JPH04128347A - Sintered alloy for valve gear mechanism for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve the compactibility of a powdered raw material and to obtain superior wear resistance by means of short-time sintering by markedly reducing Ni content and increasing Mn content in an iron-base alloy having a specific composition containing Cr, Mo, Ni, Sn, V, etc. CONSTITUTION:This sintered alloy has a composition consisting of, by weight, 1.5-4% C, 1.5-4% Mn, 8-28% Cr, <=2% Ni, 0.3-3% V, <=5% Sn, 0.7-7% Mo and/or W, 0.1-2% of either or both of <=1% P and <=2% B, and the balance Fe and also has a structure where granular metal carbide is dispersed in a martensitic iron matrix. When Ni is contained by >2.5% in this alloy, powder becomes hard and compactibility is deteriorated, and, at the time of addition in the form of Ni powder, long-time sintering is required for the purpose of diffusion. As to Mn content, the amount not lower than the lower limit is necessary to improve wear resistance, and, when Mn content exceeds the upper limit, the problem of oxidation during sintering is taken place and wear resistance as well as strength is deteriorated.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to rocker arms and valve lifters, which are members that make up the valve mechanism of an internal combustion engine and which are in sliding contact with a cam and require high-temperature wear resistance. The present invention relates to iron-based sintered alloys suitable for such applications.

[Prior art] Various sintered alloys for valve train mechanisms have been proposed that are superior in wear resistance and cost, in place of conventional heat-treated steel materials, alloyed cast iron materials, or members coated with hard chromium plating or self-fluxing alloys. has been done.

The sintered alloy described in JP-A No. 63-7350 is one of them, and has a composition (wt%) of 01 to 4%, 5 to 30% Cr, M
O1-5%, Ni5.5-10%, Sn 0.2-5
%, at least one of W and V 0.1-4%, P and B
It is a sintered alloy that is used after heat treatment, with a small amount of 0.05 to 5% of one type, the balance being Fe and unavoidable impurities. It has improved abrasion resistance.

However, when producing the sintered alloy, it was necessary to make the sintering time longer than usual.

Since the alloy powder is too hard when compression molded using the alloy powder with the above composition, C is in the form of graphite powder, Sn is in the form of tin powder, and P or B is in the form of iron phosphorus powder and ferroboron powder. It is possible to add Ni in the form of nickel powder and use Cr-MO-W-V system alloy iron powder as the alloy iron powder and add Ni in the form of nickel powder. The former alloy iron powder contains a large amount of Ni (6 to 12% by weight), making it difficult to obtain a powder compressibility of 8 (8%) and high density. Alternatively, the compressibility problem can be solved by adding the entire nickel powder in the form of nickel powder.However, in the latter case, short sintering times result in insufficient nickel diffusion and the heat-treated material has a lower hardness than desired. , resulting in poor wear resistance.

Therefore, in the latter case, sufficient sintering time is required for diffusion.

[Problems to be Solved by the Invention] The present invention provides a sintered alloy that has good compression moldability of raw material powder, can be sintered in a short time, and has wear resistance superior to conventional materials. This is an attempt to solve the shortcomings of

[Means for Solving the Problems] In order to solve the above problems, the present invention provides C: 1.5 to 4% by weight, Mn: 1.5 to 4% by weight, and Cr: 8 to 28% by weight.
, Ni: 2% by weight or less, V: 0.3 to 3% by weight, Sn:
5% by weight or less, at least one of Mo and W20.7~
7% by weight, at least one of 1% by weight or less of P and 2% by weight or less of B: 0.1 to 2% by weight, Fe and unavoidable impurities, the balance, and granular metal carbide is present in the martensitic iron matrix. The present invention provides a sintered alloy for a valve mechanism of an internal combustion engine, which is characterized by a dispersed structure.

[Function] Compared to the prior art described above, the present invention achieves the object by significantly reducing the Ni content and containing a large amount of Mn.

The sintered alloy according to the present invention improves the wear resistance of the material itself by dispersing hard metal carbide particles in a martensite matrix, and at the same time improves the wear resistance of the material itself by controlling the type, amount, and mutual combination of metal carbides. The selection also contributes to reducing wear on the mating cam material.

Next, the effects of each component will be explained.

Cr: Cr strengthens the matrix, forms hard carbides, improves hardenability, and improves wear resistance, and can be added in the form of alloyed iron powder.

The content is stable in the range of 8 to 28% by weight for sintered alloys, and causes little wear (but is less than 8% by weight, but more than 28% by weight, but causes significant wear).

V, Mo, and W: These elements strengthen the matrix like Cr, and react with C to form hard carbides to improve wear resistance.

It also has the effect of increasing the hardening effect.

In (2), the carbide is relatively hard, and when it coexists with Cr, Mo, and W, it is effective in wear resistance at 0.3% by weight or more.

If it is added in excess of 3% by weight, the material becomes brittle, making it easier to wear out the mating material.

Mo and W exhibit similar properties, but Mo is more effective. When coexisting with the carbide-forming elements Cr and V, it is effective if at least one of them is 0.7% by weight or more. On the other hand, addition of more than 7% by weight tends to cause wear of the mating material.

These elements can be added together with the Cr in the form of alloyed iron powder.

Ni: An element that diffuses into iron to strengthen the matrix and improve compatibility with the mating material, but if added in excess of 2.5% by weight to the above-mentioned alloyed iron powder, the powder will become hard. Compressibility deteriorates.

On the other hand, when added in the form of nickel powder, long sintering times are required to diffuse it. From this, it is sufficient to add 2.5% by weight or less to the above-mentioned alloyed iron powder, which corresponds to 2% by weight in terms of sintered alloy.

Mn:] Can be added in the form of nirifungan powder.

It has a greater effect on improving the hardening effect than other elements.

It has the ability to form carbides and contributes to improving hardness, but V, Mo
, does not have a very strong affinity like W, so it has a large effect of strengthening the matrix and improving compatibility with the mating material. It improves toughness and fracture load resistance and is similar to the action of Ni.

It is necessary to add 1.5% by weight or more to improve wear resistance, but if more than 4% by weight is added, there is a problem of oxidation during sintering, which reduces strength and wear resistance. .

Sn: Can be added in the form of tin powder. It melts and diffuses into the matrix to promote sintering and strengthen the base, but if it is added in an amount exceeding 5% by weight,
It makes pores and carbide particles coarser, lowering strength and worsening wear resistance.

P and B: Can be added in the form of iron phosphorus or iron boron alloy powder.

It has the effect of promoting sintering and increasing the density of the sintered alloy.

Either one kind may be added, or both may be added. The desired effect can be obtained when the amount added is 0.1% by weight or more, but 1% by weight in the case of P, 2% by weight in the case of B, and 2% by weight in the case of both.
If it is added in excess of this amount, the liquid phase will be excessive, resulting in large dimensional changes during sintering and making the material brittle.

C: Reacts with iron and the aforementioned carbide-forming elements.

It can be added in the form of graphite powder, and 1.5 to 4% by weight is required to produce sufficient carbide, and addition of more than 4% by weight causes brittleness.

[Example] First, graphite powder, tin powder, ferromanganese powder, ferroboron powder, iron phosphorus powder, Cr-■-Mo-W-Ni alloy iron powder, and zinc stearate powder were prepared, and the results shown in Table 1 were prepared. It was blended to have the composition shown.

Next, these mixed powders are compression molded into a pad shape,
A sample was prepared by performing sintering and heat treatment under the following conditions.

Sintering atmosphere: Vacuum (1x 10=mmHg) Sintering temperature:
1130°C Sintering time: 30 minutes Quenching conditions: Rapid cooling in oil from 900°C Tempering conditions = 180°C Note that sample number 34.35 is a conventional material, and Ni is added in the form of nickel powder. Further, the sintering time was 60 minutes for sample number 34 and 30 minutes for sample number 35, and the rest was the same as in the example.

Each sample was attached to a rocker arm body and installed in a water-cooled inline 4-cylinder engine, and the total amount of wear on the pads and cams was examined by a bench test in which the camshaft was rotated by a motor. The mating cam was made of low-alloy cast iron with a chilled cam top surface, and the lubricating oil was an engine oil equivalent to S A E #30 with 2.5% water added, and the engine was operated continuously for 50 hours at a rotational speed of 650 rpm. .

Table 1 shows the measurement results.

The evaluation of the amount of wear was 25 μm compared to the standard of 40 μm for conventional materials.
% lower at 30 μm.

Samples 1 to 7 represent the effect of the amount of Cr added, and 8 to 2
There is less wear when the content is 8% by weight Cr.

Samples 8 to 12 represent the effects of V, Mo, and W;
Good results have been shown when the content of MO and W is 0.7 to 7% by weight. If the amount added is too large, it will attack the opponent cam.

Samples 13 to 14 are about Ni, and the alloy iron powder contains 2,
When Ni was added in an amount exceeding 5% by weight, the compressibility of the powder deteriorated.

Samples 15 to 18 show good results when the Mn content is 1.5 to 4% by weight. Adding too much will actually lower the strength (and increase pad wear).

Samples 19-26 show the effects of P and B.

The effect is observed when the amount added is 0.1% by weight, and the best results are obtained when the amount is 0.5 to 1% by weight. If P exceeds 1% by weight and B exceeds 2% by weight, it tends to become brittle and wear increases.

Samples 27 to 30 show the effect of Sn. As the amount added increases, the wear decreases, reaching a minimum value at 3% by weight, and above that, the wear increases again, and when it exceeds 5% by weight, the addition is inappropriate.

Samples 31 to 33 have the effect of C. 1.5-4% by weight C
The amount of wear is maintained at a low level.

Sample 34 is a conventional material sintered for 60 minutes and has good wear resistance, but sample 35, which is sintered for 30 minutes, has a large amount of wear.

[Effects of the Invention] The sintered alloy for valve train mechanisms of the present invention has good moldability of the raw material powder, exhibits superior wear resistance than conventional materials even after short firing times, and is cost effective in producing the alloy. The engine quality can be improved in use.

Claims (1)

[Claims] 1 C: 1.5-4% by weight Mn: 1.5-4% by weight Cr: 8-28% by weight Ni: 2% by weight or less V: 0.3-3% by weight Sn: 5 At least one of Mo and W: 0.7 to 7% by weight, at least one of P, up to 1% by weight, and B, up to 2% by weight
A sintered alloy for a valve mechanism of an internal combustion engine, consisting of seeds: 0.1 to 2% by weight, Fe and the balance of unavoidable impurities, and characterized by a structure in which granular metal carbides are dispersed in a martensitic iron base.