JPS6237710B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a sealing material made of sintered alloy that has excellent heat resistance and wear resistance, and more specifically, it is used for sealing rings for turbocharger exhaust manifolds, piston rings for internal combustion engines, etc. The present invention relates to a method for manufacturing a sealing material. Generally, FC and
FCD-based cast iron or resin are often used, but even if they have a fair degree of wear resistance, they may lack heat resistance. On the other hand, sintered alloys tend to be used for piston rings, etc., but this is because sintered alloys have 10 to 20% of pores, which act as oil pockets to retain lubricating oil and improve wear resistance. It is intended to take advantage of the property of improving seizing resistance. However, the pores inherent in the sintered alloy reduce the effective cross-sectional area of the sintered sealing material, resulting in an increase in the actual stress of the sealing material and a deterioration in heat resistance. Reducing the pore volume ratio is effective in compensating for this drawback and improving the heat resistance of sintered alloys, but this requires the use of special techniques such as sinter forging and hot pressing, which increases the cost of sintered products. It is economically disadvantageous. Other techniques for improving the heat resistance of sintered sealing materials include Cr, Ni, and
There is a method of pre-mixing powders such as Co, Mo, and W into iron powder, but since sintering generally uses a solid phase diffusion reaction, Ni and Co are excluded.
It is extremely difficult to uniformly diffuse and dissolve Cr, Mo, W, etc. into the Fe matrix of a sintered alloy. Therefore, the method of mixing the powder of the heat resistance improving element and the iron powder as described above cannot expect a significant improvement in heat resistance. The present invention provides the manufacture of a sintered metal seal that can solve the above-mentioned problems. Hereinafter, the required performance of the sealing material and the problems of the conventional method will be specifically explained using a turbocharger exhaust manifold side seal ring as an example. In recent years, an increasing number of internal combustion engines are equipped with turbochargers as a means of improving fuel efficiency and increasing output of automobiles. The turbocharger exhaust manifold side seal ring (hereinafter referred to as seal ring) is exposed to high temperatures due to the influence of high-temperature exhaust gas, and must seal lubricating oil at high temperatures.
Therefore, maintaining tension is one of the important characteristics of a seal ring, and therefore, high heat resistance is required as a performance of the sealing material. Furthermore, since the rotational speed of the turbocharger's turbine is at a high speed of up to several hundred thousand rpm, the sealing material must also have high performance in terms of wear resistance (including properties that do not abrade the mating material) and seizure resistance. be done. FC and
FCD cast iron, resin, etc. clearly lack heat resistance for seal rings, so currently ingot materials such as high-speed steel, austenitic cast steel, high Cr cast steel, and stainless steel are generally used for seal rings. Although these melt-produced materials have excellent heat resistance, the seal ring has a small diameter, requires a large number of processing steps, and has the disadvantage that the material yield is extremely low. Furthermore, these melt-produced materials have problems in seizure resistance and wear resistance. On the contrary,
Sintered alloys have a high degree of freedom in material composition, and since the pores have internal pressure, improvements in heat resistance, wear resistance, etc. can be easily implemented. Moreover, since sintered alloys can be manufactured with extremely high dimensional accuracy, it is possible to greatly reduce the number of processing steps, and the material yield is also extremely good. However, when heat resistance is imparted to sintered alloys by adjusting the material composition as described above, the technique of simply mixing powder of heat-resistant elements with iron powder and then sintering the material results in a remarkable improvement in heat resistance. I can't wait. In order to solve the above-mentioned problems of the conventional technology and dramatically improve the heat resistance and wear resistance as a sealing material for sintered alloys, the present inventor believes that it is important that the following conditions are met. We obtained the knowledge that Pre-alloyed iron alloy powder is used and sintered at high temperature to ensure sufficient diffusion of alloying elements. For this purpose, austenitic stainless steel powder is used as the main raw material to improve the heat resistance of the sintered alloy matrix, and cobalt powder is added to diffuse and form a solid solution in the matrix during sintering. In this way, heat resistance is further improved compared to using a single powder. The wear resistance of the sintered alloy is generally good due to the oil retaining effect of the internal pressure pores, but it can be further improved by adding hard particles. That is, the hard particles, which are relatively harder than the sintered alloy matrix, form the primary sliding surface, while the relatively soft matrix forms a lubricating oil pool due to initial wear, similar to the internal pressure pores. Therefore, not only the wear resistance but also the seizure resistance is further improved than if only due to the oil retaining effect of the pores. In addition to adding hard particles with appropriate hardness, when graphite powder is added, Cr in the austenitic stainless steel matrix reacts with graphite during sintering, precipitating fine Cr carbides, which improves wear resistance. The properties and seizure resistance should be further improved. The present invention, which satisfies the above conditions and conditions, has a particle size of 150 μm and a Bitkers hardness _{of Hv} 500 to 1500.
A mixed powder containing 1 to 20% by volume of the following hard particle powder, 0.5 to 2% by weight of graphite powder, 2 to 10% by weight of cobalt powder, and the balance consisting of austenitic stainless steel powder is pressed into powder. The present invention provides a method for manufacturing a heat-resistant and wear-resistant sintered metal sealing material having a relative density of 80 to 95% by molding and sintering. The reasons for the limitations of the present invention will be described below and further explained. If the hardness of the hard particles is less than _Hv 500, there is no effect of improving wear resistance and seizure resistance _;
If the hardness of the particles exceeds Hv, the wear of the mating material will increase, so it is appropriate that the hardness of the hard particles is between _Hv 500 and 1500. As such hard particles, at least one of high alloys, ferroalloys, and intermetallic compounds with high contents of Co, Cr, etc. can be used. In addition, coarse powder with a hard particle size exceeding 150 μm will cause problems such as non-uniformity during mixing of the raw powder and reduced formability during molding.
150μm or less is required. In addition, if the volume ratio of hard particles to the total mixed powder is less than 1%, wear resistance and seizure resistance will be insufficient, and if it exceeds 20%, compactability will decrease, so the ratio of hard particles should be 1 to 20% by volume.
% is appropriate. Preferably it is 3 to 10%. If only the above-mentioned hard particles were added to the austenitic stainless steel powder, the matrix would have a simple austenitic structure, so the wear resistance and seizure resistance of the matrix would be insufficient.
% by weight of graphite powder is added. Graphite powder reacts with Cr in austenitic stainless steel during sintering,
It precipitates mainly in the grain boundaries of austenitic stainless steel as fine chromium carbides, further improving wear resistance and seizure resistance. 0.5% by weight of graphite powder
If the graphite powder content is less than 2% by weight, wear resistance and seizure resistance will be insufficient, while if the graphite powder content exceeds 2% by weight, excessive chromium carbide will precipitate at the austenite grain boundaries and the material will become brittle, so the amount of graphite powder added should be 0.5 to 2% by weight. %, preferably 0.7 to 1.5% by weight are suitable. Furthermore, by adding cobalt powder, cobalt diffuses into the austenite matrix during sintering to form a solid solution, further improving heat resistance. The amount is 2
If it is less than 10% by weight, it will not be effective in improving heat resistance, and if it exceeds 10% by weight, the compactability will decrease, so the appropriate amount of cobalt powder to be added is 2 to 10% by weight, preferably 3 to 8% by weight. It is. The remainder was made of austenitic stainless steel powder because austenite has a stable structure at high temperatures and, as mentioned above, provides an excellent effect by providing a matrix that realizes the formation of chromium carbides and the diffusion and solid solution of cobalt. be. The heat resistance of sintered alloys is also affected by the amount of pores present. That is, when the proportion of inherent pores increases, the effective cross-sectional area of the sintered material decreases, the actual stress increases, and the heat resistance decreases, so the higher the relative density of the sintered material, the better. However, it is difficult to reduce the porosity to 5% or less using the cold forming and sintering methods commonly used to produce sintered alloys. From the above, the relative density of the sintered material is 80 to 95%.
limited to. The sintering conditions in the present invention are that after compacting the mixed powder at 5 to 10 tons/ ^cm2 ,
It is desirable to adopt conditions of heating to ℃ in a vacuum, hydrogen, or decomposed ammonia atmosphere. Examples will be described below and a more detailed explanation will be added. Example 1 A predetermined amount of the various powders shown in Table 1 was weighed, mixed for 30 minutes with a V-type mixer, and then molded under a pressure of 7 tons/
^cm2 , and finally sintered at 1200°C for 1 hour in a decomposed ammonia gas atmosphere. However, the hard particle powder and stainless steel powder were set to -100 mesh (149 μm). The graphite powder and cobalt powder were -325 mesh (44 μm). After sintering, the nominal diameter is 20mm and the width is 1.6mm by machining.
A seal ring with a thickness of 1.1 mm was made and a tension reduction test was conducted. Tension reduction tests were carried out by loading the seal ring into a cast iron cylinder with the same dimensions as the seal ring's nominal diameter, and testing it at 350℃, 400℃, and 450℃.
This was carried out by heating in Ar gas for 10 hours. The amount of change in the free gap between before and after the test was determined and taken as the tension reduction rate. Table 1 also shows each characteristic value and tension reduction rate after sintering. In the table, the amount of hard particle powder added was calculated by measuring the density of each powder and calculating the volume ratio. The relative density of the sintered body was calculated by determining the porosity using a microscope (1-porosity).

【table】

[Table] From the results in Table 1, it is clear that the material of the present invention has excellent heat resistance. FIGS. 1 and 2 show the metal structure of the material A of the present invention shown in Table 1 (magnifications are 100 times and 500 times, respectively). In Figure 2, a is a hard particle, b is a fine carbide, and c
indicates a matrix of austenitic stainless steel and d indicates pores, and it is understood that excellent performance is achieved by suitably finely dispersing these constituent phases a, b, c, and d according to the method of the present invention. . Example 2 A predetermined amount of the various powders shown in Table 2 was weighed and mixed in a V-type mixer for 30 minutes, and a pin (wear test piece) was produced under the same molding and sintering conditions as in Example 1. The wear test was conducted using a rotor pin type wear tester shown in FIG. The material of rotor B as a mating material is JIS SUM43 by quenching and tempering.
It was set as HRC35. Rotor B of φ40mm and φ10
mm, length 15mm pin A is polished to approximately 1.
It had a finish roughness of ~2 μm RZ. We performed a wear test by applying a load in the direction of the arrow while lubricating it by dropping SAE #30 engine oil.
The wear amount of the pin is measured by the long axis of the wear scar, and the wear amount of the rotor as a mating material is measured by measuring the amount of dent with a roughness meter at a load of 2 kg, a friction speed of 150 m/min, and a friction distance of 5000.
It was measured under the conditions of m. Furthermore, the friction speed was increased to 200 m/min, the load was increased, and the load at which seizure occurred was determined and the seizure limit load was determined. The results are also shown in Table 2. It is clear that the material of the present invention exhibits not only its own wear resistance, but also less wear of the mating material and higher seizure resistance than the comparative example.

[Table] Example 3 Inventive materials A and (Comparative Example E) shown in Table 1 of Example 1 were tested on an actual machine. The turbocharger tested had a turbine blade diameter of φ56.
mm, the compressor blade diameter is φ54mm, and the seal ring for the exhaust manifold side has a nominal diameter of φ17.5mm, and the width
It was machined to 1.6mm and 0.9mm thick and tested on an actual machine. As a comparative example, the currently used austenitic cast steel (20%Cr-20%Ni-10%Co-5%
W-2%Mo-1.4%Si-1.6%C, balance Fe) was also subjected to actual machine testing. The test conditions were a turbocharger installed on a 4-cylinder 2.3 diesel engine, and a 200Hr endurance run at 4200rpm and full load. The change in the free joint gap before and after this test was taken as the tension reduction rate, and the amount of wear in the width direction of the seal ring was determined as the sum of the amount of wear on both sides. The results are shown in Table 3.

[Table] From the above results, the present invention has been developed as a sintered alloy seal having excellent heat resistance and wear resistance, not only for use in turbocharger seal rings, but also as piston rings, valve seats, etc. for internal combustion engine seals. It is clear that it provides a method for producing a material that can be used as a material.

[Brief explanation of the drawing]

1 and 2 are metallurgical micrographs of the material A of the present invention shown in Table 1 of Example 1, and FIG. 3 is a drawing schematically showing a rotor pin type abrasion tester. A... Pin, B... Rotor, a... Hard particles, b... Fine chromium carbide, c... Austenite matrix, d... Holes.

Claims (1)

[Claims] 1 Particle size with Vickers hardness _Hv 500 to 1500
Hard particle powder of 150μm or less 1-20% by volume
, graphite powder 0.5 to 2% by weight, and cobalt powder 2
By compacting and sintering a mixed powder containing ~10% by weight and the balance consisting of austenitic stainless steel powder, the relative density is 80~95.
A method for producing a heat-resistant, wear-resistant sintered metal sealing material having a