JP4584158B2 - Valve seat material made of iron-based sintered alloy for internal combustion engines - Google Patents

Description

  The present invention relates to a valve seat material for an internal combustion engine, and more particularly, to a valve seat material made of an iron-based sintered alloy suitable for a gas fuel engine, which has further improved strength and wear resistance and low counterattack properties.

  In an internal combustion engine (engine) that uses liquid fuel such as gasoline or light oil, the lubricity between the valve and the valve seat is maintained by the fuel and the combustion products, so that the wear of the valve seat is suppressed to some extent. However, engines using gas fuels such as LPG and CNG have fewer combustion products than metal liquid fuels, making metal contact between the valve and the valve seat easier, and increasing wear on the valve seat. Tend to. Under such circumstances, there has been a demand for further improvement in wear resistance of valve seats for gas fuel engines.

As a means for improving the wear resistance of the valve seat, a method of dispersing a large amount of Fe-W hard particles, Fe-Mo hard particles, carbide hard particles, etc. in the base of the valve seat has been used conventionally. . However, when the dispersion amount of these hard particles is increased, there arises a problem that the attacking property of the counterpart increases and the wear of the valve increases.
In order to solve such a problem, for example, in Patent Document 1, as a base component, C: 0.5 to 1.5% by weight, Cr and / or V: a total of 0.5 to 10.0% by weight, or a group consisting of Ni, Co and Mo At least one element selected from: a total of 2.0 to 20.0 wt%, and a valve seat for an internal combustion engine that contains at least the balance Fe and 26 to 50 wt% of cobalt-based hard particles Has been. It is said that the valve seat manufactured by the technique described in Patent Document 1 can be suitably used for a gas fuel engine under severe use conditions in which contact wear between metals is likely to occur.

  Patent Document 2 discloses a high-speed tool steel phase in which the overall composition is made of the balance Fe, including appropriate amounts of C, Si, Cr, Ni, Mo, W, Co, and V, in which metal carbides are dispersed. A valve for an internal combustion engine having a structure in which a cobalt alloy hard phase in which a compound is dispersed, an iron alloy phase containing Co-Ni-Mo-C, and an intermediate residue in which a cobalt alloy hard phase diffuses into other phases are mixed in a patchy state Seating materials have been proposed. According to the technique described in Patent Document 2, the high temperature wear resistance of the valve seat material is improved, and the life of the valve seat for the LPG internal combustion engine can be extended.

Further, Patent Document 3 discloses that the entire composition includes a proper amount of Co, Mo, Cr, V, Si, C, Ni and the balance Fe, and is in a mixed structure of bainite or bainite and sorbite, and martensite and austenite. In addition, a valve seat material for a high-load engine having a metal structure in which a hard phase surrounded by a diffusion phase in which Co is diffused around a hard phase made of Mo silicide has been proposed. According to the technique described in Patent Document 3, the wear resistance is improved, and it is said that it is suitable as a valve seat material for a high load engine such as a CNG engine.
Japanese Patent Laid-Open No. 11-12697 Japanese Patent No. 2706561 JP 2002-285293 A

  In recent gas fuel engines, further improvement in engine performance is aimed at, and the use environment of the valve seat is becoming more severe. For this reason, the further improvement of the intensity | strength and abrasion resistance of the valve seat used is requested | required. However, the valve seat manufactured by the above-described prior art has a problem that it is not possible to secure a sufficiently satisfactory characteristic for such a requirement.

  The present invention advantageously solves such problems of the prior art, has a predetermined strength even under severe use environment for gas fuel engines, and can maintain excellent wear resistance, and has excellent wear resistance. The object is to propose a valve seat material made of an iron-based sintered alloy for an internal combustion engine.

In order to achieve the above-described problems, the present inventors diligently studied various factors that affect the wear resistance. As a result, in order to improve strength and wear resistance under harsh usage environments such as in gas fueled engines, it is important to disperse a large amount of hard particles with low opponent aggression in the base phase. In order to disperse a large amount of hard particles in the base, it has been found that a material having a density of 6.7 g / cm ³ or more and a crushing strength of 350 MPa or more is required. As a result, it has been found that hard particles can be prevented from detaching from the matrix phase, and that high strength and excellent wear resistance can be ensured over a long period of time in a severe use environment. The present invention has been completed based on the above findings and further studies.

That is, the gist of the present invention is as follows.
(1) A valve seat material made of an iron-based sintered alloy for an internal combustion engine in which hard particles are dispersed in a base phase of an iron-based sintered alloy, wherein the base phase is in mass% and C: 0.3 to A base phase composition containing 1.5% and a total of 1 to 20% of one or more selected from Ni, Co, Mo, Cr, and V, the balance being Fe and inevitable impurities And the hard particles include intermetallic compounds mainly composed of Fe, Mo, Si, intermetallic compounds mainly composed of Co, Mo, Si, and intermetallic compounds mainly composed of Ni, Mo, Si. Hard particles containing one or more of them, having a Vickers hardness of 500 HV0.1 to 1200 HV0.1, 35 % to 60% by mass, and having a density of 6.7 g / cm ³ or more A valve seat material made of an iron-based sintered alloy for an internal combustion engine, having a crushing strength of 420 MPa or more.

(2) In (1), the matrix phase is, by mass%, C: 0.3 to 1.5%, one or more selected from Ni, Co, and Mo, or further Cr, V A valve seat material made of an iron-based sintered alloy for an internal combustion engine, containing 1 to 20% in total of one or two selected from among them.
(3) In (1) or (2), the hard particles are intermetallic compounds mainly composed of Fe, Mo, Si, intermetallic compounds mainly composed of Co, Mo, Si, Ni, Mo, Si Hard particles containing one or more of the intermetallic compounds whose main component is bismuth and containing, by mass%, Si: 1 to 15%, Mo: 20 to 60%, Cr, Ni, Co An iron-based sintered alloy valve seat material for an internal combustion engine having a composition comprising 10% to 70% of one or more selected from Fe and the balance of inevitable impurities.

  (4) In (3), the hard particles contain, in mass%, Si: 1 to 15%, Mo: 20 to 60%, or Cr: 25% or less and / or Co: 10 to 40%. And Fe-based hard particles having a composition consisting of Fe and inevitable impurities in the balance, in mass%, including Si: 1 to 15%, Mo: 20 to 60%, or further including Cr: 5 to 25%, Co-based hard particles with the balance consisting of Co and inevitable impurities, and in mass%, Si: 1-15%, Mo: 20-60%, or Cr: 5-25% and / or Co: A valve seat material made of an iron-based sintered alloy for an internal combustion engine, characterized in that it contains 10% or less and the balance is any one of Ni-based hard particles having a composition consisting of Ni and inevitable impurities.

(5) A valve seat material made of an iron-based sintered alloy for an internal combustion engine, wherein the solid lubricant is contained in an amount of 0.2 to 5% by mass in any one of (1) to (4).
(6) In any one of (1) to (5), as raw material powder, alloy element powder or low alloy steel powder is mixed with pure iron powder so as to have the matrix phase composition, and further mixed with hard particles to a mixed powder, compression molding - through the steps repeated twice sintering, or once compression molding - after the sintering step forging - internal combustion engine characterized by comprising been manufactured through a process of performing sintering Iron-based sintered alloy valve seat material.

  According to the present invention, it is possible to easily and stably manufacture a valve seat that can ensure excellent wear resistance as well as excellent strength even under severe use environment such as in a gas fuel engine, and a remarkable industrial effect. Play.

The valve seat material of the present invention is an iron-based sintered alloy valve seat material for internal combustion engines in which hard particles are dispersed in the base phase of the iron-based sintered alloy. Hereinafter, the mass% related to the composition is simply expressed as%.
In the valve seat material of the present invention, the base phase is C: 0.3 to 1.5%, and one or two or more selected from Ni, Co, Mo, Cr and V in total 1 to 20%. And having a matrix phase composition composed of the remaining Fe and inevitable impurities.

First, the reason for limiting the composition of the base phase will be described.
C: 0.3-1.5%
C is added to promote diffusion during sintering, but is an element that dissolves in the matrix and increases the strength of the matrix phase. Need. On the other hand, when the content exceeds 1.5%, cementite is likely to be generated in the matrix, and a liquid phase is likely to be generated during sintering, the stability of the structure is lowered, and the dimensional change of the product is increased. For this reason, in the present invention, C in the base phase is limited to a range of 0.3 to 1.5%.

One or more selected from Ni, Co, Mo, Cr, V: Total 1-20%
Ni, Co, Mo, Cr, and V are all elements that improve the wear resistance of the matrix, and in the present invention, a total content of 1% or more is required. On the other hand, even if it contains more than 20% in total, the effect is saturated and an effect commensurate with the content cannot be expected and it is economically disadvantageous. Note that Ni, Co, and Mo have a greater effect on improving high-temperature strength and toughness than Cr and V, and preferably contain one or more selected from Ni, Co, and Mo. Therefore, one or more selected from Ni, Co, Mo, Cr and V, preferably one or more selected from Ni, Co and Mo, or even Cr, V It is preferable to limit 1 type or 2 types selected from 1 to 20% in total.

The balance other than the above components in the matrix phase is composed of Fe and inevitable impurities.
In the valve seat material of the present invention, hard particles having a Vickers hardness of 500 HV0.1 to 1200 HV0.1 are dispersed 35 to 60% by mass in the matrix phase having the matrix phase composition described above. Consists of iron-based sintered alloy.
The hard particles are dispersed in the matrix phase in order to ensure wear resistance. However, if the hardness of the hard particles is less than 500 HV0.1, desired wear resistance cannot be ensured. On the other hand, if it exceeds 1200HV0.1, the opponent aggression will increase. For this reason, the hardness of the hard particles is limited to the range of 500 HV0.1 to 1200 HV0.1 in terms of Vickers hardness. The hard particles dispersed in the matrix phase contain Si: 1 to 15%, Mo: 20 to 60% in terms of mass% with respect to the entire hard particles from the viewpoint of wear resistance, self-lubrication, and opponent attack, Cr An intermetallic compound containing Fe, Mo, Si as a main component, having a composition comprising 10 to 70% of one or more selected from Ni, Co, and Fe, Co, Mo, Si Hard particles containing one or more of intermetallic compounds containing Ni, Mo and Si as main components.

  Specifically, the hard particles to be dispersed in the matrix phase in the present invention include, by mass% with respect to the entire hard particles, Si: 1 to 15%, Mo: 20 to 60%, or Cr: 25% or less. And / or Co: 10-40% Fe-based hard particles having a composition consisting of Fe and inevitable impurities, the mass% of the entire hard particles, Si: 1-15%, Mo: 20-60% In addition, or in addition, Cr: 5 to 25%, Co-based hard particles having a composition consisting of Co and inevitable impurities, and the mass% based on the whole hard particles, Si: 1 to 15%, Mo: 20 to 60 %, Or further, Cr: 5 to 25% and / or Co: 10% or less, the balance being Ni-based hard particles composed of Ni and inevitable impurities, or a composite thereof Is preferred.

If the hard particles dispersed in the matrix phase are less than 35 % by mass with respect to the entire valve seat material, the intended wear resistance cannot be ensured. On the other hand, if it is contained in a large amount exceeding 60%, the production cost is increased and it is economically disadvantageous, the moldability is deteriorated, the opponent aggression is increased, and the bond strength with the base is lowered. For this reason, in the present invention, the hard particles are limited to a range of 35 to 60% by mass% with respect to the entire valve seat material.

Further, the valve seat material of the present invention may contain a solid lubricant in an amount of 0.2 to 5% by mass with respect to the entire valve seat material for the purpose of improving machinability. By dispersing the solid lubricant in the matrix phase, the cutting tool can be protected, and it becomes a starting point of cutting, and the machinability is further improved. As solid lubricant, MnS, sulfides such as MoS _2, fluorides such as CaF _2, oxides such MgSiO ₂ can be exemplified. If the solid lubricant is less than 0.2%, the above-mentioned effects are not observed. On the other hand, even if the content exceeds 5%, the strength decreases. For this reason, it is preferable that the solid lubricant is limited to a range of 0.2 to 5% by mass. In addition, More preferably, it is 0.5 to 3%.

Furthermore, the valve seat material of the present invention is characterized by having a density of 6.7 g / cm ³ or more and a crushing strength of 420 MPa or more. The “crushing strength” referred to here is a value determined even in accordance with the provisions of JIS Z 2507.
When the density is less than 6.7 g / cm ³ , the bonding force between the hard particles and the base is insufficient, and the wear resistance is further lowered, so that the desired wear resistance in the severe environment of the gas fuel engine can be secured. become unable. For this reason, the density was limited to 6.7 g / cm ³ or more. The amount is preferably 6.8 g / cm ³ or more.

Further, in the present invention, the crushing strength is set to 420 MPa or more in order to improve the bonding force between the hard particles and the base and to ensure the desired wear resistance in the severe environment of the gas fuel engine. If the crushing strength is less than 420 MPa, the bonding force between the hard particles and the matrix is insufficient, wear resistance is insufficient, and cracks and chips are likely to occur during processing of the valve seat (product). In addition, Preferably it is 450 MPa or more.

The above-described valve seat material of the present invention is forged after the process of repeating compression molding-sintering twice or once after the compression molding-sintering process in order to stably secure the above-described density and crushing strength. It is preferably manufactured through a step of molding-sintering.
Below, the preferable manufacturing method of the valve seat material of this invention is demonstrated.
First, as the raw material powder, pure iron powder, alloy powder, graphite powder and further one or more of Ni powder, Mo powder, Co powder, or further Cr powder so as to have the matrix phase composition described above. One or more of the V powders are blended so as to have the above-described matrix phase composition, and further, the above-described hardness or the hard particle powder having the above-described composition is blended so as to have the above-described content. Alternatively, a solid lubricant powder is blended so as to have the above-mentioned content, preferably zinc stearate or the like is blended as a lubricant, and mixed and kneaded to obtain a mixed powder. In the present invention, even if a predetermined amount of these alloying element powders is blended with pure iron powder as described above so as to have the matrix phase composition described above, low alloy steel powder and alloying iron powder containing these elements are included. May be blended in a predetermined amount, or both may be used in combination.

  Subsequently, these mixed powders are filled in a valve seat-shaped mold having a predetermined size, subjected to a primary compression molding-sintering step of compression molding and pre-sintering to obtain a primary sintered body. Next, the compression-molding-sintering process is repeated twice. The compression-molding-sintering process is performed twice by subjecting the primary-sintered body to re-compression molding and then subjecting it to a secondary compression molding-sintering process. It is preferable that As a result, a sintered body (valve seat material) having a desired density and crushing strength is obtained.

The compression molding is preferably press molding such as a mechanical press or a hydraulic press. Sintering is preferably performed in a reducing atmosphere or in a vacuum, preferably in a temperature range of 1100 to 1200 ° C.
Moreover, in this invention, it may replace with the process of repeating a compression molding-sintering process twice , and it is good also as a forge- sintering process after a single compression molding-sintering process .

Note that a low melting point metal such as Pb, Cu, or Zn may be infiltrated into the pores of the obtained sintered body. By infiltrating the low melting point metal into the pores, it is possible to further improve the wear resistance and the counterpart material attack.
The obtained sintered body (valve seat material) is cut as necessary to obtain a product valve seat.

  Hereinafter, based on an Example, this invention is demonstrated in detail.

  The pure iron powder and the alloy element powder have the matrix phase composition shown in Table 1, and the hard particles having the types and hardnesses shown in Table 2 have the contents shown in Table 1, or further in Table 1. Each of the types of solid lubricants shown was blended so as to have the contents shown in Table 1, and further zinc stearate as a lubricant was blended, and mixed and kneaded with a V-type mixer to obtain a mixed powder. The blending amount of zinc stearate as a lubricant was 1.0 part by weight based on 100 parts by weight of the total amount of pure iron powder, alloy element powder, hard particles and solid lubricant.

Further, in some valve seat materials, instead of a part of pure iron powder and alloy element powder, low alloy powder A (Cr: 3.0 mass%, Mo: 0.2 mass%, V: 0.3 mass%, Bal .: Fe), low alloy powder B (Cr: 1.0 mass%, Mo: 0.3 mass%, Bal .: Fe) was used.
Next, the mixed powder was filled into a mold, compression-molded with a mechanical press machine, and formed into a 27? Mm x 22? Mm x 7.0mm valve seat-like shaped body, and then pre-sintered to obtain a primary sintered body. The compression molding-sintering process in which the primary sintered body obtained is recompressed into a valve seat with a finished size (27φmm × 22φmm × 6.5mm) using a hydraulic press and then re-sintered to form a sintered body Was repeated twice (2P2S). In some sheet materials, a forging-sintering step (FS) for forging and sintering was performed after a single compression molding-sintering step (1P1S). The sintering was a heat treatment (sintering treatment) in which heating was performed at 1160 ° C. in a reducing atmosphere.

A valve seat was completed using the obtained sintered body as a valve seat material. About the obtained valve seat, while measuring the density and the crushing strength, the wear resistance was investigated.
The density was determined using the Archimedes method, and the crushing strength was determined in accordance with the provisions of JIS Z 2507. The abrasion resistance was evaluated by the following test.
The obtained valve seat was mounted on a 2000 CC, in-line 4-cylinder, 4-cycle natural gas engine, the operating conditions were 6000 rpm / WOT (fully open operation), and the test time was 24 hours. The mating valve material was heat-resistant steel SUH35 as a base material and the valve face portion was plated with trivalloy. The wear resistance was evaluated by measuring the amount of sinking after wear of the valve seat and the valve on the exhaust side.
The obtained results are shown in Table 3.

  It can be seen that in all of the examples of the present invention, even on the exhaust side exposed to a severe environment in the gas fuel engine, the wear amount of the valve seat and the valve as the counterpart material is small, and the wear resistance and the opponent attack property are improved.

  On the other hand, it can be seen that the comparative example outside the scope of the present invention has much wear on the valve seat, or more wear on the valve, resulting in deterioration of wear resistance and great opponent attack.

Claims (6)

A valve seat material made of an iron-based sintered alloy for internal combustion engines in which hard particles are dispersed in a matrix phase of an iron-based sintered alloy, wherein the matrix phase is in mass%, and C: 0.3 to 1.5%. , Ni, Co, Mo, Cr, containing one or more selected from the group consisting of 1 to 20% in total, and having a matrix composition comprising the balance Fe and inevitable impurities, As the hard particles, one of an intermetallic compound mainly composed of Fe, Mo and Si, an intermetallic compound mainly composed of Co, Mo and Si, and an intermetallic compound mainly composed of Ni, Mo and Si. Contains 35 or 60% by mass of hard particles having a Vickers hardness of 500HV0.1 to 1200HV0.1, including a seed or two or more, and a density of 6.7 g / cm ³ or more, 420 MPa A valve seat material made of an iron-based sintered alloy for an internal combustion engine, having the above-mentioned crushing strength.   The base phase is, by mass%, C: 0.3 to 1.5%, one or more selected from Ni, Co, and Mo, or one selected from Cr and V, or The valve seat material made of an iron-based sintered alloy for an internal combustion engine according to claim 1, wherein the total amount of the two types is 1 to 20%.   The hard particles are one of an intermetallic compound containing Fe, Mo and Si as main components, an intermetallic compound containing Co, Mo and Si as main components, and an intermetallic compound containing Ni, Mo and Si as main components. 1 or 2 selected from Cr, Ni, Co, and Fe, which are hard particles containing seeds or two or more, and containing, by mass%, Si: 1 to 15%, Mo: 20 to 60%. 3. The iron-based sintered alloy valve seat material for an internal combustion engine according to claim 1, wherein the composition comprises 10% to 70% of seeds or more and the balance consists of inevitable impurities.   The hard particles contain, by mass%, Si: 1 to 15%, Mo: 20 to 60%, or further contain Cr: 25% or less and / or Co: 10 to 40%, with the balance being Fe and inevitable Fe-based hard particles with a composition consisting of general impurities, in mass%, Si: 1-15%, Mo: 20-60%, or even Cr: 5-25%, the balance being Co and inevitable impurities Co-based hard particles having a composition of: Si: 1 to 15%, Mo: 20 to 60%, or further containing Cr: 5 to 25% and / or Co: 10% or less, the balance The valve seat material made of an iron-based sintered alloy for an internal combustion engine according to claim 3, wherein is one of Ni-based hard particles having a composition comprising Ni and inevitable impurities.   The valve seat material made of an iron-based sintered alloy for an internal combustion engine according to any one of claims 1 to 4, wherein the solid lubricant is contained in an amount of 0.2 to 5% by mass.   As a raw material powder, a process in which alloy element powder or low alloy steel powder is blended with pure iron powder so as to have the matrix phase composition and further mixed with hard particles, and compression molding-sintering is repeated twice. The iron-based sintered alloy for an internal combustion engine according to any one of claims 1 to 5, wherein the iron-based sintered alloy for an internal combustion engine is manufactured through a process of performing forging and sintering after a single compression molding and sintering process. Made valve seat material.