WO2005038065A1

WO2005038065A1 - Fe-Al-C SINTERED ALLOY VALVE SHEET HAVING EXCELLENT OXIDATION RESISTANCE AT HIGH TEMPERATURE AND HIGH STRENGTH

Info

Publication number: WO2005038065A1
Application number: PCT/JP2004/015121
Authority: WO
Inventors: Koichiro Morimoto; Kunio Hanata; Takashi Nishida; Tomohiro Sakai
Original assignee: Mitsubishi Materials Pmg Corporation
Priority date: 2003-10-16
Filing date: 2004-10-14
Publication date: 2005-04-28
Also published as: JP2005120416A

Abstract

[PROBLEMS] To provide a valve sheet made of an Fe-Al-C sintered alloy which exhibits excellent resistance to oxidation at a high temperature and high strength. [MEANS FOR SOLVING PROBLEMS] A valve sheet made of an Fe-Al-C sintered alloy which comprises an Fe-Al-C sintered alloy having a chemical composition, in mass %, that Al: 20 to 30 %, C: 0.5 to 1.5 % and the balance: Fe and inevitable impurities, and a Fe-Al-C solid solution single phase structure.

Description

Specification

Valve seat made of sintered Fe-A1-C alloy with excellent high-temperature resistance to oxidation and high strength

Technical field

The present invention has excellent high-temperature oxidation resistance and high strength, and exhibits excellent wear resistance over a long period of time, particularly when incorporated in an engine of an LP gas vehicle that is a low-emission vehicle. Related to valve seats made of Fe-A1-C sintered alloy.

Background art

[0002] Conventionally, many valve seats made of an Fe-based sintered alloy have been proposed as valve seats for various types of automobile engines, and among them, in terms of mass% (hereinafter,% indicates mass%),

Al: 5-30%,

C: 0.2-3%,

Containing Fe and the balance consisting of Fe and unavoidable impurities, and a two-phase mixed structure of Fe—A1 alloy phase and Fe—C phase, or Fe—A1 alloy phase, Fe—C phase, and carbon (C) phase Attention has been focused on a valve seat made of a sintered Fe—A1-C alloy having a three-phase mixed structure.

[0003] In addition, the above-mentioned conventional valve seat made of a sintered Fe-A1-C alloy can be used under normal conditions, that is, in an atmosphere of ammonia decomposition gas or RX decomposition gas at a temperature of 1050-1150 ° C. Even if sintering for 2 hours, a sintered body with a specified strength is manufactured due to the poor sinterability of the powders of Fe powder, A1 powder and carbon powder used as raw material powders. Therefore, the raw material powder is blended into a predetermined composition, mixed, and press-formed into a green compact at a current density of 5 to 100 AZmm2 by current press molding sintering (press pressure is usually lOOMPa).

Patent Document 1: JP-A-2002-146495

Patent Document 2: JP 2002-146496

Disclosure of the invention

Problems to be solved by the invention

[0004] In recent years, the speed and output of automobiles have been remarkably increased, and the weight and size of automobiles have been remarkable. On the other hand, LP gas vehicles are attracting attention as low-emission vehicles due to their environmental friendliness and low exhaust gas. Therefore, the exhaust gas from the engines of the LP gas vehicles tends to be hotter, and therefore, the structure of the engine is low. The valve seat, which is a member, is exposed to high-temperature exhaust gas, which can reach 800-900 ° C, as well as the contact pressure from the valve, which is the same member, while avoiding thinning and reduction in diameter. It is not possible at present.

[0005] The valve seat made of the conventional Fe-A1-C sintered alloy has a two-phase mixed structure and a three-phase mixed structure as described above, and has the Fe-C phase of the constituent phases. Is inferior to high-temperature oxidation resistance, and particularly when incorporated in an engine of an LP gas vehicle, the high-temperature low exhaust gas causes the oxidation of the Fe—C phase to proceed relatively quickly, Wear is accelerated by the cause, and in the case of the two-phase mixed structure and the three-phase mixed structure, the strength of the phase boundary is low due to insufficient sinterability, so that it is sufficient for thinning and diameter reduction. Strength cannot be secured.

Means for solving the problem

[0006] In view of the above, the present inventors have paid particular attention to the above-mentioned conventional valve seat made of a sintered Fe-A1-C alloy and intended to improve its high-temperature oxidation resistance and strength. As a result of the research conducted, when manufacturing valve seats made of Fe-A1-C sintered alloy, as mentioned above, Fe powder, A1 powder, and carbon (C) powder were used as raw material powders. In the case of sintering conditions of 0.5 to 2 hours at a temperature of 1050 to 1150 ° C in an atmosphere such as ammonia decomposed gas or RX decomposed gas for 0.5 to 2 hours, It has a two-phase mixed structure and a three-phase mixed structure, similar to the conventional valve seat made of sintered Fe-A1-C sintered alloy, and the sinterability (adhesion) between these constituent phases is much worse. Therefore, the valve seat is stronger than the conventional Fe-A1-C sintered alloy valve seat. Although it is low in strength and cannot be produced, it also has low resistance to high-temperature oxidation at the phase boundary in addition to the Fe-C phase. Powder, preferably Fe—50% A1 alloy powder, and carbon (C) powder, and these raw powders are mixed in a specific composition, that is,

Al: 20-30%,

C: 0.5-1.5%, Fe: remaining,

The green compact obtained by blending with the blending composition of the above, mixing under normal conditions, and press-molding, in a vacuum, preferably in a vacuum of lOPa or less, is relatively higher than the normal sintering temperature described above! After sintering at a temperature of 120 0-1300 ° C for 13 hours, the manufactured valve seats completely dissolve Fe-A1 alloy and carbon (C) in Fe during sintering. As a result, the valve seat made of a Fe—A1—C solid solution has a Fe—A1—C solid solution single phase structure. The research results show that the results will be further improved.

[0007] The present invention has been made based on the above research results,

Al: 20-30%,

C: 0.5-1.5%,

Excellent high-temperature oxidation resistance and high strength composed of Fe-A1-C sintered alloy with Fe-A1-C solid solution single-phase structure, with the composition containing iron and the balance being Fe and inevitable impurity power It is characterized by a valve seat made of a sintered Fe-A1-C alloy having the following characteristics.

Next, the reason why the composition of the Fe—A1-C sintered alloy constituting the valve seat of the present invention is limited as described above will be described.

(a) Al

As described above, the Fe—A1—C solid solution single phase structure of the Fe—A1—C sintered alloy constituting the valve seat of the present invention includes Fe powder, Fe—Al alloy powder, and carbon (C) as raw material powders. It can be formed by using powder, limiting the content ratio of A1 and C as described above, and performing high-temperature vacuum sintering, and has higher strength and strength because the phase boundary does not exist. The Fe—A1-C solid solution itself, which is hardly colored, also has the strength of the Fe component, the high-temperature oxidation resistance of the A1 component, and the hardness by the action of the C component. However, if the content of the A1 component is less than 20%, the desired excellent high-temperature oxidation resistance cannot be secured, while if the content exceeds 30%, the Fe-A1 alloy powder as the raw material powder is blended. If the ratio becomes too large, it becomes difficult to completely dissolve in Fe at the time of sintering, and a two-phase mixed structure and a three-phase mixed structure that cause deterioration in strength and high-temperature oxidation resistance will appear. Therefore, the content ratio of A1 component was determined to be 20-30%. (b) C

The C component, which is a Fe—Al—C solid solution, has the effect of improving its hardness and thereby improving the wear resistance of the valve sheet, but is desirable if its content is less than 0.5%. When the content ratio exceeds 1.5%, complete solid solution in Fe during sintering becomes difficult as in the case of A1, and a two-phase mixed structure and three-phase The content and the content of the C component were determined to be 0.5 to 1.5% because the mixed structure resulted in a rapid decrease in strength and high-temperature oxidation resistance.

The invention's effect

The valve seat made of a sintered Fe—A1—C alloy of the present invention is composed of a sintered Fe—A1—C alloy having a single phase structure of a solid solution of Fe—A1—C. Because the phase structure has excellent high-temperature oxidation resistance and high strength, especially when incorporated into the engine of an LP gas vehicle, which is a low-emission vehicle, the exhaust gas power S800 — Despite reaching a high temperature of 900 ° C, it exhibits excellent abrasion resistance over a long period of time, and enables thinning and small diameter molding.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, a valve seat made of a sintered Fe—A1-C alloy of the present invention will be specifically described with reference to examples.

Example

As raw material powders, Fe powder and Fe—50% A1 alloy powder having a sieve mesh size of 0.2 mm and carbon (C) powder having an average particle diameter of: The mixture was blended in the composition shown in 1 and 0.8% of zinc stearate was added as a binder to the above-mentioned blended powder at a ratio of 0.8% and mixed with a mixer for 30 minutes. 3mm X inner diameter: 31mm X height: 6.5mm Press molded into a ring-shaped molded body having a size of 6.5mm, this molded body was heated at 400 ° C for 20 minutes in a vacuum of 3Pa under the conditions described above. After removing the binder, it was sintered in a vacuum of 3 Pa and held at 1250 ° C, which is relatively higher than the normal sintering temperature, for 1.5 hours under vacuum and high-temperature sintering. Outer Diameter: 40mm X Inner Diameter: 34mm X Height: 6mm Machined into a dimension and also subjected to a contact surface truing process, the present invention Fe-A1-C sintered alloy valve seal (Hereinafter, referred to as the present invention sintering Roh Rebushito) 1 one 7 Was manufactured respectively.

For the purpose of comparison, Fe powder having an average particle size of 5 μm, A1 powder having an average particle size of 20 μm, and carbon (C) powder having an average particle size of 10 m were used as raw material powders. The raw material powder was blended into the blending composition shown in Table 1, 0.8% zinc stearate was added as a binder to the blended powder at a ratio of 0.8%, and the mixture was mixed with a mixer for 30 minutes. , Outer diameter: 43mm X inner diameter: 31mm X height: 6.5mm Press-molded into a ring-shaped molded body with dimensions of 6.5mm, and after debinding the molded body under the same conditions, the pressure of lOOMPa was increased. Ca卩energized press molded and sintered at conditions of 3 seconds holding at a current density of 25 AZmm ² while example, as a result of the sintered body outer diameter: 40 mm X inner diameter: 34 mm X height: machined to the dimension of 6mm Also, by applying contact surface processing, the conventional valve seat made of Fe-A1-C sintered alloy (hereinafter referred to as conventional sintered valve sheet) 117 Each was produced.

[0013] The structures of the sintered valve seat 117 of the present invention and the conventional sintered valve seat 117 obtained as a result were observed using a metallographic microscope. The sintered valve seat 117 shows a single-phase structure of the Fe—A1—C solid solution with a deviation, and the conventional sintered valve seat 117 has a two-phase mixed structure of the Fe—A1 alloy phase and the Fe—C phase. Or, it showed a three-phase mixed structure of Fe-A1 alloy phase, Fe-C phase and carbon (C) phase. Table 1 also shows the results of measuring the radial crushing strength for the purpose of evaluating the strength. Table 1 also shows the Vickers hardness.

[Table 1] Composition (mass High-speed operation wear test result

E ring

Seed hardness

Sintered structure

(HV) Strength Max.

AI C Fe (Pa) Wear depth Maximum wear

(jU m) Depth (m)

1 20 1 Remaining solid solution single phase 331 874 1 6 1 2

2 22.5 1 Remaining solid solution single phase 355 932 1 2 1 3

True

3 25 1 Remaining empty Solid solution single phase 374 1056 1 0 1 3

Akira r 4 27.5 1 Residual solid solution single phase 382 989 1 1 1 5

Bake 5 30 1 Residual solid solution single phase 391 93 1 3 1 8

Ending ending

6 25 0.5 Residual solid solution single phase 343 850 1 4 1 6

7 25 1 5 Remaining solid solution single phase 389 904 1 2 1 9

1 20 1 Remaining 2 phases mixed 231 451 1 1 3 21

Through

B Z 22.5 1 Remaining Feng 2 phase mixed 258 483 02 24

j

Follow 3 25 1 Remaining 2 phases mixed 277 502 98 35

Coming

4 27. 5 1 Remaining 3 phases mixed 284 514 95 48

Grilled

Success

Conclusion 1 5 30 1 Remaining 3 phases mixed 290 526 91 55

h

6 25 0.5 Afterburning 2-phase mixture 251 468 35 21

Conclusion

7 25 1.5 3 remaining phases mixed 283 433 109 47 Next, the sintered valve seat 117 of the present invention and the conventional sintered valve seat 117 are assembled into an engine of an LP gas vehicle having a displacement of 5000 cc, respectively.

Rotation speed: 3000rpm,

Counterpart material (valve): JIS · SUH35 (heat resistant steel) body with stellite 12 overlaid with lmm thickness,

Test time: 200 hours,

A high-speed operation wear test of the actual machine was performed under the following conditions. After the test, the maximum wear depth was measured, and also the maximum wear depth of the knob, which was the mating material, was measured. The results are also shown in Table 1.

[0015] From the results shown in Table 1, it can be seen that the sintered valve seat 117 of the present invention made of Fe-A1-C sintered bond gold having a single-phase structure of Fe-A1-C solid solution has the above-mentioned Fe — A1— C solid solution The single-phase structure has excellent high-temperature oxidation resistance, so when it is incorporated into the engine of an LP gas vehicle, which is a low-emission vehicle, it is accompanied by high-speed driving and high output of the vehicle. Despite the fact that the exhaust gas reaches a high temperature of 800-900 ° C, it exhibits extremely low aggressiveness and excellent wear resistance over a long period of time. Conventional sintered valve seat composed of a Fe—A1—C sintered alloy with a ^two- phase mixed structure of phases or a three-phase mixed structure of Fe—A1 alloy phase, Fe—C phase, and carbon (C) phase 7, under the severe operating conditions described above, in addition to the Fe-C phase, especially the phase boundary portion has poor high-temperature oxidation resistance. Since Sani 匕進 line Hayagu this wear is accelerated due to those, those leading to relatively short time service life.

As described above, the valve seat made of a sintered Fe—A1-C alloy according to the present invention can be used not only for a gasoline engine and a diesel engine, but also for a high speed and high output of an automobile. Has reached a high temperature of 800-900 ° C and has low exhaust gas, so the contact between the valve seat and valve takes the form of direct metal-to-metal contact. In such a case, excellent wear resistance is exhibited over a long period of time, and since it has high strength, it is possible to reduce the thickness and diameter of the vehicle. And it can respond satisfactorily to miniaturization.

Claims

The scope of the claims

Fe containing Al: 20-30%, C: 0.5-1.5% by mass%, the balance being Fe and unavoidable impurities, and Fe-A1-C solid solution single-phase structure — Valve seat made of Fe-A1-C sintered alloy with excellent high-temperature oxidation resistance and high strength composed of A1-C sintered alloy