JPH11141316A - Valve seat body having two layer structure and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a valve seat body having two layer structure composed of one layer which has high abrasion resistance, corrosion resistance, high hardness and strength against breakage on its seat side, and the other layer which has high heat conduction, high extendability and resistance against droppage on its cylinder head side. SOLUTION: A valve seat 1 for an internal combustion engine has an annular base 4 and an annular seat part 2 provided with a tapred face, to which an engine valve 3 is attached. The base 4 is sintered material of iron-based powder mixture containing C: 0.45 to 0.6 wt.%, Ni: 1 to 5 wt.%, Mo: 0.4 to 2 wt.%, Cu: 1 to 2 wt.%. The annular seat part 2 is sintered material of iron-based powder mixture containing C: 1.0 to 1.2 wt.%, Ni: 2 to 4 wt.%, Co: 4 to 6 wt.%, Mo: 6 to 8 wt.%, Nb: 0.2 to 2 wt.%, Cr: 1 to 5 wt.%, CaF2 : 0.9 to 1.1 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve seat body which ensures airtightness in a cylinder when seating a valve for an internal combustion engine and has excellent escape resistance and a method of manufacturing the same.

[0002]

2. Description of the Related Art As valves and seats of internal combustion engines, those formed by powder metallurgy are used because of high productivity, high dimensional accuracy, and good material yield. For valve seats for internal combustion engines, the matrix is strengthened by using a high alloy material as the sintering material, or hard materials such as intermetallic compounds, carbides and nitrides are added to the sintering material. Being manufactured. It is preferable that the valve sheet sintered body further has a necessity of maintaining airtightness in the valve cylinder and preventing overheating of the valve by radiating heat from the valve to the cylinder head.

[0003] Conventionally, in valve seats, there are cases in which different materials are used for a base portion and a seat portion. For example,
Although there is a sintered two-layer valve / seat body, the strength is low as a whole due to the use of inexpensive materials for the base part. However, it was not possible to obtain a product satisfying the above requirements, and it was not adopted.

[0004]

As described in the prior art, using a high alloy material as a sintering material, the valve seat has high hardness and at the same time enhances machinability, but the high alloy material is Due to the high cost, the manufacturing cost is high. The present invention is also directed to an internal combustion engine comprising two layers: an annular base (i.e., a joint), an annular seat (i.e., a seat) having a tapered face on which an engine valve is seated. An object of the present invention is to provide an inexpensive valve seat for an internal combustion engine by substituting a sintered body material in a valve seat. As the characteristics required for the valve / seat body, wear resistance, corrosion resistance, high hardness, high fracture toughness, and the like are required on the valve contact side, that is, on the seat portion. On the other hand, high thermal conductivity and high toughness are required at the cylinder head side of the valve / seat body, that is, at the joint. Accordingly, it is an object of the present invention to provide a valve seat body having each of the above contradictory characteristics.

On the other hand, with the recent increase in engine output and the appearance of lean-burn engines, it is inevitable that engine valves will be heated to higher temperatures, and it is required to further improve their cooling performance. For this purpose, it is effective to increase the thermal conductivity of the valve seat body to improve the heat transfer to the cylinder head.However, the conventional valve seat body made of iron-based material has poor wear resistance. Although the valve seat body contains an alloy having excellent wear resistance, the cost is increased and a manufacturing disadvantage is caused.

Further, in recent years, the demand for cost, performance, and the like has become severe in the valve train parts industry, and it is an object to provide a valve seat having a two-layer structure in order to cope with these demands.

Therefore, according to the present invention, a layer having abrasion resistance, corrosion resistance, high hardness and high fracture toughness is formed on the valve contact side, and high thermal conductivity, high toughness and ductility are formed on the cylinder head side. It is an object to obtain a valve seat having a layer having good properties. In other words, an object of the present invention is to obtain a valve seat body having a two-layer structure at a high temperature (valve joining side) and a low temperature side (cylinder head side).

[0008]

According to the present invention, the valve / seat body is specialized and specialized for the seat portion and the base portion, and the specific means are as follows. (1) In a valve seat for an internal combustion engine comprising an annular base portion and an annular seat portion having a tapered face surface on which an engine valve is seated, the base portion is iron-based and C: 0. .45 to 0.6% by weight, Ni: 1 to 5% by weight, Mo: 0.4 to 2% by weight, Cu: 1 to 2% by weight. The sheet part is iron-based, C: 1.0 to 1.2% by weight, Ni: 2
-4% by weight, Co: 4-6% by weight, Mo: 6-8% by weight, Nb: 0.2-2% by weight, Cr: 1-5% by weight, C
aF ₂ : A valve seat for an internal combustion engine, which is a sintered product of a powder mixture of a composition of 0.9 to 1.1% by weight.

(2) In the above item (1), the composition of the sheet portion is Nb: 1.4 to 2.0% by weight, Cr: 3 to 5% by weight, and a carbide such as NbC or CrC is a matrix. Precipitated therein, the wear resistance can be further improved.

(3) In a method of manufacturing a valve seat body for an internal combustion engine comprising an annular base portion and an annular seat portion having a tapered face on which an engine valve is seated, iron is used as the base portion. On a base, C: 0.45-0.
6% by weight, Ni: 1 to 5% by weight, Mo: 0.4 to 2% by weight, Cu: 1 to 2% by weight of an alloy powder having a composition ratio of pulverized and mixed. As parts, based on iron, C: 1.0 to 1.2% by weight, Ni: 2 to 4% by weight, Co: 4 to 6% by weight, Mo: 6 to 8% by weight, Nb:
0.2 to 2% by weight, Cr: 1 to 5% by weight, CaF ₂ :
A composition in which a powder of an alloy composition of 0.9 to 1.1% by weight is mixed is used, and each of the powder compositions is integrally formed as a base portion and a sheet portion, molded, fired and sintered. Then, a sub-zero treatment (immersion in liquid nitrogen) is performed to transform the austenite to martensite as much as possible, and further a tempering treatment is performed to produce the valve seat body for an internal combustion engine.

(4) In the method of the above item (3), the composition of the sheet portion is Nb: 1.2.
To 2.0% by weight, Cr: 3 to 5% by weight, NbC,
CrC carbides are precipitated in the matrix,
It can improve abrasion resistance.

The first characteristic required for the valve seat body is that it is resistant to falling off, and when the temperature in the cylinder head increases, the valve seat body having a high temperature and the cylinder head having a relatively low temperature are required. The difference between the coefficients of thermal expansion is
Although thermal stress is generated in the base portion, it is necessary to ensure strength and a low coefficient of thermal expansion such that the base portion can withstand the thermal stress under severe conditions and does not fall off.

The second required property is abrasion resistance, that is, high hardness and high strength are required even in a high-temperature region in order to be able to withstand interference with the valve even when it comes into direct contact with the valve. Is done. At the same time, wear resistance is important as a valve material. It is difficult to obtain a material that simultaneously satisfies the above two required characteristics, and such a material becomes very expensive.

Therefore, in the present invention, the valve / seat body is divided into two layers and classified, that is, the characteristics are different between the valve side and the cylinder head side, so that the characteristics corresponding to each requirement can be obtained. The problem was solved by having an alloy powder layer.

[0015]

FIG. 1 shows a valve seat (1) according to the present invention. The valve seat body (1) has a tapered face (5) in contact with the valve (3) as shown.
And an annular base portion (4) provided with an annular seat portion (2). The seat (2) of the valve seat body is a valve
With the reciprocating motion of (3), the valve hits the outer surface (5) of the valve (3), and at that point (5), airtightness must be maintained between the valve and the seat (2). The face of the valve (3)
(5) and the surface (6) are heated to the highest temperature, and at the same time, it is necessary that the portion has high wear resistance, high corrosion resistance, and high fracture toughness. And the high temperature heat
In order to escape quickly to the (4) side, it must be quickly transmitted to the base side (4) in contact with the cylinder head of the valve seat body (1).

With respect to such required characteristics of the valve seat body, the present invention provides a valve seat body composed of two layers of a specific powder composition each having the above-described required characteristics. It has been found to satisfy. Further, the present invention provides a method for manufacturing a valve seat having such a structure.

The manufacturing method of the valve seat according to the present invention is as follows. In a method for manufacturing a valve seat body for an internal combustion engine, comprising an annular base portion and an annular seat portion having a tapered face surface on which an engine valve is seated, an iron base is used as the base portion, and C:
0.45 to 0.6% by weight, Ni: 1 to 5% by weight, Mo:
An alloy powder having an alloy composition ratio of 0.4 to 2% by weight and Cu: 1 to 2% by weight is pulverized, and a powder mixture obtained by mixing is used. 0 to
1.2% by weight, Ni: 2 to 4% by weight, Co: 4 to 6% by weight, Mo: 6 to 8% by weight, Nb: 0.2 to 2% by weight, C
r: 1 to 5% by weight, and CaF ₂ : 0.9 to 1.1% by weight. Using a powder mixture obtained by mixing powders of alloys, using each of the composition powders, a base and a sheet, respectively. The parts are integrated, molded, fired and sintered, subjected to sub-zero treatment (immersion in liquid nitrogen), transferred from austenite to martensite as much as possible, and further tempered.

The composition of the sheet part is as follows: Nb: 1.2 to 2.0% by weight, Cr: 3 to
It is preferable that the content is 5% by weight, and carbides of NbC and CrC are precipitated in the matrix to further improve wear resistance.

The structure of the valve seat is as follows. The sintered powder metal composition of the base is iron-based and has a C content of 0.45 to 0.6% by weight.
If C is less than 0.45% by weight, the hardness for valve seats is insufficient, and if it exceeds 0.6% by weight, the hardness is saturated and no further effect can be expected. Ni is 1
-5% by weight. If Ni is less than 1% by weight, matrix strengthening cannot be achieved, and if Ni exceeds 5% by weight, austenite remains. Mo ranges from 0.4 to 2% by weight. Mo
Is less than 0.4% by weight, the wear resistance is not improved and 2% by weight
If it exceeds, the strength is reduced. Cu is in the composition range of 1-2% by weight of the alloy. When Cu is less than 1% by weight, the density does not increase, and when it exceeds 2% by weight, liquid phase leaks.

The metal composition of the annular sheet portion is based on iron and is as follows. C is 1.0 ~
If it is less than 1.0% by weight, the strength cannot be secured, and if it exceeds 1.2% by weight, a liquid phase is generated and a uniform structure cannot be obtained. Ni: 2 to 4% by weight. If Ni is less than 2% by weight, the reinforcement of the base portion cannot be sufficiently achieved. If Ni exceeds 4% by weight, austenite remains. Co is 4 to 6% by weight. If Co is less than 4% by weight, the reinforcement of the base is insufficient.
If the effect saturates and increases further, there is no effect. Mo
Is from 6 to 8% by weight, and dispersed in the substrate as Mo particles and FeMo particles. If Mo is less than 6% by weight, sufficient abrasion resistance cannot be obtained. descend. Nb is 0.2 to 2% by weight, and Nb is 0.1% by weight.
If it is less than 2% by weight, the wear resistance due to carbide formation cannot be secured, and if it exceeds 2% by weight, the sheet portion becomes brittle. Cr
Is from 1 to 5% by weight. If Cr is less than 1% by weight, the wear resistance cannot be improved by carbide, and if it exceeds 5% by weight,
Sinterability deteriorates. CaF ₂ serves as a lubricant, and is 0.9 to 1.1% by weight. When CaF ₂ is less than 0.9% by weight, the lubricating effect is lost, and when it exceeds 1.1% by weight, compressibility is reduced. Gets worse.

The following technical effects are obtained by the valve / seat body in which the alloy composition as described above is made into two layers of the base part and the seat part. That is, the base portion is a low-cost, pearlite-based heat-resistant alloy material due to its alloy composition, resulting in a low price, and the sheet portion is a martensitic crystal and has a high hardness. Further, in the two-layer valve seat body of the present invention, in the sectional view of FIG. 1, the upper base layer (4) is exposed to repeated high-temperature heating and cooling as compared with the seat layer (2). When a strong stress is applied, the cylinder tends to yield, causing a displacement with respect to the cylinder (7), and a gap therebetween is likely to occur. On the other hand, the sheet (2) has a high heat resistance, so that the yield is low. However, the valve seat body of the present invention is hard to come off as a whole because it firmly sticks to the inner wall of the cylinder part (7), and the pull-out resistance increases.

Further, according to the manufacturing method as described above, the valve seat body can be manufactured with a small number of manufacturing steps of agitation-integral molding-sintering-subzero treatment-tempering.

Next, the valve seat body of the present invention is manufactured by the following manufacturing method.

First, a raw material powder is prepared as follows. Raw material powder is iron-based alloy (carbonyl iron powder)
And alloy powder to form an annular base of the valve seat body, based on iron, C: 0.45 to 0.6% by weight, Ni: 1 to 5% by weight, Mo: 0.4 ~ 2% by weight, C
u: pulverized so as to have an alloy composition ratio of 1 to 2% by weight;
Mix.

Next, as an annular seat portion having a tapered face surface on which the engine valve is seated, an iron alloy and an alloy are similarly formed on an iron base and C: 1.0 to 1.2.
% By weight, Ni: 2 to 4% by weight, Co: 4 to 6% by weight, M
o: 6 to 8% by weight, Nb: 0.2 to 2% by weight, Cr: 1
The powder is mixed to a composition ratio of about 5% by weight, pulverized, and further, CaF ₂ powder is mixed at a rate of 0.9 to 1.1% by weight.

The above two kinds of mixed alloy powder compositions are each provided with two layers of a base part and a sheet part, for example,
Using a floating die press, 600-70
Integrally molded at a pressure of 0 MPa, in a vacuum atmosphere, about 1
Treat at 150 ° C. for about 90 minutes and sinter and sinter. next,
The sintered body valve / sheet body was immersed in liquid nitrogen and subjected to a sub-zero treatment for transforming austenite to martensite as much as possible. The obtained sintered body was further subjected to a tempering treatment and then cut to obtain an accurate valve seat shape.

A sample of the obtained two-layer sintered valve sheet is cut and observed under a microscope. Further, when Nb, Cr or a carbide thereof was added, it was observed that carbides of NbC and CrC were precipitated in the matrix. Such carbides appear to further improve the wear resistance of the valve seat.

The sintering of the molded two-layer valve seat was performed in a vacuum to promote sintering. A holding temperature of 1150 ° C. and a holding time of 9
It was baked for 0 minutes.

Next, as a sheet portion, a sintered body was prepared from the composition shown in Table 1 under the above conditions, and the mechanical properties and the wear amount were measured for each. Table 1 shows the results. The measurement conditions were as follows: a sintered body of the composition of Example 4 in Table 2 was used as a base, and a sintered body of the composition of Table 1 was used as a seat portion. The engine was tested at a rotational speed of 3000 RPM.
The temperature of the valve face surface rises to about 650 ° C, and the valve seat portion at that time becomes 250 ° C. The test was performed in the atmosphere.

[0029]

[Table 1]

Next, as a base portion, a sintered body of the composition shown in the following table was similarly attached to an engine and a valve and tested. Table 2 shows the results. Examples 1 to 3 of the base composition are not in the composition range of the present invention. It can be seen that Example 4, which is the composition range of the present invention, has good characteristics and can be used.

[0031]

[Table 2]

Accordingly, the results shown in Tables 1 and 2 show that the sintered body of the composition of the present invention is effective as a valve seat.

[0033]

The valve seat of the present invention has the following effects. (1) By forming the valve seat into a two-layer structure, a valve seat satisfying the above two required characteristics can be obtained. (2) The manufacturing cost of the valve seat can be reduced. Since it is no longer necessary to use an expensive hard alloy as in the related art, a valve seat body which is inexpensive and has good machinability can be obtained.

(3) According to the valve seat of the second aspect,
The valve seat body has improved wear resistance. (4) According to the manufacturing method of the third aspect, the special structure and the special composition can be manufactured with a small number of manufacturing steps. Therefore, various developments are easy and expected in the future. (5) According to claim 4, it is possible to provide a method of manufacturing a valve seat body having improved wear resistance containing carbide to some extent.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view illustrating the structure of a valve seat according to the present invention.

[Explanation of symbols]

 (1) Valve seat body (2) Annular seat part (3) Valve (4) Annular base part (5) Contact surface between valve and valve seat body (6) Hot surface of valve seat body ( 7) Cylinder section

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22C 38/48 B22F 5/00 Z

Claims (4)

[Claims] 1. A valve seat for an internal combustion engine comprising an annular base portion and an annular seat portion having a tapered face on which an engine valve is seated, wherein the base portion is iron-based and C : 0.45 to 0.6% by weight, Ni: 1 to 5% by weight, Mo: 0.4 to 2% by weight, C
u: a sintered product of a powder mixture of a composition of 1 to 2% by weight, wherein the annular sheet portion is iron-based and C: 1.0 to 1.2.
% By weight, Ni: 2 to 4% by weight, Co: 4 to 6% by weight, M
o: 6 to 8% by weight, Nb: 0.2 to 2% by weight, Cr: 1
The valve seat body for an internal combustion engine as described above, which is a sintered product of a powder mixture of a composition having a composition of about 5 to 5% by weight and CaF ₂ : 0.9 to 1.1% by weight. 2. The composition of the sheet portion, wherein Nb: 1.4 to
2.0% by weight, Cr: 3 to 5% by weight, NbC, C
The valve seat body according to claim 1, wherein carbides of rC are precipitated in the matrix to improve wear resistance. 3. A method of manufacturing a valve seat body for an internal combustion engine comprising an annular base portion and an annular seat portion having a tapered face on which an engine valve is seated, wherein the base portion is an iron base. And C: 0.45 to 0.6% by weight, Ni: 1 to 5% by weight, Mo: 0.4 to 2% by weight,
Cu: alloy powder having an alloy composition ratio of 1 to 2% by weight is pulverized and mixed, while the annular sheet portion is iron-based, C: 1.0 to 1.2% by weight, Ni: 2 ~ 4% by weight,
Co: 4 to 6% by weight, Mo: 6 to 8% by weight, Nb: 0.
2-2 wt%, Cr: 1 to 5 wt%, CaF _2: 0.9
As a composition obtained by mixing powders of an alloy composition of about 1.1% by weight, each of the above compositions was used as a base and a sheet,
The valve for an internal combustion engine as described above, wherein the valve is integrated, molded, sintered and sintered, subjected to a sub-zero treatment (immersed in liquid nitrogen) to transform austenite to martensite as much as possible, and further subjected to a tempering treatment. Manufacturing method of sheet body. 4. The composition of the sheet portion is as follows: Nb: 1.4 to 2.0% by weight, Cr: 3 to 5%.
The method for producing a valve seat body according to claim 3, wherein NbC and CrC are precipitated in the matrix to further improve wear resistance.