JP2002155301A - Iron-based powdery mixture for powder metallurgy and iron based sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an iron-based powdery mixture capable of producing a sintered compact having excellent appearance properties and machinability. SOLUTION: The iron-based powdery mixture contains iron-based powder whose surface is stuck with graphite powder as powder for alloying and the fluoride of alkaline earth metals as powder for improving machinability and a free lubricant. The iron based powdery mixture contains the fluoride powder of alkaline earth metals as powder for improving machinability 0.1 to 0.7 mass% to the total of the iron-based powder, the powder for alloying and the powder for improving machinability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron-based mixed powder for powder metallurgy, and in particular, can prevent a heating element of a sintering furnace, a conveyor belt and the like from being contaminated by S (sulfur), and a sintered body. The present invention relates to an iron-based mixed powder for powder metallurgy capable of improving the machinability of steel.

[0002]

2. Description of the Related Art Advances in powder metallurgy technology have made it possible to manufacture components having complicated shapes with high dimensional accuracy in a near-net shape. Iron-based powder metallurgy products, iron-based powder,
Alloy powders such as copper powder and graphite powder, zinc stearate,
A metal mold is filled with an iron-based mixed powder mixed with a lubricant such as lithium stearate, and then molded under pressure, and then subjected to a sintering process to form a sintered body, and then cut as necessary. , And products. The sintered body manufactured in this manner has a high content ratio of vacancies, and has higher cutting resistance than a metal material obtained by a melting method. Therefore, conventionally, Pb, Se, Te, S, MnS, BaS
Various powders, such as CaS and CaS, have been added to iron-based mixed powders or alloyed with iron powders.

However, since Pb has a low melting point of 330 ° C., it melts during the sintering process, and it is difficult to disperse uniformly in the matrix without solid solution in iron. However, there is a problem that the mechanical properties of the sintered body are significantly deteriorated because the sintered body is embrittled. In addition, S, MnS, BaS,
Alternatively, when a compound containing S such as CaS is mixed, H ₂ S generated during sintering contaminates the refractory of the sintering furnace, the mesh belt for transportation, the heating element, etc., and shortens the life of those parts. was there. In addition, there is also a problem of poor appearance of the sintered body, and mixing of a compound powder containing S as a powder for improving machinability into an iron-based mixed powder has been avoided.
When BaS, CaS, etc. remain in the sintered body, BaS, CaS
There is also a problem that the sintered body is easily rusted due to the hygroscopicity of S.

To solve such a problem, for example, Japanese Patent Laid-Open No.
-198201 discloses that Ca: 0.001 to 0.10%, O: 0.05 to
A sintering steel powder which gives a sintered body having good machinability containing 1.0% is disclosed. However, JP-A-57-19820
The sintered body manufactured from the sintering powder described in JP-A-1 does not contain S, so there is no problem of sintering furnace contamination.However, calcium oxide has a hygroscopic property, There is a problem that the moldability is deteriorated and the molding becomes unstable.

Japanese Patent Application Laid-Open No. 63-137137 discloses that a graphite powder obtained by adhering a part or all of an alkaline earth fluoride equivalent to 0.1 to 1.2% by weight to the surface of a raw iron powder is used as the raw iron powder. A method for producing a sintered steel which is added to powder, mixed and sintered is disclosed. The sintered steel manufactured in this way is said to have excellent machinability. However, JP-A-63-137137
According to the technology described in Japanese Patent Application Publication No. H10-115, in order to attach the alkaline earth fluoride to the surface of the graphite powder, it is necessary to use a finely ground alkaline earth fluoride to a particle size of about 1/10 of the graphite powder particle size. In addition, there is a problem that an additional step of pulverizing an alkaline earth fluoride is added, which leads to an increase in production cost.

Japanese Patent Publication No. 7-507358 discloses that 0.1 to 0.6% by weight of calcium fluoride CaF _{2 is} contained in an iron-based powder composition.
There has been proposed a powder composition containing the compound for improving the machinability. However, impurities contained in calcium fluoride CaF ₂ affect dimensional changes and mechanical properties,
It is necessary to use calcium fluoride with high purity, and there is a problem in cost. Calcium fluoride was in a free state, and the obtained machinability was not always satisfactory.

Japanese Patent Application Laid-Open No. 9-279204 discloses a CaO—Al ₂ O ₃ —SiO ₂ -based composite oxide mainly composed of iron powder and having an anorthite phase and / or a gehlenite phase and having an average particle size of 50 μm or less. Of iron-based mixed powders for powder metallurgy containing 0.02 to 0.3% by weight of the above powder. However, if the CaO-Al ₂ O ₃ -SiO ₂ based composite oxide used has few impurities and does not use a powder having a restricted particle size, there is a problem that the powder properties and the sintered body properties are reduced. .

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, prevents contamination of a heating element of a sintering furnace, a conveyor belt, and the like. It is another object of the present invention to provide an iron-based mixed powder capable of improving the machinability of an iron-based sintered body.

[0009]

Means for Solving the Problems In order to achieve the above object, the present inventors have made intensive studies on the effects of various factors on the machinability of a sintered body. As a result, first, the present inventors have found that fluoride powder of alkaline earth metal is effective as a powder for improving machinability from the viewpoint of improving the appearance properties of the sintered body and preventing sintering furnace contamination. I thought. Furthermore, the present inventors use alkaline earth metal fluoride powder as a machinability improving powder, and fix the machinability improving powder together with graphite powder in a concave portion on the surface of the iron-based powder with a binder, It has been found that the machinability of the sintered body is significantly improved. This is because when an iron-based mixed powder in which graphite powder and machinability improving powder are fixed to surface recesses is pressed and sintered to form a sintered body, the lubricant and binder are volatilized in the sintering process. In addition, in the state after so-called dewaxing, the graphite powder and the alkaline earth metal fluoride powder can be brought into direct contact with each other, whereby the machinability of the sintered body is significantly improved.

The present invention has been completed based on the above-mentioned findings and further studies. That is, the present invention is an iron-based mixed powder obtained by mixing an iron-based powder, an alloy powder containing graphite powder, a machinability improving powder, a binder, and a lubricant, wherein the lubricant As a free lubricant in a free state, wherein the powder for improving machinability is a fluoride powder of an alkaline earth metal, and 0.1 to 0.7% by mass based on the total amount of the iron-based powder, the powder for alloy, and the powder for improving machinability. In addition, the present invention is an iron-based mixed powder for powder metallurgy, characterized in that the graphite powder and the machinability improving powder are fixed to the surface of the iron-based powder by the binder and included. Preferably, the alkaline earth metal fluoride powder is at least one of calcium fluoride, magnesium fluoride, strontium fluoride, and barium fluoride.

In the present invention, the content of the alloy powder is preferably 0.5 to 7% by mass based on the total amount of the iron-based powder, the alloy powder and the machinability improving powder. Also,
In the present invention, the powder for alloy is preferably graphite powder, or furthermore, metal powder and / or alloy powder.
The content of the graphite powder is preferably 0.5 to 7% by mass with respect to the total amount of the iron-based powder, the alloy powder and the machinability improving powder. More preferably, it is 0.5 to 5% by mass.

In the present invention, the content of the binder is preferably 0.1 to 1.0 part by weight based on 100 parts by weight of the total amount of the iron-based powder, the alloy powder and the machinability improving powder. Further, in the present invention, the content of the lubricant is a total amount of iron-based powder, alloy powder and machinability improving powder of 10
It is preferably 0.1 to 0.5 part by weight based on 0 part by weight.

Further, the present invention is an iron-based sintered body obtained by pressing any one of the above-mentioned iron-based mixed powders, molding the iron-based mixed powder, and further sintering.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The iron-based mixed powder for powder metallurgy according to the present invention is an iron-based mixed powder obtained by mixing an iron-based powder, an alloy powder containing graphite powder, a machinability improving powder, a binder and a lubricant. Powder. In the present invention, as the iron-based powder, pure iron powder such as atomized iron powder and reduced powder, or steel powder obtained by pre-alloying an alloy element in place of iron powder (pre-alloyed steel powder), or partially alloyed alloy element Any of the obtained steel powders (partially alloyed steel powders) can be suitably used. Needless to say, these may be mixed and used.

As the alloy powder contained in the iron-based mixed powder, graphite powder or metal powder such as copper powder and / or alloy powder can be selected and contained according to desired product characteristics. The content of the alloy powder is 0.5 to 7 with respect to the total amount of the iron-based powder, the alloy powder and the machinability improving powder.
It is preferred to be in the range of mass%. The content of the machinability improving powder in the iron-based mixed powder is 0.1 to 0.7% by mass based on the total amount of the iron-based powder, alloy powder and machinability improving powder. If the content of the powder for improving machinability is less than 0.1% by mass, the effect of improving machinability is small, while if the content exceeds 0.7% by mass, the effect is saturated and the compressibility of the iron-based mixed powder is reduced.

In the present invention, the powder for improving machinability is
Alkaline earth metal fluoride powder. Alkaline earth metal fluoride powders include calcium fluoride (CaF ₂ ), magnesium fluoride (MgF ₂ ), and strontium fluoride (Sr
It is preferable to use at least one of F ₂ ) and barium fluoride (BaF ₂ ). Among them, calcium fluoride (CaF ₂ ) is preferred from the viewpoint of improving machinability.

In the present invention, the powder for improving machinability is
The binder is fixed to the surface of the iron-based powder together with the graphite powder, which is a powder for the alloy, in particular, to the recesses on the surface of the iron-based powder. For this reason, the alkaline earth metal fluoride powder as a machinability improving powder, the average particle size is 45μm or less, more preferably 25μm
It is preferable to set the following. The average particle size in the present invention uses a value measured by a laser diffraction type particle size distribution measuring device.

Further, in the present invention, in order to fix the graphite powder and the powder for improving machinability on the surface of the iron-based powder, a binder is contained in the iron-based mixed powder. The content of the binder in the iron-based mixed powder is preferably 0.1 to 1.0 part by weight based on 100 parts by weight of the total amount of the iron-based powder, the alloy powder and the machinability improving powder. If the binder content is less than 0.1 parts by weight,
The effects described above are small, while if the content exceeds 1.0 part by weight, the fluidity of the iron-based mixed powder, particularly the dispensing property from the hopper, is deteriorated.

The binder may be one or more selected from stearic acid, oleic acid amide, a molten mixture of stearic acid amide and ethylene bisstearic acid amide, and ethylene bisstearic acid amide. Is preferred. Further, a hot melt of zinc stearate and one or more of oleic acid, spindle oil and turbine oil may be used.

The iron-based mixed powder of the present invention contains a lubricant as a free lubricant in a free state. The free lubricant referred to in the present invention refers to a lubricant that does not adhere to any of the iron-based powder, the alloy powder, and the machinability improving powder, and exists in the iron-based mixed powder in a free state. When the lubricant is used as a free lubricant, it is easily softened or melted by frictional heat during pressure molding in a mold, and the ejection force of the molded body is reduced.

In the present invention, the compounding amount of the free lubricant is preferably 0.1 to 0.5 part by weight based on 100 parts by weight of the total amount of the iron-based powder, the alloy powder and the machinability improving powder. If the amount of the free lubricant is less than 0.1 part by weight, the flow characteristics of the iron-based mixed powder will be reduced.On the other hand, if the amount exceeds 0.5 part by weight, the flow characteristics will not be remarkably improved, and On the contrary, the density of the body decreases, and the density of the sintered body decreases.

In the present invention, the free lubricant may be one or more selected from thermoplastic resin powder, zinc stearate and lithium stearate, or may be a thermoplastic resin powder, zinc stearate, One or more selected from lithium stearate are further added with stearic acid, oleic acid amide, stearic acid amide, a molten mixture of stearic acid amide and ethylenebisstearic acid amide, ethylenebisstearic acid amide, molecular weight It is preferable to use one or more selected from polyethylene having a molecular weight of 10,000 or less and a molten mixture of ethylene bisstearic acid amide and polyethylene having a molecular weight of 10,000 or less.

The thermoplastic resin powder contains at least one selected from the group consisting of monomeric acrylates, methacrylates, and aromatic vinyl compounds in an amount of 50% by mass or more based on the total amount of the thermoplastic resin powder. It is preferable to form a thermoplastic resin powder having a primary average particle size of 0.03 to 5 μm, an agglomeration average particle size of 5 to 50 μm, and an average molecular weight of 30,000 to 5,000,000 as measured by a solution specific viscosity method.

The primary average particle size as referred to in the present invention is, as shown in FIG. 1, individual particles (primary particles 1) of a thermoplastic resin powder.
Mean particle size 3. In addition, the agglomerated average particle size is a particle size of the agglomerated particles 2 formed by aggregating the primary particles 1.
Means the average. The primary average particle diameter is obtained by observing the aggregated particles with a scanning electron microscope and measuring and averaging the diameters (primary particle diameters) of about 50 primary particles forming the aggregated particles from a photographed image. . The aggregated average particle size is obtained by observing the aggregated particles with a scanning electron microscope and measuring and averaging the particle sizes of about 50 aggregated particles from a photograph taken in the same manner.

In the present invention, the average molecular weight is measured by a solution specific viscosity method. The solution specific viscosity method is a method of dissolving 0.2 g of a sample resin in 50 ml of tetrahydrofuran.
The viscosity A at ° C is determined as the ratio of the viscosity (B) of the solvent (tetrahydrofuran) at the same temperature to the viscosity B, A / B (specific viscosity). This is a method for determining the average molecular weight of the sample resin.

When the content of at least one selected from the group consisting of acrylic acid esters, methacrylic acid esters and aromatic vinyl compounds is less than 50% by mass based on the total amount of the thermoplastic resin powder. There is a possibility that the fluidity of the iron-based mixed powder may not be sufficiently improved. The monomer may be any one of an acrylic acid ester, a methacrylic acid ester, and an aromatic vinyl compound, or may be a combination of two or more kinds.

Examples of the acrylate include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, t-butyl acrylate, n-hexyl acrylate, and cyclohexyl acrylate. , 2-ethylhexyl acrylate, n-octyl acrylate and the like.

The methacrylic acid esters include, for example, methyl methacrylate, ethyl methacrylate,
n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate,
Examples thereof include n-octyl methacrylate. Among these monomers, methyl methacrylate can be particularly preferably used.

As the aromatic vinyl compound, for example, styrene, α-methylstyrene, divinylbenzene and the benzene nucleus of these monomers are substituted with a methyl group, an ethyl group, a propyl group or a butyl group. Monomers such as vinyltoluene and isobutylstyrene can be exemplified. Further, another monomer copolymerizable with at least one monomer of the above-mentioned acrylic acid ester, methacrylic acid ester and aromatic vinyl compound is preferably used in an amount of from 0 to 45% based on the total amount of the monomers. What added by mass% and made into a thermoplastic resin may be used as a free lubricant.

Other monomers copolymerizable with the above three monomers include, for example, acrylic acid, methacrylic acid,
2-ethylacrylic acid, crotonic acid, unsaturated monocarboxylic acids such as cinnamic acid, maleic acid, itaconic acid, fumaric acid, citraconic acid, unsaturated dicarboxylic acids such as chloromaleic acid and anhydrides thereof, monomethyl maleate, Monoesters of unsaturated dicarboxylic acids such as monobutyl maleate, monomethyl fumarate, monoethyl fumarate, monomethyl itaconate, monoethyl itaconate and monobutyl itaconate, and derivatives thereof, glycidyl methacrylate, glycidyl acrylate, glycidyl-p-vinylbenzoate, methyl Glycidyl itaconate, ethyl glycidyl maleate, glycidyl vinyl sulfonate, glycidyl ethers, butadiene monoxide, vinylcyclohexene monoxide, 5,6-epoxyhexene, 2
Epoxide olefins such as -methyl-5,6-epoxyhexene; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl esters such as vinyl acetate, vinyl propionate, vinyl myristate, vinyl oleate and vinyl benzoate And non-conjugated diene compounds such as 1,4-hexadiene, dicyclopentadiene, and ethylidene norbornene, and conjugated diene compounds such as butadiene, isoprene, 1,3-pentadiene, and cyclopentadiene.

As the copolymerizable monomer, a crosslinkable monomer having two or more double bonds having substantially the same reactivity is used in an amount of 0.1 to 2% by mass based on the total amount of the monomer. It may be added. Crosslinkable monomers include ethylene glycol diacrylate, ethylene glycol dimethacrylate, butylene glycol diacrylate, butylene glycol dimethacrylate, trimethylolpropane diacrylate, trimethylolpropane dimethacrylate, trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate. Hexanediol diacrylate, hexanediol dimethacrylate, oligoxyethylene diacrylate, oligoxyethylene dimethacrylate, aromatic divinyl monomers such as divinylbenzene, triallyl trimellitate, triallyl isocyanurate and the like.

The primary average particle size of the thermoplastic resin powder is 0.03 to 5.
It is preferably 0 μm. If the primary average particle size is less than 0.03 μm, the production cost of the iron-based mixed powder is high, and it is expensive as an industrial product. On the other hand, if it exceeds 5.0 μm, the density of the molded body (hereinafter, also simply referred to as compressibility) decreases. It is more preferable that the primary average particle size is 0.05 to 3.0 μm.

The agglomerated average particle size of the thermoplastic resin powder is as follows:
It is preferred to be in the range of 5 to 50 μm. If the agglomeration average particle size is less than 5 μm, the fluidity of the iron-based mixed powder and the hopper discharge property are reduced. On the other hand, if it exceeds 50 μm, the tensile strength of the sintered body will be lower than that of the conventional product. The aggregation average particle size is 10 to 40
It is more preferably set to μm. Furthermore, as the thermoplastic resin powder, two or more kinds of thermoplastic resin powders having different primary average particle diameters can be mixed. In this case, the mixed thermoplastic resin powder has a primary average particle diameter of It is preferable to adjust the mixing ratio so that the average value of the powder is 0.03 to 5.0 μm.

The average molecular weight of the thermoplastic resin powder measured by the solution specific viscosity method is preferably in the range of 30,000 to 5,000,000. If the average molecular weight is less than 30,000, the production cost of the iron-based mixed powder becomes too high, and the product becomes expensive. On the other hand, when the average molecular weight exceeds 5,000,000, the fluidity and hopper discharge of the iron-based mixture are lower than those of the conventional product. The method for producing the thermoplastic resin powder described above is not particularly limited in the present invention,
Any method conventionally used for producing fine resin powders such as polymethyl methacrylate is suitable. Among these methods, in particular, a polymerization method in which the particle size is not extremely fine and spherical particles are obtained, for example, a fine suspension polymerization method,
Emulsion polymerization and seeded emulsion polymerization are suitable.

In the iron-based mixed powder of the present invention, the graphite powder, which is a powder for alloy, and the powder for improving machinability are provided on the surfaces of
In particular, it is attached and fixed to the surface of the concave portion. The greater the degree of adhesion of the graphite powder and the powder for improving machinability, the more the machinability is improved. In the present invention, the degree of adhesion between the machinability improving powder and the graphite powder is preferably 60% or more. The degree of adhesion of graphite powder is expressed by the following equation (1): Degree of adhesion of graphite powder = (C content in powder having a particle size of 200 mesh or more and 100 mesh or less) / (C content of iron-based mixed powder as a whole) (1)

The adhesion of the powder for improving machinability is expressed by the following equation (2): Degree of adhesion of powder for improving machinability = (F content in powder having a particle size of 200 mesh or more and 100 mesh or less) / (iron F content of the whole base mixed powder) ... (2)

Next, a preferred method for producing the iron-based mixed powder of the present invention will be described. First, to an iron-based powder, an alloy powder containing graphite powder, a machinability improving powder composed of the alkaline earth metal fluoride having the above-described content, and the above-described binder are added, mixed and mixed. I do. Then, if one kind of binder is used, these mixtures are separated from the melting point by 10%.
Heat to a temperature higher than ~ 100 ° C, while if there are two or more binders, heat to a temperature above (lowest melting point + 10 ° C) and below the highest melting point, and mix while heating (up to this point) Primary mixing) to melt at least one binder. In addition, it is preferable that all heating temperatures are limited to the above-mentioned values or less in order to prevent the functional deterioration of the binder due to thermal decomposition.

After the at least one binder is melted and mixed, the primary mixture is cooled. As a result, the machinability improving powder composed of the graphite powder and the alkaline earth metal fluoride is firmly fixed to the surface of the iron-based powder, particularly to the surface concave portions. Thereafter, a lubricant, preferably of the type and amount described above, is added to these primary mixtures and mixed below the minimum melting point of the lubricant, preferably at room temperature (this is referred to as secondary mixing). The mixing method may be a commonly known mixing method, and need not be particularly limited.

The iron-based mixed powder of the present invention may be produced by the following steps (1) to (4). (1) To an iron-based powder, a powder for alloying and a powder for improving machinability are added, and after further spraying a liquid binder,
Mix. As the liquid binder, one or more of oleic acid, spindle oil, and turbine oil are preferably used. (2) Zinc stearate is further added to these mixtures and mixed to form a primary mixture. The addition amount of zinc stearate is the total amount of one or more of oleic acid, spindle oil, and turbine oil,
It is preferably 0.1 to 1.0 part by weight based on 100 parts by weight of the total amount of the alloy powder and the machinability improving powder. (3) The primary mixed powder is secondarily mixed while being heated to 110 to 150 ° C. By this heating, at least one of zinc stearate and oleic acid, spindle oil and turbine oil is selected.
A heated melt with more than one seed is formed. If the heating temperature of the secondary mixing is lower than 110 ° C., the adhesion of the graphite powder and the powder for improving the machinability is small and the machinability deteriorates. On the other hand, when the temperature exceeds 150 ° C., the iron-based powder may be oxidized, and when oxidized, the iron powder becomes hard and the compressibility decreases.

Then, by cooling the secondary mixed powder, the graphite powder and the machinability improving powder are firmly fixed to the surface of the iron-based powder, especially to the concave portions. (4) A lubricant is further added to the secondary mixed powder in which the graphite powder and the machinability improving powder are fixed on the surface of the iron-based powder, and the mixture is tertiarily mixed to obtain an iron-based mixed powder. The tertiary mixing temperature is preferably lower than the minimum value of the melting point of the lubricant to be added. The temperature is more preferably room temperature. The amount of the lubricant to be added is preferably 0.1 to 0.5 part by weight based on 100 parts by weight of the total amount of the iron-based powder, the iron powder for the alloy and the powder for improving the machinability. The lubricant added in the tertiary mixing becomes a free lubricant, and is present in the mixed powder in a free state without binding to the iron-based powder or the like.

The kind of the lubricant to be added in the tertiary mixing is the same as the above-mentioned free lubricant, and there is no problem. Further, as the method for producing the iron-based mixed powder of the present invention, the above-mentioned two production methods are preferable. For example, after mixing a binder dissolved or dispersed in an organic solvent with an iron-based powder, a powder for an alloy, and a powder for improving machinability, the organic solvent is evaporated to form an alloy powder on the surface of the iron-based powder, improving machinability. In the method in which the powder is fixed and then the lubricant is added and mixed, the graphite powder and the machinability improving powder are fixed to both the concave and convex portions of the surface of the iron-based powder. The powders for improvement are less likely to adhere to each other, and the effect of improving machinability is reduced.

The iron-based mixed powder of the present invention can be applied to any of the production processes in general powder metallurgy. After molding, it is sintered to form a sintered body, and may be processed as it is by sintering, such as cutting, to produce a product.Or, after molding and sintering, heat treatment such as immersion quenching, bright quenching, induction hardening, etc. It is also possible to apply it to the product.

[0043]

(Example 1) Water atomized iron powder (KIP301A manufactured by Kawasaki Steel Co., Ltd.) was used as an iron-based powder, and graphite powder (average particle size: 23) was used as an alloy powder in 1 kg of the iron-based powder.
μm), electrolytic copper powder (average particle size: 25 μm), powder for improving machinability shown in Table 1, and a binder of the type shown in Table 1 were further charged into a heating mixer and thoroughly mixed. . The amount of the alloying powder and the machinability improving powder was set to the amount (% by mass) shown in Table 1 with respect to the total amount of the iron-based powder, the alloying powder, and the machinability improving powder. The amount was the amount (parts by weight) shown in Table 1 with respect to 100 parts by weight of the total of the iron-based powder, the alloy powder, and the machinability improving powder.

Next, based on the lowest melting point and the highest melting point of the mixed binder, the mixture was heated while mixing at the temperature shown in Table 1 (this is referred to as primary mixing) to obtain a primary mixture. Subsequently, the mixture was cooled to 85 ° C. or lower while mixing. Further, the primary mixture is cooled to 40 ° C., and a lubricant (free lubricant) of the type and amount shown in Table 1 is added, and the mixture is uniformly mixed (called secondary mixing), and then discharged from the heating mixer. did. The amount of the free lubricant was set to the amount (parts by weight) shown in Table 1 with respect to 100 parts by weight of the total amount of the iron-based powder, the alloy powder, and the machinability improving powder.

Table 2 shows the relationship between the symbols and types of lubricants other than the thermoplastic resin powder, zinc stearate, and lithium stearate added during the secondary mixing. Table 3 shows the relationship between the symbols and types of the thermoplastic resin powder used at the time of the secondary mixing, their composition, polymerization method, primary particle diameter, aggregated average particle diameter, and molecular weight. In addition, as a comparative example, some iron-based mixed powders do not contain powder for improving machinability (iron-based mixed powder N
o.1-12), and those using MnS as a powder for improving machinability (iron-based mixed powder No.1-15) (conventional example). Also,
As a comparative example, an example (iron-based mixed powder No. 1-14) of mixing at room temperature for 30 minutes using a V-type mixer without adding a binder was also included.

For the obtained iron-based mixed powder, first, the adhesion of graphite powder and the adhesion of alkaline earth metal fluoride powder were examined. With respect to each iron-based mixed powder, a powder having a particle size of 200 mesh or more and 100 mesh or less is sieved, and the C content and the F content of the powder and the entire iron-based mixed powder are determined by analysis. The degree of adhesion was calculated by equation (2).

The degree of adhesion of graphite powder is expressed by the following equation (1): Degree of adhesion of graphite powder = (C content in powder having a particle size of 200 mesh or more and 100 mesh or less) / (C content of iron-based mixed powder as a whole) According to (1), the adhesion of the machinability improving powder (alkaline earth metal fluoride powder) is given by the following equation (2): The adhesion of the machinability improving powder = (200 mesh or more and 100 mesh or less) It was calculated by the following formula: (F content in powder having particle size) / (F content in entire iron-based mixed powder).

Then, the obtained iron-based mixed powder was inserted into a mold, compression-molded at a surface pressure of 480 MPa, and a disc-shaped test piece for drilling test having an outer diameter of 60 mm and a height of 10 mm, 10 × 10 A rectangular parallelepiped molded product of × 55 mm was obtained. The density of the rectangular solid was measured using the Archimedes method. The Archimedes method is a method for measuring the density by immersing a molded article as an object to be measured in water and measuring the volume.

Next, these test piece compacts were sintered at 1130 ° C. for 20 minutes in a RX atmosphere using a mesh belt furnace to obtain sintered compacts. About these sintered bodies (test pieces)
A drilling test was performed under the conditions of a rotation speed of 10,000 rpm and a feed rate of 0.012 mm / rev, and the number of drillings (pieces) was determined. Number of perforations (pieces)
Is the number of holes opened before the drill (1.2 mm φ made of Heiss) breaks.

Table 4 shows the results.

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

[Table 3]

[0054]

[Table 4]

In each of the examples of the present invention, the density of the compact was high,
The graphite powder and the machinability improving powder have a high degree of adhesion, a large number of perforations, and a sintered body excellent in machinability can be formed, and have excellent properties as an iron-based mixed powder for powder metallurgy. On the other hand, all the comparative examples outside the range of the present invention had a low density of the compact or a low machinability. In addition, an iron-based mixed powder containing a machinability improving powder containing S (iron-based mixed powder No.1-1
5) In the (conventional example), poor appearance was observed in the sintered body. (Example 2) Water atomized iron powder (trade name: KIP301A manufactured by Kawasaki Steel) was used as the iron-based powder, and 1 kg of the iron-based powder was used.
In addition, graphite powder (average particle size: 23 μm) and electrolytic copper powder (average particle size: 25 μm) as alloying powders, powders for improving machinability of the type shown in Table 5, and oleic acid shown in Table 5 as a binder Selected from oil, spindle oil and turbine oil
After spraying the seed or two or more kinds, primary mixing for mixing was performed. The amount of the binder is iron-based powder,
It is expressed in parts by weight based on 100 parts by weight of the total amount of the powder for alloying and the powder for improving machinability.

Next, the amount of zinc stearate shown in Table 5 was further added to the primary mixed powder as a binder, and the mixture was charged into a heating mixer and mixed well to obtain a mixture. Then, this mixture was heated while mixing at the temperature shown in Table 5 to obtain a secondary mixture. Subsequently, the secondary mixture was cooled to below 85 ° C. while mixing. In addition, 40 ℃
After cooling to room temperature, the types and amounts of free lubricants shown in Table 5 were added, and the mixture was tertiarily mixed to be uniform, and then discharged from the heating mixer to obtain an iron-based mixed powder. The relationship between the symbols and types of the lubricants other than the thermoplastic resin powder, zinc stearate, and lithium stearate added during the tertiary mixing is described in Example 1.
As shown in Table 2, Table 3 shows the relationship between the symbols and types of the thermoplastic resin powder used during the tertiary mixing, their composition, polymerization method, primary particle size, aggregate particle size, and molecular weight, as in Example 1.

Some iron-based mixed powders do not contain powder for improving machinability (iron-based mixed powder No. 2-12), and those using MnS as the machinability improving powder (iron-based mixed powder) No.2
-15) (conventional example) is also included. As a comparative example, 30 mi at room temperature (RT) using a V-type mixer without adding a binder.
n An example of mixing (iron-based mixed powder No. 2-14) was also included. About the obtained iron-based mixed powder, the adhesion of the graphite powder and the adhesion of the alkaline earth metal fluoride powder were examined in the same manner as in Example 1.

Then, the obtained iron-based mixed powder was inserted into a mold, compression-molded at a surface pressure of 480 MPa in the same manner as in Example 1, and a disc-shaped disk for a drilling test having an outer diameter of 60 mm and a height of 10 mm. The test piece was a 10 × 10 × 55 mm rectangular solid. The density of the rectangular solid was measured by the Archimedes method in the same manner as in Example 1.

Next, these test piece compacts were sintered at 1130 ° C. for 20 minutes in a RX atmosphere using a mesh belt furnace to obtain sintered bodies. About these sintered bodies (test pieces)
As in the first embodiment, the rotation speed is 10,000 rpm, and the feed rate is 0.012 mm / re.
A drill perforation test was performed under the conditions of v, and the number of perforations (pieces) was determined. Table 6 shows the results.

[0060]

[Table 5]

[0061]

[Table 6]

Each of the examples of the present invention has a high compact density,
Further, the graphite powder and the powder for improving machinability have a high degree of adhesion, a large number of perforations can be formed, and a sintered body excellent in machinability can be formed, and have excellent properties as an iron-based mixed powder for powder metallurgy. On the other hand, the comparative examples out of the range of the present invention all had low molded body density or low adhesion of the graphite powder and the powder for improving machinability, resulting in reduced machinability. Also, an iron-based mixed powder containing an S-containing powder for improving machinability (iron-based mixed powder No. 2-15)
In (conventional example), poor appearance was observed in the sintered body.

[0063]

As described above, according to the present invention,
The machinability can be improved without deteriorating the mechanical properties of the sintered body. Further, according to the present invention, the powder for improving machinability can be a powder containing no S, and the production of a sintered product can be performed without causing furnace contamination or harmful effects on the sintered body during sintering by S. It has a significant industrial effect.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing definitions of a primary average particle size and an aggregation average particle size.

[Explanation of symbols]

 1 primary particle 2 aggregated particle 3 primary particle size 4 aggregated particle size

Continuation of the front page (72) Inventor Akio Sonobe 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Kawasaki Steel Co., Ltd. Chiba Works Co., Ltd. F term (reference) 4K018 BA13 BC28 HA10

Claims (3)

[Claims] 1. An iron-based mixed powder obtained by mixing an iron-based powder, an alloy powder containing graphite powder, a machinability improving powder, a binder, and a lubricant, wherein the lubricant is Including as a free lubricant in a free state, the machinability improving powder is an alkaline earth metal fluoride powder, and the alkaline earth metal fluoride powder is an iron-based powder, an alloy powder and a machinability improving powder. An iron-based mixed powder for powder metallurgy, comprising 0.1 to 0.7% by mass with respect to the total amount, and comprising the graphite powder and the machinability improving powder fixed to the surface of the iron-based powder by the binder. 2. The alkaline earth metal fluoride powder,
The iron-based mixed powder for powder metallurgy according to claim 1, wherein the powder is at least one of calcium fluoride, magnesium fluoride, strontium fluoride, and barium fluoride. 3. An iron-based sintered body obtained by subjecting the iron-based mixed powder for powder metallurgy according to claim 1 to pressure molding and further sintering.