JPH0555589B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an iron-based sintered alloy for valve seats, and more specifically, by uniformly dispersing hard particles of a specific composition in an Fe-C base structure, it can be used as a valve seat. The present invention relates to an iron-based sintered alloy for valve seats that has excellent wear resistance and is less likely to damage engine valves, which are sliding mating materials. [Prior Art] Recently, there has been an increasing demand for improvements in automobile engines, such as higher output and higher revolutions, 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 other words, in engine valves, valve seats, etc., it not only improves their own wear resistance, but also reduces damage to the mating material on which they slide.
It is strongly desired to improve processability and reduce costs. As conventional sintered alloys for valve seats, those made by adding intermetallic compounds such as ferromolybdenum or composite carbides to iron-based alloys have been adopted as excellent sintered alloys for valve seats. For example, Tokukai Akira
The valve train member described in Publication No. 57-108246 has a hard phase made of metal carbide dispersed in a network of martensite bases for the purpose of achieving both wear resistance of the member itself and reduction of damage to mating members. In addition, the free-cutting wear-resistant sintered mesh described in Japanese Patent Publication No. 51-44684 is made of a sintered alloy containing chromium, molybdenum, and vanadium in order to achieve both wear resistance and machinability. Kelmet is infiltrated into the pores. However, since such sintered alloys are made by distributing each component homogeneously and adjusting the composition of the entire alloy, there is a limit to the ability to achieve both of the conflicting properties described above, and the recent strict demands have been met. There is a problem in that sufficient durability cannot be ensured with respect to the characteristics. [Object of the Invention] The present invention was made to solve the problems of the prior art as described above, and it is possible to , for valve seats that have excellent wear resistance as a valve seat, can reduce damage to the mating material on which it slides, and can be manufactured at low cost with good workability. The purpose is to provide iron-based sintered alloys. [Structure of the Invention] According to the present invention, such an object is achieved by
Mainly pearlite structure obtained by mixing powder for base structure with alloy powder for hard particles in the range of 5 to 20% by weight, compacting, and sintering.
An iron-based sintered alloy for valve seats consisting of a structure in which hard particles are uniformly dispersed in an Fe-C base structure, wherein the powder for the base structure is graphite powder in a weight ratio of 0.5 to 1.6%, and the balance is substantially The alloy powder for hard particles has a weight ratio of C; 1.0.
~2.0%, Cr; 5.0~20.0%, Mo; 0.2~3.0%,
V: 0.1 to 1.0%, the remainder essentially consisting of Fe, with finely precipitated Cr of 10μ or less inside the alloy powder;
Contains carbides such as Mo and V, average particle size: 40~
This is achieved using an iron-based sintered alloy for valve seats, which is characterized by a hardness of 150μ and a hardness of 300 to 700 Hv. [Action of the invention] The action of the present invention will be explained below. In addition, in the following description, all contents of alloying elements will be explained in terms of weight ratio (%). First, the reason for limiting the range of each component constituting the alloy powder for hard particles used in the iron-based sintered alloy for valve seats of the present invention will be explained. In the present invention, C is effective because it reacts with Fe, Cr, Mo, and V to form carbides and improve wear resistance, but if it is less than 1.0%, the amount of carbides is small, so the above-mentioned wear resistance The improvement effect is not sufficient, and on the other hand, if it exceeds 2.0%, the amount of carbides becomes excessive, and the diffusion of C from the hard particles into the surrounding base structure during sintering is promoted, which may cause the hard particles to disappear. It was set at 1.0 to 2.0% due to the nature of In addition, Cr, Mo, and V are effective in improving wear resistance because they react with C to form carbides.
If Cr is less than 5.0%, Mo is less than 0.2%, and V is less than 0.1%, the above-mentioned wear resistance improvement effect will not be sufficient due to the small amount of carbide, while Cr is 20.0% and Mo is 3.0%.
%, when V exceeds 1.0%, the amount of carbide becomes excessive,
In particular, since V forms a large amount of hard VC carbide and increases damage to sliding mating materials (engine valves), Cr; 5.0 to 20.0%;
Mo: 0.2-3.0%, V: 0.1-1.0%. Next, the particle size of the fine carbides precipitated inside the alloy powder for hard particles is set to 10μ or less because
This is because if the carbide particle size exceeds 10μ, damage to the sliding mating material (engine valve) increases. The reason why the average particle size of the alloy powder for hard particles is set to 40 to 150μ is that if it is less than 40μ, it will diffuse into the matrix during sintering, whereas if it is larger than 150μ, the alloy powder for hard particles will be dispersed in the raw material powder. This is because if it exists, the raw material powder cannot be sufficiently compacted when the raw material powder is compacted. In addition, the hardness of the alloy powder for hard particles is Hv300 ~
700 because if it is less than Hv300, the effect of improving wear resistance as a hard particle is not sufficient.
This is because if the hardness exceeds the hardness, the hard particles become too hard, increasing the damage to the sliding mating material (engine valve). Furthermore, in the present invention, the amount of dispersion of the alloy powder for hard particles into the matrix structure consisting of pearlite structure is
The reason for setting the weight ratio to be 5 to 20% is because if the amount of dispersed alloy powder for hard particles is less than 5%, the amount of hard particles will be small and the effect of improving wear resistance will not be sufficient. This is because if it exceeds 20%, damage to the sliding mating material (engine valve) increases. With the structure described above, the wear resistance of the structure as a whole and the damage resistance to the mating material are maintained by the composition, hardness, and content of the hard particles, and the average particle size is adjusted to Processability is improved by enlarging the portion consisting only of soft base. Next, the reason for limiting the range of components of the raw material powder used to form the sintered alloy base structure in the material of the present invention will be explained. During the sintering process, C reacts with Fe to form a pearlite structure to strengthen the base structure, and is also effective as it dissolves in the base structure and promotes the sintering reaction, but if it is less than 0.5%, the above-mentioned On the other hand, if it is added in excess of 1.6%, a large amount of cementite will precipitate and the sintered body will become brittle.
It was set at 0.5-1.6%. The iron-based sintered alloy for valve seats of the present invention having the limited configuration as described above has a matrix structure mainly composed of pearlite structure through sintering treatment.
Obtained as a structure in which hard particles with an average particle size of 40 to 150 μ and containing finely precipitated carbides of Cr, Mo, V, etc. of 10 μ or less are uniformly dispersed in the range of 5 to 20% by weight. . [Example] Hereinafter, one example of the present invention will be described based on the attached table. Table 1 shows the composition of the alloy powder for hard particles used in producing the material of the present invention and the diameter of fine carbide particles contained within the alloy powder. The hard particle raw material powder to be dispersed in the base structure of the pearlite structure was adjusted to the composition shown in Table 1 and melted, and then made into -100 mesh alloy powder by a water spray method. Next, as shown in Table 2, this alloy powder for hard particles was added to the iron powder for matrix structure in the proportions shown in Table 2, and graphite powder and zinc stearate were further added to form a mixture for compaction. It was made into an alloy powder. For example, the material of the present invention has the composition shown in Table 1, and contains alloy powder for hard particles with a carbide particle size of 4μ, 12% by weight, graphite powder at 1.2%, as shown in Table 2. The mixture was blended so that the balance was Fe powder, and 0.8% of zinc stearate, which is generally used as a lubricant, was added to obtain a mixed alloy powder for compaction. Similarly, in the present invention material, the first
The alloy powder for hard particles having the composition shown in Table 1 and the carbide particle size shown in Table 1 was added at the mixing ratio shown in Table 2, and graphite powder and zinc stearate were added in the same manner as the present invention material. It was added to obtain a mixed alloy powder for powder compaction. Next, for the comparison material, the composition of the alloy powder for hard particles was changed to high Cr (30%), high Mo (7%), and high C (2.5%).
%). In addition, the comparative material has a composition of alloy powder for hard particles with low Cr (less than 5%) and low C (less than 1%). In addition, the comparative material has a high V (3%) composition of the alloy powder for hard particles and a coarse carbide grain size (15μ) exceeding 10μ, so that a large amount of VC carbide is precipitated. The mixed powder for compacting thus produced was compacted at 6 tons/cm ² to form a compact of φ40 mm x 8 mm, and then heated for 1100 min in ammonia decomposition gas.
A sintering treatment was performed at ℃ for 1 hour. The base of the sintered body of the material of the present invention, which was sintered as described above, had a pearlite structure. This sintered body was machined into a valve seat shape. Then, this valve seat was press-fitted into the aluminum alloy cylinder head of a 4-cylinder, 1600 c.c. engine as an exhaust valve seat, and an engine bench durability test was conducted. As for the engine bench durability test conditions, unleaded gasoline was used as the fuel, and the engine was operated continuously for 200 hours at 6600 rpm and full load. The results of this engine bench durability test were evaluated by measuring the amount of increase in the contact surface width of the valve seat and the amount of engine valve wear after the end of the test. The engine bench durability test results are also shown in Table 2. As is clear from Table 2, in the comparative material, the composition of the alloy powder for hard particles is high Cr, high Mo, and high C, so the amount of carbide precipitation is excessive.
It is understood that the amount of wear on the sliding mating material (engine valve) is large. In addition, in the comparison material, the composition of the alloy powder for hard particles is less than 5% Cr and less than 1% C, so the amount of carbide decreases, the wear resistance decreases, and the amount of wear on the valve seat increases. It is understood that In addition, the comparison material has a high V composition of alloy powder for hard particles and a carbide particle size of over 10μ, so a large amount of hard VC carbide precipitates, resulting in the amount of wear on the sliding mating material (engine valve). It is understood that there are more and more Compared to the above-mentioned comparative materials, the inventive materials showed superior engine bench durability test results, with a valve seat contact area addition of 0.2 mm or less and engine valve wear of 8 μ or less. It shows.

【table】

〔Effect of the invention〕

As is clear from the above, according to the iron-based sintered alloy for valve seats according to the present invention, by uniformly dispersing hard particles having a specific composition and having an appropriately adjusted particle size in the Fe-C base structure, As a valve seat, it has excellent wear resistance, and can reduce damage to the mating material on which it slides.Furthermore, since the part consisting only of relatively soft base tissue is widely distributed in the structure, it is easy to process. It has the advantage of good properties and can be manufactured at low cost.

Claims (1)

[Claims] 1 Fe-C base tissue powder, weight ratio 5
A valve consisting of a structure in which hard particles are uniformly dispersed in an Fe-C base structure mainly composed of pearlite structure obtained by mixing alloy powder for hard particles in the range of ~20, compacting, and sintering. A ferrous sintered alloy for sheets, wherein the powder for the base structure consists of graphite powder in a weight ratio of 0.5 to 1.6%, and the remainder substantially consists of iron powder, and the alloy powder for the hard particles has a weight ratio of 0.5 to 1.6%. ,C;
1.0~2.0%, Cr: 5.0~20.0%, Mo; 0.2~3.0%,
V: 0.1 to 1.0%, the remainder essentially consisting of Fe, with finely precipitated Cr of 10μ or less inside the alloy powder;
Contains carbides such as Mo and V, average particle size: 40~
An iron-based sintered alloy for valve seats, characterized by a hardness of 150μ and a hardness of Hv300 to 700.