JP2018172768A - Heat-resistant sintering material having excellent oxidation resistance, high temperature wear resistance, and salt damage resistance, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-resistant sintering material that has excellent oxidation resistance and is also excellent in both of high temperature wear resistance and salt damage resistance, and a method for producing the heat-resistant sintering material.SOLUTION: A heat-resistant sintering material that is excellent in oxidation resistance, high temperature wear resistance, and salt damage resistance, has a structure in which hard phases are dispersed in a host phase. The total composition has a structure consisting of, in mass%, Cr: 20-38%, Mo: 0.5-3%, Si: 3-7%, C: 0.5-2.5%, with the balance being Fe and unavoidable impurities. The host phase comprises Fe-Cr-Mo-Si, the hard phase comprises Cr-Fe-Mo-C, and the material has a porosity of 2.0% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to heat-resistant sintering excellent in oxidation resistance, high-temperature wear resistance, and salt damage resistance, and a method for producing the same.

Turbo of the internal combustion engine that uses the energy of exhaust gas to rotate the turbine at high speed, drives the centrifugal compressor using the rotational force, and sends the compressed air into the engine to increase the thermal efficiency of the internal combustion engine The charger is known.
A turbocharger attached to an internal combustion engine is provided with a nozzle mechanism and a valve mechanism for diverting a part of exhaust gas and adjusting the amount of flow into the turbine.
The mechanical parts such as bearings and bushes incorporated in this turbocharger are always exposed to high-temperature and corrosive exhaust gas discharged from the engine, and are also movable parts and have excellent sliding characteristics. desired.

In sliding parts exposed to this type of high temperature and corrosive exhaust gas, conventionally, heat resistant parts made of high Cr cast steel melt or sintered material have been used.
As an example of a conventionally known turbocharger component, Cr: 32.4 to 48.4%, Mo: 2.9 to 10.0%, Si: 0.9 to 2.9%, P in mass ratio : 0.3 to 1.8%, C: 0.7 to 3.9%, the entire composition composed of Fe and unavoidable impurities, sintered with a density ratio of 90% or more and carbide dispersed in the matrix A material is known (see Patent Document 1).

JP 2016-188409 A

The properties desired for this type of conventional heat-resistant parts, including the sintered material described in Patent Document 1, include oxidation resistance, wear resistance (self-wear resistance), salt damage resistance, and the like. Development of melted or sintered materials of high Cr cast steel that can be satisfied is underway.
For example, an alloy having a composition of Fe-34Cr-2Mo-2Si-1.2C is known as a molten material for ferritic high Cr cast steel, and Fe-34Cr-2Mo- as a sintered material for ferritic high Cr cast steel. A sintered alloy having a composition of 2Si-2C is known.

Conventionally, bushes that may be exposed to the outside among turbo parts are required to be resistant to salt damage in addition to oxidation resistance and wear resistance.
On the other hand, even if it is a high Cr cast steel containing 34% Cr as a whole composition, the amount of parent phase Cr is about 28%, and this high Cr cast steel is excellent in salt damage resistance but lacks oxidation resistance. However, a significant improvement is desired in terms of wear resistance. Further, since the sintered material described in Patent Document 1 which is a sintered material of high Cr cast steel has a large amount of precipitation of chromium carbide which is a hard phase, the amount of Cr in the parent phase is reduced. For this reason, the sintered material described in Patent Document 1 has a problem that the salt damage resistance cannot be satisfied.
On the other hand, the melted material has less hard phase in the structure, so the amount of Cr in the parent phase is large and the salt damage resistance is excellent, but there is a problem that the wear resistance is inferior because there are few hard phases. .

Therefore, if the amount of Mo added is increased and the amount of Cr carbide dispersed is increased, the hard phase can be increased, but most of Mo will be included in the hard phase, and the parent phase due to carbide precipitation. The amount of Cr reduction cannot be reduced. Therefore, the periphery of the matrix phase is not entirely covered with the hard phase, so that the salt damage resistance is still inadequate even for a material with an increased amount of Mo.
As described above, the prior art has not provided a material that can satisfy both the characteristics of wear resistance and salt damage resistance while having oxidation resistance.
For this reason, conventional materials are difficult to achieve both wear resistance and salt damage resistance, and have been used at the expense of either wear resistance or salt damage resistance.

  In the above background, the present inventor has intensively studied the wear resistance and salt damage resistance in the sintered material. By using a chromium carbide-based precipitate as a hard phase for obtaining wear resistance, The amount of Cr in the steel decreases, but it has been found that the hardness of the parent phase can be increased by diffusing Si in the parent phase to compensate for the decrease in hardness due to the decrease in the amount of Cr, and the wear resistance can be improved even if the hard phase is small. . Utilizing this relationship, the inventors have found that it is possible to provide a heat-resistant sintered material that has both oxidation resistance and excellent wear resistance and salt damage resistance, and has reached the present invention.

  The present invention has been made in view of the circumstances as described above, and provides a heat-resistant sintered material having both oxidation resistance and excellent wear resistance and salt damage resistance, and a method for producing the same. With the goal.

(1) In order to solve the above-mentioned problems, the heat-resistant sintered material of the present invention has a structure in which a hard phase is dispersed in a matrix phase, and the total composition is Cr: 20 to 38%, Mo: 0. 5 to 3%, Si: 3 to 7%, C: 0.5 to 2.5%, the balance is composed of Fe and inevitable impurities, and the parent phase is composed of Fe-Cr-Mo-Si The hard phase is made of Cr—Fe—Mo—C and has a porosity of 2.0% or less.

When the hard phase containing Cr, Fe, Mo, and C is dispersed in the matrix containing Fe, Cr, Mo, and Si, the strength of the matrix is increased by adding Si, and the chromium carbide-based structure is added. Abrasion resistance can be improved by the dispersion of the hard phase. Further, a dense sintered material can be obtained by reducing the porosity to obtain a dense structure. For this reason, there is little possibility that corrosion will progress to the inside even if it is exposed to corrosive liquid or gas, and a sintered material excellent in salt damage resistance can be obtained.
Therefore, it is possible to provide a heat-resistant sintered material that can achieve both excellent salt damage resistance and wear resistance while maintaining excellent oxidation resistance.

(2) In addition to Cr, Mo, Si, and C in the overall composition of the present invention, B: 0.08 to 0.8% or P: 0.2 to 1.2% is contained, with the balance being Fe and inevitable A configuration that is an impurity can be employed.
(3) In the present invention, it is possible to adopt a configuration in which the parent phase is made of a ferrite fabric, and 10 to 40% by volume of hard particles made of Cr—Fe—Mo—C are dispersed in the ferrite fabric.

(4) The method for producing a heat-resistant sintered material having excellent oxidation resistance, high-temperature wear resistance, and salt damage resistance according to the present invention comprises at least Fe, Cr, and Si, and further contains Mo as required. Additive powder containing at least Si and C, and further containing at least one of Fe, Cr, and Mo, if necessary, Cr: 20-38%, Mo: 0.5-3%, Si: 3 to 7%, C: 0.5 to 2.5%, the step of mixing so that the balance is composed of Fe and inevitable impurities to obtain a mixed powder, and pressing the mixed powder to obtain a green compact And a structure in which the green compact is heated to 1100 to 1280 ° C. and a hard phase containing Cr, Fe, Mo, and C is dispersed in a matrix containing Fe, Cr, Mo, and Si. And a step of forming a sintered body having a porosity of 2.0% or less.

When preparing the raw material powder, the base powder containing at least Fe, Cr and Si, and further containing Mo if necessary, contains at least Si and C, and if necessary, further contains at least one of Fe, Cr and Mo. When the additive powder containing is mixed, the raw material powder can be adjusted in a state where the amount of Si contained in the base powder is suppressed. And Si contained in additive powder can be diffused at the time of sintering, and Si content by the side of a mother phase can be made high in the range of 3.5 to 7.0%.
If the base powder contains the desired high concentration of Si from the beginning, the base powder becomes too hard, and when the raw material powder is pressed into a green compact, the density cannot be increased. The porosity cannot be lowered.
For this reason, by using the above-mentioned raw material mixed powder, the strength of the matrix after sintering can be increased, and an excellent wear-resistant heat-resistant sintered material can be produced in combination with the precipitation of the hard phase. In addition, a heat-resistant sintered material excellent in salt damage resistance can be obtained by including a high concentration of Si in the matrix and lowering the porosity.

(5) In the production method of the present invention, FeB powder is added to the mixed powder so that the B: 0.08 to 0.8% with respect to the total composition, or the FeP powder with respect to the total composition is P: 0.2. It can mix so that it may become -1.2%.
(6) In the production method of the present invention, the hard phase can be dispersed in an amount of 10 to 40% by volume in the matrix phase by the step of forming the sintered body.

The present invention contains a specific amount of Fe, Cr, Mo, Si, and C in the overall composition, and a hard phase containing Cr, Fe, Mo, and C is dispersed in a parent phase containing Fe, Cr, Mo, and Si. The strength of the matrix phase is increased by increasing the amount of Si contained in the matrix and contained in the matrix phase, and the wear resistance can be improved by the dispersion of the chromium carbide hard phase. Further, a dense sintered material can be obtained by reducing the porosity to obtain a dense structure. For this reason, there is little possibility that corrosion will progress to the inside even if it is exposed to corrosive liquid or gas, and a sintered material excellent in salt damage resistance can be obtained.
Therefore, it is possible to provide a heat-resistant sintered material that can achieve both excellent salt damage resistance and wear resistance while maintaining excellent oxidation resistance.
For this reason, the heat-resistant sintered material of the present application is always exposed to mechanical parts such as bearings and bushes incorporated in the turbocharger, high-temperature and corrosive exhaust gas discharged from the engine, and is a movable part with sliding characteristics. It can be effectively applied as a mechanical component that is excellent in terms of surface.

The perspective view which shows an example of the bearing member formed with the sintered sliding material which concerns on this invention. The schematic diagram which shows an example of the metal structure of a coaxial receiving member. The structure photograph which shows an example of the metal structure of the sample manufactured in the Example. The graph which shows the result of having measured the relationship between the whole Cr amount and the amount of mother phase Cr about a part of Example sample.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a cylindrical bearing member 1 made of a heat-resistant sintered material according to the present invention. This bearing member 1 is used for a bearing incorporated in a nozzle mechanism or a valve mechanism for a turbocharger as an example. FIG. 2 is a schematic diagram of an enlarged structure photograph of the heat-resistant sintered material constituting the bearing member 1.
As an example, the heat-resistant sintered material includes a plurality of amorphous hard phases 3 containing Fe, Cr, Mo, and C dispersed in a parent phase 2 containing Fe, Cr, Mo, and Si as shown in FIG. Have an organization. Further, a plurality of pores (pores) 5 indicated by black circles are scattered in the structure shown in FIG.
As an example, the mother phase 2 contains Cr: 15 to 35% by mass, Mo: 0.4 to 2.5%, Si: 3.5 to 7.0%, and a composition comprising the balance Fe and inevitable impurities. Have. In order to obtain such a mother phase 2, it is necessary to contain 20 to 38% of Cr as a whole composition.
As an example, the hard phase 3 contains Cr: 40 to 75% by mass, Mo: 1.0 to 4.5%, C: 5.0 to 8.5%, and the balance Fe and inevitable impurities. Have. The volume fraction of the hard phase 3 with respect to the whole structure is preferably in the range of 10 to 40%.
Moreover, the whole composition contains Cr: 20-38%, Mo: 0.5-3.0%, Si: 3.0-7.0%, C: 0.5-2.5% in mass% In addition, it is preferably a heat-resistant sintered material having a composition composed of the remaining Fe and inevitable impurities and having a porosity of 2.0% or less in the entire structure.

The parent phase 2 containing Fe, Cr, Mo and Si is made of Fe—Cr—Mo—Si as an example, and the hard phase 3 containing Fe, Cr, Mo and C is made of Cr—Fe—Mo—C as an example. This is a carbide phase.
In addition, about the composition of the mother phase 2 and the hard phase 3, it turns out that it is the above-mentioned composition from the EDX analysis (energy dispersive X-ray fluorescence analysis) result of the Example sample mentioned later.

Hereinafter, the reasons for limiting each composition ratio in the heat-resistant sintered material of this embodiment will be described.
“Cr content: 20 to 38% by mass”
From the viewpoint of oxidation resistance, the amount of Cr in the mother phase 2 must be at least 12% by mass in the matrix, and 28% by mass in order to satisfy salt damage resistance in addition to oxidation resistance. It is necessary to be included above. However, since Si and Mo also contribute to oxidation resistance and salt damage resistance, the Cr content should be 15% by mass or more. Moreover, when it exceeds 35 mass%, there is also an influence of Si addition, and although there is little Cr amount, there exists a possibility that a (sigma) phase may be formed and it may become very weak. Moreover, since salt damage resistance also deteriorates, it is preferable that the amount of Cr of the mother phase 2 is 15 to 35% by mass.
Since the amount of Cr in the parent phase 2 decreases due to the precipitation of the hard phase 3, in order to satisfy 15 to 35% by mass as the amount of Cr in the mother phase 2, it is necessary to make the Cr content 20 to 38% by mass as a whole.

“Mo amount: 0.5 to 3.0 mass%”
Mo contributes to improvement of salt damage resistance. Containing 0.5% by mass or more of Mo contributes to improvement of salt damage resistance, and the improvement effect is effective even if it exceeds 3.0% by mass, but the effect is saturated. Since Mo is an expensive element, it is desirable in terms of cost to have a small Mo content. In addition, since it contributes to the formation of the σ phase of Cr in the parent phase 2, the upper limit of the Mo content should be 3.0% by mass. Is preferred. In order to make the amount of Mo of the mother phase 2 0.4 mass% or more, it is preferable that Mo is contained 0.5 mass% or more as a whole.

“Si amount: 3.0 to 7.0 mass%”
To satisfy the salt damage resistance, the amount of Si in the mother phase 2 needs to be 3.5% or more. For that purpose, the Si amount as a whole is required to be 3.0% by mass or more. When the total amount of Si exceeds 7.0% by mass, the material becomes too hard and the machinability is deteriorated, which may result in a material lacking in mass productivity. Therefore, the total Si amount needs to be 3.0 to 7.0% by mass from the viewpoint of salt damage resistance, wear resistance, and mass productivity.

“C amount: 0.5 to 2.5 mass%”
When the total amount of C is less than 0.5% by mass, the amount of precipitated hard phase 3 is small and the wear resistance is not satisfied. On the other hand, when the total amount of C exceeds 2.5% by mass, the amount of the hard phase 3 precipitated becomes too large, and the amount of Cr in the parent phase 2 is decreased, so that the salt damage resistance is not satisfied. Therefore, the amount of C contained in the whole needs to be 0.5-2.5 mass%.
“Porosity: 2.0% or less”
When the porosity is large, the surface area increases and oxidation is likely to occur. Therefore, the smaller the porosity, the better the oxidation resistance and salt damage resistance, and the porosity is preferably 2.0% or less.

"Production method"
The method for producing the heat-resistant sintered material will be described in detail later. As an example, Fe-Cr-Mo-Si alloy powder as a base powder, SiC powder as an additive, and FeB powder as a sintering aid are used. The mixed powder obtained by weighing and uniformly mixing the above composition range is press-molded at a pressure of about 490 to 980 MPa, and the obtained press-molded body is obtained at 1100 to 1280 ° C. for 0.5 to 2 hours. Obtained by sintering to a certain extent.
The base powder may be Fe-Cr-Si alloy powder instead of Fe-Cr-Mo-Si alloy powder. FeP powder can be used instead of FeB powder as a sintering aid, but the sintering aid may be omitted.
In addition to SiC, the additive powder may be mixed with FeSi powder, CrSi powder, C powder, FeCr alloy powder, FeMo alloy powder or the like so as to have the above-mentioned composition range with respect to the base powder.

When each of the powders described above is used, the particle size (D50) of each powder is preferably about 5 to 100 μm.
When FeB powder is used as a sintering aid, the amount of B added to the whole is preferably in the range of 0.08 to 0.8%.
When FeP powder is used as a sintering aid, the amount of P added to the whole is preferably 0.2 to 1.2%.
As the sintering aid, FeP may be used in addition to FeB, or a mixture thereof may be used. When the particle size of the powder to be used is 5 to 20 μm to make a fine powder, these sintering aids are omitted. May be.

When preparing a raw material mixed powder, if a raw material powder having a particle size of about 30 to 100 μm is used, if a sintering aid is added at about 0.4 to 4.0% and sintered, the desired heat resistance is obtained. A sintered material can be manufactured. When the sintering aid is not used, the target heat-resistant sintered material can be produced by making the particle size of the raw material powder as fine as about 5 to 20 μm.
When using the raw material powder having the above-mentioned particle size and using FeB as a sintering aid, the amount of B added to the whole is less than 0.08% in order to reduce the density so that the oxidation resistance, salt damage resistance, Any of the wear resistance may deteriorate. If the amount of B added to the whole exceeds 0.8%, deformation after sintering becomes large, and the target shape cannot be maintained. For example, when the bearing member 1 as shown in FIG. 1 is used, the inner diameter or the outer diameter may change, and the product shape may not be maintained.
When the raw material powder having the above-mentioned particle size is used and FeP is used as a sintering aid, the amount of P added to the whole is less than 0.2%, any of oxidation resistance, salt damage resistance, and wear resistance. When the amount of addition exceeds 1.2%, salt damage resistance and wear resistance are reduced.

As a raw material powder, a powder having a particle size (D50) of 10 μm can be sufficiently produced. However, when the particle size is 10 μm or less, the surface area ratio increases with respect to the volume of the powder, the amount of oxygen in the powder increases, and the sinterability increases. descend. Therefore, if a fine powder having a particle size of 5 μm or less is used, a porosity of 2% or less may not be achieved. In the case of fine powder, for example, one having a particle size of 5 to 20 μm can be used, and in the case of a raw material powder having a particle size larger than that, it is necessary to add a sintering aid.
Since the base powder has a large amount of Cr and is easily oxidized, Si is required to suppress the amount of oxygen. The amount of Si can be made slightly lower than 1%, but about 0.5 to 0.8% is contained to suppress the amount of oxygen. For this reason, it is desirable that the base powder contains about 1% Si. The Si amount of the matrix 2 can be adjusted to 3.5% or more by adding a necessary amount of CrSi powder as a Si source.

The mixed powder is put into a mold of a press apparatus and press-molded to obtain a green compact having a desired shape, for example, a cylindrical shape.
In the case of molding, various methods such as hot isostatic pressing (HIP) and cold isostatic pressing (CIP) may be employed in addition to molding by a press device.
For example, the green compact is sintered in a vacuum atmosphere or a nitrogen atmosphere at a predetermined temperature within a range of 1100 to 1280 ° C. for about 0.5 to 2 hours, thereby allowing the mother body containing Fe, Cr, Mo, and Si. For example, a cylindrical bearing member 1 shown in FIG. 1 made of a heat-resistant sintered material in which a carbide-based hard phase containing Cr, Fe, Mo, and C is dispersed in the phase can be obtained.
The heat-resistant sintered material constituting the bearing member 1 has, for example, a metal structure in which a carbide-based hard phase 3 is dispersed in a FeCrMoSi matrix phase 2 as shown in FIG. FIG. 2 is a schematic diagram of a photograph in which a part of the structure is magnified by an optical microscope with respect to an example of a heat-resistant sintered material sample manufactured in Examples described later. As shown in FIG. 2, in the metal structure of the heat-resistant sintered material 1, pores 5 generated during sintering may remain (approximately 2.0% or less).

  When FeCrMoSi alloy powder, FeB powder, and SiC powder are mixed, press-molded and then sintered, FeB becomes a liquid phase and wets and spreads at the grain boundaries of other powder particles, thereby filling pores. Therefore, the grain boundary between the FeCrMoSi alloy powder and the SiC powder can be filled with FeB in a liquid phase, so that the porosity after sintering can be reduced. Therefore, it can be set as a high-density sintered material.

Fe and B constituting the FeB powder have a eutectic point at 1174 ° C. with a composition of Fe-4 mass% B as is clear from the FeB binary phase diagram. The liquid phase acts as a sintering aid and improves the sintered density. Therefore, it is possible to obtain a sintered body having a low porosity and a high density after sintering, that is, a dense sintered body having a low porosity. The low porosity makes it difficult for corrosive liquids and gases to enter the sintered body from the outside, contributing to an improvement in oxidation resistance.
When sintering at the above temperature, Fe, Cr, Mo, and C existing around the FeCrMoSi alloy powder are interdiffused, so that the carbide-based hard phase 3 is precipitated and dispersed between these hard phase 3 matrix phases. Become an organization. That is, it becomes a structure in which the hard phase 3 which is a carbide-based precipitate having a Cr—Fe—Mo—C composition is dispersed between the Fe—Cr—Mo—Si matrix. A suitable wear resistance can be obtained by the dispersion of the hard phase 3.

The Fe-Cr-Mo-Si alloy powder used as the base powder contains Si, but if more than 1% of Si is added to the base powder, it becomes too hard and difficult to compress during press molding. The amount of Si to be added is preferably 1.0% or less.
When producing a heat-resistant sintered material using a base powder containing 1.0% or less of Si, as an additive to contain 3.0 to 7.0% by mass of Si in the matrix 2 after sintering Use SiC powder. By sintering at the above-mentioned temperature and pressure conditions, Si diffuses from the SiC powder to the base powder side, and the hard phase 3 is deposited on the base mainly composed of the base powder. Si diffuses from the SiC powder to the substrate side, the amount of Si on the substrate side increases so as to be added to the amount of Si contained in the base powder, and an amount of hard according to the amount of C contained in the additive Phase 3 is precipitated, and a heat-resistant sintered material having the structure shown in FIG. 2 is obtained.

The mother phase 2 made of Fe-Cr-Mo-Si containing Cr, Mo, and Si in the Fe base ensures oxidation resistance and salt damage resistance. Further, 3.0 to 7.0% added to the mother phase 2 The strength of the parent phase 2 can be increased due to the influence of Si. Further, an amount of Cr—Fe—Mo—C hard phase 3 corresponding to the amount of C supplied from the additive SiC is precipitated, and the wear resistance of hard phase 3 and the strength improvement effect of parent phase 2 are in phase. As a result, excellent wear resistance is obtained.
When the hard phase 3 is formed, the hard phase 3 takes some Cr from the mother phase 2, but Si is diffused in the mother phase to contain 3.0 to 7.0% of high concentration Si in the mother phase. Thus, the salt damage resistance of the mother phase can be improved and the strength of the mother phase can be increased.

  In the present embodiment, the ring-shaped bearing member 1 is configured using the above-described heat-resistant sintered material. However, the heat-resistant sintered material of the present embodiment is a shaft member provided in a nozzle mechanism or a valve mechanism of a turbocharger. Of course, it can be widely applied to rod members, bearing members, plates and the like.

In the heat-resistant sintered material obtained by the manufacturing method described above, since both the parent phase and the hard phase contain a sufficient amount of Cr, it exhibits good oxidation resistance and salt resistance, and the hard phase is harder than the parent phase Since it consists of a hard phase and the strength of the parent phase is improved by the mother phase containing a large amount of Si, it has good wear resistance in addition to good oxidation resistance and salt damage resistance.
Therefore, the above-described bearing member 1 is applied to a bearing portion such as a turbocharger, and is excellent in oxidation resistance, salt resistance, and resistance even when it is slid by a shaft while being exposed to high-temperature exhaust gas. Excellent wear resistance.

  In addition, the heat-resistant sintered material of this embodiment can be used as a constituent material of the shaft of the turbocharger, as well as various mechanical parts provided in an environment exposed to high-temperature corrosive gas with respect to oxidation resistance, salt damage resistance, and wear resistance. Of course, it can be used as a component.

EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further in detail, this invention is not limited to these Examples.
As raw material powder, Fe-Cr-Mo-Si alloy powder (base powder), FeB powder (sintering aid) and SiC powder (additive) shown in Table 1 are prepared, and these powders are shown in the following table. After blending so as to have the final component composition and mixing with a V-type mixer for 30 minutes, this mixed powder was press-molded at a molding pressure of 490 to 980 MPa to produce a cylindrical green compact.
Next, this green compact was sintered in a vacuum atmosphere at a temperature of 1100 to 1280 ° C. for 0.5 to 2.0 hours to obtain a cylindrical heat-resistant sintered material.
Each heat-resistant sintered material was formed into a suitable shape for each of the following tests and used for each test.

Further, as another test example, so as to have the composition shown in Table 1 below, any powder of SiC, FeSi, or CrSi is used as the Si source with respect to the base powder, and C (carbon powder) is used as the C source. In order to adjust the Cr amount and the Mo amount, any powder of CrSi, FeCr, FeMo is used. 1-No. 31 samples were prepared.
Further, a heat-resistant sintered material sample was manufactured by properly using either the FeB or FeP powder as a sintering aid and the case where the sintering aid is omitted, and using the following other additive powders as additives.

When the samples No. 1 to 31 were prepared, the average particle size of the powder used was FeCrMoSi alloy powder (D50 = 100 μm), FeCrSi alloy powder (D50 = 100 μm), FeCr alloy powder (D50 = 40 μm), SiC powder. (D50 = 10 μm), C powder (D50 = 20 μm), CrSi powder (D50 = 10 μm), and FeMo powder (D50 = 60 μm) were used. Further, FeB powder (D50 = 30 μm) and FeP powder (D50 = 30 μm) were used as sintering aids.
When the samples No. 26 to 31 were prepared, fine powder of FeCrMoSi alloy powder (D50 = 8 μm) was used.

"Porosity"
The porosity was measured by Archimedes method.
"Oxidation resistance test"
In the oxidation resistance test, a ring-shaped heat-resistant sintered material (bearing member) having a size of outer diameter: 20 mm × inner diameter: 10 mm × height: 5 mm and having the composition components shown in Tables 1 to 5 below. Obtained and tested.
The conditions were maintained at 800 ° C. in the atmosphere for 100 hours, and the oxidation increase was determined from the change in weight and the surface area of the sample. The criterion for determining the amount of increase in oxidation was 1 mg / cm ² or less as ◯, and when exceeding this value, it was marked as x.

"Abrasion resistance test"
In order to perform the roll-on block test, a test was performed in which a cylindrical shaft was placed on the block and rotated 90 ° reciprocally. The measurement was performed at a temperature of 600 ° C. for 30 minutes, and the amount of wear was evaluated with 2000 reciprocations.
The amount of wear was measured by taking a photograph of the wear surface with a 3D microscope and measuring the wear depth. The shape of the abrasion test piece is a rectangular parallelepiped block made of a sintered material having a thickness of 50 × 10 × 5 mm. The shaft of the mating member is a stainless steel rod made of SUS316 having a diameter of 8 mm and a length of 150 mm. The stainless steel rod was pressed against the block at a load of 80 N, and tested by reciprocating as a motor rotation shaft.
Judgment criteria of the abrasion resistance test were ○ for samples of less than 40 μm and x for samples of 40 μm or more.

"Salt damage resistance test"
The salt damage resistance was grasped by a salt spray test (according to JISZ2371). The appearance area ratio of rust on the appearance was evaluated by spraying a salt solution with a 5% NaCl aqueous solution (35 ° C., 24 hours), and a sample having a corrosion area ratio of 1% or less due to the occurrence of rust was accepted. The test piece is a ring-shaped test piece having an outer diameter of 20 mm, an inner diameter of 10 mm, and a height of 5 mm.
The symbol ○ indicates that the corrosion area ratio due to rust is 1% or less, and the symbol X indicates that the corrosion area ratio due to rust exceeds 1%.
The above test results are shown in Table 1 below.

About heat resistance sintered material sample No. 1-31 for every total composition (whole composition) shown in Table 1, about the oxidation resistance test result (oxidation increase), the measurement result of porosity, those determination results, and salt damage resistance The test results of the rust area ratio and the wear amount and the determination result of the wear resistance are shown.
From the results shown in Table 1, the overall composition is% by mass: Cr: 20-38%, Mo: 0.5-3%, Si: 3-7%, C: 0.5-2.5%, the balance being Fe And the composition is composed of inevitable impurities, the parent phase is composed of an Fe—Cr—Mo—Si based alloy, the hard phase is composed of a Cr—Fe—Mo—C based alloy, and the porosity is 2.0% or less. No. 1-3, 8, 9, 18, 21-23, 26, 27, 29-31 heat resistant sintered material, excellent oxidation resistance, high temperature wear resistance, salt resistance It is clear that it is excellent.

Samples Nos. 4 and 5 use FeB as a sintering aid, fill the gap in the green compact with FeB as the liquid phase during sintering, and lower the total B amount from the lower limit of the desired B amount when keeping the porosity low. This is a reduced example. When the raw material powder having a particle size in the above range was used, both the oxidation resistance and salt damage resistance deteriorated when the amount of FeB added as a sintering aid was as small as 0.06%.
On the contrary, when the raw material powder having a particle size in the above range is used, if the amount of FeB added as a sintering aid is too large, 0.90%, the oxidation resistance, salt damage resistance, and wear resistance are improved. However, the No. 6 sample was greatly deformed after sintering, and the No. 7 sample was difficult to maintain its shape. From this result, when the raw material powder having the above-mentioned particle size is used and FeB is used as the sintering aid, the addition amount of the sintering aid B is desirably in the range of 0.08 to 0.8%.

The sample No. 10 is a sample in which the Cr amount of the entire composition is less than the desired range of 20 to 38%, but results in poor salt damage resistance, and the sample No. 11 is the amount of Cr of the entire composition. However, the salt damage resistance was inferior, although the sample was more than the desired range of 20 to 38%.
The sample No. 12 is a sample in which the amount of C in the overall composition is less than the desired range of 0.5 to 2.5%, but results in poor wear resistance. Although it was a sample in which the amount of C was larger than the desirable range of 0.5 to 2.5%, the salt damage resistance was inferior.

The sample No. 14 is a sample in which the Si amount of the entire composition is excessively less than the desired range of 3.0 to 7.0%, but results in inferior salt damage resistance. Although it was a sample in which the Si amount of the composition was slightly less than the desired range of 3.0 to 7.0%, the salt damage resistance was slightly inferior.
The sample of No. 16 was a sample in which the amount of Si in the entire composition was larger than the desired range of 3.0 to 7.0%, but was excellent in oxidation resistance, salt damage resistance, and wear resistance. However, it was impossible to process the sintered product.
The sample of No. 17 is a sample to which Mo is not added, but results in inferior salt damage resistance. The sample of No. 19 is an example in which Mo is increased from the upper limit of the desired range, but is inferior in salt damage resistance. As a result.

The No. 20 sample has the same composition as the No. 1 sample, but as a result of sintering to a low density by lowering the sintering temperature by 60 ° C., the heat-resistant sintered material has a low density and a high porosity. , Salt damage resistance decreased and wear resistance also decreased.
The sample of No. 21 was a sample using FeP instead of FeB as a sintering aid, and was excellent in oxidation resistance and excellent in salt damage resistance and wear resistance.
The sample No. 22 is a sample containing a small amount of P within the desired range, and the sample No. 23 is a sample containing a large amount of P within the desired range, both of which have excellent oxidation resistance, salt damage resistance and wear resistance. It was also excellent.
The sample of No. 24 was a sample with less P than the desired range, and the sample of No. 25 was a sample with more P than the desired range, but the salt damage resistance decreased and the wear resistance also decreased. Therefore, when FeB and FeP are added as sintering aids, and the heat-resistant sintered material is produced by mixing the powder raw materials having the above-mentioned particle diameters, the addition amount of the sintering aid P is 0.2 to 1. A range of 2% is desirable.
The sample of No. 26 is an example using a fine powder of FeCrMoSi alloy powder (D50 = 10 μm) instead of using a sintering aid, but it has excellent oxidation resistance, salt damage resistance and wear resistance. Was also excellent.
The sample of No. 27 is No. 27. No. 28 sample was obtained by lowering the sintering temperature from 40 ° C., and the target heat-resistant sintered material was obtained. A sintered material could not be obtained.

The sample of No. 29 was manufactured using the sample of Example 1 and a fine powder (D50 = 10 μm) having a similar composition in the amount of Cr, Mo and Si without using a sintering aid, No. The sample of .30 is the heat-resistant sintered material produced by using the fine powder (D50 = 10 μm) having the same composition in the amount of Cr, Mo and Si as the sample of Example 2, and the sample of No. 31 is the sample of Example 3. And a heat-resistant sintered material produced using fine powder (D50 = 10 μm) having a similar composition in the amounts of Cr, Mo and Si.
From the results of these samples, it was found that even if the sintering aid was omitted, the desired heat-resistant sintered material could be obtained by refining the mixed powder.
The sample No. 29 was subjected to EDX (energy dispersive X-ray fluorescence analyzer) analysis of the parent phase and the hard phase. As a result, the matrix has a composition of mass%, Cr: 20.3%, Mo: 1.3%, Si: 3.9%, and the balance Fe, the hard phase is mass%, and Cr: 62.%. It had a composition of 0%, Mo: 3.5%, C: 6.1%, and the balance Fe.
From this analysis result, it was clarified that the parent phase was an Fe—Cr—Mo—Si phase and the hard phase was a CrFeMoC phase. For other samples, it was confirmed by EDX analysis that the parent phase was a Fe—Cr—Mo—Si phase and the hard phase was a CrFeMoC phase.

  3 is an enlarged photograph of the surface structure of the sample No. 2 shown in Table 1. As shown in this structural photograph, the heat-resistant sintered material sample exhibited a structure in which an amorphous hard phase (Cr—Fe—Mo—C phase) was dispersed in a matrix phase (Fe—Cr—Mo—Si phase). . In addition, a plurality of fine pores indicated by black circles were dispersed in the structure.

4 is a graph showing the results of measuring the relationship between the total Cr amount and the parent phase Cr amount for the samples No. 1 to No. 20.
As for the amount of the mother phase Cr, 28% or more of Cr is required in the mother phase in order to satisfy the oxidation resistance and salt damage resistance, but Si and Mo also contribute to oxidation resistance and salt damage resistance. 15% or more of Cr is required in the matrix. When the amount of the mother phase Cr exceeds 30%, there is an influence of Si addition, and the σ phase tends to be generated and becomes brittle. Therefore, the amount of the mother phase Cr is preferably in the range of 15 to 35%. In consideration of this, it can be seen from the relationship shown in FIG. 4 that it is preferable to adjust the total Cr content to a range of 20 to 38% in order to obtain a 15 to 35% matrix Cr content.

  DESCRIPTION OF SYMBOLS 1 ... Bearing member (heat-resistant sintered material), 2 ... Mother phase (Fe-Cr-Mo-Si phase), 3 ... Hard phase (Cr-Fe-Mo-C phase), 4 ... Hole (pore).

Claims (6)

  It has a structure in which a hard phase is dispersed in a matrix phase, and the total composition is Cr: 20-38%, Mo: 0.5-3%, Si: 3-7%, C: 0.5- 2.5%, the balance being Fe and inevitable impurities, the parent phase is Fe-Cr-Mo-Si, the hard phase is Cr-Fe-Mo-C, and the porosity is 2 A heat resistant sintered material excellent in oxidation resistance, high temperature wear resistance and salt damage resistance, characterized by being 0.0% or less.   In addition to Cr, Mo, Si, and C, the total composition contains B: 0.08 to 0.8% or P: 0.2 to 1.2%, and the balance is Fe and inevitable impurities. The heat-resistant sintered material having excellent oxidation resistance, high-temperature wear resistance, and salt damage resistance according to claim 1.   The acid resistance according to claim 1 or 2, wherein the matrix phase is made of a ferrite fabric, and hard particles made of Cr-Fe-Mo-C are dispersed in the ferrite fabric in an amount of 10 to 40% by volume. Heat-resistant sintered material with excellent heat resistance, high-temperature wear resistance, and salt damage resistance. An additive powder containing at least Si, C, and optionally containing at least one of Fe, Cr and Mo with respect to a base powder containing at least Fe, Cr and Si, and further containing Mo, if necessary.
Cr: 20 to 38%, Mo: 0.5 to 3%, Si: 3 to 7%, C: 0.5 to 2.5%, and the balance of Fe and inevitable impurities in mass% A step of mixing to obtain a mixed powder, a step of pressing the mixed powder to produce a green compact, and a step of heating the green compact to 1100 to 1280 ° C. to contain Fe, Cr, Mo, and Si It has a structure in which a hard phase containing Cr, Fe, Mo, and C is dispersed therein, and includes a step of forming a sintered body having a porosity of 2.0% or less. A method for producing heat-resistant sintered materials with excellent wear resistance and salt damage resistance.   FeB powder is mixed with the mixed powder so that B: 0.08 to 0.8% of the total composition, or FeP powder is mixed with P: 0.2 to 1.2% of the total composition. The method for producing a heat-resistant sintered material having excellent oxidation resistance, high-temperature wear resistance, and salt damage resistance according to claim 4.   The oxidation resistance, high-temperature wear resistance according to claim 4 or 5, wherein the hard phase is dispersed in the matrix by 10 to 40% by volume in the step of forming the sintered body. A method for producing a heat-resistant sintered material excellent in salt damage resistance.