TWI406957B - High-frequency iron loss low non-directional electromagnetic steel sheet and its manufacturing method - Google Patents

Abstract

Disclosed is a non-oriented electromagnetic steel plate having a low high-frequency iron loss. The non-oriented electromagnetic steel plate has an aluminum concentration gradient in the thickness-wise direction and is characterized in that the whole steel plate comprises, by mass, C: not more than 0.005%, Si: 2% to 4%, Mn: not more than 1%, and Al: 0.1% to 8% with the balance consisting of Fe and unavoidable impurities and the concentration of Al (% by mass) in the direction of the thickness of the plate satisfies the following formula (1). 0.1 s-Xc)/t < 100 (1) where Xs: concentration of Al at the surface of the steel plate, % by mass; Xc: concentration of Al at the center of the steel plate, % by mass; and t: depth from the surface of the steel plate at which the concentration of Al (% by mass) is Xc + 0.05(Xs - Xc), mm.

Description

Non-directional electromagnetic steel plate with low frequency iron loss and manufacturing method thereof Field of invention

The present invention relates to a non-oriented electrical steel sheet using a low-frequency iron loss as a material of a motor core (iron core).

Background of the invention

In recent years, interest in electric vehicles has increased in view of environmental protection or energy saving, and the driving motor has to be rotated and miniaturized at a high speed, and the driving frequency is set to be around 800 Hz.

In addition, since the high-frequency component of the driving frequency is overlapped with the driving frequency at the time of driving, the non-oriented electrical steel sheet which is a core material of the motor must have excellent mechanical properties capable of high-speed rotation and miniaturization, and at the same time It has magnetic properties superior to those in the high frequency range of 400 Hz to 2 kHz, particularly iron loss characteristics.

The iron loss includes overcurrent loss and hysteresis loss. The overcurrent loss is proportional to the square of the plate thickness and inversely proportional to the inherent resistance. Therefore, in order to reduce the overcurrent loss, try to (i) thin the plate thickness from the beginning; And/or (ii) increasing the amount of Si and/or the amount of Al and increasing the inherent resistance while increasing the strength of the steel sheet (rotor rigidity).

For example, Patent Document 1 discloses a non-oriented electrical steel sheet that defines a ratio of a Si amount to an Al amount and a relationship between W _10/400 (W/kg) and a sheet thickness (mm), and is not disclosed in Patent Document 1. Although the directional electromagnetic steel plate can reduce the iron loss near 400 Hz, the iron loss characteristics in the frequency range of frequencies greater than 400 Hz are not necessarily good, and the motor core (iron core) material driven at a frequency of 800 Hz or more or 800 Hz or higher is required. Not appropriate.

As mentioned earlier, in order to reduce overcurrent loss, (i) thinning the thickness of the plate while (ii) increasing the amount of Si and/or Al is effective, however, the increase in Si and/or Al in the steel reduces the steel plate. The processability hinders the thinning of the steel sheet. Therefore, if the Si and/or Al in the steel is simply increased, the material having the iron loss characteristic in the frequency domain of 800 Hz or even more than 1000 Hz is improved. Industrially, it cannot be manufactured stably.

In order to develop a thin non-oriented electrical steel sheet having excellent iron loss characteristics in a frequency domain of 800 Hz or even more than 1000 Hz, a new method is required.

Patent Document 2 discloses a method of forming an Al plating film or an Al-Mn alloy plating film on one or both sides of a cold-rolled steel sheet by a melt plating method or a molten salt electrolytic plating method. Then, alloying annealing is performed to produce a non-oriented electrical steel sheet excellent in magnetic properties.

The method of Patent Document 2 is to reduce the iron loss W _15/50 which is a characteristic in the commercial frequency field (an average power loss of 1 kg at a maximum of 1.5 T magnetization by 50 Hz AC), and, for this purpose, by plating - a method of alloying annealing, in which Al and/or Mn constituting an action of increasing electrical resistance is at least alloyed with Fe as a whole, or preferably Al is uniformly diffused to the entire steel sheet, however, by This method also fails to reduce iron loss in the high frequency field.

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2007-247047

[Patent Document 2] Japanese Patent Publication No. 07-258863

Invention

An object of the present invention is to reduce the high-frequency iron loss of a non-oriented electrical steel sheet, and an object of the invention is to provide a non-oriented electrical steel sheet which can be used as a motor core (iron core) material driven in a high frequency region of 400 Hz to 2 kHz.

The inventors focused on the eddy current flowing only to a depth of 50 μm from the surface of the steel sheet in the high frequency region of 400 Hz to 2 kHz, and at the same time, a method for increasing the resistance in the depth field of 50 μm from the surface of the steel sheet was examined.

If the method of alloying the plating film by annealing after the Al plating film having a thickness of several tens of μm is applied, the Al plating cost increases, and if Al is uniformly diffused to the entire steel plate, Since Al also diffuses to the surface layer portion where the eddy current does not flow when used at a high frequency, Al diffused to the center portion is in vain for high-frequency use. The inventors have found that high-frequency iron loss can be reduced by plating Al on the surface of the steel sheet with a large increase rate of electric resistance and diffusing Al to a proper depth and forming a gradient of Al concentration on the surface of the steel sheet to a predetermined depth.

The present invention has been completed based on the foregoing findings, and the gist thereof is as follows.

(1) A non-oriented electrical steel sheet having a low-frequency iron loss, which has a concentration gradient of aluminum in the thickness direction, and the entire steel sheet contains, by mass%: C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less and Al: 0.1% to 8%, and the remainder is composed of Fe and unavoidable impurities, and the Al concentration (% by mass) in the thickness direction satisfies the following formula (1).

0.1<(Xs-Xc)/t<100 ...(1)

Xs: Al concentration (% by mass) on the surface of the steel sheet

Xc: Al concentration (mass%) at the center of the steel plate

t: Al concentration (% by mass) is the distance from the surface of the steel sheet (mm) to Xc+0.05 (Xs-Xc)

(2) A non-oriented electrical steel sheet having a low-frequency iron loss, which has a concentration gradient of aluminum in the thickness direction, and the entire steel sheet contains, by mass%: C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less and Al: 0.1% to 8%, and the remainder is composed of Fe and unavoidable impurities, and the Al concentration (% by mass) in the thickness direction satisfies the following formula (2).

0.1<(Xs'-Xc)/t<100 (2)

Xs': maximum Al concentration (% by mass) near the surface of the steel sheet

Xc: Al concentration (mass%) at the center of the steel plate

t: Al concentration (% by mass) becomes Xc+0.05 (Xs-Xc) at a distance from the surface of the steel sheet (mm)

(3) The non-oriented electrical steel sheet having a low-frequency iron loss as described in the above (1), wherein the entire steel sheet is further selected from the group consisting of P: 0.3% or less, S: 0.04% or less, and N: 0.02% or less. At least one of Cu, 5% or less, Nb: 1% or less, Ti: 1% or less, B: 0.01% or less, Ni: 5% or less, and Cr: 15% or less, and more At least one selected from the group consisting of Mo, W, Sn, Sb, Mg, Ca, Ce, and Co is 0.5% or less.

(4) The non-oriented electrical steel sheet having a low-frequency iron loss as described in the above (2), wherein the entire steel sheet is further selected from the group consisting of P: 0.3% or less, S: 0.04% or less, and N: 0.02% or less. At least one of Cu, 5% or less, Nb: 1% or less, Ti: 1% or less, B: 0.01% or less, Ni: 5% or less, and Cr: 15% or less, and more At least one selected from the group consisting of Mo, W, Sn, Sb, Mg, Ca, Ce, and Co is 0.5% or less.

(5) The non-oriented electrical steel sheet having a low-frequency iron loss as described in the above (1), wherein the thickness of the non-oriented electrical steel sheet is 0.1 mm to 0.3 mm.

(6) The non-oriented electrical steel sheet having a low-frequency iron loss as in the above (2), wherein the thickness of the non-oriented electrical steel sheet is 0.1 mm to 0.3 mm.

(7) The non-oriented electrical steel sheet having a low-frequency iron loss as described in the above (1), wherein the non-oriented electrical steel sheet has an iron loss W _10/300 of 40 W/kg or less.

(8) The non-oriented electrical steel sheet having a low-frequency iron loss as described in the above (2), wherein the non-oriented electrical steel sheet has an iron loss W _10/800 of 40 W/kg or less.

(9) A method for producing a non-oriented electrical steel sheet having low high-frequency iron loss, comprising: (w) a procedure of annealing a hot-rolled steel sheet to obtain an annealed hot-rolled steel sheet, and the hot-rolled steel sheet is mass-dependent % contains: C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less, Al: 0.1% to 4%, and more preferably selected from P: 0.3% or less, S: 0.04% or less, N. : at least one of 0.02% or less, Cu: 5% or less, Nb: 1% or less, Ti: 1% or less, B: 0.01% or less, Ni: 5% or less, and Cr: 15% or less. Further, it further contains at least one selected from the group consisting of Mo, W, Sn, Sb, Mg, Ca, Ce, and Co in a total amount of 0.5% or less, and the remainder is derived from Fe and inevitable impurities. (x1) a process of cold rolling the annealed hot-rolled steel sheet and obtaining a cold-rolled steel sheet; (y1) performing Al plating on the surface of the cold-rolled steel sheet and obtaining a procedure of Al-plating cold-rolled steel sheet; and (z) The procedure for annealing the Al-plated cold-rolled steel sheet described above.

(10) A method for producing a non-oriented electrical steel sheet having low high-frequency iron loss, comprising: (w) a procedure of annealing a hot-rolled steel sheet to obtain an annealed hot-rolled steel sheet, and the hot-rolled steel sheet is mass-dependent % contains: C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less, Al: 0.1% to 4%, and more preferably selected from P: 0.3% or less, S: 0.04% or less, N. : at least one of 0.02% or less, Cu: 5% or less, Nb: 1% or less, Ti: 1% or less, B: 0.01% or less, Ni: 5% or less, and Cr: 15% or less. Further, it further contains at least one selected from the group consisting of Mo, W, Sn, Sb, Mg, Ca, Ce, and Co in a total amount of 0.5% or less, and the remainder is derived from Fe and inevitable impurities. (x2) A procedure of performing Al plating on the surface of the annealed hot-rolled steel sheet and obtaining an Al-plated hot-rolled steel sheet: (y2) a procedure of cold-rolling the Al-plated hot-rolled steel sheet and obtaining an Al-plated cold-rolled steel sheet And (z) a procedure for annealing the aforementioned Al-plated cold-rolled steel sheet.

(11) A method of producing a non-oriented electrical steel sheet having a low-frequency iron loss as described in (9) above, wherein the Al plating is performed by melt plating.

(12) A method for producing a non-oriented electrical steel sheet having a low-frequency iron loss as described in (10) above, wherein the Al plating is performed by melt plating.

(13) A method for producing a non-oriented electrical steel sheet having a low-frequency iron loss as described in (9) above, wherein the Al plating is performed by vapor deposition.

(14) A method of producing a non-oriented electrical steel sheet having a low-frequency iron loss as described in (10) above, wherein the Al plating is performed by vapor deposition.

(15) A method for producing a non-oriented electrical steel sheet having a low-frequency iron loss as described in (9) above, wherein the annealing is performed at 1000 ° C or lower for 1 hr or longer.

(16) A method for producing a non-oriented electrical steel sheet having a low-frequency iron loss as described in (10) above, wherein the annealing is performed at 1000 ° C or lower for 1 hr or longer.

(17) The method for producing a non-oriented electrical steel sheet having a low-frequency iron loss as described in (9) above, wherein the non-oriented electrical steel sheet having a low high-frequency iron loss has a concentration gradient of aluminum in a thickness direction, and the entire steel sheet Depending on the mass%, C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less, and Al: 0.1% to 8%, and the remainder is composed of Fe and unavoidable impurities, and The Al concentration (% by mass) in the thick direction satisfies the following formula (3).

0.1<(Xs-Xc)/t<100 ...(3)

Xs: Al concentration (% by mass) on the surface of the steel sheet

Xc: Al concentration (mass%) at the center of the steel plate

t: Al concentration (% by mass) becomes Xc+0.05 (Xs-Xc) at a distance from the surface of the steel sheet (mm)

(18) The method for producing a non-oriented electrical steel sheet having a low-frequency iron loss as described in (9) above, wherein the non-oriented electrical steel sheet having a low high-frequency iron loss has a concentration gradient of aluminum in a thickness direction, and the entire steel sheet Depending on the mass%, C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less, and Al: 0.1% to 8%, and the remainder is composed of Fe and unavoidable impurities, and The Al concentration (% by mass) in the thick direction satisfies the following formula (4).

0.1<(Xs'-Xc)/t<100 (4)

Xs': maximum Al concentration (% by mass) near the surface of the steel sheet

Xc: Al concentration (mass%) at the center of the steel plate

t: Al concentration (% by mass) becomes Xc+0.05 (Xs-Xc) at a distance from the surface of the steel sheet (mm)

(19) The method for producing a non-oriented electrical steel sheet having a low-frequency iron loss as described in (10) above, wherein the non-oriented electrical steel sheet having a low high-frequency iron loss has a concentration gradient of aluminum in a thickness direction, and the entire steel sheet Depending on the mass%, C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less, and Al: 0.1% to 8%, and the remainder is composed of Fe and unavoidable impurities, and The Al concentration (% by mass) in the thick direction satisfies the following formula (5).

0.1<(Xs-Xc)/t<100 ...(5)

Xs: Al concentration (% by mass) on the surface of the steel sheet

Xc: Al concentration (mass%) at the center of the steel plate

t: Al concentration (% by mass) becomes Xc+0.05 (Xs-Xc) at a distance from the surface of the steel sheet (mm)

(20) The method for producing a non-oriented electrical steel sheet having a low-frequency iron loss as described in (10) above, wherein the non-oriented electrical steel sheet having a low high-frequency iron loss has a concentration gradient of aluminum in a thickness direction, and the entire steel sheet Depending on the mass%, C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less, and Al: 0.1% to 8%, and the remainder is composed of Fe and unavoidable impurities, and The Al concentration (% by mass) in the thick direction satisfies the following formula (6).

0.1<(Xs'-Xc)/t<100 (6)

Xs': maximum Al concentration (% by mass) near the surface of the steel sheet

Xc: Al concentration (mass%) at the center of the steel plate

t: Al concentration (% by mass) becomes Xc+0.05 (Xs-Xc) at a distance from the surface of the steel sheet (mm)

Simple illustration

Fig. 1A is a graph showing the Al concentration distribution in the thickness direction of Al plating after annealing at 900 °C for 1 hr.

Fig. 1B is a graph showing the Al concentration distribution in the thickness direction of Al plating after annealing at 900 °C for 10 hr.

Fig. 2 is a graph showing the relationship between the film thickness of plating and the magnetic flux density B3 (T) after annealing after annealing at 900 ° C for 1 hr and 10 hr after Al plating.

Fig. 3 is a graph showing the relationship between the film thickness of the plating and the iron loss W _10/400 (W/kg) after annealing at 900 ° C for 1 hr and 10 hr after Al plating.

Fig. 4 is a graph showing the relationship between the film thickness of the plating and the iron loss W _10/800 (W/kg) after annealing at 900 ° C for 1 hr and 10 hr after Al plating.

Fig. 5 is a graph showing the relationship between the film thickness of the plating and the iron loss W _10/1200 (W/kg) after annealing at 900 ° C for 1 hr and 10 hr after Al plating.

Fig. 6 is a graph showing the relationship between the film thickness of the plating and the iron loss W _10/1700 (W/kg) after annealing at 900 ° C for 1 hr and 10 hr after Al plating.

The best form for implementing the invention

The non-oriented electrical steel sheet (steel sheet of the present invention) according to the present invention contains, by mass%: C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less, and Al: 0.1% to 4%, and the remainder It is composed of Fe and unavoidable impurities, and the Al concentration (% by mass) in the thickness direction satisfies the following formula (1) or the following formula (2).

0.1<(Xs-Xc)/t<100 ...(1)

0.1<(Xs'-Xc)/t<100 (2)

Xs: Al concentration (% by mass) on the surface of the steel sheet

Xs': maximum Al concentration (% by mass) near the surface of the steel sheet

Xc: Al concentration (mass%) at the center of the steel plate

t: Al concentration (% by mass) becomes Xc+0.05 (Xs-Xc) at a distance from the surface of the steel sheet (mm)

First, the reason for specifying the chemical composition of the steel sheet of the present invention will be described, and % means % by mass.

Since the C system is an element which deteriorates the iron loss after strain relief annealing, it is set to 0.005% or less in order to prevent the effect from occurring.

Since the Si system is an element effective for increasing the electric resistance and reducing the iron loss, it is added in an amount of 2% or more. However, if it is excessively added, the cold calendering property is remarkably deteriorated, so that it is 4% or less.

Like Si, Mn is used to increase the effective element of resistance. However, if it is added by more than 1%, grain growth during annealing is inhibited, so it is set to 1% or less, and Mn can make S in steel. It is harmless (MnS), so it is preferable to add 0.1% or more.

Similarly to Si, since Al is an element effective for increasing electrical resistance and reducing iron loss, it is added in an amount of 0.1% or more, and preferably 0.5% or more.

However, if it is excessively added, since the castability of steel deteriorates, the Al system of the mother steel sheet (the steel sheet before the Al plating is applied) is set to 4% or less.

Al increases the amount of Al in the steel by plating-annealing from the surface into the steel. However, in the portion where Al is excessively increased, the saturation magnetic flux density is lowered and the magnetic properties of the steel are deteriorated, so plating is performed. - The total amount of Al in the total thickness of the steel sheet after annealing is 8%.

P is an element which has a remarkable effect of improving the tensile strength. However, it is not necessary to add it to the steel sheet of the present invention. If it is more than 0.3%, the embrittlement is severe, and processing such as hot rolling and cold rolling on an industrial scale becomes difficult. The content is preferably 0.3% or less, and more preferably 0.2% or less, still more preferably 0.15% or less.

The content of S is preferably as low as possible and is preferably 0.04% or less, more preferably 0.02% or less, still more preferably 0.01% or less.

Since Cu has an effect of increasing strength in a range that does not adversely affect magnetic properties, it may contain Cu and has an upper limit of 5%.

Nb is not only intrinsic Nb, but also Nb mainly forms carbonitrides in steel sheets, and is used to retard the recrystallization of steel sheets, and also by fine Nb precipitates, because it does not have magnetic properties. The effect of increasing the strength of the range of adverse effects may also be 1% or less.

Similarly to C, since N degrades magnetic properties, it is preferably 0.02% or less.

In addition, most of the elements used in the high-strength electromagnetic steel sheets of the prior art are not only the cost of addition, but also have a lot of adverse effects on the magnetic properties, so it is not necessary to add them. When it is intentionally added, Ti, B, Ni, and/or Cr are added in accordance with the recrystallization retardation effect, the high-strengthening effect, the cost increase, and the magnetic property deterioration. In this case, the addition amount is preferably Ti: 1% or less. B: 0.01% or less, Ni: 5% or less, and Cr: 15% or less.

Further, other trace elements are not affected by the inevitable content of ore or crumb, and even if added for various known purposes, the effects of the present invention are not impaired. Further, it also includes an element which forms at least a precipitate of fine carbides, sulfides, nitrides, and/or oxides and exhibits an absolute recrystallization delay effect, and these fine precipitates have a large adverse effect on magnetic properties. Further, since the steel sheet of the present invention can obtain a sufficient recrystallization retardation effect by Cu or Nb, it is not necessary to add these elements. The inevitable content of these trace elements is usually 0.005% or less for each element. However, it may be contained in an amount of 0.01% or more for various purposes. In this case, depending on the cost or magnetic properties, Mo, W, Sn, The content of Sb, Mg, Ca, Ce, and Co is preferably set to 0.5% or less in total.

In the present invention, Al plating is performed on the surface of the mother steel sheet having the above composition, and then annealing is performed to diffuse Al into the steel.

The Al-plated mother steel plate has been subjected to annealed hot-rolled steel sheets (annealed hot-rolled steel sheets) or cold-rolled steel sheets which have been cold-rolled annealed hot-rolled steel sheets. Annealing is performed on the surface of the cold-rolled steel sheet which has been cold-rolled to the thickness of the product. However, when Al is plated on the surface of the annealed hot-rolled steel sheet, it is cold-rolled to the thickness of the product and then annealed.

The thickness of the mother steel sheet is not particularly limited, and may be appropriately determined in consideration of the thickness of the steel sheet of the final product and the reduction ratio in the calendering procedure. There is no particular limitation on the thickness of the steel sheet of the final product, however, From the viewpoint of the reduction of the loss, it is preferably from 0.1 mm to 0.3 mm.

In view of the material for the motor driven in the high-frequency field and the viewpoint of cost, etc., the method of performing Al plating on the mother steel sheet is suitable for plating, molten salt electrolysis, or hot plating from an aqueous solution or a non-aqueous solvent. It is also possible to use vapor phase plating such as PVD or CVD.

The thickness of the Al plating is not particularly limited. However, since the thickness of the plating is reduced to 1/5 by cold rolling until the thickness of the product is formed by plating the Al on the annealed hot-rolled steel sheet, it is preferable to The thickness of the plating calculated by reducing the thickness is, for example, predetermined to be 0.1 mm to 0.3 mm, and when the annealed hot-rolled steel sheet is plated with Al, the thickness reduction by cold rolling is preferably calculated. Made inside to 30 μm.

After Al plating is applied to the mother steel sheet, annealing is performed to diffuse Al into the steel, and an Al concentration gradient satisfying the above formula (1) or (2) is formed (this point is as will be described later). The annealing condition (temperature, time) is not particularly limited as long as it is a condition for forming the Al concentration gradient. However, if batch annealing is used, it is preferably "1000 ° C or less, 1 hr or more". Annealing conditions can also be set on the premise of continuous annealing.

Next, the steel sheet of the present invention is characterized in that the Al concentration after Al plating-annealing satisfies the above formula (1) or formula (2).

Fig. 1 shows an Al formed in a thickness of 1 μm (Y in the first figure), 3 μm (X in the first figure), and 10 μm (W in Fig. 1) in a 0.3 mm-thick cold-rolled steel sheet (master steel sheet). The film is coated and then annealed to form an Al concentration distribution in the thickness direction of the sheet. Further, the cold-rolled steel sheet contains: C: 0.003%, Si: 3.1%, Mn: 0.3%, Al: 1.1%, and the remainder is Fe and inevitable impurities.

Fig. 1A shows that when annealing at 900 °C for 1 hr, Fig. 1B shows annealing at 900 °C for 10 hr. Further, in Fig. 1, for comparison, the Al concentration distribution at the time of annealing without performing Al plating (Z in Fig. 1) is also shown.

As can be seen from the first and second graphs, the Al concentration (% by mass) in the thickness direction is substantially linearly decreased from the Al concentration (% by mass) on the surface or the maximum Al concentration (% by mass) in the vicinity of the surface toward the center portion of the steel sheet.

The inventors measured the iron loss characteristics and the magnetic flux density of a steel sheet having an Al concentration (% by mass) in the thickness direction and annealed steel sheet without Al plating, and the annealing also constitutes a function of recrystallizing the steel sheet. In order to confirm the difference in magnetic properties depending on the presence or absence of the Al concentration gradient, the steel plate without Al plating was also annealed by the same annealing conditions.

Fig. 2 is a graph showing the relationship between the film thickness of the plating at 900 ° C for 1 hr and 10 hr after Al plating and the magnetic flux density B3 (T) after annealing, and the second figure is shown in the L direction (calendering direction). And the average value of B3(T) measured in the C direction (perpendicular to the rolling direction) _(the vertical axis is represented by B3(T) _(L+C ) in Fig. 2). The magnetic flux density B3 (T) tends to decrease due to annealing. However, by appropriately selecting the Al plating thickness and the annealing time, it is possible to secure 1.2 T or more.

Fig. 3 is a graph showing the relationship between the film thickness of the plating and the iron loss W _10/400 (W/kg) after annealing at 900 ° C for 1 hr and 10 hr after Al plating, and the third figure is shown in the L direction (calendering) The average value of W _10/400 (W/kg) measured in the direction and the C direction (perpendicular to the rolling direction) _(the vertical axis is represented by W _10/400 (W/kg) _(L+C) in Fig. 3 ), by appropriately selecting the Al plating thickness and the annealing time, W _10/400 (W/kg) can be lowered.

Figures 4 to 6 show the iron loss W _10/800 (W/kg) and the iron loss W _{10/1200 in} the film thickness and high frequency field of the plating at 900 ° C for 1 hr and 10 hr after Al plating. (W/kg) and iron loss W _10/1700 (W/kg), however, the iron loss W _10/800 (W/kg) _(L+C) is the L direction (rolling direction) and the C direction (and The average value of W _10/800 (W/kg) in the rolling direction is perpendicular, and the iron loss W _10/1200 (W/kg) _(L+C) is the L direction (rolling direction) and the C direction (with the rolling direction) Vertical) The average value of W _10/1200 (W/kg), in addition, the iron loss W _10/1700 (W/kg) _(L+C) is the L direction (rolling direction) and the C direction (vertical to the rolling direction) The average value of W _10/1700 (W/kg).

As can be seen from Figures 4 to 6, the high-frequency iron loss characteristics can be improved by annealing at 900 ° C for 10 hours after Al plating, compared to the annealed steel sheet without Al plating.

Therefore, as shown in Fig. 1, it is considered that the reason why the iron loss characteristic in the high-frequency field is improved is that the Al concentration in the depth region of 50 μm from the surface of the steel sheet rises by Al diffusion by annealing. And increased by the iron loss characteristics in the field.

The inventors further investigated the correlation between the Al concentration (% by mass) distribution after annealing and the high-frequency iron loss.

As a result, it was found that in order to reduce the high-frequency iron loss, the Al concentration (% by mass) in the thickness direction must satisfy the following formula (1).

0.1<(Xs-Xc)/t<100 ...(1)

Xs: Al concentration (% by mass) on the surface of the steel sheet

Xc: Al concentration (mass%) at the center of the steel plate

t: Al concentration (% by mass) becomes Xc+0.05 (Xs-Xc) at a distance from the surface of the steel sheet (mm)

When the value of (Xs-Xc)/t is 0.1 or less, Al is uniformly diffused and distributed to substantially the entire field of the steel sheet, and the iron loss in the surface portion of the steel sheet is not lowered, so (Xs-Xc)/t The value is set to be greater than 0.1, and more desirably greater than 0.5, more desirably greater than 5, and more preferably greater than 20.

When the value of (Xs-Xc)/t is 100 or more, the gradient of the Al concentration becomes steep in the narrow range, and the rising characteristic at the time of excitation is remarkably deteriorated, so the value of (Xs-Xc)/t It is set to be less than 100, and desirably less than 60, and more desirably less than 40.

Further, the depth t is not particularly limited as long as it is a surface layer portion having a high-frequency induced eddy current (a depth region of 50 μm from the surface).

In the above formula (1), the Al concentration (Xs) on the surface of the steel sheet is used. However, since the maximum Al concentration (Xs') in the vicinity of the surface of the steel sheet is actually used when the Al concentration distribution is actually calculated, the above formula (1) may be used instead. The following formula (2) is used. In this case, the vicinity of the surface of the steel sheet means a range in which the uppermost layer of the base iron located under the insulating film and the forsterite film is used as a starting point in the electromagnetic steel sheet, and The location is 5 μm away from the center of the steel plate as the end point.

0.1<(Xs'-Xc)/t<100 (2)

Xs': maximum Al concentration (% by mass) near the surface of the steel sheet

In the present invention, the above formulas (1) and (2) can be used as needed.

(First embodiment)

Next, the first embodiment of the present invention will be described. However, the conditions of the first embodiment are examples of conditions for confirming the workability and effects of the present invention, and the present invention is not limited to the one condition example, as long as it is The present invention can adopt various conditions without departing from the gist of the present invention and achieving the object of the present invention.

On a 2.0 mm thick hot-rolled steel sheet composed of Fe: 0.003%, Si: 3.1%, Mn: 0.3%, Al: 1.1% and the remainder consisting of Fe and unavoidable impurities, 1000% by mass After annealing for 1 minute at °C, cold rolling is performed to a thickness of 0.3 mm, and (a) the original is not fixed; (b) 1.5 μm thick Al vapor deposition is applied to both sides of the steel sheet; (c) A 4 μm thick Al vapor deposition was performed on both sides; (d) 8 μm thick vapor deposition was performed on both sides of the steel sheet; and (e) Al vapor deposition of 30 μm thickness was applied to both sides of the steel sheet. Next, annealing was performed at 900 ° C for 6 hours, and Al was diffused into the steel by the annealing while re-crystallizing the steel sheet.

The magnetic properties were measured by a single-plate magnetic measuring device, and the Al concentration in the thickness direction was measured by EPMA line analysis of the steel plate cross section orthogonal to the rolling direction (L direction).

As is clear from Table 1, when the Al concentration is in the range of the concentration gradient (the above formula (1) or (2)) defined in the present invention, the high-frequency iron loss is small.

Industry availability

According to the present invention, it is possible to provide a non-oriented electrical steel sheet which has excellent high frequency which can be used as a motor core (iron core) material driven in a high frequency region of 400 Hz to 2 kHz. Since the iron loss characteristic has an appropriate magnetic property as a core of a motor or a transformer, the present invention has a large usability in the electric appliance manufacturing industry in which a non-oriented electrical steel sheet is used as a material.

Fig. 1A is a graph showing the Al concentration distribution in the thickness direction of Al plating after annealing at 900 °C for 1 hr.

Fig. 1B is a graph showing the Al concentration distribution in the thickness direction of Al plating after annealing at 900 °C for 10 hr.

Fig. 2 is a graph showing the relationship between the film thickness of plating and the magnetic flux density B3 (T) after annealing after annealing at 900 ° C for 1 hr and 10 hr after Al plating.

Fig. 3 is a graph showing the relationship between the film thickness of the plating and the iron loss W _10/400 (W/kg) after annealing at 900 ° C for 1 hr and 10 hr after Al plating.

Fig. 4 is a graph showing the relationship between the film thickness of the plating and the iron loss W _10/800 (W/kg) after annealing at 900 ° C for 1 hr and 10 hr after Al plating.

Fig. 5 is a graph showing the relationship between the film thickness of the plating and the iron loss W _10/1200 (W/kg) after annealing at 900 ° C for 1 hr and 10 hr after Al plating.

Fig. 6 is a graph showing the relationship between the film thickness of the plating and the iron loss W _10/1700 (W/kg) after annealing at 900 ° C for 1 hr and 10 hr after Al plating.

Claims (19)

A non-oriented electrical steel sheet having a low-frequency iron loss is characterized by having a concentration gradient of aluminum in the thickness direction, and the entire steel sheet contains, by mass%: C: 0.005% or less, Si: 2% to 4%, Mn: 1 % or less and Al: 0.1% to 8%, and the remainder is composed of Fe and unavoidable impurities, and the Al concentration (% by mass) in the thickness direction satisfies the following formula (1), that is, 0.1 < (Xs-Xc)/t<100 (1) Xs: Al concentration (% by mass) on the surface of the steel sheet Xc: Al concentration (% by mass) at the center of the steel sheet t: Al concentration (% by mass) becomes Xc + 0.05 (Xs- Xc) is the depth (mm) of the surface of the steel sheet. A non-oriented electrical steel sheet having a low-frequency iron loss is characterized by having a concentration gradient of aluminum in the thickness direction, and the entire steel sheet contains, by mass%: C: 0.005% or less, Si: 2% to 4%, Mn: 1 % or less and Al: 0.1% to 8%, and the remainder is composed of Fe and unavoidable impurities, and the Al concentration (% by mass) in the thickness direction satisfies the following formula (2), that is, 0.1 < (Xs'-Xc)/t<100...(2)Xs': maximum Al concentration (mass%) near the surface of the steel sheet Xc: Al concentration (mass%) at the center of the steel sheet t: Al concentration (% by mass) becomes Xc+ 0.05 (Xs-Xc) is the depth (mm) of the surface of the steel sheet. The non-oriented electrical steel sheet having a low-frequency iron loss as in the first aspect of the patent application, wherein the entire steel sheet is further selected from the group consisting of P: 0.3% or less, S: 0.04% or less, and N: 0.02% or less. Cu: 5% or less, Nb: At least one selected from the group consisting of 1% or less, Ti: 1% or less, B: 0.01% or less, Ni: 5% or less, and Cr: 15% or less, and more preferably 0.5% or less in total selected from the group consisting of At least one of the group consisting of Mo, W, Sn, Sb, Mg, Ca, Ce, and Co. A non-oriented electrical steel sheet having a low-frequency iron loss as in the second aspect of the patent application, wherein the entire steel sheet is further selected from the group consisting of P: 0.3% or less, S: 0.04% or less, and N: 0.02% or less. Cu: at least one of 5% or less, Nb: 1% or less, Ti: 1% or less, B: 0.01% or less, Ni: 5% or less, and Cr: 15% or less, and further includes 0.5% or less is at least one selected from the group consisting of Mo, W, Sn, Sb, Mg, Ca, Ce, and Co. A non-oriented electrical steel sheet having a low-frequency iron loss as in the first aspect of the patent application, wherein the thickness of the non-oriented electrical steel sheet is 0.1 mm to 0.3 mm. A non-oriented electrical steel sheet having a low-frequency iron loss as in the second aspect of the patent application, wherein the thickness of the non-oriented electrical steel sheet is 0.1 mm to 0.3 mm. A non-oriented electrical steel sheet having a low-frequency iron loss as in the first _aspect of the patent application, wherein the non-oriented electrical steel sheet has an iron loss W _10/800 of 40 W/kg or less. A non-oriented electrical steel sheet having a low-frequency iron loss as in the second _aspect of the patent application, wherein the non-oriented electrical steel sheet has an iron loss W _10/800 of 40 W/kg or less. Method for manufacturing non-oriented electrical steel sheet with low high-frequency iron loss, including There is a procedure of (w) annealing a hot-rolled steel sheet and obtaining annealed hot-rolled steel sheet, and the hot-rolled steel sheet contains, by mass%: C: 0.005% or less, Si: 2% to 4%, Mn: 1 % or less, Al: 0.1% to 4%, and more preferably selected from P: 0.3% or less, S: 0.04% or less, N: 0.02% or less, Cu: 5% or less, Nb: 1% or less, Ti: 1 At least one of the group consisting of % or less, B: 0.01% or less, Ni: 5% or less, and Cr: 15% or less, and further containing 0.5% or less in total, selected from Mo, W, Sn, and Sb. At least one of a group consisting of Mg, Ca, Ce, and Co, and the remainder being composed of Fe and unavoidable impurities; (x1) a process of cold rolling the annealed hot-rolled steel sheet and obtaining a cold-rolled steel sheet; (y1) a procedure of performing Al plating on the surface of the cold-rolled steel sheet to obtain an Al-plated cold-rolled steel sheet; and (z) a step of annealing the Al-plated cold-rolled steel sheet at 1000 ° C or lower for 1 hr or more. A method for producing a non-oriented electrical steel sheet having a low-frequency iron loss, comprising the following steps: (w) annealing a hot-rolled steel sheet to obtain an annealing hot-rolled steel sheet, and the hot-rolled steel sheet contains: C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less, Al: 0.1% to 4%, and more preferably selected from P: 0.3% or less, S: 0.04% or less, and N: 0.02%. Hereinafter, at least one of Cu, 5% or less, Nb: 1% or less, Ti: 1% or less, B: 0.01% or less, Ni: 5% or less, and Cr: 15% or less is used. Further, it further contains at least one selected from the group consisting of Mo, W, Sn, Sb, Mg, Ca, Ce, and Co in a total amount of 0.5% or less, and the remainder is derived from Fe and inevitable impurities. (x2) a procedure of performing Al plating on the surface of the annealed hot-rolled steel sheet and obtaining an Al-plated hot-rolled steel sheet; (y2) a procedure of cold-rolling the Al-plated hot-rolled steel sheet and obtaining an Al-plated cold-rolled steel sheet And (z) Next, the procedure for annealing the aforementioned Al-plated cold-rolled steel sheet. A method of producing a non-oriented electrical steel sheet having a low-frequency iron loss as low as in the ninth aspect of the patent application, wherein the Al plating is performed by melt plating. A method for producing a non-oriented electrical steel sheet having a low-frequency iron loss as in claim 10, wherein the Al plating is performed by melt plating. A method for producing a non-oriented electrical steel sheet having a low-frequency iron loss of a ninth aspect of the patent application, wherein the Al plating is performed by vapor deposition. A method for producing a non-oriented electrical steel sheet having a low-frequency iron loss as low as in claim 10, wherein the Al plating is performed by vapor deposition. A method for producing a non-oriented electrical steel sheet having a low-frequency iron loss according to claim 10, wherein the annealing is performed at 1000 ° C or lower for 1 hr or longer. The method for manufacturing a non-oriented electrical steel sheet having low high-frequency iron loss according to the ninth application patent, wherein the non-oriented electromagnetic steel sheet having low high-frequency iron loss has a concentration gradient of aluminum in a thickness direction, and the entire steel sheet is quality % contains: C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less, and Al: 0.1% to 8%, and the remainder is composed of Fe and unavoidable impurities, and the thickness direction The Al concentration (% by mass) satisfies the following formula (3), that is, 0.1 < (Xs - Xc) / t < 100 (3) Xs: Al concentration (% by mass) on the surface of the steel sheet Xc: Al in the center of the steel sheet Concentration (% by mass) t: Al concentration (% by mass) is a depth (mm) of the surface of the steel sheet from Xc + 0.05 (Xs - Xc). The method for manufacturing a non-oriented electrical steel sheet having low high-frequency iron loss according to the ninth application patent, wherein the non-oriented electromagnetic steel sheet having low high-frequency iron loss has a concentration gradient of aluminum in a thickness direction, and the entire steel sheet is The mass% contains: C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less, and Al: 0.1% to 8%, and the remainder is composed of Fe and unavoidable impurities, and the thickness is thick. The Al concentration (% by mass) in the direction satisfies the following formula (4), that is, 0.1 < (Xs' - Xc) / t < 100 (4) Xs': maximum Al concentration (% by mass) near the surface of the steel sheet Xc : Al concentration (mass%) of the center of the steel plate t: Al concentration (% by mass) is a depth (mm) of the surface of the steel sheet from Xc + 0.05 (Xs - Xc). The method for manufacturing a non-oriented electrical steel sheet having low high-frequency iron loss according to claim 10, wherein the non-oriented electromagnetic steel sheet having low high-frequency iron loss has a concentration gradient of aluminum in a thickness direction, and the entire steel sheet is quality The amount % contains: C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less, and Al: 0.1% to 8%, and the remainder is composed of Fe and unavoidable impurities, and the thickness is thick. The Al concentration (% by mass) in the direction satisfies the following formula (5), that is, 0.1 < (Xs - Xc) / t < 100 (5) Xs: Al concentration (% by mass) on the surface of the steel sheet Xc: center of the steel sheet Al concentration (% by mass) t: Al concentration (% by mass) is a depth (mm) from the surface of the steel sheet of Xc + 0.05 (Xs - Xc). The method for manufacturing a non-oriented electrical steel sheet having low high-frequency iron loss according to claim 10, wherein the non-oriented electromagnetic steel sheet having low high-frequency iron loss has a concentration gradient of aluminum in a thickness direction, and the entire steel sheet is The mass% contains: C: 0.005% or less, Si: 2% to 4%, Mn: 1% or less, and Al: 0.1% to 8%, and the remainder is composed of Fe and unavoidable impurities, and the thickness is thick. The Al concentration (% by mass) in the direction satisfies the following formula (6), that is, 0.1 < (Xs' - Xc) / t < 100 (6) Xs': maximum Al concentration (% by mass) near the surface of the steel sheet Xc : Al concentration (mass%) of the center of the steel plate t: Al concentration (% by mass) is a depth (mm) of the surface of the steel sheet from Xc + 0.05 (Xs - Xc).