JP5427664B2 - SOFT MAGNETIC POWDER FOR Dust Magnetic Material, Dust Magnetic Material Using the Same, and Manufacturing Method - Google Patents

Description

  The present invention relates to a soft magnetic powder for dust magnetic material containing iron as a main component, a dust magnetic material using the same, and a method for producing a dust magnetic material.

  A powder magnetic material produced by compression-molding soft magnetic powder under high pressure is used for magnetic cores such as motors and reactors for power supply circuits. The magnetic core of the dust is generally isotropic in magnetic properties and can be easily formed into a three-dimensional shape. For example, when applied to an electric motor such as a motor compared to a laminated magnetic core manufactured by laminating silicon steel plates It is expected to contribute to the reduction in size and weight. In particular, a compact magnetic body using Fe powder as a soft magnetic powder is inexpensive and has the advantages of high density and high magnetic flux density due to the high ductility of Fe powder. It is becoming active.

  In addition to high magnetic flux density as a necessary characteristic of the dust magnetic material, it is important that energy loss generated during use under an alternating magnetic field called iron loss is low. Iron loss is mainly expressed as the sum of eddy current loss and hysteresis loss. Eddy current loss is energy loss caused by eddy current flowing between Fe powder particles constituting the dust magnetic material. As a device for reducing eddy current loss, it is necessary to coat a thin insulating film on the surface of the Fe powder for magnetic material.

  On the other hand, the hysteresis loss is a loss generated with the movement of the domain wall inside the Fe powder, and the lattice distortion inside the Fe powder, that is, the vacancies and interstitial atoms (so-called point defects) that are structural defects that generate it. It is strongly influenced by the presence of lattice defects such as dislocations and grain boundaries, impurity atoms other than Fe which are chemical defects, and precipitates composed of them. In order to reduce the hysteresis loss, it is necessary to heat-treat the compact after the Fe powder compression molding to reduce the strain inside the Fe powder introduced by the molding process.

  Moreover, since the shape is determined only by compacting as a disadvantage of the compacted magnetic body, there is a problem that the strength as an iron core is extremely low. When a motor is constructed using a dust magnetic material, the strength of the pressure magnetic material is 10 to 30 MPa, which is significantly lower than that of an iron plate such as an electromagnetic steel plate, and is also susceptible to impact. Therefore, it is necessary to take strength measures that can withstand at least the handling load when manufactured as a motor, the torque reaction force generated between the stator and the rotor when operating as a motor, and external impact and vibration. The

  As a method of improving the strength of the magnetic powder magnetic body, a method of using an iron core embedded in a resin (Patent Document 1), or a strength improvement method by devising the particle size of the metal magnetic powder and the insulating coating material of the powder ( Patent Document 2) is shown.

As another method for improving the strength of the powder magnetic body, there is a method of performing heat treatment in an oxidizing atmosphere such as water vapor or air atmosphere after the compacting. For example, Patent Document 3 shows an example in which iron powder mixed with an organic lubricant after insulating inorganic coating is heat-treated in water vapor at a temperature of 300 to 600 ° C. after compacting. Here, by performing heat treatment in water vapor at 520 ° C. on the magnetic material after compacting, the bending strength is 100 MPa or more (145 MPa), 1T (Tesla), 400 Hz iron loss W10 / 400 is 44 W / kg. As a result, it has been reported that a material having excellent properties such as relatively high strength and low iron loss is obtained as a powder magnetic material. According to the literature 3, as a reason for improving the strength of the magnetic powder body by heat treatment in water vapor, it is explained that a film formed by oxidation is formed on the surface of the iron powder, and the binding force between the iron powders increases through the oxide film. .
All of the conventional techniques for improving the strength of the dust magnetic material have problems. When embedding a dust core with resin, there are problems such as an increase in weight as a motor and a complicated manufacturing process. Moreover, the method of excessively increasing the particle size of the iron powder has a drawback that leads to an increase in eddy current loss.

  Moreover, in the heat treatment of the magnetic powder compact in an oxidizing atmosphere such as water vapor or air atmosphere, there is a problem that iron loss increases due to the growth of the oxide film. In the group of the present inventors, 0.4% organic lubricant was mixed with iron powder coated with an insulating inorganic coating, and after forming, heat treatment at 500 ° C. or higher, or heat treatment for 10 minutes in air As a result, the iron loss W10 / 400 value of the magnetic powder body increased by 1.4 to 1.5 times compared to the case of heat treatment in an inert atmosphere of nitrogen gas. The increase in iron loss during heat treatment in water vapor and in the atmosphere is thought to be due to the fact that the thickness of the film increases due to oxidation and the strength increases, while the influence of oxidation proceeds to the inside of the iron powder.

JP 2008-029142 A JP 2007-129045 A Special table 2008-544520 gazette

  The object of the present invention is to appropriately control the growth of an oxide film formed on the surface of the iron powder and the effect of oxidation on the inside of the iron powder during the heat treatment in the oxidizing atmosphere of the powdered magnetic material. An object of the present invention is to provide a soft magnetic powder for a dust magnetic body that prevents the increase in iron loss of the body and provides the strength required for manufacture and use as a motor component, a dust magnetic body using the same, and a manufacturing method .

The present invention is a soft magnetic powder for dusting magnetic material containing iron as a main component, wherein the powder has 0.005 to 0.03 mass% of Ce and 0.001 of at least one of Nb and Ti. -0.02 mass% and 0.25 mass% or less of inevitable metal impurities, the powder includes an oxide layer formed on the surface and precipitated particles precipitated in an internal matrix, and the precipitated particles The average particle size of is 0.02 μm or more and 0.5 μm or less.

  According to the present invention, by appropriately controlling the growth of the oxide film formed on the surface of the iron powder and the effect of oxidation inside the iron powder during the heat treatment in the oxidizing atmosphere of the powder magnetic material, It is possible to provide a soft magnetic powder for a dusting magnetic material that prevents an increase in iron loss of the body and provides strength necessary for manufacturing and use as a motor component.

It is a figure which shows the manufacturing process of water atomized Fe powder.

  The powder magnetic body of the present invention uses iron powder produced by a water atomization method as a raw material. The iron powder after water atomization is subjected to a heat treatment in a reducing atmosphere containing hydrogen at a temperature of 800 to 1000 ° C. for the purpose of reducing gas impurities mainly for oxygen, thereby purifying the iron powder. The surface of the purified iron powder is coated with a material having excellent insulating properties such as phosphoric acid, and a powder compact is formed by pressing as a composite powder to which a lubricant is added. Finally, heat treatment is performed at 400 to 600 ° C. and applied to various products as a soft magnetic member for the purpose of removing the strain that is a factor that hinders the magnetic properties of the green compact.

  The iron powder as a raw material is produced by a water atomizing method, contains a large amount of O produced by reaction with water during pulverization, and does not have as much C and S content as a gas atomized powder. Oxygen atoms interfere with compaction moldability and strain removal (primary recrystallization at a lower temperature) by heat treatment during molding. Therefore, there is a risk of increasing iron loss. Therefore, in the present invention, in order to reduce the action of the gas impurities O, C, N, elements having a strong affinity with the gas impurities O, C, N are controlled to be added within an appropriate composition range, and those remaining in the powder are added. A material structure control method and a material manufacturing method have been devised in which the parent phase of the water atomized Fe powder is further cleaned by taking out from the parent phase as a precipitate together with the above-described additive elements.

  In the present invention, in order to reduce the action of the gas impurities O, C, N, sufficient hydrogen heat treatment is performed after water atomization to reduce the amount of gas impurities contained in the powder, and the affinity to the gas impurities is high. Strong elements are added within a suitable composition range, and the remaining gas impurities are aggregated as oxides, carbides, nitrides, and complex compounds thereof. Furthermore, the mother phase of the water atomized iron powder is further cleaned by taking out from the parent phase as a precipitate together with the additive element. Specifically, at least one of Ce, Nb, and Ti is added as an additive element. The addition amount must be added within an appropriate range that can reduce the deformation resistance of the powder, the primary recrystallization temperature, and the iron loss of the green compact.

  Further, it is possible to reduce the amount of gas impurities contained in the powder by performing sufficient hydrogen heat treatment. If the powder is heat treated in a reducing atmosphere containing hydrogen gas in a temperature range of 800 ° C. to 1000 ° C. after being powdered by the water atomization method, the gas impurity concentration can be reduced. Further, the remaining gas impurities are also aggregated as precipitates together with the additive elements, and are coarsened to clean the powder matrix. As a result, it is possible to provide a new inexpensive soft magnetic Fe powder, a material structure control technique for manufacturing the powder, and a material manufacturing method.

  Here, a method for producing an Fe powder containing impurity elements and a stabilizing element for immobilizing them will be described. The Fe powder of the present invention is produced by a water atomization method. Raw material iron is selected so as to satisfy the following composition range of inevitable impurities including Cr, Mn, and Si, put in a container such as a crucible, and heated to a high temperature to be in a molten state, but selected from Ce and Nb or Ti One or more elements to be added simultaneously are added and stirred to homogenize. At this stage, the molten iron having a predetermined chemical composition is rapidly solidified by spraying high-pressure water, and then pulverized and recovered.

  The Fe powder for compacting used in the present invention contains a large amount of O as described above immediately after the water atomization treatment. The surface layer is covered with an oxide layer, and a large amount of oxygen is rapidly cooled and dissolved in the inner matrix. In order to reduce O in the water atomized powder, it is effective to use heat treatment in a reducing gas containing hydrogen in addition to the above-described treatment of adding Ce and Nb or Ti. The temperature range in which this effect is remarkable is 800 ° C. or higher and 1000 ° C. or lower. Above 1000 ° C, powder aggregation and sintering are promoted too much, and below 800 ° C is not preferable from the safety aspect of hydrogen treatment.

  The amount of addition of Ce and Nb or Ti, which are additive elements, depends on the content of gas impurities (O, C, N) and especially on the inevitable impurities that are likely to be strongly bonded to O. As such inevitable impurities, the influence of Si, Mn, Cr, which is present as a large amount of impurities, is particularly large. It is desirable that the amount of Si, Mn, and Cr is 0.15% or less in terms of mass%, and the total amount of O, C, and N is 0.05% (approximately 0.18% in terms of atomic%) or less. In order to obtain desirable characteristics of the powder for forming green powder, the amount of unavoidable impurities in the powder subjected to the hydrogen heat treatment is 0.25% by mass in terms of element% of atomic number 9 or more, considering economy and productivity. % Or less and an element having an atomic number of 8 or less needs to be in a range of 0.05% or less. Many of the elements having an atomic number of 9 or more are metal elements. In particular, there is a tendency to contain a large amount of Cr, Mn, and Si in production, and a restriction is necessary.

  Cr can be expected to have an aggregating effect on O, C, and N, and its content is 0.03% or less by mass%. When the content exceeds 0.03% by mass%, it reacts with O diffused from the surface of the Fe powder in the production process to form many stable Cr oxides. Therefore, it is not preferable because the thermal recovery of the strain of the green compact is delayed to increase the hysteresis loss.

  Mn is abundant in production. The Mn content is 0.1% or less by mass. If it exceeds 0.1% by mass, it reacts with O diffused from the surface in the process of producing Fe powder in the same manner as Cr to form a large number of stable Mn oxides, thereby forming a compacted compact. This is not preferable because the thermal recovery of the strain is delayed and the hysteresis loss is increased.

  Si has a small oxide generation free energy, is easy to form an oxide, and is more stable, so it is difficult to coarsen. Therefore, it is preferable to suppress the content as much as possible and to make it 0.02% or less by mass%. If it exceeds 0.02% by mass, it reacts with O diffused from the surface to the inside during the production process of iron powder to form a large number of stable Si oxides. Delays recovery and increases hysteresis loss.

Of the inevitable impurity elements having an atomic number of 8 or less, C, O, and N account for the majority. In the water atomized powder, the total amount of C and N is 0.002% or less in mass%. For the reasons described above, the amounts of C and N are low and can be further reduced by hydrogen heat treatment. O accounts for the majority of gas impurities.
The amount of O in the water atomized powder subjected to hydrogen heat treatment, including the surface oxide layer, is approximately 0.05% at maximum (approximately 0.18% in atomic%) at the maximum, and the total amount of C, O, and N is 0.1% in mass%. 05% or less is preferable.

  Next, effects of the additive elements essential in the present invention will be described. Ce plays an effective role in the removal of O in the iron powder. O which is frozen into Fe powder by rapid cooling during the water atomization treatment is removed in the above-described hydrogen heat treatment in the range of 800 ° C. to 1000 ° C., and the remaining amount is precipitated as an oxide containing Nb during the heat treatment. The precipitate is coarsened to clean the powder matrix. The oxide may be a complex oxide with other metal elements contained in Fe. The effect of reducing the deformation resistance of the Fe powder, the primary recrystallization temperature, and the iron loss of the green compact is increased by the cleaning.

  Another effect of Ce addition becomes important at the stage of heat treatment for removing strains after the insulating coating treatment and the iron powder mixed with the lubricant are compacted by pressing. In the present invention, the strain recovery heat treatment of the green compact is carried out in an oxidizing atmosphere in which 20% or less of oxygen is added to the atmosphere or an inert gas for the purpose of imparting sufficient strength to the compact as described later. In the heat treatment stage in an oxidizing atmosphere, an oxide film mainly composed of iron is formed on the surface of each iron powder constituting the molded body. In the present invention material, however, the oxide film is densified by containing Ce. Suppresses excessive increase in film thickness. Further, the oxide film containing Ce has an action of suppressing diffusion of oxygen into the iron powder during the heat treatment. Due to the effect of adding Ce, the dust magnetic material of the present invention is subjected to strain recovery heat treatment in an oxidizing atmosphere. Even later, it is possible to exhibit excellent magnetic properties without increasing iron loss.

  The amount of Ce added is preferably 0.05% or less because the density of the oxide in the iron powder particularly increases when the mass percentage exceeds 0.05% and the cleaning effect of the parent phase accompanying coarsening is impaired. Addition in the range of 0.05% to 0.003% is preferable because when the content is less than 0.002%, the effect of cleaning the parent phase and the effect of densifying the oxide film during strain recovery heat treatment are reduced.

  Nb and Ti play an effective role in removing O, C, and N. O, C, and N that are frozen into Fe powder by rapid cooling during the water atomization treatment are removed in the hydrogen reduction heat treatment in the range of 800 ° C. to 1000 ° C., and the residual amount is converted into an oxide containing Nb or Ti during the heat treatment. Or precipitate as a very small amount of carbides and nitrides, and the precipitates become coarser with the treatment time to clean the powder matrix. The oxide may be a complex oxide with other metal elements contained in Fe. The effect of reducing the deformation resistance of the Fe powder, the primary recrystallization temperature, and the iron loss of the green compact is increased by the cleaning.

  In the present invention, Nb or Ti has another important role. Oxygen impurities remaining inside the iron powder at the stage of the hydrogen reduction heat treatment react with the additive elements Ce, Nb, Ti or Cr, Mn, Si, etc. contained as inevitable impurities, and precipitate as oxides. Nb and Ti act as a nucleus of precipitation when these types of oxides precipitate, and have the effect of aggregating different types of oxide particles around them. Due to the aggregation effect of the oxides of Nb and Ti, many fine oxide particles are removed from the inside of the iron powder, and cleaning of the iron powder is promoted. The effect of the oxide aggregation during the precipitation is not exhibited by the addition of Ce. On the other hand, Nb or Ti has little effect of densifying the oxide film during strain recovery heat treatment of Ce. For this reason, in this invention, the outstanding material characteristic can be exhibited by adding Nb or Ti to iron powder simultaneously with Ce.

  The amount of Nb added is preferably 0.03% or less, and is preferably 0.002% or less because the density of the oxide increases particularly when the amount exceeds 0.03% by mass% and the effect of cleaning the parent phase accompanying coarsening is impaired. Since the effect is further reduced by cutting off, a range of 0.002% to 0.03% is preferable.

  The added amount of Ti is stronger in bonding strength with O, C, and N than Nb, and when the atomic percent exceeds 0.02%, the density of the precipitates increases, and it is more stable and coarse. Since the cleaning effect of the parent phase is further impaired, it is preferable to set a limit of 0.02% or less, and since a sufficient effect can be expected up to 0.002%, 0.002% to 0.02%. A range of 02% is more preferred. When Nb is added simultaneously with Ti, the total content including Nb is preferably in the range of 0.002% to 0.03%.

  The hydrogen heat treatment water atomized iron powder of the present invention is added with hydrogen heat treatment and Ce, N, or Ti for reducing O, C, and N gas impurities that inhibit (resistance) plastic deformation in compression molding of the powder. Therefore, the average micro Vickers hardness of the powder is reduced to 120 or less. Therefore, the molding pressure for obtaining the same molded body density is also reduced as compared with the conventional powder molded body.

  The water atomized iron powder subjected to the hydrogen reduction heat treatment of the present invention is excessively plastically deformed under high pressure by molding to obtain a green compact. An insulating film is applied to the iron powder surface for the purpose of reducing the magnetic properties of the compacted body, especially eddy current loss. As long as the insulation film has sufficient insulating properties, it is not particularly specified, but iron phosphate glass (Fe-PO), which has both heat resistance and insulation properties, or an inorganic material with a similar chemical composition is used. Is preferred. Moreover, you may employ | adopt the composite insulating film which laminated | stacked the organic type film | membrane etc. on the outer side of iron phosphate glass.

  For the purpose of imparting moldability at the time of compacting, it is preferably used for molding as a composite powder in which a lubricant is mixed in iron powder subjected to an insulating film. The material of the lubricant is not particularly specified, but conventionally known materials may be used, and specific examples thereof include metal salt powders such as zinc stearate and lithium stearate and other waxes. If the addition amount of the lubricant is excessively increased, the density of the green compact is lowered, which becomes a factor that hinders magnetic properties. Moreover, when there is little addition amount, moldability, such as extraction becoming difficult, will fall. It is preferable to add a lubricant in the range of 0.05 to 0.8 mass%.

  For the purpose of removing distortion and improving magnetic properties, particularly reducing hysteresis loss, the above-mentioned green compact is subjected to heat treatment at 400 to 600 ° C. The strain-removing heat treatment of the molded body is originally preferably performed in an inert gas atmosphere such as nitrogen or argon for the purpose of preventing an increase in iron loss due to oxidation. However, it is a disadvantage that the strength of the green compact molded by heat treatment in an inert gas atmosphere is as low as 10 to 30 MPa. In the present invention, the strain-removing heat treatment is performed in an oxidizing atmosphere, specifically in the atmosphere or an atmosphere containing oxygen of 20% by mass or less in an inert gas to oxidize iron powder and thereby improve the strength of the green compact. To improve.

The iron powder of the present invention is compacted in a state in which an insulating coating is coated on the surface and a lubricant is added. For this reason, the bonding force between the iron powders constituting the green compact is very weak, and the bonding force at the interface hardly increases even after the strain removing heat treatment in the inert gas atmosphere. On the other hand, in the strain removal heat treatment in an oxidizing atmosphere such as air or water vapor, an oxide film mainly composed of Fe ₃ O ₄ is formed on the iron powder surface. The oxide film on the surface of different iron powder comes into contact with the powder interface, and the oxide layer is partially bonded, whereby the strength of the green compact is greatly improved. On the other hand, when the thickness of the oxide film due to heat treatment is excessively increased, there is a problem that a part of the insulating film such as iron phosphate glass previously applied is destroyed, leading to an increase in eddy current loss. Further, oxygen penetrates into the iron powder below the oxide film by diffusion, so that the purity of the iron powder is lowered and hysteresis loss is also increased. As described above, the heat treatment in the oxidizing atmosphere is effective for improving the strength of the compact, but there is a problem that leads to a decrease in magnetic properties due to an increase in iron loss.

  In the material of the present invention, this problem is addressed by adding Ce. In the iron powder of the present invention, a trace amount of Ce is contained inside the oxide film formed on the surface of the iron powder when the green compact is heat-treated in an oxidizing atmosphere. Although the amount of Ce contained in the oxide film is small, it has the effect of reducing the formation rate of the oxide film during heat treatment and densifying the film. As a result, in the iron powder of the present invention material, the oxide film becomes dense and thin, thereby suppressing the breakdown of the insulating film and suppressing an increase in eddy current loss. At the same time, the formation of a dense oxide film on the surface of the iron powder also suppresses an increase in hysteresis loss by reducing the diffusion of oxygen into the iron powder during the heat treatment.

  On the other hand, since the present invention material has a thin oxide film, the strength of the molded body after the heat treatment is reduced to about 60% of that of a conventional iron powder molded body to which Ce is not added. However, handling strength when incorporated as a product such as a motor and sufficient strength to withstand external impact and vibration after commercialization can be secured sufficiently, so there are no particular problems when used as a soft magnetic member. Does not occur.

  As described above, the dust magnetic body of the present invention imparts sufficient strength to the dust compact by the strain-removing heat treatment in the oxidizing atmosphere, and suppresses an increase in iron loss due to oxidation by addition of Ce. It is possible and is characterized in that it balances the strength and magnetic properties of the member.

〔Example〕
Hereinafter, further details will be described in Examples.

  In this example, Ce and Nb or Ti were added to several kinds of pure Fe, and various characteristics of the water atomized powder produced were investigated.

  FIG. 1 shows a process for producing water atomized Fe powder. Pure Fe was selected to have a predetermined chemical composition, additive elements were blended, the materials were dissolved, molten Fe was pulverized and rapidly solidified using high-pressure water to form Fe powder (Steps 1 and 2). The Fe powder with an oxide film on the surface is sieved so that the average particle size is 100 to 150 μm, and the selected powder is 880 ° C. ± 4 ° C. for 2 hours in an atmosphere where dry hydrogen flows to reduce gas impurities. And heat-treated (steps 3 and 4). Since aggregation between some powders progressed during the heat treatment, the powders were mechanically pulverized with consideration given to avoiding distortion as much as possible in order to separate individual powders (step 5). Here, when there is a concern about the introduction of strain, annealing may be performed after pulverization in a reducing atmosphere containing hydrogen or in vacuum at 600 ° C. for 30 minutes to 1 hour (step 6). In this implementation, Step 6 was performed for 30 minutes in a vacuum. The blackened powder surface immediately after water atomization turned pale gray by hydrogen heat treatment.

  After completion of the heat treatment in step 6, an insulating coating made of a phosphoric acid-based inorganic material was applied to the surface of the iron powder by chemical treatment. The thickness of the phosphoric acid insulating layer was in the range of 50 to 100 nm. A powdered zinc stearate-based lubricant was added to the iron powder after the insulation treatment, and the mixture was put into a V-type stirrer and stirred and mixed for homogenization.

  Using the powder mixed with the lubricant, compacting was performed by a hydraulic press machine to produce a ring-shaped compacted product having an outer diameter of 50 mm, an inner diameter of 40 mm, and a thickness of 5 mm. The molding pressure was 1180 MPa. The obtained green compact was subjected to a strain removing heat treatment at 520 ° C. for 30 minutes in an oxidizing atmosphere in which 5% oxygen gas was mixed in pure nitrogen gas to release the strain during molding. . For comparison with the oxidizing atmosphere, heat treatment (inert heat treatment) was performed in pure nitrogen gas at the same temperature and time.

  Magnetic properties of the molded body were evaluated by applying a winding of 200 turns on the primary side and 60 turns on the secondary side to the molded body after heat treatment using a 0.5 mm copper wire, and the magnetic flux density B ( T), and iron loss W (W / kg) at a magnetic flux density of 1T and a frequency of 400 Hz were determined. The density of the molded body was measured by Archimedes method. In addition, an 11 × 30 × 5 mm plate-like molded / heat treated body was produced from each iron powder sample under the same molding and strain removing heat treatment conditions as the ring molded body, and the bending strength by three-point bending was determined.

  Table 1 shows the analytical value of the chemical composition of the iron powder sample at the time when the hydrogen reduction heat treatment was performed after water atomization.

  Among samples A to H, A is a comparative material that does not contain Ce, Nb, and Ti, and B to H are iron powders of the present invention. B, C, and D were iron powders to which Ce and Nb were added. The Ce concentration was changed from 0.009 to 0.024%, and Nb was added at a concentration of 0.010% or less. For E, F and G, Ce and Ti were added, the Ce concentration was changed from 0.007 to 0.022%, and Nb was added at a concentration of 0.011% or less. H was Nb, Ti was not added, and Ce was added alone by 0.022%. As a result of analyzing the oxygen concentration of each iron powder, all the iron powders had a value of 500 ppm or less.

  Table 2 shows the material characteristics of the molded body.

  In Table 2, the characteristics are arranged according to the atmosphere of 520 ° C. strain removal heat treatment (oxidative heat treatment, inert heat treatment). Density, B, W, and bending strength were evaluated for the molded body subjected to heat treatment for removing strain in an oxidizing atmosphere. The molded body density shows a value of 7.50 or more for all samples. The density value did not correlate with the addition amount of Ce, Nb, Ti or the oxygen concentration, and it was found that there was no influence on the density of the chemical composition. The value of the magnetic flux density B was correlated with the compact density, and the tendency of the value to change in proportion to the density was confirmed.

  The iron loss W after the oxidative heat treatment was comparatively high at 55 W / kg in the comparative powder A, and W was a low value of less than 44 to 46 W / kg in the six types of the inventive materials B to G. Inventive powders B to G were added with Nb or Ti simultaneously with Ce, and the effect of improving the iron loss by adding the elements was confirmed. On the other hand, in Sample H to which only Ce was added alone, W was 49 W / kg, which was slightly higher than B to G. The bending strength after the oxidative heat treatment was the highest at 160 MPa in the comparative powder A, and the strengths of other invention powders B to H were 100 MPai or less, which was lower than A.

  As a result of the inert heat treatment in the nitrogen atmosphere in Table 2, the measured value of W is lower in all samples than in the oxidizing heat treatment. The decrease in W during the inert heat treatment is presumed to be due to the absence of the influence of oxidation. The difference in W between the oxidizing atmosphere and the inert atmosphere, ΔW, varies depending on the sample. In the comparative powder A, ΔW = 9 W / kg, whereas in the inventive powders BH, ΔW is 2-4 W / kg. It was found that the difference became smaller. The reason why the above-described ΔW of the powder of the present invention is lower than that of the comparative powder A is considered to be that the deterioration of the characteristics due to oxidation was suppressed by adding Ce to the powder of the present invention.

  On the other hand, the bending strength of the molded body during the inert heat treatment is a remarkably low value of about 30 MPa or less for all the samples. By performing the heat treatment in an inert environment free from the influence of oxidation in this way, the iron loss of the green compact is reduced, while the strength of the green compact is very low. Such a poor balance between magnetic properties and mechanical properties has been one of the problems of conventional powder magnetic materials.

  The results of the iron loss W and the bending strength of the newly developed powders B to G after the oxidative heat treatment in Table 2 are considered to eliminate the above-mentioned characteristic balance defect to some extent. The bending strength after heat treatment in the oxidizing atmosphere of B to G is lower than that of the comparative powder A, but it can be seen that the value increases three times or more as compared with the strength during the inert heat treatment. Further, the iron loss of B to G after the oxidative heat treatment decreases with a width of 10 W / kg or more as compared with the comparative powder A. Thus, in the present invention powder to which Ce and Nb or Ti are added, an increase in iron loss can be suppressed by performing an oxidative heat treatment on the molded body as compared with the additive-free comparative powder, and at the same time as in the inert heat treatment. The results showed that the intensity could be increased by more than 3 times. Such a characteristic that balances the magnetic characteristics and strength of the iron powder of the present invention is considered to be beneficial when used as a soft magnetic member such as a motor core.

  In the comparative powder A of Example 1 and the newly developed powder C, a structure observation sample was collected from a molded body subjected to heat treatment for removing strain in an oxidizing atmosphere, and the iron powder surface was oxidized by SEM (scanning electron microscope). The film was observed. For the observation sample, a part of the ring molded body was cut, polished after resin embedding, and subjected to observation.

  In the compact of Comparative Powder A, formation of an oxide film by heat treatment was confirmed at the iron powder interface near the press surface. As a result of measuring the thickness of the coating on the surface of the iron powder from the SEM photograph, the film thickness is about 12 μm on average, and there are portions where the thickness exceeds 20 μm in the vicinity of the fine vacant wall of the powder interface. confirmed. On the other hand, in the compact of the powder C of the present invention, it was confirmed that the oxide film on the surface of the iron powder had an average thickness of 1.8 μm and was very thin compared to A. The thicknesses of both oxide films are influenced by the addition of an additive element, particularly Ce, and it is presumed that in the powder C of the present invention, the oxidation rate was lowered by Ce, and the film became thin.

  The Fe powder, soft magnetic material, dust core and manufacturing method thereof of the present invention can be used for, for example, a motor core, a solenoid valve, a reactor, or a general electromagnetic component.

Claims (8)

A soft magnetic powder for powdered magnetic material mainly composed of iron,
The powder is composed of a 0.005 to 0.03 wt% of Ce, Nb, and 0.001 to 0.02 wt% of at least one of Ti, the inevitable metallic impurities 0.25 wt% or less And
The powder includes an oxide layer formed on the surface, and precipitated particles precipitated in the internal matrix.
An average particle diameter of the precipitated particles is 0.02 μm or more and 0.5 μm or less. In claim 1,
The powder contains at least one of Cr, Mn, and Si as the inevitable metal impurities,
A soft magnetic powder for a magnetic powder compact, characterized in that the respective contents are Cr: 0.03 mass% or less, Mn: 0.1 mass% or less, and Si: 0.02 mass% or less. In claim 1,
A soft magnetic powder for a dusting magnetic material, comprising an inorganic insulating coating layer on a surface. Iron was cooled by blowing water into the molten alloy as a main component, it is composed of a 0.005 to 0.03 wt% of Ce, Nb, and 0.001 to 0.02 wt% of at least one of Ti After obtaining a finely divided alloy,
Heat treatment in a temperature range of 800 ° C. to 900 ° C. in a reducing atmosphere containing hydrogen;
Compacting the alloy powder,
A method for producing a magnetic powder compact comprising heat-treating the powder compact at 450 to 600 ° C. In claim 4,
An inorganic insulating coating layer is provided on the surface of the alloy powder that has been heat-treated at a temperature range of 800 ° C. to 900 ° C. in a reducing atmosphere containing hydrogen,
Mix organic lubricants,
A method for producing a powder magnetic material, comprising compacting an alloy powder having the inorganic insulating coating layer. In claim 4,
The method for producing a dust magnetic material, characterized in that the atmosphere of the heat treatment after forming the dust magnetic material is air or an oxidizing atmosphere in which 10% or less of oxygen is mixed in an inert gas. A powder magnetic body obtained by the production method according to claim 6,
It has an oxide film mainly composed of Fe ₃ O ₄ having an average thickness of 2 μm or less, which is formed by the heat treatment in the oxidizing atmosphere on the iron surface constituting the dust magnetic body. Powder magnetic material.   A motor using a dust magnetic material using the soft magnetic powder for dust magnetic material according to any one of claims 1 to 3.

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