JPH0347950A - Iron-base sintered alloy for valve seat - Google Patents

Abstract

PURPOSE:To obtain the iron-base sintered alloy improved in wear resistance and strength by providing a composition containing respectively prescribed amounts of C and one or more elements among W, V, Nb, and Ta and also providing a structure in which most of the above elements W, V, Nb, and Ta are uniformly distributed in the form of solid solution in an iron matrix. CONSTITUTION:An iron-base sintered alloy for valve seat which has a composition consisting of, by weight, 0.8-2.5% C, 3-14% of one or more kinds among W, V, Nb, and Ta, and the balance Fe with inevitable impurities and also has a structure in which most of W, V, Nb, and Ta are uniformly dispersed in the form of solid solution in an iron matrix is provided. Further, it is necessary to use an Fe-X type (where X means one or more elements among W, V, Nb, and Ta or contains Mo other than the above) powder as an iron powder to be the principal component of powdery raw materials in order to disperse W, V, Nb, and Ta uniformly into the matrix. The resulting powder mixture of respective elements mentioned above is sintered at 1100-1200 deg.C, by which the desired iron-base sintered alloy for valve seat can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in iron-based sintered alloys for valve seats of internal combustion engines, and more particularly, to improvements in iron-based sintered alloys for valve seats of internal combustion engines, and more particularly, to improve wear resistance and strength of valve seats. Regarding iron-based sintered alloys.

[Conventional technology]

In recent years, as internal combustion engines have become smaller and have higher output, and the use of unleaded gasoline, harsher conditions such as high rotation, high temperature, and high surface pressure have been imposed than before, and valve seats have also become more wear-resistant. is required. Furthermore, with the adoption of a supercharger, the thermal and mechanical loads placed on the valve seat tend to further increase.

In order to meet the trend of internal combustion engines, the materials for +-'1m Sekigawa valves are being changed from molten lumber to sintered alloy materials. That is, for the purpose of improving the wear resistance, high temperature strength, and oxidation resistance of the valve seat, C', N11Co, W, Mo
By adding elements such as , V, Nb, Ta, etc. for alloying purposes, or as ferroalloy, carbide, or composite alloy powder, they were distributed as hard particles in the matrix. For example, when adding MO, it becomes Fe-
It was added as Mo (ferromolybdenum) particles.

[Problem to be solved by the invention]

Although the addition of the above-mentioned alloying elements improves and improves the wear resistance, it has the drawback of increasing costs. Furthermore, there are many unknown points as to whether the addition of such alloying elements has a commensurate effect. In addition, when they are used as hard particles, they are difficult to diffuse into the base iron, so although the area around the hard particles is strengthened, other parts are not strengthened, so the base is strengthened by dispersion reinforcement. It was not expected that the alloying elements would be strengthened by solid solution and alloying with the base.

The present invention was made in view of these conventional problems, and provides a high-performance valve seat for high-load engines that can cope with increased thermal and mechanical loads due to higher output and higher rotation speeds of internal combustion engines. The purpose of the present invention is to provide an iron-based sintered alloy for valve seats that is suitable as a material.

[Means to solve the problem]

In view of the above, the present inventors previously proposed a FeMo-C-based material obtained by sintering iron powder in which Mo is uniformly dissolved in solid solution (Japanese Patent Application Laid-Open No. 161144/1982).
, subsequent research revealed that instead of Mo, W, V, N'b
STa or Mo, Wl V, Nb, Ta 1
It has been found that similar effects can be obtained by simultaneous addition of more than one type of compound.

Based on the above discovery, the present invention provides C: 0.8 to 2.5% by weight, any one or more of W, V, Nb, Ta, or the total of these and Mo: 3 to 14% by weight %, the balance consists of Fe and unavoidable impurities, and the W, V, Nb,
Provided is an iron-based sintered alloy for a valve seat, characterized in that it has a structure in which most of Ta and Mo elements are uniformly distributed in solid solution in an iron matrix.

That is, in the present invention, W, V, Nb, Ta
Alternatively, by using an alloy powder material in which these and Mo are uniformly distributed and dissolved in the iron base, these elements can be uniformly dispersed and the wear resistance improvement effect of these elements can be maximized. It was utilized.

Next, the reasons for limiting the components and structure of the iron-based sintered alloy for valve seats according to the present invention will be explained.

W, V, Nb5Ta are elements from Group 5 or 6 of the periodic table, and like Cr, they form a solid solution in iron, increasing strength and heat resistance, and combining with carbon to form carbides, which improves wear resistance. It has the effect of increasing sex. If the amount is less than 3% by weight, the abrasion improving effect will not be sufficient, and if it exceeds 14% by weight, the moldability during powder molding will decrease and the material will become hard and brittle, which is not preferable. Therefore, W, V, Nb,
Ta needs to be 3 to 14% by weight in total,
In particular, it is preferably 5 to 10% by weight. Furthermore, since all of these elements have similar effects on improving wear resistance,
A combination of two or more types may be included.

In addition, along with one or more of these elements, Mo
can also be added. When Mo is added, the total amount of Mo, WSV, Nb, and Ta is 3 to 14% by weight for the same reason as above. M again.

The content is preferably 5 to 10% by weight.

In order to uniformly distribute W, V, Nb, Ta, or these and Mo in the base, the iron powder, which is the main ingredient of the raw material powder, uniformly distributes and solid-solves Mo, W, V, Nb, and Ta. Fe-X system (X: W, V, Nb,
It is necessary to use a powder containing at least one type of Ta or a powder containing Ta and Mo. Although various powders can be used, it is preferable to use powder produced by an atomization method. At this time, a part (amount exceeding 3% by weight) of Mo%W, V, Nb, Ta is 3
It may be added as a fine metal powder of 25 mesh or less. In this case, alloying elements (W,
Adjust the content of V, Nb, TaSMo) or
Alternatively, by blending a corresponding amount of a small amount of iron powder that does not contain alloying elements, the content of alloying elements in the resulting sintered alloy can be adjusted to a predetermined value.

Carbon dissolves in the iron matrix to increase its strength, and reacts with the above elements to form carbides. The amount of added Mo, W,
Depending on the amounts of V, Nb, and Ta and the amounts of other alloying elements, the range is inevitably determined as a range in which ferrite and coarse carbides are not generated. The amount of carbon corresponding to the range of the amounts of Mo, W, V, Nb, and Ta described above is 0.8 to 2.5%. If the carbon percentage is lower than the eutectoid composition, soft ferrite is produced, which deteriorates wear resistance, which is undesirable.On the other hand, if the carbon percentage is too high, coarse carbides are produced, making it difficult to process and making the material brittle, which is not desirable. do not have. However, ferrite,
Although it is preferable that coarse carbides do not occur, in reality it is difficult to strictly control the amount of carbon because the amount of oxygen in the raw material powder depends on the atmosphere of the sintering furnace.
The following ferrites and coarse carbides are allowed to form.

In addition to the above-mentioned elements, base reinforcement elements such as Co and B may be added in an amount of up to 10 atomic %.

The particle size of the sintering powder is preferably 325 mesh or less; if the powder is coarser than this range, it is difficult to obtain a uniform solid solution structure, and if the particle size is finer than this range, commensurate effects cannot be obtained.

The sintering is performed at a temperature of 110[deg.]C to 1200[deg.]C. If the sintering temperature is below 1100°C, the strength after sintering will be low and sufficient wear resistance will not be obtained, so it is not preferable;
If it exceeds tJa, a large amount of liquid phase will be generated and the carbide will become coarse, which is not preferable. Therefore, sintering is 1100-120
It is necessary to carry out at 0°C. Sintering time is generally 30 to 120
After sintering to a certain extent in about minutes, heat treatment is performed as necessary to adjust the structure and hardness.

〔Example〕

Hereinafter, the present invention will be specifically explained based on Examples.

Example 1 Graphite powder with a mesh size of 325 was added to iron powder having a peak particle size of 150 to 200 mesh and containing 5% by weight of W in a uniform solid solution so that the final composition was 2.1% by weight. Ta. Furthermore, in order to improve mold release during mold molding, 0.6% by weight of zinc stearate was added as a lubricant, and the resulting mixed powder was molded in a press at a molding pressure of 7 t/cn. Dewaxing was performed at 650°C for 1 hour. Furthermore, 1
After sintering at 200°C for 1 hour, the furnace was cooled to 900°C.
Gas cooling was performed from 00°C.

After cooling, it was processed to create a test piece (valve seat) with an outer diameter of 46 mm, an inner diameter of 30 mm, and a height of 7.5 mm.

Furthermore, heat treatment was performed so that the hardness became around HRB95.

Examples 2 to 10, Comparative Examples 1 to 4 In the same manner as in Example 1, Mo, W,
Test pieces were also created for systems containing V and NbXTa singly or in combination.

In addition, as a comparative material, test pieces were prepared by adding W, V, Nb, and Ta ferroalloys to iron powder of the same particle size so as to have the composition shown in Table 1, under the same conditions as Example ①. made. In addition, W in each ferroalloy
The contents of XV, Nb, and Ta were as follows.

W: 80% by weight V: 50% by weight Nb: 65% by weight 7a: 65! ,! I) % Table 1 shows the composition of each sintered alloy.

No. table (Note) *: Each chemical component was added as a ferroalloy.

The outer diameter 46 mm x inner diameter 30 mm x height 7
After processing a 5 mm test piece into a predetermined valve seat shape, its suitability as a valve seat material was evaluated by a durability test using a unit wear test.

FIG. 1 schematically shows the unit wear tester used.

In this test machine, the valve 3 raised by the cam 2 rotated by a drive device (not shown) repeatedly hits the valve seat 1 with an impact by the expansion and contraction of the spring 5 at the bottom of the valve stem 4. It has become. Further, a gas burner 6 is disposed above the valve 3, and a nozzle 8 for blowing compressed air to the cylinder head 7 is disposed on the side.
The structure is such that the surface of the valve 3 is heated and maintained at a constant temperature by adjusting the amount of propane gas supplied to the gas burner 6 and the air volume of the nozzle 8.

Using such a wear tester, tests were conducted under the test conditions shown below assuming the usage conditions of intake valve seats.
The amount of wear on the valve seat was determined from the amount of sinking of the reference valve.

(Test conditions) Valve material: 5IIH-36 Valve surface temperature: 650°C Valve seat temperature: 300°C Number of revolutions: 300 rpm Test time: 5 hours The test results are shown in Table 2. As is clear from Table 2,
The sintered alloy valve seat of the present invention has significantly improved wear resistance compared to conventional valve seats containing ferroalloy. Additionally, the amount of wear on the mating valve has been significantly reduced.

1 2 The iron-based sintered alloy for seat sheets shown in Table 1 is made by sintering iron powder in which alloying elements are uniformly dissolved in solid solution, so most of the alloying elements are uniformly dissolved in the iron matrix. This improves wear resistance and strength. Therefore, it can be suitably used for valve seats for high-load engines.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a single wear tester. 1...Valve seat 2...cam 3... Valve

Claims (2)

[Claims] (1) C: 0.8-2.5% by weight, W, V, Nb, Ta
Any one or two or more of: 3 to 14% by weight, balance F
consisting of e and unavoidable impurities, the above-mentioned W, V, Nb, Ta
An iron-based sintered alloy for valve seats, characterized by having a structure in which most of the elements are uniformly distributed as a solid solution in the iron matrix. (2) The iron-based sintered alloy for valve seats according to claim 1 contains a total of 3 to 14% by weight of Mo and one or more of W, V, Nb, and Ta. An iron-based sintered alloy for valve seats featuring: