JP2009007592A - Method for manufacturing non-oriented electrical steel sheet for rotor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a non-oriented electrical steel sheet which possesses both excellent mechanical characteristic and magnetic characteristic required as a rotor for a motor rotating at high speed and also, is contributed to reduction in weight of the rotor. <P>SOLUTION: The method for manufacturing the nonoriented electrical steel sheet for the rotor includes: a hot-rolling process for applying the hot-rolling to a steel ingot or a steel slab containing, by mass, ≤0.06% C, ≤3.5% Si, 0.05-3.0% Mn, >2.5% to 6.0% Al, ≤0.30% P, ≤0.04% S, ≤0.02% N, and 0.02% the total content of at least one kind selected from a group composed of Nb, Ti, Zr and V and the balance Fe with impurities; a cold-rolling process for applying once or twice or more times inserting an intermediate annealing to the obtained hot-rolled steel plate obtained with the above hot-rolling process, and applying a continuous annealing to the steel plate before the finish cold-rolling at 850-1200°C for 10 sec-5 min; and a soaking-treating process for obtaining the steel sheet having <90% area ratio of a recrystallized portion by applying soaking treatment to cold-rolled steel sheet obtained with the above cold-rolling process. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  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. In addition, all parts are being reduced in weight for the purpose of improving the fuel efficiency of automobiles, but reducing the weight of the drive motor is also an important issue. 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 sufficient to use punched electrical steel sheets, but non-oriented electrical steel sheets that have both the magnetic and mechanical properties necessary for rotors and that contribute to weight reduction have been found. There was no current situation.

  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 strengthening by such precipitates is relatively ineffective, it is necessary to contain about 3.0% of Si as shown in Examples of Patent Document 3 and Patent Document 4, In the method, 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 having Si: 1.6 to 2.8% and limiting the 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 proposes a high-strength electrical steel sheet having excellent magnetic properties. However, since it is based on making the content of Ti and Nb into an inevitable impurity level or reducing it, high intensity | strength cannot be obtained stably.

  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 sheet 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-A-2005-113185

  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 inventors have made various studies on the steel structure that should be possessed by non-oriented electrical steel sheets having both magnetic and mechanical properties suitable for rotors, and have focused on increasing the strength by dislocation strengthening, which has not been studied at all. did. The new knowledge that dislocations remaining in the recovery state have a relatively small effect on iron loss has been obtained, and this technology is completely opposite to the complete recrystallized ferrite structure, which is the technical recognition of conventional non-oriented electrical steel sheets. Based on the idea, the magnetic and mechanical characteristics required for the rotor can be obtained by making the steel sheet structure a recovered structure in which a large amount of dislocations remain (hereinafter referred to as “recovered structure”). I found. Furthermore, in order to obtain a recovery structure, it is important to contain Nb, Zr, Ti and V in a solid solution state, and it is necessary to set the contents of Nb, Zr, Ti and V within a predetermined range. I found out. Based on these findings, 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 manufacturing method thereof have been proposed (Japanese Patent Laid-Open No. 2006-9048, No. 2006-70296).

  However, in the preferred embodiment described in JP-A-2006-9048 and the invention described in JP-A-2006-70296, Nb, Zr, Ti and V in amounts exceeding the contents of C and N are included. Since it is required to reduce the C content, there is room for improvement from the viewpoint of manufacturing cost. In addition, there is room for consideration for the demand for higher strength. Furthermore, there is room for improvement in terms of contributing to weight reduction of the rotor.

  The present invention has been made in view of the above circumstances, and is a non-oriented electrical steel sheet that has excellent mechanical and magnetic properties necessary for a rotor of a motor that rotates at high speed and contributes to weight reduction. The main purpose is to provide a method.

  Therefore, the present inventors have studied in detail a method for stably obtaining a recovery structure even if the C content is high, which can contribute to weight reduction of the rotor, and positively contain Al. It has been found that, by optimizing the annealing conditions performed before the cold rolling, a light weight reduction effect by reducing the specific gravity can be obtained, and a stable recovery structure can be obtained. Furthermore, the conditions of annealing performed before the final cold rolling are optimized for steel sheets containing Al positively and containing Nb, Zr, Ti and V in excess of the C and N contents. As a result, in addition to the effect of reducing the weight by reducing the specific gravity, it was found that the strength could be further increased. The present invention has been completed based on these new findings.

  That is, in the present invention, by mass%, C: 0.06% or less, Si: 3.5% or less, Mn: 0.05% or more and 3.0% or less, Al: more than 2.5% and 6.0% Hereinafter, P: 0.30% or less, S: 0.04% or less, N: 0.02% or less, and total of at least one element selected from the group consisting of Nb, Ti, Zr and V Once in a hot rolling process in which hot rolling is performed on a steel ingot or steel slab containing 0.02% or more and the balance being Fe and impurities, and the hot rolled steel sheet obtained by the hot rolling process. Alternatively, a cold rolling process in which cold rolling is performed twice or more with intermediate annealing, and the steel sheet before the final cold rolling is subjected to continuous annealing at a temperature of 850 ° C. to 1200 ° C. for 10 seconds to 5 minutes. And subjecting the cold-rolled steel sheet obtained by the cold-rolling process to a soaking treatment, the surface of the recrystallized portion Ratio to provide a method of manufacturing a non-oriented electrical steel sheet for a rotor and having a soaking step of obtaining a steel sheet less than 90%.

  According to the present invention, the recovery structure can be obtained by positively containing Al and appropriately controlling the contents of Nb, Zr, Ti and V, and the annealing conditions applied to the steel sheet before the final cold rolling. It is possible to obtain a non-oriented electrical steel sheet having a low specific gravity and a high strength, mainly composed of. Such strengthening of the steel sheet does not accompany the strengthening of the steel sheet used for cold rolling, that is, the base material of the cold rolling, and therefore has the advantage of being able to suppress breakage during cold rolling. Have. Furthermore, according to the present invention, a non-oriented electrical steel sheet having not only mechanical properties but also good magnetic properties and a low specific gravity can be obtained by using a steel ingot or steel slab having a predetermined steel composition. Therefore, according to the present invention, it is possible to satisfy the magnetic characteristics and mechanical characteristics necessary for a rotor of a drive motor, for example, without using expensive steel components as in the past or through a special process, and the rotor. It is possible to stably manufacture a non-oriented electrical steel sheet for a rotor that contributes to a reduction in weight of the rotor.

In the present invention, it is preferable that the steel ingot or steel slab contains at least one element selected from the group consisting of Nb, Zr, Ti and V in a range satisfying 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.)
This is because the strength of the steel sheet can be further improved by setting the contents of Nb, Zr, Ti and V within the above ranges.

  According to the present invention, a non-oriented electrical steel sheet that has both excellent mechanical and magnetic properties required as a rotor for a motor that rotates at high speed, and that can contribute to weight reduction, is stable without causing a significant increase in cost. Can be manufactured. Therefore, it can sufficiently cope with the high speed and light weight of the motor in the drive motor field of electric vehicles and hybrid vehicles, and its industrial value is extremely high.

  The characteristics necessary for the electrical steel sheet used in the rotor referred to in the present invention are mechanical characteristics, and yield point and 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.

  Further, the second 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 third characteristic required for the electrical 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 excessively low, a desired torque cannot be obtained. However, this is not the case when the output of the motor is secured not by torque but by rotation speed. Since drive motors and servo motors in recent years tend to rotate at high speed, it is recalled that the magnetic flux density of the material used for the rotor is acceptable even if the magnetic flux density is lower than the material used for the stator.

  The fourth characteristic necessary for the electrical steel sheet used for the rotor is specific gravity. Usually, the weight reduction of the motor is achieved by the miniaturization of the motor. For miniaturization of the motor, it is extremely effective to increase the magnetic flux density of the electromagnetic steel sheet used for the stator, and the influence of the magnetic flux density of the electromagnetic steel sheet used for the rotor on the miniaturization is small. Therefore, in order to reduce the weight of the motor as a rotor, there is no other way to reduce the weight of the rotor of the given shape, but it is necessary to reduce the weight of the electromagnetic steel sheet for the rotor, that is, to reduce the specific gravity of the electromagnetic steel sheet for the rotor. Is done.

  The present inventors diligently studied non-oriented electrical steel sheets that satisfy these characteristics. First, based on the above idea, various studies were made on the steel structure that should be possessed by the non-oriented electrical steel sheet having both magnetic properties and mechanical properties suitable for the rotor. 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 dislocation strengthening as a strengthening mechanism, it was found that dislocations remaining in the recovery state have a relatively small effect on iron loss. From these results, the magnetic properties required for the rotor are achieved by using a recovery structure in which a large amount of dislocations remain, contrary to the completely recrystallized ferrite structure that is the technical recognition of conventional non-oriented electrical steel sheets. And the knowledge that the mechanical properties are achieved.

  The recovery structure can be obtained by allowing dislocations introduced at the time of processing to a predetermined plate thickness to remain by suppressing annihilation by appropriate soaking. 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 recovery structure, it is necessary to suppress recrystallization in a soaking process usually performed after cold rolling. Moreover, in order to reduce specific gravity without deteriorating mechanical characteristics and magnetic characteristics, it is necessary to positively contain Al. In order to suppress recrystallization at the time of soaking in a steel sheet containing a large amount of Al, it is important to contain Nb, Zr, Ti and V in a solid solution state, and to contain Nb, Zr, Ti and V is required.

  In the preferred embodiment described in Japanese Patent Laid-Open No. 2006-9048 and the invention described in Japanese Patent Laid-Open No. 2006-70296, Nb, Zr, Ti and V in amounts exceeding the contents of C and N may be contained. Although it is necessary, in the present invention, even if the content of Nb, Zr, Ti and V is less than the content of C and N, by optimizing the conditions of annealing performed before the final cold rolling Dislocation disappearance and recrystallization during soaking performed after the final cold rolling can be suppressed. Further, when Nb, Zr, Ti and V are contained in excess of the contents of C and N, compared to the inventions described in JP-A-2006-9048 and JP-A-2006-70296, It is possible to further increase the strength of the steel sheet. Furthermore, since Al is actively contained, the effect of reducing the weight by reducing the specific gravity can be obtained.

  Even if the content of Nb, Zr, Ti and V is less than or equal to the content of C and N, the leveling performed after the final cold rolling can be performed by optimizing the annealing conditions performed before the final cold rolling. The reason why dislocation disappearance and recrystallization during heat treatment can be suppressed, and when Nb, Zr, Ti and V are contained in excess of the contents of C and N, before the final cold rolling. Although it is not clear why the steel sheet can be further strengthened by optimizing the annealing conditions, the present inventors presume as follows.

That is, even if the content of Nb, Zr, Ti and V is less than the content of C and N, recrystallization can be suppressed, and sufficient strength can be ensured by annealing performed before the final cold rolling. By carrying out at a relatively high temperature, the precipitates of the above elements were re-dissolved, and the dislocation disappearance and recrystallization suppression effect due to Nb, Zr, Ti and V in a substantially solid solution state were obtained. Inferred. In addition, when Nb, Zr, Ti and V are contained in excess of the contents of C and N, the strength is further improved as in the above, compared with the annealing performed before the final cold rolling. This is presumably because the precipitates of the above elements were re-dissolved by carrying out at a high temperature, and the amounts of Nb, Zr, Ti and V in the solid solution increased. Further, solid solution C and solid solution Nb, Zr, Ti and V generated by re-dissolution of precipitates have an interaction, and dislocation and solid solution C, dislocation and solid solution Nb, Zr, Ti and V Since there is also an interaction, the effect of suppressing the disappearance of dislocations by the conditions of annealing performed before the final cold rolling and the optimization of the Nb, Zr, Ti and V contents is Nb, Zr, Ti and V-containing This is higher than the effect of suppressing the disappearance of dislocations due to the optimization of the amount alone, and this is considered to have contributed to the further increase in strength.
Hereinafter, the manufacturing method of the non-oriented electrical steel sheet for rotors of this invention is demonstrated in detail.

The manufacturing method of the non-oriented electrical steel sheet for rotors of this invention is the mass%, C: 0.06% or less, Si: 3.5% or less, Mn: 0.05% or more and 3.0% or less, Al : More than 2.5% 6.0% or less, P: 0.30% or less, S: 0.04% or less, N: 0.02% or less, from the group consisting of Nb, Ti, Zr and V A hot rolling process in which hot rolling is performed on a steel ingot or steel slab containing at least one selected element in total of 0.02% or more and the balance being Fe and impurities, and the above hot rolling process The obtained hot-rolled steel sheet is subjected to cold rolling at least once with intermediate annealing or intermediate annealing, and the steel sheet before the final cold rolling is subjected to a temperature of 850 ° C. to 1200 ° C. for 10 seconds to 5 minutes. The cold rolling process in which the following continuous annealing is performed, and the cold rolled steel sheet obtained by the cold rolling process is soaked. Subjected to physical, area ratio of recrystallized portion is characterized in that it has a soaking step of obtaining a steel sheet less than 90%.
Hereinafter, the steel ingot or steel piece and each process in the manufacturing method of the non-oriented electrical steel sheet for rotors of this invention are demonstrated.

1. Steel ingot or steel slab The steel ingot or steel slab used in 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: more than 2.5%, 6.0% or less, P: 0.30% or less, S: 0.04% or less, N: 0.02% or less, and a group consisting of Nb, Ti, Zr and V At least one element selected from the group consisting of 0.02% or more in total, with the balance being Fe and impurities.
“%” Indicating the content of each element means “mass%” unless otherwise specified.
Hereinafter, the steel composition will be described.

(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, the C content is preferably reduced in order to suppress the disappearance of dislocations and the progress of recrystallization that proceed in the soaking process after cold rolling by solute Nb, Zr, Ti, and V. However, excessive reduction of the C content increases the steelmaking cost, and even if the C content is high, if the precipitate is re-dissolved by annealing under predetermined conditions before the final cold rolling. In view of the effect of suppressing the disappearance of dislocations and recrystallization during soaking after cold rolling, 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. If the C content is 0.01% 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 Therefore, it is desirable from the viewpoint of further strengthening and 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. More preferably, it is less than 2.0%. When Si is used as a deoxidizing agent, it is necessary to contain 0.01% or more, but in the present invention, since Al is also actively contained as a deoxidizing agent, the lower limit value of the Si content Is not particularly limited. From the viewpoint of increasing the strength of the steel sheet by solid solution strengthening, it is desirably 0.2% or more, and more desirably 1.0% 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. Furthermore, it has an effect of greatly reducing the specific gravity, and is an extremely important alloy element in the present invention aimed at contributing to weight reduction of the rotor. However, when Al is contained in a large amount, the alloy cost increases, and cracks during cold rolling are induced as in the case of Si, and the manufacturing cost increases due to a decrease in the yield of the steel sheet. However, since the contribution to cold rollability deterioration is lower than that of Si, a large amount is allowed to be contained, and the Al content is more than 2.5% from the viewpoint of reducing specific gravity and eddy current loss. Preferably it is 3.0% or more. In order to obtain a desired electrical resistance and achieve a reduction in eddy current loss after securing a tensile strength of 800 MPa or more, 3.5% or more is preferable. From the viewpoint of suppressing the cost increase and the cold rolling deterioration, the upper limit value of the Al content is 6.0%.

(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. From the viewpoint of ensuring strength, the P content is 0.01% or more, preferably 0.02% or more.

(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 the disappearance and recrystallization of dislocations during the soaking process performed after the final cold rolling with the solute 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. 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 Therefore, it is desirable from the viewpoint of further strengthening and manufacturing cost.

(8) Nb, Zr, Ti and V
In order to obtain the mechanical and magnetic properties necessary for the rotor by suppressing the disappearance and recrystallization of dislocations during soaking, and obtaining a recovery structure, Nb, It is necessary to contain Zr, Ti or V. In the present invention, dislocation disappearance and recrystallization regardless of the value of Nb / 93 + Zr / 91 + Ti / 48 + V / 51− (C / 12 + N / 14) by optimizing the annealing conditions before the final cold rolling. Therefore, it is not necessary to consider the contents of C and N described above as the contents of Nb, Zr, Ti and V. However, by annealing under predetermined conditions before the final cold rolling, the precipitate is re-dissolved, thereby suppressing the disappearance and recrystallization of dislocations during soaking, and obtaining a recovery structure. , Ti and V must contain at least one element selected from the group consisting of 0.02% or more in total.

  In addition, dislocation disappearance and recrystallization suppression are particularly affected by solute Nb and solute Ti among Nb, Zr, Ti and V, and recover even when the soaking temperature during soaking is increased. Since it is easy to obtain a structure, it is preferable to positively contain Nb or Ti. The Nb content is preferably 0.02% or more, and more preferably 0.03% or more. From the viewpoint of securing strength, it is preferably over 0.05%. The Ti content is preferably 0.01% or more, and more preferably 0.02% or more.

Furthermore, in order to effectively suppress the disappearance and recrystallization of dislocations during the soaking process and achieve further increase in strength, at least one element selected from the group consisting of Nb, Zr, Ti and V is added as follows: It is preferable to contain in the range which satisfies Formula (2).
Nb / 93 + Zr / 91 + Ti / 48 + V / 51- (C / 12 + N / 14)> 0 (2)
(Here, in the formula (2), Nb, Zr, Ti, V, C and N indicate the content (mass%) of each element.)

  The left side of the above formula (2) represents the difference between the contents of Nb, Zr, Ti and V and the contents of C and N. The positive value indicates that the carbide, nitride or carbonitride This corresponds to containing Nb, Zr, Ti or V in a solid solution state in which no precipitate such as a product is formed. In the present invention, the precipitate is re-dissolved by annealing under a predetermined condition before the final cold rolling, so that the above formula (2) has already been solid-solved before the annealing under the predetermined condition. It indicates that Nb, Zr, Ti or V in the state is contained.

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 the recovery structure is obtained.
However, when excessively containing solute Nb, Zr, Ti and V, dislocation disappearance and recrystallization are suppressed even during hot rolling, which may cause uneven defects on the surface of the steel sheet. When the layers are stacked, the space factor may be reduced, and the motor efficiency may be reduced. In particular, in the present invention in which Al is contained in a large amount exceeding 2.5%, the recrystallization temperature is increased due to high alloying, and Japanese Patent Laid-Open Nos. 2006-9048 and 2006-70296 are disclosed. There is a concern about the deterioration of the surface properties than the steel sheet disclosed in. Moreover, a crack may arise at the time of cold rolling. Accordingly, in the present invention in which Al is actively contained, the upper limit value of the content of solute Nb, Zr, Ti and V is determined from such a viewpoint, and Nb, Zr, Ti and V are represented by the following formula (1). It is preferable to contain in the range shown by.
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 of the present invention, the above formula (1) in which the term of S 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) 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.

  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 in 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. .

  In addition, since the present invention achieves both magnetic properties and mechanical properties by suppressing recrystallization, Sn, Sb, Se, Bi, Ge contributes to high strength by suppressing recrystallization by grain boundary segregation. , Te and B may be included. When these elements are contained, the content of each element is Sn: 0.5% or less, Sb: 0.5% or less, Se from the viewpoint of suppressing the occurrence of cracks and cost increase in hot rolling. : 0.3% or less, Bi: 0.2% or less, Ge: 0.5% or less, Te: 0.3% or less, B: 0.01% or less are preferable. 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.

Further, 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, from the group consisting of Ca, Mg and REM for the purpose of improving magnetic properties by controlling the form of sulfide. At least one selected may be included.
Here, REM refers to a total of 17 elements including 15 elements of 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.

  In addition, unlike the conventional technique based on the recrystallized structure, the present invention increases the strength by using a recovered structure in which many dislocations remain. The inclusion of the elements that have been made can be tolerated to a higher level. 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. Hot Rolling Step The hot rolling step in the present invention is a step of hot rolling a steel ingot or steel slab (hereinafter also referred to as “slab”) having the above-described steel composition.
In this step, the steel having the above-described steel 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 temperature is not particularly limited, but is preferably set to 1000 ° C. to 1300 ° C. from the viewpoint of cost and hot rollability. More preferably, it is 1050 degreeC-1250 degreeC.
Moreover, various conditions of hot rolling are not specifically limited, For example, what is necessary is just to carry out according to general conditions, such as finishing temperature of 700 to 950 degreeC and coiling temperature of 750 degrees C or less.

  A hot-rolled steel sheet is usually subjected to cold rolling after removing scales generated on the surface of the steel sheet during hot rolling by pickling. When hot-rolled sheet annealing described later is applied to the hot-rolled steel sheet, it may be pickled either before hot-rolled sheet annealing or after hot-rolled sheet annealing.

3. Cold rolling step The cold rolling step in the present invention is performed by subjecting the hot rolled steel sheet obtained by the hot rolling step to cold rolling twice or more sandwiching the intermediate annealing and the final cold rolling. In this step, the steel sheet before rolling is subjected to continuous annealing at a temperature of 850 ° C. to 1200 ° C. for 10 seconds to 5 minutes. By performing such a cold rolling process, the steel sheet is finished to a predetermined plate thickness, and dislocations necessary for obtaining the intended strength are introduced.

Here, “the steel plate before the final cold rolling” means that the hot rolled steel plate is used when the product is subjected to cold rolling only once without intermediate annealing to finish the product sheet thickness. This means that when the hot-rolled steel sheet is subjected to two or more cold rolling sandwiching intermediate annealing to finish the product sheet thickness, it means the cold-rolled steel sheet before the final cold rolling.
In addition, there are cases where the mechanical properties and thickness of the product are adjusted by performing cold working after the soaking process described later, but the cold working is not cold rolling, but the number of cold rolling described above. Does not count.

  In addition, “the steel sheet before the final cold rolling is subjected to continuous annealing at a temperature of 850 ° C. or more and 1200 ° C. or less for 10 seconds or more and 5 minutes or less” is performed only once without performing intermediate annealing. In this case, it means that hot-rolled sheet steel is subjected to hot-rolled sheet annealing under predetermined conditions, and when performing cold rolling more than once with intermediate annealing, before the final cold-rolling. Means that the cold-rolled steel sheet is subjected to intermediate annealing under predetermined conditions. That is, in the present invention, when cold rolling is performed only once without performing intermediate annealing, the hot-rolled sheet annealing conditions are optimized, and cold rolling is performed twice or more with intermediate annealing. In this case, dislocation disappearance and recrystallization during soaking can be suppressed by optimizing the conditions of the intermediate annealing before the final cold rolling.

  In the present invention, it is necessary to subject the steel plate before the final cold rolling to continuous annealing at a temperature of 850 ° C. to 1200 ° C. for 10 seconds to 5 minutes. That is, when cold rolling is performed only once without intermediate annealing, it is performed by hot-rolled sheet annealing, or when cold rolling is performed twice or more with intermediate annealing, the final cold In the intermediate annealing before rolling, continuous annealing is performed at a temperature of 850 ° C. or higher and 1200 ° C. or lower for 10 seconds to 5 minutes. If the annealing temperature is less than the above range, the time required to dissolve the precipitates is prolonged, resulting in poor productivity, and if the annealing temperature exceeds the above range, the equipment is overloaded and the steel plate is overloaded. A scale is formed on the surface layer, and the surface properties of the product deteriorate due to poor pickling. Further, if the holding time is less than the above range, the solid solution of the precipitate becomes insufficient, so the effect of the present invention cannot be obtained, and if the holding time exceeds the above range, a scale is formed on the surface of the steel sheet, resulting in poor pickling. As a result, the surface properties of the product deteriorate. In order to improve the effect of suppressing the disappearance of dislocations and recrystallization, it is preferable that the annealing temperature is 900 ° C. or higher and the holding time is 30 seconds or longer. A more preferable holding time is 60 seconds or more.

  The reason why the annealing performed before the final cold rolling is continuous annealing is that the cooling rate after annealing is larger in the continuous annealing than in the case of box annealing, so that the solid solution precipitate is reprecipitated during cooling. This is because it can be suppressed. The effect of this invention can be acquired if the cooling rate in the continuous annealing line used for the hot-rolled sheet annealing of a non-oriented electrical steel sheet is generally employ | adopted. A preferable lower limit of the cooling rate is set to 10 ° C./s from the viewpoint of suppressing reprecipitation during cooling and from the viewpoint of suppressing a long cooling time. From the viewpoint of suppressing reprecipitation, the larger the cooling rate, the better. Therefore, the upper limit of the cooling rate is not particularly limited, but 100 ° C./s or less is preferable from the viewpoint of suppressing an excessive load on the equipment. You may use the equipment which has a cooling rate larger than the above-mentioned value, such as a water cooling equipment and a roll cooling equipment.

  In this step, the sheet may be finished to a predetermined thickness by one cold rolling, or may be finished by two or more cold rolling sandwiching intermediate annealing. From the viewpoint of productivity, if the product sheet thickness is up to 0.35 mm, it is preferable to finish the sheet to a desired sheet thickness by a single cold rolling after performing hot-rolled sheet annealing.

  Since the effect of the present invention can be obtained if dislocations are sufficiently introduced, various conditions for cold rolling, such as the steel sheet temperature during cold rolling, the rolling reduction, and the rolling roll diameter, are not particularly limited, The material is appropriately selected depending on the steel composition of the material to be rolled, the thickness of the target steel sheet, and the like. Light processing may be performed for the purpose of correcting the flatness of the steel sheet before being subjected to the soaking process. Light processing in that case is not counted in the number of cold rolling.

  Moreover, when performing cold rolling only once without performing intermediate annealing, it is necessary to subject hot-rolled steel sheet to hot-rolled sheet annealing under predetermined conditions, but hot-rolled sheet annealing is an essential process, When performing cold rolling twice or more with intermediate annealing, hot-rolled sheet annealing may or may not be performed before cold rolling. When hot-rolled sheet annealing is performed, there is an advantage that the ductility of the steel sheet is improved and breakage in cold rolling can be suppressed.

  When performing cold rolling at least twice with intermediate annealing and performing hot-rolled sheet annealing before cold rolling, the conditions for intermediate annealing before final cold rolling may be optimized. Therefore, various conditions of hot-rolled sheet annealing such as annealing temperature, holding time, method (continuous annealing / box annealing) at the time of hot-rolled sheet annealing are not particularly limited, depending on the steel composition of the hot-rolled steel sheet, etc. Shall be selected. In addition, when performing intermediate annealing twice or more, it is only necessary to optimize the conditions of intermediate annealing before the final cold rolling as described above, so intermediate annealing other than the intermediate annealing before the final cold rolling is performed. As for, various conditions of intermediate annealing such as annealing temperature, holding time, method (continuous annealing / box annealing) during intermediate annealing are not particularly limited, and are appropriately selected depending on the steel composition of the material to be rolled, etc. To do.

4). Soaking process The soaking process in the present invention is a process in which the cold-rolled steel sheet obtained by the above-described cold-rolling process is soaked to obtain a steel sheet having an area ratio of recrystallized portions of less than 90%.

  The area ratio of the recrystallized portion is determined from the viewpoint of ensuring the mechanical characteristics necessary for the rotor. From the viewpoint of suppressing deformation during high-speed rotation, the area ratio of the recrystallized portion is less than 90%. 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 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 field of view in the longitudinal cross-sectional structure photograph of the non-oriented electrical steel sheet for rotor obtained by the present invention. It can be measured based on a photograph. 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.

  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, the content of Nb, Zr, Ti, and V and the annealing conditions applied to the steel sheet before the final cold rolling are optimized, so that the effect of suppressing recrystallization is great. Even when the C content is large, the dislocation disappearance and the recrystallization suppressing effect are sufficiently exhibited under the soaking condition of a normal non-oriented electrical steel sheet. 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 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, the more the progress of recrystallization is suppressed. However, if the soaking temperature is too 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 an effect of improving the iron loss as compared with the state of cold rolling by soaking, the iron loss increases when the soaking temperature is too low. Furthermore, when the soaking temperature is too 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 any method of box annealing and continuous annealing, but it is desirable to carry out 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. It is preferable to perform the correction process which corrects the flatness and shape of a steel plate after a process.

  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.

5). Other Steps In the present invention, after the soaking step, it is preferable to perform a coating step of applying an insulating film made of only an organic component, only an inorganic component, or an organic-inorganic composite to the steel sheet surface according to a general method. . From the viewpoint of reducing environmental burden, an insulating film not containing chromium may be applied. 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.

  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.
[Example 1]
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. and a winding temperature of 580 ° C., and the thickness is 2. A 0 mm hot rolled steel sheet was obtained. Among these, hot-rolled sheet annealing is omitted for hot-rolled steel sheets of steels A to H, or hot-rolled sheet annealing is performed by box annealing or continuous annealing, and the thickness is reduced by a single cold rolling. Finished to 0.35 mm. Then, the soaking | uniform-heating process by the continuous annealing hold | maintained for 30 second at the annealing temperature of 700 degreeC was performed. Table 2 below shows the hot-rolled sheet annealing conditions.

The obtained steel sheet was examined for magnetic properties, mechanical properties, area ratio of recrystallized portion and specific gravity.
Mechanical properties were evaluated by performing a tensile test using a JIS No. 5 test piece with the rolling direction as the longitudinal direction and yield point: YP and tensile strength: TS.
As magnetic characteristics, specimens were collected according to JIS C 2550, and the iron loss W _10/400 at a maximum magnetic flux density of 1.0 T and an excitation frequency of 400 Hz was measured.
As the area ratio of the recrystallized portion, the ratio of the recrystallized grains in the field of view was calculated using a longitudinal cross-sectional optical microscope photograph taken at a magnification of 100 times.
About specific gravity, the weight in water and the weight in air were measured, and it evaluated by the Archimedes method which considered the density of the water in measurement temperature.
The results are shown in Table 2.

Steel plates with test numbers 1-1 to 1-3 and 1-13 to 1-15 using steels A and E whose contents of Nb, Ti, Zr and V are outside the scope of the present invention Since recrystallization cannot be suppressed, the mechanical properties were inferior regardless of hot-rolled sheet annealing conditions. In the steel sheets of test numbers 1-4 to 1-12 using steels B, C and D in which the contents of Nb, Ti, Zr and V are within the scope of the present invention, the hot-rolled sheet annealing conditions are defined by the present invention. Only when the conditions were satisfied, recrystallization during soaking was suppressed, and excellent mechanical properties could be obtained. The content of Nb, Ti, Zr and V is in a preferred range defined in the present invention (0 <Nb / 93 + Zr / 91 + Ti / 48 + V / 51− (C / 12 + N / 14) <5 × 10 ⁻³ ), and In the steel sheets of test numbers 1-16 to 1-24 using steels F, G and H in which the C content is within the preferred range specified by the present invention (0.01% or less), hot rolled sheet annealing is performed according to the present invention. The mechanical properties were improved when the conditions specified in (1) were satisfied.

[Example 2]
Among the hot-rolled steel sheets described in Example 1, with respect to the hot-rolled steel sheets of Steels D and H, the intermediate sheet thickness is 1 under various hot-rolled sheet annealing conditions and intermediate annealing conditions shown in Table 3 below. Two cold rollings with a thickness of 0.0 mm were performed to finish the plate thickness to 0.27 mm. Then, the soaking | uniform-heating process by the continuous annealing hold | maintained for 30 second at the annealing temperature of 700 degreeC was performed.
The obtained steel sheet was examined in the same manner as in Example 1 for the magnetic properties, mechanical properties, area ratio and specific gravity of the recrystallized portion. The results are shown in Table 3.

In the steel sheets of test numbers 2-1 to 2-6 using the steel D in which the contents of Nb, Ti, Zr and V are within the scope of the present invention, intermediate annealing which is annealing before the final cold rolling is performed. Only when the conditions specified in the invention were satisfied, recrystallization during soaking was suppressed, and excellent mechanical properties were obtained. The content of Nb, Ti, Zr and V is in a preferred range defined in the present invention (0 <Nb / 93 + Zr / 91 + Ti / 48 + V / 51− (C / 12 + N / 14) <5 × 10 ⁻³ ), and In the steel sheets of test numbers 2-7 to 2-12 using steel H in which the C content is in the preferred range specified by the present invention (0.01% or less), intermediate annealing which is annealing before the final cold rolling Improved the mechanical properties when the conditions specified in the present invention were satisfied.

[Example 3]
Of the hot-rolled steel sheets described in Example 1, hot-rolled steel sheets under various conditions shown in Table 4 below are used for hot-rolled steel sheets of steels D, H, I, J, K, L, M, and N. Annealing was performed. Subsequently, except for test number 3-16, the sheet thickness was finished to 0.35 mm by one cold rolling. Test No. 3-16 was finished to a sheet thickness of 0.35 mm by two cold rolling operations in which the intermediate sheet thickness was 1.0 mm and the intermediate annealing was continuously annealed at 1000 ° C. for 1 minute. Thereafter, these steel sheets were subjected to soaking treatment by continuous annealing that was held at various temperatures for 30 seconds. The reason why test number 3-16 using steel L was cold-rolled twice is to suppress breakage during cold rolling.
The obtained steel sheet was examined in the same manner as in Example 1 for the magnetic properties, mechanical properties, area ratio and specific gravity of the recrystallized portion. The results are shown in Table 4.

Even in the case of steel D in which the contents of Nb, Ti, Zr and V are within the scope of the present invention, the temperature and time during hot-rolled sheet annealing as in test numbers 3-1 and 3-2 When it was out of the range, the progress of recrystallization could not be suppressed and the mechanical properties were inferior. In addition, when the soaking temperature was excessively high as in test number 3-6, recrystallization proceeded and the mechanical properties were inferior.
The content of Nb, Ti, Zr and V is in a preferred range defined in the present invention (0 <Nb / 93 + Zr / 91 + Ti / 48 + V / 51− (C / 12 + N / 14) <5 × 10 ⁻³ ), and In the steel H in which the C content is in a preferable range (0.01% or less) defined in the present invention, even if the hot soaking is performed under the conditions defined in the present invention, the same soaking temperature is obtained. Improved mechanical properties.

  The steel plate with test number 3-13 has a high Si content, the steel plate with test number 3-14 has a high Al content, and the steel plate with test number 3-15 has a high P content. Sometimes broke. The steel sheets of Test Nos. 3-16 had a high C and Mn content, and the steel structure was a martensite structure, so the iron loss increased significantly. The steel plate of test number 3-17 broke during cold rolling because the contents of Nb, Zr, Ti and V exceeded the preferable range specified in the present invention. The steel plate of Test No. 3-18 had a high specific gravity due to the low Al content.

  From the above-mentioned Examples 1 to 3, even when finishing to a desired sheet thickness by one cold rolling, it is a case to finish to a desired sheet thickness by two or more cold rolling sandwiching intermediate annealing. However, when the steel composition and annealing conditions performed before the final cold rolling are within the scope of the present invention, a non-oriented electrical steel sheet that satisfies the magnetic and mechanical properties required for the rotor can be obtained. It was. The specific gravity obtained was found to be as low as 7.31 to 7.35. These specific gravity levels can reduce the weight of the rotor having the same shape by 3 to 4% compared to the case where the steel plate of test number 3-18 is used.

Claims (2)

  In mass%, C: 0.06% or less, Si: 3.5% or less, Mn: 0.05% or more and 3.0% or less, Al: more than 2.5% and 6.0% or less, P: 0.0. 30% 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 in total 0.02% or more A hot rolling process in which a steel ingot or steel slab containing Fe and impurities is hot-rolled, and a hot rolled steel sheet obtained by the hot rolling process is sandwiched once or intermediately. A cold rolling process in which cold rolling is performed more than once, and the steel sheet before the final cold rolling is subjected to continuous annealing at a temperature of 850 ° C. to 1200 ° C. for 10 seconds to 5 minutes, and the cold rolling The cold-rolled steel sheet obtained by the process is subjected to soaking, and the area ratio of the recrystallized portion is less than 90% Method for producing a non-oriented electrical steel sheet for a rotor and having a soaking step of obtaining a plate. The steel ingot or steel slab contains at least one element selected from the group consisting of Nb, Zr, Ti, and V in a range satisfying the following formula (1). Method for non-oriented electrical steel sheet for rotors.
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.)