JPH07109024B2 - Sintered alloy for valve seat of internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to a valve seat for an internal combustion engine that stably functions with both unleaded gasoline and leaded gasoline.

[Prior Art] Since the exhaust gas regulations of automobiles, the valve seats of internal combustion engines have been improved on the premise of unleaded gasoline (about 0.5 g Pb / gallon). A sintered material in which lead is impregnated has good wear resistance and has been put to practical use.

Further, a valve seat of this type is disclosed in JP-A-51-37011 and JP-B-5.
As described in JP-A No. 1-44684 and JP-A No. 60-258449, a sintered material obtained by impregnating the pores of a sintered alloy steel with a copper-lead alloy is mentioned.

However, in the world, Europe, Australia, the Middle East, etc. are still using leaded gasoline (for example, about 3 g Pb / gallon) for the purpose of improving engine output.

In the case of an engine using leaded gasoline as a fuel, combustion products such as lead oxide, lead sulfide, and lead sulfate adhere to the valve and valve seat surfaces during combustion, and are easily worn by ordinary sintered alloys. Site-based heat-resistant steel ingot material is generally used.

[Problems to be Solved by the Invention] As described above, valve seats for gasoline engines are classified into those suitable for unleaded gasoline and those suitable for leaded gasoline. For example, the above Japanese Patent Publication No. 55-36242. When the valve seat of No. 1 is applied to a leaded gasoline engine, wear becomes noticeable. Also, the same result can be obtained by applying a valve seat made of molten martensitic heat-resistant steel to an unleaded gasoline engine. Therefore, it would be extremely convenient if it can be used for lead-free, lead-free, domestic or export specifications.

An object of the present invention is to provide a valve seat that is resistant to wear regardless of whether the fuel of the internal combustion engine is unleaded gasoline or leaded gasoline.

[Means for Solving the Problems] In order to achieve the above object, the present invention is achieved by configuring the material of the valve seat as follows. That is, the composition is C1.2-2.7% by weight ratio, Si0.2-2.5%, Cr1
The total composition of Cu and Pb is 15-25% by weight in the total composition in the iron matrix in which the hard metal carbide consisting of 1 to 27%, Mo 0.6 to 4%, V2.5% or less and the balance of Fe is dispersed. The sintered alloy is characterized in that the weight ratio of Cu: Pb is 80:20 to 60:40.

[Action] Next, the action of each element will be described.

First, the base composition will be described.

Cr: A component that forms a solid solution in the iron matrix to improve the high temperature strength and combines with C to precipitate a hard carbide in the matrix and contribute to the improvement of wear resistance. If the content is less than 11%, the matrix strength is too low. Also, it is easily oxidized and worn when used. on the other hand,
Even if it exceeds 27%, the effect is small relative to the amount added, and unleaded gasoline has the property of being easily warped due to warping.

Like Mo; Cr, it is a carbide-forming element and has the same function as Cr. If it is less than 0.6%, the effect is small, and if it exceeds 4%, oxidative wear increases.

V; Forms the same carbides as Cr and Mo. V-carbides are relatively hard. Less addition is effective, and if too much is added, the valve of the other party will be worn away, so less than 2.5% is preferable.

Si; an element added for the purpose of preventing oxidative wear, 0.2
% Addition, the effect appears, and even if added over 2.5%, the effect is small compared to the addition.

It acts as a solid solution in C; Fe, strengthens the matrix, and combines with Cr, Mo, and V to precipitate hard carbides. If it is less than 1.2%, the amount of carbide produced is small and wear resistance cannot be expected. Also,
If it exceeds 2.7%, the carbides become coarse and increase the wear of the mating valve during use.

As mentioned above, the characteristic of the iron base is that the Vickers hardness is Hv2000-3000.
Hard precipitated carbide (Cr, Fe) 7 C3, (Cr, Mo, Fe) 7
It is configured to contain a large amount of C3 and VC.

Next, the dispersion composition will be described.

Cu and Pb; Cu partially diffuse into the base and strengthen the base. Further, part of the copper phase remains in the form of a copper phase, and the thermophilic conductivity of copper has the effect of improving the heat dissipation of the valve seat during use.

On the other hand, Pb has a function of preventing adhesive wear with the valve during use, and is a highly effective component for unleaded gasoline. However, in leaded gasoline, it reacts with sulfur contained in the fuel to produce combustion products, which adhere to the seat face and accelerate wear.

When Cu and Pb coexist in a given state, both lead-free and lead-containing properties are less likely to wear. The weight ratio of Cu and Pb is 8
The range from 0:20 to 60:40 is good. C when the ratio of Cu is more than 80
The property of u appears remarkably and wear becomes large in unleaded gasoline. Further, when the ratio of Cu is less than 60, the property of Pb appears and wear becomes large in leaded gasoline. In addition, Cu and Pb
It is important that the structure is a structure dispersed in the base, and Pb is contained in Cu.
Is preferably dispersed in an alloy state. This structure is obtained by infiltrating Cu-Pb into the iron-based sintered body and Cu-Pb in the alloy iron powder.
It is obtained by a method of blending Pb powder, molding and sintering. Cu
If the total content of Pb and Pb is less than 15% in the total composition, the above-mentioned action and effect are small, and if it exceeds 25%, the amount of matrix is reduced accordingly and the strength is lowered and the wear resistance is also deteriorated.

[Examples] Hereinafter, examples will be described in detail.

Example 1 Example 1 is a comparison of wear characteristics of materials in which copper is dispersed, lead is dispersed, and copper-lead is dispersed in a base material.

First, 0.8% zinc stearate was added to alloy iron powder with a composition of Fe-18.5Cr-1.2Mo-0.6V-0.5Si-1.8C and a grain size of 100 mesh or less to form a mixed powder, and the predetermined size of the valve seat shape was determined. After compression molding, the temperature was set to 11 in an ammonia decomposition gas atmosphere furnace.
Sintered at 50 ° C.

Then, a molded body of Cu-3Co alloy powder and a molded body of Cu-30Pb alloy powder were prepared, and each of them was subjected to infiltration treatment at a temperature of 1150 ° C. in an ammonia decomposition gas atmosphere furnace together with the sintered body, and a sample for wear test. 1 and sample 2 were prepared. Cu-Co alloy
Co is added for the purpose of not corroding the base material during infiltration. The other type is Sample 3 in which the sintered body is heated and held in a decompression container, immersed in a Pb molten metal, pressurized with nitrogen gas, and infiltrated with lead.
Prepared.

Table 1 shows the measurement results of the infiltration amount, radial crushing strength, and thermal conductivity of these samples.

The infiltration amount is about 19%, and the radial crushing strength is higher in the composition with more copper,
The composition with more copper also has better thermal conductivity.

The wear resistance was evaluated by using a 2000 cc, 6-cylinder engine, processing the sample into a predetermined shape, and mounting the sample, followed by preload operation at a rotation speed of 6000 rpm.

Heat-resistant steel 21-4N was used as the material of the valve, and the fuel was tested with leaded gasoline (3 g, Pb / gallon) and unleaded gasoline (0.5 gPb / gallon). Fig. 1 shows the results of measuring the amount of wear of the valve seat after operating for 200 hours.

According to this, it is understood that the copper infiltration sample 1 is good for leaded gasoline, but has large wear for unleaded gasoline. On the contrary, the lead-infiltrated sample 3 has extremely large wear in the case of leaded gasoline. The copper-lead alloy infiltrated sample 2 has good wear resistance both with lead and without lead.

Example 2 Example 2 investigates the effect of the Pb content of a Cu-Pb alloy in a copper-lead dispersion material having good wear resistance in both leaded gasoline and unleaded gasoline.

The alloy iron powder is the same as in Example 1, and the Cu-Pb alloy powder has a Pb content of 10
%, 20%, 30%, and 40% are prepared, and each alloy iron powder contains Cu
-Pb alloy powder of 20% constant and zinc stearate 0.8% were added to form mixed powders, each of which was molded to have a sintering density of 8.0 g / cm ³ , and then sintered under the same conditions as in Example 1 to obtain a sample. 4-7 were created.

The engine test was conducted under the same conditions as in Example 1, and the measurement results of the valve seat wear amount after the test are shown in FIG. The results of Sample 1 and Sample 3 of Example 1 are additionally shown in the figure.

According to this, when the Pb amount of the added Cu-Pb alloy is in the range of 20 to 40%, the result shows that the wear is small with both of the two types of fuel. Also, it can be seen that when the amount is less than 20%, unleaded gasoline increases, and when the amount exceeds 40%, unleaded gasoline increases wear.

Example 3 Example 3 was based on the results of Examples 1 and 2 and had a Cu-30% content.
The relation between the amount added to iron alloy powder and wear was investigated, using Pb alloy as a representative.

The same alloy iron powder Cu-30Pb alloy powder as in Example 1 was prepared, and Cu-
30Pb alloy 10%, 15%, 20%, 25%, and 30% were compounded, 0.8% of zinc stearate was added to each to make a mixed powder, and the mixture was molded to have a sintered density of 8.0 g / cm ³ . A sample was prepared by sintering under the same conditions as in Example 1. Example 1 engine test
Under the same conditions as above, the valve seat wear measurement result after the test is
Shown in the figure.

According to this, when the addition amount of the Cu-30Pb alloy is within the range of 15 to 25%, both leaded gasoline and unleaded gasoline have little wear, but outside the range, wear resistance becomes inferior.

Example 4 In Example 4, the relationship between the composition of the ferroalloy forming the matrix and the wear resistance, and comparison with the conventional material were performed.

The composition in Table 2 shows the main components excluding Fe and unavoidable impurities of the alloy iron powder in% by weight.
Pb alloy was kept constant at 20% and zinc stearate was added at 0.8% to form a mixed powder, which was molded to a sintered density of 8.0 g / cm ³ and then sintered under the same conditions as in Example 1 to obtain Sample 6 ~ 15 created. Samples 6-9 are materials of the invention.

Further, Samples 16 and 17 are conventional materials and are shown by the overall composition. Specimen 16 is Japanese Examined Sho 55 which has a proven record in unleaded gasoline valve seats.
-No. 36242 is a material obtained by infiltrating lead into an iron-based sintered alloy containing Co, Ni, and C, and sample 17 is a valve seat that is machined from SUH4 heat-resistant steel.

The engine test was conducted under the same conditions as in Example 1, and Table 3 shows the measurement results of the amount of wear of the valve seat after the test.

According to this, the samples of the base iron alloy composition of the present invention show less wear results for both leaded gasoline and unleaded gasoline, but it is understood that the comparative materials of Samples 10 to 15 have large wear amounts. Note that among the comparative materials, Samples 11 and 12 have a relatively small amount of wear, but they are not preferable because they wear the mating valve.

It can be seen that the conventional material shows excellent properties for one fuel, but it significantly wears for the other fuel.

[Advantages of the Invention] As described in detail above, the valve seat of the present invention can suppress wear in both a leaded gasoline engine and a leaded gasoline engine to a small extent, and functions stably over a long period of time. Like

[Brief Description of Drawings] FIG. 1 is a graph showing wear results of valve seats in which various materials are infiltrated into a sintered iron alloy, and FIG. 2 is a Pb content of Cu-Pb alloy powder blended with iron alloy powder. Graph showing the relationship between wear and valve seat wear, No. 3
The figure is a graph showing the relationship between the amount of Cu—Pb alloy powder added to the iron alloy powder and the wear of the valve seat.

Claims (1)

[Claims] 1. A composition of C1.2-2.7% by weight and Si0.2-2.5 by weight.
%, Cr11 to 27%, Mo0.6 to 4%, V2.5% or less, and a balance of Fe in a carbide-dispersed iron matrix, the total of Cu and Pb is dispersed by 15 to 25% in the total composition weight ratio, and A sintered alloy for a valve seat of an internal combustion engine, characterized in that a weight ratio of Cu: Pb is 80:20 to 60:40.