KR20030054427A - Method for Manufacturing Grain-Oriented Electrical Having Low Core Loss and High Magnetic Induction - Google Patents

Abstract

PURPOSE: A method for manufacturing grain-oriented electrical steel sheet having low core loss and high magnetic induction is provided. CONSTITUTION: The method includes the steps of reheating a steel slab comprising Si 2.0 to 4.0 wt.%, sol.Al 0.006 to 0.040 wt.%, N 0.006 to 0.012 wt.%, 0.007 wt.% or less of S, 0.5 wt.% or less of Cu, Mn 0.08 to 1.0 wt.%, 0.015 wt.% or less of C, a balance of Fe and incidental impurities at 1100 to 1250°C, followed by hot rolling; annealing the hot rolled steel sheet at 900 to 1200°C; cold rolling the annealed steel sheet at a reduction ratio of greater than 90 % to the thickness of less than 0.27 mm; annealing the cold rolled steel sheet under an atmospheric condition including nitrogen ion at 750 to 950 deg.C in order to penetrate nitrogen ion into the steel sheet in an amount of 0.0010 to 0.0300 %; applying an annealing separator primarily consisting of MgO, followed by coiling; heating the steel sheet under an atmospheric condition including 5 to 90 % nitrogen to the temperature range of 1150 to 1250°C; and soaking the steel sheet in pure hydrogen atmosphere for more than 10 hrs, followed by cooling.

Description

Method for Manufacturing Grain-Oriented Electrical Having Low Core Loss and High Magnetic Induction}

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used as a core material of a large rotor, such as a generator and various transformers and electronic devices, and more particularly, a grain-oriented electrical steel sheet having excellent magnetic properties with low iron loss and high magnetic flux density. It relates to a method of manufacturing.

In general, the grain-oriented electrical steel sheet is characterized by having excellent magnetic properties in the rolling direction by arranging all grains in the (110) [001] direction through cold rolling and annealing processes.

Ordinary oriented electrical steel sheet contains 2-4% silicon and MnS or MnSe as grain growth inhibitor, and melted to make slab and then reheated-hot rolled-preannealed-two cold rolled with intermediate annealing -Decarbonization-Application of fusion inhibitor-Finished into final product through the very complicated process of final high temperature annealing.

These complex processes are essential in the general manufacturing method that causes secondary recrystallization using MnS or MnSe as grain growth inhibitors.

Secondary recrystallization of the grain-oriented electrical steel sheet suppresses the normal growth of the first recrystallized particles by grain growth inhibitors, and only particles having an aggregate structure having some excellent magnetic properties selectively undergo abnormal growth.

In order to induce secondary recrystallization, precipitates such as MnS, a grain growth inhibitor, should be finely precipitated to effectively suppress normal growth of the primary recrystallized grain.

To deposit MnS finely, the slab must be reheated at a very high temperature of 1400 ° C. where MnS can be dissolved.

In addition, a certain amount of carbon should be added to prevent coarse growth of columnar tissue and central segregation of sulfur, which adversely affects the magnetism generated when the slab is reheated at a high temperature.

The carbon causes ferrite-austenite phase transformation to inhibit the formation of columnar tissues, to promote the employment of AlN, a grain growth inhibitor, and to inhibit central segregation of sulfur.

However, when carbon remains in the final product, it precipitates even in a low temperature range of 200 ° C., thereby greatly increasing the iron loss, thereby greatly reducing the efficiency of the electronic device.

Therefore, carbon must be removed prior to secondary recrystallization annealing through decarbonization annealing.

Many studies have been made to improve the complicated manufacturing process of electrical steel sheet.

Initially, a method of manufacturing a grain-oriented electrical steel sheet having high magnetic flux density characteristics by shortening the cold rolling process by one time and combining MnS and AlN was developed.

This method was able to secure the magnetic properties of high magnetic flux density and low iron loss than conventional oriented electrical steel sheet, but the carbon content was increased and the slab heating was performed at high temperature of 1400 ℃. Slab wash had a problem of falling error rate.

Since then, many researches have been conducted to reduce the slab reheating temperature in order to improve the slab high temperature heating and improve productivity.

Most of these studies are performed by reheating the slab at a temperature below about 1300 ℃ where the slab does not melt, hot rolling, and then adding grain growth inhibitors necessary for secondary recrystallization in the post-hot-rolling process. Concentrated on how to prepare.

This method is very different from the conventional method of controlling the secondary recrystallization by completely employing the grain growth inhibitor by high temperature slab heating and then finely depositing it in the hot rolling step.

In addition, nitriding treatment is performed to add grain growth inhibitors at the stage after the hot rolling. Since nitriding treatment is not carried out when carbon is present in steel, it is usually carried out in the next step after decarbonization annealing. shall.

For this reason, it is necessary to expand additional manufacturing facilities because an annealing furnace capable of nitriding treatment is required separately from decarbonization annealing.

The present invention is to control the content of carbon added in the steelmaking step extremely low to lower the slab heating temperature to 1250 ℃ or less and omit the decarbonization annealing process and cold-rolled final product thickness of 0.27mm or less by one-time cold rolling method By reinforcing additional grain growth inhibitors by rolling and nitriding annealing, an object of the present invention is to provide a method for more economically manufacturing oriented electrical steel sheet having lower iron loss and higher magnetic flux density.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the present invention, C: 0.015wt% or less, Si: 2.0 ~ 4.0wt%, acid soluble Al: 0.006 ~ 0.040wt%, N: 0.006 ~ 0.012wt%, S: 0.007wt% or less, Cu: 0.5wt % Or less, Mn: 0.08 ~ 1.0wt%, remainder Fe and other unavoidable impurities, the slab is reheated to 1100 ~ 1250 ℃ and hot rolled, followed by short time hot roll annealing at 900 ~ 1200 ℃ After cold rolling the thickness of final product to 0.27mm or less by one cold rolling method with rolling rate over 90%, decarburization process is skipped and 0.0010 using gas atmosphere containing nitrogen ion at the temperature of 750 ~ 950 ℃. Nitriding annealing in which ˜0.0300 wt% of nitrogen ions are introduced to the steel sheet is carried out, followed by winding up by applying a fusion inhibitor containing MgO as a main component, and then 1150 to 1250 ° C. in a water atmosphere containing 5 to 90% of nitrogen. It is heated up to the temperature range of and it cracks and cools more than 10 hours in 100% water atmosphere. The present invention relates to a method for producing a grain-oriented electrical steel sheet having low iron loss and high magnetic flux density by performing annealing.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

When the oriented electrical steel sheet is processed and used by end users, the magnetic properties of the material deteriorate with time.

This phenomenon is called magnetic aging, which mainly causes the residual carbon, which is dissolved in the material, to precipitate as carbide, such as Fe ₃ C, at the grain boundary due to the thermal energy generated when the product is used. As a result, the magnetic properties are reduced.

Of course, other impurities also cause self-aging, but they do not cause as much loss as carbon, so the residual carbon content in the production of the product is not more than 30 ppm.

Efforts to prevent the deterioration of the magnetic properties of the final product by managing such carbon from the initial steelmaking stage continued, but this was not possible in the existing component system that requires full employment of grain growth inhibitors in the slab heating stage.

In this regard, Korean Patent Laid-Open Publication No. 1998-034055 re-heats a slab at a temperature of 1220 ~ 1280 ° C and uses two cold rolling methods while managing carbon content at an extremely low level of 0.002wt% in a component system using AlN as a grain growth inhibitor. Therefore, a method of manufacturing a general grain electrical steel sheet having a magnetic flux density of 1.87 Tesla level is presented.

However, in the above method, the slab temperature is a sufficiently high temperature at which the crystal grains of the slab are coarse to form stretched grains in the hot rolled sheet when carbon is extremely low.

When the stretched grain is present in the hot rolled plate, the stretched grain is also present in the cold rolling process and the annealing process, which in turn hinders the secondary recrystallization and degrades the magnetic properties. In the case of using the two cold rolling method and the product thickness is 0.3mm, the magnetic flux density is only about 1.87 Tesla.

Accordingly, the present inventors heated the slab at a temperature below 1250 ° C., which is a temperature at which crystal grains do not grow coarsely while reducing the carbon content in the steelmaking step to a level where no decarburization process is required, and then hot rolling is performed to produce coarse stretched grains. The method of positive suppression and the method of manufacturing oriented electrical steel sheets with high magnetic flux density of 1.89 Tesla or higher were studied.

As a result, in addition to AlN, a grain growth inhibitor added in the steelmaking step, by introducing nitrogen ions into the steel plate in a later step, the AlG precipitates can be omitted by adding additional AlN precipitates in addition to the existing AlN, thereby eliminating the decarburization process. It has been found that slab heating below 1250 ° C., which does not form coarse grains, is possible even in a component system containing a small amount of carbon steel.

In addition, with the introduction of additional grain growth inhibitors, it is possible to produce oriented electrical steel sheets even by one-time cold-rolling. Especially, by cold rolling to a thickness of 0.27mm or less, excellent directionality with excellent magnetic properties with high magnetic flux density and low iron loss. A method of manufacturing electrical steel sheet has been developed.

The result of this study is an advanced technology than Korean Patent Publication No. 1998-034055, which omits the decarburization process due to the combined inhibitory power of AlN, which is an existing grain growth inhibitor, and AlN, which is additionally formed by nitrogen ions introduced into the steel sheet in the subsequent process In the component system containing carbon steel, slab can be heated up to 1250 ℃ and cold rolled once with a thickness of 0.27mm or less can produce oriented electrical steel sheet with low iron loss and high magnetic flux density.

Below. The reason for component limitation of this invention is demonstrated in more detail.

The Si is an element that plays a role of lowering iron core loss, that is, iron loss by increasing the resistivity of the material as the basic composition of the electrical steel sheet, when the content is less than 2.0wt%, the resistivity decreases and the iron loss property is deteriorated, and more than 4.0wt%. When excessively contained, the brittleness of the steel becomes large, the cold rolling property becomes extremely poor, and at the same time, the secondary recrystallization becomes unstable, so the content of Si is preferably set to 2.0 to 4.0 wt%.

The Mn has the effect of reducing the iron loss by increasing the specific resistance similar to Si and to reduce the iron loss when added to less than 0.08wt% as an element to facilitate the solid solution of AlN by forming austenite when reheating the slab It is weak and lacks austenite formation, which does not help sufficient employment of AlN.

However, when 1.0 wt% or more is added, the strength of the steel increases, which causes the plate shape to become uneven during cold rolling and prevents secondary recrystallization by causing phase transformation during high temperature annealing.

Therefore, the content of Mn is preferably limited to 0.08 to 1.0wt%.

The Al component is an important element to form the precipitate of AlN together with N to secure the grain growth inhibitory force, and the acid content of Al which can form AlN by reacting with N is important rather than the total Al content.

If the acid-soluble Al content is less than 0.006wt%, the secondary recrystallization becomes unstable because it does not form enough precipitates to suppress the growth of the grains, and when added more than 0.040wt%, the amount of precipitates is too high, 2 As a result of the strong inhibition of the growth of all primary recrystallized particles, including Goss grains, the core of the secondary recrystallization, no secondary recrystallization is formed.

Therefore, the content of the acid-soluble Al is preferably set to 0.006 ~ 0.040wt%.

N is an essential component in secondary recrystallization because it inhibits the growth of primary recrystallized grains by reacting with acid-soluble Al to form AlN precipitates.

When N is added at 0.012wt% or more in the steelmaking step, coarse AlN is formed in the slab, and the effect of inhibiting crystal growth is reduced, and a blister occurs on the surface of the steel sheet, thereby deteriorating the surface characteristics of the product.

On the other hand, when less than 0.006wt% is added in the steelmaking step, it is impossible to form sufficient AlN as the primary crystal growth inhibitor, so that the primary recrystallized microstructure grows coarsely and the secondary recrystallization becomes unstable.

Therefore, the content of the acid soluble N is preferably set to 0.012 to 0.006wt%.

Cu is an austenite forming element and contributes to the solid solution and fine precipitation of AlN to stabilize the secondary recrystallization. In addition, Cu combines with S to form a precipitate called Cu ₂ S. In the component system of the present invention, Cu ₂ S formation not only prevents central segregation of S, but also forms Cu ₂ S rapidly at a temperature lower than the temperature at which MnS is formed. Since it is effective in suppressing the formation of MnS having a high solid solution temperature, it is preferable to add a certain amount.

If the Cu is added more than 0.5wt% Cu not only adversely affect the insulating film formation by the oxide produced during the decarbonization annealing, but also the iron loss increases due to the coarse size of the secondary recrystallized grains is limited to less than 0.5wt% It is desirable to.

The S is a component that acts as an inhibitor by forming a precipitate in the form of emulsion with Cu or Mn, but is managed as low as possible because the sulfide is not used as an inhibitor in the present component system.

Particularly, in the case of MnS, since the solid solution temperature is very high, in order to prevent the precipitate from being formed in the steelmaking step, it is preferable that the S is contained in an amount of 0.007 wt% or less.

Hereinafter, the reason why the content of C is set to 0.015 wt% or less will be described.

The C is a component that promotes austenite transformation of steel when added to 0.02wt% to refine the hot-rolled structure during hot rolling and promotes the solubility and precipitation of AlN to increase the effect as a grain growth inhibitor. If it remains, it forms carbide and causes magnetic deterioration. Therefore, it was necessary to manage it to less than 0.0030wt% in the final product through the decarburization process.

However, the present inventors investigated the minimum carbon steel content condition that does not require the decarburization process through experiments.

Other components were changed without changing the content of carbon steel as shown in Table 1, vacuum melted, made a slab and heated up to 1200 ℃, then hot rolled and then subjected to hot-rolled sheet annealing, once cold rolled to 0.23mm Then, an additional decarburization step was omitted and annealing was performed in a gas atmosphere containing a temperature of 850 ° C. and nitrogen ions.

Then, MgO was applied to the annealing plate and the final high temperature annealing was performed to form secondary recrystallization.

After hot annealing, the carbon content and magnetic properties remaining in the steel sheet were measured, and the results are shown in Table 1 below.

Changes in Residual Carbon Content (wt%) by Manufacturing Process Magnetic flux density (Tesla) Iron hand (W17 / 50) Steel carbon content Hot rolled sheet Hot Rolled Annealing Final Annealed Plate 0.0050 0.0030 0.0020 0.0010 1.915 0.913 0.0090 0.0055 0.0033 0.0014 1.928 0.932 0.0150 0.0084 0.0051 0.0022 1.917 0.891 0.0190 0.0125 0.0087 0.0036 1.911 1.083

As shown in Table 1, when the carbon steel content was 0.019wt%, the residual carbon content did not decrease below 0.0030wt% even after hot rolling, hot rolling annealing and hot annealing after slab heating.

For this reason, the secondary recrystallization was good and the magnetic flux density was good, but the iron loss was found to be somewhat inferior.

However, when the carbon content is less than 0.015wt%, after the final high temperature annealing, the residual carbon content is reduced to less than 0.0030wt%, and the magnetic flux density and iron loss characteristics are also excellent.

Therefore, in order to successfully carry out the object of the present invention, the content of carbon added in the steelmaking step is preferably limited to 0.015wt% or less.

The steel component of the present invention is as described above, and the other components are composed of Fe and inevitable trace impurities. The silicon steel material as described above can be used as the material of the present invention even when manufactured using any conventional dissolution method, ingot method, performance method, or the like.

Hereinafter, manufacturing conditions are demonstrated.

The steel slab formed as described above is heated to a temperature of 1100 ~ 1250 ℃.

When the steel slab is heated to a temperature above 1250 ° C., the AlN precipitate present in the slab may be added to the steelmaking step and reprecipitated as a fine precipitate having grain growth inhibition, but the grains of the slab grow very coarsely. do. When the slab is hot rolled, coarse crystal grains form a microstructure elongated in the rolling direction.

The presence of many of these stretched grains in the hot rolled sheet prevents the growth of Goss grains, making secondary recrystallization very difficult.

Therefore, the grains of the slab are heated to a temperature of 1250 ° C. or less where they do not grow coarsely, and then hot rolled. Then, the hot-deformed grains are recrystallized again in the subsequent hot-rolled sheet annealing process to make microstructures without stretch grains and at the same time, The heat treatment is performed so that the same solid solution and re-precipitation of AlN precipitate as the heating step occurs.

However, when the slab heating temperature is less than 1100 ℃, it takes a lot of time for the AlN solid solution and the strain stress during hot rolling is very large, thereby increasing the load of the hot rolling process.

Therefore, the heating temperature of the steel slab is preferably set to 1100 ~ 1250 ℃.

Then, hot rolling is hot rolled to a thickness of 1.5 ~ 3.0mm in consideration of the optimal cold rolling rate, and then wound at a temperature of 600 ℃ or less.

The hot-rolled sheet annealing recrystallizes the crystal grains deformed by hot rolling to make a uniform microstructure without stretching grains, and also forms a fine precipitate by solid solution and reprecipitation of AlN precipitates in the same manner as the slab heating step. By controlling the growth of the former primary crystal structure helps to form a microstructure favorable to the secondary recrystallization. In order to perform this role, heat treatment is required for a short time in the temperature range of 900 ~ 1200 ℃.

At temperatures below 900 ° C, the precipitation tends to be coarse because there is more precipitation than solid solution. In this case, since the grain growth inhibitory power is lowered, coarse precipitates may be dissolved by heating to a temperature of 900 ° C. or higher, and the precipitates may have a uniform size distribution.

However, when heated to a temperature of 1200 ° C or more, the grains grow coarse, and most of the small precipitates are dissolved and the size distribution of the overall precipitates is increased as the fine particles are reprecipitated in the subsequent cooling process. Such precipitate distribution causes secondary recrystallization to be non-uniform, making it difficult to secure stable magnetic properties.

Therefore, the temperature range of the hot rolled sheet annealing is preferably 900 ~ 1200 ℃.

After the hot-rolled sheet annealing as described above, after the pickling, cold rolling is performed to a thickness of 0.27 mm or less at a rolling rate of 90% or more.

In addition to the purpose of making the thickness of the final product, cold rolling has only the ideal Goss grains in the steel sheet, and the ideal Goss grains are secondary recrystallized at high temperature annealing to secure excellent magnetic properties.

Therefore, in the ultra low carbon component system such as the component system of the present invention, the cold crystallinity must be 90% or more so that ideal crystals exist.

If the cold rolling rate is less than 90%, pseudo-gos grains deviating from the ideal (110) [001] orientation are present and the magnetic properties are degraded by secondary recrystallization at high temperature annealing.

In addition, it is important to secure excellent magnetic flux density in order to lower the core loss, but it is most effective to lower the thickness of the product. Therefore, in order to obtain magnetic properties of low iron loss and high magnetic flux density, cold rolling should be over 90% and cold rolling should be less than 0.27mm thick.

After the cold rolling as described above, the decarburization process is omitted, and heat treatment is performed for a short time in a gas atmosphere containing nitrogen ions in order to secure additional crystal growth inhibition.

This is a heat treatment step necessary to effectively apply the annealing separator MgO prior to high temperature annealing, and can increase productivity because the decarburization step, which is a feature of the present invention, can be omitted.

In addition, there is no need for a humidification apparatus necessary for the decarburization process, and the amount of the surface oxide layer generated in the decarburization reaction can be reduced.

In many cases of the surface oxide layer, formation of the surface of the inorganic oxide layer after the final high temperature annealing is very likely to cause surface defects.

Thus, elimination of the decarburization process can significantly reduce the occurrence of surface defects upon high temperature annealing as well as the effect of increased productivity.

On the other hand, by performing annealing for a short time in a gas atmosphere containing nitrogen ions to secure an additional crystal growth inhibitor, which is AlN grains by suppressing coarse grain formation by heating the electrical steel slab of the component system of the present invention to 1100 ~ 1250 ℃ This is to reinforce the weakened inhibitory effect of the growth inhibitory agent.

In other words, by annealing in a gas atmosphere containing nitrogen ions, nitrogen ions are introduced into the steel sheet to form additional AlN precipitates. It is to form a re-crystallization.

In order to effectively introduce nitrogen ions into the steel sheet, heat treatment should be performed at a temperature range of 750 ~ 950 ℃, and to contain nitrogen ions, cracked ammonia gas is used.

When the annealing temperature is less than 750 ° C, nitrides such as Si ₃ N ₄ are formed by the introduced nitrogen ions, and the nitrides are sensitive to temperature and easily decomposed, so that they do not have grain growth inhibition.

On the other hand, when the annealing temperature is 950 ° C or higher, even when nitrogen ions are introduced into the steel sheet to form AlN precipitates, the size of the primary recrystallized grain becomes very coarse and the secondary recrystallization becomes unstable by forming a nonuniform microstructure.

On the other hand, the total amount of nitrogen ions introduced into the steel sheet from the atmosphere gas containing nitrogen ions is preferably set to 0.0010 to 0.0300 wt%.

When the nitrogen ion is introduced into the steel sheet at 0.0010wt% or less, the precipitation amount of the additionally precipitated AlN is very small so that the growth of crystal grains cannot be strongly inhibited. When the nitrogen ion is introduced into the steel sheet at 0.0300wt% or more, additional AlN precipitates are generated. Since even goth crystal grains are inhibited from growth and secondary recrystallization does not occur, an appropriate amount of nitrogen ion introduced into the steel sheet is preferably 0.0010 to 0.0300 wt%.

The steel sheet annealed in a gas atmosphere containing nitrogen ions is coated with MgO, an annealing separator, and then heated up to a temperature range of 1150 to 1250 ° C. in a hydrophobic atmosphere containing 5 to 90% nitrogen, followed by 100% hydrogen. Final high temperature annealing is performed for 20 hours or more in a gas atmosphere.

The temperature increase rate at the time of high temperature annealing is about 10-20 degreeC / hr.

When nitrogen is added to the high temperature annealing atmosphere gas, AlN precipitates are not easily decomposed in the steel sheet, so that the suppressive force can be maintained at a relatively high temperature, thereby increasing the secondary recrystallization temperature to obtain excellent magnetic properties.

If the nitrogen gas is 5% or less during the high temperature annealing, there is almost no effect of suppressing the decomposition of AlN precipitates. If the nitrogen gas is contained more than 90%, the inorganic surface oxide layer formation becomes unstable and the surface quality of the electrical steel sheet is greatly reduced.

In addition, decomposition of AlN precipitates is strongly suppressed, so that secondary recrystallization does not occur even at a high temperature of 1200 ° C.

As described above, the carbon content in the steelmaking step is reduced to the level where no decarburization process is required, and the cold rolling rate is 90% or more and the thickness of 0.27mm or less is once cold-rolled, and the AlN and cold precipitated by hot rolling and annealing are applied. By annealing the rolled steel sheet in a gas atmosphere containing nitrogen ions, additional AlN precipitates are formed to strongly inhibit the growth of grains other than the Goss orientation, resulting in highly oriented electrical steel sheets with excellent magnetic properties with high magnetic flux density and low iron loss. It can manufacture.

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

(Example 1)

In the steelmaking step, carbon is added below 0.015wt%, Si: 3.12wt%, Mn: 0.45wt%, acid soluble Al: 0.015wt%, N: 0.011wt%, S: 0.005wt%, Cu: 0.47wt%, A slab consisting of the balance Fe and other unavoidable impurities was produced.

The slab was reheated at 1050, 1100, 1200, 1250, 1280 ° C. for 3.5 hours and hot rolled to make a 3.0 mm thick hot rolled sheet.

The hot rolled sheet was annealed in a nitrogen atmosphere at 1100 ° C. for a short time, then quenched and pickled.

Cold rolling is performed once by cold rolling to 0.27mm, followed by annealing using a gas atmosphere containing nitrogen ions at a temperature of 800 ° C, and 25% N ₂ +75 up to 1200 ° C after MgO is applied. After heating up in a gas atmosphere of% H _2, the mixture was changed to 100% hydrogen atmosphere and annealed for 20 hours.

Changes in the stretch ratio and magnetic properties of the hot rolled sheet according to the slab heating temperature are shown in Table 2 below.

Reheat slab Hot Rolled Sheet Elongation B10 (Tesla) Iron loss (W17 / 50) 1050 ℃ 10% 1.877 1.252 Comparative Material 1 1100 ℃ 15% 1.912 0.955 Invention 1 1200 ℃ 20% 1.932 0.983 Invention 2 1250 ℃ 40% 1.925 0.975 Invention 3 1300 ℃ 80% 1.830 1.563 Comparative Material 2

As shown in Table 2, when the slab heating temperature is higher than 1250 ° C. (Comparative Material 2), the ratio of stretched grains to the microstructure after hot rolling is greatly increased to 80%. Even cold rolling of% does not recrystallize and thus adversely affects secondary recrystallization.

On the other hand, when the slab heating temperature is 1050 ° C (Comparative Material 1), although the ratio of elongated grains of the hot rolled sheet is low, the employment of AlN, a grain growth inhibitor, is insufficient, resulting in non-uniform precipitation distribution. It can be seen that the magnetic properties are somewhat inferior to that of the inventive material (1-3) due to unstable formation.

(Example 2)

C: 0.012wt%, Si: 3.15wt%, Mn: 0.18wt%, Acid Soluble Al: 0.025wt% N: 0.010wt%, S: 0.004wt%, Cu: 0.48wt%, Remnant Fe and Other Unavoidable Impurities The slab was made and reheated at a temperature of 1220 ° C. for 4.0 hours, followed by hot rolling to make hot rolled plates having different thicknesses.

Then, the hot rolled sheet was annealed at a temperature of 1050 ° C. for a short time and then quenched.

The annealed plate was pickled and cold rolled at 0.35 ~ 0.18mm by changing the cold rolling rate.

The cold rolled steel sheet was annealed at a temperature of 900 ° C. using a gas atmosphere containing nitrogen ions so that a certain amount of nitrogen ions were introduced into the steel sheet to further precipitate new AlN.

In addition, the high temperature annealing was carried out in a water quenching atmosphere containing 50% N ₂ , and the change in magnetic properties according to the cold rolling rate and the amount of nitrogen ions was simultaneously investigated. The results are shown in Table 3 below.

Cold rolling rate Product thickness (mm) Nitrogen ion addition amount (ppm) Magnetic flux density (Tesla) Iron loss (W17 / 50) 85% 0.35 150 1.851 1.362 Comparative Material 3 87% 0.30 100 1.895 1.205 Comparative Material 4 90% 0.30 80 1.905 1.107 Comparative Material 5 91% 0.27 200 1.922 0.976 Invention 4 91% 0.23 150 1.941 0.944 Invention 5 91% 0.20 5 1.885 1.224 Comparative Material 6 92% 0.20 130 1.938 0.939 Invention 6 93% 0.18 250 1.946 0.921 Invention 7 93% 0.18 380 1.782 1.506 Comparative Material7

As shown in Table 3, when the cold rolling rate is less than 90%, Goss grains having similar orientations other than the ideal Goss grains are also subjected to secondary recrystallization, thereby obtaining high magnetic flux density characteristics of 1.90 Tesla or more. Even if a cold rolling ratio of more than 90% is secured, when the product thickness is 0.30mm, the iron loss improvement effect due to the thickness reduction is insignificant, and thus low iron loss of less than 1.0 W / kg cannot be obtained.

On the other hand, when the cold rolled sheet was annealed in a gas atmosphere containing nitrogen ions and the amount of nitrogen ion added was 0.0010 to 0.0300 wt%, the magnetic flux density of 1.90 Tesla or more was secured, but when the nitrogen ion was added to less than 0.0010 wt%, It can be seen that the density is somewhat inferior. This was introduced into the nitrogen-ion steel sheet in the atmosphere gas and precipitated additional AlN, which strongly inhibited the growth of grains like AlN precipitates that were previously precipitated by hot rolling and hot-rolled sheet annealing, thus making the ideal Goss grain more stable. By recrystallization, the magnetic flux density is excellent.

However, when the amount of nitrogen ion added is more than 0.0300wt%, the precipitated amount of additional AlN is so large that it inhibits the growth of even goth grains, so that secondary recrystallization does not occur completely. Can be.

As described above, the present invention not only improves productivity by significantly lowering the carbon content in the steelmaking step and thus eliminating the decarburization process after cold rolling, but also the cold rolling rate of 90% or more and the final thickness of 0.27mm or less. By reinforcing the grain restraint by cold rolling and nitriding, there is an effect that can provide a method for manufacturing a grain-oriented steel sheet which can further improve iron loss and magnetic flux density.

Claims (1)

Si: 2.0 ~ 4.0wt%, Acid Soluble Al: 0.006 ~ 0.040wt%, N: 0.006 ~ 0.012wt%, S: 0.007wt% or less, Cu: 0.5wt% or less, Mn: 0.08 ~ 1.0wt% , C: 0.015wt% or less, steel slab composed of remainder Fe and other unavoidable impurities, reheated to 1100 ~ 1250 ℃ and hot rolled, followed by short time hot roll annealing at a temperature of 900 ~ 1200 ℃, followed by cold rolling After cold rolling of the final product to 0.27mm or less by one-time cold-rolling method of more than 90%, decarburization process is omitted and using a gas atmosphere containing nitrogen ions at a temperature of 750 ~ 950 ℃, 0.0010 ~ 0.0300 wt Nitride annealing in which% nitrogen ions are introduced into the steel sheet is applied, and it is wound up by applying a fusion inhibitor containing MgO as a main component, and then in a water introduction atmosphere containing 5 to 90% nitrogen to a temperature range of 1150 to 1250 ° C. A high temperature annealing is performed in which the temperature is elevated and cracked and cooled for at least 10 hours in a 100% water atmosphere. Method for producing a grain-oriented electrical steel sheet having a low iron loss and high magnetic flux density, characterized in that