JP3225649B2 - Wear resistant iron-based sintered alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron-based sintered alloy having excellent wear resistance and useful for sintered parts such as valve seats, piston rings or exhaust system collars used in internal combustion engines.

[0002]

2. Description of the Related Art Conventional valve seat materials include Fe.
Intermetallic compounds such as ferromolybdenum (Fe-Mo) and ferrochrome (Fe-Cr) or Fe-C for the purpose of improving wear resistance of -C-Co-Ni-based material and Fe-C-based material
-Cr-Mo-V alloy or the like is used (JP-A-56-154110).

Further, Fe— containing Cr and Mo
A sintered alloy in which iron-based hard particles composed of Cr, Mo, V, etc. are dispersed in a C base structure to improve abrasion resistance and aggressiveness to a partner (Japanese Patent Laid-Open No. 60-224762), and Fe-C-
A sintered alloy in which hard particles made of FeMo and FeW are dispersed in a Co-Ni base matrix and impregnated with a Pb alloy or the like to improve wear resistance (Japanese Patent Laid-Open No. 62-202058)
Gazette).

[0004] The characteristics required for the valve seat material include corrosion resistance and heat resistance in addition to wear resistance.
Hard particles are mainly responsible for wear resistance, and corrosion resistance and heat resistance are mainly responsible for base structures, and the two are combined to ensure durability.

[0005]

In recent years, there has been a growing demand for improvement in automobile engines for longer life, higher output, higher rotation speed, measures for purifying exhaust gas, or measures for improving fuel efficiency. For this reason, it has become unavoidable for engine valves and valve seats in automobile engines to withstand more severe use environments than ever before, and heat resistance and wear resistance are further improved, and at high temperatures. It has become necessary to improve the corrosion resistance of steel.

[0006] However, the formation of the base of the conventional iron-based valve seat material is based on the alloying elements Ni, C
After mixing elemental powders of the respective elements such as o, Mo, etc., the mixed powder is molded and sintered as a raw material to obtain Ni, Co, Mo.
Etc. are diffused in iron. For this reason, it is difficult to completely diffuse these alloy elements into iron, and it is difficult to improve properties corresponding to the added amount.

Therefore, in order to efficiently bring out the effect of alloying element addition, it is conceivable to alloy the alloying element with iron in advance.
The solid solution hardening reduces the compressibility of the alloyed iron powder, making it difficult to increase the density of the green compact, which is disadvantageous for improving the durability. In addition, there is a high demand for improvement in properties such as heat resistance, abrasion resistance, and corrosion resistance, and appropriate components are required.

The present invention has been made to solve the above-mentioned problems of the iron-based sintered alloy used for the conventional iron-based valve seat material, and has been adapted to the severe use environment of recent valve seat materials. It is an object of the present invention to provide an iron-based sintered alloy having further improved heat resistance, corrosion resistance, and wear resistance.

[0009]

In view of the fact that when alloying an additive element with iron powder, the alloy powder is solid-solution hardened and the compressibility is reduced, the present inventors have proposed an additive element which does not form a solid solution hardening even when alloyed. Research on the composition range of As a result, it has been found that the compressibility of the alloy powder can be ensured in the specific composition range of the additive element. Further, when using the alloy powder of the specific composition range, repeated studies on the corrosion resistance and wear resistance of the sintered body, a combination of specific additional elements,
The present inventors have found that by dispersing the hard particles, the corrosion resistance and wear resistance of the sintered body are significantly improved, and completed the present invention.

The iron-based sintered alloy of the present invention having excellent wear resistance contains, by weight, 2-15% of Co and 3-10% of Mo, with the balance being an iron-based alloy composed of unavoidable impurities and Fe. Based on the alloy powder, Fe-55 to 70% Mo-0.5% or less C,
Fe-55 to 70% Cr-0.5% or less C, Fe-75
One or more hard particles of up to 85% W-0.5% or less C
2 to 30% in total of more than seeds, 0.3 to 1.7% of graphite powder
And a molding lubricant, and then molded and sintered.

[0011]

The iron-based sintered alloy of the present invention has a weight ratio of Co;
Since the base structure was sintered using an alloy powder containing 15%, Mo; 3 to 10%, the homogeneity of solid solution of the alloy element in the base material was high, and the solid solution was less than the conventional method of mixing the element powder. Excellent corrosion resistance, oxidation resistance and wear resistance can be obtained with the amount of alloy.

Further, since the contents of Co and Mo in the iron-base alloy base powder are restricted to the above-mentioned composition ranges, the compressibility is less reduced, and the compressibility is slightly lowered as compared with the conventional method of mixing element powders. However, there is no danger of affecting the oxidation resistance and corrosion resistance, which are strongly related to the density, and the characteristics corresponding to the added amount can be improved. Further, since hard particles are dispersed in the matrix, the abrasion resistance is excellent.

[0013] In the iron-based sintered alloy of the present invention, the sintered alloy obtained by mixing the conventional element powders has variations in Mo and Co concentrations.
Where austenite-forming element Co has high Co concentration, it becomes austenite, and where ferrite-forming element Mo is high, it becomes pearlite and has a mixed structure, resulting in poor abrasion resistance. Therefore, the base becomes bainite and has excellent wear resistance.

Next, the reason why the composition range of alloying elements and the like in the present invention is limited will be described. Fe-2 to 15% Co-2 to 10% Mo alloy powder; this alloy powder forms the matrix of the material of the present invention, and Co forms a solid solution in the matrix to strengthen it and improve heat resistance. When the content is less than 2%, the effect is insufficient. On the other hand, when the content is more than 15%, the effect is further improved, but the economy is low. １５15%.

Mo forms a solid solution in the matrix and strengthens it, and also has the effect of improving the strength and corrosion resistance in a high-temperature region. It is effective in improving sex. These effects are
If the content is less than 3%, the content is insufficient, and if it exceeds 10%, although the effect is improved, the compressibility of the powder is reduced.

Fe-Mo, Fe-Cr, Fe-W (hard particle powder): 2 to 30% Fe-Mo, Fe-Cr, Fe-W powder is dispersed in the matrix and contributes to improvement of wear resistance. I do. If the addition amount of the hard particles is less than 2%, the improvement of the wear resistance is insufficient, and even if it exceeds 30%, the improvement is small for the addition, and the moldability is lowered. The addition amount was 2 to 30%.
The hard powder particles preferably have a particle size of 149 μm or less. If the particle size exceeds 149 μm, the particles will not be uniformly dispersed in the matrix.

Graphite powder; 0.3 to 1.7% Graphite is dissolved in the matrix as a carbon component to strengthen the matrix, and partly forms carbide with Fe or Mo in the matrix to improve wear resistance. The effect is shown. If the added amount is less than 0.3%, the above effect cannot be expected,
Further, if added in excess of 1.7%, the sintered alloy will be embrittled, so the amount added is limited to 0.3-1.7%. Preferably, the particle size of the graphite powder particles is 45 μm or less. If the particle size exceeds 45 μm, the carbon concentration becomes non-uniform.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in comparison with comparative examples to clarify the features of the present invention. Embodiment 1 of the present invention
-8, Co; 4.4%, Mo; 4.1% by weight.
Iron-based sprayed alloy powder A in which the balance is substantially Fe, Co: 4.1%, Mo; 7.2% in weight ratio Iron-based sprayed alloy powder B in which the balance is substantially Fe (177 μm or less)
Was manufactured by the atomizing method, and commercially available pure iron powder (particle size: 177 μm or less) and ferromolybdenum powder (Fe-
61% Mo-0.6% Si-0.03% C), ferrochrome powder (Fe-60% Cr-0.3% Si-0.002)
% C), ferrotungsten powder (Fe-79% W-0.
2% Si-0.03% C) were ground to a particle size of 149 μm or less, graphite powder and a lubricant zinc stearate were prepared, weighed so as to have a composition shown in Table 1, and then weighed. A compact of 6.9 g / cm ³ was molded.

Further, as comparative materials 1 to 3, iron-based sprayed alloy powder A, sprayed iron powder, Co powder, Mo powder, and ground to a particle size of 149
μm or less ferromolybdenum powder (Fe-61% Mo)
-0.6% Si-0.03% C) and ferrotungsten powder (Fe-79% W-0.2% Si-0.03%)
C), prepare graphite powder and lubricant zinc stearate,
After weighing so as to have the composition shown in Table 1, the density was 6.9 g.
/ Cm ³ was molded. The obtained green compacts of Examples and Comparative Examples were decomposed in an atmosphere of decomposed ammonia gas to 138.
The alloy was sintered at a temperature of 3 K for 2.4 Ks for a period of 2.4 Ks to produce each example and comparative material.

[0020]

[Table 1]

Each of the obtained examples and comparative materials was processed into a valve seat ring, and abrasion resistance was examined using a valve / valve seat tester simulating an actual machine. This test apparatus reproduces the beating wear of the valve and the valve seat by a mechanism that heats the valve and the valve seat by burning propane gas and opens and closes the valve by driving a cam.

In the test, the valve material was set to JIS SUH4, the temperature of the valve was controlled to 1023K, the temperature of the valve seat was maintained to 623K, and the number of rotations of the cam was set to 2000 rpm.
pm and the operation time was 36 Ks, and the amount of valve seat wear was measured as the increase in the contact width of the valve seat. The results obtained are shown in FIG.

As shown in FIG. 1, the contact width increase of the comparative material is 90 to 120 μm, whereas the contact width increase of the embodiment of the present invention is 45 to 75 μm. Was confirmed to have excellent wear resistance. Although the sintered body compositions of Example 3 and Comparative Material 3 and Example 4 and Comparative Material 1 were the same, the wear amount was reduced to about half of that of Comparative Example. It can be seen that the abrasion resistance of the material was superior to that of the conventional material.

This is a feature of the present invention. By forming Fe-Mo-Co in advance as an alloy powder, the homogeneity is superior to that obtained by mixing element powders as a comparative material. It was possible to obtain a base structure, and it was possible to obtain an iron-based sintered alloy having the same composition and excellent wear resistance.

[0025]

As described above, the wear-resistant iron-based sintered alloy of the present invention has a weight ratio of Co: 2 to 15% and Mo: 3 as described above.
One or two of hard particles of ferromolybdenum powder, ferrochrome powder, and ferrotungsten powder with respect to an iron-based alloy powder containing 10% to 10%, with the balance being unavoidable impurities and Fe.
2 to 30% in total of more than seeds, 0.3 to 1.7% of graphite powder
It is obtained by mixing, molding, and sintering, and has a high degree of solid solution uniformity of the alloying element in the base material. In comparison, excellent corrosion resistance, oxidation resistance and wear resistance can be obtained with a small amount of alloy. Since the composition range of the alloying element is restricted to the above composition range, the compressibility is less reduced, and as compared with the conventional method of mixing the element powders, the compressibility is slightly reduced but almost the same, and the density and relevance are reduced. There is no risk of affecting strong oxidation resistance and corrosion resistance. Further, since the hard particles are dispersed, the wear resistance is further improved, and Co and Mo are uniformly dissolved in the Fe base, so that the base becomes bainite and the wear resistance is excellent.

[Brief description of the drawings]

FIG. 1 is a diagram showing the wear amount of an example of the present invention and a comparative example in a wear test.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-111848 (JP, A) JP-A-63-317646 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00 304 B22F 1/00 B22F 5/00 C22C 33/02

Claims (1)

(57) [Claims] 1. A weight ratio of Co: 2 to 15%, Mo: 3
Fe-55 to 70% Mo-0.5 with respect to an iron-based alloy powder containing 10% to 10%, with the balance being unavoidable impurities and Fe.
% Or less C, Fe-55 to 70% Cr-0.5% or less C,
Fe-75 to 85% W-0.5% or less C of hard particles 1
2-30% in total of two or more species, graphite powder 0.3
An iron-based sintered alloy having excellent wear resistance, which is obtained by mixing, shaping, and sintering a mixture of about 1.7% with a forming lubricant.