JP2012036459A - Non-oriented magnetic steel sheet and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-oriented magnetic steel sheet which has good magnetic properties in the L-direction and C-direction, the L-direction magnetic properties being in particular excellent, and to provide a production method for the non-oriented magnetic steel sheet.SOLUTION: The non-oriented magnetic steel sheet has a chemical composition comprising, by mass, 0.005% or less of C, 1.0-4.0% of Si, 0.1 to 3.0% of sol.Al, 0.1 to 3.0% of Mn, 0.2% or less of P, 0.01% or less of S and 0.01% or less of N and the balance Fe with unavoidable impurities, and further satisfying Si+sol.Al/2+Mn/4+5P≤4.0. The non-oriented magnetic steel sheet has: a steel matrix in which the average crystal grain diameter is 40 to 180 μm; magnetic properties satisfying (2×W+W)/3≤40×{(2×B+B)/3+t-0.2}-56; a specific resistance at room temperature of 40×10to 75×10Ωm; and a sheet thickness of 0.1 to 0.35 mm.

Description

  The present invention relates to a non-oriented electrical steel sheet and a method for producing the same. More specifically, the present invention can be used mainly for stator cores of high-efficiency divided iron core motors such as compressor motors such as air conditioners and refrigerators, drive motors and generators such as electric vehicles and hybrid vehicles. The present invention relates to a suitable non-oriented electrical steel sheet and a method for producing the same.

  Due to the need to reduce greenhouse gases, products with low energy consumption are being developed in the fields of automobiles, home appliances, and the like. For example, in the automobile field, there are low fuel consumption vehicles such as a hybrid drive vehicle combining a gasoline engine and a motor, and a motor drive electric vehicle. In the field of home appliances, there are high-efficiency air conditioners, refrigerators and the like that consume less electricity annually. The technology common to these is a motor, and high efficiency of the motor is an important technology.

  The motors as described above are often multipolar, and it is known that the motor efficiency of the multipolar motor is greatly influenced by the magnetic characteristics of the teeth portion of the stator (stator). In many conventional motors, an integrally punched iron core is used for the stator. In the case of integral punching, the direction of each tooth portion takes various directions with respect to the rolling direction of the electromagnetic steel sheet. For this reason, non-oriented electrical steel sheets having good magnetic properties in the entire circumferential direction have been required for the integrally punched iron core material.

  On the other hand, in recent years, the number of cases in which a split core that is advantageous in terms of winding design and yield is employed for the stator is increasing. In the case of a split iron core, the direction of the tooth portion can be matched with a direction in which the magnetic properties of the electromagnetic steel sheet are good, for example, a rolling direction (hereinafter also referred to as “L direction”).

  Unidirectional electrical steel sheets are known as electrical steel sheets having excellent magnetic properties in the L direction. However, the unidirectional electrical steel sheet is not suitable as a split core material in which a considerable amount of magnetic flux also flows in the C direction because the magnetic properties in the direction perpendicular to the rolling direction (hereinafter also referred to as “C direction”) are extremely poor. Furthermore, in order to manufacture such a unidirectional electrical steel sheet, there is a problem that the manufacturing cost is high because a special facility capable of high-temperature long-time secondary recrystallization annealing and decarburization annealing is required.

Therefore, in Patent Document 1 and Patent Document 2, in order to solve the problem that the magnetic properties in the C direction are poor with respect to the unidirectional electromagnetic steel sheet, a technique related to the electromagnetic steel sheet for the split core in which the iron loss in the C direction is reduced. Is disclosed.
Patent Documents 3 to 5 disclose techniques related to non-oriented electrical steel sheets for split iron cores.

  Conventionally, a two-time cold rolling method is known as a method for enhancing the magnetic properties of a non-oriented electrical steel sheet (see Patent Documents 6 to 9).

JP 2004-100025 A Japanese Patent Laid-Open No. 2004-100026 JP 2008-127600 A JP 2008-127608 A JP 2008-127612 A JP 51-151215 A JP 59-74225 A Japanese Patent Laid-Open No. 11-236618 JP 2000-17330 A

  As described above, in the case of a split iron core, the direction of the tooth portion can be matched with a direction in which the magnetic properties of the electromagnetic steel sheet are good, for example, the rolling direction (L direction). In this case, the direction of the yoke part through which a considerable amount of magnetic flux flows next to the direction of the tooth part coincides with the direction perpendicular to the rolling direction (C direction). Accordingly, non-oriented electrical steel sheets having good magnetic properties in the L direction and C direction are suitable for the material for the split iron core, and non-oriented electrical steel sheets having particularly excellent magnetic properties in the L direction are most suitable. . That is, it is most suitable as a material for a split core that the magnetic properties obtained by weighted averaging the L direction and the C direction weighted in the L direction are good.

  However, although the electrical steel sheets disclosed in Patent Document 1 and Patent Document 2 are aimed at reducing iron loss in the C direction, it is said that a lower magnetic flux density in the C direction is preferable. However, it is not suitable as a material for a split core through which a considerable amount of magnetic flux flows. In addition, in order to manufacture these electrical steel sheets, similar to the unidirectional electrical steel sheets, special equipment capable of secondary recrystallization annealing and decarburization annealing at a high temperature for a long time is required. have.

Patent Documents 3 to 5 disclose non-oriented electrical steel sheets for split iron cores, but anisotropy of magnetic flux density B ₅₀ when magnetized at a magnetizing force of 5000 A / m has been studied. However, the anisotropy of the iron loss that is more important than the magnetic flux density in the high-speed rotating motor has not been studied.

  In addition, the non-oriented electrical steel sheet manufacturing methods disclosed in Patent Document 6 and Patent Document 7 are intended to reduce anisotropy, and are disclosed in Patent Document 8 and Patent Document 9. The method for producing a grain-oriented electrical steel sheet is intended to improve simple average magnetic properties in the L direction and the C direction, both of which obtain a non-oriented electrical steel sheet with good circumferential magnetic properties. The purpose is that. Therefore, it cannot be said that it is suitable as a non-oriented electrical steel sheet for a split iron core.

  Thus, the non-oriented electrical steel sheet having good magnetic properties in the L direction and the C direction is suitable for the magnetic steel sheet for the split iron core, and the non-oriented electrical steel sheet having particularly excellent magnetic properties in the L direction. Is most suitable, and the magnetic properties obtained by weighted averaging of the L direction and the C direction weighted in the L direction are required to be satisfactory. The fact is that nothing has been done.

  The present invention has been made in view of the above circumstances, and its problem is mainly fixing high-efficiency divided core motors such as compressor motors such as air conditioners and refrigerators, drive motors and generators such as electric vehicles and hybrid vehicles. To provide a non-oriented electrical steel sheet that is suitable for use in a child (stator) core, has good magnetic properties in the L direction and C direction, and particularly excellent in the magnetic properties in the L direction, and a method for manufacturing the same. is there.

  In order to solve the above problems, the present inventors have investigated in detail the magnetic properties in the L direction and the C direction. As a result, in order to obtain a non-oriented electrical steel sheet having excellent magnetic properties in the L direction and C direction and particularly excellent in the magnetic properties in the L direction, the L direction and the C direction weighted in the L direction are set. It was important to improve the weighted average magnetic properties, and for this purpose, it was found that increasing the magnetic property anisotropy was effective. And in order to obtain such magnetic characteristics, it was found that it is important to adopt the cold rolling method twice and to optimize the rolling reduction, intermediate annealing conditions, and finish annealing conditions. The gist of the present invention based on such new findings is as follows.

That is, the present invention relates to mass%, C: 0.005% or less, Si: 1.0% or more and 4.0% or less, sol. Al: 0.1% to 3.0%, Mn: 0.1% to 3.0%, P: 0.2% or less, S: 0.01% or less, and N: 0.01% or less And the balance is made of Fe and impurities, has a chemical composition satisfying the following formula (1), has a steel structure with an average crystal grain size of 40 μm or more and 180 μm or less, and satisfies the following formula (2) A non-oriented electrical steel sheet having magnetic properties, having a specific resistance at room temperature of 40 × 10 ⁻⁸ Ωm or more and 75 × 10 ⁻⁸ Ωm or less, and a thickness of 0.10 mm or more and 0.35 mm or less. provide.
Si + sol. Al / 2 + Mn / 4 + 5P ≦ 4.0 (1)
(2 × W _{10 / 400L} + W _{10 / 400C} ) / 3
≦ 40 × {(2 × B _50L + B _50C ) /3+t−0.2} −56 (2)
(here,
Si, sol. Al, Mn, P: Content of each element (% by mass)
W _{10 / 400L} : Iron loss in the rolling direction at an excitation magnetic flux density of 1.0 T and an excitation frequency of 400 Hz (W / kg)
W _{10 / 400C} : Iron loss in the direction perpendicular to rolling at an excitation magnetic flux density of 1.0 T and an excitation frequency of 400 Hz (W / kg)
B _50L : Magnetic flux density (T) in the rolling direction when magnetized with a magnetizing force of 5000 A / m
_B50C : Magnetic flux density (T) in the direction perpendicular to the rolling direction when magnetized with a magnetizing force of 5000 A / m
t: Plate thickness (mm)
It is. )

  In the above invention, the chemical composition is one or two selected from the group consisting of Sn: 0.1% or less and Sb: 0.1% or less in mass%, instead of a part of the Fe. You may contain the above. This is because the texture can be improved by improving the texture of the non-oriented electrical steel sheet.

  Moreover, in the said invention, it replaces with a part of said Fe, and the said chemical composition may contain Ca: 0.01% or less by the mass%. This is because the crystal characteristics can be improved and the magnetic properties can be improved.

This invention provides the manufacturing method of the non-oriented electrical steel sheet characterized by having the following process (A)-(D).
(A) A first cold rolling process in which hot rolling steel sheet having the above chemical composition and specific resistance is subjected to cold rolling at a rolling reduction of 10% or more and 75% or less (B) obtained by the first cold rolling process. An intermediate annealing step for subjecting the cold-rolled steel plate to an intermediate annealing to be held in a temperature range of 700 ° C. to 900 ° C. for 1 hour to 40 hours (C) 50% to 85% to the intermediate annealing steel plate obtained by the intermediate annealing step Second cold rolling step (D) in which cold rolling is performed at the following rolling reduction to obtain a sheet thickness of 0.10 mm or more and 0.35 mm or less. The following formula is applied to the cold rolled steel plate obtained by the second cold rolling step. Finish annealing step for performing finish annealing satisfying (3) and (4) 900 ≦ A ≦ 1200 (3)
9-2 × A / 300 ≦ B ≦ 14-2 × A / 300 (4)
(Here, A represents the finish annealing temperature (° C.), and B represents the tension (MPa) applied during finish annealing.)

  The method for producing a non-oriented electrical steel sheet of the present invention is based on box annealing in which the hot-rolled steel sheet used in the first cold rolling step is held in a temperature range of 700 ° C. to 900 ° C. for 1 hour to 40 hours, or In addition, a hot-rolled sheet annealing step for performing hot-rolled sheet annealing by continuous annealing that is held in a temperature range of 900 ° C. or higher and 1100 ° C. or lower for 1 second or more and 300 seconds or less may be provided. This is because the magnetic properties can be further enhanced.

  The non-oriented electrical steel sheet according to the present invention can be expected to improve the motor efficiency of the split iron core type motor. Moreover, since the manufacturing method of the non-oriented electrical steel sheet which concerns on this invention does not require special equipment, it is excellent also in terms of manufacturing cost.

Reduction ratio and X value (X = 40 × {(2 × B _50L + B _50C ) /3+t−0.2} −56− (2 × W) in the first cold rolling step and the second cold rolling step in the examples. It is a graph which shows the relationship with _{10 / 400L} + W _{10 / 400C} ) / 3). Finish annealing temperature and tension at the time of finish annealing and X value (X = 40 × {(2 × B _50L + B _50C ) /3+t−0.2} −56− (2 × W _{10 / 400L} + W _{10 / 400C)} ) / 3) is a graph showing the relationship.

  Hereinafter, the non-oriented electrical steel sheet and the manufacturing method thereof according to the present invention will be described in detail.

A. Non-oriented electrical steel sheet The non-oriented electrical steel sheet of the present invention is mass%, C: 0.005% or less, Si: 1.0% or more and 4.0% or less, sol. Al: 0.1% to 3.0%, Mn: 0.1% to 3.0%, P: 0.2% or less, S: 0.01% or less, and N: 0.01% or less And the balance is composed of Fe and impurities, has a chemical composition satisfying the above formula (1), has a steel structure with an average crystal grain size of 40 μm to 180 μm, and satisfies the above formula (2) It has magnetic characteristics, has a specific resistance at room temperature of 40 × 10 ⁻⁸ Ωm or more and 75 × 10 ⁻⁸ Ωm or less, and a plate thickness of 0.10 mm or more and 0.35 mm or less.

  Hereafter, each structure in the non-oriented electrical steel sheet of this invention is demonstrated in detail.

1. Chemical Composition First, the reasons for limiting the chemical composition of the steel sheet will be described. Note that “%” indicating the content of each element means “% by mass” unless otherwise specified.

  C is an element that is contained as an impurity and deteriorates magnetic properties. For this reason, C content shall be 0.005% or less. Preferably, it is 0.003% or less.

  Si is an element effective for increasing the specific resistance of a steel sheet and reducing iron loss. Therefore, the Si content is 1.0% or more. Preferably it is 1.5% or more. On the other hand, when Si is excessively contained, the magnetic flux density is remarkably lowered. For this reason, Si content shall be 4.0% or less. Preferably it is 3.5% or less.

  Al is an element effective for increasing the specific resistance of the steel sheet and reducing iron loss. Therefore, sol. The Al content is 0.1% or more. Preferably it is 0.6% or more. On the other hand, when Al is excessively contained, the magnetic flux density is remarkably lowered. For this reason, sol. The Al content is 3.0% or less. Preferably it is 2.5% or less.

  Mn is an element effective for increasing the specific resistance of the steel sheet and reducing iron loss. Therefore, the Mn content is 0.1% or more. On the other hand, if the Mn content is increased, Mn is economically disadvantageous because of its higher alloy cost than Si and Al. For this reason, Mn content shall be 3.0% or less. Preferably it is 2.5% or less.

  P is an element generally contained as an impurity. However, P has an effect of improving the magnetic properties by improving the texture of the non-oriented electrical steel sheet, and therefore may be positively contained. However, since P is also a solid solution strengthening element, if the P content is excessive, the steel sheet becomes hard and cold rolling becomes difficult. Therefore, the P content is 0.2% or less.

Si, Al, Mn, and P have a high solid solution strengthening ability, and if excessively contained, cold rolling becomes difficult. Therefore, the following formula (1) is satisfied.
Si + sol. Al / 2 + Mn / 4 + 5P ≦ 4.0 (1)
(Here, Si, sol.Al, Mn, and P are the contents (mass%) of each element.)

  S is contained as an impurity and combines with Mn in the steel to form fine MnS, inhibits the growth of crystal grains during annealing, and degrades the magnetic properties of the non-oriented electrical steel sheet. For this reason, S content shall be 0.01% or less. Preferably it is 0.005% or less.

  N is contained as an impurity and combines with Al to form fine AlN, which inhibits the growth of crystal grains during annealing and deteriorates magnetic properties. For this reason, N content shall be 0.01% or less. Preferably it is 0.005% or less.

  Sn and Sb have the effect of improving the texture by improving the texture of the non-oriented electrical steel sheet. Therefore, you may contain 1 type or 2 types of Sn and Sb. However, even if it is made excessive, the effect of the above action is saturated, which is economically disadvantageous. Therefore, the contents of Sn and Sb are both 0.1% or less. In order to more reliably obtain the effect of the above action, it is preferable to contain either 0.01% or more of Sn and Sb.

  Ca is an element effective for inclusion control, and when it is contained appropriately, crystal grain growth is improved. Therefore, Ca may be contained. However, even if it contains excessively, the effect by the said effect | action will be saturated and it will become economically disadvantageous. Therefore, the Ca content is 0.01% or less. In order to more reliably obtain the effect of the above action, the Ca content is preferably 0.0003% or more.

2. Average crystal grain size If the crystal grain size is too large or too small, the iron loss will deteriorate. Therefore, the average crystal grain size is set to 40 μm or more and 180 μm or less.
The average crystal grain size may be the average value of the crystal grain sizes measured by the cutting method in the plate thickness direction and the rolling direction in the longitudinal sectional structure photograph. An optical micrograph can be used as the longitudinal cross-sectional structure photograph. For example, a photograph taken at a magnification of 50 times may be used.

3. Magnetic Properties Non-oriented electrical steel sheets that have good magnetic properties in the L direction and C direction and particularly excellent magnetic properties in the L direction are suitable for the material for the split core. For this reason, it is important to improve the magnetic characteristics obtained by weighted averaging of the L direction and the C direction weighted in the L direction. Therefore, in the present invention, an index obtained by weighting the magnetic characteristics in the L direction twice as much as the magnetic characteristics in the C direction is used.

  The iron loss can be reduced by reducing the thickness or increasing the specific resistance by increasing the content of the alloy element. However, if the thickness is reduced, the number of punches at the time of motor production increases and the productivity deteriorates. Further, when the content of the alloy element is increased, the ratio of iron atoms in the electrical steel sheet is reduced, and the magnetic flux density is reduced. That is, iron loss and magnetic flux density, and iron loss and motor productivity are generally in a trade-off relationship. For this reason, the balance required for these characteristics depends on the motor design, and iron loss is relative when emphasizing high magnetic flux density or increasing plate thickness with emphasis on motor productivity. It is allowed to be high.

For this reason, the present invention has magnetic characteristics satisfying the following formula (2).
(2 × W _{10 / 400L} + W _{10 / 400C} ) / 3
≦ 40 × {(2 × B _50L + B _50C ) /3+t−0.2} −56 (2)
here,
W _{10 / 400L} : Iron loss in the rolling direction at an excitation magnetic flux density of 1.0 T and an excitation frequency of 400 Hz (W / kg)
W _{10 / 400C} : Iron loss in the direction perpendicular to rolling at an excitation magnetic flux density of 1.0 T and an excitation frequency of 400 Hz (W / kg)
B _50L : Magnetic flux density (T) in the rolling direction when magnetized with a magnetizing force of 5000 A / m
_B50C : Magnetic flux density (T) in the direction perpendicular to the rolling direction when magnetized with a magnetizing force of 5000 A / m
t: Plate thickness (mm)
It is.

4). Specific resistance Compressor motors such as air conditioners and refrigerators, drive motors and generators such as electric vehicles and hybrid vehicles are used in high-speed rotation regions, and non-oriented electrical steel sheets, which are core materials, have low iron loss in high-frequency regions. Things are desirable. As the specific resistance is increased by increasing the amount of alloy such as Si, Al, Mn, etc., the high-frequency iron loss is reduced. However, if the amount of alloy is excessively increased, the alloy cost and the magnetic flux density are problematic. Therefore, the specific resistance at room temperature is set to 40 × 10 ⁻⁸ Ωm or more and 75 × 10 ⁻⁸ Ωm or less. More preferably, it is 45 × 10 ⁻⁸ Ωm or more and 70 × 10 ⁻⁸ Ωm or less.
The specific resistance at room temperature may be measured by a known four-terminal method. The sample used for the measurement may be a non-oriented electrical steel sheet from which the insulating coating on the surface has been removed, or a sample for measuring resistivity from a hot-rolled steel sheet or slab.

5. Thickness As mentioned above, compressor motors such as air conditioners and refrigerators, drive motors such as electric cars and hybrid cars, and generators are used in high-speed rotation areas. Therefore, non-oriented electrical steel sheets that are core materials are used in high-frequency areas. Those with low iron loss are desirable. A thinner plate thickness is preferable for reducing iron loss under high frequency conditions. Therefore, the plate thickness is 0.35 mm or less. Preferably it is 0.30 mm or less. On the other hand, excessive thinning significantly reduces the productivity of steel plates and motors. Therefore, the plate thickness is 0.10 mm or more. Preferably it is 0.15 mm or more.

6). Manufacturing method It is suitable to manufacture the non-oriented electrical steel sheet of the present invention by a manufacturing method of the non-oriented electrical steel sheet described later.

B. Manufacturing method of non-oriented electrical steel sheet The manufacturing method of the non-oriented electrical steel sheet of the present invention includes the following steps (A) to (D).
(A) A first cold rolling process in which hot rolling steel sheet having the above chemical composition and specific resistance is subjected to cold rolling at a rolling reduction of 10% or more and 75% or less (B) obtained by the first cold rolling process. An intermediate annealing step for subjecting the cold-rolled steel plate to an intermediate annealing to be held in a temperature range of 700 ° C. to 900 ° C. for 1 hour to 40 hours (C) 50% to 85% to the intermediate annealing steel plate obtained by the intermediate annealing step A second cold rolling step (D) in which cold rolling at the following reduction rate is performed to obtain a plate thickness of 0.10 mm or more and 0.35 mm or less is applied to the cold rolled steel plate obtained by the second cold rolling step. Finish annealing process for performing finish annealing satisfying (3) and (4)

  Hereinafter, each process in the manufacturing method of the non-oriented electrical steel sheet according to the present invention will be described.

1. First Cold Rolling Step In the first cold rolling step, the hot rolled steel sheet having the above-described chemical composition is subjected to cold rolling at a reduction rate of 10% to 75%.
If the rolling reduction in the first cold rolling process is less than 10% or more than 75%, the intended magnetic properties may not be obtained. Therefore, the rolling reduction in the first cold rolling step is set to 10% or more and 75% or less.
Other conditions for cold rolling, such as the temperature of the steel sheet during cold rolling and the diameter of the rolling roll, are not particularly limited, and are appropriately selected depending on the chemical composition of the hot rolled steel sheet, the thickness of the target steel sheet, etc. To do.
A hot-rolled steel sheet is usually subjected to cold rolling after removing the scale formed on the surface of the steel sheet during hot rolling by pickling. As will be described later, when hot-rolled sheet annealing is performed on the hot-rolled steel sheet, it may be pickled either before or after hot-rolled sheet annealing.

2. Intermediate annealing step In the intermediate annealing step, the cold-rolled steel sheet obtained by the first cold rolling step is subjected to intermediate annealing that is maintained in a temperature range of 700 ° C to 900 ° C for 1 hour to 40 hours.
If the annealing temperature in the intermediate annealing (hereinafter also referred to as “intermediate annealing temperature”) is less than 700 ° C. or the time for holding in the temperature range of 700 ° C. or more is less than 1 hour, the crystal grains after the intermediate annealing Is not coarsened, the target magnetic characteristics may not be obtained. On the other hand, special equipment is required to raise the intermediate annealing temperature above 900 ° C., resulting in an increase in cost. Moreover, even if it keeps in the temperature range of 700 degreeC or more over 40 hours, an effect will be saturated and it will become disadvantageous in cost. Therefore, the intermediate annealing is held in a temperature range of 700 ° C. to 900 ° C. for 1 hour to 40 hours.
Other conditions for the intermediate annealing are not particularly limited.

3. Second cold rolling step In the second cold rolling step, the intermediate annealed steel sheet obtained by the intermediate annealing step is subjected to cold rolling at a reduction ratio of 50% or more and 85% or less to be 0.10 mm or more and 0.35 mm. The thickness is as follows.
If the rolling reduction in the second cold rolling process is less than 50% or more than 85%, the intended magnetic properties may not be obtained. Therefore, the rolling reduction in the second cold rolling step is set to 50% or more and 85% or less.
Further, for the reason described in the above-mentioned section “A. Non-oriented electrical steel sheet”, the sheet thickness after the second cold rolling is set to 0.10 mm or more and 0.35 mm or less.

4). Finish annealing step In the finish annealing step, finish annealing that satisfies the following formulas (3) and (4) is applied to the cold-rolled steel sheet obtained by the second cold rolling step.
900 ≦ A ≦ 1200 (3)
9-2 × A / 300 ≦ B ≦ 14-2 × A / 300 (4)
Here, A indicates the finish annealing temperature (° C.), and B indicates the tension (MPa) applied during finish annealing.

If the annealing temperature in finish annealing (hereinafter also referred to as “finish annealing temperature”) is less than 900 ° C., the average crystal grain size may be less than 40 μm due to insufficient grain growth, and sufficient magnetic properties may not be obtained. On the other hand, if the finish annealing temperature exceeds 1200 ° C., the grain growth proceeds excessively and the average crystal grain size exceeds 180 μm, and sufficient magnetic properties may not be obtained. In addition, such high temperature annealing may require special equipment, which may increase costs. Therefore, the finish annealing temperature is set to 900 ° C. or more and 1200 ° C. or less.
Regarding the tension at the time of finish annealing, if the annealing is performed at a tension lower than the lower limit defined by the formula (4), the iron loss in the L direction is deteriorated and desired magnetic properties cannot be obtained. On the other hand, if annealing is performed with a tension higher than the upper limit defined by the formula (4), there is a risk of the flatness of the steel sheet and the breakage during annealing. Therefore, the tension at the time of finish annealing is set to a value defined by the equation (4).
Other conditions for finish annealing are not particularly limited.

5. Hot-rolled sheet annealing process The hot-rolled steel sheet to be subjected to the first cold rolling process may be subjected to hot-rolled sheet annealing. By performing hot-rolled sheet annealing, better magnetic properties can be obtained.
Hot-rolled sheet annealing may be performed by either box annealing or continuous annealing. When performing by box annealing, it is preferable to hold | maintain in the temperature range of 700 degreeC or more and 900 degrees C or less for 1 hour or more and 40 hours or less. When performing by continuous annealing, it is preferable to hold | maintain in the temperature range of 900 degreeC or more and 1100 degrees C or less for 1 second or more and 300 seconds or less.
Other conditions for hot-rolled sheet annealing are not particularly limited.

6). Strain relief annealing When the non-oriented electrical steel sheet after finish annealing is subjected to strain relief annealing, the iron loss in the L direction deteriorates. Therefore, the non-oriented electrical steel sheet after finish annealing should not be subjected to strain relief annealing.

7). Hot rolling process The hot-rolled steel sheet used in the cold rolling process can be obtained by subjecting a steel ingot or steel slab (hereinafter also referred to as “slab”) having the above chemical composition and specific resistance to hot rolling. it can.

In hot rolling, a steel having the above chemical composition is made into a slab by a general method such as a continuous casting method or a method of rolling a steel ingot, and is charged into a heating furnace and hot rolled. At this time, when the slab temperature is high, hot rolling may be performed without charging the heating furnace.
Various conditions for hot rolling are not particularly limited.

8). Other Steps After the finish annealing step, according to a general method, a coating for applying an insulating film made of only an organic component, only an inorganic component, or an organic-inorganic composite to the steel sheet surface may be applied. From the viewpoint of reducing the environmental burden, an insulating coating that does not contain chromium may be applied. Further, the coating may be an insulating coating that exhibits adhesive ability by heating and pressing. As a coating material exhibiting adhesive ability, an acrylic resin, a phenol resin, an epoxy resin, a melamine resin, or the like can be used.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

Hereinafter, the present invention will be described specifically by way of examples and comparative examples.
A slab having the chemical composition and specific resistance shown in Table 1 below was hot rolled into a hot rolled steel sheet having a thickness of 1.8 mm to 2.7 mm, and pickled. About these pickled steel sheets, with the exception of a part, the first cold rolling process and the second cold rolling process in which the intermediate annealing is sandwiched without subjecting the hot-rolled sheet annealing to a finished sheet thickness of 0.20 mm to 0.35 mm. A rolled steel sheet was used. The first cold rolling process and the second cold rolling process in which a part is subjected to hot-rolled sheet annealing by box annealing at 800 ° C. for 10 hours or continuous annealing at 1000 ° C. for 20 seconds to sandwich intermediate annealing under various conditions Thus, a cold-rolled steel sheet having a finished sheet thickness was obtained. The remainder was subjected to hot-rolled sheet annealing by continuous annealing at 950 ° C. for 180 seconds to obtain a cold-rolled steel sheet having a finished sheet thickness by a single cold rolling process. These cold-rolled steel sheets were subjected to finish annealing that was held at a temperature of 850 ° C. to 1180 ° C. for 10 seconds under a tension of 1 MPa to 6 MPa to obtain non-oriented electrical steel sheets having an average crystal grain size of 35 μm to 167 μm. A portion of the non-oriented electrical steel sheet thus obtained was subjected to strain relief annealing at 800 ° C. for 2 hours.

These non-oriented electrical steel sheets were magnetized with an iron loss W _{10 / 400L in} the L direction and an iron loss W _{10 / 400C in} the C direction and a magnetizing force of 5000 A / m when magnetized at a magnetic flux density of 1.0 T and a frequency of 400 Hz. The magnetic flux density B _{50L in} the L direction and the magnetic flux density B _50C in the C direction were measured. Then, it was confirmed whether or not the above formula (2) was satisfied for these magnetic characteristic values. The X value in Table 2 is a value calculated from the following formula (5). When the formula (2) is satisfied, X ≧ 0.
X = 40 × {(2 × B 50L + B 50C) /3+t-0.2} -56- (2 × W 10 / 400L + W 10 / 400C) / 3 (5)

  The results are shown in Table 2 together with the production conditions. FIG. 1 shows the relationship between the rolling reduction ratio and the X value in the first cold rolling step and the second cold rolling step, and FIG. 2 shows the relationship between the finish annealing temperature and the tension during finish annealing and the X value. .

Steel plate No. In Nos. 1 to 15, since the rolling reduction of the cold rolling twice, the intermediate annealing conditions, the finish annealing conditions, and the average crystal grain size are within the predetermined ranges, desired magnetic characteristics were obtained. Steel plate No. As shown in FIGS. 16 and 17, desired magnetic properties could be obtained even when hot-rolled sheet annealing was performed.
On the other hand, no. No. 18 was not subjected to cold rolling twice with intermediate annealing in between. 19 and 20, the reduction ratio in the second cold rolling step, No. 21 is the rolling reduction in the first cold rolling process, No. 21. In No. 22, the finish annealing temperature and average grain size, In Nos. 23 and 24, since the tension during finish annealing was out of the predetermined range, none of the desired magnetic properties could be obtained. No. As shown in 25 and 26, when the intermediate annealing is continuous annealing, desired magnetic properties could not be obtained. No. Comparing 1 and 27, when the stress relief annealing at 800 ° C. for 2 hours is performed after the finish annealing, the iron loss in the C direction decreases, but the iron loss in the L direction increases. Could not get.

Claims (5)

In mass%, C: 0.005% or less, Si: 1.0% or more and 4.0% or less, sol. Al: 0.1% to 3.0%, Mn: 0.1% to 3.0%, P: 0.2% or less, S: 0.01% or less, and N: 0.01% or less Containing, the balance consisting of Fe and impurities, having a chemical composition satisfying the following formula (1),
Having a steel structure with an average crystal grain size of 40 μm or more and 180 μm or less,
It has magnetic properties satisfying the following formula (2),
A non-oriented electrical steel sheet having a specific resistance at room temperature of 40 × 10 ⁻⁸ Ωm or more and 75 × 10 ⁻⁸ Ωm or less, and a plate thickness of 0.10 mm or more and 0.35 mm or less.
Si + sol. Al / 2 + Mn / 4 + 5P ≦ 4.0 (1)
(2 × W _{10 / 400L} + W _{10 / 400C} ) / 3
≦ 40 × {(2 × B _50L + B _50C ) /3+t−0.2} −56 (2)
(here,
Si, sol. Al, Mn, P: Content of each element (% by mass)
W _{10 / 400L} : Iron loss in the rolling direction at an excitation magnetic flux density of 1.0 T and an excitation frequency of 400 Hz (W / kg)
W _{10 / 400C} : Iron loss in the direction perpendicular to rolling at an excitation magnetic flux density of 1.0 T and an excitation frequency of 400 Hz (W / kg)
B _50L : Magnetic flux density (T) in the rolling direction when magnetized with a magnetizing force of 5000 A / m
_B50C : Magnetic flux density (T) in the direction perpendicular to the rolling direction when magnetized with a magnetizing force of 5000 A / m
t: Plate thickness (mm)
It is. )   The chemical composition contains one or more selected from the group consisting of Sn: 0.1% or less and Sb: 0.1% or less in mass% instead of part of the Fe. The non-oriented electrical steel sheet according to claim 1.   The non-oriented electrical steel sheet according to claim 1 or 2, wherein the chemical composition contains Ca: 0.01% or less in mass% instead of part of the Fe. A method for producing a non-oriented electrical steel sheet comprising the following steps (A) to (D):
(A) Cold rolling with a reduction ratio of 10% or more and 75% or less on the hot-rolled steel sheet having the chemical composition according to any one of claims 1 to 3 and the specific resistance according to claim 1. A first cold rolling step of applying;
(B) An intermediate annealing step for subjecting the cold-rolled steel sheet obtained by the first cold rolling step to an intermediate annealing for holding in a temperature range of 700 ° C. to 900 ° C. for 1 hour to 40 hours;
(C) A second cold rolling step in which the intermediate annealed steel sheet obtained by the intermediate annealing step is subjected to cold rolling at a reduction ratio of 50% or more and 85% or less to obtain a plate thickness of 0.10 mm or more and 0.35 mm or less. And (D) a finish annealing step of subjecting the cold-rolled steel sheet obtained by the second cold rolling step to finish annealing that satisfies the following formulas (3) and (4).
900 ≦ A ≦ 1200 (3)
9-2 × A / 300 ≦ B ≦ 14-2 × A / 300 (4)
(Here, A represents the finish annealing temperature (° C.), and B represents the tension (MPa) applied during finish annealing.)   The hot-rolled steel sheet to be subjected to the first cold rolling step is subjected to box annealing that is held in a temperature range of 700 ° C. to 900 ° C. for 1 hour to 40 hours or in a temperature range of 900 ° C. to 1100 ° C. for 1 second. The method for producing a non-oriented electrical steel sheet according to claim 4, further comprising a hot-rolled sheet annealing step for performing hot-rolled sheet annealing by continuous annealing for 300 seconds or less.

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