JP5613134B2 - Rotor core for permanent magnet motor - Google Patents

Description

  The present invention relates to a rotor iron core used in a permanent magnet motor and a rotor provided with the rotor iron core.

  An SPM (Surface Permanent Magnet) motor is known as a permanent magnet motor. FIG. 1 is a partially enlarged view schematically showing an example of the structure of an SPM motor. The SPM motor 1 has a permanent magnet on the surface of a rotor core 2 (2a is an end surface of the rotor core, 2b is a side surface of the rotor core). 3 and a stator 7 in which a coil 6 is wound around a stator iron core 5. As shown in FIG. 1, the rotor core 2 may have a shaft 8 inserted therein, or may not use the shaft 8 and may use a columnar (solid) stator core (not shown). ). SPM motors have a simple structure, and are widely used as industrial motors and automobile motors because they are excellent in miniaturization (weight reduction) and motor characteristics (high torque).

  The stator iron core is usually produced by punching a laminate of electromagnetic steel sheets, and the rotor iron core is produced by cutting the remaining material after the stator iron core is punched. In order to improve motor characteristics, the stator core material is required to have low iron loss in an alternating magnetic field, and electromagnetic steel sheets have been developed with a focus on reducing iron loss in an alternating magnetic field. For example, in order to increase the electrical resistance of an electromagnetic steel sheet, a large amount of Si or Al is contained, and an insulating layer is formed on the steel sheet surface.

  On the other hand, since the magnetic flux carried by the rotor core is mostly DC component, it is desired that the magnetic flux density is high in the DC magnetic field. However, when Si or Al is positively added, the ferrite phase ratio contained in the magnetic steel sheet is lowered, and it is difficult to obtain a high magnetic flux density in a DC magnetic field. Therefore, when a rotor core cut out from an electromagnetic steel sheet to which Si or Al is positively added is used, there is a limit in maximizing the performance of the SPM motor.

  In recent years, in order to increase the winding density of the stator, it has been studied to separately form the stator core. Therefore, it is not necessary to manufacture the rotor core using the remaining material after the stator core is punched out, and it has been considered to select suitable materials for the stator core and the rotor core.

  It is known that a pure iron-based soft magnetic material may be used to increase the magnetic flux density in a DC magnetic field. By forming the soft magnetic material into the shape of the rotor core by forging, it can be expected to reduce the manufacturing cost and improve the motor characteristics.

  Patent Document 1 proposes a permanent magnet rotor in which a plurality of permanent magnets are bonded and fixed to an outer surface of a rotor core made of a magnetic material with an adhesive. This document discloses a technique for increasing the adhesive strength between the rotor core and the permanent magnet by forming an Al film on the surface of the rotor core or the permanent magnet.

Patent Document 2 discloses a magnetic circuit member for an alternating current electromagnetic valve that has high electrical resistance, has excellent high-speed response, can be mass-produced, and can reduce product cost. In this document, it is possible to improve the machinability and cold forgeability by using electromagnetic soft iron or low carbon steel as the base material of the magnetic circuit member, and the electrical resistance is increased by containing Al in the magnetic circuit member. It is described that eddy current loss can be reduced. As a method for incorporating Al in the magnetic circuit member, a magnetic circuit member made of electromagnetic soft iron is embedded in a mixture of Al powder and Al ₂ O ₃ powder and NH ₄ Cl added, and 900 ° C. in a hydrogen stream. A method of performing a heat treatment for 3 hours is adopted.

JP 2003-224944 A JP-A-63-3318380

  As a result of studies by the present inventors, as proposed in Patent Document 1, when an Al coating is formed between the rotor iron core and the permanent magnet (that is, the side surface of the rotor iron core), the magnetoresistance of the rotor iron core is reduced. It has been found that the motor characteristics of the permanent magnet motor provided with the increase and the rotor iron core are deteriorated.

  Further, as proposed in Patent Document 2, when Al is diffused in a magnetic circuit member by a powder coating method, the Al concentration on the surface of the member varies, and a layer having a significantly high Al concentration (for example, It was found that when a layer containing 20% by mass or more of Al) is formed, the portion becomes a nonmagnetic phase and the motor characteristics deteriorate.

  By the way, it has been found that the motor characteristics are greatly influenced by the amount of iron loss of the rotor core, and that the iron loss of the rotor core is generated at the end of the rotor core due to leakage magnetic flux (AC magnetic field) from the stator core. Therefore, in order to reduce the iron loss of the rotor core, it is conceivable to make the rotor core longer than the stator core, but there is a problem that the motor cannot be reduced in size.

  The present invention has been made in view of such circumstances, and a rotor core for a permanent magnet motor that can manufacture a motor having motor characteristics equal to or higher than that of a permanent magnet motor provided with a rotor core manufactured using an electromagnetic steel sheet. Is to provide. Another object of the present invention is to provide a rotor for a permanent magnet motor provided with the rotor core.

  The rotor core for a permanent magnet motor according to the present invention that has solved the above problems has a chemical composition of the parent phase of C: 0.002 to 0.02% (meaning mass%; the same applies hereinafter). Si: 3% or less (excluding 0%), Mn: 0.1 to 0.5%, P: 0.03% or less (excluding 0%), S: 0.03% or less (0% Cu: 0.1% or less (not including 0%), Ni: 0.1% or less (not including 0%), Cr: 1.6% or less (not including 0%), Al : 0.002 to 0.04%, N: 0.005% or less (excluding 0%), balance: iron and inevitable impurities, which is a rotor core for a columnar or cylindrical permanent magnet motor.

And the rotor core for permanent magnets of the present invention is
(A) When an Al diffusion layer in which the Al amount decreases from the outermost surface side of the end portion toward the center portion and when the Al concentration on the end surface is measured at a plurality of locations, the maximum value (Al _max ) and the minimum The value (Al _min ) ratio (Al _max / Al _min ) is 1.0 to 1.5, or
(B) The Sn diffusion layer in which the Sn amount decreases from the outermost surface side of the end portion toward the center portion, and the maximum value (Sn _max ) and the minimum when the Sn concentration on the end surface is measured at a plurality of locations. value ratio _{(Sn min) (Sn max /} Sn min) has a gist in that 1.0 to 1.5.

  Of the Al diffusion layers, the thickness of the optimum Al diffusion layer containing 1% by mass or more of Al is preferably 40 μm or more. The Al concentration in the end face is preferably 18% by mass or less (excluding 0% by mass).

  Of the Sn diffusion layers, the thickness of the optimum Sn diffusion layer containing 1% by mass or more of Sn is preferably 40 μm or more. The Sn concentration in the end face is preferably 18% by mass or less (not including 0% by mass).

  It is recommended that the ferrite fraction in the matrix metal structure is 99 area% or more and the ferrite grain size number is 5.5 or less.

  The parent phase may further contain B: 0.006% or less (excluding 0%) as another element.

  The present invention also includes a permanent magnet motor rotor in which a permanent magnet is fixed to the outer surface of the permanent magnet motor rotor core, and a permanent magnet motor including the rotor.

  According to the present invention, since the Al diffusion layer or the Sn diffusion layer is formed at the end portion of the rotor core, the Al diffusion layer or the Sn diffusion layer can increase the electric resistance of the end portion and reduce the eddy current loss. As a result, since the magnetic characteristics of the rotor core are improved, the permanent magnet motor having the rotor core has good motor characteristics.

FIG. 1 is a partially enlarged view schematically showing an example of the structure of an SPM motor. FIG. 2 is a schematic diagram showing the shape of a test piece in which the rotor core and the shaft used in the examples are combined. FIG. 3 is a graph showing the relationship between torque applied to the evaluation motor and motor efficiency. FIG. 4 is a graph showing the relationship between the rotation speed of the evaluation motor and the motor efficiency.

The present inventors have repeatedly investigated the relationship between the motor characteristics of a permanent magnet motor and the rotor core provided in the permanent magnet motor. as a result,
(1) Leakage magnetic flux from the stator causes eddy current loss at the end of the rotor core, and this eddy current loss has an adverse effect on the motor characteristics of the permanent magnet motor;
(2) In order to reduce this eddy current loss, a pure iron-based steel material having a high magnetic flux density may be used as a material for the rotor core, and the electrical resistance at the end of the rotor core may be increased.
(3) The present invention has been completed by finding that an Al diffusion layer or a Sn diffusion layer may be formed in order to increase the electric resistance.

  That is, the rotor core of the present invention can reduce the iron loss of the rotor core itself by using a high magnetic flux density material with a small amount of C as the material, and locally increasing the electrical resistance at the end, and further reducing the stator core itself. Since the iron loss at the end due to the magnetic flux leaked from can be reduced, the motor characteristics can be improved. In order to suppress the iron loss reduction at the end, it is effective to form an Al diffusion layer or a Sn diffusion layer. For example, the end surface has an Al coating or a Sn coating and is processed into the shape of a rotor core. By heat-treating the steel material, Al or Sn formed on the surface of the end face is uniformly diffused into the steel material. According to this method, since Al or Sn diffuses and penetrates uniformly from the end face of the steel material, a portion where Al or Sn is excessively concentrated locally does not occur on the surface of the end face. Accordingly, it has been clarified that the non-magnetic phase is not formed on the end face and the deterioration of the motor characteristics can be prevented.

  Hereinafter, the rotor core of the present invention will be described in detail.

  The rotor core of the present invention has a columnar shape (for example, a columnar shape) or a cylindrical shape (for example, a cylindrical shape), and an Al diffusion layer or an Sn diffusion layer is formed at the end. The columnar shape includes a substantially columnar shape (for example, a substantially columnar shape) provided with a stepped portion in which rings having different diameters are stacked in the axial direction, and the cylindrical shape is a stack of rings having different diameters in the axial direction. This means that it includes a substantially cylindrical shape (for example, a substantially cylindrical shape) provided with a level difference. The end surface means a surface perpendicular to the axial direction of the rotor core. The end means the vicinity including the end face, and refers to, for example, a region from the end face to a depth of about 500 μm.

<About Al diffusion layer>
The Al diffusion layer means a region where the amount of Al is larger than the amount of Al contained in the parent phase and the amount of Al decreases from the outermost surface side of the end toward the center. Since the eddy current loss generated on the end face can be reduced by tilting the Al concentration at the end, the motor characteristics can be effectively improved.

  The Al diffusion layer is preferably formed with an Al diffusion layer containing 1% by mass or more of Al (hereinafter referred to as an optimal Al diffusion layer). If the Al content is less than 1% by mass, the electrical resistance at the end cannot be sufficiently increased, so that eddy current loss cannot be reduced and the motor characteristics cannot be sufficiently improved.

  The thickness of the optimum Al diffusion layer is preferably 40 μm or more. By setting the thickness to 40 μm or more, the electric resistance at the end can be sufficiently increased, so that the eddy current loss is reduced and the motor characteristics can be further improved. The thickness of the optimum Al diffusion layer is more preferably 50 μm or more, further preferably 70 μm or more, and particularly preferably 100 μm or more. Note that the upper limit of the thickness of the optimum Al diffusion layer is not particularly limited, and may be, for example, more than 250 μm, but may be 500 μm or less from the viewpoint of suppressing cost increase due to heat treatment.

The rotor iron core of the present invention has a ratio (Al _max / Al _min ) between the maximum value (Al _max ) and the minimum value (Al _min ) of 1.0 to 1.5 when the Al concentration on the end face is measured at a plurality of locations. is there. If the ratio exceeds 1.5, the variation in Al concentration at the end face increases, and a nonmagnetic phase is locally generated, resulting in deterioration of motor characteristics. The ratio is preferably 1.0 to 1.3.

  The maximum value of Al concentration at the end face is preferably 18% by mass or less (not including 0% by mass). If the maximum Al concentration exceeds 18% by mass, the spontaneous magnetization may be reduced, and the motor characteristics may be deteriorated. Therefore, the maximum Al concentration is preferably 18% by mass or less, more preferably 15% by mass or less, and still more preferably 10% by mass or less.

<< Sn diffusion layer >>
The Sn diffusion layer means a region where the amount of Sn decreases from the outermost surface side of the end toward the center. Since the eddy current loss generated on the end face can be reduced intensively by inclining the Sn concentration at the end, the motor characteristics can be effectively improved.

  Since the Sn diffusion layer exhibits the same effect as the Al diffusion layer, the reason for its definition is the same.

  That is, the Sn diffusion layer is preferably formed with an Sn diffusion layer containing 1% by mass or more of Sn (hereinafter referred to as an optimal Sn diffusion layer). If Sn is less than 1% by mass, the electric resistance at the end cannot be sufficiently increased, so eddy current loss cannot be reduced and the motor characteristics cannot be improved sufficiently.

  The thickness of the optimum Sn diffusion layer is preferably 40 μm or more. By setting the thickness to 40 μm or more, the electric resistance at the end can be sufficiently increased, so that the eddy current loss is reduced and the motor characteristics can be further improved. The thickness of the optimum Sn diffusion layer is more preferably 50 μm or more, further preferably 70 μm or more, and particularly preferably 100 μm or more. Note that the upper limit of the thickness of the optimum Sn diffusion layer is not particularly limited, and may be, for example, more than 250 μm, but may be 500 μm or less from the viewpoint of suppressing cost increase due to heat treatment.

The rotor core of the present invention has a ratio (Sn _max / Sn _min ) between the maximum value (Sn _max ) and the minimum value (Sn _min ) of 1.0 to 1.5 when the Sn concentration at the end face is measured at a plurality of locations. is there. If the ratio exceeds 1.5, the variation in Sn concentration at the end face increases, so a nonmagnetic phase is locally generated and the motor characteristics deteriorate. The ratio is preferably 1.0 to 1.3.

  The maximum value of the Sn concentration at the end face is preferably 18% by mass or less (not including 0% by mass). If the maximum Sn concentration exceeds 18% by mass, the spontaneous magnetization may be reduced, which may deteriorate the motor characteristics. Accordingly, the maximum Sn concentration is preferably 18% by mass or less, more preferably 15% by mass or less, and still more preferably 10% by mass or less.

  The Al concentration or the Sn concentration in the end portion and the end surface is determined by, for example, an electron probe X in a region from the end surface to a depth of 500 μm on the cut surface exposed by cutting so as to be parallel to the axial direction of the rotor core. What is necessary is just to measure several places (for example, four or more places) with a line microanalyzer (Electron Probe X-ray Micro Analyzer; EPMA).

  Next, the component composition of the rotor core according to the present invention will be described.

  In the rotor core of the present invention, the chemical composition of the parent phase is C: 0.002 to 0.02%, Si: 3% or less (not including 0%), Mn: 0.1 to 0.5%, P: 0.03% or less (not including 0%), S: 0.03% or less (not including 0%), Cu: 0.1% or less (not including 0%), Ni: 0.1 % Or less (not including 0%), Cr: 1.6% or less (not including 0%), Al: 0.002 to 0.04%, and N: 0.005% or less (not including 0%) ) And the balance: iron and inevitable impurities. The reason for specifying such a range is as follows.

  C is an important element for securing the strength of the rotor core. However, when C is excessively contained, C dissolved in the steel distorts the Fe lattice, lowers the magnetic moment, and decreases the magnetic flux density, so that the motor characteristics deteriorate. Accordingly, the C content is 0.02% or less, preferably 0.015% or less, more preferably 0.01% or less. Since the rotor core (particularly, the SPM rotor core) is required to have a high magnetic flux density, it is desirable that the C amount be as small as possible. However, the effect of reducing the C amount and increasing the magnetic moment is saturated when the C amount is about 0.002%. Moreover, if the amount of C is reduced too much, the strength of the rotor iron core will be too low. Therefore, C is 0.002% or more, preferably 0.003% or more, more preferably 0.004% or more.

  Si is an element that acts as a deoxidizer during melting. Si also has the effect of reducing the magnetic anisotropy and increasing the magnetic flux density to improve the motor characteristics. In order to exhibit such an effect effectively, it is preferable to contain Si 0.001% or more. More preferably, it is 0.003% or more, More preferably, it is 0.005% or more. However, these effects are saturated even if Si is contained in excess of 3%. Moreover, when it contains excessively, the cold forgeability at the time of shape | molding steel materials in the shape of a rotor iron core will deteriorate significantly. Therefore, the amount of Si is 3% or less, preferably 2.5% or less, more preferably 2.00% or less.

  Mn is an element used as a deoxidizer during melting. Moreover, in steel, it combines with S to form sulfide (MnS) and has an action of suppressing embrittlement due to S. Furthermore, sulfide precipitates around sulfides and oxides in steel to form composite precipitates, increasing the electrical resistivity of the rotor core and reducing eddy current loss, improving motor characteristics Has an effect. In order to exhibit such an effect, Mn is 0.1% or more, preferably 0.15% or more, more preferably 0.2% or more, and particularly preferably 0.25% or more. However, when Mn becomes excessive, the ferrite phase becomes unstable, the magnetic moment decreases, the magnetic flux density decreases, and the motor characteristics deteriorate. Therefore, Mn is 0.5% or less, preferably 0.45% or less, more preferably 0.4% or less.

  P is an element that segregates at grain boundaries and degrades hot workability and cold workability. Therefore, P is 0.03% or less, preferably 0.02% or less, more preferably 0.01% or less. It is desirable that P is reduced as much as possible.

  S combines with Mn or the like to form a sulfide (for example, MnS), increases the electrical resistivity of the rotor core, reduces eddy current loss, and has an effect of improving motor characteristics. However, when S is contained excessively, magnetic properties and cold forgeability are lowered by FeS produced at a grain boundary in large quantities and MnS produced in steel. Therefore, S is 0.03% or less, preferably 0.02% or less, more preferably 0.015% or less.

  Cu is an element that improves the strength by dissolving in ferrite. Moreover, it has the effect | action which raises an electrical resistivity and reduces eddy current loss and improves a motor characteristic. In order to effectively exhibit such an action, Cu is preferably contained in an amount of 0.005% or more, and more preferably 0.01% or more. However, if it is contained excessively, the magnetic flux density is lowered, the motor characteristics are deteriorated, and the cold forgeability is also deteriorated. Therefore, Cu is 0.1% or less, preferably 0.08% or less, more preferably 0.05% or less.

  Ni is an element having the same action as Cu. That is, it is an element that improves the strength by dissolving in ferrite. Moreover, it has the effect | action which raises an electrical resistivity and reduces an eddy current loss and improves a motor characteristic. In order to effectively exhibit such an action, Ni is preferably contained in an amount of 0.005% or more, and more preferably 0.01% or more. However, if it is contained excessively, the magnetic flux density is lowered, the motor characteristics are deteriorated, and the cold forgeability is also deteriorated. Therefore, Ni is 0.1% or less, preferably 0.08% or less, more preferably 0.05% or less.

  Cr is an element that acts to increase the electrical resistance of the rotor core, reduce eddy current loss, and improve motor characteristics. It also has the effect of improving the motor characteristics by making the metal structure of the rotor core ferrite. In order to effectively exhibit these actions, Cr is preferably contained in an amount of 0.005% or more, more preferably 0.01% or more, and further preferably 0.1% or more. However, when Cr exceeds 1.6%, the magnetic moment is lowered and a high magnetic flux density cannot be obtained. Therefore, Cr is 1.6% or less, preferably 1% or less, more preferably 0.5% or less.

  Al is an element that has the effect of improving the motor characteristics by combining with N in the steel to form AlN and suppressing the deterioration of the magnetic characteristics due to solute N. Therefore, Al is made 0.002% or more, preferably 0.003% or more. However, if it is contained excessively, a large amount of AlN is formed, the growth of crystal grains is inhibited by this AlN, and the grain boundaries increase, thereby deteriorating the magnetic properties. Further, Al that is not bonded to N dissolves in the ferrite and acts to increase the strength, so that the deformation resistance increases and the cold forgeability deteriorates. Therefore, Al is 0.04% or less, preferably 0.02% or less, more preferably 0.015% or less.

  If N is contained excessively, a large amount of AlN is formed, and this AlN inhibits the growth of crystal grains and increases the grain boundaries, so that the magnetic characteristics deteriorate and the motor characteristics deteriorate. Further, when N is contained excessively and the solid solution N increases, the magnetic characteristics are lowered and the motor characteristics are deteriorated. Furthermore, the steel material is age-hardened by excessive N, cracks are generated during cold forging, and cold forgeability deteriorates. Therefore, N is 0.005% or less, preferably 0.004% or less, more preferably 0.003% or less.

  The balance of the steel material is iron and inevitable impurities. As inevitable impurities, elements mixed in depending on the situation of raw materials, materials, manufacturing equipment, etc. are allowed.

  The steel material may further contain B: 0.006% or less (not including 0%) as another element.

B is an element for precipitating solute N in steel as BN, and by reducing the solute N, it is possible to suppress deterioration of cold forgeability due to dynamic strain aging and to reduce the magnetic moment of the ferrite structure. It can be increased to improve the magnetic properties. In addition, it has the effect of reducing AlN that inhibits crystal grain growth and increasing the Ac ₃ point to expand the ferrite stabilization region. Can be realized. In order to exhibit such an effect effectively, it is preferable to make it contain 0.001% or more, More preferably, it is 0.0015% or more. However, if contained excessively, Fe ₂ B precipitates along the grain boundary, the grain boundary strength decreases, and the magnetic properties and cold forgeability deteriorate. Therefore, the B content is 0.006% or less, preferably 0.005% or less, more preferably 0.004% or less.

  Next, a manufacturing method that can be suitably used in manufacturing the rotor core of the present invention will be described.

  The rotor core can be manufactured by heat-treating a steel material having an Al film or a Sn film on the end face of a columnar or cylindrical steel material that satisfies the chemical component composition. That is, by forming an Al film or Sn film on the end face of the steel material and heat-treating it, Al or Sn can be diffused and penetrated uniformly from the end face to the inside. As a result of this diffusion permeation, the Al diffusion layer or Sn diffusion layer can be formed at the end, and these diffusion layers become high electrical resistance layers, and eddy current loss is reduced. As a result, motor characteristics can be improved. As described above, in the present invention, Al or Sn is uniformly diffused and penetrated from the surface to the inside, so that it is possible to prevent the Al concentration or the Sn concentration from being locally increased.

  The steel material before heat treatment has an Al film or Sn film on the surface of the end surface, and may be processed into a columnar or cylindrical part shape, and the step of forming the Al film or Sn film on the end surface of the steel material; The order of the steps for processing the steel material into the part shape is not particularly limited. That is, the steel material may be processed into a part shape and then an Al film or Sn film may be formed, or an Al film or Sn film may be formed on the steel material and processed into a part shape. The component shape is a columnar shape or a cylindrical shape, and may be a columnar shape or a cylindrical shape, for example. The processing to the part shape may be performed by cold forging, for example.

  The thickness of the Al film may be, for example, 5 to 20 μm. Preferably it is 8-18 micrometers.

  The method for forming the Al film is not particularly limited, and examples thereof include chemical vapor deposition (CVD), physical vapor deposition (PVD), and plating. Examples of the plating method include a molten Al plating method and an electric Al plating method. Among these, it is preferable to manufacture by the hot Al plating method.

  When forming an Al film by the hot-dip Al plating method, for example, a pure Al plating bath or an Al plating bath containing 15% by mass or less (not including 0%) of Si is used as a plating bath. May be set to 800 ° C. or lower (for example, 650 to 700 ° C.), and the immersion time may be set to 1 to 10 minutes.

  On the other hand, the thickness of the Sn film may be 5 to 20 μm, for example. Preferably it is 8-18 micrometers.

  The method for forming the Sn film is not particularly limited, and examples thereof include chemical vapor deposition (CVD), physical vapor deposition (PVD), and plating. Examples of the plating method include a hot Sn plating method and an electric Sn plating method. Among these, it is preferable to manufacture by an electric Sn plating method.

  The heat treatment is preferably performed at a heating temperature of 850 ° C. or higher and a heating time of 1 hour or longer. When the heating temperature is lower than 850 ° C. or the heating time is shorter than 1 hour, Al or Sn does not sufficiently diffuse and penetrate from the surface side toward the inside, so that a desired Al diffusion layer or Sn diffusion layer cannot be formed. Sometimes.

  The heating temperature is more preferably 900 ° C. or higher, further preferably 950 ° C. or higher, and particularly preferably 1000 ° C. or higher. The heating temperature is desirably set as high as possible in order to diffuse and infiltrate Al or Sn from the surface side toward the inside. Moreover, since heat treatment at a high temperature can prevent the formation of a nonmagnetic phase such as FeAl at the end, magnetic characteristics can be improved and motor characteristics can be improved.

  The heating time is more preferably 3 hours or longer, and still more preferably 5 hours or longer. The heating time is desirably set as long as possible in order to diffuse and penetrate Al or Sn from the surface side toward the inside. However, if the heating time is too long, the productivity will deteriorate, so the upper limit is preferably set to 15 hours, for example.

It is recommended that the heat treatment be performed in an inert gas atmosphere (for example, an N ₂ gas atmosphere or an Ar gas atmosphere) or a reducing atmosphere in order to suppress oxidation of the surface layer portion. As the reducing gas, for example, hydrogen may be contained.

  What is necessary is just to let the temperature increase rate when heating to the said heating temperature be 100-400 degreeC / hour, for example. Moreover, what is necessary is just to let the temperature fall rate when cooling to room temperature after heat processing be 100-400 degreeC / hour, for example.

  The obtained rotor iron core can manufacture a rotor for a permanent magnet motor by fixing a permanent magnet to the outer surface. The permanent magnet may be fixed by a known method, and for example, an adhesive can be used. The permanent magnet may be fixed as an integral type magnetized with multiple poles along the outer periphery of the rotor core, or may be fixed as divided for each magnetic pole.

  When the rotor core is cylindrical, a metal (for example, steel) shaft may be inserted into the shaft position.

  On the other hand, a permanent magnet motor can be manufactured by preparing a stator manufactured using a magnetic steel sheet or the like and winding the coil around the stator and combining it with the rotor for the permanent magnet motor.

  Since the rotor core of the present invention has improved magnetic characteristics at the end, the permanent magnet motor provided with this rotor core has good motor characteristics. The permanent magnet motor can be used, for example, as an electrical component (for example, an SPM motor) that is driven through a magnetic force among components mounted on an automobile or an industrial machine.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

[No. 1-15, 17-21]
Steels having the chemical composition shown in Table 1 below (the balance being iron and inevitable impurities; steel types a to c and steel types e) were melted in a 240 ton converter, an 80 ton converter, or a 50 kg vacuum furnace. The melted material melted in the 240 ton converter or 80 ton converter was hot-rolled to produce a rolled material having a diameter of 50 mm. A steel ingot obtained from a smelted material melted in a 50 kg vacuum furnace was forged to produce a forged material having a diameter of 50 mm, and then subjected to a heat treatment of 30 minutes heating → air cooling by simulating hot rolling. .

  The rolled material or the forged material after heat treatment was cut into the shape of a rotor core, and the obtained rotor core for test was attached to an evaluation motor, and the motor characteristics were evaluated. As an evaluation motor, a commercially available SPM motor [Minebea DC brushless motor (24DCM-371), rated rotational speed: 3000 rpm, rated torque: 0.159 Nm] was prepared. The rotor core provided in the evaluation motor was taken out, and the rolled material or the forged material after heat treatment was cut so as to have the same shape. FIG. 2B shows the shape of a test piece in which a test rotor core and a shaft are combined. In FIG. 2B, reference numeral 2 denotes a test rotor core, 2a denotes an end surface of the test rotor core, and 8 denotes a shaft. As shown in FIG. 2, the test rotor core 2 has a substantially cylindrical shape with a maximum diameter of 27 mm and a maximum height of 34 mm, and is provided with a level difference in the vicinity of both ends such that rings with different diameters are stacked. 2A is a view of the member shown in FIG. 2B viewed from the left side of the drawing, and FIG. 2C is a view of the member shown in FIG. 2B viewed from the right side of the drawing. Each shows. The “integrated product” of the rotor structure shown in Table 2 below means that the rotor core 2 and the shaft 8 are integrally formed by forging and cutting a lump of strip steel.

  An Al coating or Sn coating was formed on the end face or the entire surface of the obtained test rotor core by the following procedure, and this was heat-treated to form an Al diffusion layer or an Sn diffusion layer (No in Tables 2 and 3 below). .7, 12, 15, 16, 21). The end surface 2a of the test rotor core is the both end surfaces of the upper bottom surface and the lower bottom surface, and the entire surface of the test rotor core means all of the upper bottom surface, the lower bottom surface, and the side surfaces (FIG. 1, FIG. 2). Table 2 below shows the position where the film was formed. In the table, “-” means that no film is formed.

<About Al film>
The Al film was formed by a hot Al plating method or a powder coating method.

In the molten Al plating method, the test rotor iron core was immersed in a molten Al plating bath (bath temperature: 670 ° C.) containing about 10% by mass of Si for 2 minutes to form an Al film. The adhesion amount of the Al film was 41 g / m ² . Subsequently, after heating to a temperature shown in the following Table 2 in a hydrogen reduction atmosphere at a temperature rising rate of 300 ° C./hour, heat treatment was performed by holding at this temperature for 3 hours. After the heat treatment, it was cooled to room temperature at a temperature drop rate of 300 ° C./hour.

In the above-mentioned powder coating method, a mixed powder obtained by mixing equal amounts of Al powder (500 g) and Al ₂ O ₃ powder (500 g) and 10 g of NH ₄ Cl is put in a stainless steel case, and the above-described rotor for test is contained therein. The iron core was embedded and heat-treated in a hydrogen reduction atmosphere at 900 ° C. for 3 hours.

<< Sn film >>
The Sn film was formed by an electric Sn plating method.

In the electric Sn plating method, an Sn film having an adhesion amount of about 95 g / m ² (thickness of about 13 μm) was formed on the end face or the entire surface of the test rotor core. Subsequently, after heating to a temperature shown in the following Table 2 in a hydrogen reduction atmosphere at a temperature rising rate of 300 ° C./hour, heat treatment was performed by holding at this temperature for 3 hours. After the heat treatment, it was cooled to room temperature at a temperature drop rate of 300 ° C./hour.

  Next, the Al concentration or the Sn concentration at the end of the rotor core for test obtained by heat treatment was measured using EPMA (“JXA-8900RL (device name)” manufactured by JEOL Ltd.). In the measurement, the area from the Al film formation surface or the Sn film formation surface to a depth of 500 μm on the cut surface exposed by cutting so as to be parallel to the axial direction of the rotor core for test was measured with the EPMA beam. The diameter was 1 μm, and the measurement was performed at 1 μm intervals. As a result, the Al coating or Sn coating formed on the surface of the test rotor core diffused into the test rotor core by heat treatment. Further, the end portion of the test rotor core obtained by heat treatment has the gradient composition in which the Al amount or the Sn amount on the outermost surface is the largest and the Al amount or the Sn amount decreases toward the center, and the Al diffusion layer Or it turned out that Sn diffused layer is formed.

  When the Al coating or Sn coating is formed on the entire surface of the rotor core for test, and this is heat-treated, the Al concentration or Sn concentration is measured for the side surface of the rotor core for test by the above procedure, and Al diffusion is performed. It was confirmed that a layer or a Sn diffusion layer was formed.

  Next, the thickness of the optimum Al diffusion layer containing 1 mass% or more of Al or the thickness of the optimum Sn diffusion layer containing 1 mass% or more of Sn is measured at the end of the rotor core for test obtained by heat treatment. did. The measurement results are shown in Table 2 below.

  Next, for the test rotor core obtained by heat treatment, the Al concentration or Sn concentration (diffusion element concentration) on the outermost surface is subjected to line analysis using the above EPMA, and the maximum value (Max) and the minimum value (Min) ) The line analysis was performed on two lines and shifted by 90 ° so that the lines intersected at a right angle. The maximum value (mass%) and the minimum value (mass%) of the measurement results are shown in Table 2 below. Further, the ratio between the maximum value and the minimum value (Max / Min) is calculated and shown in Table 2 below.

The maximum value (Max) when the Al diffusion layer is provided is Al _max , the minimum value (Min) is Al _min , and the maximum value (Max) when the Sn diffusion layer is provided is Sn _max and the minimum value (Min). Corresponds to Sn _min .

  As apparent from Table 2 below, when the Al film was formed by the hot-dip Al plating method, there was almost no variation in the measurement result of the Al concentration on the outermost surface after the heat treatment. Further, when the Sn film was formed by the electric Sn plating method, there was almost no variation in the measurement result of the Sn concentration on the outermost surface after the heat treatment. Therefore, the electrical resistivity on the outermost surface after the heat treatment becomes substantially uniform, and there is little local bias in the electrical resistivity, so that it can be expected that the influence of eddy currents associated with the varying magnetic field during motor rotation can be efficiently suppressed.

  On the other hand, when the Al coating was formed by the powder coating method, the measurement result of the Al concentration varied, and the ratio between the maximum value and the minimum value exceeded 1.5. Therefore, it is considered that the electric resistivity at the outermost surface after the heat treatment is locally biased, and the influence of the eddy current accompanying the fluctuating magnetic field during motor rotation cannot be effectively suppressed.

  Next, the rotor core for test obtained by heat treatment is cut so that the longitudinal section (cut surface parallel to the shaft) is exposed with respect to the shaft, and the outermost surface at the center position in the longitudinal direction of the rotor core for test The metal structure was observed with an optical microscope at the part (outer peripheral side) and the D / 4 position (D is the diameter of the test rotor core). The observation was performed after the vertical section was polished and immersed in a 5% picric acid alcohol solution for 15 to 30 seconds to cause corrosion. The observation magnification was 100 times and 400 times, and the metal structure was identified. In any of the tested rotor cores, the outermost surface portion and the metal structure at the D / 4 position were the same. The results of the observed metal structure are shown in Table 3 below. “Ferrite” in Table 3 below means that the ferrite fraction in the metal structure is 99 area% or more, and “ferrite + pearlite” includes 5 area% or more pearlite, with the balance being ferrite. It means that there is.

  Further, the particle size number of the ferrite at the D / 4 position was determined by the method defined in JIS G0552. The number of measurement points of the ferrite particle size number was four, and the average value was calculated. The calculation results are shown in Table 3 below.

  Next, the electrical resistivity of the test rotor core was evaluated by the following procedure. The electrical resistivity was calculated from the ratio to the energization current by a commonly used energization method (four-terminal method). The test was performed using a test piece of 2 mm square × 200 mm length collected from the rolled material or the forged material after the heat treatment, and the distance between the voltage terminals was 60 mm. The test piece was not formed with an Al diffusion layer or an Sn diffusion layer, and the electrical resistance of the base material was measured. In addition, the energization direction is carried out in two forward and reverse directions to eliminate the influence of contact resistance, bias current, thermoelectromotive force and the like. The measurement results are shown in Table 3 below.

  Next, the obtained test rotor iron core was attached to the evaluation motor, and the motor characteristics were evaluated.

  The motor characteristics were applied by controlling the torque applied to the evaluation motor by adjusting the input power to the evaluation motor in a state where the AC servo motor (3 kW) was directly connected to the evaluation motor as a load source. The motor efficiency at each torque was measured. Further, the maximum value and the lower limit of the allowable rotational speed when the maximum value of the motor efficiency, the motor efficiency at the rated torque (0.159 Nm), and the motor efficiency of 78% or more were secured were measured. “Ss200ss020” (manufactured by Ono Sokki) was used as the torque detector, and “MP981” (manufactured by Ono Sokki) was used as the rotational speed detector. Further, a value obtained by subtracting the lower limit from the upper limit of the allowable rotational speed was calculated. The results are shown in Table 3 below.

  In the present invention, the maximum value of the motor efficiency is 82.0% or more, and the motor efficiency at the rated torque is 82.0% or more. When the motor efficiency is 78% or more, the lower limit is subtracted from the upper limit of the allowable rotational speed. Is a case of satisfying all of 670 or more, and a comparative example is a case of not satisfying any of the criteria.

  On the other hand, No. in Table 2 and Table 3 below. 7, 12, 15, and 21 are examples in which neither the Al diffusion layer nor the Sn diffusion layer was formed in the rotor core. Among these, No. in Table 2 and Table 3 below. 7, 12, and 21 cut the rolled material or the forged material after the heat treatment into the shape of the rotor core provided in the motor for evaluation, and obtained rotor cores for test were obtained at 850 ° C., 3 It is an example using what performed magnetic annealing of time. That is, these are examples in which the Al film and the Sn film are not formed, and the heat treatment after the film formation is not performed.

  The metal structure, ferrite crystal grain size, and electrical resistivity of the test rotor core obtained by magnetic annealing were measured in the same procedure as described above, and the measurement results are shown in Table 3 below.

  Next, the test rotor core obtained by magnetic annealing was attached to the evaluation motor, and the measurement was performed in the same procedure as described above. The measurement results are shown in Table 3 below.

  No. in Table 2 and Table 3 below. 15 is an example in which the rolled material is cut into the shape of the rotor core provided in the evaluation motor. That is, no. No. 15 is an example in which neither the magnetic annealing nor the formation of the Al film and the Sn film is performed, and the heat treatment after the film formation is not performed.

  The metal structure, ferrite crystal grain size, and electrical resistivity of the test rotor core obtained by cutting were measured in the same procedure as described above, and the measurement results are shown in Table 3 below.

  Next, the rotor iron core for test obtained by cutting was attached to the motor for evaluation, and measured by the same procedure as described above. The measurement results are shown in Table 3 below.

[No. 16]
No. in Table 2 and Table 3 below. 16 is an example using the steel type d shown in Table 1 below (the balance is iron and inevitable impurities). The steel type d is a non-oriented electrical steel sheet that is generally available on the market (“50H600” made by Nippon Steel, which is a 50A600 equivalent steel specified by JIS C2552, thickness 0.5 mm). No. No. 16 uses a laminate of the magnetic steel sheet in the shape of the rotor core (see FIG. 2) provided in the evaluation motor. That is, no. No. 16 is an example in which neither the magnetic annealing nor the formation of the Al film and the Sn film is performed, and the heat treatment after the film formation is not performed. The “laminated steel sheet” shown in Table 2 below refers to a laminate obtained by punching and laminating the non-oriented electrical steel sheet, and performing a caulking process and a partial weld joint to produce a rotor core. It means that the shaft is combined. The component composition of the shaft is the same as that of the non-oriented electrical steel sheet.

  The metal structure, ferrite grain size, and electrical resistivity of the obtained test rotor core were measured in the same procedure as described above, and the measurement results are shown in Table 3 below.

  Next, the obtained test rotor iron core was attached to the evaluation motor and measured in the same procedure as described above. The measurement results are shown in Table 3 below.

  Next, FIG. 3 shows the relationship between the torque applied to the evaluation motor and the motor efficiency. FIG. 4 shows the relationship between the rotation speed of the evaluation motor and the motor efficiency. 3 and 4, No. 1 shown in Table 3 below as a representative value. The results of 1, 3, 4, 7, 16 are shown. In FIG. 3 and FIG. As a result of No. 1, □ is No. 3. As a result, Δ is No. As a result of No. 4, ◆ is No. As a result of No. 7, ■ is No. 16 results are shown respectively.

  As is clear from FIGS. 3 and 4, the motor efficiencies of the test pieces with respect to the torque applied to the evaluation motor tend to be almost equal, but the rotor core obtained by laminating electromagnetic steel sheets is used. No. No. 16 shows that the decrease in motor efficiency increases remarkably as the motor speed increases.

  The following Table 1 to Table 3 can be considered as follows. No. 1, 5, 8, 10, 17, 19 are examples that satisfy the requirements defined in the present invention, and the evaluation motor provided with the obtained rotor core satisfies the target motor efficiency, In addition, motor efficiency of 78% or more can be realized in a wide rotational speed range. No. 1 provided with an Al diffusion layer. 1 and No. No. 17 provided with a Sn diffusion layer. 5 and No. 19 is compared with the example (No. 17 and No. 19) using the steel type e to which B is added rather than the example (No. 1 and No. 5) using the steel type a to which B (boron) is not added. It can be seen that the magnetic properties are further improved.

  On the other hand, no. 2 to 4, 6, 7, 9, 11 to 16, 18, 20, and 21 are examples that do not satisfy any of the requirements defined in the present invention, and the evaluation motor including the obtained rotor iron core is In some cases, the target motor efficiency is not satisfied, and the rotation speed region in which the motor efficiency of 78% or more can be realized is narrow. Specifically, no. Reference numeral 16 is a conventional example using a rotor core obtained by laminating electromagnetic steel sheets, and the motor efficiency does not reach the target standard.

  No. Nos. 7, 12, 15, and 21 are examples in which neither an Al diffusion layer nor an Sn diffusion layer is formed at the end of the rotor core, and the motor efficiency of the evaluation motor equipped with this rotor core is the target. The rotation speed region for achieving motor efficiency of 78% or more is narrower than the standard has been reached.

No. In No. 2, since the Al diffusion layer is formed at the end of the rotor core, the rotational speed region for achieving motor efficiency of 78% or more is as wide as 930. However, since the Al diffusion layer is formed by the powder coating method, the ratio between the maximum value (Al _max ) and the minimum value (Al _min ) exceeds 1.5, and the Al concentration on the outermost surface varies. Yes. Moreover, since the Al concentration on the outermost surface exceeds 18% by mass, a nonmagnetic phase part is also generated. Therefore, eddy current loss occurred locally, and the motor efficiency itself did not reach the target standard.

  No. No. 13 is an example in which an Al diffusion layer is formed at the end of the rotor core. However, since the chemical composition of the matrix does not satisfy the requirements defined in the present invention, the magnetic properties necessary for the rotor core are insufficient. The motor efficiency does not reach the target standard, and the rotational speed region for achieving motor efficiency of 78% or more is narrow.

  No. 3, 4, 9, 14, and 18 are examples in which an Al diffusion layer is formed on the entire surface of the rotor core. The motor efficiency does not reach the target standard, and the motor efficiency is 78% or more. The rotational speed region to achieve is narrow.

  No. Nos. 6, 11, and 20 are examples in which an Sn diffusion layer is formed on the entire surface of the rotor core. The motor efficiency does not reach the target standard, and a motor efficiency of 78% or more is achieved. The rotation speed region is narrow.

Claims (9)

The chemical composition of the parent phase is
C: 0.002 to 0.02% (meaning mass%, the same shall apply hereinafter),
Si: 3% or less (excluding 0%),
Mn: 0.1 to 0.5%
P: 0.03% or less (excluding 0%),
S: 0.03% or less (excluding 0%),
Cu: 0.1% or less (excluding 0%),
Ni: 0.1% or less (excluding 0%),
Cr: 1.6% or less (excluding 0%),
Al: 0.002 to 0.04%,
N: 0.005% or less (excluding 0%),
The rest: iron and inevitable impurities
It is a rotor core for a columnar or cylindrical permanent magnet motor,
(A) When an Al diffusion layer in which the Al amount decreases from the outermost surface side of the end portion toward the center portion and when the Al concentration on the end surface is measured at a plurality of locations, the maximum value (Al _max ) and the minimum The value (Al _min ) ratio (Al _max / Al _min ) is 1.0 to 1.5, or
(B) The Sn diffusion layer in which the Sn amount decreases from the outermost surface side of the end portion toward the center portion, and the maximum value (Sn _max ) and the minimum when the Sn concentration on the end surface is measured at a plurality of locations. value (Sn _min) ratio (Sn _max / Sn _min) is the rotor iron core permanent magnet motor, characterized in that 1.0 to 1.5.   The rotor core according to claim 1, wherein, in the Al diffusion layer, the thickness of the optimum Al diffusion layer containing 1% by mass or more of Al is 40 µm or more.   The rotor core according to claim 1 or 2, wherein an Al concentration in the end face is 18 mass% or less (not including 0 mass%).   2. The rotor core according to claim 1, wherein among the Sn diffusion layers, an optimum Sn diffusion layer containing 1 mass% or more of Sn is 40 μm or more.   The rotor core according to claim 1 or 4, wherein the Sn concentration in the end face is 18 mass% or less (excluding 0 mass%). The ferrite fraction in the matrix metal structure is 99 area% or more,
The rotor core according to any one of claims 1 to 5, wherein the average value of the grain number numbers of the ferrite crystal grains is 5.5 or less. The parent phase further includes other elements,
The rotor core according to any one of claims 1 to 6, wherein B: 0.006% or less (excluding 0%) is contained.   A rotor for a permanent magnet motor, wherein a permanent magnet is fixed to the outer surface of the rotor core for a permanent magnet motor according to any one of claims 1 to 7.   A permanent magnet motor comprising the rotor for a permanent magnet motor according to claim 8.

Images