealing or high temperature annealing) to obtain a final secondary recrystallized structure, depending on the type of inhibitor used. . This is to properly configure the manufacturing process in order to maximize the role of the inhibitor described above.

As an example of the method of using the MnS as an inhibitor, Japanese Patent Application No. 30-3651 by MF Littmann discloses a technique for obtaining a stable secondary recrystallized structure through two cold rolling including intermediate annealing. There is a problem that a high magnetic flux density cannot be obtained by the method, and the manufacturing cost is high due to two cold rolling.

As an example of the method using MnS + AlN, there is a technique disclosed in Japanese Unexamined Patent Application Publication No. 40-15644. In this method, cold rolling is performed once at a high reduction ratio of 80% or more to produce a grain-oriented electrical steel sheet, and a product having high magnetic flux density. There is an advantage to get it. However, in industrial production, it is difficult to strictly control each process condition.

As a technique for producing a grain-oriented electrical steel sheet using the MnS (or MnSe) + Sb, there is a technique of Japanese Patent Application No. 51-13469. This method has a high magnetic flux density but has to be cold rolled twice and toxic and has the disadvantage of using expensive elements such as Sb and Se.

However, these techniques have more fundamental problems than those mentioned above. That is, in each method, in order to obtain a precipitate having a desired size and distribution and use it as an inhibitor, the slab must be reheated to a high temperature before hot rolling. This is necessary to control the size and distribution of the precipitates as desired in the hot rolling process, and is based on the technical idea that MnS or AlN should be heated to a sufficiently high temperature. That is, MnS, AlN, etc. contained in the cast steel component must be completely dissolved (highly referred to as 'complete incorporation') by heating for a long time at high temperature, and then made into a precipitate having an appropriate size and distribution during hot rolling and cooling. In theory, 1,300 ° C in the method using MnS, 1,350 ° C in the method using MnS + AlN, and 1,320 ° C or higher in the method using MnS (or MnSe) + Sb to be completely employed. In actual industrial production, however, it is necessary to obtain a uniform temperature distribution to the inside in consideration of the size of the slab, etc., so that the surface portion of the slab is reheated to a temperature close to 1,400 ° C.

However, when the slab is heated at a high temperature for a long time, it is expensive to manufacture due to a large amount of heat used, and the surface portion of the slab flows down to a molten state, resulting in a high maintenance cost of the furnace, shortening the life span, and being developed on the surface of the slab. There is a problem in that the columnar tablet, which is a coagulation structure, grows coarse and generates a deep crack in the width direction of the plate in a subsequent hot rolling process, thereby significantly lowering the error rate. Therefore, by producing a grain-oriented electrical steel sheet by lowering the reheating temperature of the slab, many advantages can be obtained in terms of manufacturing cost and error rate. However, as described above, if the slab is not completely dissolved at a high temperature, it is difficult to control the precipitate. This makes it impossible to manufacture a grain-oriented electrical steel sheet.

Recently, many methods have been studied to lower the heating temperature of the slab and not to make the inhibitor in the hot rolling step. In other words, it does not obtain the inhibitor entirely from the elements contained in the small steel component, it forms a precipitate in a suitable place during the manufacturing process. This was made possible by incomplete solution and nitriding treatment, as shown in Japanese Patent Application No. 1-230721 and Japanese Patent Application No. 1-283324. In other words, this method has the technical idea that the slab is heated to 1,200 ° C. or less, incompletely formed, leaving unreacted Al, and then, after cold rolling, nitrogen is added to the steel and reacted as a precipitate by annealing. Thus produced (Al, Si) N functions as an inhibitor. The above-mentioned nitriding treatment method includes applying an annealing separator containing a compound having nitriding ability to a steel sheet, incorporating a nitriding gas into the atmosphere gas during the elevated temperature of the high temperature annealing process, and nitriding after cracking in the decarburization process. Nitriding steel sheets in a gas atmosphere with high performance.

In addition, Japanese Patent Application Laid-Open No. 2-228425 discloses a method of making nitrogen precipitate in a steel by a nitriding process performed before hot rolling or final cold rolling. 2-294428 discloses a technique for performing nitriding and decarburization during decarbonization after completion of cold rolling. However, in the case of these methods, there is a problem that secondary recrystallization becomes unstable. Therefore, Japanese Patent Application Laid-Open No. 3-2324 discloses a method of preferentially performing decarbonization, growing the crystal grains to a certain extent or more, and nitriding with ammonia gas.

All of the above methods use a method in which nitrogen, generated by ammonia decomposition at about 500 ° C. or above, is introduced into the steel sheet by nitriding with ammonia gas, wherein nitrogen that has entered the steel sheet is already present in the steel. Phosphorus reacts with phosphorus Al, Si, Mn, etc. to become nitride, and becomes the most stable (Al, Si) N thermodynamically during the high temperature annealing process. In this way, it is possible to produce a grain-oriented electrical steel sheet by low temperature heating of the slab.

However, in order to make (Al, Si) N finally used as an inhibitor, it is necessary to go through the following manufacturing process. In other words, in order to maximize the amount of Al that can be reacted in the nitriding process, the slab heating temperature should be lowered to 1,200 ° C. or lower so that Al and N contained in the small steel component do not bond, thereby incompleteizing. In practice, the slab is reheated at a temperature of 1,150 ° C. or lower to minimize the high capacity of AlN. However, this results in lower starting and finishing temperatures of subsequent hot rolling, which places a lot of load on the rolling equipment, and is significantly lower than the reheating temperature of general carbon steel, thus preventing the simultaneous production of grain-oriented electrical steel sheet and general steel. I still hold it.

Therefore, there is a demand for development of a manufacturing method capable of stably producing oriented electrical steel sheet while removing the load of hot rolling by setting the slab reheating temperature to 1200 to 1300 ° C.

Accordingly, the present inventors conducted research and experiments to solve the above-mentioned problems of the conventional methods, and based on the results, the present invention proposes the present invention, and the present invention lowers the slab reheating temperature by adding REM in the steel component. Since it is to provide a method for producing a grain-oriented electrical steel sheet can be omitted even nitriding process, the purpose is.

The present invention for achieving the above object,

By weight%, C: 0.02 to 0.1%, Si: 1.0 to 4.8%, Mn: 0.2% or less, S: 0.035% or less, Al: 0.005 to 0.02%, N: 0.005% or less, Cu: 0.1 to 0.25%, Steel slab consisting of 0.04% ≤ REM ≤ 0.13%, balance Fe and other unavoidable impurities is reheated and hot rolled at 1200 ~ 1300 ° C, hot rolled annealed at 900 ~ 1150 ° C, cold rolled, decarbonized and hot annealed. It relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties comprising the.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In general, the method of manufacturing the grain-oriented electrical steel sheet varies depending on the type of inhibitor and the method of forming the same. Until now, the research on the method of manufacturing the grain-oriented electrical steel sheet has been conducted from high temperature heating to low temperature heating. That is, a method of completely solidifying the components contained in the small steel component through slab high temperature heating and controlling the precipitates in hot rolling as an inhibitor, and using a method of forming precipitates in annealing after incomplete solution through slab low temperature heating. It is developed.

However, the inventors of the present invention, by forming a precipitate using REM and using it as an inhibitor, it is possible to stably develop secondary recrystallization at high temperature annealing and obtain excellent magnetic flux density while maintaining slab heating temperature the same as that of ordinary steel. It was found that the present invention was completed.

Hereinafter, a steel component and a manufacturing process are demonstrated.

C is an element added to refine the hot rolled structure. After performing the function of hot rolling, C is an impurity and should be removed because it adversely affects the magnetic properties. When 3% of Si is contained, when about 0.018% of C is contained, α-γ transformation occurs during hot rolling, thereby miniaturizing the hot rolled structure. In the present invention, since the content of Si is 1.0 to 4.8% by weight, The content of C is preferably added at least 0.020%. However, if C remains in the final product, it causes self-aging and deteriorates the characteristics of electrical equipment such as transformers. Therefore, the final product is strictly controlled to be 0.003% or less through the decarburization process. In addition, if the content of C is so great that coarse carbides are precipitated, the removal becomes difficult, so the upper limit is preferably set to 0.1%.

Si is an element that significantly improves iron loss by increasing the specific resistance of steel, and is an essential element in the production of grain-oriented electrical steel sheet. The amount of addition is determined by various limiting factors, and in practice, the content is generally about 2.95 to 3.5%. This is a range determined by being able to stably cold roll industrially. In the present invention, it is preferable to set it at 1.0 to 4.8%, because when it is 1.0% or less, the addition effect is insignificant and there is no significant meaning, and when it is more than 4.8%, rolling is impossible.

Mn is an ingredient that increases the electrical resistance and lowers the iron loss. In order to obtain such an effect, Mn should be added at 0.05% or more, but if the content is too high, the magnetic flux density will be reduced. It is preferable.

S reacts with Mn and REM in steel to form MnS or REM-S, which is used as a primary recrystallization inhibitor. If the content is high, S is segregated in the center of slab heating and adversely affects the microstructure. It is desirable to manage.

Al is an element that acts as an inhibitor by binding to N added in the steel during annealing to form AlN. In general, acid-soluble Al is known to form the most appropriate AlN at about 0.03%. In the present invention, since the content of N is small, it is preferable to set the content range of Al to 0.02%.

It is preferable that N is not included in the steel, but in practice, the amount of nitrogen contained as an impurity cannot be completely removed. Therefore, N is preferably controlled at 0.005% or less, which can be easily controlled in steelmaking.

Cu is an austenite forming element such as Mn, and AlN contributes to solid solution and fine precipitation to stabilize secondary recrystallization. In addition, by forming a precipitate called Cu ₂ S in combination with S has the effect of suppressing grain growth. The content of Cu is preferably set to 0.1 to 0.25%. The reason is that if the content is less than 0.1%, the above effect is insignificant. Because.

REM is a characteristic element of the present invention. The secondary steel sheet is formed by forming REM-S or REM-N-shaped precipitates or inclusions by combining with REM alone or with nitrogen or sulfur contained as impurities in the small steel component. It is responsible for successfully recrystallization. The REM refers to rare earth metal elements, and includes one or two or more thereof in the present invention, which is composed of Ce (cerium), La (lanthanum), Nd (neodymium), Pr (pracidium), or the like. have. It is preferable to add the content in 0.04 to 0.13%, More preferably, it is 0.08 to 0.12%. The reason is that if the content of the REM is less than 0.04%, the effect is insignificant, and if more than 0.13%, the inclusions of the REM are present to deteriorate the magnetic properties. In addition, when the content of the REM is 0.08 ~ 0.12%, it is possible to lower the content of Mn having an effect of increasing the electrical resistance and lowering the iron loss to 0.01% or less, thereby the MnS of S used as the primary recrystallization inhibitor The content can also be lowered to 0.008% or less.

The steel slab formed as described above may be reheated in a temperature range of 1200 to 1300 ° C. which is a reheating temperature of general steel. At this time, when the heating temperature is less than 1200 ° C., the slab temperature is too low, making it difficult to hot roll, and reheating cannot be performed like other types of ordinary steel, and productivity is also lowered. If it is 1300 ℃ or more does not significantly affect the magnetic properties, it is not preferable because the benefits from the low temperature heating of the slab is greatly reduced.

On the other hand, in the slab heating process, S and N present in the steel react with REM to form sulfides, and Mn remains as sulfides.

The hot rolled hot rolled plate after the slab heating is preferably annealed at 900 ~ 1150 ℃ to improve the uniformity and pickling properties of the hot rolled structure. In the conventional method, partial employment and reprecipitation of precipitates during hot-rolled sheet annealing have occurred, and thus, a method of quenching is maintained when the temperature reaches about 900 ° C. after maintaining at 1100 to 1150 ° C. to obtain a stable distribution of precipitates. It is not necessary to consider such control cooling is not necessary.

Thereafter, the hot rolled sheet is cold rolled to the final product thickness and then subjected to annealing for decarburization, wherein the atmosphere in the annealing furnace is a mixed gas atmosphere of wet hydrogen + nitrogen. In this process, C of the steel sheet is removed and the particle size of the primary recrystallization is controlled.

On the other hand, conventionally, in the decarbonization annealing process, N is impregnated into the steel, but in the present invention, since the preformed REM alone or the nitride or sulfide compounded with the REM is formed as an inhibitor from the slab heating process, the immersion treatment is performed. Becomes unnecessary.

After decarbonization annealing as described above, an annealing separator containing MgO as a main component is applied to the surface of the steel sheet and subjected to high temperature annealing in the form of a coil. The high temperature annealing is composed of a temperature rising section for developing a secondary recrystallization structure and a pure annealing section for removing impurities, and the temperature rising rate of the temperature rising section affects the growth behavior of the precipitate. If the temperature increase rate is too fast, the secondary recrystallization becomes unstable, and if it is too slow, the annealing time is long and uneconomical, so it is preferable to set it at 10 to 40 ° C / hr. Since the pure annealing is a process of removing harmful elements in the steel by maintaining in a reducing atmosphere, it is preferable to use 100% hydrogen.

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

(Example)

The steel slab formed as shown in Table 1 was reheated at 1250 ° C. for 2 hours, and then hot rolled to obtain a hot rolled plate having a thickness of 2.3 mm. The hot rolled sheet was annealed at 950 ° C. for 5 minutes, cooled, and then cold rolled to a thickness of 0.3 mm. The cold rolled plates were decarburized for 5 minutes in a mixed gas atmosphere of 25% hydrogen + 75% nitrogen with a dew point of 51 ° C in a furnace maintained at 850 ° C. MgO, an annealing separator, was applied to this steel sheet to perform high temperature annealing to cause secondary recrystallization. The high temperature annealing was heated to 1,200 ° C. at a rate of 15 ° C./hr in a 25% hydrogen + 75% nitrogen atmosphere, and then maintained in a 100% hydrogen atmosphere for 10 hours, followed by quenching.

Next, the magnetic properties were measured magnetic flux density (B ₁₀ ) induced under a magnetic field of 1000A / m, the results are shown in Table 1 below.

division Chemical composition (% by weight) Magnetic flux density (Tesla) C Si Cu Mn S Sol.Al N REM Comparative Steel 1 0.047 3.15 0.17 0.072 0.024 0.026 0.0092 － 1.78 Comparative Steel 2 0.069 0.028 0.014 0.0010 0.03 1.84 Inventive Steel 1 0.068 0.027 0.014 0.0007 0.05 1.87 Inventive Steel 2 0.066 0.028 0.015 0.0009 0.10 1.88 Invention Steel 3 0.0063 0.0050 0.015 0.0008 0.10 1.93 Inventive Steel 4 0.0011 0.0014 0.010 0.0006 0.10 1.94 Comparative Steel 3 0.0013 0.0020 0.010 0.0008 0.15 1.83

As shown in Table 1, the inventive steels (1) to (4) of the present invention to which REM was added, the formation of secondary recrystallization gradually improved at high temperature annealing, and the magnetic flux density of the comparative steels (1) to (3). It can be seen that the contrast is high. In addition, in the case of the inventive steels (3) and (4) in which the amount of REM added is 0.1%, the content of Mn is 0.01% or less, and the content of S is 0.008% or less, the magnetic flux density is further improved to show excellent magnetic properties. Able to know.

According to the present invention as described above, it is possible to manufacture a grain-oriented electrical steel sheet having excellent magnetic properties without controlling the hot rolled material heating temperature, there is an effect that can improve productivity and workability.

Claims (2)

By weight%, C: 0.02 to 0.1%, Si: 1.0 to 4.8%, Mn: 0.2% or less, S: 0.035% or less, Al: 0.005 to 0.02%, N: 0.005% or less, Cu: 0.1 to 0.25%, Steel slab consisting of 0.04% ≦ REM ≦ 0.13%, balance Fe and other unavoidable impurities is reheated and hot rolled at 1200 ~ 1300 ° C, hot rolled annealed at 900 ~ 1150 ° C, cold rolled, decarbonized and hot-annealed. Method for producing a grain-oriented electrical steel sheet having excellent magnetic properties comprising a. The method of manufacturing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein Mn is 0.01% or less, S is 0.008% or less, and REM is 0.08 to 0.12%.