Patent Description:
Recently, as awareness of eco-friendly automobiles has been increased to reduce the generation of fine dust and greenhouse gas emissions, there has been a rapid increase in demand for non-oriented electrical steel sheets used for automobile driving motors. Unlike conventional internal combustion engine vehicles using engines, engines for environmentally friendly vehicles (hybrid, plug-in hybrid, electric, and fuel cell vehicles) are replaced by driving motors. In addition, various motors other than driving motors are required.

The driving range of eco-friendly vehicles is closely related to the efficiency of various motors including driving motors, and the efficiency of these motors is directly related to the magnetism of the electrical steel sheet. Therefore, in order to increase the driving range, it is necessary to use a non-oriented electrical steel sheet which is excellent in magnetic properties.

Since a driving motor of automobile must exhibit excellent characteristics in all areas ranging from low speed to high speed, unlike normal motors, it is necessary to output a large torque at a low speed or an acceleration, and decrese a loss at a constant speed or a high speed driving.

In order to obtain such characteristics, a non-oriented electrical steel sheet which is a motor iron core material must have a large magnetic flux density characteristic at a low speed rotation and a small high frequency iron loss at a high speed rotation. Moreover, high mechanical strength is required because it must withstand the centrifugal force generated at a high speed rotation.

As a non-oriented electrical steel sheet for eco-friendly automobiles, a non-oriented electrical steel sheet containing a segregation element, such as Sn, Sb, and P, has been proposed. However, this is problematic in that brittleness is so strong that cold rolling is difficult. Accordingly, there has been proposed technique of lowering the content of Si and increasing the addition amount of Al and Mn to improve the cold rolling property or of lowering the content of Sn, Sb, and P used as a segregation element to further improve the cold rolling property. However, when concentrating on productivity such as cold rolling, magnetic properties are degraded and motor characteristics are deteriorated. <CIT> discloses a non-Oriented Electrical Steel Sheet and Production Process Thereof, which can optionally comprise <NUM>-<NUM>% of Ge. <CIT> discloses a non-oriented electrical sheet comprising by weight, <=<NUM>% C, <NUM> to <NUM>% Si, <NUM> to <NUM>% Mn, <=<NUM>% P, <=<NUM>% S, <=<NUM>% Al, <=<NUM>% N, <NUM> to <NUM>% Ge and the balance Fe with inevitable impurities.

The present invention is to provide a non-oriented electrical steel sheet including a new additive element that can replace Sn, Sb, and P.

The present invention is to provide a method for manufacturing a non-oriented electrical steel sheet.

A non-oriented electrical steel sheet according to the present invention comprising: by weight, <NUM> to <NUM>% of Si, <NUM> to <NUM>% of Al,.

The non-oriented electrical steel sheet and manufacturing method according to an embodiment of the present invention are excellent in productivity as well as in magnetic properties.

The terms "first," "second," "third" and the like are used to illustrate different parts, components, areas, layers and/or sections, but are not limited thereto. The terms are only used to differentiate a specific part, component, area, layer or section from another part, component, area, layer or section. Accordingly, a first part, component, area, layer or section, which will be mentioned hereinafter, may be referred to as a second part, component, area, layer or section.

The singular number used here includes the plural number as long as the meaning of the singular number is not distinctly opposite to that of the plural number. The term "comprises," used herein refers to the concretization of a specific characteristic, region, integer, step, operation, element and/or component, but does not exclude the presence or addition of other characteristic, region, integer, step, operation, element and/or component.

When it is said that any part is positioned "on" or "above" another part, it means the part is directly on the other part or above the other part with at least one intermediate part. In contrast, if any part is said to be positioned "directly on" another part, it means that there is no intermediate part between the two parts.

Unless otherwise specified, all the terms including technical terms and scientific terms used herein have the same meanings commonly understandable to those skilled in the art relating to the present disclosure. The terms defined in generally used dictionaries are additionally interpreted to have meanings corresponding to relating scientific literature and contents disclosed now, and are not interpreted either ideally or very formally unless defined otherwise.

Unless otherwise stated, % means % by weight, and <NUM> ppm is <NUM>% by weight. In an embodiment of the present invention, the term "further includes an additional element" means an additional amount of the additional element substituted for the remainder of iron (Fe).

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In an embodiment of the present invention, in addition to optimizing the composition in the non-oriented electrical steel sheet, particularly the main additive components of Si, Al, and Mn, the addition amount of Ga and Ge, which are trace elements, is limited to remarkably improve the set tissue and the magnetism.

The non-oriented electrical steel sheet according to the present invention includes, by weight, <NUM> to <NUM>% of Si, <NUM> to <NUM>% of Al, <NUM> to <NUM>% of Mn, individually or in a total amount of <NUM> to <NUM>% of at least one of Ga and Ge, and the remainder including Fe and unavoidable impurities.

First, the reason for limiting the components of the non-oriented electrical steel sheet will be described.

Silicon (Si) increses the resistivity of the material to lower the iron loss. If Si is added to little, the effect of improving the high frequency iron loss may be insufficient. On the contrary, when Si is added too much, the hardness of the material may increase and the cold rolling property may be extremely deteriorated. Thus, the productivity and punching property may become poor. Therefore, Si is added in the above-mentioned range.

Aluminum (Al) plays a role of lowering the iron loss by increasing the resistivity of the material. If Al is added too little, it may not be effective in the reduction of high frequency iron loss, and nitride is formed finely, which may deteriorate the magnetism. On the other hand, if Al is added too much, various problems may occur in all processes such as steelmaking and continuous casting, and thus the productivity may be greatly lowered. Therefore, Al is added in the above-mentioned range.

Manganese (Mn) enhances the resistivity of the material to improve the iron loss and form sulfide. When it is added too little, MnS may precipitate finely to deteriorate the magnetism. If it is added too much, the magnetic flux density may be reduced by promoting the formation of [<NUM>] set tissue, which may be disadvantageous to the magnetism. Therefore, Mn is added in the above-mentioned range.

Gallium (Ga) and germanium (Ge) are segregated on the surface and grain boundaries of the steel sheet, thereby suppressing surface oxidation during annealing and improving the set tissue. In one embodiment of the present invention, at least one of Ga and Ge is included. That is, Ga alone may be included, or Ge alone may be included, or Ga and Ge may be included at the same time. When Ge alone is included, <NUM> to <NUM>% by weight of Ge is included. When Ga alone is included, <NUM> to <NUM>% by weight of Ga is included. When Ga and Ge are included at the same time, the total amount of Ga and Ge is <NUM> to <NUM>% by weight. If at least one of Ga and Ge is added too little, there is no such effect. If it is added too much, it is segregated in the grain boundaries to deteriorate the toughness of the material, thereby decreasing the productivity against magnetic improvement. Specifically, Ga and Ge may be included at the same time. Further, <NUM> to <NUM>% by weight of Ga and <NUM> to <NUM>% by weight of Ge may be included. More specifically, <NUM> to <NUM>% by weight of Ga and <NUM> to <NUM>% by weight of Ge may be conatined.

Nitrogen (N) not only forms fine and long AlN precipitates inside the base material but also forms fine nitride by binding with other impurities to inhibit grain growth and deteriorate iron loss. Thus, is limited to <NUM> wt% or less, more specifically <NUM> wt% or less.

Carbon (C) causes self-aging and binds with other impurity elements to generate carbide to degrade the magnetic properties. Thus, it is limited to <NUM>% by weight or less, more specifically <NUM>% by weight or less.

Sulfur (S) reacts with Mn to form a sulfide such as MnS to reduce grain growth and suppress the migration of the magnetic domain. Thus, it is limited to <NUM> wt% or less. More specifically, it may be preferably limited to <NUM> wt% or less.

Titanium (Ti) plays a role of suppressing grain growth and magnetic domain formation by forming carbide or nitride. Thus, i1 is limited to <NUM> wt% or less, more specifically <NUM> wt% or less.

Niobium (Nb) plays a role of suppressing the grain growth and the magnetic domain formation by forming carbide or nitride. Thus, i1 is limited to <NUM> wt% or less, more specifically <NUM> wt% or less.

Vanadium (V) plays a role of suppressing the grain growth and the magnetic domain formation by forming carbide or nitride. Thus, i1 is limited to <NUM> wt% or less, more specifically <NUM> wt% or less.

Unavoidable impurities such as Mo, Mg, Cu and the like may be included in addition to the above-mentioned elements. Although these elements are included in trace amounts, they may cause deterioration of magnetism through the formation of inclusions in the steel. Therefore, it is controlled as follows: Mo and Mg:
not more than <NUM> wt%, respectively, and Cu: not more than <NUM> wt%.

The non-oriented electrical steel sheet according the present invention satisfies the following Formula <NUM>. <MAT> ([Si], [Al], [Mn], [Ga] and [Ge] represent the content (% by weight) of Si, Al, Mn, Ga and Ge, respectively.

When the value of the Formula <NUM> is less than <NUM>, the effect of addition of Ga and Ge may be insignificant, and thus the magnetism may be deteriorated. When the value of the Formula <NUM> exceeds <NUM>, a large amount of Ga and Ge are added. The set tissue may be deteriorated and the saturation magnetic flux density may decrease. Thus, the effect of improving high frequency magnetic properties may be lost. The non-oriented electrical steel sheet according to the present invention satisfies the following Formula <NUM>. <MAT> ([Si], [Al] and [Mn] represent the content (% by weight) of Si, Al and Mn, respectively.

When the value of the above-described Formula <NUM> is satisfied, the cold rolling property can be ensured.

While the non-oriented electrical steel sheet according to the invention comprises individually or in a total amount of <NUM> to <NUM>% of at least one of Ga and Ge,.

In one embodiment of the present invention, a certain amount of Ga and Ge may be added to improve the set tissue. More specifically, when the XRD test is performed on the area of <NUM>/2t to <NUM>/4t of the steel sheet thickness, the strength ratio of the set tissue can satisfy P200/(P211 + P310) ≥ <NUM>. In this case, <NUM>/2t means <NUM>/<NUM> of the thickness of the entire steel sheet, <NUM>/4t means <NUM>/<NUM> of the thickness of the entire steel sheet. P200 means the surface strength of the set tissue in which the <<NUM>> direction lies parallel to the vertical direction of the steel sheet within <NUM> degrees, P211 means the surface strength of the set tissue in which the <<NUM>> direction lies parallel to the vertical direction of the steel sheet within <NUM> degrees, and P310 means the surface strength of the set tissue in which the <<NUM>> direction lies parallel to the the vertical direction of the steel sheet within <NUM> degrees, in XRD test. The set tissue in which the <<NUM>> direction lies parallel to the vertical direction of the steel sheet within <NUM> degrees (i.e., ND//<<NUM>>) includes the axis of the easy magnetization. Thus, the larger the ratio is, the more favorable the magnetism is. In addition, a set tissue in which the <<NUM>> direction lies parallel to the vertical direction of the steel sheet within <NUM> degrees (i.e., ND//<<NUM>>) and a set tissue in which the <<NUM>> direction lies parallel to the vertical direction of the steel sheet within <NUM> degrees (i.e., ND//<<NUM>>) are close to the axis of hard magnetization. Thus, the smaller the ratio is, the more favorable the magnetism is. In the embodiment of the present invention, the magnetic improvement effect may be obtained in the low magnetic field region through the improved set tissue. Further, it may play a key role in improving the high frequency iron loss.

The non-oriented electrical steel sheet according to an embodiment of the present invention may have an average diameter of grains of <NUM> to <NUM>µm. The highfrequency iron loss is excellent in the above-mentioned range.

The non-oriented electrical steel sheet according to an embodiment of the present invention has improved magnetic permeability and coercive force and is suitable for high-speed rotation. As a result, when applied to motors of eco-friendly automobiles, it can contribute to improvement in mileage. Specifically, the non-oriented electrical steel sheet according to the present invention has a magnetic permeability at <NUM> A/m of <NUM> or more and a coercive force at B=<NUM>. 0T of <NUM> A/m or less.

The non-oriented electrical steel sheet according to an embodiment of the present invention may have a resistivity of <NUM> to 75Ω·cm. If the resistivity is too high, the magnetic flux density may be deteriorated and become unsuitable for a motor.

A method of manufacturing a non-oriented electrical steel sheet according to the present invention includes: heating the slab including, by weight, <NUM> to <NUM>% of Si, <NUM> to <NUM>% of Al, <NUM> to <NUM>% of Mn, individually or in a total amount of <NUM> to <NUM>% of at least one of Ga and Ge, and the remainder including Fe and unavoidable impurities, and satisfying the following Formula <NUM>; hot rolling the slab to produce a hot-rolled sheet; cold rolling the hot-rolled sheet to produce a cold-rolled sheet; and finally annealing the cold-rolled sheet.

First, the slab is heated. The reason why the addition ratio of each composition in the slab is limited is the same as the reason for limiting the composition of the non-oriented electrical steel sheet described in the above, so repeated description is omitted. The composition of the slab is substantially the same as that of the non-oriented electrical steel sheet because the composition of the slab does not substantially change during the manufacturing process, such as hot rolling, hot-rolled sheet annealing, cold rolling, and final annealing, which will be described later.

The slab may be produced by the steps as follows: producing a molten steel; adding Si alloy iron, Al alloy iron, and Mn alloy iron to the molten steel; and adding at least one of Ga and Ge to the molten steel and continuously casting the molten steel. Si alloy iron, Al alloy iron, Mn alloy iron, Ga, Ge and the like can be adjusted so as to correspond to the composition range of the above-mentioned slab.

The slab is charged into a heating furnace and heated to <NUM> to <NUM>. When heated at a temperature exceeding <NUM>, the precipitate may be redissolved and precipitated finely after hot rolling.

The heated slab is hot-rolled to <NUM> to <NUM> to produce a hot-rolled sheet. In the step of producing the hot-rolled sheet, the finishing temperature may be <NUM> to <NUM>.

After the step of producing the hot-rolled steel sheet, the step of annealing the hot-rolled steel sheet may be further included. At this time, the hot-rolled sheet annealing temperature may be <NUM> to <NUM>. If the annealing temperature of the hot-rolled sheet is less than <NUM>, the tissue may not grow or grow finely. Thus, the synergistic effect of the magnetic flux density may be small. If the annealing temperature exceeds <NUM>, the magnetic properties may be rather deteriorated and the rolling workability may become poor due to the deformation of the plate shape. More specifically, the temperature range may be <NUM> to <NUM>. More specifically, the annealing temperature of the hot-rolled sheet is <NUM> to <NUM>. The annealing of hot-rolled sheet may be performed in order to increase the orientation favorable to magnetism as required, and may be omitted.

Next, the hot-rolled sheet is pickled and cold-rolled to a predetermined thickness. But the hot-rolled sheet can be cold-rolled to a final thickness of <NUM> to <NUM> by applying a reduction ratio of <NUM> to <NUM>%, which may be differentiated according to the thickness of the hot-rolled sheet.

The final cold-rolled sheet is subjected to final annealing so as to have an average dimater of grains of <NUM> to <NUM>µm. The final annealing temperature may be <NUM> to <NUM>. If the final annealing temperature is too low, recrystallization may not occur sufficiently. Further, if the final annealing temperature is too high, the rapid growth of grains may occur and the magnetic flux density and the high frequency iron loss may deteriorate. More specifically, the final annealing can be performed at a temperature of <NUM> to <NUM>. In the final annealing process, all the processed tissues formed in the previous cold rolling step can be recrystallized (i.e., <NUM>% or more).

Hereinafter, the present invention will be described in more detail with reference to examples. However, these embodiments are only for illustrating the present invention, and the present invention is not limited thereto.

Slabs were prepared as shown in Table <NUM> below. The contents of C, S, N, Ti, Nb, V, and the like other than those shown in Table <NUM> were all controlled to <NUM>% or less. The slab was heated to <NUM> and hot-rolled at <NUM> to produce a hot-rolled sheet having a thickness of <NUM>. The hot-rolled sheet was annealed at <NUM> for <NUM> minutes and pickled. Thereafter, the sheet was cold-rolled to a sheet thickness of <NUM>, and then subjected to final annealing at a temperature of <NUM> for <NUM> seconds. The magnetic properties were determined as the average value by means of a single sheet tester in the rolling direction and in the vertical direction, and were shown in Table <NUM> below. The magnetic permeability is the magnetic permeability at <NUM> A/m and the coercive force is the coercive force at B=<NUM>. For the set tissue, the steel sheet was cut to <NUM>/2t and XRD (X-ray diffraction) test method was used to calculate the strength of each face.

As shown in Table <NUM> and Table <NUM>, in the case of the inventive steels, the set tissue was improved and the magnetic permeability was large and the coercive force was small. On the other hand, in the case of the comparative steels in which the amount of addition of Ga and Ge was outside the range of the present invention, the set tissue was not improved, so that the magnetic permeability and the coercive force were weakened and the grain growth was poor.

Claim 1:
A non-oriented electrical steel sheet, comprising: by weight, <NUM> to <NUM>% of Si, <NUM> to <NUM>% of Al, <NUM> to <NUM>% of Mn, individually or in a total amount of <NUM> to <NUM>% of at least one of Ga and Ge, and the remainder being Fe and unavoidable impurities, and optionally further comprising
N: <NUM>% or less excluding <NUM>%, C: <NUM>% or less excluding <NUM>%, S: <NUM>% or less excluding <NUM>%, Ti: <NUM>% or less excluding <NUM>%, Nb: <NUM>% or less excluding <NUM>%, and V: <NUM>% or less excluding <NUM>% and optionally comprising Mo and Mg: not more than <NUM> wt%, respectively, and Cu: not more than <NUM> wt%, wherein Mo, Mg and Cu belong to the unavoidable impurities, wherein the non-oriented electrical steel sheet satisfies the following Formula <NUM> and Formula <NUM>,
wherein the non-oriented electrical steel sheet has a magnetic permeability at <NUM> A/m of <NUM> or more and a coercive force at B=<NUM>.0T of <NUM> A/m or less,
wherein the magnetic permeability and the coercive force are determined by the average value of the rolling direction and the vertical direction using a single sheet tester, <MAT>
wherein [Si], [Al], [Mn], [Ga], and [Ge] represent the content, % by weight, of Si, Al, Mn, Ga, and Ge, respectively, <MAT>
wherein [Si], [Al], and [Mn] represent the content, % by weight, of Si, Al and Mn, respectively.