JP4948636B2 - Hard particles for blending sintered alloys, wear-resistant iron-based sintered alloys, and valve seats - Google Patents

Description

  The present invention relates to hard particles suitable for blending into a sintered alloy, in particular, hard particles suitable for improving the wear resistance of a sintered alloy, and further, wear-resistant iron-based fired containing the hard particles. The present invention relates to a bonding gold and a valve seat formed of the sintered alloy.

  Conventionally, sintered alloys based on iron may be applied to valve seats and the like. The sintered alloy may contain hard particles in order to further improve the wear resistance. When hard particles are included, powder of hard particles is mixed with powder having a composition of low alloy steel or stainless steel, and a compacted body is formed with this mixed powder, and then the compacted body is sintered. Generally, a sintered alloy is used.

  As such hard particles, for example, by mass: Mo: 20 to 60%, C: 0.2 to 3%, Ni: 5 to 40%, Mn: 1 to 15%, Cr: 0.1 to 10% In other words, hard particles composed of inevitable impurities and Fe have been proposed (see, for example, Patent Document 1).

  When a sintered alloy based on iron is produced using these hard particles, the adhesion between the hard particles and the iron base that is the base material can be improved. Furthermore, favorable solid lubricity can be ensured by including Mo in hard particles.

JP 2001-181807 A

  By the way, when the valve seat of the internal combustion engine is manufactured with the sintered alloy described in Patent Document 1, since the hard particle Mo acts as a solid lubricant, the lubricity of the sliding surface between the valve and the valve seat is improved. Can be increased.

  However, when the valve is opened and closed, the valve seat and the valve do not simply slide relative to each other. In particular, the valve on the exhaust side is in a higher temperature environment than the intake side, and in this environment, the valve seat and the valve are intermittently in contact with the opening and closing of the valve, and at the time of this contact both slide relatively. Therefore, adhesive wear at the time of contact and abrasive wear at the time of sliding are mixed (composite). When such a wear form is strictly considered, the wear resistance of the valve seat may not be sufficiently improved only by improving the lubricity.

  The present invention has been made in view of the above-described problems, and the object of the present invention is to make it possible to improve wear resistance even when a combined wear form is developed in a high temperature environment. It is another object of the present invention to provide hard particles for bonding gold, an abrasion-resistant iron-based sintered alloy containing the hard particles, and a valve seat formed of the sintered alloy.

  As a result of intensive studies to solve the above problems, the inventors have effectively improved the hardness of the hard particles while maintaining the lubrication characteristics of the hard particles so far, which is effective for wear resistance in the environment. I thought it was. And, as a means for realizing this, adding yttrium (Y), which is more oxidizing than other elements, to the hard particles is a method for increasing the hardness of the hard particles while ensuring the lubricating properties of the hard particles. However, we have obtained new knowledge that it is the most effective method.

  The present invention is based on such new knowledge, the hard particles for blending sintered alloy is hard particles blended as a raw material in the sintered alloy, Mo: 20-40% in mass%, C: 0.5 to 1.0%, Ni: 5 to 30%, Mn: 1 to 10%, Cr: 1 to 10%, Co: 5 to 30%, Y: 0.05 to 2%, the balance being It consists of inevitable impurities and Fe. In the present specification, unless otherwise specified,% means mass%.

According to the present invention, yttrium is very easy to oxidize in the atmosphere as compared with other elements. Therefore, by adding Y (yttrium) to the hard particle component, the hard particle has an oxide of yttrium (Y ₂ O ₃ ) is formed and this oxide is dispersed in the hard particles. Thereby, the hard particles are strengthened by dispersion, and the hardness of the hard particles can be increased. Moreover, adhesion wear can be suppressed by the oxide of yttrium, and the wear resistance can be further improved. Further, when the sintered alloy containing hard particles is cut, the sintered alloy is difficult to adhere to the cutting tool, and therefore the machinability of the sintered alloy can be improved by the oxide of yttrium.

Here, when adding less than 0.05% of yttrium to the mass of the hard particles, even if yttrium oxide (Y ₂ O ₃ ) is formed in the hard particles, this is sufficient. It is not possible to obtain a hardness enough to expect the wear resistance of a sintered alloy using sinter.

  On the other hand, as yttrium is added to the hard particles, the hardness of the hard particles can be increased. However, when the yttrium is added in excess of 2% with respect to the mass of the hard particles, the hard particles become brittle. As a result, the wear resistance of the sintered alloy produced by using this is reduced. The other components of the hard particles and the technical significance of the content thereof will be described in detail in the following embodiments and examples.

  A wear-resistant iron-based sintered alloy is also disclosed as the present invention using the hard particles for compounding a sintered alloy thus configured. The wear-resistant iron-based sintered alloy according to the present invention is obtained by mixing a powder comprising the sintered alloy compounding hard particles with a base iron-based powder so that the sintered alloy compounding hard particles are dispersed. A sintered wear-resistant iron-based sintered alloy, wherein the hard particles for blending the sintered alloy contain 10 to 60% by mass with respect to the wear-resistant iron-based sintered alloy. More preferred.

  According to the present invention, the sintered alloy is based on an iron-based metal at the time of sintering, and hard particles are connected. When the hard particles are less than 10% by mass with respect to the sintered alloy, the sintered alloy has resistance to hard particles. In some cases, the wear effect cannot be fully exhibited. On the other hand, when the amount of hard particles exceeds 60% by mass, the ratio of the iron base decreases, and as a result, the hard particles may not be held with sufficient adhesion to the sintered alloy. As a result, in an environment where wear occurs, such as a contact / sliding environment, the hard particles fall off from the sintered alloy, which may promote wear of the sintered alloy.

  Furthermore, it is preferable that the valve seat is formed of the wear-resistant iron-based sintered alloy thus configured. According to the present invention, even in a case where a wear form in which the above-described adhesive wear at the time of contact and abrasive wear at the time of sliding are mixed is exhibited in a high temperature environment, the solid particles of the conventional hard particles The hardness of the hard particles can be increased without impairing the lubricity. Thereby, the abrasion resistance of the valve seat can be further improved as compared with the conventional one.

  According to the sintered alloy in which the hard particles of the present invention are blended, the solid lubricity and hardness can be improved even in the case where a wear form in which abrasive wear and adhesive wear are combined under high temperature environment. Thus, the wear resistance can be further improved.

The figure which showed the abrasion test result of the valve seat of Examples 1-4 and Comparative Examples 1-3. The figure which showed the abrasion test result of the valve seat of Examples 5-10 and Comparative Examples 4-15. The figure which showed the abrasion test result of the valve seat of Examples 11-15 and Comparative Examples 16 and 17. The figure for demonstrating the abrasion test of an Example and a comparative example.

  Hereinafter, embodiments of the present invention will be described in detail. The hard particles according to this embodiment are hard particles (sintered alloy compounding particles) blended as a raw material in a sintered alloy, and are particles having a higher hardness than the base of the sintered alloy. Hard particle | grains are Mo: 20-40% by mass%, C: 0.5-1.0%, Ni: 5-30%, Mn: 1-10%, Cr: 1-10%, Co: 5- 30%, Y: 0.05-2%, the balance is inevitable impurities and Fe.

  Such hard particles can be manufactured by an atomizing process in which a molten metal in which the above-described composition is blended in the above-described ratio is prepared and the molten metal is atomized. As another method, a solidified body obtained by solidifying a molten metal may be pulverized by mechanical pulverization. The atomization process may be either a gas atomization process or a water atomization process, but a gas atomization process that provides round particles is more preferable in consideration of sinterability and the like. Moreover, as a gas atomization process, if it can oxidize Y (yttrium) by manufacturing (sintering) a sintered alloy, it will be, for example, non-oxidizing atmosphere (inert such as nitrogen gas or argon gas) Gas atomization may be performed in a gas atmosphere or in a vacuum.

  Here, as the lower limit value and the upper limit value of the composition of the hard particles described above, the reasons for limiting the composition to be described later, and further, in the range, considering hardness, solid lubricity, adhesion, cost, etc. Depending on the importance of each characteristic of the applied member, it can be changed as appropriate.

  First, among the composition of hard particles, Mo forms Mo carbide to improve the hardness and wear resistance of the hard particles, and solid solution of Mo and Mo carbide forms a Mo oxide film and is improved. It is effective for improving the solid lubricity.

  When the amount of Mo is less than the above lower limit value, the solid lubricity in the hard particles becomes insufficient. When the above upper limit is exceeded, the adhesion with the iron-based matrix is reduced during sintering. The more preferable Mo content in the hard particles is 21 to 39% by mass.

  Of the composition of the hard particles, C combines with Mo to form Mo carbide, and is effective in improving the hardness and wear resistance of the hard particles.

  If C is less than the above lower limit, the wear resistance is insufficient, and if C is more than the above upper limit, the density of the sintered alloy is lowered. The more preferable content of C in the hard particles is 0.7 to 0.9% by mass.

  Of the hard particle composition, Ni increases the austenite at the base of the hard particles, increases the solid solution amount of Mo, and improves the wear resistance. Further, the hard particle Ni is effective for diffusing into the base of the sintered alloy to increase the austenite in the base, increasing the solid solution amount of Mo, and improving the wear resistance.

  If Ni is less than the above lower limit, the solid solution amount of Mo is reduced and wear resistance is insufficient, and if Ni is more than the above upper limit, the sintered alloy is easily seized, As a result, adhesive wear is likely to occur. The more preferable Ni content in the hard particles is 6 to 28% by mass.

  Of the hard particle composition, Mn efficiently diffuses from the hard particle to the base of the sintered alloy during sintering under the hard particle composition, which is effective in improving the adhesion between the hard particle and the base. It is. Furthermore, Mn can be expected to increase austenite at the base.

  If Mn is too smaller than the above lower limit, the amount of diffusion to the base is small, so the adhesion between the hard particles and the base is reduced, and if Mo is more than the above upper limit, Density decreases. The more preferable content of Mn in the hard particles is 1 to 9% by mass.

  Of the hard particle composition, Cr is effective in suppressing the oxidation of the hard particles because the use environment temperature is high and when the generation of the oxide film on the hard particles increases, the oxide film peels off the hard particles. .

  If the Cr is less than the above lower limit, the oxide film on the hard particles becomes too thick and is subject to oxidative wear. If the Cr is more than the above upper limit, formation of an oxide film that becomes a solid lubricant is formed. Will be suppressed. The more preferable content of Cr in the hard particles is 2 to 9% by mass.

  Of the composition of the hard particles, Co is effective for increasing the austenite at the base of the hard particles and the base of the sintered alloy and improving the hardness of the hard particles.

  If Co is less than the above lower limit value, it is difficult to expect the above-described effect, and if Co is more than the above upper limit value, wear resistance may be lowered. The more preferable Co content in the hard particles is 7 to 29% by mass.

Of the composition of the hard particles, Y is very easy to oxidize in the atmosphere as compared with other elements. Therefore, by adding Y to the hard particle components, the hard particles have yttrium oxide (Y ₂ O ₃ ) And the oxide is dispersed within the hard particles, strengthening the hard particles. This oxidation of yttrium can be manifested not only during the production of hard particle powders, but also during molding and then when used as a sintered alloy in a high temperature environment. Furthermore, since the oxide of yttrium is present on the surface of the sintered alloy (hard particles), adhesive wear can be suppressed and the wear resistance can be improved.

Here, if Y is less than the above lower limit, even if an oxide of yttrium (Y ₂ O ₃ ) is formed in the hard particles, the wear resistance of the sintered alloy using this is sufficient. It is not possible to obtain a hardness that can be expected.

  On the other hand, as yttrium is added to the hard particles, the hardness of the hard particles can be increased. However, when the yttrium is added in excess of 2% with respect to the mass of the hard particles, the hard particles become brittle. Therefore, the wear resistance of the sintered alloy produced by using this is reduced. In this case, the hardness of the hard particles becomes too high when molding a powder in which hard particles and base iron powder particles are mixed, so that the density of the molded green compact is low. turn into. As a result, the density of the sintered alloy obtained by sintering the formed body is lowered, and thereby the wear resistance of the sintered alloy is lowered.

  The average particle size of the hard particles can be appropriately selected according to the use and type of the iron-based sintered alloy, but can be about 20 to 250 μm. However, it is not limited to this. The hardness of the hard particles depends on the amount of Y added and can be about Hv 600 to 700. However, the present invention is not limited to this. In short, it is only necessary that the hard particles are hard to be used, such as a sintered alloy base.

  Then, using such hard particles for compounding sintered alloy, the powder composed of the hard particles for compounding sintered alloy is dispersed into a base iron-based powder so that the hard particles for compounding sintered alloy are dispersed. Mix. At this time, the hard particles are more preferably contained in an amount of 10 to 60% by mass with respect to the entire mixed powder (that is, the wear-resistant iron-based sintered alloy).

  Since the hard particles are dispersed in the base of the sintered alloy and constitute a hard phase that enhances the wear resistance of the sintered alloy, if the proportion of hard particles is less than 10% by mass, the wear resistance of the sintered alloy is Not enough. If the ratio of hard particles exceeds 60% by mass, not only the opponent attack property is increased, but also the retention properties of the hard particles are difficult to be secured.

  Further, as the mixed powder, an iron-based powder (for example, pure iron powder or low alloy steel powder) serving as a base of the wear-resistant iron-based sintered alloy may be used, and carbon powder may be further added thereto. The low alloy steel powder can employ Fe-C based powder. For example, when the low alloy steel powder is 100% by mass, C: 0.2 to 5% by mass, and the balance is composed of inevitable impurities and Fe. A thing with can be adopted.

  Thus, the obtained mixed powder is shape | molded to a compacting body, and this compacting body is sintered. As a sintering temperature, about 1050 to 1250 ° C., in particular, about 1100 to 1150 ° C. can be adopted. As a sintering time at the above-described sintering temperature, 30 to 120 minutes, more preferably 45 to 90 minutes can be employed. The sintering atmosphere may be a non-oxidizing atmosphere such as an inert gas atmosphere, and examples of the non-oxidizing atmosphere include a nitrogen atmosphere, an argon gas atmosphere, and a vacuum atmosphere.

  The base of the iron-based sintered alloy obtained by sintering preferably contains a structure containing pearlite in order to ensure its hardness. As the structure containing pearlite, a pearlite structure, a mixture of pearlite-austenite The structure may be a pearlite-ferrite mixed structure or a pearlite-cementite mixed structure. In order to ensure wear resistance, it is preferable that the amount of ferrite having low hardness is small. Although the hardness of the base depends on the composition, it is about Hv120 to 300, and can be adjusted by heat treatment conditions, the amount of carbon powder added, and the like. However, the composition and hardness are not limited as long as the wear resistance such as adhesion between the hard particles and the base is not lowered.

  And you may form the valve seat of the exhaust valve of an internal combustion engine with an abrasion-resistant iron-based sintered alloy. This is a case where a wear pattern in which adhesion wear at the time of contact between the valve seat and the valve and abrasive wear at the time of sliding occurs in a high temperature environment, such as a valve seat on the exhaust side of an internal combustion engine. However, the hardness of the hard particles can be increased without deteriorating the solid lubricity of the hard particles so far. Thereby, the abrasion resistance of the valve seat can be further improved as compared with the conventional one.

Below, the example which carried out the present invention concretely is described with a comparative example.
[Example 1]
A valve seat made of a sintered alloy containing hard particles according to Example 1 was manufactured by the method described below. Specifically, alloy powder was produced from a molten metal having the composition shown in Table 1 by gas atomization using an inert gas (nitrogen gas). These were classified into a range of 44 μm to 180 μm to obtain hard particle powder. The hard particle powder, graphite powder, and pure iron powder were mixed by a mixer to form a mixed powder as a mixed material. Here, the hard particle powder was 30% by mass with respect to the mixed powder, the graphite powder was 0.6% by mass, and the rest was pure iron powder.

Using a molding die, the mixed powder blended as described above was compression molded into a ring-shaped test piece with a pressure of 78.4 × 10 ⁷ Pa (8 tonf / cm ² ) to form a green compact. The green compact was sintered in an inert atmosphere (nitrogen gas atmosphere) at 1120 ° C. for 60 minutes to form a sintered alloy (valve seat) according to the test piece.

[Examples 2 to 4]
A valve seat was manufactured in the same manner as in Example 1. The difference from Example 1 is that the composition of the hard particles is as shown in Table 1, that is, Y contained in the hard particles of the valve seat (sintered alloy) is successively 0.2 mass%, 1.0. It is the point made into the mass% and 2.0 mass%.

[Comparative Example 1]
A valve seat was manufactured in the same manner as in Example 1. The difference from Example 1 is that the composition of the hard particles is as shown in Table 1, that is, the composition of the hard particles of the valve seat (sintered alloy) is set to the composition and content shown in Patent Document 1 described above. Is a point.

[Comparative Example 2]
A valve seat was manufactured in the same manner as in Example 1. The difference from Example 1 is that the composition of the hard particles is as shown in Table 1, that is, Y contained in the hard particles of the valve seat (sintered alloy) was 0 mass% (not contained). Is a point.

[Comparative Example 3]
A valve seat was manufactured in the same manner as in Example 1. The difference from Example 1 is that the composition of the hard particles is as shown in Table 1, that is, the Y contained in the hard particles of the valve seat (sintered alloy) is 5.0% by mass.

<Abrasion test>
Next, a wear test was performed on the wear resistance of the sintered alloy using the testing machine shown in FIG. 4 to evaluate the wear resistance. In this wear test, as shown in FIG. 4, the propane gas burner 10 is used as a heating source, and the ring-shaped valve seat 12 made of a sintered alloy produced as described above and the valve face 14 of the valve 13 slide. The part was a propane gas combustion atmosphere. The valve face 14 is obtained by soft nitriding the SUH 11. The temperature of the valve seat 12 is controlled to 200 ° C., a load of 18 kgf is applied by the spring 16 when the valve seat 12 and the valve face 14 are in contact, and the valve seat 12 and the valve face 14 are And an abrasion test for 8 hours was conducted.

  The amount of wear (wear depth) of the valve seat at this time was measured. The result is shown in FIG. The wear amount ratio shown in FIG. 1 is normalized by assuming the wear amount of the valve seat of Comparative Example 1 to be 1.

<Hardness test>
The hardness of the hard particles according to Examples 2 to 4 and Comparative Example 2 was measured using a micro Vickers hardness meter with a measurement load of 0.1 kgf. The results are shown in Table 2 below.

<Result 1>
As shown in FIG. 1, the wear amount ratios of the valve seats of Examples 1 to 4 were smaller than those of Comparative Examples 1 to 3. As shown in Table 2, the hardness of the hard particles increases with an increase in the Y content (addition amount) of the hard particles, and the rate of increase in hardness is the Y content (addition amount) of the hard particles. It declined with the increase.

<Evaluation 1>
From the result 1, it can be seen that by adding Y to the hard particles, the hardness of the hard particles is increased, and as a result, the wear resistance of the valve seat is improved. This is presumably because the oxide of Y (Y ₂ O ₃ ) was finely dispersed in the hard particles, thereby strengthening the hard particles. When the Y content is less than 0.2% by mass, strengthening by the oxide of Y may not be sufficient, and when it exceeds 2% by mass, sufficient resistance is obtained due to embrittlement of the hard particles. Abrasion is not expected.

[Examples 5 to 10]
A valve seat was manufactured in the same manner as in Example 1. The difference from Example 1 is the content of each composition of hard particles. Specifically, as shown in Table 2, the hard particles are, in mass%, Mo: 20 to 40%, C: 0.5 to 1.0%, Ni: 5 to 30%, Mn: 1 to 10%. , Cr: 1 to 10%, Co: 5 to 30%, and Y: 0.05 to 2%. The amount of each composition contained in the hard particles is adjusted.

[Comparative Examples 4 to 15]
A valve seat was manufactured in the same manner as in Example 1. The difference from Example 1 is the amount of each composition contained in the hard particles, as shown in Table 3. Specifically, in the hard particles of Comparative Examples 4 and 5, in the composition of the present invention, the content of only Mo was out of the range of Mo: 20 to 40%. In the hard particles of Comparative Examples 6 and 7, in the composition of the present invention, the content of only C was out of the range of C: 0.5 to 1.0%. The hard particles of Comparative Examples 8 and 9 were such that the content of only Ni out of the composition of the present invention was out of the range of Ni: 5 to 30%. The hard particles of Comparative Examples 10 and 11 were such that the content of only Mn out of the composition of the present invention was out of the range of Mn: 1 to 10%. The hard particles of Comparative Examples 12 and 13 were such that the content of only Cr out of the composition of the present invention was out of the range of Cr: 1 to 10%. The hard particles of Comparative Examples 14 and 15 were such that the content of only Co in the composition of the present invention was out of the range of Co: 5 to 30%.

<Abrasion test>
A wear test similar to the wear test of the valve seat of Example 1 was performed on the valve seats of Examples 5 to 10 and the valve seats of Comparative Examples 4 to 15. The result is shown in FIG. The wear amount ratio shown in FIG. 2 is normalized by setting the wear amount of the valve seat of Comparative Example 1 to 1. FIG. 2 also shows the wear amount ratio of the valve seat of Comparative Example 1.

<Result 2>
As shown in FIG. 2, the wear amount ratio of the valve seats of Examples 5 to 10 was smaller than those of Comparative Examples 4 to 15.

<Evaluation 2>
From the result 2, hard particles are, in mass%, Mo: 20 to 40%, C: 0.5 to 1.0%, Ni: 5 to 30%, Mn: 1 to 10%, Cr: 1 to 10%, It can be said that the wear amount of the valve seat was reduced by adjusting the amount of each composition contained in the hard particles so as to fall within the ranges of Co: 5 to 30% and Y: 0.05 to 2%.

[Examples 11 to 15]
A valve seat was manufactured in the same manner as in Example 2. The difference from Example 2 is that, as shown in Table 4 below, the hard particle powder is successively 10% by mass, 20% by mass, 30% by mass, 50% by mass, and 60% by mass with respect to the mixed powder. The graphite powder was added in the same amount as in Example 2.

[Comparative Examples 16 and 17]
A valve seat was manufactured in the same manner as in Example 2. The difference from Example 2 is that the powder of hard particles is sequentially 5% by mass and 70% by mass as shown in Table 4 below with respect to the mixed powder, and the same amount of graphite powder is added as in Example 2. This is the point.

<Abrasion test>
A wear test similar to the wear test of the valve seat of Example 1 was performed on the valve seats of Examples 11 to 15 and the valve seats of Comparative Examples 16 and 17. The result is shown in FIG. The wear amount ratio shown in FIG. 3 is normalized with the wear amount of the valve seat of Comparative Example 1 being 1, and the wear amount ratio of the valve seat of Comparative Example 1 is also shown.

<Result 2>
As shown in FIG. 3, the wear amount ratio of the valve seats of Examples 11 to 15 was smaller than those of Comparative Examples 16 and 17.

<Evaluation 2>
From the results 2, it is preferable that the hard particles for blending sintered alloy is contained in an amount of 10 to 60% by mass with respect to the wear-resistant iron-based sintered alloy. If the effect of the wear resistance by the particles cannot be sufficiently exhibited, and the ratio is large outside this range, the ratio of the iron base is reduced, and as a result, the hard particles are sufficiently adhered to the sintered alloy. It is considered impossible.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed.

  It can be suitably used for a valve system (for example, a valve seat, a valve guide) of an engine that uses compressed natural gas, liquefied petroleum gas, or gasoline as fuel under a high temperature use environment.

Claims (3)

  Hard particles blended as a raw material in the sintered alloy, and in mass% Mo: 20-40%, C: 0.5-1.0%, Ni: 5-30%, Mn: 1-10%, Hard particles for blending sintered alloy, characterized in that Cr: 1 to 10%, Co: 5 to 30%, Y: 0.05 to 2%, and the balance consisting of inevitable impurities and Fe. A powder comprising the sintered alloy compounding hard particles is mixed with a base iron-based powder so as to disperse the sintered alloy compounding hard particles according to claim 1 and sintered, and then the wear-resistant iron group is sintered. A sintered alloy,
10. The wear resistant iron-based sintered alloy, wherein the hard particles for blending the sintered alloy are contained in an amount of 10 to 60% by mass with respect to the wear-resistant iron-based sintered alloy.   A valve seat formed of the wear-resistant iron-based sintered alloy according to claim 2.

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