JPH0555593B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention was mainly developed for valve seats of internal combustion engines.
This invention relates to a sintered alloy with high wear resistance. Since the mid-1960s, intense technological innovation has been carried out in automobile engines, first to comply with exhaust gas regulations, and then to achieve greater power performance and lower fuel consumption than before the regulations, and the operating conditions for engines have become increasingly harsh. It's coming. As a result, the conventional materials that make up the engine's valve mechanism lack heat resistance, wear resistance, etc., and there is an urgent need to develop alternative materials, and the applicant has also successively developed new materials as shown below. I've been doing it. 17968 (filed in 1945) 36242 (filed in 1950) 36242 (filed in 1950) 56547 (filed in 1953) 37343 (filed in 1955) Materials that meet the characteristics are materials that reduce costs while maintaining the required characteristics, and materials that meet increasingly strict requirements. However, as engine improvements have continued since then, the requirements for the properties of valve seat materials, particularly wear resistance, have recently become more stringent. Additionally, the type of fuel (unleaded gasoline, leaded gasoline, LPG...) also has a large effect on valve seat wear.
Due to the nature of automobiles as international products, it is natural that it is desirable to have quality that can be broadly adapted to various conditions that differ depending on the destination. The present invention was made based on these circumstances, and based on past experience, the above alloys, that is, Ni 0.5 to 3%, Mo 0.5 to 3%, Co 5.5 to
7.5%, C0.6-1.2% and the balance Fe as a main component.As a result, this composition has a selected hard phase in the matrix, namely Mo33-36%, Si4-12%.
and Co balance (63-52%) intermetallic compounds or Mo26-30% Cr7-9%, Si1.5-2.5% and Co
The balance (65.5-58.5%) is 5-25% intermetallic compounds.
The intended purpose was achieved by dispersing the materials. Incidentally, these intermetallic compounds are commercially available as alloy powders having the above-mentioned composition ranges, the former being commercially available from Cabot Co. under the trade name Tribaloy, and the latter being commercially available from Fukuda Metal Foil Powder under the trade name Kobamet. The properties of the alloy of the present invention can be improved depending on the characteristics of the engine by post-treatment after sintering. For example, infiltrating lead into the pores of the sintered material is effective when the operating temperature is relatively low but wears easily, or when the fuel does not contain anti-friction components such as LPG. Therefore, it is effective to re-compress the sintered material to make it more dense, especially in cases where high temperatures and high compression ratios occur, such as in diesel engines, or where sludge adheres due to the regular use of leaded gasoline. . In order to further stabilize the alloy structure,
After sintering, it is desirable to perform quenching and tempering for refining. However, when performing lead infiltration, the infiltration temperature is high at around 550°C, so an effect similar to that of thermal refining can be obtained. The present invention will be described in detail below with reference to examples. First, alloy powder with a composition excluding carbon from the base composition, that is, 1.5% Ni, 1.5% Mo and 6.5% by weight
Atomized alloy iron powder with a grain size of 100 mesh or less containing %Co was prepared as the main raw material, and Mo28% and Cr8 were prepared as the main raw material to form a hard phase dispersed in the base.
%, Si2% and Co62% intermetallic compound powder (kobamet) was prepared. Next, we prepared a sample. First, as a comparative sample that does not contain a hard phase, we mixed the above alloyed iron powder with 1% graphite powder and 0.8% zinc stearate as a lubricant to give a powder density of 6.9 g/ ^cm3 . After forming into a predetermined shape, sintering was performed in an ammonia decomposition gas furnace at a temperature of 1200°C for 20 minutes. Furthermore, as an example of the present invention, a sample (sample 1) was prepared in which a predetermined amount of the above-mentioned intermetallic compound powder was added to alloyed iron powder, and the blending of graphite and lubricant, molding, and sintering were the same as in the case of the comparative sample. did. Among the samples thus obtained, FIG. 1 shows the test results of mechanical properties at high temperatures for the comparison sample and sample 1 of the present invention having a hard phase content of 15%. Since the valve seat is generally only fixed in a mounting hole in the cylinder by an interference fit, if its strength is insufficient, there is a risk that it will fall off during operation when heating and cooling are repeated. Also, for the same reason,
A smaller coefficient of thermal expansion is desirable. Looking at FIG. 1 from this point of view, the comparative sample indicated by the broken line shows high radial crushing strength at low temperatures, but it significantly decreases at high temperatures. On the other hand, the sample of the present invention shown by the solid line maintains stable strength from the low temperature range to the high temperature range, and exhibits higher strength than the comparative sample at 400°C or higher. It can also be seen that this is superior in terms of thermal expansion coefficient. In addition, in the case of the present invention sample (Sample 2) in which the hard phase of Sample 1 was replaced with the hard phase of the second invention, that is, a predetermined amount of intermetallic compound powder (Tribaloy) containing 34% Mo, 8% Si, and 58% Co, The coefficient of expansion is the temperature
At 100°C, it is equal to Sample 1, and after that it gradually decreases as the temperature rises, and at 500°C, it shows a value of 12.5 compared to 12.8 of Sample 1. In addition, the radial crushing strength of sample 1 is 72,500 at 100℃.
67Kg/ ^mm2 at ℃, while sample 2 is 70 at 100℃, 500℃
65Kg/mm ² , which is a decrease of about 2Kg/mm ² over the entire curve. This is thought to be due to the difference in toughness between the two hard phases. Data for sample 2 is omitted from illustration to avoid complexity. Next, to examine the effect of the hard phase content, lead was infiltrated into the pores of each sample at 550°C, and the amount of wear on each valve seat was compared using a simulated engine test machine. This testing machine uses LPG combustion gas to heat the valve and valve seat to a predetermined temperature while driving the camshaft with a motor.The temperature, rotation speed, valve spring pressure, etc. can be set arbitrarily, and the test machine can undergo severe damage in a short period of time. tests can be conducted. The material of the valve is heat-resistant steel 21-4N. Figure 2 shows the test results of continuous operation for 30 hours with the valve seat temperature set at 350°C using this testing machine, and the measurement results of the radial crushing strength of each sample at room temperature. The data in this figure is for a sample (sample 3) in which lead was infiltrated into sample 1, whose hard phase content was varied from 5% to 25%. However, the data for the content of 0 are for the comparative sample mentioned above. It is something. The radial crushing strength decreases as the content of the hard phase increases, but even with a content of 25%, it maintains a strength that does not pose any practical problems. The wear of the valve seat increases rapidly up to a hard phase content of 5%.
After that, it decreased slowly until it reached around 20%, and after that there was almost no change. Therefore, in order to avoid variations in wear resistance, the content of the hard phase is set at a lower limit of 5%, most preferably about 15%, and an upper limit of 25%. In addition, in the sample (sample 4) in which lead was infiltrated into sample 2 in which the hard phase was replaced, the radial crushing strength was approximately 4 kg/mm ² lower than in the case of sample 3, and the wear amount was lower than that of sample 3. %, it increases by 9μ, and for 10% or more, it increases by about 2μ. Next, FIG. 3 shows the results of a test in which the valve seat temperature was changed using the above-mentioned simulated engine test machine. The solid line in the figure is the present invention sample 32 with a hard phase content of 15%, the broken line is the same comparative sample as in Figure 2, and the dashed line is the sample according to the above (Japanese Patent Publication No. 59-37343).
That is, in a base consisting of alloyed iron powder containing 3% Cr, 0.3% each of Mo and V, equal amounts of each of the above alloyed iron powders which are the main raw materials of the present invention material, and 1% carbon, 35% Mo,
This is a conventional material in which 15% of the hard phase of 10% Si and 55% Co is dispersed. From this graph, it can be seen that the comparison sample has a low temperature of 200℃ and a temperature of 400℃.
Although there is little wear at temperatures around 350°C, there is significantly more wear at the intermediate temperatures of around 350°C.
It shows a minimum value around ℃, but the wear before and after that is significant, especially in the low temperature range, so both are pros and cons. On the other hand, it can be seen that the sample of the present invention not only has less wear than the former two, but also has stable wear resistance over the entire range from low to high temperatures. The test results for other samples of the present invention are not shown in the figures and are shown in Table 1 together with the data for Sample 3. The lead infiltrated into the pores of the sintered material prevents wear through solid lubricant action, and as the data shows, this effect is particularly noticeable in low-temperature environments, and is almost meaningless at high temperatures where lead melts. becomes. Therefore, the third
The fourth invention is suitable for engines that use unleaded fuel and have a low operating environment (which applies to most domestic specification cars); when using leaded fuel or for engines with high design temperatures, A valve seat made of the sintered material according to the first or second invention, which is recompressed as necessary, is more suitable. Next, Figure 4 shows the results of a bench durability test using a 4-cylinder 2000 c.c. LPG engine (rotation speed constant 6000 rpm; fuel used was unleaded gasoline). The contents of each sample are the same as in the case of FIG. As is clear from the figure, the comparative sample that does not contain a hard phase has the most wear, followed by the conventional sample that contains a hard phase but has a different base, and the sample of the present invention (sample 3) shows the best results. There is. Regarding sample 4, the data is as shown in Table 2, and although the amount of wear is slightly greater than that of sample, it is clearly superior to the conventional one. Next, FIG. 5 shows the relationship between the sintering temperature and the wear resistance and radial crushing strength of the obtained sintered material when producing the alloy according to the present invention. Combining these items, the sintering temperature will be around 30℃ around 1200℃.
A value within this range is suitable, but a lower value within this range is preferred in terms of preventing diffusion of the hard phase. As stated at the beginning, the base of the material of the present invention is an alloy obtained by the applicant's previous invention (Japanese Patent Publication No. 36242/1982). Therefore, I will quote and explain the summary from this bulletin.
In the base of the material of the present invention, Ni and Mo mainly contribute to improving the strength, but if it is less than 0.5%, it is insufficient, and on the other hand, if it is added in an amount of 3% or more, it is not cost effective. Moreover, when Mo is added in excess, oxidation resistance decreases. When Co is less than 5.5%, it lacks high-temperature hardness and is prone to wear, while when it exceeds 7.5%, the raw material powder becomes hard and compression molding becomes difficult. From the viewpoint of control of the sintering process and quality stability, a suitable content of C is 0.6 to 1.2%. When blending these components, it is conceivable to blend each single component, but it is desirable to use an alloy iron powder containing all components other than carbon. As a result, it is possible to reliably obtain a desired alloy that not only prevents segregation during blending but also has little interdiffusion between the matrix and the hard phase. Regarding the overall composition of the sintered alloy according to the present invention,
The present invention is significant in that a predetermined amount of the selected hard phase is dispersed in the above-mentioned matrix, and the composition, structure, and properties of the alloy are specified thereby.
This dispersion hardening type structure is created by blending a predetermined amount of intermetallic compound powder with a predetermined composition to form a hard phase with alloy powder having a predetermined composition to form a matrix. Therefore, the overall composition is the result of induction from the respective compositions of the base and hard phase and the proportions of the two, that is, nickel and carbon (because they are not included in the hard phase) are:
Each range is common to the first and second terms,
In the case of nickel, the upper limit is 2.9% when 5% hard phase is mixed into a base with a 3% Ni content, and the Ni content is 0.5%.
The lower limit is 0.3% when 25% of the hard phase is blended into the base of 25%. On the other hand, since cobalt is included in both the base and the hard phase, its composition range is different between the first and second terms.
To illustrate the case of the second term, the lower limit is 7% when 5% of a hard phase with a Co content of 52% is blended into a base with a Co content of 5.5%, and a base with a Co content of 63% in a base with a Co content of 7.5%. The upper limit is 22% when 25% of the hard phase is mixed. Furthermore, since Si and Cr are not included in the matrix, their composition range is determined by their content in the hard phase and the amount added to the matrix. Table 3 shows the range of each component determined in this way and its basis. The components and composition range of the hard phase are the same as those of the selected commercially available intermetallic compound, since the blended intermetallic compound powder forms the hard phase as is. The specifications for intermetallic compounds are set by the raw material powder manufacturer. As intermetallic compounds suitable for the hard phase in the present invention, there are two types of products described on pages 4 to 5.
It is said that the material containing Cr (trade name: Kobamet) exhibits the desired characteristics over a wider temperature range.
However, no particular difference was observed between the two under the test conditions and temperature range of the engine test described above. As detailed above, the valve seat alloy according to the present invention exhibits uniformly excellent wear resistance from low to high temperatures,
It has characteristics that are almost unrestricted by the characteristics of the engine or the type of fuel. Therefore, although it contains a large amount of Co in both the base and the hard phase and is relatively expensive, it is extremely suitable for applications where quality is paramount.

【table】

【table】

【table】 [Brief explanation of the drawing]

Figure 1 is a graph showing the mechanical properties of a sintered alloy for valve seats at high temperatures; Figure 2 is a graph showing the relationship between the amount of hard phase contained in the matrix and wear resistance and radial crushing strength; The figure is a graph showing the relationship between valve seat temperature and wear amount using a simulated engine test machine.
The figure is a graph showing the results of the bench durability test, and FIG. 5 is a graph showing the relationship between the sintering temperature, wear resistance, and radial crushing strength of the alloy according to the present invention.

Claims (1)

[Claims] 1. Overall composition is 0.3 to 2.9% Ni and 1.7 to 2.9% Mo by weight.
9.8%, Co8~22%, C0.4~1.2% Cr0.3~2.3%,
Si0.1~0.7% and Fe balance, and Ni0.5~3%,
Mo0.5~3%, Co5.5~7.5%, C0.6~1.2% and
In the base of Fe remainder, Mo26~30%, Cr7~9%
A high-temperature wear-resistant sintered alloy characterized by exhibiting a structure in which a hard phase of 1.5 to 2.5% Si and 5 to 25% of the remaining Co is dispersed. 2 The overall composition is Ni0.3~2.9%, Mo2.1~ by weight.
11.3%, Co7~22%, C0.4~1.2%, Si0.1~3% and the balance of Fe, and Ni0.5~3%, Mo0.5~3%,
It is characterized by exhibiting a structure in which 5 to 25% of the hard phase of 33 to 36% Mo, 4 to 12% of Si, and the remainder of Co is dispersed in a base of 5.5 to 7.5% of Co, 0.6 to 1.2% of C, and the remainder of Fe. High temperature wear resistant sintered alloy. 3 Overall composition is Ni0.3~2.9%, Mo1.7~ by weight
9.8%, Co8~22%, C0.4~1.2% Cr0.3~2.3%,
Si0.1~0.7% and Fe balance, and Ni0.5~3%,
Mo0.5~3%, Co5.5~7.5%, C0.6~1.2% and
In the base of Fe remainder, Mo26~30%, Cr7~9%
A high-temperature wear-resistant sintered alloy which is an alloy exhibiting a structure in which a hard phase of 1.5 to 2.5% Si and 5 to 25% of the remainder Co is dispersed, and the pores of which are infiltrated with lead. 4 The overall composition is Ni0.3~2.9% and Mo2.1~ by weight.
11.3%, Co7~22%, C0.4~1.2%, Si0.1~3% and the balance of Fe, and Ni0.5~3%, Mo0.5~3%,
An alloy exhibiting a structure in which a hard phase of 33 to 36% Mo, 4 to 12% Si, and the remainder of Co is dispersed in a matrix of 5 to 25% of Co5.5 to 7.5%, C0.6 to 1.2%, and Fe remainder, A high-temperature wear-resistant sintered alloy whose pores are infiltrated with lead.