KR101568835B1 - Oriented electrical steel sheet and method for manufacturing the same - Google Patents

Abstract

A method of manufacturing a directional electrical steel sheet is disclosed. A method for producing a grain-oriented electrical steel sheet according to the present invention comprises the steps of: 2.8 to 3.6% Si, 0.020 to 0.040% of Si, 0.20% or less of Mn (excluding 0%), 0.0030 to 0.0075% : 0.04 to 0.07%, S: 0.0060% or less (excluding 0%), P: 0.02% to 0.075%, the balance being Fe and other unavoidable impurities; Reheating the slab; Hot-rolling the slab to produce a hot-rolled steel sheet; Annealing the hot-rolled steel sheet by hot-rolling; Cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet; Subjecting the cold-rolled steel sheet to decarburization annealing and steep annealing; Applying and annealing the annealing separator to perform final annealing; And a continuous temperature gradient is given when annealing the hot rolled sheet. The temperature at the start of annealing is 920 to 930 占 폚, and the temperature at the end of annealing is 910 to 920 占 폚.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a directional electric steel sheet,

The present invention relates to a grain-oriented electrical steel sheet and a method for producing the same, and more particularly, to a grain-oriented electrical steel sheet with improved magnetic properties and iron loss by controlling annealing conditions and a method for producing the same.

The oriented electrical steel sheet has a so-called Goss texture in which the orientation of all the grains on the steel sheet face is {110} plane and the crystal orientation in the rolling direction is parallel to the <001> axis, This is a very good soft magnetic material.

A method for producing a grain-oriented electrical steel sheet is a method for producing a hot-rolled steel sheet by heating a slab containing 2% or more Si and hot-rolling the slab.

The hot-rolled steel sheet thus produced is subjected to hot-rolled sheet annealing, cold rolling, and primary recrystallization annealing.

After the primary recrystallization annealing is completed, the annealing separator is applied and rolled, and secondary recrystallization annealing is performed.

The magnetic properties of the oriented electrical steel sheet depend on how well the {110} <001> texture is formed in the secondary recrystallization. That is, when the {110} plane and the <001> direction in the rolling direction are arranged in parallel exactly on the rolled surface, the magnetic properties are excellent.

On the other hand, in order to stably induce the secondary recrystallization, it is important to determine the grain size of the primary recrystallization, which is the driving force of the secondary recrystallization, and the size and distribution of the grain growth inhibitor, which is a precipitate that suppresses the growth of the primary recrystallization.

In order to obtain a strong inhibition of grain growth, it is known that the number of fine precipitates having a size of several hundreds to 2,000 microns is increased as much as possible and uniformly distributed, thereby increasing the inhibition of grain growth.

The secondary recrystallization annealing of the grain-oriented electrical steel sheet is heat-treated in the form of coils wound with the annealing separator applied. When MgO as the annealing separator is coated, MgO is mixed with water to be coated, so that the coil to be a material of high temperature annealing is a form in which hydrated MgO containing a large amount of water is coated on the surface of the steel sheet and wound.

Therefore, when the secondary recrystallization annealing is performed, the inside of the coil is disadvantageous in releasing hydrated water and an oxidizing atmosphere is formed. Therefore, the phenomenon that the inhibitor of the grain growth is oxidized and decomposed by moisture at a temperature lower than the temperature at which the secondary recrystallization occurs is easily generated.

For this reason, the temperature distribution and the atmospheric conditions between the inside and the outside of the coil are changed, and the magnetic characteristics are varied depending on the position of the steel sheet. Especially, in the case of the inside of the coil, it is difficult to form a stable secondary recrystallization atmosphere, There arises a problem that causes deterioration.

DISCLOSURE OF THE INVENTION The present invention has been made in order to solve such problems and it is an object of the present invention to provide a directional electric steel sheet which has a low iron loss uniformly and has excellent magnetic properties without any deviation according to the position of the steel sheet in the final annealing of the coil state in the subsequent coil state, And to provide a manufacturing method thereof.

A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises: 2.8 to 3.6% by weight of Si; 0.020 to 0.040% by weight of an acid soluble Al; 0.20% , 0.004 to 0.0075%, C: 0.04 to 0.07%, S: 0.0060% or less (excluding 0%), P: 0.02% to 0.075%, the balance being Fe and other unavoidable impurities; Reheating the slab; Hot-rolling the slab to produce a hot-rolled steel sheet; Annealing the hot-rolled steel sheet by hot-rolling; Cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet; Subjecting the cold-rolled steel sheet to decarburization annealing and steep annealing; Applying an annealing separator and winding and performing final annealing; The annealing may be performed at a temperature of 920 to 930 ° C at the beginning of annealing, and at a temperature of 910 to 920 ° C at the end of annealing.

The temperature at the start of the annealing may be 1.075 to 2.2% higher than the temperature at the end of annealing.

According to another aspect of the present invention, there is provided a method of manufacturing a directional electrical steel sheet,

(Excluding 0%), N: 0.0030 to 0.0075%, C: 0.04 to 0.07%, S: 0.0060% or less (by weight), Si: 2.8 to 3.6% in weight%, acid soluble Al: 0.020 to 0.040% 0%), P: 0.02% to 0.075%, the balance being Fe and other unavoidable impurities; Reheating the slab; Hot-rolling the slab to produce a hot-rolled steel sheet; Annealing the hot-rolled steel sheet by hot-rolling; Cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet; Subjecting the cold-rolled steel sheet to decarburization annealing and steep annealing; Applying an annealing separator and winding and performing final annealing; / RTI &gt;

The annealing temperature up to 45 to 55% of the entire length of the hot-rolled sheet during annealing of the hot-rolled sheet may be 920 to 930 캜, and the remainder of the annealing temperature may be 910 to 920 캜.

The annealing temperature up to 45 to 55% of the total length of the hot-rolled sheet may be 1.075 to 2.2% higher than the annealing temperature of the remaining portion.

The slab may further include at least one of Sn and Sb in an amount of 0.01 to 0.045%.

In the step of reheating the slab, the reheating temperature may be 1050 to 1250 ° C.

The decarburization annealing and the steep annealing can be performed at a temperature ranging from 800 to 950 ° C.

The final annealing may be performed in a mixed atmosphere of nitrogen and hydrogen gas at a temperature rising period before the secondary recrystallization, and in a hydrogen atmosphere after completion of secondary recrystallization.

The method for manufacturing a grain-oriented electrical steel sheet according to the present invention controls the conditions at the time of annealing the hot-rolled steel sheet to adjust the size of the precipitates inside and outside the coil wound around the secondary recrystallization annealing. Therefore, it is possible to provide a method of manufacturing a grain-oriented electrical steel sheet in which a secondary recrystallization can be stably performed even in the inside of a coil when secondary recrystallization annealing is performed.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below. 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.

According to another aspect of the present invention, there is provided a method of manufacturing a directional electrical steel sheet,

First, in terms of% by weight, Si: 2.8 to 3.6%, acid soluble Al: 0.020 to 0.040%, Mn: 0.20% or less (excluding 0%), N: 0.0030 to 0.0075%, C: 0.04 to 0.07%, S: (Excluding 0%), P: 0.02% to 0.075%, and the balance of Fe and other unavoidable impurities.

The slab may further include at least one of Sn and Sb in an amount of 0.01 to 0.045%.

The reason for limiting the components of the present invention will be described.

[Si: 2.8 to 3.6 wt%]

Si is a basic composition of an electric steel sheet and plays a role of lowering the core loss by increasing the resistivity of the material.

When the Si content is less than 2.8 wt%, the resistivity is decreased, and the eddy current loss is increased to deteriorate the iron loss characteristic. In addition, during high temperature annealing, phase transformation between ferrite and austenite occurs, and the secondary recrystallization becomes unstable as well as the structure is severely damaged.

When the Si content exceeds 3.6 wt%, the mechanical properties of the electrical steel sheet increase in brittleness and the toughness is decreased, so that the plate rupture incidence rate during rolling is intensified and the formation of secondary recrystallization becomes unstable.

[Acid soluble Al: 0.020 to 0.040 wt%]

Al serves as a grain growth inhibitor by forming nitrides of (Al, Si, Mn) N and AlN type.

When Al is less than 0.020 wt%, sufficient effect as an inhibitor can not be expected because the number and volume to be formed are considerably low.

When Al is more than 0.040 wt%, a coarse nitride is formed and the crystal grain growth inhibiting ability is lowered.

[Mn: 0.20 wt% or less (excluding 0%)]

Mn has an effect of reducing the total iron loss by decreasing the eddy current by increasing the resistivity.

(Al, Si, Mn) by reacting with nitrogen introduced by the nitriding treatment together with Si to form a precipitate of N, thereby suppressing the growth of the primary recrystallized grains and causing secondary recrystallization.

If Mn is more than 0.20 wt%, 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 , thereby hindering formation of a base coat formed during high temperature annealing, and the surface quality is lowered.

In addition, since high temperature annealing induces phase transformation between ferrite and austenite, aggregate structure is severely damaged and magnetic properties are greatly deteriorated.

Therefore, the content of Mn is preferably 0.20 wt% or less.

[N: 0.0030 to 0.0075 wt% or less]

N is an element that reacts with Al to form AlN.

If N exceeds 0.0075 wt% in the steelmaking process, surface defects due to nitrogen diffusion are caused in the step after hot rolling, excessive nitrides are formed and the rolling property is lowered. If it is less than 0.0030 wt%, the crystal growth inhibitor can not be sufficiently produced.

[C: 0.04 to 0.07 wt%]

C is an element that causes phase transformation between ferrite and austenite and is an essential element for improving the rolling property of an electric steel sheet, but deteriorates magnetic properties formed due to the aging effect when remaining in the final product.

When the content is less than 0.04 wt%, phase transformation between ferrite and austenite does not occur, resulting in non-uniformity of slab and hot rolled microstructure.

If it exceeds 0.07 wt%, not only a sufficient decarburization effect can not be obtained in the decarburization annealing process, but also the secondary recrystallization texture is damaged due to the phase transformation phenomenon, and magnetic properties are deteriorated due to magnetic aging .

[S: 0.0060wt% or less (excluding 0%)]

S is an element that reacts with Mn to form MnS.

When S is more than 0.0060 wt%, precipitates of MnS are formed in the slab to inhibit grain growth, and it is difficult to control the microstructure in the subsequent process due to segregation at the center of the slab during casting.

[P: 0.02 to 0.075 wt%]

P is segregated in grain boundaries to interfere with grain boundary movement and at the same time has a role of suppressing grain growth and has an effect of improving {110} < 001 >

When the content of P is less than 0.02 wt%, there is no addition effect. When the content of P is more than 0.075 wt%, the brittleness is increased and the rolling property is greatly deteriorated, so that the content is preferably 0.005 to 0.05 wt%.

[At least one Sn or Sb: 0.01 to 0.045 wt%]

Sn and Sb are crystal grain growth inhibitors because they are elements that interfere with grain boundary movement as grain boundary segregation elements.

Also, by increasing the grain fraction of the Goss orientation in the primary recrystallized texture, the number of Goss bearing nuclei growing in the secondary recrystallized texture increases and the size of the secondary recrystallized microstructure is reduced.

However, if it is added in an excess amount, it is not possible to secure a good surface due to segregation in the lower part of the oxide layer, and there is a problem in that the brittleness increases due to excessive segregation in the grain boundary, so that at least one of Sn and Sb is preferably 0.01 to 0.045 wt%.

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

First, Si: 2.8 to 3.6%, Si: 0.020 to 0.040%, Mn: 0.20% or less (excluding 0%), N: 0.0030 to 0.0075%, C: 0.04 to 0.07%, and S: 0.0060% (Excluding 0%), P: 0.02% to 0.075%, the remainder being Fe and other unavoidable impurities, and continuously casting molten steel containing at least one of Sn and Sb in an amount of 0.01 to 0.045% .

The slab is charged into a furnace and reheated at 1050 to 1250 ° C. The total amount of nitrogen recycled to the slab in the step of reheating the slab may be 20 to 70 ppm.

The preferred size of the primary recrystallized grains in the component system of the electrical steel sheet according to the embodiment of the present invention is about 15 to 25 占 퐉.

If the size of the primary recrystallized grains is less than 15.0 탆, the crystal growth driving force is large and the temperature at which the secondary recrystallization starts is lowered, and the primary recrystallization is suppressed, while the selective growth period in which only the secondary recrystallization grows becomes narrow do. In this case, the conditions for the growth of a good secondary recrystallized structure are not well established, so that the degree of secondary recrystallization is poor and the secondary recrystallized grain size becomes large.

On the other hand, if the size of the primary recrystallized grains is larger than 25.0 탆, the crystal growth driving force is small and the temperature at which the secondary recrystallization starts is increased, and the primary recrystallization is suppressed while the selective growth period in which only the secondary recrystallization grows becomes narrower.

In this case, in the region where the secondary recrystallization does not grow in the secondary recrystallization forming region, the size of the primary recrystallized grains becomes larger, and the specimen passes through in the thickness direction.

These crystal grains are then left without being extinguished even after the refining annealing, resulting in a problem that secondary recrystallization fine grains are produced.

The reheated slab is hot rolled to produce a hot rolled steel sheet.

The hot rolled steel sheet can be manufactured by hot rolling to a thickness of 1.5 to 4.0 mm.

The hot-rolled sheet is subjected to hot-rolled sheet annealing. The hot-rolled sheet annealing can be carried out in a continuous annealing furnace. And the distribution of the precipitates of the grain growth inhibitor and the size of the precipitates are determined during annealing of the hot rolled sheet.

In the manufacturing process of the grain oriented electrical steel sheet according to the related art, the phenomenon that the grain growth inhibitor is oxidized and decomposed by moisture at a temperature lower than the temperature at which the secondary recrystallization occurs in the coil easily occurs during the secondary recrystallization annealing.

In order to solve this problem, a continuous temperature gradient is given when annealing the hot-rolled steel sheet, and the size of the precipitate formed at the front end of the hot-rolled steel sheet is larger than that of the precipitate formed at the rear end of the hot-rolled steel sheet.

In order to increase the size of the precipitate produced at the front end of the hot-rolled steel sheet to be larger than that of the precipitate generated at the rear end of the hot-rolled steel sheet, the temperature at the beginning of annealing is 920 to 930 ° C, have.

The temperature at the start of the annealing may be 1.075 to 2.2% higher than the temperature at the end of annealing.

As described above, by controlling the size of the precipitate inside the coil and the outside of the coil, it is possible to prevent the decomposition of the grain growth inhibitor present inside the coil wound up during the secondary recrystallization annealing, which will be described later.

The front end portion of the hot-rolled steel sheet becomes the inside of the coil after winding, and the rear end portion of the hot-rolled steel sheet becomes the outside of the coil after winding.

The annealing temperature up to 45 to 55% of the entire length of the hot rolled sheet can be carried out at 920 to 930 占 폚, and the annealing temperature at the remainder can be carried out at 910 to 920 占 폚, instead of the continuous temperature gradient when annealing the hot rolled sheet.

The annealing temperature up to 45 to 55% of the total length of the hot-rolled sheet may be 1.075 to 2.2% higher than the annealing temperature of the remainder.

The above-described control can prevent the phenomenon that the grain growth inhibitor inside the coil is decomposed during the secondary recrystallization annealing.

Thereafter, the cold rolling is performed by using a reverse mill or a tandem mill to perform cold rolling twice or more times including cold rolling or intermediate annealing to produce a cold rolled sheet having a final product thickness.

After the cold rolling is finished, decarburization annealing and steep annealing are performed. The decarburization annealing and the steep annealing can be performed at a temperature ranging from 800 to 950 ° C.

Further, it is possible to control the amount of nitrogen remaining in the steel sheet after the decarburization annealing and the nitriding annealing to be maintained at 100 to 300 ppm.

If it is less than 100 ppm, nitrogen may not form inhibitor properly. If it exceeds 300 ppm, it may take an excessive time to remove nitrogen in the final annealing process.

After performing decarburization annealing and steep annealing, MgO as an annealing separator is applied and final annealing is performed.

The final annealing is performed in a mixed atmosphere of nitrogen and hydrogen gas at a temperature rising to 1200 ° C, and can be maintained for 10 hours or longer in a hydrogen atmosphere after reaching 1200 ° C.

The final annealing is performed for formation of {110} < 001 > texture by secondary recrystallization, formation of a vitreous film by reaction of MgO with an oxide layer formed upon decarburization, and insulation removal and removal of impurities that impair magnetic properties.

As a final high-temperature annealing method, the nitride as a grain growth inhibitor is protected by maintaining a mixed gas of nitrogen and hydrogen at a temperature rising period before the secondary recrystallization, so that the secondary recrystallization is well developed. After completion of the secondary recrystallization, For a long time to remove impurities.

Hereinafter, the present invention will be described more specifically by way of examples.

[Example]

A slab composed of 3.15% of Si, 0.052% of C, 0.09% of Mn, 0.029% of Sol-Al, 0.005% of S, 0.0049% of N and impurities inevitably mixed with Fe was heated at 1150 ° C, mm thick.

The hot-rolled steel sheet was subjected to cracking treatment at different temperatures at the beginning of annealing and at the end of annealing as shown in Table 1.

After the annealing was completed, cold-rolling was performed to a final thickness of 0.23 mm, and then primary recrystallization annealing was performed. Then, MgO coating was performed, secondary recrystallization annealing was performed, and an insulating liquid containing an inorganic material as a main component was applied, and the magnetic properties of the inside and the outside of the coil were measured.

The magnetism was represented by iron loss until it was magnetized at 50 Hz to 1.7 Tesla.

Hot-rolled sheet Annealing Cracking temperature (℃) Iron loss (W / kg) Remarks Temperature at annealing end Temperature at the start of annealing Outside coil Inside coil 900 900 0.88 0.90 Comparative material 910 910 0.84 0.87 Comparative material 910 920 0.84 0.85 Invention material 910 930 0.84 0.84 Invention material 920 920 0.88 0.85 Comparative material 930 920 0.92 0.85 Comparative material

As shown in Table 1, the outer periphery of the high temperature annealing was subjected to a crack treatment at 910 to 920 ° C, and the inner periphery of the high temperature annealing, in which the precipitate was liable to be decomposed by moisture, was subjected to a heat treatment at 920 to 930 ° C, Uniform and excellent iron loss was obtained in both the inner and outer parts when the inner part was cracked 10 to 20 ° C higher than the outer part.

That is, by controlling the annealing temperature of the hot-rolled sheet in the present invention, the size of the precipitate at the front end of the hot-rolled sheet is larger than the size of the precipitate at the rear end, And no phenomenon of oxidation and decomposition by moisture at the temperature occurred.

Therefore, the grain-oriented electrical steel sheet produced by the present invention has uniform iron loss at both the front end and the rear end.

It can be seen that the grain-oriented electric steel sheet produced by the present invention has a uniform iron loss at the front end and the rear end of the steel sheet with a difference in iron loss of 1.2% or less.

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 (25)

(Excluding 0%), N: 0.0030 to 0.0075%, C: 0.04 to 0.07%, S: 0.0060% or less (by mass), Si: 2.8 to 3.6% by mass%, acid soluble Al: 0.020 to 0.040% 0%), P: 0.02% to 0.075%, the balance being Fe and other unavoidable impurities;
Reheating the slab;
Hot-rolling the slab to produce a hot-rolled steel sheet;
Annealing the hot-rolled steel sheet by hot-rolling;
Cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet;
Subjecting the cold-rolled steel sheet to decarburization annealing and steep annealing; And
Applying and annealing the annealing separator to perform final annealing;
/ RTI &gt;
A continuous temperature gradient is applied to the annealing temperature of the front end portion and the rear end portion of the hot-rolled steel sheet during the annealing of the hot-rolled steel sheet, the annealing temperature at the front end of the hot-rolled steel sheet is 920 to 930 ° C, To 920 &lt; 0 &gt; C. The method according to claim 1,
Wherein the annealing temperature at the front end of the hot-rolled steel sheet is 1.075 to 2.2% higher than the annealing temperature at the rear end of the hot-rolled steel sheet. The method according to claim 1,
Wherein the slab further comprises at least one of Sn and Sb in an amount of 0.01 to 0.045%. The method of claim 3,
Wherein the reheating temperature in the step of reheating the slab is 1050 to 1250 占 폚. 5. The method of claim 4,
The decarburization annealing and the steep annealing are carried out in a temperature range of 800 to 950 캜. 6. The method of claim 5,
Wherein the final annealing is performed in a mixed atmosphere of nitrogen and hydrogen gas in a temperature rising period before the secondary recrystallization and in a hydrogen atmosphere after completion of secondary recrystallization. (Excluding 0%), N: 0.0030 to 0.0075%, C: 0.04 to 0.07%, S: 0.0060% or less (by mass), Si: 2.8 to 3.6% by mass%, acid soluble Al: 0.020 to 0.040% 0%), P: 0.02% to 0.075%, the balance being Fe and other unavoidable impurities;
Reheating the slab;
Hot-rolling the slab to produce a hot-rolled steel sheet;
Annealing the hot-rolled steel sheet by hot-rolling;
Cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet;
Subjecting the cold-rolled steel sheet to decarburization annealing and steep annealing; And
Applying and annealing the annealing separator to perform final annealing;
/ RTI &gt;
Wherein the annealing temperature up to 45 to 55% of the total length of the hot-rolled sheet during annealing of the hot-rolled sheet is 920 to 930 占 폚, and the remainder of annealing temperature is 910 to 920 占 폚. 8. The method of claim 7,
Wherein the annealing temperature up to 45 to 55% of the total length of the hot-rolled sheet is 1.075 to 2.2% higher than the annealing temperature of the remaining portion. 8. The method of claim 7,
Wherein the slab further comprises at least one of Sn and Sb in an amount of 0.01 to 0.045%. 10. The method of claim 9,
Wherein the reheating temperature in the step of reheating the slab is 1050 to 1250 占 폚. 11. The method of claim 10,
The decarburization annealing and the steep annealing are carried out in a temperature range of 800 to 950 캜. 12. The method of claim 11,
Wherein the final annealing is performed in a mixed atmosphere of nitrogen and hydrogen gas in a temperature rising period before the secondary recrystallization and in a hydrogen atmosphere after completion of secondary recrystallization. delete delete delete delete delete delete delete delete delete delete delete delete delete