CN107614158B

CN107614158B - Mixed powder for iron-based powder metallurgy, method for producing same, sintered body produced using same, and method for producing sintered body

Info

Publication number: CN107614158B
Application number: CN201680029964.6A
Authority: CN
Inventors: 赤城宣明
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2015-05-27
Filing date: 2016-04-27
Publication date: 2020-06-09
Anticipated expiration: 2036-04-27
Also published as: EP3321000A4; KR102102584B1; EP3321000B1; KR20180008732A; CN107614158A; US20180141117A1; JP6480265B2; EP3321000A1; WO2016190038A1; JP2016222943A

Abstract

The mixed powder for iron-based powder metallurgy of the present invention comprises: an iron-based powder; and a CaS raw material powder containing one or more selected from the group consisting of type III anhydrous calcium sulfate, type II anhydrous calcium sulfate, calcium sulfate dihydrate, calcium sulfide, and calcium sulfate hemihydrate, wherein the CaS raw material powder is covered with either or both of a lubricant and a binder.

Description

Mixed powder for iron-based powder metallurgy, method for producing same, sintered body produced using same, and method for producing sintered body

Technical Field

The present invention relates to a mixed powder for iron-based powder metallurgy and a method for producing the same, and a sintered body and a method for producing a sintered body produced using the same, and more particularly, to a mixed powder for iron-based powder metallurgy and a method for producing the same, which contains a calcium sulfide powder or a calcium sulfate hemihydrate powder coated with either or both of a lubricant and a binder, and a sintered body and a method for producing a sintered body produced using the same.

Background

Powder metallurgy is widely used as an industrial production method for various machine parts. In the step of iron-based powder metallurgy, first, an iron-based powder, an alloy powder such as a copper (Cu) powder or a nickel (Ni) powder, a graphite powder, and a lubricant are mixed to prepare a mixed powder. Then, the mixed powder is filled into a die, press-molded, and sintered to produce a sintered body. Finally, the sintered body is subjected to cutting such as drilling and turning, thereby obtaining a machine component of a desired shape.

The sintered body is preferably processed so that the sintered body can be used as a machine component without performing cutting processing. However, the sintering may cause uneven shrinkage of the raw material powder. In recent years, mechanical parts are required to have high dimensional accuracy and complicated shapes. Therefore, it is increasingly necessary to perform cutting processing on the sintered body. Under such a technical background, machinability is imparted to the sintered body so as to smoothly process the sintered body.

As a method for imparting the machinability, manganese sulfide (MnS) powder is added to a mixed powder. The addition of the manganese sulfide powder is effective for cutting at a relatively low speed such as drilling. However, the addition of manganese sulfide powder has the following problems: in recent years, the cutting is not always effective even in high-speed cutting, and the sintered body is contaminated, and the mechanical strength is lowered.

Patent document 1 (Japanese patent laid-open publication No. 52-16684) discloses a method for imparting machinability, in addition to the addition of manganese sulfide described above. Patent document 1 discloses a sintered steel which is derived from an iron-based raw material powder containing iron powder, carbon and copper in required amounts, and contains 0.1 to 1.0% of calcium sulfide (CaS), 0.1 to 2% of carbon (C) and 0.5 to 5.0% of copper (Cu).

The proposal disclosed in patent document 1 in which calcium sulfide is included in the iron-based raw material powder has problems such as a significant decrease in the strength of mechanical parts, and an unstable quality (product quality) due to a change over time in the mixed powder. Further, when the sintered steel disclosed in patent document 1 is machined by a cutting tool, it is difficult to finely divide the chips. For this reason, it is difficult to say that the sintered steel disclosed in patent document 1 is excellent to the extent of satisfying the current chip disposability requirements.

The present invention has been made in view of the above problems, and an object thereof is to: provided is a mixed powder for iron-based powder metallurgy, which can produce a sintered body having stable quality and performance.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. JP 52-16684

Disclosure of Invention

The sintered body of the present invention is obtained by sintering the mixed powder for iron-based powder metallurgy.

The method for producing the mixed powder for iron-based powder metallurgy according to the present invention comprises: a step of covering a CaS raw material powder containing one or more selected from the group consisting of type III anhydrous calcium sulfate, type II anhydrous calcium sulfate, calcium sulfate dihydrate, calcium sulfide, and calcium sulfate hemihydrate with either or both a lubricant and a binder; and a step of mixing the coated CaS raw material powder and the iron-based powder.

The method for producing a sintered body of the present invention comprises: and sintering the mixed powder for iron-based powder metallurgy produced by the production method to obtain a sintered body containing CaS in a weight ratio of 0.01 wt% to 0.1 wt%.

Detailed Description

In order to achieve the above object, the present inventors investigated why the sintered body disclosed in patent document 1 deteriorates in quality and performance with the passage of time. Further, the present inventors have found that: if the sintered body contains calcium sulfide and calcium sulfate hemihydrate (hereinafter, these two components are referred to as "CaS component"), the quality and performance of the sintered body are degraded. Namely, the present inventors have found that: the CaS component absorbs moisture in the atmosphere and changes into calcium sulfate dihydrate (CaSO)₄·2H₂O); the CaS component is aggregated into coarse particles of 63 μm or more by a hardening reaction. Accordingly, it is clear that: the CaS component is unevenly dispersed in the mixed powder or the sintered body to lower the machinability of the sintered body; furthermore, moisture adsorbed by the CaS component expands during sintering to form water vapor, which lowers the strength of the sintered body.

The present inventors have further studied the structure of the CaS component which is less likely to absorb moisture based on the above findings, and have completed the present invention shown below.

According to the present invention, it is possible to provide a mixed powder for iron-based powder metallurgy, which can produce a sintered body having stable quality and performance.

The mixed powder for iron-based powder metallurgy according to the present invention and the method for producing the same will be specifically described below.

< mixed powder for iron-based powder metallurgy >

The mixed powder for iron-based powder metallurgy according to the present invention is a mixed powder obtained by mixing an iron-based powder with a CaS raw material powder containing at least one selected from the group consisting of type III anhydrous calcium sulfate, type II anhydrous calcium sulfate, calcium sulfate dihydrate, calcium sulfide, and calcium sulfate hemihydrate. The CaS raw material powder is characterized in that: covered with either or both of a lubricant and a binder. Various additives such as 3-membered oxides, 2-membered oxides, alloy powders, graphite powders, lubricants, binders, and the like may be added to the mixed powder as appropriate. In addition to these, the mixed powder for iron-based powder metallurgy may contain a trace amount of inevitable impurities in the production process of the mixed powder. The mixed powder for iron-based powder metallurgy of the present invention is filled into a die or the like, molded, and then sintered to obtain a sintered body. The sintered body thus produced can be used for various machine parts by cutting. The use and production method of the sintered body will be described later.

< iron-based powder >

The iron-based powder is a main constituent constituting the iron-based powder metallurgy mixed powder, and is preferably contained at a weight ratio of 60 wt% or more with respect to the entire iron-based powder metallurgy mixed powder. The weight% of the iron-based powder refers to a ratio of the total weight of the mixed powder for iron-based powder metallurgy excluding the lubricant. Hereinafter, when the weight% of each component is defined, the definition refers to the weight ratio of the total weight of the iron-based powder metallurgy mixed powder excluding the lubricant.

As the iron-based powder, there can be used: pure iron powder such as atomized iron powder and reduced iron powder; partially diffusing alloyed steel powder; fully alloying steel powder; or a mixed type steel powder obtained by partially diffusing the alloy components in the fully alloyed steel powder. The volume average particle diameter of the iron-based powder is preferably 50 μm or more, more preferably 70 μm or more. When the volume average particle diameter of the iron-based powder is 50 μm or more, handling properties are excellent. The volume average particle diameter of the iron-based powder is preferably 200 μm or less, and more preferably 100 μm or less. When the volume average particle size of the iron-based powder is 200 μm or less, the iron-based powder can be easily formed into a precise shape and can have sufficient strength.

< CaS raw material powder >

The mixed powder for iron-based powder metallurgy of the present invention is characterized in that: the lubricant composition contains a CaS raw material powder containing one or more selected from the group consisting of type III anhydrous calcium sulfate, type II anhydrous calcium sulfate, calcium sulfate dihydrate, calcium sulfide and calcium sulfate hemihydrate, and is covered with either or both of a lubricant and a binder. By using the CaS raw material powder covered with the lubricant and/or the binder, the water absorption of the CaS raw material powder can be suppressed, and thus various properties of the sintered body can be stably improved.

Conventionally, calcium sulfide (CaS) and dihydrate gypsum (CaSO) have been added as raw materials to be sintered into CaS₄·2H₂O), type III anhydrous calcium sulfate (type III CaSO)₄) Semi-hydrated gypsum (CaSO)₄·1/2H₂O), and the like. However, the above components absorb moisture with the passage of time, and the machinability of the sintered body may be deteriorated. Further, moisture absorbed in a raw material that becomes CaS by sintering may expand during sintering to form steam, which lowers the density of a sintered body, or high-temperature steam may oxidize an iron-based powder in a sintered body, which lowers the strength of the sintered body. In contrast, in the present invention, since the CaS raw material powder covered with the lubricant or the binder is added as described above, the CaS raw material powder is less likely to absorb moisture even when stored in a state of being included in the mixed powder for iron-based powder metallurgy for a certain period of time. By this effect, various characteristics (sintered body density, compression ring strength, machinability, etc.) of the predetermined sintered body are stabilized. Further, the coated CaS raw material powder becomes CaS after sintering, and the machinability of the sintered body can be improved.

The CaS raw material powder preferably contains one or both of calcium sulfide and calcium sulfate hemihydrate as a main component, and may further contain calcium sulfate dihydrate (CaSO)₄2H2O), form II anhydrous calcium sulfate (form II CaSO)₄) Type III anhydrousCalcium sulfate (type III CaSO)₄) And the like.

Here, "CaS raw material powder is covered with either or both of a lubricant and a binder" includes: a mode in which the entire surface of the CaS raw material powder is covered with either or both of the lubricant and the binder; and, partially covered. The thickness of the lubricant and/or the binder is not particularly limited as long as the type III calcium sulfate anhydrous, calcium sulfate dihydrate, calcium sulfide, and calcium sulfate hemihydrate do not contact the external atmosphere. The thickness is preferably uniform on the surface of the CaS raw material powder, but a thick portion or a thin portion may be locally present.

The amount of the lubricant added may be appropriately set, and is preferably 0.1 wt% or more and 1.5 wt% or less with respect to the weight of the iron-based powder metallurgy mixed powder. The amount of the binder to be added may be appropriately set, and is preferably 0.02 wt% or more and 0.5 wt% or less with respect to the weight of the iron-based powder metallurgy mixed powder. When the lubricant and the binder are excessively added, the compressibility during extrusion is reduced, and the density is reduced. Conversely, if the amount of lubricant or binder is too small, the CaS raw material powder is likely to come into contact with the outside air, or is difficult to be released from the die during extrusion molding, and thus the die may be damaged.

The coating with the lubricant can be performed by mixing the CaS raw material powder with the lubricant in a mixing vessel and then heating. Alternatively, a coated CaS raw material powder may be prepared in advance, or a lubricant may be coated on the surface of the CaS raw material powder by a hot-melt method. The hot-melt method is a process in which, first, a lubricant is filled into a mixing vessel together with each powder other than the lubricant, which constitutes the mixed powder for iron-based powder metallurgy. Subsequently, the respective powders were mixed while being heated, and then cooled to room temperature. In this way, each powder constituting the mixed powder for iron-based powder metallurgy is covered with the lubricant.

Further, as another covering method, the entire powder except the lubricant among the respective powders constituting the mixed powder for iron-based powder metallurgy is filled in the mixing container. Then, a binder solution in which a binder is dissolved in a solvent is added to the mixing vessel and mixed. Then, the solvent contained in the binder solution is volatilized. Finally, the CaS feedstock powder may be covered with a lubricant and/or binder by adding a lubricant. In this case, each powder is covered with the lubricant and/or the binder. The details of this step will be described later.

The CaS raw material powder is preferably contained in the iron-based mixed powder for powder metallurgy so that the weight ratio of CaS after sintering is 0.01 wt% or more and 0.1 wt% or less. The CaS raw material powder is more preferably contained so that the weight ratio of CaS after sintering becomes 0.02 wt% or more, and still more preferably contained so that the weight ratio of CaS after sintering becomes 0.03 wt% or more. Sintered bodies containing CaS in such a weight ratio are particularly excellent in machinability. On the other hand, the CaS raw material powder is preferably contained so that the weight ratio of CaS after sintering becomes 0.09 wt% or less, and more preferably 0.08 wt% or less. By including CaS in such a weight ratio, the strength of the sintered body can be improved.

Here, the "weight ratio of CaS after sintering" refers to a weight ratio of CaS in a sintered body obtained by sintering the mixed powder for iron-based powder metallurgy. The weight ratio of CaS contained in the sintered body after sintering can be adjusted by the weight ratio of CaS raw material powder contained before sintering.

The weight ratio of CaS contained in the sintered body is calculated by collecting a sample piece obtained by processing the sintered body by drilling or the like, quantitatively analyzing the weight of Ca contained in the sample piece, and converting the obtained weight of Ca into the weight of CaS. The conversion is performed by dividing by the atomic weight of Ca (40.078) and multiplying by the molecular weight of CaS (72.143). Ca hardly reacts and does not disappear during sintering, so that the weight of Ca does not change before and after sintering, and Ca and S are bonded in a ratio of 1: 1.

The volume average particle diameter of the CaS raw material powder is preferably 0.1 μm or more, more preferably 0.5 μm or more, and still more preferably 1 μm or more. The volume average particle diameter of the CaS raw material powder is preferably 60 μm or less, more preferably 30 μm or lessThe particle diameter is more preferably 20 μm or less. The CaS raw material powder having such a volume average particle diameter can be obtained, for example, by pulverizing a commercially available CaS raw material powder with a known pulverizer and classifying the powder. The CaS raw material powder composed of type II calcium sulfate anhydrite can be obtained by, for example, heating hemihydrate gypsum at 350 ℃ to 900 ℃ for 1 hour to 10 hours, and then pulverizing and classifying the hemihydrate gypsum. The smaller the volume average particle diameter of the CaS raw material powder is, the smaller the addition amount of the CaS raw material powder is, the higher the machinability of the sintered body can be. The volume average particle diameter is a particle diameter D of 50% in the cumulative value in the particle size distribution obtained by using a laser diffraction particle size distribution measuring apparatus (Microtrac "MODEL 9320-X100" manufactured by Nikkiso K.K.)₅₀The value of (c).

< Lubricant >)

The lubricant covering the CaS raw material powder is added to suppress the hygroscopicity of type III calcium sulfate anhydrous, calcium sulfate dihydrate, calcium sulfide, and calcium sulfate hemihydrate. The lubricant also has the following functions: a compact obtained by compressing an iron-based powder metallurgy mixture powder in a die is easily taken out of the die. That is, by adding a lubricant to the iron-based powder metallurgy mixture powder, the drawing pressure (drawing pressure) at the time of drawing the compact from the die can be reduced, and cracks in the compact and damage to the die can be prevented. In addition, in the case of using the hot-melt method, the lubricant functions to adhere the alloy powder and the graphite powder to the surface of the iron-based powder, and therefore, segregation of the iron-based mixed powder can also be prevented. In addition to the lubricant for covering the CaS raw material powder, the lubricant may be added during the production of the iron-based powder metallurgy mixed powder, or the lubricant may be applied to the surface of the die when the iron-based powder metallurgy mixed powder is filled into the die.

The lubricant is preferably contained in an amount of 0.01 wt% or more, more preferably 0.1 wt% or more, and still more preferably 0.2 wt% or more, based on the weight of the iron-based powder metallurgy mixed powder. By setting the content of the lubricant to 0.01 wt% or more, the effect of suppressing contact between the CaS raw material powder and the outside air and stabilizing the performance of the sintered body can be easily obtained. The lubricant is preferably contained in an amount of 1.5 wt% or less, more preferably 1.2 wt% or less, and still more preferably 1.0 wt% or less, based on the weight of the iron-based powder metallurgy mixed powder. By setting the content of the lubricant to 1.5 wt% or less, a sintered body with high density and high strength can be easily obtained.

The lubricant is preferably a wax-based lubricant, and more preferably an amide-based lubricant, from the viewpoint of improving the performance of adhering the alloy powder, graphite powder, or the like to the surface of the iron-based powder and easily reducing segregation of the iron-based mixed powder. Examples of the amide-based lubricant include stearic acid monoamide, fatty acid amide, and amide wax. As the lubricant other than the amide-based lubricant, one or more selected from the group consisting of a hydrocarbon-based wax, zinc stearate, and a crosslinked alkyl (meth) acrylate resin may be used.

< Binder >

The binder for covering the CaS raw material powder is added to suppress the hygroscopicity of type III calcium sulfate anhydrous, calcium sulfate dihydrate, calcium sulfide, and calcium sulfate hemihydrate and to prevent segregation of the iron-based mixed powder. The binder also has the function of adhering the alloying powder to the surface of the iron-based powder. In addition to the binder for covering the CaS raw material powder, the binder may be added during the process of producing the mixed powder for iron-based powder metallurgy.

In the step of covering the CaS raw material powder with the binder, first, the binder is dissolved in an organic solvent such as toluene, thereby preparing an organic solvent containing the binder. The organic solution was then mixed with CaS feedstock powder. Finally, the organic solvent is evaporated, thereby covering the CaS raw material powder with the binder.

More preferably, at least one selected from the group consisting of styrene-butadiene rubber, isoprene rubber, butene-based polymer, and methacrylic polymer is used as the binder. As the butene-based polymer, it is preferable to use: 1-butene homopolymer consisting of butene alone; alternatively, a copolymer of butene and an olefin. As the olefin, a lower olefin is preferable, and ethylene or propylene is preferable. As the methacrylic polymer, one or more selected from the group consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, ethylhexyl methacrylate, lauryl methacrylate, methyl acrylate and ethyl acrylate can be used.

The binder is preferably contained in an amount of 0.01 wt% or more, more preferably 0.05 wt% or more, based on the weight of the iron-based powder metallurgy mixed powder. The moisture absorption of calcium sulfate type III, calcium sulfate dihydrate, calcium sulfide, and calcium sulfate hemihydrate can be suppressed by containing the binder in an amount of 0.01 wt% or more. The binder is preferably contained in an amount of 0.5 wt% or less, more preferably 0.4 wt% or less, and still more preferably 0.3 wt% or less, based on the weight of the iron-based powder metallurgy mixed powder. By setting the content of the binder to 0.5 wt% or less, a molded body having a high density can be easily obtained at the time of extrusion molding.

< 3-membered oxide >

In order to improve the machinability when the sintered body is machined for a long time, a 3-membered oxide may be added. The 3-membered oxide remarkably improves the machinability of the sintered body in cooperation with the addition of the CaS raw material powder. Here, the 3-membered oxide means a composite oxide of 3 elements, specifically, a composite oxide of 3 elements selected from the group consisting of Ca, Mg, Al, Si, Co, Ni, Ti, Mn, Fe, and Zn is preferable, and a Ca — Al — Si oxide, a Ca — Mg — Si oxide, and the like are more preferable. Examples of the Ca-Al-Si based oxide include 2 CaO. Al₂O₃·SiO₂And the like. Examples of the Ca-Mg-Si based oxide include 2CaO MgO 2SiO₂And the like. Among them, 2 CaO. Al is preferably added₂O₃·SiO₂.2 CaO. Al mentioned above₂O₃·SiO₂With TiO contained in or on the coating applied in or on the cutting tool₂Since the reaction forms a protective film on the surface of the cutting tool, the wear resistance of the cutting tool can be significantly improved.

The shape of the 3-membered oxide is not particularly limited, and is preferably: spherical; alternatively, the circular shape is slightly deformed, that is, has a substantially circular shape.

The lower limit of the volume average particle diameter of the 3-membered oxide is preferably 0.1 μm or more, more preferably 0.5 μm or more, and still more preferably 1 μm or more. The smaller the volume average particle diameter, the smaller the amount of the additive, the more the machinability of the sintered body tends to be improved. The upper limit of the volume average particle diameter of the 3-membered oxide is preferably 15 μm or less, more preferably 10 μm or less, and still more preferably 9 μm or less. When the volume average particle diameter is too large, it is difficult to improve the machinability of the sintered body. The volume average particle diameter of the 3-membered oxide is a value measured by the same measurement method as the above-mentioned CaS raw material powder.

The lower limit of the content of the 3-membered oxide is preferably 0.01% by weight or more, more preferably 0.03% by weight or more, and still more preferably 0.05% by weight or more. The upper limit of the content of the 3-membered oxide is preferably 0.25% by weight or less, more preferably 0.2% by weight or less, and still more preferably 0.15% by weight or less. By including the above-described components in such a weight ratio, a sintered body excellent in machinability in long-term cutting can be obtained while suppressing the cost. By using a 3-membered oxide in combination with a CaS raw material, the machinability in long-term cutting can be improved even if the amount of the 3-membered oxide added is small.

The weight ratio of the 3-membered oxide to CaS after sintering is preferably 1: 9 to 9: 1, more preferably 3: 7 to 9: 1, and still more preferably 4: 6 to 7: 3. By containing the two components in such a weight ratio, the machinability of the sintered body can be remarkably improved.

< 2-membered oxide >

In order to improve the machinability at the initial stage of cutting when the sintered body is cut, a 2-membered oxide may be added. Here, the 2-membered oxide means a composite oxide of two elements, specifically, a composite oxide of two elements selected from the group consisting of Ca, Mg, Al, Si, Co, Ni, Ti, Mn, Fe, and Zn is preferable, and a Ca — Al oxide, a Ca — Si oxide, and the like are more preferable. Examples of the Ca-Al based oxide include CaO-Al₂O₃、12CaO·7Al₂O₃And the like. As Ca-Si based oxidesExamples thereof include 2 CaO. SiO₂And the like.

The shape, volume average particle diameter, measurement method, and weight ratio of the 2-membered oxide are preferably the same as those of the 3-membered oxide.

< 2-membered oxide and 3-membered oxide >

The mixed powder for iron-based powder metallurgy of the present invention preferably contains both a 2-membered oxide and a 3-membered oxide in a total amount of 0.02 wt% to 0.3 wt% in total. The total weight of the oxides is preferably 0.05 wt% or more, and more preferably 0.1 wt% or more. From the viewpoint of cost, the smaller the weight ratio of the 2-membered oxide to the 3-membered oxide is, the more preferable. The total weight of the oxides is preferably 0.25 wt% or less, and more preferably 0.2 wt% or less. When the total weight of the oxides is 0.25 wt% or less, the compression ring strength of the sintered body can be ensured to be sufficient.

The weight ratio of the 2-membered oxide to CaS after sintering is preferably 1: 9 to 9: 1, more preferably 3: 6 to 9: 1, and still more preferably 4: 6 to 7: 3. By including the two components in such a weight ratio, a sintered body excellent in machinability at the initial stage of cutting can be produced.

Powder for alloy

In order to promote the bonding of the iron-based powders to each other and to improve the strength of the sintered body after sintering, an alloying powder may be added. The alloy powder is preferably contained in an amount of 0.1 to 10 wt% based on the whole iron-based powder mixture. When the content is 0.1 wt% or more, the strength of the sintered body can be improved, and when the content is 10 wt% or less, the dimensional accuracy of the sintered body at the time of sintering can be secured.

Examples of the alloy powder include: nonferrous metal powders such as copper (Cu) powder, nickel (Ni) powder, Mo powder, Cr powder, V powder, Si powder, and Mn powder; cuprous oxide powder, and the like. One of them may be used alone, or two or more of them may be used in combination.

< method for producing mixed powder for iron-based powder metallurgy >

The mixed powder for iron-based powder metallurgy of the present invention can be produced, for example, by the following production methods (1) to (3).

(1) The surface of the CaS feedstock powder was covered with a lubricant. Then, the coated CaS raw material powder, the iron-based powder, and the powders of the other components were mixed by a mechanical stirring mixer, thereby producing a mixed powder for iron-based powder metallurgy.

(2) Instead of covering the surface of the CaS raw material powder with a lubricant in advance, powders of all the components were mixed in a closed container while heating. Then, the surfaces of all the powders were covered with a lubricant by a hot-melt method to prepare a mixed powder for iron-based powder metallurgy.

(3) All the powders except the lubricant in each powder constituting the mixed powder for iron-based powder metallurgy are added to a closed vessel. Thereafter, an organic solution in which a binder is dissolved is added to the sealed container and mixed, and then the organic solvent is volatilized. Finally, a lubricant is added to the closed container to mix the powders constituting the mixed powder for iron-based powder metallurgy. Thereby, the surfaces of all the powders except the lubricant were covered with the lubricant and/or the binder, and the mixed powder for iron-based powder metallurgy was produced. The volume average particle diameter of the CaS raw material powder is preferably 0.1 to 60 μm.

The heating temperature in the hot-melt method varies depending on the melting point of the lubricant, and is preferably 50 ℃ or higher and 150 ℃ or lower, for example. When the heating temperature is 50 ℃ or higher, the fluidity of the lubricant is easily improved. When the heating temperature is 150 ℃ or lower, the oxidation of the iron-based powder can be suppressed in the step of producing the mixed powder, and the cost required for heating can be reduced.

The heating time in the hot melt method is preferably 10 minutes to 5 hours. The heating time can be shortened as the heating temperature is higher. In the case where the heating time is short, it may be difficult to cover the entire surface of the CaS raw material powder with the lubricant and/or the binder.

The mixed powder for iron-based powder metallurgy of the present invention can be produced, for example, as follows: the iron-based powder and the CaS raw material powder prepared above were mixed by using a mechanical stirring mixer, thereby preparing the powder. In addition to these powders, various additives such as 3-membered oxides, alloying powders, graphite powders, 2-membered oxides, binders, lubricants and the like may be added as appropriate. Examples of the mechanical agitation type mixer include a high-speed mixer, a vertical screw mixer, a V-type mixer, and a double cone mixer. The mixing order of the powders is not particularly limited. The mixing temperature is not particularly limited, but is preferably 150 ℃ or lower from the viewpoint of suppressing oxidation of the iron-based powder in the mixing step.

< method for producing sintered body >

The mixed powder for iron-based powder metallurgy prepared as described above is filled into a mold, and then a pressure of 300MPa to 1200MPa is applied to produce a powder compact. The molding temperature in this case is preferably 25 ℃ to 150 ℃.

The green compact produced as described above is sintered by a usual sintering method to obtain a sintered body. The sintering conditions may be a non-oxidizing atmosphere or a reducing atmosphere. The green compact is preferably sintered at a temperature of 1000 to 1300 ℃ for 5 to 60 minutes in a nitrogen atmosphere, a mixed atmosphere of nitrogen and hydrogen, or an atmosphere of hydrocarbon or the like.

< sintered body >

The sintered body produced as described above preferably contains 0.01 wt% to 0.1 wt% of CaS. The upper limit of CaS in the sintered body is preferably 0.09 wt% or less, more preferably 0.08 wt% or less. The lower limit of CaS in the sintered body is preferably 0.02 wt% or more, and more preferably 0.03 wt% or more. The sintered body can be processed with various tools such as a cutting tool as needed, and can be used as a machine component of an automobile, an agricultural implement, an electric tool, and a home electric appliance. Examples of the cutting tool for machining the sintered body include a drill, an end mill, a cutting tool for slicing, a cutting tool for turning, a reamer, and a tap.

According to the mixed powder for iron-based powder metallurgy of the above embodiment, since the surfaces of calcium sulfide and calcium sulfate hemihydrate are covered with the lubricant or the binder, the hygroscopicity of these components can be suppressed, and various properties of the sintered body can be stably improved.

The mixed powder for iron-based powder metallurgy further contains at least one 3-membered oxide selected from the group consisting of Ca-Al-Si-based oxides and Ca-Mg-Si-based oxides, and therefore, the machinability during long-term cutting can be improved.

Since the mixed powder for iron-based powder metallurgy contains the CaS raw material powder so that the weight ratio of CaS after sintering is 0.01 wt% or more and 0.1 wt% or less, the sintered body after sintering is excellent in machinability.

The weight ratio of the 3-component oxide to the sintered CaS is 3: 7-9: the mode 1 includes a 3-membered oxide and CaS raw material powder, and therefore, the machinability in long-term cutting can be improved.

Since the volume average particle diameter of the CaS raw material powder is 0.1 μm or more and 60 μm or less, the machinability of the sintered body can be improved.

The sintered body produced using the above-mentioned mixed powder for iron-based powder metallurgy is stable and excellent in various properties such as machinability. Further, the mixed powder for iron-based powder metallurgy produced by the above production method exhibits stable performance because the CaS raw material powder does not easily absorb moisture.

Examples

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

(example 1)

First, a commercially available calcium sulfide powder was classified by a sieve at-63/+ 45 μm (volume average particle diameter of 54 μm). Adding the classified calcium sulfide powder into a closed container according to the weight of the sintered CaS reaching 0.5 wt%. To the closed container, 0.75 wt% of an amide lubricant (product name: ACRAWAX C (manufactured by LONZA corporation)) was added. Then, the mixture was heated to 100 ℃ and mixed for 10 minutes to coat the surface of the calcium sulfide powder with the amide-based lubricant.

Then, 2 wt% of copper powder (product name: CuATW-250 (manufactured by Futian Metal foil industries, Ltd.)) and 0.8 wt% of graphite powder (product name CPB (manufactured by Nippon graphite industries, Ltd.)) were mixed with the above-prepared lubricant-coated calcium sulfide powder with respect to a pure iron powder (product name: 300M (manufactured by Tokuwa Kaisho Co., Ltd.)) to prepare a mixed powder for iron-based powder metallurgy. The graphite powder was added in an amount such that the amount of carbon after sintering became 0.75 wt%. The coated calcium sulfide powder was added in an amount to bring the weight of the sintered CaS to 0.5 wt%.

(example 2)

In example 1, calcium sulfide powder and amide-based lubricant (product name: ACRAWAX C (manufactured by LONZA corporation)) were charged into a closed container and heated to 100 ℃, while in example 2, the powder of all the components used in example 1 was charged into a closed container, heated to 100 ℃ by hot-melt method and mixed for 30 minutes, thereby covering the surface of the powder of all the components with the amide-based lubricant. Then, the mixture was cooled to room temperature, thereby preparing an iron-based mixed powder for powder metallurgy.

(example 3)

In example 3, the same powders as in example 2 were mixed except that the amide-based lubricant used in example 2 was replaced with a toluene solution containing styrene-butadiene rubber. The toluene solution was added so that the weight of styrene-butadiene rubber after toluene volatilization became 0.1 wt%. Then, toluene was volatilized at 100 ℃ to coat the surfaces of CaS raw material particles with styrene-butadiene rubber. Then, the same amount of the amide-based lubricant used in example 1 as that used in example 1 was added and mixed to prepare an iron-based powder metallurgy mixed powder of example 3.

Comparative examples 1 to 3

A mixed powder for iron-based powder metallurgy was produced in the same manner as in example 1, except that no CaS raw material powder was added in comparative example 1. In comparative examples 2 and 3, iron-based mixed powders for powder metallurgy were produced in the same manner as in example 1, except that the CaS raw material powders shown in the column of "CaS component" in table 1 were used and were not covered with a lubricant and a binder.

Two kinds of sintered bodies were produced using the mixed powders for iron-based powder metallurgy of the above examples and comparative examples. One is a sintered body using the mixed powder for iron-based powder metallurgy immediately after production (hereinafter referred to as "immediate sintered body"), and the other is a sintered body using the mixed powder for iron-based powder metallurgy after 10 days from production (hereinafter referred to as "post-10-day sintered body").

The manufacturing steps of the instant sintered body are as follows: first, a mixed powder for iron-based powder metallurgy immediately after production was filled in a die, followed by forming to obtain a ring shape having an outer diameter of 64mm, an inner diameter of 24mm and a thickness of 20mm and a forming density of 7.00g/cm³The test piece of (1); the annular test piece was then placed at 10% H by volume₂－N₂The resultant was sintered at 1130 ℃ for 30 minutes in an atmosphere to prepare a sintered body. On the other hand, a sintered body after 10 days was produced in the same manner as the immediate sintered body, except that the mixed powder for iron-based powder metallurgy left in the air for 10 days after the production was filled in the die.

TABLE 1

< evaluation >

In table 1, the evaluation results of the compact density, sintered body density, compression ring strength, and tool wear amount are described as "sintered body immediately after 10 days". In this description, the left value of the diagonal line represents the evaluation result of the instant sintered body, and the right value represents the evaluation result of the sintered body after 10 days.

The compact density and sintered body density of the sintered body immediately after and after 10 days of each example and each comparative example were measured based on the japan powder metallurgy association standard (JPMAM 01). The compression ring strength was measured by JISZ 2507-2000. The higher the compression ring strength, the less likely the sintered body to be broken, indicating that the strength is higher.

The sintered bodies produced in the examples and comparative examples were measured for the tool wear (. mu.m) of the cutting tool at the time of cutting by a tool microscope using a cermet plate (ISO model: SNGN120408 non-breaker) having a peripheral speed of 160m/min, a cutting depth of 0.5mm/pass, a feed of 0.1mm/rev, and a dry condition turning of 1150 m. The results are shown in the column "tool wear" in table 1. The smaller the value of the tool wear amount, the more excellent the machinability of the sintered body.

From the results of the examples and comparative examples shown in table 1, it is understood that: by coating the CaS raw material powder with the lubricant or the binder as in each example, the properties (sintered body density, compression ring strength, and tool wear) of the instant sintered body and the sintered body after 10 days were almost equivalent. On the other hand, comparative examples 2 and 3 contained CaS itself or hemihydrate gypsum as the CaS component, but the surfaces thereof were not subjected to any covering treatment, and thus various characteristics of the sintered body after 10 days were significantly deteriorated as compared with the instant sintered body.

It is considered that the reason why the quality and properties of the sintered body were deteriorated after 10 days in comparative examples 2 and 3 was: during the standing of the mixed powder for iron-based powder metallurgy for 10 days, CaS or gypsum hemihydrate in the mixed powder for iron-based powder metallurgy absorbs moisture. That is, it is considered that, in comparative examples 2 and 3, when stored in the atmosphere for 10 days, CaS itself or hemihydrate gypsum in the mixed powder for iron-based powder metallurgy absorbs water, and thus the density of the sintered body decreases or the compressive strength decreases. In comparative example 1, since the CaS component was not contained, the tool wear amount of the sintered body was significantly high both immediately after sintering and after 10 days, and the machinability of the sintered body was significantly low.

The results shown in table 1 clearly show that: by covering the CaS raw material powder with the lubricant or the binder, various characteristics (sintered body density, compression ring strength, and tool wear) of the sintered body were almost equal even after 10 days and the quality and performance of the sintered body were stable, and the effect of the present invention was exhibited.

Claims

1. A mixed powder for iron-based powder metallurgy, which is used for producing a sintered body having stable quality and performance, is a mixed powder for iron-based powder metallurgy, which is obtained by mixing an iron-based powder and a CaS raw material powder coated with either or both of a lubricant and a binder, and which comprises:

an iron-based powder; and

a CaS raw material powder containing calcium sulfide and at least one selected from the group consisting of type III anhydrous calcium sulfate, type II anhydrous calcium sulfate and calcium sulfate hemihydrate, wherein,

the CaS feedstock powder is covered with either or both of a lubricant and a binder,

the CaS raw material powder is contained so that the weight ratio of CaS after sintering is 0.01 to 0.1 wt%.

2. The mixed powder for iron-based powder metallurgy according to claim 1, further comprising one or more 3-membered oxides selected from the group consisting of Ca-Al-Si-based oxides and Ca-Mg-Si-based oxides.

3. The mixed powder for iron-based powder metallurgy according to claim 2, wherein the weight ratio of the 3-membered oxide to the sintered CaS is 3: 7-9: the mode 1 includes the 3-membered oxide and the CaS raw material powder.

4. The mixed powder for iron-based powder metallurgy according to claim 1, wherein the CaS raw material powder has a volume average particle diameter of 0.1 μm or more and 60 μm or less.

5. A sintered body obtained by sintering the mixed powder for iron-based powder metallurgy according to claim 1.

6. A method for producing a mixed powder for iron-based powder metallurgy, which is used for producing a sintered body having stable quality and performance, is a method for producing a mixed powder for iron-based powder metallurgy, which is obtained by mixing an iron-based powder and a CaS raw material powder coated with either or both of a lubricant and a binder, and which comprises:

a step of covering a CaS raw material powder containing calcium sulfide and one or more selected from the group consisting of type III anhydrous calcium sulfate, type II anhydrous calcium sulfate, and calcium sulfate hemihydrate with either or both of a lubricant and a binder; and

a step of mixing the coated CaS feedstock powder and the iron-based powder.

7. A method for producing a sintered body, comprising:

a step of sintering the mixed powder for iron-based powder metallurgy manufactured by the manufacturing method according to claim 6 to obtain a sintered body,

the sintered body contains CaS in a weight ratio of 0.01 wt% or more and 0.1 wt% or less.