JPH0137466B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a valve seat for an internal combustion engine, and particularly to a valve seat made of a composite of two different types of sintered alloys. With the use of unleaded gasoline, sintered alloy valve seats have become widely used for internal combustion engines due to the desire for better wear resistance. The presence of sintered pores that contribute to the wear resistance of a valve seat made of a composite metal is considered to be a problem in the strength of the valve seat. When a conventional valve seat is assembled into an aluminum alloy cylinder head, even if it is shrink-fitted, cold-fitted, or press-fitted, if the valve seat thickness is appropriate, there is no fear of it falling off from the cylinder head. However, in order to improve engine output, the valve opening area of the cylinder head is increased, and as a method to do so, it is necessary to reduce the thickness of the valve seat, but in this case, problems such as valve seat falling off and deformation occur. arise. Furthermore, in engines that use cast iron cylinder heads, such as diesel engines, there may be a problem of the valve seat falling off due to the difference in thermal expansion coefficient between the valve seat and the cast iron cylinder head. These thin-walled valve seats and valve seats incorporated into cast iron cylinder heads are required to have strength and rigidity, especially under high-temperature conditions. On the other hand, a valve seat made of sintered alloy contains a large amount of expensive elements in order to satisfy heat resistance and wear resistance. This is a two-layer composite sintered valve seat with the second member 2 to be formed, thereby improving the effects of compounding such as economical efficiency, machinability, and thermal conductivity. In recent years, attempts have been made to improve the strength of the valve seat itself by increasing the density of the second member on the cylinder head side of the composite sintered valve seat by forging. In addition, the valve seat on the exhaust side in particular tends to become extremely hot due to exhaust gas, and high-temperature corrosion wear tends to progress.Therefore, it is necessary to improve thermal conductivity and reduce heat accumulation in the valve seat as much as possible, so a copper alloy is added to the sintered alloy. Some products can be used after infiltration. The purpose of the present invention is to satisfy the above-mentioned strength, rigidity, abrasion resistance, and thermal conductivity related to abrasion resistance as a valve seat, as well as the conditions for a composite valve seat, and the composite sintered valve seat of the present invention It consists of the following five configurations. (1) The first sintered alloy forming the first member on the side facing the valve contains 8 to 14% by volume of hard particles of 250 mesh or less, 0.5 to 1.7% by weight of C,
Ni0.5~2.5%, Cr3.0~8.0%, Mo0.1~0.9%,
It is an iron-based sintered alloy consisting of 1.0 to 3.8% W, 4.5 to 8.5% Co, and the balance substantially Fe. (2) The first sintered alloy is an iron-based sintered alloy in which the amount of pores formed by atomized iron powder is 6 to 13% by volume, and the amount of independent pores is 0.4 to 1.2% by volume. It's gold. (3) A second member forming the second member on the cylinder head side.
Sintered alloy weight% C0.5~1.4%, P0.1~0.4
The balance is an iron-based sintered alloy consisting essentially of Fe. (4) Iron-based alloy in which the second sintered alloy is formed from atomized powder, the pore content is 6 to 12% by volume, and the independent pore content is 0.5 to 2.5% by volume. It is a sintered alloy. (5) Both the first sintered alloy and the second sintered alloy are infiltrated with a copper alloy. The most distinctive feature of the composite sintered valve seat of the present invention is that it improves the balance between independent pores and continuous pores that inevitably exist in sintered alloys, and also has a synergistic effect combined with the infiltration treatment effect. ,
This maximizes the effectiveness of a composite sintered alloy valve seat. In other words, two types of base iron powder for sintered alloy valve seats are normally used: reduced iron powder and atomized powder, and in order to obtain a relatively high density sintered alloy, the particle size must be fine and approximately spherical. Atomized powder is used. However, as mentioned above, in the case of sintered alloys for valve seats that require a large amount of alloy particles necessary for wear resistance, these alloy particles are blended as a single powder, and furthermore, extremely fine carbon powder or cobalt powder is blended. Therefore, the density of the sintered alloy and its pore distribution differ depending on the powder used, and the amount of continuous pores and the amount of independent pores also differ. Furthermore, in a sintered alloy infiltrated with a copper alloy, the continuous pores are infiltrated with the copper alloy, which improves the strength and thermal conductivity of the sintered alloy. In the valve seat under these conditions, internal stress is generated due to the difference in coefficient of thermal expansion between the copper alloy and the sintered alloy, and as heating and cooling are repeated, the strength of the sintered alloy progresses to decrease. Conversely, if the amount of independent pores is large, the infiltration of the copper alloy will not reach the independent pores, resulting in a decrease in the strength and thermal conductivity of the sintered alloy. In addition, in the case of a composite sintered valve seat, the strength and coefficient of thermal expansion of the first sintered alloy and the second sintered alloy are required to be as similar as possible, and the valve seat is required to be homogeneous. The raw material powder and manufacturing conditions used must be appropriate. In the present invention, in order to satisfy these conditions for a composite valve seat, the first sintered alloy, which requires wear resistance, contains 8 to 14% by volume of hard particles of 250 mesh or less, and the base is An iron-based sintered alloy is required in which the amount of pores formed by the atomized iron powder is 6 to 13% by volume, and more preferably the amount of independent pores is 0.4 to 1.2% by volume. The first sintered alloy has a close relationship with the second sintered alloy described later, but its most distinctive feature is that the amount of pores is 6 to 13% by volume. The reason is that if the amount of pores exceeds 13% by volume, the strength of the sintered alloy itself will be low, and when it is infiltrated with copper alloy and used, a decrease in high-temperature strength is unavoidable, so it is recommended that the amount of pores be less than 13% by volume. necessary and 6
If it is less than % by volume, the amount of copper alloy infiltrated will be too small, which will lower the thermal conductivity and reduce the high-temperature wear resistance of the first sintered alloy, and the amount of pores will be 6 to 13% by volume. is necessary. On the other hand, independent pores that are not infiltrated with copper alloy are
It is desired that the content is 0.4 to 1.2% by volume. The reason is that improvements in thermal conductivity and strength due to copper infiltration are inhibited because the independent pores are not infiltrated with copper.
It is necessary that the amount of sintered pores be 1.2% or less, but conversely, in order to reduce the number of independent pores to the total amount of pores, it is unavoidable to increase the amount of sintered pores themselves.
In addition, the effect of independent pores, which has the function of adjusting the difference in thermal expansion coefficient between the copper alloy infiltrated layer and the sintered alloy, is lost and the high temperature strength of the sintered alloy decreases, so the amount of independent pores is 0.4%.
It is preferable that there be at least one of them. In order to obtain a sintered alloy having such sintered pores, it is necessary that the sintered alloy has 8 to 14% by volume of hard particles of 250 mesh or less, and that the iron-based alloy powder forming the base is It needs to be an atomized powder. As mentioned above, the atomized powder is fine and approximates a spherical shape, so it has excellent compression moldability and has a high density, which is necessary for adjusting the continuous pore ratio.
By using hard particles that contribute to wear resistance as a fine powder with a mesh size of 250 mesh or less and blending them into the iron-based alloy atomized powder at a volume % of 8 to 14 volume %, the above-mentioned independent pores and total pores can be obtained. A balance is achieved. In other words, the hard particles must exist in the required volume % on the valve contact surface of the first sintered alloy to directly form a sliding surface with the valve, and in order to have sufficient wear resistance. is required to be at least 8% by volume. However, if the amount of hard particles is too large, the strength of the sintered alloy will decrease, and if the amount of hard particles is too large in the mixture of atomized powder and hard particles, the amount of sintered pores will be excessive. Depending on these conditions, the amount of hard particles needs to be 8 to 14% by volume. Furthermore, the particle size of these hard particles must be fine powder of 250 mesh or less, and if relatively large particles of 250 mesh or more are used, the overall porosity ratio will increase as described above. , and the fluidity of the blended powder decreases, resulting in a decrease in compactability and a decrease in sintered alloy density. It is preferable that the first sintered alloy is composed of the following sintered alloy. (Component weight%) C0.5-1.7, Ni0.5-2.5, Cr3.0
~8.0, Mo0.1~0.9, W1.0~3.8, Co4.5~8.5,
The remainder consists essentially of Fe, with Cu9.5~ in the sintered pores.
Including 14%. This first sintered alloy forms hard particles compared to, for example, the valve seat alloy of Japanese Patent Publication No. 51-13093.
It is characterized by improved surface strength and wear resistance by suppressing the amounts of Cr, Co, and W, and by making the hard particles more fine. To explain each additive element, C is essential for matrix adjustment. If it exceeds 1.7%, the amount of cementite becomes excessive and machinability and strength decrease. If it is less than 0.5%, the amount of ferrite in the matrix becomes excessive and the matrix hardness decreases. 0.5 to 1.7 because wear resistance deteriorates due to a decrease in
%, more preferably in the range of 1.0 to 1.5%. Regarding Ni, it dissolves in the matrix and contributes to improving heat resistance, but if it is less than 0.5%, no heat resistance effect can be obtained, and if it exceeds 2.5%, hardenability deteriorates, resulting in loss of hardness uniformity and wear resistance. The content is selected in the range of 0.5 to 2.5%, more preferably 0.8 to 2.3%, since this may cause deterioration of properties. C-Cr for Cr, W, Co
-W-Co-Fe is added as hard particles and contributes to wear resistance, and is also dissolved in the matrix and contributes to improving heat resistance and strength.
The limiting values of W and Co are determined by the above-mentioned limited range of hard particle amount and the C-Cr-W-Co-Fe particle components described below, and 3.0 for Cr.
If it is less than 4.5%, the heat resistance effect will be lost; for W, if it is less than 1.0%, the high temperature strength will decrease, and if it is less than 4.5%, the high temperature strength and C-Cr will decrease.
-The bonding strength between the hard particles of W-Co-Fe and the matrix decreases, with Cr3.0-8.0%, W1.0-3.8%,
Co4.5-8.5%, more preferably Cr3.5-7.5%,
W1.3~3.3% and Co5.0~8.0% are selected and the amount of hard particles is adjusted. Furthermore, when Mo is added as Fe-Mo, it forms hard particles that contribute to wear resistance, but if it exceeds 0.9%, economic efficiency and powder compactability deteriorate compared to the wear resistance effect. Also, if it is less than 0.1%, the amount of hard particles will be too small and the high temperature strength will also decrease, so 0.1 to 0.9%, more preferably 0.3 to 0.7%.
selected within the range. More specifically, the first sintered alloy having such components includes Fe powder, C powder, Co powder, Ni powder,
This is achieved by mixing and sintering Fe-Mo powder and C-Cr-Co-W-Fe alloy powder.
For W-Fe powder, preferably C2.0-3.0%,
Co7.0~1.5%, W15~25%, Cr55~70%, Fe1.0
It is preferable that the alloy powder is selected in the range of ~8.0%. Such alloy powder has a large amount of Cr compared to an alloy called stellite, and by reducing the amount of Co, the hardness of the alloy particles themselves can be increased. Its presence increases the bonding strength between the hard particles and the base. The first sintered alloy of the present invention has been explained below,
In the present invention, extremely excellent effects can be achieved by forming a composite sintered valve seat using the above-described first sintered alloy and a second sintered alloy that is optimally combined with the second sintered alloy. The second sintered alloy has C0.5 to 1.4% by weight,
P0.1-0.4%, the remainder is a component consisting essentially of Fe,
The amount of pores formed by atomized powder is 6 to 12
% by volume, more preferably an iron-based sintered alloy in which the amount of independent pores among the pores is 0.5 to 2.5% by volume. First of all, the amount of sintered pores has an effect on the strength of the sintered alloy, as well as the effect of infiltration, as mentioned above. Therefore, the use of a low-alloy sintered alloy is an absolute prerequisite for improving the economical effects, machinability, and productivity of composite materials. Furthermore, when the second sintered alloy and the first sintered alloy are combined, they are formed in advance into two layers in the form of a powder compact and sintered under the same temperature, atmosphere, and time conditions. The second sintered alloy and the first sintered alloy are required to have approximately similar sintering shrinkage, and in practical use, approximately similar coefficients of thermal expansion are required to prevent internal distortion of the valve seat as a whole. Furthermore, it is necessary to relatively improve the thermal conductivity, which is likely to be insufficient in the first sintered alloy. Under such conditions, in the present invention, the total pore content of the first sintered alloy is set to 6 to 12%. The amount of pores is
If it exceeds 12% by volume, not only will the strength of the sintered alloy itself decrease, but also, especially in the case of the second sintered alloy, which is a low alloy, the difference in thermal expansion coefficient with the copper alloy to be infiltrated will increase. Since the alloy is susceptible to a decrease in high-temperature strength, the total pore content is preferably 12% by volume or less, more preferably in the range of 0.5 to 3% relative to the first sintered alloy. On the other hand, the amount of sintered pores is 6
If the amount of sintered pores is less than 6% by volume, the amount of pores infiltrated becomes too small and the effect of improving thermal conductivity cannot be obtained, and the sintered pores must be selected in the range of 6 to 12% by volume. be. Moreover, as mentioned above, if the second sintered alloy pore content is lower than the first sintered alloy pore content by more than 3 volume%, the difference in thermal expansion coefficient due to copper infiltration will be excessive between both sintered alloys, which is preferable. do not have. On the other hand, if the second sintered alloy has a low porosity, which is less than 0.5% compared to the first sintered alloy, the second sintered alloy itself is inferior in strength as a material than the first sintered alloy. If the amount of sintered pores or the amount of pores in the second sintered alloy is relatively large, the strength of the second sintered alloy will be inferior to the first sintered alloy. It is preferable that there is a difference in the amount of sintered pores between the first sintered alloy and the first sintered alloy in the range of 0.5 to 3% by volume. Furthermore, the amount of independent pores in the second sintered alloy is
It needs to be 2.5% or less. This is the second
As described below, the sintered alloy is uniformly dispersed and undergoes local sintering shrinkage due to the influence of P added to achieve the above-mentioned range of sintered pores, resulting in an increase in the amount of independent pores. However, if the amount of independent pores exceeds 2.5% by volume, copper infiltration will not occur in the independent pores, resulting in a significant decrease in thermal conductivity and strength. It is necessary to do the following. Conversely, in order to reduce the amount of independent pores to less than 0.5%, not only is it necessary to increase the amount of sintered pores, but also the strength of the second sintered alloy is relatively poor. The amount of independent pores, which has an adjustment function for deterioration of high-temperature strength due to the difference in thermal expansion coefficient with the copper infiltrated layer, is too small, resulting in a decrease in high-temperature strength. 0.5 of volume
Selected in the range ~2.5% by volume. In order to obtain such a sintered alloy having total pores and independent pores, the second sintered alloy must have C0.5 to C0.5 in weight%.
It is a sintered alloy consisting of 1.4% P, 0.1 to 0.4% P, and the remainder substantially Fe, and it needs to be formed of atomized powder. The reason for using atomized powder is that, as is generally known, it has excellent compression moldability and can form a green compact with a relatively high density, thereby reducing the amount of sintered pores. Furthermore, in the present invention, copper infiltration is essential to improve thermal conductivity, strength, and rigidity, and copper infiltration causes copper to infiltrate into pores and partially diffuse into the base sintered alloy. Therefore, it is characterized in that an improvement in strength is achieved. That is, copper is an element that normally causes sintering expansion and has a strong effect on low alloy iron-based sintered alloys such as the second sintered alloy, but in the present invention, such copper 0.1-0.4% P for infiltration
This is solved by using iron-based alloy powder containing iron. P has an effect on sintering shrinkage, offsets the sintering expansion effect of copper, and is also effective in reducing the amount of pores in the sintered alloy itself. If P is less than 0.1%, No effect, on the contrary P0.4%
If it exceeds Fe-P-C, machinability and toughness deteriorate due to steadite crystallization, and sintering shrinkage progresses too much, resulting in an excessive amount of independent pores and a decrease in the amount of infiltration. is 0.1 to 0.4% by weight, preferably 0.1
Must be selected in the range of ~0.3%. Also, C is essential for base adjustment of the second sintered alloy,
If it is less than 0.5%, the amount of ferrite will be high and the hardness will be low, resulting in a decrease in strength. If it exceeds 1.4%, the amount of cementite will be excessive, which will not only make the matrix brittle but also deteriorate machinability, so the C range is 0.5 to 1.4%. Preferably, it should be selected between 0.9 and 1.4%. Examples of the composite sintered valve seat of the present invention will be described below. First, as a raw material powder for the second sintered alloy of the present invention
Mix 77% atomized iron powder containing 0.3% P, 1% -325 mesh C powder, and the remaining atomized iron powder, fill it into a powder mold, and then mix and mix the raw material powder for the first sintered alloy below. and fill it onto the first sintered alloy powder. C powder (-325 mesh) 1.2% Co powder (5μ or less) 6.0% Ni powder (-325 mesh) 2.0% Fe-Mo powder (-250 mesh) 1.0% C2.5-Co10-W19-Cr6.35-Fe5 Alloy powder (-
250 mesh) 11.5% Remaining atomized iron powder The above two layers of powder were compacted at a compacting pressure of 6t/ ^cm2 , sintered at 1110℃ for 60 minutes in a reducing atmosphere, and the copper alloy for infiltration was placed on it. Infiltration treatment was performed at ℃60min. Further, after holding at 880℃ for 30 minutes, oil-cooling quenching and tempering test pieces for measuring the physical properties below and test pieces for the tests described below (outer diameter φ31, inner diameter φ25, height 7 mm)
It was created. When the physical properties of this valve seat were measured, they were as follows: 1. First sintered alloy (component weight%) C1.20%, Ni1.73%, Cr7.30%,
Mo0.45%, W2.19%, Co7.15%, Cu12.51% Fe with residual trace impurities (hardness) HRC 33.0 (porosity) 11.8% (before infiltration) (independent porosity) 0.51% 2 Second sintered alloy (component weight%) C1.1%, P0.20%, Cu11.2% Fe with residual trace impurities (hardness) HRC 24 (porosity) 9.9% (before infiltration) (independent) Porosity) 1.6% 3 Physical properties as a composite material (modulus of elasticity) 18600Kg/mm ² (Coefficient of thermal expansion) (RT→400℃) 1.305×10 ^-5 /℃ (Thermal conductivity) (400℃)
10.9×10 ^-2 Ccl/cm・sec・℃ (Tensile strength) 93.4Kg/mm ^2Here , the second sintered alloy and the first sintered alloy obtained through the powder and manufacturing process under the same conditions as described above. When the physical properties of each individual were measured, 4. First sintered alloy (modulus of elasticity) 19400Kg/mm ² (coefficient of thermal expansion) (RT→400℃) 1.244×10 ^-5 /℃ (thermal conductivity) (400 ℃)
10.4×10 ^-2 Cal/cm・sec・℃ (Tensile strength) 96.8Kg/mm ² 5 Second sintered alloy (modulus of elasticity) 18000Kg/mm ² (Coefficient of thermal expansion) (RT→400℃) 1.367×10 ⁵ /℃ (thermal conductivity) (400℃)
13.0×10 ^-2 Cal/cm・sec・℃ (Tensile strength) 91.0Kg/mm ^2Here , each measured value hollow porosity is the theoretical density and actual density before infiltration, and independent porosity is after infiltration. This is calculated from the after density and the amount of pores. In this way, the first and second sintered alloys each have a high tensile strength of 90 Kg/mm ² or more and an elastic modulus of 17000 Kg/mm ² or more, either alone or as a composite material. , furthermore, the difference in thermal expansion coefficient between the first sintered alloy and the second sintered alloy is 10% or less, and the thermal conductivity is
Since it has a high temperature of over 10×10 ^-2 Cal/cm・sec・℃, it has excellent strength, rigidity, and wear resistance against falling off when it is assembled into a cylinder head as a valve seat. The valve seat of the present invention thus obtained
200x micrographs are shown in Figures 2 and 3. Second
Both Fig. 3 and Fig. 3 show the metal structure of the sintered alloy subjected to nital corrosion, and the photograph in Fig. 2 shows the first sintered alloy, and Fig. 3 shows the second sintered alloy. A shown in FIGS. 2 and 3 is a continuous hole and is infiltrated with copper, and B is an independent hole that is not infiltrated with copper. C indicates hard particles. Figures 4 and 5 are 200x micrographs showing the metal structure of a composite sintered alloy valve seat 2 infiltrated with copper alloy as in the present invention but corroded with nital liquid for comparison as described later. FIG. 4 shows the sintered alloy used for the first member on the valve contact side, and FIG. 5 for the second member on the cylinder head side. Comparing the metal structures of the valve seats of the present invention shown in FIGS. 2 and 3 with the conventional valve seats shown in FIGS. 4 and 5, it is clear that the hard particles C in the present invention are smaller in size. Moreover, the continuous pores indicated by A are also fine and have a small area, and furthermore, it is clear that the structure of the valve seat of the present invention is extremely dense. The valve seat of the present invention will be compared with a conventional composite sintered valve seat, and its effects will be explained. (Comparative composite sintered valve seat 1) (First sintered alloy) C powder (-325 mesh.0.75%, Ni powder (-
325 mesh) 1.2%, Fe-Mo powder (-150 mesh) with Mo content of 0.35%, C1.4-Cr55-W26-
Co 17.6% alloy powder (-150 mesh) 18% Co
A mixed powder of 5.5% powder (less than 5μ) and residual reduced iron powder (-100 mesh). (Second sintered alloy) C powder (-325 mesh) 1.12%, Fe-Mo powder (-150 mesh) with Mo content of 0.57%, Cu powder (-
Mixed powder of 4.04% (120 mesh) and residual reduced iron powder (-100 mesh). Comparative composite sintered valve seat 1 was formed by mold-pressing and sintering such powder under the same conditions as the above-described valve seat of the present invention, and after sintering,
Comparative composite sintered valve seat 2 was created by copper infiltration and heat treatment. The physical properties of the comparative composite sintered valve seats 1 and 2 described above were measured in the same manner as the valve seat of the present invention, and the results are shown below.

[Table] The comparison valve seat and the valve seat of the present invention were subjected to a press-fit test, a pull-out load test, a wear test, and a drop-off test and a wear test as actual machine tests, as shown below. (Press-fit test and pull-out test) (Test method) As shown in Fig. 6, an aluminum alloy cylinder head sample 5 with an outer diameter of 86 mm and a height of 25 mm and having concentric holes of 31 mm in diameter and 27 mm in the center for fitting the valve seat 12 was used. Valve seat 12 by changing the tightening distance
is press-fitted, and while cooling the cooling part 51 of the cylinder head sample 5 with water, the flame of the burner is heated to the valve seat 12.
Heating at 400°C for 3 minutes at the center and then cooling with an air jet for 3 minutes was repeated 200 times. In this test, the rigidity of the valve seat is evaluated based on the relationship between the initial pressure-fitting load of the valve seat into the cylinder head and the interference margin, and the test evaluates the rigidity of the valve seat based on the relationship between the initial pressure-fitting load of the valve seat into the cylinder head and the interference margin. This test evaluates the strength of the valve seat against falling off. Comparison valve seat 1, which is not infiltrated, is the conventional one with an outer diameter of φ31 mm and an inner diameter of φ23 mm and a wall thickness of 4.
Comparative valve seat 2 and the valve seat of the present invention have an outer diameter of φ31 mm, an inner diameter of φ25 mm, and a wall thickness of 3 mm.
A thin-walled valve seat was used. (Test Results) The results of the punch test are shown in Figure 7. As shown in FIG. 7, the valve seat of the present invention has a pull-out load that is approximately 1.3 times that of the comparative valve seat 2 which has the same wall thickness and shape, and also has a pullout load that is approximately 1.3 times that of the comparative valve seat 1 which has the same wall thickness and shape. It was confirmed that they had the same pull-out load and superior drop strength. Also, Fig. 8 shows the results of the valve seat press-fit test, and the results of this test, where stiffness is evaluated, are 1.3 times that of comparative valve seat 2 with the same wall thickness, and similar to comparative valve seat 1 with 1.3 times the wall thickness. Stiffness was demonstrated. As described above, the composite sintered valve seat of the present invention has superior strength and rigidity compared to conventional valve seats, so it has excellent resistance to falling off from the cylinder head, and at the same time has improved thermal conductivity and first sintered bond. The following wear test shows that the gold structure is strengthened and densified, resulting in excellent wear resistance. (Abrasion Test) (Abrasion Test Method) The above-described valve seats according to the present invention and comparative valve seats 1 and 2 are used as test materials. The test machine sprayed a propane gas flame onto the valve seat surface to heat the valve seat surface to 300 to 500℃, and rotated the valve against the valve seat via a spring, 3000 times/with a valve spring load of 35 kg. Evaluation is made by measuring the wear area of the contact surface between the valve seat and the valve after 8×10 ⁵ times. In addition, Stellite No. 6 metal was used for the contact surface of the valve. (Wear test results) Fig. 9 shows the amount of wear on the valve seat, and Fig. 10 shows the amount of wear on the valve. Both Figures 9 and 10 show the amount of wear as the temperature changes, and both the valve and valve seat of the present invention and the conventional product.
It was confirmed that sufficient wear resistance was maintained at 0.04 mm ² or less. Furthermore, test results of actual machine operation of the valve seat of the present invention and conventional comparison valve seats 1 and 2 are shown below. (Actual machine test) (Test conditions) 1500c.c., OHC, gasoline engine 5500rpm full load 400 hours continuous operation Comparison valve seat 1 Outer diameter φ31mm Inner diameter φ23mm Comparison valve seat 2 and invention valve seat Outer diameter φ31mm, inner diameter φ25mm Valve: Stellite No. 6 metallized valve (test results) After the test, no falling off or deformation of the comparative valve seats 1 and 2 and the valve seat of the present invention was observed. Also, according to the wear test results shown in Fig. 11, which shows the average amount of wear of the test valve seats and valves for each cylinder, the amount of wear of the valve seat of the present invention is 0.04 mm ² or less, and even when combined with the amount of valve wear, The wear amount is 0.05 mm ² or less, which is the same as that of comparison valve seats 1 and 2, and is sufficient for practical use. As is clear from the strength test, wear test, and actual machine test of the valve seat, in the composite sintered valve seat of the present invention, the amount of sintered pores in the first sintered alloy and the second sintered alloy are reduced. In addition, the balance between the sintered pores and the amount of sintered pores was appropriate, and by controlling the amount of independent pores, the effect of infiltration was fully utilized, and the strength and high-temperature strength were improved. As a result, it is evaluated that the resistance to falling off from the cylinder head has been improved. Furthermore, the reason why it has wear resistance comparable to that of conventional high-alloy sintered valve seats is that the pore content of the first sintered alloy is controlled to be low and the structure including hard particles is refined. This is thought to be due to not only improved surface strength but also markedly improved thermal conductivity.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a composite sintered valve seat, Fig. 2 is a 200x micrograph showing the metallographic structure of the first sintered alloy of the present invention, and Fig. 3 is a 200x micrograph showing the metallographic structure of the second sintered alloy of the present invention. A magnified micrograph, Figure 4 shows the conventional 1st
A 200x micrograph showing the metallographic structure of a sintered alloy. Figure 5 is a 200x micrograph showing the metallographic structure of a conventional secondary sintered alloy.
Fig. 6 is a cross-sectional view of a test cylinder head sample of the valve seat of the present invention, Fig. 7 is a graph showing the pullout load test results of the valve seat of the present invention from the cylinder head, and Fig. 8 is the valve seat of the present invention. 9 and 10 are graphs showing the results of the wear test of the valve seat of the present invention, respectively.
FIG. 1 is a graph showing the results of a wear test of the valve seat of the present invention in an actual machine. Explanation of the numbers: 1...First member, 2...Second member, 3...Cylinder head, 4...Valve, 5...
...Cylinder head sample, 12...Composite sintered valve seat, A...Continuous holes, B...Independent holes, C...
...Hard particles.

Claims (1)

[Claims] 1 In a valve seat formed of two different types of sintered alloys and further infiltrated with a copper alloy, the first sintered alloy forming the first member on the valve contact side is a hard metal of 250 mesh or less. Particles by volume%
Contains 8-14% in weight, C0.5-1.7% in weight%,
Ni0.5~2.5%, Cr3.0~8.0%, Mo0.1~0.9%,
It is an iron-based sintered alloy consisting of W1.0~3.8%, Co4.5~8.5%, and the balance substantially Fe, and the amount of pores formed by the atomized iron powder is 6~13% by volume, and The iron-based sintered alloy has an independent pore content of 0.4 to 1.2% by volume, and the second sintered alloy forming the second member on the cylinder head side has C0.5 to 1.2% by weight.
1.4%, P0.1~0.4% The balance is an iron-based sintered alloy consisting essentially of Fe, and the amount of pores formed by the atomized iron powder is 6~12% by volume, and it has independent pores. It is an iron-based sintered alloy having a pore volume of 0.5 to 2.5% by volume, and is characterized in that both the first sintered alloy and the second sintered alloy are infiltrated with a copper alloy. Composite sintered valve seat.