KR101899453B1 - Method for manufacturing grain oriented electrical steel sheet - Google Patents

Abstract

A method for producing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises: 3.2 to 4.0% Si, 0.03 to 0.09% C, 0.015 to 0.040% Al, 0.04 to 0.15% Mn, 0.001 to 0.005%, S: 0.01% or less (excluding 0%), and the balance comprising Fe and other unavoidable impurities; Hot rolling the slab to produce a hot rolled sheet; Hot-rolled sheet annealing for 30 to 300 seconds at a cracking temperature of 900 to 980 캜; A step of cold-rolling the hot-rolled sheet after annealing of the hot-rolled sheet to produce a cold-rolled sheet; A first recrystallization annealing of the cold rolled sheet; And secondary recrystallization annealing the cold rolled sheet after the primary recrystallization annealing has been completed.
[Formula 1]
[Mn] x [S]? 0.0004
(In Expression 1, [Mn] and [S] are the contents (% by weight) of Mn and S in the slab, respectively.)

Description

[0001] METHOD FOR MANUFACTURING GRAIN ORIENTED ELECTRICAL STEEL SHEET [0002]

To a method for producing a directional electrical steel sheet. More specifically, the present invention relates to a method of producing a grain-oriented electrical steel sheet capable of achieving both productivity and magnetic properties at the same time.

Directional electrical steel sheets are used as core materials for static devices such as transformers, motors, generators and other electronic devices. Since the final product of grain-oriented electrical steel sheet has an aggregate texture (aka goss texture) in which the grain orientation is oriented in the {110} < 001 > direction and has excellent magnetic properties in the rolling direction, the transformer, the motor, It can be used as an iron core material for electronic devices, etc. In order to reduce energy loss, iron loss is required to be low, and magnetic flux density is required for miniaturization of power generation equipment.

The iron loss of a directional electric steel sheet is divided into history hands and eddy current hands. In order to reduce double eddy current hands, it is necessary to reduce the plate thickness or increase the specific resistivity. One of the concrete methods to increase specific resistivity is to produce high quality oriented electrical steel sheet products with high Si content.

In general, as the Si content of the oriented electrical steel sheet is increased, the specific resistivity of the product is increased to lower the iron loss, so that it is possible to produce a high-grade product, but productivity problems such as a reduction in the real- .

In particular, the directional electric steel sheet of the slab low-temperature heating method requires a high cold rolling reduction ratio compared with the high-temperature heating method for securing the magnetic properties. For this purpose, the thickness of the hot-rolled steel sheet must be increased to increase the frequency of fracture during cold rolling. Furthermore, in order to produce a high Si-containing directional electric steel sheet product of the low-temperature heating method in order to increase the brittleness of the high-Si-containing material and to improve the cold rolling property, a technique for reducing the occurrence of fracture during cold rolling is further required. For this purpose, several methods have been tried to improve the cold rolling property of high Si containing materials and to improve industrial productivity.

One of the methods for improving the cold rolling property to solve this problem is to improve the quality of the edge of the rolled edge portion and to reduce the occurrence of edge crack by processing the processed surface after the rolling edge trim. A method of performing trimming at a high temperature, and a method of reducing edge unevenness in hot rolling.

In addition, since a large number of ruptures occur during rolled winding at the time of starting the two-pass rolling, a method of optimizing the one-pass cold rolling rate for securing ductility at the start of two-pass rolling has been proposed. However, it is not a way to improve the original characteristics of the material, so there is a limit to its improvement. Even if the conventional methods are applied, it is not possible to fundamentally solve the fracture due to the occurrence of the edge crack due to the inherent characteristics of the high-Si steel sheet.

The microstructure of the grain-oriented electrical steel sheet prior to cold rolling has a pearlite bainite ferrite phase mixed therein. After the annealing of the hot-rolled steel sheet, decarburization of the surface, particularly, the edge portion is locally generated, resulting in a ferrite single phase in which no transformation phase such as pearlite or bainite or martensite is present, and grain growth occurs depending on the annealing temperature.

In the hot-rolled sheet annealing, in order to raise the plate temperature to a high temperature in the heating zone, the edge portions where the heating is concentrated during the temperature increase are all ferrite-like due to local decarburization, and grain growth occurs vigorously. In general, when the structure is fine, crack initiation resistance is excellent. In the presence of coarseness at the edge portion, the frequency of occurrence of edge crack locally increases, the crack length formed during rolling increases, It is likely to continue.

On the other hand, if the precipitates are fine and non-uniformly present before the cold rolling, crystal grains are unevenly distributed in the subsequent steps, and eventually incomplete secondary recrystallization or non-uniform secondary recrystallization are made to impair product characteristics. Therefore, the magnetization is secured by controlling the heat treatment temperature in order to maximally employ fine precipitates causing unevenness and to precipitate coarse precipitates.

That is, in order to secure the magnetic properties of the electrical steel sheet product, it is essential to control the fine precipitates through annealing at a sufficiently high temperature. On the contrary, in order to reduce the edge cracking which causes plate breakage during cold rolling and to secure productivity, the annealing temperature of the hot-rolled sheet must be lowered.

In one embodiment of the present invention, a method of manufacturing a directional electrical steel sheet is provided. More specifically, the present invention is to provide a method for producing a grain-oriented electrical steel sheet capable of simultaneously achieving cold rolling productivity and magnetic property improvement.

A method for producing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises: 3.2 to 4.0% Si, 0.03 to 0.09% C, 0.015 to 0.040% Al, 0.04 to 0.15% Mn, 0.001 to 0.005%, S: 0.01% or less (excluding 0%), and the balance comprising Fe and other unavoidable impurities; Hot rolling the slab to produce a hot rolled sheet; Hot-rolled sheet annealing for 30 to 300 seconds at a cracking temperature of 900 to 980 캜; A step of cold-rolling the hot-rolled sheet after annealing of the hot-rolled sheet to produce a cold-rolled sheet; A first recrystallization annealing of the cold rolled sheet; And secondary recrystallization annealing the cold rolled sheet after the primary recrystallization annealing has been completed.

[Formula 1]

[Mn] x [S]? 0.0004

(In Expression 1, [Mn] and [S] are the contents (% by weight) of Mn and S in the slab, respectively.)

The slab may further include 0.03 to 0.15% by weight, 0.01 to 0.05% by weight of P, and 0.02 to 0.15% by weight of Cr, respectively, of at least one of Sb and Sn.

The slab may further contain 0.01 to 0.2% by weight of Cu and 0.01 to 0.05% by weight of Mo.

After the hot-rolled sheet annealing step, it can be cooled from a starting temperature of 700 to 850 DEG C to 300 DEG C at a cooling rate of 10 DEG C / sec to 300 DEG C / sec.

After the step of annealing the hot-rolled sheet, the elongation of the hot-rolled sheet may be 20% or more.

In the step of heating the slab, it may be heated to 1050 to 1200 캜.

The grain-oriented electrical steel sheet according to an embodiment of the present invention can precisely control the content of Mn and S in the slab and the temperature condition at the time of annealing of the hot-rolled steel sheet, so that the productivity is excellent and the magnetic and productivity Is excellent.

Fig. 1 is an RD sectional photograph of an edge portion after the hot-rolled sheet annealing in Inventive Material 1. Fig.
Fig. 2 is an RD sectional photograph of the edge portion after the hot-rolled sheet annealing in the comparative member 4. Fig.

The terms first, second and third, etc. are used to describe various portions, components, regions, layers and / or sections, but are not limited thereto. These terms are only used to distinguish any moiety, element, region, layer or section from another moiety, moiety, region, layer or section. Thus, a first portion, component, region, layer or section described below may be referred to as a second portion, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms as used herein include plural forms as long as the phrases do not expressly express the opposite meaning thereto. Means that a particular feature, region, integer, step, operation, element and / or component is specified and that the presence or absence of other features, regions, integers, steps, operations, elements, and / It does not exclude addition.

When referring to a portion as being "on" or "on" another portion, it may be directly on or over another portion, or may involve another portion therebetween. In contrast, when referring to a part being "directly above" another part, no other part is interposed therebetween.

Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Commonly used predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or very formal meanings unless defined otherwise.

Unless otherwise stated,% means% by weight, and 1 ppm is 0.0001% by weight.

In an embodiment of the present invention, the term further includes an additional element, which means that an additional amount of the additional element is substituted for the remaining iron (Fe).

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

A method for producing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises: 3.2 to 4.0% Si, 0.03 to 0.09% C, 0.015 to 0.040% Al, 0.04 to 0.15% Mn, 0.001 to 0.005%, S: 0.01% or less (excluding 0%), and the balance comprising Fe and other unavoidable impurities; Hot rolling the slab to produce a hot rolled sheet; Hot-rolled sheet annealing for 30 to 300 seconds at a cracking temperature of 900 to 980 캜; A step of cold-rolling the hot-rolled sheet after annealing of the hot-rolled sheet to produce a cold-rolled sheet; A first recrystallization annealing of the cold rolled sheet; And secondary recrystallization annealing the cold rolled sheet after the primary recrystallization annealing has been completed.

Hereinafter, each step will be described in detail.

First, the slab is heated.

The slab is composed of 3.2 to 4.0% of Si, 0.03 to 0.09% of C, 0.015 to 0.040% of Al, 0.04 to 0.15% of Mn, 0.001 to 0.005% of N, 0.01% And the remainder comprises Fe and other unavoidable impurities.

Hereinafter, each component of the slab will be described.

Si: 3.2 to 4.0 wt%

Silicon (Si) plays a role in lowering the core loss, that is, the iron loss, by increasing the resistivity of the oriented electrical steel sheet material. When the Si content is too small, the resistivity decreases and the effect of lowering the iron loss is deteriorated. In the case of excessive content, the brittleness of the steel increases and the toughness decreases, so that rolling is difficult due to plate breakage during the rolling process. And falls below the plate temperature required for pass aging during cold rolling, and the formation of secondary recrystallization becomes unstable. In one embodiment of the present invention, the content of Mn and S in the slab and the temperature condition at the time of annealing the hot-rolled steel sheet are precisely controlled, so that even if the Si content is relatively large, the productivity is excellent.

C: 0.03 to 0.09 wt%

Carbon (C) is an element which induces the formation of austenite phase. As the C content increases, ferrite-austenite phase transformation is activated during the hot rolling process, and the elongated hot rolled steel strip structure formed during the hot rolling process is increased, The ferrite grain growth is suppressed during the annealing process. In addition, as the C content increases, the tensile strength of the hot rolled steel strip structure is increased, which is higher than that of the ferrite structure. The initial grain size of the annealed hot rolled steel sheet, . This is because the effect of the pass aging during cold rolling becomes large due to the residual C existing in the steel sheet after the annealing of the hot-rolled sheet, thereby increasing the goss fraction in the primary recrystallized grains. Therefore, the higher the C content, the longer the decarburization time during decarburization and the deterioration of productivity, and if the decarburization at the initial stage of heating is insufficient, the primary recrystallization grains become uneven and the secondary recrystallization becomes unstable . Thus limiting the carbon content in the slab to the aforementioned range. On the other hand, the oriented electrical steel sheet which is decarburized in the course of the primary recrystallization annealing and the like during the production of the grain-oriented electrical steel sheet may contain 0.005 wt% or less of carbon.

Al: 0.015 to 0.040 wt%

Aluminum (Al) binds with N and precipitates into AlN. However, N and AlN type nitrides, which are fine precipitates (Al, Si, Mn), are formed in the annealing for decarburization and nitriding at the same time. More than a certain amount of solid solution Al is needed. If the content is too small, the number and the volume fraction of the precipitates to be formed are low, so that the effect of inhibiting the growth of grain growth is not sufficient. If the content is too high, the precipitates grow coarser and the effect of inhibiting grain growth is deteriorated. Therefore, the content of Al can be adjusted to the above-mentioned range.

Mn: 0.04 to 0.15 wt%

Manganese (Mn) has the same effect of decreasing the eddy current loss by increasing the resistivity as Si, and not only has the effect of reducing iron loss, but also reacts with S present in the steel to form Mn compound or react with Al and nitrogen ions (Al, Si, Mn) N type nitride to form a grain growth inhibitor. If Mn is too small, fine MnS may be unevenly precipitated in the hot-rolled steel and the magnetic properties may be lowered. If the content thereof is too large, the austenite phase transformation ratio increases during the secondary recrystallization annealing, so that the goss texture is seriously damaged and the magnetic properties can be abruptly increased. Therefore, the content of Mn can be adjusted to the above-mentioned range.

N: 0.001 to 0.005 wt%

Nitrogen (N) reacts with Al or the like to form AlN micro precipitates, inhibiting grain boundary migration to inhibit grain boundary growth, and fine grain size. When these fine AlN are appropriately distributed, as described above, it is possible to appropriately fine-structure the structure after cold rolling to ensure proper primary recrystallization grain size. If the content is excessive, however, the primary recrystallized grain becomes excessively fine , And as a result, the driving force causing crystal grain growth during the secondary recrystallization increases due to the fine crystal grains, so that the crystal grains having a grain orientation other than goth can grow, which is not preferable. If N is contained too much, the amount of fine precipitates of AlN precipitated during the hot rolling process is increased to cause unevenness, and further severe annealing of the hot-rolled sheet is required. Therefore, in this patent, N is set to 0.005 wt% or less. When a nitriding process for increasing the nitrogen content is performed between the cold rolling and the secondary recrystallization annealing, it is sufficient that N of the slab is contained in the above-mentioned range.

S: not more than 0.010% by weight

Sulfur (S) is preferably an element which has a high solidus temperature at the time of hot rolling and is not contained in the segregated element as much as possible, but it is a kind of impurities contained in steel making. Also, since S forms MnS and affects the primary recrystallized grain size, the S content is preferably limited to 0.010% or less, more preferably 0.006% or less. The lower limit of S may be 0.001% by weight.

When the Mn and S contents are contained so as to satisfy the following formula 1, the MnS precipitates are fine and precipitate in an appropriate amount after the hot rolling, and then the precipitates are re-precipitated at a temperature in the range of 900 to 980 캜 for annealing the hot- . As a result, it is possible to reduce the occurrence of judgment during cold rolling of the high-Si-containing material, and the first and second recrystallized grain size uniformities are improved, and the magnetic properties are excellent and the product characteristics become uniform.

[Formula 1]

[Mn] x [S]? 0.0004

(In Expression 1, [Mn] and [S] are the contents (% by weight) of Mn and S in the slab, respectively.)

Sn, Sb, P

Phosphorus (P), tin (Sn), and antimony (Sb) can segregate in grain boundaries and can play an auxiliary role of suppressing grain growth and improve the primary recrystallization texture. It is an effective element because it has an effect of forming a magnetic flux density stably.

When P is added in an amount of 0.01 wt% or more, the effect is exhibited. When the addition amount exceeds 0.05 wt%, brittleness is strong and cold rolling becomes difficult.

Sn and Sb exhibit the effect at a content of 0.03% by weight or more. When the content exceeds 0.15% by weight, the grain boundary segregation effect is too strong, and it is difficult to secure a good surface by suppressing the formation of a surface oxide layer during decarburization annealing, The first order recrystallization is not uniform and the final magnetic property is not stable. From the viewpoint of mechanical properties, brittleness is increased due to excessive segregation at grain boundaries, which may lead to rolling property disadvantage. Accordingly, one or more of Sb and Sn may be contained individually or in a total amount of 0.03 to 0.15% by weight. That is, it may contain 0.03 to 0.15 wt% of Sb alone, 0.03 to 0.15 wt% of Sn alone, or 0.03 to 0.15 wt% of Sb and Sn, respectively.

Cr: 0.02 to 0.15 wt%

Chromium (Cr) is an element that promotes oxidation. Addition of an appropriate amount of chromium suppresses the formation of a dense oxide layer in the surface layer and helps to form a fine oxide layer in the depth direction. With addition of Sb and Sn, addition of a Cr content in an appropriate range makes it easier to form a primary recrystallization with excellent uniformity. By adding Cr, decarburization and sedimentation due to the increase of Sb and Sn contents are delayed to overcome the phenomenon that the primary recrystallized grains are uneven, thereby forming primary recrystallized grains having excellent uniformity and enhancing the magnetic properties. According to the content of Sb and Sn, when the Cr content is added in the above range, the internal oxide layer is formed deeper and the rate of decay and decarburization is increased. Therefore, the formation of dense and thin oxide layer due to the addition of Sb and Sn leads to the formation of 1 It is possible to overcome the difficulty in controlling the size and ensuring uniformity of the tea recrystallization. When the Cr content is less than the lower limit, the effect is insufficient, and when the Cr content is over the upper limit value, the oxide layer is excessively formed, the effect is decreased, and the cost is increased due to the addition of the expensive alloy.

Cu: 0.01 to 0.2 wt%

Copper (Cu) binds with S and precipitates as CuS. It mainly forms (Mn, Cu) S form by mixing with MnS, and plays a role of inhibiting grain growth. In addition, as in the case of Mo, Cu causes a large amount of Goss grains having a precise orientation to be formed in the structure of the hot-rolled surface portion, thereby reducing grain size after secondary recrystallization and reducing eddy current loss, The magnetic flux density is also increased because the Goss particles of the magnetic layer grows much. When Cu is added, if it is added too little, the effect is not sufficient. If the content is too large, precipitates grow to a great extent and the effect of suppressing grain growth is deteriorated.

Mo: 0.01 to 0.05 wt%

Molybdenum (Mo) is known to cause secondary recrystallization in grain-oriented electrical steel sheets, which is generated during hot rolling and remains on the surface of the specimen after cold rolling and primary recrystallization heat treatment, resulting in secondary recrystallization. When molybdenum (Mo) is added during the hot rolling of the oriented electrical steel sheet, grains having a precise bearing orientation are formed in the surface of the hot rolled steel sheet, and the grains remaining after the first recrystallization heat treatment are left much larger, . Therefore, after the secondary recrystallization, the crystal grain size decreases and the eddy current loss becomes small, so that the iron loss of the final product decreases, and the magnetic flux density also increases due to the large number of goss particles growing in the correct orientation.

In addition, Mo plays an important role in suppressing grain growth by segregating in grain boundaries as in Sn, and plays a role of controlling the secondary recrystallization so that it occurs at high temperature. Therefore, it plays a role of growing Goss particles of more accurate orientation Thereby increasing the magnetic flux density. Mo is a very effective grain growth inhibiting element because it has a relatively large size of the atom and a very high melting point of 2623 ° C, so that the diffusion rate in iron is low and the segregation effect can be maintained well to a high temperature.

When the content of Mo is too small, the effect of improving the magnetic properties is small, but the effect is not only small, but the effect of improving the degree of integration of the goss texture is low and the effect of compensating the grain growth inhibition by the particles existing in the matrix is small The effect of improving the magnetic properties is insufficient. On the other hand, when the content is too large, the crystal grain growth inhibiting ability is excessively increased and the crystal grain size of the primary recrystallized microstructure must be decreased in order to increase the grain growth driving force relatively. Therefore, the decarburization annealing must be performed at a low temperature, It is impossible to secure a good surface. Therefore, when Mo is further contained, it can be added in the above-mentioned range.

Ni: 0.03 to 0.1 wt%

Nickel (Ni) is an element that enhances the final magnetic flux density by complementing the saturation flux density which is caused by the decrease of magnetic anisotropy due to the upward of the Si content. Ni, like C, activates the austenite phase transformation of the austenite forming element in the heat treatment step after hot rolling and hot rolling as the austenite forming element, and has the effect of promoting the microstructure of the structure and particularly promoting the formation of the goss grain in the subsurface portion. It is possible to increase the Goss fraction in sizing and to improve the uniformity of the size of the primary recrystallized grains so as to increase the magnetic flux density of the final product and further to add Ni to lower the lower limit of the C content according to the Si content It plays a role. When the additive amount is less than the lower limit of the Ni addition amount, the effect is insufficient. When the additive amount exceeds the upper limit value, the addition effect is not large and the cost increase due to the addition of the expensive alloy is caused. Therefore, when Ni is further contained, it can be added in the above-mentioned range.

Ti: 0.005 wt% or less

Titanium (Ti) is a strong nitrite forming element. It becomes TiN in the preheating step and lowers the N content. It causes fine precipitation to make crystal grains uneven and makes secondary recrystallization unstable, so it is limited to 0.005 wt% or less.

The slab of this composition is heated. The slab may be heated at a temperature of 1200 ° C or less, more specifically, at a low temperature of 1150 ° C or less to partially refine the precipitate. If the heating temperature of the slab is increased, the manufacturing cost of the steel sheet is increased, and the heating furnace can be repaired by melting the surface of the slab and the lifetime of the heating furnace can be shortened. In addition, if the slab is heated to a temperature of 1050 to 1200 ° C, the columnar structure of the slab is prevented from being grown to a great extent, thereby preventing cracks from being generated in the width direction of the plate in the subsequent hot rolling step, .

Next, the slab is hot-rolled to produce a hot-rolled sheet. The hot rolling temperature is not limited, and in one embodiment hot rolling may be terminated at 950 ° C or lower. Thereafter, it is water-cooled and can be wound at 600 ° C or less. The hot-rolled steel sheet can be produced from hot-rolled steel sheets having a thickness of 2.0 to 3.5 mm by hot rolling.

In the hot-rolled steel sheet, hot-rolled steel sheet and steel sheet were stretched in a hot rolling direction to form non-uniformly, and coarse precipitates and carbides existing in the slab were introduced into the hot- . Such uneven and coarse microstructures, precipitates, and carbides deteriorate the rolling properties of the material during cold rolling, which is a subsequent process, and cause frequent plate breakage during rolling. Therefore, it is important that the hot rolled annealed material is annealed to have a uniform microstructure and fine and uniformly distributed precipitates.

Next, the hot-rolled sheet is subjected to hot-rolled sheet annealing. And can be annealed at a cracking temperature of 900 to 980 캜 for 30 to 300 seconds. The step of annealing the hot-rolled sheet may include a first heating step and a second heating step before reaching the cracking temperature.

In this case, the first heating step is a step of heating the hot-rolled sheet to 750 to 850 ° C, and the second heating step is a step of raising the hot-rolled sheet after the first heating step to the cracking temperature of the cracking step. Specifically, the first heating step is a step of raising the hot rolled sheet after the hot rolling step to 750 to 850 캜. The second heating step is a step of raising the hot rolled sheet after the first heating step, that is, the hot rolled sheet heated to 750 to 850 캜, to the cracking temperature in the cracking step. Rate of temperature rise (t ₁₎ of the first temperature raising step may be from 5 to 45 ℃ / sec. If the rate of temperature rise (t ₁ ) in the _first heating step is too fast, the edge crack occurrence number at the edges of the cold-rolled sheet may increase sharply. The rate of temperature rise (t ₂ ) in the _second heating step may be 1 to 6 ° C / sec. If the rate of temperature rise (t ₂ ) of the second heating step is too fast, the number of edge cracks at the edges of the cold-rolled sheet may increase sharply.

The cracking temperature may be 900 to 980 占 폚, and the annealing time, that is, the ashing time may be 30 to 300 seconds. The rolling property in the cold rolling process can be improved through the precisely controlled cracking temperature and annealing time, and the magnetic properties of the finally produced directional electric steel sheet are also improved.

After the hot-rolled sheet annealing step, it can be cooled from a starting temperature of 700 to 850 DEG C to 300 DEG C at a cooling rate of 10 DEG C / sec to 300 DEG C / sec. If the cooling rate is too low, the carbides precipitate and the primary recrystallization texture is disadvantageously adversely affected. If the cooling rate is too high, the plate shape may be distorted during the cooling process and stress may remain in the material. A very slight transformation phase such as a knight is left in a large amount, and the rolling characteristics may be dulled during cold rolling.

The hot-rolled sheet thus annealed in the hot-rolled sheet has a high elongation, so that the rolling property in the cold-rolling step is improved. The elongation at this time means the elongation rate obtained in the tensile test after the hot-rolled sheet is subjected to tensile specimen processing in accordance with JIS13B standard.

Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. Cold rolling is carried out by using a cold rolling method using a reverse rolling mill or a tandem rolling mill in a plurality of cold rolling processes including one cold rolling, a plurality of cold rolling or an intermediate annealing to produce cold-rolled steel sheets having a thickness of 0.15 mm to 0.35 mm can do. Further, warm rolling in which the temperature of the steel sheet is maintained at 100 캜 or higher during cold rolling can be performed. In addition, the final rolling reduction through cold rolling can be from 50 to 95%.

As described above in the embodiment of the present invention, since the hardness of the hot-rolled sheet after the annealing of the hot-rolled sheet is low and the work hardening index is low, the edge crack occurrence number formed at the end portion in the thickness direction of the cold- . In an embodiment of the present invention, an edge crack means a crack having a depth of 5 mm or more existing at an end portion (edge portion) in the thickness direction of the cold-rolled sheet after cold rolling. Specifically, edge cracks may occur at four or less per 50 cm in the longitudinal direction of the cold-rolled steel sheet.

Next, the cold-rolled cold-rolled sheet is subjected to primary recrystallization annealing. Primary recrystallization occurs in which the core of the goss grain is generated in the primary recrystallization annealing step. Decarburization and soaking of the steel sheet can be achieved during the primary recrystallization annealing process. The first recrystallization annealing can be performed in a mixed gas atmosphere of steam, hydrogen and ammonia for decarburization and soaking. It can be annealed at a temperature of 800 ° C to 900 ° C and a dew point temperature of 50 ° C to 70 ° C for decarburization. When the temperature exceeds 900 DEG C, the recrystallized grains grow to a great extent and the crystal growth driving force falls, so that stable secondary recrystallization is not formed. The annealing time is not a serious problem in achieving the effect of the present invention, but it is preferable to treat the annealing within 5 minutes in consideration of productivity.

In the formation of nitrides such as (Al, Si, Mn) N and AlN, which are precipitates, by introducing nitrogen ions into the steel sheet using ammonia gas for nitriding, after decarburization and recrystallization are finished, There is no problem in exerting the effects of the present invention in any of the methods of performing the steeping treatment at the same time so as to perform the treatment at the same time or performing the decarburization annealing after the steeping treatment is performed first.

Next, the cold-rolled sheet having undergone the primary recrystallization annealing is subjected to secondary recrystallization annealing. Secondary recrystallization annealing is performed to form a {110} < 001 > aggregate structure in which the {110} planes of the steel sheet are parallel to the rolling surface and the < 001 > direction is parallel to the rolling direction. At this time, after the annealing separator is applied to the cold-rolled sheet having undergone the primary recrystallization annealing, secondary recrystallization annealing can be performed. At this time, the annealing separator is not particularly limited, and an annealing separator containing MgO as a main component may be used.

The {110} < 001 > texture is formed by secondary recrystallization in the secondary recrystallization annealing step, insulating property is imparted by the formation of a glassy film by the reaction of MgO with the oxide layer on the surface formed through the primary recrystallization annealing heat treatment, Impurities that impair the characteristics are removed. In the second recrystallization annealing step, the nitride, which is a particle growth inhibitor, is protected by maintaining a mixed gas of nitrogen and hydrogen at the temperature rising period before the secondary recrystallization, so that the secondary recrystallization can be well developed. After the secondary recrystallization is completed Any method of using a 100% hydrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen has no problem in exerting the effect of the present invention, and the impurities are removed for a long time.

Thereafter, an insulating film may be formed on the surface of the grain-oriented electrical steel sheet or a magnetic domain refining treatment may be carried out, if necessary. In one embodiment of the present invention, the alloy component of the grain-oriented electrical steel sheet refers to a base steel sheet excluding a coating layer such as an insulating coating.

Hereinafter, the present invention will be described in more detail with reference to examples. However, these embodiments are only for illustrating the present invention, and the present invention is not limited thereto.

Example 1

The slabs consisting of the components in Table 1 and Table 2 and impurities inevitably incorporated with the remainder Fe were heated at 1180 占 폚 for 210 minutes and then hot-rolled to a thickness of 2.3 m.

The hot-rolled steel sheet was annealed at a temperature and time according to the conditions shown in Table 3 below, cooled to 760 ° C, quenched in water, and pickled. The annealed sheet of the hot-rolled sheet was processed to JIS-13B standard and subjected to a tensile test to measure elongation. The results are summarized in Table 3. When the elongation is 20% or more, it is indicated as excellent, and when it is less than 20%, it is indicated as poor. Fig. 1 is an RD sectional view of the edge portion after annealing the hot rolled steel sheet in Inventive Material 1, and Fig. 2 is an RD sectional photograph of the edge portion after annealing the hot rolled steel sheet in the comparative material 4. As shown in Figs. 1 and 2, it can be confirmed that crystal grains are uniformly generated when annealing is performed at an annealing temperature of a suitable hot-rolled sheet. On the other hand, the comparative material 4 can be confirmed that the crystal grains are generated unevenly.

The hot-rolled and annealed sheet was hot-rolled once to a thickness of 0.23 mm. The cold-rolled plate was maintained at a temperature of about 860 ° C in a humid atmosphere of hydrogen and a mixed gas of nitrogen and ammonia for 180 seconds to carry out primary recrystallization annealing including simultaneous decarburization and nitriding so that the carbon content was 50 ppm or less and the nitrogen content was 200 ppm Respectively.

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. The final annealing was carried out under a mixed atmosphere of 25 vol% nitrogen and 75 vol% hydrogen until 1200 deg. C, and after reaching 1200 deg. C, maintained in a 100 vol% hydrogen atmosphere for 10 hours or longer and then cooled.

Iron loss and magnetic flux density were measured using a single sheet measurement method. Iron loss from 50 Hz to 1.7 Tesla was measured, and the magnetic flux density (Tesla) induced under a magnetic field of 800 A / m was measured.

(weight%) C Si Mn S Al N Mn x S Inventory 1 0.063 3.43 0.1 0.004 0.03 0.004 0.0004 Inventory 2 0.064 3.46 0.075 0.004 0.03 0.004 0.0003 Inventory 3 0.065 3.46 0.075 0.004 0.03 0.004 0.0003 Invention 4 0.067 3.5 0.05 0.008 0.03 0.004 0.0004 Invention Article 5 0.063 3.43 0.1 0.004 0.03 0.004 0.0004 Inventions 6 0.068 3.48 0.05 0.004 0.03 0.004 0.0002 Invention 7 0.064 3.46 0.075 0.004 0.03 0.004 0.0003 Invention 8 0.065 3.43 0.1 0.004 0.03 0.004 0.0004 Invention 9 0.065 3.43 0.05 0.004 0.03 0.004 0.0002 Comparison 1 0.063 3.45 0.15 0.004 0.03 0.005 0.0006 Comparative material 2 0.067 3.49 0.1 0.008 0.03 0.005 0.0008 Comparative material 3 0.065 3.44 0.1 0.004 0.03 0.005 0.0004 Comparison 4 0.066 3.48 0.1 0.004 0.03 0.005 0.0004 Comparative material 5 0.064 3.47 0.1 0.004 0.03 0.004 0.0004 Comparative material 6 0.065 3.43 0.075 0.004 0.03 0.004 0.0003

(weight%) Sn Sb P Cr Cu Mo Inventory 1 0.06 0 0.02 0.05 0 0 Inventory 2 0.06 0 0.02 0.05 0 0 Inventory 3 0.06 0 0.02 0.05 0 0 Invention 4 0.06 0 0.02 0.05 0 0 Invention Article 5 0.06 0 0.02 0.05 0.05 0 Inventions 6 0.06 0 0.02 0.05 0.2 0 Invention 7 0.05 0.04 0.02 0.05 0 0 Invention 8 0.06 0.02 0.02 0.05 0 0 Invention 9 0.06 0 0.02 0.05 0.2 0.03 Comparison 1 0.06 0 0.02 0.05 0 0 Comparative material 2 0.06 0 0.02 0.05 0 0 Comparative material 3 0.06 0 0.02 0.05 0 0 Comparison 4 0.06 0 0.02 0.05 0 0 Comparative material 5 0.06 0 0.02 0.05 0 0 Comparative material 6 0.08 0.1 0.02 0.05 0 0

Annealing condition of hot-rolled sheet Young's modulus Magnetic property Remarks Annealing temperature (캜) Ashes Time (sec) B ₈ (T) _{W 15/50 (W / kg} ) Inventory 1 900 180 Great 1.933 0.766 - Inventory 2 980 180 Great 1.937 0.783 - Inventory 3 980 40 Great 1.939 0.747 - Invention 4 980 300 Great 1.937 0.777 - Invention Article 5 930 180 Great 1.94 0.787 - Inventions 6 950 180 Great 1.936 0.763 - Invention 7 950 180 Great 1.944 0.738 - Invention 8 980 180 Great 1.941 0.76 - Invention 9 980 180 Great 1.944 0.78 - Comparison 1 1000 180 Great 1.902 0.894 Magnetic irregularity Comparative material 2 950 180 Great 1.899 0.895 Magnetic irregularity Comparative material 3 880 180 Bad 1.903 0.879 Large number of edge cracks Comparison 4 1050 180 Bad 1.906 0.874 Large number of edge cracks Comparative material 5 980 20 Great 1.898 0.879 Magnetic irregularity Comparative material 6 1000 180 Bad 1.905 0.89 Magnetic irregularities / surface defects

As can be seen from Tables 1 to 3, when both of the annealing temperature and time of Equation 1 and the hot-rolled sheet of the present invention are satisfied, it is confirmed that the magnetic properties are excellent and the rolling characteristics are excellent. On the other hand, when the annealing temperature and time of Eq. 1 of the present invention and some of the annealing temperature and time are not satisfied, it can be confirmed that the magnetic properties deteriorate or the rolling characteristics deteriorate and a large number of edge cracks are formed.

Example 2

The slab consisting of the components in Table 4 and the balance of Fe and inevitably entrained impurities was heated at 1180 占 폚 for 210 minutes and then hot-rolled to a thickness of 2.3 m.

The hot-rolled steel sheet was annealed at a temperature and a time condition shown in Table 5 below and then cooled by air cooling to 300 deg. C at a cooling start temperature of 800 deg. C, and at 30 deg. C / sec by quenching in boiling water at 100 deg. The annealed sheets of the hot-rolled sheets were processed in accordance with JIS-13B standard and subjected to a tensile test to measure elongation. The results are summarized in Table 5. When the elongation is 20% or more, it is indicated as excellent, and when it is less than 20%, it is indicated as poor.

The hot-rolled and annealed sheet was cold-rolled to a thickness of 0.23 mm. The cold-rolled plate was maintained at a temperature of about 860 ° C in a humid atmosphere of hydrogen and a mixed gas of nitrogen and ammonia for 180 seconds to carry out primary recrystallization annealing including simultaneous decarburization and nitriding so that the carbon content was 50 ppm or less and the nitrogen content was 200 ppm Respectively.

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. The final annealing was carried out under a mixed atmosphere of 25 vol% nitrogen and 75 vol% hydrogen until 1200 deg. C, and after reaching 1200 deg. C, maintained in a 100 vol% hydrogen atmosphere for 10 hours or longer and then cooled.

(weight%) C Si Mn S Al N Sn P Inventions 10 0.063 3.43 0.1 0.004 0.03 0.004 0.06 0.02 Comparison 7 0.068 3.48 0.05 0.004 0.03 0.004 0.06 0.02

Annealing condition of hot-rolled sheet Young's modulus Magnetic property Remarks Annealing temperature (캜) Ashes Time (sec) Cooling start temperature
(° C) B ₈ (T) _{W 15/50 (W / kg} ) Inventions 10 950 180 800 Great 1.933 0.766 Comparison 7 1050 180 800 Bad 1.937 0.783 Large number of edge cracks

As shown in Tables 4 and 5, it can be confirmed that when both of the annealing temperature and time of Equation 1 and the hot-rolled sheet of the present invention are satisfied, the magnetic properties are excellent and the rolling characteristics are excellent. On the other hand, when the annealing temperature and time of Eq. 1 of the present invention and some of the annealing temperature and time are not satisfied, it can be confirmed that the magnetic properties deteriorate or the rolling characteristics deteriorate and a large number of edge cracks are formed.

It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims and their equivalents. It will be understood that the invention may be practiced. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (6)

(% By weight), Si: 3.2 to 4.0%, C: 0.03 to 0.09%, Al: 0.015 to 0.040%, Mn: 0.04 to 0.15%, N: 0.001 to 0.005% And the remainder comprises Fe and other unavoidable impurities, heating the slab satisfying formula 1 below;
Hot rolling the slab to produce a hot rolled sheet;
Annealing the hot-rolled sheet for 30 to 300 seconds at a cracking temperature of 900 to 980 캜;
Cooling the hot rolled sheet after completion of annealing of the hot rolled sheet from a starting temperature of 700 to 850 占 폚 to 300 占 폚 at a cooling rate of 10 占 폚 / sec to 300 占 sec / sec;
Cold-rolling the cooled hot-rolled sheet to produce a cold-rolled sheet;
Subjecting the cold-rolled sheet to primary recrystallization annealing; And
And secondary recrystallization annealing the cold rolled sheet after the primary recrystallization annealing has been completed.
[Formula 1]
[Mn] x [S]? 0.0004
(In Expression 1, [Mn] and [S] are the contents (% by weight) of Mn and S in the slab, respectively.) The method according to claim 1,
Wherein the slab comprises 0.03 to 0.15 weight%, P is 0.01 to 0.05 weight%, and Cr is 0.02 to 0.15 weight%, respectively, of at least one of Sb and Sn. The method according to claim 1,
Wherein the slab further comprises 0.01 to 0.2% by weight of Cu and 0.01 to 0.05% by weight of Mo. delete The method according to claim 1,
Wherein the hot-rolled sheet has an elongation of 20% or more after the annealing of the hot-rolled sheet. The method according to claim 1,
And heating the slab at a temperature of 1050 to 1200 占 폚 in the step of heating the slab.

Images