JP2003268401A - Method for manufacturing sintered member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a sintered member, which causes little dimensional change of a sintered compact, and reduces dimensional variation among the sintered compacts due to difference among lots of a raw material powder. <P>SOLUTION: The method for manufacturing the sintered member has a raw material powder preparation step of blending a carbon powder which superfluously contains a amount corrected by calculation for an amount of at least oxygen contained in the raw iron powder, to the raw iron powder. The above preparation step can include blending the carbon powder which superfluously contains a amount corrected by calculation for an amount of oxygen and further carbon contained in the raw iron powder, to the raw iron powder. In addition, the method for manufacturing the sintered member is characterized by sintering the member to be sintered, at a calculated temperature according to a relational expression between the amount of oxygen contained in the raw iron powder and the sintering temperature of the sintered compact. Furthermore, the method for manufacturing the sintered member is characterized by sintering the member to be sintered, for a duration of time a relational expression between the amount of oxygen in the raw iron powder and the sintering time of the sintered compact. The method for manufacturing the sintered member can include a dimension correction step and a heat treatment step after the above sintering step, as needed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a sintered member, and more particularly, to a sintered member which has high dimensional accuracy and reduces fluctuations in dimensions between lots of raw iron powder. It relates to a manufacturing method.

[0002]

2. Description of the Related Art A sintered member is made by forming raw material powder into a powder compact, and sintering the powder compact at a temperature below the melting point to form a sintered compact. It is manufactured by subjecting the sintered body to dimensional correction and heat treatment. Since the size of a sintered body obtained by sintering a powder compact changes due to expansion or contraction that occurs during sintering, it is generally performed in advance to allow for the amount of dimensional change to correct the die size. .
However, the dimensional change amount of the sintered body varies due to various factors during the manufacturing process, so that a dimensional correction process or finishing process is further required, which causes a cost increase.

The dimensional variation of the sintered body in industrial production is
There are intra-lot and intra-lot variations. Although the intra-lot variation is relatively small, the dimensional variation between lots is often greater than the intra-lot variation, which greatly reduces the dimensional accuracy of the sintered member.

Factors that affect the dimensional change of the sintered body during the manufacturing process include the amount of fine powder of the raw material powder, the composition (particularly the amount of carbon), the compacting density, the sintering temperature or the sintering time.

It is well known that the amount of fine powder in the raw iron powder is one of the factors that change the amount of shrinkage in the sintering process. For example, in Japanese Patent Laid-Open No. 4-210402,
Disclosed is a method for manufacturing a sintered member, which reduces the dimensional change during sintering and improves the dimensional accuracy of the sintered body by adjusting the particle size of the raw iron powder. That is, the average particle size 4
A raw material powder in which iron coarse powder of 0 to 200 μm and iron fine powder having an average particle diameter of 20 μm or less are mixed by 5 to 30% by weight is used.

[0006] Here, it is necessary to control the amount of fine powder within a certain value range regardless of the production lot of the raw iron powder. For this purpose, there arises a problem that the obtained raw material powder must be classified by some method and blended again, and it is also necessary to hold a considerable amount of inventory.

The amount of dimensional change during sintering varies depending on the amount of carbon added. Usually, in order to improve the mechanical properties of the sintered member, a certain amount of carbon is mixed with the raw iron powder to obtain the raw powder. However, on the other hand, the raw material iron powder contains oxygen as an impurity, and a part of this blended carbon is consumed to reduce the iron powder during sintering.
Therefore, the amount of carbon in the sintered member varies depending on the amount of oxygen contained in the raw iron powder, and as a result, the size of the sintered member varies. The raw iron powder has a process of removing oxygen in its manufacturing process, but the amount of oxygen varies greatly depending on the manufacturing lot. However, heretofore, sufficient consideration has not been given to the fluctuation of the oxygen content in the raw iron powder.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and the dimensional change of the sintered member is small, and the dimensional variation of the sintered member due to the lot of raw material powder is reduced. The present invention is intended to provide a method for manufacturing a sintered member.

[0009]

A method for producing a sintered member according to the present invention comprises a raw material powder preparation step of blending at least raw material iron powder and carbon powder to prepare a raw material powder, and molding the raw material powder. In a method for manufacturing a sintered member, which comprises a forming step of forming a powder compact and a sintering step of sintering the powder compact to form a sintered body, the raw material powder preparing step comprises:
It is characterized in that it is a step of blending carbon powder to which a carbon powder correction amount calculated from at least the oxygen amount contained in the raw iron powder is added.

The raw material powder preparation step is a step of blending carbon powder to which a carbon powder correction amount calculated from the oxygen amount and carbon amount contained in the raw iron powder is added.

The method for producing a sintered member according to the present invention comprises a raw material powder preparation step of blending at least raw material iron powder and carbon powder to prepare a raw material powder, and molding the raw material powder to form a powder compact. In a method of manufacturing a sintered member, which comprises a forming step and a sintering step of sintering a powder formed body into a sintered body, the sintering step includes the amount of oxygen contained in the raw iron powder and the sintering member. It is characterized in that it is a step of sintering at a sintering temperature adjusted by a correction temperature calculated from a relational expression with the sintering temperature.

Further, the method for producing a sintered member according to the present invention comprises a raw material powder preparation step of blending at least raw material iron powder and carbon powder to prepare a raw material powder, and molding the raw material powder to obtain a powder compact. In a method for manufacturing a sintered member, which comprises a forming step of forming and a sintering step of sintering a powder compact into a sintered body, the sintering step includes the amount of oxygen contained in the raw iron powder and the sintering. It is characterized in that it is a step of sintering for a sintering time adjusted by a correction time calculated from a relational expression with the sintering time of the member.

In the method for manufacturing a sintered member according to the present invention, a post-treatment process such as a dimension correcting process or a heat treatment process can be provided after the sintering process, if necessary.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION (Adjustment by Amount of Added Carbon) The method for producing a sintered member according to the present invention is a method in which a carbon powder as a raw material is added with a carbon powder correction amount calculated from at least the oxygen amount contained in the raw iron powder. It is characterized by having a raw material powder preparation step of blending with iron powder.

Further, in the raw material powder preparing step, a carbon powder correction amount calculated from the oxygen amount of the raw iron powder and the carbon amount can be calculated and blended into the raw iron powder.

The raw iron powder can be produced by a method such as a direct reduction method or an atomizing method. The particle size distribution of the iron powder is not particularly limited as long as it is usually used for producing a sintered body, but the iron coarse powder is about 20 to 200 μm and 45 μm.
It is desirable to contain 5 to 20% by weight of the following (325 mesh) fine iron powder. When the iron coarse content is 200 μm or more, a high density of the sintered body cannot be obtained. In addition, 20% by weight of iron fine powder
If the above content is included, the density becomes high, but it is not suitable because the dimensional change after sintering is large.

The oxygen content of the raw iron powder is "JPMAP05-
1992 Method for determination of total oxygen content of metal powder by reduction extraction method "
It is preferable to carry out. A carbon powder correction amount is calculated from the obtained oxygen amount, blended with the raw iron powder, and mixed to obtain a raw powder.

The relationship between the amount of carbon and the rate of dimensional change depends on the alloy composition, particle size distribution, powder shape, etc. of the raw iron powder used. Therefore, it is desirable to previously determine the relationship between the carbon content and the dimensional change rate of the raw iron powder to be used by experiments.

An example thereof is shown in FIG. The raw iron powder was Fe-3% Cr-0.3% Mo- obtained by the water atomizing method.
0.3% V powder. In FIG. 1, the amount of carbon in the sintered member was set to three levels of 0.8, 1.0 and 1.2%. G in the figure
-D (◆) indicates the dimensional change rate of the powder compact with respect to the molding die. Similarly, SG (■) is a sintered body for the powder compact, SD (Δ) is a sintered body for the molding die, and H is H.
-S (x) is H- of the sintered body after heat treatment of the sintered body.
D (*) indicates the dimensional change rate of the sintered member after heat treatment with respect to the mold. For example, when the amount of carbon is 0.8%, the powder compact expands by about 0.26% with respect to the mold, and the sintered compact yields 0% of the powder compact. By contracting 0.09% and performing heat treatment, the sintered member is expanded 0.04% from the sintered body. It can be seen that, based on the molding die, the sintered member after the heat treatment expanded by about 0.2% (the dimension was not corrected after sintering). Further, since the rate of change in size increases in proportion to the increase in the amount of carbon, it is necessary to keep the amount of carbon in the sintered member constant in order to suppress the variation in size.

Since the amount of carbon in the sintered member depends on the amount of oxygen in the raw iron powder, the amount of oxygen in the raw iron powder can be grasped before adjusting the raw powder to keep the carbon amount after sintering constant. The carbon amount may be corrected so that

From FIG. 1, the relationship between the amount of carbon in the sintered member and the dimensional change rate of the sintered member with respect to the mold is as follows: dimensional change rate% = 0.306 × carbon amount% -0.319 (1) It was That is, when the oxygen content of the raw iron powder is 0, if 1.042% of carbon is blended, the dimensional change rate after sintering becomes 0, and the carbon content of the sintered member becomes 1.042%. is there. However, in reality, since the raw iron powder contains oxygen, a part of the blended carbon is C + O → CO during sintering.
The carbon content in the sintered member is changed by that amount, resulting in the dimensional change rate represented by the equation (1).

The mass ratio of carbon to oxygen is 3: 4. Therefore, if the carbon content is increased by 3/4 × (oxygen content%) with respect to the target carbon content of the sintered member, the oxygen in the raw material iron will be reduced and consumed by the increased carbon content, and therefore the target value is calculated. It is possible to obtain a sintered body having a carbon amount, and it is possible to eliminate the dimensional variation of the sintered member due to the variation of the oxygen amount in the raw iron powder.

The amount of added carbon can be roughly determined by the following equation (2).

Target carbon amount (%) = − 3/4 × oxygen amount (%) + added carbon amount (%) (2) As the added carbon, commonly used natural graphite or artificial graphite can be used. The particle size of graphite is not particularly limited, but an average particle size of several μm to several tens of μm is suitable.

The raw iron powder and the added carbon may be mixed by a usual method. A lubricant such as zinc stearate or amide wax may be added during mixing.
Further, segregation prevention treatment may be performed with a binder or the like.
The lubricant may be applied to the mold without being mixed with the raw material powder.

The raw material powder obtained above is filled in a molding die and compression-molded. Molding conditions are not particularly limited, but in the case of a structural member by uniaxial compression molding, the surface pressure is 400 to 800M.
It is preferable to carry out at Pa. If the surface pressure is 400 MPa or less, a sufficient density of the sintered body cannot be obtained, and if it is 800 MPa or more, equipment restrictions may occur. However, this is not the case when the density needs to be further increased depending on the application.

Sintering is preferably carried out in a vacuum atmosphere, a protective atmosphere, or a non-carburizing reducing atmosphere. In the case of a carburizing atmosphere, the carbon content of the sintered member may fluctuate due to variations in the atmosphere, and the effect may be impaired.
In the case of vacuum sintering, the degree of vacuum before heating is 10 ^-3 torr.
In the following, an inert gas may be introduced as necessary in the dewaxing sintering process. Sintering temperature is generally 1100-
At 1300 ° C, the holding time is 10-60 minutes. When the sintering temperature is 1100 ° C. or lower, the growth of the neck between the sintered powders is slow and it is difficult to obtain strength. If the temperature is 1300 ° C. or higher, the sintering equipment will be restricted. Sintering retention time is 1
If the time is less than 0 minutes, the growth of the neck is insufficient, so that it is difficult to obtain the strength. Further, there is no particular restriction on the temperature rising rate at the time of sintering, but it is important to stabilize the conditions because the temperature rising rate may greatly affect the dimensional change depending on the component of the iron fine powder. . Further, the cooling condition is generally around 20 ° C./min, but it can be freely selected depending on the productivity and the need for structure control.

In order to suppress variations in sintering time,
It is desirable to avoid stacking by using a continuous furnace such as a mesh belt rather than a batch type vacuum sintering furnace. This is because in the high temperature range where sintering is performed, radiation is dominant in heat transfer, so if stacking is performed, there will be a delay in temperature rise to the internal work, and as a result, sintering will occur depending on the work loading position. This is because there is a difference in time.

After sintering, dimensional correction can be performed if necessary. The dimensional correction can be performed by a usual method and there is no particular limitation.

If desired, heat treatment may be performed after sintering to improve mechanical properties and the like. As a heat treatment method, general hardening treatment such as induction hardening tempering, carburizing quenching tempering, bright quenching tempering, or nitriding treatment can be used, and the conditions are not particularly limited. However, for carburizing and quenching, stabilizing the carbon potential is important for ensuring dimensional accuracy.

As the post-treatment, steam treatment for the purpose of sealing or rust prevention, shot peening for the purpose of applying residual stress, etc. can be applied.

The raw iron powder may contain carbon depending on the method of producing the powder. Particularly in the case of atomized powder produced by a part of vacuum reduction, 0.001 to 0.1%
It contains some carbon. Therefore, it is desirable to consider the amount of carbon originally contained in the raw iron powder. That is, in order to further reduce the dimensional variation of the sintered member depending on the lot of the raw iron powder, the amount of oxygen of each lot of the raw iron powder is analyzed at the same time as the amount of oxygen of each lot, and the amount of added carbon is adjusted. It is desirable to do. In this case, the added carbon amount can be roughly modified from the equation (2) to obtain the added carbon amount% = target carbon amount% + 3/4 oxygen amount% -analytical carbon amount%. Here, the amount of analyzed carbon is the amount of carbon contained in the raw iron powder. (Adjustment by Sintering Temperature) The method for manufacturing a sintered member according to the present invention is a method of sintering a sintered member from a relational expression between the amount of oxygen contained in the raw iron powder and the sintering temperature of the sintered member. Characterized by sintering at a temperature.

That is, the dimensional variation of the sintered body due to the amount of added carbon consumed by oxygen in the raw iron powder, the amount of added carbon and the sintering time, that is, the productivity is constant,
This is a method of suppressing it by adjusting the sintering temperature.
More specifically, by knowing the relationship between the oxygen content of the raw iron powder and the sintering temperature, it is possible to obtain the sintering temperature for each lot that corrects the deviation of the dimensional change due to the fluctuation of oxygen and perform the sintering. It is intended to reduce the dimensional variation of the sintered member.

An example of the relationship between the dimensional change rate of the sintered member and the sintering temperature is shown in FIG. FIG. 2 is a sintered member with respect to the sintering temperature and the mold size when the same raw iron powder as in FIG. 1 is used to powder-form a raw material powder to which a certain amount of carbon has been added, and further sintered and heat-treated. It shows the relationship with the dimensional change rate of.

The sintering temperature is 10 up to 1230 to 1270 ° C.
It was set to 5 levels in increments of ° C. Sintering retention time is all 30 ± 0.
It was 5 minutes. As can be seen from FIG. 2, the sintering temperature is 12
At 30 ° C, the dimensional change rate is -0.15%.
It was -0.37% at 0 degreeC. That is, the dimensional change rate increases to the negative side in proportion to the increase of the sintering temperature. From this FIG. 2, the relational expression of dimensional change rate = −0.0054 × (sintering temperature ° C.) + 6.454 (3) was obtained.

Since a certain amount of carbon is added to the raw iron powder, as already mentioned, the dimensional change due to the amount of oxygen in the raw iron powder is as follows.

Assuming that the dimensional change rate of the sintered member having a carbon amount C ₁ (%) after sintering is X ₁ (%), from the equation (1), X ₁ =
The 0.306 × C ₁ -0.319. If the median amount of carbon after sintering is C ₀ (%), the dimensional change rate X ₀
(%) Can be expressed as X ₀ = 0.306 × C ₀ -0.319.

Since the dimensional change rate is the dimensional change rate with respect to the molding die, the dimensional change rate between the sintered bodies, that is, the variation, is based on the dimensional change rate of the sintered member including the median carbon content. It may be considered that ΔX (%) = X ₁ −X ₀ . That is, ΔX = 0.306 × (C ₁ −C ₀ ). C ₁
-C ₀ can be calculated from the formula (2) as follows: C ₁ -C ₀ = −3 / 4 × (O ₁ −O
₀ ). Here, O ₁ is the amount of oxygen in the raw iron powder when the carbon content of the sintered member is C ₁ . Similarly, O ₀ is the amount of oxygen in the raw iron powder when the carbon content of the sintered member reaches C ₀ .

Oxygen amount deviation ΔO depending on the lot of raw iron powder
Assuming that (%) is ΔO = O ₁ −O ₀ , the dimensional change rate ΔX (%) (variation) due to the oxygen content deviation of the raw iron powder lot
Can be represented by ΔX = 0.306 × (−3 / 4 × ΔO).

On the other hand, the dimensional change rate depending on the sintering temperature is
Since it is given by the formula (3), when the sintering temperature is T ₁ (° C.) (the oxygen amount in the raw iron powder is O ₁ , that is, the sintering temperature when the carbon amount of the sintered member is C ₁ ) The dimensional change rate Y ₁ (%) is
Y ₁ = −0.0054 × T ₁ +6.454, and the sintering reference temperature is T ₀ (° C.) (the amount of oxygen in the raw iron powder is O ₀ , that is, the amount of carbon in the sintered member is C). If the sintering reference temperature is ₀ ), the dimensional change rate Y at the sintering reference temperature Y
₀ (%) can be expressed as Y ₀ = −0.0054 × T ₀ +6.454.

Therefore, the temperature deviation from the sintering reference temperature ΔT
If the rate of dimensional change due to (℃) is ΔY (%), then ΔY =
Y ₀ −Y ₁ = −0.0054 × (T ₀ −T ₁ ) = − 0.00
54 × ΔT.

In order to reduce the dimensional variation of the sintered member, the deviation ΔX of the dimensional change rate of the sintered member due to the fluctuation of the oxygen content in the raw iron powder is defined as the deviation of the dimensional change rate due to the adjustment of the sintering temperature. It may be canceled by ΔY and ΔX + ΔY = 0. That is, 0.306 × (−3 / 4 × ΔO) + (− 0.0054 × ΔT) = 0 (4).

Since the deviation ΔO (%) of the oxygen amount is obtained from each oxygen analysis value of the raw iron powder, the temperature deviation (correction temperature) ΔT (° C.) from the sintering reference temperature is obtained from the equation (4). be able to.

As described above, the sintering temperature of the raw material iron powder is determined for each lot, and in principle, the sintering temperature is kept constant for each lot, so that the dimensional variation between the lots of the sintered member is determined. Can be reduced. (Adjustment by Sintering Time) In the method for manufacturing a sintered member according to the present invention, the sintered member is sintered by a relational expression between the oxygen content of the raw iron powder and the sintering time of the sintered member. It is characterized by being sintered in time.

That is, the dimensional variation of the sintered member due to the added carbon amount consumed by oxygen in the raw iron powder is suppressed by adjusting the sintering time while keeping the added carbon amount and the sintering temperature constant. is there. More specifically,
By knowing the relationship between the oxygen content of the raw iron powder and the sintering time, the sintering time for which the variation of the dimensional change rate of the sintered member is set to 0 is obtained for each lot, and the sintering is performed. It is intended to reduce the dimensional variation.

An example of the relationship between the dimensional change rate of the sintered member and the sintering time is shown in FIG. 3 is a raw material powder similar to that shown in FIG. 1, to which a certain amount of carbon is added and powder-molded as a raw material powder, and the powder compact is sintered and heat-treated. With respect to the dimensional change rate of the sintered member. The sintering time was set to three levels of 20, 30, and 40/40. The sintering temperatures were all 1250 ± 2 ° C.

As can be seen from FIG. 3, at a sintering temperature of 20 minutes, the dimensional change rate is −0.14%, and at 40 minutes, it is −0.
It was 26%. That is, the rate of dimensional change increases to the negative side in proportion to the extension of the sintering time. From FIG. 3, the relational expression of dimensional change rate% = − 0.0060 × (sintering time min) −0.023 (5) was obtained.

From the same idea as in the case of the sintering temperature, the equation (6) can be derived by using the equations (1), (2) and (5).

0.306 × (−3 / 4 × ΔO) + (− 0.0060 × Δt) = 0 (6) The deviation ΔO (%) of the oxygen amount is each oxygen analysis value of the raw iron powder. Therefore, the time deviation (correction time) Δt (min) from the sintering reference time can be obtained from the equation (6). Here, the time deviation Δt (min) = t ₀ −t ₁ , where t ₀ is the sintering reference time when the oxygen content in the raw iron powder is O ₀ , that is, when the carbon content of the sintered member is C _0. , T ₁ are the sintering times when the amount of oxygen in the raw iron powder is O ₁ , that is, the amount of carbon in the sintered member is C ₁ .

As described above, the sintering time for each lot of the raw material iron powder is determined, and in principle, the sintering time is set to be constant for each lot, so that the dimension of the sintered member between the lots is determined. Variations can be reduced.

It should be noted that, as the above-mentioned method of adjusting by the amount of added carbon, adjusting by the sintering temperature, and adjusting by the sintering time, it is advisable to select or combine methods having less restrictions in the process. INDUSTRIAL APPLICABILITY The present invention is effective in reducing the dimensional fluctuation of the sintered member due to the fluctuation of the oxygen content of the raw material powder. Various factors of dimensional variation are known. When a combination of means for canceling out these fluctuation factors is used in the same manner as in the present invention, it is expected that the dimensional variation of the sintered member is further reduced.

[0052]

EXAMPLES The present invention will be described in more detail below with reference to examples. (Example 1) Fe-3.0% Cr-0.
3% Mo-0.3% V (made by Kawasaki Steel), iron coarse powder particle size 45 to 250 μm, particle size 45 μm (325 mesh)
20 lots of raw material iron powder containing 9.8 to 19.3% by weight of the following iron fine powder were prepared.

First, the oxygen content of each lot is calculated as "JPMA
P05-1992 reduction extraction method for determination of total oxygen content of metal powder ”. The average value (the same value as the median value) of the oxygen content of all 20 lots was 0.165%. Since the carbon content of the sintered member is obtained by the equation (2),
If 1.0% graphite is added to the raw iron powder, this 2
The average carbon content after sintering of 0 lot is 0.87%. Therefore, here, the carbon content to be added is corrected and added in accordance with the oxygen content of each lot of the raw iron powder so that the target carbon content after sintering will be 0.87%. That is, the added carbon amount (X)% = 0.87 + 3/4 (oxygen amount%) (7).

Out of the 20 lots of raw iron powder, the oxygen amount of Lot No. 1 having the smallest oxygen content was 0.09.
Substituting this into the above relational expression (7) between the amount of added carbon and the amount of oxygen gives X = 0.94%.

The obtained amount of added carbon was adjusted to an average particle size of about 5 μm.
Natural graphite (manufactured by Nippon Graphite Co., Ltd.) was weighed and blended with the raw iron powder, and mixed with a V-type mixer for 30 minutes to obtain raw powder. Ten samples of about 22 g were arbitrarily sampled from this raw material powder, and made of a cemented carbide mold (inner diameter: 25.2305 mm,
(Thickness: 45 mm), and pressure molding was performed at a surface pressure of 900 MPa. At this time, a suspension of zinc stearate in ethyl alcohol was applied to the inner surface of the mold and naturally dried to obtain a lubricant.

The powder compact after pressure molding has a size of 6 ± 0.1 m
It was m thick.

Among the 20 lots of the raw iron powder, the lot number 2 with the highest oxygen content had an oxygen content of 0.25%.
When calculated in the same manner as above, the amount of added carbon is 1.0575%, so an equivalent amount of graphite was weighed and added to the raw iron powder.
Then, mixing and pressure molding were carried out in the same manner as above to obtain 10 powder compacts. Further, the remaining 18 raw iron powder lots were similarly processed to obtain a total of 200 powder compacts.

Next, the 200 powder compacts obtained above were vacuumed at room temperature to a degree of vacuum of 10 ^-3 torr or less (10 ^-4 torr).
In a vacuum sintering furnace at a temperature of 1250 ± 1 ° C. for 30 ± 0.5 minutes. The heating rate was 20 ° C./min. After sintering and holding, the temperature was cooled from 1250 ° C. to 300 ° C. at an average cooling rate of 30 ° C./min by controlling a nitrogen gas fan. Then, it was cooled in air to obtain 200 sintered bodies.

The obtained sintered body was further subjected to soaking treatment at 850 ° C. for 30 minutes in a vacuum quenching furnace and put into quenching oil at 80 ° C. for quenching treatment. At this time, the rate of temperature increase from room temperature to soaking temperature was 15 ° C./min. Subsequently, tempering treatment was performed at 180 ° C. for 60 minutes in an atmospheric furnace to obtain a sintered member.

The diameter of each of the 200 sintered members thus obtained was measured at 2 points using a laser scanning micrometer in a thermostatic chamber at 20 ± 0.5 ° C., and the average value was calculated. .

The dimensional variation of these sintered members was 17.8 μm in the range from the maximum value and the minimum value of the obtained 200 sintered members. The carbon content of the 200 sintered bodies was 0.85 to 0.88%. (Comparative Example 1) From the same 20 lots of raw material iron powder as in Example 1, lot number 1 with the minimum oxygen content and lot number 2 with the same oxygen content as in Example 1 were used. 1.0% graphite was added. That is, this is a case where the correction of the added carbon amount based on the oxygen amount of the raw iron powder is not performed. The powder molding method, sintering, and heat treatment were performed in the same manner as in Example 1 to obtain 20 sintered members.

The diameter dimension of the sintered member was measured with a laser micrometer as in Example 1. When the maximum value and the minimum value were obtained from the data of 20 pieces, the dimensional variation of the sintered member was 24.3 μm. The carbon content of the 20 sintered bodies was 0.81 to 0.93%. (Example 2) From lots of raw iron powder of 20 lots similar to Example 1, lot number 1 of minimum oxygen amount and lot number 2 of maximum oxygen amount similar to those of Example 1 were used. A raw material powder was prepared by adding 1.0% graphite. Mixing and powder molding were performed in the same manner as in Example 1 and 10
Individual powder compacts were obtained.

The sintering temperature deviation (correction temperature) was obtained from the oxygen content of each lot using the equation (4), and the sintering temperature for each lot was determined. The sintering time was 30 ± 0.5 minutes in all cases.

The median oxygen amount in the lot of Example 20 was 0.165%. The sintering reference temperature T ₀ was 1250 ° C.

The oxygen deviation ΔO of lot number 1 is 0.09.
% -0.165% =-0.075%. Therefore,
Since the corrected temperature (temperature deviation value) ΔT of lot number 1 is calculated as 1250−T ₁ = + 3.2 ° C. from the equation (4), the sintering temperature T ₁ of lot number ₁ is 1247 ° C. And it is sufficient. Further, in lot number 2, the oxygen deviation is +0.
Since it is 075%, it is sufficient to perform the same calculation and sinter at 1253 ° C.

In this way, 10 sintered bodies were obtained in lot number 1 and 10 sintered bodies in lot number 2 as in Example 1. The obtained sintered body was subjected to the same heat treatment as in Example 1 to obtain a sintered member.

The dimensional variation of these sintered members is 1 from the maximum value and the minimum value of the obtained 20 sintered members.
It was 8.2 μm. (Example 3) From 20 lots of raw iron powder similar to that of Example 1, 1.0% graphite was added to each lot for all lots similar to Example 1 to adjust the raw material powder. did.
Mixing and powder molding were performed in the same manner as in Example 1 and 1 for each lot.
Zero powder compacts were obtained.

The sintering time deviation (correction time) was determined from the oxygen content of each lot using the equation (5), and the sintering time for each lot was determined. The sintering temperature was 1250 ± 1 ° C in all cases.

The median amount of oxygen in 20 lots of the raw material iron powder of this example was 0.165%. The sintering reference time t ₀ was set to 30 minutes.

The oxygen deviation of lot number 1 is 0.09%-
It becomes 0.165% =-0.075%. Therefore, (6)
From the formula, the correction time (time deviation value) Δt of this lot is 3
0-t ₁ = + 2.9 minutes, and the sintering time may be 27.1 minutes. Also, with lot number 2, the oxygen deviation is +
Since it is 0.075%, it is sufficient to perform the same calculation and sinter in 32.9 minutes.

In this way, as in Example 1, 10 sintered bodies were obtained from lot number 1 and 10 sintered bodies from lot number 2. The obtained sintered body was subjected to the same heat treatment as in Example 1 to obtain a sintered member.

The dimensional variation of these sintered members is 1 from the maximum value and the minimum value of the obtained 20 sintered members.
It was 8.5 μm.

In summary, in the method for manufacturing a sintered member according to the present invention, in the case of 20 lots of the raw material iron powder, a) the amount of added carbon, the sintering temperature and the sintering time were constant (comparative example). In 1), the dimensional variation of the sintered member is 2
It was 4.3 μm. B) Adjust the amount of added carbon according to the amount of oxygen in the raw iron powder,
When the sintering temperature and the sintering time are constant (Example 1)
In addition, the dimensional variation of the sintered member was 17.8 μm. C) When the sintering temperature was adjusted with the amount of added carbon and the sintering time being constant (Example 2), the dimensional variation of the sintered member was 18.2 μm. D) When the amount of added carbon and the sintering temperature were kept constant and the sintering time was adjusted (Example 3), the dimensional variation of the sintered member was 18.5 μm. As a result, it was found that the method of the present invention is extremely effective in reducing the dimensional variation of the sintered member.

[0074]

According to the method of manufacturing a sintered member of the present invention,
By knowing the oxygen content of the raw iron, the dimensional change rate of the sintered member can be predicted. Therefore, by adjusting the amount of added carbon according to the amount of oxygen in each lot, or by adjusting the sintering temperature and sintering time while keeping the amount of added carbon constant, the lot of raw material iron powder of the sintered member size can be adjusted. The variation can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a carbon content of a sintered member and a dimensional change rate between respective steps.

FIG. 2 is a diagram showing a relationship between a sintering temperature and a dimensional change rate of a sintered body with respect to a mold.

FIG. 3 is a diagram showing a relationship between a sintering time and a dimensional change rate of a sintered body with respect to a mold.

Claims (6)

[Claims] 1. A raw material powder preparation step of blending at least raw iron powder and carbon powder to prepare a raw material powder, a molding step of compacting the raw material powder to form a powder compact, and baking the powder compact. In the method for manufacturing a sintered member, which comprises a sintering step of binding the material into a sintered body, the raw material powder preparing step includes adding a carbon powder correction amount calculated from at least an oxygen amount contained in the raw iron powder. A method for manufacturing a sintered member, characterized in that it is a step of mixing carbon powder. 2. The raw material powder preparation step is a step of blending carbon powder to which a carbon powder correction amount calculated from an oxygen amount and a carbon amount contained in the raw iron powder is added.
A method for manufacturing a sintered member according to claim 1. 3. A raw material powder preparation step of blending at least raw iron powder and carbon powder to prepare a raw material powder, a molding step of compacting the raw material powder to form a powder compact, and baking the powder compact. In a method of manufacturing a sintered member, which comprises a sintering step of binding to form a sintered body, the sintering step includes a relationship between an oxygen amount contained in the raw iron powder and a sintering temperature of the sintered member. A method of manufacturing a sintered member, comprising a step of sintering at a sintering temperature adjusted by a correction temperature calculated from a formula. 4. A raw material powder preparation step of blending at least raw iron powder and carbon powder to prepare a raw material powder, a molding step of compacting the raw material powder to form a powder compact, and burning the powder compact. In a method for manufacturing a sintered member, which comprises a sintering step of binding to form a sintered body, the sintering step includes a relationship between an oxygen amount contained in the raw iron powder and a sintering time of the sintered member. A method of manufacturing a sintered member, comprising a step of sintering for a sintering time adjusted by a correction time calculated from a formula. 5. The method for manufacturing a sintered member according to claim 1, further comprising a dimension correcting step after the sintering step. 6. The method for producing a sintered member according to claim 1, further comprising a heat treatment step after the sintering step.