KR20210078630A - Non-oriented electrical steel sheet with low core-loss and high strength after stress relief annealing and method for manufacturing the same - Google Patents

Abstract

The present disclosure relates to a non-oriented electrical steel sheet manufacturing method and a non-oriented electrical steel sheet manufactured thereby. The method includes the following steps of: heating a slab including no more than 0.005 wt% of C, 2.8-4.0 wt% of Si, no more than 0.1 wt% of P, 0.1-2.0 wt% of Al, 0.2-2.5 wt% of Mn, no more than 0.003 wt% of N, no more than 0.005 wt% of Ti and Nb, no more than 0.05 wt% of Cu, no more than 0.003 wt% of S, 0.005-0.025 wt% of V, and the remaining of Fe and inevitable mixed impurities, and satisfying the following formula 1; manufacturing a hot-rolled plate by hot-rolling the slab; manufacturing a cold-rolled plate by cold-rolling the hot-rolled plate; and finally annealing the cold-rolled plate. [Formula 1] (51*[C])/12-0.002 <= [V] <= (51*[C])/12+0.004 (In the formula 1, [C] and [V] refer to contents (wt%) of C and V respectively). Therefore, the present invention is capable of improving and stably securing an iron loss property.

Description

High-strength non-oriented electrical steel sheet with low iron loss after SRA and manufacturing method thereof

The present disclosure relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, it relates to a non-oriented electrical steel sheet having excellent high strength before SRA and excellent iron loss after SRA, and a method for manufacturing the same.

Recently, eco-friendly vehicles such as hybrid electric vehicles (HEVs) or electric vehicles (EVs) are growing along with international carbon dioxide reduction activities, and related R&D is being carried out widely. In particular, since a driving motor used in an eco-friendly vehicle has a harsher environment than a general motor in terms of durability and efficiency, an electric steel sheet suitable for this is required.

In the case of a drive motor, it is necessary to obtain a large output with a limited size, and accordingly, a rotation speed of 10000 rpm or more is required. In this case, since the centrifugal force received by the rotor of the motor is proportional to the square of the rotation speed, it exceeds the yield strength that a general electrical steel sheet can withstand during high-speed rotation, which acts as a factor threatening the stability and durability of the motor. Therefore, a high-strength material is required for the rotor of the machine rotating at high speed.

In addition, in the case of a material used as a rotor of a motor, it is necessary to reduce the eddy current loss caused by high frequency in addition to strength. As the loss becomes large, the overall efficiency of the motor is reduced.

Therefore, it is necessary to study the manufacturing technology of electrical steel sheet that can satisfy both high strength characteristics and low iron loss characteristics. As a part of this, a technology to improve strength by forming a structure other than ferrite in steel, a technology to improve strength by adding alloying elements, and control the grain size before cold rolling or additional processing to 20㎛ or more to lose iron A technique for reconciling characteristics and strength characteristics has been proposed.

However, in the technology of forming structures other than ferrite, iron loss and magnetic flux density rapidly deteriorate due to the presence of non-magnetic abnormal structures of pearlite, martensite, and austenite in the steel, and when used in a rotor, the efficiency of the motor rapidly decreases. It has the disadvantage of being reduced. The technology of adding alloying elements also has a problem of rapidly deteriorated magnetism, and there are limitations depending on the place of use. In addition, the effect of the technique of controlling the grain size before cold rolling to 20㎛ or more is a characteristic that appears in the process and intermediate products performed in conventional electrical steel sheets, and the effect is insignificant in high-strength electrical steel sheets with many non-recrystallized structures. In comparison with the case of using a material whose crystal grain size is controlled to be smaller than this, there is a problem in that it is difficult to effectively improve the magnetic properties.

In addition, the iron loss of high-alloy non-oriented electrical steel sheets containing large amounts of Si/Al/Mn etc. by improving cleanliness and texture at the same thickness by using segregation elements or elements with high oxygen affinity in terms of improving iron loss Efforts have been made to improve

Conventionally, in order to achieve this object, Mo, Y, Bi, P, etc. have been actively used, and techniques such as improvement of texture by segregation and improvement of iron loss by coarsening of precipitates have been proposed.

However, segregation elements such as Bi and P are segregated at grain boundaries to deteriorate cold rolling properties, and when applied to a high-alloy non-oriented electrical steel sheet having high Si, there is a problem in that the real rate is lowered, and in the case of Y, additional oxides are formed Therefore, the magnetism is rather deteriorated, and when Mo is added due to its insignificant effect, it exhibits less magnetic improvement than the iron loss deviation, resulting in low economic feasibility.

An object of the present invention is to provide a non-oriented electrical steel sheet used as a part of an electric device such as a generator or an automobile motor, and a method for manufacturing the same. More specifically, a method for manufacturing a non-oriented electrical steel sheet that allows both high-strength characteristics that can withstand high-speed rotating machines subjected to high stress and magnetic characteristics of low iron loss for energy efficiency, and non-oriented electricity manufactured thereby We would like to provide a steel plate.

Non-oriented electrical steel sheet of an embodiment of the present disclosure by weight%, C: 0.005% or less, Si: 2.8 to 4.0% or less, P: 0.1% or less, Al: 0.1 to 2.0%, Mn: 0.2 to 2.5%, N: 0.003% or less, Ti or Nb: 0.005% or less, Cu: 0.05% or less S: 0.003% or less, V: 0.005 to 0.025%, the balance Fe and other unavoidably mixed impurities, and satisfies the following formula 1, The average grain size may be 20 μm or less.

[Equation 1]

(51*[C])/12-0.002 ≤ [V] ≤ (51*[C])/12+0.004

(In Formula 1, [C] and [V] represent the contents (% by weight) of C and V, respectively.)

The non-oriented electrical steel sheet may have an average particle diameter of VC precipitates of 1 to 10 nm.

The non-oriented electrical steel sheet may have a density of 4*10 ¹⁵ to 1*10 ¹⁹ pieces/m ³ of VC precipitates.

The non-oriented electrical steel sheet may have an average particle diameter of AlN precipitates of 20 nm or less, and a density of 10 * 10 ¹⁴ pieces/m ³ or less.

The non-oriented electrical steel sheet may have an average particle diameter of at least one precipitate of NbC and TiC of 10 nm or less, and a density of 10 * 10 ¹⁵ pieces/m ³ or less.

The non-oriented electrical steel sheet may have an average particle diameter of CuS precipitates of 10 nm or less, and a density of 10 * 10 ¹⁵ pieces/m ³ or less.

The non-oriented electrical steel sheet may have a yield strength of 480 MPa or more before SRA.

The non-oriented electrical steel sheet may have an iron loss (W _10/400 ) after SRA of 28*t+4.4 or less when the final rolling thickness is t.

The manufacturing method of the non-oriented electrical steel sheet of an embodiment of the present disclosure by weight%, C: 0.005% or less, Si: 2.8 to 4.0% or less, P: 0.1% or less, Al: 0.1 to 2.0%, Mn: 0.2 to 2.5% , N: 0.003% or less, Ti, Nb: 0.005% or less, Cu: 0.05% or less, S: 0.003% or less, V: 0.005 to 0.025%, the remainder Fe and other unavoidably mixed impurities, and the following formula 1 heating a slab that satisfies manufacturing a hot-rolled sheet by hot-rolling the slab; manufacturing a cold-rolled sheet by cold-rolling the hot-rolled sheet; and final annealing of the cold-rolled sheet, wherein the final annealing of the cold-rolled sheet may have a final annealing temperature of 720 to 820°C.

[Equation 1]

(51*[C])/12-0.002 ≤ [V] ≤ (51*[C])/12+0.004

(In Formula 1, [C] and [V] represent the contents (% by weight) of C and V, respectively.)

In the step of heating the slab, the slab heating temperature may be 1100 to 1250 ℃.

manufacturing a hot-rolled sheet by hot-rolling the slab; After annealing the hot-rolled sheet, the hot-rolled sheet annealing temperature may be 850 to 1200 ℃.

In the step of cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet; in, the cold rolling may be performed once or performed two or more times with an intermediate annealing therebetween.

final annealing the cold-rolled sheet; Thereafter, it may include the step of coating an insulating film on the final annealed steel sheet.

The average grain size on the final annealed steel sheet may be 20㎛ or less.

final annealing the cold-rolled sheet; Thereafter, the step of SRA (Stress Relief Annealing) of the final annealed steel sheet may be further included.

SRA (Stress Relief Annealing) of the final annealed steel sheet; may be performed at a temperature of 700 to 1000 ℃ range.

According to one embodiment of the present disclosure, high strength properties can be achieved by controlling the average size of the recrystallized grains after cold rolling.

In particular, according to one embodiment of the present disclosure, by inputting the V (vanadium) content in proportion to the C (carbon) content in the range in which the crystal growth property does not deteriorate inside the base iron, the VC precipitates are reduced to a size that does not affect the magnetism. can be controlled

Accordingly, it is possible to provide a non-oriented electrical steel sheet having high strength and magnetic flux density characteristics that can be used in the rotor before the SRA treatment.

In addition, according to one embodiment of the present disclosure, by effectively suppressing magnetic deterioration due to C after final annealing, iron loss characteristics can be improved and stably secured, and after SRA, it can have low iron loss enough to be used in a stator. .

Therefore, the non-oriented electrical steel sheet of one embodiment of the present disclosure can select both properties before and after SRA treatment.

1 is a vanadium content graph according to the carbon content of Examples of the present disclosure showing the relationship with the iron loss.
2 shows the relationship between the thickness of the cold-rolled steel sheet and the iron loss after SRA of the embodiments of the present disclosure.

Terms such as first, second and third are used to describe, but are not limited to, various parts, components, regions, layers and/or sections. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first part, component, region, layer or section described below may be referred to as a second part, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is for the purpose of referring to specific embodiments only, and is not intended to limit the invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite. The meaning of "comprising," as used herein, specifies a particular characteristic, region, integer, step, operation, element and/or component, and includes the presence or absence of another characteristic, region, integer, step, operation, element and/or component. It does not exclude additions.

When a part is referred to as being “on” or “on” another part, it may be directly on or on the other part, or the other part may be involved in between. In contrast, when a part refers to being "directly above" another part, the other part is not interposed therebetween.

In addition, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

Although not defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Commonly used terms defined in the dictionary are additionally interpreted as having a meaning consistent with the related technical literature and the presently disclosed content, and unless defined, they are not interpreted in an ideal or very formal meaning.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

The present disclosure relates to the influence of various alloying elements in manufacturing non-oriented electrical steel sheets where high-frequency iron loss is important for driving motors for eco-friendly vehicles, and recrystallization behavior by adjusting various process factors of hot rolling, cold rolling and final annealing. As a result of considering the structure change characteristics, it is intended to provide a method of providing a non-oriented electrical steel sheet with low high-frequency iron loss even after SRA by appropriately controlling C precipitates using V.

In addition, as a result of studying the high frequency iron loss characteristics after SRA of a non-oriented electrical steel sheet in which Si has a high alloy amount of 2.8 wt% or more, the present disclosure indicates that C-based precipitates present in the steel sheet are an important factor affecting the iron loss. We want to understand and control it. In general, it is known that C-based precipitates having a high remelting temperature weaken the (001) texture, which is advantageous in magnetism, and further impede the movement of magnetic domains to deteriorate iron loss. However, the precipitates having a low remelting temperature not only improve the texture when the hot-rolled sheet annealing temperature is relatively high, but also have a small size of the precipitates, which can act as a positive factor for magnetism.

Accordingly, the present disclosure discovers that VC precipitates formed by combining V with C can play such a role due to a low re-melting temperature, and intends to utilize them in a non-oriented electrical steel sheet and a method for manufacturing the same. In the case of VC precipitates, when the V content is appropriately controlled, the remelting temperature is around 700 ° C., which is lower than the final annealing temperature as well as the SRA heat treatment temperature, so that there is an effect of improving the texture during recrystallization, and the size is 1 to 10 Does not degrade magnetism below nm.

Hereinafter, each step will be described in detail.

The method for manufacturing a non-oriented electrical steel sheet according to the present disclosure is C: 0.005% or less, Si: 2.8 to 4.0% or less, P: 0.1% or less, Al: 0.1 to 2.0%, Mn: 0.2 to 2.5%, N by weight% : 0.003% or less, Ti, Nb: 0.005% or less, Cu: 0.05% or less, S: 0.003% or less, V: 0.005 to 0.025%, remainder Fe and other unavoidably mixed impurities, and the following formula 1 is satisfied heating the slab to preparing a hot-rolled sheet by hot-rolling the slab; manufacturing a cold-rolled sheet by cold-rolling the hot-rolled sheet; It may include the step of final annealing the cold-rolled sheet.

[Equation 1]

(51*[C])/12-0.002 ≤ [V] ≤ (51*[C])/12+0.004

(In Formula 1, [C] and [V] represent the contents (% by weight) of C and V, respectively.)

Through the manufacturing process, carbon (C) present in the steel is combined with vanadium (V) to form VC precipitates, and the average particle diameter of the formed VC precipitates may be 1 to 10 nm or less. Specifically, the average particle diameter of the VC precipitates may be 2 nm to 8 nm. In addition, the density of the VC precipitates may be 4*10 ¹⁵ to 1*10 ¹⁹ pieces/m ³ .

By controlling the final annealing temperature to 720 to 820 °C in the final annealing step, the average grain size can be generated to 20㎛ or less. Specifically, the final annealing temperature may be 740 to 820 °C, more specifically 740 to 800 °C, or 740 to 780 °C.

The non-oriented electrical steel sheet of one embodiment of the present disclosure prepared by the above method may have a yield strength of 480 MPa or more. Specifically, the yield strength may be 480 to 600 MPa.

In addition, the non-oriented electrical steel sheet of the embodiment of the present disclosure may have a magnetic flux density of 1.63T or more.

In addition, the non-oriented electrical steel sheet of the present disclosure may form AlN precipitates by combining Al inside the steel with N. The formed AlN precipitates may inhibit crystal growth or further interfere with magnetic domain movement to deteriorate magnetism. Therefore, in the non-oriented electrical steel sheet of the present disclosure, the smaller the average particle diameter of the AlN precipitate, the better, and may be 20 nm or less. Specifically, the average particle diameter may be 1 to 20 nm, more specifically 1 to 18 nm, and more specifically 1 to 15 nm. In addition, the AlN precipitates in the non-oriented electrical steel sheet of the present disclosure may have a density of 10 * 10 ¹⁴ pieces/m ³ or less. Specifically, 1*10 ¹⁴ to 10*10 ¹⁴ pieces/m ³ , more specifically 3*10 ¹⁴ to 7*10 ¹⁴ pieces/m ³ .

In addition, in the non-oriented electrical steel sheet of the present disclosure, Nb and Ti in the steel may be combined with C to form NbC and TiC precipitates. Since the formed NbC and TiC precipitates are finely precipitated at around 900° C. and may have a fatal effect on magnetism, the size and density must be controlled. Therefore, in the non-oriented electrical steel sheet of the present disclosure, the smaller the average particle diameter of any one or more precipitates of NbC and TiC, the better, for example, may be 10 nm or less. Specifically, the average particle diameter may be 1 to 10 nm. More specifically, it may be 1 to 9 nm, more specifically 1 to 7 nm. In addition, the density of any one or more precipitates of NbC and TiC in the non-oriented electrical steel sheet of the present disclosure may be 10 * 10 ¹⁵ pieces/m ³ or less. Specifically, 1*10 ¹⁵ to 10*10 ¹⁵ pieces/m ³ , and more specifically 3*10 ¹⁵ to 8*10 ¹⁵ pieces/m ³ .

In addition, in the non-oriented electrical steel sheet of the present disclosure, Cu inside the steel may combine with S to form CuS precipitates. The formed CuS precipitates are generally precipitated as sulfides smaller than coarse MnS, which can deteriorate magnetism, so the size and density must be controlled. Therefore, the non-oriented electrical steel sheet of the present disclosure may have an average particle diameter of CuS precipitates of 10 nm or less. Specifically, the average particle diameter may be 1 to 10 nm, more specifically 4 to 8 nm. In addition, the non-oriented electrical steel sheet of the present disclosure may have a density of 10*10 ¹⁵ pieces/m ³ of CuS precipitates or less. Specifically, the density may be 1*10 ¹⁵ to 10*10 ¹⁵ pieces/m ³ , more specifically 3*10 ¹⁵ to 7*10 ¹⁵ pieces/m ³ .

First, the reason for the component limitation of the non-oriented electrical steel sheet of the present invention will be described. Unless otherwise specified, the content in the following means % by weight.

[C: 0.005 wt% or less]

C causes magnetic aging in the final product to reduce magnetic properties during use, so it should be contained in an amount of 0.005 wt% or less. Since the lower the content of C is, the more preferable it is for magnetic properties, so it is more preferable to limit it to 0.004 wt% or less in the final product.

[Si: 2.8 to 4.0 wt% or less]

Si is added as a main component to increase specific resistance to lower eddy current loss during iron loss, and to have high strength characteristics before SRA. In the present invention, in order to sufficiently improve high frequency low iron loss and strength, 2.8 wt% or more should be added. However, if Si is contained in excess of 4.0 wt%, even if the structure before cold rolling is improved, cold rolling property is deteriorated and plate breakage occurs. Therefore, it is preferable to limit the Si content to 4.0 wt% or less.

[P: 0.1 wt% or less]

P is added to increase resistivity and improve magnetic properties by improving texture. However, it is preferable to limit the content of P to 0.1% by weight or less because cold rolling property deteriorates when excessively added.

[S: 0.003 wt% or less]

Since S forms fine precipitates, MnS and CuS, and deteriorates magnetic properties by hindering crystal growth, it is desirable to manage it low, and the S content is limited to 0.003 wt% or less in the present invention.

[Al: 0.3 to 2.0 wt%]

Al is an effective component for reducing eddy current loss by increasing specific resistance, and has a lower effect than Si, but has an effect of increasing strength when added. When Al is added in an amount of less than 0.3% by weight, AlN is finely precipitated to deteriorate magnetism, whereas when Al is added in excess of 2.0% by weight, workability is deteriorated, so it is preferable to limit the Al content to 0.3 to 2.0% by weight. Do.

[Mn: 0.2 to 2.5 wt%]

When Mn is added in an amount of less than 0.2 wt %, fine MnS precipitates are formed to inhibit crystal growth, and thereby deteriorate magnetism. Therefore, it is preferable to add it in an amount of 0.2 wt % or more, so that the MnS precipitate is coarsely formed. In addition, when Mn is added in an amount of 0.2 wt % or more, it is possible to prevent the S component from being precipitated as CuS, which is a finer precipitate, thereby preventing deterioration of magnetism. However, when Mn is added excessively, the magnetism is rather deteriorated, so the content of Mn is preferably 0.2 to 2.5 wt%.

[N: 0.003 wt% or less]

N is preferably contained as little as possible because it forms fine and long AlN precipitates inside the base material and inhibits grain growth to deteriorate iron loss, and in the present invention, the N content is limited to 0.003 wt% or less.

[Ti,Nb: 0.005 wt% or less]

Ti and Nb inhibit grain growth by forming fine Ti(Nb)CN precipitates. When Ti and Nb are contained in excess of 0.005% by weight, many fine precipitates are generated to deteriorate the texture to deteriorate magnetism, and to inhibit crystal growth in the SRA process, so the Ti content is limited to 0.005% by weight or less.

[Cu: 0.05 wt% or less]

Like Mn, Cu combines with S to form precipitates, inhibits grain growth, and impairs magnetic domain movement, thereby deteriorating iron loss. In particular, the CuS precipitate is limited to 0.5 wt % or less because the size of the CuS precipitate is small and the deterioration effect is large.

[V: 0.005 to 0.25 wt%]

In the present invention, V is an essential element for improving iron loss by combining with C to form VC having a low remelting temperature to improve the texture. The formation of VC precipitates serves to bind C, thereby suppressing the formation of Fe carbides that deteriorate iron loss. As a result, iron loss can be improved by suppressing Fe carbide formation by forming VC precipitates. In order to play this role, V must be added within the range satisfying the following formula 1 within the range of 0.005 to 0.25 wt%, in this case, the VC precipitate has a small size of 1 to 10 nm or less, and the VC precipitate density can be controlled in the range of 4*10 ¹⁵ to 1*10 ¹⁹ pieces/m ³ to prevent deterioration of iron loss.

[Equation 1]

(51*[C])/12-0.002 ≤ [V] ≤ (51*[C])/12+0.004

(In Formula 1, [C] and [V] represent the contents (% by weight) of C and V, respectively.)

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

The method for manufacturing a non-oriented electrical steel sheet of the present invention is first heated by charging the slab having the above composition into a heating furnace. The heating temperature of the slab is preferably 1100 to 1250 ℃. When the slab is heated to a temperature exceeding 1250° C., the precipitates that harm magnetism are re-dissolved and can be finely precipitated after hot rolling.

When the slab is heated, then hot rolling is performed, and the hot rolled sheet is wound up. The wound hot-rolled sheet is subjected to annealing of the hot-rolled sheet if necessary. It is preferable to perform hot-rolled sheet annealing in manufacturing high-grade electrical steel sheet without phase transformation, and it is effective to improve the texture of the final annealed sheet to improve magnetic flux density. When performing hot-rolled sheet annealing, it is preferable to perform hot-rolled sheet annealing at a temperature of 850 to 1200 °C. If the hot-rolled sheet annealing temperature is less than 850° C., the structure does not grow or grows fine, so it is difficult to expect a synergistic effect of magnetic flux density. When the annealing temperature of the hot-rolled sheet is higher than 1200°C, the magnetic properties are rather deteriorated, and the rolling workability may be deteriorated due to the deformation of the sheet shape.

After performing the hot-rolled sheet annealing as described above, the hot-rolled sheet is pickled and cold-rolled to manufacture a cold-rolled sheet having a desired thickness. Cold rolling may be carried out by one cold rolling or by performing cold rolling two or more times with intermediate annealing therebetween as needed.

Since the thickness of the cold-rolled cold-rolled sheet is closely related to the high-frequency iron loss of the final sheet, in the present disclosure, where high-frequency characteristics are important, the thickness of the cold-rolled sheet may be 0.30 mm or less. As the thickness of the cold-rolled sheet increases, the iron loss deteriorates, so the thickness of the cold-rolled sheet is preferably 0.30 mm or less (see FIG. 2 ).

The cold rolled sheet is subjected to final annealing. The final annealing is carried out within the range of 720 to 820° C. so that the grain size in the cross section of the steel sheet is 20 μm or less. When the heat treatment is performed at a temperature lower than 720°C, the grain size becomes too small, the strength is high, but there are many non-recrystallized structures, and the magnetic flux density is low, so it is not suitable for use as a rotor. On the other hand, in the case of final annealing heat treatment at a temperature higher than 820 ° C, the grain size grows to 20 μm or more, and the magnetic flux density is high, but the strength is low, which is not suitable when high yield strength is required as in the present disclosure.

The final annealed steel sheet can be treated with an insulating film in a conventional way and shipped to a customer. When coating the insulating film, it is possible to apply a conventional coating material, and any of chromium-based (Cr-type) or chromium-free (Cr-free type) can be used without limitation.

After performing the final annealing step, a SRA (Stress Relief Anneaning) step may be further included. The temperature during SRA may be 700 to 1000°C.

As described above, in the non-oriented electrical steel sheet according to one embodiment of the present disclosure, crystal grains grow in the SRA process to improve iron loss characteristics. Specifically, after the SRA step, the grain size may be 30 to 300 μm, and after SRA, C and V present in the steel combine to exist as VC precipitates of 1 to 10 nm, thereby suppressing magnetic degradation due to C aging. can As the grain size increases after SRA, the effect of increasing the magnetic flux density can be obtained.

Accordingly, high strength characteristics can be obtained by maintaining the grain size at 20 μm or less before SRA, and high magnetic flux density characteristics can be obtained as the grain size grows to 30 to 300 μm after SRA.

Accordingly, when the thickness of the non-oriented electrical steel sheet of the embodiment of the present disclosure is t, the iron loss after SRA (W40/100) may be 28*t+4.4 or less. When the thickness of the steel sheet is 0.25mm, the iron loss W40/100 after SRA may be 11.4W/kg or less.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are for illustrative purposes only, and the present invention is not limited thereto.

Example

By weight, a slab made of alloy components and impurities having the composition shown in Tables 1 and 2 below was reheated to 1130° C., and then hot-rolled to 2.0 mm to prepare a hot-rolled sheet. Each manufactured hot-rolled sheet was wound at 620°C, cooled in air, and annealed at 1020°C for 2 minutes. Then, after pickling the hot-rolled sheet, cold rolling was performed so as to have a thickness of 0.25 to 0.30 mm. Then, the cold-rolled sheet was subjected to final annealing for 2 minutes under the conditions shown in Table 2 under atmospheric conditions of 20% hydrogen and 80% nitrogen. Thereafter, SRA was performed in a nitrogen atmosphere at 800° C. for 1 hour.

Analysis of magnetism and precipitates before and after SRA was performed. The iron loss and magnetic flux density were measured in the rolling direction and the rolling direction perpendicular to the rolling direction using a single plate measuring device ^{of 60*60mm 2 size and averaged, and the VC precipitate size was measured using a transmission electron microscope replication method.} The results are shown in Table 2. The average grain size was calculated, and the yield strength was determined as a value at a 0.2% offset by performing a tensile test by manufacturing a specimen of KS 13B standard.

steel grade thickness
(mm) Si
(weight%) Al
(weight%) Mn
(weight%) N
(weight%) P
(weight%) Nb
(weight%) Ti
(weight%) Cu
(weight%) A 0.25 3.6 0.5 0.8 0.0015 0.01 0.002 0.002 0.01 A-1 0.2 3.6 0.5 0.8 0.0015 0.01 0.002 0.002 0.01 A-2 0.23 3.6 0.5 0.8 0.0015 0.01 0.002 0.002 0.01 A-3 0.27 3.6 0.5 0.8 0.0015 0.01 0.002 0.002 0.01 A-4 0.3 3.6 0.5 0.8 0.0015 0.01 0.002 0.002 0.01 B 0.25 3 1.1 0.6 0.0015 0.01 0.002 0.002 0.01 C 0.25 2.5 1.5 0.6 0.0015 0.01 0.002 0.002 0.01 D 0.25 3.5 0.8 0.5 0.0015 0.01 0.01 0.002 0.01 E 0.25 3.5 0.8 0.5 0.0015 0.01 0.002 0.01 0.01 F 0.25 3.5 0.8 0.5 0.0015 0.01 0.002 0.002 0.1 G 0.25 3.6 0.002 0.8 0.0015 0.01 0.002 0.002 0.01

Bungang
Bell final
Annealing
Temperature
(℃) ingredient Characteristics before SRA Post-SRA characteristics remark C content
(weight%) 51*[C]/12-0.002
(weight%) 51*[C]/12+0.004
(weight%) V content
(weight%) grain
size
(μm) surrender
burglar
(MPa) Magnetic flux density (B50, T) High frequency
iron loss
(W10/400, W/kg) VC average size (nm) VC density (pcs/m ³ ) A 770 0.002 0.007 0.013 0.002 16 562 1.62 11.8 2 3*10 ¹⁸ Comparative Goods 1 A 770 0.002 0.007 0.013 0.005 15 542 1.63 11.6 2 8*10 ¹⁸ Comparative Goods 2 A 770 0.002 0.007 0.013 0.008 13 545 1.64 11 4 6*10 ¹⁶ invention material 1 A 770 0.002 0.007 0.013 0.01 14 544 1.63 10.8 6 2*10 ¹⁶ invention material 2 A 770 0.002 0.007 0.013 0.012 13 546 1.63 10.9 7 1*10 ¹⁶ invention material 3 A 770 0.002 0.007 0.013 0.015 12 555 1.62 11.9 20 5*10 ¹⁴ Comparative Goods 3 A 770 0.002 0.007 0.013 0.02 9 558 1.62 11.9 25 2*10 ¹⁴ Comparative Goods 4 A 770 0.003 0.011 0.017 0.008 12 558 1.62 11.8 4 2*10 ¹⁸ Comparative Goods 5 A 770 0.003 0.011 0.017 0.012 11 535 1.63 10.9 6 3*10 ¹⁶ Invention 4 A 770 0.003 0.011 0.017 0.015 13 549 1.64 11.2 8 1*10 ¹⁶ invention 5 A 770 0.003 0.011 0.017 0.02 11 545 1.62 11.8 13 3*10 ¹⁵ Comparative Goods 6 A 770 0.004 0.015 0.021 0.01 10 558 1.62 11.8 3 5*10 ¹⁸ Comparative Goods 7 A 770 0.004 0.015 0.021 0.016 9 564 1.63 11.1 5 8*10 ¹⁶ invention 6 A 770 0.004 0.015 0.021 0.018 10 538 1.64 10.9 8 2*10 ¹⁶ invention 7 A 770 0.004 0.015 0.021 0.025 9 553 1.62 11.8 15 3*10 ¹⁵ Comparative Goods 8 A 770 0.006 0.024 0.030 0.02 8 552 1.64 11.7 10 3*10 ¹⁷ Comparative Goods 9 A 770 0.006 0.024 0.030 0.028 10 565 1.63 12 15 5*10 ¹⁵ Comparative Goods 10 A 770 0.006 0.024 0.030 0.035 9 543 1.62 12 25 1*10 ¹⁵ Comparative Goods 11 A 700 0.002 0.007 0.013 0.01 2 650 1.59 10.8 6 2*10 ¹⁶ Comparative Goods 12 A 720 0.002 0.007 0.013 0.01 7 600 1.63 10.9 6 2*10 ¹⁶ invention 8 A 740 0.002 0.007 0.013 0.01 9 580 1.64 10.9 7 1*10 ¹⁶ invention 9 A 760 0.002 0.007 0.013 0.01 10 550 1.64 10.9 7 1*10 ¹⁶ invention 10 A 780 0.002 0.007 0.013 0.01 12 540 1.64 10.8 7 1*10 ¹⁶ Invention 11 A 800 0.002 0.007 0.013 0.01 15 500 1.65 11 7 1*10 ¹⁶ Invention 12 A 820 0.002 0.007 0.013 0.01 16 480 1.65 11.1 8 8*10 ¹⁵ invention material 13 A 840 0.002 0.007 0.013 0.01 25 470 1.65 11.1 8 8*10 ¹⁵ Comparative Goods 13 A-1 770 0.003 0.011 0.017 0.008 13 551 1.62 10.3 4 2*10 ¹⁸ Comparative Goods 14 A-1 770 0.003 0.011 0.017 0.012 15 545 1.63 9.7 6 3*10 ¹⁶ invention material 14 A-1 770 0.003 0.011 0.017 0.015 13 534 1.64 9.8 8 1*10 ¹⁶ invention 15 A-1 770 0.003 0.011 0.017 0.02 13 531 1.62 10.2 13 3*10 ¹⁵ Comparative Goods 15 A-2 770 0.003 0.011 0.017 0.008 14 558 1.62 11 4 2*10 ¹⁸ Comparative Goods 16 A-2 770 0.003 0.011 0.017 0.012 13 528 1.63 10.7 6 3*10 ¹⁶ Invention 16 A-2 770 0.003 0.011 0.017 0.015 10 538 1.64 10.6 8 1*10 ¹⁶ invention 17 A-2 770 0.003 0.011 0.017 0.02 12 546 1.62 11 13 3*10 ¹⁵ Comparative Goods 17 A-3 770 0.003 0.011 0.017 0.008 13 562 1.64 12.3 4 2*10 ¹⁸ Comparative Goods 18 A-3 770 0.003 0.011 0.017 0.012 11 551 1.64 11.8 6 3*10 ¹⁶ invention material 18 A-3 770 0.003 0.011 0.017 0.015 12 541 1.64 11.7 8 1*10 ¹⁶ invention material 19 A-3 770 0.003 0.011 0.017 0.02 10 550 1.64 12.4 13 3*10 ¹⁵ Comparative Goods 19 A-4 770 0.003 0.011 0.017 0.008 13 544 1.64 12.9 4 2*10 ¹⁸ Comparative Goods 20 A-4 770 0.003 0.011 0.017 0.012 13 544 1.64 12.7 6 3*10 ¹⁶ invention 20 A-4 770 0.003 0.011 0.017 0.015 10 548 1.64 12.6 8 1*10 ¹⁶ invention 21 A-4 770 0.003 0.011 0.017 0.02 13 545 1.64 13 13 3*10 ¹⁵ Comparative Goods 21 B 770 0.002 0.007 0.013 0.01 13 500 1.64 11.2 7 1*10 ¹⁶ invention material 22 C 770 0.002 0.007 0.013 0.01 12 470 1.64 11.1 7 1*10 ¹⁶ Comparative Goods 22 D 770 0.002 0.007 0.013 0.01 5 580 1.64 14 8 7*10 ¹⁵ Comparative Goods23 E 770 0.002 0.007 0.013 0.01 3 580 1.64 13.5 8 5*10 ¹⁵ Comparative Goods24 F 770 0.002 0.007 0.013 0.01 6 560 1.64 12.3 7 1*10 ¹⁶ Comparative Goods25 G 770 0.002 0.007 0.013 0.01 10 490 1.67 13.4 4 6*10 ¹⁶ Comparative Goods 26

Among the properties before and after SRA shown in Table 2, Comparative Materials 1 to 11 and Inventive Materials 1 to 7 are shown in FIG. 1 in order to examine the amounts of V and C for the 0.25 mm product and magnetic properties after SRA.

In the case of invention materials 1 to 7 in which the V content satisfies the range of (51*[C])/12-0.002 ≤ [V] ≤ (51*[C])/12+0.004, the iron loss is lower than 11.4 W/kg The iron loss values are shown. In the case of Comparative Materials 10 and 11, the content of V was within the corresponding range, but the content of C was higher than 0.005%, so that the VC size was 10 nm or more, indicating that the iron loss deteriorated.

Therefore, in order to realize excellent characteristics with low high-frequency iron loss of 11.4W/Kg or less after SRA suitable for an eco-friendly vehicle driving motor, V is added in proportion to the amount of C as shown in Invention Materials 1 to 7 in Table 2, but the C content is 0.005 % should not be exceeded.

In order to see the effect of the final annealing temperature, the final annealing temperature was changed to 700 to 840 ℃ for the A component system in Table 1. In the case of invention materials 8 to 13 of Table 2, the magnetic flux density was 1.63T or more and the strength was 480 MPa or more, which was suitable for use as a rotor of a high-efficiency motor, but comparative materials 12 and 13 had excessively small crystal grains or 20㎛. In excess, one of magnetic flux density and strength was found to be inadequate. Accordingly, it can be seen that it is necessary to control the final annealing temperature in the range of 720 ~ 820 °C.

In order to see the effect of iron loss after heat treatment according to the V content and the thickness of the final product plate, A-1,A-2,A-3,A-4 with the thickness changed from 0.2 to 0.3mm for the A component system in Table 1 The iron loss after heat treatment of the specimen is shown in FIG. 2 . It can be seen that in the case of invention materials 4,5,14-21 in Table 2, in which V effectively suppresses the aging of C, the iron loss has a value of 28*product thickness (mm)+4.4.

The test results of B, C, D, E, and F of Table 1 dissolved in order to understand the influence of impurities such as Si, Nb, Ti, and Cu are shown in Inventive Materials 22 and Comparative Materials 22 to 25 in Table 2. In the case of B, where Si is higher than 2.8%, both strength and iron loss are within the appropriate range, but in the case of C with Si as low as 2.5%, the yield strength is 470MPa, which is not significant compared to the existing electrical steel sheet, so the rotor of high-speed rotating machine was unsuitable for In the case of D and E melt material containing 100ppm or more of Ti and Nb, respectively, the properties before SRA were excellent, but after heat treatment, the properties deteriorated due to growth inhibition, etc. It was not suitable for the same reason. In the case of Comparative Material 26, which contained a very small amount of Al as 0.002, the magnetic flux density was high, but the specific resistance value was low, the high frequency iron loss was high, and the strength was relatively low, making it unsuitable.

Therefore, when it is necessary to selectively utilize the rotor strength and the iron loss of the stator through a subsequent process such as stress relief annealing, Si is added at 2.8wt% or more, and V is added in proportion to C, but Ti, Nb, S By controlling the amount to be less than a certain amount and controlling the final annealing temperature to be smaller than 20 μm in grain size, an electrical steel sheet having suitable properties can be manufactured.

Table 3 below shows the average sizes and densities of AlN, (Nb, Ti)C, (Nb, Ti)N and CuS precipitates by measuring them.

Psalter
number AlN (Nb,Ti)(C,N) CuS remark Average size (nm) Density (pcs/m ³ ) Average size (nm) Density (pcs/m ³ ) Average size (nm) Density (pcs/m ³ ) One 13 4*10 ¹⁴ 9 2*10 ¹⁵ 8 3*10 ¹⁵ Comparative Goods 1 2 12 3*10 ¹⁴ 5 7*10 ¹⁵ 8 5*10 ¹⁵ Comparative Goods 2 3 18 4*10 ¹⁴ 8 5*10 ¹⁵ 4 7*10 ¹⁵ invention material 1 4 12 7*10 ¹⁴ 8 3*10 ¹⁵ 6 5*10 ¹⁵ invention material 2 5 12 4*10 ¹⁴ 7 8*10 ¹⁵ 7 7*10 ¹⁵ invention material 3 6 18 5*10 ¹⁴ 8 3*10 ¹⁵ 6 7*10 ¹⁵ Comparative Goods 3 7 13 5*10 ¹⁴ 6 5*10 ¹⁵ 5 5*10 ¹⁵ Comparative Goods 4 8 11 3*10 ¹⁴ 7 7*10 ¹⁵ 8 6*10 ¹⁵ Comparative Goods 5 9 11 5*10 ¹⁴ 7 3*10 ¹⁵ 4 3*10 ¹⁵ Invention 4 10 11 6*10 ¹⁴ 5 3*10 ¹⁵ 8 5*10 ¹⁵ invention 5 11 14 7*10 ¹⁴ 5 3*10 ¹⁵ 6 7*10 ¹⁵ Comparative Goods 6 12 17 7*10 ¹⁴ 8 5*10 ¹⁵ 7 5*10 ¹⁵ Comparative Goods 7 13 14 5*10 ¹⁴ 5 3*10 ¹⁵ 7 7*10 ¹⁵ invention 6 14 17 6*10 ¹⁴ 9 7*10 ¹⁵ 7 4*10 ¹⁵ invention 7 15 16 4*10 ¹⁴ 6 4*10 ¹⁵ 5 4*10 ¹⁵ Comparative Goods 8 16 13 3*10 ¹⁴ 9 3*10 ¹⁵ 6 3*10 ¹⁵ Comparative Goods 9 17 18 3*10 ¹⁴ 9 4*10 ¹⁵ 4 4*10 ¹⁵ Comparative Goods 10 18 15 4*10 ¹⁴ 6 2*10 ¹⁵ 5 4*10 ¹⁵ Comparative Goods 11 19 14 4*10 ¹⁴ 7 7*10 ¹⁵ 6 5*10 ¹⁵ Comparative Goods 12 20 17 7*10 ¹⁴ 6 3*10 ¹⁵ 7 3*10 ¹⁵ invention 8 21 11 5*10 ¹⁴ 6 6*10 ¹⁵ 8 7*10 ¹⁵ invention 9 22 15 3*10 ¹⁴ 8 8*10 ¹⁵ 4 4*10 ¹⁵ invention 10 23 17 7*10 ¹⁴ 6 5*10 ¹⁵ 8 4*10 ¹⁵ Invention 11 24 14 6*10 ¹⁴ 7 8*10 ¹⁵ 4 5*10 ¹⁵ Invention 12 25 14 5*10 ¹⁴ 5 7*10 ¹⁵ 5 7*10 ¹⁵ invention material 13 26 15 5*10 ¹⁴ 6 7*10 ¹⁵ 7 4*10 ¹⁵ Comparative Goods 13 27 17 4*10 ¹⁴ 9 4*10 ¹⁵ 7 3*10 ¹⁵ Comparative Goods 14 28 17 7*10 ¹⁴ 5 8*10 ¹⁵ 6 4*10 ¹⁵ invention material 14 29 13 6*10 ¹⁴ 8 7*10 ¹⁵ 4 3*10 ¹⁵ invention 15 30 17 4*10 ¹⁴ 5 5*10 ¹⁵ 7 3*10 ¹⁵ Comparative Goods 15 31 15 7*10 ¹⁴ 9 6*10 ¹⁵ 5 3*10 ¹⁵ Comparative Goods 16 32 17 3*10 ¹⁴ 8 4*10 ¹⁵ 4 4*10 ¹⁵ Invention 16 33 11 4*10 ¹⁴ 6 8*10 ¹⁵ 7 6*10 ¹⁵ invention 17 34 11 3*10 ¹⁴ 5 4*10 ¹⁵ 6 4*10 ¹⁵ Comparative Goods 17 35 14 6*10 ¹⁴ 6 3*10 ¹⁵ 4 4*10 ¹⁵ Comparative Goods 18 36 12 6*10 ¹⁴ 6 5*10 ¹⁵ 6 4*10 ¹⁵ invention material 18 37 18 6*10 ¹⁴ 7 2*10 ¹⁵ 5 3*10 ¹⁵ invention material 19 38 12 6*10 ¹⁴ 5 2*10 ¹⁵ 8 4*10 ¹⁵ Comparative Goods 19 39 17 7*10 ¹⁴ 8 4*10 ¹⁵ 7 6*10 ¹⁵ Comparative Goods 20 40 15 3*10 ¹⁴ 7 8*10 ¹⁵ 5 7*10 ¹⁵ invention 20 41 18 6*10 ¹⁴ 8 8*10 ¹⁵ 6 6*10 ¹⁵ invention 21 42 11 5*10 ¹⁴ 8 4*10 ¹⁵ 6 4*10 ¹⁵ Comparative Goods 21 43 14 7*10 ¹⁴ 5 3*10 ¹⁵ 8 7*10 ¹⁵ invention material 22 44 11 6*10 ¹⁴ 5 3*10 ¹⁵ 5 3*10 ¹⁵ Comparative Goods 22 45 16 4*10 ¹⁴ 14 4*10 ¹⁷ 4 4*10 ¹⁵ Comparative Goods23 46 17 7*10 ¹⁴ 19 4*10 ¹⁶ 4 7*10 ¹⁵ Comparative Goods24 47 18 4*10 ¹⁴ 5 3*10 ¹⁵ 21 4*10 ¹⁸ Comparative Goods25 48 4 8*10 ¹⁵ 6 7*10 ¹⁵ 6 7*10 ¹⁵ Comparative Goods 26

The present invention is not limited to the embodiments, but may be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains may develop other specific forms without changing the technical spirit or essential features of the present invention. It will be appreciated that this may be practiced. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (16)

In wt%, C: 0.005% or less, Si: 2.8 to 4.0% or less, P: 0.1% or less, Al: 0.1 to 2.0%, Mn: 0.2 to 2.5%, N: 0.003% or less, Ti or Nb: 0.005% or less, Cu: 0.05% or less S: 0.003% or less, V: 0.005 to 0.025%, the remainder including Fe and other unavoidably mixed impurities, satisfying the following formula 1, and having an average grain size of 20 μm or less, non-directional electricity grater.
[Equation 1]
(51*[C])/12-0.002 ≤ [V] ≤ (51*[C])/12+0.004
(In Formula 1, [C] and [V] represent the contents (% by weight) of C and V, respectively.) According to claim 1,
The non-oriented electrical steel sheet has an average particle diameter of VC precipitates of 1 to 10 nm, non-oriented electrical steel sheet. According to claim 1,
The non-oriented electrical steel sheet has a density of 4*10 ¹⁵ to 1*10 ¹⁹ pieces/m ³ of VC precipitates, a non-oriented electrical steel sheet. According to claim 1,
The non-oriented electrical steel sheet has an average particle diameter of AlN precipitates of 20 nm or less, and a density of 10 * 10 ¹⁴ pieces/m ³ or less, a non-oriented electrical steel sheet. According to claim 1,
The non-oriented electrical steel sheet has an average particle diameter of at least one precipitate of NbC and TiC of 10 nm or less, and a density of 10 * 10 ¹⁵ pieces/m ³ or less, a non-oriented electrical steel sheet. According to claim 1,
The non-oriented electrical steel sheet has an average particle diameter of CuS precipitates of 10 nm or less, and a density of 10 * 10 ¹⁵ pieces/m ³ or less, a non-oriented electrical steel sheet. According to claim 1,
The non-oriented electrical steel sheet has a yield strength of 480 MPa or more before SRA, a non-oriented electrical steel sheet. According to claim 1,
The non-oriented electrical steel sheet has an iron loss after SRA (W _10/400 ) of 28*t+4.4 or less when the final rolling thickness is t, non-oriented electrical steel sheet. By weight%, C: 0.005% or less, Si: 2.8 to 4.0% or less, P: 0.1% or less, Al: 0.1 to 2.0%, Mn: 0.2 to 2.5%, N: 0.003% or less, Ti, Nb: 0.005% or less, Cu: 0.05% or less, S: 0.003% or less, V: 0.005 to 0.025%, the balance Fe and other unavoidably mixed impurities, heating the slab satisfying the following formula 1;
manufacturing a hot-rolled sheet by hot-rolling the slab;
manufacturing a cold-rolled sheet by cold-rolling the hot-rolled sheet;
final annealing of the cold-rolled sheet;
In the final annealing of the cold-rolled sheet, the final annealing temperature is 720 to 820° C.
[Equation 1]
(51*[C])/12-0.002 ≤ [V] ≤ (51*[C])/12+0.004
(In Formula 1, [C] and [V] represent the contents (% by weight) of C and V, respectively. 10. The method of claim 9,
In the step of heating the slab;
The slab heating temperature is 1100 to 1250 ℃, non-oriented electrical steel sheet manufacturing method. 10. The method of claim 9,
manufacturing a hot-rolled sheet by hot rolling the slab; Since the
Comprising the step of annealing the hot-rolled sheet, the hot-rolled sheet annealing temperature is 850 to 1200 ℃, non-oriented electrical steel sheet manufacturing method. 10. The method of claim 9,
manufacturing a cold-rolled sheet by cold-rolling the hot-rolled sheet; in,
The cold rolling is carried out once or twice or more with an intermediate annealing therebetween, a non-oriented electrical steel sheet manufacturing method. 10. The method of claim 9,
final annealing the cold-rolled sheet; Since the,
A method of manufacturing a non-oriented electrical steel sheet, comprising the step of coating an insulating film on the final annealed steel sheet. 10. The method of claim 9,
The average grain size on the final annealed steel sheet is 20㎛ or less, a method of manufacturing a non-oriented electrical steel sheet. 10. The method of claim 9,
final annealing the cold-rolled sheet; after
Further comprising the step of SRA (Stress Relief Annealing) of the final annealed steel sheet, the method of manufacturing a non-oriented electric field sheet. 16. The method of claim 15,
SRA (Stress Relief Annealing) of the final annealed steel sheet;
A method for manufacturing a non-oriented electrical steel sheet, wherein the temperature is performed in the range of 700 to 1000 ℃.

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