JP3434527B2 - Sintered alloy for valve seat - Google Patents

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 a reciprocating internal combustion engine (engine), and more particularly to a valve seat made of a sintered alloy.

[0002]

2. Description of the Related Art Since a valve seat is used so as to be in contact with intake and exhaust valves of an engine,
High heat resistance and wear resistance are required due to severe thermal and mechanical loads. Therefore, by dispersing high alloy powder particles of high hardness in the matrix,
A valve seat made of an iron-based sintered alloy with improved wear resistance has been proposed (for example, molybdenum (Mo) particles in Japanese Patent Publication No. 50-14603 and C-Cr- in Japanese Patent Publication No. 57-19188). As Ni-Mo-Nb-Fe particles and the like in which two kinds of hard particles are further dispersed in a matrix, C-Cr in JP-B-51-44483 is disclosed.
-W-Co-Fe and Fe-Mo particles, JP-B-51-
13093 gazette C-Cr-W-Co-Fe, Fe
-Mo particles etc.). Of these hard particles, Fe-
Mo and C-Cr-W-Co-Fe have high hardness, and C-C
The r-Ni-Mo-Nb-Fe had the characteristic of having a medium hardness. In addition, Ni and Cr are also added to the matrix to improve the strength and heat resistance of the matrix itself.

Generally, an oxide film generated on the valve seat during engine operation is present between the valve and the metal to prevent contact between the valve seat and the metal, resulting in adhesion wear and seizure. There is a preventive action. However, in the case of an engine with a special fuel such as a gas engine (for example, for a co-generator) or a hydrogen engine, since the combustion is close to complete combustion, almost no oxide film is formed on the valve seat. Under the use of such special fuel and severe load conditions, the above-mentioned valve seat material cannot be adopted. Therefore, for a valve seat used in such an engine, for example, a sintered material infiltrated with a lead alloy or a sintered material added with CaF ₂ (see JP-A-3-225008) is adopted.

[0004] In the case of a lead infiltration sintered material, it is necessary to reheat and infiltrate by using a lead bath or the like after the material is sintered, so that the productivity is inferior. It lowers the durability of the furnace and deteriorates the working environment. Further, the CaF ₂ -added sintered material disclosed in JP-A-3-225008 is further inferior in productivity because it is subjected to forging after sintering and then sintered again.

Therefore, the present inventor has proposed a sintered alloy for a valve seat, in which two kinds of hard particles having different hardness and CaF ₂ are dispersed in a matrix, in Japanese Patent Application No. 4-13249 (Jan. 28, 1992). Application) Further, a non-metallic mineral containing Al ₂ O ₃ and a sintered alloy in which hard alloy particles are dispersed in a matrix have been proposed in Japanese Patent Laid-Open No. 122052 .

[0006]

With the increase in power of internal combustion engines, valve seats are required to have higher heat resistance and wear resistance, and particularly under wear conditions in which an oxide film is not formed on the face surface. Alternatively, under severe wear conditions where the wear resistance and lubricity of the oxide film itself are not sufficient, the sintered alloy in which the hard alloy particles and the solid lubricant (CaF ₂ ) are dispersed is Their own wear resistance is not sufficient, while hard alloy particles and ceramic particles (Al
_The sintered alloy in which ₂ O ₃ ) is dispersed has a great attacking property against the valve of the mating material.

It is an object of the present invention to meet severe wear conditions, especially
It is intended to provide a sintered alloy for a valve seat, which can be used under a wear condition in which an oxide film is not formed on the face surface, has excellent wear resistance of itself, and has a small opponent attack property.

[0008]

The present invention has been made to solve the above problems, and its gist is that a matrix of a sintered alloy skeleton contains a die alloy tool steel powder as a raw material, and Carbon: 1.0 to 1.3 wt%, Chromium: 1.5 to 3.4 wt%, balance Fe and unavoidable impurities in the matrix of the sintered alloy skeleton, Carbon: 1 to 4 wt%, Chromium: 10 to 30 wt%, nickel: 2 to 15 wt%, molybdenum: 10 to 30 wt%, cobalt: 20 to 40 wt%, niobium: 1 to 5 wt%, hardness HV500 consisting of balance Fe and unavoidable impurities
To 900 hard particles (A), ferromolybdenum particles (B) that are hard alloy particles having a hardness of HV1000 or more, and one or two hardnesses of titanium nitride and silicon nitride, HV1500.
The above ceramic particles (C) and CaF ₂ particles (D)
With respect to the sintered alloy skeleton, A: 20 to 30 wt%, B: 1 to 10 wt%, C: 1 to 10 wt%, D: 0.5 to 7 wt%, provided that A + B + C: less than 40 wt% And the copper or copper alloy is dispersed in the pores of the skeleton in a proportion of 10 with respect to the sintered alloy skeleton.
A sintered alloy for a valve seat, which is infiltrated in an amount of up to 20 wt%.

Further , the present invention provides the above-mentioned (1) above.
The ceramic particles (C) are titanium nitride particles.
A sintered alloy for a valve seat, which is characterized by:

Furthermore, the present invention provides the above-mentioned (1),
The alloy steel powder for a metal mold is SKD11 powder, and the sintered alloy
It is a sintered alloy for valve seats, characterized in that it is contained in an amount of 5 to 15 wt% with respect to the skeleton . It is also desirable that the skeleton matrix has a tempered martensite structure.

[0011]

In the present invention, if the dispersed particles in the matrix are only the hard alloy particles and the solid lubricant (CaF ₂ ), the wear resistance at high temperature is not sufficient, and the hard alloy particles and the ceramic particles ( Considering the fact that Al ₂ O ₃ ) alone has a great attacking property against the partner material, these hard alloy particles, solid lubricants and ceramic particles are used together to improve wear resistance and reduce the partner attacking property. . CaF ₂ particles are used as a solid lubricant to suppress cohesive wear due to metal contact, to optimize three types of particles having different hardnesses and their proportions to be dispersed in a matrix of a sintered alloy, and to strengthen the matrix. By this, valve seat (sintered alloy)
The wear of the valve itself, which is the material of sliding contact, is minimized. Since the strength is not sufficient only with a sintered skeleton composed of these four types of particles and a matrix, copper or a copper alloy is infiltrated to compensate for this. Further, alloy tool steel for molds (SKD11) particles are added to improve the heat resistance of the matrix.

Regarding the composition of the matrix, carbon (C)
Strengthens the matrix and gives a martensitic structure by quenching. If the C content is less than 1.0 wt%, a sufficient martensitic structure cannot be obtained, while if it exceeds 1.3 wt%, cementite precipitates and becomes brittle. Chromium (Cr) forms a solid solution in the matrix to enhance its high temperature strength and prevents the hard alloy particles from falling off or sinking into the matrix. If the amount of Cr is less than 1.5 wt%, these effects are poor. On the other hand, if it exceeds 3.4 wt%, the improvement in high temperature strength is small relative to the addition, and the sinterability is impaired.

The two types of hard alloy particles (A) and (B) dispersed in the matrix enhance the wear resistance of the matrix, and the hard alloy particles (A) having a hardness of HV500 to 900 alone are sufficient for forming the matrix. Hard alloy particles (B) with increased wear and hardness of HV 1000 or more
Since the wear of the valve of the mating material will increase if only with these, these two types of hard alloy particles are used in combination in consideration of balance.

If the proportion of the hard alloy particles (A) is less than 20% by weight, sufficient wear resistance cannot be obtained, and if it exceeds 30% by weight, the bonding force between the hard particles and the matrix is lowered and cracks are generated during powder molding. It becomes easy to enter and molding becomes difficult,
The life of the molding die is shortened, and the dimensional change (shrinkage) during sintering becomes large. If the proportion of the hard alloy particles (B) is less than 1 wt%, the effect of addition is not obtained and 1
If it exceeds 0 wt%, cracks are likely to occur during powder molding, molding becomes difficult, and the life of the molding die is shortened.
Moreover, the wear of the valve face portion of the mating material becomes large. Hard alloy particles (A) are Fe-Cr, Fe-M
Materials such as o, Fe-Nb, Ni, Co and graphite are blended so as to have the following composition, melted and cast into a steel ingot,
It is preferable that the steel ingot is mechanically crushed and classified to obtain an alloy powder having a size of 150 mesh or less.

Carbon: 1-4 wt% Chromium: 10-30 wt% Nickel: 2-15 wt% Molybdenum: 10-30 wt% Cobalt: 20-40 wt% Niobium: 1-5 wt% Iron and unavoidable impurities The balance is such that the alloy powder particles have hardness (H
The mechanical characteristics including V500 to 900) can be adjusted appropriately. This alloy powder is manufactured by
It was proposed in Japanese Patent No. 188.

The hard alloy particles (B) are preferably low carbon ferro-molybdenum particles (powder) of 200 mesh or less, but if the particles are harder than HV1000, a high alloy containing tungsten (W). (C-Cr
Hard particles such as —W—Co alloy and C—Cr—W—Fe alloy) may be used.

The ceramic particles (C) have high hardness and stable titanium nitride (TiN) and silicon nitride (Si).
N ₃ ), etc. can be used, and if it is less than 1 wt%, the wear resistance at high temperature is not sufficient, and if it exceeds 10 wt%, the formability is impaired, the strength and toughness are deteriorated, and the attacking property to the mating material is deteriorated. It gets bigger.

The CaF ₂ particles are a solid lubricant stable at high temperature and have an action of preventing metal-metal contact between the valve seat and the valve to suppress cohesive wear. If it exceeds 7 wt%, the strength of the valve seat will be reduced and the amount of wear will increase. Moreover, in the case of an exhaust valve seat for a diesel engine, CaF ₂ particles tend to fall off. In other solid lubricants (molybdenum disulfide <MoS ₂ >, graphite), MoS ₂ -based solid lubricants are easily decomposed by heat during sintering, and the amount of graphite required for the sintering is in a dispersed state. Since it is difficult to precipitate with Ca, Ca without such defects
F ₂ is excellent as a solid lubricant for sintering.

Further, the above-mentioned hard particles A, B and C
If the total ratio of the above exceeds 40 wt%, cracks are likely to occur during powder molding, the moldability is impaired, and the life of the molding die is shortened. Alloy tool steel for molds (for example, S
KD11) particles have the effect of increasing the heat resistance of the matrix. Therefore, if less than 5% by weight, the effect is poor, and if more than 15% by weight, the green compact tends to crack, and high temperature The increase in strength is also saturated.

The sintered body satisfying the above-mentioned requirements has pores in the skeleton, and if the pores are filled with copper or a copper alloy at an infiltration amount of 10 to 20 wt% depending on the amount of the pores. For example, the wear resistance and heat resistance can be improved by increasing the strength and thermal conductivity of the sintered body. 20 wt%
If it exceeds, the high temperature strength and the creep strength will decrease.

[0021]

EXAMPLES The present invention will be described in detail below with reference to the accompanying drawings by way of example embodiments and comparative examples of the present invention. Raw material powders used for producing the sintered alloys of Examples and Comparative Examples are prepared. As the hard particles (A), Fe-C
r, Fe-Mo, Fe-Nb, Ni, Co and graphite were blended so as to have the composition described below, melted, cast into a steel ingot, and the steel ingot was mechanically crushed and classified. The alloy powder is 150 mesh or less. Carbon: 2 wt% Chromium: 20 wt% Nickel: 8 wt% Molybdenum: 20 wt% Cobalt: 32 wt% Niobium: 2 wt% Iron and unavoidable impurities: balance In this way, hardness HV600-800, maximum particle size 1
Hard particles (A) having a diameter of 00 μm and an average particle diameter of 50 μm are prepared.

Hard particles (B) have a hardness of HV130.
0, a low-carbon ferro-molybdenum powder having a maximum particle size of 75 μm and an average particle size of 30 μm is prepared. Ceramic particles (C)
The hardness is HV2000 or more, the maximum particle size is 44 μm,
Titanium nitride having an average particle size of 10 μm is prepared.

As CaF ₂ particles (D), powder having a maximum particle size of 150 μm and an average particle size of 45 μm is prepared.
SKD11 steel powder, Fe-3% Cr steel powder, and graphite (C) powder are prepared as materials forming the matrix of the iron-based sintered alloy (skeleton). The SKD11 steel powder has a maximum particle size of 160 μm and an average particle size of 60 μm.

As shown in Table 1, these raw material powders were prepared in a predetermined ratio, 1 wt% of zinc stearate was added and mixed, and compression molding was carried out at a molding pressure of 7 ton / cm ² to obtain a powder compact (density). : 6.0 to 6.7 g / cm ³ , ring shape) is formed. A predetermined amount of a copper alloy for infiltration (for example, a Cu-Fe-Mn-based alloy) is placed on the top of this compact, and sintering is performed at a temperature of 1120 ° C for 30 minutes in an ammonia decomposition gas atmosphere. Infiltration is performed at the same time as this sintering, and the infiltration amount of the copper alloy is as follows when the compact (skeleton) density is in this range.
The infiltration amount is in the range of 10 to 20 wt%.

[0025]

[Table 1]

As shown in Table 1, the sample No. 1-3,
Sample Nos. 5 and 6 are examples of the present invention. 7,8,1
0 to 13 are comparative examples. Sample No. 7, 8 and 10
Is a sample having less hard particles (C) than the limited range.
Sample No. 11 is a case where the hard alloy particles (B) are less than the limited range of the present invention. No. 12 is the case where there are no ceramic particles (D), and Sample No. No. 13 is a case where there is no hard alloy particle (A + B) and ceramic particle (D), and sintering forging is performed without infiltration with copper.

Obtained sintered alloy ring (valve seat)
Is machined and then subjected to a quenching / tempering treatment including a subzero treatment so that the matrix has a tempered martensite structure. This process contributes to prevent the valve seat from falling off the cylinder head. Then, finish processing is performed. The obtained sintered alloy ring (valve seat) is attached to a valve seat wear tester as shown in FIG. 1 and a wear test is conducted under the following conditions to measure the wear of the valve seat and the face surface of the mating valve. The valve seat is heated by the gas burner, and the combustion state of the gas burner is set to complete combustion so that no oxide film is formed on the surface of the valve seat.

Test conditions: Valve material: STL # 12 (Stellite alloy) Valve seat temperature: 300 ° C Camshaft rotation speed: 2000 rpm Test time: 10 hours

In the valve seat abrasion tester, as shown in FIG. 1, the face surface of the valve 4 is the spring 5 against the sintered alloy ring (valve seat) 3 fitted in the seat holder 2 of the frame 1. To abut. The valve 4 is lifted upward by the cam shaft 7 rotated by the electric motor 6 via the rod 8, returned by the spring 5, and hits the sintered alloy ring (valve seat) 3 by such a reciprocating motion. Then, the valve 4 is heated by the gas burner 9, and the temperature of the sintered alloy ring (valve seat) 3 is measured by the thermocouple 10. Valve 4,
Parts such as the spring 5, the camshaft 8 and the rod 8 are actual engine parts.

Table 1 shows the obtained measured values of wear amount. From these wear amount results, in the valve seat according to the present invention (Sample Nos. 1 to 3 , 5, 6 ), both the wear amount of the valve seat itself and the wear amount of the mating material valve are smaller than those in the comparative example. I understand. Further, it was confirmed by observing the sliding surface and cross-sectional structure of the valve seat (sample) after the test that no oxide film was formed. The valve seat according to the present invention comprises a base layer and a contact layer having different compositions as proposed in Japanese Patent Publication No. 56-44123.
It can also be used for the contact layer in a layer composite sintered valve seat.

[0031]

As explained above, in the sintered alloy valve seat according to the present invention, CaF ₂ addition to the solid lubricant, 2
By combining hard alloy particles of various types and ceramic particles, strengthening the matrix, improving the heat resistance of alloy tool steel addition, and infiltration strengthening of the skeleton, even if the valve seat itself is subjected to severe load conditions with a special fuel that does not generate an oxide film. Has excellent wear resistance and does not cause much wear of the mating valve. Further, the valve seat according to the present invention can be easily manufactured according to the conventional method for manufacturing a sintered alloy valve seat.

[Brief description of drawings]

FIG. 1 is a schematic partial cross-sectional view of a valve seat abrasion machine.

[Explanation of symbols]

1 ... frame 2 ... Sheet holder 3 ... Valve seat (sintered alloy ring) 4 ... Valve 5 ... Spring 7 ... Camshaft 8 ... Rod

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI F01L 3/02 F01L 3/02 F (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 33/02 B22F 3 / 00 C22C 38/00-38/60

Claims (3)

(57) [Claims] 1. A matrix of sintered alloy skeletons comprising:
In addition to including alloy tool steel powder for molds as a raw material, carbon: 1.0 to 1.3 wt%, chromium: 1.5 to 3.4 wt%, balance Fe and unavoidable impurities. In the matrix, carbon: 1 to 4 wt%, chromium: 10 to 30 wt%, nickel: 2 to 15 wt%, molybdenum: 10 to 30 wt%, cobalt: 20 to 40 wt%, niobium: 1 to 5 wt%, balance Fe and unavoidable HV500 consisting of static impurities
To 900 hard particles (A), ferromolybdenum particles (B) that are hard alloy particles having a hardness of HV1000 or more, and one or two hardnesses of titanium nitride and silicon nitride, HV1500.
The above ceramic particles (C) and CaF ₂ particles (D)
With respect to the sintered alloy skeleton, A: 20 to 30 wt%, B: 1 to 10 wt%, C: 1 to 10 wt%, D: 0.5 to 7 wt%, provided that A + B + C: less than 40 wt% And the copper or copper alloy is dispersed in the pores of the skeleton in a proportion of 10 with respect to the sintered alloy skeleton.
A sintered alloy for a valve seat, which is infiltrated in an amount of up to 20 wt%. 2. The ceramic particles (C) are titanium nitride.
The valve system according to claim 1, wherein the valve system is a particle.
Sintered alloy for steel sheets. 3. The alloy steel powder for a die is SKD11 powder.
The sintered alloy for a valve seat according to claim 1 , wherein the sintered alloy is contained in an amount of 5 to 15 wt% with respect to the sintered alloy skeleton .