KR101504704B1 - 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, 0.1% or less (excluding 0%), S: not more than 0.03% (excluding 0%), Mn: 0.1 to 2.0% (C, N) and Nb (C, N) precipitates in the steel sheet are 20 nm or less in size, which is composed of Nb: 0.2% or less (excluding 0%) and the balance Fe and other inevitably incorporated impurities. A non-oriented electrical steel sheet and a method of manufacturing the same.

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 method of manufacturing a high strength non-oriented electrical steel sheet capable of withstanding high- .

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.

However, when a high-strength electrical steel sheet is used, it is necessary to apply different materials to the rotor and the stator. In this case, the amount of scrap is increased and the cost of the material cost is increased. Restrictions follow.

Therefore, it is necessary to study the manufacturing technology of the high strength electric steel sheet which is lower in manufacturing cost than the existing products. In order to realize high-strength electrical steel sheet production, there have been proposed a technique in which strength is improved by forming a structure other than ferrite in steel and a technique in which an alloy element such as Nb, V, Cu is added to improve strength.

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 Nos. 2008-50685, WO2008 / 013015 and Korean Patent Laid-Open No. 2009-0007745 disclose a technique in which a high-strength electrical steel sheet is made by using Nb-based carbide and Ni or the like, .

However, when Cu is added, there is a problem that defects are generated on the surface during continuous casting and hot rolling reheating due to a low melting point of Cu, and there is a problem that expensive Ni is added in order to suppress it. In the case of Japanese Laid-Open Patent Application No. 2008-50685, Ni is used to finely disperse and effectively use Nb-based carbide. However, Ni is an expensive element, which causes a large cost burden.

In order to solve the above problems, the present invention provides a non-oriented electrical steel sheet having improved strength by finely dispersing precipitates 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 0.02% or less (excluding 0%), N is 0.002 to 0.02%, Si is 4.0% or less (excluding 0%), P is 0.1% (Excluding 0%), S: not more than 0.03% (excluding 0%), Mn: not more than 0.1 to 2.0%, Al: not more than 0.1% (C, N) and Nb (C, N) precipitates in the steel sheet are 20 nm or less, the balance being Fe and other inevitably incorporated impurities, A steel sheet may be provided.

The size of the AlN precipitate in the steel sheet is 100 nm or less, and the size of the crystal grains in the steel sheet is 30 mu m or less.

The yield strength of the steel sheet is _{550 MPa} or more and the steel loss (W _10/400 ) of the steel sheet is 60 W / kg or less.

In one or more embodiments of the present invention, the content of C is 0.02% or less (excluding 0%), the content of N is 0.002 to 0.02%, the content of Si is 4.0% or less (excluding 0%), the content of P is 0.1% (Excluding 0%), S: not more than 0.03% (excluding 0%), Mn: 0.1 to 2.0%, Al: not more than 0.1% (Exclusive of 0%), and the remaining Fe and other inevitably incorporated impurities, to produce a casting plate; A step of annealing the casting plate or omitting the casting plate and pickling the casting plate; Performing cold rolling twice or more while cold rolling or intermediate annealing is performed one time; And finally annealing the cold-rolled steel sheet. In the casting step, the molten steel is cooled at a rate of 50 ° C / s or higher before rolling, thereby providing a non-oriented steel sheet manufacturing method.

In the museum casting step, state, and characterized in that the thickness of the typesetting of 1 ~ 3mm, the yield strength after the final annealing, the steel sheet is at least 550MPa, the final iron loss of the steel sheet after annealing (W _10/400) is 60W / Kg Or less.

The final annealing step is performed in a temperature range of 700 ° C to 900 ° C.

According to the embodiment of the present invention, by rapid cooling through casting, even in a component system in which Si and Al are comparatively high and no phase transformation is present, it is possible to manufacture a high strength non-oriented electrical steel sheet by dispersing Ti, Nb or Al- have.

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 embodiment according to the present invention, when Ti, Al and Nb are included to manufacture a high strength nonoriented electrical steel sheet, rapid cooling is performed through strip casting to produce small and uniform Ti, Al, Nb Carbonitride was obtained to produce a non-oriented electrical steel sheet excellent in strength.

In order to manufacture the non-oriented electrical steel sheet according to the embodiment of the present invention, first, 0.02% or less of C, 0.002 to 0.02% of N, 4.0% or less of Si, 0.1% or less of P, , Molybdenum containing not more than 2.0% of Mn, not more than 2.0% of Al, not more than 0.1% of Al, not more than 0.01% of N, not more than 0.1% of Ti and not more than 0.2% of Nb, The casting was carried out using a casting machine of 1 to 3 mm.

In the embodiment according to the present invention, the molten steel (more specifically, the surface of the molten steel) is cooled at a rate of 50 to 400 ° C / s before passing through the casting roll and rolling. The temperature of the surface of the molten steel is about 1400 to 1500 ° C, and the temperature before rolling after passing through the casting roll is about 900 to 1100 ° C. In addition, the larger the cooling rate is, the more effective it is, and in a general performance process, 50 DEG C / s or more, which is more than 10 DEG C / s, is sufficient. Therefore, the present invention is not limited to the above numerical range.

The size of precipitates of TiN (C, N) and Nb (C, N) is 20 nm or less by annealing in a temperature range of 700 ° C. to 900 ° C. within 2 minutes after cold- Or less, thereby improving the strength.

Hereinafter, the reason for restricting the composition of the non-oriented electrical steel sheet according to the embodiment of the present invention will be described. Unless specifically stated otherwise, the following amounts refer to weight percentages.

C: 0.02% or less (excluding 0%)

C has the effect of improving the texture and increasing the strength, but it causes magnetic aging in the final product and deteriorates the magnetic properties during use, so that the content of C is limited to 0.02 wt% or less in the examples according to the present invention. The lower the content of C is, the more preferable it is for the magnetic properties, and it is more preferable to limit it to 0.01 wt% or less, and more preferably to 0.005 wt% in the final product.

N: 0.002 to 0.02%

N is preferably contained in a certain amount since N is combined with Ti, Al, Nb and the like to form carbonitride. Therefore, by including 0.002% or more, strength improvement due to fine precipitates can be expected. However, if it is added in excess of 0.02%, the size of the precipitate becomes coarse and its effect becomes small, so the content of N in the examples according to the present invention is limited to the above range.

Si: 4.0% or less (excluding 0%)

Si is added as a component to lower the eddy loss in the iron loss by increasing the resistivity. However, if Si is contained in an amount exceeding 4.0%, cold rolling property is deteriorated and plate breakage occurs. Therefore, the Si content in the examples according to the present invention is limited to 4.0% or less.

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 has the effect of forming MnS and CuS, which are fine precipitates, to improve the strength. However, when the content exceeds 0.03%, the effect is saturated and the magnetism deteriorates. Therefore, the S content is limited to 0.03% or less in the present invention.

Mn: 0.1 to 2.0%

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 Mn is added in an amount exceeding 2.0%, the magnetic property is deteriorated. Therefore, the content of Mn in the examples according to the present invention is limited to 0.1 to 2.0%.

Al: 0.1% or less (excluding 0%)

Al is an effective component for increasing the resistivity and lowering the eddy current loss. However, when Al exceeds 0.1%, the size of the AlN precipitates becomes coarse and the effect of retarding crystal grain growth becomes low. Therefore, the Al content in the examples according to the present invention is limited to 0.1% or less.

Ti: 0.1% or less (excluding 0%)

Ti is an element that forms fine TiN and TiC precipitates to suppress grain growth and increase the strength. However, when it exceeds 0.1%, it becomes difficult to control the size of the precipitate such as TiN. Therefore, the content of Ti is limited to 0.1% in the examples according to the present invention.

Nb: not more than 0.2% (excluding 0%)

Nb is an element that forms fine NbN and NbC precipitates to suppress grain growth and increase the strength. However, when it exceeds 0.2%, the magnetic property is excessively deteriorated and it becomes difficult to control the size of the precipitate, so that the content of Nb in the embodiment according to the present invention is limited to 0.2%.

Further, in the method of manufacturing the non-oriented electrical steel sheet according to the embodiment of the present invention, molten steel having the above composition is directly cast with a thickness of 1 to 3 mm using a twin roll casting facility. The casting speed and the material of the roll surface (difference between the breaking point and the temperature of the molten steel) are selected in consideration of workability. However, Ti, Al and Nb-based carbonitrides dissolve in order to improve the strength of the precipitates. In the vicinity of 1400 to 1500 占 폚 so as to have a cooling rate of 50 占 폚 / s or higher to around 900 占 폚, which is the pre-rolling temperature after passing through the roll. The cooling rate can be controlled by a casting roll.

In particular, TiN differs depending on the content. However, since it dissolves at a temperature of 1400 ° C or higher, a minute precipitate may be formed due to rapid cooling immediately after casting, and a cooling rate of 50 ° C / s or higher Lt; / RTI > A commonly used method for forming fine precipitates is precipitation by phase transformation. In the case of an electrical steel sheet, the phase transformation is limited by the high Si content.

In order to generate the phase transformation intentionally, Ni or Mn may be added. However, Ni is an expensive element, and Mn is difficult to add enough to cause phase transformation because it lowers the magnetization ability. Therefore, the rapid cooling by the casting of the cast steel proposed in the present invention can be effectively used without using a phase transformation to make fine precipitates at a low cost.

In the embodiment according to the present invention, when the thickness exceeds 3 mm, the cooling rate may be reduced, and the cold rolling rate may increase during cold rolling to adversely affect magnetism. However, when the thickness is less than 1 mm, And cooling speed, but the production is delayed and the productivity is lowered, which may lead to a problem in work stability.

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> There is no need for separate annealing before cold rolling. Particularly, as in the embodiment according to the present invention, when a high-strength electrical steel sheet is produced by positively using precipitates, there is a possibility of making the size of the precipitate large by annealing the casting plate. In this case, It is advantageous.

After the casting plate annealing is performed or omitted as described above, the steel is pickled and cold-rolled to produce a cold-rolled sheet having a desired thickness. The cold rolling may be carried out by cold rolling one time or by performing cold rolling twice or more while intermediate annealing is carried out 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 increase the strength, the annealing temperature is 700 to 900 ° C. and the time is within 2 minutes in consideration of workability and the like. The control of the final annealing temperature is intended to limit grain growth and prevent growth of the precipitate.

Generally, when the precipitate is more than 100 nm, the size of the precipitate becomes larger than the thickness of the magnetic domain wall, which causes a great obstacle to the movement of the magnetic domain, thereby increasing the iron loss. Further, when the size is increased, The restraining force against movement is reduced and the strength is reduced. Further, since the strength increases as the grain size is smaller, it is necessary to limit the grain size to 30 mu m or less.

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

[Example 1]

Molten steel consisting of four kinds of alloy components and other impurities having the composition shown in the following Table 1 was cast to a thickness as shown in Table 2 through continuous slab casting or casting. In the case of continuous casting in slabs, the steel sheet was reheated to 1150 DEG C and then hot rolled to 2.3 mm to prepare a hot rolled sheet. The rolled sheet was wound at 620 DEG C and then cooled in air. Then, the hot rolled sheet was pickled, Cold rolling was carried out so as to have a thickness. In case of casting casting, the casting plate was cooled at a cooling rate corresponding to Table 2, then rolled at 650 ° C, cooled in air, pickled, and cold rolled to a thickness of 0.35 mm.

At this time, the cooling rate shown in Table 2 means the average cooling rate from the molten steel temperature to 900 占 폚. The cold-rolled sheet made by the above two different conditions was subjected to final annealing at 800 ° C. for 2 minutes under the atmosphere of hydrogen 20% and nitrogen 80%, and then cut into a size of 60 mm × 60 mm and measured with SST (Single Sheet Tester). The size of the precipitates was arbitrarily taken at 10 points in the range of 5 占 퐉 占 5 占 퐉 using the TEM method using the replica method. The tensile strength was measured using three specimens cut into the KS-13B standard at a tensile force of 20 MPa / And a value at a 0.2% offset was determined.

Steel grade Si
(weight%) Al
(weight%) Mn
(weight%) C
(weight%) N
(weight%) Ti
(weight%) Nb
(weight%) P
(weight%) A 3.1 0.03 0.2 0.01 0.007 0.02 0.02 0.01 B 1.9 0.03 0.2 0.01 0.006 0.03 0.03 0.02 C 3.1 0.03 0.2 0.01 0.007 0.2 0.02 0.01 D 3 0.3 0.2 0.01 0.007 0.03 0.02 0.01 E 3.12 0.03 0.2 0.01 0.007 0.03 0.3 0.01

Specimen Number Steel grade Casting plate Cooling rate (° C / s) Yield strength
(Mpa) (Ti, Nb)
(C, N) Average size (nm) AlN average size (nm) W10 / 400 (W / Kg) Remarks Thickness (mm) One A 250 (slab) 0.5 511 42 110 65 Comparison 1 2 A 4 40 542 23 90 61 Comparative material 2 3 A 2.5 60 621 15 45 42 Inventory 1 4 A 2 100 650 10 30 38 Inventory 2 5 B 250 (slab) 0.5 450 43 105 75 Comparative material 3 6 B 4.1 40 515 25 86 65 Comparison 4 7 B 2.5 60 583 12 45 45 Inventory 3 8 B 1.8 100 592 9 29 40 Invention 4 9 C 250 (slab) 0.5 410 120 115 62 Comparative material 5 10 C 4.1 40 440 82 93 60 Comparative material 6 11 C 2.5 60 520 62 45 41 Comparison 7 12 C 2 100 540 40 23 39 COMPARISON 8 13 D 250 (slab) 0.5 412 40 520 67 Comparative material 9 14 D 4.1 40 443 25 320 66 Comparative material 10 15 D 2.5 60 545 14 205 45 Comparative material 11 16 D 2 100 570 9 120 40 Comparative material 12 17 E 250 (slab) 0.5 400 80 125 64 Comparative material 13 18 E 4.1 40 442 64 110 60 Comparative material 14 19 E 2.5 60 521 50 90 39 Comparative material 15 20 E 2 100 541 34 23 38 Comparative material 16

From the results in Table 2, it can be seen that when the casting is carried out as a slab or when the casting plate is thicker than 4 mm and the cooling rate is 50 ° C / s or less, the size of the (Ti, Nb) And it is not suitable as a high strength non-oriented electrical steel sheet.

In the case of inventive materials 1 to 4, the average size of (Ti, Nb) (C, N) was 20 nm or less and the size of AlN was finely dispersed to 100 nm or less or 50 nm or less at a cooling rate of 50 ° C / As a result, it has a characteristic of being able to connect a yield strength of 550 Mpa or more and a magnetic property of 60 W / Kg or less.

In the case of the comparative materials 1 to 16, there is a sufficient time for the precipitates to coarsen at a cooling rate of 50 ° C / s or less, or Ti, Nb or Al is added in an excessive amount, There are some conditions that an average size is 20 nm or more, a size of AlN is 100 nm or more, a grain growth retarding effect is low, and a strength improvement effect is small and an iron loss is 60 W / Kg or less. There was no condition to make.

Therefore, it is necessary to control the precipitate size to be 20 nm or less in order to simultaneously improve strength and iron loss for the steel types shown in Table 1 having Si of 2% or more. For this purpose, the maximum content of carbonitride forming elements Ti, Nb and Al And it is necessary to control the cooling rate to 50 DEG C / s or more.

[Example 2]

Molten steel consisting of an alloy component and other impurities having the composition shown in A and B in Table 1 below was cast to 2.3 mm in thickness by casting. The cooling rate up to 900 占 폚 was 70 占 폚 / s immediately after the casting, followed by cooling at 620 占 폚, air cooling, pickling, and cold rolling to a thickness of 0.35 mm. The cold-rolled sheet was finally annealed at the temperature shown in Table 3 under an atmosphere of 20% of hydrogen and 80% of nitrogen. The magnetic properties were measured in a rolling direction and a direction perpendicular to the rolling direction using a single plate measuring machine of 60 × 60 mm ² size. The yield strength was measured by preparing a specimen of KS 13B standard and performing a tensile test at a 0.2% offset .

Specimen Number Steel grade Final annealing temperature
(° C) Yield strength
(MPa) Grain size (탆) W10 / 400 (W / Kg) Remarks One A 680 920 - 67 Comparison 1 2 A 750 670 3 52 Inventory 1 3 A 850 580 21 38 Inventory 2 4 A 950 480 40 35 Comparative material 2 5 B 680 812 - 71 Comparative material 3 6 B 750 640 4 54 Inventory 3 7 B 850 560 25 42 Invention 4 8 B 950 451 41 39 Comparison 4

From the results shown in Table 3, when the final annealing temperature is between 700 ° C and 900 ° C, it is possible to obtain an appropriate crystal grain size, so that iron loss and yield strength can be compatible with each other.

The comparative materials 1 and 3 had an annealing temperature of 700 ° C or less and a high yield strength but were unrecrystallized to have an iron loss of 60 W / Kg or more, and Comparative Samples 2 and 4 had an annealing temperature of 900 ° C or more and a good iron loss The yield strength is low, so that the high-strength electrical steel sheet does not match the characteristics sought.

Therefore, by maintaining the final annealing temperature at 700 ° C to 900 ° C as in inventive materials 1 to 4, a high strength non-oriented electrical steel sheet to be produced by the present invention can be obtained.

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)

C: not more than 0.02% (excluding 0%), N: 0.002 to 0.02%, Si: not more than 4.0% (excluding 0%), P: not more than 0.1% (excluding 0%), S: not more than 0.03% , Ti: not more than 0.1% (excluding 0%), Nb: not more than 0.2% (excluding 0%), Mn: not more than 0.1 to 2.0% Fe and other inevitably incorporated impurities,
Wherein the size of the Ti (C, N) and Nb (C, N) precipitates in the steel sheet is 20 nm or less. The method according to claim 1,
Wherein the size of the AlN precipitate in the steel sheet is 100 nm or less. 3. The method according to claim 1 or 2,
Wherein the grain size of the steel sheet is 30 占 퐉 or less. The method of claim 3,
Wherein the yield strength of the steel sheet is 550 MPa or more. The method of claim 3,
_Wherein an iron loss (W _10/400 ) of the steel sheet is 60 W / kg or less. C: not more than 0.02% (excluding 0%), N: 0.002 to 0.02%, Si: not more than 4.0% (excluding 0%), P: not more than 0.1% (excluding 0%), S: not more than 0.03% (Excluding 0%), Mn: 0.1 to 2.0%, Al: not more than 0.1% (excluding 0%), Ti: not more than 0.1% (excluding 0%), Nb: not more than 0.2% And other inevitably incorporated impurities into a casting roll to produce a casting plate directly;
A step of annealing the casting plate or omitting the casting plate and pickling the casting plate;
Performing cold rolling twice or more while cold rolling or intermediate annealing is performed one time; And
And finally annealing the cold-rolled steel sheet,
Wherein the molten steel is cooled at a rate of 50 DEG C / s or higher before the rolling in the casting step. The method according to claim 6,
Wherein the casting step has a casting plate having a thickness of 1 to 3 mm. 8. The method according to claim 6 or 7,
Wherein the yield strength of the steel sheet after the final annealing is 550 MPa or more. 9. The method of claim 8,
_Wherein an iron loss (W _10/400 ) of the steel sheet after the final annealing is 60 W / Kg or less. 9. The method of claim 8,
Wherein the final annealing step is performed in a temperature range of 700 ° C to 900 ° C.