JPH0633185A - Production of sintered alloy for valve seat excellent in wear resistance - Google Patents

Abstract

PURPOSE:To produce an iron-base sintered alloy for valve seat excellent in heat, corrosion and wear resistances by mixing powders of carbon, Co, FeMo, etc., with a powder of iron-base alloy of specific composition at specific ratio, applying compacting and sintering to the resulting powder mixture, and then subjecting the resulting sintered compact to subzero treatment and to tempering treatment. CONSTITUTION:As a ferrous matrix structure constituting a matrix, a powder of an iron-base alloy having a composition consisting of, by weight, 1.0-5.0% Cr, <=0.2% O, 0.1% C, and the balance Fe with inevitable impurities is used. A powder mixture is prepared by mixing 0.3-2.0% carbon powder, 3.0-30% of one or more kinds among the powders of Co, Ni, and Fe, and 2.0-20% of one or more kinds among the powders of FeMo, FeW, and FeCr are mixed with the iron-base alloy powder. This powder mixture is compacted and sintered. Then the resulting sintered compact is subjected to subzero treatment, by which a martensite or sorbite structure is formed. Further, the strain resulting from this treatment is removed by tempering treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sintered alloy for a valve seat of an automobile internal combustion engine.

[0002]

2. Description of the Related Art A valve seat is a member incorporated in a cylinder head of an internal combustion engine, and seals mixed gas and combustion gas by seating a valve face of a mushroom-shaped valve. Since the valve moves up and down at high speed in combustion gas and repeatedly sits on and leaves the valve seat, the valve seat requires heat resistance, corrosion resistance, and wear resistance, as well as aggression against the material that does not wear the mating valve. To be done.

As a conventional valve seat material, Fe-
C-Co-Ni-based materials and Fe-C-based materials aiming at improvement of wear resistance, intermetallic compounds such as ferromolybdenum (Fe-Mo) and ferrochrome (Fe-Cr), or Fe-C-
The one to which a Cr-Mo-V alloy or the like is added is used (Japanese Patent Laid-Open No. 56-154110).

Further, Fe-containing Cr and Mo
Impregnated with a sintered alloy (Japanese Patent Laid-Open No. 60-224762), Pb alloy, etc., in which iron-based hard particles composed of Cr, Mo, V, etc. are dispersed in the C base structure to improve wear resistance and opponent attack. Fe-C in the formed Fe-C-Co-Ni matrix structure
A sintered alloy in which hard particles made of a -Cr-Mo-V alloy are dispersed (Japanese Patent Laid-Open No. 60-251258) is disclosed.

Further, in Japanese Patent Laid-Open No. 60-258449, a Fe-C-Co-Ni based matrix structure having a mixed structure of an austenite structure, a pearlite structure and a ferrite structure is provided with a hard layer composed of an Fe-Mo alloy layer. An iron-based sintered alloy for a valve seat is disclosed in which particles are uniformly dispersed and the hard particles are diffused in a matrix structure and firmly bonded.

[0006]

However, recently, in automobile engines, there has been an increasing demand for improvement in long life, high output, high rotation, exhaust gas purification measures, or fuel consumption improvement measures. For this reason, it has become more unavoidable than ever to withstand harsh operating environments for engine valves and valve seats in automobile engines, further improving heat resistance and wear resistance, and at high temperatures. There is a growing need to improve the corrosion resistance of aluminum.

The present invention has been invented to meet the demand for higher performance of conventional sintered alloys for valve seats, which accompanies the recent increase in output of automobile engines and improvement in fuel consumption. Another object of the present invention is to provide a method for producing an iron-based sintered alloy for a valve seat, which can further improve wear resistance.

[0008]

In order to improve the corrosion resistance and wear resistance at high temperatures, the inventors of the present invention have studied the chemical composition, structure, etc. of the matrix structure of the iron-based sintered alloy material for valve seats. , Repeated intensive research. As a result, it was newly found that the matrix structure must be uniform in order to exhibit excellent heat resistance and wear resistance. Therefore,
It was found that excellent heat resistance and wear resistance can be obtained by using an iron-based alloy powder as the base structure.

Further, as a result of repeated research on the structure of the iron-based alloy serving as a base, it was found that excellent wear resistance can be obtained by forming a martensite structure or a sorbite structure by subzero treatment. Furthermore, Co, Ni
Alternatively, Fe was added to strengthen the matrix structure in a solid solution, and hard particles such as FeMo, FeW, and FeCr are dispersed to improve wear resistance, thereby completing the present invention.

The method for producing an iron-based sintered alloy for valve seats having excellent wear resistance according to the present invention is, by weight ratio, Cr: 1.0 to
Iron-based alloy powder containing 5.0%, O; 0.2% or less, C; 0.1% or less, the balance being Fe and inevitable impurities, carbon powder 0.3 to 2.0%, Co Powder, Ni powder, Fe powder 1 type or 2 types or more 3.0 to 30%
And one or more of FeMo, FeW, and FeCr powders, 2.0 to 20% are mixed, the mixed powder is compression-molded, and then sintered, and the sintered body is subjected to subzero treatment and tempering treatment. That is the summary.

[0011]

[Function] Cr is added to the Fe-based matrix structure that constitutes the matrix.
Since the iron-based alloy powder containing is used, the structure is made uniform and heat resistance and corrosion resistance can be improved. Also,
By regulating the O content of the alloy powder, the effect of Cr addition was secured, and the Fe-based matrix structure was made into a martensite structure or sorbite structure by subzero treatment, so that the heat resistance and corrosion resistance were further improved.

3% to 30% of Co, Ni or Fe was solid-dissolved in the Fe-based matrix structure constituting the matrix, so that the strength was improved and excellent heat resistance and corrosion resistance were obtained. Further, since one or more of FeMo, FeW, and FeCr powders were mixed at 2.0 to 20%, wear resistance could be improved.

Next, the reason for limiting the composition range of the components constituting the sintered alloy in the present invention will be described. First, the reasons for limiting the composition range of the iron-based alloy powder forming the matrix structure will be described. Cr: 1.0 to 5.0% Cr is contained in order to improve the heat resistance and corrosion resistance of the matrix structure. If the Cr content is less than 1.0%, the above effect cannot be obtained, and if it exceeds 5.0%, the above effect is not significantly improved, and the compactness of the powder is lowered, so that the density of the compact is also reduced. Therefore, the content is 1.0 to
Limited to 5.0%.

O: 0.2% or less If O exceeds 0.2%, not only does the compressibility deteriorate, but it also binds to Cr and hinders the effect of Cr. It was set to 2%. C: 0.1% or less C is contained in an amount exceeding 0.1%, so that the compressibility decreases, so the upper limit of the content is made 0.1%.

Next, the reason for limiting the composition range of the alloy powder, hard particle powder, etc. added to the iron-based alloy powder forming the matrix structure will be explained. Carbon powder: 0.3 to 2% C has the effect of forming a solid solution in the matrix to strengthen it and form carbides with the Cr component to improve wear resistance.
If the content is less than 0.3%, the above effect cannot be obtained, and if the content exceeds 2%, coarse cementite precipitates and embrittlement becomes remarkable, so the content is limited to 0.3 to 2%. did.

One or more of Co powder, Ni powder and Fe powder; 3.0 to 30% These components form a solid solution in the matrix to strengthen it, and
Although it has an effect of improving heat resistance, if it is less than 3.0%, the above effect cannot be obtained, and if it exceeds 30%, the effect is not further improved. Limited to 0-30%. When carbonyl iron is used as the Fe powder, it contributes to the promotion of sintering and the effect of improving the density is obtained.

One of FeMo, FeW and FeCr powders
Fe-Mo (Hv600-) containing 60 to 70% of 2.0 to 20% Mo
1300), and Fe-W containing 75 to 85% W.
(Hv500 to 1000) and Fe-Cr (Hv1100 to 1800) containing 60 to 70% of Cr have high hardness, and when they are uniformly dispersed, they act as hard particles to improve wear resistance. Although it is effective, if it is less than 2%, the effect is small, and if it exceeds 20%, the other valve material is greatly attacked and the other material is worn, and in addition, the machinability is deteriorated. The amount of dispersion is 2.
It was set to 0 to 20%.

The sub-zero treatment is carried out in order to sufficiently advance the martensitic transformation in order to stabilize the unstable structure in which a large amount of austenite was present. Further, the tempering treatment is necessary for removing the strain of the martensitic transformation generated in the subzero treatment.

[0019]

EXAMPLES Examples of the present invention will be described in comparison with comparative examples to clarify the effects of the present invention. As raw material powder, C
r-based alloy powder (O; 0.2 or less, C; 0.1 or less), reduced iron powder, FeCr powder, Co powder of 75 μm or less, Ni powder, intermetallic compound FeMo powder, intermetallic compound FeW powder After further preparing natural graphite powder having a particle size of 25 μm or less and lubricant zinc stearate powder, blending these raw material powders so as to have the compositions shown in Tables 1 and 2, and adding 0.8% of lubricant. The powder was mixed with a powder mixing device.

Table 1 is an example of the present invention, Table 2 is a comparative example, Comparative Example 1 does not use Cr alloy powder, Comparative Example 2 shows Co powder, Ni powder and Fe powder. The additive amount is 2% or less, the comparative example 3 is 20% or more of the Co powder, the Ni powder and the Fe powder, and the comparative example 4 is the dispersion amount of hard particles such as FeMo, FeW and FeCr. 2% or less, Comparative Example 5 is FeMo, FeW,
The amount of hard particles such as FeCr dispersed is 20% or more, the amount of graphite powder added is less than 0.3% in Comparative Example 6, and the amount of graphite powder added is 2.0% in Comparative Example 7. In the case of exceeding, the comparative example 8 omits the sub-zero treatment.

[0021]

[Table 1]

[0022]

[Table 2]

Various powder compacts of test pieces were molded from the mixed powder under a molding pressure of 700 MPa. The compacted green compact was held in a reducing atmosphere at a temperature of 1453K for 900 seconds for sintering. Sintered various test piece compacts were made at 213K for 18
Hold for 00 seconds, perform sub-zero processing, then 773K
And held for 6000 seconds for tempering. However, in Example, re-compression was performed at 1000 MPa after sintering, and in Comparative Example 8, the sub-zero treatment was omitted.

With respect to the obtained test piece, the proportion of martensite and bainite in the matrix structure, hardness, and the amount of wear by the Ogoshi-type wear test were measured. The measurement results are shown in Table 3. The measurement was performed according to JPMA (Japan Powder Metallurgy Association Standard). The Ogoshi abrasion test conditions are shown below. Counterpart material S45C Sliding speed 0.250mm / sec Friction distance 200m Final load 32N

[0025]

[Table 3]

As shown in Table 3, in Comparative Example 1, since no Cr alloy powder was used, the martensite / bainite ratio was as low as 5%, the hardness was HV210, and the wear amount was 5.01 mm. Inferior in wear resistance. In Comparative Example 2, the added amount of Co powder, Ni powder, and Fe powder was 2% or less, so the hardness was low at Hv435 and the strength was insufficient, and in Comparative Example 3, the added amount of Co powder, Ni powder, and Fe powder. Was 20% or more, the ratio of martensite and bainite was as small as 52%, and the wear amount was 3.08 mm, and the wear resistance was poor.

In Comparative Example 4 in which the dispersion amount of hard particles such as FeMo, FeW, FeCr is 2% or less, the hardness is low, the wear amount is 3.97 mm, and the wear resistance is inferior.
In Comparative Example 5 in which the dispersion amount of hard particles such as W and FeCr is 20% or more, although the hardness was high, the wear amount was 5.1.
It was as large as 5 mm. In Comparative Example 6, the amount of graphite powder added was 0.
Since it was less than 3%, the martensite ratio was as small as 12% and the hardness was low and the wear resistance was inferior. In Comparative Example 7, the addition amount of the graphite powder was more than 2.0%. Although it was high, the wear amount was 4.95 mm and the wear resistance was poor. Further, Comparative Example 8 had a smaller amount of wear than the other Comparative Examples, but the amount of wear of the mating material was more than double that of the other Comparative Examples,
It could not be used as a valve seat material.

On the other hand, Examples 1 to 9 of the present invention shown in Table 1
Has a martensite and bainite ratio of 73 to 88.
%, The hardness is Hv 460 to 565, sufficient hardness and strength, and the wear amount is 2.11 to 2.42 mm, which proves to be excellent in wear resistance. The effect of the invention was confirmed.

[0029]

EFFECTS OF THE INVENTION The method for producing an iron-based sintered alloy for valve seats having excellent wear resistance according to the present invention comprises Cr: 1.0 to 5.0% and O; 0 in the Fe-based matrix structure constituting the matrix. .2
%, C; 0.1% or less, and the balance was used, and an iron-based alloy powder consisting of Fe and unavoidable impurities was used, so that the structure was made uniform and heat resistance and corrosion resistance could be improved. Further, by controlling the O content of the alloy powder,
Since the effect of adding Cr was secured and the Fe-based matrix structure was made into a martensite structure or a sorbite structure by subzero treatment, the heat resistance and corrosion resistance were further improved. Carbon powder 0.3 to 2.0% and Co, Ni or Fe 3 to 3 in the Fe-based matrix structure forming the matrix.
Since the solid solution was 0%, strength was improved and excellent heat resistance and corrosion resistance were obtained. In addition, FeMo, Fe
One or more of W and FeCr powders 2.0 to 2
Since 0% was mixed, wear resistance could be improved.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C22C 38/40 (72) Inventor Hiroshi Okajima 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (72) Inventor Yoshitaka Takahashi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Automobile Co., Ltd. (72) Inventor Takashi Maejima 5-1 Kurisuno Kinuzukacho, Yamashina-ku, Kyoto City Nippon Powder Powder Co., Ltd. (72) Inventor Hideki Kato 5-1, Kitsusu-cho, Kurusuno, Yamashina-ku, Kyoto

Claims (1)

[Claims] 1. A weight ratio of Cr: 1.0 to 5.0%,
O: 0.2% or less, C: 0.1% or less, the balance being F
Fe-based alloy powder consisting of e and unavoidable impurities, carbon powder 0.3 to 2.0%, Co powder, Ni powder, Fe powder, one or more kinds 3.0 to 30%, FeM
o, FeW, and FeCr powders, one or more of which are mixed in a proportion of 2.0 to 20%, and the mixed powder is compression-molded and then sintered, and the sintered body is subjected to subzero treatment and tempering treatment. A method for producing an iron-based sintered alloy having excellent wear resistance for valve seats.