KR101504703B1 - Non-oriented electrical steel steet and manufacturing method for the same - Google Patents

Abstract

The present invention relates to a non-oriented electrical steel sheet and a method of manufacturing the same, and more particularly, to a non-oriented electrical steel sheet and a method of manufacturing the same, which comprises 0.005% or less (excluding 0%) of C, 1.0 to 2.5% , Ti: not more than 0.03% (excluding 0%), Mn: 0.1 to 1.0%, Al: 4.0 to 6.0%, N: not more than 0.003% Fe and other inevitably incorporated impurities, and the crystals in the (001) direction in the vertical direction of the steel sheet are 30% or more. A non-oriented electrical steel sheet and a method of manufacturing the same are disclosed.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof, and more particularly, to a non-oriented electrical steel sheet and a method of manufacturing the same, To a method of manufacturing a directional electrical steel sheet and a non-oriented electrical steel sheet produced thereby.

Recently, as interest in the efficient use of energy has increased, efficiency of motors used in electric devices such as large generators, hybrid electric vehicles (HEVs), and environmentally friendly vehicles such as electric vehicles (EVs) In the United States. As part of this effort, efforts are being made to achieve faster rotational speeds than conventional motors by modulating the frequency with BLDC motors.

Particularly, in the case of a motor used in a driving section of a hybrid vehicle or an electric vehicle, it is necessary to obtain a large output with a limited size, and a rotational speed of 10,000 rpm or more is required. Therefore, a high-strength material is required for a rotor of a device rotating at a high speed.

In addition, in the case of a material used as a rotor of a motor, it is necessary to reduce eddy current loss caused by high frequency in addition to strength. When a high strength carbon steel or an integral type rotor is formed for the purpose of improving strength, The loss is increased and the overall efficiency of the motor is reduced.

Therefore, it is necessary to study the manufacturing technology of the electric steel sheet which can satisfy both the high strength characteristics and the low iron loss characteristics. As a part of this, as a technique of improving the strength by forming a structure other than ferrite in the steel and a technique of improving the strength by adding alloying elements such as Nb, V, and Cu, a technique of increasing the grain size in the state before cold rolling or further processing A technique has been proposed in which iron loss characteristics and strength characteristics are controlled to be controlled to 20 탆 or more.

Particularly, in Korean Patent Laid-Open Nos. 2005-033349, 2004-315956, 2004-339603, and 2007-039754, Cu is added in an amount of about 1 to 4%, and the product is heat- A method of minimizing deterioration of magnetic properties and maximizing the strength is proposed by generating Cu precipitates of several nm in size inside.

Japanese Patent Laid-Open No. 2009-7592 has attempted to make both iron loss and high strength compatible by using a large amount of Al and using Nb and Ti precipitates in proper amounts.

However, when Cu is added, iron loss is reduced to 20% or more, which is lower than that of other Nb and Ti precipitates, but iron loss is deteriorated in the rotor when employed. When a large amount of Al is contained, The mold flux was deteriorated due to the strong reducing power of Al during the casting by the continuous casting method and thus it could not be produced.

In order to solve the above problems, the present invention provides a non-oriented electrical steel sheet having excellent magnetic properties and high strength by controlling the amount of Al added by using a casting method, and a method for manufacturing the same.

In one or more embodiments of the present invention, the content of C is not more than 0.005% (excluding 0%), Si is 1.0 to 2.5%, P is not more than 0.1% (excluding 0%), S is not more than 0.03% (Excluding 0%), Ti: not more than 0.01% (excluding 0%), the remainder being Fe and other inevitably (excluding 0%), Mn: 0.1 to 1.0%, Al: 4.0 to 6.0% And the crystals in the (001) direction in the vertical direction of the steel sheet are 30% or more of the non-oriented electrical steel sheet.

The grain diameter of the steel sheet is 0.05 to 0.2 mm, and the yield strength of the steel sheet is 550 MPa or more.

The electrical steel sheet is characterized by having a steel sheet thickness of 0.3 mm and an iron loss (W _10/400 ) of 15 W / Kg or less.

In one or more embodiments of the present invention, the content of C is 0.005% or less, the content of Si is 1.0-2.5%, the content of P is 0.1% or less (excluding 0%), the content of S is 0.03% or less (excluding 0% , Al: not more than 0.003% (excluding 0%), Ti: not more than 0.01% (excluding 0%), the balance being Fe and other inevitably incorporated impurities Casting a molten steel comprising a mixture of molybdenum and molybdenum; A step of annealing the casting plate or omitting the casting plate annealing step, and then pickling it; Subjecting the pickled casting plate to cold rolling twice or more while cold rolling or intermediate annealing is performed; And performing final annealing in a temperature range of 900 to 1100 ° C after cold rolling, wherein the surface temperature of the molten steel is controlled to be 50 to 200 ° C higher than the solidification temperature, thereby providing a non-oriented electrical steel sheet manufacturing method .

The casting step is characterized in that the casting plate has a thickness of 1 to 3 mm, and Ar and He are used as the atmosphere gas in the casting step.

The crystals in the (001) direction in the vertical direction of the steel sheet after the final annealing is 30% or more, and the yield strength of the steel sheet after the final annealing is 550 MPa or more.

And an iron loss (W _10/400 ) of not more than 15 W / Kg at a steel sheet thickness of 0.33 mm after the final annealing.

According to the embodiment of the present invention, it is possible to manufacture a non-oriented electrical steel sheet having low iron loss and high strength by avoiding deterioration in workability due to high Al generated during continuous casting by casting casting while controlling the content of Al.

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.

In the examples according to the present invention, in order to produce a non-oriented electrical steel sheet having excellent magnetic properties and high strength, 4% or more of Al was added and Si was appropriately added to obtain strength and low iron loss simultaneously. %, The mold flux which is used in the slab manufacturing process is denatured and the workability is rapidly deteriorated, so that the continuous operation is impossible.

In order to solve this problem, a high strength electrical steel sheet having both magnetism and strength was manufactured by manufacturing a product using a twin roll casting method which does not use a mold flux. The mold flux in the embodiment according to the present invention is an important consumable supplementary material used as an additive in the continuous casting process of steel, and is used as a mold for improving the initial solidification of molten steel in the mold and producing a steel shell of good surface quality. Is put on the molten steel surface in the mold.

First, the reason for restricting the component of the non-oriented electrical steel sheet in the embodiment according to the present invention will be described. In the following, unless otherwise stated, the unit of content is weight percent (wt%).

C: 0.005% or less (excluding 0%)

C has the effect of improving the texture and increasing the strength, but in the examples according to the present invention, it is necessary to limit to extremely low levels in order to realize low iron loss, so that it is contained in an amount of 0.005% by weight or less. The lower the content of C is, the better the magnetic properties are. Therefore, the final product is preferably limited to 0.01% by weight or less, more preferably 0.005% by weight.

Si: 1.0 to 2.5%

Si increases the resistivity and lowers the eddy loss in the iron loss, and at the same time has an effect of increasing the strength. In the present invention, it is added at the same time as Al and is an effective element for achieving both strength and iron loss. However, if the content of Si is more than 2.5%, it is preferable to limit the Si content to not more than 2.5%, because the hardness of the material is increased and the cold rolling property is lowered due to the added Al, The content of Si in the examples according to the present invention is limited to the above range because there is a limit to increase the strength even if excessive amount of Al is added.

P: 0.1% or less (excluding 0%)

P is added to increase resistivity, improve texture and improve magnetism. However, the P content in the examples according to the present invention is limited to 0.1% or less because the cold rolling property deteriorates at the time of excessive addition.

S: 0.03% or less (excluding 0%)

S is preferably controlled to be low because it forms fine precipitates MnS and CuS to deteriorate magnetic properties. In the examples according to the present invention, the S content is limited to 0.03% or less.

Mn: 0.1 to 1.0%

When Mn is added in an amount of less than 0.1%, fine MnS precipitates are formed to suppress crystal growth, thereby deteriorating magnetism. Therefore, it is added at 0.1% or more so that MnS precipitates are formed to a great extent. When Mn is added in an amount of 0.1% or more, precipitation of the S component into CuS, which is a more fine precipitate, can be prevented to prevent deterioration of magnetic properties. However, if the Mn is added excessively, the magnetic property is lowered, so the content of Mn in the examples according to the present invention is limited to 0.1 to 1.0%.

Al: 4.0 to 6.0%

Al is an effective component for increasing the resistivity and lowering the eddy loss, and at the same time, it increases the strength. In the case of the present invention, a large amount of Al is added for the purpose of reducing iron loss because of the high limit of the amount of addition, and more than 4.0% is added in order to optimize strength and iron loss. However, if it is added in an amount exceeding 6.0%, since the cold rolling property is deteriorated rapidly, the content of Al in the embodiment of the present invention is limited to the above range.

N: 0.003% or less (excluding 0%)

N is preferably as small as possible because it forms fine and long AlN precipitates inside the base material to suppress grain growth and thereby lower the iron loss. In the examples according to the present invention, the N content is limited to 0.003% or less.

Ti: 0.01% or less (excluding 0%)

Ti forms fine TiN and TiC precipitates to suppress grain growth to increase the strength. However, in the embodiment of the present invention, the effect is not used because it is intended to improve the strength by Cu precipitates. Therefore, magnetic deterioration due to Ti addition should be minimized. When Ti is contained in an amount of more than 0.01%, many minute precipitates are generated to deteriorate the texture and deteriorate the magnetism, so that the Ti content in the examples according to the present invention is limited to 0.01% or less.

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

A method for producing a non-oriented electrical steel sheet according to the present invention is characterized by comprising the steps of: C: not more than 0.005% (excluding 0%), Si: not more than 1.0 to 2.5% (excluding 0%), P: not more than 0.1% ), S: not more than 0.03% (excluding 0%), Mn: 0.1 to 1.0%, Al: 4.0 to 6.0%, N: not more than 0.003% (excluding 0%), Ti: not more than 0.01% Fe and other inevitably mixed impurities is cast into a 1 to 3 mm piece using a twin roll casting and subjected to cold rolling without or after intermediate hot rolling and then subjected to final annealing to obtain a non- .

In the embodiment according to the present invention, the molten steel having the above composition is directly cast to a thickness of 1 to 3 mm using a twin roll casting facility to produce a non-oriented electrical steel sheet.

In this case, the casting speed during casting, the material of the roll surface (the difference between the breaking point and the molten steel temperature) and the like are selected in consideration of workability. However, when a large amount of Al is added as in the embodiment of the present invention, The inert gas such as Ar or He is used as the atmosphere to perform casting.

Since the saturation magnetic flux density of the final product plate may be in a state where a large amount of Al is added, it is important to make a texture in such a direction as to improve the magnetic flux density. In the double roll casting method, Which is advantageous. In order to strengthen the (001) texture, it is effective to sharply increase the temperature difference inside the material during cooling. In the embodiment of the present invention, the temperature of the surface of the molten steel is set so that the temperature of 50 to 200 DEG C It is sufficient if the temperature is higher than 50 캜.

If the thickness of the casting plate exceeds 3 mm, the cooling rate may be reduced, and then the cold rolling rate may be increased during cold rolling to adversely affect the magnetism. If the thickness of the steel sheet is less than 1 mm, However, since the productivity is low due to the delay in production of the product, there is a problem in operational stability. Therefore, the casting plate thickness in the embodiment of the present invention is limited to 1 to 3 mm.

Casting annealing may be omitted or omitted for the purpose of improving the texture after casting. In the case of a general hot-rolled steel sheet, the rolled steel sheet remains untouched, and when it is cold-rolled, the <111> aggregate structure unfavorable to magnetism is likely to increase. However, in the casting plate, there are many <001> The grain size becomes coarse, and no separate annealing is required before cold rolling.

However, annealing may be carried out in order to facilitate the casting of the casting plate or to grow fine crystal grains under the influence of intermediate hot rolling during casting of the casting product.

After the casting plate annealing is performed or omitted as described above, it is pickled and cold-rolled to produce a cold-rolled sheet having a desired thickness. The cold rolling may be performed by cold rolling at least twice, or by cold rolling at one time or intermediate annealing if necessary.

The cold-rolled cold-rolled sheet is subjected to final annealing. When annealing, add 5% or more of hydrogen to prevent oxidation of the surface and keep the dew point at zero. In order to optimize the iron loss, the grain size is annealed to a size of 0.05 to 0.2 mm. The annealing temperature at this time is 900 to 1100 ° C and the time is within 5 minutes considering the workability and the like.

The final annealed product is a high-strength non-oriented electrical steel sheet having excellent magnetic properties with a (001) texture remaining in the original casting plate and having a crystal orientation of (001) of 30% or more. In addition, in the embodiment of the present invention, after the punching and laminating, there is a case where a heat treatment process is performed to improve the magnetism through stress relief of the rubbing surface. In the case of the embodiment according to the present invention, There is no particular limitation on the heat treatment after the punching and stacking.

The electrical steel sheet produced by the above method is capable of continuous casting of 10,000 m or more without the denaturation of the mold flux due to a high addition amount of Al and the surface temperature of molten steel passing through twin rolls is 50 to 200 ° C (001) texture structure favorable to magnetism is present in the final product sheet by 30% or more so that the yield strength of the final product sheet is _{550 MPa} or more and the iron loss (W _10/400 ) is 15 W / Kg Or less and a method for producing the same.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[Example 1]

The molten steel consisting of 0.2% of Mn, 0.01% of P, 0.003% of C, 0.002% of N, and other impurities was mixed with the alloy composition of the composition such as Si, Al, The superheat degree, which is the difference between the surface temperature and the solidification temperature, was controlled as shown in Table 1. In order to prevent oxidation and nitrification of the surface of the molten steel, Ar gas was used as the upper atmosphere of the molten steel Respectively. In case of casting, casting was carried out immediately after casting at 650 ° C, then cooled in air, pickled and cold rolled to a thickness of 0.30 mm. The cold - rolled sheet was annealed to a grain size of 0.1 mm under atmospheric conditions of 20% hydrogen and 80% nitrogen, and then analyzed for texture together with the mechanical and magnetic properties of the final product.

Mechanical properties were measured by three tensile specimens manufactured with KS-13A, and the average values were obtained. The magnetic properties were measured by SST (single sheet tester) using a 60 mm × 60 mm veneer. In order to obtain the (001) fraction by analyzing the texture, the x-ray pole figure was taken and the fraction of the crystals oriented in the vertical direction (001) from the surface of the specimen to the inside was integrated , Where the offset angle was 15 °.

Specimen Number Si content
(weight%) Al content
(weight%) Superheat degree
(° C) Yield strength
(Mpa) Iron loss
W10 / 400
(W / Kg) (001)
Fraction
(%) Remarks One 0.5 5 80 380 16.1 45 Comparison 1 2 0.6 6.5 79 420 14.5 50 Comparative material 2 3 1.5 3 82 510 16.8 48 Comparative material 3 4 1.4 4.8 120 580 14.5 68 Inventory 1 5 1.6 4.7 102 600 14.8 60 Inventory 2 6 1.5 4.6 70 585 14.9 42 Inventory 3 7 1.5 4.7 40 590 15.4 19 Comparison 4 8 1.5 5.6 82 595 14 52 Invention 4 9 1.5 6.7 83 Cold rolled plate break Comparative material 5 10 2.3 3.5 79 540 14.1 49 Comparative material 6 11 2.3 4.5 81 610 13.8 53 Invention Article 5 12 2.3 5 85 630 13.2 52 Inventions 6 13 2.3 6.3 85 Cold rolled plate break Comparison 7 14 3.5 0.7 84 450 13.6 62 COMPARISON 8 15 3.6 1.5 82 Cold rolled plate break Comparative material 9 16 3.5 3.5 83 Cold rolled plate break Comparative material 10 17 3.4 5 75 Cold rolled plate break Comparative material 11

From the results shown in Table 1, the comparative materials 1 to 3 having Si of 1.5 wt% or less have low yield strength and are difficult to use for high strength steels. When Si is more than 2.3 wt% as in comparative materials 7 and 9 to 11 In order to realize a high strength steel, when the Al is increased, plate breakage occurs and the product can not be manufactured. Also, as in Comparative Examples 5, 6, and 8, even if Si is at an appropriate level, when the Al content is less than 4 wt%, or when the Al content is more than 6 wt%, the strength is insufficient or plate rupture occurs during cold rolling. In the case of the comparative material 4, the superheat degree was lower than 50 占 폚, and the (001) fraction was less than 30%, resulting in the magnetic dislocation.

Inventive materials 1 to 6 had a superheated degree of Si and Al ranging from 1 to 2.5 wt% and 4 to 6 wt%, respectively, at a temperature of 50 to 200 ° C. At that time, the yield strength was 550 MPa or more and W _{10 /} The strength and the iron loss were both excellent at 15 W / Kg.

[Example 2]

And a molten steel consisting of 2.0 wt% of Si, 0.2 wt% of Mn, 0.01 wt% of P, 0.003 wt% of C, 0.002 wt% of N, and other impurities, Cast to 250 mm through slab casting or 2.2 mm thick through casting. In the case of the slab, the work was continued until the casting was stopped due to an abnormality in the heat, and the thickness of the slab was 2.2 mm thick by the amount of the work.

Table 2 shows the amount of work up to the point where the aluminum content in the molten steel is oxidized and nitrided to cause the main composition to fall sharply.

The comparative material 1 was relatively low in Al content, and the slabs could produce hot-rolled sheets of more than 10,000 m. However, in the case of comparative materials 2 and 3, the amount of hot-rolled sheets that can be produced rapidly decreased. However, since the embodiment according to the present invention includes not less than 4% of Al, the comparative material 1 is not the invention of the invention. In the case of inventive materials 1 to 5 containing Al of 4% or more, It is expected that it is difficult to actually mass-produce it.

However, in case of using casting casting, it is possible to operate without overheating more than 10,000m, and actual mass production was possible. However, when the atmosphere above the molten steel was changed to nitrogen as in comparative materials 4 to 8, Al-based nitride was generated and the flow of molten steel was inhibited to deteriorate the operability. Therefore, it was found that it is effective to investigate the effect of the Al - based gas which does not react with Al in the high Al operation.

Specimen Number Al content
(weight%) When molding casting
Molten steel atmosphere Slab casting possible
Hot rolled plate length (m) Mold Casting Amount (m) Remarks One 1.2 argon 15000 28000 Comparison 1 2 2 argon 5625 25000 Comparative material 2 3 3.5 argon 1875 19800 Comparative material 3 4 4.2 argon 1500 18000 Inventory 1 5 4.8 argon 937.5 17900 Inventory 2 6 5 argon 1312.5 18200 Inventory 3 7 6.1 argon 750 18500 Invention 4 8 7 argon 562.5 17300 Invention Article 5 4 4.2 nitrogen - 8500 Comparison 4 5 4.8 nitrogen - 7500 Comparative material 5 6 5 nitrogen - 6900 Comparative material 6 7 6.1 nitrogen - 7200 Comparison 7 8 7 nitrogen - 5400 COMPARISON 8

While the present invention has been described in connection with certain exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (10)

(Excluding 0%), S: not more than 0.03% (excluding 0%), Mn: 0.1 to 1.0%, C: not more than 0.005% , Al: 4.0 to 6.0%, N: 0.003% or less (excluding 0%) and Ti: 0.01% or less (excluding 0%), the balance being Fe and other inevitably incorporated impurities,
Wherein the crystals in the (001) direction in the vertical direction of the inner side of the steel sheet are 30% or more. The method according to claim 1,
Wherein the grain size of the steel sheet is 0.05 to 0.2 mm. 3. The method of claim 2,
Wherein the yield strength of the steel sheet is 550 MPa or more. 3. The method of claim 2,
And an iron loss (W _10/400 ) of 15 W / Kg or less at a steel sheet thickness of 0.3 mm. (Excluding 0%), S: not more than 0.03% (excluding 0%), Mn: 0.1 to 1.0%, Al: 4.0 to 4.0% , The balance being Fe and other inevitably incorporated impurities, in an amount of 0.01% or less, 6.0% or less, N: 0.003% or less (excluding 0% Lt; / RTI &gt;
A step of annealing the casting plate or omitting the casting plate annealing step, and then pickling it;
Subjecting the pickled casting plate to cold rolling twice or more while cold rolling or intermediate annealing is performed; And
And performing final annealing in a temperature range of 900 to 1100 DEG C after cold rolling,
Wherein the surface temperature of the molten steel is controlled to be 50 to 200 占 폚 higher than the solidification temperature. 6. The method of claim 5,
Wherein the thickness of the casting plate in the casting step is 1 to 3 mm. The method according to claim 6,
Wherein Ar and He are used as an atmospheric gas in the step of casting the natural product. The method according to claim 6,
Wherein the crystals in the (001) direction in the inner vertical direction of the steel sheet after the final annealing are 30% or more. 9. The method according to any one of claims 5 to 8,
Wherein the yield strength of the steel sheet after the final annealing is 550 MPa or more. 9. The method according to any one of claims 5 to 8,
_{Wherein an} iron loss (W _10/400 ) of the steel sheet after the final annealing is not more than 15 W / Kg at a thickness of 0.33 mm.