JPH0770720A - Ferrous sintered alloy for valve seat - Google Patents

Abstract

PURPOSE:To provide the ferrous sintered alloy for valve seats having improved corrosion resistance by infiltrating the holes of a ferrous sintered compact with a lead metal dispersed with a specific amt. of fine powder particles of an Ni alloy. CONSTITUTION:The holes of the ferrous sintered compact having about 10-20vol.% porosity are infiltrated with an infiltrating material dispersed with 3-35% fine particles (0.4-2.1mu particle diameter) of the Ni alloy in the lead metal when the entire part is assumed to be 100wt.%. The ferrous sintered compact is constituted by dispersing hard particles into a matrix. This matrix consists of 6-11% Ni alloy, 5-1.2% Co and the balance substantially iron when the entire part of the sintered compact is assumed to be 100wt.%. The hard particles are composed of >=1 kinds among FeMo, FeCr and FeW and contain 4 to 16% thereof. The fine particles of the Ni alloy is composed of a high-corrosion resistant alloy contg. 35-65% Ni, 12-27% Mo, 5-30% Cr and 2-10% Fe, etc., when the entire part of the infiltrating material is assumed to be 100wt.%. As a result, the ferrous sintered alloy for valve seats suppressed in abrasion loss is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferrous sintered alloy for valve seats. The alloy of the present invention can be used in a valve train of an internal combustion engine.

[0002]

2. Description of the Related Art Valves in a valve train of an internal combustion engine are likely to become hot. In particular, an exhaust valve exposed to high-temperature combustion gas tends to have a high temperature. Therefore, there is a direct contact with the hot valve,
The contact surface of the sliding valve seat also becomes hot, and wear easily progresses. Particularly in the case of an internal combustion engine that uses leaded gasoline fuel, a corrosive lead compound such as PbO is generated on the valve surface, so that the contact surface of the valve seat is likely to be corroded, and therefore the contact surface is excessively large. Wear may occur.

Therefore, conventionally, in order to suppress the corrosion reaction due to the lead compound or the like, the pores of the sintered alloy forming the valve seat are infiltrated with copper or the like having excellent heat conductivity so that the contact surface temperature of the valve seat is increased. There is known a valve seat that lowers the emission (Japanese Patent Laid-Open No. 60-251258, etc.). Further, in the valve seat, lead holes are infiltrated into the holes on the contact surface side, and copper is infiltrated into the opposite side, and the lubrication action of lead in the solid state is achieved.
There is also known a valve seat that combines the strength increase effect and the heat transfer effect improvement effect of copper (Japanese Patent Publication No. Sho 55-78118, Japanese Patent Laid-Open No. 61-104048).

Further, conventionally, as an iron-based sintered alloy for valve seats in which hard particles are dispersed, carbides such as Cr, Mo and V are contained, the average particle size is 40 to 150 μm, and the hardness Hv300.
Also known is one in which hard particles of .about.700 are dispersed in a mixed structure of austenite and pearlite (Japanese Patent Laid-Open No. Sho 60).
-251258).

[0005]

Even if the heat transfer of the valve seat is improved by lead infiltration or the like, when the contact surface of the valve seat becomes hot, the contact surface exceeds the melting point of the infiltrant. There are cases. In this case, the infiltrant may be melted and gradually released from the pores of the sintered alloy to the outside, and the lubricating effect of the infiltrant in the solid state may be reduced.

[0006] For example, in an internal combustion engine of a high output type using leaded gasoline fuel or a stoichiometric air-fuel ratio (theoretical air-fuel ratio) to improve fuel economy, the combustion temperature rises and the contact surface of the valve seat is increased. However, even if the heat conductivity is improved by infiltration of lead or the like, the temperature of the contact surface may exceed the melting point of 327 ° C. of lead which is the infiltration material. As a result, the infiltrated lead is melted and gradually released onto the contact surface of the valve seat, reducing the lubrication effect of lead in the solid state, and the contact surface of the valve seat partially contacts the valve surface directly. More opportunities to do. Further, in this type of internal combustion engine, a large amount of lead compounds are produced and the corrosion reaction is active, so that there is a problem that the aggressiveness of the lead compounds increases.

Further, the iron-based sintered alloy forming the valve seat, particularly in the case of element powder type, does not have a microscopically uniform structure, and diffusion of alloy elements such as Co and Ni for strengthening the matrix is observed. Inevitably a large amount and a small amount coexist. The portion where the amount of diffusion of alloying elements is large becomes an austenite phase and has excellent high temperature wear resistance and corrosion resistance. However, the portion where the diffusion amount of the alloy element is small becomes a pearlite phase or bainite phase which is inferior in high temperature wear resistance and corrosion resistance to the austenite phase. Therefore, when the corrosion reaction by the lead compound is active, the pearlite phase and the bainite phase are preferentially corroded, and wear progresses from this part, which may cause excessive wear on the contact surface of the valve seat.

The present invention has been made in view of the above circumstances, and an object thereof is whether a lead compound which easily causes corrosion of a tissue is produced or a combustion temperature is high. An object of the present invention is to provide an iron-based sintered alloy for valve seats that can suppress the amount of wear.

[0009]

The iron-based sintered alloy for a valve seat according to claim 1 is composed of an iron-based sintered body and an infiltrant infiltrated into the pores of the iron-based sintered body. The infiltrant is characterized by being composed of fine powder particles made of a Ni-based alloy dispersed in lead-based metal in an amount of 3 to 35% when the entire infiltrant is 100% by weight. Is. In the present invention,% means wt% unless otherwise specified. The porosity of the sintered body before infiltrating the infiltrant is vol% and is, for example, 10 to 20.
Can be%.

In the iron-based sintered alloy for a valve seat according to claim 2, the iron-based sintered body is composed of a matrix and hard particles dispersed in the matrix, and the matrix is 100% of the entire sintered body. Ni-based alloy is 6 to 11%, C is 0.5 to 1.2%, and the balance is substantially iron.
The Ni-based alloy has a Ni content of 3% when the Ni-based alloy is 100%.
5-65%, Mo 12-27%, Cr 5-30%,
An alloy having a composition containing 2 to 10% of Fe and 80 to Ni.
90%, 2 to 20% of Si, and 1 to 7% of Cu, and at least one kind of alloy having a composition. The infiltrant contains 9% of fine powder particles when the entire infiltrant is 100%. ~ 21%,
The balance is substantially a lead composition, and the fine powder particles have a Ni content of 35 to 65% and an M content of 100% based on the entire fine powder particles.
o is 12 to 27%, Cr is 5 to 30%, and Fe is 2 to 10%.
% High corrosion resistant alloy containing 80 to 90% Ni and Si
2 to 20% of Cu and 1 to 7% of Cu, and at least one kind of high corrosion resistant alloy, and the particle size of Ni-based fine powder particles is 0.4 to 2.1 μm. is there.

In the iron-based sintered alloy for a valve seat according to claim 3, the hard particles are composed of at least one of FeMo, FeCr and FeW, and when the whole sintered body is 100%, 4% to 4%.
It is characterized by containing 16%. [Reasons for Limiting Mixing Ratio of Each Component] The preferable mixing ratio of each component in the above-described iron-based sintered alloy for valve seats will be described separately for the matrix, the infiltrant, and the hard particles. 1. Matrix <C content> It is preferable that the sintered body contains C.
C is a typical element that strengthens iron by forming a solid solution in iron, and is a matrix obtained in a sintered body (usually a structure consisting of at least one of austenite phase, pearlite phase, bainite phase, etc.).
To form a solid solution in the sintered body to improve the strength and hardness of the sintered body. But,
If the mixing ratio of C in the matrix is less than 0.5%, the amount of C element diffused into the iron by heating during sintering is small and the above effect is not sufficiently exhibited. The diffusion amount becomes too large, the precipitation amount of cementite (Fe ₃ C) increases, and the matrix of the sintered body becomes brittle, so the C amount in the matrix is preferably 0.5 to 1.2%.

<Ni-based alloy> It is preferable that the matrix of the sintered body contains a Ni-based alloy. This Ni-based alloy is a corrosion resistant Ni alloy having excellent corrosion resistance in a high temperature / corrosive atmosphere, and those called Hastelloy D and Hastelloy C can be adopted. By heating at the time of sintering, Ni element diffuses from this Ni-based alloy to the surrounding iron-based material, further stabilizing the matrix in the austenite phase, and further improvement in high-temperature strength and corrosion resistance can be expected. The matrix preferably contains a Ni-based alloy in an amount of 6 to 11% when the entire sintered body is taken as 100%. If it is less than 6%, the wear amount of the valve seat is large, and if it exceeds 11%, the wear amount of the valve seat does not decrease so much.

The Ni-based alloy has a Ni content of 35 to 65%, a Mo content of 12 to 26%, and a C content of 100%.
Ni-M having a composition containing 5 to 30% r and 2 to 10% Fe
It can be composed of an o-Cr alloy. Ni-based alloy is Ni
Of 80% to 90%, Si of 2% to 20%, and Cu of 1% to 7%. In this case, Mn is preferably 3% or less and Al is 3% or less.

Next, the reasons for limiting the composition of the Ni-based alloy will be described separately for the Ni-Mo-Cr-based alloy and the Ni-Si-Cu-based alloy. Ni-Mo-Cr alloy Ni: Increases corrosion resistance in an oxidizing / corrosive atmosphere with other alloy components, but if Ni is less than 35%, its effect is small. The amount of diffusion is insufficient, and there are few regions that stabilize in the austenite phase). However, when Ni exceeds 65%, the effects of other alloy components are impaired and the effect of improving corrosion resistance saturates.
35-65% addition of Ni is preferable.

When added to Mo: Ni, it has the effect of improving the corrosion resistance in an oxidizing atmosphere, and further combines with the carbon diffused from the base material to form Mo carbide, and also improves the wear resistance. Effect is small, and 2
If it exceeds 7%, the formation of carbides becomes too much, the Ni-based alloy becomes brittle, and the attacking property of the other party also increases.
It is preferable to add 12 to 27% of Mo.

Cr: Passivates in an oxidizing atmosphere to improve the corrosion resistance of Ni-based alloys at high temperatures. However, if it is less than 5%, its effect is scarce, and if it exceeds 30%, its effect saturates. -30% is preferable. When it is added to Fe: Ni-Mo alloy, around 6% (2
(10% to 10%), the corrosion resistance becomes minimum and the amount of Mo or Ni can be reduced (replaced by Fe), so that Fe is preferably 2 to 10%.

Ni-Si-Cu system alloy Ni: Ni-Mo-Cr system, if less than 80%, the effect of improving corrosion resistance is small, and if more than 90%, the effects of other alloy components are impaired and the corrosion resistance is deteriorated. Since the improvement effect is saturated, Ni is preferably 80 to 90%. When it is added to Si: Ni, it forms a hard phase of Ni silicide and further improves the corrosion resistance, but if it is less than 2%, its effect is small, and if it exceeds 20%, the hard phase is formed too much and becomes brittle. Moreover, since the opponent's aggression increases,
Si is preferably 2 to 20%.

When it is added to Cu: Ni, the solid solution forms a solid solution to increase the hardness, and further improves the corrosion resistance in an oxidizing atmosphere. Since the effect is saturated, Cu is preferably 1 to 7%. Addition to Mn: Ni stabilizes the Ni-based alloy in the austenite phase and improves high-temperature strength, but if it exceeds 3%, the effect is saturated, so 3% or less is preferable.

When it is added to Al: Ni, the corrosion resistance is improved, but its effect is relatively small, and when it exceeds 3%, it is N.
In order to make the i alloy brittle, 3% or less is preferable. 2. Infiltrant The base of the infiltrant is lead and a lead-based alloy, and the lead content can be appropriately selected according to the type of sintered alloy. The fine powder particles made of a Ni-based alloy dispersed in this infiltrant are alloys having excellent corrosion resistance in a high temperature corrosive atmosphere. The fine powder particles made of a Ni-based alloy can have the same composition as the Ni-based alloy mixed in the matrix of the sintered body. That is, the fine powder particles have a Ni content of 35 to 6 when the fine powder particles are 100%.
It can be composed of an alloy having a composition containing 5%, Mo 12 to 27%, Cr 5 to 30%, and Fe 2 to 10%. The fine powder particles contain 80 to 90% Ni, 2 to 20% Si, and C.
It can be composed of an alloy having a composition containing 1 to 7% of u. In this case, Mn is preferably 3% or less and Al is 3% or less.

In the alloy of the present invention, fine powder particles are contained in an amount of 3 to 35% when the entire infiltration material is taken as 100%. This is because the effect of improving wear resistance and its saturation are taken into consideration. In particular,
It is preferably contained in 9 to 21%. This is because with the addition of the fine powder particles, the valve seat wear amount greatly decreases to around 9%, the wear amount reaches a steady value from around 21%, and the wear resistance improving effect tends to be saturated. The particle size of the fine powder particles is preferably 0.4 to 2.1 μm. As will be described later, since the valve seat wear amount is minimized when the fine powder particles have a particle size in the range of 0.4 to 2.1 μm, the pore size of the sintered body in which the infiltrant is infiltrated is usually 5 to 5. It is about 15 μm, so that the fine powder particles can easily enter the pores of the sintered body during infiltration. 3. Hard particles Hard particles greatly improve the wear resistance of the sintered alloy.
As hard particles, FeMo particles, FeW particles, FeCr
Particles can be adopted.

Here, FeMo has a hardness Hv1300 to 1
400, FeW are Hv 1100 to 1200, and FeCr are Hv 1600 to 1700, which are high hardness intermetallic compounds, and can greatly improve the wear resistance of the matrix of the iron-based sintered alloy. If the amount of hard particles added is less than 4%,
The effect of improving the wear resistance is insufficient, and when it exceeds 16%, the amount of wear of the mating material (valve face) increases, exceeds the allowable level, and the machinability deteriorates. Is preferred. However, FeCr has extremely high hardness, and if the addition amount exceeds 10%, the opponent attack property becomes large. Therefore, the upper limit of the addition amount (whether alone or in combination) is preferably 10%.

[0022]

[Function] When the temperature of the contact surface of the valve seat becomes high and exceeds the melting point of the infiltrant, the infiltrant mixed with the fine powder particles becomes in a molten state, gradually escaping from the pores of the sintered alloy to the outside of the outermost layer. Is released. At that time, the fine powder particles mixed with the infiltrant are also discharged to the outside. Since the fine powder particles are made of a Ni-based alloy, their melting point is higher than that of the infiltrant,
The solid state is maintained, and the fine powder particles move on the contact surface of the valve seat due to the seating of the valve, reach the minute recesses on the contact surface, and enter the recesses. Therefore, the progress of the corrosion reaction in the recess is suppressed, and the corrosion resistance of the contact surface of the valve seat is improved.

[0023]

【Example】

[Structure of Examples] Examples will be described below together with comparative examples. FIG. 2 shows a cross section of a valve train of a main part including the valve seat 100 and the valve 200. In this example, in forming the iron-based sintered body that constitutes the valve seat 100, 1
Iron powder, graphite powder, and Ni-based alloy powder manufactured to about 00 mesh (particle size 150 μm) are used. Further, FeMo powder (particle size 20 to 50 μm) as hard particles is also used. These powders are thoroughly mixed to obtain a mixed powder.

As shown in Table 1, as the above Ni-based alloy powder, Ni-Mo-Cr system is used in Examples 1, 3, 3, 5 and 7. In addition, as the above Ni-based alloy powder, Example 2, Example 4,
In Example 6, a Ni-Si-Cu system is adopted. The ratio of each component is as shown in Table 1. Next, the manufacturing method will be described. Using the sintering mold 2 composed of the molds 2a to 2c shown in FIGS. 3A and 3B, the above-mentioned mixed powder 1 was filled in the sintering mold 2 and punched at a pressure of 7 ton / cm ^3. The mold 2e is pressed to mold the ring-shaped green compact 1A. Then, the green compact 1A is heated and held at 1100 to 1150 ° C. for 45 minutes in an ammonia decomposing gas atmosphere to sinter the green compact 1A to obtain a sintered body 3 shown in FIG. 3 (C). This sintered body 3
Has a density of 6.6 to 7.0 g / cm ³ and a void ratio of about 10 to 20 vol%.

The above-mentioned sintering conditions will be described. In the green compact 1A, the powder particles are simply connected by mechanical meshing. Therefore, it is sintering that further heats each powder to bond each powder particle at the atomic level, but usually the heating conditions are below the melting point of each component, and each powder remains in the solid state between powders. The heating temperature and heating time at which atoms are sufficiently diffused are selected in consideration of productivity. Considering this, the sintering conditions are selected as follows.

(Sintering heating temperature) In the above-mentioned embodiments, the main component of the matrix is iron, and the sintering reaction between the iron and the Ni alloy is important. The melting point of iron is 1535 ℃, N
The melting point of i alloy is 51Ni-19Mo-17Cr-6Fe
In this case, since the temperature is 1350 ° C., the heating temperature (1100 to 1150 ° C.) usually set when iron is the main component was selected. In this heating temperature range, the density of the sintered body becomes 6.6 to 7.0 g / cm ³ when it is held for a time (1 to 2 hours) where the atomic diffusion between the powders is saturated, and the desired porosity is obtained. About 1
0-20 vol% is obtained.

(Sintering heating time) Iron and Ni are elements which are alloyed with each other. At the initial stage of the sintering reaction, Ni atoms wrap the surface of the iron powder by surface diffusion, and then the iron powder. Ni atoms diffuse into the interior of the alloy to form an alloy. The diffusion amount of Ni atoms increases with heating time when the heating temperature is constant, and reaches a saturation value after a certain time. In FIG. 4, sintering heating temperatures of 1100 ° C. and 11
Heat retention time and Ni diffusivity at 50 ° C. (ratio of area where Ni element diffused in arbitrary cross section of sintered body ... EP
The relationship of elemental analysis by a MA analyzer is shown. As shown in the characteristic line of FIG. 4, the change in Ni diffusivity depends on the sintering heating temperature, that is, the higher the temperature (1150 ° C.), the more Ni
The diffusion rate is high and diffusion is quick, but in the end Ni
The diffusivity reaches the same saturation level regardless of the temperature difference.
Therefore, 45 minutes at which the diffusivity reaches a saturated state at a sintering heating temperature of 1100 ° C. was set as the sintering heating holding time.

Next, the infiltrant used in the examples will be described. That is, in this example, fine powder particles of Ni-based alloy having a particle size of about 0.5 to 2 μm are used. Table 1 shows the composition and particle size of the fine powder particles in each example.

[0029]

[Table 1]

Then, 10% by weight to 20% by weight of fine powder particles are mixed in a lead melt at a ratio shown in Table 1 when the total amount of the infiltration material is 100%, and the mixture is stirred. After that, the lead melt is solidified into particles with a particle size of about 1 mm by atomization,
As a result, a granular infiltrant containing fine powder particles is obtained. Then, as shown in FIG. 3D, the granular infiltration material 4 is spread on a graphite tray 5, and the sintered body 3 is placed thereon. In that state, above the melting point of lead in the ammonia decomposition gas atmosphere 400
The sintered body 3 is heated together with the infiltrant 4 to ˜420 ° C., and the melt of the infiltrant 4 is infiltrated into the pores of the sintered body 3 by a capillary phenomenon, whereby fine powder particles made of a Ni-based alloy. Into the pores of the sintered body 3.

Finally, the infiltrated sintered body 3 is appropriately machined to form a valve seat. FIG. 5 is an enlarged view schematically showing a cross-sectional structure near the outermost layer of the contact surface of the sintered alloy valve seat. As shown in FIG. 5, in the matrix, the Ni-based alloy 103 is dispersed in the iron-based material 102 composed of the pearlite phase or bainite phase in which C is solid-solved, and the Ni element is surrounded by the Ni element 103. A diffused austenite phase 104 is formed. Further, the infiltrant 8 is infiltrated into the continuous pores of the matrix,
The infiltrant 8 contains fine powder particles 11 made of a Ni-based alloy. Further, hard particles are dispersed in the matrix.

By the way, in an internal combustion engine using leaded gasoline fuel, PbO and P which are highly corrosive on the exhaust side valve are used.
bSO ₄ is generated, and the contact surface of the valve seat that is in direct contact with the valve is strongly corroded by PbO or PbSO ₄ . The contact surface of such a valve seat is taken with an electron microscope (S
When observed by EM), there is relatively little corrosion in the austenite phase. However, the pearlite phase and bainite phase having a small amount of Ni diffusion are strongly corroded, and many fine recesses are formed on the surface, and it can be seen that the corrosion further progresses at the bottom of the fine recesses. [Effects of Embodiments] According to the embodiments of the present invention described above, the effect of reducing the amount of wear of the valve seat is obtained. It is speculated that such an effect of reducing the amount of wear is due to the following mechanism. That is, when the temperature of the contact surface of the valve seat exceeds the melting point of lead (327 ° C.), the lead infiltrant 8 mixed with fine powder particles becomes in a molten state, and the sintered alloy as shown in FIG. Is gradually released to the outside from the pores in the outermost layer of
The light is emitted to the contact surface 101 and becomes the emission portion 9. At that time,
The fine powder particles 11 mixed with the infiltration material 8 are also carried out to the contact surface 101 at the same time. Since the fine powder particles 11 made of this Ni-based alloy have a high melting point of 1230 ° C. or 1350 ° C., the solid state is maintained, and the valve is seated in the Y1 direction (FIG. 6 (B)). With the rotation in the Y2 direction (Fig. 6 (C)), the contact surface 1 of the valve seat 1
Fine powder particles 11 move to the corrosion progressing region K1 on 01,
Reaching the minute recesses 13 in the above-described corrosion progressing region K1,
As shown in FIG. 6C, the fine powder particles 11 enter the recess 13. Further, the fine powder particles 11 are buried in the recess 13 due to the seating force of the valve and the combustion pressure. Therefore, the progress of the corrosion reaction in the recess 13 is suppressed, and the corrosion resistance of the contact surface 101 of the valve seat is improved. Therefore, even in an internal combustion engine that uses leaded gasoline fuel that easily induces wear and has a high combustion temperature, the wear resistance of the exhaust side valve seat is maintained, and a large increase in wear is effectively avoided.

In order to confirm the effect of reducing the amount of wear of the valve seat, valve seats were made by trial using the sintered alloys of the examples and the comparative example, and lead cylinders of 2200 cc (4 valves per cylinder) with 4 cylinders. It was incorporated into the exhaust side of a cylinder head of an internal combustion engine using gasoline fuel, and the durability was tested under the operating conditions of full load × 200 hours (air-fuel ratio = 13 to 14) at 6000 rpm. The test results are shown in FIG. The upper part of the vertical axis of FIG. 1 represents the valve seat wear amount, and the lower part of the vertical axis represents the valve face wear amount.

As shown in FIG. 1, in each of the examples, the valve seat wear amount was less than half that of the comparative example. Therefore, the effect of improving the wear resistance by mixing the fine powder particles of the Ni-based alloy with the lead infiltration material was confirmed, and the effect of suppressing the progress of lead compound corrosion was also confirmed. [Test Example] (Test Example 1) Using the sintered alloy manufactured as described above, the relationship between the mixing ratio of the Ni-based alloy in the matrix of the sintered body and the valve seat wear amount in a corroded state was tested. The test was conducted as follows. That is, as shown in FIG.
00 in PbO powder 303 and heated in furnace 305 at 600 ° C. for 1 hour. By this heating, the PbO powder 303 does not melt (melting point of PbO is 880 ° C.), but the corrosion reaction proceeds at the contact portion between the test piece 300 and the PbO powder 303, and the contact surface of the valve sheet of the test piece 300 is corroded. It becomes a state. Next, as shown in FIG. 8, the valve sheet-shaped test piece 300 and the valve 400 (manufactured by SUE50) were assembled into a valve unit abrasion tester, and the valve 400 was heated by the burner 500 while actually operating the valve of the internal combustion engine. Relative motion is performed under the same conditions as the system. The test conditions are as follows: temperature per valve seat: 350 ° C, valve sliding speed: engine speed 4
000 rpm equivalent, valve spring load: 4 kgf,
Test time: 10 hours.

As shown in FIG. 9, when the seat contact width before the test is α1 and the seat contact width after the test is α2, the valve seat wear amount is the contact surface width increase amount of the valve seat, that is, (α2 -Α1) was measured and obtained. The valve face wear amount was obtained by measuring β of the valve. The test results are shown in FIG. As you can see from the special line P1 in Fig. 10, N
The wear amount of the valve seat decreases as the mixing ratio of the i-based alloy increases, but the wear amount approaches a steady value when the Ni-based alloy exceeds 5%, and the wear amount starts when it exceeds 15 wt%. Is slightly increasing. The higher the mixing ratio of this Ni-based alloy, the worse the machinability and the higher the material cost. Therefore, the mixing ratio range of the Ni-based alloy is 6 to 1
It can be seen that 1 wt%, that is, the vicinity of the region M1 shown in FIG. 10 is preferable.

Test Example 2 FeMo, F as hard particles
Using each particle of eW and FeCr, the relationship between the amount of hard particles added to the sintered body and the valve seat wear amount in a corroded state was tested. The test conditions were the same as in Test Example 1. F
eMo has a hardness of Hv1300 to 1400, FeW has a hardness of Hv1100 to 1200, and FeCr has a hardness of Hv16.
It is as high as 00 to 1700 and greatly improves the wear resistance of the matrix of the iron-based sintered body. The test results are shown in FIG.
As shown by the characteristic line P2 in FIG. 11, if the addition rate of hard particles is less than 4%, this effect is insufficient, and if it exceeds 16%, the wear amount of the valve face, which is the mating material, increases and the allowable level is increased. As it exceeds, the cutting property of itself deteriorates,
The mixing range of the hard particles is preferably 4 to 16 wt%, that is, near the region M2 shown in FIG. The test results when FeCr is used are shown by characteristic lines P5 and P6 in FIG.
In this case, the vicinity of the area M3 is preferable.

Test Example 3 The relationship between the mixing ratio of fine powder particles made of a Ni-based alloy contained in the infiltrant and the wear resistance of the valve seat after corrosion was tested. The test conditions were the same as in Test Example 1. The test results are shown in FIG. Characteristic line P of FIG.
As can be understood from 4, when the mixing ratio of the fine powder particles made of the Ni-based alloy is increased, the valve seat wear amount greatly decreases up to around 9%, and the valve seat wear amount reaches a steady value from around 21 wt%. However, the effect of improving wear resistance tends to be saturated. Therefore, the mixing ratio of fine powder particles is 9 to 2
It is preferably 1%, that is, near the region M4 shown in FIG.

Next, the relationship between the particle size of the fine powder particles and the wear amount of the valve seat was tested. The test conditions were the same as in Test Example 1. The test results are shown in FIG. As shown in FIG. 13, the wear amount of the valve seat becomes the minimum in the range of the particle size of 0.5 to 2 μm, so that the vicinity of the region M5 shown in FIG. 13 is preferable.

[0039]

According to the valve seat-like sintered alloy of the present invention, the corrosion resistance of the contact surface of the valve seat can be improved. The reason is speculated as follows. That is, when the contact surface temperature of the valve seat becomes high and exceeds the melting point of the infiltrant, the infiltrant enters a molten state and is gradually discharged together with the fine powder particles from the pores in the outermost layer of the sintered alloy to the outside. Since the fine powder particles are made of a Ni-based alloy, their melting point is higher than that of the infiltrant, and the solid state is maintained, and the fine powder particles move on the contact surface of the valve seat due to the seating of the valve and the like. It reaches the fine recesses on the surface and enters into the recesses, the progress of the corrosion reaction in the recesses is suppressed, and the corrosion resistance of the contact surface of the valve seat is improved.

Therefore, according to the valve seat-like sintered alloy of the present invention, the valve can be used even in an internal combustion engine that uses a leaded gasoline fuel that easily induces corrosion, or an internal combustion engine that has a high combustion temperature due to the air-fuel ratio. The abrasion resistance of the sheet is retained, and the amount of abrasion can be reduced. Therefore, it is advantageous to prevent combustion gas loss due to wear of the valve seat and melting damage of the valve due to combustion gas loss. Further, it is advantageous for suppressing uneven wear of the valve seat due to the circumferential temperature distribution of the valve seat.

[Brief description of drawings]

FIG. 1 is a graph showing test results.

FIG. 2 is a sectional view showing a main part of a valve mechanism.

FIG. 3 is a process diagram showing a process of producing a green compact and infiltrating the green compact.

FIG. 4 is a graph showing the relationship between the heating and holding time in sintering and the Ni diffusivity.

FIG. 5 is a cross-sectional view schematically showing the structure near the contact surface of the valve face.

FIG. 6 is a cross-sectional view schematically showing a process in which fine powder contained in the infiltrant is discharged to the contact surface of the valve face.

FIG. 7 is a cross-sectional view showing a state where a test piece is heated and held in PbO powder.

FIG. 8 is a configuration diagram schematically showing a state under test.

FIG. 9 is a configuration diagram showing a width increase amount per sheet.

FIG. 10 is a graph showing the relationship between the Ni-based alloy mixing ratio and the valve seat wear amount.

FIG. 11 is a graph showing the relationship between the amount of hard particles added and the amount of valve seat wear and the amount of valve face wear.

FIG. 12 is a graph showing the relationship between the mixing ratio of fine powder particles in the infiltrant and the valve seat wear amount.

FIG. 13 is a graph showing the relationship between the particle size of fine powder particles in the infiltrant and the valve seat wear amount.

[Explanation of symbols]

In the figure, 3 is a sintered body, 8 is an infiltrant, 11 is fine powder particles, 1
01 is a contact surface, 102 is an iron base, 104 is an austenite phase, and 303 is a PbO powder.

Claims (3)

[Claims] 1. An iron-based sintered body and an infiltrant infiltrated into the pores of the iron-based sintered body, wherein the infiltrant is 100% by weight of the entire infiltrant. In this case, the iron-based sintered alloy for a valve seat, characterized in that fine powder particles made of a Ni-based alloy are dispersed in 3 to 35% of a lead-based metal. 2. An iron-based sintered body is composed of a matrix and hard particles dispersed in the matrix, and the matrix has 100% of the whole sintered body.
The Ni-based alloy has a composition of 6 to 11%, C of 0.5 to 1.2%, and the balance substantially iron. When the Ni-based alloy is 100%,
Ni 35-65%, Mo 12-27%, Cr 5-5
Ni-Mo-Cr having a composition containing 30% and 2 to 10% Fe
80-90% of Ni-based alloy and 2-20 of Si
%, And at least one Ni-Si-Cu alloy having a composition containing Cu of 1 to 7%. The infiltrant contains 9% of the fine powder particles when the entire infiltrant is taken as 100%. .About.21%, the balance being substantially lead. The fine powder particles have a Ni content of 35 to 65%, a Mo content of 12 to 27%, and a Cr content of 5 to 5 when the whole of the fine powder particles is 100%. High corrosion resistance alloy containing 30%, Fe 2 to 10%, Ni 80 to 90%, Si 2 to 20%, Cu 1
2. The iron system for a valve seat according to claim 1, wherein the iron powder is a high corrosion resistant alloy having a composition of ˜7%, and the fine powder particles have a particle size of 0.4 to 2.1 μm. Sintered alloy. 3. The hard particles are FeMo, FeCr, FeW.
Of at least one of the
The iron-based sintered alloy for valve seats according to claim 2, wherein the content is 4% to 16%.