JP2009299102A - Nonoriented silicon steel sheet for rotor and production method therefor - Google Patents

Abstract

A main object of the present invention is to provide a non-oriented electrical steel sheet having excellent mechanical characteristics and magnetic characteristics required as a rotor of a motor that rotates at high speed, and a method for manufacturing the same.
In the present invention, C: 0.06% or less, Si: 1.0% to 4.0%, Mn: 0.05% to 3.0%, Al: 2.% by mass. 5% or less, P: 0.25% or less, S: 0.04% or less, N: 0.02% or less, and at least one element selected from the group consisting of Nb, Zr, Ti and V is represented by the following formula (1) is contained in a range satisfying, the balance is Fe and impurities, the area ratio of the recrystallized portion is less than 90%, the tensile strength in the 45 ° direction from the rolling direction is 600 MPa or more, and the 45 ° direction from the rolling direction. The above object is achieved by providing a non-oriented electrical steel sheet for a rotor characterized by having a magnetic flux density B ₅₀ of 1.68 T or more.
0 <Nb / 93 + Zr / 91 + Ti / 48 + V / 51- (C / 12 + N / 14) <5 × 10 ^-3 (1)
(Here, in the formula (1), Nb, Zr, Ti, V, C and N indicate the content (mass%) of each element.)
[Selection figure] None

Description

  The present invention relates to a non-oriented electrical steel sheet used for a rotor of a high-efficiency motor such as a drive motor for an electric vehicle or a hybrid vehicle, a servo motor for a robot, a machine tool, and the like, and a method for manufacturing the same. In particular, the present invention relates to a non-oriented electrical steel sheet having excellent mechanical characteristics and magnetic characteristics suitable as a rotor of a permanent magnet embedded motor that rotates at high speed, and a method for manufacturing the same.

  Due to the recent increase in global environmental problems, energy conservation and environmental countermeasure technologies have been developed in many fields. The automobile field is no exception, and technologies for reducing exhaust gas and improving fuel efficiency are advancing rapidly. It is no exaggeration to say that electric vehicles and hybrid vehicles are the culmination of these technologies, and the performance of automobile drive motors (hereinafter also simply referred to as “drive motors”) greatly affects the performance of automobiles.

  Many drive motors use permanent magnets, and are composed of a stator (stator) portion provided with windings and a rotor (rotor) portion provided with permanent magnets. Recently, a shape in which a permanent magnet is embedded in a rotor (permanent magnet embedded motor; IPM motor) has become mainstream. Further, with the advancement of power electronics technology, the rotational speed can be arbitrarily controlled, and there is a tendency to increase the speed. Therefore, the rate at which the iron core material is excited in a high frequency range higher than the commercial frequency (50 to 60 Hz) is increased, and not only the magnetic characteristic at the commercial frequency but also the improvement of the magnetic characteristic at 400 Hz to several kHz is required. It has become like this. In addition, since the rotor is constantly subjected not only to centrifugal force during high-speed rotation but also to stress fluctuations associated with fluctuations in the rotational speed, the rotor core material is also required to have mechanical characteristics. In particular, since the IPM motor has a complicated rotor shape, the core material for the rotor needs to have mechanical characteristics sufficient to withstand centrifugal force and stress fluctuation in consideration of stress concentration. Also, in the field of servo motors for robots and machine tools, it is predicted that the rotation speed will increase in the same way as drive motors.

  Conventionally, the stator of the drive motor has been manufactured mainly by stacking non-oriented electrical steel sheets that have been stamped, but the rotor has also been manufactured by a lost wax casting method or a sintering method. This is because the stator requires excellent magnetic properties and the rotor requires robust mechanical properties. However, since the motor performance is greatly influenced by the air gap between the rotor and the stator, the above-described rotor has a problem in that the necessity for precision machining is required and the core manufacturing cost is significantly increased. From the viewpoint of cost reduction, it is only necessary to use a punched electrical steel sheet, but the current situation is that no non-oriented electrical steel sheet having both the magnetic and mechanical properties necessary for the rotor has been found. .

As an electrical steel sheet having excellent mechanical properties, for example, in Patent Document 1, in addition to 3.5 to 7% Si, one or two of Ti, W, Mo, Mn, Ni, Co and Al are used. Steel sheets containing the above in a range not exceeding 20% have been proposed. In this method, solid solution strengthening is used as a steel strengthening mechanism. However, in the case of solid solution strengthening, the cold rolled base metal is also strengthened at the same time, so cold rolling is difficult, and in this method, a special process called warm rolling is indispensable. There is room for improvement such as improvement and yield improvement. Further, the magnetic flux density B ₅₀ obtained is 1.56～1.61T, there is a problem that the magnetic flux density is low as compared with conventional non-oriented electrical steel sheet.

Patent Document 2 discloses a steel sheet containing B and a large amount of Ni in addition to 2.0 to 3.5% Si and 0.1 to 6.0% Mn, and having a crystal grain size of 30 μm or less. Has been proposed. In this method, solid solution strengthening and strengthening by refinement of crystal grain size are used as the strengthening mechanism of steel. However, strengthening by grain refinement is relatively ineffective, so it is essential to contain a large amount of expensive Ni in addition to about 3.0% Si as shown in the example of Patent Document 2. However, the problem of frequent cracking during cold rolling and the problem of increased alloy costs remain. Further, the magnetic flux density B ₅₀ obtained is 1.63～1.65T, there is a problem that the magnetic flux density is low as compared with conventional non-oriented electrical steel sheet.

  Furthermore, Patent Documents 3 and 4 propose steel sheets containing Nb, Zr, B, Ti, V, or the like in addition to 2.0 to 4.0% Si. In these methods, precipitation strengthening by precipitates of Nb, Zr, Ti or V is used in addition to solid solution strengthening by Si. However, since such strengthening by precipitates is relatively ineffective, it is necessary to make Si about 3.0% as shown in Examples of Patent Document 3 and Patent Document 4, and in particular, the method of Patent Document 3 Then, it is necessary to contain a large amount of expensive Ni. Therefore, the problem that cracks frequently occur during cold rolling and the problem of increased alloy costs remain.

  Patent Documents 5 and 6 propose steel sheets containing Ti, Nb and V, or P and Ni, respectively, after limiting Si and Al to 0.03 to 0.5%. In these methods, precipitation precipitation strengthening of carbide and solid solution strengthening of P are used rather than solid solution strengthening by Si. However, in these methods, there is a problem that a strength level necessary for a rotor of a drive motor, which will be described later, cannot be ensured, and as shown in Examples of Patent Documents 5 and 6, 2.0% There is a problem that the above Ni content is essential and the alloy cost is high.

  Further, Patent Document 7 proposes a non-oriented electrical steel sheet for embedded permanent magnet motors with Si: 1.6 to 2.8% and limited crystal grain size, internal oxide layer thickness, and yield point. Has been. However, at the yield point of the steel plate by this method, the strength is insufficient as a rotor of a drive motor that rotates at high speed.

  Patent Document 8 and Patent Document 9 propose a technique that uses precipitation strengthening of Cu as a strengthening mechanism of a non-oriented electrical steel sheet. Although these techniques can achieve excellent magnetic properties and mechanical properties, so-called aging heat treatment for the purpose of precipitation of Cu is required. Therefore, for example, it involves a change in the heat treatment process by the user, and there are many problems for practical use.

  As non-oriented electrical steel sheets stipulated in JIS C 2552, so-called high-grade non-oriented electrical steel sheets (35A210, 35A230, etc.) have the highest alloy content and high strength, but the mechanical property level is high as described above. The strength is insufficient as a rotor of a drive motor that is below the tension electromagnetic steel plate and rotates at high speed.

JP 60-238421 A JP-A-1-162748 Japanese Patent Laid-Open No. 2-8346 JP-A-6-330255 JP 2001-234302 A JP 2002-146493 A JP 2001-172752 A JP 2004-84053 A JP 2004-3000535 A

  As mentioned above, the solid solution strengthening and precipitation strengthening conventionally proposed as methods for increasing the strength of non-oriented electrical steel sheets also strengthens the base material of cold rolling, so cracks frequently occur during cold rolling. In the case of increasing the strength by refining crystal grains, the amount of strengthening is insufficient, so that it is not possible to realize a strength that can be practically used as a rotor. In addition, the present inventors have also examined transformation strengthening, but it has been found that the transformation structure such as martensite significantly increases iron loss in transformation strengthening, and realizes magnetic characteristics that can be practically used as a rotor application. I can't. Furthermore, increasing the strength by precipitation strengthening of Cu requires the addition of a heat treatment step, and there remains a problem in practical use. Under such circumstances, the present inventors have focused on increasing the strength by strengthening dislocations, and disclosed in JP-A-2006-9048, JP-A-2006-70296, JP-A-2007-16278, JP-A-2007-23351, No. 2007-31755 proposes a non-oriented electrical steel sheet for rotors. The technical essence is to suppress the recrystallization that proceeds during the soaking process by solid solution Nb, Zr, Ti, V, and to control the steel structure to a recovery structure. According to the present technology, it is possible to realize a strength that can be practically used as a rotor application without cracking during cold rolling, which was a problem of the prior art. Further, there is no need to add an aging heat treatment step such as strengthening by precipitation strengthening of Cu.

  Thus, the non-oriented electrical steel sheet for rotors by strengthening dislocations that overcomes the problems of the prior art, but in order to further improve the fatigue characteristics, which is the most important performance as the practical performance of the rotor, The conventional examination which evaluates only by the rolling direction was insufficient. Further, the above-described conventional technique has a problem that the magnetic flux density is lowered. However, it has been desired to further improve the magnetic flux density even in the non-oriented electrical steel sheet for rotors by dislocation strengthening.

  The present invention has been made in view of the above problems, and provides a non-oriented electrical steel sheet having excellent mechanical characteristics and magnetic characteristics necessary as a rotor of a motor that rotates at high speed, and a method for manufacturing the same. The main purpose.

  The present inventors have intensively studied to improve the practical performance of a rotor using a non-oriented electrical steel sheet for rotors utilizing dislocation strengthening. First, as a result of investigating the fatigue characteristics, which is the most important performance, it was found that even in a rotor using the same steel plate, there is a difference in fatigue characteristics. As a result of analyzing the cause focusing on the anisotropy of the steel sheet, it was found that the mechanical properties showed significant anisotropy, and it was easy to induce fatigue failure when repeated loading was applied in the direction of the lowest strength. did. There was no variation in strength anisotropy for each steel sheet, and it was found to be anisotropy peculiar to non-oriented electrical steel sheets utilizing dislocation strengthening. Therefore, in the non-oriented electrical steel sheet for rotors by dislocation strengthening, the direction in which fatigue failure is likely to occur is always the same, and if the direction is strengthened, fatigue failure in all directions is inevitably suppressed, and the fatigue characteristics of the rotor Can be improved reliably. Furthermore, as a result of investigating the anisotropy of the magnetic flux density, it was found that the magnetic flux density could be greatly improved if the direction in which fatigue fracture is likely to occur was strengthened. These findings cannot be grasped by the conventional evaluation method that evaluates the mechanical characteristics only in the rolling direction or by the average characteristics in the plate surface, and can surely contribute to the improvement of the practical performance of the rotor. . The above-described conventional steel sheets listed as electromagnetic steel sheets having excellent mechanical properties are also evaluated for mechanical properties only in the rolling direction or by average properties in the plate surface, and the strength obtained by such evaluation is the rotor. The probability of being an indicator of fatigue fracture suppression is low. By increasing the strength of a specific direction of a steel plate having specific anisotropy, the practical performance of the rotor can be reliably improved. These new findings were obtained to complete the present invention.

That is, the present invention is mass%, C: 0.06% or less, Si: 1.0% or more and 4.0% or less, Mn: 0.05% or more and 3.0% or less, Al: 2.5% Hereinafter, at least one element selected from the group consisting of P: 0.25% or less, S: 0.04% or less, N: 0.02% or less, Nb, Zr, Ti and V is represented by the following formula (1 ), The balance is Fe and impurities, the area ratio of the recrystallized portion is less than 90%, the tensile strength in the 45 ° direction from the rolling direction is 600 MPa or more, and the magnetic flux is in the 45 ° direction from the rolling direction. Provided is a non-oriented electrical steel sheet for rotors having a density B ₅₀ of 1.68 T or more.
0 <Nb / 93 + Zr / 91 + Ti / 48 + V / 51- (C / 12 + N / 14) <5 × 10 ^-3 (1)
(Here, in the formula (1), Nb, Zr, Ti, V, C and N indicate the content (mass%) of each element.)

  In the present invention, the strength and magnetic flux density can be increased by appropriate control of the steel composition and the area ratio of the recrystallized portion, so that a non-oriented electrical steel sheet for rotors with good mechanical and magnetic properties can be obtained. it can. As a result, the practical performance of the rotor can be improved.

  Moreover, it is preferable that the non-oriented electrical steel sheet for rotors of this invention contains Nb more than 0.02% instead of a part of said Fe. This is because Nb enhances the effect of suppressing recrystallization and increases the strength and productivity of the steel sheet.

Furthermore, the non-oriented electrical steel sheet for rotors according to the present invention contains at least one element selected from the group consisting of Cu, Ni, Cr, Mo, Co, and W instead of a part of the Fe described below. It is preferable to contain by mass%.
Cu: 0.01% to 8.0% Ni: 0.01% to 2.0% Cr: 0.01% to 15.0% Mo: 0.005% to 4.0% Co: 0.01% or more and 4.0% or less W: 0.01% or more and 4.0% or less The strength of the steel sheet can be further increased by the action of increasing the strength of the above elements.

Further, the non-oriented electrical steel sheet for a rotor of the present invention contains at least one element selected from the group consisting of Sn, Sb, Se, Bi, Ge, Te and B instead of a part of the Fe. It is preferable to contain by the following mass%.
Sn: 0.5% or less Sb: 0.5% or less Se: 0.3% or less Bi: 0.2% or less Ge: 0.5% or less Te: 0.3% or less B: 0.01% or less This is because recrystallization can be effectively suppressed by grain boundary segregation of elements.

Furthermore, the non-oriented electrical steel sheet for a rotor of the present invention contains at least one element selected from the group consisting of Ca, Mg and REM in the following mass%, instead of a part of the Fe. Is preferred.
Ca: 0.03% or less Mg: 0.02% or less REM: 0.1% or less Magnetic properties can be further improved by the sulfide form controlling action of the above elements.

  Further, the present invention provides a hot rolling process in which hot rolling is performed on a steel ingot or steel slab having the above steel composition, and heat in which hot rolled steel sheet obtained by the hot rolling process is subjected to hot rolling sheet annealing. A sheet annealing process, a cold rolling process in which the steel sheet after the hot-rolled sheet annealing is subjected to a single cold rolling to obtain a final sheet thickness, and a cold-rolled steel sheet obtained by the cold rolling process are subjected to soaking treatment. A non-oriented electrical steel sheet for a rotor having a soaking process, wherein the area ratio of the recrystallized portion of the steel sheet before the cold rolling process is less than 40%, and the soaking process in the soaking process is performed. Provided is a method for producing a non-oriented electrical steel sheet for a rotor, characterized in that the heat treatment temperature is 700 ° C. or higher and 900 ° C. or lower.

  According to the present invention, the non-oriented electrical steel sheet for rotors utilizing dislocation strengthening can improve the strength in the direction in which fatigue failure is most likely to be induced and also increase the magnetic flux density. Can be produced.

  According to the present invention, a non-oriented electrical steel sheet having excellent mechanical properties and magnetic properties necessary as a rotor of a motor that rotates at high speed can be stably manufactured without causing an increase in alloy costs and an increase in heat treatment processes. Is possible. Therefore, it can sufficiently cope with the increase in the rotational speed in the field of drive motors of electric vehicles and hybrid vehicles, and its industrial value is extremely high.

  The characteristics required for the electromagnetic steel sheet used in the rotor referred to in the present invention are mechanical characteristics first and indicate tensile strength. This is intended to suppress not only the deformation of the rotor during high-speed rotation but also the fatigue failure caused by stress fluctuations.

  The second characteristic necessary for the electromagnetic steel sheet used for the rotor is the magnetic flux density. In a motor that utilizes reluctance torque, such as an IPM motor, the magnetic flux density of the material used for the rotor also affects the torque. If the magnetic flux density is low, a desired torque cannot be obtained.

  Furthermore, the third characteristic necessary for the electromagnetic steel sheet used for the rotor is iron loss. The iron loss generated in the rotor does not dominate the motor efficiency itself, but the permanent magnet is demagnetized by the iron loss in the rotor, that is, heat generation, so that the motor performance is indirectly deteriorated. Accordingly, it is recalled that the upper limit of the iron loss value of the material used for the rotor is determined from the viewpoint of the heat resistance temperature of the permanent magnet, and is allowed even if the iron loss value is higher than the material used for the stator.

  The present inventors have made various studies on the steel structure to be possessed by the non-oriented electrical steel sheet having both magnetic properties and mechanical properties suitable for these rotors. As a result, the strength of the cold-rolled base metal is strengthened by solid solution strengthening and precipitation strengthening, so it is inevitable to break during cold rolling. And it turned out that iron loss increases remarkably in transformation structures, such as martensite. Therefore, attention has been focused on increasing the strength by strengthening dislocations, which has not been studied at all. And we obtained the knowledge that the dislocations remaining in the recovery state have a relatively small effect on iron loss, and this technology is completely opposite to the completely recrystallized ferrite structure, which is the technical recognition of conventional non-oriented electrical steel sheets. Based on the idea, the magnetic properties and mechanical properties required for the rotor described above can be obtained by making the structure of the steel sheet a recovered structure in which a large amount of dislocations remain (hereinafter referred to as “recovered structure”). I found out that Furthermore, in order to obtain a recovery structure, it was found that the contents of Nb, Zr, Ti and V in a solid solution state must be within a predetermined range, and based on these findings, dislocation strengthening was utilized. Non-oriented electrical steel sheets for rotors have been proposed (Japanese Patent Laid-Open Nos. 2006-9048, 2006-70296, 2007-16278, 2007-23351, and 2007-31755). The present inventors have studied in detail for the purpose of further improving the practical performance of a rotor using these non-oriented electrical steel sheets for rotors, and focusing on the anisotropy of mechanical properties, strengthening of dislocations. The present inventors have found that the practical performance of the utilized non-oriented electrical steel sheet for rotors can be reliably improved, and completed the present invention. Hereinafter, the knowledge that led to the completion of the present invention will be described.

  By mass%, C: 0.002%, Si: 3.0%, Mn: 0.2%, Al: 1.0%, N: 0.002%, P: 0.01%, S: 0.00. Hot rolled to 002%, Nb: 0.08% steel to 2.3 mm, then hot-rolled sheet annealed at 800 ° C. for 10 hours, further cold rolled to 0.35 mm, 750 ° C. And soaking was performed for 20 seconds. A rotor of an IPM motor was manufactured from the obtained steel plate and subjected to a fatigue test. As a result, it has been found that even in a rotor manufactured from the same steel plate, a difference in fatigue characteristics may occur. As a result of analyzing this cause, it was clear that remarkable anisotropy was observed in the mechanical characteristics represented by tensile strength, and it was clear that the fatigue characteristics differed depending on the direction of repeated stress loading even in the same steel sheet. became.

  The specific anisotropy is as shown in FIG. 1 and is characterized by a low tensile strength in the 45 ° direction from the rolling direction. FIG. 2 shows the results of a fatigue test carried out at a stress ratio of 0.05 and a repetition rate of 60 Hz using a fatigue test piece having a rolling direction, a 45 ° direction from the rolling direction, and a perpendicular direction from the rolling direction as the longitudinal direction. As shown in FIG. 2, it can be seen that the fatigue characteristics in the 45 ° direction from the rolling direction are inferior to those in the other directions.

  As a result of the same investigation on various non-oriented electrical steel sheets utilizing dislocation strengthening, no difference was found between the steel sheets in the anisotropy of such tensile strength, and non-oriented electrical steel sheets utilizing dislocation strengthening. It turned out to be a characteristic anisotropy. Further, due to this, in the non-oriented electrical steel sheet for rotors by dislocation strengthening, the direction in which fatigue failure is likely to occur was always found to be 45 ° from the rolling direction. From these, in the case of increasing the strength by strengthening dislocations, if the tensile strength in the 45 ° direction from the rolling direction is improved, the fatigue characteristics in all directions are inevitably improved, and the fatigue characteristics of the rotor are surely improved. I came to remember that I could do it.

  The anisotropy of the mechanical properties of dislocation strengthened steel is due to the recovery structure and the rolling texture remains strong. Therefore, as a result of investigating the magnetic flux density that is also strongly influenced by the texture, it was found that the higher the magnetic flux density in the 45 ° direction from the rolling direction, the higher the tensile strength in the 45 ° direction from the rolling direction. In order to strongly leave the rolling texture, it is effective to suppress the disappearance of the rolling texture formed by hot rolling during hot-rolled sheet annealing. Therefore, it is effective to suppress recrystallization during hot-rolled sheet annealing, and the area ratio of the recrystallized part of the steel sheet after hot-rolled sheet annealing, that is, the area ratio of the recrystallized part of the steel sheet before cold rolling is predetermined. It is necessary to be in the range.

  These findings cannot be grasped by the conventional evaluation method that evaluates the mechanical properties only in the rolling direction or by the average properties in the plate surface, and were found for the first time after conducting a fatigue test as a rotor. is there. The above-described conventional steel sheets listed as electromagnetic steel sheets having excellent mechanical properties are also evaluated for mechanical properties only in the rolling direction or by average properties in the plate surface, and the strength obtained by such evaluation is the rotor. The probability of being an indicator of fatigue fracture suppression is low. By increasing the strength of a specific direction for a steel plate with specific anisotropy, such as a non-oriented electrical steel plate utilizing dislocation strengthening, the practical performance of the rotor can be reliably improved. . There is no so-called variation in the anisotropy of the non-oriented electrical steel sheet utilizing dislocation strengthening. Therefore, it is easy to manage in terms of steel plate manufacturing, and easily reflected in the design of the rotor. This is similar to the fact that the anisotropy of the magnetic properties of the unidirectional electrical steel sheet having strong anisotropy is sufficiently reflected in the design of the transformer. These new findings were obtained to complete the present invention.

Hereinafter, the non-oriented electrical steel sheet for rotors of the present invention and the manufacturing method thereof will be described in detail.
A. Non-oriented electrical steel sheet for rotors The non-oriented electrical steel sheet for rotors of the present invention is mass%, C: 0.06% or less, Si: 1.0% or more and 4.0% or less, Mn: 0.00%. 05% or more and 3.0% or less, Al: 2.5% or less, P: 0.25% or less, S: 0.04% or less, N: 0.02% or less, Nb, Zr, Ti and V Containing at least one element selected from the group within a range satisfying the above formula (1), the balance being Fe and impurities, the area ratio of the recrystallized portion being less than 90%, 45 ° direction from the rolling direction The tensile strength is 600 MPa or more, and the magnetic flux density B _{50 in the} 45 ° direction from the rolling direction is 1.68 T or more.
“%” Indicating the content of each element means “mass%” unless otherwise specified.
Hereinafter, the steel composition, the area ratio of the recrystallized portion, the tensile strength, and the magnetic flux density in the non-oriented electrical steel sheet for rotor of the present invention will be described.

1. Steel composition (1) C
Since C is combined with Nb, Zr, Ti and V to form a precipitate, it leads to a decrease in the content of solid solution Nb, Zr, Ti and V. Therefore, in the present invention in which recrystallization is suppressed by solute Nb, Zr, Ti and V, the C content is preferably reduced. However, excessive reduction of the C content increases the steelmaking cost, and even if the C content is large, if the contents of Nb, Zr, Ti and V are increased accordingly, solid solution Nb, Zr, Ti In view of securing the V and V contents, the upper limit of the C content is set to 0.06%. Preferably it is 0.04% or less, More preferably, it is 0.02% or less. In particular, if the C content is 0.01% or less, the contents of Nb, Zr and Ti necessary to satisfy the condition of Nb / 93 + Zr / 91 + Ti / 48 + V / 51− (C / 12 + N / 14)> 0 This is desirable from the viewpoint of alloy cost.

(2) Si
Si is an element that has the effect of increasing electrical resistance and reducing eddy current loss. However, when a large amount of Si is contained, cracks during cold rolling are induced, and the manufacturing cost increases due to a decrease in the yield of the steel sheet. Therefore, the Si content is 4.0% or less. From the viewpoint of suppressing cracking, 3.5% or less is preferable. From the viewpoint of increasing the strength of the steel sheet by solid solution strengthening and reducing iron loss, the Si content is set to 1.0% or more. Preferably it is 1.2% or more.

(3) Mn
Mn has the effect of increasing electrical resistance and reducing eddy current loss, similar to Si. However, if Mn is contained in a large amount, the alloy cost increases, so the upper limit of the Mn content is 3.0%. On the other hand, the lower limit of the Mn content is determined from the viewpoint of fixing S, and is 0.05%.

(4) Al
Al increases eddy current loss in the same manner as Si because it increases electric resistance. However, when Al is contained in a large amount, the alloy cost increases and the leakage of magnetic flux occurs due to the decrease of the saturation magnetic flux density, so that the motor efficiency decreases. From these viewpoints, the upper limit of the Al content is 2.5%. Moreover, when using Al as a deoxidizer, it is necessary to contain 0.01% or more, but since Si may be used as a deoxidizer, the lower limit of the Al content is not particularly limited.

(5) P
P has the effect of increasing the strength of the steel sheet by solid solution strengthening, but when it contains a large amount of P, it induces cracks during cold rolling. Therefore, the P content is 0.25% or less.

(6) S
S is an impurity inevitably mixed in the steel. However, since the cost increases to reduce it in the steelmaking stage, the upper limit of the S content is 0.04%.

(7) N
Since N is combined with Nb, Zr, Ti and V to form a precipitate, the content of solute Nb, Zr, Ti and V is reduced. Therefore, in the present invention in which recrystallization is suppressed by solute Nb, Zr, Ti and V, the N content is preferably reduced. However, in view of the fact that the contents of solute Nb, Zr, Ti and V can be secured if the contents of Nb, Zr, Ti and V are increased accordingly even if the N content is large, The upper limit is 0.02%. Preferably it is 0.01% or less, More preferably, it is 0.005% or less. If the N content is 0.005% or less, the contents of Nb, Zr, Ti and V necessary to satisfy the condition of Nb / 93 + Zr / 91 + Ti / 48 + V / 51− (C / 12 + N / 14)> 0 This is desirable from the viewpoint of alloy cost.

(8) Nb, Zr, Ti and V
In order to suppress the disappearance and recrystallization of dislocations during the soaking process and obtain a recovery structure, it is necessary to contain Nb, Zr, Ti or V in a solid solution state in which no precipitate is formed. For that purpose, it is necessary to contain Nb, Zr, Ti or V in a larger amount than C and N in terms of atomic fraction, and at least one selected from the group consisting of Nb, Zr, Ti and V It is necessary to contain seed elements in a range that satisfies the following formula (2).
0 <Nb / 93 + Zr / 91 + Ti / 48 + V / 51- (C / 12 + N / 14) (2)
(Here, in the formula (2), Nb, Zr, Ti, V, C and N indicate the content (mass%) of each element.)

The greater the content of solute Nb, Zr, Ti, and V, the greater the effect of suppressing the disappearance and recrystallization of dislocations, and the more effective is the recovery structure. However, when excessively containing solute Nb, Zr, Ti and V, cracks may occur during cold rolling. The upper limit of the content of solid solution Nb, Zr, Ti and V is determined from this viewpoint, and Nb, Zr, Ti and V must be contained within the range represented by the following formula (1).
0 <Nb / 93 + Zr / 91 + Ti / 48 + V / 51- (C / 12 + N / 14) <5 × 10 ^-3 (1)
(Here, in the formula (1), Nb, Zr, Ti, V, C and N indicate the content (mass%) of each element.)

  Here, considering sulfides, the contents of Nb, Zr, Ti and V in a solid solution state are also affected by the S content. However, since the influence of S on the recrystallization inhibitory effect was not recognized within the range of the S content described above, the above formula (1) in which the S term was omitted was adopted in the present invention. The reason why the influence of S was not recognized is not clear, but it is considered that S was fixed by Mn by, for example, crystallization as MnS from a region where S at the end of solidification was concentrated.

  Among the solid solution Nb, Zr, Ti and V, since the recrystallization inhibiting effect of the solid solution Nb is the largest, it is preferable to actively contain Nb in the present invention, and the Nb content exceeds 0.02%. Is preferred. More preferably, it is 0.04% or more.

(9) Cu, Ni, Cr, Mo, Co and W
In the present invention, since recrystallization is not reduced but recrystallization itself is suppressed, both magnetic properties and mechanical properties are achieved, so Cu, Ni, At least one element selected from the group consisting of Cr, Mo, Co, and W can be contained. Since these elements have the effect of increasing the strength of the steel sheet, they are effective and preferable for further increasing the strength of the steel sheet.

  Cu has the effect of increasing the specific resistance of the steel sheet and reducing iron loss. However, excessive inclusion of Cu leads to surface defects and cracking during cold rolling, so the Cu content is preferably 0.01% or more and 8.0% or less. The present invention can achieve the magnetic characteristics and mechanical characteristics required for a rotor without using Cu precipitation strengthening, so even if Cu is contained, the so-called aging heat treatment type non-oriented electrical steel sheet exemplified as the prior art Needless to say, it is essentially different.

  If Ni and Mo are excessively contained, cracks during cold rolling and an increase in cost are caused. Therefore, the Ni content is 0.01% or more and 2.0% or less, and the Mo content is 0.005% or more. It is preferable to make it 0% or less.

  Cr has the effect of increasing the specific resistance of the steel sheet and reducing iron loss. It also has the effect of improving corrosion resistance. However, since the cost increases when Cr is excessively contained, the Cr content is preferably 0.01% or more and 15.0% or less.

  Since Co and W are excessively contained and cost increases, the Co content may be 0.01% or more and 4.0% or less, and the W content may be 0.01% or more and 4.0% or less. preferable.

(10) Sn, Sb, Se, Bi, Ge, Te and B
Since the present invention aims to achieve both magnetic properties and mechanical properties by suppressing recrystallization, it consists of Sn, Sb, Se, Bi, Ge, Te, and B, which have the effect of suppressing recrystallization by grain boundary segregation. It is preferable to contain at least one element selected from the group. When these elements are contained, the content of each element is Sn: 0.5% or less, Sb: 0.5% or less, from the viewpoint of suppressing the occurrence of cracks and cost increase in the hot rolling process. Preferably, Se is 0.3% or less, Bi is 0.2% or less, Ge is 0.5% or less, Te is 0.3% or less, and B is 0.01% or less. In order to reliably obtain the recrystallization suppressing effect by these elements, the content of each element is Sn: 0.001% or more, Sb: 0.0005% or more, Se: 0.0005% or more, Bi: 0.0005. % Or more, Ge: 0.001% or more, Te: 0.0005% or more, and B: 0.0002% or more are preferable.

(11) Ca, Mg and REM
Since the influence of S on the recrystallization suppression effect was not recognized within the range of the S content defined in the present invention, in the present invention, it is composed of Ca, Mg and REM for the purpose of improving magnetic properties by controlling the form of sulfide. At least one selected from the group can be contained.
Here, REM refers to a total of 17 elements of 15 elements having atomic numbers 57 to 71 and 2 elements of Sc and Y.

  When these elements are contained, the content of each element is preferably Ca: 0.03% or less, Mg: 0.02% or less, and REM: 0.1% or less. In order to reliably obtain the above effects, the content of each element is preferably set to Ca: 0.0001% or more, Mg: 0.0001% or more, and REM: 0.0001% or more.

(12) Others Since the present invention is different from the conventional technique based on the recrystallized structure, it enhances the strength by using a recovered structure in which many dislocations remain, and thus the conventional technique based on the recrystallized structure. It is possible to tolerate the inclusion of elements that were limited in For example, Ta, Hf, As, Au, Be, Zn, Pb, Tc, Re, Ru, Os, Rh, Ir, Pd, Pt, Ag, Cd, Hg, and Po are limited to 0.01% or less in total. However, it can be tolerated up to 0.1%.

2. Area ratio of recrystallized portion With the progress of recovery, which is the previous stage of recrystallization, the area ratio of the recrystallized portion remains zero and the yield point and the tensile strength decrease. After the start of recrystallization, the yield point and the tensile strength further decrease with an increase in the area ratio of the recrystallized portion. Here, the area ratio of the recrystallized portion is determined from the viewpoint of securing the mechanical characteristics necessary for the rotor, and is less than 90%. Preferably it is 70% or less, More preferably, it is 40% or less, and if it is 30% or less, it is more preferable from a viewpoint of fatigue fracture suppression. From the viewpoint of mechanical properties, the area ratio of the recrystallized part is preferably as low as possible, and the area ratio of the recrystallized part is preferably set to zero so that it is completely in an unrecrystallized state (recovered structure).

  Here, the area ratio of the recrystallized portion indicates the ratio of the recrystallized grains in the visual field in the longitudinal sectional structure photograph of the non-oriented electrical steel sheet for rotors of the present invention. It can be measured originally. As the longitudinal cross-sectional structure photograph, an optical microscope photograph can be used. For example, a photograph taken at a magnification of 100 times may be used.

3. Tensile strength With the drive motors of electric and hybrid vehicles in recent years, the tensile strength is reduced from the viewpoint of fatigue fracture suppression due to the complexity of the rotor shape, the larger rotor diameter, the larger embedded permanent magnet, etc. 600 MPa or more is necessary. Since the present invention is premised on a non-oriented electrical steel sheet utilizing dislocation strengthening, it requires 600 MPa or more in the tensile strength in the 45 ° direction from the rolling direction due to its unique anisotropy. Preferably it is 650 MPa or more, More preferably, it is 680 MPa or more. By setting the tensile strength in this direction within the above range, fatigue failure can be suppressed / reduced in all directions of the steel sheet.

4). Magnetic flux density The electrical steel sheet having excellent mechanical properties according to the prior art has a problem that the magnetic flux density is lower than that of a normal non-oriented electrical steel sheet. In the present invention, this point is also improved, and the magnetic flux density B ₅₀ in the 45 ° direction from the rolling direction is set to 1.68 T or more. Increasing the magnetic flux density in this direction also has the effect of improving the tensile strength. Therefore, it is preferably 1.69 T or more, more preferably 1.70 T or more.

B. Next, the manufacturing method of the non-oriented electrical steel sheet for rotors of this invention is demonstrated. The method for producing a non-oriented electrical steel sheet for a rotor of the present invention includes a hot rolling process in which hot rolling is performed on a steel ingot or steel slab having the above steel composition, and a hot process obtained by the hot rolling process. It is obtained by a hot-rolled sheet annealing process for subjecting a rolled steel sheet to hot-rolled sheet annealing, a cold-rolling process in which the steel sheet after the hot-rolled sheet annealing is subjected to a single cold rolling to obtain a final sheet thickness, and the cold-rolling process. A non-oriented electrical steel sheet for a rotor having a soaking process for subjecting the cold-rolled steel sheet to a soaking process, wherein the area ratio of the recrystallized portion of the steel sheet before the cold-rolling process is 40% The soaking temperature in the soaking process is 700 ° C. or more and 900 ° C. or less.

According to the present invention, by setting the area ratio of the recrystallized portion of the steel sheet before cold rolling within a predetermined range, the effect of improving the mechanical and magnetic properties in the 45 ° direction from the rolling direction is produced, and the soaking process Recrystallization is suppressed by keeping the temperature at a predetermined range, and the recovery structure is mainly composed of a recovery structure in which a large amount of dislocations remain by suppressing the disappearance of dislocations introduced during processing to a predetermined plate thickness. This makes it possible to increase the strength. In addition, since there is no need to increase the strength of the steel sheet used for cold rolling as in the conventional solid solution strengthening and precipitation strengthening, that is, the base material of cold rolling, it is possible to suppress breakage during cold rolling. . Moreover, neither expensive steel components as in the prior art nor special processes are required.
Hereinafter, each process in the manufacturing method of such a non-oriented electrical steel sheet for rotors is demonstrated.

(1) Hot rolling process The hot rolling process in this invention is a process of hot-rolling the steel ingot or steel slab (henceforth "slab") provided with the steel composition mentioned above. In addition, about the steel composition of a steel ingot or a steel piece, since it is the same as that of what was described in the term of the "A. non-oriented electrical steel sheet for rotors" mentioned above, description here is abbreviate | omitted.

In this step, the steel having the above-described 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 in a heating furnace and subjected to hot rolling. At this time, when the slab temperature is high, hot rolling may be performed without charging the heating furnace.
The slab heating temperature is not particularly limited, but is preferably 1000 ° C. to 1300 ° C. from the viewpoint of cost and hot rolling properties. More preferably, it is 1050 degreeC-1250 degreeC.
Various conditions for hot rolling are not particularly limited, but the finishing temperature is preferably 700 ° C. to 950 ° C., and the winding temperature is preferably 750 ° C. or less.

(2) Hot-rolled sheet annealing process In this invention, hot-rolled sheet annealing is given to the hot-rolled steel sheet obtained by the said hot-rolling process. By performing the hot-rolled sheet annealing process, the ductility of the steel sheet is improved, and breakage in the cold rolling process can be suppressed.
Hot-rolled sheet annealing may be performed by either box annealing or continuous annealing, but as described later, the area ratio of the recrystallized portion of the steel sheet before cold rolling needs to be within a predetermined range. .

(3) Cold rolling process The cold rolling process in this invention is a process which makes the steel plate after the said hot-rolled sheet annealing process the final board thickness by one cold rolling. In this step, the steel sheet after the hot-rolled sheet annealing step is subjected to one cold rolling and finished to a predetermined plate thickness.

  The plate thickness is preferably 0.15 mm or more and 0.80 mm or less. If the plate thickness is less than the above range, excessive processing is required, and there is a risk that ear cracks or breakage may occur during cold rolling. Moreover, not only productivity in the soaking process described later is deteriorated, but also the space factor and caulking strength may be lowered. On the other hand, if the plate thickness exceeds the above range, the eddy current loss increases, and thus the motor efficiency may be reduced. Moreover, since the amount of dislocations introduced during cold rolling is reduced, the mechanical properties of the product may be deteriorated. From such a viewpoint, a more preferable plate thickness is 0.20 mm or more and 0.70 mm or less.

  In cold rolling at least twice with intermediate annealing, the rolling texture formed by hot rolling and cold rolling tends to disappear during intermediate annealing, and the mechanical properties in the 45 ° direction from the rolling direction deteriorate. Therefore, the present invention is limited to one cold rolling.

(4) Soaking process The soaking process in the present invention is a process of soaking the cold-rolled steel sheet obtained by the above-described cold rolling process at 700 ° C. or more and 900 ° C. or less. The gist of the present invention is to suppress the recrystallization that proceeds in the soaking process and leave the dislocations. Therefore, when the recrystallization suppressing effect is small, it is necessary to make the soaking temperature significantly lower than the soaking temperature of a normal non-oriented electrical steel sheet. Assuming soaking in a continuous annealing line of a normal non-oriented electrical steel sheet, it cannot be subjected to soaking until the furnace temperature is lowered and stabilized. Furthermore, once the furnace temperature is lowered, the normal non-oriented electrical steel sheet cannot be subjected to soaking treatment until the furnace temperature rises to the soaking temperature of the normal non-oriented electrical steel sheet and stabilizes. . From these facts, it can be easily imagined that the productivity is remarkably lowered when the recrystallization suppressing effect is small.

  In the present invention, since it is subjected to soaking in a state in which proper amounts of solute Nb, Zr, Ti and V are contained, the effect of suppressing recrystallization is great. Therefore, even if the soaking temperature in the soaking process is high, a recovery structure can be obtained, and it is not necessary to provide a special soaking temperature opportunity, so that productivity can be improved. Specifically, if the soaking temperature is 900 ° C. or lower, desired mechanical properties can be obtained. From the viewpoint of mechanical properties, it is preferably 850 ° C. or lower, more preferably 800 ° C. or lower. The lower the soaking temperature is, the more the recrystallization progress is suppressed. However, the space factor when the steel plate is laminated on the rotor without being corrected may be lowered. Moreover, when soaking temperature is low, it leads to an iron loss increase. Furthermore, when the soaking temperature is low, the productivity is significantly reduced as described above. From these viewpoints, the lower limit of the soaking temperature is set to 700 ° C. These soaking temperatures are within the range to be implemented with a normal non-oriented electrical steel sheet, and do not hinder productivity.

  In the present invention, soaking is performed in a continuous annealing line from the viewpoint of productivity. In the box annealing, the flatness of the steel sheet may be lowered or the shape may be deteriorated due to coil winding (also referred to as a coil set) due to being subjected to annealing in a coil state. This is because a correction process for correcting the flatness and shape may be necessary later, and the productivity is greatly deteriorated.

(5) Area ratio of recrystallized portion of steel plate before cold rolling In the present invention, it is necessary to improve the tensile strength in the 45 ° direction from the rolling direction in order to improve the practical performance of the rotor. For this purpose, it is important to suppress the disappearance of the rolling texture formed by hot rolling during hot-rolled sheet annealing. Therefore, it is important to suppress recrystallization during hot-rolled sheet annealing, and the area ratio of the recrystallized part of the steel sheet after hot-rolled sheet annealing, that is, the area ratio of the recrystallized part of the steel sheet before cold rolling is 40. %. From the viewpoint of improving the tensile strength in the 45 ° direction from the rolling direction, the lower the area ratio of the recrystallized portion of the steel sheet before cold rolling, the better. Therefore, the area ratio is set to zero and the completely recrystallized state (recovered structure) ) Is preferable. The method for measuring the area ratio of the recrystallized portion is as described above. Since it is thicker than the thickness of the product after hot-rolled sheet annealing, for example, a longitudinal sectional structure photograph with a photographing magnification of 50 times may be used.

  Here, the area ratio of the recrystallized portion of the steel sheet before cold rolling is within a predetermined range excludes adjusting the area ratio of the recrystallized portion to a predetermined range by omitting hot-rolled sheet annealing. . This is because cracking during cold rolling, which was a problem of the prior art, occurs due to omission of hot-rolled sheet annealing. In the present invention, it is important to perform hot-rolled sheet annealing and adjust the area ratio of the recrystallized portion of the steel sheet before cold rolling to a predetermined range.

(6) Others In the present invention, after the soaking process, according to a general method, a coating process is performed in which an insulating coating composed of only an organic component, only an inorganic component, or an organic-inorganic composite is applied to the steel sheet surface. Is preferred. Further, the coating process may be a process of applying an insulating coating that exhibits adhesive ability by heating and pressurizing. 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.

  Note that the non-oriented electrical steel sheet for rotors manufactured according to the present invention is the same as that described in the above-mentioned section “A. Non-oriented electrical steel sheet for rotors”, so the description here is as follows. Omitted.

  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.

[Examples 1 to 18]
Steels having the steel compositions shown in Table 1 below are melted in vacuum, these steels are heated to 1150 ° C, hot-rolled at a finishing temperature of 820 ° C, wound up at 580 ° C, and the thickness is 2.1 mm. A hot rolled steel sheet was obtained. Thereafter, hot-rolled sheet annealing was performed under various conditions, and finished to a sheet thickness of 0.35 mm by one cold rolling. The obtained cold-rolled steel sheet was subjected to soaking treatment that was held at various temperatures for 20 seconds.

[Comparative Examples 1 to 10]
Using steel having the steel composition shown in Table 1 above, hot rolling was performed under various conditions after hot rolling in the same manner as in Examples 1 to 18, and Comparative Examples 1 to 1 were performed in a single cold rolling. 3 and 5-8 were finished to a plate thickness of 0.35 mm, Comparative Example 4 to 0.7 mm, Comparative Example 9 to 1.0 mm, and Comparative Example 10 to 0.12 mm. The obtained cold-rolled steel sheet was subjected to soaking treatment that was held at various temperatures for 20 seconds. Here, the total of Ta, Hf, As, Au, Be, Zn, Pb, Tc, Re, Ru, Os, Rh, Ir, Pd, Pt, Ag, Cd, Hg, and Po in steels A to V The content was 0.01% or less.

[Evaluation]
About the steel plates of Examples 1 to 18 and Comparative Examples 1 to 10, the area ratio of the recrystallized portion of the steel plate before cold rolling, the area ratio of the recrystallized portion of the steel plate after soaking, the mechanical properties, and the magnetic properties were evaluated. .

An optical micrograph of the longitudinal section of the steel sheet taken at a magnification of 50 times was taken at a magnification of 50 times, and the area ratio of the recrystallized portion of the steel sheet after soaking was taken at a magnification of 100 times. The ratio of recrystallized grains in the field of view was calculated using optical micrographs of the longitudinal section of each steel sheet. The mechanical properties were evaluated by tensile strength: TS by a tensile test using a test piece taken in the longitudinal direction at a 45 ° direction from the rolling direction. Magnetic properties were measured by measuring magnetic flux density B ₅₀ (magnetic flux density at a magnetizing force of 5000 A / m) in a 45 ° direction from the rolling direction with a 55 mm square single plate test piece. In Table 2, the evaluation result about the steel plates of Examples 1-18 and Comparative Examples 1-10 is shown.

  Since the steel plate of Comparative Example 1 had a high Si content and omitted hot-rolled sheet annealing, it broke during cold rolling. The steel plate of Comparative Example 2 had a low magnetic flux density due to its high Al content. Since the steel plate of Comparative Example 3 had a high P content, it broke during cold rolling. The steel plate of Comparative Example 4 had a high content of C and Mn and a low magnetic flux density because the steel structure was a martensite structure. In the steel sheet of Comparative Example 5, since the contents of Nb, Zr, Ti and V are outside the scope of the present invention, recrystallization is not suppressed, the area ratio of the recrystallized portion is increased, and the tensile strength and magnetic flux density are inferior. It was. The steel plate of Comparative Example 6 broke during cold rolling because the contents of Nb, Zr, Ti and V exceeded the upper limit of the range of the present invention. In Comparative Example 7, the area ratio of the recrystallized portion of the steel sheet before cold rolling was high, and both the tensile strength and the magnetic flux density were inferior. In Comparative Example 8, the area ratio of the recrystallized portion of the steel sheet after soaking was high, and both the tensile strength and the magnetic flux density were inferior. In Comparative Example 9, since the finish thickness of the cold rolling was thick, the amount of dislocations introduced by the cold rolling was not sufficient, and both the tensile strength and the magnetic flux density were inferior. In Comparative Example 10, since the cold-rolled finished sheet thickness was thin, ear cracks occurred after cold rolling, and could not be used for the subsequent steps.

  On the other hand, in the steel plates of Examples 1 to 18 that satisfy all the requirements defined in the present invention, both the magnetic properties and the mechanical properties showed excellent values. Further, comparing Example 5 and Example 6, it was found that the magnetic characteristics and mechanical characteristics did not change even when the S content changed.

It is a figure which shows the anisotropy of the tensile strength of the non-oriented electrical steel sheet using dislocation strengthening. It is a figure which shows the fatigue test result of the non-oriented electrical steel sheet using dislocation strengthening.

Claims (6)

In mass%, C: 0.06% or less, Si: 1.0% to 4.0%, Mn: 0.05% to 3.0%, Al: 2.5% or less, P: 0.00%. 25% or less, S: 0.04% or less, N: 0.02% or less, at least one element selected from the group consisting of Nb, Zr, Ti and V within a range satisfying the following formula (1) And the balance is Fe and impurities, the area ratio of the recrystallized portion is less than 90%, the tensile strength in the 45 ° direction from the rolling direction is 600 MPa or more, and the magnetic flux density B _{50 in the} 45 ° direction from the rolling direction is 1. A non-oriented electrical steel sheet for a rotor, characterized by being 68T or more.
0 <Nb / 93 + Zr / 91 + Ti / 48 + V / 51- (C / 12 + N / 14) <5 × 10 ^-3 (1)
(Here, in the formula (1), Nb, Zr, Ti, V, C and N indicate the content (mass%) of each element.)   The non-oriented electrical steel sheet for a rotor according to claim 1, wherein Nb exceeds 0.02% instead of a part of the Fe. The at least one element selected from the group consisting of Cu, Ni, Cr, Mo, Co, and W is contained in the following mass% in place of a part of the Fe. Item 3. The non-oriented electrical steel sheet for rotors according to Item 2.
Cu: 0.01% to 8.0% Ni: 0.01% to 2.0% Cr: 0.01% to 15.0% Mo: 0.005% to 4.0% Co: 0.01% or more and 4.0% or less W: 0.01% or more and 4.0% or less 2. Instead of a part of the Fe, at least one element selected from the group consisting of Sn, Sb, Se, Bi, Ge, Te and B is contained in the following mass%. The non-oriented electrical steel sheet for rotors according to any one of claims 1 to 3.
Sn: 0.5% or less Sb: 0.5% or less Se: 0.3% or less Bi: 0.2% or less Ge: 0.5% or less Te: 0.3% or less B: 0.01% or less 5. Instead of a part of Fe, at least one element selected from the group consisting of Ca, Mg, and REM is contained in the following mass%. The non-oriented electrical steel sheet for rotors according to claim 1.
Ca: 0.03% or less Mg: 0.02% or less REM: 0.1% or less A hot rolling process in which hot rolling is performed on a steel ingot or steel slab having the steel composition according to any one of claims 1 to 5, and hot rolling obtained by the hot rolling process It is obtained by a hot-rolled sheet annealing process for subjecting a steel sheet to hot-rolled sheet annealing, a cold-rolling process in which the steel sheet after the hot-rolled sheet annealing is made into a final sheet thickness by a single cold rolling, and the cold-rolling process. A method of producing a non-oriented electrical steel sheet for a rotor having a soaking process for soaking a cold rolled steel sheet,
The area ratio of the recrystallized portion of the steel sheet before the cold rolling step is less than 40%,
A method for producing a non-oriented electrical steel sheet for a rotor, wherein a soaking temperature in the soaking process is 700 ° C. or more and 900 ° C. or less.

Images