KR101461785B1 - Mehtod for manufacturing low core loss grain-oriented elecrrical steel sheet having exceelent energy efficiency - Google Patents

Abstract

The present invention relates to a method of manufacturing a low iron-loss directional electrical steel sheet having a high energy efficiency. In one embodiment of the present invention, Depositing aluminum on the substrate; Heating the directional electrical steel sheet having the aluminum deposition layer at a rate of 110 ° C / min or more, diffusion heat treatment at 1050 to 1150 ° C, and cooling at a rate of 110 ° C / min or more; And electrolytically polishing the cooled directional electrical steel sheet. The present invention also provides a method for manufacturing a directional electrical steel sheet.
INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a low iron loss directional electric steel sheet which is free from cavities and secondary phases and has an energy efficiency of 15% or more as compared with the conventional method.

Description

[0001] METHOD FOR MANUFACTURING LOW CORE LOSS GRAIN-ORIENTED ELECRICAL STEEL SHEET HAVING EXCEALENT ENERGY EFFICIENCY [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a low iron loss directional electric steel sheet having excellent energy efficiency and more particularly to a method of manufacturing a low iron loss directional electric steel sheet which can be used as a component of an electric appliance such as a large- .

Recently, as the interest in efficient use of energy has increased, there has been an increasing problem of energy cost due to depletion of fossil fuel. Therefore, development of a low iron loss directional electric steel sheet is required for efficient use of electric energy. In order to reduce the iron loss indicating the amount of energy loss, a method of increasing the specific resistivity of the steel sheet by increasing the amount of silicon tetrachloride can be used. However, the addition of silicon at 3.3% or more causes problems such as plate breakage during cold rolling. As a result, the method of increasing the amount of silicon in the initial stage is still being studied, but it has not yet been put to practical use. Therefore, in order to manufacture a low-loss steel sheet having excellent energy efficiency, a method of finding a substitute material for solving the problem of excessive silicon addition and a point of adding a resistivity material for preventing plate breakage in cold rolling, The systematic aspect of the addition method has been studied in two ways.

First, the addition of aluminum and silicon-aluminum alloys, which exhibit a resistivity-increasing characteristic similar to that of silicon in terms of adding substitute materials, has been proposed. The resistivity of aluminum is not as good as that of silicon, but it has the most similar properties to other materials and is known to exhibit much better properties in terms of elongation.

However, when the amount of aluminum is increased, there is a problem in that it is difficult to increase the content due to the problem of texture control through secondary recrystallization and the easy oxidation characteristic of aluminum.

On the other hand, as a system aspect, a method of controlling the cold rolling method and the temperature after increasing the amount of silicon in the initial raw material has been proposed. On the other hand, as a method of adding silicon to the final product after the completion of the cold rolling, , Hot dip galvanizing, and plasma deposition.

Typically, NKK succeeded in the production of non-oriented products by adding 3.3% of silicon, completing cold rolling and secondary recrystallization, and then further diffusing the resistivity elements by CVD. However, in the case of the CVD technique, since silicon tetrachloride (SiCl ₄ ), which is a toxic and highly corrosive reactive gas, is used as a raw material for silicon deposition, there is a disadvantage in that it requires a facility investment for safety. In addition, There is a disadvantage that it is necessary.

As a result, studies on physical vapor deposition methods such as hot dip coating and plasma deposition have been made. As shown in FIG. 1, when hot dip coating of silicon, aluminum or silicon-aluminum alloy, intermetallic commpound is formed at the interface between the specimen and the plating layer And there is a problem of cavity formation due to the Kirkendall effect when the aluminum or silicon-aluminum alloy is plated, and it is still in the research stage.

In addition, when silicon is deposited using the plasma deposition method, as shown in FIG. 2, the surface state is deteriorated due to the formation of cavities and secondary phases formed in the steel sheet due to the cavities and the curtain- . On the other hand, there is no research on the plasma deposition method using aluminum or other alloying elements.

In the case where the inner cavity and the surface deterioration due to the secondary phase and the cavity and the curcumin effect are generated at the interface between the substrate iron and the plating layer, the magnetization is adversely affected and the energy loss is greater . That is, iron loss is increased.

As a result, there has been no successful method of adding a resistivity element by physical vapor deposition until now, and there is still a problem of secondary phase and co-occurrence. Therefore, there is a need for research on plasma deposition method using aluminum and other alloying elements to be.

The present invention is intended to provide a method of manufacturing a low iron loss directional electrical steel sheet which is capable of preventing cavitation and secondary phase from occurring and preventing surface deterioration by penetrating a substitute material of silicon with a physical vapor deposition method.

According to an embodiment of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: depositing aluminum by physical vapor deposition in which an aluminum target is sputtered using plasma in a vacuum atmosphere at 300 to 400 ° C so that an aluminum deposition layer is formed on a directionally oriented electrical steel sheet after completion of secondary recrystallization; Heating the directional electrical steel sheet having the aluminum deposition layer at a rate of 110 ° C / min or more, diffusion heat treatment at 1050 to 1150 ° C, and cooling at a rate of 110 ° C / min or more; And electrolytically polishing the cooled directional electrical steel sheet. The present invention also provides a method for manufacturing a directional electrical steel sheet.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a low iron loss directional electric steel sheet which is free from cavities and secondary phases and has an energy efficiency of 15% or more as compared with the conventional method.

In addition, since the low iron-strength directional electrical steel sheet provided by the present invention does not use the chemical vapor deposition method, it can solve the pollution inducing and corrosion problems of the equipment, and the internal cavity generation and surface deterioration And also can be suitably applied to a large-sized transformer or a motor requiring low iron loss.

Fig. 1 is an example of a photograph of a microstructure of a material after hot-dip coating of silicon, aluminum or a silicon-aluminum alloy.
FIG. 2 is an example of a photograph of a microstructure of a workpiece after plasma-deposited and heat-treated with silicon.
FIG. 3 is an example of a photograph of a microstructure of a workpiece after plasma-deposited aluminum, followed by diffusion heat treatment at a heating rate of 10 ° C / min, followed by gradual cooling.
FIG. 4 is an example of a photograph of microstructure inside a material after plasma-deposited aluminum according to an embodiment of the present invention, followed by diffusion heat treatment by applying a rapid heating and cooling method.
5 is a microstructure photograph of the side surface of FIG. 4 observed.
FIG. 6 is a microstructure photograph of the upper surface of FIG. 4 observed. FIG.
FIG. 7 is a microstructure photograph of an upper surface of a workpiece subjected to an electrolytic polishing process according to an embodiment of the present invention. FIG.

The inventors of the present invention have studied a systematic aspect of addition of a new resistivity material that can replace silicon and a point of addition of a resistivity material in a directional electric steel sheet manufacturing process in the production of a grain- Aluminum was deposited on the grain-oriented electrical steel sheet subjected to the cold rolling and the second recrystallization in the course of performing cold rolling and secondary recrystallization, and then subjected to diffusion annealing through rapid heating and rapid cooling in the heat treatment in a specific temperature range, , It is possible to produce a grain-oriented electrical steel sheet having excellent surface characteristics and low iron loss properties.

Hereinafter, a method for producing the grain-oriented electrical steel sheet of the present invention will be described.

First, a directional electrical steel sheet having been subjected to cold rolling and secondary recrystallization is prepared. The steel sheet applicable to the present invention can be used in any directional steel sheet commonly used in the related art. For example, a grain oriented steel sheet containing about 3% of Si can be used. Further, in the present invention, the thickness of the electric steel sheet is not particularly limited, and a steel sheet having a thickness range generally used in this technical field can be used. For example, an electrical steel sheet having a thickness of 220 to 230 mu m can be used. The cold rolling and the secondary recrystallization may also be performed under ordinary conditions used in the related art.

Then, aluminum is preferably deposited by physical vapor deposition using a plasma in a vacuum atmosphere at 300 to 400 ° C so that an aluminum deposition layer is formed on the directionally oriented electrical steel sheet after the secondary recrystallization. The temperature range is an atmospheric temperature for vacuum deposition of aluminum. By maintaining the steel sheet at a high temperature of 300 ° C or higher, the aluminum particles can have a high thermal energy and can be preferably deposited on the surface of the steel sheet. If the vacuum deposition is performed at a holding temperature of less than 300 캜, the adhesion between aluminum and aluminum is stronger than the adhesion between an electrical steel sheet and aluminum, so that the electrical steel sheet and the aluminum deposition layer are easily peeled off. In addition, it is difficult to secure a good contact state between the steel sheet and the aluminum deposition layer, so that the aluminum deposition layer can not easily penetrate into the steel sheet during the diffusion annealing process (diffusion heat treatment) There is a possibility that rapid diffusion does not occur inside. Further, if the oxygen atmosphere is exposed to the atmosphere for a long time, a large amount of oxygen may be introduced into the pores, which may cause iron loss to increase. Therefore, the steel sheet holding temperature needs to be 300 DEG C or higher. However, if the steel sheet holding temperature is higher than 400 ° C, aluminum may be oxidized or a secondary phase may be formed, and if it is too large, the aluminum may be melted. Therefore, Lt; / RTI > On the other hand, if the vacuum atmosphere is not maintained during the temperature control, the steel sheet is oxidized due to the high temperature, and it may be difficult to obtain the characteristics of the product required in the present invention.

Thereafter, aluminum is deposited using plasma to form an aluminum deposition layer on the grain-oriented electrical steel sheet. By using the plasma deposition method, the formation of the secondary phase which occurs during the hot dip coating can be suppressed, and the iron loss reducing effect can be exhibited. Of course, even if the plasma deposition method is used, as the present invention proposes, if the heating rate and the cooling rate can not be controlled during the diffusion heat treatment, a secondary phase may occur.

At this time, it is preferable that the aluminum is deposited on both surfaces of the directional electrical steel sheet. In the case of depositing aluminum only on the end face of a steel sheet, a phenomenon occurs in which the steel sheet is bent toward the deposited face due to the difference in thermal expansion coefficient between the aluminum-deposited surface and the non-deposited surface in the annealing process.

Thereafter, the directional electric steel sheet having the aluminum deposition layer formed thereon is preferably heated at a rate of 110 ° C / min or more to diffuse heat treatment (anneal) at 1050 to 1150 ° C to diffuse the aluminum deposition layer into the directional electric steel sheet. By rapidly heating the aluminum deposition layer at a high temperature of 110 ° C / min or more at such a high temperature as described above, the aluminum deposition layer is instantaneously brought into a liquid state and diffused into the steel sheet by diffusion heat treatment in this state, . When the heating rate is less than 110 ° C / min, co-generation due to the curcumed effect occurs at 10 to 20 μm from the surface of the steel sheet in the thickness direction to increase the iron loss, so that the heating rate is 110 ° C./min or more . The higher the heating rate, the more advantageous it is, so the upper limit is not particularly limited. However, it is difficult to exceed 220 캜 / min in the limit of the process.

If the diffusion heat treatment temperature is less than 1050 DEG C, the time required for diffusion of aluminum becomes longer, so that the amount of aluminum oxidized on the surface becomes larger than the amount of aluminum deposited on the steel sheet. As a result, And the amount of oxygen diffused into the steel sheet also increases, thereby affecting hysteresis loss. The higher the diffusion heat treatment temperature is, the more advantageous it is, so the upper limit is not particularly limited. However, in order to ensure productivity, it is preferable that the diffusion heat treatment temperature does not exceed 1150 占 폚. The diffusion heat treatment temperature is more preferably in the range of 980 to 1130 ° C, and more preferably in the range of 970 to 1120 ° C.

At this time, it is preferable that the diffusion heat treatment is performed for 0.5 to 6 hours. If the diffusion heat treatment time is less than 0.5 hour, the aluminum may not diffuse into the material and the internal properties may not be uniform, If the time exceeds 6 hours, not only aluminum but also the time for diffusing oxygen in the atmosphere into the material becomes longer, so that inclusions that can cause the increase of iron loss due to the bonding of aluminum to oxygen inside the material . Therefore, the diffusion heat treatment is preferably performed for 0.5 to 6 hours, more preferably for 1 to 4 hours.

The diffusion heat treatment is preferably performed at a high degree of vacuum of 1 x 10 ^-4 torr or less. When annealing is performed in an atmosphere of 1 × 10 ^-4 torr or less, the rate of oxidation of aluminum to oxide by residual oxygen in the atmosphere is minimized, and the diffusion amount ratio to aluminum deposition amount can be increased to 90% or more. However, when annealing is performed under a low vacuum of more than 1 × 10 ^-4 torr, the diffusion amount ratio to the aluminum deposition amount becomes 50% or less, which is disadvantageous in that the aluminum loss rate is increased when the aluminum oxide is removed in the final electrolytic polishing process . Therefore, it is preferable that the deposition of aluminum is performed at a high degree of vacuum of 1 x 10 < ^-4 > torr or lower, and a higher vacuum degree is more advantageous. Therefore, in the present invention, the lower limit of the vacuum degree is not particularly limited. However, due to the limitations of the apparatus performance, the vacuum degree is less likely to be less than 1 x 10 < ^-10 > torr.

Alternatively, the diffusion heat treatment may be performed in a hydrogen atmosphere. In this case, by controlling the dew point, the amount of internal water vapor and the influence of oxygen are excluded, thereby preventing oxidation of aluminum. Furthermore, since there is little oxygen in the chamber, there is an advantage that aluminum can be deposited at a relatively low degree of vacuum.

Meanwhile, the Al content of the electrical steel sheet obtained through the diffusion heat treatment is preferably in the range of 1 to 3% by weight. If the Al content is less than 1 wt%, the iron loss reduction effect may not be sufficient. If the Al content is more than 3 wt%, the loss ratio may increase.

After the diffusion heat treatment, it is preferable to cool at a rate of 110 ° C / min. As described above, it is possible to obtain an effect of reducing the amount of oxygen diffused into the material through rapid cooling at 110 ° C / min or more. When the cooling rate is less than 110 ° C / min, the amount of oxygen increases and the loss rate may increase. On the other hand, the higher the cooling rate is, the more advantageous the effect is obtained, so the upper limit is not particularly limited. However, it is difficult for the cooling rate to exceed 220 캜 / min at the limit of the process.

FIG. 3 is an example of a photograph of a microstructure of a workpiece after plasma-deposited aluminum, followed by slow heating and diffusion heat treatment, followed by gradual cooling. As can be seen from FIG. 3, when the rapid heating and cooling system proposed by the present invention is not used, it can be seen that cavities are formed in the steel sheet due to the curcumin effect at 10 to 20 μm in the thickness direction from the surface of the steel sheet.

FIG. 4 is an example of a photograph of microstructure of a workpiece after plasma-deposited aluminum according to an embodiment of the present invention, followed by diffusion heat treatment by applying a rapid heating and cooling system. As can be seen from FIG. 4, in the case of manufacturing the electrical steel sheet according to the embodiment of the present invention, it can be seen that the inner cavity due to the curtain-like effect does not occur, unlike in FIG.

Fig. 5 is a microstructure photograph of the surface of Fig. 4 observed. Fig. As can be seen from FIG. 5, even though the aluminum vapor deposition layer is diffusion-heat treated on the electrical steel sheet using the diffusion heat treatment conditions proposed in the present invention, the formation of the inner cavity is prevented, but the surface layer is problematic. A part of the aluminum deposition layer which has not yet penetrated into the electrical steel sheet remains on the electrical steel sheet and a cavity is formed at the interface between the aluminum deposition layer and the directional electrical steel sheet. This phenomenon is mainly caused by two factors. First, due to the rapid heating at a high temperature, a volume difference occurs due to a difference in thermal expansion coefficient between the aluminum deposition layer and the base steel, thereby causing peeling in a certain region of the aluminum deposition layer and the base iron interface. Second, a good contact state can not be ensured in a certain region between the aluminum deposition layer and the base metal, which causes a difference in the diffusion rate even in the aluminum deposition layer, resulting in a density difference between the interfaces. This density difference causes a volume difference, which eventually results in peeling.

Further, when the magnetic properties of the electric steel sheet subjected to the diffusion heat treatment process proposed by the present invention were measured, it was found that the iron loss was increased rather than before the diffusion heat treatment. The reason why the eddy loss is increased is also divided into two . First, the thickness of the steel sheet is also increased due to the deposition of aluminum. It is generally known that the increase in the steel sheet thickness leads to an increase in iron loss due to Edison current. Second, the uneven surface state acts as an obstacle to the eddy current flow, which leads to increased eddy loss.

FIG. 6 is a microstructure photograph of the upper surface of FIG. 4 observed. FIG. As can be seen from FIG. 6, since the aluminum deposition layer rapidly becomes a liquid state due to rapid heating at a high temperature, aluminum is diffused into the steel sheet by diffusion heat treatment in this state. At this time, aluminum Which is then melted and cooled to form a non-uniform surface.

Accordingly, after the diffusion heat treatment step, the surface of the steel sheet is preferably mirror-polished through an electrolytic polishing step. The electrolytic polishing process has the effect of not only removing the surface of the steel sheet but also a cavity formed between the steel sheet surface and the remaining aluminum deposition layer. The electrolytic polishing is preferably carried out using a solution comprising 10 to 40 mass% of perchloric acid and 60 to 90 mass% or less of acetic acid. If the content of the perchloric acid is less than 10 mass% or the content of acetic acid is more than 90 mass%, the pickling time increases and the amount of the oxidized layer oxidized again more than the amount of the oxide removed from the surface increases. On the other hand, when the content of the perchloric acid exceeds 40 mass% or the content of the acetic acid is less than 60 mass%, the pickling time is increased and the amount of the oxidized layer oxidized again rather than the amount of the oxidized layer removed from the surface is increased. Therefore, it is preferable to use a solution comprising 10 to 40% by weight of perchloric acid and 60 to 90% by weight of acetic acid as the electrolytic polishing.

It is preferable that the electric current at the electrolytic polishing has a range of 6 mA / cm 2 or more. If the current is less than 6 mA / cm 2, the amount of corrosion to the acid is greater than the amount of electrolytic polishing, which causes electrolytic polishing or polishing time to be infinite. On the other hand, when the current exceeds 60 mA / cm 2, an excessive current flows and it is difficult to obtain a uniform reaction on the entire surface of the workpiece, so that the uniformity of the surface may be lowered.

FIG. 7 is a microstructure photograph of an upper surface of a workpiece subjected to an electrolytic polishing process according to an embodiment of the present invention. FIG. As shown in FIG. 7, it can be seen that the surface of the material subjected to the electrolytic polishing process is in a very smooth state as compared with FIG. 6, and it is easy to deduce that a low iron loss electrical steel sheet having excellent energy efficiency can be manufactured have.

As described above, according to the method for manufacturing a grain-oriented electrical steel sheet proposed by the present invention, by solving the problem of increase in iron loss due to generation of cavities and secondary phases and surface deterioration, and by improving the energy efficiency by more than 15% It is possible to provide a low iron loss directional electric steel sheet which can be preferably applied to a motor or the like. In addition, because physical vapor deposition is used, pollution and facility erosion caused by chemical vapor deposition can be solved.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are only illustrative of the present invention in more detail and do not limit the scope of the present invention.

(Example)

The surface of the grain-oriented electrical steel sheet having a thickness of 0.23 mm and an Si content of 3% is cleaned with alcohol to remove impurities as much as possible. The steel sheet is then inserted into a vacuum furnace for sputtering and is discharged at a vacuum degree of 1 x 10 ^-5 torr or less Thereafter, the steel sheet was heated to 300 DEG C under a vacuum condition. Thereafter, argon gas was introduced into the vacuum furnace so as to have a degree of vacuum of 1 × 10 ^-3 torr to 1 × 10 ^-2 torr, and then a DC voltage was applied to the steel sheet to plasma-vacuum aluminum. In this case, the purity of the aluminum target used was 99.999%. In order to uniformly deposit on both surfaces of the steel sheet, the surface of the steel sheet was evaporated and then exhausted. Deposition method was used. The aluminum deposition layer was deposited to a thickness of 20 탆 in an amount of 10 탆 per surface so that the aluminum deposition layer was 2% by weight of the total weight of the electrical steel sheet. Thereafter, the aluminum deposition layer was cooled to 100 캜 or less and then desorbed in a vacuum furnace. Thereafter, the aluminum-deposited steel sheet was inserted into a heat-treated vacuum furnace evacuated at a vacuum degree of 1 x 10 ^-5 torr or less and heat-treated under the conditions shown in Table 1 below. Thereafter, electrolytic polishing was carried out for 6 minutes in order to make the surface of the steel sheet mirror-finished. The electrolytic polishing solution used was a mixture of 10% by mass of perchloric acid and 90% by mass of acetic acid, the voltage was 3 to 5 V / cm 2 and the current was 6 mA / cm 2. The steel plate was connected to the anode, Pure iron was connected. Thereafter, the steel sheet was washed with alcohol, and the residual alcohol on the surface was removed. Then, the iron loss of the steel sheet was measured using a 6 cm / 6 cm SST (single sheet tester) magnetometer. The results are shown in Table 1 Respectively.

division Diffusion heat treatment Steel sheet thickness after electrolytic polishing
(탆) Al content in steel sheet
(weight%) Magnetic measurement results (W _17/50 ) Heating rate
(° C / min) Heat treatment temperature
(° C) Heat treatment time
(time) Cooling rate
(° C / min) diffusion
Before heat treatment diffusion
After heat treatment Inventory 1 110 1100 One 110 220 One 1.10 1.04 Inventory 2 110 1100 2.5 110 215 2 1.09 1.00 Inventory 3 110 1100 4 110 217 2.5 1.10 0.95 Comparative Example 1 110 950 4 110 221 2 1.17 1.18 Comparative Example 2 10 1100 8.5 110 220 2 1.09 1.08 Comparative Example 3 5 1100 14.5 110 218 2 1.12 1.10

As can be seen from Table 1, in the case of Examples 1 to 3, which satisfy the manufacturing conditions proposed by the present invention, iron loss is greatly reduced compared to that before diffusion heat treatment. Particularly, as the Al content is increased, Also, it can be seen that the iron loss decreased by about 5 ~ 15%.

However, in the case of Comparative Examples 1 to 3, which do not satisfy the conditions proposed by the present invention, the heating rate, the cooling rate and the heat treatment temperature are not satisfied and it is found that there is almost no iron loss reduction effect. It is expected that the heating rate and the heat treatment temperature do not satisfy the conditions of the present invention, so that the hysteresis loss due to the inflow of oxygen into the inside and the eddy loss have been affected as the heat treatment time becomes longer.

Claims (7)

Depositing aluminum by physical vapor deposition in which an aluminum target is sputtered using a plasma in a vacuum atmosphere at 300 to 400 ° C so that an aluminum deposition layer is formed on the grain-oriented electric steel sheet after the secondary recrystallization is completed;
Heating the directional electrical steel sheet having the aluminum deposition layer at a rate of 110 ° C / min or more, diffusion heat treatment at 1050 to 1150 ° C, and cooling at a rate of 110 ° C / min or more; And
And electrolytically polishing the cooled directional electrical steel sheet. The method according to claim 1,
Wherein the aluminum is deposited on both surfaces of the directional electrical steel sheet. The method according to claim 1,
Wherein the diffusion heat treatment is performed for 0.5 to 6 hours. The method according to claim 1,
Wherein the diffusion heat treatment is performed at a degree of vacuum of 1 x 10 ^-5 torr or less, or in a hydrogen atmosphere. The method according to claim 1,
Wherein the directional electrical steel sheet has an Al content of 1 to 3% by weight after the diffusion heat treatment. The method according to claim 1,
Wherein the electrolytic polishing is carried out using a solution comprising 10 to 40 mass% of perchloric acid and 60 to 90 mass% of acetic acid. The method according to claim 1,
Wherein the electric current during the electrolytic polishing is 6 to 60 mA / cm 2.

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