Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/05—Mixtures of metal powder with non-metallic powder
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/12—Metallic powder containing non-metallic particles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/10—Sintering only
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/12—Both compacting and sintering
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0207—Using a mixture of prealloyed powders or a master alloy
  • C22C33/0228—Using a mixture of prealloyed powders or a master alloy comprising other non-metallic compounds or more than 5% of graphite
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2302/00—Metal Compound, non-Metallic compound or non-metal composition of the powder or its coating
  • B22F2302/25—Oxide
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/05—Mixtures of metal powder with non-metallic powder
  • C22C1/051—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor
  • C22C1/053—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor with in situ formation of hard compounds
  • C22C1/055—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor with in situ formation of hard compounds using carbon

Definitions

• the present invention relates to a mixed powder for iron-based powder metallurgy and a sintered body prepared by using the same, and more particularly to a mixed powder for iron-based powder metallurgy containing binary oxides and ternary oxides at a specific weight ratio and a sintered body prepared by using the same.
• Powder metallurgy is widely used as a method for industrial production of various kinds of mechanical parts.
• a procedure for the iron-based powder metallurgy is such that, first, a mixed powder is prepared by mixing an iron-based powder with a powder for alloy such as a copper (Cu) powder or a nickel (Ni) powder, a graphite powder, and a lubricant. Next, this mixed powder is put into a mold to perform press-molding, and the resultant is sintered to prepare a sintered body. Finally, this sintered body is subjected to cutting such as drilling process or turning on a lathe, so as to be prepared into a mechanical part having a desired shape.
• a mixed powder is prepared by mixing an iron-based powder with a powder for alloy such as a copper (Cu) powder or a nickel (Ni) powder, a graphite powder, and a lubricant.
• this mixed powder is put into a mold to perform press-molding, and the resultant is sintered to prepare
• An ideal for powder metallurgy is such that the sintered body is processed to be made usable as a mechanical part without performing cutting on the sintered body.
• the aforesaid sintering may generate non-uniform contraction of the raw material powder.
• the dimension precision required in the mechanical parts is increasing, and the shapes of the parts are becoming more complex. For this reason, it is becoming essential to perform cutting on the sintered body. From such a background, machinability is imparted to the sintered body so that the sintered body can be smoothly processed.
• MnS manganese sulfide
• Addition of the MnS powder is effective for cutting at a comparatively low speed, such as drilling.
• addition of a manganese sulfide powder is not necessarily effective for cutting at a high speed that is performed in recent years, and raises problems such as generation of contamination on the sintered body and decrease in the mechanical strength.
• Patent Literatures 1 to 4 additives disclosed, for example, in Patent Literatures 1 to 4 are proposed as techniques other than the addition of manganese sulfide.
• Patent Literature 1 Japanese Examined Patent Application Publication No. S52-16684 discloses a sintered steel in which 0.1 to 1.0% of calcium sulfide, 0.1 to 2% of carbon (C), and 0.5 to 5.0% of copper (Cu) are incorporated into an iron-based raw material powder obtained by allowing a needed amount of carbon and copper to be contained in an iron powder.
• Patent Literature 2 Japanese Unexamined Patent Application Publication No. 2008-502807 derived from International Patent Application discloses a metallurgy powder composition comprising a powder containing calcium aluminate.
• the powder containing calcium aluminate contains 51 to 57 wt% of alumina, 31 to 37 wt% of calcium oxide, less than 6.0 wt% of SiO 2 , less than 2.5 wt% of Fe 2 O 3 , less than 3.0 wt% of TiO 2 , less than 2.0 wt% of MgO, less than 0.2 wt% of K 2 O, and less than 0.2 wt% of sulfur.
• Patent Literature 3 Japanese Unexamined Patent Application Publication No. 2010-236061 discloses an iron-based mixed powder containing an oxide powder of SiO 2 -CaO-MgO at a ratio of 0.01 to 1.0 parts by mass relative to 100 parts by mass of an iron-based powder.
• Patent Literature 4 Japanese Unexamined Patent Application Publication No. H09-279204 discloses an iron-based mixed powder for powder metallurgy mainly made of iron powder and containing 0.02 to 0.3 wt% of a CaO-Al 2 O 3 -SiO 2 composite oxide powder having an average particle size of 50 ⁇ m or less.
• This excessive amount of CaO reacts with other oxides or sulfur or is singly present, whereby the characteristics of the sintered body are hardly stabilized.
• the present invention has been made in view of the aforementioned current circumstances, and an object thereof is to provide a mixed powder for iron-based powder metallurgy capable of preparing a sintered body that is excellent in machinability both at an initial stage of starting the cutting and in a long period of time of cutting.
• a mixed powder for iron-based powder metallurgy of the present invention comprises at least one ternary oxide selected from the group consisting of Ca-Al-Si oxides and Ca-Mg-Si oxides, and at least one binary oxide selected from the group consisting of Ca-Al oxides and Ca-Si oxides, wherein the ternary oxide and the binary oxide are contained in a sum weight of 0.025 wt% or more to 0.3 wt% or less.
• the present invention is also directed to a sintered body prepared by sintering the mixed powder for iron-based powder metallurgy described above.
• the present inventor has confirmed a mechanism of reaction between the oxide (2CaO•Al 2 O 3 •SiO 2 powder) contained in the sintered body and the titanium oxide (TiO 2 ) powder contained in a cutting tool or in the coating of a cutting tool. Specifically, a mixed powder of 2CaO•Al 2 O 3 •SiO 2 powder and TiO 2 powder was heated in ambient air under no pressure applied, and the reaction product thereof was analyzed by X-ray diffraction.
• the present inventor has assumed that, in a state of immediately after the start of cutting in which the edge temperature of the cutting tool is low, the reaction between a ternary oxide and TiO 2 in the tool does not occur sufficiently, and a protection coating film is hardly formed. Also, the present inventor has confirmed that, in a state in which a predetermined period of time has passed from the start of cutting and the edge temperature of the cutting tool is high, Ca in the ternary oxide reacts with TiO 2 on the tool surface to form a protection coating film on the tool surface, and also various binary oxides are formed.
• the present inventor has assumed that, in cutting for a long period of time, the ternary oxide exhibits an effect of suppressing tool wear more than the binary oxide because Ca in the binary oxide reacts with TiO 2 on the surface of the cutting tool to be lost, and hard Al 2 O 3 , SiO 2 are generated to provoke tool wear.
• the present inventor has found out that the machinability at an initial stage of cutting is enhanced by the binary oxide, and machinability in cutting for a long period of time is enhanced by the ternary oxide that hardly generate hard Al 2 O 3 , SiO 2 , thereby completing the present invention shown below.
• a mixed powder for iron-based powder metallurgy capable of preparing a sintered body that is excellent in machinability both at an initial stage of starting the cutting and in a long period of time of cutting.
• a mixed powder for iron-based powder metallurgy of the present invention is preferably formed by mixing an iron-based powder with a ternary oxide and a binary oxide.
• Various kinds of additives such as powders for alloy, graphite powders, lubricants, binders, and machinability improvers may be appropriately added into this mixed powder.
• the mixed powder may contain a slight amount of inevitable impurities during the process of producing the mixed powder for iron-based powder metallurgy.
• the mixed powder for iron-based powder metallurgy of the present invention may be put into a mold or the like to be molded and thereafter sintered to give a sintered body.
• the sintered body thus prepared may be subjected to cutting process, so as to be made usable in various kinds of mechanical parts. The use and the production method of this sintered body will be described later.
• the iron-based powder is a main constituent component constituting the mixed powder for iron-based powder metallurgy, and is preferably contained at a weight ratio of 60 wt% or more relative to the total amount of the mixed powder for iron-based powder metallurgy.
• wt% of the iron-based powder as used herein refers to the occupied ratio relative to the total weight of the constituent components of the mixed powder for iron-based powder metallurgy other than the lubricants.
• the definition refers to the occupied weight ratio relative to the total weight of the constituent components of the mixed powder for iron-based powder metallurgy other than the lubricants.
• the above iron-based powder usable in the present invention may be, for example, a pure iron powder such as an atomized iron powder or a reduced iron powder, a partially diffused alloyed steel powder, a completely alloyed steel powder, a hybrid steel powder obtained by partially diffusing alloy components into a completely alloyed steel powder, or the like.
• a volume-average particle size of the iron-based powder is preferably 50 ⁇ m or more, more preferably 70 ⁇ m or more. When the volume-average particle size of the iron-based powder is 50 ⁇ m or more, the handling property is excellent. Further, the volume-average particle size of the iron-based powder is preferably 200 ⁇ m or less, more preferably 100 ⁇ m or less. When the volume-average particle size of the iron-based powder is 200 ⁇ m or less, a precision shape can be readily molded, and also a sufficient strength can be obtained.
• the mixed powder for iron-based powder metallurgy of the present invention contains both of a binary oxide and a ternary oxide in a sum weight of 0.025 wt% or more to 0.3 wt% or less.
• the binary oxide can improve the machinability at an initial stage of cutting when the sintered body is used in a cutting process.
• the ternary oxide can improve the machinability when cutting is performed for a long period of time.
• the sum weight of the oxides is preferably 0.03 wt% or more, more preferably 0.04 wt% or more, still more preferably 0.05 wt% or more, and particularly preferably 0.1 wt% or more.
• the weight ratio of the binary oxide and ternary oxide is preferably as small as possible.
• the sum weight of the oxides is preferably 0.25 wt% or less, more preferably 0.2 wt% or less. When the sum weight of the oxides is 0.25 wt% or less, the radial crushing strength of the sintered body can be sufficiently ensured.
• the binary oxide means a composite oxide of two types of elements
• the ternary oxide means a composite oxide of three types of elements.
• the binary oxide is preferably a composite oxide of two types of elements selected from the group consisting of Ca, Mg, Al, Si, Co, Ni, Ti, Mn, Fe, and Zn, and is more preferably a Ca-Al oxide, a Ca-Si oxide, or the like.
• the Ca-Al oxide may be, for example, CaO•Al 2 O 3 , 12CaO•7Al 2 O 3 , or the like.
• the Ca-Si oxide may be, for example, 2CaO•SiO 2 or the like.
• the ternary oxide to be used is preferably a composite oxide of three types of elements selected from the group consisting of Ca, Mg, Al, Si, Co, Ni, Ti, Mn, Fe, and Zn, and is more preferably a Ca-Al-Si oxide, a Ca-Mg-Si oxide, or the like.
• the Ca-Al-Si oxide may be, for example, 2CaO ⁇ Al 2 O 3 ⁇ SiO 2 or the like.
• the Ca-Mg-Si oxide may be, for example, 2CaO•MgO•2SiO 2 or the like. Among these, it is preferable to add 2CaO•Al 2 O 3 •SiO 2 .
• a shape of the binary oxide and the ternary oxide is not particularly limited; however, the binary oxide and the ternary oxide preferably have a spherical shape or a crushed spherical shape, that is, a shape that is round as a whole.
• the volume-average particle size of the binary oxide and the ternary oxide is preferably 0.1 ⁇ m or more, more preferably 0.5 ⁇ m or more, and still more preferably 1 ⁇ m or more. There is a tendency such that, according as the volume-average particle size is smaller, the machinability of the sintered body can be improved by a smaller amount of addition. Further, the volume-average particle size of the binary oxide and the ternary oxide is preferably 15 ⁇ m or less, more preferably 10 ⁇ m or less, and still more preferably 9 ⁇ m or less. When the volume-average particle size is too large, it is difficult to improve the machinability of the sintered body.
• the above volume-average particle size is a value of the particle size D 50 at an accumulated value of 50% in the particle size distribution obtained by using a laser diffraction particle size distribution measurement device (Microtrac "MODEL9320-X100” manufactured by Nikkiso Co., Ltd.).
• a laser diffraction particle size distribution measurement device Microtrac "MODEL9320-X100” manufactured by Nikkiso Co., Ltd.
• the content of the binary oxide is preferably 0.01 wt% or more, more preferably 0.03 wt% or more, and still more preferably 0.05 wt% or more. Further, the content of the binary oxide is preferably 0.25 wt% or less, more preferably 0.2 wt% or less, and still more preferably 0.15 wt% or less. When the binary oxide is contained at such a weight ratio, it is possible to obtain a sintered body having an excellent machinability at an initial stage of cutting while suppressing the costs.
• the content of the ternary oxide is preferably 0.01 wt% or more, more preferably 0.03 wt% or more, and still more preferably 0.05 wt% or more. Further, the content of the ternary oxide is preferably 0.25 wt% or less, more preferably 0.2 wt% or less, and still more preferably 0.15 wt% or less. When the ternary oxide is contained at such a weight ratio, it is possible to obtain a sintered body having an excellent machinability even in cutting for a long period of time while suppressing the costs.
• the weight ratio of the ternary oxide and the binary oxide is preferably 9 : 1 to 1 : 9, more preferably 9 : 1 to 3 : 7, and still more preferably 7 : 3 to 4 : 6.
• these two kinds of oxides are contained at such a weight ratio, a sintered body that can be easily machined both at an initial stage of cutting and in cutting for a long period of time can be prepared.
• a powder for alloy is added for the purpose of promoting bonding between the iron-based powders and enhancing the strength of the sintered body after the sintering.
• Such a powder for alloy is contained preferably at a ratio of 0.1 wt% or more to 10 wt% or less relative to the whole of the mixed powder for iron-based powder metallurgy.
• the ratio is 0.1 wt% or more, the strength of the sintered body can be enhanced.
• the ratio is 10 wt% or less, the dimension precision of the sintered body at the time of sintering can be ensured.
• the powder for alloy may be, for example, a non-ferrous metal power such as copper (Cu) powder, nickel (Ni) powder, Mo powder, Cr powder, V powder, Si powder, or Mn powder, a copper suboxide powder, or the like. These may be used either alone as one kind or in combination of two or more kinds.
• a non-ferrous metal power such as copper (Cu) powder, nickel (Ni) powder, Mo powder, Cr powder, V powder, Si powder, or Mn powder, a copper suboxide powder, or the like.
• a lubricant is added so that the molded body obtained by compressing the mixed powder for iron-based powder metallurgy in a mold can be readily taken out from the mold.
• a lubricant is added into the mixed powder for iron-based powder metallurgy, the withdrawing pressure at the time of taking the molded body out from the mold can be reduced, so that cracking of the molded body and damage of the mold can be prevented.
• the lubricant may be added into the mixed powder for iron-based powder metallurgy or may be applied onto the surface of the mold.
• the lubricant When the lubricant is added into the mixed powder for iron-based powder metallurgy, the lubricant is contained preferably at a ratio of 0.01 wt% or more, more preferably at a ratio of 0.1 wt% or more, relative to the weight of the mixed powder for iron-based powder metallurgy. When the content of the lubricant is 0.01 wt% or more, the effect of reducing the withdrawing pressure of the sintered body can be readily obtained. Further, the lubricant is contained preferably at a ratio of 1.5 wt% or less, more preferably at a ratio of 1.2 wt% or less, relative to the weight of the mixed powder for iron-based powder metallurgy. When the content of the lubricant is 1.5 wt% or less, a sintered body having a high density can be readily obtained, and a sintered body having a high strength can be obtained.
• the lubricant that can be put to use may be one or more selected from the group consisting of metal soap (lithium stearate, calcium stearate, zinc stearate, or the like), stearamide, fatty acid amide, amide wax, hydrocarbon-based wax, and cross-linked alkyl (meth)acrylate resin.
• metal soap lithium stearate, calcium stearate, zinc stearate, or the like
• stearamide fatty acid amide
• amide wax hydrocarbon-based wax
• cross-linked alkyl (meth)acrylate resin it is preferable to use an amide-based lubricant from the viewpoint of having a good performance of allowing the powder for alloy, graphite powder, or the like to adhere onto the iron-based powder surface and being capable of readily reducing the segregation of the iron-based mixed powder.
• a binder is added for the purpose of allowing the powder for alloy and the graphite powder to adhere onto the iron-based powder surface.
• the binder that is put to use may be a butene-based polymer, a methacrylate-based polymer, or the like.
• the butene-based polymer it is preferable to use a 1-butene homopolymer made of butene alone or a copolymer of butene and alkene.
• the alkene herein referred to is preferably a lower alkene, and is preferably ethylene or propylene.
• methacrylate-based polymer it is possible to use at least one selected from the group consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, ethylhexyl methacrylate, lauryl methacrylate, methyl acrylate, and ethyl acrylate.
• the binder is contained preferably at a ratio of 0.01 wt% or more, more preferably at a ratio of 0.05 wt% or more, and still more preferably at a ratio of 0.1 wt% or more, relative to the weight of the mixed powder for iron-based powder metallurgy.
• the binder is contained preferably at a ratio of 0.5 wt% or less, more preferably at a ratio of 0.4 wt% or less, and still more preferably at a ratio of 0.3 wt% or less, relative to the weight of the mixed powder for iron-based powder metallurgy.
• the machinability improver is added for the purpose of improving the machinability of the sintered body obtained by sintering the mixed powder for iron-based powder metallurgy.
• the machinability improver to be used is preferably calcium sulfide.
• calcium sulfide it is preferable that the surface of the powder made of calcium sulfide is coated, or alternatively, the powder of calcium sulfide is heated to 300°C to 900°C in advance to change the powder into a form of II type calcium sulfate, because calcium sulfide has moisture absorptivity and may deteriorate the stability of performance.
• an organic material such as an amide-based polymer material or styrene•butadiene rubber can be used.
• the machinability improver is contained preferably at a ratio of 0.01 wt% or more, more preferably at a ratio of 0.05 wt% or more, and still more preferably at a ratio of 0.1 wt% or more, relative to the weight of the mixed powder for iron-based powder metallurgy.
• the machinability improver is contained preferably at a ratio of 1 wt% or less, more preferably at a ratio of 0.4 wt% or less, and still more preferably at a ratio of 0.3 wt% or less, relative to the weight of the mixed powder for iron-based powder metallurgy.
• the mixed powder for iron-based powder metallurgy of the present invention can be prepared by mixing the iron-based powder with the ternary oxide and the binary oxide with use of, for example, a mechanical agitation mixer.
• various kinds of additives such as a powder for alloy, a graphite powder, a lubricant, and a binder may be suitably added.
• the mechanical agitation mixer may be, for example, a high-speed mixer, a Nauta Mixer, a V-type mixer, a double-cone blender, or the like.
• the order of mixing these powders is not particularly limited.
• the mixing temperature is not particularly limited; however, the mixing temperature is preferably 150°C or lower in view of suppressing oxidation of the iron-based powder in the mixing step.
• a pressure of 300 MPa or higher to 1200 MPa or lower may be applied to produce a pressed-powder molded body.
• the molding temperature during this time is preferably 25°C or higher to 150°C or lower.
• the pressed-powder molded body prepared in the above is sintered by an ordinary sintering method to obtain a sintered body.
• the sintering conditions may be a non-oxidizing atmosphere or a reducing atmosphere.
• the above pressed-powder molded body is preferably sintered at a temperature of 1000°C or higher to 1300°C or lower for 5 minutes or more to 60 minutes or less in an atmosphere such as a nitrogen atmosphere, a mixed atmosphere of nitrogen and hydrogen, or a hydrocarbon atmosphere.
• the sintered body thus prepared can be used as a mechanical part of an automobile, an agricultural instrument, a power tool, a home electrical appliance, or the like by being processed with various kinds of tools such as a cutting tool in accordance with the needs.
• a cutting tool may be, for example, a drill, an end mill, a cutting tool for milling, a cutting tool for turning on a lathe, a reamer, a tap, or the like.
• the mixed powder for iron-based powder metallurgy contains a binary oxide
• a sintered body having an excellent machinability at an initial stage of cutting can be obtained.
• the mixed powder for iron-based powder metallurgy contains a ternary oxide
• a sintered body having an excellent machinability in cutting for a long period of time can be obtained.
• the sum weight of the binary oxide and the ternary oxide is within the above range, the machinability at an initial stage of cutting and the machinability in cutting for a long period of time are highly compatible with each other.
• the mixed powder for iron-based powder metallurgy contains the ternary oxide and the binary oxide at a weight ratio of 9 : 1 to 1 : 9, a good balance is provided between the machinability at an initial stage of cutting and the machinability in cutting for a long period of time.
• the mixed powder for iron-based powder metallurgy contains the ternary oxide and the binary oxide in a sum weight of 0.05 wt% or more to 0.2 wt% or less, a sintered body having an excellent balance between the machinability at an initial stage of cutting and the machinability in cutting for a long period of time can be prepared.
• a pure iron powder (trade name: ATOMEL 300M (manufactured by Kobe Steel, Ltd.) was mixed with 2 wt% of copper powder (trade name: CuATW-250 (manufactured by Fukuda Metal Foil & Powder Co., Ltd.)), a binary oxide and/or a ternary oxide having a composition in wt% shown in the section of "binary oxide” and/or “ternary oxide” in Table 1, graphite powder (trade name: CPB (manufactured by Nippon Graphite Industries, Co., Ltd.)), and 0.75 wt% of zinc stearate, so as to prepare a mixed powder for iron-based powder metallurgy.
• the graphite powder was added at an amount such that the amount of carbon after the sintering would be 0.75 wt%.
• those having a volume-average particle size of 2 ⁇ m were used.
• the above mixed powder for iron-based powder metallurgy was put into a mold, and a test piece was molded so as to have a ring shape with an outer diameter of 64 mm, an inner diameter of 24 mm, and a thickness of 20 mm and to have a molding density of 7.00 g/cm 3 .
• this test piece having a ring shape was sintered at 1130°C for 30 minutes in a 10 vol% H 2 -N 2 atmosphere, so as to prepare a sintered body.
• the sintered body thus prepared was turned on a lathe by using a cermet tip (ISO type number: SNGN120408 non-breaker) under conditions with a circumferential speed of 160 m/min, a cutting rate of 0.5 mm/pass, and a feed rate of 0.1 mm/rev, and with a dry type, so as to measure a tool wear amount of the cutting tool.
• a wear amount ( ⁇ m) of the cutting tool after the sintered body was cut for 330 m from the start of cutting and a wear amount ( ⁇ m) of the cutting tool after the sintered body was cut for 1150 m from the start of cutting were measured with a tool microscope.
• the sintered body density was a value as determined by making measurements in accordance with Japan Powder Metallurgy Association Standard (JPMA M 01).
• the radial crushing strength was a value as determined by making measurements in accordance with JIS Z 2507-2000. The higher the radial crushing strength is, the less likely the sintered body is broken, so that the sintered body has a higher strength.
• Examples 1 to 6 are each a sintered body containing a binary oxide and a ternary oxide in combination.
• Comparative Example 1 is a sintered body containing neither a binary oxide nor a ternary oxide.
• Comparative Examples 3 and 4 are each a sintered body containing a ternary oxide alone.
• Comparative Examples 2, 5 and 6 are each a sintered body containing a binary oxide alone.
• a component disclosed in Patent Literature 1 (CaO•Al 2 O 3 ) is used.
• a component disclosed in Patent Literature 3 (2CaO•MgO•2SiO 2 ) is used.
• Comparative Example 4 a component disclosed in Patent Literature 4 (2CaO•Al 2 O 3 •SiO 2 ) is used.
• Comparative Example 1 When Comparative Example 1 is compared with Comparative Examples 2, 5, and 6, it will be understood that the addition of a binary oxide produces an effect of suppressing the initial wear of the cutting tool. Further, when Comparative Example 1 is compared with Comparative Examples 3 and 4, it will be understood that the addition of a ternary oxide produces an effect of suppressing the wear of the cutting tool in cutting for a long period of time.
• Example 7 to 18 a mixed powder for iron-based powder metallurgy and a sintered body were prepared in the same manner as in Example 1 except that the sum weight of the binary oxide and the ternary oxide was fixed to 0.1 wt% and that the weight ratio and the composition thereof were changed to the composition and wt% shown in the sections of "binary oxide” and "ternary oxide” in Table 2.
• evaluation of the tool wear amount was made by the same method as in Example 1. The results of these are shown in the following Table 2.
• Example 19 to 21 and Comparative Examples 7 to 9 a mixed powder for iron-based powder metallurgy and a sintered body were prepared in the same manner as in Example 1 except that the weights of the binary oxide and the ternary oxide were changed to the composition and wt% shown in the sections of "binary oxide” and "ternary oxide” in Table 3. On the sintered body thus prepared, evaluation of the wear amount was made by the same method as in Example 1. The results of these are shown in the following Table 3.

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