JP2006274359A - Alloy powder for forming hard phase and ferrous powder mixture using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alloy powder for forming a hard phase appropriate for forming the hard phase of a wear resistant sintering member for a valve seat material exhibiting excellent high temperature wear resistance. <P>SOLUTION: The composition is, by mass, 48 to 60% Mo, 3 to 12% Cr, 1 to 5% Si, and the balance Fe and inevitable impurities. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an alloy powder for forming a hard phase suitable for forming a hard phase of a wear-resistant sintered member used for a valve seat material of an automobile engine, and an iron-based mixture that becomes a raw material powder suitable for an abrasion-resistant sintered member. Relates to powder.

  In recent years, the operating conditions of automobile engines have become more severe due to higher performance, and the valve seats used in engines are also required to withstand more severe use environment conditions than ever before. When used in such a harsh environment, high wear resistance is required and high strength that does not cause a sag phenomenon is required.

  As such a sintered alloy for valve seats, many have been proposed and implemented using a Co—Mo—Si hard phase as a hard phase (for example, Patent Documents 1 to 4). This hard phase is formed in the matrix by applying Co-Mo-Si alloy powder to the raw material powder and sintering, and hard particles mainly composed of Mo silicide precipitate in groups in the Co-based alloy matrix. This is a precipitate-dispersed hard phase. This Co-Mo-Si hard phase has the advantage that it enhances the wear resistance of the valve seat and also has a low aggression against the mating member because the Mo silicide has a self-lubricating property. Has been applied.

  The hard phase is a Co-based alloy having a Mo content of 40% by mass or less, and a sintered alloy containing this hard phase has a considerable high temperature wear resistance and high strength. However, in recent years, a sintered alloy having high temperature wear resistance and high strength has been desired. Therefore, as these improved inventions, by mass ratio, Si: 1.0 to 12%, Mo: 20 to 50%, Mn: 0.5 to 5.0%, and the balance is at least of Fe, Ni, Co An alloy powder for forming a wear-resistant hard phase composed of one kind and inevitable impurities is disclosed (see Patent Document 5).

Japanese Examined Patent Publication No. 59-037343 Japanese Patent Publication No. 05-055593 Japanese Patent Publication No. 07-098985 Japanese Patent Laid-Open No. 02-163351 JP 2002-356704 A

  Thus, in accordance with the demands of the times, a sintered alloy suitable as a valve seat material having more excellent wear resistance has been proposed. However, in recent years, there has been a demand for higher wear resistance of valve seat materials due to higher engine output and the like. On the other hand, it is also desired to be inexpensive due to the demand for cost reduction, and there is an urgent need to develop materials with a high price-performance ratio.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide a hard phase forming powder for a valve seat material having higher wear resistance and a high price-performance ratio.

  The present inventors analyzed the wear state between a valve seat and a valve under a high-power engine in recent years, and plastic flow and adhesion occur based on a base portion other than hard particles. Was found to be the cause of wear. Therefore, as a countermeasure, the inventors have found that the Mo content can be increased to increase the Mo silicide amount and reduce the wear base point. Moreover, the knowledge that the pinning effect of hard particles can be increased by increasing the Mo content and precipitating an integrated Mo silicide was also obtained. Based on these findings, the present inventors have reached the conclusion that the wear resistance can be greatly improved since the occurrence of plastic flow and adhesion can be minimized.

  Specifically, by adopting inexpensive Fe as the balance from the base described in the above-mentioned Patent Document 5 and eliminating Mn, increasing the amount of Mo without increasing the hardness of the powder, the precipitated Mo silicide It is the gist of the present invention to increase the number of objects and to deposit them together at the same time. It is also important to reduce the hardness of the powder and increase the amount of added Mo by optimizing the amount of Si to the necessary amount to produce the necessary Mo silicide. The present invention has been completed based on such findings.

  Therefore, this invention was made | formed based on the said countermeasure, and as for the alloy powder for hard phase formation concerning this invention, the whole composition is a mass ratio, Mo: 48-60%, Cr: 3-12%, Si: 1 to 5%, and the balance is Fe and inevitable impurities.

  The iron-based mixed powder for wear-resistant sintered alloy according to the present invention is obtained by adding 5 to 40% by mass of the above-mentioned hard phase forming alloy powder to an iron alloy base powder. It is said.

  According to the present invention, by increasing the amount of hard particles dispersed as compared with the prior art, the base point of wear can be reduced, and the hard particles can be integrated and precipitated to effect the pinning effect of the hard particles. Therefore, the occurrence of plastic flow and adhesion can be minimized. For this reason, it is possible to further improve the wear resistance of the hard particles, exhibit excellent high-temperature wear resistance, and provide a wear-resistant sintered alloy that is inexpensive and has a high price-performance ratio.

Hereinafter, the alloy powder for forming a hard phase according to the present invention and the iron-based mixed powder using the same will be described with reference to the drawings and numerical basis.
(1) Alloy powder for forming a hard phase The alloy powder for forming a hard phase of the present invention has an effect of using inexpensive Fe as a base material, diffusing to a base during sintering, and contributing to improvement of hard particle adhesion. The grounds for limiting the numerical values of each component composition of the hard phase forming alloy powder will be described below.

  Mo: Mo is mainly bonded to Si to form Mo silicide excellent in wear resistance and lubricity, and contributes to improvement in wear resistance of the sintered alloy. In addition, some of them also take in Cr and become Mo silicide precipitation type hard particles formed of a Mo—Cr—Si alloy. When the Mo content is less than 48% by mass, the Mo silicide is not integrated and deposited, and the conventional granular Mo silicide is dispersed in the Co-based hard phase, so that the wear resistance is conventional. It stops to the extent. On the contrary, if the Mo content exceeds 60% by mass, the effect of increasing the amount of Mo and the amount of reduction of Si, which will be described later, is increased, the hardness of the powder is increased, and the compressibility during molding is impaired. . Moreover, since the hard phase to be formed becomes brittle, part of the hard phase is lost due to impact, and the wear resistance is reduced by the action of the abrasive powder. Therefore, the Mo content is set to 48 to 60% by mass.

  Cr: Cr contributes to strengthening of the Fe alloy base of the hard phase. It also diffuses to the base and contributes to the improvement of the wear resistance of the base. If the Cr content is less than 3% by mass, these effects are poor. Conversely, if the Cr content exceeds 12% by mass, the amount of oxygen in the powder increases and an oxide film is formed on the powder surface to inhibit the progress of the sintering, and the oxide film hardens the powder so that it is compressible. Decrease. For this reason, since the intensity | strength of a sintered alloy falls and causes a fall of abrasion resistance, the upper limit of Cr content was 12 mass%. As described above, the Cr content was set to 3 to 12% by mass.

  Si: Si mainly reacts with Mo to form Mo silicide excellent in wear resistance and lubricity, and contributes to improvement in wear resistance of the sintered alloy. When the Si content is less than 1% by mass, a sufficient Mo silicide cannot be obtained, so that a sufficient wear resistance improving effect cannot be obtained. On the other hand, if the Si content is excessive, Si that diffuses to the base without reacting with Mo increases. Si hardens the base but also makes it brittle. For this reason, a certain amount of Si diffusion to the base is effective in terms of fixing the hard phase to the base. However, excessive diffusion of Si is not preferable because it reduces the wear resistance of the base and increases the opponent's aggressiveness. Here, if the amount of Si that does not react with Mo is reduced, an appropriate amount of Mo can be provided without increasing the hardness of the powder. Therefore, the upper limit of the Si content is set to 5 mass% where Si diffused to the base without reacting with the Mo amount starts to increase. As described above, the Si content is set to 1 to 5% by mass.

(2) Iron-based mixed powder The iron-based mixed powder of the present invention is obtained by adding 5 to 40% by mass ratio of the above-mentioned hard phase forming alloy powder to an iron alloy base powder. Here, the greater the amount of hard phase forming powder added, the better the wear resistance. However, if the added amount is less than 5% by mass with respect to the entire iron-based mixed powder, the effect of improving the wear resistance is poor. On the other hand, when the addition amount exceeds 40% by mass, the compressibility of the mixed powder is lowered, the density and strength after sintering are lowered, and the wear resistance is also lowered. Therefore, the addition amount of the hard phase forming alloy powder is set to 5 to 40% by mass with respect to the entire iron-based mixed powder.

  By sintering the green compact obtained by compacting the iron-based mixed powder into a predetermined shape at 1000 to 1200 ° C. in a non-oxidizing atmosphere, the composition is in mass ratio in the iron alloy matrix. , Mo: 48 to 60%, Cr: 3 to 12%, Si: 1 to 5%, the balance consisting of Fe and inevitable impurities, and a precipitate mainly composed of Mo silicide and precipitated A wear-resistant sintered alloy in which the base hard phase is dispersed by 5 to 40% by mass is obtained. In this wear-resistant sintered alloy, as shown in FIG. 1, the hard phase in which hard particles mainly composed of Mo silicide are integrally deposited in the Fe alloy matrix becomes a metal structure dispersed in the matrix structure. . This hard phase is hard and has a low affinity with the counterpart valve, Mo silicide, and further improves wear resistance, and hard particles made of Mo silicide are deposited together. Therefore, even in an environment where metal contact occurs, the base pinning effect prevents wear due to plastic flow and adhesion of the base. Further, since inexpensive Fe is used as the base material for the hard phase, the hard phase forming powder itself is inexpensive, and a wear-resistant sintered alloy having a high price-performance ratio can be obtained.

  On the other hand, FIG. 2 is a schematic diagram showing a conventional wear-resistant sintered alloy. In this wear-resistant sintered alloy, a hard phase surrounded by a diffusion phase (white phase) in which Co is diffused around a hard phase mainly made of Mo silicide is dispersed in the matrix. This hard phase is hard, but hard particles made of Mo silicide are not deposited together, so the pinning effect of the base is weak, and wear due to plastic flow and adhesion of the base is sufficiently prevented Can not do it. Further, since expensive Co is used as a base material, the wear-resistant sintered alloy itself is expensive.

  The recommended sintering temperature for obtaining the metal structure shown in FIG. 1 is 1000 to 1200 ° C. If the sintering temperature is less than 1000 ° C., the sintering is insufficient and satisfactory wear resistance cannot be obtained. Conversely, when the sintering temperature exceeds 1200 ° C., the hard phase melts and disappears, and each component necessary for the Mo silicide to be integrated and precipitated diffuses and flows out to the base, and the Mo silicide precipitates in a granular form. Will be.

  The composition of the iron alloy base powder and the metal structure obtained thereby are not particularly limited, and Fe alloy bases such as those in Patent Documents 1 to 3 can be used. That is, the wear resistance can be improved by simply replacing the Co-based hard phase used in these conventional techniques with the Fe-based hard phase of the present invention.

  The following is an example of an iron alloy base powder for obtaining a recommended wear-resistant sintered alloy. The structure of the iron alloy base powder and the metal structure obtained thereby will be described.

  In the present invention, the recommended iron alloy base powder has a mass ratio of Mo: 1.5 to 5.0%, and iron-based alloy powder having a composition consisting of Fe and inevitable impurities, and 0.3 to This is a powder for an iron alloy base to which 1.2% of graphite powder is added.

  When Mo is given as a solid solution in steel, the bainite region on the CCT diagram is expanded and the base structure is made bainite at the cooling rate after sintering without taking a special cooling step such as isothermal treatment. Have Bainite is a structure that is hard and strong next to martensite, and is not as hard as martensite. Therefore, the aggressiveness of the mating member is low, and it is a suitable structure for ensuring its own wear resistance. In order to uniformly exert the effect of Mo throughout the entire base, it is effective to apply the base forming powder forming the base in the form of Fe-Mo alloy powder. However, when the amount of Mo in the alloy powder is less than 1.5% by mass, the effect of bainite formation on the base is poor, and low-strength pearlite is likely to be generated. On the other hand, if it exceeds 5.0% by mass, the alloy powder becomes too hard and the compressibility of the alloy powder is impaired. As a result, the strength and wear resistance of the matrix are lowered.

  C is added to combine with Fe in the steel to form bainite in the matrix structure. This C is added in the form of graphite powder because the powder becomes hard when it is given as a solid solution in the alloy powder and the compressibility is impaired. If the amount of graphite powder to be added is less than 0.3% by mass, ferrite with extremely low strength is generated in a part of the matrix. On the other hand, if it exceeds 1.2 mass%, C dissolved in supersaturation on the Fe base will be precipitated as hard and brittle cementite, and the strength and wear resistance will be reduced.

  When the iron alloy base powder having such a configuration is used, the overall composition of the wear-resistant sintered alloy is, by mass ratio, Mo: 3.81 to 2699%, Si: 0.05 to 2.0. %, Cr: 0.15 to 4.8%, C: 0.3 to 1.2%, and the balance becomes Fe and inevitable impurities, and the metal structure of the wear-resistant sintered alloy obtained after sintering is shown in FIG. As shown in FIG. 3, the hard phase in which the Mo silicide is integrally deposited on the Fe alloy base is dispersed in the bainite base.

  The iron-base alloy powder may further contain Ni: 3% by mass or less. By including Ni in the iron-based alloy powder (Fe—Mo alloy powder), the hardenability of the base structure is improved, and the bainite structure obtained after sintering becomes the lower bainite structure, thereby improving strength and resistance. Abrasion is improved. However, if the Ni content exceeds 3% by mass, the iron-based alloy powder becomes hard and the compressibility is impaired.

  When the iron alloy base powder having this configuration is used, the overall composition of the wear-resistant sintered alloy is, by mass ratio, Mo: 3.81 to 2699%, Si: 0.05 to 2.0%, Cr: 0.15 to 4.8%, Ni: 2.84% by mass or less, C: 0.3 to 1.2%, and the balance becomes Fe and inevitable impurities, and wear-resistant sintered obtained after sintering The gold metal structure is the same as the above structure, in which the hard phase in which the Mo silicide is integrally deposited on the Fe alloy base is dispersed in the bainite base (FIG. 3). Higher and more wear resistant.

  Moreover, you may add 13 mass% or less Ni powder to the said iron alloy base powder (mixed powder of an iron base alloy powder and graphite powder). In this case, Ni diffuses from the Ni powder added in the form of a simple powder to the matrix during sintering to improve the hardenability of the matrix, and the metal structure of the diffusion part is hard martensite to improve the abrasion resistance of the matrix. Can be improved. Also, the original Ni powder portion has a high Ni concentration, and the portion remains as soft austenite, improving the conformability of the wear-resistant sintered alloy and reducing the counter attack of hard martensite. Have When Ni plain powder having such an action is added to the above iron alloy base powder, the amount of martensite in the bainite base increases as the addition amount increases, As the amount of austenite increases, the base hardness of the wear-resistant sintered alloy increases and the wear resistance improves. Further, when the amount of Ni powder added is about 10% by mass, the amount of martensite is maximized, the base hardness of the wear resistant sintered alloy is maximized, and the self wear resistance is maximized. Furthermore, when the amount of Ni added is increased, the amount of austenite increases and the amount of martensite starts to decrease, and the base hardness of the wear-resistant sintered alloy decreases. The effect of lowering the opponent's aggression is increased. However, if the amount of Ni powder exceeds 13% by mass, soft austenite increases excessively, resulting in a decrease in wear resistance. Since the addition of Ni powder has these functions, the addition of Ni powder of 13% by mass or less to the above-mentioned iron alloy base powder makes it possible to wear the wear-resistant sintered alloy with its own wear resistance and opponent attack. The conformability can be adjusted according to the required characteristics.

  When the iron alloy base powder having such a configuration is used, the overall composition of the wear-resistant sintered alloy is, by mass ratio, Mo: 3.81 to 2699%, Si: 0.05 to 2.0. %, Cr: 0.15-4.8%, Ni: 15.45% by mass or less, C: 0.3-1.2%, and the balance becomes Fe and inevitable impurities, and wear resistance obtained after sintering As shown in FIG. 4, in the sintered alloy, the hard phase in which the Mo silicide is integrally deposited on the Fe alloy matrix is dispersed in the matrix exhibiting a mixed structure of bainite, martensite, and austenite. It will be a thing.

[Influence of composition of alloy powder for forming hard phase]
The Fe-6.5Co-1.5Mo-Ni alloy powder disclosed in the above-mentioned document 2 is prepared as the base forming alloy powder, and 25% by mass of the hard phase forming alloy powder having the composition shown in Table 1, graphite powder 1.1% by mass and a molding lubricant (0.8% by mass of zinc stearate) were added and mixed, and the mixed powder was molded into a ring of φ30 × φ20 × h10 at a molding pressure of 650 MPa. Next, these compacts were sintered in an ammonia decomposition gas atmosphere at 1180 ° C. for 60 minutes to prepare samples 01 to 16. Table 1 also shows the results of simple wear tests on the above samples.

  Note that the simple wear test was performed in a state in which tapping and sliding input were applied at a high temperature. Specifically, the ring-shaped test piece was processed into a valve seat shape having a 45 ° tapered surface on the inner diameter surface, and the sintered alloy was press-fitted into an aluminum alloy housing. Then, a disk-shaped counterpart material (valve) partially having a 45 ° taper surface on the outer surface made of the SUH-36 material is moved up and down by a motor-driven eccentric cam, thereby moving the sintered alloy and The taper surfaces with the mating material were repeatedly collided. That is, the operation of the valve repeats the opening operation of separating from the valve seat by the eccentric cam rotated by the motor drive and the seating operation on the valve seat by the valve spring, thereby realizing the vertical piston motion. In this test, the counterpart material was heated with a burner, and the temperature was set so that the sintered alloy became 250 ° C., the number of hits of the simple wear test was 2800 times / minute, and the repetition time was 15 hours. Thus, the wear amount of the valve seat and the wear amount of the valve after the test were measured and evaluated.

(Relation between wear amount and Mo amount in hard phase forming alloy powder)
The sintered alloy (sample number 02 to 05) in which the Mo amount in the hard phase forming alloy powder is in the range of 48 to 60% by mass has a low and stable wear amount of the valve seat and the valve. It can be seen that it exhibits wear resistance. On the other hand, the sintered alloy (sample No. 01, 06) in which the Mo amount deviates from the range of 48 to 60% by mass has a particularly high valve seat wear amount, and the valve wear amount is relatively high. high. Accordingly, it was confirmed that excellent wear resistance was achieved when the Mo content in the alloy powder for forming the hard phase was in the range of 48 to 60% by mass.

(Relationship between wear amount and Cr amount in hard phase forming alloy powder)
In the sintered alloy (sample number 03,08-10) in which the Cr amount in the hard phase forming alloy powder is in the range of 3 to 12% by mass, the wear amount of the valve seat and the valve is stably low. It can be seen that it exhibits good wear resistance. On the other hand, in the sintered alloy (sample numbers 07 and 11) in which the Cr amount deviates from the range of 3 to 12% by mass, the wear amount of the valve seat is particularly high. Therefore, it was confirmed that excellent wear resistance was achieved when the Cr content in the hard phase forming alloy powder was in the range of 3 to 12 mass%.

(Relation between wear amount and Si amount in hard phase forming alloy powder)
In the sintered alloy (sample numbers 03, 13, and 14) in which the Si amount in the hard phase forming alloy powder is in the range of 1 to 5% by mass, the wear amount of the valve seat and the valve is stably low. It can be seen that it exhibits good wear resistance. On the other hand, in the sintered alloy (sample numbers 12 and 15) in which the Si amount deviates from the range of 1 to 5% by mass, the wear amount of the valve seat is particularly high. Accordingly, it was confirmed that excellent wear resistance was achieved when the Si content in the hard phase forming alloy powder was in the range of 1 to 5 mass%.

(Comparison between the hard phase of the present invention and the conventional hard phase)
Metals of samples (sample numbers 02 to 05, 08 to 10, 13, 14) using the above-described hard phase forming alloy powders of the present invention and samples of conventional Co-based hard phase forming alloy powders (sample number 16) As a result of observation of the structure, in the sample using the hard phase forming alloy powder of the present invention, as shown in FIG. 1, it was confirmed that precipitates mainly composed of Mo silicide were integrated and precipitated. It was. On the other hand, in the sample of the conventional alloy powder for forming a Co-based hard phase, it was confirmed that precipitates mainly composed of Mo silicide as shown in FIG. It was.

  In Table 1, when comparing a sample of the conventional Co-based hard phase forming alloy powder and a sample of the hard phase forming alloy powder having the above component composition within the range of the present invention, the hard phase forming alloy within the range of the present invention In any case, the powder samples can reduce the valve seat wear amount and the valve wear amount, and the total wear amount can be reduced as compared with the case where the conventional Co-based hard phase forming alloy powder is used. I understand. In particular, the amount of wear of the valve is significantly reduced, as confirmed by observation of the metal structure, Mo silicide having lubricity is integrally deposited.

[Effect of addition amount of hard phase forming alloy powder]
While preparing the Fe-6.5Co-1.5Mo-Ni alloy powder disclosed in Document 2 above as the base forming alloy powder, preparing the hard phase forming alloy powder used in Sample 03 of Example 1, The addition amount of the alloy powder for forming the hard phase was set to the amount shown in Table 2, and molded into a ring of φ30 × φ20 × h10 under the same conditions as in Example 1. Next, these compacts were sintered in an ammonia decomposition gas atmosphere at 1180 ° C. for 60 minutes to prepare Samples 17 to 23. Table 2 shows the results of simple wear tests on the above samples.

(Relationship between amount of wear and amount of hard phase forming alloy powder added)
Sintered alloys (sample numbers 03, 18-22) in which the addition amount of the alloy powder for forming the hard phase with respect to the total mass of the mixed powder is in the range of 5 to 40% by mass have stable valve seat and valve wear. It can be seen that it is low and exhibits good wear resistance. On the other hand, in the sintered alloy (sample numbers 17 and 23) in which the addition amount of the alloy powder for forming the hard phase is out of the range of 5 to 40% by mass, the wear amount of the valve seat is particularly high. Therefore, it was confirmed that if the addition amount of the alloy powder for forming the hard phase with respect to the total mass of the mixed powder is in the range of 5 to 40% by mass, excellent wear resistance is realized. In addition, all the sintered alloys of the present invention (sample numbers 03 and 18 to 22) have less wear on both the valve seat and the valve than the conventional sintered alloy (sample number 16). Good results have been obtained.

[Influence of sintering temperature]
While preparing the Fe-6.5Co-1.5Mo-Ni alloy powder disclosed in Document 2 above as the base forming alloy powder, preparing the hard phase forming alloy powder used in Sample 03 of Example 1, A ring of φ30 × φ20 × h10 was molded under the same conditions as in Example 1. Next, these compacts were sintered at the temperatures shown in Table 3 for 60 minutes in an ammonia-decomposing gas atmosphere to prepare samples 24-28. The results of conducting a simple wear test on the above samples are also shown in Table 3.

(Relation between wear amount and sintering temperature)
Sintered alloys with a sintering temperature in the range of 1000 to 1200 ° C. (sample numbers 3, 25 to 27) have a stable and low wear amount of the valve seat and valve, and exhibit good wear resistance. I understand. On the other hand, the sintered alloy (sample numbers 24 and 28) whose sintering temperature deviates from the range of 1000 to 1200 ° C. has a particularly high amount of wear of the valve seat. Therefore, it was confirmed that if the sintering temperature is in the range of 1000 to 1200 ° C., excellent wear resistance is realized. Note that the sintered alloy of the present invention (sample numbers 03, 25 to 27) is better in terms of the total wear amount of the valve seat and the valve than the sintered alloy of the conventional example (sample number 16). The result is obtained.

[Influence of hard phase]
Whether the Fe-3Cr-0.3Mo-0.3V alloy powder disclosed in Patent Document 1 and the Fe-6.5Co-1.5Mo-1.5Ni alloy powder are prepared alone as the base forming alloy powder Alternatively, a mixed powder prepared by mixing these alloy powders at a ratio of 1: 1 was prepared. Moreover, the Fe-50Mo-10Cr-3Si alloy of this invention and the conventional Co-3Cr-0.3Mo-0.3V alloy were prepared as the alloy powder for hard phase formation, respectively. Then, 25% by mass of the hard-phase-forming alloy powder and 1.1% by mass of the graphite powder are added to the base-forming powder in the proportions shown in Table 4, and formed into a ring of φ30 × φ20 × h10 under the same conditions as in Example 1. did. Next, these compacts were sintered in an ammonia decomposition gas atmosphere at 1180 ° C. for 60 minutes to prepare Samples 03, 16, and 29 to 32. The results of conducting a simple wear test on the above samples are also shown in Table 4.

(Relationship between wear amount and hard phase)
Whichever base forming alloy powder is used, when the hard phase forming alloy powder of the present invention is used (sample numbers 03, 29, 30), the conventional hard phase forming alloy powder is used. It can be seen that the wear amount of the valve seat and the valve is stably lower than that in the case of (Sample Nos. 16, 31, 32), and the wear resistance is good. Therefore, it was confirmed that if the alloy powder for forming a hard phase of the present invention is used, excellent wear resistance is realized.

[Influence of composition of alloy powder for base formation]
The base powder having the composition shown in Table 5 was prepared, and 25% by mass of the hard phase forming alloy powder used in Sample 03 of Example 1 and the amount of graphite powder shown in Table 5 were added. A ring of φ30 × φ20 × h10 was molded under the same conditions as in Example 1. Next, these compacts were sintered in an ammonia decomposition gas atmosphere at 1180 ° C. for 60 minutes to prepare Samples 33 to 49. The results of simple wear tests on the above samples are also shown in Table 5.

(Relationship between the amount of wear and the amount of Mo in the base-forming alloy powder)
In the sintered alloy (sample numbers 34 to 37) in which the Mo amount in the base forming alloy powder is in the range of 1.5 to 5.0% by mass, the wear amount of the valve seat and the valve is stably low. It can be seen that it exhibits good wear resistance. On the other hand, in the sintered alloy (sample numbers 33 and 38) in which the Mo amount deviates from the range of 1.5 to 5.0 mass%, the wear amount of the valve seat is particularly high, and the wear of the valve The amount is also relatively high. Therefore, it was confirmed that if the amount of Mo in the hard phase forming alloy powder is in the range of 1.5 to 5.0 mass%, excellent wear resistance is realized.

(Relationship between wear amount and Ni amount in base forming alloy powder)
A sintered alloy (Sample No. 36) having Mo content of 3.5% by mass in the base-forming alloy powder, and Mo: 3.5% by mass and Ni in the ratio shown in Table 5 were given in the base-forming alloy powder. By comparing the sintered alloys (sample numbers 45 to 49), it is possible to confirm the influence when Ni is dissolved in the base forming alloy powder. From these sintered alloys, wear resistance is improved by giving Ni in the base-forming alloy powder containing 3.5% by mass of Mo, and the wear resistance is further improved as the Ni content increases. I know that. However, this effect has a peak Ni content of 2% by mass. When the Ni content is 3% by mass, the wear resistance is almost the same as that with no addition, and when the Ni content further increases, It can be seen that the wear rate decreases and the wear amount increases. Therefore, the wear resistance can be further improved by including Ni in the base-forming alloy powder containing Mo, but addition exceeding 3% by mass decreases the wear resistance, so the upper limit of the addition amount is 3% by mass. It was confirmed that it was necessary.

(Metal structure observation results)
Observation of the metal structure of the sintered alloy (sample numbers 34 to 37, 45 to 48) using the base-forming alloy powder in the component composition range of the present invention described above, Mo silicide as shown in FIG. It was confirmed that the hard phase in which precipitates mainly composed of selenium precipitate together has a metal structure dispersed in the bainite matrix structure.

[Influence of composition of raw material powder]
The base-forming alloy powder used in Sample 36 of Example 5 was prepared, and 25% by mass of the hard-phase forming alloy powder used in Sample 03 of Example 1 was added. A raw material powder obtained by adding and mixing graphite powder and Ni powder in a proportion was molded into a ring of φ30 × φ20 × h10 under the same conditions as in Example 1. Next, these compacts were sintered in an ammonia decomposition gas atmosphere at 1180 ° C. for 60 minutes to prepare samples 50 to 60. The results of conducting a simple wear test on the above samples are also shown in Table 6.

(Relationship between the amount of wear and the amount of graphite powder added)
In the sintered alloy (sample numbers 36 and 51 to 54) in which the amount of the graphite powder in the raw material powder is in the range of 0.3 to 1.2% by mass, the wear amount of the valve seat and the valve is stably reduced. It can be seen that it exhibits good wear resistance. On the other hand, the sintered alloy (sample numbers 50 and 55) in which the addition amount of the graphite powder deviates from the range of 0.3 to 1.2% by mass has a particularly high wear amount of the valve seat, Valve wear is also relatively high. Therefore, it was confirmed that excellent wear resistance was achieved when the amount of graphite powder added to the raw material powder was in the range of 0.3 to 1.2 mass%.

(Relationship between wear amount and Ni powder addition amount)
By comparing the sintered alloy containing no Ni powder in the raw material powder (sample number 36) and the sintered alloy (sample number 56-60) obtained by adding Ni powder in the ratio shown in Table 6 to the raw material powder, The effect of adding Ni powder to the powder can be confirmed. From these sintered alloys, it can be seen that the wear resistance is improved by adding Ni to the raw material powder, and the wear resistance is further improved as the Ni content increases. However, this effect peaked at 10% by mass of Ni powder added, and when the added amount of Ni powder was 13% by mass, the wear resistance was almost the same as that of the unadded one. It can be seen that as the amount increases, the wear resistance decreases and the amount of wear increases. Therefore, the wear resistance can be further improved by adding Ni powder to the raw material powder. However, the addition of Ni powder exceeding 13% by mass decreases the wear resistance, so the upper limit of the addition amount needs to be 13% by mass. It was confirmed that there is.

(Metal structure observation results)
When the metal structure of the sintered alloy (sample numbers 56 to 59) using the raw material powder having the Ni addition amount of 13% by mass or less was observed, a precipitate mainly composed of Mo silicide as shown in FIG. It was confirmed that the hard phase in which the precipitates are integrally formed exhibits a metal structure that is dispersed in a matrix structure that exhibits a mixed structure of bainite, austenite, and martensite.

  The sintered alloy of the present invention can be applied to valve seats whose operating conditions have become more severe in recent years due to higher performance of automobile engines due to improved wear resistance.

It is a schematic diagram showing the metal structure of the wear-resistant sintered member obtained by using the iron-based mixed powder of the present invention. It is a schematic diagram showing the metal structure of the conventional abrasion-resistant sintered member. It is a schematic diagram showing the metal structure of the wear-resistant sintered alloy obtained by using the iron-based mixed powder of the present invention. It is a schematic diagram showing the metal structure of the wear-resistant sintered alloy obtained by using the iron-based mixed powder of the present invention.

Claims (6)

  Hard phase forming alloy characterized in that the overall composition is, by mass ratio, Mo: 48-60%, Cr: 3-12%, Si: 1-5%, the balance being Fe and inevitable impurities Powder.   An iron-based mixed powder for a wear-resistant sintered member, comprising 5 to 40% by mass of the hard phase forming alloy powder according to claim 1 added to an iron alloy matrix powder.   The iron alloy base powder has a mass ratio of Mo: 1.5 to 5.0%, and the iron base alloy powder having a balance of Fe and inevitable impurities, and 0.3 to 1.2% graphite. The iron-based mixed powder for wear-resistant sintered members according to claim 2, wherein powder is added.   The iron-based mixed powder for wear-resistant sintered members according to claim 3, wherein the iron-based alloy powder further contains Ni: 3% or less by mass ratio.   5. The iron-based mixed powder for wear-resistant sintered members according to claim 3, wherein the iron alloy base powder further contains 13% or less of Ni powder by mass ratio. The iron alloy base powder is further selected from among lead powder, molybdenum disulfide powder, manganese sulfide powder, boron nitride powder, magnesium metasilicate mineral powder, bismuth powder, bismuth oxide powder, chromium sulfide powder, calcium fluoride powder. The iron-based mixed powder for wear-resistant sintered members according to any one of claims 3 to 5, wherein at least one kind is contained in a mass ratio of 2% or less.

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