JPH0555591B2 - - 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, a Fe-C-Co-Ni base structure consisting of a mixed structure of an austenite structure and a pearlite structure has a specific composition. By uniformly dispersing hard particles and, if necessary, infiltrating with a Pb alloy or Cu alloy, the valve seat itself has excellent wear resistance. This applies to a ferrous sintered alloy for valve seats that is less likely to damage engine valves, which are the mating material. [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 reduce the cost. However, as conventional sintered alloys for valve seats, those made by adding intermetallic compounds such as ferromolybdenum and composite carbides to iron-based alloys have been adopted as excellent sintered alloys for valve seats.
Such sintered alloys have a problem in that they cannot ensure sufficient durability to meet the recent strict requirements for properties as described above. Therefore, in view of the current state of durability of conventional valve seats as described above, the inventors have developed a method to uniformly disperse hard particles with a specific composition and particle size adjustment in an Fe-C base structure mainly consisting of pearlite structure. We have already proposed an iron-based sintered alloy for valve seats that has excellent wear resistance as a valve seat and is less likely to damage engine valves, which are the mating material on which it slides. Name: "Iron-based sintered alloy for valve seats," Applicant: Toyota Motor Corporation, April 19, 1980). In addition, as another invention, a valve seat can be made to have even more excellent wear resistance by using an infiltration treatment with an infiltration alloy of Pb alloy or Cu alloy for the iron-based sintered alloy for valve seats of the above invention. A steel-based sintered alloy has also been proposed (name of invention;
"Iron-based sintered alloy for valve seats", applicant: Toyota Motor Corporation, filing date: concurrently filed with this case). [Object of the Invention] The present invention was made to solve the problems of the prior art as described above.
- By uniformly dispersing hard particles with a specific composition and particle size adjustment in the Co-Ni matrix structure, and further infiltrating with a Pb alloy or Cu alloy as necessary. , it has excellent wear resistance as a valve seat, and can also reduce damage to the mating material it slides on.
Moreover, it is an object of the present invention to provide an iron-based sintered alloy for valve seats that can be manufactured at low cost. [Structure of the Invention] According to the present invention, such an object is achieved by
-Co-Ni based powder for base tissue, weight ratio: 5
Consists of a mixed structure of austenite and pearlite structures obtained by mixing alloy powder for hard particles in the range of ~20%, compacting, and sintering.
An iron-based sintered alloy for valve seats consisting of a structure in which hard particles are uniformly dispersed in a Fe-C-Co-Ni base structure, wherein the powder for the base structure has a weight ratio of graphite powder; 0.5 to 1.6. %, at least one of Co powder and Ni powder; 3.0 to 15.0%, the remainder substantially consisting of iron powder, and the alloy powder for hard particles is
In terms of weight ratio, C; 1.0 to 2.0%, Cr; 5.0 to 20.0%,
Mo: 0.2~3.0%, V: 0.1~1.0%, remainder substantially
A valve made of Fe, having carbides of Cr, Mo, V, etc. finely precipitated within the alloy powder of 10μ or less, and having an average particle size of 40 to 150μ and a hardness of Hv300 to 700. The iron-based sintered alloy for sheets and the Fe-C-Co-Ni-based base structure powder are mixed with alloy powder for hard particles in a weight ratio range of 5 to 20%, and after compaction, sintering is performed. An iron-based sintered alloy for valve seats consisting of a structure in which hard particles are uniformly dispersed in a Fe-C-Co-Ni base structure consisting of a mixed structure of an austenite structure and a pearlite structure obtained through a coagulation treatment and an infiltration treatment. The base tissue powder is graphite powder in a weight ratio of 0.5 to 1.6.
%, at least one of Co powder and Ni powder; 3.0 to 15.0%, the remainder substantially consisting of iron powder,
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, finely precipitated inside the alloy powder with a particle size of 10μ or less
Contains carbides such as Cr, Mo, and V, average particle size: 4.0~
150μ, hardness: Hv300 to 700 hard particles, and the infiltration treatment is for a valve seat characterized by infiltrating 5 to 25% by weight of an infiltration alloy of Pb alloy or Cu alloy. This is achieved by using iron-based sintered alloys. [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. C in the alloy powder for hard particles dispersed in the material of the present invention 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 2.0, the wear resistance improvement effect mentioned above is not sufficient.
It was set at 1.0 to 2.0% because the amount of carbide exceeding 1.0% would be excessive and could promote the diffusion of C from the hard particles into the surrounding matrix structure during sintering, causing the hard particles to disappear. . In addition, Cr, Mo, and V react with C to form carbides, so they are effective in improving wear resistance, but Cr
When Cr is less than 5.0%, Mo is less than 0.2%, and V is less than 0.1%, the amount of carbide formed is small, so the wear resistance improvement effect described above is not sufficient.On the other hand, Cr is 20.0%,
If Mo exceeds 3.0% and V exceeds 1.0%, an excessive amount of carbides will be formed.
Because it forms a large amount of carbide and increases the damage to the sliding mating material (engine valve),
Cr: 5.0-20.0%, 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 base 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, the reason why the amount of the alloy powder for hard particles dispersed in the powder for the matrix structure consisting of a mixed structure of austenite structure and pearlite structure in the material of the present invention is set to 5 to 20% by weight is that the alloy powder for hard particles is If the amount of dispersion is less than 5%, the effect of improving wear resistance will not be sufficient due to the small amount of hard particles.On the other hand, if the amount of dispersed alloy powder for hard particles exceeds 20%, it will cause damage to the sliding mating material (engine valve). This is because it increases damage. 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 the components of the base structure 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. During the sintering process, C is effective because it reacts with Fe and dissolves in the matrix structure consisting of a mixed structure of austenite and pearlite structures to promote the sintering reaction, but if it is less than 0.5%, the above effect will not be achieved. However, if it is added in excess of 1.6%, a large amount of cementite structure will precipitate and the sintered body will become brittle, so it was set at 0.5 to 1.6%. In addition, Co and Ni are effective because they dissolve in the matrix structure and strengthen the matrix structure and improve heat resistance, but if it is less than 3%, the improvement effect is not sufficient, and if it exceeds 15%, it will burn out. The content was set at 3 to 15% because it softens the alloy material and reduces wear resistance. In addition, the infiltration alloy of Pb alloy or Cu alloy is
It is effective because it is infiltrated into the sintered body and its lubricating effect improves wear resistance, and its sealing effect also improves machinability. If it is less than 25%, the improvement effect will not be sufficient, and if it exceeds 25%, the strength will drop significantly, so it was set at 5 to 25%. In addition, when using a Cu alloy as an infiltration alloy, Pb; 20 to 40%, the balance consisting of Cu.
It is desirable to use a so-called Kelmet alloy. [Example] Hereinafter, one example of the present invention will be described based on the attached table. The chemical composition of the alloy powder for hard particles used in the present invention material, the particle size of fine carbides contained in the alloy powder, and the alloy powder for hard particles in the mixed alloy powder for compaction described below. The mixing ratio of
Shown in the table. The alloy powder for hard particles to obtain a hard phase to be dispersed in a matrix structure consisting of a mixed structure of austenite structure and pearlite structure is prepared by adjusting each component to the composition shown in Table 1 and melting it, and then using a water spray method to obtain -
100 meshes of alloy powder were produced. Next, this alloy powder for hard particles was added to the iron powder for matrix structure of each component shown in Table 2 at the mixing ratio shown in Table 1, and further graphite powder and zinc stearate were added to form a powder for compaction. A mixed alloy powder was prepared. For example, in the material of the present invention, alloy powder for hard particles having the composition shown in Table 1 and containing carbide particle size of 4μ is used at 12% by weight, and graphite powder is added as shown in Table 2. 1.1%, Co powder 8
%, the remainder is Fe powder, and further,
Zinc stearate, commonly used as a lubricant,
0.8% was added to make a mixed alloy powder for compaction. Similarly, in the present invention material, the first
As shown in the table, the alloy powder for hard particles whose composition and contained carbide particle size were adjusted was added at the mixing ratio shown in Table 1, and in addition, in the same manner as the present invention material, the powder was added as shown in Table 2. Co powder or Ni
The mixed alloy for powder compaction was made into a powder by adding 0.8% zinc stearate. Next, as a comparative material, the composition of the alloy powder for hard particles was high Cr (29%) and high Mo (5%), and the average grain size of carbides in the alloy powder for hard particles was coarse particles exceeding 10 μ. It is. In addition, the comparative material has a composition of low C (0.7%) and low Cr (3%) of the alloy powder for hard particles, and a blending ratio of the alloy powder for hard particles of less than 5% (3%). The Co content of the tissue powder is increased to more than 15% (19%). In addition, the comparative material has a blending ratio of alloy powder for hard particles exceeding 25% (29%), and a content of Ni in powder for matrix structure exceeding 15% (20%). be. The mixed powder for compacting thus produced was compacted at 6 ton/cm ² to form a powder compact of φ40 mm x 8 mm, and then heated for 1100 min in ammonia decomposition gas.
After the sintering treatment for 1 hour at °C, no infiltration treatment was performed for the inventive material and the comparative material;
The sintered bodies were manufactured by performing infiltration treatment with a Pb alloy for the and comparative materials, and by performing the infiltration treatment with a Kelmet alloy for the present invention materials and comparative materials. The matrix of the sintered body of the material of the present invention, which was sintered as described above, had a mixed structure of an austenite structure and a pearlite structure. The sintered body subjected to the sintering treatment and, if necessary, the infiltration treatment as described above, was machined and finished into a valve seat shape. The valve seat thus produced was press-fitted as an exhaust valve seat into the aluminum alloy cylinder head of a 4-cylinder, 1600 c.c. engine, 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 on-board engine durability test evaluated the durability of the valve seat 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, the composition of the alloy powder for hard particles of the comparative material was high Cr (29%) and high Mo (5%).
%), and since the average grain size of carbides in the alloy powder for hard particles is coarse grains exceeding 10μ, the amount of carbide precipitated is excessive.
Since no Pb alloy or Cu alloy infiltration alloy is added, the amount of wear on the sliding mating material (engine valve) is high. In addition, in the comparison material, the composition of the alloy powder for hard particles was C (0.7%) and low Cr (3%), and the blending ratio of the alloy powder for hard particles was less than 5% (3%).
Since the Co content of the base structure powder is high (19%) exceeding 15%, the amount of carbide formed is small, which softens the base structure of the sintered alloy and reduces wear resistance. Valve seat wear is increasing. In addition, the comparison material has a large amount (29%) of the alloy powder for hard particles, which not only causes a large amount of wear on the valve seat, but also has a high Ni content in the powder for the matrix structure. Since this amount exceeds 15% (20%), the amount of wear on the sliding mating material (engine valve) is also increasing. Compared to the above comparative materials, the inventive materials have an increase in the contact surface of the valve seat of 0.2 mm or less, as is clear from the results of the engine bench durability test, and the amount of wear of the engine valves. It also shows excellent durability with a thickness of less than 8μ.

【table】

〔Effect of the invention〕

As is clear from the above, the iron-based sintered alloy for valve seats according to the present invention has a mixed structure of an austenite structure and a pearlite structure.
Uniformly disperse hard particles with a specific composition and particle size adjustment in the Fe-C-Co-Ni base structure, and
By using infiltration treatment with a Pb alloy or Cu alloy as necessary, the valve seat itself has excellent wear resistance and also reduces damage to the mating material on which it slides. It has the advantage that it can be manufactured at low cost.

Claims (1)

[Claims] 1 Fe-C-Co-Ni matrix powder is mixed with alloy powder for hard particles in a weight ratio of 5 to 20%, and after compacting, sintering is performed. obtained by
An iron-based sintered alloy for a valve seat consisting of a structure in which hard particles are uniformly dispersed in a Fe-C-Co-Ni-based base structure consisting of a mixed structure of an austenite structure and a pearlite structure, wherein the powder for the base structure comprises: In terms of weight ratio, graphite powder; 0.5 to 1.6%; at least one of Co powder and Ni powder; 3.0 to 15.0%; the remainder substantially consists of iron powder; ;
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, finely precipitated inside the alloy powder with a particle size of 10μ or less
Contains carbides such as Cr, 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. 2 Fe-C-Co-Ni based powder for matrix structure is mixed with alloy powder for hard particles in a range of 5 to 20% by weight, and after compaction, sintering and infiltration are performed. An iron-based sintered alloy for a valve seat comprising a structure in which hard particles are uniformly dispersed in an Fe-C-Co-Ni-based matrix structure consisting of a mixed structure of an austenite structure and a pearlite structure, the powder for the matrix structure is graphite powder; 0.5 to 1.6%; at least one of Co powder and Ni powder; 3.0 to 15.0%; the remainder substantially consists of iron powder; ,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, finely precipitated inside the alloy powder with a particle size of 10μ or less
Contains carbides such as Cr, Mo, and V, average particle size: 40~
150 μ, hardness: Hv 300 to 700 hard particles, and the infiltration treatment includes infiltrating 5 to 25% by weight of an infiltration alloy of Pb alloy or Cu alloy. Iron-based sintered alloy.