JP5823697B2 - Ferrous sintered alloy valve seat - Google Patents

Description

  The present invention relates to a valve seat for an internal combustion engine, and more particularly, to a valve seat made of an iron-based sintered alloy that is used under lean conditions of lubrication 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. Further, 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, where fuel is directly injected into the cylinder, the sliding surface of the valve and 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 Patent Document 1, for example, a solid lubricant such as calcium fluoride is dispersed in a large amount in the base to enhance self-lubrication, thereby improving wear resistance under no lubrication. Ferrous sintered alloys 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.

Japanese Patent Laid-Open No. 2003-166025

  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 valve seat of the present invention is a valve seat made of an iron-based sintered alloy in which at least two kinds of hard particles different in hardness from a solid lubricant are dispersed, and the solid lubricant is 0.2 to 0.8% by mass%. The two kinds of hard particles are made up of first hard particles and second hard particles, and hard particles having an average particle size of 50 to 150 μm and Vickers hardness Hv 800 to 1200 as the first hard particles are 2 to 2% by mass. 8%, hard particles having an average particle diameter of 10 to 150 μm and Vickers hardness Hv of 400 to 490 are dispersed as 5% to 15% by mass% as the second hard particles .

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 in mass%, Mo: 40-70%, Si: 0.1-2.0%, the balance is Fe-Mo-Si alloy particles consisting of Fe and inevitable impurities, 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 in 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 0.2 to 0.8% by mass% of the solid lubricant and dispersing at least two kinds 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, a wide temperature range from low temperature range to high temperature range at about 150 to 350 ° C under lean conditions of lubrication Excellent wear resistance even when used in 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 figure which showed the evaluation result by the single body wear tester of the valve seat of the Example of this invention, and a comparative example. (A) And (b) is the evaluation result which showed the abrasion loss of the valve seat and valve | bulb in the test temperature of 150 degreeC and 250 degreeC, respectively by the relative ratio. It is the figure which showed the evaluation result by the single body wear tester of the valve seat of the Example of this invention, and a comparative example. (A) And (b) is the evaluation result which showed the total amount of wear of the valve seat and valve | bulb in test temperature 150 degreeC and 250 degreeC, respectively by the relative ratio.

  The valve seat made of an iron-based sintered alloy according to 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 decreases. The average particle size of the solid lubricant is preferably 2 to 50 μm, and by dispersing uniformly in the matrix, the self-lubricating property and the machinability are improved as well as the wear resistance.

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 have an average particle size has a Vickers hardness of Hv800~1200 at 50 to 150 [mu] m, is assumed to be distributed 2% to 8% in 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 in mass%. 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 harder than the base, the average particle size has a Vickers hardness of Hv400～ 490 at 10 to 150 m, is assumed to be distributed 5-15% in mass%. More preferably, the average particle size is 20 to 130 μm. In particular, Fe-C-Cr-Mo consisting of mass%, C: 0.2-0.5%, Cr: 0.5-5%, Mo: 1-5%, V: 2-5%, 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 to 2%, based on the total amount of raw material powder, that is, iron powder, pre-alloy 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 form a green compact, and the green compact is sintered in a temperature range of 1050 to 1200 ° C. in a vacuum or a 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 preferably an atmosphere using NH ₃ gas or a mixed gas of N ₂ and H ₂ .

Examples 1-2 (J1-J2), Reference Examples 1-3 (R1-R3) and Comparative Examples 1-6 (C1-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 as shown in Table 1 and the first hard particles L to R of the 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.

* 固体潤滑材の平均粒径はMnSが7μm、BNが10μmであった。

* The average particle size of the solid lubricant was 7 μm for MnS and 10 μm for BN.

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. Thus, the base part containing the tempered martensite phase and the pearlite phase, and two types of hard particles having different hardness in the base (Fe-Mo-Si alloy and Fe-C-Cr-Mo-V alloy) And the ring-shaped sintered compact of Examples 1-2 (J1-J2) and Reference Examples 1-3 (R1-R3) which disperse | distributed solid lubricant (MnS and / or BN) was 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 ( Comparative Examples 3 and 4 (C3, C4)) were used in the same steps as in Examples 1 to 2 (J1 to J2) and Reference Examples 1 to 3 (R1 to R3) using Comparative Powders 1 to 6 (C1 A ring-shaped sintered body of ~ C6) was obtained. The Vickers hardness of the base portion and the 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. Thermocouples 5 and 6 are embedded in the valve seat 4, 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 temperatures 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 and FIG. 2 ((a) test temperature 150 ° C., (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 the Fe—Mo—Si alloy is added and dispersed in the hard particles is 1. In Examples 1 to 2 (J1 to J2) and Reference Examples 1 to 3 (R1 to R3) according to the present invention, the valve seat wear amount at any of test temperatures 150 ° C. and 250 ° C. is different from that of Comparative Example 3 (C3). The valve wear amount of the counterpart material was also reduced, and excellent wear resistance and relatively gentle attack of the counterpart material were exhibited in both the low temperature range and the high temperature range. Moreover, also about the total amount of wear of a valve seat and a valve, Examples 1-2 (J1-J2) by this invention and Reference Examples 1-3 (R1-R3) are below half of comparative example 3 in 150 ° C and 250 ° C. The wear resistance is remarkably improved in a wide temperature range from a low temperature range to a high 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)) have improved wear resistance at the test temperatures of 150 ° C and 250 ° C, but have a remarkable wear resistance in a wide temperature range from low to high temperatures. I couldn't improve. 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.

1 Burner
2 Valve seat holder
3 Valve
4 Valve seat
5 Thermocouple (high temperature side)
6 Thermocouple (low temperature side)
7 cams

Claims (5)

A valve seat made of an iron-based sintered alloy in which at least two kinds of hard particles having different hardness from a solid lubricant are dispersed, wherein the solid lubricant is dispersed by 0.2 to 0.8% by mass , and the two kinds of hard The particles are composed of first hard particles and second hard particles, and the first hard particles are hard particles having an average particle size of 50 to 150 μm and Vickers hardness Hv 800 to 1200 in 2% to 8% by mass, and the second hard particles. A valve seat made of an iron-based sintered alloy, wherein hard particles having an average particle diameter of 10 to 150 μm and Vickers hardness Hv of 400 to 490 are dispersed as particles in an amount of 5 to 15% by mass . The first hard particles are, by mass%, Mo: 40 to 70%, Si: 0.1 to 2.0%, the balance being Fe-Mo-Si alloy 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 consisting of Fe and unavoidable impurities The valve seat made of an iron-based sintered alloy according to claim 1 , The composition of the matrix in which the solid lubricant and the at least two kinds of hard particles having different hardness are dispersed is C: 0.5 to 2.5%, Si: 0.4 to 2%, Mo: 0.5 to 5%, Ni 3. The iron-based sintered alloy valve seat according to claim 1 , wherein the valve seat is made of 1 to 5%, and the balance is Fe and inevitable impurities. 4. The valve seat made of an iron-based sintered alloy according to claim 3 , wherein the base includes a tempered martensite phase and a pearlite phase. 5. 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.

Images