WO2012099239A1

WO2012099239A1 - Iron-based sintered alloy valve seat

Info

Publication number: WO2012099239A1
Application number: PCT/JP2012/051191
Authority: WO
Inventors: 林太郎高橋; 浩二逸見; 周一鹿内
Original assignee: 株式会社リケン
Priority date: 2011-01-20
Filing date: 2012-01-20
Publication date: 2012-07-26
Also published as: JP2012149584A; EP2666981A4; MX2013008435A; JP5823697B2; US20130291822A1; CN103328776A; EP2666981A1

Abstract

The purpose of the present invention is to provide an iron-based sintered alloy valve seat that can be used in a DI-type internal combustion engine adapted for enhanced fuel economy, lower emissions, and higher output, the seat being highly wear-resistant across a wide temperature range. To achieve this purpose, the added amount of a solid lubricant dispersed in a base material for the iron-based sintered alloy valve seat is limited, and at least two types of hard particles of different hardness levels are dispersed in the base material, whereby high strength and self-lubricating properties are simultaneously obtained, and wear resistance is improved across a wide temperature range, even under no lubrication.

Description

Ferrous sintered alloy valve seat

The present invention relates to a valve seat for an internal combustion engine, and more particularly to an iron-based sintered alloy valve seat used under lean conditions in a lubricated state by in-cylinder fuel injection. *

In the internal combustion engine, in order to respond to the environment, the fuel consumption is improved, the emission is reduced, and the output is increased, and the components that make up the combustion chamber are widely used due to the increased load of the combustion state and the increased load of the engine specifications. There is a demand for further improvement in wear resistance at temperatures. The valve seats that are the seats of the intake and exhaust valves and have the function of keeping the combustion chamber secret are also exposed to the combustion pressure during combustion and are repeatedly subjected to strong impacts due to the reciprocating motion of the valves. In addition, the valve is rotatable around the valve shaft at the same time as the reciprocating motion, and the sliding surface of the valve seat that contacts the valve requires wear resistance. In particular, in DI (Direct Injection) internal combustion engines in which fuel is directly injected into the cylinder, the sliding surface between the valve and the valve seat slides without lubrication by the fuel without lubrication. In addition, there is a need for improved wear resistance. For this reason, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-166025, a large amount of solid lubricant such as calcium fluoride is dispersed in the base to enhance self-lubrication, thereby preventing wear under no lubrication. Ferrous sintered alloys with improved properties have been used for valve seats.

However, in the valve seat of the conventional iron-based sintered alloy in which calcium fluoride is dispersed in a large amount in the base as a solid lubricant, the strength of the sintered body is low, and the wear resistance in the low temperature range is not sufficient, There was a problem in application in a wide operating temperature range. Further, the conventional iron-based sintered alloy valve seat containing only ferromolybdenum as hard particles also has insufficient wear resistance in a wide operating temperature range. *

In view of the above problems, the present invention is an iron-based sintered alloy having high wear resistance in a wide temperature range that can be used for a DI-type internal combustion engine corresponding to improvement in fuel consumption, low emission, and high output. It is an object to provide a valve seat made by the manufacturer.

As a result of diligent research, the inventors of the present invention limited the amount of solid lubricant added to the base of the iron-based sintered alloy valve seat and contained at least two types of hard particles having different hardness in the base. By dispersing, it was conceived that high strength and self-lubricating properties can be simultaneously imparted, and wear resistance can be remarkably improved in a wide temperature range even under non-lubrication.

That is, the present invention is an iron-based sintered alloy valve seat in which at least two kinds of hard particles having different hardness and a solid lubricant are dispersed, and the solid lubricant is dispersed in an amount of 0.2 to 0.8% by mass. It is characterized by that.

The at least two types of hard particles having different hardnesses are composed of first hard particles and second hard particles. As the first hard particles, hard particles having an average particle diameter of 50 to 150 μm and a Vickers hardness of Hv 800 to 1200 are mass%. It is preferable to disperse 2 to 8%, and as the second hard particles, it is preferable to disperse 5 to 15% by mass of hard particles having an average particle diameter of 10 to 150 μm and a Vickers hardness Hv of 400 to 750. As the hard particles, Fe—Mo alloy particles, Fe—Cr—Mo—V alloy particles, and Co—Mo—Cr alloy particles can be used. In particular, the first hard particles are, by mass%, Mo: 40 to 70%, Si: 0.1 to 2.0%, the balance is Fe-Mo-Si alloy particles composed of Fe and inevitable impurities, and the second hard particles are C : 0.2-0.5%, Cr: 0.5-5%, Mo: 1-5%, V: 2-5%, the balance being Fe-C-Cr-Mo-V alloy particles consisting of Fe and inevitable impurities desirable.

Furthermore, the composition of the base part in which at least two kinds of the hard particles having different hardness and the solid lubricant are dispersed is mass%, C: 0.5 to 2.5%, Si: 0.4 to 2%, Mo: 0.5 to 5% Ni: 1 to 5%, the balance is preferably made of Fe and inevitable impurities, and the matrix phase preferably contains a tempered martensite phase and a pearlite phase.

Furthermore, as the solid lubricant, one or more powders selected from sulfides such as MnS and MoS ₂ and nitrides such as BN are preferable, and the average particle diameter is preferably 2 to 50 μm.

The valve seat made of an iron-based sintered alloy according to the present invention has a high strength and high dispersion by dispersing a solid lubricant in 0.2 to 0.8% by mass and dispersing at least two types of hard particles having different hardness in the base. Self-lubricating properties can be imparted simultaneously, and wear resistance can be significantly improved in a wide temperature range even without lubrication. Two types of hard particles are composed of a part of the elements constituting one hard particle, forming a solid solution or a compound with the element in the matrix to strengthen the matrix and the element constituting the other hard particle. By suppressing solid solution in the substrate and increasing softening resistance, it contributes to improvement of wear resistance at high and low temperatures. As a result, as a valve seat used in DI type internal combustion engines in which fuel is directly injected into the cylinder, it can be used in a wide range of temperatures from low to high temperatures at low temperatures of about 150 to 350 ° C under the condition of lean lubrication. Excellent wear resistance even when used. The iron-based sintered alloy valve seat of the present invention is particularly preferably applicable as an intake valve seat.

It is the figure which showed the outline of the single-piece | unit abrasion test used for evaluation of the iron-base sintered alloy valve seat of this invention. It is the result of evaluation by the single wear tester of the valve seat of the example of the present invention and a comparative example, and shows the amount of wear of the valve seat and the valve at a test temperature of 150 ° C. in a relative ratio. It is the evaluation result by the single wear tester of the valve seat of the example of the present invention, and a comparative example, and it is a figure showing the amount of wear of the valve seat in the test temperature of 250 ° C by the relative ratio. It is the result of evaluation by a single wear tester of the valve seat of the example of the present invention and the comparative example, and is a diagram showing the total wear amount of the valve seat and the valve at a test temperature of 150 ° C. in a relative ratio. It is the result of evaluation by the single wear tester of the valve seat of the example of the present invention and the comparative example, and is a diagram showing the total wear amount of the valve seat and the valve at a test temperature of 250 ° C. in a relative ratio.

The iron-based sintered alloy valve seat of the present invention is composed of a base, at least two kinds of hard particles having different hardness dispersed in the base, and a solid lubricant. The solid lubricant dispersed in the base is 0.2 to 0.8% by mass. When the solid lubricant is dispersed in excess of 0.8%, the powder bonding strength is reduced during powder compression molding, the strength of the sintered body is reduced, and sufficient wear resistance cannot be obtained. On the other hand, if it is less than 0.2%, the machinability is poor. The average particle size of the solid lubricant is preferably 2 to 50 μm. By uniformly dispersing the solid lubricant in the matrix, the wear resistance as well as the self-lubricity and the machinability are improved.

The solid lubricant is preferably one or more selected from sulfides such as MnS and MoS ₂ and nitrides such as BN (boron nitride). When two or more kinds of solid lubricants are used, it is more preferable that at least one kind is uniformly dispersed with an average particle diameter of 2 to 10 μm and other kinds with an average particle diameter of 10 to 50 μm. Solid lubricants with an average particle size of 2 to 10 μm improve machinability by being finely dispersed, and solid lubricants with a particle size range of 10 to 50 μm improve self-lubricating properties by being relatively coarse. And wear resistance is improved.

Regarding the hard particles dispersed in the matrix, the first hard particles are harder than the second hard particles, and the second hard particles are harder than the matrix phase. Due to the presence of the intermediate hardness hard particles, the hardness of the base phase and the hard particles can be balanced, and the attack of the mating material can be suppressed while maintaining the wear resistance.

The first hard particles preferably have an average particle size of 50 to 150 μm, a Vickers hardness of Hv 800 to 1200, and are dispersed 2 to 8% by mass. In particular, it is preferable to use Fe—Mo—Si alloy particles of an intermetallic compound consisting of Mo: 40 to 70%, Si: 0.1 to 2.0%, and the balance of Fe and inevitable impurities. By using it together with the second hard particles described later, diffusion of the alloy element into the matrix is suppressed, the matrix structure is not altered, softening resistance can be increased, attack on the counterpart material can be suppressed, and self wear resistance It becomes possible to improve the property.

The second hard particles are preferably harder than the matrix, have an average particle size of 10 to 150 μm, a Vickers hardness of Hv 400 to 750, and are preferably dispersed 5 to 15% by mass. More preferably, the average particle size is 20 to 130 μm. In particular, Fe-C-Cr-Mo consisting of C: 0.2 to 0.5%, Cr: 0.5 to 5%, Mo: 1 to 5%, V: 2 to 5%, the balance being Fe and inevitable impurities. It is preferable to use -V alloy particles. By dispersing relatively fine second hard particles in the matrix, some of the alloy elements (for example, Cr and V) form solid solutions or carbides in the matrix to strengthen the matrix and the first hard particles Suppresses diffusion of the alloy element into the base material. As a result, it is possible to suppress attacks on the counterpart material and to improve the self wear resistance.

The base portion preferably has a composition of C: 0.5 to 2.5%, Si: 0.4 to 2%, Mo: 0.5 to 5%, Ni: 1 to 5% and the balance of Fe and inevitable impurities in mass%. . C dissolves in the base and strengthens the base, and combines with other alloy elements to form carbides, improving wear resistance. In addition, Si improves the wear resistance by forming an oxide film, and Mo improves the wear resistance by lowering the oxidation start temperature of the valve seat as well as improving the hardenability and base strength. Ni improves wear resistance by improving the strength and hardness of the base. The microscopic structure preferably includes a mixed structure of tempered martensite and pearlite. In this case, the microstructural structure has appropriate toughness and excellent wear resistance. Of course, fine carbides are dispersed in the mixed structure.

In the production of the iron-based sintered alloy valve seat of the present invention, as a raw material of the base phase, metal powder of each alloy element, graphite powder, etc. may be added to iron powder, and an alloy alloyed in advance with a predetermined composition Powder (pre-alloy alloy powder) may be used. At least two types of hard particle powders and solid lubricant powders having different hardnesses are blended into the iron powder and / or prealloy alloy powder and alloy element powder constituting the matrix phase, and the mixed powder is used as raw material powder. Stearate, etc., may be blended as a mold release material in an amount of 0.5-2% of the total amount of raw material powder, that is, iron powder, prealloy alloy powder, alloy element powder, hard particles, and solid lubricant powder. good. The mixed powder is compressed and molded by a molding press or the like to be molded into a green compact, and the green compact is sintered in a temperature range of 1050 to 1200 ° C. in a vacuum or non-oxidizing (or reducing) atmosphere. It is tempered in the temperature range of 500-700 ° C. The sintered body after tempering may be sealed with a resin or the like.

When the sintering temperature is less than 1050 ° C., diffusion bonding is insufficient and a predetermined strength cannot be obtained. On the other hand, if sintering is performed at a temperature exceeding 1200 ° C., abnormal diffusion occurs between the hard particles and the matrix, resulting in deterioration of wear resistance. Specifically, the non-oxidizing (or reducing) atmosphere is desirably an atmosphere using NH ₃ gas, a mixed gas of N ₂ and H ₂ , or the like.

Examples 1 to 5 (E1 to E5) and Comparative Examples 1 to 6 (C1 to C6)
Pure iron powder with a particle size distribution having a peak at 150 to 200 mesh and / or prealloy alloy powder consisting of Mo: 2.5%, Si: 1%, C: 0.02%, the balance being iron (including inevitable impurities) Predetermined amounts of Mo powder, Si powder, Ni powder, and graphite powder with the blending amounts of base parts A to K shown in Fig. 1, and L to R first hard particles of Fe-Mo-Si alloy shown in Table 2 And the second hard particles of S to Y of the Fe—C—Cr—Mo—V alloy shown in Table 3 and the solid lubricant powder shown in Table 4 were blended in the ratios (mass%) shown in Table 4, respectively. A mixed powder was prepared by kneading with a mixer.

These mixed powders are filled into a molding die, compressed and molded with a molding press at a surface pressure of 6.5 t / cm ² , and then sintered in a vacuum atmosphere at 1120 ° C., outer diameter 37.6 mmφ, inner diameter 26 mmφ, thickness An 8 mm ring-shaped sintered body was produced. Thereafter, a tempering treatment was performed at 650 ° C. In this way, the base part including the tempered martensite phase and the pearlite phase, and two types of hard particles (Fe-Mo-Si alloy and Fe-C-Cr-Mo-V alloy) having different hardness in the base Then, ring-shaped sintered bodies of Examples 1 to 5 (E1 to E5) in which a solid lubricant (MnS and / or BN) was dispersed were obtained. As comparative examples, the total amount of solid lubricant is 1% or more (Comparative Examples 1 (C1), 2 (C2), 4-6 (C4-C6)), and only one type of hard particle powder ( Using the mixed powders of Comparative Examples 3 and 4 (C3, C4)), ring-shaped sintered bodies of Comparative Examples 1 to 6 (C1 to C6) were obtained in the same steps as in Examples 1 to 5. The Vickers hardness of the base portion and hard particles of the obtained sintered body was measured with a micro Vickers hardness meter at a load of 50 to 100 g. The results are also shown in Table 4.

The obtained ring-shaped sintered body was processed into a valve seat, and the wear resistance was evaluated using a single wear tester shown in FIG. The valve seat 4 is press-fitted into a valve seat holder 2 which is a cylinder head equivalent material and set in a testing machine. The wear test is performed in conjunction with the rotation of the cam 7 while the valve 3 and the valve seat 4 are heated by the burner 1. Done by moving 3 up and down. The valve seat 4 is embedded with thermocouples 5 and 6 and the heating power of the burner 1 is adjusted so that the contact surface of the valve seat has a predetermined temperature. The valve seat 4 was worn by being repeatedly struck by the valve 3, and the amount of wear was calculated as the receding amount of the contact surface by measuring the shape of the valve seat and the valve before and after the test. Here, a valve made of SUH alloy (JIS standard: JIS G 4311) having a size suitable for the valve seat was used. The test conditions were a temperature of 150 ° C. and 250 ° C., a cam rotation speed of 2500 rpm, and a test time of 5 hours. The test results are shown in Table 5, FIG. 2 (a) (test temperature 150 ° C.), and FIG. 2 (b) (test temperature 250 ° C.).

The amount of wear of the valve seat is shown as a relative ratio when the amount of wear in Comparative Example 3 (C3) in which only Fe—Mo—Si alloy is added and dispersed in hard particles is taken as 1. In Examples 1 to 5 (E1 to E5) according to the present invention, the valve seat wear amount was reduced compared to Comparative Example 3 (C3) at the test temperatures of 150 ° C. and 250 ° C., and the valve wear amount of the counterpart material was also reduced. It showed reduced wear resistance and relatively mild attack on the mating material in both low and high temperature ranges. Also, the total wear amount of the valve seat and the valve is less than half of Comparative Example 3 in Examples 1 to 5 (E1 to E5) according to the present invention at 150 ° C. and 250 ° C., from the low temperature range to the high temperature range. The wear resistance is remarkably improved in a wide temperature range. On the other hand, the total amount of solid lubricant is 1% or more (Comparative Example 1 (C1), 2 (C2), 4-6 (C4-C6)), and only one type of hard particle powder (Comparative Example 3) , 4 (C3, C4)) has improved wear resistance at test temperatures of 150 ° C and 250 ° C, but has a remarkable wear resistance in a wide temperature range from low to high temperatures. An improvement could not be obtained. In the embodiment of the present invention, the valve seat wear amount and the wear amount of the counterpart material are small in a wide temperature range from the low temperature range to the high temperature range as compared with the comparative example, the wear resistance is improved, and the aggressiveness of the counterpart material is improved. Has also declined.

Claims

An iron-based sintered alloy valve seat in which at least two kinds of hard particles having different hardness and a solid lubricant are dispersed, wherein the solid lubricant is dispersed in an amount of 0.2 to 0.8% by mass%. Valve seat made of iron-based sintered alloy.
At least two kinds of hard particles having different hardness are composed of a first hard particle and a second hard particle. As the first hard particles, hard particles having an average particle diameter of 50 to 150 μm and a Vickers hardness Hv 800 to 1200 in mass%. 2. The iron according to claim 1, wherein hard particles having an average particle diameter of 10 to 150 μm and Vickers hardness Hv 400 to 750 as 2nd hard particles are dispersed in an amount of 5 to 15% by mass. Base sintered alloy valve seat.
The first hard particles are Fe-Mo-Si alloy composed of Mo: 40 to 70%, Si: 0.1 to 2.0%, the balance being Fe and inevitable impurities, and the second hard particles are C : 0.2-0.5%, Cr: 0.5-5%, Mo: 1-5%, V: 2-5%, the balance being Fe-C-Cr-Mo-V alloy consisting of Fe and inevitable impurities 3. The valve seat made of an iron-based sintered alloy according to claim 1, wherein the valve seat is made of an iron-based sintered alloy.
The composition of the matrix in which at least two kinds of the hard particles having different hardness and the solid lubricant are dispersed is mass%, C: 0.5 to 2.5%, Si: 0.4 to 2%, Mo: 0.5 to 5%, Ni: 4. The iron-based sintered alloy valve seat according to claim 1, comprising 1 to 5%, the balance being Fe and inevitable impurities.
5. The iron-based sintered alloy valve seat according to claim 4, wherein the base includes a tempered martensite phase and a pearlite phase.
6. The iron-based firing according to claim 1, wherein the solid lubricant is at least one selected from sulfides and nitrides, and has an average particle size of 2 to 50 μm. Bonded valve seat.