JPS5810460B2 - Engine cylinder head manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an engine cylinder head equipped with a valve seat having excellent high temperature resistance and wear resistance.

In the era when leaded gasoline could be used as a fuel for automobiles, the lead content in gasoline adhered to the valve seat, which reduced the metal contact between the exhaust valve and the valve seat, making the valve seat resistant even under high temperatures. Abrasion was not much of a problem.

However, from the viewpoint of exhaust gas regulations, it is now mandatory to use unleaded gasoline, and under these circumstances, it is difficult to expect the anti-wear effect of lead, which is superior in terms of strength and abrasion resistance. Cobalt-containing iron-based alloys, which are high-temperature materials, are beginning to be widely used for valve seats.

However, cobalt metal tends to be in short supply worldwide, and there are problems such as unstable supply, unstable prices, and abnormally high prices. is becoming increasingly necessary.

For this reason, valve seat materials with low cobalt content have been proposed, but conventional materials of this kind are used as valve seat materials for leaded gasoline engines and LPG engines, which have different combustion temperatures and atmospheres than unleaded gasoline engines. However, there were problems in that it was unsuitable and lacked versatility.

Therefore, the present invention exhibits excellent wear resistance in high-temperature oxidizing atmospheres without containing cobalt, and is versatile enough to be used regardless of the type of fuel used, such as unleaded gasoline, leaded gasoline, and LPG. The basic objective is to provide a method for manufacturing an engine cylinder head with a valve seat.

Generally, this type of valve seat material is required to have the following properties.

(a) Must have strength (hardness) at high temperatures to withstand metal contact with valve bodies such as exhaust valves.

(b) Good workability and rigidity.

This is because, after the valve seat is press-fitted into the cylinder head, it is usually necessary to cut the valve seat using the valve body as a reference in order to improve the precision of the contact surface with the valve body and obtain good airtightness.

(c) The thermal expansion coefficient should be close to that of the cylinder head material.

That is, if the thermal expansion coefficients of the two valves are too different, a large thermal stress will be generated on the valve seat due to the temperature increase during operation, resulting in so-called sagging.

The present invention exhibits extremely good machinability when press-fitted into a cylinder head, and therefore has excellent workability, and when it is subsequently used as a valve seat at high temperatures, it gradually hardens under heat, and therefore has excellent durability. The present invention aims to provide a method for manufacturing an engine cylinder head that satisfies both workability and product performance by using a sintered metal valve seat that exhibits high temperature and wear resistance.

The secondary hardening type sintered alloy for valve seats used in the method of the present invention is made by combining pre-prepared hard particles containing Ni and Mo as main components and alloy powder for adding Mo to a raw material powder containing iron powder as a main component. After being blended and mixed in the powder, the powder is compacted, and then the compact is sintered.

During this sintering, it is preferable to infiltrate Cu as described later to improve thermal conductivity.

The above-mentioned secondary hardening sintered alloy for valve seats is formed into the desired valve seat in advance, and after sintering, it can be used as is.
Install it as a valve seat and perform cutting to match it with the valve.

Therefore, the workability of the valve seat at this stage is extremely good because it is not hardened.

The adjusted valve seat is used as is, and the secondary hardening type sintered alloy forming the valve seat is secondary hardened by the high heat generated by engine combustion.

This secondary hardening is brought about by Mo added as the alloy powder for Mo addition gradually precipitating as Mo carbide or Mo composite carbide.

Therefore, the valve seat is hardened and its high temperature resistance and wear resistance are improved to a desirable degree.

As the alloy powder for adding Mo, as described later, pe
Binary eutectic alloys of rro-Mo or ternary eutectic alloys of Fe-MO-C can be advantageously used.

The secondary hardening sintered alloy for valve seats used in the method of the present invention has the following chemical components and characteristics.

(I) Chemical component (1) C Component C maintains the hardness of the matrix even at high temperatures, and at the same time, when reheated (during operation), it precipitates together with MO in the form of molybdenum carbide MomCn. It can induce a secondary hardening phenomenon and improve wear resistance at high temperatures.

If it is less than 0.6% by weight, the effect is substantially lost and wear resistance decreases, and if it exceeds 2.2% by weight, it becomes brittle and cannot withstand use.

(2) Si component The Si component is an element necessary for manufacturing hard particles, and does not directly contribute to the functionality of the valve seat.

That is, when producing hard particles, whether using the atomization method or the grinding method, it is essential for increasing the fluidity of the molten metal, and is unavoidably contained in the hard particles.
It is necessarily present in an amount of 0.1 to 0.7%.

(3) Ni component The Ni component exists in both the matrix and the hard particles.

In the matrix, Ni is effective in improving high-temperature strength and improving quench hardness.

In the hard particles, it forms a compound with Mo, giving the hard particles their hardness.

Moreover, its hardness is Hv600 to Hv900, and the hardness decreases little at high temperatures.

Since the hardness is within the above range, it can be used as a valve seat even if the material of the face of the valve body is Stellite, T254N, or TNMC457 (no overlay).

If the Ni component is 2.1% or less, the above effects will be insufficient,
When it exceeds 5.5%, machinability deteriorates and wear on the valve body side increases.

(4) Mo component Mo is present in both the matrix and the hard particles.

In the hard particles, as described above, Ni forms a compound with Ni to improve the hardness of the alloy.

On the other hand, like Ni, Mo in the matrix is effective in improving high-temperature strength and hardening hardness, and at the same time, by providing a Mo concentration gradient, even a small amount of Mo added can locally cause secondary hardening. be able to.

In order to obtain the above effects, 0.45 to 2.5% by weight is required.

Further, Mo from the hard particles is 1.25 to 5.0% by weight.

This is essential for imparting wear resistance by hard particles.

Therefore, the total amount of Mo is required to be 1.7 to 7.5% by weight.

If it is less than 1.7%, the above effect cannot be obtained effectively, and 7.5%
If it exceeds %, it is not only disadvantageous in terms of cost, but also the green compact density becomes low, which is disadvantageous in terms of manufacturing, and processability also deteriorates.

(5) Cu component Cu added by infiltration is about 6 to
8% is solid solution and the remaining 14-16% fills the pores.

Cu dissolved in the matrix is effective in improving high-temperature strength and high-temperature hardness, as well as improving hardening properties.

Cu filling the pores has the effect of improving the thermal conductivity of the valve seat.

When the valve body is an exhaust valve, the heat on the valve face is mainly released through the valve seat, so the better the thermal conductivity of the valve seat, the lower the temperature on the valve face. Even low-grade materials with low high-temperature hardness can be used as valve materials.

This is one of the reasons why the valve seat manufactured using the valve seat material according to the present invention can be used for both Stellite overlay valves and valves without overlay.

At the same time, by improving thermal conductivity through Cu infiltration,
The valve seat material according to the present invention can be used regardless of the type of fuel used.

That is, the combustion temperature is unleaded gasoline minus leaded gasoline <h,
P and G increase in order, so as a valve seat material,
High temperature resistance is required depending on the type of fuel used, but the valve seat material according to the present invention has excellent thermal conductivity.
Leaded gasoline has a higher combustion temperature than unleaded gasoline, P
, G as fuel.

If the amount of Cu infiltration is less than 13%, the amount of Cu that fills the pores will decrease and the above effect cannot be expected, and if it is more than 22%, the proportion of the matrix will decrease and the wear resistance will decrease, making it economically difficult. It will be disadvantageous.

(1) Density The density of the secondary hardened sintered alloy for the valve seat used in the method of the present invention is determined by the density of the green compact (the ratio occupied by the matrix) and the amount of Cu infiltration.

Green density is 7. When it is lower than ll/CC, the hardness decreases and the wear resistance and set resistance decrease.

When the amount of Cu infiltrated is small and is less than 7.1 g/cc, thermal conductivity deteriorates and the above-mentioned effects cannot be obtained.

The structure of the secondary hardened sintered alloy for valve seats used in the method of the present invention is composed of hard particles, a Cu alloy phase, and fine pearlite.

The hard particle phase is determined by the amount and size of the hard particle powder added.

The weight ratio is preferably 5 to 20%.

Further, it is desirable that the size of the hard particle powder is 180 μm or less.

The amount and size of the Cu alloy phase are determined by the green compact density and the amount of infiltration, and these amounts and sizes are as described above.

The reason why the matrix is made of fine pearlite is to improve wear resistance and ensure high temperature hardness.

(1) Mo master alloy The alloy powder for adding Mo is Fe-M.

(50-70% by weight), Ferro-Mo powder 1Fe-
Mo(i2~1g wt%)-C(3,5~4.5wt%
) can be used, and are added in an amount of 0.6 to 5.0% by weight and 2.5 to 20% by weight, respectively.

In addition to the methods described above, methods for adding Mo include (1) using atomized powder, and (2) adding in the form of pure Mo.

■0.5 to 2 in the form of Mo-C (molybdenum carbide)
．． A method of adding 78% by weight is considered, but in method (2), the MO concentration gradient becomes smaller, so the amount of Mo added is reduced to 2%.
．． It is necessary to increase the amount to 0% by weight or more, and as the amount of Mo increases, the compressibility of the powder deteriorates and the strength of the green compact decreases, making it impractical. At a sintering temperature of 1,100 to 1,200°C, diffusion is slow, so alloying does not proceed, and MO remains as pure S, resulting in poor secondary hardenability, and methods ① and ② are not preferred. It is.

(1) Hard powder As the hard powder, those having the following components are used.

In addition, its tensile strength is 30 to 45 kg/mm2, and its hardness is H.
v600-900, particle size -80mesh.

The effects of the above hard powder are basically as follows.

(1) Even at high temperatures, the hardness of the hard particles does not decrease significantly and can compensate for the decrease in hardness of the base metal, making it possible to maintain high-temperature hardness.

(2) Therefore, even under lead-free conditions, sliding properties are good and seizure resistance is improved.

(3) Since the hard particles exist dispersed in the base metal,
As for machinability, it is possible to obtain good machinability equivalent to that of ordinary sintered alloys.

(4) The base metal can be strengthened by hard particles,
Abrasion resistance at high temperatures can be improved.

Next, a method for manufacturing a cylinder head according to the present invention will be explained.

First, we will discuss the manufacturing method for the valve seat material.

As raw material powder, pure iron powder or alloy iron powder has a content of 5 to 20%.
% of hard particle powder, an appropriate amount of the alloy powder for adding Mo, an appropriate amount of graphite powder, and 0.5-2.0% of zinc stearate as a lubricant. After mixing, the compression pressure was 4-4.
Compacting at 6t/ffl, placing Cu alloy infiltrant on top of the compact, and heating at 1100°C or higher at 118°C in a non-oxidizing atmosphere.
Sintering is performed at a temperature of 0° C. or lower for 10 minutes or more and 60 minutes or less.

After sintering, it is hardened. Leave to cool as is without tempering.

Next, a method of manufacturing a cylinder head using this valve seat material will be explained.

The valve seat material manufactured by the method described above is press-fitted as is into the valve seat mounting part of the cylinder head, and then finishing processing (cutting) is performed based on the valve body, which is the mating part of the valve seat. Improves adhesion with the valve body.

The hardness of the sintered body is HRC approximately 28, and the workability is extremely good.

Then, when the engine is assembled and operated, the valve seat is heated to a high temperature by combustion heat, and this heating causes MO and C to precipitate in the form of molybdenum girbide, causing a secondary hardening phenomenon, resulting in a decrease in hardness. It will improve.

As mentioned above, the secondary hardening phenomenon occurs when reheating.
This is a phenomenon in which Mo, which was in solid solution, precipitates in the form of MomCn and hardens.

If such a material is used as a material for a valve seat, as mentioned above, it has a low hardness after sintering and is easy to process.
(0 to 600°C), secondary hardening occurs and only the outermost surface is hardened, exhibiting favorable wear resistance.

Next, examples of the present invention will be shown.

Example-1 Chemical components are 28.8% Ni and 35.0% Mo.

4.8% Si, remaining Fe, 5.0% hard particle powder with a particle size of -80 mesh, and chemical components are 16.3% Mo.

1.60% C1 balance Fe, 10.0% alloy powder with particle size -80mesh, 1.1% graphite powder with particle size -80mesh
0%, 2.16% Ni powder with particle size -350mesh,
Contains 81.74% Fe powder with a particle size of -80mesh, and 0.7% zinc stearate as a lubricant.
and mixed for 30 minutes using a V-type mixer to obtain a mixed powder.

This mixed powder was compacted into a shape of 15 mmφ x 35 mmφ x 10 mmt at a compression pressure of 5 Ot/ffl, and molded onto the compact so that the final content was 15.52%. The Cu infiltrant was installed and pre-sintered (dewaxed) by holding it at 800°C for 30 minutes in ammonia decomposition gas as a protective atmosphere, and then 1130°C.
The mixture was held at ℃ for 20 minutes to perform sintering, and then slowly cooled to obtain a sintered body.

The chemical composition, density, and hardness at this time were as shown in the table.

Cut out a valve seat test piece from this sintered body and heat it with a gas burner so that the temperature near the valve seating part is 750°C and the valve seat surface temperature is 450°C when the engine speed is 5,000 r, p, m. A 40-hour wear test was conducted without lubrication, and the results are shown in the table, comparing the cases where the valve side was filled with stellite and the case where 2l-4N material was used.

Example-2 Chemical components are 25.5% Ni and 30.0% Mo.

4.8% Si, residual Fe, 5.0% hard particle powder with particle size -80mesh, chemical components 8.5% Mo, 0.85%
2.5% C1 residual Fe, particle size -80mesh alloy powder
, 0.6% graphite powder with particle size -80mesh, particle size -3
50mesh Ni powder 0.83%, particle size 80mes
92.27% of the Fe powder of h was blended, 0.7% of zinc stearate was added as a lubricant, and the mixture was mixed for 30 minutes using a ■ type mixer to obtain a mixed powder.

This mixed powder was compacted into a shape of 15 mmφ x 35 mmφ x 10 mmt at a compression pressure of s, ot/cm2, and a Cu infiltrated material was molded on top of the compact so that the final content was 20.0%. as a protective atmosphere.
Preliminary sintering was carried out by holding at 800° C. for 30 minutes in an ammonia decomposition gas.

Next, sintering is performed by holding at 1130°C for 30 minutes,
A sintered body was obtained by slow cooling.

The chemical composition, density, and hardness at this time are as shown in the table.

In addition, a valve seat test piece was cut out from this sintered body and subjected to an abrasion test under the same test conditions as above. The results are shown in the table.

Example-3 Chemical components are 20.5% Ni, 30% Mo, 3.5% Si
, remaining Fe, 20% hard particle powder with particle size -80 mesh
, the chemical composition is 8.5% Mo, 0.85% C1 balance Fe, the particle size is 180 mesh alloy powder 18.3%, the particle size is -8
0mesh graphite powder 1.2%, particle size, 350mes
Blend 1.4% of h Ni powder and 69.2% of Fe powder of -80mesh particle size, add 0.7% of zinc stearate as a lubricant, and mix for 30 minutes with a ■ type mixer. A mixed powder was obtained.

This mixed powder was compressed under a pressure of 5. It was compacted at Ot/cm2 and heated at 800°C in ammonia decomposition gas as a protective atmosphere.
Pre-sintering was carried out by holding for 30 minutes at 1130
Sintering was carried out by holding at a temperature of 20 minutes, followed by gradual cooling to obtain a sintered body.

The chemical composition, density, and hardness at this time are as shown in the table.

In addition, a valve seat test piece was cut out from this sintered body and subjected to an abrasion test under the same test conditions as above. The results are shown in the table.

In the above table, Conventional Examples 1 and 2 are both sintered materials, Conventional Example 1 is not infiltrated with Cu, and Conventional Example 2 is infiltrated with Cu.

Further, for the above Example 1, the degree of secondary curing by reheating is shown in FIG.

In FIG. 1, the hardness was measured for the samples heat-treated for 2 hours at each of the above-mentioned heating temperatures.

At the stage of sintering, the HRC28 was
Maximum HRC45 when heated at 500-600℃
It is possible to obtain a certain degree of hardness.

Note that the dotted line in FIG. 1 shows the change in hardness when a material heated at 300° C. for 2 hours is further heated.

As is clear from the comparison between the dotted line and the solid line, it is understood that the first heating after sintering is important.

Therefore, due to secondary hardening, the amount of wear is reduced as shown in the table.
Those using L-F, materials that do not contain cobalt (21
-4N), conventional examples 1 and 2
It decreases by a large margin compared to .

The amount of wear described above is the result of measuring the amount of sinking of the exhaust valve under the same conditions, and is the sum of the amount of wear of the exhaust valve and the amount of wear of the valve seat.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the degree of secondary hardening of the secondary hardening sintered alloy for valve seats according to the present invention.

Claims (1)

[Claims] I C 0.6-2.2% by weight, Si 0.1-0.7% by weight Ni 2.1-5.5% by weight, Mo 1.7-7.5% by weight, the balance substantially consisting of Fe. Alternatively, a valve seat material, which is a sintered body containing 13 to 22% Cu by infiltration and in which 5 to 20% by weight of hard particles mainly composed of Ni and Mo are dispersed in the matrix, is used in the engine. A method of manufacturing a cylinder head for an engine, which comprises press-fitting the valve seat material into the cylinder head, subjecting it to finishing processing, and then operating the engine to harden the valve seat material using the heat of combustion.