JP2763826B2 - Sintered alloy for valve seat - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sintered alloy for a valve seat of an internal combustion engine having excellent wear resistance at high temperatures and excellent machinability.

<Conventional technology> In recent years, the types of fuels used in automobile engines have been diversified, and with the trend toward higher performance, it can be used with any fuel and has more durability. Some valve seats require such, and various sintered alloys used for such components have been proposed.

In order to respond to such needs, the present applicants first show uniformly excellent wear resistance in a range from a low temperature region to a high temperature region, and are not restricted by the characteristics of the engine and the type of fuel. As a sintered alloy, JP-A-62-102424
A sintered alloy as described in Japanese Unexamined Patent Publication (Kokai) No. H10-206, was developed.

This sintered alloy is C0.6-1.2%, Ni0.5-3%,
In the base of 0.5 to 3% of Mo, 5.5 to 7.5% of Co and the balance of Fe, Cr7
It is characterized in that the hard phase, which is an intermetallic compound of -9%, Mo26-30%, Si1.5-2.5% and the balance of Co, is dispersed in 5-25%, and is also suitable for LPG fuel. As described above, there has been proposed one characterized in that lead is infiltrated into the pores.

<Problems to be Solved by the Invention> However, among the conventional materials described above, a material that does not infiltrate lead exhibits excellent wear resistance particularly when used in a high temperature area, but when cutting, Has the drawback of being difficult to cut, and there has been a demand for this type of sintered material having good machinability.

On the other hand, conventional materials that are infiltrated with lead and are also suitable for LPG fuel exhibit good wear resistance when used at a temperature of 327 ° C or lower, but the material strength decreases at higher temperatures. There is a tendency to exhibit less wear resistance than expected, and further improvements have been desired.

The present invention has been made in view of the above-described circumstances, and has as its object to obtain a sintered alloy for a valve seat having high material strength at high temperatures and good machinability.

<Means for Solving the Problems> In order to achieve the above objects, the present invention has a composition in which the total composition is C 0.4 to 1.2%, Ni 0.3 to 2.9%, and Cr 0.3 to 2.
3%, Mo 1.7 to 9.8%, Co 8 to 22%, Si 0.1 to 0.7%, lubricant
0.5-2% and Fe remaining, and C0.6-1.2%, Ni0.5-3
%, Mo 0.5-3%, Co 5.5-7.5% and the balance of Fe
r 7 to 9%, Mo 26 to 30%, Si 1.5 to 2.5% and the balance of the hard phase of Co balance 5 to 25%, exhibiting a structure in which 0.5 to 2% of the lubricating substance is dispersed in the grain boundaries. Is a magnesium metasilicate mineral, or a magnesium metasilicate mineral and a magnesium orthosilicate mineral, or at least one of a magnesium metasilicate mineral or a magnesium orthosilicate mineral and at least one of boron nitride or manganese sulfide
Seeds are dispersed.

In addition, the total composition is C0.4-1.2%, Ni0.3-2.9% by weight.
%, Cr 0.3 to 2.3%, Mo 1.7 to 9.8%, Co 8 to 22%, Si 0.1 to 0.7
%, Pb 3% or less, lubricating substance 0.5-2% and Fe remaining, and C
0.6 to 1.2%, Ni 0.5 to 3%, Mo 0.5 to 3%, Co 5.5 to 7.5%, and Fe base 9 to 7%, Mo 26 to 30%, Si 1.5 to 2.
5% to 25% of the hard phase with 5% and the balance of Co, 3% or less of Pb in the grain boundaries or vacancies, and 0.5 to 2% of the lubricating material dispersed in the grain boundaries. Magnesium silicate mineral, or magnesium metasilicate mineral and magnesium orthosilicate mineral, or at least one of magnesium metasilicate mineral or magnesium orthosilicate mineral and at least one of boron nitride or manganese sulfide
The magnesium metasilicate mineral powder is at least one of enstatite powder, clinoenstatite powder, ensteinite powder and hyperstain powder, and the magnesium orthosilicate mineral powder is At least one of forsterite powder and chrysolite powder
It is a seed.

The base phase is the same as the sintered alloy composition described in JP-B-55-36242, in which the elements Ni and Mo mainly contribute to the improvement in strength, Co improves the high-temperature hardness, and C is the graphite powder. Added in form and alloyed during sintering. The hardness of the base phase is about MHV3
It is about 00-380.

The hard particles are alloys described in JP-A-62-10244. Of the intermetallic compounds disclosed, Mo 33-36%,
A cobalt alloy with 4-12% Si is suitable.

In particular, engines for LPG fuel are susceptible to abrasive wear (mechanical destructive wear) caused by contact between materials because the interface between the valve and the valve seat is dry. However, these Co-based alloy hard particles are effective in reducing the wear. is there.

The base structure is a structure in which the above-mentioned intermetallic compound is dispersed, and has a hardness of about MHV 800 to 970.

The addition amount of the Co-based alloy hard particles is 5% or more, and the wear resistance is stable, and 10 to 20% is preferable. However, the addition of more than 25% has no effect for the cost.

Disperse the CO-based alloy hard particles in the iron base as above,
When lead is further added to this material, the wear resistance is improved and the machinability is improved when the lubricating component is not contained in the fuel such as LPG.

However, the material to which lead is added is 327 ° C, which is higher than the melting point of lead.
Since there is a phenomenon in which the material strength decreases as the above and the lead content increases, it is desirable to keep the lead amount to 3% or less.

The addition of lead is susceptible added in the form of lead powder to the or the powder mixture infiltration and filling the lead in holes in the usual infiltration, when the sintered body density is 7.2 g / cm ³ Contains about 10% lead
Therefore, the impregnation amount is controlled by the lead infiltration temperature, pressure and infiltration time.

Lead reduces high temperature strength, but is presumed to be related to the volume expansion of molten lead.

The decrease in strength is usually easy to change because the temperature of each part of the valve seat is not uniform, so that the airtightness is reduced and the output is reduced or uneven wear is caused.

When the content of lead is 3% or less, the high temperature strength satisfies the requirement.

On the other hand, if the amount of lead is reduced to zero or less than 3%, machinability becomes a problem, but magnesium metasilicate minerals,
By adding specific amounts of the magnesium orthosilicate-based mineral, boron nitride, and manganese sulfide, machinability equivalent to that in which a large amount of lead is added can be obtained without lowering the high-temperature material strength.

Magnesium silicate is a solid lubricant interposed at the grain boundaries of the matrix, and magnesium metasili
cate) is represented by MgSiO ₃ and it is said that there are several types with different crystal structures, but orthorhombic enstatite, clinoenstatite monoclinic , Oblique pyroxene).

Further, those purified from natural ores are generally in the form of a solid solution of Mg silicate and Fe silicate, or a solid solution of this solid solution and Mg silicate, (Mg, Fe ) SiO
₃ and such forms include ensteinite and hypersthen.

In the present invention, the above magnesium metasilicate and the silicate containing the same are referred to as magnesium metasilicate minerals.

On the other hand, magnesium orthosil
icate) is represented by Mg ₂ SiO ₄ and is an ore that is industrially called forsterite (folsterite).
It is generally in the form of a solid solution with a silicate of Mg or Fe as in the above, and such a form includes chrysolite (chrysolite, olivine).

Chrysolite is the forsterite (Mg ₂ Si
O ₄ ) and fayalite (fayalite, Fe ₂ SiO ₄ ), or even a solid solution containing tephroite (tephroite, Mn ₂ SiO ₄ )
It is represented by (Mg, Fe) ₂ SiO ₄ or (Mg, Fe, Mn) ₂ SiO ₄ .

In the present invention, the above-described magnesium orthosilicate and the silicate containing the same are referred to as magnesium orthosilicate-based minerals.

As for the lubricating effect, the effect is recognized when added at 0.5% by weight or more, and the effect increases as the added amount is increased. It is not preferable because it becomes low.

Although talc is known as magnesium silicate, talc (Mg ₃ Si ₄ O ₁₁ .H ₂ O) dehydrates crystallization water during sintering, contaminating the sintering furnace gas, Is not preferable because silicon dioxide (SiO ₂ ) may be attached to the sliding member.

Magnesium metasilicate minerals and orthosilicate magnesium minerals have a specific gravity of about 3.2 to 3.9 and are cleaved, so they act as solid lubricants, improving the alloy's free-cutting properties, sliding properties, conformability, and wear resistance. I do.

When the magnesium metasilicate-based mineral and the magnesium orthosilicate-based mineral are compared, the latter is harder and harder to be cleaved. Therefore, it is desirable to use the magnesium metasilicate-based mineral in combination with the magnesium metasilicate-based mineral.

The powder of the magnesium silicate based mineral having such properties is added to the metal powder, compression molded and sintered, but the friction with the molding die is reduced during powder molding, and the moldability is reduced. Get better.

Further, it is relatively stable against heat and can be manufactured by the usual sintering method of powder metallurgy.

In order to further improve the machinability and wear resistance of the sintered alloy, at least one of boron nitride and manganese sulfide is added to a metal matrix in addition to one or both of a magnesium metasilicate-based mineral and a magnesium orthosilicate-based mineral. If dispersed, the boron nitride and manganese sulfide act as a solid lubricant, improving the wear resistance of the sintered part.

Comparing both boron nitride and manganese sulfide, boron nitride is superior in machinability and manganese sulfide is superior in wear resistance.

Further, the amount of addition is adjusted to be in the range of 0.1 to 2% by weight in total with the magnesium silicate-based mineral for the same reason as described above for the lubricating action of the magnesium silicate-based mineral.

The combination ratio of magnesium silicate based mineral and at least one of boron nitride and manganese sulfide is not limited,
Since the cost of boron nitride and manganese sulfide is as high as about 10 to 30 times that of the magnesium silicate-based mineral, it is preferable to reduce the cost to half or less from the viewpoint of cost.

<Action> The sintered alloy for a valve seat according to the present invention is characterized in that Ni and Mo are added to strengthen the matrix, Co is added to improve the high-temperature hardness, and Co is added.
Alloy structure that reduces abrasive wear by adding hard alloy-based alloy particles and furthermore, disperses a predetermined amount of magnesium metasilicate-based mineral, magnesium orthosilicate-based mineral, boron nitride, manganese sulfide, etc. in a specific combination at grain boundaries As a result, it is possible to obtain a sintered alloy for a valve seat having high material strength at high temperatures and good cutability.

<Example> Hereinafter, an example will be described.

 Compositions and blending ratios are weight ratios.

 In preparing a sample, the following raw material powder was prepared.

(1) Base-forming alloy iron powder Fe-1.5% Ni-1.5% Mo-6.5% Co alloy iron powder (2) Cobalt alloy powder for forming hard particles Co-28% Mo-8% Cr-2% Si alloy powder (3) Natural graphite powder (4) Lubricating substance a; Enstatite powder b; Forsterite powder c; Boron nitride powder d; Manganese sulfide powder (5) Zinc stearate powder Comparative material 1: Conventional material for base formation Cobalt alloy powder to ferroalloy powder
15%, natural graphite powder 1% and zinc stearate powder 0.8%
Was mixed into a ring shape, and then sintered at a temperature of 1200 ° C. for 20 minutes in an ammonia decomposition gas furnace.

Comparative materials 2 to 6: This is a material obtained by infiltrating lead in the comparative material 1 and varying the infiltration temperature and time to prepare samples having different amounts of lead impregnation.

Comparative Materials 7-9 and Invention Materials 1-7: Enstatite powder, an example of magnesium metasilicate-based mineral, forsterite, an example of magnesium orthosilicate-based mineral, and powders of boron nitride and manganese sulfide, This is a sample obtained by adding a predetermined amount to the same mixed powder as in No. 1 and molding and sintering.

Invention materials 8 to 9: Samples in which the enstatite powder of invention material 2 was lead-impregnated into a sintered body containing 1%.

The radial crushing strength, machinability and wear resistance of these samples at high temperatures were measured.

 The radial crushing strength is a value measured at a temperature of 400 ° C.

In addition, the machinability is measured by using a lathe to adjust the outer diameter of the sample to 0.5 m.
The cutting resistance value (main component force) when cutting was performed at 0.1 mm per feed at a feed rate of 0.1 mm was measured.

The wear resistance was measured by cutting each sample to the specified size of the valve seat, mounting it on a simulated engine tester, setting the temperature of the valve seat to 400 ° C with LPG fuel gas, and operating the valve seat continuously for 30 hours. Expressed in quantity.

This tester has a mechanism for driving a camshaft by a motor, and can arbitrarily set a temperature, a rotation speed, a valve spring pressure, and the like, and can perform a severe test in a short time.

 The results of the above measurements for each sample are shown in the table.

As is clear from these results, the comparative materials 1 to 6 show the effect of lead. As the lead content increases, the machinability improves, but the radial crushing strength and wear resistance decrease.

Therefore, the lead content is preferably 3% or less from the radial crushing strength and the wear amount.

Comparative materials 7 to 8 and invention materials 1 to 3 show the effect of the added amount of enstatite powder, and the machinability becomes better as the added amount of enstatite powder increases.

Further, the abrasion resistance is also improved, and is best when the content is 1 to 2%, but tends to deteriorate when the content is 3%, and the radial crushing strength is further reduced.

For this reason, enstatite improves machinability and improves abrasion resistance at a specific amount.However, addition of the enstatite lowers the density of the base material, lowering the radial crushing strength. It also indicates that sex is worse.

Comparative material 9 shows the effect of the amount of forsterite powder added, and is inferior in machinability as compared with enstatite.

Inventive material 4 shows that machinability is improved when enstatite and forsterite coexist.

Invention materials 5 to 7 show the effects of boron nitride and manganese sulfide. It can be seen that boron nitride is particularly effective in improving machinability, and manganese sulfide is particularly effective in improving wear resistance.

Inventive materials 8 to 9 have good machinability, but are slightly inferior in radial crushing strength and wear resistance because they contain lead.

<Effects of the Invention> As described above, the sintered alloy for a valve seat according to the present invention is characterized in that Ni and Mo are added to strengthen the matrix, Co is added to improve the high-temperature hardness, and a Co-based alloy is formed. Hard particles are added to reduce abrasive wear, and an alloy structure is formed by dispersing a predetermined amount of magnesium metasilicate mineral, magnesium orthosilicate mineral, boron nitride, manganese sulfide, etc. in a specific combination at grain boundaries. This makes it possible to obtain a sintered alloy for a valve seat of an internal combustion engine, which has high material strength at high temperatures and good cutability.

Further, since it is relatively stable to heat and does not undergo dehydration / decomposition during sintering, it has an effect that it can be manufactured at low cost by ordinary sintering means. .

──────────────────────────────────────────────────続 き Continuing on the front page (72) Akira Fujiki, Inventor Nissan Motor Co., Ltd., 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture (72) Inventor Makoto Kano 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (56) References JP-A-1-255604 (JP, A) JP-A-4-157137 (JP, A) JP-A-62-11024 (JP, A) JP-A-63-118047 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C22C 38/00 304

Claims (3)

(57) [Claims] (1) The total composition is C 0.4-1.2% by weight, Ni 0.3-
2.9%, Cr 0.3 to 2.3%, Mo 1.7 to 9.8%, Co 8 to 22%, Si 0.1 to
0.7%, lubricating substance 0.5-2% and Fe remaining, and C0.6-1.
In the matrix of 2%, Ni 0.5-3%, Mo 0.5-3%, Co 5.5-7.5% and the balance of Fe, Cr 7-9%, Mo 26-30%, Si 1.5-2.5% and C
o The remaining hard phase is 5 to 25% and the lubricating substance is 0.5 to 2% at the grain boundaries.
The lubricating substance is a magnesium metasilicate mineral, or a magnesium metasilicate mineral and a magnesium orthosilicate mineral, or at least one of a magnesium metasilicate mineral or a magnesium orthosilicate mineral. A sintered alloy for a valve seat, wherein at least one of boron nitride and manganese sulfide is dispersed. 2. The total composition is C 0.4-1.2% by weight, Ni 0.3-
2.9%, Cr 0.3 to 2.3%, Mo 1.7 to 9.8%, Co 8 to 22%, Si 0.1 to
0.7%, Pb3% or less, lubricating substance 0.5-2% and Fe remaining, and C0.6-1.2%, Ni0.5-3%, Mo0.5-3%, Co5.5-7.5%
And in the base of Fe balance, Cr7-9%, Mo26-30%, Si1.5-
The hard phase of 2.5% and the balance of Co is 5 to 25%, Pb is 3% or less in the grain boundaries or vacancies, and 0.5 to 2% of the lubricating material is dispersed in the grain boundaries. A magnesium silicate mineral, or a magnesium metasilicate mineral and a magnesium orthosilicate mineral, or at least one of a magnesium metasilicate mineral or a magnesium orthosilicate mineral and at least one of boron nitride or manganese sulfide are dispersed. A sintered alloy for a valve seat. 3. The magnesium metasilicate mineral powder is at least one of enstatite powder, clinoenstatite powder, ensteinite powder and hyperstain powder, and the magnesium orthosilicate mineral powder is forsterite powder and chrysolite powder. The sintered alloy for a valve seat according to claim 1, wherein the sintered alloy is at least one kind.