KR101594598B1 - Method for manufacturing the oriented electrical steel sheet - Google Patents

Abstract

A method of manufacturing a directional electrical steel sheet according to the present invention includes the steps of: providing an electrical steel slab; Reheating the slab; Hot-rolling the slab to produce a hot-rolled steel sheet; Cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet; A first recrystallization annealing step of the cold-rolled steel sheet; And secondary recrystallization annealing the electric steel sheet after the primary recrystallization annealing has been completed; And the secondary recrystallization annealing is performed in a state in which an electric field is applied.

Description

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

The present invention relates to a method for producing a grain-oriented electrical steel sheet, and more particularly, to a method for producing a grain-oriented electrical steel sheet capable of shortening the annealing time during secondary recrystallization annealing.

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.

In general, magnetic properties can be expressed by magnetic flux density and iron loss, and high magnetic flux density can be obtained by precisely aligning the orientation of the crystal grains in the {110} < 001 > orientation.

The oriented electrical steel sheet having excellent magnetic properties should strongly develop the goss texture in the {110} < 001 > orientation in the rolling direction of the steel sheet. In order to form such a texture, the grains of Goss orientation are secondary recrystallization Unsteady grain growth must be formed.

In order to develop such a goss texture, various process conditions such as component control during steelmaking, slab reheating in hot rolling and hot rolling process control, hot-rolled sheet annealing, primary recrystallization annealing, and secondary recrystallization annealing are very precise It must be strictly controlled.

The production of directional electrical steel sheets is carried out through a two-stage cold rolling, primary recrystallization and secondary recrystallization processes including slab reheating, hot rolling, hot-rolled sheet annealing, one cold rolling or intermediate annealing.

Among them, the secondary recrystallization annealing step is divided into a temperature rising section for forming the secondary recrystallization of the Goss grain and a annealing annealing section for improving the iron loss.

In order to stably induce secondary recrystallization of the Goss particles in the temperature rising period, the temperature is elevated to a secondary recrystallization starting temperature of 1050 to 1100 ° C at a slow rate of 40 ° C / hr or less.

Immediately after the second recrystallization of the Goss grains is completed, N and S as the precipitate forming elements are not completely removed, so that precipitates are formed again upon cooling, and there are many island grains inside the Goss secondary recrystallized grains, and iron loss is poor.

Therefore, the annealing annealing is performed at a temperature of 1100 ° C or more for 30 hours or longer at which the secondary recrystallization is completed to remove the island grains in the residual N, S and secondary recrystallized grains to improve iron loss.

The annealing annealing process, which is performed at a temperature of 1100 占 폚 or more for 30 hours or more for a long time, is a step required for securing low iron loss, but there is a problem that the productivity of the grain oriented electrical steel sheet is lowered and energy consumption for maintaining the high temperature is large.

SUMMARY OF THE INVENTION The present invention provides a directional electrical steel sheet capable of effectively reducing residual N and S by applying an electric field in a secondary recrystallization section to shorten secondary recrystallization annealing annealing time and providing a manufacturing method thereof .

The method for producing a grain-oriented electrical steel sheet according to the present invention comprises the steps of: providing an electric steel sheet slab containing 2.0 to 6.5% Si by weight and comprising the balance Fe and other unavoidable impurities; Hot-rolling the slab to produce a hot-rolled steel sheet; Cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet; A first recrystallization annealing step of the cold-rolled steel sheet; And secondary recrystallization annealing the electric steel sheet after the primary recrystallization annealing has been completed; And the secondary recrystallization annealing is performed in a state in which an electric field is applied.

The secondary recrystallization annealing includes a temperature increasing step and a refining annealing step, and the refining annealing step can be carried out while applying an electric field.

The magnitude of the electric field may be from 1 kV / cm to 3 kV / cm.

The annealing atmosphere in the secondary recrystallization annealing step is heat treated using a mixed gas of hydrogen and nitrogen in the temperature rising step, and can be cracked using hydrogen gas in refining annealing.

The temperature raising step may be performed at a temperature raising rate of 40 ° C / hr or less in a temperature range of 1050 to 1100 ° C, and the refining annealing may be performed at a temperature of 1100 ° C or more.

Further comprising a step of annealing the hot-rolled steel sheet after the step of manufacturing the hot-rolled steel sheet, wherein the annealing of the hot-rolled steel sheet can be carried out at a temperature of 900 ° C or higher.

The step of producing the cold-rolled steel sheet may be performed by cold rolling twice or more including cold rolling or intermediate annealing once, and warm rolling may be carried out during cold rolling to maintain the temperature of the steel sheet at 100 캜 or higher.

And performing decarburization annealing and steep annealing on the cold-rolled steel sheet after the step of manufacturing the cold-rolled steel sheet, wherein the step of performing the decarburization annealing and the steep annealing of the cold-rolled steel sheet can simultaneously perform the decarburization annealing and the steep annealing .

The decarburization annealing and the steep annealing may be performed such that the amount of nitrogen formed in the steel sheet is 100 to 300 ppm.

Wherein the slab contains 2.0 to 6.5% of Si, 0.005 to 0.04% of Al, 0.20% or less of Mn (not including 0%), 0.01% or less of N, 0.01 to 0.10% % Or less (excluding 0%), and the remainder may be a slab composed of Fe and other unavoidable impurities.

INDUSTRIAL APPLICABILITY The method for producing a grain-oriented electrical steel sheet according to the present invention shortens the annealing time in the secondary recrystallization process, thereby increasing the productivity.

In addition, it is possible to shorten the annealing time to reduce the energy for production of the electric steel sheet, thereby improving the economical efficiency.

Further, since the atomic diffusion rate in the electric steel sheet is increased during the refining annealing, island grains in the secondary N, S and GOSS secondary recrystallized grains are smaller than conventional electric steel sheets after finishing annealing, It is possible to provide an electrical steel sheet excellent in magnetic quality than a steel sheet.

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.

A method of manufacturing a directional electrical steel sheet according to the present invention includes the steps of: providing an electrical steel slab; Reheating the slab; Hot-rolling the slab to produce a hot-rolled steel sheet; Cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet; A first recrystallization annealing step of the cold-rolled steel sheet; And secondary recrystallization annealing the electric steel sheet after the primary recrystallization annealing has been completed; And the secondary recrystallization annealing is performed in a state in which an electric field is applied.

The magnitude of the electric field may be from 1 kV / cm to 3 kV / cm.

The secondary recrystallization annealing includes a temperature increasing step and a refining annealing step, and the refining annealing step can be carried out while applying an electric field.

The annealing atmosphere in the secondary recrystallization annealing step is heat-treated using a mixed gas of hydrogen and nitrogen in the temperature rising step, and can be cracked using hydrogen gas in refining annealing.

The temperature raising step may be performed at a temperature raising rate of 40 ° C / hr or less in a temperature range of 1050 to 1100 ° C, and the refining annealing may be performed at a temperature of 1100 ° C or more.

Hereinafter, the operation of the present invention will be described.

In the production process of the grain-oriented electrical steel sheet, precipitate is used as a grain growth inhibitor to induce secondary recrystallization stably at a high temperature, and secondary recrystallization occurs at a temperature at which precipitates are decomposed.

However, if N and S, which are precipitate-forming elements, remain on the electric steel sheet after the completion of the secondary recrystallization annealing, precipitates are formed again upon cooling to interfere with the movement of the magnetic domains, thereby deteriorating iron loss. Since the second recrystallization of the Goss particles occurs at a very high speed, a large number of island grains exist in the Goss grains immediately after the completion of the second recrystallization, and these island grains also interfere with the movement of the magnetic domains. Thereby making the iron loss worse.

Therefore, in order to produce a grain-oriented electrical steel sheet with low iron loss, a refining annealing process for performing a long time heat treatment at a high temperature after the completion of secondary recrystallization is essentially performed.

Increasing the diffusion rate of the atoms accelerates the diffusion of remaining N and S after the formation of the secondary recrystallization, shortening the time for removing N and S, promoting the diffusion of the base material Fe, Time can be shortened.

There are many free electrons in the metal material. When an electric field is applied from the outside, the surface is charged to the opposite electrode to the external electrode, and a potential difference is generated between the surface and the center. Thus, the electro-chemical potential difference occurs, and the mobility of the vacancies having a relatively negative polarity in the metal is increased. The increase in the mobility of the public will eventually increase the diffusion rate of the iron atoms.

Therefore, if the heat treatment is performed in the state of applying the electric field in the annealing step during the secondary recrystallization annealing step, the diffusion of remaining N and S after the formation of the secondary recrystallization is promoted, and the time for removing N and S can be shortened, The diffusion of the base material Fe is promoted and the island grain removal time can be shortened.

In addition, if the annealing is performed by applying an electric field, the removal of N and S is more effective than the prior art. Therefore, in the grain-oriented electrical steel sheet having undergone the secondary recrystallization annealing by the present invention, the content of N and S remaining in the steel sheet can be controlled to 10 ppm or less, respectively.

The hot-rolled sheet annealing may further include annealing the hot-rolled sheet after the step of preparing the hot-rolled steel sheet so as to have a uniform recrystallized microstructure and a fine precipitate distribution before the cold rolling, .

The step of producing the cold-rolled steel sheet may be performed by cold rolling at least two times including cold rolling or intermediate annealing, and hot rolling may be performed during cold rolling to maintain the temperature of the steel sheet at 100 ° C or higher.

The step of performing decarburization annealing and steep annealing on the cold-rolled steel sheet after the step of producing the cold-rolled steel sheet, wherein the step of performing the decarburization annealing and the steep annealing on the cold-rolled steel sheet is performed simultaneously with the decarburization annealing and the steep annealing .

The decarburization annealing and the steep annealing may be performed such that the amount of nitrogen formed in the steel sheet is 100 to 300 ppm. If it is less than 100 ppm, nitrogen may not form an inhibitor properly. If it exceeds 300 ppm, it may take an excessive time to remove nitrogen in the second recrystallization annealing process.

Further, the slab contains 2.0 to 6.5% of Si and the balance consists of Fe and other unavoidable impurities.

The slab may contain not more than 0.005 to 0.04% of Al, not more than 0.20% of Mn (not including 0%), not more than 0.01% of N, not more than 0.01 to 0.10% of C, not more than 0.01% of S ) May be further included.

The reason why the component system is limited will be described.

[Si: 2.0 to 6.5 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 2.0 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.

If the Si content exceeds 6.5 wt%, the mechanical properties of the electrical steel sheet increase in brittleness and the toughness decreases, so that the plate fracture occurrence rate during the rolling process becomes intense and the formation of secondary recrystallization becomes unstable.

[Al: 0.005 to 0.04 wt%]

In addition to AlN precipitated at the time of hot rolling and annealing of hot-rolled steel sheet, Al also has nitrogen ions introduced by ammonia gas in the annealing step after cold rolling combined with Al, Si and Mn existing in solid state in steel, Si, &lt; / RTI &gt; Mn) N and AlN type nitride to form a strong grain growth inhibitor.

When the content of Al is less than 0.005 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]

Mn has an effect of reducing the total iron loss by decreasing the eddy current loss by increasing the resistivity and reacting with the nitrogen introduced by the nitriding treatment together with Si to form precipitates of N (Al, Si, Mn) Which causes secondary recrystallization.

When 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, Since the phase transformation between ferrite and austenite is induced, the aggregate structure is seriously damaged and magnetic properties are greatly deteriorated. Therefore, the content of Mn is 0.20 wt% or less.

[N: 0.01 wt% or less]

N is an element which reacts with Al to form AlN. When N exceeds 0.01 wt% in the steelmaking process, surface defects are caused by nitrogen diffusion in the step after hot rolling, and nitride is excessively formed in the slab state, Resulting in a complicated subsequent process and an increase in manufacturing cost.

Further, in the annealing step after the cold rolling, N necessary for further forming nitrides such as N and AlN during the nitriding treatment using ammonia gas (Al, Si, Mn) can be reused.

[C: 0.01 to 0.10 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 having a high brittleness and poor rolling property, but a carbide formed due to a magnetic aging effect when remaining in the final product It is an element that deteriorates magnetic properties.

If C is contained in an amount of less than 0.01 wt%, the phase transformation between ferrite and austenite does not work properly, resulting in nonuniformity of the slab and hot rolled microstructure.

If it exceeds 0.10 wt%, a sufficient decarburization effect can not be obtained in the decarburization annealing process, the secondary recrystallization texture is damaged due to the phase transformation phenomenon, and magnetic properties are deteriorated due to magnetic aging .

[S: 0.010 wt% or less]

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

When S is contained in an amount exceeding 0.01 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.

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

[Example 1]

The slab comprising 3.18% of Si, 0.056% of C, 0.11% of Mn, 0.0052% of S, 0.0051% of N and 0.028% of Al and 0.028% of Al and the balance of Fe and other inevitably incorporated impurities, After the reheating temperature was elevated to 1,150 占 폚 for 180 minutes, hot rolling was performed to produce a hot rolled sheet having a thickness of 2.3 mm. The hot-rolled sheet was heated to a temperature of 1100 占 폚 or higher, held at 910 占 폚 for 90 seconds, quenched in water, pickled, and cold-rolled to a thickness of 0.30 mm. The cold-rolled steel sheet was held at a temperature of 870 DEG C in a humid atmosphere of hydrogen and a mixed gas of nitrogen and ammonia for 180 seconds to perform simultaneous decarburization and nitridation annealing so that the nitrogen content became 200 ppm. In the secondary recrystallization annealing, the mixture atmosphere of 25% nitrogen + 75% hydrogen was raised at a temperature elevation to 1200 ° C, and purification annealing was performed at 1200 ° C.

In order to confirm the effect of applying the electric field in the annealing annealing, the change of iron loss was measured according to the annealing annealing time while the electric field was applied by applying a voltage to the electrode.

Electric field strength
(kV / cm) Electrode voltage
polarity Annealing time
(hr) Magnetic flux density
(B8, Tesla) Iron loss
(W17 / 50, W / kg) division
- - 0 1.928 1.45 Comparison 1 - - 5 1.929 1.25 Comparative material 2 - - 10 1.929 1.17 Comparative material 3 - - 15 1.930 1.10 Comparison 4 - - 20 1.930 1.03 Comparative material 5 - - 25 1.930 0.99 Comparative material 6 - - 30 1.931 0.95 Comparison 7 - - 50 1.931 0.92 COMPARISON 8 - - 80 1.931 0.90 Comparative material 9 - - 120 1.932 0.88 Comparative material 10 2 cathode 3 1.928 1.24 Inventory 1 2 cathode 6 1.929 1.11 Inventory 2 2 cathode 9 1.930 0.96 Inventory 3 2 cathode 12 1.930 0.94 Invention 4 2 cathode 15 1.930 0.91 Invention Article 5 2 cathode 18 1.931 0.89 Inventions 6 2 cathode 21 1.931 0.88 Invention 7 2 cathode 24 1.931 0.88 Invention 8 2 cathode 27 1.932 0.88 Invention 9 2 cathode 30 1.932 0.88 Inventions 10

As shown in Table 1, when the magnitude of the electric field is 2 kV / cm when the annealing annealing is performed, the annealing annealing time is shortened. The iron loss after annealing for 30 hours was 0.95 W / kg (Comparative Example 9), but the iron loss after annealing for 18 hours after the electric field application was 0.89 W / kg (Inventive Material 6) after general annealing annealing without applying electric field. The iron loss is extremely excellent.

[Example 2]

A slab composed of 3.16% of Si, 0.053% of C, 0.98% of Mn, 0.0052% of S, 0.0049% of N, 0.028% of acid soluble Al and 0.028% of the balance Fe and other inevitably incorporated impurities The slab was heated at a reheating temperature of 1150 占 폚 for 180 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 1100 占 폚 or higher, held at 910 占 폚 for 90 seconds, quenched in water, pickled, and cold-rolled to a thickness of 0.30 mm. The cold-rolled steel sheet was held at a temperature of 870 DEG C in a humid atmosphere of hydrogen and a mixed gas of nitrogen and ammonia for 180 seconds to perform simultaneous decarburization and nitridation annealing so that the nitrogen content became 200 ppm. In the secondary recrystallization annealing, the mixture atmosphere of 25% nitrogen + 75% hydrogen was raised at a temperature elevation to 1200 ° C, and purification annealing was performed at 1200 ° C.

In order to confirm the influence of the direction of the applied electric field in the annealing annealing, the iron loss was measured after performing the annealing annealing in the state where the positive electrode and the negative electrode were applied to the electrode voltage.

Electric field strength
(kV / cm) Electrode voltage
polarity Annealing time
(hr) Magnetic flux density
(B10, Tesla) Iron loss
(W17 / 50, W / kg) division
- - 5 1.929 1.26 Comparative material 11 2 anode 5 1.930 1.12 Invention invention 11 2 cathode 5 1.929 1.14 Invention 12 - - 10 1.930 1.16 Comparative material 12 2 anode 10 1.930 0.96 Invention invention 13 2 cathode 10 1.930 0.94 Invention Article 14 - - 15 1.930 1.08 Comparative material 13 2 anode 15 1.930 0.91 Invention material 15 2 cathode 15 1.931 0.90 Invention material 16

As shown in Table 2, iron loss is lower when annealing annealing is performed for the same time by applying an external electric field in the annealing annealing. Even if the direction of the electric field is changed by applying the polarity of the external electrode applying the electric field to the positive electrode and the negative electrode, the difference in the effect does not greatly change, and the influence of the electric field is greatly influenced on the improvement of the iron loss.

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 (23)

(Inclusive of 0%), N: not more than 0.01% (inclusive of 0%), C: 0.01 to 0.10% (inclusive) %, S: not more than 0.01% (not including 0%) and the balance Fe and other unavoidable impurities;
Reheating the slab;
Hot-rolling the slab to produce a hot-rolled steel sheet;
Cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet;
A first recrystallization annealing step of the cold-rolled steel sheet; And
A second recrystallization annealing step of subjecting the electrical steel sheet after the primary recrystallization annealing to completion; / RTI &gt;
Wherein the secondary recrystallization annealing includes a temperature increasing step and a refining annealing step, and the refining annealing step is carried out while applying an electric field. delete The method according to claim 1,
Wherein the electric field has a size of 1 kV / cm to 3 kV / cm. The method of claim 3,
Wherein the annealing atmosphere in the secondary recrystallization annealing step is a heat treatment using a mixed gas of hydrogen and nitrogen in a temperature rising step and a hydrogen gas is used in refining annealing. 5. The method of claim 4,
Wherein the temperature raising step raises the temperature at a temperature raising rate of 40 ° C / hr or less at a temperature interval of 1050 to 1100 ° C and performs refining annealing at a temperature of 1100 ° C or more. 6. The method of claim 5,
Further comprising the step of annealing the hot-rolled steel sheet at a temperature of 900 ° C or higher after the step of manufacturing the hot-rolled steel sheet. The method according to claim 6,
The step of producing the cold-rolled steel sheet comprises the steps of cold-rolling two or more times including cold rolling or intermediate annealing, and performing hot rolling to maintain the temperature of the steel sheet at 100 DEG C or higher during cold rolling Way. 8. The method of claim 7,
Further comprising the step of performing decarburization annealing and steep annealing simultaneously on the cold-rolled steel sheet after the step of producing the cold-rolled steel sheet. 9. The method of claim 8,
Wherein the amount of nitrogen formed in the steel sheet in the simultaneous decarburization annealing and the steep annealing is 100 to 300 ppm. delete 10. The method according to any one of claims 1 to 9,
Wherein the content of residual N and S in the electric steel sheet after the secondary recrystallization annealing is 10 ppm or less, respectively. delete delete delete delete delete delete delete delete delete delete delete delete