KR20140118298A - Oriented electrical steel sheet and method of manufacturing the same - Google Patents

Abstract

Disclosed are an oriented electrical steel sheet capable of ensuring excellent electromagnetic properties by performing low temperature heat treatment after homogenization heat treatment; and a method of manufacturing the same. According to the present invention, the method of manufacturing the oriented electrical steel sheet comprises: a hot rolling step of cooling a slab after groove rolling the slab comprising carbon (C), silicon (Si), and the remainder consisting of Fe and inevitable impurities; a cold rolling step of cold rolling the steel by attaching silica fabrics to the surface of the steel after pickling the cooled steel; a homogenization heat treating step of diffusing silicon inside the steel by homogenization heat treating the cold rolled steel; and a low temperature heat treating step of low temperature heat treating the homogenization heat treated steel at 500-700°C for 0.5-2 hours.

Description

TECHNICAL FIELD [0001] The present invention relates to a directional electric steel sheet and a method of manufacturing the same. BACKGROUND ART [0002]

The present invention relates to a directional electrical steel sheet and a method of manufacturing the same, and more particularly, to a directional electrical steel sheet capable of ensuring excellent electromagnetic characteristics by performing a low temperature heat treatment after a homogenization heat treatment and a method of manufacturing the same.

Directional electric steel sheets used as iron core materials of transformers and motors can increase the content of silicon (Si) and drastically reduce iron loss. The grain oriented electrical steel sheet has a crystal orientation of (110) plane in the steel sheet face and a crystal orientation in the rolling direction is composed of grains having a goss texture parallel to the [001] axis, It is a magnetic material.

The characteristics required for such a directional electric steel sheet are high magnetic flux density and low iron loss. The magnetic flux density is determined according to the degree of arrangement of one axis in the rolling direction. If the magnetic flux density is high, the same performance can be exhibited even if the iron core material is used in a small amount.

Conventional electric steel sheets have a problem in that brittleness is increased due to a high silicon content and it is difficult to manufacture using the rolling. Thus, conventional electrical steel sheets have been fabricated either by chemical vapor deposition using SiCl ₄ or by high temperature diffusion using SiO ₂ fabrics.

A related prior art is Korean Patent Laid-Open Publication No. 10-2011-0063187 (published on Jun. 10, 2011), which discloses a low iron loss high specific gravity directional electric steel sheet.

It is an object of the present invention to provide a method for producing a grain-oriented electrical steel sheet in which the content of silicon is 6.4 to 6.6% by weight to satisfy excellent electromagnetic characteristics.

Another object of the present invention is to provide a grain-oriented electrical steel sheet produced by the above-described method and having an iron loss value (W / Kg) of 0.33 or less at a magnetic flux density of 1.0 T and a frequency of 60 Hz.

According to an aspect of the present invention, there is provided a method for manufacturing a grain-oriented electrical steel sheet, which comprises: subjecting a slab plate made of carbon (C), silicon (Si), and remaining iron (Fe) step; A cold rolling step of pickling the cooled steel and then cold-rolling a silica cloth on the surface of the steel; A homogenizing heat treatment step of subjecting the cold-rolled steel to homogenization heat treatment to diffuse silicon into the steel; And a low-temperature heat treatment step of subjecting the homogenized heat-treated steel to a low-temperature heat treatment at 500 to 700 ° C for 0.5 to 2 hours.

According to another aspect of the present invention, there is provided a grain-oriented electrical steel sheet comprising 0.0017 wt% or less of carbon (C), 6.4 to 6.6 wt% of silicon (Si), and balance iron (Fe) and unavoidable impurities (W / Kg) at a magnetic flux density of 1.0 T and a frequency of 60 Hz is controlled to be 0.33 or less by controlling the regular phase of FeSi and Fe ₃ Si by performing a low temperature heat treatment after performing a homogenization heat treatment .

The directional electrical steel sheet and the method of manufacturing the same according to the present invention strictly restrict the content of silicon to 6.4 to 6.6% by weight, and after the homogenization heat treatment is performed, the low temperature heat treatment is performed to control the regularity of FeSi and Fe ₃ Si , And the iron loss value (W / Kg) at a magnetic flux density of 1.0 T and a frequency of 60 Hz can be 0.33 or less.

Therefore, the grain-oriented electrical steel sheet and the manufacturing method thereof according to the present invention have a low iron loss effect, and as a result, excellent electromagnetic characteristics can be exhibited.

1 is a process flow diagram illustrating a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention.
Fig. 2 is a graph showing the iron loss test results for the specimen according to Example 1 and Comparative Example 1. Fig.
3 is a photograph showing the microstructure of the specimen according to Comparative Example 1. Fig.
4 is a photograph showing the microstructure of the specimen according to Example 1. 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. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

Hereinafter, a directional electrical steel sheet according to a preferred embodiment of the present invention and a method of manufacturing the same will be described in detail with reference to the accompanying drawings.

Electric steel sheet

The electric steel sheet according to the present invention aims at exhibiting an iron loss (W / Kg) of 0.33 or less at a magnetic flux density of 1.0 T and a frequency of 60 Hz.

To this end, the electrical steel sheet according to the present invention is composed of 0.0017 wt% or less of carbon (C), 6.4 to 6.6 wt% of silicon (Si), and the balance of iron (Fe) and unavoidable impurities.

At this time, the electric steel sheet is subjected to a homogenizing heat treatment and then subjected to a low-temperature heat treatment, whereby the regular phase of FeSi and Fe ₃ Si is controlled.

The steel sheet may contain at least one of manganese (Mn): 0.01 to 0.50 wt%, phosphorus (P): 0.003 wt% or less, sulfur (S): 0.001 wt% .

Hereinafter, the role and content of each component included in the electrical steel sheet according to the present invention will be described.

Carbon (C)

Carbon (C) is present in the iron (Fe) atomic lattice structure in the solid state, and moves in the molding process, and it disturbs the dislocation movement as a dislocation in the dislocation portion, thereby deteriorating the molding characteristics of the product.

In particular, the magnetic aging phenomenon refers to a phenomenon in which the temperature of the transformer itself rises when a user uses a directional electric steel plate assembled and transformed into a transformer, and thus the remaining carbon component in the material becomes a carbide such as Fe ₃ C. This carbide precipitates on the grain boundaries to prevent the magnetic flux from migrating, thereby deteriorating the magnetic properties. This can be solved by performing the decarburization annealing process before the heat treatment.

However, when the content of carbon (C) is more than 0.0017 wt%, the magnetic aging phenomenon may be conspicuous even though homogenization heat treatment is performed. Therefore, carbon (C) is preferably limited to a content ratio of 0.0017 wt% or less of the total weight of the electrical steel sheet according to the present invention.

Silicon (Si)

Silicon (Si) is a basic composition of an electric steel sheet, and it plays a role of lowering the core loss (iron loss) by increasing the resistivity of the material.

The silicon (Si) is preferably added at a content ratio of 6.4 to 6.6 wt% of the total weight of the electrical steel sheet according to the present invention. When the content of silicon (Si) is less than 6.4% by weight, there is a problem that the resistivity decreases and the iron loss characteristic deteriorates. On the other hand, when the content of silicon (Si) exceeds 6.6% by weight and is added in excess, brittleness of the steel increases and cold rolling becomes extremely difficult.

Manganese (Mn)

Manganese (Mn) lowers the solidification temperature of the precipitate during reheating and prevents cracks on both ends of the material during hot rolling.

Therefore, manganese (Mn) is preferably added in an amount of 0.01 to 0.50% by weight based on the total weight of the electrical steel sheet according to the present invention. When the content of manganese (Mn) is less than 0.01% by weight, the risk of cracking due to cracking during hot rolling is increased. On the other hand, when the content of manganese (Mn) exceeds 0.50 wt%, the adhesion of the forester coating is deteriorated.

In (P)

Phosphorus (P), like carbon, has a small atomic radius and is high in mobility in iron (Fe) crystals, and because of this atomic size, this element preferentially locates in the defect part of crystal grain boundaries. In this way, phosphorus (P), which is preferentially located in the defect region, blocks explosive iron (Fe) diffusion through the crystal grain boundaries, thereby inhibiting the formation of the gamma-alloy phase in the initial alloying process.

However, if the content of phosphorus (P) is higher than necessary, diffusion of iron (Fe) is suppressed to require excessive alloying temperature, and generation of a gamma-alloy phase is promoted in accordance with such temperature rise, It is also a factor. Therefore, phosphorus (P) is preferably limited to a content ratio of 0.003% by weight or less of the total weight of the electrical steel sheet according to the present invention.

Sulfur (S)

Sulfur (S) plays a role in forming precipitates of manganese (Mn) and emulsions, but if the content of sulfur is excessive, it may become difficult to solidify and diffuse the center segregation part during reheating in the hot rolling process.

Therefore, sulfur (S) is preferably limited to a content ratio of 0.001% by weight or less of the total weight of the electrical steel sheet according to the present invention.

Aluminum (Al)

Aluminum (Al) is ultimately made of nitride of (Al, Si, Mn) N type and serves as an inhibitor.

However, when a large amount of aluminum (Al) is added in excess of 0.01 wt% in the present invention, the nitride of Al series precipitates and grows too much, so that the effect as an inhibitor becomes insufficient. Therefore, in the present invention, the content of aluminum is limited to not more than 0.01% by weight of the total weight of the electrical steel sheet.

1 is a process flow diagram illustrating a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention.

Referring to FIG. 1, a method for manufacturing a directional electrical steel sheet according to an embodiment of the present invention includes a hot rolling step S110, a cold rolling step S120, a homogenizing heat treating step S130, and a low temperature heat treating step S130 .

Hot rolling

In the hot rolling step (S110), a steel consisting of carbon (C), silicon (Si), and remaining iron (Fe) and inevitable impurities is rolled and then cooled.

Specifically, in the hot rolling step, the slab plate made of carbon (C): not more than 0.0017 wt%, silicon (Si): not more than 2.0 wt%, and the balance of iron (Fe) and unavoidable impurities is reheated at 1150 to 1250 캜, Rolling at a temperature of ~ 1000 ° C, followed by cooling at 500 ~ 600 ° C.

The slab plate may further contain at least one of manganese (Mn): 0.01 to 0.50 wt%, phosphorus (P): 0.003 wt% or less, sulfur (S): 0.001 wt% May be included.

At this time, the rolling of the steel in the unidirectional state can cause generation of the aggregate structure that is related to the magnetic property, that is, the Goss structure, by causing the strain by causing rolling in the steel structure. As a result, it is possible to impart excellent magnetic properties to the wire material even if only the coiling is performed in a hot state. Such finish rolling is preferably carried out at 900 to 1000 占 폚. If the finish rolling temperature is less than 900 占 폚, the surface load of the steel may be caused by the process load, and the rolling roll may be broken. On the other hand, when the finish rolling temperature exceeds 1000 캜, the strain can be effectively exerted due to an increase in ductility at the time of rolling.

Cold rolling

In the cold rolling step (S120), after pickling the cooled steel, a silica cloth is attached to the surface of the steel and cold-rolled. At this time, it is preferable to adhere the silicon fabric to the surface of the steel with a thickness of 10 mu m or less.

The cold rolling is preferably carried out at a reduction ratio of 60 to 80%. When the reduction rate of the cold rolling is less than 60%, the deformation effect of the hot-rolled steel is small. On the contrary, when the reduction rate exceeds 80%, there is a problem of raising the process cost due to excessive rolling without increasing the effect further.

Homogenization heat treatment

In the homogenization heat treatment step (S130), the cold-rolled steel is subjected to a homogenizing heat treatment to diffuse silicon into the steel. At this time, silicon is diffused into the cold-rolled steel to increase the content of silicon in the finally produced steel to 6.4 to 6.6 wt%. By increasing the content of silicon, the low iron loss effect can be improved.

At this time, the homogenization heat treatment is preferably performed at 1100 to 1200 ° C for 5 to 15 hours. If the homogenization annealing temperature is less than 1100 ° C, it may be difficult to uniformly distribute the ordered phases of FeSi and Fe ₃ Si. On the other hand, when the homogenization heat treatment temperature exceeds 1200 ° C, it acts as a factor for raising the manufacturing cost and time without further increase of the effect, which is not economical.

In addition, when the homogenization heat treatment time is less than 5 hours, there is a great possibility that silicon diffusion can not be smoothly performed. On the other hand, when the homogenizing heat treatment time exceeds 15 hours, it serves only as an allowance to raise the manufacturing cost of the electric steel sheet without further increase in the effect.

The homogenization heat treatment is preferably performed in a high purity hydrogen (H ₂ ) atmosphere in order to prevent unnecessary oxidation of the surface of the steel sheet. At this time, the homogenization heat treatment can be performed by the continuous annealing method and the box annealing method, but in consideration of sufficient diffusion of silicon, the box annealing method is more preferably used.

Low temperature heat treatment

In the low temperature heat treatment step (S140), the homogenized heat treated steel is subjected to low temperature heat treatment at 500 to 700 ° C for 0.5 to 2 hours.

The low temperature heat treatment is carried out for the purpose of inducing the growth of the regular phase of FeSi and Fe ₃ Si to a large width. Particularly, the regular growth of FeSi and Fe ₃ Si plays a role of reducing the pinning site during the magnetization process, thereby reducing the iron loss and improving the electromagnetic characteristics.

In this step, when the low temperature heat treatment temperature is less than 500 占 폚 or the low temperature heat treatment time is less than 0.5 hour, it may be difficult to grow the regular phase of FeSi and Fe ₃ Si to a large extent. On the contrary, when the low temperature heat treatment temperature exceeds 700 DEG C or the low temperature heat treatment time exceeds 2 hours, it can be a factor to increase the manufacturing cost and time without further increase of the effect, which is not economical.

The low temperature heat treatment is preferably performed in a high purity hydrogen (H ₂ ) atmosphere in order to prevent unnecessary oxidation of the surface of the steel sheet. At this time, the low temperature heat treatment can be carried out by the continuous annealing method and the box annealing method, but when considering the regular growth of FeSi and Fe ₃ Si, the box annealing method is more preferably used.

The electric steel sheet manufactured in the above steps S110 to S140 is subjected to a homogenizing heat treatment and then subjected to a low temperature heat treatment at 500 to 700 ° C for 0.5 to 2 hours so that the regular phase of FeSi and Fe ₃ Si is controlled, The iron loss value (W / Kg) at 1.0 T and the frequency of 60 Hz can be 0.33 or less.

Thus, the electric steel sheet produced according to the present invention induces a large-scale growth of the ordered phase of FeSi and Fe ₃ Si through the low-temperature heat treatment, thereby reducing the iron loss due to the reduction of the pinning site during the magnetization process The electromagnetic characteristics can be improved.

Therefore, the electric steel sheet produced according to the present invention has an advantage that the electric power loss can be suppressed through the improvement of the electromagnetic characteristics, and the electromagnetic lifetime can be improved.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

1. Specimen Manufacturing

Example 1

The steel consisting of 0.0015 wt% of C, 3.0 wt% of Si, 0.1 wt% of Mn and the balance of Fe and unavoidable impurities was reheated at 1180 캜, finished at 940 캜, and then cooled to 520 캜.

Thereafter, after pickling the cooled steel, a silica cloth (manufactured by Hansol New Materials Co., Ltd.) having a thickness of 30 탆 was attached to the surface of the steel and cold-rolled at a reduction ratio of 75%.

Thereafter, homogenization heat treatment was performed at 1100 占 폚 for 10 hours, and then low temperature heat treatment was performed at 600 占 폚 for 1 hour. At this time, the homogenization heat treatment and the low temperature heat treatment were performed in a box annealing manner under a hydrogen gas atmosphere.

Example 2

A specimen was prepared in the same manner as in Example 1 except that the homogenization heat treatment was performed at 1150 ° C for 15 hours and then the low temperature heat treatment was performed at 650 ° C for 50 minutes.

Example 3

A specimen was prepared in the same manner as in Example 1, except that the low temperature heat treatment was performed at 700 占 폚 for 40 minutes.

Comparative Example 1

The steel consisting of 0.0014 wt% of C, 3.0 wt% of Si, 0.5 wt% of Mn, and the balance of Fe and unavoidable impurities was reheated at 1180 캜, followed by finish rolling at 940 캜, followed by cooling to 520 캜.

Thereafter, after pickling the cooled steel, a silica cloth (manufactured by Hansol New Materials Co., Ltd.) having a thickness of 30 탆 was attached to the surface of the steel and cold-rolled at a reduction ratio of 75%.

Thereafter, homogenization heat treatment was performed at 1300 ° C for 8 hours. At this time, the homogenization heat treatment was carried out in a box annealing manner under a hydrogen gas atmosphere.

Comparative Example 2

A specimen was prepared in the same manner as in Comparative Example 1, except that the homogenization heat treatment was performed at 900 占 폚 for 4 hours.

2. Iron Loss Measurement

Table 1 shows the results of iron loss measurements on the specimens prepared according to Examples 1 to 3 and Comparative Examples 1 and 2, and FIG. 2 shows the iron loss values of the specimens according to Example 1 and Comparative Example 1 Fig. At this time, the iron loss value was measured at a magnetic flux density of 1.0 T and a frequency of 60 Hz.

[Table 1]

Referring to Table 1 and FIG. 2, it can be confirmed that the iron losses (W / Kg) at a magnetic flux density of 1.0 T and a frequency of 60 Hz are 0.33 or less in Examples 1 to 3 in which the low temperature heat treatment was performed after the homogenization heat treatment.

On the other hand, in the specimens prepared according to Comparative Examples 1 and 2 in which only homogenization heat treatment was performed without performing low temperature heat treatment, the iron loss values (W / Kg) at magnetic flux density 1.0 T and frequency 60 Hz were 0.366 W / Kg and 0.351 W / Kg, respectively.

FIG. 3 is a photograph showing the microstructure of the specimen according to Comparative Example 1, and FIG. 4 is a photograph showing the microstructure of the specimen according to Example 1. FIG.

As shown in FIGS. 3 (a) and 3 (b), in the case of the test piece prepared according to Comparative Example 1, it can be confirmed that the regular growth of FeSi and Fe ₃ Si is not properly performed. On the other hand, as shown in FIGS. 4 (a) and 4 (b), in the case of the specimen produced according to Example 1, the regular phases of FeSi and Fe ₃ Si grew to a large extent by the low temperature heat treatment, It is considered that the pinning site decreased during the magnetization process due to the regular growth of FeSi and Fe ₃ Si.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

S110: Hot rolling step
S120: Cold rolling step
S130: homogenization heat treatment step
S140: low temperature heat treatment step

Claims (5)

A hot rolling step in which a slab plate made of carbon (C), silicon (Si) and the balance iron (Fe) and unavoidable impurities is subjected to a co-milling process and then cooled;
A cold rolling step of pickling the cooled steel and then cold-rolling a silica cloth on the surface of the steel;
A homogenizing heat treatment step of subjecting the cold-rolled steel to homogenization heat treatment to diffuse silicon into the steel; And
And a low-temperature heat treatment step of subjecting the homogenized heat-treated steel to a low-temperature heat treatment at 500 to 700 ° C for 0.5 to 2 hours.
The method according to claim 1,
The homogenization heat treatment
Wherein said step (c) is carried out at 1100 to 1200 ° C for 5 to 15 hours.
The method according to claim 1,
Each of the homogenization heat treatment and the low temperature heat treatment
Wherein the annealing is carried out in a box annealing manner.
0.0017 wt% or less of carbon (C), 6.4 to 6.6 wt% of silicon (Si), and the balance of iron (Fe) and unavoidable impurities,
(W / Kg) at a magnetic flux density of 1.0 T and a frequency of 60 Hz is controlled to be 0.33 or less by controlling a regular phase of FeSi and Fe ₃ Si by performing a low temperature heat treatment after performing a homogenization heat treatment. Electric steel plate.
6. The method of claim 5,
The steel sheet
, At least one of manganese (Mn): 0.01 to 0.50 wt%, phosphorus (P): 0.003 wt% or less, sulfur (S): 0.001 wt% or less and aluminum (Al) As shown in Fig.

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