JPH06146823A - Valve seat for engine - Google Patents

Abstract

PURPOSE:To provide an engine valve seat having a high strength and excellent wear and abrasion resistance. CONSTITUTION:An engine valve seat is a Fe base valve seat 5 pressed in an Al-alloy cylinder head 2 of an engine, and the metallographic structure of matrix is a multiphase structure having an austenite phase and a martensite phase, and at a seating part 14 where an exhaust valve 6 is seated, the existing quantity of the martensite phase is greater than that of the austenite phase, and on the other hand, at a pressing in part 15 pressed in the cylinder head 2, the existing quantity of the austenite phase is greater than that of the martensite phase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve seat for an engine, and in particular, Fe which is press-fitted into an Al alloy cylinder head.
System valve seats.

[0002]

2. Description of the Related Art Conventionally, as this type of valve seat, there is known a valve seat having a matrix metallographic structure of a pearlite phase.

[0003]

However, the conventional valve seat has relatively low strength such as tensile strength, compressive strength, radial crushing strength, etc., and the amount of struck and worn by the engine valve is relatively large. Top, increase the amount of engine valve wear,
There is such a problem. Further, since the valve seat is used by being press-fitted into the Al alloy cylinder head, the press-fitting margin must be increased due to the difference in thermal expansion between the Al alloy and Fe, and there is a limit to the thinning of the valve seat.

In view of the above, the present invention has high strength and excellent wear resistance, and can suppress wear of an engine valve, which is a mating member, and further achieve thinning. It is an object of the present invention to provide the valve seat described above.

[0005]

The present invention relates to an engine A
In the Fe-based valve seat press-fitted into the 1-alloy cylinder head, the metallic structure of the matrix is a multiphase structure having an austenite phase and a martensite phase, and in the seating portion where the engine valve is seated, the amount of the martensite phase present is austenite. The amount of the austenite phase is larger than that of the martensite phase in the press-fitting portion that is press-fitted into the cylinder head.

[0006]

When the metal structure of the matrix has the mixed phase structure as described above, the strength of the valve seat can be improved by supplementing the brittleness due to the martensite phase with the austenite phase having elongation. Further, the press-fitting portion has a large amount of austenite phase, and its coefficient of thermal expansion is close to that of the Al alloy that is the material for forming the cylinder head, so it is possible to reduce the press-fitting margin and achieve a thin valve seat. Thereby, the inner diameter of the valve seat can be expanded to improve the intake and exhaust efficiency. On the other hand, since the seating portion has a large amount of martensite phase, the amount of wear caused by the engine valve being hit is small, and the wear of the engine valve, which is a mating member, can be suppressed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a cylinder head 2 of an engine 1 is made of an Al alloy, and its exhaust port 3
The Fe-based valve seat 5 is press-fitted into the recess 4 formed on the inlet side of the. The valve head 7 of the exhaust valve 6 as an engine valve is on the combustion chamber side and faces the valve seat 5, and the valve stem 8 is slidably fitted in the valve guide 9 of the cylinder head 2. A valve spring 12 is contracted between a pair of retainers 10 and 11 mounted on the valve stem 9, and a rocker arm 13 abuts on an end surface of the valve stem 9.

As shown in FIG. 2, the metal structure of the matrix in the valve seat 5 is a mixed phase structure having an austenite phase and a martensite phase, and the seat portion 14 on which the valve head 7 of the exhaust valve 6 is seated has a martensite structure. The abundance of the phase is larger than the abundance of the austenite phase. On the other hand, in the press-fitting portion 15 that is press-fitted into the recess 4 of the cylinder head 2, the abundance of the austenite phase is larger than the abundance of the martensite phase.

When the matrix has a metallographic structure of the mixed phase structure as described above, the strength of the valve seat 5 can be improved by supplementing the brittleness due to the martensite phase with the austenite phase having elongation. Further, since the press-fitting portion 15 has a large amount of austenite phase and its thermal expansion coefficient is close to that of the Al alloy which is the material for forming the cylinder head, it is possible to reduce the press-fitting allowance and to make the valve seat 5 thinner. As a result, the inner diameter of the valve seat 5 can be expanded and the exhaust efficiency can be improved. On the other hand, since the seating portion 14 has a large amount of the martensite phase, the amount of wear caused by the exhaust valve 6 being hit is small, and the wear of the exhaust valve 6 can be suppressed.

In manufacturing the valve seat 5, a step of manufacturing an Fe-based sintered material having a matrix having at least an austenite phase in a metal structure by a powder metallurgy method, and aging of the Fe-based sintered material, And a step of performing a secondary hardening treatment by processing or the like.

The metallic structure of the matrix in the Fe-based sintered material is, for example, a single-phase structure composed of only an austenite phase, a mixed-phase structure composed of an austenite phase and a martensite phase, or a mixed-phase structure composed of an austenite phase and a pearlite phase. Alternatively, it has a multiphase structure composed of an austenite phase, a martensite phase and a pearlite phase. Fine MC type or M _{6 in} these matrices
C-type carbides (where M is a metal carbide forming element) are dispersed.

The secondary hardening treatment may be carried out alone, but as a simple method, a Fe-based sintered material is incorporated into the engine 1 as shown in FIGS. It is done by driving. That is, when the Fe-based sintered material is heated by the combustion heat as the engine 1 is operated, the valve head 7 of the exhaust valve 6 is seated on the seat portion 14 of the Fe-based sintered material at the same time, and then separated, and this is repeated. In the Fe-based sintered material, a temperature distribution appears such that the seat portion 14 has the highest temperature and the press-fit portion 15 has the lowest temperature. At the same time, the seat portion 14 is struck by the exhaust valve 6 to be processed. Seat 14
In, the phase change progresses more rapidly than in the press-fitting section 15,
As a result, in the seating portion 14, the abundance of the martensite phase becomes larger than the abundance (remaining amount) of the austenite phase,
On the other hand, in the press-fitting portion 15, the existing amount (residual amount) of the austenite phase is larger than the existing amount of the martensite phase, whereby the valve seat 5 is obtained. In such a secondary hardening treatment, precipitation of fine metal carbides and intermetallic compounds occurs in the martensite phase together with the phase change.

Next, the composition of the Fe-based valve seat 5 will be described. The valve seat 5 contains a metal carbide forming element, an austenite forming element and C as essential components, and uses hard powder, P and a self-lubricating material as selective components, and the balance is substantially Fe (Si, Mn, (Including S). (A) Metal Carbide Forming Element At least one selected from W, Mo, V, Ti, Nb, Ta and B corresponds to this kind of element, and when these elements are M, it is MC or M ₆ Form a metal carbide represented by C. The content of the metal carbide forming element is usually 0.4 to 15% by weight, preferably 6 to 12% by weight. If the content of this element is less than 0.4% by weight, the hardness may not be sufficiently increased by the secondary curing, and the wear resistance may not be sufficiently improved. On the other hand, if it exceeds 15% by weight, the amount of carbide precipitated in the sintered material becomes too large, the hardness is increased more than necessary, and the machinability may be deteriorated. However, V, Ti and Nb
When using at least one of these, it is preferable that the content thereof be 0.4 to 2% by weight in order to mitigate the aggressiveness to the engine valve. When W and Mo are used in combination, the content may be up to 15% by weight.

The metal carbide-forming element precipitates fine MC-type or M ₆ C-type carbides having a grain size of usually 2 μm or less in the austenite phase during sintering, and becomes a nucleus by aging treatment to grow further. Increase the amount of precipitation. on the other hand,
The amount of C in the matrix decreases as the amount of this metal carbide increases, and as a result, the martensite transformation point (hereinafter, M
(referred to as s point), and martensitic transformation occurs at the engine environmental temperature of 200 to 400 ° C. (B) Austenite forming element At least one selected from Ni, Co, Cu and Cr corresponds to this kind of element. This austenite forming element is contained in the matrix and has the effect of improving heat resistance, corrosion resistance and strength, suppresses martensite transformation or pearlite transformation during sintering, and also by aging, beating by engine valves, etc. Martensitic transformation is induced to form an austenite phase that undergoes secondary hardening. When kept at high temperature for a long time, Ni ₃ Ti, Ni ₃ Mo, Ni
₃ Precipitate intermetallic compounds such as Nb and NiAl that contribute to hardness improvement.

The content of the austenite forming element is usually 5 to 35% by weight, preferably 10 to 30% by weight. When the content of this element is less than 5% by weight, heat resistance, corrosion resistance and strength cannot be sufficiently improved, and an austenite phase may not be sufficiently formed. On the other hand, if the content exceeds 35% by weight, the austenite phase may be stabilized and secondary curing may not occur. (C) Regarding C C has an action of lowering the Ms point, and its content is usually 0.2 to 1.2% by weight, preferably 0.4 to 0.8.
% By weight. If the C content is less than 0.2% by weight, free ferrite may be precipitated in the matrix to hinder the improvement of wear resistance. On the other hand, the content is 1.
If it exceeds 2% by weight, free cementite may be precipitated in the matrix during sintering and machinability may be impaired, and the Ms point becomes too low at 100 ° C or lower to prevent martensitic transformation due to aging or the like. Therefore, the secondary hardening may not occur and the hardness and wear resistance may not be improved. In addition, C means that contained in the matrix by diffusion from carbon powder or other powders. For example, carbon in carbides that may be added as a hard phase or bonded carbon and free carbon contained in other hard powders. Is excluded. (D) Hard powder The hard powder has a function of improving the wear resistance by being dispersed in the matrix. However, when the amount of the hard powder dispersed is large, the workability and the strength are deteriorated, and at the same time, the hardness of the valve seat is increased. Manufacturing cost rises. Considering these points, the upper limit of the content of the hard powder is set to 30% by weight.

The hard powder is, for example, W-Cr-Co.
-C based stellite alloy powder, W-Cr-Co-C-Fe
Stellite alloy powder, Eatite alloy powder, Mo
Applicable are —Fe alloy powder, Cr—Mo—VC—Fe alloy powder, Co—Mo—Cr—Si alloy powder, and ceramic powders such as carbides, oxides and nitrides. The hardness Hv of the hard powder is generally 900 or more. (E) About P P has the function of improving the sinterability between particles during the sintering of a high alloy powder having a poor compacting property to form a high density and high strength sintered body. The content of P is usually 0.1 to 0.6% by weight, preferably 0.2 to 0.4% by weight. If the content is less than 0.1% by weight, the sinterability improving effect may not be sufficient. On the other hand, if the content exceeds 0.6% by weight, steadite may be precipitated at the grain boundaries, which may lead to a decrease in machinability and toughness. The above content range relates to the case where P is positively blended, and does not include a trace amount of P that is inevitably contained in the raw material powder. (F) Self-lubricating material The self-lubricating material is used by adding it alone or by being contained in the Fe powder, and is precipitated at the grain boundaries or in the grains of the matrix. Examples of self-lubricating materials include fluorides, sulfides, lead oxides, and the like. The content of the self-lubricating material is usually 0.2 to 5
%, Preferably 0.5 to 3% by weight. If the content is less than 0.2% by weight, the compounding effect of the self-lubricating material, that is, the effect of improving self-lubricating property to improve wear resistance may not be sufficient. On the other hand, if it exceeds 5% by weight, strength and corrosion resistance may be deteriorated.

In the production of the Fe-based sintered material, the density of the green compact is usually set to 6.8 g / cm ³ or more.
Further, the sintering process is performed in a non-oxidizing atmosphere in order to prevent the constituent elements from being oxidized. The sintering temperature and the sintering time are difficult to unconditionally determine because they vary depending on the blending ratio of each component, the shape and size of the green compact, etc., but normally the sintering temperature is 1100 to 1200 ° C. The sintering time is set to 20 to 60 minutes. In this case, an austenite phase capable of forming martensite in the use environment can be formed in the matrix by adjusting the cooling rate in the sintering process or performing solution treatment of the Fe-based sintered material. The hardness of Fe-based sintered material, H _R B is about 1
It is 00 or less and has good workability. Further, since the material has excellent wear resistance, heat resistance and strength, and further has good corrosion resistance, for example, even when it is used for a valve seat of an engine that uses alcohol as a fuel, formic acid generated by the combustion of alcohol is used. There is little effect of corrosion due to.

Next, a specific example will be described.

Table 1 shows compositions of Examples (1) to (4) and Comparative Examples relating to the Fe-based valve seat. This composition is, of course, the same as that of the Fe-based sintered material.

[0020]

[Table 1] In order to manufacture the Fe-based sintered material for each valve seat, Fe-based base powder, first hard powder, second hard powder, third hard powder and MnS powder as a self-lubricating material were prepared.

Table 2 shows the composition of the Fe-based base powder.

[0022]

[Table 2] Table 3 shows the composition of the alloy powder which comprises the 1st-3rd hard powder.

[0023]

[Table 3] Next, the Fe-based sintered material for the valve seat of Example (1) was manufactured by the following method. First, with respect to the Fe-based base powder, 0.6 wt% C powder (graphite powder), 4 wt% Ni powder, 2 wt% Co powder, 10 wt% first hard powder, and 15 wt% A raw material powder was prepared by blending the third hard powder and 0.5% by weight of MnS powder, and 1.0% by weight of zinc stearate (lubricant for mold) was added to the raw material powder, and a V-type blender was used. Mixed for 15 minutes to obtain a mixed powder.

A powder compact having a shape corresponding to the valve seat is formed from the mixed powder by using a hydraulic press machine, and then the compact is fired at 1160 ° C. for 30 minutes using an AX gas furnace. A binding treatment was applied, and then the Fe-based sintered material was manufactured by cooling at a cooling rate of 20 ° C./min.

The hardness Hv _0.025 of the matrix in this Fe-based sintered material was 381, and the austenite phase content was 36.3% in area ratio.

Next, the Fe-based sintered material was subjected to an aging treatment, and the relationship between the aging temperature and the aging time and the hardness Hv _0.025 was examined, and the results shown in Table 4 were obtained.

[0027]

[Table 4] Further, when the relationship between the aging temperature and the aging temperature and the existing amount (area ratio) of the retained austenite phase was investigated, the results shown in Table 5 were obtained.

[0028]

[Table 5] As is clear from Table 4 and Table 5, at each aging temperature,
It is understood that the hardness increases as the aging time elapses and the existing amount of the retained austenite phase decreases, which causes the secondary hardening phenomenon. Therefore, by incorporating the Fe-based sintered material into the engine and operating it, the material is subjected to a secondary hardening treatment at 200 to 400 ° C., and the metal structure of the seating portion and the press-fitting portion is set as described above. The valve seat of the specified embodiment (1) can be obtained.

Next, Fe for valve seat of Example (2)
The sintered material was manufactured by the following method. First, 0.4 wt% of C powder (graphite powder), 6 wt% of Ni powder, 2 wt% of Co powder, and 10 wt% of the Fe-based base powder.
A raw material powder was prepared by blending 1% by weight of the first hard powder, 15% by weight of the second hard powder and 0.5% by weight of MnS powder, and 1.0% by weight of zinc stearate (gold Mold lubricant) was added and mixed for 15 minutes with a V-type blender to obtain a mixed powder.

A powder compact having a shape corresponding to the valve seat is formed from the mixed powder by using a hydraulic press machine, and then the compact is fired at 1160 ° C. for 30 minutes using an AX gas furnace. A binding treatment was applied, and then the Fe-based sintered material was manufactured by cooling at a cooling rate of 20 ° C./min.

The hardness Hv _0.025 of the matrix in this Fe-based sintered material was 475, and the existing amount of the austenite phase was 33.5% in area ratio.

Next, the Fe-based sintered material was subjected to an aging treatment, and the relationship between the aging temperature and the aging time and the hardness Hv _0.025 was examined, and the results shown in Table 6 were obtained.

[0033]

[Table 6] Further, when the relationship between the aging temperature and the aging temperature and the existing amount (area ratio) of the retained austenite phase was investigated, the results shown in Table 7 were obtained.

[0034]

[Table 7] As is clear from Table 6 and Table 7, at each aging temperature,
It is understood that the hardness increases as the aging time elapses and the existing amount of the retained austenite phase decreases, which causes the secondary hardening phenomenon. Therefore, as in the above, by incorporating the Fe-based sintered material into the engine and operating it, the material is subjected to a secondary hardening treatment at 200 to 400 ° C. The valve seat of the embodiment (2) specified as above can be obtained.

Next, the Fe-based sintered material for valve seat of Example (3) was manufactured by the following method. First, 0.4 wt% of C powder (graphite powder), 6 wt% of Ni powder, 2 wt% of Co powder, and 10 wt% of the Fe-based base powder.
A raw material powder is prepared by blending 1% by weight of the first hard powder, 15% by weight of the second hard powder and 0.2% by weight of P powder.
To this raw material powder, 1.0% by weight of zinc stearate (lubricant for mold) was added and mixed with a V-type blender for 15 minutes to obtain a mixed powder.

Using a hydraulic press, a green compact having a shape corresponding to the valve seat is formed from the mixed powder, and then the green compact is fired at 1160 ° C. for 30 minutes using an AX gas furnace. A binding treatment was applied, and then the Fe-based sintered material was manufactured by cooling at a cooling rate of 20 ° C./min.

The hardness Hv _0.025 of the matrix in this Fe-based sintered material was 564, and the austenite phase content was 35% in area ratio.

Further, Fe for valve seat of Example (4)
The sintered material was manufactured by the following method. First, 0.6% by weight of C powder (graphite powder), 4% by weight of Ni powder, 2% by weight of Co powder, and 10% by weight of Fe-based base powder.
A raw material powder is prepared by blending 1% by weight of the first hard powder, 15% by weight of the second hard powder and 0.2% by weight of P powder.
To this raw material powder, 1.0% by weight of zinc stearate (lubricant for mold) was added and mixed with a V-type blender for 15 minutes to obtain a mixed powder.

Using a hydraulic press, a green compact having a shape corresponding to the valve seat was formed from the mixed powder, and then the green compact was baked at 1160 ° C. for 30 minutes using an AX gas furnace. A binding treatment was applied, and then the Fe-based sintered material was manufactured by cooling at a cooling rate of 20 ° C./min.

The hardness Hv _0.025 of the matrix in this Fe-based sintered material was 425, and the austenite phase content was 40% in area ratio.

Next, F corresponding to the embodiments (1) to (3)
By incorporating the e-based sintered material and the Fe-based sintered material corresponding to the comparative example into the exhaust port side of the engine and operating the engine, a valve seat corresponding to those materials is obtained and their seats and exhausts are obtained. When the wear condition of the valve head in the valve was examined, the results shown in FIG. 3 were obtained. The metallic structure of the matrix in the comparative valve sheet was composed of the pearlite phase.

The operating condition of the engine is that the cam rotation speed is 30
00 rpm, valve rotation 20 rpm, operating time
Approx. 9 hours (1.6 x 10 ⁶ contacts), engine temperature 200 ° C, valve spring load 25 kg (set), 62 kg (lift), exhaust valve material N
CF440 (material equivalent to Inconel).

It is apparent from FIG. 3 that Examples (1) to (3) have better wear resistance than the Comparative Example and that the exhaust valve is also suppressed from wearing.

The valve seat according to the present invention is also applied to the intake port side.

[0045]

EFFECTS OF THE INVENTION According to the present invention, by specifying the metal structure as described above, it has high strength and excellent wear resistance, and further suppresses wear of the engine valve which is a counterpart member. Further, it is possible to provide a valve seat that can achieve further thinning.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an engine.

FIG. 2 is an enlarged sectional view of a main part of a valve seat.

FIG. 3 is a graph showing wear conditions of a valve seat and an exhaust valve.

[Explanation of symbols]

 1 Engine 2 Cylinder Head 5 Valve Seat 6 Exhaust Valve (Engine Valve) 14 Seating Part 15 Press Fitting Part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsutomu Saka, 1-4-1, Chuo, Wako-shi, Saitama, Honda R & D Co., Ltd. (72) Inventor, Osamu Kawamura 1111 Nogi, Nogi-cho, Shimotsuga-gun, Tochigi Japan Piston Ring Co., Ltd.Tochigi Plant (72) Inventor Teruo Takahashi 1111 Nogi, Nogi-cho, Shimotsuga-gun, Tochigi Japan Piston Ring Co., Ltd. Tochigi Plant (72) Inventor Shin 1111 Nogi, Nogi-cho, Shimotsuga-gun, Tochigi Japan Piston Ring Stocks Company Tochigi factory

Claims (1)

[Claims] 1. An Fe-based valve seat (5) press-fitted into an Al alloy cylinder head (2) of an engine (1), wherein the matrix metallographic structure is a mixed phase structure having an austenite phase and a martensite phase. In the seating part (14) on which the valve (6) is seated, the amount of the martensite phase is larger than that of the austenite phase, while in the press-fitting part (15) press-fitted into the cylinder head (2), the austenite phase is present. A valve seat for an engine, characterized in that the abundance of phases is greater than the abundance of martensite phases.