JP3449110B2 - Iron-based mixed powder for powder metallurgy and method for producing sintered body using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention makes it easy to adjust the dimensional change rate during sintering without impairing the strength of the sintered body, and further, in both turning and drilling, high-speed cutting and The present invention relates to an iron-based powder for powder metallurgy which gives a sintered body having excellent machinability in any of low-speed cutting, and a method for producing a sintered body using the same.

[0002]

2. Description of the Related Art Powder metallurgy is a promising technology as an industrial production method for various machine parts and is widely used.
In reality, in most cases, the sintered parts are finally subjected to some machining due to the constraints of press molding using a mold. Therefore, to further simplify machining after sintering,
It is desirable to suppress the amount of machining as much as possible by enhancing the controllability of the dimensional change rate during sintering, but concrete improvement studies from this point of view have not been conducted so much. It has also been confirmed that the machinability of sintered parts is poorer than that of ingots of the same composition. The cause is that the pores present in the sintered body impede heat dissipation due to heat conduction. It has been pointed out that the temperature of the cutting part is increased and the cutting tool is subjected to intermittent impact.

Therefore, in order to improve the machinability of the sintered material,
Conventionally, MnS powder has been added to iron-based powder for powder metallurgy together with C (graphite) powder and other alloying element powder for improving physical properties,
A method of improving the machinability of the sintered body is adopted. MnS
It is considered that the machinability improving effect brought about by containing the powder is that flaking of the cutting tip is promoted by MnS.

As another machinability improving method, for example, Japanese Patent Laid-Open No. 63-93483 discloses a method of mixing glass, boron nitride, talc, etc. in a raw material powder, and Japanese Patent Laid-Open No. 7-33.
No. 78 discloses a method of adding sepiolite, attapulgite, zeolite, etc., and further, "Journal of Precision Engineering" V
ol. 61, No. 2, p238-242 (1995)
Include, as a machinability improving component, a grenite powder and MnS.
A method for multiple addition of powders is disclosed. In these conventional techniques, the reason why the machinability improving effect is obtained by the complex oxide such as gehlenite is that these complex oxides are melted by the cutting heat and form a protective coating on the machined surface of the cutting tool. It is considered. However, according to the additional tests confirmed by the present inventors, the conventional machinability improving method using a complex oxide cannot always stably obtain a satisfactory modifying effect.

[0005]

SUMMARY OF THE INVENTION The present invention has been made by paying attention to the above-mentioned prior art, and its purpose is to:
Good dimensional change rate controllability during sintering,
It is intended to provide an iron-based mixed powder for powder metallurgy, which provides a sintered product having excellent mechanical properties (strength, fatigue properties, etc.) and having stable machinability.

[0006]

The iron-based mixed powder for powder metallurgy according to the present invention, which has been able to solve the above-mentioned problems, is mainly composed of iron powder and has an average particle size having an anorthite phase and / or a grenite phase. CaO-Al of 50 μm or less
The powder of the ₂ O ₃ —SiO ₂ -based composite oxide was added to 0.02 to 0.
Its characteristic is that it contains 3% by weight. In the present invention, the composite oxide has an average particle size of 12
By using those having a thickness of not more than μm, the modifying effect can be exhibited more reliably and stably.

Further, as the iron powder used above, the S content is 0.15 to 0.5% by weight, and the Mn content is the chemical equivalent of the Mn amount + 0.3% by weight or less. If iron powder containing a certain S and Mn in a solid solution state is used, or if a mixed powder containing 0.1 to 0.7% by weight of MnS powder having an average particle size of 65 μm or less is used as another component, the firing It is preferable because the machinability of the bonded body can be further improved. Further, if necessary, the above-mentioned mixed powder of the present invention contains an appropriate amount of graphite as a carburizing-strengthening component, or an appropriate amount of a metal powder for improving physical properties in accordance with required characteristics to improve the physical properties of a sintered product. Furthermore, in order to improve the compaction density during compaction molding, a lubricant such as wax or metal soap is added, or in order to promote uniform dispersion of the additive as described above, light oil, oil and fat, SB
It is also effective to add a rubber such as R and a segregation preventing agent such as a polyhydric alcohol fatty acid ester.

The method for producing a sintered body according to the present invention means that the mixed powder for powder metallurgy as described above is compacted to form 650 to 15
It has a characteristic that it is sintered at 00 ° C. By specifying such a sintering temperature, the characteristics of the above iron-based mixed powder for powder metallurgy are effectively utilized, and under excellent dimensional change rate controllability. It is possible to obtain a sintered body having excellent strength and machinability.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION First, as the iron-based powder for powder metallurgy used in the present invention, reduced iron powder (collectively referred to as ore reduced iron powder, mill scale reduced iron powder, sponge iron powder, etc.), atomized iron powder, It may be a commonly used one such as electrolytic iron powder and is not particularly limited, but it is desirable that the content of hard oxide impurities such as SiO ₂ that inhibits machinability is small. In addition, the present inventors have examined the existence form of Mn contained in the iron powder and the influence of the content thereof.
It has been confirmed that the n content is preferably as small as possible within the range in which the strength is not deteriorated when the n content is present without binding with sulfur or oxygen.

The effect of improving the turning property by the addition of gehlenite is suggested in the above "Journal of Precision Engineering",
It has been clarified that the addition of gehlenite does not cause a change in the dimensional change rate or strength deterioration and may contribute to the improvement of the transverse rupture strength in some cases. However, when the present inventors actually conducted a follow-up test, the expected machinability improvement effect could not be obtained.

Therefore, the present inventors have found that Gerenite (Ge)
Hlenite, powder CaO-Al ₂ O ₃ -SiO ₂ composite oxide having a _{2CaO · Al 2 O 3 · SiO} 2) phase (hereinafter again called gehlenite powder), and which further melting temperature is lower than the composite Anorthite (CaO.Al ₂ O ₃ .2Si), which is considered to act effectively as an oxide-based protective film forming component
O ₂₎ phase CaO-Al ₂ O ₃ -SiO ₂ composite oxide having a (hereinafter, focused on) that anole site powder,
In order to make more effective use of its characteristics on a practical scale, details of the powder particle size, addition amount, sintering temperature and dimensional change behavior during sintering, strength and machinability of the sintered body and its heat-treated body are detailed. I examined it.

As a result, it has been found that the addition of the grenite powder and the anolsite powder causes a clear change in the dimensional change behavior in the sintering process. That is, as the amount of the grenenite powder or the anorthite powder mixed in the iron-based mixed powder for powder metallurgy increases,
The apparent α → γ transformation completion point that occurs at around 950 ° C. shifts to the high temperature side, and the dimensional change rate (expansion amount) at the time of the α → γ transformation completion is reduced. Further general iron-based powder,
By the normal soaking and holding performed at 1000 to 1300 ° C., the sintering of the iron powder particles progresses to cause shrinkage, but when the raw material powder contains the grenite powder or the anolsite powder, the shrinkage amount at this time Was confirmed to change. That is, when a grenenite powder or an anorthite powder is contained, the final sintered body can be obtained depending on the type and blending amount of iron powder and auxiliary materials (graphite, metal powder for improving physical properties, etc.) or the sintering method. It has a considerable effect on the dimensions of.

Then, the present inventors have studied the effect of the gerenite powder and the anolsite powder on the dimensional change behavior during sintering, and as a result, have found the following facts. That is, since Si contained in gehrenite and anorthite is an element that easily forms a carbide, C (generally blended as a graphite powder), which is generally blended as a carburizing-strengthening component, diffuses into iron and forms a solid solution. Delaying, the apparent α → γ transformation completion temperature shifts to the high temperature side, and when a large amount of gehlenite powder or anorthite powder is included, the probability that there will be gehlenite powder or anorthite powder between the iron powder particles will increase. The shrinkage amount due to the sintering of the iron powders during the soaking is small, and even in the cooling process after the completion of the soaking, the grenenite powder or the anorthite powder has a smaller thermal expansion coefficient than that of Fe. If it is interposed between the system powders, the amount of shrinkage during cooling becomes small, and finally it tends to expand.

It was also confirmed that the particle diameters of the grenite powder and the anolsite powder also significantly affect the dimensional change behavior during sintering, the strength of the sintered body, and the machinability. That is, when the iron-based powder for powder metallurgy contains a grenenite powder or an anorthite powder as a machinability improving component, depending on their particle size, it is filled in the voids generated between the iron powder particles during compaction molding. The probability of going and the probability of existing between iron powder particles will change considerably.

Therefore, in consideration of the behavior of the above-mentioned grenite powder and anorthite powder and the influence on the dimensional change during sintering, the preferable grain size constitution and content of these powders, MnS, graphite powder and other auxiliary materials As a result of detailed examinations including grain size and addition amount, sintering temperature and diffusion of C, shrinkage amount of the sintered body due to soaking, heat shrinkage during cooling, etc. If a proper amount of Gerenite powder and / or anorthite powder with a proper particle size composition is included in the mixed powder, it has stable strength characteristics under excellent dimensional controllability, good machinability and turning property. The inventors of the present invention have come to the present invention by knowing that a sintered body having excellent machinability by drilling as well as high-speed cutting as well as high-speed cutting can be obtained.

The reasons for setting each of the requirements defined in the present invention will be described in detail below based on experimental data.

[Suitable Particle Sizes of Gerenite Powder and Anolsite Powder] First, the average particle size of the grenite powder and anolsite powder is 50 μm or less, and more preferably 1.
The reason for defining 0 μm or less will be clarified. C
The oxides of a, Al, and Si are respectively converted into Gehlenite (2CaO.Al ₂ O ₃ .SiO _2).
2 ) and anorthite (Ca)
O.Al ₂ O ₃ .2SiO ₂ ) was mixed, heated and melted, and then cooled and crushed to produce a grenite powder and anorthite powder. At this time, the average particle size was adjusted to 2 to 150 μm by adjusting the crushing time, the opening of the sieving mesh, and the airflow classification conditions.

The obtained grenenite powder and anolsite powder were mixed with commercially available atomized steel powder (Kobe Steel,
Product name "Atmel 300M"), atomized copper powder (manufactured by Fukuda Metal Co., product name "CuAtG-200"), graphite powder (manufactured by Nippon Graphite Co., product name "J-CPB") and a lubricant with a high-speed mixer. Fe-2 wt% Cu-
0.8 wt% graphite-0.1 wt% (gerenite or anolsite) +0.75 wt% lubricant (-
Was used to prepare an iron-based mixed powder for powder metallurgy of 1 ton, and + means an external content, that is, an external content.

1 ton of the mixed powder having the above composition was charged into the raw material hopper of the continuous molding press, and the outer diameter was 64 mm and the inner diameter was 24.
mm, a thickness of 20 mm, and a compact density of 7.0 g / cm ³ about 2400 compacts were compacted. The compact was continuously sent to a mesh belt type continuous sintering furnace and 10% H ₂
Sintering was performed in an atmosphere of -N ₂ under the condition of 1120 ° C. for 30 min, and the outer diameter dimensional change rate, radial crushing strength (pressure resistance when a pressure in the crushing direction was applied to an annular sintered body), P Average turning time per piece of carbide tip and its variation R
investigated. In the turning test, one out of every 10 pieces was sampled in the order of compacting and sintering, 10 pieces were piled up and fixed to a jig, and the outer periphery was turned by a dry method.
The turning conditions are: peripheral speed V: 200 m / min, feed f:
0.01 mm / rev, cut t: 0.5 mm,
Carbide tip has a tool flank wear of 0.3 mm
It was evaluated by the time to reach. The results are shown in Table 1.

[0020]

[Table 1]

As is clear from Table 1, in order to keep the variation of the outer diameter dimensional change rate, the radial crushing strength, and the variation of the lathe turning time at a high level, the average particle diameters of the grenenite powder and the anorthite powder are large. It must be used that the powder has a particle size of 50 μm or less, and it can be confirmed that all the values become extremely worse when a coarse powder having a particle size of more than 50 μm is used. In particular, when fine powder having an average particle size of 10 μm or less is used, the average turnable time is significantly improved and the variations are also significantly reduced. This improves homodispersibility of iron powder of gerenicite powder and anorthite powder, and also improves the contact probability between the tool and the grenite or anolsite during cutting, effectively exerting the surface protection effect of the tool. It seems to be because.

[Segregation Preventing Effect of Organic Binder and / or Oil] In the iron-based mixed powder for powder metallurgy of the present invention, in addition to the main iron powder and the above-mentioned grenite powder and / or anorthite powder, usually carburizing is carried out. Graphite is contained as a reinforcing component, and moreover, metal powder such as Cu powder is often contained. Since these have various specific gravities, particle sizes, etc., they can be handled from a powder conveying process such as handling or a screw feeder or from a raw material hopper. Segregation occurs during the supply process, which causes variations in the characteristics of the sintered parts.

As a method of preventing these, there is known a method of blending fats and oils or a co-melt of a fatty acid and a metal soap as shown in JP-A-3-162502 and fixing the alloy powder on the surface of the iron-based powder particles. Has been. Therefore, in order to effectively utilize such a technique, the present inventors have an average particle size of 9.
The anti-segregation effect of the external addition of the anti-segregation agent was investigated for the mixed powder of Invention Example 3 shown in Table 1 using 9 μm of a grenite powder.

The results are shown in Tables 2 and 3. When styrene-butadiene rubber (abbreviated as SBR) was used as an organic binder for preventing segregation, the addition amount was about 0.
At 2% (hereinafter, unless otherwise specified, means% by weight), the effect of improving the variation in the turnable time saturates, and at 0.3%, the Ratler value, which is one of the evaluation methods of the strength of the molded body, is poor. There is a tendency to become. Therefore, when SBR is used as the segregation preventive agent, it is desirable to suppress the addition amount to about 0.2% or less. This tendency is due to ethylene glycol di-stearate (EGDS
And abbreviation) are used in the same manner.

On the other hand, when light oil or fatty acid is used, the effect of reducing the variation in the turnable time can be seen, but the fluidity, which is a measure of the difficulty when the powder is filled in the mold, does not include these. It tends to be worse than in Example 3,
Therefore, in the case of light oil, it is desirable to control the content to about 0.03% or less, and for the fatty acid, to control it to about 0.10% or less.

In addition, SBR and light oil or fatty acid, EGD
Even when S and fatty acids are used in combination, the effect of their addition can be effectively exerted by appropriately adjusting the addition amount thereof.

As is apparent from these experiments, also in the present invention, the addition of an organic binder, a segregation preventing agent such as light oil, a fatty acid, etc., reduces the variation in the turnable time, and further, the sintered material. It is possible to extend the average turnable time by homogenizing.

[0028]

[Table 2]

[0029]

[Table 3]

[Preferable Content of Gerenite Powder and Anolsite Powder] In this experiment, the rationale for defining the content ratio of the grenite powder and / or the anolsite powder in the mixed powder to 0.02 to 0.3% is clarified. To Commercially available 0.5% Ni-1.0% Mo prealloyed atomized steel powder (Kobe Steel, trade name "46F4
H ”) as the main component, and the graphite powder content is 0.6
%, The content of the grenite powder or the anorthite powder was changed in the range of 0 to 0.5% to prepare a mixed powder,
Using these, a ring-shaped green compact was molded and sintered in the same manner as described above, and a turning test and a radial crushing strength test were performed in the same manner as described above. The turning test is performed after sintering, and the radial crushing strength is after sintering and heat treatment (bright quenching /
It measured about each after tempering.

The results are shown in Table 4, and as the contents of the gehlenite powder and the anorthite powder increased, the time during which the sintered body could be turned per one cemented carbide chip became longer, but the content was 0. At 01%, there is almost no significant difference with the additive-free material. Therefore, in order to effectively utilize the effect, the content should be 0.02% or more.
On the other hand, focusing on the radial crushing strength of the sintered body / heat-treated body, the content rate of the grenenite powder and the anolsite powder was 0.07.
%, The radial crushing strength becomes maximum, and 0.10% in the sintered body
And the heat-treated body exceeds 0.3% and is contained in an excessively large amount, the strength becomes lower than that of the additive-free material. Therefore, from the viewpoints of both turning time and strength, it can be seen that the content of the gehlenite / annolsite powder should be set in the range of 0.02 to 0.3%.

[0032]

[Table 4]

[Control of Dimensional Change Rate 1: Relationship between Addition Amount of Gerenite Powder and / or Anorthite Powder and Sintering Temperature] In this experiment, the contents of the garenite powder and the anolsite powder in the mixed powder were the The influence on the dimensional change rate at the time of setting was examined. As iron-based powder, commercially available 4% Ni-1.5% Cu-0.5
% Mo partially diffused steel powder (Kobe Steel, trade name "48
00DFC ”) was used to prepare a test powder in which the content of graphite powder was 0.6% and the content of gerenite powder or anorthite powder was varied in the range of 0 to 1.0%. Was powder molded into a ring-shaped test piece having an outer diameter of 64 mm, an inner diameter of 24 mm, and a thickness of 10 mm in the same manner as described above, and then was subjected to 11% in a 10% H ₂ —N ₂ atmosphere.
Sintering was carried out at 20 ° C. × 30 min or 1250 ° C. × 30 min, and the mold-based outer diameter dimensional change rate was investigated.

The results are shown in FIGS.
Even when sintering is performed at 0 ° C., when a small amount of the grenenite powder or the anolsite powder is added, the outer diameter dimensional change rate in the same compact density shows a shrinkage (−) tendency, and the content rate is about 0.05 to 0. The shrinkage amount becomes maximum at 0.1%. After that, the dimensional change rate of the outer diameter gradually shows an expansion tendency as the content rate increases.

On the basis of these tendencies, considering the case where sintering is performed at 1120 ° C. using a mixed powder containing a grenite powder, for example, by setting the content of the grenite powder to about 0.18%, It is possible to obtain almost the same dimensional change rate as the additive-free material. Therefore, it becomes possible to effectively utilize the machinability improving effect by containing the gehlenite powder without using a dedicated mold.

Further, even when the same amount of gerenic powder or anorthite powder is contained, the degree of influence on the dimensional change rate is slightly different depending on the sintering temperature. That is, in the mixed powder of the present invention containing the grenite powder and / or anorthite powder, as described above, the radial crushing strength is improved as compared with the additive-free material, so the strength is lower than that of the additive-free material. Without this, the sintering temperature can be finely adjusted to match the dimensional change rate.

For example, FIG. 5 shows 0.3% of grenite powder.
FIG. 3 is a graph showing the relationship between the sintering temperature and the outer diameter dimensional change rate of mixed powders with and without addition, and as is clear from this figure, compaction molding using mixed powders without addition of gerenite powder If a dimensional change rate similar to that in the case of sintering a body at 1250 ° C. is to be obtained with a mixed powder having a content rate of 0.3% of grenite powder, the sintering temperature is 1230.
It is sufficient to set the temperature to ℃, and thereby, it is possible to obtain the heat-treated body strength and the dimensional change rate equivalent to those obtained by sintering the additive-free material at 1250 ℃.

[Control of Dimensional Change Rate 2: Mechanism of Variation in Dimensional Change Rate] In FIGS. 1 to 4 described above, the influence of the contents of the gerenic powder and the anorthite powder on the dimensional change rate (DC) during sintering is clarified. However, in order to further clarify the cause that affects the dimensional change rate, a dilatometer (thermal expansion meter) was used for the study.

As a result, as shown in FIGS. 6 and 7, both the grenenite powder and the anorthite powder were 800 to 9
The effect is to move the apparent α → γ transformation completion point seen around 50 ° C. to the high temperature side and to reduce the expansion amount at the completion of α → γ transformation. This is because Si contained in anorthite and gehlenite is an element that easily forms a carbide, so that the solid solution of C derived from the graphite powder contained in the mixed powder into the iron powder is delayed, and the apparent α → γ transformation occurs. It is considered that the completion shifts to the high temperature side.

Further, the amount of shrinkage during soaking (holding at 1250 ° C. in FIGS. 6 and 7) is also affected by the inclusion of the gehlenite powder or the anolsite powder. That is, in a small amount of the grenite powder and anorthite powder contained, the amount of shrinkage during soaking is larger than that of the additive-free material, whereas when contained in a large amount, between the iron powder particles,
It seems that gerenite powder and anorthite powder that do not react with iron powder enter and inhibit the shrinkage due to sintering.Thus, the dimensional change rate of the sintered body depends on the content ratio of the gerenite powder and anorthite powder. It is considered to be the main cause of fluctuation. And the extent of the influence depends on the sintering temperature and the composition (see Fig. 1-Fig. 1).
4, 6, 7).

Further, in the cooling process after the completion of the soaking, the shrinkage gradient is changed by adding a large amount of the grenite powder and the anolsite powder. In other words, when a large amount of gerenic powder or anorthite powder having a smaller coefficient of thermal expansion than metal exists between the iron powder particles, the thermal expansion of the entire sintered body is suppressed, so that the expansion tendency when cooled to room temperature is more It is expected to become stronger.

[Reasons for Defining Sintering Temperature] Next, the temperature for sintering a green compact using the iron-based mixed powder of the present invention is 6
The reason for defining 50 to 1500 ° C will be described. Generally, the lower the sintering temperature, the more gradual the degree of sintering and the better the machinability of the obtained sintered body. However, in the state where sintering has hardly progressed, cracking, chipping, or deformation of the work piece during handling (attaching the work piece (sintered body) to the cutting machine (catching, mounting)) There is a fear that such problems will occur.

On the other hand, when the sintering temperature is increased, the strength of the sintered body is increased, but generally known problems such as an increase in thermal energy cost and a decrease in machinability are caused, and the grenite powder is produced. In the mixed powder of the present invention containing the oranol site powder, for example, as shown in the state diagram of FIG. 8, there is a possibility that a portion slightly deviated from the theoretical bond ratio obtained from the chemical formula may be decomposed. These decomposed products act as impure inclusions in the sintered body and deteriorate machinability. Therefore, in order to suppress such thermal decomposition, it is necessary to suppress the sintering temperature to 1500 ° C. or lower.

By the way, Table 5 below shows commercially available 0.5% Ni.
-1.0% Mo prealloy type atomized steel powder (Kobe Steel Co., Ltd., trade name "46F4H") is the main component, the graphite powder content is 0.6%, the content of the grenite powder or anorthite powder is 0.1. The results of examining the degree of damage to the sintered body when the ring-shaped green compact was molded in the same manner as described above using the mixed powder (%) and the sintering temperature was variously changed are shown. In this experiment, the number of test materials (1) that were cracked or chipped when ten of the above-mentioned ring-shaped powder compacts that were compacted were stacked and fixed to a jig.
It was evaluated by the number per 000 pieces). As is clear from this table, in order to obtain a sintered body of sufficient strength without impairing the machinability of the sintered body, the sintering temperature should be 650 to 1
It is understood that the temperature should be set to 500 ° C, preferably 700 to 1500 ° C.

[0045]

[Table 5]

[Effect of Turning Property by Containing Gerenite Powder and Anorthite Powder in Comparison with MnS Powder Containing Material] Iron powder-2% Cu-0.5% C (carbon) is used as a basic composition, and MnO and MnS are used. The amount of iron is almost equal, but iron powders having different Mn and S contents are used, and a mixed powder containing 0.1% of a grenite powder or anorthite powder having an average particle diameter of 15 μm is used. Forming density 6.90 g / cm ³
The powder compact of was produced. This molded body is 1130 ° C x 3
Sintering was carried out for 0 minutes, and a machinability test piece was prepared in the same manner as above for the obtained sintered body. Further, as a known MnS powder additive used for improving machinability, 0.5
% Iron powder (manufactured by Mitsui Kinzoku Co., Ltd.) containing MnS powder, was similarly compacted and sintered, and used as a standard for machinability evaluation.

In the machinability test, a P-type cemented carbide tip was used as a cutting tool, dry type, incision t = 0.5 mm, feed f =
0.1 mm / rev, peripheral speed V = 70 to 200 m / min
Turned in. The results are shown in Table 6. The tool life ratio in the table means that the tool life time (time until the wear amount of the tool reaches a predetermined value) of the sintered body using the 0.5% MnS powder additive under the same turning condition is 1, It is shown as a relative value to this value.

As is clear from Table 6, when the amount of Mn contained in the iron powder used as the base is in a state other than MnO and MnS, it is preferable that it is as small as possible within the range that does not affect the strength. I understand. Furthermore, in a sintered body using a material containing a grenite powder and anorthite powder,
0.5 in high-speed turning with a peripheral speed of 120 m / min or more
It can be confirmed that a remarkable machinability improvement effect is exhibited as compared with the% MnS powder additive.

[0049]

[Table 6]

[Effect of Combined Addition of Gerenite + MnS Powder: Effect of Particle Size] In the above description, it has been clarified that the machinability during high-speed turning is remarkably improved by containing the grenite powder and the anolsite powder. . However, it is difficult to increase the peripheral speed (diameter x π x number of revolutions) excessively in the inner / outer periphery processing of a small-diameter sintered part, or in the case of a large-sized part, due to the performance restrictions of the processing machine in the inner diameter processing. In many cases, cutting under low speed conditions is required. Therefore, the present inventors also studied improvement of turning workability in a low speed region.

That is, iron powder-2% Cu-0.5% C was used as the basic composition, the content rate of the grenite powder or anorthite powder was fixed at 0.1%, and the particle size of the MnS powder was as shown in Table 7. For the mixed powder with various additions and addition amounts, powder compaction and sintering (1130 ° C. × 30 m
in), the machinability test of the test material obtained was performed, and the tool life ratio when the tool life time of the sintered body using the 0.5% MnS powder additive was set to 1 in the same manner as above. The results are shown in Table 7.

[0052]

[Table 7]

As is clear from Table 7, when the MnS powder used in combination with the grenite powder or the anorthite powder is coarse, the contribution to the improvement of the tool life is small, but the average particle size is about 65 μm. If a fine powder of less than 0.5 is used, machinability close to that of the 0.5% MnS powder additive can be obtained even with a small amount. Regarding the content of MnS powder, when the content is less than 0.1%, the life extension effect is not so great, but when 0.1% or more of MnS powder is used together, it is particularly effective in extending the tool life during low speed cutting. It seems to work. However, if the MnS content becomes too large, the mechanical properties and fatigue properties of the sintered body will be adversely affected, so the MnS powder content is preferably controlled to 0.7% or less.

That is, when the grenenite powder or the anolsite powder and MnS powder are used in combination, the average particle size is 65.
By using 0.1 to 0.7% of MnS powder having a particle size of μm or less together, it is possible to effectively utilize the combined effect of both. Especially in the low-speed turning region where the cutting speed is slow and the temperature of the tool does not rise sufficiently and machinability improvement (tool protection) due to the formation of a protective film of gehlenite or anorthite cannot be expected satisfactorily.
By effectively exhibiting the turning property improving effect of the powder, it becomes possible to secure excellent machinability over the entire range from low speed cutting to high speed cutting.

The improvement of the machinability improvement effect by the combined use with MnS powder suggested in the above-mentioned "Journal of Precision Engineering" is that MnO existing as an impurity in MnS in high-speed turning at 100 to 200 m / min. However, in order to facilitate the attachment of gehrenite to the tool surface, in the present invention, as described above, the cutting speed is slow and the temperature of the tool does not rise sufficiently, thus forming a protective film for gehrenite and anorthite. Even in the low-speed turning area where the machinability improvement (tool protection) due to is insufficient, the machinability in such a machining area is supplemented by MnS powder in order to exert satisfactory turning machinability. .

That is, in the present invention, in the sintered body in which the MnS powder is used in combination with the grenite or anorthite powder,
The machinability improvement at low speed is secured by MnS powder, and the machinability in the high-speed cutting area is taken care of by the protective coating derived from the grenite powder and / or anorthite powder, so to speak, a two-step machinability improvement function. A major feature of this is that it is possible to stably ensure excellent machinability not only in high-speed cutting but also in a low-speed cutting region by providing it.

[Example of combined use of Mn.S prealloy type iron powder + gerenite powder and / or anolsite powder] In the above, when the grenite powder or anorthite powder is used in combination with MnS powder, high speed machining from a low speed machining range of the sintered body is carried out. It was shown that the machinability in the entire machining area over the area was improved. However, in the method of containing MnS powder, if left in the air, the MnS powder deteriorates and the machinability improving effect decreases, so special measures must be taken to store the mixed powder. Therefore, when sintering is performed in an H ₂ atmosphere, H ₂ S is generated, which not only damages the sintering furnace but also contaminates the working environment. The inclusion of MnS powder causes the sintered body to deteriorate in strength. And strengthening elements such as Cu, Ni, Mo, etc. must be additionally contained. If MnS powder is contained, the dimensional change rate at the time of sintering will change. Therefore, basic data is prepared according to the MnS powder content. At the same time, a unique problem arises with the use of MnS powder, such as having to prepare a dedicated mold.

Therefore, in order to improve the problems inherent to the use of MnS powder, the inventors of the present invention do not include MnS as a powder, but rather add it in a solid solution state in the iron powder as the main component. We also wondered if a similar machinability improvement effect could be obtained by this method, and conducted research from this perspective. Further, in other experiments, the inventors of the present invention showed that the machinability when applied to the turning process and the drilling process may differ depending on the type of the machinability improving component mixed in the mixed powder. Since I knew that, I also examined from that perspective.

First, in FIG. 9, Fe-2% Cu-0.5% C
The dry drilling test result (VL diagram) of a sintered material using a mixed powder having a basic composition of (Kobe Steel Co., Ltd., trade name "Atmel 300M") is shown. As is clear from this figure, the material containing 0.1% gerenic powder has a shorter tool life in drilling a high-speed drill than the additive-free material. This is because the cutting mechanism is different between turning and drilling, increasing the peripheral speed of the tool in drilling, making it difficult for the protective film (bererk) of Gerenite to adhere to the HSS tool, and the inclusion of Gerenite as an inclusion. It can be considered that it has a positive effect. On the other hand, 0.5%
The MnS powder added material shows a remarkable improvement effect even with high-speed drilling, but the above-mentioned problems occur.

In FIG. 10, iron powder containing Mn and S in a solid solution state (Mn.S prealloy type iron powder: composition is shown in Table 8) was used, and 0.1% by weight of gerenicite was added thereto. The results of a drilling test of a sintered body using the mixed powder contained as a raw material are shown. By using Mn.S prealloy type iron powder as a base iron powder, 0.5% is obtained.
It can be seen that it is possible to secure substantially the same drill piercing property as the sintered body using the mixed powder containing the MnS powder. With this method, MnS powder can be used without causing the above-mentioned problems caused by using MnS powder.
It becomes possible to obtain a machinability improving effect comparable to that containing S powder.

[0061]

[Table 8]

In this case, regarding the S content contained in the iron powder, if the S content is less than 0.15% by weight, the machinability improving effect is poor, and if it exceeds 0.5% by weight, the compressibility is remarkably reduced. The S content in the powder should be in the range of 0.15-0.5% by weight. On the other hand, Mn in the iron powder does not contribute to the improvement of the machinability by itself, but is contained in the iron powder.
Is an element that fixes desaturation to prevent desulfurization during sintering and effectively exerts the machinability improving effect of S. Therefore, its content rate is
It also depends on the relationship with the S content or the degree of desulfurization that occurs during sintering.

That is, when the sintering is performed in a hydrogen-containing atmosphere gas such as AX gas (ammonia decomposition gas: H ₂ = 75%, N ₂ = 25%) or butane modification gas, the desulfurization reaction (H ₂ + S → H ₂ S) progresses, Mn is required to fix S as MnS, and the fixing effect is S
It is effectively exhibited by containing Mn in a chemical equivalent amount or more with respect to the amount. However, if the Mn content exceeds the chemical equivalent and the Mn content becomes excessively high, MnO is produced in the iron powder manufacturing process, which adversely affects the compressibility. In order to avoid such obstacles, the Mn content should be the chemical equivalent to the S content +
It should be kept below 0.3% by weight.

However, recently, for the purpose of improving dimensional accuracy and the like, the number of cases where sintering is performed in an N ₂ atmosphere is increasing, and in such a case, desulfurization at the time of sintering is not a problem, and S
It is not necessary to include Mn for fixing, in this case Mn
It does not matter even if you do not add.

By the way, Table 9 below shows iron powder-2% Cu-
0.3% in commercially available atomized iron powder with 0.5% C as basic composition (Kobe Steel, trade name "Atmel 300M")
Of Mn powder (average particle size: 45 μm) and 0.1% of grenenite powder (particle size: 15 μm) were added in combination, iron powder with various S content changes, and 0.1% of grenite powder (particle size: 15 μm) ), A powder compact having a compacting density of 6.9 g / cm ³ was produced,
The results of a machinability test and a desulfurization experiment of a sintered body are shown for a test material obtained by sintering at × 30 min.

The machinability test was carried out by dry type outer peripheral turning with a cutting speed V = 70 and 200 m / min and a cut t =
The life was set to 0.5 mm, the feed rate f = 0.1 mm / rev, and the flank wear of the tool VB = 0.3 mm. Also,
Since the desulfurization reaction easily proceeds in the sintering atmosphere containing hydrogen gas as described above, the surface of the sintered product was chemically analyzed and S added.
When the reduction rate from (including the calculated value) was 4% or more, it was determined that there was desulfurization. AX in the table means the ammonia decomposition gas used as the sintering atmosphere gas (H ₂ = 75%, N _2
2 = 25%).

[0067]

[Table 9]

In Table 9, except for Reference Examples 21 and 22,
The MnS powder additive material and the S-containing iron powder material are desulfurized by sintering in a hydrogen-containing atmosphere, but no desulfurization is observed in an N ₂ atmosphere. From this, it is understood that it is not necessary to fix S by Mn when sintering is performed in an N ₂ atmosphere. In addition, the tool life equivalent to or higher than that of Reference Example 20 in which 0.3% MnS powder was added was set to low speed (70 m / mi).
n) In order to secure by turning, the amount of S dissolved in iron powder should be 0.15% or more. As the amount of S increases, the tool life ratio during low-speed cutting is particularly remarkable. You can confirm that it will be improved. The tool life ratio of Reference Example 24 is good, but the compressibility of the powder is adversely affected.
The content is preferably 0.5% or less, which does not cause such defects.

Next, Table 10 shows the same test method as in Table 9 above.
The results of studying desulfurization during sintering in an atmosphere containing hydrogen using anolsite are shown. Mn / S in the table
Means how many times the amount of Mn in the iron powder corresponds to the amount of S, and Mn / S for fixing all S in the iron powder as MnS is 1.71, so Mn on that basis
The excess or deficiency of the amount is represented by (%).

[0070]

[Table 10]

As is clear from Table 10, Mn / S
Of less than 1.71 causes desulfurization during sintering. On the other hand, an excessive amount of Mn is mostly MnO in the iron powder manufacturing process, and it can be seen that there is a tendency to increase the tool life ratio particularly in high-speed turning.
If it exceeds 3%, the compressibility of the iron powder will deteriorate, so even if it is added excessively, its amount should be suppressed to (1.71 × S amount + 0.3%) or less.

[0072]

The present invention is constituted as described above, and by using an anolsite powder and / or a grenite powder having an average particle size of 50 μm or less, more preferably 10 μm or less as a machinability improving component, Iron for powder metallurgy that can easily adjust the dimensional change rate during sintering without deteriorating the strength of the sintered body and has excellent machinability not only for turning but also for drilling. It has been possible to provide a system mixed powder.

In addition to the anolsite powder and / or the grenenite powder, the Mn having the specified average particle size is specified.
When S powder is used together, a sintered body having excellent machinability not only in high speed cutting but also in low speed cutting can be obtained. Furthermore, instead of using MnS powder together, a predetermined amount of base iron powder is used. If the iron powder containing Mn and S in a solid solution state is used, it is possible to avoid the problem caused by using the MnS powder. Further, in the present invention, graphite powder and / or metal powder for improving physical properties, which are preferably blended with an iron-based powder for ordinary powder metallurgy, or a lubricant or an anti-segregation agent is blended to effectively utilize those characteristics. Is also possible.

By setting the sintering temperature after compaction molding of these mixed powders in the range of 650 to 1500 ° C., the characteristics of the iron-based mixed powder for powder metallurgy described above are effectively utilized to the maximum and stable. With the above dimensional accuracy, it becomes possible to efficiently obtain a sintered product having excellent strength and machinability.

[Brief description of drawings]

FIG. 1 is a graph showing the results of investigating the relationship between the density of compacts and the rate of change in outer diameter during sintering (1120 ° C.) when the content of the grenenite powder in the mixed powder was changed.

FIG. 2 is a graph showing the results of examining the relationship between the density of a compact and the rate of change in outer diameter at the time of sintering (1250 ° C.) when the content of the grenenite powder in the mixed powder was changed.

FIG. 3 is a graph showing the results of examining the relationship between the compact density and the outer diameter change rate during sintering (1120 ° C.) when the content of the anolsite powder in the mixed powder was changed.

FIG. 4 is a graph showing the results of examining the relationship between the compact density and the outer diameter change rate during sintering (1250 ° C.) when the content of the anolsite powder in the mixed powder was changed.

FIG. 5 is a graph showing a sintering temperature and an outside diameter dimensional change rate during sintering of a material without addition of a gehlenite powder and a material with addition of 0.3%.

FIG. 6 is a graph showing mixed powders having different contents of gehlenite powder.
It is a graph which shows the behavior of dimensional change at the time of sintering and cooling.

FIG. 7 is a graph showing the behavior of dimensional changes during sintering and cooling of mixed powders having different contents of anolyte powder.

FIG. 8 is a CaO—Al ₂ O ₃ —SiO ₂ system phase diagram.

FIG. 9 is a graph showing the relationship between the cutting speed and the tool life of the material added with a grenite powder, the material added with a MnS powder, and the material without an additive.

FIG. 10 is a graph showing the relationship between cutting speed and tool life when Mn.S prealloyed iron powder is used as the iron powder and a grenite powder is contained.

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B22F 1/00

Claims (7)

(57) [Claims] 1. An iron-based mixed powder for powder metallurgy, which comprises mainly iron powder and has an anorthite phase and / or a grenenite phase and an average particle size of 50 μm or less CaO—Al ₂
Add powder of O ₃ —SiO ₂ composite oxide to 0.02 to 0.3
An iron-based mixed powder for powder metallurgy, characterized in that the iron-based mixed powder is contained in a weight percentage. 2. The iron-based mixed powder for powder metallurgy according to claim 1, wherein the composite oxide has an average particle diameter of 12 μm or less. 3. The iron powder has an S content of 0.15 to 0.5% by weight, and an Mn content of the iron powder is a chemical equivalent of the Mn amount +
The iron-based mixed powder for powder metallurgy according to claim 1 or 2, which is 0.3% by weight or less. 4. The iron-based mixed powder for powder metallurgy according to claim 1, which contains 0.1 to 0.7% by weight of MnS powder having an average particle diameter of 65 μm or less as another component. 5. The iron-based mixed powder for powder metallurgy according to claim 1, further comprising graphite powder and / or metal powder for improving physical properties as other components. 6. The iron-based mixed powder for powder metallurgy according to claim 1, wherein a lubricant or an anti-segregation agent is added as another component. 7. A compacting the powder metallurgical iron-based mixed powder according to any of claims 1 to 6, 650-1500
A method for producing a sintered body, which comprises sintering at ℃.