KR19980044908A - Manufacturing method of oriented electrical steel sheet - Google Patents

Abstract

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used for iron cores, such as transformers, the second recrystallization annealing without eliminating the decarburization process using ultra-low carbon, without taking the control method of the inhibitor by precipitation annealing In the high temperature annealing process, the inhibitor is reinforced to effectively suppress the growth of primary recrystallized grains, thereby producing the grain-oriented electrical steel sheet by the low temperature reheating method.

Description

Manufacturing method of oriented electrical steel sheet

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used for iron cores such as transformers, and more particularly, to a method for producing grain-oriented electrical steel sheet having excellent economy by low temperature slab heating.

In general, a grain-oriented electrical steel sheet has an aggregate structure of {110} 1 orientation in the rolling direction, and a manufacturing method was first proposed by Goss (N, P, GOSS) in US Patent 1,965,559, and then has been studied by various researchers. And the magnetic properties have been improved by improving the process.

A grain-oriented electrical steel sheet having an aggregate structure of {110} 1 orientation is produced by effective control of fine precipitates and segregation elements called inhibitors.

The manufacture of the grain-oriented electrical steel sheet undergoes a secondary recrystallization process in which grains having a {110} 1 orientation are preferentially grown among the first recrystallized grains.

In this process, the inhibitor is known to function to prevent the first recrystallization from growing significantly and to allow the grain growth of the {110} 1 orientation to preferentially grow in the subsequent second recrystallization.

Currently, industrially produced oriented electrical steel sheet uses one of MnS, MnS + AIN, and MnS (Se) + Sb as an inhibitor. Therefore, the core of the present technique is to obtain a secondary recrystallized structure having an aggregate structure of {110} 1 orientation through the different manufacturing process using the above-mentioned inverter using the above-mentioned inverter.

The process of developing secondary texture in the manufacturing process to develop the {110} 1 orientation texture is called high temperature annealing. The annealing process is an annealing separator to prevent sticking between steel sheets in any method using an inhibitor, and to react with an oxide layer formed on the surface of the steel sheet to form a glassy film, thereby providing insulation. It is performed by applying (mainly MgO).

Finally, an insulation coating is applied to a plate having an aggregate structure of the {110} 1 orientation obtained in this step to obtain a product.

The above-mentioned precipitates are important as conditions to be in order to function as an inhibitor as follows.

Precipitates should be evenly distributed in sufficient quantity and in an appropriate size so that growth can be inhibited until the first recrystallization occurs just before the secondary recrystallization, and thermally stable to the high temperature just before the secondary recrystallization occurs and not easily decomposed.

MnS, MnS + AIN, and MnS (Se) + Sb mentioned above are satisfied and used industrially. A typical method for producing a grain-oriented electrical steel sheet using MnS + AIN is shown in Japanese Patent Publication No. 40-15644. In this method, a grain-oriented electrical steel sheet is produced by cold rolling once with a high reduction ratio of 80% or more.

On the other hand, a representative method for producing a grain-oriented electrical steel sheet using MnS (or MnSe) + Sb described above is shown in Japanese Patent Publication No. 51-13469, in which the cold rolled two times to produce a grain-oriented electrical steel sheet do.

However, the above methods all have to reheat the slab to 1,300 ° C. or higher in order to obtain a precipitate having a desired size distribution. This is based on the technical idea that MnS or AIN must be above this temperature in order to be employed.

That is, MnS or AIN contained in the mild steel component is heated and heated at high temperature for a long time to be hot rolled, and then cooled to make a precipitate having an appropriate size and distribution.

In fact, industrial production is reheating to a temperature close to 1,400 ℃ in order to obtain a uniform temperature distribution to the inside in consideration of the size of the slab.

However, when the slab is heated to a high temperature, the following problems occur.

First, the cost of manufacturing is high due to the large amount of heat used. Second, the surface part of the slab flows down to the molten state, resulting in a high cost of repairing the furnace, shortening the lifespan. In the subsequent hot rolling process, deep cracks are generated in the width direction of the plate, thereby significantly lowering the error rate.

For the same reason, lowering the slab reheating temperature of a grain-oriented electrical steel sheet can have many effects in terms of manufacturing cost and error rate.

In order to solve the above problems, methods that do not use MnS having high employment temperature have recently been developed. This can be achieved by making the precipitate at a suitable place in the manufacturing process, without relying entirely on the inverter from the elements contained in the steel composition.

Representative method that does not use the above MnS is presented in Japanese Patent Publication No. Hei 2-228425, which is to provide a high-speed high-density oriented electrical steel sheet with low slab reheating temperature and excellent characteristics, hot rolled Nitrogen is introduced into the steel by a nitriding process prior to plate or final cold rolling to form precipitates.

Another method not using MnS described above is disclosed in Japanese Patent Application Laid-Open No. 2-294428, which simultaneously performs nitriding and decarburization at the time of decarbonization followed by completion of cold rolling. However, this method has a problem that the secondary recrystallization becomes unstable.

In addition, Japanese Patent Application Laid-Open No. 3-2324 can be cited as a method that does not use the above-described MnS. This method is an improvement of Japanese Patent Publication No. 2-294428 in which secondary recrystallization becomes unstable. It is a method of nitriding with ammonia gas after growing to a certain degree or more.

The manufacturing process of the grain-oriented electrical steel sheet is a process of hot slab heating, hot rolling, precipitation annealing, cold rolling, decarbonization annealing, high temperature annealing.

Therefore, many attempts have been made to simplify the long manufacturing process of such oriented electrical steel sheets.

However, each process has a metallurgical meaning, so the omission of one process is possible only by substituting its effects in the other process.

As a representative example, eliminating decarburization requires new components or process improvements that can give the effect of refining the hot-rolled sheet grains, which is the role of carbon, and to omit precipitation annealing, it is necessary to make precipitates that can function as inhibitors in other fixtures. will be.

In fact, efforts have been made to pursue economic feasibility by eliminating the decarburization process using molten steel containing ultra-low carbon and many methods have been proposed. As an example, Japanese Patent Publication 54-112317, Japanese Patent Publication 55-073818, Japanese Patent Publication 57-114614, Japanese Patent Publication 58-100627, Japanese Patent Publication 61-91319, Japanese Patent Publication 61-83421 Japanese Patent Laid-Open No. 1-119644, Japanese Patent Laid-Open No. 1-212721, Japanese Patent Laid-Open No. 1-309923, Japanese Patent Laid-Open 1-309924, Japanese Patent Laid-Open No. 2-30714, Japanese Patent Laid-Open No. 2-141532, Japan JP-A 3-111516, JP-A-3-287721, JP-A 5-9666, and the like. However, these methods have not been practical because of the fact that secondary recrystallization development is not stable and the process conditions are tightly controlled, so there are many problems in actual industrial use.

By the above-mentioned nitriding treatment method, it is possible to manufacture a grain-oriented electrical steel sheet by low temperature heating. Therefore, a lot of attempts have been made to develop a technique that uses this technique and achieves cost reduction by shortening the process. As a specific method, it is typical to omit the decarbonization process by reducing the amount of carbon in the steel, and to eliminate the precipitation annealing by allowing the formation of inhibitors in the latter part of the process by nitriding.

As a result, a number of methods have recently been proposed to pursue economic feasibility by combining the nitriding treatment and the use of ultra low carbon to omit or simplify the decarburization process.

For example, Japanese Patent Laid-Open No. 7-197127, Japanese Patent Laid-Open No. 7-197129, Japanese Patent Laid-Open No. 6-346147, Japanese Patent Laid-Open No. 7-26328, Japanese Patent Laid-Open No. 70640, Japanese Patent Laid-Open No. 7-70639, Japanese Patent Japanese Unexamined Patent Publication No. 7-97630 proposes a method of eliminating or simplifying decarbonization, and Japanese Patent Publication No. 7-179942 proposes a method of eliminating precipitation annealing.

However, all of these techniques are to be carried out separately by nitriding annealing instead of omitting precipitation annealing or decarbonization annealing. Therefore, there is a problem that can not fully take advantage of the economics resulting from the omission of the process has not been industrialized.

As mentioned above, the above-mentioned nitriding loss is all nitrided with ammonia gas. In order to carry out nitriding, a new facility is required, or a facility for controlling ammonia into an existing furnace must be retrofitted.

Therefore, it is possible to manufacture a grain-oriented electrical steel sheet by low temperature reheating by the above-described method, but it is applicable only when a new process is added or a significant modification of the conventional equipment is performed. Therefore, these methods do not greatly benefit the problem of pursuing economic feasibility, because the advantages obtained by low-temperature reheating and the addition of nitriding treatment do not fully utilize the advantages of cost reduction through the omission of a true process.

Therefore, in order to use the current manufacturing equipment of oriented electrical steel sheet as it is, and to produce a product with economical value as if the process is omitted, the low temperature ash heating does not involve the elimination of the process and the addition of a new process and the renovation of the equipment near to the new construction. There is a need for a method for producing a grain-oriented electrical steel sheet.

The present invention has been invented to solve the above problems, the present invention omits the decarburization process using ultra-low carbon, high temperature annealing process of the second recrystallization annealing without taking the control method of the inhibitor by precipitation annealing It is an object of the present invention to provide a method for manufacturing a grain-oriented electrical steel sheet by a low temperature reheating method by reinforcing the inhibitor in effectively inhibiting the growth of primary recrystallized grains.

Features of the present invention having such a purpose are wt% C: 0.1% or less, Si: 1.0-4.8%, Al: 0.010-0.05%, Mn: 0.05-2%, N: 110 ppm or less, S: 0.01% or less , Ni: 0.2-2.0%, remainder Fe and other unavoidable impurities, reheat the steel sheet slab to a temperature of 1,100 ~ 1,250 ℃, hot roll, and then pickling and cold rolling, and then applying an annealing separator, To produce a grain-oriented electrical steel sheet without any additional nitriding process by omitting precipitation annealing and decarbonization annealing at high temperature, but adding a cast steel component of 0.1% or less, adding Ni: 0.2-2.0%, and preparing an annealing separator. Si ₃ N ₄ was added to MgO and applied to the surface of the steel sheet, followed by high temperature annealing, eliminating precipitation annealing and decarbonization annealing, and nitriding in a high temperature annealing process without the addition of a nitriding step. By recrystallization to produce a grain-oriented electrical steel sheet.

The present invention is wt% C: 0.1% or less, Si: 1.0-4.8%, Al: 0.010-0.05%, Mn: 0.05-2%, N: 100ppm or less, S: 0.01% or less, Ni: 0.2-2.0% The steel sheet slab containing the remaining Fe and other unavoidable impurities was reheated and hot rolled at a low temperature of 1,100-1,250 ° C., followed by pickling and cold rolling, followed by application of an annealing separator and high temperature annealing. Producing a grain-oriented electrical steel sheet by omitting the decarbonization annealing process;

In the preparation of the annealing separator, nitride of Si such as Si ₃ N ₄ is added to MgO and coated on the surface of the steel sheet, followed by high temperature annealing, followed by nitriding using nitrogen released by decomposition of Si ₃ N ₄ in a temperature rising process of high temperature annealing. The specific resistance is increased by diffusing Si into the steel sheet to produce a grain-oriented electrical steel sheet having low iron loss.

Hereinafter, the present invention will be described in detail.

In the present invention, C is an element added to refine the hot rolled structure, and after performing the function during hot rolling, it becomes an impurity and thus has to be removed because it adversely affects the magnetic properties. Originally, when manufacturing a grain-oriented electrical steel sheet, 0.025% or more must be included to undergo a two-phase region of α + γ during hot rolling to obtain a grain refinement effect.

However, in the present invention, the amount of C is 0.1% or less, and by adding Ni, which is a γ-forming element, to enlarge the two-phase region, it replaces the micronizing function of the tissue, which is the role of C.

Therefore, it is preferable not to add C separately but to use the amount contained as an impurity at the time of addition of another element as it is. Preferably, it is desirable to prevent the magnetic aging when used as a final product with an ultra low carbon of 0.0030% or less.

Si is a component added to increase the electrical resistance of the steel sheet to lower the iron loss. If the content is more than 4.8%, the cold rolling is impossible, and if it is less than 1.0%, the additive content is not effective. It is preferable to set it to 4.8 wt%.

Al is finally made into AIN, (Al, Si) N and (Al, Si, Mn) N type nitride and acts as an inhibitor, and if the content is less than 0.010%, sufficient effect to the inhibitor can be expected. If too high and too high, Al-based nitride grows coarsely, and the ability of the inhibitor is lowered. Therefore, the Al content is preferably set at 0.010 to 0.05%.

Since N is used by reinforcing in the high temperature annealing process, an amount sufficient to enter impurities during melting is sufficient. However, even if nitrogen is deliberately added, there is no other effect. However, when it exceeds 100 ppm, hot rolling is difficult, so the N content is preferably selected to be 100 ppm or less.

Mn is an element having an effect of lowering iron loss as an element that increases electrical resistance. When the content is too large, Mn causes a decrease in magnetic flux density. Therefore, the Mn content is preferably selected to 0.05 to 0.2%.

S is preferably a high solubility temperature at the time of hot rolling and is not contained as much as possible as a segregation element. In consideration of the amount of impurities contained in the steel rewound, the content of S is preferably 0.01% or less.

Ni is an element added to replace the function of C as a γ region expansion element. When Ni is added at 0.2% or less, it is not effective. When Ni is more than 2.0%, hot rolling workability is deteriorated.

The reheating temperature of the electrical steel slab is preferably selected to be 1,100 ~ 1,250 ℃, the reason is that when the reheating temperature is less than 1,100 ℃ it is difficult to work during hot rolling, and when the temperature is above 1,250 ℃, there is no significant effect on the magnetic properties, This is because the benefits from cold reheating are greatly reduced.

The heated steel sheet slabs are hot rolled and cold rolled in a conventional manner.

After applying the annealing separator to the steel sheet prepared as described above, a grain-oriented electrical steel sheet having excellent magnetic properties is produced by obtaining an {110} 1 texture in the rolling direction by secondary recrystallization by high temperature annealing.

Since the oxide layer does not develop on the surface layer of the steel sheet due to the omission of the decarburization process at the time of high temperature annealing, it is disadvantageous to form a glassy film. It must be kept in one state. In order to keep gas in a humid state, what is necessary is just to make furnace point into 0 degreeC or more, but it is preferable to keep it at 10-30 degreeC preferably.

As the annealing separator, Si-based nitride should be added based on MgO. The addition of nitrides other than Si-based metals has a nitriding effect. However, in the case of metal nitrides, the glassy film formation state is poor, and the iron loss improvement effect due to diffusion of Si cannot be obtained. That is, it is most preferable that nitrogen generated as the added Si-based nitride decomposes into the steel sheet, and Si enters into the steel by diffusion.

At the time of the high temperature annealing, a mixed gas of nitrogen and hydrogen is used as the atmospheric gas, and a preferable composition of the mixed gas is 5 to 95% N ₂ +95 to 5% H ₂ . This is because if nitrogen is not contained in the atmosphere, the nitrogen concentration in the steel sheet may be high and nitrogen may escape into the atmosphere having a relatively low nitrogen concentration.

Nitrogen is decomposed into the steel at 500 ℃ or higher during the high temperature annealing, and the temperature of the secondary recrystallization is estimated to be 900 to 1,100 ° C.

The slower the temperature rise rate in this region is, the more favorable it is for the safety of nitriding, diffusion of Si, and secondary recrystallization structure development. However, if it is too slow, it is preferable to select 15 to 40 ° C / hr because of economical problems.

Hereinafter, the metallurgical characteristics of the present invention will be described.

In the electrical steel sheet slab of the present invention, sulfur (S) is not added and hot rolling is performed at a heating temperature of 1,250 ° C. or lower. Therefore, sulfides such as MnS having a solid solution temperature of 1,300 ° C. or higher cannot be used as an inhibitor.

In addition, at temperatures below 1,250 ° C., A1N is a low temperature that cannot be completely dissolved, and thus AIN-based precipitates do not have an appropriate size and distribution that can be used as an inhibitor. Therefore, there is no precipitate in a state that can be used as an inhibitor until the stage just before hot annealing. During the high temperature annealing process, the Si ₃ N ₄ is gradually decomposed to become silicon (Si) and nitrogen (N ₂ ) and uniformly diffuse into the steel sheet.

Nitrogen combines with Al in steel to form AlN-based nitrides, or nitrogen combines with Si in steel to form Si-based nitrides or Al and Si composite nitrides, although a small number of them, Al, Si and Mn Will form.

In this process, nitride-like precipitates are generated that can be used as an inhibitor, and as the temperature increases, nitrides of Si-based thermodynamically unstable are decomposed. Therefore, ultimately, nitrides such as AIN, (Al, Si) N, and (Al, Si Mn) N act as inhibitors.

On the other hand, Si is more actively diffused into the steel at higher temperatures, the Si content as a whole increases. Si is the most effective element for increasing the electrical resistivity. Iron loss, the most important characteristic of oriented electrical steel sheets, can be largely divided into hysteresis loss and eddy current loss. The eddy current loss is inversely related to the loss of the eddy current caused by the use of the steel sheet as an iron core. In fact, increasing the amount of Si by 0.2% at 1.7 Tesla and 50 Hz is known to improve the iron loss of 0.06w / kg.

A feature of the present invention is to manage the steel as a very low carbon to eliminate the need for decarburization, to replace the function of carbon by the addition of Ni, and to control the precipitate used as an inhibitor in the precipitation annealing process, added during high temperature annealing Nitride is added to the additive of the annealing separator to replace the nitriding process by the decomposition thereof, thereby producing a grain-oriented electrical steel sheet without the need for additional nitriding process.

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

Example 1

Wt% aromatic containing C: 0.0030%, Si: 3.11%, Mn: 0.14%, S: 0.004%, Sol, Al: 0.027%, N: 0.0040%, Ni: 0.5% and the balance is substantially Fe The electrical steel slab was reheated at 1,250 ° C. for 2 hours to prepare a hot rolled sheet having a thickness of 2.3 mm.

The hot rolled plate was pickled and cold rolled to 0.30mm thickness without intermediate annealing. An annealing separator containing 5% of Si ₃ N ₄ was added to MgO, followed by high temperature annealing to form a secondary recrystallized texture of {110} 1. Got it.

At this time, the high temperature annealing was heated at a temperature increase rate of 15 ℃, up to 1,150 ℃ 75% N ₂ + 25% H ₂ atmosphere, after reaching 1,150 ℃ 100% H _{2 to} maintain for 10 hours to decompose the nitride and remove impurities Was performed. Up to 800 ° C, a 75% N ₂ + 25% H ₂ atmosphere gas was passed through a humidifier so that the dew point was 30 ° C.

After the high temperature annealing was finished, the excess annealing separator was removed, and then subjected to stress removal annealing at 800 ° C. for 100 hours in an atmosphere of 100% N ₂ to obtain a magnetic flux density (B ₁₀ ) at a storage capacity of 1,000 A / m at 1.7 Tesla and 50 Hz. The iron loss of W _17/50 was measured as follows.

Magnetic flux density (B ₁₀ ): 1.838Tesla

Iron loss (W _17/50): 1.24w / kg

Example 2

wt: C: 0.0079%, Si: 3.15%, Mn: 0.14%, S: 0.004%, Sol. A grain-oriented electrical steel slab containing Al: 0.027%, N: 0.0040%, and Ni: 1.0%, the balance being substantially made of Fe, was reheated at 1,250 ° C for 2 hours to prepare a hot rolled sheet having a thickness of 2.3 mm.

The hot rolled plate was pickled and cold rolled to 0.30mm thickness without intermediate annealing. An annealing separator containing 5% of Si ₃ N ₄ was added to MgO, followed by high temperature annealing to form a secondary recrystallized texture of {110} 1. Got it.

At this time, the high temperature annealing was heated at a temperature rising rate of 15 ℃, up to 1,150 was 75% N ₂ + 25% H ₂ atmosphere, and after reaching 1,150 ℃ 100% H ₂ maintained for 10 hours to decompose the nitride and remove impurities Was performed. Up to 800 ° C, a 75% N ₂ + 25% H ₂ atmosphere gas was passed through a humidifier so that the dew point was 10 ° C. After the high temperature annealing was finished, the excess annealing separator was removed, and then subjected to stress removal annealing at 800 ° C. in a 100% N ₂ atmosphere for 5 hours to obtain a magnetic flux density (B ₁₀ ) at a storage capacity of 1,000 A / m at 1.7 Tesla and 50 Hz. The iron loss (W _17/50 ) was measured as follows.

Magnetic flux density (B ₁₀ ): 1.843Tesla

Iron loss (W _17/50): 1.22w / kg

As described above, the present invention manages the steel component as ultra low carbon, eliminating the need for decarburization, replaces the function of carbon by adding Ni, and does not control the precipitate used as an inhibitor in the precipitation annealing process, and at the time of high temperature annealing. By adding nitride to the additive of the annealing separator to be added and replacing the nitriding process by the decomposition thereof, there is an effect that a grain-oriented electrical steel sheet can be manufactured without the need for additional nitriding process.

Claims (1)

In manufacturing a grain-oriented electrical steel sheet used as an iron core of a transformer or the like, C: 0.1% or less, Si: 1.0-4.8%, Al: 0.010-0.05%, Mn: 0.05-2%, N: 110 ppm or less in wt%, S: 0.01% or less, Ni: 0.2-2.0%, remainder Fe and other unavoidable impurities. Reheat the steel sheet slab to a temperature of 1,100 ~ 1,250 ℃, hot roll, and then pickling and cold rolling, followed by annealing separator After coating, and annealing at high temperature to omit the precipitation annealing and decarbonization annealing to produce a grain-oriented electrical steel sheet without the addition of a separate nitriding process, the steel component is less than C: 0.1%, Ni: 0.2-2.0% is added, In the annealing separator, Si ₃ N ₄ is added to MgO and coated on the surface of the steel sheet, followed by high temperature annealing, thus eliminating precipitation annealing and decarbonization annealing and nitriding in a high temperature annealing process without adding a nitriding process. } Directional transfer characterized by obtaining a second recrystallized tissue of 1 The method of the steel sheet.