WO2009128428A1

WO2009128428A1 - High-strength non-oriented magnetic steel sheet and process for producing the high-strength non-oriented magnetic steel sheet

Info

Publication number: WO2009128428A1
Application number: PCT/JP2009/057453
Authority: WO
Inventors: 有田　吉宏; 村上　英邦; 義行牛神; 猛久保田
Original assignee: 新日本製鐵株式会社
Priority date: 2008-04-14
Filing date: 2009-04-13
Publication date: 2009-10-22
Also published as: JPWO2009128428A1; KR20100122116A; JP4659135B2; CN102007226A; EP2278034B1; EP2278034A1; US20110056592A1; TW200946695A; BRPI0910984A2; TWI404806B; EP2278034A4; PL2278034T3; BRPI0910984B8; BRPI0910984B1; CN102007226B

Abstract

Disclosed is a high-strength non-oriented magnetic steel sheet, comprising by mass C: 0.002% or more and 0.05% or less, Si: 2.0% or more and 4.0% or less, Mn: 0.05% or more and 1.0% or less, N: 0.002% or more and 0.05% or less, and Cu: 0.5% or more and 3.0% or less. Al content is 3.0% or less. The following formulae (1) and (2) are satisfied. In formulae (1) and (2), [Nb] represents Nb content, %; [Zr] represents Zr content, %; [Ti] represents Ti content, %; [V] represents V content, %; [C] represents C content, %; and [N] represents N content, %. The balance consists of Fe and unavoidable impurities. The percentage area of recrystallized crystals is 50% or more. The yield strength in a tensile test is 700 MPa or more. The break elongation is 10% or more. The eddy-current loss We_10/400 (W/kg) satisfies formula (3) in relation with the thickness t (mm) of the steel sheet. 2.0 × 10^-4 ≤ [Nb]/93 + [Zr]/91 + [Ti]/48 + [V]/51 (1) 1.0 × 10^-3 ≤ [C]/12 + [N]/14 - ([Nb]/93 + [Zr]/91 + [Ti]/48 + [V]/51) ≤ 3.0 × 10^-3 (2) We_10/400 ≤ 70 × t² (3)

Description

High strength non-oriented electrical steel sheet and manufacturing method thereof

The present invention relates to a high-strength non-oriented electrical steel sheet suitable for iron core materials for motors for electric vehicles and motors for electric devices, and a method for manufacturing the same.

In recent years, due to the increase in energy saving of electric appliances worldwide, higher performance characteristics have been required for non-oriented electrical steel sheets used as iron core materials for rotating machines. In particular, recently, a demand for a small high-power motor is high as a motor used in an electric vehicle or the like. Such electric vehicle motors are designed to enable high speed rotation and high torque.

High-speed rotary motors are also used in electrical equipment such as machine tools and vacuum cleaners. However, the outer shape of the high-speed rotation motor for electric vehicles is larger than the outer shape of the high-speed rotation motor for electric devices. Further, as a high-speed rotation motor for an electric vehicle, a DC brushless motor is mainly used. In a DC brushless motor, a magnet is embedded in the vicinity of the outer periphery of the rotor. In this structure, the width of the bridge portion on the outer peripheral portion of the rotor (the width from the outermost outer periphery of the rotor to the steel plate between the magnets) is very narrow as 1 to 2 mm depending on the place. For this reason, high-speed rotary motors for electric vehicles are required to have higher strength steel plates than conventional non-oriented electrical steel plates.

Patent Document 1 describes a non-oriented electrical steel sheet in which Mn and Ni are added to Si to enhance solid solution. However, sufficient strength cannot be obtained even with this non-oriented electrical steel sheet. Further, the toughness tends to decrease with the addition of Mn and Ni, and sufficient productivity and yield cannot be obtained. Moreover, the price of the added alloy is high. In particular, in recent years, the price of Ni has soared due to the global demand balance.

Patent Documents 2 and 3 describe non-oriented electrical steel sheets that are strengthened by dispersing carbonitrides in steel. However, sufficient strength cannot be obtained even with these non-oriented electrical steel sheets.

Patent Document 4 describes a non-oriented electrical steel sheet reinforced with Cu precipitates. However, the heat treatment conditions are restricted when manufacturing the non-oriented electrical steel sheet. For this reason, the required strength and magnetic properties cannot be obtained.

Japanese Patent Laid-Open No. Sho 62-256917 Japanese Patent Laid-Open No. 06-330255 Japanese Patent Laid-Open No. 10-018005 JP 2004-084053 A

An object of the present invention is to provide a high-strength non-oriented electrical steel sheet that can easily obtain high strength and magnetic characteristics and a method for producing the same.

The present invention is summarized as follows in order to solve the above problems.

(I) In mass%,
C: 0.002% to 0.05%,
Si: 2.0% to 4.0%,
Mn: 0.05% or more and 1.0% or less,
N: 0.002% or more and 0.05% or less, and Cu: 0.5% or more and 3.0% or less,
Al content is 3.0% or less,
The content (%) of Nb is [Nb], the content (%) of Zr is [Zr], the content (%) of Ti is [Ti], the content (%) of V is [V], When the content (%) is [C] and the content (%) of N is [N], the expressions (1) and (2) are satisfied,
The balance consists of Fe and inevitable impurities,
The recrystallization area ratio is 50% or more,
The yield stress of the tensile test is 700 MPa or more,
The elongation at break is 10% or more,
A high-strength non-oriented electrical steel sheet, wherein the eddy current loss We _10/400 (W / kg) satisfies the formula (3) in relation to the thickness t (mm) of the steel sheet.
2.0 × 10 ⁻⁴ ≦ [Nb] / 93 + [Zr] / 91 + [Ti] / 48 + [V] / 51 (1)
1.0 × 10 ⁻³ ≦ [C] / 12 + [N] / 14 − ([Nb] / 93 + [Zr] / 91 + [Ti] / 48 + [V] / 51) ≦ 3.0 × 10 ⁻³ (2)
We _10/400 ≦ 70 × t ² (3)

(II) The high-strength non-oriented electrical steel sheet according to (I), further comprising Ni: 0.5% to 3.0% by mass.

(III) The high-strength non-oriented electrical steel sheet according to (I) or (II), further containing Sn: 0.01% to 0.10% by mass%.

(IV) The high-strength non-directional electromagnetic wave according to any one of (I) to (III), further comprising, by mass%, B: 0.0010% to 0.0050% steel sheet.

(V) In mass%,
C: 0.002% to 0.05%,
Si: 2.0% to 4.0%,
Mn: 0.05% or more and 1.0% or less,
N: 0.002% or more and 0.05% or less, and Cu: 0.5% or more and 3.0% or less,
Al content is 3.0% or less,
The content (%) of Nb is [Nb], the content (%) of Zr is [Zr], the content (%) of Ti is [Ti], the content (%) of V is [V], When the content (%) is [C] and the content (%) of N is [N], the expressions (1) and (2) are satisfied,
Producing a slab with the balance being Fe and inevitable impurities;
A step of hot rolling the steel to obtain a hot rolled sheet;
Pickling the hot-rolled rolled sheet; and
Next, by performing cold rolling of the hot-rolled rolled sheet, a step of obtaining a cold-rolled sheet,
A step of finish annealing the cold-rolled sheet;
Have
A method for producing a high-strength non-oriented electrical steel sheet, characterized in that the soaking temperature T (° C.) of the finish annealing and the Cu content a (mass%) of the cold-rolled sheet satisfy the formula (4).
T ≧ 200 × a + 500 (4)

(VI) The non-high-strength non-direction according to (V), further comprising a step of annealing the hot-rolled sheet between the step of obtaining the hot-rolled plate and the step of pickling. Method for producing an electrical steel sheet.

(VII)% by mass,
C: 0.002% to 0.05%,
Si: 2.0% to 4.0%,
Mn: 0.05% or more and 1.0% or less,
N: 0.002% or more and 0.05% or less, and Cu: 0.5% or more and 3.0% or less,
Al content is 3.0% or less,
The content (%) of Nb is [Nb], the content (%) of Zr is [Zr], the content (%) of Ti is [Ti], the content (%) of V is [V], When the content (%) is [C] and the content (%) of N is [N], the expressions (1) and (2) are satisfied,
Producing a slab with the balance being Fe and inevitable impurities;
A step of hot rolling the steel to obtain a hot rolled sheet;
Next, a step of pickling the hot rolled sheet,
Next, by performing cold rolling of the hot-rolled rolled sheet, a step of obtaining a cold-rolled sheet,
A step of finish annealing the cold-rolled sheet;
Have
A high-strength non-oriented electrical steel sheet, wherein the hot rolling coiling temperature is 550 ° C or lower, and the ductile brittle fracture surface transition temperature in the Charpy impact test of the hot rolled plate is 70 ° C or lower. Manufacturing method.
2.0 × 10 ⁻⁴ ≦ [Nb] / 93 + [Zr] / 91 + [Ti] / 48

(VIII)% by mass,
C: 0.002% to 0.05%,
Si: 2.0% to 4.0%,
Mn: 0.05% or more and 1.0% or less,
N: 0.002% or more and 0.05% or less, and Cu: 0.5% or more and 3.0% or less,
Al content is 3.0% or less,
The content (%) of Nb is [Nb], the content (%) of Zr is [Zr], the content (%) of Ti is [Ti], the content (%) of V is [V], When the content (%) is [C] and the content (%) of N is [N], the expressions (1) and (2) are satisfied,
Producing a slab with the balance being Fe and inevitable impurities;
A step of hot rolling the steel to obtain a hot rolled sheet;
Next, a step of annealing the hot rolled sheet,
Next, a step of pickling the hot rolled sheet,
Next, by performing cold rolling of the hot-rolled rolled sheet, a step of obtaining a cold-rolled sheet,
A step of finish annealing the cold-rolled sheet;
Have
A high cooling rate of the annealing from 900 ° C. to 500 ° C. is 50 ° C./sec or more, and a ductile brittle fracture surface transition temperature in the Charpy impact test of the hot-rolled sheet is 70 ° C. or less. A method for producing a strength non-oriented electrical steel sheet.

The present inventors investigated the reason why the strength and magnetic properties of the conventional steel strengthening method utilizing Cu precipitates are greatly influenced by the heat treatment conditions. As a result, it has been found that in order to strengthen the steel sheet by precipitation of Cu, a high annealing temperature at which Cu is once dissolved is required in finish annealing after cold rolling.

However, it has also been found that simply increasing the finish annealing temperature coarsens the crystal grains and reduces the strengthening allowance due to Cu precipitation.

It was also found that when the coarsening of crystal grains and Cu precipitation strengthening overlap, the elongation at break in the tensile test is significantly reduced. This remarkable decrease in the elongation at break particularly when the motor core is punched from the steel sheet is cracked at the punched end surface, which leads to a significant decrease in the yield and productivity of the motor core. For this reason, it is desirable to avoid a significant decrease in breaking elongation.

Therefore, the present inventors have further studied earnestly on a method for solving these problems while enjoying precipitation strengthening of Cu. As a result, by adding a certain amount of C, N, Nb, Zr, Ti, and V, it is possible to achieve both Cu precipitation strengthening and crystal grain refinement, and solve the above-mentioned problems. I found out that I can do it.

Furthermore, the magnetic property required for the rotor, which is the main application of the high-strength electrical steel sheet, is eddy current loss (We) at a high frequency of 400 Hz or higher, and C, N, Nb, Zr, Ti, And it has been found that refinement of crystal grains by containing V and V is effective.

Here, the experimental results that led to the present invention will be described.

(Experiment 1)
In a laboratory vacuum melting furnace, by mass%, Si: 3.1%, Mn: 0.2%, Al: 0.5%, Cu: 2.0%, C, N, Nb, Steels with Zr, Ti and V mass% in Table 1 were prepared, heated at 1100 ° C. for 60 minutes, and then immediately hot-rolled to obtain hot-rolled sheets having a plate thickness of 2.0 mm. Thereafter, the hot-rolled sheet was pickled and a cold-rolled sheet having a thickness of 0.35 mm was obtained by one cold rolling. The cold-rolled sheet was subjected to a finish annealing at 800 ° C. to 1000 ° C. for 30 seconds. Table 2 shows the measurement results of various properties after finish annealing.

As shown in Table 2, in materials C and D in which Nb, Zr, Ti, and V satisfy Expression (1), yield strength and elongation at break are high, and eddy current loss is low, and good characteristics are obtained. It was. With respect to the material A that hardly contained C, N, Nb, Zr, Ti, and V, the yield strength and the elongation at break were both low, and the eddy current loss was high. This is because crystal grains are coarsened in the final annealing at 900 ° C. and 1000 ° C.

For material B, the recrystallization rate in finish annealing at 900 ° C. was low. This is presumably because a slight amount of Nb was precipitated immediately before recrystallization of finish annealing, and recrystallization was delayed. Further, it is speculated that in the finish annealing at 1000 ° C., Nb was dissolved, the crystal grains were coarsened, and the same result as that of the material A was expressed.

For material C with good characteristics, Nb precipitates are dispersed and deposited moderately, and for material D, Ti precipitates are dispersed and deposited moderately, and crystal grain growth at 900 ° C. and 1000 ° C. It is inferred that On the other hand, Cu was once dissolved at the final annealing temperatures of 900 ° C. and 1000 ° C., and further precipitated finely during the cooling of the final annealing, so that the precipitation strengthening of Cu could be utilized to the maximum. As a result, it is presumed that high yield strength and elongation at break and low eddy current loss were obtained.

Material E had high yield strength but low elongation at break. This is thought to be due to the adverse effect of excess C. In any of the conditions, recrystallization was not performed by finish annealing at 800 ° C. This is presumably because Cu that had been dissolved before annealing precipitated during annealing and delayed recrystallization.

(Experiment 2)
In a laboratory vacuum melting furnace, by mass%, Si: 2.8%, Mn: 0.1%, Al: 1.0%, Cu: 1.8%, C, N, Nb, Steels with Zr, Ti, and V mass% in Table 3 were prepared, heated at 1150 ° C. for 60 minutes, and then immediately hot-rolled to obtain a hot-rolled sheet having a thickness of 2.2 mm. Thereafter, the hot-rolled sheet was pickled and a cold-rolled sheet having a thickness of 0.35 mm was obtained by one cold rolling. The cold-rolled sheet was subjected to a finish annealing at 800 ° C. to 1000 ° C. for 30 seconds. Table 4 shows the measurement results of various characteristics after finish annealing.

As shown in Table 4, in the materials H and I in which Nb, Zr, Ti, and V satisfy the formula (1), the yield strength and elongation at break are high, and the eddy current loss is low, and good characteristics are obtained. It was. For the material F containing almost no C, N, Nb, Zr, Ti, and V, the yield strength and elongation at break were both low, and the eddy current loss was high. This is because crystal grains are coarsened in the final annealing at 900 ° C. and 1000 ° C.

For Material G, the recrystallization rate in the final annealing at 900 ° C. was low. This is presumably because a slight amount of Nb was precipitated immediately before recrystallization of finish annealing, and recrystallization was delayed. Further, it is speculated that in the finish annealing at 1000 ° C., Nb was dissolved, the crystal grains were coarsened, and the same result as the material F was expressed.

For material H, which has good characteristics, Nb precipitates are moderately dispersed and precipitated. For material I, Ti precipitates are moderately dispersed and precipitated, and crystal grain growth at 900 ° C. and 1000 ° C. It is inferred that On the other hand, Cu was once dissolved at the final annealing temperatures of 900 ° C. and 1000 ° C., and further precipitated finely during the cooling of the final annealing, so that the precipitation strengthening of Cu could be utilized to the maximum. As a result, it is presumed that high yield strength and elongation at break and low eddy current loss were obtained.

Material J had high yield strength but low elongation at break. This is thought to be due to the adverse effect of excess N. In any of the conditions, recrystallization was not performed by finish annealing at 800 ° C. This is thought to be because Cu, which had been dissolved before annealing, precipitated during annealing and delayed recrystallization.

Finish annealing at 800 ° C. has so far been performed as a process for refining crystal grains. That is, this finish annealing has been carried out for the purpose of once dissolving Cu to increase the strength, recrystallizing the steel sheet, and preventing coarsening of the crystal grains. However, from Experiments 1 and 2, it was found that even if the annealing temperature was adjusted while adding Cu, it was difficult to obtain sufficient strength by itself. In other words, it is difficult to achieve both mechanical characteristics and magnetic characteristics with the conventional technology. On the other hand, according to the present invention described below, both mechanical characteristics and magnetic characteristics can be achieved.

Next, the reasons for limiting the numerical values in the high-strength non-oriented electrical steel sheet according to the present invention will be described. Hereinafter,% means mass%.

C is an element necessary for crystal grain refinement. Fine carbides have the effect of increasing nucleation sites during recrystallization and further suppressing crystal grain growth. In order to enjoy the effect, the C content is 0.002% or more. In particular, when N is less than 0.005%, the preferable C content is 0.01% or more, more preferably 0.02% or more. On the other hand, if added over 0.05%, the elongation at break is significantly reduced. Therefore, the upper limit of the C content is 0.05%.

Si is an element effective for reducing eddy current loss and also effective for solid solution strengthening. However, when it adds excessively, cold-rolling property will fall remarkably. Therefore, the upper limit of the Si content is 4.0%. On the other hand, from the viewpoints of solid solution strengthening and eddy current loss, the lower limit is made 2.0%.

Mn is an element effective for lowering eddy current loss and increasing strength in the same manner as Si. However, even if the Mn content exceeds 1.0%, the effect is not improved and saturation occurs. Therefore, the upper limit of the Mn content is 1.0%. On the other hand, the lower limit is made 0.05% from the viewpoint of sulfide formation.

Al is an element effective for increasing the specific resistance like Si. However, if the Al content exceeds 3.0%, the castability deteriorates. Therefore, considering the productivity, the upper limit of the Al content is set to 3.0%. There is no particular lower limit. However, from the viewpoint of stabilizing deoxidation (preventing nozzle clogging during casting), the Al content in the case of Al deoxidation is 0.02% or more, and the Al content in the case of Si deoxidation is 0.01%. % Or more is preferable.

N is an element necessary for crystal grain refinement. Fine nitride has the effect of increasing the number of nucleation sites during recrystallization and further suppressing crystal grain growth. In order to enjoy the effect, the N content is set to 0.002% or more. When N is contained more than the normal level by 0.005 or more, the effect of suppressing crystal grain growth becomes more remarkable. Since this effect is greater as the N content is higher, the N content is preferably further increased to 0.01% or more, and more preferably 0.02 or more. In particular, when the C content is less than 0.005%, the effect obtained by the addition of N is more pronounced. On the other hand, if added over 0.05%, the elongation at break is significantly reduced. Therefore, the upper limit of the N content is 0.05%.

Cu is an important element that brings about precipitation strengthening. If it is less than 0.5%, it will dissolve completely in the steel and the effect of precipitation strengthening will not be obtained, so the lower limit of the Cu content is 0.5%. The upper limit is set to 3.0% considering that the strength is saturated.

Ni is an effective element that can increase the strength of a steel sheet without making it too brittle. However, since it is expensive, it may be added according to the required strength. When adding, in order to fully obtain the effect, it is preferable to contain 0.5% or more. The upper limit is set to 3.0% in consideration of cost. Moreover, it is preferable to add 1/2 or more of Cu addition amount from a viewpoint of suppressing the beard wrinkle which generate | occur | produces by addition of Cu.

Sn has the effect of improving the texture and suppressing nitriding and oxidation during annealing. In particular, the effect of improving the magnetic flux density that is lowered by the addition of Cu is great. When enjoying these effects, if less than 0.01%, the desired effect cannot be obtained. On the other hand, if the content exceeds 0.10%, there is a possibility that an increase in lashes may be caused. Therefore, the addition amount of Sn is preferably 0.01% or more and 0.10% or less.

B segregates at the grain boundaries and has the effect of increasing the toughness of the hot-rolled sheet and hot-rolled annealed sheet. When enjoying this effect, if it is less than 0.0010%, the desired effect cannot be obtained. On the other hand, if it exceeds 0.0050%, slab cracking may occur during casting. Therefore, the addition amount of B is preferably 0.0010% or more and 0.0050% or less.

The four elements Nb, Zr, Ti, and V have the effect of generating carbides or nitrides and suppressing the coarsening of the crystal grain size. And when the formula (1) comprised using the value which remove | divided the mass% of each element by atomic weight is satisfy | filled, a remarkable effect expresses. [Nb] indicates the Nb content (% by mass), [Zr] indicates the Zr content (% by mass), [Ti] indicates the Ti content (% by mass), and [V] indicates V Content (mass%).
2.0 × 10 ⁻⁴ ≦ [Nb] / 93 + [Zr] / 91 + [Ti] / 48 + [V] / 51 (1)

In the formula (1), when the value on the right side is less than 2.0 × 10 ⁻⁴ , the precipitation amount is insufficient, and a sufficient crystal grain suppression effect cannot be obtained. Therefore, the lower limit of the value on the right side is 2.0 × 10 ⁻⁴ . On the other hand, since the excessive content of these elements is dissolved in steel and does not affect the properties of the steel, the upper limit is not particularly specified. However, considering the characteristics and cost, the value on the right side is preferably 1.0 × 10 ⁻² or less.

Formula (2) that defines the relationship among the six elements C, N, Nb, Zr, Ti, and V is an important parameter for miniaturizing crystal grains in combination with Formula (1). [C] indicates the C content (% by mass), and [N] indicates the N content (% by mass).
1.0 × 10 ⁻³ ≦ [C] / 12 + [N] / 14 − ([Nb] / 93 + [Zr] / 91 + [Ti] / 48 + [V] / 51) ≦ 3.0 × 10 ⁻³ (2)

Formula (1) merely defines the maximum amount of carbide or nitride that can be generated, and the crystal growth of the final annealing cannot be sufficiently suppressed only by this condition.

The second term of the formula (2) is obtained by subtracting the right side of the formula (1) from the sum of values obtained by dividing the mass% of C and N by the atomic weight, and an excessive amount of C that does not form carbonitrides. This is a parameter indicating the amount of N.

This excess C and / or N is extremely important in making crystal grains fine. This is because when C and / or N is excessively contained, the carbonitride precipitates with an appropriate dispersion before the finish annealing, and the crystal grain growth during the annealing can be reliably suppressed.

In the present invention, carbides, nitrides, and carbonitrides have a very important role. Among these, nitrides and carbonitrides are useful, and nitrides have a remarkable effect. That is, when carbide and nitride are compared, nitride is more effective for the effect of the present invention, and nitride contributes to the effect of the present invention in a smaller amount. In addition, when the same amount of carbide and nitride are compared, nitride can provide a more favorable effect, and undesirable side effects can be suppressed. As used herein, “preferable effect” means crystal grain refinement, increased strength, and stability at high temperatures, and “unfavorable side effects” include increased iron loss, cracks originating from precipitates ( In particular embrittlement).

The mechanism by which the properties of non-oriented electrical steel sheets change depending on the type of precipitates is not clear, but the effects of precipitate size, morphology (anisotropic), consistency with the parent phase, precipitation location, etc. It is thought that it is because they have received it. In addition, it is considered that the size and the like of these precipitates are influenced by the difference in the solubility of the constituent elements, the difference in the crystal structure of the precipitate, the difference in the size of the constituent atoms, and the like.

Thus, since the N content is appropriate in consideration of not only the contents of Nb, Zr, Ti, and V but also the balance with the content of C and the thermal history in the manufacturing process, the present invention Then, nitride is formed preferentially as compared with the conventional electromagnetic steel sheet. As a result, crystal grain growth at a high temperature is suppressed, and an increase in iron loss and embrittlement can be suppressed.

In addition, since carbonitrides have various configurations depending on the formation process, their characteristics and functions are not unambiguous, but it can be said that they exhibit a more favorable action than at least precipitates consisting of carbides. . Accordingly, the ratio of the N content to the C content is preferably high, and [N] / [C] is preferably 3 or more, and more preferably 5 or more. The composition of nitride is, for example, whether carbide is an initial formation, nitride is an initial formation, has a structure similar to carbide in the growth process, or is similar to nitride in the growth process. It is considered to change due to the effect of having a structure.

When the value (parameter value) of the second term of the formula (2) is less than 1.0 × 10 ⁻³ , the thermal stability of the carbonitride is weakened. For example, if the recrystallization is delayed immediately after the recrystallization of the finish annealing and the annealing temperature is further increased, the precipitates are re-dissolved, the crystal grains become coarse, and the formation of stable fine grains is difficult. Become. On the other hand, if C and / or N is excessive to a level where the parameter value exceeds 3.0 × 10 ⁻³ , quenching occurs during cooling, and the elongation and toughness of the steel sheet deteriorate.

For the above reason, the lower limit of the parameter value in the equation (2) is 1.0 × 10 ⁻³ and the upper limit is 3.0 × 10 ⁻³ .

When the recrystallization area ratio of the high-strength non-oriented electrical steel sheet itself is less than 50%, the product characteristics, particularly the elongation at break, are significantly reduced. Therefore, the recrystallization area ratio is set to 50% or more.

The yield stress in the tensile test is set to 700 MPa or more in consideration of the strength required for a rotor that rotates at high speed. The yield stress specified here is the lower yield point.

The elongation at break is 10% or more from the viewpoint of suppressing cracks in the punched end face of the motor core.

Eddy current loss is loss caused by current flowing through a steel plate during excitation. When this loss is large, the motor core easily generates heat and causes demagnetization of the magnet. Since the eddy current loss We _10/400 is _highly dependent on the plate thickness of the steel plate, the plate thickness t (mm) is used as a parameter, and the allowable range of heat generation by the rotor is expressed as 70 × t as shown in Equation (3). ² or less.
We _10/400 ≦ 70 × t ² (3)

As a method for calculating this eddy current loss, a two-frequency method is used. For example, assuming that the iron loss at frequency f ₁ is W ₁ and the iron loss at frequency f ₂ is W ₂ at a maximum magnetic flux density Bmax of _{1.0 T} , the eddy current loss We _10/400 of W _10/400 is “(W ₂ / f ₂ −W ₁ / f ₁ ) / (f ₂ −f ₁ ) × 400 × 400 ”.

Since the calculation is possible if there is a plurality of iron loss values with different frequencies at a maximum magnetic flux density Bmax of 1.0 T, the measurement frequency is not particularly specified. However, if possible, it is preferable to calculate at a frequency close to 400 Hz, for example, a frequency range of about 100 to 800 Hz. The maximum magnetic flux density Bmax is the maximum magnetic flux density that is excited when the iron loss is measured.

Next, the reasons for limiting the numerical values in the method for producing a high-strength non-oriented electrical steel sheet according to the present invention will be described.

In the finish annealing, high strength can be obtained by temporarily dissolving Cu and precipitating it during cooling. Therefore, the soaking temperature T (° C.) of finish annealing must be equal to or higher than the solid solution temperature of Cu. This solid solution temperature depends on the Cu content. Assuming that the Cu content is a (mass%), if the temperature is 200 × a + 500 or higher (° C.), Cu completely dissolves, so as shown in the equation (4), the soaking temperature of finish annealing T (° C.) is 200 × a + 500 or more.
T ≧ 200 × a + 500 (4)

When the coiling temperature during hot rolling exceeds 550 ° C., carbonitride and Cu precipitates remarkably reduce the toughness of some hot rolled sheets. Therefore, the coiling temperature during hot rolling is set to 550 ° C. or lower. Regarding the toughness of the hot-rolled sheet, the ductile brittle fracture surface transition temperature in the Charpy impact test is set to 70 ° C. or less from the viewpoint of suppressing fracture during cold rolling.

Regarding the annealing of hot-rolled sheets, if the cooling rate from 900 ° C. to 500 ° C. is lower than 50 ° C./sec, the toughness of the hot-rolled annealed sheet is significantly reduced by carbonitrides and Cu precipitates. Therefore, the cooling rate in this temperature range is set to 50 ° C./sec or more. Regarding the toughness of the steel sheet after annealing, the ductile brittle fracture surface transition temperature in the Charpy impact test is set to 70 ° C. or less from the viewpoint of suppressing fracture during cold rolling.

The annealing temperature of the hot-rolled sheet is not particularly specified, but 900 ° C. or higher is preferable because the purpose of annealing the hot-rolled sheet is to recrystallize the hot-rolled sheet and promote grain growth. On the other hand, from a brittle viewpoint, 1100 degrees C or less is preferable.

The transition temperature defined here is a temperature at which the ductile fracture surface ratio is 50% in the transition curve showing the relationship between the test temperature and the ductile fracture surface ratio, as defined in Japanese Industrial Standards (JIS). You may employ | adopt the temperature corresponding to the average value of the absorbed energy in a ductile fracture surface rate is 0% and 100%.

The length and height of the specimen used for the Charpy impact test shall be the size specified in JIS. On the other hand, the width of the test piece is the thickness of the hot rolled plate. Accordingly, the size is 55 mm in length in the rolling direction, the height is 10 mm, and the width is about 1.5 mm to 3.0 mm depending on the thickness of the hot rolled sheet. Further, in the test, it is preferable to stack a plurality of test pieces and bring them closer to a thickness of 10 mm which is a normal test condition.

Example 1
In a vacuum melting furnace, by mass%, Si: 2.9%, Mn: 0.2%, Al: 0.7%, and Cu: 1.5%, C, N, Nb, Zr, Steels having different mass percentages of Ti and V were prepared, heated at 1150 ° C. for 60 minutes, and then immediately hot-rolled to obtain a hot-rolled plate having a plate thickness of 2.3 mm. Thereafter, the hot-rolled sheet was pickled and a cold-rolled sheet having a thickness of 0.5 mm was obtained by one cold rolling. This cold-rolled sheet was subjected to finish annealing at 900 ° C. for 60 seconds. Table 5 shows the measurement results of the components and various characteristics.

In the sign a1 that does not satisfy the expression (1), the yield stress and the eddy current loss We _10/400 are out of the range defined in the present invention. Further, in the symbols a14 to a17 that do not satisfy the formula (2), the recrystallization rate and the elongation at break were out of the ranges defined in the present invention. In the code | symbol a20 in which C content exceeds the upper limit of the range prescribed | regulated by this invention, and does not satisfy Formula (2), the breaking elongation was remove | deviated from the range prescribed | regulated by this invention. Good characteristics were obtained with other samples (reference symbols a2, a3, a18, and a19) in which each requirement is within the range defined by the present invention.

(Example 2)
In a vacuum melting furnace, by mass%, Si: 3.7%, Mn: 0.1%, Al: 0.2%, and Cu: 1.4%, C, N, Nb, Zr, Steels having different mass percentages of Ti and V were prepared, heated at 1150 ° C. for 60 minutes, and then immediately hot-rolled to obtain a hot-rolled plate having a plate thickness of 2.3 mm. Thereafter, the hot-rolled sheet was pickled and a cold-rolled sheet having a thickness of 0.5 mm was obtained by one cold rolling. This cold-rolled sheet was subjected to finish annealing at 900 ° C. for 60 seconds. Table 6 shows the measurement results of the components and various characteristics.

In the sign b1 not satisfying the expression (1), the yield stress and the eddy current loss We _10/400 are out of the range defined in the present invention. In addition, in the symbols b14 to b17 that do not satisfy the formula (2), the recrystallization rate and the elongation at break were outside the ranges defined in the present invention. Similarly, in the code | symbol b20 which does not satisfy Formula (2), breaking elongation was remove | deviated from the range prescribed | regulated by this invention. Good characteristics were obtained in other samples (reference numerals b2, b3, b18, and b19) in which each requirement is within the range defined by the present invention.

(Example 3)
In a vacuum melting furnace, in mass%, C: 0.022%, Mn: 0.5%, Al: 2.0%, N: 0.003%, Ni: 1.0%, Nb: 0.031 %, Zr: 0.004%, Ti: 0.003%, and V: 0.004%, a steel with varying amounts of Si and Cu was prepared and heated at 1120 ° C for 120 minutes, Immediately hot-rolled, a hot-rolled sheet having a thickness of 2.0 mm was obtained. Thereafter, the hot-rolled sheet was pickled and a cold-rolled sheet having a thickness of 0.25 mm was obtained by one cold rolling. The cold-rolled sheet was subjected to a finish annealing at 1000 ° C. for 45 seconds. Table 7 shows the measurement results of the Si amount, the Cu amount, and various characteristics.

In 1.8% samples (symbols c1 to c5) having a Si content lower than the range defined in the present invention, the yield stress and eddy current loss We _10/400 were outside the range defined in the present invention. . Further, in the 4.1% sample (reference numerals c21 to c25) in which the Si content exceeds the range specified in the present invention, the elongation at break was extremely low.

Furthermore, even if the Si content is within the range defined by the present invention, the samples with Cu less than 0.5% (reference numerals c6, c11, and c16) have low yield stress, and are defined by the present invention. It was out of range. Further, the samples with Ni / Cu of 0.5 or more (reference numerals c1 to c4, c6 to c9, c11 to c14, c16 to c19, and c21 to c24) did not show baldness.

Example 4
In a vacuum melting furnace, in mass%, C: 0.003%, Si: 3.3%, Mn: 0.2%, Al: 0.7%, N: 0.022%, Ni: 1.5 %, Nb: 0.032%, Zr: 0.004%, Ti: 0.003%, and V: 0.003%, and a steel in which the B content and the Sn content were changed was produced at 1110 ° C. Was heated for 80 minutes and then immediately hot rolled to obtain a hot rolled plate having a thickness of 2.7 mm. The coiling temperature in this hot rolling was 530 ° C. Thereafter, this hot rolled sheet is subjected to annealing (intermediate annealing) at 1050 ° C. for 60 seconds, further pickled, and a cold rolled sheet having a sheet thickness of 0.35 mm by one cold rolling. Obtained. This cold-rolled sheet was subjected to finish annealing at 950 ° C. for 60 seconds. Table 8 shows the B amount, Sn amount, transition temperature after intermediate annealing, and magnetic flux density after finish annealing.

The transition temperature of the hot-rolled annealed sheet was low when the amount of B was 0.0010% or more and d6 to d25. A high magnetic flux density was obtained with the codes d2 to d5, d7 to d10, d12 to d15, d17 to d20, and d22 to d25 having an Sn content of 0.010% or more. It should be noted that slab cracking occurred in the signs d21 to d25 where the B amount exceeded 0.0050%, and baldness occurred in d5, d10, d15, d20, and d25 where the Sn amount exceeded 0.010%. .

(Example 5)
In a vacuum melting furnace, in mass%, C: 0.028%, Si: 2.9%, Mn: 0.8%, Al: 1.4%, N: 0.012%, Ni: 1.4 %, Nb: 0.003%, Zr: 0.04%, Ti: 0.003%, and V: 0.003%, and steel with varying amounts of Cu was prepared, and 90 minutes at 1120 ° C. After heating, it was immediately hot rolled to obtain a hot hot rolled sheet having a thickness of 2.0 mm. Thereafter, this hot-rolled sheet is subjected to hot-rolled sheet annealing at 950 ° C. for 60 seconds, further pickled, and a cold-rolled sheet having a thickness of 0.35 mm is obtained by one cold rolling. It was. This cold-rolled sheet was subjected to finish annealing while changing the soaking temperature. Table 9 shows the results of the amount of Cu, the temperature of finish annealing, and various characteristics.

Samples where the soaking temperature satisfies the formula (4) (in the case of the symbols e1 to e10, e13 to e15, e18 to e20, and e23, the yield stress, breaking elongation, and We _10/400 are within the range defined by the present invention. And good characteristics were obtained.

In samples where the soaking temperature does not satisfy the formula (4) (reference numerals e11, e12, e16, e17, e21, and e22), the recrystallization area ratio is less than 50% and / or the elongation at break is less than 10%. It was outside the range defined by the invention.

(Example 6)
In a vacuum melting furnace, in mass%, C: 0.027%, Si: 3.6%, Mn: 0.1%, Al: 1.8%, N: 0.005%, Ni: 2.0 %, Nb: 0.003%, Zr: 0.004%, Ti: 0.03%, and V: 0.01%. These steel slabs were heated at 1170 ° C. for 90 minutes and immediately hot rolled to obtain hot rolled sheets having a plate thickness of 2.5 mm. During the production of this hot-rolled sheet, the winding temperature was changed. Furthermore, the produced hot rolled sheet was annealed at 1000 ° C. for 60 seconds to obtain an annealed sheet. During this annealing, the cooling rate from 900 ° C. to 500 ° C. was changed. Charpy test pieces were produced from these hot-rolled plates and annealed plates, and the transition temperature was measured by an impact test. The results are shown in Table 10.

Good toughness with a transition temperature of 70 ° C. or lower was obtained for samples with a winding temperature of 550 ° C. or lower (reference symbols f1 to f3). For the annealed plate, regardless of the coiling temperature, in the samples (reference numerals f8 to f10, f13 to f15, and f18 to f20) where the cooling rate from 900 ° C. to 500 ° C. is 50 ° C./sec or more, the transition temperature is Good toughness of 70 ° C. or less was obtained.

According to the present invention, a non-oriented electrical steel sheet having excellent strength can be provided at a low cost without sacrificing the yield and productivity in manufacturing the motor core and the steel sheet.

Claims

% By mass
C: 0.002% to 0.05%,
Si: 2.0% to 4.0%,
Mn: 0.05% or more and 1.0% or less,
N: 0.002% or more and 0.05% or less, and Cu: 0.5% or more and 3.0% or less,
Al content is 3.0% or less,
The content (%) of Nb is [Nb], the content (%) of Zr is [Zr], the content (%) of Ti is [Ti], the content (%) of V is [V], When the content (%) is [C] and the content (%) of N is [N], the expressions (1) and (2) are satisfied,
The balance consists of Fe and inevitable impurities,
The recrystallization area ratio is 50% or more,
The yield stress of the tensile test is 700 MPa or more,
The elongation at break is 10% or more,
A high-strength non-oriented electrical steel sheet, wherein the eddy current loss We 10/400 (W / kg) satisfies the formula (3) in relation to the thickness t (mm) of the steel sheet.
2.0 × 10 −4 ≦ [Nb] / 93 + [Zr] / 91 + [Ti] / 48 + [V] / 51 (1)
1.0 × 10 −3 ≦ [C] / 12 + [N] / 14 − ([Nb] / 93 + [Zr] / 91 + [Ti] / 48 + [V] / 51) ≦ 3.0 × 10 −3 (2)
We 10/400 ≦ 70 × t 2 (3)
The high strength non-oriented electrical steel sheet according to claim 1, further comprising Ni: 0.5% to 3.0% by mass.
The high-strength non-oriented electrical steel sheet according to claim 1, further comprising Sn: 0.01% to 0.10% by mass.
The high-strength non-oriented electrical steel sheet according to claim 2, further comprising Sn: 0.01% or more and 0.10% or less in mass%.
The high-strength non-oriented electrical steel sheet according to claim 1, further comprising, in mass%, B: 0.0010% or more and 0.0050% or less.
The high-strength non-oriented electrical steel sheet according to claim 2, further comprising, in mass%, B: 0.0010% or more and 0.0050% or less.
The high-strength non-oriented electrical steel sheet according to claim 3, further comprising, in mass%, B: 0.0010% or more and 0.0050% or less.
The high-strength non-oriented electrical steel sheet according to claim 4, further comprising, in mass%, B: 0.0010% or more and 0.0050% or less.
% By mass
C: 0.002% to 0.05%,
Si: 2.0% to 4.0%,
Mn: 0.05% or more and 1.0% or less,
N: 0.002% or more and 0.05% or less, and Cu: 0.5% or more and 3.0% or less,
Al content is 3.0% or less,
The content (%) of Nb is [Nb], the content (%) of Zr is [Zr], the content (%) of Ti is [Ti], the content (%) of V is [V], When the content (%) is [C] and the content (%) of N is [N], the expressions (1) and (2) are satisfied,
Producing a slab with the balance being Fe and inevitable impurities;
A step of hot rolling the steel to obtain a hot rolled sheet;
Pickling the hot-rolled rolled sheet; and
Next, by performing cold rolling of the hot-rolled rolled sheet, a step of obtaining a cold-rolled sheet,
A step of finish annealing the cold-rolled sheet;
Have
A method for producing a high-strength non-oriented electrical steel sheet, characterized in that the soaking temperature T (° C.) of the finish annealing and the Cu content a (mass%) of the cold-rolled sheet satisfy the formula (4).
2.0 × 10 −4 ≦ [Nb] / 93 + [Zr] / 91 + [Ti] / 48 + [V] / 51 (1)
1.0 × 10 −3 ≦ [C] / 12 + [N] / 14 − ([Nb] / 93 + [Zr] / 91 + [Ti] / 48 + [V] / 51) ≦ 3.0 × 10 −3 (2)
T ≧ 200 × a + 500 (4)
The high-strength non-oriented electrical steel sheet according to claim 9, further comprising a step of annealing the hot-rolled plate between the step of obtaining the hot-rolled plate and the step of pickling. Manufacturing method.
% By mass
C: 0.002% to 0.05%,
Si: 2.0% to 4.0%,
Mn: 0.05% or more and 1.0% or less,
N: 0.002% or more and 0.05% or less, and Cu: 0.5% or more and 3.0% or less,
Al content is 3.0% or less,
The content (%) of Nb is [Nb], the content (%) of Zr is [Zr], the content (%) of Ti is [Ti], the content (%) of V is [V], When the content (%) is [C] and the content (%) of N is [N], the expressions (1) and (2) are satisfied,
Producing a slab with the balance being Fe and inevitable impurities;
A step of hot rolling the steel to obtain a hot rolled sheet;
Next, a step of pickling the hot rolled sheet,
Next, by performing cold rolling of the hot-rolled rolled sheet, a step of obtaining a cold-rolled sheet,
A step of finish annealing the cold-rolled sheet;
Have
A high-strength non-oriented electrical steel sheet, wherein the hot rolling coiling temperature is 550 ° C or lower, and the ductile brittle fracture surface transition temperature in the Charpy impact test of the hot rolled plate is 70 ° C or lower. Manufacturing method.
2.0 × 10 −4 ≦ [Nb] / 93 + [Zr] / 91 + [Ti] / 48 + [V] / 51 (1)
1.0 × 10 −3 ≦ [C] / 12 + [N] / 14 − ([Nb] / 93 + [Zr] / 91 + [Ti] / 48 + [V] / 51) ≦ 3.0 × 10 −3 (2)
% By mass
C: 0.002% to 0.05%,
Si: 2.0% to 4.0%,
Mn: 0.05% or more and 1.0% or less,
N: 0.002% or more and 0.05% or less, and Cu: 0.5% or more and 3.0% or less,
Al content is 3.0% or less,
The content (%) of Nb is [Nb], the content (%) of Zr is [Zr], the content (%) of Ti is [Ti], the content (%) of V is [V], When the content (%) is [C] and the content (%) of N is [N], the expressions (1) and (2) are satisfied,
Producing a slab with the balance being Fe and inevitable impurities;
A step of hot rolling the steel to obtain a hot rolled sheet;
Next, a step of annealing the hot rolled sheet,
Next, a step of pickling the hot rolled sheet,
Next, by performing cold rolling of the hot-rolled rolled sheet, a step of obtaining a cold-rolled sheet,
A step of finish annealing the cold-rolled sheet;
Have
A high cooling rate of the annealing from 900 ° C. to 500 ° C. is 50 ° C./sec or more, and a ductile brittle fracture surface transition temperature in the Charpy impact test of the hot-rolled sheet is 70 ° C. or less. A method for producing a strength non-oriented electrical steel sheet.
2.0 × 10 −4 ≦ [Nb] / 93 + [Zr] / 91 + [Ti] / 48 + [V] / 51 (1)
1.0 × 10 −3 ≦ [C] / 12 + [N] / 14 − ([Nb] / 93 + [Zr] / 91 + [Ti] / 48 + [V] / 51) ≦ 3.0 × 10 −3 (2)