KR20160078171A - Grain orientied electrical steel sheet and method for manufacturing the same - Google Patents

Abstract

According to an embodiment of the present invention, in an oriented electrical steel sheet, a base steel sheet comprises: 0.001-0.5 wt% of La; an amount equal to or less than 0.0055 wt% of S (excluding 0 wt%); 0.005-0.5 wt% of Mn; and the remainder consisting of Fe and inevitable impurities.

Description

TECHNICAL FIELD [0001] 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 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.

Further, there is a problem that the manufacturing complexity and the cost burden are incurred in order to remove the constituent components of the precipitate after the completion of the secondary recrystallization, at a high temperature of 1200 ° C for 30 hours or more for a long time.

In this refinement annealing process, AlN precipitates are decomposed into Al and N, and Al moves to the surface of the steel sheet and reacts with oxygen in the surface oxide layer to form Al ₂ O ₃ oxide.

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.

One embodiment of the present invention is to provide a directional electrical steel sheet.

Yet another embodiment of the present invention is to provide a method of manufacturing a grain-oriented electrical steel sheet.

The grain-oriented electrical steel sheet according to one embodiment of the present invention comprises 0.001 to 0.5% of La, 0.0055% or less of S (does not include 0%), and 0.005 to 0.5% of Mn in weight% And the remainder includes Fe and other unavoidable impurities.

Wherein said base steel sheet comprises 1.0 to 7.0% of Si, 0.0050% or less of C, 0.005% or less of Al (not including 0%) and 0.003% or less of N (not including 0% As shown in FIG.

In the above electric steel sheet, the area ratio of crystal grains having a grain size of 1 mm or less may be 10% or less.

In the electrical steel sheet, the average grain size of crystal grains having a grain size of 1 mm or more may be 10 mm or more.

Further, it may contain La segregated at grain boundaries.

A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises 0.001 to 0.5% of La, 0.0055% or less of S and 0.005 to 0.5% of Mn, Heating the slab comprising unavoidable impurities; Hot rolling the slab to produce a hot rolled sheet; Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; A step of subjecting the cold-rolled sheet to primary recrystallization annealing, and a secondary recrystallization annealing of the electric steel sheet after the primary recrystallization annealing has been completed.

The slab contains, by weight%, 1.0% to 7.0% of Si, 0.001% to 0.1% of C, 0.005% or less of Al (not including 0%) and 0.003% or less ).

In the step of heating the slab, the slab heating temperature may be lower than 1280 ° C.

After the hot rolling step, annealing the hot-rolled sheet may be further performed.

The primary recrystallization annealing may be performed at an annealing temperature of 750 ° C or higher.

The grain-oriented electrical steel sheet according to an embodiment of the present invention stably forms goth grain, thereby having low iron loss and excellent magnetic properties.

In addition, since AlN and MnS are not used as the crystal growth inhibitor, it is unnecessary to reheat the slab at a temperature higher than 1300 ° C.

In addition, since the purification annealing at a high temperature for removing precipitates such as AlN and MnS is reduced, the manufacturing cost is reduced.

Further, there is no need to remove N and S or the like after high-temperature annealing, and surface defects due to the N and S gasification reactions do not exist in the annealing annealing process.

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.

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

A method of manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention will be described.

First, a slab containing 0.001% to 0.5% of La, 0.003% or less of S and 0.005% to 0.5% of Mn, and the balance of Fe and other unavoidable impurities is provided in terms of% by weight. Wherein the slab contains, by weight%, 1.0% to 7.0% of Si, 0.0050% or less of C, 0.005% or less of Al (not including 0%) and 0.003% or less .

La is added in an amount of 0.001% or more, and thus acts as a grain growth inhibitor during the secondary recrystallization annealing process. However, if 0.5% is exceeded, the rolling properties may be deteriorated and the rolling cracks may increase.

In one embodiment of the present invention, S helps La to act as a grain growth inhibitor. However, when 0.0055% is exceeded, the grain size of the primary recrystallized grains is affected and the magnetic properties may be lowered. Therefore, the content of S in the slab may be 0.0055% or less, more specifically 0.0035% or less. The content of S in the electrical steel sheet may be 0.0055% or less. Further, if S in the electrical steel sheet is removed by refining annealing, the content of S in the electrical steel sheet may be 0.0015% or less.

Mn is added as a resistivity element in an amount of 0.005% or more to improve the magnetic property, but if it exceeds 0.5%, it may cause a phase change after the secondary recrystallization, which may adversely affect magnetism.

Also, in one embodiment of the present invention, since the content of S is controlled, the MnS compound may not be formed.

When the Si content is less than 1.0%, the resistivity decreases and the iron loss characteristic deteriorates. In addition, when the Si content in the slab exceeds 4.5%, cold rolling becomes difficult. However, since the Si powder can be applied to the surface of the steel sheet after cold rolling or the Si can be diffused into the steel sheet after being deposited on the surface of the steel sheet, the Si content in the final steel sheet may become larger than the Si content in the slab. However, when the Si content exceeds 7% in the grain oriented electrical steel sheet, the Si content in the grain oriented electrical steel sheet may be less than 7% since it is difficult to process the transformer.

C is an austenite stabilizing element, which is added to the slab in an amount of 0.001% or more, thereby suppressing the slab center segregation of S in addition to the effect of making the coarse columnar structure finer. It also promotes work hardening of the steel sheet during cold rolling, thereby promoting the formation of secondary recrystallization nuclei in the {110} < 001 > orientation in the steel sheet. However, if the C content in the slab exceeds 0.1%, hot-rolled edge-crack may occur. It is subjected to decarburization annealing at the time of producing the electric steel sheet, and the C content in the electric steel sheet after decarburization annealing may be 0.0050 wt% or less. More specifically 0.0030% by weight or less.

Since Al forms a bond with nitrogen in the steel to form AlN precipitates, in one embodiment of the present invention, the Al content can be suppressed positively to avoid Al-based nitride and oxide formation. Therefore, Al may not be added in one embodiment of the present invention, but it may be 0.005% or less in the slab and the electric steel sheet, considering the amount of steel that is inevitably incorporated during the steelmaking process.

N is AlN, (Al, Mn) N , (Al, Si, Mn) N, Si 3 N 4 , N may not be added in one embodiment of the present invention. However, the amount of N in the slab and the electric steel sheet may be 0.0055% or less, considering the amount that is inevitably incorporated during the steelmaking process. More specifically, it may be 0.0035% or less. Further, the content of N in the electrical steel sheet may be 0.0015% or less.

Components such as Ti, Mg, and Ca are preferably not added because they react with oxygen in the steel to form oxides. However, considering the impurities in the steel, the content of each component in the slab and the electric steel sheet may be 0.005% or less.

The slab is heated. The heating temperature of the slab is not limited, but if the slab is heated to a temperature of 1280 ° C or lower, the slab is prevented from growing in a large scale. Therefore, it is possible to prevent the plate from being cracked in the subsequent hot rolling process. Therefore, the reheating temperature of the slab may be 1000 ° C or more and 1280 ° C or less.

When the reheating of the slab is completed, hot rolling is performed. The hot rolling temperature and the cooling temperature are not limited. In one embodiment, hot rolling may be terminated at 950 占 폚 or lower, and the hot rolling may be performed at a temperature of 600 占 폚 or less.

The hot-rolled hot-rolled sheet can be subjected to cold-rolling without performing annealing of the hot-rolled sheet or annealing of the hot-rolled sheet if necessary.

In the case of performing hot-rolled sheet annealing, the hot-rolled steel sheet can be heated to a temperature of 900 캜 or more, cooled and then cracked to make the hot-rolled steel sheet uniform.

Cold rolling can be carried out by using a reverse mill or a tandem mill to produce a cold rolled sheet having a thickness of 0.1 mm to 0.5 mm by a plurality of cold rolling methods including one cold rolling, multiple cold rolling or intermediate annealing . Further, warm rolling in which the temperature of the steel sheet is maintained at 100 캜 or higher during cold rolling can be performed.

The cold-rolled steel sheet is subjected to primary recrystallization annealing. In the first recrystallization annealing, primary recrystallization occurs in which nuclei of decarburization and goth grain are produced.

The primary recrystallization annealing may be to hold the cold rolled sheet at a temperature of 750 DEG C or higher for 30 seconds or more. The primary recrystallization is difficult to occur at a temperature lower than 750 DEG C, and it is difficult to secure a sufficient primary recrystallization time when the temperature is maintained at less than 30 seconds.

Further, in the method of manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention, the nitriding annealing step may be omitted after decarburization annealing. In the method for producing a grain-oriented electrical steel sheet using conventional AlN as a grain growth inhibitor, nitriding annealing is required for the formation of AlN. However, in the method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention, a nitriding annealing process is not necessary since AlN is not used as a grain growth inhibitor.

The steel sheet subjected to the first recrystallization annealing is coated with an annealing separator containing MgO and subjected to secondary recrystallization annealing. The cracking temperature during the secondary recrystallization annealing may be 900 ° C to 1250 ° C.

In the method for producing a grain-oriented electrical steel sheet according to an embodiment of the present invention, the finishing annealing step can be omitted after the secondary recrystallization annealing is completed.

In the method for producing a grain-oriented electrical steel sheet using conventional MnS and AlN as grain growth inhibitors, purification annealing at a high temperature for a long period of time to remove precipitates such as AlN and MnS was required. However, The burden of refining annealing is alleviated.

The grain-oriented electrical steel sheet according to one embodiment of the present invention comprises 0.001 to 0.5% of La, 0.0055% or less of S (does not include 0%), and 0.005 to 0.5% of Mn in weight% And the remainder includes Fe and other unavoidable impurities.

Wherein said base steel sheet comprises 1.0 to 7.0% of Si, 0.0050% or less of C, 0.005% or less of Al (not including 0%) and 0.003% or less of N (not including 0% As shown in FIG. The reason for the composition limitation in the base steel sheet is as described in the slab for the reason of the component limitation.

In the above electric steel sheet, the area ratio of crystal grains having a grain size of 1 mm or less may be 10% or less. When the area ratio of the crystal grains having a grain size of 1 mm or less is more than 10%, the grain growth may not be sufficient and the magnetic properties may be lowered.

In the electrical steel sheet, the average grain size of crystal grains having a grain size of 1 mm or more may be 10 mm or more. If the average grain size of the crystal grains having a grain size of 1 mm or more is less than 10 mm, the grain growth may be insufficient and the magnetic properties may be lowered. The average grain size of the grains having a grain size of 1 mm or more may be 70 mm or less. When the distance exceeds 70 mm, the magnetic domain width may become large and the magnetism may be deteriorated.

In addition, the electrical steel sheet may contain La segregated at grain boundaries. This is because La acts as a grain growth inhibitor.

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 1]

Mn, and S as shown in Table 1 and containing the remainder Fe and impurities in a weight percentage of 3.2%, Si: 0.051%, N: 0.005%, and Al: Lt; / RTI &gt;

The slab was heated at a temperature of 1150 캜 for 90 minutes, and hot-rolled to produce a hot-rolled sheet having a thickness of 2.6 mm.

The hot-rolled sheet was heated to a temperature of 1050 占 폚 or higher, held at 910 占 폚 for 90 seconds, cooled with water and pickled. Followed by cold rolling to a thickness of 0.29 mm.

The cold-rolled steel sheet was subjected to primary recrystallization annealing after being heated in a furnace, and maintained at a hydrogen gas atmosphere of 50 vol% and nitrogen: 50 vol% mixed gas atmosphere, a dew point temperature of 60 ° C, and an annealing temperature of 850 ° C for 120 seconds. After the primary recrystallization annealing, carbon was 0.0030 wt%.

Thereafter, MgO was applied and then wound in a coil to perform secondary recrystallization annealing.

In the final annealing, the temperature was raised to 1200 ° C in a mixed gas atmosphere of nitrogen: 25% by volume and hydrogen: 75% by volume at the time of temperature elevation. After reaching 1200 ° C, the atmosphere was maintained in a 100%

Sample number La content
(weight %) Mn content
(weight %) S content
(weight %) Magnetic flux density (B10, Tesla) Remarks division A 0 0 0 1.50 Comparison 1 B 0.02 0 0 1.53 Comparative material 2 C 0.9 0 0 1.55 Comparative material 3 D 0.1 0 0 1.53 Comparison 4 E 0.2 0 0 1.53 Comparative material 5 F 0 0.05 0.0018 1.55 Comparative material 6 G 0.005 0.05 0.0015 1.88 Inventory 1 H 0.04 0.05 0.0016 1.90 Inventory 2 I 0.06 0.05 0.0020 1.92 Inventory 3 J 0.1 0.05 0.0018 1.91 Invention 4 K 0.2 0.05 0.0018 1.88 Invention Article 5 L 0.8 0.05 0.0018 - Cracking Comparison 7

As can be seen from Table 1, when the content of La, Mn and S satisfies the range according to one embodiment of the present invention, it can be seen that the magnetic property is excellent.

[Example 2]

C: 0.053%, Mn: 0.097%, S: 0.005%, Al: 0.029%, and N: 0.004% in order to compare the grain size of the Al-based nitride with that of the grain- And a sample M composed of the remaining Fe and other inevitably incorporated impurities was prepared.

The sample M was subjected to the steps up to cold rolling in the same manner as in Example 1. The cold plate was heated in a furnace and then subjected to decarburization and nitriding by maintaining 50 vol% of hydrogen and 50 vol% of nitrogen, a dew point of 60 deg. C, and an annealing temperature of 850 deg. C for 120 seconds to reduce carbon to 30 ppm or less, 200 ppm.

The I and M samples of Example 1 were coated with MgO as an annealing separator and finally annealed in a coiled state. When the temperature was raised to 1200 ° C in the final annealing, the atmosphere was varied as shown in Table 2. After reaching 1200 캜, it was maintained in a 100% by volume hydrogen atmosphere for 20 hours or longer and then furnace-cooled.

Sample number La content
(weight %) Mn content
(weight %) S content
(weight %) Atmosphere at high temperature annealing Magnetic flux density (B10, Tesla) division I 0.06 0.05 0.0020 100 vol% hydrogen 1.92 Inventions 6 I 0.06 0.05 0.0020 25 vol% nitrogen and 75 vol% hydrogen 1.92 Invention 7 M 0 0.097 0.005 100 vol% hydrogen 1.80 COMPARISON 8 M 0 0.097 0.005 25 vol% nitrogen and 75 vol% hydrogen 1.91 Comparative material 9

In Table 2 and Table 1, when comparing the magnetic properties of I and M samples, I, which uses La as an inhibitor, exhibits the same magnetic properties regardless of the atmospheric conditions at the time of elevating the high temperature annealing, while the component system M using precipitates as inhibitors It was found that the magnetism varies greatly depending on the atmosphere at the time of heating.

[Example 3]

And the balance contains La in an amount of 3.2% by weight, C: 0.051%, N: 0.005%, Al: 0.029%, Mn: 0.05%, and S: 0.0015% Fe and impurities were prepared.

The slab was heated at a temperature of 1150 ° C for 90 minutes, and hot-rolled to obtain a hot-rolled steel sheet having a thickness of 2.3 mm.

The hot-rolled sheet was heated to a temperature of 1050 占 폚 or higher, held at 910 占 폚 for 90 seconds, quenched in boiling water, and pickled. Followed by cold rolling to a thickness of 0.262 mm. The cold-rolled steel sheet was heated in a furnace and then subjected to decarburization treatment for 120 seconds at a hydrogen gas mixture atmosphere of 50 vol% and nitrogen: 50 vol%, a dew point of 60 deg. C, and an annealing temperature of 850 deg. 30 ppm or less.

This steel sheet was coated with MgO as an annealing separator, and finally annealed in a coiled state. In the final annealing, the temperature was raised to 1200 DEG C in a mixed gas atmosphere of nitrogen of 25 vol% and hydrogen of 75 vol%, and after reaching 1200 DEG C, it was maintained in a 100 vol% hydrogen atmosphere for 20 hours and then cooled.

La content
(weight %) Area ratio (%) of crystal grains having a grain size of 1 mm or less Average grain size (mm) of crystal grains having a grain size of 1 mm or more Magnetic flux density (B10, Tesla) division 0 100 - 1.53 Comparative material 10 0.06 2 25 1.92 Invention 8

In Table 3, the area ratio (%) of the crystal grains having a grain size of 1 mm or less in the electric steel sheet according to an embodiment of the present invention is 10% or less, and the average grain size of crystal grains having a grain size of 1 mm or more is 10 mm or more Respectively.

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 (10)

, 0.001% to 0.5% of S, 0.0055% or less of S (does not include 0%) and 0.005% to 0.5% of Mn, and the remainder contains Fe and other unavoidable impurities Directional electrical steel sheet.
The method according to claim 1,
Wherein said base steel sheet comprises 1.0 to 7.0% of Si, 0.0050% or less of C, 0.005% or less of Al (not including 0%) and 0.003% or less of N (not including 0% Further comprising the steps of:
3. The method of claim 2,
Wherein the area ratio of the crystal grains having a grain size of 1 mm or less with respect to 100% of the total grain area in the above-mentioned electric steel sheet is 10% or less.
The method of claim 3,
In the electrical steel sheet, an average grain size of crystal grains having a grain size of 1 mm or more is 10 mm or more.
5. The method according to any one of claims 1 to 4,
A grain oriented electrical steel sheet containing La segregated in grain boundaries.
By weight, heating a slab comprising 0.001% to 0.5% of La, 0.0055% or less of S and 0.005% to 0.5% of Mn, the balance comprising Fe and other unavoidable impurities;
Hot rolling the slab to produce a hot rolled sheet;
Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet;
Subjecting the cold-rolled sheet to primary recrystallization annealing; And
A second recrystallization annealing step of subjecting the electrical steel sheet subjected to the first recrystallization annealing to completion;
Wherein the method comprises the steps of:
The method according to claim 6,
The slab contains, by weight%, 1.0% to 7.0% of Si, 0.001% to 0.1% of C, 0.005% or less of Al (not including 0%) and 0.003% or less Wherein the method further comprises the steps of:
8. The method of claim 7,
Wherein the slab heating temperature is 1280 DEG C or less in the step of heating the slab.
9. The method of claim 8,
Further comprising the step of annealing the hot-rolled steel sheet after the hot-rolling.
10. The method of claim 9,
Wherein the primary recrystallization annealing is performed at an annealing temperature of 750 캜 or higher.