KR101568839B1 - Non-oriented electrical steel steet and manufacturing method for the same - Google Patents

Abstract

 A method of manufacturing a non-oriented electrical steel sheet is provided. A method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: 2.5 to 3.5% by weight of Si, 0.2 to 1.5% by weight of Al, 0.05 to 0.8% by weight of Mn, 0.1% (Excluding 0%), S: not more than 0.004% (excluding 0%), N: not more than 0.002% (excluding 0%), and the balance Fe and other inevitable impurities. Ca: 10 to 30 ppm or REM: Or both at the same time; Charging the slab into a heating furnace and reheating the slab; Hot rolling the slab at a temperature between 1,150 ° C and 1,200 ° C to a thickness of 1.6mm or less; Annealing the hot-rolled hot-rolled sheet to hot-rolled sheet; A step of cold picking the hot-rolled sheet, and a step of finally annealing the cold-rolled steel plate.

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 finest non-oriented electrical steel sheet which is widely used as an important part of a rotating machine and has low iron loss and high magnetic flux density.

In general, the nonoriented electric steel sheet is an important iron core material necessary for converting electrical energy into mechanical energy in a rotating machine. In order to save energy, it is important to have magnetic properties, that is, low iron loss and high magnetic flux density. Here, iron loss is the energy that turns into heat in the energy conversion process, so the lower the energy is, the more efficient the magnetic flux density becomes.

Recently, technologies for converting existing internal combustion engine vehicles into HEV (hybrid vehicle) / EV (electric vehicle) have been rapidly developed as measures to reduce fossil fuel shortage and greenhouse gas reduction. These HEV / EVs are cars that can convert some or all of the drive system into electric motors to reduce the consumption of gasoline or diesel fuel, which is a fuel for existing internal combustion engines, while achieving better fuel economy.

The motors used in such automobiles must produce a large torque at low speeds or accelerations, and at high speeds at constant speeds and at high speeds. Therefore, the nonoriented electric steel sheet, which is a motor iron core material, should have a large magnetic flux density characteristic at low speed rotation and a low iron loss at high speed. In general, high-frequency iron loss refers to iron loss at a frequency of 200 Hz or more, but the value of W10 / 400 is generally used for automotive non-oriented electrical steel sheets.

In order to improve the high-frequency iron loss, the alloy elements such as Si, Al, and Mn, which are the resistivity elements of the electric steel sheet, should be moved upward, and impurities should be reduced to facilitate the movement of the magnetic domains. However, when the non-magnetic alloy element such as Si, Al, and Mn is highly contained, the magnetic flux density becomes low. In particular, it is essential to use a material having a high magnetic flux density for a material such as an environmentally friendly electric automobile drive motor which is continuously required to be lightweight.

Japanese Patent Publication Nos. JP2000-096195 and JP2008-127659 use a method of preventing formation of a [111] texture which is detrimental to magnetism by lowering the hot-rolled thickness in order to suppress the magnetic flux density dislocation caused by the addition of alloying elements. Japanese Patent JP2008-132534 Has realized the high magnetic flux density through the casting texture and metalization by using the double roll casting method with REM and Ca addition.

However, although JP2000-096195 and JP2008-127659 prove the effect of reducing the thickness of the hot rolled steel sheet, there is a problem that it is difficult to apply the steel sheet to the actual process because there is no technique required for reducing the hot rolled steel sheet thickness. In JP2008-132534, Although the positive effect of Ca has been proposed, casting itself has limitations on mass production and it is difficult to introduce it into actual mass production facilities.

An embodiment of the present invention is to provide a non-oriented electrical steel sheet which is not deteriorated in magnetic properties even when the reheating temperature is raised to heat the final hot-rolled steel thickness during hot rolling, and has excellent magnetic properties while maintaining a high alloy, and a method for manufacturing the same.

According to an embodiment of the present invention, a steel sheet comprising 2.5 to 3.5% by weight of Si, 0.2 to 1.5% by weight of Al, 0.05 to 0.8% by weight of Mn, 0.1% : Not more than 0.004% (excluding 0%), N: not more than 0.002% (excluding 0%) and the balance Fe and other unavoidable impurities, and Ca: 10 to 30 ppm or REM: 20 to 80 ppm, ; Charging the slab into a heating furnace and reheating the slab; Hot rolling the slab at a temperature between 1,150 ° C and 1,200 ° C to a thickness of 1.6mm or less; Annealing the hot-rolled hot-rolled sheet to hot-rolled sheet; There is provided a method for producing a non-oriented electrical steel sheet comprising pickling the hot-rolled sheet, cold-rolling and finally annealing the cold-rolled steel sheet.

At this time, the hot-rolled sheet annealing can be performed at a temperature of 850 to 1,150 ° C.

At this time, the hot rolled sheet can be cold rolled at a reduction ratio of 70 to 95%.

At this time, the final annealing may be performed at a temperature of 900 to 1,050 DEG C such that the crystal grain diameter becomes 50 to 150 mu m.

At this time, at the step of manufacturing the slab, at least one of Ca or REM may be added at the same time or at the same time in the refining step in the slab manufacturing process.

At this time, Ca may be added in the form of CaSi.

At this time, the electric steel sheet may have a magnetic flux density of 1.68 T or more and an iron loss (W10 / 400) of 12.5 W / Kg or less based on a thickness of 0.27 mm. According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: 2.5 to 3.5 wt% of Si, 0.2 to 1.5 wt% of Al, 0.05 to 0.8 wt% of Mn, 0.1 wt% S: not more than 0.004% (excluding 0%), N: not more than 0.002% (excluding 0%) and the balance of Fe and other unavoidable impurities, Ca: 10 to 30 ppm or REM: 20 to 80 ppm, And then reheated at a temperature of 1,150 ° C. to 1,200 ° C., hot-rolled to 1.6 mmt or less, and then hot-rolled and annealed, followed by cold rolling and final annealing to obtain a steel sheet having a thickness of 0.27 mm Directional electric steel sheet having a magnetic flux density of 1.68 T or more and an iron loss (W10 / 400) of 12.5 W / kg or less.

At this time, the steel sheet may be 0.30 mm to 0.15 mm thick after the cold rolling.

At this time, the steel sheet may have a crystal grain diameter of 50 to 150 mu m after the final annealing.

At this time, the steel sheet can be annealed at a temperature of 850 to 1,150 ° C.

At this time, the steel sheet can be cold-rolled at a reduction ratio of 70 to 95%.

At this time, the steel sheet may be subjected to final annealing at a temperature of 900 to 1,050 ° C.

According to one embodiment of the present invention, it is possible to minimize the magnetic suppression due to hot rolling reheating temperature including Ca, REM and the like, thereby making it possible to thin the hot rolled sheet thickness and finally to manufacture a high- There is a way to do this.

The non-oriented electrical steel sheet according to an embodiment of the present invention can contribute to the improvement of the efficiency of the automotive drive motor.

FIG. 1 is a graph showing changes in iron loss and magnetic flux density according to the amount of Ca change after fixing the reheating temperature at 1,160 ° C. and the hot-rolled steel thickness at 1.4 mmt in the method of manufacturing the non-oriented electrical steel sheet according to an embodiment of the present invention.
FIG. 2 is a graph showing changes in iron loss and magnetic flux density according to a change amount of REM after fixing the reheating temperature at 1,160 ° C. and the hot-rolled steel thickness at 1.4 mmt in the method of manufacturing the non-oriented electrical steel sheet according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

According to one embodiment of the present invention, a steel sheet according to the present invention comprises 2.5 to 3.5% of Si, 0.2 to 1.5% of Al, 0.05 to 0.8% of Mn, 0.1% or less of P (excluding 0% 0.004% or less (excluding 0%), N: 0.002% or less (excluding 0%) and the balance of Fe and other unavoidable impurities, Ca: 10 to 30 ppm or REM: 20 to 80 ppm, , The slab is heated at a temperature of 1150 to 1200 ° C. during hot rolling and the final thickness of the hot rolling is made to be 1.6 mmt or less to obtain a magnetic flux density of 1.68 T or more at the time of manufacturing a product of 0.27 mm t, 400) of 12.5 W / Kg or less can be provided.

 First, the reason why the range of the constituent elements constituting the non-oriented electrical steel sheet according to the embodiment of the present invention and the addition ratio between the constituent elements are limited will be described.

Unless otherwise stated, the unit of content is weight percent (wt%).

[Si: 2.5 to 3.5% by weight]

When Si is added in an amount of less than 2.5%, the effect of improving the high-frequency iron loss is insufficient. When the Si content exceeds 3.5%, the hardness of the material increases, It is undesirable to heat.

[Al: 0.5 to 1.5% by weight]

Al increases the resistivity of the material and lowers the iron loss and forms nitride. When Al is added in an amount less than 0.5%, there is no effect on reduction of high-frequency iron loss, and nitride is formed finely to deteriorate magnetism. When Al is added in excess of 1.5%, problems occur in all processes such as steelmaking and continuous casting, .

 [Mn: 0.05 to 0.8% by weight]

Mn improves the resistivity of the material to improve the iron loss and form sulphide. When the Mn content is less than 0.05%, the MnS is precipitated finely and deteriorates the magnetic properties. If Mn is added in excess of 0.8%, the magnetic flux density is reduced by promoting the formation of [111] texture unfavorable to magnetism, so that the addition amount of Mn is preferably limited to 0.05 to 0.8%.

[P: 0.1 wt% or less] (excluding O%)

P is mostly employed in the steel to improve the iron loss, but when it is more than 0.1%, it is segregated in the grain boundaries to deteriorate the toughness of the material, which lowers the productivity and saturation.

[S: 0.004% or less] (excluding O%)

Since S forms fine precipitates MnS and CuS to deteriorate magnetic properties, it is preferable to control it at a low level. It is preferable to remove the refining process as much as possible as an element indispensably present in steel. However, , The S content is limited to 0.004% or less in the present invention.

[N: 0.002% or less] (excluding O%)

N is preferably as small as possible because it forms fine and long AlN precipitates inside the base material to suppress grain growth and thereby lower the iron loss. In the present invention, the N content is limited to 0.002% or less.

[Ca: 10 to 30 ppm]

Ca is a key element for suppressing the redissolution of the precipitate when the slab is reheated in the present invention. Ca is added in the form of CaSi, which not only reduces S during refining but also binds with S or binds with (Mn, Cu) S to stabilize the precipitate. The effect is insignificant at less than 10 ppm, and when it is more than 30 ppm, the amount of precipitate due to Ca itself increases, which lowers iron loss and magnetic flux density, so that the range is limited to 10 to 30 ppm.

[REM: 20 to 80 ppm]

REM has strong chemical bonding force with 17 elements including 15 scandium and yttrium in 15 lanthanide elements and stabilizes oxides and sulfides. For REM injection, misch metal Is used. The effect is insignificant at less than 20 ppm, and when it exceeds 80 ppm, the amount of precipitate due to REM itself increases, which lowers iron loss and magnetic flux density, so that the range is limited to 20 to 80 ppm.

 [Other unavoidable impurity element]

In addition to the above impurity elements, inevitably incorporated impurities such as C, S, N, and Ti may be included.

C causes self-aging, so it is preferable to limit it to 0.004% or less (excluding O%), preferably to 0.003% or less.

Since S and N form sulphide and nitride, respectively, the growth of grain growth is negligible. Therefore, it is preferable that S and N are limited to 0.004% or less (excluding O%), preferably 0.003% or less.

Ti promotes the growth of the [111] texture, which is an undesirable crystal orientation in the non-oriented electrical steel sheet, and is therefore preferably limited to 0.004% or less (excluding O%), more preferably 0.002% or less.

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

In the method of manufacturing the non-oriented electrical steel sheet according to the present invention, it is preferable to use a high purity alloy element in order to minimize the pickup of impurities in the steelmaking step, and Ca or REM must be added in the refining step.

In particular, Ca is highly volatile, so it is desirable to add CaSi in the form of CaSi, and to minimize volatilization time by adding in the final refining step, RH or LF. The molten steel thus controlled is solidified in a continuous casting process to produce a slab.

The slab is charged into a furnace and reheated at 1,150 ° C to 1,200 ° C. In order to prevent redeposition of the precipitate during reheating, it is preferable to reheat at a low temperature as much as possible. However, in order to reduce the deformation resistance of the hot rolled steel sheet to 1.6 mm or less as in the embodiment of the present invention, There is a need.

When heated above 1,150 ℃, S-type precipitates can be rapidly redissolved. Ca and REM added at the time of steelmaking effectively inhibit redissolution.

When reheating to 1,200 ° C or higher, the effect of Ca or REM is limited, and the intended characteristics of the present invention can not be realized, and it is essential to limit the reheating temperature to 1,150-1,200 ° C.

Limiting the thickness of the hot-rolled plate to 1.6 mm or less is to minimize the (111) recrystallized texture structure which is disadvantageous to magnetism by minimizing the cold reduction rate.

Electric steel sheets for HEV / EV are particularly limited to reduce the total content of Si, Al, and Mn, which are the resistive elements, in order to increase magnetic flux density, because it is essential to reduce high frequency iron loss along with magnetic flux density.

Therefore, a method of decreasing the resistivity element to increase the magnetic flux density is not applicable, but the magnetic flux density should be improved through improvement of the final assembly texture. In order to improve the texture, in one embodiment of the present invention, the hot rolled sheet thickness is limited to 1.6 mm or less in order to effectively reduce the cold rolling reduction ratio.

The hot-rolled hot-rolled sheet is subjected to hot-rolled sheet annealing at a temperature of 850 to 1,150 ° C to increase the crystal orientation favorable to magnetism.

If the annealing temperature of the hot-rolled sheet is less than 850 캜, the structure does not grow or grows finely and the synergistic effect of the magnetic flux density is small. If the annealing temperature exceeds 1,150 캜, the magnetic properties are rather deteriorated. The temperature range is limited to 850 to 1,150 ° C. More preferably, the annealing temperature of the hot-rolled sheet is 950 to 1,150 ° C.

Then, the hot rolled sheet is pickled and cold rolled at a reduction ratio of 70 to 95% to have a predetermined thickness. The electric steel sheet used for HEV / EV has a thickness of 0.30 mm to 0.15 mm Lt; / RTI >

The cold-rolled cold-rolled sheet is subjected to final annealing. If the final annealing temperature is less than 750 캜, recrystallization does not sufficiently occur. If the final annealing temperature exceeds 1,050 캜, the crystal grain diameter becomes too large and the high-frequency iron loss tends to heat. Therefore, final annealing is performed at a temperature of 900 to 1,050 캜 Lt; / RTI >

Hereinafter, the present invention will be described in more detail by way of examples.

A slab composed of 3.4% of Si, 0.6% of Al, 0.4% of Mn, 0.002% of N, 0.003% of C, 0.05% of P, 0.002% of S and 0.0015% of N and other unavoidable impurities and Ca and REM in Table 1 And then subjected to hot rolling at the reheating temperature and thickness shown in Table 1, followed by hot-rolled sheet annealing at 1100 ° C.

Hot - rolled annealed sheets were cold - rolled at 0.27mm after pickling and analyzed for magnetic properties after final annealing at 950 ℃ at 20% hydrogen and 80% nitrogen for 1 minute. The magnetic measurements were averaged in the rolling direction and in the direction perpendicular to the rolling direction using a 60 x 60 mm2 size single piece measuring machine.

Psalter
number Ca
(ppm) REM
(ppm) Reheat temperature
(T) Hot rolled thickness
(mm) However,
W10 / 400
(W / Kg) Magnetic flux density
B50
(Tesla) Remarks One 5 2 1130 2.3 13.7 1.645 Comparison 1 2 4 3 1130 1.8 13.2 1.654 Comparative material 2 3 5 2 1130 1.6 Inoperable Comparative material 3 4 6 One 1130 1.4 Inoperable Comparison 4 5 5 3 1160 2.3 14.2 1.634 Comparative material 5 6 6 2 1160 1.8 14 1.628 Comparative material 6 7 7 3 1160 1.6 13.9 1.632 Comparison 7 8 5 3 1160 1.4 13.7 1.633 COMPARISON 8 9 4 2 1160 1.2 13.8 1.634 Comparative material 9 10 20 2 1160 2.3 13.2 1.644 Comparative material 10 11 22 One 1160 1.8 12.7 1.652 Comparative material 11 12 23 3 1160 1.6 12.4 1.682 Inventory 1 13 24 2 1160 1.4 12.2 1.69 Inventory 2 14 19 3 1160 1.2 12 1.695 Inventory 3 15 4 40 1160 2.3 13.2 1.644 Comparative material 12 16 7 42 1160 1.8 13.1 1.652 Comparative material 13 17 6 38 1160 1.6 12.3 1.682 Invention 4 18 3 35 1160 1.4 12.2 1.69 Invention Article 5 19 4 36 1160 1.2 12.1 1.695 Inventions 6 20 20 2 1190 2.3 13.2 1.642 Comparative material 14 21 22 One 1190 1.8 12.9 1.649 Comparative material 15 22 23 3 1190 1.6 12.2 1.681 Invention 7 23 24 2 1190 1.4 12.3 1.688 Invention 8 24 19 3 1190 1.2 12.1 1.693 Invention 9 25 4 40 1190 2.3 13.3 1.641 Comparative material 16 26 7 42 1190 1.8 12.9 1.646 Comparative material 17 27 6 38 1190 1.6 12.2 1.681 Inventions 10 28 3 35 1190 1.4 12 1.687 Invention invention 11 29 4 36 1190 1.2 11.8 1.691 Invention 12 30 24 2 1160 1.4 12.2 1.69 Invention invention 13 31 3 45 1220 1.4 13.2 1.66 Comparative material 18

Ca and REM each contain ~ 20ppm and ~ 40ppm, and the inventive materials 1 to 13, in which the hot-rolled steel sheet was rolled to a thickness of 1.2 to 1.6 mm and the reheating temperature was 1160 to 1190 ° C, all had an iron loss of 12.5 W / Kg or less and 1.68 T While the comparative materials 1 to 18, which did not satisfy this condition, showed iron loss or magnetic flux density lower than expected.

In order to investigate the optimum contents of Ca and REM, the iron loss and magnetic flux density are shown in Figs. 1 and 2, respectively, when the reheating temperature is fixed to 1,160 ° C and the hot-rolled thickness is fixed to 1.4 mmt. As shown in FIG. 1 and FIG. 2, the iron loss is 12.5 W / Kg or less at 10 to 30 ppm for Ca, 20 to 80 ppm for REM, and 1.68 T or more.

In order to investigate the influence of the content of other alloying elements, a steel ingot as shown in Table 2 was prepared. Each material was reheated at 1,160 ° C, then hot rolled at 1.4 mmt and annealed at 1100 ° C.

Hot - rolled annealed sheets were cold - rolled at 0.27mm after pickling and analyzed for magnetic properties after final annealing at 950 ℃ at 20% hydrogen and 80% nitrogen for 1 minute. The magnetic measurements were averaged in the rolling direction and in the direction perpendicular to the rolling direction using a 60 x 60 mm2 size single piece measuring machine.

Psalter
number Si
(wt%) Al
(wt%) Mn
(wt%) P
(wt%) S
(ppm) N
(ppm) However,
W10 / 400
(W / Kg) Magnetic flux density,
B50
(T) Remarks One 3.4 0.7 0.5 0.05 0.002 0.0015 12.1 1.685 Inventory 1 2 2.7 0.7 0.5 0.05 0.002 0.0015 12.5 1.715 Inventory 2 3 2.3 0.7 0.5 0.05 0.002 0.0015 13.4 1.73 Comparison 1 4 3.7 0.7 0.5 0.05 0.002 0.0015 Inoperable Comparative material 2 5 3.4 0.1 0.5 0.05 0.002 0.0015 12.8 1.69 Comparative material 3 6 3.4 0.3 0.5 0.05 0.002 0.0015 12.5 1.695 Inventory 3 7 3.4 2 0.5 0.05 0.002 0.0015 11.4 1.65 Comparison 4 8 3.4 0.7 One 0.05 0.002 0.0015 11.8 1.66 Comparative material 5 9 3.4 0.7 0.5 0.12 0.002 0.0015 Inoperable Comparative material 6 10 3.4 0.7 0.5 0.05 0.005 0.0015 13.1 1.67 Comparison 7 11 3.4 0.7 0.5 0.05 0.002 0.004 13.2 1.65 COMPARISON 8

In the case of inventive materials 1 to 3 according to the embodiment of the present invention, excellent iron loss and magnetic flux density were achieved at the same time. In the case of comparative materials 1 and 3, where the amount of the alloy was too small, iron loss was insufficient, and excessive comparative materials 2, 4, 5 and 6 were not rolled. In the case of the comparative materials 7 and 8 including the impurities which are outside the scope of the present invention, both the iron loss and the magnetic flux density were not satisfied.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (13)

(Excluding 0%), S: not more than 0.004% (provided that the content of Si is not more than 0.1% by weight), the content of Si is from 2.5 to 3.5% by weight, the content of Al is from 0.2 to 1.5% (Except 0%), N: 0.002% or less (excluding 0%) and the balance Fe and other unavoidable impurities, and Ca: 10 to 30 ppm or REM: 20 to 80 ppm or both step;
Charging the slab into a heating furnace and reheating the slab at 1,150 ° C to 1,200 ° C;
Hot rolling the slab to a hot rolled sheet thickness of 1.6 mm or less;
Annealing the hot-rolled hot-rolled sheet to hot-rolled sheet;
A step of cold picking the hot rolled sheet,
And finally annealing the cold-rolled steel sheet. The method according to claim 1,
Wherein the hot-rolled sheet annealing is performed at a temperature of 850 to 1,150 캜. 3. The method of claim 2,
Wherein the hot-rolled sheet is cold-rolled at a reduction ratio of 70 to 95%. The method of claim 3,
Wherein the final annealing is performed at a temperature of 900 to 1,050 占 폚 so as to have a grain size of 50 to 150 占 퐉. 5. The method of claim 4,
In the step of manufacturing the slab, at least one of Ca or REM is added at the same time or at the same time during the refining step in the slab manufacturing process. 6. The method of claim 5,
Wherein the Ca is added in the form of CaSi. 7. The method according to any one of claims 1 to 6,
Wherein the electric steel sheet has a magnetic flux density of 1.68 T or more and an iron loss (W10 / 400) of 12.5 W / Kg or less based on a thickness of 0.27 mm. (Excluding 0%), S: not more than 0.004% (provided that the content of Si is not more than 0.1% by weight), the content of Si is from 2.5 to 3.5% by weight, the content of Al is from 0.2 to 1.5% (Except 0%), N: 0.002% or less (excluding 0%) and the balance Fe and other unavoidable impurities, and Ca: 10 to 30 ppm or REM: 20 to 80 ppm or both Rolled at a temperature of 1,150 to 1,200 占 폚, hot-rolled to 1.6 mm or less, and then subjected to hot-rolling, followed by cold rolling and final annealing to obtain a magnetic flux density of 1.68 T or more And an iron loss (W10 / 400) of 12.5 W / Kg or less. 9. The method of claim 8,
Wherein the steel sheet is 0.30 mm to 0.15 mm thick after the cold rolling. 10. The method of claim 9,
Wherein the steel sheet has a grain size of 50 to 150 占 퐉 after the final annealing. 11. The method of claim 10,
Wherein the steel sheet is a hot-rolled steel sheet annealed at a temperature of 850 to 1,150 캜. 12. The method of claim 11,
The steel sheet is cold-rolled at a reduction ratio of 70 to 95%. 13. The method of claim 12,
Wherein the steel sheet is subjected to final annealing at a temperature of 900 to 1,050 占 폚.

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