JP5079417B2 - Manufacturing method of high temperature corrosion resistant wear resistant sintered parts - Google Patents

Description

  The present invention provides a high-temperature corrosion-resistant and wear-resistant ceramic suitable for components that require corrosion resistance and wear resistance in a high-temperature environment, particularly various components of turbochargers attached to internal combustion engines and valve seats of internal combustion engines. The present invention relates to a method for manufacturing a bonded part.

  The components of the turbocharger and the valve seat of the internal combustion engine are required to have heat resistance, corrosion resistance, and wear resistance because they are in contact with exhaust gas that is high temperature corrosive gas. Further, the components of the turbocharger are in sliding contact with the nozzle vane, and the valve seat of the internal combustion engine is in sliding contact with the valve. For this reason, these parts are required to have wear resistance at high temperatures. Therefore, in turbocharger components, conventionally, for example, high Cr cast steel or a material obtained by applying Cr surface treatment to improve corrosion resistance and wear resistance to SCH22 class stipulated in JIS standards has been used. . In recent years, application of sintered materials (Patent Documents 1 and 2, etc.) has also been performed. Further, in the valve seat of an internal combustion engine, various sintered materials (Patent Document 3 etc.) have been conventionally used, and those with improved corrosion resistance (Patent Document 4 etc.) have been proposed.

  Patent Document 1 proposes a sintered alloy in which cobalt alloy particles containing Si, Cr, and Mo and free carbon are dispersed in a nickel-chromium stainless steel base in which metal carbide is dispersed. The base is made of austenitic stainless steel to provide heat resistance, and metal carbides mainly composed of chromium are dispersed in the base to increase the strength of the base. Furthermore, hard cobalt intermetallic compound particles are dispersed to increase the resistance to adhesive wear, and the strength of wear resistance is achieved by the solid lubricating action of free graphite.

  In Patent Document 2, the composition is composed of Cr: 25 to 45%, Mo: 1 to 3%, Si: 1 to 3%, C: 0.5 to 1.5%, the balance Fe and inevitable impurities by mass ratio. A mixed powder obtained by adding 1.0 to 3.3% by mass of Fe: P to 10 to 30% by mass of Fe—P powder and 0.5 to 1.5% by mass of graphite powder to the Fe alloy powder is used. It has been. After molding this mixed powder, by sintering, Cr: 23.8 to 44.3%, Mo: 1.0 to 3.0%, Si: 1.0 to 3.0% by mass ratio, A composition comprising P: 0.1 to 1.0%, C: 1.0 to 3.0%, the balance Fe and inevitable impurities is obtained. This can be used as a turbocharger turbo part in which Mo carbide and Cr carbide are dispersed in a Fe-Cr base.

Japanese Examined Patent Publication No. 05-041693 Japanese Patent No. 3784003 Japanese Patent No. 3661823 Japanese Patent No. 3354401

  In recent years, due to environmental problems, energy saving problems, and the like, higher efficiency of internal combustion engines than ever is required. In order to cope with this, the ultra lean combustion of the internal combustion engine has been advanced, and accordingly, the exhaust gas has become higher temperature. Therefore, turbocharger components and internal combustion engine valve seats are also required to be improved in corrosion resistance and wear resistance in a higher temperature environment. Under such circumstances, the components of the turbocharger described in Patent Document 1 are ones in which chromium carbide is precipitated and dispersed in the base. However, in this case, chromium carbide precipitates along the grain boundary, so that the strength decreases. Further, the precipitation of chromium carbide reduces the amount of Cr in the vicinity of the grain boundary, which easily causes grain boundary corrosion. Moreover, the components of the turbocharger described in Patent Document 2 are manufactured by liquid phase sintering. This is because a relatively large amount of Cr carbide or Mo carbide is dispersed in a large amount and is difficult to machine. Furthermore, the sintered alloy for valve seats described in Patent Document 3 is considered to have lower corrosion resistance than the above-mentioned Patent Documents 1 and 2 because the base is a high-speed tool steel system. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a high-temperature corrosion-resistant and wear-resistant sintered part that is further improved in corrosion resistance and wear resistance in a high-temperature environment and that can be easily machined.

The manufacturing method of the high-temperature corrosion-resistant wear-resistant sintered part of the present invention is, by mass ratio, Cr: 15 to 35%, Ni: 3.5 to 22%, Mo : 5% or less, Nb : 0.1 to 0.1 1.0% , using a raw material powder obtained by mixing and mixing 15-50% of the hard phase forming powder with the stainless steel powder having the balance of Fe and inevitable impurities, and the graphite powder in the amount represented by Equation 1, The raw material powder is compacted into a desired shape, and the obtained molded body is sintered . The hard phase forming powder is, by mass ratio, Mo: 20 to 60%, Cr: 3 to 12%, Si: 1 A method for producing a high-temperature, corrosion-resistant, wear-resistant sintered part, comprising ˜12% and the balance: Co and inevitable impurities .

  In the method for producing a high-temperature corrosion-resistant wear-resistant sintered part of the present invention, as the hard phase forming powder, by mass ratio, Mo: 20 to 60%, Cr: 3 to 12%, Si: 1 to 12%, and The balance: It is preferable to use a material comprising Co and inevitable impurities.

The high-temperature corrosion-resistant wear-resistant sintered part obtained by the production method of the present invention exhibits excellent wear resistance due to precipitation and dispersion of carbides together with a heat-resistant hard phase in a stainless steel composition base. Further, most of the carbides are composed of at least Nb carbides of Mo and Nb, and there are very few carbides of Cr. For this reason, there is almost no fall of the amount of Cr contained in a base, and good corrosion resistance is obtained in each part of parts. Furthermore, since the carbide precipitates finely in the matrix, machining is easy.

(Composition of raw material powder)
The outline of the manufacturing method of the high-temperature corrosion-resistant wear-resistant sintered part of the present invention is as follows. First, a heat-resistant hard phase is dispersed in a base having a stainless steel composition. Furthermore, at least Nb is provided as a solid solution of Mo and Nb, which have higher carbide forming ability than Cr, and C that is bonded to Mo and Nb is provided. In the base of the stainless steel composition thus obtained, Mo carbide and Nb carbide are preferentially precipitated and dispersed as metal carbide. Thereby, precipitation of Cr carbide can be suppressed.

  From the viewpoint of imparting corrosion resistance to the base of sintered parts after sintering, it is effective against Cr, which is an effective element for oxidizing acids such as nitric acid, and non-oxidizing acids such as hydrochloric acid and sulfuric acid. Both Ni which is an effective element are used together. In addition, since it is necessary to uniformly apply the effects of Cr and Ni to the entire base, stainless steel powder provided by dissolving both Cr and Ni in iron powder is used.

  The base of the sintered body after sintering exhibits good corrosion resistance against oxidizing acids by setting the Cr amount to 12% by mass or more. Therefore, even if a small part of Cr contained in the stainless steel powder is precipitated as a carbide during sintering, the present invention ensures that a sufficient amount of Cr remains at the base of the sintered body after sintering. The base Cr content is set to 15 mass% or more. On the other hand, when the amount of Cr in the stainless steel powder exceeds 35% by mass, a brittle σ phase is formed, and the compressibility of the stainless steel powder is significantly impaired. From these things, in this invention, the amount of Cr of the stainless steel powder used as a main raw material powder shall be 15-35 mass%.

  The base of the sintered body after sintering can improve the corrosion resistance against non-oxidizing acid by setting the Ni amount to 3.5% by mass or more, and non-oxidizing at 10% by mass or more regardless of the Cr amount. Good corrosion resistance to acid can be obtained. On the other hand, even if Ni exceeds 22% by mass in the base of the sintered body, the effect of improving corrosion resistance does not change, and since Ni is an expensive element, the upper limit of the amount of Ni contained in the stainless steel powder Was 22 mass%. Therefore, in the present invention, the amount of Ni in the stainless steel powder is 3.5 to 22% by mass, preferably 10 to 22% by mass.

  In addition, the corrosion resistance of steel is superior to the ferrite structure because the austenite structure has a crystallographically higher atomic density. For this reason, it is more preferable to adjust the amount of Cr and the amount of Ni so that the base structure of the sintered body obtained after sintering becomes an austenite structure and to make it contain in the stainless steel powder. For example, in the annealed structure diagram of an Fe—Cr—Ni alloy, the horizontal axis represents the Cr content, the vertical axis represents the Ni content, point A: the Cr content is 15 mass%, the Ni content is 7.5 mass%, and the B point: Cr amount is 18% by mass, Ni amount is 6.5% by mass, point C: Cr amount is 24% by mass and Ni amount is 18% by mass. Since an austenite structure is obtained in a region where the amount of Ni is larger than the polygonal line connecting point A, point B, and point C, adjustment may be made so that the amount of Cr and the amount of Ni are included in this region.

As the base of the above-mentioned stainless steel composition, elements such as Cu, Al, Mn, Si, Se, P, S, and N may be additionally contained as conventionally performed. That is, the base of the above stainless steel composition can contain 1 to 4% of Cu for the purpose of improving acid resistance, corrosion resistance, spot corrosion resistance or imparting precipitation hardenability. Moreover, 0.1-5% of Al can be contained for the purpose of improving weldability, improving heat resistance, or imparting precipitation curability. Furthermore, 0.3% or less of N can be contained for the purpose of adjusting crystal grains and reducing the amount of Ni, and 5.5 to 10% of Mn can be contained for the purpose of reducing the amount of Ni. Si can be contained in an amount of 0.15 to 5% for the purpose of improving oxidation resistance, heat resistance, and sulfuric acid resistance, and Se, P, and S can be contained for the purpose of improving intergranular corrosion resistance and improving free cutting properties.
(Formation of metal carbide)

  In the present invention, high temperature wear resistance is improved by dispersing a hard phase having heat resistance and a metal carbide in the base structure. Among these metal carbides, when a large amount of chromium carbide precipitates, the corrosion resistance of the base is lowered. Therefore, Mo and Nb, which have higher carbide forming ability than Cr, are dissolved in the stainless steel powder. Since Mo and Nb are selectively combined with C added to the raw material powder in the form of graphite powder during sintering, it suppresses the formation of Cr carbide in the base of the stainless steel composition of the sintered part I can do it. Further, unlike Cr carbide, Mo and Nb carbides do not precipitate along the grain boundaries, but precipitate in the grains, so that a decrease in strength can be suppressed. In order to uniformly apply the effect of carbide formation by Mo and Nb to the entire sintered part, it is necessary to dissolve Mo and Nb in the above-mentioned stainless steel powder. Further, when C is given as a solid solution in a stainless steel powder, the powder becomes hard and compressibility is impaired. Therefore, it is necessary to provide C in the form of graphite powder and to mix the above stainless steel powder and graphite powder.

The above Mo, the Nb, Mo is MoC, Mo ₂ C, etc., Nb is NbC, believed to precipitate carbides in the form of such _Nb 4 _{C 3.} Some of them are considered to precipitate in the form of M ₆ C type such as (Fe, Mo) ₆ C and M ₂₃ C ₆ type such as (Fe, Mo) ₂₃ C ₆ . Since it is difficult to control the ratio of these carbides, it is necessary to set the amount of C to be added, that is, the amount of graphite powder added, with a certain range. From such a viewpoint, the amount of graphite powder added to the Mo amount is (0.05 to 0.25) × Mo amount, and the amount of graphite powder added to the Nb amount is (0.12 to 0.25) × Nb amount. Set. Here, when the addition amount of graphite powder is less than the set amount with respect to each element, the amount of precipitated metal carbide decreases and the effect of improving the wear resistance becomes poor. On the other hand, if the amount of graphite powder added exceeds the set amount for each element, excess C forms carbides with the base Cr, and a local Cr concentration lowering portion is formed. This leads to a decrease in corrosion resistance.

In addition, about the addition amount of the graphite powder to a stainless steel powder, it is necessary to add more than the amount spent for said metal carbide formation. This is because graphite powder is consumed to reduce the oxide film on the surface of the stainless steel powder, moisture adsorbed on the powder surface, and the like as CO gas during sintering. The amount of additional C may be 0.3% by mass or less. For this reason, the amount of graphite powder added to the stainless steel powder can be expressed as follows.

  In addition, since the amount of C (addition amount of graphite powder) with respect to Mo and Nb is set with a certain width as described above, a small portion of the base Cr may precipitate as carbide. However, since the Cr amount of the base is set to 15% by mass or more as described above, the Cr amount of the base is 12% by mass even if Cr carbide or a composite carbide with Mo or Nb is precipitated in a small part. It does not fall below and good corrosion resistance can be maintained.

By dispersing the metal carbide in the matrix, the plastic flow of the matrix is suppressed and the wear resistance is improved. In order to form this metal carbide, Mo needs to be 1.5% by mass or more, and Nb needs to be 0.1% by mass or more. By the way, Mo and Nb for forming metal carbides are given as a solid solution in stainless steel powder because it is necessary to exert the effect uniformly on the whole base, but a large amount of Mo and Nb is dissolved in stainless steel powder. And the hardness of the stainless steel powder is increased, the compressibility is significantly lowered, and the compact density is not increased. As a result, the density of the sintered body after sintering is lowered, and the strength and wear resistance are significantly lowered. For this reason, the upper limit of the amount of Mo given by dissolving in a stainless steel powder is 5 mass%, and the upper limit of Nb is 1 mass%. Since these metal carbides are dispersed in the matrix in a fine form (φ10 μm or less), they are excellent in machinability such as cutting.
(Formation of hard phase)

  In the high-temperature corrosion-resistant wear-resistant sintered part of the present invention, in order to disperse the hard phase in the matrix in addition to the metal carbide, the powder for forming the hard phase is further added to the stainless steel powder and the graphite powder. Add the raw material powder. When the amount of the hard phase forming powder added to the raw material powder is less than 15% by mass, the hard phase dispersed in the matrix is scarce and the effect of improving the wear resistance is poor. On the other hand, when it exceeds 50 mass%, the compressibility of the raw material powder is lowered, and the density of the molded body is lowered. As a result, the density of the obtained sintered body is lowered, and the strength and wear resistance of the sintered body are impaired. Moreover, since the amount of pores increases due to a decrease in the density of the sintered body, pitting corrosion is likely to proceed, and corrosion resistance is also impaired.

The hard phase of the high-temperature corrosion-resistant wear-resistant sintered part needs to have hardness and corrosion resistance in a high-temperature environment. From this point, use a Fe-Mo intermetallic compound, a hard phase in which molybdenum silicide is dispersed in the cobalt-based alloy matrix, a hard phase in which Cr carbide is dispersed in the Ni-Cr-based alloy matrix of Patent Document 4, or the like. Can do. Among these, those in which molybdenum silicide is dispersed have both wear resistance and lubricity, and are particularly suitable. The cobalt-based hard phase is formed by adding 15 to 50% by mass of a hard phase forming powder to a powder obtained by mixing the stainless steel powder and the graphite powder, and molding and sintering the powder. Specifically, as a hard phase forming powder, a cobalt-based alloy powder having a composition of Mo: 20 to 60%, Cr: 3 to 12%, Si: 1 to 12%, and the balance of Co and inevitable impurities. Is mentioned. In this cobalt-based alloy powder, if the amount of Mo and the amount of Si are less than the above ranges, the amount of molybdenum silicide precipitated in the alloy base of the heat-resistant hard phase is reduced, and the effect of improving the wear resistance is reduced. Moreover, when the amount of Mo and Si exceeds the above range, the amount of alloy elements dissolved in the hard phase forming powder becomes excessive, the hardness of the powder is remarkably increased, and the compressibility of the raw material powder is impaired. On the other hand, Cr contributes to strengthening of the hard phase cobalt base, and the effect is reduced when the Cr content is not within the above range. On the other hand, if the Cr amount exceeds the above range, the hardness of the powder is remarkably increased and the compressibility of the raw material powder is impaired.
(Method for manufacturing high-temperature corrosion-resistant and wear-resistant sintered parts)

A raw material powder composed of a stainless steel powder containing at least 0.1 to 1.0% of Nb of Mo and Nb, a hard phase forming powder, and a graphite powder is used. As in the past, this raw material powder is filled in a mold hole of a mold having a mold hole of a desired shape, and compacted by an upper and lower punch to form a molded body of a desired shape. The obtained molded body is sintered to become a high-temperature corrosion-resistant wear-resistant sintered part. As an example of the structure of the obtained molded body, it can be represented as shown in FIG. In the structure of the molded body, metal carbide is precipitated and dispersed in a stainless steel matrix containing a hard phase, and pores are included. Here, if the sintering temperature is less than 1000 ° C., the bonding between the powders due to sintering becomes insufficient and the strength becomes poor, and a sufficient amount of metal carbide is not formed, resulting in poor wear resistance. On the other hand, when the sintering temperature exceeds 1300 ° C., the amount of shrinkage due to sintering becomes large and the film is easily deformed, and the dimensional accuracy is lowered. For this reason, the range of 1000-1300 degreeC is suitable for sintering temperature.

  The above high-temperature corrosion-resistant wear-resistant sintered parts can be manufactured by using a conventional machinability-improving substance addition method in combination for improving machinability. The method is a method in which at least one of magnesium silicate mineral, boron nitride, manganese sulfide, calcium fluoride, and chromium sulfide is dispersed in the pores or powder grain boundaries of the above wear-resistant sintered part. . These machinability improving materials are stable even at high temperatures, and even when added to the raw powder in the form of powder, they do not decompose during the sintering process, and are dispersed in the above locations as machinability improving materials to improve machinability. Can improve. By using this machinability improving substance addition method in combination, the machinability of the wear-resistant sintered member can be further improved. Further, if the machinability improving substance powder is added excessively, the strength of the wear-resistant sintered member is impaired, and the wear resistance is reduced. For this reason, when using the machinability improving substance addition method in combination, the upper limit of the addition amount should be limited to 5.0% by mass.

[First embodiment]
The raw material powder is a stainless steel powder having the composition shown in Table 1 and a hard phase-forming powder and graphite powder consisting of Mo: 28%, Si: 2.5%, Cr: 8% and the balance of Co and inevitable impurities. Used as. These powders were added and mixed at a ratio shown in Table 1, and compacted into a disk shape having a diameter of 30 mm and a thickness of 10 mm at a molding pressure of 1.2 GPa. The green compact thus obtained was sintered at 1200 ° C. × 1 Hr in a decomposed ammonia gas atmosphere to prepare samples Nos. 01-13. About these samples, the carbon amount (bonding C amount) couple | bonded with the sample was measured using the carbon analyzer (made by Horiba, Ltd.). Then, the amount of carbon lost by sintering (the amount of loss C) was determined by subtracting the amount of bonded C from the amount of graphite powder added. Moreover, the ratio (C ratio) of the amount of bonded C to the amount of Mo or Nb in the stainless steel powder was calculated. These samples were subjected to an oxidation test and a reciprocating sliding friction test, and the amount of wear after the test was measured. These results are shown in Table 2 and FIGS.

The oxidation test was carried out by placing each test piece in an alumina crucible, placing it in a muffle furnace, and heating it in an air atmosphere at a temperature of 900 ° C. for 100 hours. And the weight difference before and behind a test was measured, and the value which remove | divided this by the geometric surface area was evaluated as oxidation increase (g / m < ² >).

  The reciprocating sliding friction test is a friction test in which the disk-shaped test piece is slid back and forth while pressing the side surface of a roll (counter member) having a diameter of 15 mm and a thickness of 22 mm with a predetermined load. In this test, the surface of molten steel equivalent to JIS standard SUS316 is chromized as a roll material (the surface is coated with chromium and a hard iron-chromium intermetallic compound layer is formed to provide wear resistance, seizure resistance, corrosion resistance, etc. Used to improve the process. A reciprocating sliding friction test was performed under the test conditions of load: 40 N, reciprocating sliding frequency: 20 Hz, reciprocating sliding amplitude: 1.5 mm, test time: 20 min, test temperature: room temperature.

  From the sample numbers 01 to 07 in Tables 1 and 2, it is possible to examine the influence of the ratio (C ratio) of the bond C amount to the Mo amount in the stainless steel powder. From these, the oxidation increase shows a tendency to increase with an increase in the C ratio (an increase in the amount of graphite powder added). Since the addition amount of graphite powder increases as the C ratio increases, it is considered that not only Mo carbides are formed, but also the added C is combined with Cr in the matrix, and Cr carbides are gradually formed. . For this reason, it is thought that some Cr density | concentrations in a base fell and corrosion resistance fell. In particular, in the sample number 07 in which the C ratio exceeds 0.25, the increase rate of the oxidation increase is large. Sample number 01 shows a large wear amount. This is presumably because Mo carbides are hardly generated since the amount of bond C is not recognized. On the other hand, the amount of wear tends to decrease as the C ratio increases (the amount of added graphite powder increases). This is because the amount of graphite powder added increases as the C ratio increases, and the amount of precipitated Mo carbide increases. From these, it can be seen that good corrosion resistance and wear resistance can be obtained when the C ratio to the Mo content in the stainless steel powder is in the range of 0.05 to 0.25.

  From the sample numbers 08 to 13 in Tables 1 and 2, the influence of the ratio (C ratio) of the bond C amount to the Nb amount in the stainless steel powder can be examined. The influence of the C ratio on the amount of Nb shows the same tendency as the influence of the C ratio on the amount of Mo, and good corrosion resistance and resistance in the range where the C ratio with respect to the amount of Nb in the stainless steel powder is 0.12 to 0.25. It can be seen that wear is obtained.

[Second Embodiment]
Next, stainless steel powders having different amounts of Cr and Ni and different amounts of Mo and Nb as shown in Table 3 were prepared. To this, 25% by mass of the hard phase forming powder used in the first example and graphite powder in an amount such that the C ratio to the Mo amount or Nb amount in the stainless steel was 0.2 were added and mixed. The raw material powder thus obtained was molded and sintered under the same conditions as in the first example, and samples Nos. 14 to 26 shown in Table 3 were produced. These samples were subjected to a corrosion resistance test and an abrasion resistance test under the same conditions as in the first example. The results are shown in Table 4 and FIGS. In Tables 3 and 4, the values of sample numbers 05 and 11 of the first example are shown together. Further, the value of sample number 05 is shown in FIG. 4, and the value of sample number 11 is shown in FIG.

  The influence of the amount of Mo in the stainless steel powder can be examined by the sample numbers 05 and 14 to 20 in Tables 3 and 4. Samples Nos. 14 and 15 have a large amount of wear as well as an increased amount of oxidation, and have low corrosion resistance and wear resistance. This is considered because there is almost no amount of bond C in the sample and no metal carbide is precipitated. On the other hand, in sample numbers 05 and 16 to 19 containing 1.5 to 5% by mass of Mo in the stainless steel powder, Mo carbide precipitates and exhibits good wear resistance as well as good corrosion resistance. However, in the sample of sample number 20 in which the Mo amount exceeds 5 mass%, both corrosion resistance and wear resistance tend to decrease. This is presumably because the amount of Mo dissolved in the stainless steel powder is excessive, the compressibility of the raw material powder is impaired, the compact density is lowered, and the sintered density is lowered.

  According to sample numbers 11 and 21 to 26 in Tables 3 and 4, the influence of Nb in the stainless steel powder can be examined. Nb also shows the same tendency as Mo described above, and shows good corrosion resistance and wear resistance when the amount of Nb in the stainless steel powder is 0.1 to 1% by mass, but the amount of Nb exceeds 1% by mass. As a result of the loss of compressibility of the raw material powder, both the corrosion resistance and the wear resistance tend to decrease. From these facts, it is understood that the Mo amount in the stainless steel powder is preferably 1.5 to 5% by mass and the Nb amount is preferably 0.1 to 1% by mass.

[Third embodiment]
Stainless steel powders having different amounts of Mo and Nb and different amounts of Cr and Ni as shown in Table 5 were prepared. The hard phase forming powder used in the first example: 25% by mass and graphite powder: 0.8% by mass were added thereto and mixed. The raw material powder thus obtained was molded and sintered under the same conditions as in the first example, and samples Nos. 27 to 41 shown in Table 5 were produced. These samples were subjected to a corrosion resistance test and an abrasion resistance test under the same conditions as in the first example. The results are also shown in Table 5 and FIGS.

  According to the sample numbers 27 to 33 in Table 5, the influence of the Cr amount in the stainless steel powder can be examined. In the sample No. 27 in which the Cr amount in the stainless steel powder is less than 15% by mass, since the Cr amount is small, the oxidation increase is large. On the other hand, in the sample of sample number 28 in which the amount of Cr in the stainless steel powder is 15% by mass, the increase in oxidation is remarkably suppressed as compared with sample number 27, and the effect of improving corrosion resistance is recognized. In Sample Nos. 28 to 32, when the amount of Cr in the stainless steel powder is increased, the increase in oxidation is reduced, and an improvement in corrosion resistance is observed. In addition, as the amount of Cr in the stainless steel powder increases, the amount of wear tends to decrease, and the effect of improving wear resistance is recognized. This is presumably because a part of Cr in the base was precipitated as carbides due to an increase in the amount of Cr in the base. From the results of the corrosion resistance test, it was also confirmed that the amount of Cr deposited in the base as carbides does not significantly reduce the amount of Cr in the base. On the other hand, in the sample of sample number 33 in which the Cr amount in the stainless steel powder exceeds 35% by mass, the corrosion resistance is lowered. This is presumably because a hard σ phase was generated in the stainless steel powder and the compressibility of the raw material powder was impaired. Thereby, the density of a molded object falls, the density of a sintered compact falls, the amount of pores increases, and as a result, it is thought that corrosion resistance fell. From these facts, it is understood that the Cr content in the stainless steel powder should be in the range of 15 to 35% by mass in order to obtain good corrosion resistance and wear resistance.

  The influence of the amount of Ni in the stainless steel powder can be examined by sample numbers 34 to 41 in Table 5. Sample No. 34 is an example of ferritic stainless steel containing no Ni, and the oxidation increase is small and the corrosion resistance is good. In Sample No. 35 containing 3.5% by mass of Ni, the increase in oxidation was further suppressed, and the effect of improving corrosion resistance due to the Ni content was recognized. However, even if Ni content exceeds 22 mass%, the effect of the further corrosion resistance improvement is not seen. For this reason, it can be said that the Ni content is sufficient up to 22% by mass from the viewpoint of cost. In addition, the inclusion of Ni changes the base structure from ferrite to austenite. This austenite base has a larger solid solubility limit of C than the ferrite base. For this reason, in the sample number 35 used as an austenite base, the precipitation amount of the metal carbide is decreased and the wear amount is slightly increased. However, this decrease in wear resistance is negligible and is not problematic. From these facts, it was confirmed that the inclusion of 3.5 to 22% by mass of Ni is effective in improving the corrosion resistance.

[Fourth embodiment]
A stainless steel powder having a composition by mass ratio of Cr: 25%, Ni: 20%, Mo: 1.5%, Nb: 0.2%, and the balance of Fe and inevitable impurities was prepared. Graphite powder: 0.4% by mass, and the hard phase forming powder used in the first example were added at different ratios as shown in Table 6 and mixed. The raw material powder thus obtained was molded and sintered under the same conditions as in the first example, and samples Nos. 42 to 51 shown in Table 6 were produced. These samples were subjected to a corrosion resistance test and an abrasion resistance test under the same conditions as in the first example. The results are also shown in Table 6 and FIG.

  From Table 6, the influence of the addition amount of the hard phase forming alloy powder, that is, the amount of the hard phase dispersed in the matrix after sintering can be examined. In the samples of sample numbers 42 to 44 in which the addition amount of the hard phase forming alloy powder is less than 15% by mass, the amount of wear is large because the amount of dispersion of the hard phase formed after sintering is poor. On the other hand, in the sample of Sample No. 45 with the addition amount of the hard phase forming alloy powder 15%, the wear amount is remarkably reduced, and as the addition amount of the hard phase forming alloy powder increases, the wear amount tends to decrease. Raru. When the addition amount of the hard phase forming alloy powder is 40% by mass or more (sample numbers 49 to 51), the wear amount is extremely small and becomes a constant value.

  On the other hand, the oxidation increase shows a tendency to increase as the addition amount of the hard phase forming alloy powder increases. This is because the compressibility of the raw material powder decreases as the addition amount of the hard phase forming alloy powder increases, and the compact density decreases accordingly, and the pores of the sample increase (specific surface area increases). . Further, as the addition amount of the hard phase forming alloy powder increases, the addition amount of the stainless steel powder forming the base decreases. However, since the amount of graphite powder added is constant, it is considered that not only the carbides of Mo and Nb contained in the matrix of the sample but also Cr in the matrix starts to precipitate as carbides. Therefore, it can be said that the corrosion resistance of the base tends to decrease. This increase in oxidation shows a tendency to increase at a substantially constant rate until the addition amount of the hard phase forming alloy powder is 50% by mass. On the other hand, in the sample of sample number 51 in which the addition amount of the hard phase forming alloy powder exceeds 50% by mass, the increase rate of the oxidation increase is large. From these facts, it is understood that the addition amount of the hard phase forming alloy powder should be 15 to 50% by mass.

  The high-temperature corrosion-resistant and wear-resistant sintered part obtained by the manufacturing method of the high-temperature corrosion-resistant and wear-resistant sintered part of the present invention exhibits excellent wear resistance and corrosion resistance, and is easy to machine. It is suitable for parts that require wear resistance as well as corrosion resistance and wear resistance in a high temperature environment such as a valve seat of an internal combustion engine.

It is the schematic which shows an example of the structure | tissue of the molded object obtained by the manufacturing method of the high temperature corrosion-resistant abrasion-resistant sintered part of this invention. It is a graph which shows the relationship between the oxidation increase of the sample (sample number 01-07) used in 1st Example, or the abrasion loss, and C ratio. It is a graph which shows the relationship between the oxidation increase of the sample (sample number 08-13) used in 1st Example, or the abrasion loss, and C ratio. It is a graph which shows the relationship between the oxidation increase amount or abrasion amount of the sample (sample number 05, 14-20) used in 2nd Example, and the amount of Mo in stainless steel powder. It is a graph which shows the relationship between the oxidation increase amount or abrasion amount of the sample (sample number 11,21-26) used in 2nd Example, and the amount of Nb in stainless steel powder. It is a graph which shows the relationship between the oxidation increase amount or abrasion amount of the sample (sample number 27-33) used in 3rd Example, and the Cr amount in a stainless steel powder. It is a graph which shows the relationship between the oxidation increase amount or abrasion amount of the sample (sample number 34-41) used in 3rd Example, and the amount of Ni in a stainless steel powder. It is a graph which shows the relationship between the oxidation increase amount or abrasion amount of the sample used in 4th Example, and the addition amount of hard phase formation alloy powder.

Claims (3)

Stainless steel powder with a mass ratio of Cr: 15-35%, Ni: 3.5-22%, Mo : 5% or less, Nb : 0.1-1.0% , the balance being Fe and inevitable impurities A molding obtained by compacting the raw material powder into a desired shape using a raw material powder obtained by mixing 15-50% of the hard phase forming powder and the graphite powder in the amount represented by Equation 1 The hard phase-forming powder is composed of Mo: 20 to 60%, Cr: 3 to 12%, Si: 1 to 12%, and the balance: Co and inevitable impurities. A method for producing high-temperature corrosion-resistant wear-resistant sintered parts.

  The method for producing a high-temperature corrosion-resistant wear-resistant sintered part according to claim 1, wherein the amount of Mo in the stainless steel powder is 1.5 to 5% by mass. The raw material powder further 5 mass% of manganese sulfide powder, chromium sulfide powder, according to claim 1 or 2 calcium fluoride powder, characterized in that adding and mixing at least one of magnesium silicate mineral powder A method for producing a high-temperature corrosion-resistant wear-resistant sintered part as described in 1.

Images