JPH07138611A - Production of sintered and forged product - Google Patents

Abstract

PURPOSE:To provide the process for production of the sintered and forged product which eliminates the need for reduced powder of a high cost subjected to a reduction treatment and does not require consideration for compression moldability and lubricity by abolishing green compacts and a stage for molding these green compacts. CONSTITUTION:The non-reduced ferrous powder obtd. by an atomization method is charged into the cavity 1a of a container 1 made of ceramics, by which powder aggregate having pores is obtd. This powder aggregate in the container 1 is heated and sintered in a reducing atmosphere, by which a porous sintered compact 5 is obtd. At this time, the reducing atmosphere penetrates deep into the porous sintered compact 5, by which the porous sintered compact is subjected to the reduction treatment and the oxide layer is removed. Next, a cap member 1k is mounted at the container 1 emerged from a sintering furnace to hermetically close the container 1. The hermetically closed container 1 is transferred to a forging die 6. Next, the cap member 1k is opened and the porous sintered compact 5 is dropped into a forging cavity 63 and the high- temp. porous sintered compact 5 is hot forged by the forging mold 6, by which the sintered and forged product having the high density ratio is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sintered forged product using an iron-based powder obtained by atomizing a molten metal into powder particles. The present invention can be applied to the manufacture of vehicle parts, industrial parts such as connecting rods and gears.

[0002]

2. Description of the Related Art A sintered forged product is a product obtained by forging a sintered body obtained by sintering a metal powder with a forging die with a large surface pressure, and has a significantly reduced residual porosity, which is advantageous for high strength and high toughness. Therefore, its development is being promoted in the industrial world. As such a sintered forged product, one using atomized powder obtained by spraying a molten metal as a raw material powder is known. In general, the particles of this atomized powder are covered with a relatively thick oxide layer (oxygen amount: for example, 0.4 to 0.6% by weight). This oxide layer is not preferable because it easily forms a non-sintered portion. Therefore, in the production of the conventional sintered forged product, the atomized powder reduced in order to remove the oxide layer is used.

That is, when a sintered forged product is manufactured by using atomized powder as a raw material powder, the manufacturing method is roughly classified, as shown in FIG. 15, the atomized powder obtained by reduction treatment to remove the oxide layer. And a method B for forming a sintered forged product from the reduced atomized powder. In Method A, as can be understood from FIG. 15, a raw material having a predetermined composition is used, the raw material is melted to form a molten metal, and the molten metal is atomized (sprayed) to form a fine particle powder. Is dried, the particle size is adjusted by sieving the powder to obtain a raw material powder, and the raw material powder is heated and reduced in a reducing atmosphere to remove the oxide layer. Further, since powder particles are solidified by heating during the reduction, the powder particles are crushed, and the powder is sieved again to obtain atomized powder.

Since atomized powder particles obtained by spraying the molten metal as fine particles as described above are hard, their compression moldability and lubricity are not always sufficient. Therefore, in Method B, as can be understood from FIG. 15, in order to improve compression moldability and lubricity, other powder is mixed with atomized powder in the powder mixing step to obtain a powder mixture, and the powder mixture is used as a mold. After being placed in the cavity of, the compact is pressed with a molding die to form a compact with a high density ratio, and the compact is sintered in a sintering furnace to form a sintered body with a high density ratio. The sintered body is hot forged with a forging die and post-treated to form a sintered forged product.

As described above, in the conventional manufacturing method, it is necessary to use the reduced powder whose cost is high because the oxide layer is removed by the reduction treatment, and the compacted powder having a high density ratio is obtained from the reduced powder. A sintered compact having a high density ratio is formed from the green compact, and the sintered compact is hot forged to obtain a sintered forged product having extremely few residual pores. Further, Japanese Unexamined Patent Publication No. 50-14510 uses a rotary hearth furnace having a reducing atmosphere inside and a preformed body which is a green compact formed by strong pressure by a powder molding press. Is charged into a rotary hearth furnace to heat the preformed body to about 1100 ° C in a reducing atmosphere, the heated preformed body is cooled to about 800 to 1000 ° C in a cooling furnace, and the preformed body is further cooled. A technique of hot forging with a forging die is disclosed.

[0006] In the technique according to this publication, since the preformed body which is a green compact is strongly pressed by the powder compacting press,
The density ratio is high, and especially the density ratio of the surface layer portion of the preform is high. Such a preformed body having a high density ratio is disadvantageous in permeating the reducing atmosphere deep into the preformed body and sufficiently reducing it to the deep portion. Further, in Japanese Patent Laid-Open No. 64-68406, after metal powder is vibrated and packed (density ratio of about 68%) in a ceramic container, the lower part of the container is made into a liquid phase and a solid phase by a high frequency coil in a vacuum or non-oxidizing atmosphere. Liquid phase sintering is performed by heating to the coexisting temperature range of, and the high frequency coil is further moved toward the upper part of the container in order, whereby the liquid phase sintering region is sequentially moved to obtain a sintered ingot with a density ratio of 96% or more. A technique is disclosed in which, after forming, the sintered ingot is made to have a true density by hot forging or rolling. In this case, when the vacuum is maintained in the liquid phase sintering state,
A degassing effect of gas components contained in the liquid phase can be expected, and oxygen gas and nitrogen gas remaining in the sintered ingot are reduced. In the technique according to this publication, a high density sintered ingot having a density ratio of 96% or more is obtained, and therefore liquid phase sintering is adopted. When the density ratio is high as described above, even if a reducing atmosphere is adopted as the non-oxidizing atmosphere, it is disadvantageous to permeate the reducing atmosphere deep inside the sintered ingot and to carry out the reduction treatment in the deep portion. .
Furthermore, it does not reduce at the same time as sintering. In particular, even if reducing CO gas is generated in the sintered ingot, if the atmosphere is a vacuum, it is immediately sucked and removed by the vacuum pump side, and reduction treatment at a deep portion cannot be expected.

Further, Japanese Patent Application Laid-Open No. 57-54201 discloses that
The iron-based powder compact coated with graphite is sintered, and the graphite and water in a reducing atmosphere react with each other in a water gas reaction (C + H ₂ 0 → CO + H).
_The technology intended to prevent the oxidation of the powder compact by generating ₂ ) is disclosed. In addition, JP-A-3-56602
The publication discloses a technique of spraying graphite powder immediately after a forging material made of a green compact or a sintered body is taken out of a heating furnace. This is intended to prevent oxidation of the forging material during the transfer of graphite to oxygen in the air and transfer to the forging process.

Further, in JP-A-59-182946, Fe-Cr-Co alloy powder obtained by an atomizing method is put into a graphite mold, and 300 kg at 1000 ° C in a vacuum atmosphere or a hydrogen gas atmosphere. There is disclosed a technique in which hot pressing is performed at / cm ² to perform pressure molding and sintering at the same time, followed by heat treatment to form a permanent magnet.

Japanese Patent Laid-Open No. 57-54201, mentioned above,
JP-A-3-56602, JP-A-59-18294
It is considered that the technique according to Japanese Patent Publication No. 6 also uses the reduced powder obtained by reducing and removing the oxide layer as the raw material powder, as in the conventional method shown in FIG. Further, it is considered that the density ratio of the green compact and the sintered body is high, and even if the reducing atmosphere is adopted, the reducing atmosphere is permeated deep inside the green compact and the sintered body, and the reduction treatment is performed in the deep part. It is disadvantageous to try.

Further, in Japanese Patent Laid-Open No. 53-34614,
A technique is disclosed in which a high temperature sintered body is pressed by a rotating roll in a sintering furnace to densify the surface portion of the sintered body. Even in this case, it is considered that the reduced powder obtained by removing the oxide layer by the reduction treatment is used.

[0011]

The object of the method according to claims 1 to 3 is to use unreduced iron-based powder that has not been subjected to reduction treatment as a raw material powder, and to carry out reduction treatment at high cost. It is not necessary to use powder, and the process of forming compacts and compacts, which are compacts with a high density ratio, has been eliminated, and compression moldability and lubricity are not taken into consideration. The object of the present invention is to provide a method for manufacturing a sintered forged product that can eliminate the powder mixing step for ensuring the above.

Further, the object of the method according to claims 2 and 3 is to reduce or avoid the oxidation of the porous sintered body during the transfer from the sintering reduction step to the forging step, which is advantageous for eliminating the unsintered portion. It is to provide a method for manufacturing a sintered forged product.

[0013]

[Means for Solving the Problems] Based on the above-mentioned object, the present inventor has eagerly made a development, and puts unreduced iron-based powder obtained by the atomization method and not subjected to reduction treatment into a container to obtain a density ratio. If a powder aggregate with a low density is obtained, and the powder aggregate with a low density ratio is housed in a container and heated to the sintering temperature in a reducing atmosphere to sinter, the reducing atmosphere is not only the surface layer of the powder aggregate. It penetrates deeply into the interior, and at the same time as sintering, the oxide layer can be reduced well in the deep part, and if the porous sintered body thus formed with a low density ratio is hot forged, it is not reduced. It was found that the oxide layer of iron-based powder was reduced or disappeared and a high-density sintered forged product was obtained,
The method of the present invention has been completed based on this finding.

That is, the method for producing a sintered forged product according to claim 1 uses unreduced iron-based powder obtained by the atomization method and not subjected to reduction treatment, and a container having a cavity of a predetermined shape, A step of introducing iron-based powder into the cavity of the container to obtain a powder aggregate having pores between the powder particles,
The powder aggregate in the container is heated in a reducing atmosphere to reduce it at the same time as sintering to obtain a porous sintered body, and a high-temperature porous sintered body taken out of the container is heated with a forging die. It is characterized in that the forging process is carried out in order to obtain a sintered forged product.

A method for manufacturing a sintered forged product according to claim 2 is
Using an unreduced iron-based powder obtained by an atomizing method and not subjected to reduction treatment, and a container provided with a cavity of a predetermined shape, the iron-based powder was put into the cavity of the container, and pores were provided between the powder particles. A loading step to obtain a powder aggregate, a sintering reduction step in which the powder aggregate in the container is heated in a reducing atmosphere to reduce at the same time as sintering to obtain a porous sintered body, and the porous sintered body is stored. Attach the lid member to the container and seal the container, transfer the container to the forging die in the closed state, and hot forge the high temperature porous sintered body taken out from the container with the forging die. Then, a forging step for obtaining a sintered forged product is sequentially performed.

A method for manufacturing a sintered forged product according to claim 3 is
Using an unreduced iron-based powder obtained by an atomizing method and not subjected to reduction treatment, an oxidation-suppressing powder, and a container having a cavity of a predetermined shape, the iron-based powder and the oxidation-suppressing powder are put into the cavity of the container. Then, a charging step of obtaining a powder aggregate having pores between the powder particles and having an oxidation inhibiting layer on the outside, and heating the powder aggregate in the container together with the oxidation inhibiting layer in a reducing atmosphere to simultaneously reduce the sintering. Characterized in that a sintering reduction step for obtaining a porous sintered body and a forging step for hot forging the high temperature porous sintered body taken out of the container with a forging die to obtain a sintered forged product are performed in order. It is what

[0017]

The iron-based powder used in the method of the present invention is obtained by the atomizing method and has not been subjected to unreduced treatment.
Therefore, the oxide layer remains on the surface of the iron-based powder particles. The container used in the method of the present invention has a cavity. This cavity can have a preform shape that is similar to or closely resembles that of a sintered forged product, except that if the heightwise dimension of the porous sintered body is significantly reduced during the forging process, The dimension in the depth direction needs to be considerably larger than the height of the sintered forged product. The reason is that, in the forging step, the dimension of the porous sintered body in the depth direction is greatly reduced due to the collapse of the pores, and the reduced dimension is taken into consideration.

The material of the container is preferably one that has heat resistance even at the sintering temperature of the iron-based powder and is unlikely to stick to the iron-based powder heated to a high temperature. Generally, zirconia,
Ceramics such as alumina, silicon nitride, and silicon carbide can be used. In the charging step according to the present invention, iron-based powder is charged into the cavity of the container to obtain a powder aggregate having pores between the powder particles and having a low density ratio. The pores in the powder aggregate are continuous so that the reducing atmosphere can easily penetrate into the inside of the powder aggregate, and it is preferable that there are few isolated pores. The density ratio of the powder aggregate needs to be set to a value that allows the reducing atmosphere to easily penetrate deep inside the powder aggregate, and is generally 35 to 55%.
In particular, it can be about 40 to 50%. Here, the density ratio means the ratio of the substances having the same composition to the true density.

In the sinter reduction step according to the present invention, the powder aggregate in the container is heated in a reducing atmosphere to be reduced simultaneously with sintering to obtain a porous sintered body. The sintering temperature is preferably a temperature at which solid phase sintering is performed so that a liquid phase does not occur. This is because when the liquid phase is generated, the density ratio of the porous sintered body tends to increase. The density ratio of the porous sintered body is generally the same value as the density ratio of the powder aggregate, and specifically, it is as low as usually 35 to 55%, especially 40 to 50%.
Therefore, during the sintering, the reducing atmosphere can penetrate deep inside the powder aggregate or the porous sintered body, and the reduction treatment can be well performed deep inside the porous sintered body.

In the forging step according to the method of the present invention, a high-temperature porous sintered body having a low density ratio is hot forged with a forging die, but since the forging has a large surface pressure, the pores in the porous sintered body are A sintered forged product with a large disappearance and a high density ratio and few residual pores can be obtained. In the sealing step according to the method of claim 2, the lid member is attached to the container to seal the porous sintered body in the container. This suppresses or avoids the entry of outside air into the container, and reduces or avoids the oxidation of the porous sintered body while the high temperature porous sintered body is transferred to the forging die.

In the charging step according to the method of claim 3, a powder aggregate having an oxidation suppressing layer on the outside is obtained. The oxidation suppression layer is a layer laminated on the outer side of the powder aggregate in order to reduce or avoid the oxidation of the powder aggregate. The oxidation suppression layer is
Iron-based powder with a high carbon content, carbon-based powder such as graphite powder,
It can be constituted by using an oxidation-inhibiting powder such as a fine powder having a fine or ultrafine particle size. When the oxidation suppressing layer is composed of iron-based powder with a high carbon content, when decarburization proceeds from the oxidation suppressing layer that constitutes the porous sintered body, outside air permeates into the inside of the porous sintered body. However, due to the reaction between the decarburized carbon and the oxygen in the outside air, CO gas having a reducing property (C + 1/20 ₂ → CO gas) can be expected, which reduces the oxidation of the porous sintered body. Or be avoided.

The same effect is expected when the oxidation suppressing layer is made of carbon powder such as graphite powder. Further, when the oxidation suppressing layer is made of fine powder, the oxidation suppressing layer has a high density ratio. Therefore, in the sintering that requires a relatively long time, the reducing atmosphere can permeate the inside of the porous sintered body, but a relatively short time until the porous sintered body is transferred from the sintering furnace to the forging die (for example, In several seconds to several tens of seconds), the time for the outside air to penetrate into the sintered body is insufficient, so that the oxidation of the porous sintered body is suppressed.

[0023]

EXAMPLES Examples of the method of the present invention will be described below. (First embodiment) Fe-2% Cu-0.6% C in% by weight
Using a molten metal having a composition of about 1650 to 1700 ° C, the molten metal is atomized with water to obtain a powder. An oxide layer is formed in the powder particles, and the oxygen content is generally about 0.4 to 0.6% by weight. After the powder is dried, it is sieved to obtain a raw material powder having a particle size of 80 mesh or less. Then, the raw material powder is put into the cavity 1a of the ceramics (alumina) sintering container 1 shown in FIG. 1 to obtain a powder aggregate 2. The density ratio of the powder aggregate 2 is about 40 to 50%, and pores communicating with each other remain between the powder particles. At the time of charging, neither vibration was applied to the sintering container 1 nor press for compressing the powder. Therefore, the particle spacing in the powder aggregate 2 is quite large.

The cavity 1a of the sintering container 1 has a plane shape similar to that of a sintered forged product 7 described later, but the height dimension of the powder aggregate 2 housed in the cavity 1a is H1, When the height dimension of the sintered forged product 7 is H3, H1 is considerably larger than H3. Then, as can be understood from FIG. 1, the sintering container 1 is loaded into the furnace chamber of the sintering furnace 4 in the AX gas atmosphere, and heated and held at 1150 ° C. for 20 minutes in the furnace chamber. At this time, the oxide layer on the surface of the powder particles is removed by reduction, the powder particles are bonded to each other and the powder aggregate 2 is sintered, and the porous sintered body 5 is obtained.

Here, the powder aggregate 2 and the porous sintered body 5 obtained by sintering the powder aggregate 2 have a low density ratio of about 40 to 50%. Pores that communicate with each other and communicate with the outer surface remain inside. Therefore, the AX gas atmosphere in the sintering furnace 4 can penetrate deep into the powder aggregate 2 and the porous sintered body 5, and the oxide layer in the deep portion of the porous sintered body 5 is removed by reduction. That is, reduction is performed simultaneously with sintering. The pressure of the AX gas atmosphere is about (atmospheric pressure + 2 to 6 mmaq).

Here, the AX gas is a gas obtained by decomposing ammonia through a catalyst in a high temperature range, and is H ₂ 7 in volume%.
It is a reducing gas having a composition in which 5% and 75% N ₂ are mixed, and has a low dew point (-30 to -40 ° C). Next, the lid member 1k (material: for example, made of alumina) is immediately attached to the upper surface opening of the sintering container 1 taken out from the sintering furnace 4 or inside the sintering furnace 4, and the high temperature porous sintered body 5 is stored. The sintered container 1 is sealed. As a result, the contact between the high temperature porous sintered body 5 and the outside air is blocked. This state is shown in FIG.

In this sealed state, the sintering container 1 is transferred to the forging die 6 shown in FIG. 3 by transfer means or manual work. The transfer time is as short as about 5 to 15 seconds in general. Then, as shown in FIG. 3, the sintering container 1 is turned upside down above the forging die 6. The forging die 6 includes a die die 60, a lower punch die 61, an upper punch die 62 (see FIG. 5), and a forging cavity 63.

Further, as shown in FIG. 4, the lid member 1k is attached to the arrow E1.
The opening of the sintering container 1 is opened by sliding in the direction, and the high temperature porous sintered body 5 in the sintering container 1 is dropped into the forging cavity 63 of the forging die 6. Immediately thereafter, the upper punch die 62 is lowered as shown in FIG. 5, and the porous sintered body 5 is strongly pressed in the height direction by the die punch surface of the upper punch die 62 to perform hot forging. At the time of hot forging, the temperature of the porous sintered body 5 is 1100 to 100
It is considered to be 1050 ° C and the forging surface pressure is 10 tons / c
It is about m ² . Then, the sintered forged product 7 is obtained through release and post-treatment.

In this case, the height of the porous sintered body 5 before forging is H2 (substantially the same as H1), and the height after forging is H.
When set to 3, generally (H3 / H2) = 0.35-
It will be about 0.4. Here, the target value of the carbon content of the sintered forged product 7 is about 0.45%. There may be a difference between the carbon content of the molten metal that atomizes the iron-based powder and the carbon content of the sintered forged product 7. The carbon content corresponding to this difference causes decarburization during sintering heating. It is considered that it contributed to the generation of CO gas having a reducing property. In this case, it is more advantageous for reduction.

The basic steps of the first embodiment are shown in FIG. As can be understood from the comparison between FIG. 6 according to the first embodiment and FIG. 15 according to the conventional example, it can be seen that the number of steps is reduced in the first embodiment. By the way, since the density ratio of the porous sintered body 5 is as low as 40 to 50% as described above, while the sintering container 1 containing the porous sintered body 5 is transferred from the sintering furnace 4 to the forging die 6, Moreover, outside air may permeate the high temperature porous sintered body 5 housed in the sintering container 1 and the porous sintered body 5 may start to oxidize, which may promote the oxidation. In this respect, in this example, as described above, the lid member 1k is attached to the upper opening of the sintering container 1, the sintering container 1 containing the high-temperature porous sintered body 5 is sealed, and the sintering is performed in a sealed state. Since it is transferred from the furnace 4 to the forging die 6, the contact between the high temperature porous sintered body 5 and the outside air is effectively blocked during the transfer, and the oxidation of the high temperature porous sintered body 5 is reduced. Or be avoided. In this way, since the oxidation of the porous sintered body 5 is reduced or avoided,
This is advantageous for increasing the strength and toughness of the sintered forged product 7.

This example can be applied to the manufacture of iron-based connecting rods of internal combustion engines and the manufacture of gears. (Second Example) Fe-2% Ni-0.5% M in% by weight
Using a molten metal having a composition of o-1.0% C, the molten metal is water atomized to obtain a powder. After the powder is dried, it is sieved to obtain a raw material powder having a particle size of 80 mesh or less.
The raw material powder and the raw material powder produced in Example 1 are put into the cavity 1a of the ceramic sintering container 1 to obtain a powder aggregate 2 schematically shown in FIG.

The powder aggregate 2 shown in FIG. 7 is the powder aggregate 2
Of the inner layer 2c and a cylindrical oxidation suppressing layer 2e arranged so as to cover the outer peripheral surface of the inner layer 2c. The inner layer 2c is composed of the raw material powder manufactured in Example 1. The oxidation suppressing layer 2e is composed of the raw material powder manufactured in Example 2 (having a higher carbon content than in Example 1).

Here, the powder aggregate 2 shown in FIG. 7 can be manufactured, for example, as follows. That is, as shown in FIG.
Using r and the tubular tool 1t, the tubular tool 1r and the tubular tool 1t are arranged substantially coaxially in the cavity 1a of the sintering container 1.
In this state, the iron-based powder is put into the space surrounded by the inner peripheral surface of the tubular tool 1t to obtain the inner layer 2c. After that, as can be understood from FIG. 10, the tubular tool 1r is pulled out upward to form a ring-shaped gap between the outer peripheral surface of the tubular tool 1t and the inner peripheral surface of the standing wall 1i of the sintering container 1. Then, the iron-based powder is put into the ring-shaped gap to obtain the oxidation suppressing layer 2e. After that, the tube tool 1t is also pulled out. Cylinder tool 1
The space left after t is filled with the flow of powder.

Although the oxidation suppressing layer 2e in FIG. 7 covers the outer peripheral surface of the inner layer 2c, the present invention is not limited to this, and the entire surface of the inner layer 2c may be covered as shown in FIG. The oxidation suppression layer 2e shown in FIG. 8 includes a ring layer 2x, a lower layer 2y, and an upper layer 2z which are continuous in the circumferential direction. The powder aggregate 2 shown in FIG. 8 can also be formed by utilizing the tubular tool 1r and the tubular tool 1t as described above. That is, the lower layer 2 is formed on the bottom wall of the empty sintering container 1.
After placing the iron-based powder that constitutes y, the tube tool 1r and the tube tool 1t are placed on the lower layer 2y, and the tube tool 1r is placed in the same manner as described above.
Is removed to form the ring layer 2x, and the tubular tool 1t is pulled out upward, and then the iron-based powder constituting the upper layer 2z is placed.

When the powder aggregate 2 shown in FIG. 7 having the oxidation suppressing layer 2e is formed as described above, the sintering container 1 is placed in the sintering furnace 4 in the AX gas atmosphere, as in the first embodiment. Charged with the powder aggregate 2 and 115 in an AX gas atmosphere.
Heat and hold for 20 minutes at 0 ° C. At this time, as in the first embodiment, the oxide layer on the surface of the powder particles is removed by reduction, the powder particles are bonded to each other and the powder aggregate 2 is sintered, and the porous sintered body 5 is obtained. Is obtained.

The density ratio of the powder aggregate 2 and the porous sintered body 5 obtained by sintering the powder aggregate 2 according to the second embodiment is as low as about 40 to 50% as in the first embodiment. Therefore, the AX gas atmosphere in the sintering furnace 4 can penetrate deep into the inside of the powder aggregate 2 and the porous sintered body 5, and the oxide layer in the deep portion can also be removed by reduction. That is, as in the case of Example 1, the powder aggregate 2 is reduced at the same time as the sintering to obtain the porous sintered body 5.

Next, as in the first embodiment, the sintering container 1 is transferred to the forging die 6 and the porous sintered body 5 in the high temperature state is hot forged. A sintered forged product 7 is obtained through release and post-treatment.
By the way, also in the second embodiment, as described above, the density ratio of the porous sintered body 5 is as low as about 40 to 50%. Therefore, while the porous sintered body 5 is transferred from the sintering furnace 4 to the forging die 6, outside air may permeate the high temperature porous sintered body 5 and the porous sintered body 5 may be oxidized. In this respect, in this example, since the oxidation suppressing layer 2e is made of the iron-based powder having a high carbon content, decarburization proceeds from the oxidation suppressing layer 2e forming the porous sintered body 5, so that the high temperature porous In the case where the fine sintered body 5 is transferred in the open air, even if the open air contacts the porous sintered body 5, the reducing property is reduced by the reaction between the decarburized carbon and the oxygen in the open air at a high temperature. It is possible to expect the production of CO gas (C + 1/20 ₂ → CO gas), which reduces or avoids the oxidation of the porous sintered body 5.

Further, since the outer surface of the sintered forged product 7 according to this example is formed of the oxidation suppressing layer 2e having a large carbon content, the surface hardness becomes high due to the rapid cooling after forging. Therefore, the surface characteristics are improved and the same hardness improvement effect as carburizing and quenching can be expected. (Test Example) According to the first and second embodiments described above,
A test piece according to the first example and a test piece according to the second example made of a sintered forged product were manufactured. The test piece is cylindrical (forging direction is the axial direction). And each test piece was cut | disconnected and the oxidation depth of the surface of the cut surface was measured using the optical microscope.
The measurement result is 0.05 mm for the test piece according to the first embodiment.
And the test piece according to the second example is 0.07 m.
m was good. Further, in the first embodiment, the lid member 1k
Even if it is not deposited, the oxidation depth is 0.13
mm was good.

Further, a test piece according to a comparative example was manufactured according to the conventional process shown in FIG. That is, in this comparative example, 2 wt% graphite powder and 0.6 wt% zinc stearate were mixed with water-atomized iron-based powder, and the density was 6.8 g / cm ³ (density ratio) at a surface pressure of 5 ton / cm ^2. 86%) to form a green compact, which is then sintered by heating and holding the green compact in an AX gas atmosphere at 1150 ° C. for 20 minutes to obtain a sintered body having a high density ratio (density ratio). 90%). Further, the sintered body was taken out of the sintering furnace and transferred to the forging process in the open air. Approximately 10 seconds after the sintered body was taken out of the sintering furnace, it was forged in the open air at a surface pressure of 10 ton / cm ² to obtain a sintered forged product (a density ratio of about 100%). The oxidation depth of the comparative test example manufactured in this manner was also measured and found to be 0.13 mm.

(Variation) As shown in FIG. 11, a ventilation hole 1f may be formed in the sintering container 1. This case is suitable when the height of the powder aggregate 2 is large and it is difficult for the AX gas atmosphere to penetrate to the bottom of the powder aggregate 2. In addition, an inorganic porous body having heat resistance is arranged in the boundary region between the sintering container 1 and the powder aggregate 2, and the air permeability of this porous body is utilized to
The AX gas atmosphere may penetrate into the inside of the powder aggregate 2. The porous body is preferably one that is hard to bind to the iron-based powder. As the porous body, there is an aggregate of glass fiber, rock wool and the like.

(Third Example) Fe-2% Cu by weight%
A molten metal having a composition of −0.7% C is water atomized to obtain a raw material powder. After drying the raw material powder, it is sieved to obtain a powder having a particle size of 80 mesh or less. The powder is put into the cavity 1a of the sintering container 1 to obtain a powder aggregate 2 having a low density ratio.

In this example, as shown in FIG. 12, a driving belt device 100 having a driving roller 100a, a driven roller 100b and a belt 100c is used, and an RX gas atmosphere having an inlet 4m and an outlet 4n and having a reducing property is used. The sintering furnace 4 is used. And the belt 1 holding the sintering container 1
00c is conveyed in the direction of the arrow W1, and the powder aggregate 2 is sequentially charged into the furnace chamber of the sintering furnace 4. As a result, the powder aggregate 2 was heated and held at 1150 ° C. for about 30 minutes in the furnace chamber of the sintering furnace 4.
Is sintered to obtain a porous sintered body 5.

Since the powder aggregate 2 and the porous sintered body 5 obtained by sintering the powder aggregate 2 according to the third embodiment have a low density ratio of about 40 to 50%, the reducing gas at the time of sintering is porous. It is possible to penetrate deep into the sintered body 5, and the oxide layer in the deep portion of the porous sintered body 5 is removed by reduction. That is, also in the third embodiment, as in the case of the first embodiment, the powder aggregate 2 is reduced simultaneously with sintering to obtain the porous sintered body 5.

The RX gas, which is also called an endothermic gas, is a mixture of air and hydrocarbons which is transformed so that a gas rich in CO and H ₂ is produced. In this example, as schematically illustrated in FIGS. 12 and 13, a hot working machine 8 is provided on the outlet 4n side of the sintering furnace 4. The hot working machine 8 includes a first rotating roll 81 and a second rotating roll 81.
And a rotating roll 82. Pressing protrusions 81c are formed on the peripheral portion of the first rotating roll 81 at predetermined intervals. Then, the upper surface of the sintered porous sintered body 5 is mechanically crushed by the pressing protrusion 81c of the first rotating roll 81 and pressed down. The rolling reduction is 53%. The rolling reduction is {(h ₀ −, where h ₀ is the thickness before rolling and h ₁ is the thickness after rolling).
It means h ₁ ) / h ₀ } × 100 [%]. Due to this reduction, the vicinity of the surface of the porous sintered body 5 is densified, and the density ratio near the surface becomes as high as 96%. Therefore, the plugging property of the open pores near the surface of the porous sintered body 5 is improved. Therefore, until the porous sintered body 5 is transferred to the forging die 6 (about 1
Oxidation of the surface of the porous sintered body 5 during 0 seconds is suppressed.

Then, as in the first embodiment, the porous sintered body 5 is forcibly pressed by a forging die 6 to be forged. Forging surface pressure is 8 tons /
It is about cm ² . (Test Example) A test piece was formed according to the third example, and the static fracture surface of the test piece was observed by SEM to measure the area ratio of the unsintered portion in the static fracture surface. The measurement result is shown by the characteristic line S1 in FIG. As can be understood from the characteristic line S1, the depth at which the unsintered portion was observed at an area ratio of 5% was about 0.2 mm.

On the other hand, the thickness was 0.7 mm when manufactured in the same manner as in the third embodiment but the surface densification processing was not performed by the hot working machine 8. From this measurement result, it can be seen that surface densification by the hot working machine 8 is effective in preventing oxidation.

[0047]

According to the method of claims 1 to 3, since the density ratio of the powder aggregate and the porous sintered body obtained by sintering the powder aggregate is small, the porosity during sintering in the sintering reduction step is reduced. The reducing atmosphere can penetrate deep into the porous sintered body, and the reduction treatment in the deep portion of the porous sintered body can be performed well. In this way, since it can be reduced at the same time as sintering, it is possible to use an iron-based powder that is formed by the atomization method and is not subjected to reduction treatment, which is advantageous in terms of cost, as a raw material powder. It is not necessary to use the powder as the raw material powder, which is advantageous for cost reduction.

Further, according to the method of claims 1 to 3, the powder aggregate formed by charging the iron-based powder into the cavity of the container is used, and the green compact which is a compact having a high density ratio is used. is not. Therefore, it is not necessary to consider the compression moldability and lubricity at the time of compacting. Therefore, it is possible to expect an effect that the iron-based powder having the target composition can be used as it is without the need for a powder mixing step.

Further, since the density ratio of the porous sintered body is low, outside air may permeate the inside of the porous sintered body and oxidation may progress before the porous sintered body is transferred to the forging step. There is. In this respect, according to the method of claim 2, since the porous sintered body in the container is sealed by the lid member and the porous sintered body is transferred to the forging die, that is, the forging step in the sealed state, the porous sintered body is sintered. The penetration of outside air into the body is reduced or avoided. Therefore, the oxidation of the porous sintered body is suppressed, high strength,
It is advantageous for obtaining a high toughness sintered forged product.

Further, according to the method of claim 3, since the powder aggregate having the oxidation suppressing layer on the outside is used, the oxidation of the porous sintered body is reduced or avoided before being transferred to the forging die. Therefore, it is advantageous to obtain a sintered forged product having high strength and high toughness. Further, when the oxidation suppressing layer remains on the surface layer of the sintered forged product, improvement in surface characteristics can be expected.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a state in which a sintering container containing a powder aggregate is held in a sintering furnace.

FIG. 2 is a cross-sectional view showing a state in which a lid member is attached to a sintering container containing a powder aggregate.

FIG. 3 is a cross-sectional view showing a state in which a vertically inverted sintering container is arranged so as to face a forging cavity of a forging die.

FIG. 4 is a cross-sectional view showing a state in which a porous sintered body is dropped from a vertically inverted sintering container into a forging cavity of a forging die.

FIG. 5 is a cross-sectional view showing a state in which a porous sintered body is hot forged by a forging die.

FIG. 6 is a process flow chart showing a flow of each process according to the first embodiment.

FIG. 7 is a cross-sectional view showing a state where a powder aggregate according to another example is housed in a sintering container.

FIG. 8 is a cross-sectional view showing a state where a powder aggregate according to another example is housed in a sintering container.

FIG. 9 is a cross-sectional view showing a form of obtaining a powder aggregate according to another example including an oxidation suppression layer.

FIG. 10 is a cross-sectional view showing a form of obtaining a powder aggregate according to another example including an oxidation suppression layer.

FIG. 11 is a cross-sectional view of a sintering container according to another example.

FIG. 12 is a configuration diagram according to a third embodiment schematically showing a state where the porous sintered body is pressed by a hot working machine while being sintered in a sintering furnace.

FIG. 13 is a configuration diagram according to a third embodiment schematically showing a state in which a porous sintered body is rolled down by a hot working machine.

FIG. 14 is a graph showing the relationship between the area ratio of the unsintered portion and the depth from the surface of the sintered forged product.

FIG. 15 is a process flow chart showing a flow of each process according to a conventional method.

DESCRIPTION OF SYMBOLS In the figure, 1 is a sintering container, 1a is a cavity, 1k is a lid member, 2 is a powder aggregate, 5 is a porous sintered body, 6 is a forging die,
Reference numeral 7 indicates a sintered forged product, and 8 indicates a hot working machine.

Claims (3)

[Claims] 1. An unreduced iron-based powder obtained by an atomizing method and not subjected to reduction treatment, and a container having a cavity of a predetermined shape are used, and the iron-based powder is put into the cavity of the container to obtain a powder. A charging step of obtaining a powder aggregate having pores between particles, and a sintering reduction step of heating the powder aggregate in the container in a reducing atmosphere to reduce it simultaneously with sintering to obtain a porous sintered body. A method for producing a sintered forged product, which comprises sequentially performing a hot forging process on the high-temperature porous sintered body taken out of the container with a forging die to obtain a sintered forged product. 2. An unreduced iron-based powder obtained by an atomizing method, which has not been subjected to a reduction treatment, and a container having a cavity of a predetermined shape. The iron-based powder is put into the cavity of the container to obtain a powder. A charging step of obtaining a powder aggregate having pores between particles, and a sintering reduction step of heating the powder aggregate in the container in a reducing atmosphere to reduce it simultaneously with sintering to obtain a porous sintered body. , A lid member is attached to the container containing the porous sintered body, the container is hermetically sealed, and the container is sealed and transferred to a forging die; A method for manufacturing a sintered forged product, comprising performing hot forging of the porous sintered body with the forging die to sequentially perform a forging step for obtaining a sintered forged product. 3. An iron-based powder, which is obtained by an atomizing method and is not subjected to reduction treatment, an oxidation-suppressing powder, and a container having a cavity of a predetermined shape. In a cavity of the container to obtain a powder aggregate having pores between the powder particles and having an oxidation suppression layer made of an oxidation suppression powder on the outside, and the powder aggregate in the container is charged with the oxidation suppression layer. Together with the sintering and reduction step of heating in a reducing atmosphere and simultaneously reducing with sintering to obtain a porous sintered body, and hot forging the high temperature porous sintered body taken out of the container with the forging die. And a forging step of obtaining a sintered forged product in order, and a method for manufacturing a sintered forged product.