JPH03260308A - Sintered alloy for valve seat - Google Patents

Abstract

PURPOSE:To obtain sintered alloy which has small aggressive property against a valve and good abrasion resistance, particularly even in an automobile engine driven by methanol fuel, by infiltrating Pb at only a specified rate into the sintered alloy in which specified hard particles are added in a specified base structure. CONSTITUTION:Sintered alloy used for the valve seat of an automobile engine particularly driven by methanol fuel, is constituted by infiltrating Pb in the sintered alloy made by adding specified hard particles in a specified base structure. Namely, the Pb is infiltrated by 5 to 25% of a weight ratio, into the sintered alloy formed by dispersing equally 3 to 20% the first hard perticles which is formed by including Cr: 5 to 20%, Si: 1 to 5%, Mo: 25 to 35%, Ni and/or Fe: 1 to 3%, C: 0.03 to 0.08% in a weight ratio, and the residual part thereof Co, and a second hard particles 0.5 to 1% made of FeW, in the base structure formed by including C: 0.25 to 0.55%, Ni: 8 to 11%, Co: 8 to 11% in a weight ratio, and the residual part thereof Fe and impurity element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sintered alloy for valve seats of automobile internal combustion engines.

[Prior Art] Recently, there has been an increasing demand for improvements in automobile engines, such as higher output, higher rotation speed, measures to purify exhaust gas, and measures to improve fuel efficiency. For this reason, it has become inevitable for engine valves and valve seats in automobile engines to withstand harsher usage environmental conditions than ever before.

In order to cope with such severe usage environments, hard facings have been adopted in which Co-based or Ni-based metal alloys, which have excellent wear resistance, high hardness at high temperatures, and high resistance to high-temperature corrosion, are welded to the valve face. However, this hard facing is expensive because it uses expensive metal fittings, and for this reason, intake valves that do not have metal metal fittings on the face are increasingly being used in order to reduce costs.

In addition, as a conventional valve seat material, FeC-Co
Intermetallic compounds such as ferromolybdenum (Fe-Mo) and ferrochrome (Fe-Cr) or Pe-C-Cr are added to Nj-based materials and Fe-C-based materials to improve wear resistance.
-Mo-V alloys are used (Japanese Unexamined Patent Publication No. 154110/1983).

Also, in Japanese Patent Application Laid-open No. 15349/1983, N1-Co
-CrMo-Co group in the base structure consisting of C-based iron alloy,
An iron-based sintered alloy for valve seats in which Cr-W-Co-based and Fe-Mo-based hard particles are dispersed has been disclosed, and this alloy has excellent wear resistance and is useful for increasing the output of automobile engines,
It can cope with thermal and mechanical negative ζ-work caused by high rotation speeds.

[Problems to be Solved by the Invention] Incidentally, in an engine using methanol fuel, when a knob and a knob seat similar to those in a gasoline engine are used, a problem arises in that the amount of valve wear increases. One of the reasons why the amount of valve wear increases is that the valve seat is highly aggressive toward the other valve in the corrosive atmosphere of methanol fuel. It is thought that this is largely due to the alloy particles contained in the Norklube sheet.

The present invention was made in view of the above-mentioned problems regarding the amount of valve wear in methanol engines, and it is an object of the present invention to reduce the aggressiveness of alloy particles contained in a valve seat against a mating valve, thereby improving engine performance in engines using methanol fuel. It is an object of the present invention to provide a sintered alloy for a valve seat that causes less wear on a mating valve.

[Means for Solving the Problems] The sintered alloy for valve seats of the present invention has, as its first invention, C: 0.25% to 0.55% and Ni: 8% to 11% by weight.
%, Co; 8 to If%, with the balance consisting of Fe and impurity elements, in a weight ratio of Cr; 5-20
%, Si: 1-5%, Mo: 25-35%, Ni and/or Fe; 5 to 25 percent by weight of Pb is dissolved in a sintered alloy in which 3 to 20 percent by weight of particles and 0.5 to 1 percent by weight of second hard particles made of FeW are uniformly dispersed. The gist is that it was immersed.

Further, the second invention has C, 0.25 to 0.55% by weight,
In the base structure containing Ni; 8 to 11%, Co; 8 to 11%, and the balance consisting of Fe and impurity elements, Cr is added in weight ratio.
; 5-20%, Si; 1-5%, MO; 25-35%,
Co and/or Fe; 1-3%, C, 0,03-0
．． The first hard particles containing 0.8% and the balance being Ni were uniformly dispersed at a weight ratio of 3 to 20%, and the second hard particles consisting of FeW were uniformly dispersed at a weight ratio of 0.5 to 1%. The gist is that the sintered alloy is infiltrated with Pb in a weight ratio of 5 to 25%.

[Function] The function of the present invention will be explained below. In the following description, the contents of alloying elements are all expressed in terms of weight ratio (%).

First, the reason for limiting the range of each component constituting the hard particles used in the sintered alloy for a valve seat of the present invention will be explained.

Or and Mo combine with CO or Ni, which is the base of the hard particles, to improve heat resistance and corrosion resistance. Also, some of it is combined with C 1. hard carbide to increase the hardness of the hard particles.

If the Cr content is less than 5%, the improvement in heat resistance will not be sufficient, and if it exceeds 20%, the effect will hardly change. -20%.

Similar to Cr, if the Mo content is less than 25%, the heat resistance will be insufficient, and if it exceeds 35%, the hard particles will become too hard and attack the opponent. Therefore, the Mo content is limited to 25 to 35%. did.

Si is added to increase the hardness of the hard particles by combining with Fe or C. If the Si content is less than 1%, the above effect cannot be obtained, and if the Si content exceeds 3%, the hard particles become too hard and increase the aggressiveness of the opponent.
It was limited to 3%.

C is an element necessary to increase the hardness of hard particles by combining with Or, Mo, Fe, or Si. If the C content is less than 0.303%, the above effect is insufficient, and if it exceeds 0.08%, the hard particles will become too hard.
It was limited to 0.03 to 0.08%.

Both Co and Ni are materials with high heat resistance and corrosion resistance, and contribute to improving the heat resistance and corrosion resistance of the hard particles. In addition, a part of Co and Ni diffuses into the base, improving bonding properties between the hard particles and the base, and has the effect of preventing the hard particles from falling off. When not used as a base for hard particles, each serves as an additive that improves the heat resistance and corrosion resistance of the other, while combining with Fe to harden the hard particles. If the amount added is less than 1%, the improvement in heat resistance and corrosion resistance will not be sufficient, and if it exceeds 3%, the hard particles will become too hard and increase the aggressiveness of the opponent.

Alternatively, the amount of Ni added was limited to 1 to 3%.

The first hard particles formed from the above components are Hvl O
If it is less than 00, it is characterized by low opponent aggression. If the content of the first hard particles is less than 3%, there is no effect on the wear resistance of the sintered metal, and if it exceeds 20%, formability, compressibility, and machinability decrease, and the aggressiveness of the mating material becomes large. Therefore, the content of the first hard particles was limited to 3 to 20%.

The second hard particles, FeW, are necessary to ensure the wear resistance of the sintered metal. If it is less than 0.5%, it will not have any effect on the wear resistance of the sintered metal, and if it exceeds 1%, it will increase the aggressiveness toward the other party, so the content was limited to 0.5 to 1%.

The particle diameter of any hard particles is preferably 20 to 200 μm. This is because if the particle size is less than 20 μm, the abrasion resistance will decrease, and if it exceeds 200 μm, the moldability and compressibility will decrease and the abrasion resistance will deteriorate.

Next, the reason for limiting the range of components of the base structure raw material powder used to form the base structure of the sintered alloy for valve seats of the present invention will be explained.

C solidly dissolves with Fe in the matrix to improve the strength and hardness of the sintered metal, and also combines with Cr and Mo in the hard particles to form hard carbides, further improving the hardness of the hard particles. effective. If the C content is less than 0.25%, there is no effect of reinforcing the base, and if it exceeds 0.55%, the base becomes brittle, so the C content was limited to 0.25 to 0.55%.

Ni and Co form a solid solution in the Fe base, strengthen the base, and help improve corrosion resistance and heat resistance. If the content is less than 8%, there will be no effect on corrosion resistance or heat resistance, and if the content exceeds 11%, the base will become soft and wear resistance will decrease, so the composition range was limited to 8 to 11%.

In the present invention, Pb, which is an infiltrated metal, acts as a lubricant that forms a Pb oxide layer at the contact portion between the valve and the valve seat, thereby improving the wear resistance of the valve and the valve seat. If the Pb infiltration is less than 5%, the above effect cannot be obtained, and if it exceeds 20%, the skeleton of the sintered metal will be weakened and the amount of wear will increase, so the Pb infiltration m was limited to 5 to 20%.

[Example] Examples of the present invention will be explained together with comparative examples to clarify the effects of the present invention.

The base@structure alloy powder having the composition shown in Table 1 was added with the first
Table I After combining the powders of the first hard particles and the second hard particles having the compositions shown in Table 1 in the proportions shown in Table 1, and mixing 0.8% of lead acid stearate as a lubricant, This mixed powder was filled into a mold and molded at a molding pressure of 7 t/am' to obtain a powder compact having a rough shape of a valve seat.

In addition, graphite powder (-350f
i powder), Ni powder (10 μm or less), Co powder (
lOμ- or less) and reduced iron powder (-IOO mesh)
1f)lii! An alloy atomized powder (-100 mesh) was used as the alloy powder for the i-quality particles.

Further, in Table 1, Examples 1 to 3 are the first invention in which the balance of the first hard particles is Co, and Example 4 is the second invention in which the balance of the first hard particles is Ni. . The comparative example does not contain the first hard particles but contains FeMo particles instead.

(Left below) This powder chromium was heated to 115% in an ammonia decomposition gas atmosphere.
A sintered body was obtained by sintering at a temperature of 0° C. for 60 minutes. Next, this sintered body was brought into contact with the Pb lump and heated again at a temperature of 1050° C. for 30 minutes in an ammonia decomposition gas atmosphere to infiltrate Pb into the sintered body.

The obtained sintered body is processed into an exhaust valve seat shape and the exhaust valve 1
It was installed in a 11,500cc, 4-cylinder, methanol-fueled Otto cycle engine, and a 300-hour bench durability test was conducted under full load to measure valve face wear, width increase per valve seat, and valve depression. Note that the mating valve was made of heat-resistant steel coated with CO base.

The results obtained are shown in Table 2.

(Margin below) r As is clear from the results in Table 2, the amount of valve face wear in Examples 1 to 4 was 7 to 9 μ-, which is a much smaller value than the 50 μ tone of the comparative example. It has been confirmed that the sintered alloy of the present invention reduces the aggressiveness of the valve seat to other parts, and can sufficiently withstand use even in methanol engines, which have severe conditions against corrosion. In addition, the width per valve seat is 062 to 0 in Examples 1 to 4 of the present invention as well as in the comparative example.
641, and it has become clear that the sintered alloy of the present invention can be sufficiently used in engines using methanol fuel. Regarding the amount of valve sinking, Examples 1 to 4 of the present invention
is 0.02 to 0.04 m+i and 0.12 ma+ of the comparative example
It was confirmed that the sintered alloy of the present invention has excellent wear resistance and low attackability even when using methanol fuel.

[Effects of the Invention] As explained above, the sintered alloy for valve seats of the present invention contains Cr in the iron base structure containing C5Ni and CO.
, Si, first hard particles containing Mo and Fe with the remainder being Co or Ni, and second hard particles consisting of FeW.
Pb is infiltrated into a sintered alloy in which hard particles are uniformly dispersed.
By dispersing hard particles in the iron base structure and further dispersing second hard particles with excellent wear resistance, even when using methanol fuel, there is low aggressiveness against the mating material of the valve, and it can also be used as a valve seat. Abrasion resistance is ensured,
It is extremely useful as a material for valve seats in methanol engines.

Claims (2)

[Claims] (1) C: 0.25 to 0.55%, Ni: 8 to 0.55% by weight
11%, Co; 8 to 11%, and the balance is Fe and impurity elements, in a weight ratio of Cr; 5 to 20%.
%, Si; 1 to 5%, Mo; 25 to 35%, Ni and/or Fe; 1 to 3%, C; 0.03 to 0.08%, the balance being Co. 5 to 25 percent by weight of Pb is dissolved in a sintered alloy in which 3 to 20 percent by weight of particles and 0.5 to 1 percent by weight of second hard particles made of FeW are uniformly dispersed. A sintered alloy for valve seats characterized by being immersed. (2) C: 0.25 to 0.55%, Ni: 8 to 0.55% by weight
11%, Co; 8 to 11%, and the balance is Fe and impurity elements, in a weight ratio of Cr; 5 to 20%.
%, Si; 1 to 5%, Mo; 25 to 35%, Co and/or Fe; 1 to 3%, C; 0.03 to 0.08%, the balance being Ni. 5 to 25 percent by weight of Pb is dissolved in a sintered alloy in which 3 to 20 percent by weight of particles and 0.5 to 1 percent by weight of second hard particles made of FeW are uniformly dispersed. A sintered alloy for valve seats characterized by being immersed.