JP4779474B2 - Non-oriented electrical steel sheet for rotor and manufacturing method thereof - Google Patents

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, etc., 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 magnetic and mechanical properties required 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.

  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.

  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 secured, 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.

  As non-oriented electrical steel sheets specified 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

  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.

  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 made various studies on the steel structure that should be possessed by the non-oriented electrical steel sheet having both magnetic properties and mechanical properties suitable for rotors, and have achieved high strength by work hardening that has not been studied at all. Pay attention. The new knowledge that dislocations introduced during processing have a relatively small effect on iron loss has been obtained, and this technology is completely the opposite of the completely recrystallized ferrite structure that is the technical recognition of conventional non-oriented electrical steel sheets. Based on the idea, the magnetic structure and mechanical characteristics required for the rotor can be achieved by making the structure of the steel sheet a processed structure in which a large amount of dislocations remain and a recovered structure (hereinafter referred to as “recovered structure”). It was found that it can be obtained. Furthermore, in order to obtain a recovery structure, it has been found that the contents of Nb, Zr, Ti and V need to be within a predetermined range, and based on these findings, Japanese Patent Application Nos. 2004-183554 and 2004 are disclosed. -252395 proposes a non-oriented electrical steel sheet having excellent mechanical and magnetic properties necessary for a rotor of a motor that rotates at high speed, and a method for manufacturing the same. The present inventors have examined the conditions for obtaining a recovered tissue in more detail, and found that it is most effective to contain Nb particularly among Nb, Zr, Ti and V, and this is the most effective. Completed the invention.

That is, the present invention is, in mass%, C: 0.06% or less, Si: 3.5% or less, Mn: 0.05% or more and 3.0% or less, Al: 2.5% or less, P: 0 30% or less, S: 0.04% or less, N: 0.02% or less, Nb: more than 0.02%, and at least one selected from the group consisting of Nb, Ti, Zr and V A non-oriented electrical steel sheet for a rotor comprising an element in a range satisfying the following formula (1), the balance being Fe and impurities, and an area ratio of a recrystallized portion being less than 90%: provide.
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 area ratio of the recrystallized portion is appropriately controlled, and the strength can be increased by making the steel structure in which many dislocations remain. Steel sheet. As a result, the magnetic characteristics and mechanical characteristics required for the rotor described above can also be satisfied.

Moreover, 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.

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 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 rotors 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. It is preferable.
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.

  The present invention also includes a hot rolling process in which hot rolling is performed on a steel ingot or steel slab having the above-described steel composition, and a hot rolled steel sheet obtained by the hot rolling process is subjected to one time or intermediate annealing. For a rotor characterized by having a cold rolling step for performing cold rolling at least twice and a soaking step for soaking the cold rolled steel sheet obtained by the cold rolling step at 820 ° C. or less. A method for producing a non-oriented electrical steel sheet is provided.

  In the present invention, by setting the temperature in soaking to a predetermined range, recrystallization is suppressed, and the recovered structure that has remained without annihilating dislocations introduced during processing to a predetermined plate thickness Therefore, the strength of the steel sheet can be increased. Moreover, since it does not accompany the high intensity | strength of the steel plate which uses for cold rolling, ie, the base material of cold rolling, the fracture | rupture at the time of cold rolling can be suppressed. Furthermore, by using a steel ingot or steel slab having a predetermined steel composition, it is possible to produce a non-oriented electrical steel sheet for a rotor that has not only mechanical properties but also good magnetic properties.

  Moreover, the manufacturing method of the non-oriented electrical steel sheet for rotors of this invention may have the hot-rolled sheet annealing process which performs hot-rolled sheet annealing to the said hot-rolled steel sheet. This is because by performing hot-rolled sheet annealing, the ductility of the steel sheet is improved and breakage in the cold rolling process can be suppressed.

  According to the present invention, it is possible to stably manufacture a non-oriented electrical steel sheet having both excellent mechanical properties and magnetic properties necessary as a rotor of a motor that rotates at high speed without causing a significant increase in cost. is there. 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 necessary for the electrical steel sheet used for the rotor referred to in the present invention are mechanical characteristics, which are the yield point and the 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. In drive motors of recent electric vehicles and hybrid vehicles, the rotor receives a stress amplitude of about 150 MPa under an average stress of about 250 MPa. Therefore, from the viewpoint of suppressing deformation, the yield point must be 400 MPa or more, and considering the safety factor, it is necessary to satisfy 500 MPa or more. Preferably it is 550 MPa or more. Further, from the viewpoint of suppressing fatigue failure in the stress state described above, the tensile strength is 550 MPa or more, and considering the safety factor, 600 MPa or more, preferably 700 MPa or more is required.

  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. Iron loss consists of hysteresis loss due to irreversible domain wall motion and Joule heat (eddy current loss) due to eddy currents caused by magnetization changes. The iron loss of electrical steel sheets is the sum of these totals. It is evaluated by iron loss. Although the loss generated in the rotor does not dominate the motor efficiency itself, the permanent magnet is demagnetized due to the loss of the rotor, that is, heat generation, which indirectly deteriorates the motor performance. 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 diligently studied non-oriented electrical steel sheets that satisfy these characteristics. First, based on the above-mentioned idea, various studies were made on the steel structure that the non-oriented electrical steel sheet having both magnetic characteristics and mechanical characteristics suitable for the rotor should have. 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. Furthermore, as a result of examining work hardening as a strengthening mechanism, it was found that dislocations introduced during processing have a relatively small effect on iron loss. From these results, it is required for the rotor to have a processed structure and a recovered structure in which a large amount of dislocations remain, contrary to the complete recrystallized ferrite structure that is the technical recognition of conventional non-oriented electrical steel sheets. It was found that the magnetic properties and mechanical properties can be achieved.

The processed structure and the recovered structure can be obtained by allowing dislocations introduced during processing to a predetermined plate thickness to remain without being eliminated during soaking or by suppressing the disappearance. Therefore, unlike the prior art mainly based on solid solution strengthening or precipitation strengthening, it is possible to increase the strength without increasing the strength of the cold-rolled base material, and to suppress breakage during cold rolling. In order to obtain such a processed structure and a recovered structure, it is necessary to suppress recrystallization in a soaking process that is usually performed after cold rolling. Further, in order to suppress recrystallization during soaking, it is necessary to contain Nb, Zr, Ti and V. In particular, since Nb contributes greatly, it is necessary to contain an appropriate amount centering on Nb. However, when Nb, Zr, Ti, and V are excessively contained, the surface properties deteriorate, so that it is important to optimize the contents of Nb, Zr, Ti, and V.
Hereinafter, the knowledge that led to the completion of the present invention will be described.

  The main components are mass%, Si: 2.0%, Mn: 0.2%, Al: 0.3%, N: 0.002%, P: 0.01%, C, S and Nb Steel whose content was changed to C: 0.001 to 0.04%, S: 0.0002 to 0.03%, Nb: 0.001 to 0.6%, respectively, and the main component was mass%, Si: 2.0%, Mn: 0.2%, Al: 0.3%, N: 0.002%, P: 0.01%, and the contents of C, S and Ti are C: 0 0.001 to 0.04%, S: 0.0002 to 0.03%, Ti: 0.001 to 0.3%, and hot rolled to 2.3 mm, then 800 mm Hot-rolled sheet annealed at 10 ° C for 10 hours, further cold-rolled to 0.35 mm, soaked at 700 ° C for 20 seconds or at 750 ° C for 20 seconds It was subjected to physical. The tensile strength of the steel sheet thus obtained was measured.

1 and 2, the following formula (2) defined by the contents of Nb, C, N, and Ti, C, N for each steel sheet subjected to soaking at 700 ° C. or 750 ° C. for 20 seconds. ) And (3) and the relationship between Nb ^* and Ti ^* and the tensile strength of the steel sheet.
Nb ^* = Nb / 93-C / 12-N / 14 (2)
Ti ^* = Ti / 48-C / 12-N / 14 (3)
(Here, in the formulas (2) and (3), Nb, Ti, C and N indicate the content (mass%) of each element.)

1 and 2, it was found that excellent mechanical properties can be obtained only when Nb ^* > 0 and Ti ^* > 0. Moreover, as a result of investigating the steel structure, recrystallization was suppressed only when Nb ^* > 0 and Ti ^* > 0, and the steel structure was a processed structure and a recovered structure. Nb ^* and Ti ^* correspond to the solute Nb and solute Ti contents, and it has been found that securing the solute Nb and solute Ti contents is important for suppressing recrystallization. Furthermore, if Nb and Ti are compared, the effect of suppressing recrystallization of Nb is greater than that of Ti, so it is more effective for increasing the strength. The higher the soaking temperature in soaking, the more It was also found that the difference in effect was large.

In addition, Zr and V were also examined in the same manner as described above, and it was found that it was necessary to satisfy the following formula (1) after positively containing Nb in order to suppress recrystallization. Thus, the present invention has been completed.
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.)
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: 3.5% or less, Mn: 0.05% or more. 0% or less, Al: 2.5% or less, P: 0.30% or less, S: 0.04% or less, N: 0.02% or less, Nb: more than 0.02%, Nb, Ti And at least one element selected from the group consisting of Zr and V in a range satisfying the above formula (1), the balance being Fe and impurities, and the area ratio of the recrystallized portion being less than 90% It is characterized by being.
“%” Indicating the content of each element means “mass%” unless otherwise specified .
Hereinafter, the steel composition and the area ratio of the recrystallized portion 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 or V to form a precipitate, it leads to a decrease in the content of solute Nb, Zr, Ti and V. Therefore, in order to secure the contents of solute Nb, Zr, Ti and V, it is preferable to reduce the C content. 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 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, Nb / 93 + Zr / 91 + Ti / 48 + V / 51− (C / 12 + N / 14)> 0 necessary for satisfying the condition of Nb, Zr, Ti and V Since the content is small, it is desirable from the viewpoint of manufacturing 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 3.5% or less. Moreover, 3.0% or less is preferable from a viewpoint of crack suppression. Furthermore, when using Si as a deoxidizing agent, it is necessary to contain 0.01% or more, but since Al may be used as a deoxidizing agent, the lower limit of the Si content is not particularly limited. From the viewpoint of increasing the strength of the steel sheet by solid solution strengthening, the desirable lower limit is 1.0%.

(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. From the viewpoint of increasing the strength of the steel sheet by solid solution strengthening, the desirable lower limit is 0.2%.

(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 0.30% 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, or V to form a precipitate, the content of solute Nb, Zr, Ti, and V is reduced. Therefore, in order to suppress recrystallization by the solid solution Nb, Zr, Ti and V, it is preferable to reduce the N content. 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 Nb, Zr, Ti and V contents 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 manufacturing cost.

(8) Nb, Zr, Ti and V
In order to suppress dislocation annihilation and recrystallization during soaking, and to obtain a processed structure and a recovered structure, it is necessary to contain Nb, Zr, Ti, or V in a solid solution state in which precipitates are not formed. is there. Therefore, it is necessary to contain at least one element selected from the group consisting of Nb, Zr, Ti and V in a range satisfying the following formula (4).
Nb / 93 + Zr / 91 + Ti / 48 + V / 51- (C / 12 + N / 14)> 0 (4)
(Here, in the formula (4), Nb, Zr, Ti, V, C and N indicate the content (mass%) of each element.)

The left side of the above formula (4) represents the difference between the contents of Nb, Zr, Ti and V and the contents of C and N, and this value is positive that the carbide, nitride or carbonitride It corresponds to containing Nb, Zr, Ti or V in a solid solution state in which no precipitate is formed.
As described above, since the contribution of the solid solution Nb is particularly large among these elements, Nb is positively contained in the present invention, and the Nb content exceeds 0.02%. Preferably it is 0.04% or more. The positive inclusion of Nb greatly contributes to productivity improvement as will be described later. On the other hand, the upper limit of the Nb content is set so as not to exceed the upper limit of the formula (1) described later.

As shown in FIGS. 1 and 2, when the soaking temperature during soaking is high, the more the content of solid solution Nb, Zr, Ti and V is, the more effective the effect of suppressing dislocation disappearance and recrystallization. It is effective for obtaining a processed structure or a recovered structure.
However, when excessively containing solute Nb, Zr, Ti, and V, dislocation disappearance and recrystallization are suppressed during hot rolling and hot-rolled sheet annealing, so that the structure before cold rolling is not yet obtained. Recrystallized state. As a result, surface defects called ridging are generated, which is not preferable because the space factor when laminated on an iron core is lowered and the motor efficiency is lowered. Moreover, a crack may arise at the time of cold rolling. The upper limit of the content of the solute 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.)

  In consideration of sulfide, the contents of Nb, Zr, Ti and V in the solid solution state are also affected by the S content. However, since the influence of S on the recrystallization suppressing 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.

(9) Cu, Ni, Cr, Mo, Co and W
In the present invention, since the recrystallization itself is suppressed rather than the recrystallized grain size, the recrystallization itself is suppressed to achieve both magnetic properties and mechanical properties. Therefore, 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.
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.
When Co and W are excessively contained, the cost increases. Therefore, the Co content is preferably 0.01% or more and 4.0% or less, and the W content is preferably 0.01% or more and 4.0% or less. .

(10) Sn, Sb, Se, Bi, Ge, Te and B
Since the present invention attempts 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, the present invention comprises 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 In the present invention, it is possible to contain elements other than the elements described above within a range not impairing the effects of the present invention. Unlike the prior art based on the premise of a recrystallized structure, the present invention increases strength by using a processed structure and a recovered structure in which many dislocations remain. Inclusion of limited elements can be tolerated to higher levels. For example, Ta, Hf, As, Au, Be, Zn, Pb, Tc, Re, Ru, Os, Rh, Ir, Pd, Pt, Ag, Cd, Hg, and Po are contained in a total amount of 0.1% or less. Can do.

2. Next, the reason for limiting the area ratio of the recrystallized portion in the present invention will be described together with the experimental results.
In mass%, C: 0.002%, Si: 2.8%, Mn: 0.2%, Al: 1.2%, S: 0.006%, N: 0.002%, P: 0.00. Hot rolled to 01%, Nb: 0.09% steel to 2.3 mm, hot-rolled sheet annealed at 800 ° C. for 10 hours, further cold rolled to 0.35 mm, 680-800 A soaking treatment was performed by holding at various temperatures of 1050 ° C. for 10 seconds. The tensile strength of the steel sheet thus obtained was measured.
FIG. 3 shows the relationship between the area ratio of the recrystallized portion, the yield point, and the tensile strength. With the progress of recovery, which is the pre-recrystallization stage, the yield point and tensile strength decrease while the area ratio of the recrystallized portion remains zero. After the start of recrystallization, the yield point and tensile strength further decrease as the area ratio of the recrystallized portion increases. Here, the area ratio of the recrystallized portion is determined from the viewpoint of securing the mechanical characteristics necessary for the rotor. Considering the safety factor, the area ratio of the recrystallized portion is less than 90% from the viewpoint of suppressing deformation during high-speed rotation. Preferably it is 70% or less. From the viewpoint of suppressing fatigue fracture, it is preferably 40% or less, more preferably less than 25%. From the viewpoint of mechanical properties, the area ratio of the recrystallized portion is preferably as low as possible, and it is preferable that the area ratio of the recrystallized portion is zero and the state is completely unrecrystallized (worked structure and recovery structure).

  To control the area ratio of the recrystallized portion, it is important to adjust the soaking temperature and soaking time during soaking. Since the present invention is characterized by positively containing Nb having a large effect of suppressing recrystallization, such area ratio control of the recrystallized portion is disclosed in Japanese Patent Application Nos. 2004-183554 and 2004-252395. It is easier than the developed technology and leads to improved productivity.

  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.

B. Next, the manufacturing method of the non-oriented electrical steel sheet for rotors of the present invention will be described. 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-described steel composition, and a hot process obtained by the hot rolling process. A cold rolling process in which cold rolling is performed twice or more by sandwiching the rolled steel sheet once or by intermediate annealing, and a soaking process in which the cold rolled steel sheet obtained by the cold rolling process is soaked at 820 ° C. or less. It is characterized by having.

According to the present invention, by setting the temperature in the soaking process to a predetermined range, recrystallization is suppressed, and disappearance of dislocations introduced during processing to a predetermined plate thickness is suppressed, and a large amount of The recovery structure in which dislocations are left can be the main component, which makes it possible to increase the strength of the steel sheet. 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. . Furthermore, in the present invention, since a steel ingot or steel slab having a predetermined steel composition is used, and the temperature in the soaking process is set within a predetermined range as described above, the strength is increased. For example, a non-oriented electrical steel sheet for a rotor that satisfies the magnetic and mechanical characteristics required for a rotor of a drive motor can be stably manufactured without using expensive steel components or special processes. be able to.
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 to 1300 ° C. from the viewpoint of cost and hot rolling properties. More preferably, it is 1050-1250 degreeC.
Moreover, various conditions of hot rolling are not specifically limited, For example, what is necessary is just to perform according to general conditions, such as finishing temperature 700-950 degreeC and coiling temperature 750 degrees C or less.

(2) Cold rolling process The cold rolling process in the present invention is a process in which the hot rolled steel sheet obtained by the hot rolling process is subjected to cold rolling twice or more with one or intermediate annealing. By performing such a cold rolling process, the steel sheet is finished to a predetermined thickness.
In this step, the sheet thickness may be finished by one cold rolling or may be finished by two or more cold rollings including intermediate annealing.

  In the present invention, the strength is increased by suppressing the disappearance of the dislocations introduced by cold rolling, so that sufficient strength cannot be ensured when the amount of dislocations introduced is small. Since the amount of dislocation introduced can be determined by the strength of the steel sheet, in the present invention, the tensile strength in the previous stage to be subjected to the soaking process is used as an index, and the measured value with the rolling direction as the longitudinal direction is 850 MPa or more. It is preferable to do.

The reason for this will be described based on experimental results. In mass%, C: 0.003%, Si: 2.9%, Mn: 0.2%, Al: 1.1%, S: 0.001%, N: 0.002%, P: 0.00. Steel having a composition of 01%, Nb: 0.001% (steel of Nb ^* <0 described above), C: 0.002%, Si: 2.8%, Mn: 0.2%, Al: 1 .2%, S: 0.006%, N: 0.002%, P: 0.01%, Nb: 0.09% steel (having the above-mentioned Nb ^* > 0 steel) After rolling to 2.0 mm, hot-rolled sheet annealing is performed at 750 ° C. for 10 hours, and finished to various plate thicknesses of 0.35 to 1.2 mm by one cold rolling, at 700 ° C. A soaking treatment was performed for 20 seconds. For some hot-rolled plates, after hot-rolled sheet annealing, the intermediate sheet thickness is 0.4 to 1.8 mm, and the intermediate annealing conditions are maintained at 750 ° C. for 10 hours until cold rolling is performed to 0.35 mm Finishing was similarly performed soaking at 700 ° C. for 20 seconds. These steel sheets were subjected to a tensile test with the rolling direction as the longitudinal direction before and after soaking.

FIG. 4 shows the tensile strength before and after the soaking process. Only for steels with Nb ^* > 0, the tensile strength after the soaking process can be arranged by the tensile strength before the soaking process, regardless of cold rolling once or twice. That is, in steel containing solute Nb, the tensile strength before the soaking process can be adopted as a measure of the amount of dislocations necessary to ensure the strength. The same study is performed for Ti, Zr and V, and if the steel composition of the present invention is provided, the tensile strength before the soaking process is adopted as an index of the amount of dislocation necessary for ensuring the strength. The knowledge that it can be obtained. As a necessary condition for ensuring a sufficient tensile strength after the soaking process, it has been found important to secure a tensile strength of 850 MPa or more before the soaking process.
Here, the tensile strength in the previous stage of the soaking process can be measured with a tensile specimen taken with the rolling direction as the longitudinal direction.

  Since the effects of the present invention can be obtained if sufficient dislocations are introduced, various conditions for cold rolling, such as the temperature of the steel sheet during rolling, the rolling reduction, and the diameter of the rolling roll, are not particularly limited. The material is appropriately selected depending on the steel composition of the material, the thickness of the target steel plate, and the like. Even when light processing is performed for the purpose of correcting the flatness of the steel sheet before being subjected to the soaking process, the effects of the present invention can be obtained as long as the above-described tensile strength is satisfied after the light processing.

(3) Soaking step The soaking step in the present invention is a step of soaking the cold-rolled steel sheet obtained by the cold rolling step described above at 820 ° C or lower.
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.
Since the present invention is characterized by positively containing Nb among Nb, Zr, Ti and V, the effect of suppressing recrystallization is great. Therefore, even if the soaking temperature in the soaking process is high, a processed structure and a recovered structure can be obtained, and productivity can be improved because there is no need to provide a special soaking temperature. Specifically, if the soaking temperature in the soaking process is 820 ° C. or less, desired mechanical properties can be obtained. From the viewpoint of mechanical properties, it is preferably 780 ° C. or lower, more preferably 750 ° C. or lower. This soaking temperature is within the range to be implemented with a normal non-oriented electrical steel sheet, and does not hinder productivity. The lower the soaking temperature is, the more the recrystallization progress is suppressed. However, when the soaking temperature is low, the flatness of the steel sheet is not corrected, and the space factor when laminated on the rotor may decrease. Moreover, since it has the effect of improving the iron loss as compared with the state of cold rolling by soaking, it leads to an increase in iron loss when the soaking temperature is low. Furthermore, when the soaking temperature is low, the productivity is significantly reduced as described above. Therefore, from the viewpoint of flatness correction and iron loss improvement, a preferable lower limit value of the soaking temperature is set to 500 ° C. More preferably, it is 600 degreeC or more.

The soaking process may be carried out by box annealing, but the flatness of the steel sheet decreases or the shape deteriorates due to winding of the coil (also called coil set) due to the annealing in the coil state. In some cases, a straightening process for correcting the flatness and shape of the steel sheet after the soaking process may be necessary. Therefore, it is desirable to carry out in a continuous annealing line from the viewpoint of productivity.
If recrystallization proceeds by soaking at a high temperature and the mechanical properties are lowered due to this, the number of steps is unavoidable, but processing may be performed after the soaking step to ensure strength.

(4) Hot-rolled sheet annealing process In this invention, you may perform the hot-rolled sheet annealing process which performs hot-rolled sheet annealing to the hot-rolled steel plate obtained by the said hot-rolling process. This hot-rolled sheet annealing process is a process performed between a hot rolling process and a cold rolling process.
The hot-rolled sheet annealing process is not necessarily an essential process, but 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 any method of box annealing and continuous annealing. Moreover, the various conditions of hot-rolled sheet annealing are not specifically limited, It shall select suitably by the steel composition etc. of a hot-rolled steel plate.

(5) Others In the present invention, after the soaking step, according to a general method, a coating step of applying an insulating film made of only an organic component, only an inorganic component, or an organic-inorganic composite to a steel sheet surface may be performed. preferable. 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 specifically described with reference to Examples , Reference Examples and Comparative Examples.

[Examples 18 to 26 , Reference Examples 1 to 17 ]
Steels having the steel compositions shown in Table 1 below are vacuum-melted, these steels are heated to 1150 ° C., hot-rolled at a finishing temperature of 820 ° C., wound up at 580 ° C., and a thickness of 2.0 mm. A hot rolled steel sheet was obtained. Except for some of these hot-rolled steel sheets, box annealing that is held for 10 hours in a hydrogen atmosphere or hot-rolled sheet annealing by continuous annealing that is held at 1000 ° C. for 60 seconds is performed for one cold rolling. And finished to a plate thickness of 0.35 mm. For some hot-rolled steel sheets, after the above-described hot-rolled sheet annealing, after cold rolling to an intermediate sheet thickness, box annealing that is held at 750 ° C. or 800 ° C. for 10 hours in a hydrogen atmosphere, or 1000 Intermediate annealing was performed by continuous annealing held at 60 ° C. for 60 seconds, and finished to 0.35 mm by the second cold rolling. Furthermore, some hot-rolled steel sheets were finished to 0.35 mm by performing cold rolling once or twice including intermediate annealing without performing hot-rolled sheet annealing. Thereafter, in Reference Examples 1 to 9 and 11 to 17 and Examples 18 to 26, soaking was performed by continuous annealing that was held at various temperatures for 30 seconds. In Reference Example 10, soaking was performed by box annealing that was held at 500 ° C. for 10 hours. In this way, a steel plate was produced.

[Comparative Examples 1-8]
Steel plates having the steel composition shown in Table 1 were used to produce steel plates in the same manner as in Examples 18 to 26 and Reference Examples 1 to 17 .

[Evaluation]
About the steel plates of Examples 18 to 26 , Reference Examples 1 to 17 and Comparative Examples 1 to 8, the mechanical properties of the steel plates in the pre-stage of soaking, and the area ratio, mechanical properties, and magnetic properties of the recrystallized portion after soaking And the fatigue properties were evaluated.

As the area ratio of the recrystallized portion, the ratio of the recrystallized grains in the visual field was calculated using an optical micrograph of the longitudinal section of the steel sheet taken at a magnification of 100 times.
The mechanical properties were evaluated by performing a tensile test using a JIS No. 5 test piece. The steel plate before the soaking was evaluated by tensile strength: TS, and the steel plate after the soaking was evaluated by yield point: YP and tensile strength: TS.
Regarding magnetic characteristics, a 55 mm square single plate test piece has a maximum magnetic flux density of 1.0 T, an excitation frequency of 400 Hz, an iron loss W _10/400, and a magnetic flux density B ₅₀ of 5000 A / m. It was measured. The measurement was carried out in the rolling direction and the direction perpendicular to the rolling, and the average value thereof was adopted.
As the fatigue test, a test piece was collected by punching, and subjected to a single swing electromagnetic resonance test at a frequency of 60 Hz while being punched without grinding the end face. In this fatigue test, the safety factor was taken into consideration with respect to the stress state of the drive motor, and those that did not undergo fatigue failure under the conditions of average stress: 300 MPa and stress amplitude: 180 MPa were judged to be good. The number of repetitions was up to 10 ⁷ , and the determination was made based on the presence or absence of destruction at this number of repetitions. In Table 2, those with no fatigue failure are indicated with “◯”, and those with fatigue failure are indicated with “x”.

Table 2 shows hot-rolled sheet annealing conditions, cold-rolling conditions, soaking conditions, and evaluation results for the steel plates of Examples 18 to 26 , Reference Examples 1 to 17 and Comparative Examples 1 to 8, respectively.

The steel plate of Comparative Example 1 broke during cold rolling because of the high Si content. Moreover, since the steel plate of Comparative Example 2 had a high Al content, the magnetic flux density was low. Since the steel plate of Comparative Example 3 had a high P content, it broke during cold rolling. Further, the steel sheet of Comparative Example 4 had a high C and Mn content, and the steel structure was a martensite structure, so that the iron loss was remarkably increased and the magnetic flux density was low. 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 yield point and tensile strength are inferior. It was. The steel sheet of Comparative Example 6 was inferior in yield point and tensile strength because the amount of dislocations introduced by cold rolling was not sufficient. The steel plate of Comparative Example 7 was inferior in yield point and tensile strength because the area ratio of the recrystallized portion was high. The steel plate of Comparative Example 8 broke during cold rolling because the Nb, Zr, Ti and V contents exceeded the upper limit of the range of the present invention.
On the other hand, in the steel plates of Examples 18 to 26 that satisfy the requirements defined in the present invention, both the magnetic properties and the mechanical properties showed excellent values regardless of the hot-rolled sheet annealing method and the number of cold rolling. Thus, fatigue failure did not occur even under the stress conditions described above.

In addition, it was found that even under conditions where the soaking temperature is relatively high, the recrystallization suppression effect is large, and thus the magnetic properties and mechanical properties are excellent .

Nb ^* (= Nb / 93-C / 12-N / 14) and Ti ^* (= Ti / 48-C / 12-N / 14) for a steel plate subjected to soaking at 700 ° C. for 20 seconds. It is a figure which shows the relationship with tensile strength. Nb ^* (= Nb / 93-C / 12-N / 14) and Ti ^* (= Ti / 48-C / 12-N / 14) for a steel sheet subjected to soaking at 750 ° C. for 20 seconds It is a figure which shows the relationship with tensile strength. It is a figure which shows the relationship between the area ratio of a recrystallized part, a yield point, and tensile strength. It is a figure which shows the relationship of the tensile strength before and behind a soaking process.

Claims (13)

In mass%, C: 0.06% or less, Si: 3.5% or less, Mn: 0.05% or more and 3.0% or less, Al: 2.5% or less, P: 0.30% or less, S : 0.04% or less, N: 0.02% or less, Nb: more than 0.02%, and at least one element selected from the group consisting of Nb, Ti, Zr and V is represented by the following formula (1 ), At least one element selected from the group consisting of Mo, Co, and W is contained in the following mass% , the balance is composed of Fe and impurities, and the area ratio of the recrystallized portion is non-oriented electrical steel sheet to that round rotor and less than 90%.
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.)
Mo: 0.005% to 4.0% Co: 0.01% to 4.0% W: 0.01% to 4.0%   It replaces with a part of said Fe, and contains at least 1 sort (s) of elements chosen from the group which consists of Cu, Ni, and Cr in the following mass%, The non-direction for rotors according to claim 1 characterized by things Electrical steel sheet.
  Cu: 0.01% to 8.0% Ni: 0.01% to 2.0%
  Cr: 0.01% or more and 15.0% 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%. Or the non-oriented electrical steel sheet for rotors of Claim 2.
  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 In mass%, C: 0.06% or less, Si: 3.5% or less, Mn: 0.05% or more and 3.0% or less, Al: 2.5% or less, P: 0.30% or less, S : 0.04% or less, N: 0.02% or less, Nb: more than 0.02%, and at least one element selected from the group consisting of Nb, Ti, Zr and V is represented by the following formula (1 ) contained in a range satisfying, Sn, Sb, Se, containing Bi, at least one element selected from Ge and T e or Ranaru group by mass% below, the balance being Fe and impurities , a non-oriented electrical steel sheet that times rotor to, characterized in that the area ratio is less than 90% of the recrystallized parts.
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.)
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 under   The non-oriented electrical steel sheet for a rotor according to claim 4, wherein B is contained in an amount of 0.01% by mass or less in place 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 6. The non-oriented electrical steel sheet for rotors according to Item 5.
  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% to 4.0% W: 0.01% to 4.0% In mass%, C: 0.06% or less, Si: 3.5% or less, Mn: 0.05% or more and 3.0% or less, Al: 2.5% or less, P: 0.30% or less, S : 0.04% or less, N: 0.02% or less, Nb: more than 0.02%, and at least one element selected from the group consisting of Nb, Ti, Zr and V is represented by the following formula (1 ), At least one element selected from the group consisting of Ca, Mg, and REM is contained in the following mass% , the balance is composed of Fe and impurities, and the area ratio of the recrystallized portion is non-oriented electrical steel sheet to that round rotor and less than 90%.
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.)
Ca: 0.03% or less Mg: 0.02% or less REM: 0.1% or less In mass%, C: 0.06% or less, Si: 3.5% or less, Mn: 0.05% or more and 3.0% or less, Al: 2.5% or less, P: 0.30% or less, S : 0.04% or less, N: 0.02% or less, Nb: more than 0.02%, and at least one element selected from the group consisting of Nb, Ti, Zr and V is represented by the following formula (1 ) In a range that satisfies the following: Ta, Hf, As, Au, Be, Zn, Pb, Tc, Re, Ru, Os, Rh, Ir, Pd, Pt, Ag, Cd, Hg, and Po in total A non-oriented electrical steel sheet for rotors , containing 1% or less, the balance being Fe and impurities, and the area ratio of the recrystallized portion being less than 90%.
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.)   Instead of a part of the Fe, Ta, Hf, As, Au, Be, Zn, Pb, Tc, Re, Ru, Os, Rh, Ir, Pd, Pt, Ag, Cd, Hg, and Po are 0 in total. The non-oriented electrical steel sheet for a rotor according to claim 7, wherein the non-oriented electrical steel sheet is contained in an amount of .1% by mass or less.   The at least one element selected from the group consisting of Cu, Ni, Cr, Mo, Co, and W is contained in the following mass% instead of a part of the Fe. The non-oriented electrical steel sheet for rotors according to any one of claims 9 to 9.
  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% to 4.0% W: 0.01% to 4.0%   8. 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 10 to 10. A hot rolling step of performing hot rolling steel ingot or slab having a steel composition according to any one of claims of claims 1 to 11, hot obtained by the hot rolling process rolling A cold rolling process in which the steel sheet is subjected to cold rolling at least once with intermediate or intermediate annealing, and a soaking process in which the cold rolled steel sheet obtained by the cold rolling process is soaked at 820 ° C. or less. A method for producing a non-oriented electrical steel sheet for a rotor, comprising: The method for producing a non-oriented electrical steel sheet for a rotor according to claim 12 , further comprising a hot-rolled sheet annealing step for subjecting the hot-rolled steel sheet to hot-rolled sheet annealing.

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