SE1650056A1 - Mixed powder for powder metallurgy, method of manufacturingsame, and method of manufacturing iron-based powder sinteredbody - Google Patents

Abstract

A mixed powder for powder metallurgy includes a machinability improvement powder that is crystalline layered alkaline silicate heat-treated in a range from 400 °C to 1100 °C and whose mix proportion is in a range from 0.01% to 1.0% by mass in terms of total content of an iron-based powder, an alloying powder, and the machinability improvement powder. Such a mixed powder for powder metallurgy not only enables a compact to be sintered without adversely affecting the environment in a sintering furnace, but also enables a sintered body having excellent lathe machinability and excellent drill machinability to be obtained.

Description

MIXED POWDER FOR POWDER METALLURGY, METHOD OFMANUFACTURING SAME, AND METHOD OF MANUFACTURINGIRON-BASED POWDER SINTERED BODY TECHNICAL FIELD[0001] The disclosure relates to a mixed powder for powder metallurgyobtained by mixing an iron-based powder, an alloying powder, a machinabilityimprovement powder, and a lubricant and suitable for sintered parts ofvehicles and the like and a method of manufacturing the same, and a methodof manufacturing an iron-based powder-made sintered body by forming andsintering the mixed powder. The disclosure is particularly intended to improve the machinability of an iron-based powder-made sintered body.

BACKGROUND

[0002] The development of powder metallurgy technology has enabled partswith high dimensional accuracy and complex shape to be manufactured in nearnet shape. Products made using powder metallurgy technology are thusutilized in various fields. Powder metallurgy technology has a feature ofhigh shape flexibility, as a die of the desired shape is filled with a powderwhich is then formed and sintered. Hence, powder metallurgy technology isoften used for machine parts having complex shape such as gears.

[0003] In the field of iron-based powder metallurgy, a die of a predeterminedshape is filled with an iron-based mixed powder obtained by mixing aniron-based powder (metal powder) with an alloying powder such as a copperpowder or a graphite powder and a lubricant such as zinc stearate or lithiumstearate, which is then press-formed into a compact and subjected to asintering process to obtain a sintered part. The sintered part obtained in thisway typically has high dimensional accuracy. In the case of manufacturing asintered part for which extremely strict dimensional accuracy is required,cutting work needs to be performed after sintering. The cutting workincludes processes such as lathe turning and drill boring at various cuttingspeeds.

[0004] The sintered part has high porosity, and so has a high cutting resistance as compared with a metal material processed by melting.

Ref. NO. Po134275-PcT-zz (1/29) Accordingly, to improve the machinability ofthe sintered body, Pb, Se, Te, orthe like has been conventionally added to the iron-based mixed powder inpowder form or in the form of being alloyed with the iron powder oriron-based powder.

However, the use of Pb has a problem in that, since Pb has a lowmelting point of 330 °C, Pb melts in the sintering process but does notdissolve in iron, and so it is difficult to uniformly disperse Pb in the matrix.The use of Se or Te has a problem in that the sintered body is embrittled andas a result the mechanical property of the sintered body degradessignificantly.

[0005] Besides, due to poor thermal conductivity ofthe aforementioned pores,when the sintered body is cutting, frictional heat during the cuttingaccumulates and as a result the surface temperature of the tool tends toincrease. The cutting tool thus wears easily and has a shorter life. Thisleads to the problem of an increase in cutting work cost and an increase inmanufacturing cost of sintered parts.

[0006] In view of these problems, for example, Patent Literature (PTL) ldescribes an iron powder mixture for sintered body production obtained bymixing an iron powder with 0.05% to 5% by weight a fine manganese sulfidepowder of 10 um or less.

The technique described in PTL l is supposed to improve themachinability ofthe sintered material without significant dimensional changesand strength deterioration.

[0007] PTL 2 describes an iron-based sintered body manufacturing method ofadding alkaline silicate to an iron-based powder.

The technique described in PTL 2 is supposed to improve free machinability without significant dimensional changes and strengthdeterioration, by adding 0.l% to l.0% by weight alkaline silicate.[0008] PTL 3 describes an iron-based mixed powder for powder metallurgythat is mainly composed of an iron powder and contains 0.02% to 03% byweight a CaO-AlgOg-SiOg complex oxide powder (ceramic powder) of 50 umor less in average particle size having an anorthite phase and/or a gehlenitephase.

The technique described in PTL 3 is supposed to prevent tool material Ref. NO. Po134275-PcT-zz (2/29) degradation and improve machinability, as the ceramic powder exposed on theworked surface adheres to the tool surface and forms a tool protective film(belag layer) during cutting.

[0009] PTL 4 describes an iron-based mixed powder obtained by mixing aniron-based powder, an alloying powder, a machinability improvement powderincluding a manganese sulfide powder and at least one of a calcium phosphatepowder and a hydroxyapatite powder, and a lubricant. According to PTL 4,the manganese sulfide is effective in refinement of chips, whereas the calciumphosphate powder and the hydroxyapatite powder have an effect of preventingor suppressing tool surface alteration by adhering to the tool surface andforming a belag layer during cutting.

The technique described in PTL 4 is thus supposed to improvemachinability without degradation of the mechanical property of the sinteredbody.

[0010] PTL 5 describes an improvement in mechanical workability such asmachinability by adding, to iron or an iron-based alloy, 0.3% to 3.0% byweight barium sulfate, barium sulfide, or both.

CITATION LIST Patent Literature

[0011] PTL l: JP S6l-l4780l A PTL 2: JP S60-l45353 A PTL 3: JP H9-279204 A PTL 4: JP 2006-89829 A PTL 5: JP S46-39564 B PTL 6: JP H04-l57l38 A PTL 7: JP 20l2-l4480l A PTL 8: JP 200l-ll4509 A SUMMARY(Technical Problem)[0012] However, the techniques described in PTL l and PTL 4 have a problemin that, since a manganese sulfide (MnS) powder is contained, the appearanceof the sintered body deteriorates, and also S or MnS remaining in the sintered body promotes rusting of the sintered part and lowers its anti-corrosion Ref. NO. Po134275-PcT-zz (3/29) property.

These techniques also have a problem in that, though MnS is excellentin improving machinability in a low speed range where the cutting speed is100 m/min or less, the machinability improvement effect of MnS is small inhigh speed cutting of about 200 m/min.

[0013] The technique described in PTL 2 has a problem in that, since alkalinesilicate is hygroscopic, fixation occurs in the mixed powder and causes aforming failure.

[0014] The technique described in PTL 3 has a problem in that impurities inthe ceramic powder need to be reduced and also the particle size needs to beadjusted in order to prevent decreases in powder property and sintered bodyproperty, which incurs a rising material cost. The technique described inPTL 3 also has a problem in that, though excellent in improving machinabilityat high speed, the machinability improvement effect is small in low speedcutting.

[0015] The machinability improvement by belag layer formation described inPTL 3 and PTL 4 is effective in reducing cutting power in lathe turning, buthas poor chip removability in drilling as chips are not refined. Thus, there isstill a problem with drill machinability.

[0016] The technique described in PTL 5 has a problem in that themachinability improvement effect is small in high speed cutting of about 200m/min, as in the case of using MnS.

[0017] It could therefore be helpful to provide a mixed powder for powdermetallurgy that enables obtainment of a sintered body having excellentmachinability and particularly excellent lathe machinability (hereafter alsoreferred to as lathe turnability) and excellent drill machinability, and a methodof manufacturing the same. It could also be helpful to provide a method ofmanufacturing an iron-based powder-made sintered body having excellentmachinability including both excellent lathe turnability and excellent drillworkability.

(Solution to Problem)

[0018] We made intensive research on various factors, especially alkalinesilicate, affecting the machinability of the sintered body. As a result of conducting a test of high-temperature heat treatment to reduce the Ref. NO. Po134275-PcT-zz (4/29) hygroscopicity of alkaline silicate, we discovered that alkaline silicatecrystallized in layers by the heat treatment significantly improves themachinability ofthe sintered body.

[0019] The mechanism ofthis improvement is still unclear. However, PTL 6,for example, describes that a magnesium metasilicate-based mineral or amagnesium orthosilicate-based mineral is cleavable and so functions as a solidlubricant, and as a result improves the free machinability, slidability,conformability, and wear resistance of the alloy. We assume that crystallinelayered alkaline silicate has the same mechanism.

[0020] We also discovered that crystalline layered alkaline silicate has agreater machinability improvement effect than a magnesiummetasilicate-based mineral or magnesium orthosilicate, and is effective inmachinability improvement even at relatively low speed, that is, effective inmachinability improvement in a wide range from low speed to high speed.

The mechanism of this improvement is still unclear. However, giventhat MnS and the like have been reported to have an action of fostering aductile fracture of a shear zone under low strain shear rate deformation, thesame mechanism is estimated to function more advantageously.

[0021] Based on the aforementioned discoveries, we determined thatcrystalline layered alkaline silicate can simultaneously improve machinabilityof different requirements, namely, machinability by a lathe (lathe turnability)and machinability by a drill (drill machinability).

[0022] We also discovered that lathe turnability at low speed can be furtherimproved by adding, as a machinability improvement powder (additive), notonly crystalline layered alkaline silicate but also a powder including at leastone selected from a group consisting of SiOg and MgO.

[0023] The mechanism of the synergistic machinability improvement of thesintered body is still unclear, but we assume the following.

According to the description of PTL 7, the addition of a powderincluding one selected from a group consisting of SiOg and MgO allows a softphase and a hard phase to be simultaneously dispersed in the matrix phase ofthe sintered body during the sintering process. Therefore, when a powderincluding one selected from a group consisting of SiOg and MgO is added to crystalline layered alkaline silicate, the function of the crystalline layered Ref. NO. Po134275-PcT-zz (5/29) alkaline silicate as a solid lubricant becomes more apparent, and decreases thedrag of the soft metal compound phase exerted on the tool. This facilitatesthe function of suppressing wear, deformation, or cracking of the tool, andfacilitates cracking in chips by the hard metal compound phase, contributingto enhanced removability of chips during drill boring.

We thus discovered that adding crystalline layered alkaline silicate to the additive described in PTL 7 produces the synergistic effect ofmachinability improvement in drilling.[0024] We further discovered that lathe turnability at low speed can be furtherimproved by adding, as a machinability improvement powder (additive), notonly crystalline layered alkaline silicate but also a powder including at leastone selected from a group consisting of alkali metal sulfates and alkaline earthmetal sulfates.

The mechanism of the synergistic machinability improvement of thesintered body is still unclear, but we assume the following.

According to the description of PTL 5, BaSO4 does not melt ordissolve in any metal and is soft, and such BaSO4 scatters in crystal grainboundaries and grains and develops a notch effect during cutting, thuslowering the cutting resistance and improving the machinability by cutting.[0025] Therefore, when a powder including at least one selected from a groupconsisting of alkali metal sulfates and alkaline earth metal sulfates is added tocrystalline layered alkaline silicate, the function of the crystalline layeredalkaline silicate as a solid lubricant becomes more apparent, and decreases thedrag of the soft compound phase exerted on the tool. This further enhancesthe function of suppressing wear, deformation, or cracking ofthe tool.

We thus newly discovered that adding crystalline layered alkalinesilicate to the additive described in PTL 5 produces the synergistic effect ofmachinability improvement in drilling and the like at low speed.

[0026] The disclosure is based on the aforementioned discoveries and furtherstudies. We thus provide the following. l. A mixed powder for powder metallurgy obtained by mixing aniron-based powder, an alloying powder, a machinability improvement powder,and a lubricant, wherein the machinability improvement powder comprises crystalline layered alkaline silicate heat-treated in a range from 400 °C to Ref. NO. Po134275-PcT-zz (6/29) 1100 °C, and a mix proportion ofthe machinability improvement powder is ina range from 0.0l% to 1.0% by mass in terms of total content of theiron-based powder, the alloying powder, and the machinability improvementpowder.

[0027] 2. The mixed powder for powder metallurgy according to theforegoing 1, wherein the machinability improvement powder furthercomprises at least one selected from a group consisting of an enstatite powder,a talc powder, a kaolin powder, a mica powder, a granulated slag powder, alevigated clay powder, a magnesium oxide (MgO) powder, and a powdermixture of silica (SiOg) and magnesium oxide (MgO), in a range from 10% to80% by mass in terms of total content of the machinability improvementpowder.

[0028] 3. The mixed powder for powder metallurgy according to theforegoing 2, wherein the machinability improvement powder furthercomprises an alkali metal salt powder in a range from 10% to 80% by mass interms oftotal content of the machinability improvement powder.

[0029] 4. The mixed powder for powder metallurgy according to theforegoing 3, wherein the alkali metal salt powder is one or two selected from agroup consisting of an alkali carbonate powder and an alkali metal soap.[0030] 5. The mixed powder for powder metallurgy according to any one ofthe foregoing 1 to 4, wherein the machinability improvement powder furthercomprises a calcium fluoride powder.

[0031] 6. The mixed powder for powder metallurgy according to any one ofthe foregoing 1 to 5, wherein the machinability improvement powder furthercomprises one or two selected from a group consisting of a metal boridepowder and a metal nitride powder.

[0032] 7. The mixed powder for powder metallurgy according to theforegoing 6, wherein the metal boride powder consists of at least one selectedfrom a group consisting of TiB2, ZrBQ, and NbBg, and the metal nitride powderconsists of at least one selected from a group consisting of TiN, AlN, andSi3N4.

[0033] 8. The mixed powder for powder metallurgy according to any one ofthe foregoing 1 to 7, wherein the machinability improvement powder further comprises at least one selected from a group consisting of an alkali metal Ref. NO. Po134275-PcT-zz (7/29) sulfate and an alkaline earth metal sulfate, in a range from 10% to 80% bymass in terms oftotal content ofthe machinability improvement powder.[0034] 9. A method of manufacturing a mixed powder for powder metallurgyaccording to any one ofthe foregoing 1 to 8, by preparing and then mixing aniron-based powder, an alloying powder, a machinability improvement powder,and a lubricant to obtain a mixed powder, wherein the machinabilityimprovement powder comprises crystalline layered alkaline silicateheat-treated at 400 °C to 1100 °C, and a mix proportion of the machinabilityimprovement powder is 0.01% to 1.0% by mass in terms oftotal content oftheiron-based powder, the alloying powder, and the machinability improvementpowder, and the mixing includes: primary mixing in which a part or whole ofthe machinability improvement powder and a part of the lubricant are added,as a primary mixture material, to the iron-based powder and the alloyingpowder and heated to perform mixing while melting at least one type of thelubricant, and a resulting mixture is cooled for solidification; and secondarymixing in which a remaining powder of the machinability improvementpowder and the lubricant is added, as a secondary mixture material, to themixture to perform mixing.

[0035] 10. The method of manufacturing a mixed powder for powdermetallurgy according to the foregoing 9, wherein the machinabilityimprovement powder further comprises at least one selected from a groupconsisting of an enstatite powder, a talc powder, a kaolin powder, a micapowder, a granulated slag powder, a levigated clay powder, a magnesiumoxide (MgO) powder, and a powder mixture of silica (SiOg) and magnesiumoxide (MgO), in a range from 10% to 80% by mass in terms oftotal content ofthe machinability improvement powder.

[0036] 11. The method of manufacturing a mixed powder for powdermetallurgy according to the foregoing 10, wherein the machinabilityimprovement powder further comprises an alkali metal salt powder in a rangefrom 10% to 80% by mass in terms of total content of the machinabilityimprovement powder.

[0037] 12. The method of manufacturing a mixed powder for powdermetallurgy according to the foregoing 11, wherein the alkali metal salt powder is one or two selected from a group consisting of an alkali carbonate powder Ref. NO. Po134275-PcT-zz (s/29) and an alkali metal Soap.

[0038] 13. The method of manufacturing a mixed powder for powdermetallurgy according to any one of the foregoing 9 to 12, wherein themachinability improvement powder further comprises a calcium fluoridepowder.

[0039] 14. The method of manufacturing a mixed powder for powdermetallurgy according to any one of the foregoing 9 to 13, wherein themachinability improvement powder further comprises one or two selectedfrom a group consisting of a metal boride powder and a metal nitride powder.

[0040] 15. The method of manufacturing a mixed powder for powdermetallurgy according to the foregoing 14, wherein the metal boride powderconsists of at least one selected from a group consisting of TiB2, ZrBQ, andNbBg, and the metal nitride powder consists of at least one selected from agroup consisting of TiN, AlN, and Si3N4.

[0041] 16. The method of manufacturing a mixed powder for powdermetallurgy according to any one of the foregoing 9 to 15, wherein themachinability improvement powder further comprises at least one selectedfrom a group consisting of an alkali metal sulfate and an alkaline earth metalsulfate, in a range from 10% to 80% by mass in terms of total content of themachinability improvement powder.

[0042] 17. A method of manufacturing an iron-based powder sintered body,by filling a die with a mixed powder for powder metallurgy manufactured bythe method according to any one of the foregoing 9 to 16,compression-forming the mixed powder into a compact, and subjecting thecompact to a sintering process to obtain a sintered body.

(Advantageous Effect)

[0043] It is possible to manufacture a sintered body having excellentmachinability that includes both excellent lathe turnability and excellent drillmachinability, at low cost. This remarkably reduces the manufacturing costof metal sintered parts, and so has an industrially significant advantageouseffect. Since cutting can be performed in a wide range of cutting conditionsfrom low speed to high speed, the advantageous effect is particularlynoticeable in works, such as drilling, where the cutting speed varies between center and peripheral portions.

Ref. NO. Po134275-PcT-zz (9/29) _10- Another advantageous effect is that a compact can be formed without a decrease in green density and an increase in ejection force.

DETAILED DESCRIPTION

[0044] The disclosed components and methods are described in detail below.

The disclosed mixed powder for powder metallurgy is described first.

The disclosed mixed powder for powder metallurgy is a mixed powderobtained by mixing an iron-based powder, an alloying powder, a machinabilityimprovement powder, and a lubricant.[0045] The iron-based powder may be any of the iron-based powdersincluding: a pure iron powder such as an atomized iron powder or a reducediron powder; a pre-alloyed steel powder (completely alloyed steel powder)obtained by pre-alloying an alloying element; a partial diffusion-alloyed steelpowder obtained by partially diffusing and alloying an alloying element in aniron powder; and a hybrid steel powder obtained by further partially diffusingan alloying element in a pre-alloyed steel powder (completely alloyed steelpowder). As the iron-based powder, an iron-based powder mixture includingan alloying powder and a lubricant in addition to the aforementionediron-based powder may be used.[0046] The alloying powder is, for example, a graphite powder, a non-ferrousmetal powder such as Cu (copper) powder, Mo powder, or Ni powder, acuprous oxide powder, or the like. The alloying powder is selected fromthese powders and mixed depending on the desired sintered body property.Mixing such an alloying powder with the iron-based powder increases thestrength of the sintered body, and ensures the desired sintered part strength.The mix proportion ofthe alloying powder is in a range from 0.l% to 10% bymass in terms of total content of the metal powder, the alloying powder, andthe machinability improvement powder, depending on the desired sinteredbody strength. When the mixed proportion of the alloying powder is lessthan 0.l% by mass, the desired sintered body strength cannot be ensured.When the mixed proportion of the alloying powder exceeds 10% by mass, thedimensional accuracy ofthe sintered body decreases.[0047] The machinability improvement powder is crystalline layered alkaline silicate heat-treated at 400 °C to ll00 °C. Alkaline silicate used here may be Ref. NO. Po134275-PcT-zz (10/29) _11- sodium silicate, potassium silicate, lithium silicate, or the like. Thesesubstances are water-soluble. Accordingly, when any of these substances isdirectly added to the mixed powder, its moisture absorption causes fixationbetween the powders in the mixed powder, as a result of which the fluidity ofthe powder deteriorates and a forming failure occurs.

[0048] In view of this, the alkaline silicate is heat-treated to reduce silanolgroups on the surface, thus lowering the connectivity with water. It isimportant to set the heating temperature to 400 °C to 1100 °C. When theheating temperature is less than 400 °C, the hygroscopicity reduction effect isinsufficient. When the heating temperature exceeds 1100 °C, the cost of thetreatment is not reasonable.

In the heat treatment, the alkaline silicate crystallizes into a layered structure. This structure can be observed by analysis means such as an X-raydiffractometer. The crystalline layered alkaline silicate is one type ofcrystalline alkali metal layered silicate. The crystalline alkali metal layeredsilicate is well known as a detergent builder which is a material that, whenmixed in a detergent, significantly enhances detergency. The crystallinealkali metal layered silicate is described in detail in PTL 8.[0049] When forming the mixed powder into the compact and sintering it, asoft metal compound powder is preferably added, as a machinabilityimprovement powder used together with the crystalline layered alkalinesilicate. The soft metal compound powder forms, in the matrix phase of thesintered body, soft particles (soft phase) with lower hardness than the averagehardness of the matrix phase and can form an amorphous phase at a lowtemperature because of the low melting point.

In detail, the soft metal compound powder is at least one type selectedfrom an enstatite powder, a talc powder, a kaolin powder, a mica powder, agranulated slag powder, a levigated clay powder, a magnesium oxide (MgO)powder, and a powder mixture of silica (SiOg) and magnesium oxide (MgO).[0050] Of these additives to the mixed powder as a machinabilityimprovement powder, soft minerals such as an enstatite powder, a talc powder,a kaolin powder, and a mica powder are metal compounds containing at leastSi or Mg, and O (SiOg or MgO), and a granulated slag powder is a deoxidation product represented by a chemical composition such as CaO-SiOg-AlgOg or Ref. NO. Po134275-PcT-zz (11/29) _12- MgO-AlgOg-SiOg. These powders which are compounds containing Si, Mg,and O can each form a low-melting amorphous phase and disperse in thematrix phase of the sintered body as a soft metal compound phase, whensintering the green compact formed from the mixed powder. Thelow-melting amorphous phase formed during sintering is a SiOg-MgO-basedamorphous phase.

[0051] At least one selected from a group consisting of a levigated claypowder, a magnesium oxide (MgO) powder, and a powder mixture of silica(SiOg) and magnesium oxide (MgO) which contains Si, Mg, and O as with anenstatite powder and the like may be used as a machinability improvementpowder. The powder mixture of silica (SiOg) and magnesium oxide (MgO)can equally form a low-melting amorphous phase (amorphous particles) whensintering the green compact formed from the mixed powder. The mixingratio SiO2:MgO is preferably in a range from 1:2 to 3:1 by mass.

[0052] Preferably, an alkali metal salt powder is further added as amachinability improvement powder. Further adding an alkali metal saltpowder to a powder containing SiOg and/or MgO, such as an enstatite powder,facilitates the formation of the low-melting amorphous phase when sinteringthe green compact.

[0053] During sintering, not only the alkali metal salt forms low-melting fluxby itself or by reacting with iron oxide on the surface of the iron-basedpowder, but also other oxides such as SiOg and MgO included in the mixedpowder melt in the flux to form a SiOQ-MgO-alkali metal oxide-basedamorphous phase, which disperses in the matrix phase of the sintered body asa soft phase.

Examples of the alkali metal salt include alkali carbonate and alkalimetal soap. Any one or a composite of these powders may be included.The use of alkali metal soap is advantageous in that the lubrication effect bythe metal soap improves the density ofthe green compact in powder forming.[0054] The mix proportion of the powder containing SiOg and/or MgO or thealkali metal salt powder is preferably in a range from 10% to 80% by mass interms of total content of the machinability improvement powder. When themix proportion is less than l0% by mass, the aforementioned synergetic effect cannot be expected. When the mix proportion exceeds 80% by mass, the Ref. NO. Po134275-PcT-zz (12/29) _13- machinability improvement effect at low speed decreases.

[0055] A calcium fluoride powder may further be included. The mixproportion of the calcium fluoride powder is preferably in a range from20% to 80% by mass in terms of total content of the machinabilityimprovement powder. When the mix proportion is less than 20% by mass,the desired machinability improvement effect cannot be expected. When themix proportion exceeds 80% by mass, the mechanical strength ofthe sinteredbody decreases.

[0056] A powder serving as hard particles is, for example, a metal boridepowder and/or a metal nitride powder. Examples of the metal boride powderinclude a TiB2 powder, a ZrBQ powder, and a NbBQ powder, and a NbBQpowder is particularly preferable. Examples of the metal nitride powderinclude a TiN powder, a AlN powder, and a Si3N4 powder, and a Si3N4 powderis particularly preferable.

The mix proportion of the metal boride powder and/or metal nitride powder is preferably in a range from l0% to 80% by mass in terms of totalcontent ofthe machinability improvement powder. When the mix proportionis less than l0% by mass, the desired machinability improvement effectcannot be expected. When the mix proportion exceeds 80% by mass, thepowder compressibility and the sintered body strength decrease.[0057] Moreover, when forming the mixed powder into the compact andsintering it, at least one selected from a group consisting of alkali metalsulfates and alkaline earth metal sulfates may be added as a machinabilityimprovement powder used together with the crystalline layered alkalinesilicate.

In detail, at least one selected from a group consisting of alkali metalsulfates such as sodium sulfate and lithium sulfate and alkaline earth metalsulfates such as calcium sulfate, magnesium sulfate, barium sulfate, andstrontium sulfate may be added.

[0058] These are all soft substances, and do not melt or dissolve in any metal.Such a substance scatters in crystal grain boundaries and grains, and developsa notch effect during cutting, thus lowering the cutting resistance andimproving the machinability by cutting. As a result, the function of the crystalline layered alkaline silicate as a solid lubricant becomes more Ref. NO. Po134275-PcT-zz (13/29) _14- apparent, and decreases the drag of the soft compound phase exerted on thetool. This enhances the function of suppressing wear, deformation, orcracking ofthe tool.

The mix proportion of the alkali metal sulfate or alkaline earth metalsulfate is preferably in a range from 10% to 80% by mass in terms of totalcontent ofthe machinability improvement powder. When the mix proportionis less than l0% by mass, the desired machinability improvement effectcannot be expected. When the mix proportion exceeds 80% by mass, thepowder compressibility and the sintered body strength decrease.

[0059] The mix proportion of the machinability improvement powder in themixed powder needs to be in a range from 0.01% to 1.0% by mass in terms oftotal content of the iron-based powder, the alloying powder, and themachinability improvement powder. When the mix proportion is less than0.0l% by mass, the machinability improvement effect is insufficient. Whenthe mix proportion exceeds 1.0% by mass, the green density decreases and themechanical strength of the sintered body obtained by sintering the compactdecreases. The mix proportion of the machinability improvement powder inthe mixed powder is therefore limited to a range from 0.0l% to l.0% by massin terms of total content of the iron-based powder, the alloying powder, andthe machinability improvement powder.

[0060] The mixed powder includes an appropriate amount of lubricant, inaddition to the aforementioned iron-based powder, alloying powder, andmachinability improvement powder. The lubricant is preferably metal soapsuch as zinc stearate or lithium stearate, carboxylic acid such as oleic acid, oramide wax such as stearic acid amide, stearic acid bisamide, orethylene-bis-stearamide. The mix proportion of the lubricant is notparticularly limited. As the external additive amount, the mix proportion ispreferably in a range from 0.l% to l.0% by mass in outer percentage in termsof total content of l00% by mass the metal powder, the alloying powder, andthe machinability improvement powder. When the mix proportion of thelubricant is less than 0.l% by mass in outer percentage, the friction with thedie increases and the ejection force increases, causing a shorter die life.When the mix proportion of the lubricant is large exceeding l.0% by mass in outer percentage, the forming density decreases and the density ofthe sintered Ref. NO. Po134275-PcT-zz (14/29) _15- body decreases.[0061] A preferable method of manufacturing the mixed powder is describedbelow.

The alloying powder, the machinability improvement powderincluding one or more powders of the aforementioned types and mixproportions, and the lubricant are added to the iron-based powder byrespective predetermined amounts. Desirably, they are mixed at one time orin two or more times typically using a well-known mixer, to obtain the mixedpowder (iron-based mixed powder). The machinability improvement powderdoes not necessarily need to be mixed all at once. Only a part of themachinability improvement powder may be added and mixed (primary mixing),after which the remaining part (secondary mixture material) is added andmixed (secondary mixing). The lubricant is preferably added in two times.

Here, the iron-based powder that has been subjected to segregationprevention treatment of causing a part or whole of the alloying powder and/ormachinability improvement powder to adhere to the surface of a part or wholeof the iron-based powder by a bonding material may be used. Thesegregation prevention treatment may be the segregation prevention treatmentdescribed in JP 3004800 B.

[0062] By heating to not lower than the minimum temperature of the meltingpoint of any of various types of lubricant included in the mixed powder, atleast one type of lubricant out of these lubricants melts to initiate primarymixing, and then the mixture is cooled for solidification. After this, thesecondary mixture material composed of the remaining powder of themachinability improvement powder and lubricant is added to initiatesecondary mixing.

[0063] The mixing means is not particularly limited, and may be any of theconventionally well-known mixers. Mixers that facilitate heating, such as ahigh-speed bottom stirring mixer, an inclined rotating pan-type mixer, arotating hoe-type mixer, and a conical planetary screw-type mixer, areespecially advantageous.

[0064] A preferable method of manufacturing the sintered body using themixed powder for powder metallurgy obtained by the aforementioned manufacturing method is described below.

Ref. NO. Po134275-PcT-zz (15/29) _16- First, a die is filled with the mixed powder for powder metallurgy manufactured by the aforementioned method, which is thencompression-formed into a compact. As the forming method, any of thewell-known forming methods such as press forming may be suitably used.The use of the disclosed mixed powder for powder metallurgy realizes highforming pressure of 294 MPa or more, and enables forming at normaltemperature. To ensure stable formability, it is preferable to heat the mixedpowder or the die to appropriate temperature, or apply a lubricant to the die.[0065] In the case of performing compression forming in a heatingatmosphere, the temperature ofthe mixed powder or die is preferably less than150 °C. This is because the mixed powder for powder metallurgy has highcompressibility and so exhibits excellent formability even when thetemperature is less than 150 °C, and also because degradation due to oxidationmay occur when the temperature is 150 °C or more.[0066] The compact obtained by the aforementioned forming process is thensubjected to the sintering process to form the sintered body. The temperatureof the sintering process is desirably about 70% of the melting point of themetal powder.

In the case of the iron-based powder, the temperature of the sintering process is 1000 °C or more, and preferably 1300 °C or less. When thetemperature of the sintering process is less than 1000 °C, the desired densityof the sintered body is unlikely to be achieved. A high temperature of thesintering process exceeding 1300 °C is not preferable because abnormal graingrowth tends to occur during sintering and decrease the strength of thesintered body.[0067] The atmosphere of the sintering process is preferably an inert gasatmosphere such as nitrogen or argon, an inert gas-hydrogen gas mixtureatmosphere where hydrogen is mixed with the inert gas atmosphere, or areduction atmosphere such as ammonia decomposition gas, RX gas, or naturalgas.

After the sintering process, heat treatment such as gas carburizing heattreatment or carburizing nitriding treatment is further performed according toneed, to obtain the product (sintered part, etc.) having the desired properties.

Cutting work and the like are conducted as necessary to form the product Ref. NO. Po134275-PcT-zz (16/29) _17- having predetermined dimensions.

EXAMPLES[0068] Non-limiting examples according to the disclosure are describedbelow.

As the iron-based powder, the iron-based powders (average particlesize: about 80 um in each case) shown in Table l were used. The averageparticle size was determined using laser diffractometry.

As shown in Table l, the iron-based powders used are: (A) anatomized pure iron powder; (B) a reduced pure iron powder; (C) a partialdiffusion-alloyed steel powder obtained by partially diffusing and alloying Cuas an alloying element on the surface of an iron powder; (D) a partialdiffusion-alloyed steel powder obtained by partially diffusing and alloying Ni,Cu, and Mo as an alloying element on the surface of an iron powder; (E) apre-alloyed steel powder (completely alloyed steel powder) obtained bypre-alloying Ni and Mo as an alloying element; (F) a pre-alloyed steel powder(completely alloyed steel powder) obtained by pre-alloying Mo as an alloyingelement; (G) a pre-alloyed steel powder (completely alloyed steel powder)obtained by pre-alloying Mo as an alloying element; and (H) a steel powder(hybrid alloyed steel powder) obtained by further partially diffusing andalloying Mo as an alloying element in a completely alloyed steel powderobtained by pre-alloying Mo.

[0069] [Table l] Table lIron-based powder CompositionType symbol (%: mass%)A Atomized pure iron powder FeB Reduced pure iron powder FeC Partial diffusion-alloyed steel powder Fe-2.0%CuD Partial diffusion-alloyed steel powder Fe-4.0%Ni-l.5%Cu-0.5%MoE Completely alloyed steel powder Fe-0.5%Ni-0.5%MoF Completely alloyed steel powder Fe-0.6%MoG Completely alloyed steel powder Fe-0.45%MoH Hybrid alloyed steel powder (Fe-0.45%Mo) -0. l5%Mo* *) Steel powder obtained by diffusing and alloying 0. l5%Mo in Fe-0.45%Mo completely alloyed steel powder Ref. NO. Po134275-PcT-zz (17/29) _18-

[0070] The alloying powder of each of the types and mix proportions shownin Table 2, the machinability improvement powder of each of the types andmix proportions shown in Table 2, and the lubricant of each of the types andmix proportions shown in Table 2 were added to the corresponding one oftheaforementioned iron-based powders, and primary mixing was performed usinga high-speed bottom stirring mixer. In the primary mixing, each sample washeated to 140 °C while being mixed, and then cooled to 60 °C or less. Anatural graphite powder added as the alloying powder is a powder of 5 pm inaverage particle size, and a copper powder added as the alloying powder is a powder of 20 pm in average particle size.

Ref. NO. Po134275-PcT-zz (18/29) (6Z/6ÛZZ1LDdíLZVSlOd 'ON 'Pål Table 2 11 _1111 aEzwå: Alloying powder Machinabilily irnprovement powder LubricantMassa Game Wde C Wde Pmmafymaaag , ._ P. a ._ sec da psvvasf symbol; f” r °pperp° r A1111111vs 311111151 A1111111vs 1111111111 y "uxmg P de "m rymmg °“ rymmg Rsmafks. sw 1symbol rmx _ _ Proponion of _ __ . “M Type***** Type*****pmpaasa Try” Typs; maspaapsaaa _ mifíx* “im V miïypeåíägnm a1111111vs gsap Tyge' f” pmfzaflïä) ; mixpsspsfnsa ; mapfspsaaa(massw P ”mot (mass%) ' p °f° ' F? IW* p' Wflfm] (massH/sasmsf (massfl/asassf(mass A1) (mass A1) (mass A1) D (mass A1)(mass A1) percentage) percenlage) 1 1111 ;M 1 A;99.3 Namaogšm” e _ a; 0.1 _ 0 _ 0.1 Ao; 0.1,z11; 0.3 za; 0.4 Examp1s 1 1111 ;M 2 A; 99.2 Nmmogšap e _ 11; 0.1 f 0.1 50 _ 0.2 Ao; 0.1,z11; 0.3 za; 0.4 13xa111111sM 3 A; 97.1 Namaåfšapme: Ammasd ssppsf; 2.0 a; 0.1 _ 0 _ 0.1 Ao; 01,211; 0.3 za; 0.4 Exampls Na1111~a1 g1ap1111s; _ .M 4 A; 97.0 08 A1sm1as11 ssppss; 2.0 s; 0.1 1; 0.05, m; 0.05 20 _ 0.2 AM; 0.2,13s; 0.2 L1; 0.1za0.1,13s0.3 ExammsN 1 1111 ;M 5 A; 97.05 “mmoïp e Ammasa ssppss; 2.0 a; 0.05 g; 0.05, 11; 0.05 57 _ 0.15 AM; 0.2,13s; 0.2 Li; 0.1,za0.1,1as0.3 13xa1ap1sM 6 ß: 99.2 Nmmëínphne: _ 111 0.1 1; 005,12 0.05 50 _ 0.2 Ao; 0.2,Bs; 0.2 za: 0.4 13xa111111sM 7 B; 99.2 Namraëggapme: _ s; 0.1 k;0.1 25 _ 0.2 Ao;0.2, Bs; 0.2 za; 0.4 ExamplsNa1111~a1 g1ap1111s; _ .

M s ß; 96.9 0 8 E1ssas1y1s ssppss; 2.0 a; 0.1 1; 0.1 33 s13N4;0.1 0.3 AM; 0.1, Bs; 0.1 za; 0.1,Bs0.5 121amp1sM 9 c; 98.9 Nammëímphüe: _ a; 0.1 1; 0.05, m; 0.05 25 T1132; 0.2 0.4 Ao; 0.1, za; 0.3 za; 0.4 Examp1s 1 1111 ;M 10 D;99.2 Nmwaogšmp e _ 11;0.2 a; 0.1 33 _ 0.3 Ao: 0.1.z11; 0.3 za;0.4 13xa111p1sM 11 E; 99.3 Nmmaëgfpme: _ s; 0.1 s; 0.1 50 _ 0.2 Ao; 0.2,13s;0.2 za; 0.4 ExammsM 12 F; 99.05 Na"“aå)g:'phñeí _ a; 0.2 1; 0. 1, m; 0.05 43 T1B2; 0.1 0.45 AM; 0.2, Bs; 0.2 L1; 0.1z110.1,13s0.3 Exampls N ~ 1 1111 ; M 13 (1953 amaoïap e Ammasd ssppsazo 11;0.2 1s;0.1 25 213,01 0.4 AM; 0.1,13s;0.1 za; 0.1,13s0.5 Examp1sM 14 H; 913.5 Nammëâmphne: _ s; 0.2 f; 0.25, s; 0.25 71 _ 0.7 Ao; 0. 1, za; 0.3 za; 0.4 Examp1sM 15 A; 99.4 Nmml gmpm: _ _ _ 0 _ 0 Ao; 0.1, za; 0.3 za; 0.4 Cmpmme 0.6 E11amp1s *) a: crystallirre layered sodium silicate, b: crystallirxe layered potassiurn silicate, c: crystalline layered lithium silicate, d: unheated sodiurn silicate, e: 350 °C heated sodiurn silicate**) f: enstatite, g: tale, h: kaohrr, i: mica,j: granulated slag, k: levigated clay, k MgO,m: S102, rr lithium carbonate (alkali metal salt), o: lilhium stearate (metal soap) p: sodlum sulfate, q: calclum sulfate, r: barium sulfate***) proponion of addilive group II in all ****) Proportion of all cuttabiljly improvement powder in total content of irorrbased powder, alloying powder, and cuttabfliry improvement powder improvement powder *Hm za; ams s1sa1a1s,L1; 11111111ms1sa1a1s,13s; s111y1s11s_111s_s1sa1aa11s1s, AM; stsaas as111a1sasam1as,Ao; s1s1s as111 [z 31091] [two] _6I- (Gl/OZ) ZZ1LO Table 2 (conf d) Ir _15 dïwâ: Auoyrrrg powder Moeirrrroo' ' rrrrproverrrerri powder LrrbrieorriMixed _ Primary mixing _ _ _ _ _ . _G m d « c de ° ~ room 1> rmory s dopowder syrrriool; ”I” :WW e) ”p” WW r Addmve proup1 Addrfive opp 11 g Powder r mmg mm rwmmg Rerrrerkeeyrrroo1 rrrrx A _ *_ n Proporrrorr of _ _ _ rypeflmfl* rypeßm*_ Type. mix _ _ Type Type ._ Type. mix pwporrrurr _ _ _ _proportion _ Type: mixpropomon _ _ _ _ addinve group _ n : mix proportion : mixpropornon0 propornon o, : mixproponion : mnxproportion *M proportion (mass Ar) o o(mass ./o) ( mssw) (mass m) (massy) (nmssly) II (nmssy) (mass /fl-outer (mass /o-outer' ° “ “ (mess-nr) “ pereerrrege) pereerriege)M 16 A;99.3 Nammågëapme: _ d; 0.1 _ o _ 0.1 Ao;0_1,zrrro.3 zrr;0_4 C°E““P“mlm'°. XanlzflN 1 o; r c rrrpe 511 A;97.1 amaogšap 'e Arorrraoed copper; 2.0 d;0.1 _ o _ 0.1 Ao;0.1,zrr;o.3 zrr;0.4 “šxanïlïve18 A;97.1 Nammlgapme: Aiorrrized eopper;2.0 e;0.1 _ o _ 0.1 Ao;0.1,zrr;o.3 zrr; 0.4 Ccmlmame0.8 Exerrrp1eM 19 A;9v.1 Namaàgšapm” Aiorrrazed oopper;2.0 _ f; 0.1 100 _ 0.1 Aorogzrrros zrr;0.4 CëïïalïveN 1 1.11 ; c '20 A;97.1 “maogsfap ° Arorrrized oopper;2.0 _ 1; 0.05, rrr; 0.05 25 _ 0.1 AM;o.2,1ss;o,2 Li;o.1zrr0.1,1sso.3 'Eïlïïïve21 B;97.o Nammàïapme: Eieerrolyre eopper; 2.0 _ j; 0.1 50 si3N4;o.1 0.2 AM;0.1,Bs;0.1 zrr;0.1Bs0.5 CcgxawammltšveM 22 099.3 Namialgraphne: - _ _ o _ 0 Ao;0.1,zrr;o.3 zrr;0.4 Cmparafiva0.7 ExamEle23 D;99.5 Namalgrapme: _ _ _ o _ 0 Ao;0.1,zrr;o.3 zrr;0.4 C°'“P“'a““'e0.5 Emm ie24 E;99.5 Namalgapme: _ _ _ 0 _ o Ao; 0.1,zrr;o.3 zo;0.4 C°"'P“'°“V°0.5 Erorrrr 1eM 25 F;99.25 Namalgraphne: _ _ 1; 0.1,rrr; 0.05 60 TiB2;0.1 0.25 AM;0_2,Bs;0.2 L1;0.1,zrr0.1,1sso.3 Cmnpamme0.5 Example1 o; ; c 5M 26 G;97.2 Nm” m? 'e Arorrrized eopper;2.0 _ _ o _ 0 AM;0.1,Bs;o.1 zrr; 013505 °“'P““"Ve0.8 ErrerrrpieM 27 A;99.2 Nammåïapme: _ rr;0.1 p; 0.1 50 _ 0.2 Ao;0.1,zrr;o.3 zrr;0.4 Exerrrp1e1 om ;2s A;9v.0 Nama gap e Arorrrazea oopper;2.0 e;0.1 q:o.1 20 _ 0.2 AM;o.2,Bsro.2 1.1:o.1,zrr0.1,1aso.3 Exerrrpie0.81 5 r29 A;97.o Nawaogšfapmæ Arorrrized eopper;2.0 rr;o.1 r; 0.1 20 _ 0.2 AM;0.2,Bs;o.2 L1;o.1zo0.1,1aso.3 ErorrrrpieM 30 Are-Los Nammåïaphüe: Arorrrized oopper; 2.0 e; 0.05 f; 0.05,p; 0.05 67 _ 0.15 AM;0_2,Bs;0.2 L1;0.1,zrr0.1,1sso.3 Exerrrp1e *) e; oryeieurrre 1oyered eodiorr. euroere, o; oryerenrrre 1eyered porrreerrrrrr enseore, e; eryerourrre 1eyered mirrorrr emeore, d; ordreered eodrorrr euro-rie, e; 350 °c 1reered eodrrrrrr eiisoere n) f; errerorrreg; re1o,1r; keoirrr, 1; rrrrorrj; grarrooredeogde 1ewgo1ea o1ey, 1; Mgarrr; s1o2rr udrrorrr owroorrore (euron rrrere1ee1r),o; 11r1r1rrrrr erearere (rrrem Soap) D: sodium sulfate. a: calcium sulfate, r: barium sulfate W) pr-oporrroo of eddrrrve group 11 rr. en errorrouiry rrrrproverrrerrr powder***~) Propornorr of on eonpomry rrrrproverrrerrr powder arr :om oorrrerrr of irorr-oeeed powder, enoyirrg powder, and eoneoriiry irrrproverrrerr» powder “***) Zn: zinc stearate, Li: liíhium sßearatre, BS: emyleneJnis-stearamide, AM: stearic acid monoamide, AO: oleic acid _0z- _21-

[0072] After the primary mixing, the secondary mixture material composed ofthe machinability improvement powder and lubricant of each ofthe types andmix proportions shown in Table 2 was further added, and secondary mixing ofstirring each sample for 1 minute was performed with the rotational frequencyof the mixer being 1000 rpm. After the secondary mixing, the mixed powderwas taken out of the mixer. Here, the machinability improvement powderwas added in two times, i.e. upon the primary mixing and upon the secondarymixing. The mix proportion of the machinability improvement powder isexpressed in % by mass in terms oftotal content of the iron-based powder, thealloying powder, and the machinability improvement powder. The mixproportion of the lubricant as external addition is expressed in % by mass inouter percentage in terms of total content of 100% by mass the iron-basedpowder, the alloying powder, and the machinability improvement powder.

As a result of the aforementioned steps, the mixed powder in whichthe iron-based powder, the alloying powder, and the machinabilityimprovement powder were uniformly mixed without segregation wasobtained.

As comparative examples, the iron-based powder, the alloying powder, and the lubricant of each of the types and mix proportions shown in Table 2were added and mixed at normal temperature using a V-type container rotatingmixer, thus obtaining a mixed powder.[0073] Following this, a die (two types for lathe turning test and drilling test)was filled with the obtained mixed powder, which was thencompression-formed with a pressing force of 590 MPa to obtain a compact.The compact was subjected to a sintering process at 1130 °C for 20 min in anRX gas atmosphere to obtain a sintered body.

The obtained sintered body was subjected to the lathe turning test andthe drilling test. The test methods are as follows.[0074] (1) Lathe turning test Three sintered bodies (ring-shaped, 60 mm (outer diameter) >< 20 mm(inner diameter) >< 20 mm (length)) were overlaid on each other, and their sidesurfaces were turned using a lathe. The turning condition is as follows: theuse of a cermet-made lathe turning tool; the turning speed of 100 m/min and 200 m/min; the feed rate of 0.1 mm per cycle; the turning depth of 0.5 mm; Ref. NO. Po134275-PcT-zz (21/29) _22- and the turning distance of 1000 m. After the test, the flank Wear Width ofthe turning tool Was measured. Based on the assumption that the tool lifecorresponds to approximately the Wear of 0.25 mm, in the case Where the toollife Was reached When the turning distance is less than l000 m, the sampleWas marked as “l000 m not reached”. It is thus evaluated that the sinteredbody has more excellent machinability When the flank Wear Width of thecutting tool is smaller.[0075] (2) Drilling test A sintered body (disk-shaped, 60 mm (outer diameter) >< l0 mm(thickness)) Was bored to form a through hole under the conditions of 5,000rpm in rotational frequency and 750 mm/min in feed rate, using a high speedsteel-based drill (2.6 mm in diameter). During this, the thrust component asthe cutting resistance in drilling Was measured using a tool dynamometer. Itis eValuated that the sintered body has more excellent machinability When thethrust component is smaller.

Table 3 shows each ofthe obtained results.

Ref. NO. Po134275-PcT-zz (22/29) _23-

[0076] [Tabie 3] Table 3Lathe turning test result Drilling test resultSintered . Turning speed Turning speed . .Mbody Dfd pgovíder 100m/min 200m/min Cumng reslstance RemarksNo. ym Flank Wear Flank Wear Thrust component(mm) (mm) (N)1 M 1 0.07 0.09 241 Example2 M 2 0.06 0.06 230 Example3 M 3 0.08 0.09 250 Example4 M 4 0.07 0.05 234 Example5 M 5 0.07 0.08 244 Example6 M 6 0.08 0.07 255 Example7 M 7 0.06 0.05 226 Example8 M 8 0.09 0.08 253 Example9 M 9 0.08 0.08 249 Example10 M 10 0.11 0.10 261 Example11 M 11 0.10 0.09 254 Example12 M 12 0.09 0.07 250 Example13 M 13 0.08 0.07 238 Example14 M 14 0.09 0.08 255 Example1000m not 1000m not Comparative15 M 15 reached reached 301 Example1000m not 1000m not Comparative1 16 M 6 reached reached 297 Example17 M 17 0.21 0.23 290 CmnparatlveExample18 M 18 0.18 0.19 289 CmnparatlveExample19 M 19 0.17 0.10 275 CmnparatlveExample20 M 20 0.18 0.09 286 CmnpafatlveExample21 M 21 0.20 0.12 281 CmnparatlveExample1000m not 1000m not Comparative22 22M reached reached 300 Example1000m not 1000m not Comparative2 23 M 3 reached reached 322 Example1000m not 1000m not Comparative24 M 24 reached reached 3 12 Example25 M 25 0.22 0.12 289 CmnparatlveExample26 M 26 1000m not 1000m not 294 Comparativereached reached Example27 M 27 0.06 0.08 224 Example28 M 28 0.07 0.07 220 Example29 M 29 0.07 0.06 223 Example30 M 30 0.07 0.10 233 Example Ref. NO. Po134275-PcT-zz (23/29) _24-

[0077] As shown in Table 3, Exaniples according to the disclosure all hadsn1all flank wear width of the cutting tool, which indicates excellent latheniachinability. Moreover, Exaniples had low thrust component in drill boring,and thus were sintered bodies having excellent drill niachinability, too. Onthe other hand, Comparative Exaniples outside the range of the disclosure especially had poor drill niachinability.

Ref. NO. Po134275-PcT-zz (24/29)

Claims (17)

1. A mixed powder for powder metallurgy obtained by mixing aniron-based powder, an alloying powder, a machinability improvement powder,and a lubricant, wherein the machinability improvement powder comprises crystallinelayered alkaline silicate heat-treated in a range from 400 °C to 1100 °C, and amix proportion of the machinability improvement powder is in a range from0.01% to 1.0% by mass in terms of total content ofthe iron-based powder, the alloying powder, and the machinability improvement powder.

2. The mixed powder for powder metallurgy according to claim wherein the machinability improvement powder further comprises atleast one selected from a group consisting of an enstatite powder, a talcpowder, a kaolin powder, a mica powder, a granulated slag powder, a levigatedclay powder, a magnesium oxide (MgO) powder, and a powder mixture ofsilica (SiOg) and magnesium oxide (MgO), in a range from 10% to 80% by mass in terms of total content ofthe machinability improvement powder.

3. The mixed powder for powder metallurgy according to claim2, wherein the machinability improvement powder further comprises analkali metal salt powder in a range from 10% to 80% by mass in terms oftotal content of the machinability improvement powder.

4. The mixed powder for powder metallurgy according to claim3,wherein the alkali metal salt powder is one or two selected from a group consisting of an alkali carbonate powder and an alkali metal soap.

5. The mixed powder for powder metallurgy according to any one of claims 1 to 4, Ref. NO. Po134275-PcT-zz (25/29) _26- wherein the machinability improvement powder further comprises a calcium fluoride powder.

6. The mixed powder for powder metallurgy according to any oneof claims l to 5, wherein the machinability improvement powder further comprises oneor two selected from a group consisting of a metal boride powder and a metal nitride powder.

7. The mixed powder for powder metallurgy according to claim6, wherein the metal boride powder consists of at least one selected froma group consisting of TiBg, ZrBg, and NbBg, and the metal nitride powderconsists of at least one selected from a group consisting of TiN, AlN, and Si3N4.

8. The mixed powder for powder metallurgy according to any oneof claims l to 7, wherein the machinability improvement powder further comprises atleast one selected from a group consisting of an alkali metal sulfate and analkaline earth metal sulfate, in a range from 10% to 80% by mass in terms of total content ofthe machinability improvement powder.

9. A method of manufacturing a mixed powder for powdermetallurgy according to any one of claims l to 8, by preparing and thenmixing an iron-based powder, an alloying powder, a machinabilityimprovement powder, and a lubricant to obtain a mixed powder, wherein the machinability improvement powder comprises crystallinelayered alkaline silicate heat-treated at 400 °C to ll00 °C, and a mixproportion of the machinability improvement powder is 0.0l% to l.0% bymass in terms of total content of the iron-based powder, the alloying powder,and the machinability improvement powder, and the mixing includes: primary mixing in which a part or whole of the machinability Ref. NO. Po134275-PcT-zz (26/29) _27- improvement powder and a part of the lubricant are added, as a primarymixture material, to the iron-based powder and the alloying powder andheated to perform mixing while melting at least one type ofthe lubricant, anda resulting mixture is cooled for solidification; and secondary mixing in which a remaining powder of the machinabilityimprovement powder and the lubricant is added, as a secondary mixture material, to the mixture to perform mixing.

10. l0. The method of manufacturing a mixed powder for powdermetallurgy according to claim 9, wherein the machinability improvement powder further comprises atleast one selected from a group consisting of an enstatite powder, a talcpowder, a kaolin powder, a mica powder, a granulated slag powder, a levigatedclay powder, a magnesium oxide (MgO) powder, and a powder mixture ofsilica (SiOg) and magnesium oxide (MgO), in a range from 10% to 80% by mass in terms oftotal content ofthe machinability improvement powder.

11. ll. The method of manufacturing a mixed powder for powdermetallurgy according to claim l0, wherein the machinability improvement powder further comprises analkali metal salt powder in a range from l0% to 80% by mass in terms oftotal content of the machinability improvement powder.

12. The method of manufacturing a mixed powder for powdermetallurgy according to claim ll,wherein the alkali metal salt powder is one or two selected from a group consisting of an alkali carbonate powder and an alkali metal soap.

13. The method of manufacturing a mixed powder for powdermetallurgy according to any one of claims 9 to 12,wherein the machinability improvement powder further comprises a calcium fluoride powder.

14. l4. The method of manufacturing a mixed powder for powder Ref. NO. Po134275-PcT-zz (27/29) _28- metallurgy according to any one of claims 9 to 13,wherein the machinability improvement powder further comprises oneor two selected from a group consisting of a metal boride powder and a metal nitride powder.

15. The method of manufacturing a mixed powder for powdermetallurgy according to claim 14, wherein the metal boride powder consists of at least one selected froma group consisting of TiBg, ZrBg, and NbBg, and the metal nitride powderconsists of at least one selected from a group consisting of TiN, AlN, and Si3N4.

16. The method of manufacturing a mixed powder for powdermetallurgy according to any one of claims 9 to 15, wherein the machinability improvement powder further comprises atleast one selected from a group consisting of an alkali metal sulfate and analkaline earth metal sulfate, in a range from 10% to 80% by mass in terms of total content ofthe machinability improvement powder.

17. A method of manufacturing an iron-based powder sinteredbody, by filling a die with a mixed powder for powder metallurgymanufactured by the method according to any one of claims 9 to 16,compression-forming the mixed powder into a compact, and subjecting the compact to a sintering process to obtain a sintered body. Ref. NO. Po134275-PcT-zz (28/29)