JP2010236061A - Iron based mixed powder for sintered member excellent in machinability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide iron based mixed powder suitable to obtain a sintered member excellent in machinability. <P>SOLUTION: Oxide powder of a SiO<SB>2</SB>-CaO-MgO system is mixed into iron based powder at a rate of 0.01-1.0 pts.mass to the iron based powder: 100 pts.mass. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an iron-based mixed powder for a free-cutting sintered member suitable for use in a sintered member having excellent machinability.

  Since powder metallurgy technology can produce machine parts of complicated shapes while maintaining extremely high dimensional accuracy, it is possible to greatly reduce the manufacturing costs of the machine parts. Therefore, various machine parts manufactured using powder metallurgy technology are used in various fields. Furthermore, recently, there is an increasing demand for downsizing or weight reduction of machine parts, and various powders for powder metallurgy for producing machine parts having a small size, light weight and sufficient strength have been studied.

  For example, Patent Documents 1, 2, and 3 propose raw material powder for powder metallurgy in which an alloy powder is adhered to the surface of iron powder or alloy steel powder. As described above, powders mainly composed of iron components (hereinafter referred to as iron-based powders) are usually auxiliary material powders such as copper powder, graphite powder, iron phosphide powder, manganese sulfate powder, and lubricants such as stearic acid. Zinc, aluminum stearate, etc. are added and used.

The powder obtained by mixing the above raw materials is filled into a part-shaped mold in consideration of shrinkage during sintering and the like, and after pressure molding, it is sintered in a reducing atmosphere to form a machine part.
In this sintering process, thermal diffusion between the raw powders for powder metallurgy proceeds with heating, and the material strength increases. At this time, non-uniform shrinkage due to thermal diffusion occurs, so that the material after sintering is generally adjusted to a desired size by cutting. Also, structures that are difficult to be applied by pressure molding such as horizontal holes and oblique holes are adjusted to a desired dimension by performing drilling or boring after sintering.

  The above-mentioned sintered material has a large number of pores inside the material, and the metal structure is inhomogeneous, so the hardness is inhomogeneous, and the impact transmitted to the cutting tool during cutting is intermittent. Become. In addition, since the pores inside the material are difficult to transfer heat, the frictional heat generated during cutting tends to be trapped, and the life of the cutting tool is shorter than that of other ferrous materials, which reduces the manufacturing cost of ferrous sintered parts. This is the main factor pushing up.

  On the other hand, it is conventionally known that the machinability of sintered parts is improved by adding a free-cutting component (for example, S, MnS, etc.) to an iron-based powder mixture for powder metallurgy. The free-cutting component has the effect of easily breaking the chips or forming a thin cutting edge on the cutting tool to increase the lubricity of the cutting tool (especially the rake face). As a result of contaminating the inside of the sintering furnace with S, causing appearance defects of the sintered parts, accelerating rusting, and the like, there is a problem that the parts appearance is impaired.

JP-A-01-219101 JP 02-217403 A Japanese Patent Laid-Open No. 03-162502

  The present invention advantageously solves the above-described problems, and does not adversely affect the in-furnace environment of the sintering furnace when the molded body is sintered, and has excellent machinability and good appearance. It is an object of the present invention to propose an iron-based powder mixture for a sintered member suitable for producing the above.

The inventors have made extensive studies on iron-based mixed powders for sintered parts having excellent machinability and good appearance. As a result, it has been found that it is useful to mix oxide powder, especially fine particles of SiO ₂ —CaO—MgO-based oxide powder. Furthermore, it was also found that the SiO ₂ —CaO—MgO-based oxide powder can partially replace MgO with Al ₂ O ₃ and / or TiO ₂ .
The present invention has been made based on these findings.

That is, the gist configuration of the present invention is as follows.
(1) A SiO ₂ —CaO—MgO-based oxide powder is blended in an iron-based powder for a sintered member at a ratio of 0.01 to 1.0 part by mass with respect to 100 parts by mass of the iron-based powder. An iron-based mixed powder for a free-cutting sintered member.

(2) The iron-based mixture for a free-cutting sintered member according to (1), wherein the oxide powder is obtained by substituting a part of MgO with Al ₂ O ₃ and / or TiO _2. Powder.

  (3) The iron-based mixed powder for a free-cutting sintered member according to (1) or (2), wherein the oxide powder has a melting point in the range of 1000 to 1800 ° C.

  (4) The iron-based mixed powder for a free-cutting sintered member according to any one of (1) to (3), wherein an average particle diameter of the oxide powder is 0.5 to 10 μm.

  (5) The free-cutting sintered member according to any one of (1) to (4), wherein the iron-based mixed powder further contains a lubricant and / or a binder. Iron-based mixed powder.

  (6) The lubricant or binder is one or more selected from zinc stearate, lithium stearate, calcium stearate, stearic acid monoamide, and ethylene bisstearamide. The iron-based mixed powder for a free-cutting sintered member according to any one of (1) to (5).

  (7) The free-cutting sintering according to any one of (1) to (6), wherein the iron powder or iron alloy powder used as the iron-based powder is atomized powder and / or reduced powder Iron-based mixed powder for parts.

  ADVANTAGE OF THE INVENTION According to this invention, the tool abrasion at the time of cutting is suppressed, and the sintered compact excellent in machinability can be obtained.

The present invention will be specifically described below.
In the present invention, as iron-based powder, pure iron powder such as atomized iron powder and reduced iron powder, or partially diffused alloyed steel powder and fully alloyed steel powder, and further partially diffused alloy components in fully alloyed steel powder. The hybrid steel powder etc. which were made to be illustrated are illustrated.
The present invention is characterized in that the iron-based powder is mixed with a SiO ₂ —CaO—MgO-based oxide powder for improving the machinability.

  There are various types of methods for producing the iron powder and alloy powder described above, but considering the moldability, characteristics of the molded body, characteristics of the sintered body, etc., water atomized iron powder and reduced iron powder are used. It is particularly preferred. These iron powders have irregularities on the surface of the particles, and when pressed, they are entangled and the strength of the molded body and sintered body is increased.

In the present invention, in the iron-based powder, the SiO ₂ —CaO—MgO-based oxide powder may be mixed at a ratio of 0.01 to 1.0 part by mass with respect to 100 parts by mass of the iron-based powder. is important. This is because when the mixing ratio of the oxide powder is less than 0.01 parts by mass, no improvement effect is observed in the fluidity of the iron-based powder. On the other hand, when the amount exceeds 1.0 part by mass, the density of the green compact that has been press-formed is reduced, and the density of the sintered body is also reduced, resulting in a decrease in strength of the sintered body. It is. The mixing ratio of the SiO ₂ —CaO—MgO system is not particularly limited, but is preferably mass%, SiO ₂ : 40 to 55%, CaO: 30 to 50%, and MgO: about 0 to 20%. .
Furthermore, a part of MgO of the oxide powder can be replaced with Al ₂ O ₃ and / or TiO ₂ . The amount of substitution in this case is preferably about 0.1 to 25 parts by mass with respect to 100 parts by mass of the oxide powder.

The oxide powder described above is a fine powder having an effect of improving the fluidity of iron powder, and it is preferable to use a powder having a melting point of 1000 to 1800 ° C.
In this melting point range, when the iron-based powder is molded and then sintered, the oxide is less likely to melt and react with the iron powder to grow into a coarser oxide having a lower melting point. In general, the cohesive force between atoms tends to determine elastic properties, and a low-melting substance having a relatively low cohesive force between atoms tends to have a low elastic modulus. Therefore, it is considered that the above-described oxide powder belonging to a relatively low temperature as the melting point of the oxide has a low elastic modulus among the oxides. As a result, when the sintered body is cut, the oxide powder described above can be easily deformed on the cutting surface, so that it spreads between the cutting tool and the cutting surface of the work material and suppresses wear of the tool. , It can have an effect of improving machinability.

  That is, when the melting point is less than 1000 ° C., the oxide melts and aggregates during the sintering, which may reduce the strength of the sintered body. On the other hand, when the melting point exceeds 1800 ° C., the elastic modulus increases, so that it becomes difficult for the oxide to spread on the tool surface, and the tool wear may be accelerated.

The average particle diameter of the oxide powder is preferably a value of 50% cumulative transmission distribution d ₅₀ of at measurement by a laser diffraction method is in the range of 0.5 to 10 [mu] m.
This is because it is generally known that if there are fine irregularities on the surface of the powder particles, the contact area between the particles becomes small, the adhesion between particles becomes small, and the agglomerated state of the powder is eliminated. The iron powder also has irregularities, but the surface roughness is about 10 μm in terms of arithmetic average roughness Ra, which is not sufficient to eliminate the powder aggregation state.

In other words, if the average particle size of the oxide powder is less than 0.5 μm, there is a risk of being buried in the unevenness of the iron powder surface or the lubricant present on the iron powder surface. Moreover, there exists a possibility that the oxide powder may adhere to the surface of the iron powder with aggregation.
On the other hand, when the average particle size exceeds 10 μm, it becomes equivalent to the curvature of the unevenness present on the iron powder surface from the beginning, and the significance of attaching the particles is diminished. Furthermore, the oxide powder is sintered as it is without being decomposed during sintering. Present in the body. Therefore, when the particle size of the oxide powder is too large, the strength of the sintered body is reduced. In addition, Preferably, it is the range of 1-5 micrometers.

The lubricant and binder used in the present invention may be any of conventionally known lubricants and binders, such as those that melt by heating or those that solidify by heating. Those having properties are preferred. This is because the frictional force between the powder particles is reduced, the fluidity of the powder is improved, and the particle rearrangement at the initial stage of pressure molding is promoted.
Specifically, metal soap, amide wax, polyamide, polyethylene, polyethylene oxide or the like is used. Particularly preferred are zinc stearate, lithium stearate, calcium stearate, stearic acid monoamide, and ethylene bisstearamide. These lubricants and binders may be used alone or in combination of two or more. May be used.

The above-described lubricant and binder melt at the melting point or higher, and wet the surface of each particle of the raw material powder in the mixing tank. Since water atomized iron powder and reduced iron powder have irregularities on the surface, the binder tends to accumulate locally on the irregularities. Therefore, the distribution of the lubricant and binder on the surface of the iron-based powder is not uniform.
In order to make the distribution of the lubricant and the binder uniform, it is necessary to improve the wettability between the iron-based powder surface and the lubricant and the binder. Therefore, in order to improve the wettability between the iron-based powder surface and the lubricant and binder, it is preferable to use a wetting improver.

When the wetting improver is used, it is necessary to coat the surface of the iron-based powder with the wetting improver in advance before the lubricant and binder, iron powder, and other alloy components are heated and mixed. When a silane coupling agent is used as the wetting improver, iron powder is charged into a mixing tank, and the silane coupling agent is charged therein and stirred at room temperature for about 1 to 10 minutes. Thereafter, the above-described lubricant, binder, and other alloy components are added and mixed by heating.
The mixing amount of the wetting improver is not particularly limited but is preferably about 0.01 to 0.1 mass% with respect to the iron-based powder.

Hereinafter, an example of the manufacturing process of the present invention will be specifically described.
In the present invention, for a sintered member excellent in machinability, which is prepared by mixing various alloy components such as iron powder and graphite, Cu powder, Ni powder, lubricant and binder using a mechanical stirring mixer. In the process of producing the iron-based mixed powder, oxide particles are added and mixed at the same time.

  In the present invention, a high-speed mixer, which is a kind of mechanically stirred mixer, is used to heat and mix iron powder and various alloy components such as graphite, Cu powder, and Ni powder, and a binder. In order to ensure the moldability of the powder, the addition of a lubricant improves the machinability when the final lubricant is added and mixed in the manufacturing process of an iron-based mixed powder for sintered parts with excellent machinability. It can also be produced by simultaneously adding and mixing oxide particles as particles.

  First, a predetermined amount of iron powder is charged into a high-speed mixer, and alloy components such as graphite and Cu powder and a binder are added thereto. After adding these raw materials, heating and mixing are started. The rotational speed of the rotary blade in the high-speed mixer varies depending on the size of the mixing tank and the shape of the rotary blade, but is generally about 1 to 10 m / sec at the peripheral speed of the tip of the rotary blade. Subsequently, it heat-mixes until the temperature in a mixing tank becomes more than melting | fusing point of a binder, and mixes for about 1 to 30 minutes at the temperature more than melting | fusing point. After mixing, the inside of the mixing tank is cooled. During this cooling process, the binder is solidified, and at this time, auxiliary materials such as alloy components adhere to the surface of the iron powder.

The effect of adding oxide particles that are machinability improving particles has not been clearly clarified, but the inventors consider the following.
That is, oxide particles having a melting point adjusted to 1000 to 1800 ° C. are added to the iron-based powder and sintered, so that the oxide particles are present inside the sintered body. The internal oxide particles soften due to frictional heat generation between the tool and the work material during cutting, and move or elute to the work material surface to reduce the friction between the tool and the work material. It is considered that the coating of oxide particles moved to the surface prevents oxidative deterioration of the tool due to frictional heat generation, so that tool wear and tool loss are simultaneously reduced, resulting in improved machinability.

Add 0.8mass% graphite powder (average particle size: 4μm) and 2mass% electrolytic copper powder to atomized pure iron powder (trade name: JFE Steel JIP301A) as an alloy powder. The SiO ₂ —CaO—MgO-based powder having the blending ratio and average particle size shown in Table 1 was added as a machinability improving powder to the iron-based powder composed of powder. Furthermore, a lubricant having a ratio of 0.8 mass% was added to the whole powder including the iron-based powder and the machinability improving powder, and mixed for a predetermined time to obtain an iron-based mixed powder.
In addition, as a comparative example, a powder not containing the machinability improving powder according to the present invention (Comparative Example 1) and a conventionally added MnS (Comparative Example 2) were also prepared.

After these iron-based mixed powders were filled in a mold, compression molding was performed. The shape was a ring shape with an outer diameter of 60 mm, an inner diameter of 20 mm, and a height of 25 mm in accordance with JIS Z 2507 “Sintered bearing-crushing strength test method”, and the molding density was 6.9 Mg / m ³ .
Then, these specimens were sintered in a mesh belt furnace RX mixed gas atmosphere under the conditions of 1130 ° C x 20 minutes to form a sintered body, and a lathe was formed in a cylindrical shape by stacking three of them. And the outer periphery was ground. The cutting was stopped after cutting 1000 m, and the width of the abrasive wear on the side clearance surface of the tool tip was measured.

The cutting tool was a carbide: P10 type cuboidal insert, and cutting was performed at a cutting speed of 200 m / min, a feed of 0.1 mm / rev, and a cutting depth of 0.5 mm.
The test results are also shown in Table 1.

  As shown in Table 1, all the sintered bodies using the iron-based mixed powder according to the present invention had an abrasive wear width of 0.12 mm or less on the side flank face of the chip, compared with Comparative Example 2 in which conventional MnS was added. It can be seen that it is extremely small. Further, in Comparative Example 1 in which no cutting improving material was added, the width of the abrasive wear was large, thereby increasing the cutting resistance and making 1000 m cutting difficult.

To the reduced iron powder (trade name: JFE Steel JIP255M), 0.8mass% graphite powder (average particle size: 4μm) and 2mass% atomized copper powder are added as alloy powder. This iron powder and alloy powder The SiO ₂ —CaO—MgO-based powder having the blending ratio and average particle size shown in Table 2 was added as a machinability improving powder to the iron-based powder made of. Furthermore, a lubricant having a ratio of 0.8 mass% was added to the whole powder including the iron-based powder and the machinability improving powder, and mixed for a predetermined time to obtain an iron-based mixed powder.
In addition, as a comparative example, those not containing the machinability improving powder according to the present invention (Comparative Example 3) and those added with conventionally used MnS (Comparative Example 4) were also prepared.

After these iron-based mixed powders were filled in a mold, compression molding was performed. The shape was a ring shape with an outer diameter of 60 mm, an inner diameter of 20 mm, and a height of 25 mm, as in Example 1, and the molding density was 6.9 Mg / m ³ .
Subsequently, these test piece molded bodies were made into sintered bodies under the same conditions as in Example 1, and these were set on a lathe in the form of a cylinder in which three of them were stacked, and the outer periphery was ground. The cutting was stopped after cutting 1000 m, and the width of the abrasive wear on the side clearance surface of the tool tip was measured.

The cutting tool was a carbide: P10 type cuboidal insert, and cutting was performed at a cutting speed of 200 m / min, a feed of 0.1 mm / rev, and a cutting depth of 0.5 mm.
The test results are also shown in Table 2.

  As shown in Table 2, all the sintered bodies using the iron-based mixed powder according to the present invention had an abrasive wear width of 0.14 mm or less on the side flank face of the chip, compared with the comparative example 4 in which conventional MnS was added. It can be seen that it is extremely small. Further, in Comparative Example 3 in which the powder for improving machinability was not added, the width of the abrasive wear was large, thereby increasing the cutting resistance and making it difficult to cut 1000 m.

  ADVANTAGE OF THE INVENTION According to this invention, the sintered member excellent in machinability which does not cause the lifetime reduction of a cutting tool, and does not cause the raise of manufacturing cost can be provided. Furthermore, with this sintered body excellent in machinability, it is possible to provide a machine component having a small size, light weight and sufficient strength even for a component that requires cutting.

Claims (7)

An iron-based powder for a sintered member and a SiO ₂ —CaO—MgO-based oxide powder blended at a ratio of 0.01 to 1.0 part by mass with respect to 100 parts by mass of the iron-based powder. Iron-based mixed powder for machinable sintered parts. _2. The iron-based mixed powder for a free-cutting sintered member according to claim 1, wherein the oxide powder is obtained by substituting a part of MgO with Al ₂ O ₃ and / or TiO ₂ .   The iron-based mixed powder for a free-cutting sintered member according to claim 1 or 2, wherein the oxide powder has a melting point in the range of 1000 to 1800 ° C.   The iron-based mixed powder for a free-cutting sintered member according to any one of claims 1 to 3, wherein the oxide powder has an average particle size of 0.5 to 10 µm.   The iron-based mixed powder for a free-cutting sintered member according to any one of claims 1 to 4, further comprising a lubricant and / or a binder contained in the iron-based mixed powder.   2. The lubricant or binder is one or more selected from zinc stearate, lithium stearate, calcium stearate, stearic acid monoamide, and ethylene bisstearamide. Iron-based mixed powder for a free-cutting sintered member according to any one of -5. The iron-based mixed powder for a free-cutting sintered member according to any one of claims 1 to 6, wherein the iron powder or alloy powder used as the iron-based powder is atomized powder and / or reduced powder. .