KR20160078133A - Grain-oriented electrical steel sheet and method for manufacturing the same - Google Patents

Abstract

Provided are a grain-oriented electrical steel sheet, and a method to manufacture the same. According to an embodiment of the present invention, the grain-oriented electrical steel sheet comprises: 2.0-4.5 wt% of Si; 0.03-0.09 wt% of C; 0.01-0.05 wt% of Sb; 0.03-0.08 wt% of Sn; 0.01-0.05 wt% of Mo; 0.02-0.15 wt% of Cr; and the remainder consisting of Fe and inevitable impurities. Moreover, Sn(wt%) + Sb(wt%) - 0.7Cr(wt%) is equal to or less than 0.07.

Description

TECHNICAL FIELD The present invention relates to a grain-oriented electrical steel sheet and a method of manufacturing the same. BACKGROUND ART [0002]

To a directional electric steel sheet excellent in magnetic properties and a manufacturing method thereof.

Generally, a directional electric steel sheet having excellent magnetic properties is required to strongly develop a goss texture in a {110} < 001 > orientation in the rolling direction of a steel sheet. In order to form such a texture, It is necessary to form an abnormal crystal grain growth called recrystallization.

This abnormal crystal growth occurs when normal crystal growth inhibits the movement of grain boundaries normally grown by precipitates, inclusions, or elements segregated in the grain boundaries or solid solution, unlike ordinary grain growth.

The directional electric steel sheet mainly uses a manufacturing method which causes secondary recrystallization using precipitates such as AlN and MnS as a crystal growth inhibitor. The method for producing a grain-oriented electrical steel sheet using such an AlN or MnS precipitate as a grain growth inhibitor has the following problems.

In order to use the AlN and MnS precipitates as the grain growth inhibitors, the precipitates must be distributed very finely and uniformly on the steel sheet. In order to uniformly distribute the fine precipitates in this way, the slab is heated at a high temperature of 1300 DEG C or higher for a long time to solidify coarse precipitates present in the steel, and then subjected to hot rolling in a very short period of time, .

To accomplish this, a large-scale slab heating apparatus is required. In order to suppress the precipitation as much as possible, it is necessary to control the hot rolling and the winding process very strictly, and to control the precipitates precipitated in the hot- .

In addition, when the slab is heated at a high temperature, the slab washing phenomenon occurs due to the formation of Fe ₂ SiO ₄ having a low melting point, thereby reducing the water content. In addition, there is a problem that the manufacturing complexity and the cost burden are required to perform the annealing for a long time at a high temperature of 1200? For 30 hours or more in order to remove the constituent components of the precipitate after completion of the second recrystallization.

Also, in this refinement annealing process, Al ₂ O ₃ oxide is formed as Al-N precipitates are decomposed into Al and N, and then Al moves to the surface of the steel sheet and reacts with oxygen in the surface oxidation layer. The Al-based oxide thus formed or the AlN precipitates not decomposed in the refining annealing process interfere with the movement of the magnetic domains in the steel sheet or near the surface, thereby causing the iron loss to deteriorate.

Of the segregated elements for replacing AlN, MnS, etc., Sb is an element inducing grain boundary brittleness, and when it is added at a certain level or more, the rolling property is deteriorated. In addition, a coating is formed on the surface of the primary recrystallization annealing to inhibit the oxidation reaction on the surface, thereby failing to form a good quality surface oxidation layer, resulting in deterioration of the base coating after secondary recrystallization annealing at high temperature .

Korean Patent Application No. 2011-0139480 discloses a method of controlling the time of sinking by adding Sb and Sn at the same time. However, the influence of Sn and the variation in sediment due to variation of the oxide layer are not taken into consideration, The effect is mainly observed in the decarburization annealing section where the primary recrystallization is formed, and the effect is rather reduced in the high temperature annealing section.

Therefore, it is necessary to develop a directional electric steel sheet excellent in magnetic property and excellent in rolling property and surface quality by developing a technology using an element which is superior in magnetic property improving effect than Sb and advantageous in rolling property and surface quality.

To provide a directional electrical steel sheet excellent in magnetic properties and a method for producing the same.

The grain-oriented electrical steel sheet according to one embodiment of the present invention comprises 2.0 to 4.5% of Si, 0.03 to 0.09% of C, 0.01 to 0.05% of Sb, 0.03 to 0.08% of Sn, 0.03 to 0.08% of Sn, 0.01% to 0.05% of Cr, 0.02% to 0.15% of Cr, and the balance of Fe and other unavoidable impurities, wherein the value of Sn (wt.%) + Sb (wt.%) - 0.7Cr (wt.

In the electrical steel sheet, Sb, Sn and Mo may be segregated in the grain boundaries by acting as grain growth inhibitors.

The electric steel sheet according to any one of claims 1 to 3, further comprising 0.015 to 0.040% of Al, 0.01 to 0.20% of Mn, 0.001 to 0.01% of N, 0.001 to 0.01% of S and 0.005 to 0.05% .

The average grain size of the electrical steel sheet may be 3 cm or less.

The electrical steel sheet may have a grain size of 1 cm or more and occupy 90% or more of the total area of the electrical steel sheet.

A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes: 2.0 to 4.5% Si, 0.03 to 0.09% C, 0.01 to 0.05% Sb, 0.03 to 0.08% Sn, , 0.01% to 0.05% Mo, 0.02% to 0.15% Cr, and the balance Fe and other unavoidable impurities; Heating the slab; Hot rolling the heated slab to produce a hot rolled sheet; Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; Decarbonizing and nitriding the cold rolled sheet; And secondary recrystallization annealing the steel sheet after completion of the decarburization annealing and nitriding annealing.

The value of Sn (% by weight) + Sb (% by weight) - 0.7Cr (% by weight) in the slab may be 0.07 or less. The slabs may contain 0.015% to 0.040% of Al, 0.01% to 0.20% of Mn, 0.001% to 0.01% of N, 0.001% to 0.01% of S and 0.005% to 0.05% of P, .

The decarburization annealing and the nitriding annealing may be simultaneous decarburization annealing performed simultaneously.

The decarburization annealing and nitriding annealing may be performed at a temperature ranging from 800 ° C to 950 ° C.

And the step of applying the annealing separator to the steel sheet before the secondary recrystallization annealing step after the decarburization annealing and nitriding annealing step.

The annealing separator may be one containing MgO as a main component.

The annealing separator may include MgO.

In the step of heating the slab, the heating temperature may be 1100 ° C to 1250 ° C.

The total amount of nitrogen recycled to the slab in the step of heating the slab may be 0.0020% to 0.0070% by weight.

The size of the grain of the electric steel sheet after the secondary recrystallization annealing is completed may be 3 cm or less.

In the electric steel sheet after completion of the secondary recrystallization annealing, the crystal grains having a size of 1 cm or more may occupy 90% or more of the total area of the electric steel sheet.

The value of Sn (wt%) + Sb (wt%) - 0.7Cr (wt%) in the slab may be 0.07 or less.

The slab further contains 0.015% to 0.040% of Al, 0.01% to 0.20% of Mn, 0.001% to 0.01% of N, 0.001% to 0.01% of S and 0.005% to 0.05% of P can do.

And then subjecting the hot-rolled sheet to annealing after hot-rolling.

The hot-rolled sheet annealing step may be a step of heating to a temperature of 1000 ° C to 1250 ° C, followed by crack cooling at a temperature of 850 ° C to 1,000 ° C.

The secondary recrystallization annealing may be a temperature raising step and a cracking step, and the raising temperature may be elevated to 1100 ° C to 1300 ° C in the raising temperature step and may be raised in a mixed atmosphere of nitrogen and hydrogen.

The cracking step may be performed in a hydrogen atmosphere.

According to one embodiment of the present invention, a grain-oriented electrical steel sheet having excellent iron loss and magnetic properties and a method for producing the same can be provided.

FIG. 1 is a graph showing changes in grain size uniformity due to decarburization and soaking in the simultaneous decarburization step. FIG.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims. Like reference numerals refer to like elements throughout the specification.

Thus, in some embodiments, well-known techniques are not specifically described to avoid an undesirable interpretation of the present invention. Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Whenever a component is referred to as "including" an element throughout the specification, it is to be understood that the element may include other elements, not the exclusion of any other element, unless the context clearly dictates otherwise. Also, singular forms include plural forms unless the context clearly dictates otherwise.

The grain-oriented electrical steel sheet according to one embodiment of the present invention comprises 2.0 to 4.5% of Si, 0.03 to 0.09% of C, 0.01 to 0.05% of Sb, 0.03 to 0.08% of Sn, 0.03 to 0.08% of Sn, 0.01% to 0.05% of Cr, 0.02% to 0.15% of Cr, and the balance of Fe and other unavoidable impurities, wherein the value of Sn (wt.%) + Sb (wt.%) - 0.7Cr .

In the electrical steel sheet, Sb, Sn and Mo may be segregated in the grain boundaries by acting as grain growth inhibitors.

The electric steel sheet according to any one of claims 1 to 3, further comprising 0.015 to 0.040% of Al, 0.01 to 0.20% of Mn, 0.001 to 0.01% of N, 0.001 to 0.01% of S and 0.005 to 0.05% .

The size of the grain of the electrical steel sheet may be 3 cm or less.

The electrical steel sheet may have a grain size of 1 cm or more and occupy 90% or more of the total area of the electrical steel sheet.

In order to manufacture the grain-oriented electrical steel sheet, a method of manufacturing a grain-oriented electrical steel sheet according to one embodiment as described below may be provided.

A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes: 2.0 to 4.5% Si, 0.03 to 0.09% C, 0.01 to 0.05% Sb, 0.03 to 0.08% Sn, , 0.01% to 0.05% Mo, 0.02% to 0.15% Cr, and the balance Fe and other unavoidable impurities; Heating the slab; Hot rolling the heated slab to produce a hot rolled sheet; Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; Decarbonizing and nitriding the cold rolled sheet; And secondary recrystallization annealing the steel sheet after completion of the decarburization annealing and nitriding annealing.

The value of Sn (% by weight) + Sb (% by weight) - 0.7Cr (% by weight) in the slab may be 0.07 or less. The slabs may contain 0.015% to 0.040% of Al, 0.01% to 0.20% of Mn, 0.001% to 0.01% of N, 0.001% to 0.01% of S and 0.005% to 0.05% of P, .

First, the reason for the composition limitation will be described.

Si plays a role of lowering the iron loss by increasing the resistivity of the electric steel sheet. When the Si content is less than 2.0% by weight, the resistivity is decreased, the eddy current loss is increased to deteriorate the iron loss characteristic, and the ferrite and the austenite phase transformation occurs at the high temperature annealing, so that the secondary recrystallization becomes unstable and the texture is damaged . On the other hand, when the Si content exceeds 4.5 wt%, the brittleness of the electric steel sheet is increased and the toughness is decreased, so that the occurrence rate of the plate fracture during the rolling process is intensified and the weldability is weakened to cause a load in the cold rolling operation. The temperature is lowered, and the formation of the secondary recrystallization becomes unstable.

C is an element which induces the formation of austenite phase. As the C content increases, ferrite-austenite phase transformation during the hot rolling process is activated, and the elongated hot rolled steel strip structure formed during the hot rolling process is increased, Thereby suppressing ferrite grain growth. Also, as the C content increases, the texture is improved after the cold rolling due to the increase in the stretched hot rolled band structure, which is higher in strength than the ferrite structure, and the finer grain size of the annealed hot rolled steel sheet. In particular, the Goss fraction is increased. It is considered that the effect of pass aging during cold rolling becomes large due to the residual C existing in the steel sheet after annealing the hot-rolled sheet, thereby increasing the goss fraction in the primary recrystallized grains. Therefore, the larger the C content, the longer the decarburization annealing time in decarburizing annealing, and the deterioration in productivity. If the decarburization at the initial stage of heating is insufficient, the primary recrystallization grain becomes uneven and makes the secondary recrystallization unstable. Also, since the magnetic properties may be deviated due to the magnetic aging phenomenon, the C content is preferably limited to a range of 0.03 wt% to 0.09 wt%.

Sb has the effect of increasing the grain nuclei in the goss orientation generated during the cold rolling process and improving the fraction of the grains having the goss orientation in the primary recrystallization texture. In addition, the secondary recrystallization starting temperature of the grains having a goss aggregate structure is increased when segregating in the primary recrystallization grain boundaries and performing secondary recrystallization and high temperature annealing, so that the secondary recrystallization microstructure excellent in the degree of integration can be obtained and the magnetic flux density is increased. If the content is less than 0.01% by weight, the effect is not exhibited properly. If the content is more than 0.05% by weight, the size of the primary recrystallized grains becomes too small to lower the secondary recrystallization starting temperature and deteriorate the magnetic properties, The secondary recrystallization may not be formed. Therefore, Sb is preferably in the range of 0.01 wt% to 0.15 wt%.

Sn is an element inhibiting the movement of grain boundaries as a grain boundary segregation element and is therefore known as a crystal growth inhibitor. In addition, by increasing the grain fraction of the Goss orientation in the primary recrystallized texture, the size of the secondary recrystallized microstructure is reduced because the number of the Goss bearing nuclei growing in the secondary recrystallized texture structure is decreased. As the grain size becomes smaller, The iron loss of the final product is reduced. On the other hand, Sn plays an important role in suppressing grain growth through grain segregation in grain boundaries. This not only improves the suppressing effect of suppressing the crystal growth driving force of the microcrystallized first recrystallized microstructure, (Al, Si, Mn) during the annealing process, particles causing N grain growth inhibiting effect such as N and AlN are coarsened, thereby preventing the grain growth growth inhibiting ability from being reduced. On the other hand, when the content of Sn is less than 0.03 wt%, there is no addition effect. When the content of Sn exceeds 0.08 wt%, the grain growth inhibiting ability is excessively increased and the grain size of the primary recrystallized microstructure is decreased The decarburization annealing has to be carried out at a low temperature. As a result, it is not possible to control the decarburization to a proper oxide layer, and thus a good surface can not be secured. In view of mechanical properties, the brittleness is increased due to excessive segregation of grain boundary segregation elements, which may cause plate fracture during the manufacturing process. Therefore, the content of Sn is preferably 0.03 to 0.08% by weight.

Mo is one of the main alloying elements of the present invention. Goss particles causing secondary recrystallization in the grain-oriented electrical steel sheet are generated during hot rolling, and remain in the surface portion of the specimen after the cold rolling and the first recrystallization heat treatment to cause secondary recrystallization It is known. 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. Since the size of the atom is relatively large and the melting point is very high at 2,623 ° C, Mo is considered to be a very effective grain growth inhibiting element because it has a low diffusion rate in iron and can keep the segregation effect to a high temperature.

When the content of Mo is less than 0.01% by weight, 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 small, and the effect of suppressing the growth of grains It is hard to say that there is a magnetic improvement effect because there is little effect of compensation. On the other hand, when the content is more than 0.05% by weight, the grain growth inhibiting ability is excessively increased and the grain size of the primary recrystallized microstructure must be reduced to increase the grain growth driving force relatively. Therefore, the decarburization annealing should be performed at a low temperature , Which can not be controlled by an appropriate oxide layer, so that a satisfactory surface can not be obtained. Therefore, the content of Mo is preferably 0.01 wt% or more and 0.05 wt% or less.

When Cr is added as an element promoting oxidation formation within the range of 0.02 wt% to 0.15 wt%, formation of a dense oxide layer in the surface layer is suppressed and a fine oxide layer is formed in the depth direction. The addition of Sb and Sn makes it easier to form primary recrystallization with excellent uniformity by addition of Cr in an appropriate range. 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 0.02% by weight, the effect is insignificant. When the Cr content is more than 0.15% by weight, the oxide layer is excessively formed and the effect thereof is reduced, and the cost is increased due to the addition of the expensive alloy.

(Al, Si, Mn) N and AlN-type nitride are formed in the annealing for decarburization and sedimentation at the same time, resulting in a strong grain growth inhibition It plays a role. More than a certain amount of solid solution Al is needed. If the content is less than 0.015% by weight, the number and the volume fraction of the precipitates to be formed are low and the effect of inhibiting the growth of grain growth is insufficient. If the content is too high, the precipitates grow coarser and the effect of inhibiting grain growth is deteriorated. Therefore, it is preferable to add 0.015 wt% to 0.04 wt% of acid soluble Al.

Mn has the same effect of increasing the specific resistance as Si and reducing the iron loss. It reacts with the nitrogen introduced by the nitriding treatment together with Si to form precipitates of N (Al, Si, Mn), whereby the growth of the primary recrystallized grains And it is an important element for causing secondary recrystallization. However, when it is added in an amount of more than 0.20% by weight, a large amount of (Fe, Mn) and Mn oxide are formed on the surface of the steel sheet in addition to Fe ₂ SiO ₄ to prevent formation of a base coat formed during high temperature annealing, The size of the primary recrystallized grains becomes uneven due to the nonuniformity of the phase transformation between the ferrite and the austenite in the process, and as a result, the secondary recrystallization becomes unstable. However, when Mn is contained in an amount of less than 0.001% by weight, the addition effect is insignificant, so that Mn is preferably added in an amount of 0.001 to 0.20% by weight.

N is an element that reacts with Al or the like to refine the crystal grains. When these elements 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. However, if the content is excessive, the primary recrystallization grain becomes excessively fine, As a result, due to the fine crystal grains, the driving force causing crystal grain growth during the secondary recrystallization becomes large, so that it can grow to the crystal grains of an undesirable orientation. If N is contained in an amount exceeding 0.010 wt%, the secondary recrystallization starting temperature rises and the magnetic properties deteriorate. However, when N is less than 0.001% by weight, the effect is insignificant, so N is set to 0.001 to 0.010% by weight or less. When the treatment for increasing the nitrogen amount between the cold rolling and the secondary recrystallization annealing is carried out, it may suffice that the N content of the slab is 0.006% by weight or less.

S is preferably an element which has a high solid solution temperature during hot rolling and is not contained in the segregated element as much as possible, but it is a kind of an impurity which is inevitably contained in steelmaking. Also, since S forms MnS and affects the primary recrystallized grain size, the S content is 0.010 wt% or less, and when it is controlled to less than 0.001 wt%, the management cost increases. S is more preferably 0.006% by weight or less.

P is an element exhibiting similar effects to Sn and Sb. It plays an auxiliary role in inhibiting the grain boundary migration and at the same time inhibiting grain growth by segregating into grain boundaries. In addition, it can improve {110} <001> . If the content of P is 0.005% by weight or less, there is no addition effect. If the content of P is more than 0.05% by weight, the brittleness is increased and the rolling property is greatly deteriorated. Therefore, the content is preferably limited to 0.005 to 0.05% by weight.

Sb and Sn have the effect of increasing the grain nuclei in the goss orientation generated during the cold rolling process and improving the fraction of the grains having the goss orientation in the primary recrystallized texture. In addition, the secondary recrystallization starting temperature of the grains having a goss aggregate structure is increased when segregating in the primary recrystallization grain boundaries and performing secondary recrystallization and high temperature annealing, so that the secondary recrystallization microstructure excellent in the degree of integration can be obtained and the magnetic flux density is increased. However, Sb and Sn are concentrated to the surface during the annealing of the primary recrystallization, making the internal oxide layer thin and dense, making decarburization and dipping difficult. In particular, it is very important to set the conditions for forming a stable secondary recrystallized grains because the decarburization and the nitriding process are hardly effected.

The decarburization and nitriding time are very important in the decarburization and nitriding processes, which are described in FIG. Decarburization and nitriding become difficult and decarburization and sedimentation reaction are slow, there is a possibility that the unevenness of the central portion is increased or the difference in the grain size in the thickness direction is increased, so that the unevenness of the final crystal grain can be increased. It may have a bad influence on forming a stable magnetism.

When Sb and Sn are added in an appropriate range, excellent magnetic properties can be obtained. However, as described above, it is difficult to decarburize and precipitate, thereby causing nonuniformity of the primary recrystallized grains due to fine fluctuation of the annealing furnace, The probability is lowered and the yield of obtaining the highest magnetization is deteriorated.

In order to overcome this, when Cr is appropriately added as an element promoting oxidation formation in the decarburization annealing process, formation of a dense oxide layer in the surface layer is suppressed and a fine oxide layer is formed in the depth direction. Depending on the amount of Sb and Sn added, and addition of Cr in the proper amount range, decarburization and soaking become easy, and it becomes easier to form excellent primary recrystallization and secondary recrystallization. In other words, the magnetic properties of the final product can be stably obtained, and the productivity can be maximized because the simultaneous decarburization process is stably applied.

The segregation effect of Sb and Sn is largely dominant in the first recrystallization temperature zone, and the deterrent force due to segregation in the subsequent high temperature annealing zone is reduced. In order to compensate for this, it is possible to obtain not only the first recrystallization but also the uniformity of the secondary recrystallization, by adding Mo, which is mainly segregated at high temperature, together with Sb and Sn.

In the case of reheating the slab before hot rolling, it is preferable that the heating is performed within a predetermined temperature range in which N and S to be dissolved are incompletely dissolved. If N and S are completely dissolved, a large amount of nitride or sulfide is formed after annealing of the hot-rolled steel sheet, which makes it impossible to perform hot rolling once, which is a subsequent process, and thus an additional process is required. And the size of the primary recrystallized grains becomes considerably small, so that proper secondary recrystallization may not be able to be expressed.

The directional electric steel plate slab having the above composition is reheated before the hot rolling. At this time, it is preferable to heat the slab at a low temperature of 1,250 ° C or less, for example, 1,200 ° C or less, for example, 1,100 ° C to 1,250 ° C 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 melting of the surface of the slab can repair the heating furnace and shorten the life of the heating furnace. In addition, if the slab is heated to a temperature of 1,250 ° C. or less, for example, 1,200 ° C. or less, for example, 1,100 ° C. to 1,250 ° C., the columnar structure of the slab is prevented from being grown to a great extent, It is possible to prevent the occurrence of the failure, thereby improving the error rate.

During the heating of the slab, nitrogen is reused in the slab. At this time, the total amount of nitrogen that is reused in the slab may be 0.0020% to 0.0070% by weight.

After the directional electric steel slab is reheated, hot rolling is performed. A hot rolled sheet having a thickness of 2.0 mm to 3.5 mm can be produced by hot rolling. After the hot rolled sheet is manufactured, the hot rolled sheet is annealed if necessary and then cold rolled. In the case of annealing the hot-rolled steel sheet, the steel sheet may be heated at a temperature of 1,000 ° C. to 1,250 ° C. and then cracked at a temperature of 850 ° C. to 1,000 ° C., followed by cooling. The hot-rolled sheet annealing is performed according to need, and this can be omitted. At this time, the average size of the precipitates after hot rolling or annealing the hot-rolled sheet is 300 ANGSTROM to 3000 ANGSTROM.

The cold rolling may be performed through one time of cold rolling, and may be manufactured through rolling to a final thickness of 0.15 mm to 0.35 mm. The cold-rolled sheet is subjected to decarburization, recrystallization of the deformed structure, and nitriding treatment using ammonia gas.

The decarburization annealing and the nitriding annealing may be performed simultaneously or sequentially, and the decarburization annealing and the nitriding annealing to be performed at the same time may be performed in a temperature range of 800 ° C to 900 ° C.

When nitriding annealing is performed simultaneously with decarburization annealing, it can be carried out in a mixed gas atmosphere of ammonia, hydrogen and nitrogen. According to the method in which the decarburization annealing is first performed after the temperature elevating process in the first recrystallization annealing and then the nitriding annealing is performed, precipitates such as Si ₃ N ₄ and (Si, Mn) N are generated in the surface layer portion of the steel sheet, (Al, Si, Mn) N, which is thermally stable in the final annealing process, which is a subsequent process, since the annealing temperature is controlled to 700 to 800 ° C. It is possible to perform a role as an inhibitor by re-precipitating it as a precipitate. On the contrary, when the decarburization annealing and the nitriding annealing are performed at the same time, AlN or (Al, Si, Mn) N precipitates are formed at the same time, so that the precipitates can be used as an inhibitor without transformation of the precipitates during final annealing. It is more preferable to carry out decarburization annealing and nitriding annealing at the same time.

The annealing separator can be applied to the steel sheet before the step of decarburization annealing and nitriding annealing and subsequent to the second recrystallization annealing step.

The primary recrystallized steel sheet is subjected to secondary recrystallization after the annealing separator is applied for a long period of time after the annealing separator is applied so that the {110} plane of the steel sheet is parallel to the rolling plane and the <001> direction is parallel to the rolling direction, 001 &gt; cluster texture can be formed. The annealing separator may preferably be one produced by using MgO as a main component, but is not limited thereto. For example, the annealing separator may include MgO. For example, the annealing separator may be MgO.

The purpose of the final annealing is largely in the formation of {110} < 001 > texture by secondary recrystallization, the formation of a vitreous film by the reaction of the oxide layer and MgO formed during decarburization, and the removal of impurities which impair magnetic properties. As the final annealing method, the nitride is inhibited by keeping the mixed gas of nitrogen and hydrogen at the temperature rising period before the secondary recrystallization, and the secondary recrystallization is well developed. After completion of the secondary recrystallization, 100% hydrogen It is possible to keep impurities in the atmosphere for a long time. The temperature rise in the temperature rising period may be from 1,100 ° C to 1,300 ° C.

The size of the grain of the electric steel sheet after the secondary recrystallization annealing is completed may be 3 cm or less.

In the electric steel sheet after completion of the secondary recrystallization annealing, the crystal grains having a size of 1 cm or more may occupy 90% or more of the total area of the electric steel sheet.

Hereinafter, the embodiment will be described in detail. The following examples are illustrative of the present invention only and are not intended to limit the scope of the present invention.

[Example]

0.005 wt% of Si, 0.0045 wt% of N, 0.028 wt% of Sol-Al, 0.028 wt% of P, 0.08 wt% of P, and 0.1 wt% of Sb, Sn, Cr , The amount of Mo added was changed as shown in Table 1, and the remainder of the components were vacuum-melted after forming a directional electric steel sheet containing Fe and other inevitably impurities.

Then heated at a temperature of 1,200 DEG C for 210 minutes and hot-rolled to a thickness of 2.3 mm. The hot-rolled sheet was heated at a temperature of 1,080 占 폚 and then held at 940 占 폚 for 90 seconds to anneal the hot-rolled sheet and quenched in water to be pickled.

After the pickling, the steel sheet was subjected to one-time cold-rolling at a thickness of 0.23 mm, and the cold-rolled sheet was held at a temperature of 870 ° C in a mixed hydrogen gas atmosphere of nitrogen and ammonia for 180 seconds to perform simultaneous decarburization annealing so that the nitrogen content became 200 ppm .

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. In the final annealing, a mixed atmosphere of 25 vol% nitrogen and 75 vol% hydrogen was set up to 1,200 ° C. After reaching 1,200 ° C, the furnace was maintained in a 100% hydrogen atmosphere for 10 hours and then cooled. The measured values of the respective conditions are shown in Table 1 below.

Mo
(weight%) Sn + Sb
(weight%) Cr
(weight%) Sn + Sb - 0.7Cr Average size of secondary recrystallized grains / Area fraction of grain over 1cm Iron loss
(W17 / 50, W / kg) Magnetic flux density
(B8, Tesla) division 0.0 0.04 0.08 -0.016 4.2 / 97 0.857 1.911 Comparison 1 0.03 0.13 0.06 0.088 1.5 / 85 1.021 1.880 Comparative material 2 0.05 0.09 0.02 0.076 2.8 / 88 0.915 1.903 Comparative material 3 0.1 0.12 0.06 0.078 1.6 / 87 0.970 1.882 Comparison 4 0.08 0.1 0.07 0.051 2.3 / 89 0.886 1.902 Comparative material 5 0.08 0.13 0.05 0.085 1.8 / 87 1.003 1.883 Comparative material 6 0.03 0.08 0.2 -0.060 3.5 / 95 0.928 1.894 Comparison 7 0.03 0.06 0.06 0.018 3.0 / 95 0.776 1.931 Inventory 1 0.04 0.11 0.13 0.019 2.2 / 96 0.752 1.935 Inventory 2 0.03 0.11 0.11 0.033 2.3 / 93 0.775 1.943 Inventory 3 0.01 0.09 0.05 0.055 2.8 / 94 0.809 1.934 Invention 4 0.05 0.08 0.12 -0.004 2.9 / 94 0.801 1.924 Invention Article 5 0.05 0.1 0.1 0.030 2.5 / 92 0.796 1.933 Inventions 6

As shown in Table 1, the content of Mo is 0.01 to 0.05% by weight, the content of Cr is 0.02 to 0.15% by weight, the content of Sn (% by weight) + Sb (% Cr (wt.%) ≤ 0.07 are satisfied, it is found that the inventive material has excellent magnetic characteristics and improved grain size uniformity as compared with the comparative material.

While the present invention has been described in connection with certain exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (20)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 2.0 to 4.5% of Si, 0.03 to 0.09% of C, 0.01 to 0.05% of Sb, 0.03 to 0.08% of Sn, 0.01 to 0.05% of Mo, 0.02 to 0.15% , The remainder including Fe and other unavoidable impurities,
Wherein the value of Sn (wt%) + Sb (wt%) - 0.7Cr (wt%) is 0.07 or less.
The method according to claim 1,
Wherein the electrical steel sheet comprises Sb, Sn and Mo segregated at grain boundaries.
3. The method of claim 2,
The electric steel sheet according to any one of claims 1 to 3, further comprising 0.015 to 0.040% of Al, 0.01 to 0.20% of Mn, 0.001 to 0.01% of N, 0.001 to 0.01% of S and 0.005 to 0.05% Comprising a directional electrical steel sheet.
The method of claim 3,
Wherein the average grain size of the electrical steel sheet is 3 cm or less.
5. The method of claim 4,
Wherein the electrical steel sheet has a grain size of 1 cm or more and occupies 90% or more of the total area of the electrical steel sheet.
The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 2.0 to 4.5% of Si, 0.03 to 0.09% of C, 0.01 to 0.05% of Sb, 0.03 to 0.08% of Sn, 0.01 to 0.05% of Mo, 0.02 to 0.15% , The remainder being Fe and other unavoidable impurities;
Heating the slab;
Hot rolling the heated slab to produce a hot rolled sheet;
Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet;
Decarbonizing and nitriding the cold rolled sheet; And
A second recrystallization annealing the steel sheet after the decarburization annealing and nitriding annealing are completed;
Wherein the method comprises the steps of:
The method according to claim 6,
Wherein the decarburization annealing and the nitriding annealing are simultaneously performed.
8. The method of claim 7,
Wherein the decarburization annealing and the nitriding annealing are performed in a temperature range of 800 ° C to 950 ° C.
10. The method of claim 8,
Further comprising the step of applying the annealing separator to the steel sheet after the step of decarburization annealing and nitriding annealing before the step of annealing the secondary recrystallization.
10. The method of claim 9,
Wherein the annealing separator comprises MgO.
10. The method of claim 9,
Wherein the heating temperature in the step of heating the slab is 1,100 ° C to 1,250 ° C.
12. The method of claim 11,
Wherein the total amount of nitrogen recycled to the slab in the step of heating the slab is 0.0020% to 0.0070% by weight.
13. The method of claim 12,
Wherein the size of the grain of the electric steel sheet after completion of the secondary recrystallization annealing is 3 cm or less.
14. The method of claim 13,
Wherein the crystal grains having a size of 1 cm or more occupy 90% or more of the total area of the electric steel sheet in the electric steel sheet after completion of the secondary recrystallization annealing.
15. The method according to any one of claims 6 to 14,
Wherein the value of Sn (wt%) + Sb (wt%) - 0.7Cr (wt%) in the slab is 0.07 or less.
16. The method of claim 15,
The slab further contains 0.015% to 0.040% of Al, 0.01% to 0.20% of Mn, 0.001% to 0.01% of N, 0.001% to 0.01% of S and 0.005% to 0.05% of P Wherein the method comprises the steps of:
17. The method of claim 16,
Further comprising the step of annealing the hot-rolled steel sheet after the hot-rolling.
18. The method of claim 17,
And annealing the hot-rolled sheet at a temperature of 1,000 ° C to 1,250 ° C.
19. The method of claim 18,
Wherein the secondary recrystallization annealing is performed at a temperature elevating step and a cracking step and the temperature is raised to 1,100 ° C to 1,300 ° C in the temperature increasing step and is increased in a mixed atmosphere of nitrogen and hydrogen.
20. The method of claim 19,
Wherein the cracking step is performed in a hydrogen atmosphere.

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