JPH0313546A - Ferrous sintered alloy for valve seat - Google Patents

Abstract

PURPOSE:To obtain the ferrous sintered alloy in which adhesion in a low-temp. region is prevented and which has superior wear resistance as valve seat and is capable of reducing damage to a mating material by dispersing the fine hard grains of an Fe-Cr alloy into an Fe-C-Co matrix structure and infiltrating Pb alloy, etc., into the resulting sintered alloy. CONSTITUTION:A ferrous sintered alloy for valve seat which has a composition containing, by weight ratio, 0.46-2.0% C, 1-<3% Co, 1.2-3.6% Cr, 0.06-0.40% Mo, and 0.003.0-100% V and into which Pb, Pb alloy, Cu alloy, or Sn alloy is impregnated by 5-25% is provided. In this sintered alloy, the fine hard grains of Fe-Cr alloy are dispersed in an Fe-C-Co matrix structure consisting of a mixed structure of austenitic structure and pearlitic structure. Moreover, this sintered alloy is infiltrated with infiltration alloy, such as Pb alloy and Cu alloy, and further, by reducing Co content in the Fe-C-Co matrix structure, adhesion in a low temp. region can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an iron-based sintered alloy for valve seats of automobile internal combustion engines.

[Prior Art] A cross-sectional view of a valve train of an automobile engine is shown in FIG. 1, and the face portion 16 of the intake valve 7 comes into contact with the valve seat 9 due to the vertical movement of the pulp. The operating temperature of this intake valve is 100 to 400°C, and conventionally, 5UH1, 3, 4, and 11 have been used, which have high softening resistance at the operating temperature, corrosion resistance, fatigue strength, and high temperature strength.

Recently, there has been an increasing demand for improvements in automobile engines, such as higher output, higher rotation speed, measures to purify exhaust gas, and measures to improve fuel efficiency. For this reason, it has become inevitable for engine valves and valve seats in automobile engines to withstand harsher usage environmental conditions than ever before.

In order to cope with such severe usage environments, hard facing has been adopted in which Co-based or Ni-based metal alloys, which have excellent wear resistance, high hardness at high temperatures, and high resistance to high-temperature corrosion, are welded to the valve face. However, this hard facing is expensive because it uses expensive metal fittings, and for this reason, intake valves that do not have metal metal fittings on the face are increasingly being used in order to reduce costs.

In addition, conventional valve seat materials include Fe-C-C
Ferromolybdenum (Fe-Mo) and ferrochrome (
Intermetallic compounds such as Fe-Cr) or Fe-C-Cr-
A material to which Mo-V alloy or the like is added is used (Japanese Patent Application Laid-Open No. 154110/1983).

[Problems to be Solved by the Invention] Essentially, engine valves, valve seats, etc. are required to have improved wear resistance and less damage to mating materials on which they slide. However, the intake valve that abolished the filler (SUHI, 3.4.11)
When using a valve seat in which ferromolybdenum or ferrochrome is added to an Fe-C base material, a problem may arise in which only the valve face wears.

As a countermeasure for this, Japanese Patent Laid-Open No. 60-224762 discloses Fe-0.5 to 2. O%C-0.25~4.0
%Cr-0.1-0.6%Mo-0.05-0.2%V
An Fe-based sintered alloy has been proposed, which has a composition consisting of 2 to 20% of hard particles of an Fe-Cr-based alloy dispersed therein. However, in this material, p, which is a lubricating component,
C for strengthening the base and improving heat resistance without infiltration of B
o is not added. Therefore, heat resistance and lubricity are insufficient under severe sliding conditions in the intake valve, and it is not possible to completely prevent wear on the pulp and valve seat.

Furthermore, in JP-A-60-251258, Fe-0
,5~2.0%C-0,25~4.0%Cr-0,1~
0.6%Mo-0.05~0.2%V 3~15Ni
or Co, with a pb gold alloy or Sn
An Fe-based sintered alloy has been proposed in which an alloy is infiltrated and hard particles made of an Fe-Cr-based alloy are dispersed in a range of 5 to 20%. However, although this material has a high Co content, strengthens the base, and has excellent heat resistance, it has the disadvantage of being difficult to oxidize. Therefore, when used as an intake valve seat in a low temperature atmosphere (seat temperature is 100
℃), the seat surface is not oxidized and adhesion occurs, which may cause wear of the pulp and valve seat.

The present invention was made to solve the above-mentioned problems when combining an intake valve made of 5UH1, 3, 4, 11, which is desired to be used, with an intake valve seat made of iron-based sintered alloy. It is an object of the present invention to provide a sintered alloy for a valve seat that can ensure the wear resistance of the intake valve and the valve seat even when combined with an intake valve that does not require a metal filler.

[Means for Solving the Problems] The sintered alloy for valve seats of the present invention has, as a first invention, a
i ratio rc; O, /16~2.0%, Co; 1~3
%, Cr; 1.2-3. ,, Mo; 0.06-0.
An iron-based sintered alloy for valve seats containing 40%, V: 0.003 to 0.100%, the remainder substantially consisting of Fe, and impregnated with 5 to 25% of Pb, Pb alloy, Cu alloy, or Sn alloy. impregnated with the impregnating alloy and having a weight ratio of C; 0°5 to 2
．． 0%, Co; contains less than 1.0 to 3.0%, the remainder substantially consists of Fe, and in the Fe-C-Co base structure consisting of a mixed structure of austenite structure and pearlite structure, c in weight ratio; 0.8-2.0%, Cr; 4-18%,
Contains Mo: 0.2 to 2%, ■: 0.1 to 0.5%, the balance is Fe, and contains precipitated carbides of Cr, Mo, and ■ below 10μ steel, and has a grain size of 40 ~150μ
m, hard particles with hardness Hv300-850 in weight ratio of 3-3
The gist is that it was distributed at a rate of 20%.

In addition, the second invention has a weight ratio of C;o, 46 to 2°0%.
, Co: less than 1 to 3%, Cr: 0.3 to 5.0%, the remainder substantially consists of Fe, and the valve seat is impregnated with 5 to 25% of Pb, a Pb alloy, a Cu alloy, or a Sn alloy. A steel-based sintered alloy impregnated with the impregnating alloy and having a weight ratio of C: 0°5 to 2.0%, Co: 1.0 to 3.
Fe-
In the C-Co matrix structure, the weight ratio of c; 0.8 to 2.
0%, Cr: 10-25%, the balance is Fe, and contains precipitated carbides of Cr, Mo, and ■ of 10 μm or less inside, grain size 40-150 μm, hardness Hv300.
-850 hard particles are dispersed at a weight ratio of 3 to 20%.

[Function] Hereinafter, the function of the present invention will be explained. In the following description, the contents of alloying elements are all expressed in terms of weight ratio (%).

First, the reason for limiting the range of each component constituting the hard particles used in the valve seat iron-based sintered alloy of the present invention will be explained.

C in the hard particles dispersed in the material of the present invention is Fe, C
It is effective because it reacts with r, MO1■ to form carbides and improve wear resistance, but if it is less than 0°8%, the amount of carbides is small, so the above-mentioned effect of improving wear resistance is not sufficient. On the other hand, if it exceeds 2.0%, the amount of carbide becomes excessive, so it is set at 0.8 to 2.0%.

In addition, Cr, Mo, and ■ are effective in improving wear resistance because they react with C to form carbides, but C'' is less than 4%, MO is less than 0.2%, and ■ is 0.1%. If the amount is less than 1, the amount of carbide formed is small and the above-mentioned wear resistance improvement effect is not sufficient, while Cr is 18%, Mo is 2.0%, and ■ is 0.
．． If it exceeds 5%, the amount of carbide formed will be excessive,
In particular, ■ forms a large amount of hard VC carbide and increases the damage to the sliding mating material (engine valve).
■: 0.1 to 0.5%.

In addition, in the second invention, the hard particles are Fe-Cr −
Since it was C-based, the Cr content was set to 10 to 25%. In the second invention, since it is desired to contain MO and ■ in the hard particles, Cr
This is because if the amount is less than 10%, the amount of carbide is small, and if it exceeds 25%, the amount of carbide is excessive, causing wear of the mating material. Therefore, the Cr amount was set to 10 to 25%.

Next, the reason why the amount of hard particles dispersed in the matrix structure consisting of a mixed structure of austenite structure and pearlite structure in the present invention material was set at 3 to 20% by weight is that the amount of hard particles dispersed is less than 3%. This is because the amount of hard particles is small, so the wear resistance improvement effect is not sufficient, and on the other hand, if the amount of hard particles dispersed exceeds 20%, the damage to the sliding mating material (engine valve) increases. be.

Therefore, the amount of hard particles dispersed was set to 3 to 20%.

In addition, the hardness of the hard particles is set to Hv300 to 850 because if the hardness is less than Hv300, the wear resistance improvement effect of the hard particles is not sufficient, whereas if it exceeds Hv850, the hard particles are too hard and may not slide. This is because damage to the mating material (engine valve) increases.

Next, the reason for limiting the range of components of the base structure raw material powder used to form the base structure of the iron-based sintered alloy for valve seats in the material of the present invention will be explained.

C is an effective component because it reacts with Fe and dissolves in the matrix structure consisting of a mixed structure of ausinite structure and pearlite structure to promote the sintering reaction, but if it is less than 0.5%, the above effect is not sufficient. On the other hand, if it is added in excess of 2.0%, a large amount of cementite structure will precipitate and the sintered body will become brittle, so it is set at 05 to 2.0%.

In addition, Co is effective because it solid-solves in the base structure and strengthens the base structure and improves oxidation resistance and heat resistance, but in the case of intake valves, the valve seat temperature is approximately 1
Since the temperature is as low as 00 to 400°C, if the content exceeds 3%, the oxidation of the seat surface will not progress and adhesion may occur between the seat surface and the valve face. Conversely, if the Co content is less than 1%, the heat resistance will be insufficient, so the Co content should be 1.0 to 3.
In the present invention, an infiltration alloy such as Pb, Pb alloy Cu alloy, or Sn alloy is infiltrated into the sintered body during the sintering process, and its lubricating action improves wear resistance. , is effective because it can also improve machinability through the sealing effect, but if it is less than 5%, the improvement effect is not sufficient, and if it exceeds 25%, the strength decreases significantly, so the infiltration type is ~25%.

In addition, when using a Cu alloy as an infiltration alloy, it is desirable to use a so-called gelmet alloy consisting of 20 to 40% Pb and the balance Cu.

Next, the particle size of fine carbides to be precipitated within the hard particles was adjusted to 1
The reason why the carbide particle size is 0μ or less is that if the carbide particle size exceeds 10μ, damage to the sliding mating material (engine valve) increases.

[Example] Examples of the present invention will be explained together with comparative examples to clarify the effects of the present invention.

Tables 1 and 2 Compositions of base components, impregnated metals, compositions and amounts of hard molecules added, hardness and density of sintered bodies, and counterpart materials (intake valves) used as test materials. ) are shown for each material.

(Left below) 256 After preparing and melting the hard particle raw material powder to be dispersed in the matrix structure consisting of a mixed structure of ausinite structure and pearlite structure, it has a composition shown in Table 1, and then -100
A mesh alloy powder was produced.

Next, this hard particle raw material powder was added to the iron powder for base composition of each component shown in Table 1 in the mixing ratio shown in Table 1, and further graphite powder and zinc stearate were added to form a mixture for forming a green compact. It was made into an alloy powder.

6 t of the thus prepared mixed powder for green compact molding
on/am” to form a powder compact of φ40 mm x 8 mm, and then heated to 110 mm in ammonia decomposition gas.
After the sintering treatment at 0° C. for 1 hour, infiltration treatment using a PB gold alloy was performed at the ratio shown in Table 2. The infiltrated sintered body is
It was machined into a valve seat shape. The overall composition, hardness and density of the valve seat materials are shown in Table 2.

The valve seats manufactured in this way were used for 4-cylinder, 16-cylinder
The intake valve seat is press-fitted into the aluminum alloy cylinder head of the 00cc engine, and the 5UH3
An engine bench durability test was conducted in combination with an intake valve consisting of:

The conditions for the engine bench durability test were as follows: unleaded gasoline was used as fuel, the valve seat temperature was relatively low, and oxidation did not proceed easily at 5,600 rpm and idle speed (
approximately 800 rpm), and approximately 600 rpm.
I drove for hours.

The durability test was evaluated based on the amount of wear on the valve seat, the amount of increase in the contact width of the valve seat, and the condition of the sliding surface before and after the test. The results obtained are shown in Table 3.

Table 3 (blank below) As is clear from Table 3, in Comparative Material 1 in which ferromolybdenum was used as the hard particles, there was almost no narrowing of the valve seat, indicating that the valve was subject to excessive wear. Comparative material 2 has a Co content of 0%, but the wear amount of both the valve seat and valve face is 2 to 4 of the inventive example.
Since there was no PB infiltration, surface roughness due to adhesion was observed. Comparative material 3 had a Co content of 4%, but adhesion of the valve seat material was observed, and wear of about 50 μm was observed on the valve.

On the other hand, inventive material 1 corresponding to the first invention and inventive material 2 corresponding to the second invention, the width increase amount per valve seat was 0.1 to 0.21, and comparative materials 1 to 3 The amount of wear on the valve face is 12 to 15μ, which is 1/3 to 1/12 compared to comparative materials 1 to 3. It was confirmed that the material of the present invention exhibited excellent durability.

[Effects of the Invention] As described in detail above, the iron-based sintered alloy for valve seats of the present invention contains Fe-C-Co base structure consisting of a mixed structure of an ausinite structure and a pearlite structure.
Fine hard particles made of a Cr-based alloy are dispersed and an infiltrated alloy such as a Pb alloy or a Cu alloy is infiltrated to reduce the Co content in the Fe-C-Co matrix structure. This prevents adhesion in the low temperature range, has excellent wear resistance as a valve seat, and can reduce damage to mating materials, so it can be used in combination with intake valves that do not require fillers. Also, the wear resistance and durability of the intake valve and valve seat can be ensured. This allows the use of intake valves that do not require metal fillers, making it possible to save resources and reduce engine costs.Furthermore, the hardness of the hard particles is lower compared to seat valve materials containing ferromolybdenum, which are commonly used in the past. Therefore, workability is improved.

[Brief explanation of drawings]

FIG. 1 shows a sectional view of a valve train of an automobile engine. 7...-Valve, 9... Valve seat, 16... Face part Fig. 1

Claims (2)

[Claims] (1) Weight ratio of C: 0.46~2.0%, Co: 1~
Less than 3%, Cr; 1.2-3.6, Mo; 0.06-0
．． 40%, V: 0.003 to 0.100%, the remainder substantially consists of Fe, and is impregnated with 5 to 25% of Pb, Pb alloy, Cu alloy, or Sn alloy. gold, impregnated with the impregnating alloy and having a weight ratio of C; 0. 5 to 2.0%, Co; less than 1.0 to 3.0%, the remainder substantially consists of Fe, and the Fe-C-Co base structure consists of a mixed structure of austenite structure and pearlite structure, C: 0.8-2.0%, Cr: 4-18 in ratio
%, Mo: 0.2 to 2%, V: 0.1 to 0.5%, the balance is Fe, and contains precipitated carbides of Cr, Mo, and V with a particle size of 10 μm or less inside. 40-150
μm, hard particles with hardness Hv300-850 in a weight ratio of 3
An iron-based sintered alloy for valve seats, characterized in that it is dispersed at a ratio of ~20%. (2) Weight ratio of C: 0.46~2.0%, Co: 1~
less than 3%, Cr: 0.3 to 5.0%, the remainder substantially consists of Fe, Pb, Pb alloy, Cu alloy or S
An iron-based sintered alloy for a valve seat impregnated with 5 to 25% of an n-alloy, the weight ratio of which is impregnated with the impregnated alloy is C; 0. 5 to 2.0%, Co; less than 1.0 to 3.0%, the remainder substantially consists of Fe, and the Fe-C-Co base structure consists of a mixed structure of austenite structure and pearlite structure, C: 0.8-2.0%, Cr: 10-2
5%, the remainder is Fe, and there is a 10μm inside.
For a valve seat, which contains the following precipitated carbides of Cr, Mo, and V, and is characterized in that hard particles having a particle size of 40 to 150 μm and a hardness of Hv 300 to 850 are dispersed at a weight ratio of 3 to 20%. Iron-based sintered alloy.