Patent Application
20120107168
The present invention relates to an iron-based sintered sliding member having excellent tribological property and a manufacturing method thereof.
1. Background Art
Heretofore known as iron-based materials are iron-carbon type or iron-copper-carbon type bearing materials impregnated with liquid lubricant (lubricating oil) and iron-carbon type or iron-copper-carbon type sintered materials (See Non-Patent Document 1, for example). In the case of the above-mentioned earlier iron-based sintered sliding members, at least 3 mass percent or more of carbon is needed for effectuating the solid lubrication action of carbon. In that condition, however, iron powder reacts with carbon powder in the course of sintering, causing the phenomenon of precipitation of free cementite (Fe3C) of high hardness in the sinter structure. This precipitation of free cementite of high hardness in the structure raises a problem of damaging the opposite member, for example an axle in the event of sliding against the axle (the opposite member). In the sliding use, it is an important point to avoid this phenomenon as much as possible.
2. Description of the Related Art
As methods of preventing the precipitation of free cementite, the following methods can provide a certain degree of solution: (1) mixing of a small amount, for example 0.82 mass percent or less, of carbon (graphite); and (2) sintering at a low temperature, for example 1000 degrees Celsius or less, at which free cementite does not precipitate. The method (1), however, cannot be expected to provide the solid lubricating action of mixed carbon. According to the method (2), sinter alloying is not sufficient to give high mechanical strength, and thus it is difficult to apply the method to the sliding use. Thus, there remains a problem that iron-based sintered materials obtained by these methods can not realize sufficient solid lubricating action of the contained carbon.
As another method, it is possible to consider a method of mixing graphite-stabilizing element such as silicon (See Patent Document 1, for example). However, heating at about 1200 degrees Celsius or more is required as a condition for diffusing silicon into iron to form solid solution. Thus, the method requires much higher temperature than the ordinary sintering temperature for ordinary iron-based sintering material, and this increases the manufacturing costs. Further, if sintering atmosphere is not controlled strictly, there is a possibility of oxidization of silicon. Further, there is an iron-based sintered material manufacturing method that prevents precipitation of free cementite in the structure by mixing ferrosilicon (FeSi) powder (See Patent Documents 2 and 3).
In view of the above circumstances, an object of the present invention is to provide an iron-based sintered sliding member that has no precipitation of free cementite in its structure and has excellent tribological property such as friction and wear, and to provide its manufacturing method.
As a result of various investigations aimed at solving the above problems, the present inventor focused the attention on copper and manganese as elements that promote generation of ferrite phase (α phase) structure. And, when copper and manganese are mixed in the form of copper-iron-manganese master alloy into an iron-carbon-X (metallic element) type sintering material at a prescribed ratio, the inventor found that copper and manganese are sufficiently diffused into the α phase structure to be solid-state solution in it, and the copper-iron-manganese master alloy is contained and diffused in the α phase structure without no precipitation of free cementite in the α phase structure, thus providing excellent tribological property.
The iron-based sintered sliding member of the present invention has been invented on the basis of the above finding, and is made from iron powder, copper-iron-manganese alloy powder, and carbon powder. The iron-based sintered sliding member is characterized in that: it comprises 2.67-18.60 mass % copper component, 0.12-1.20 mass % manganese component, 1.0-5.0 mass % carbon component, and iron component as a remaining part; the matrix presents pearlite structure or structure in which pearlite partially coexists with ferrite; no free cementite precipitates in the structure of the matrix; and copper-iron-manganese alloy is dispersedly contained in the structure of the matrix.
In the iron-based sintered sliding member, the copper-iron-manganese mother alloy dispersedly contained in the structure of the matrix may be dispersedly contained in net-like forms at grain boundary of the structure of the matrix.
Further, in the iron-based sintered sliding member, the copper-iron-manganese mother alloy dispersedly contained in the structure of the matrix shows the hardness of 100-120 in terms of the micro Vickers hardness (HMV). On the other hand, the structure of the matrix, i.e. the pearlite structure or the structure in which pearlite partially coexists with ferrite shows the hardness of 350-450 in terms of the micro Vickers hardness (HMV).
In the iron-based sintered sliding member of the present invention, the pearlite structure of the matrix or the structure of the matrix in which pearlite partially coexists with ferrite dispersedly contains the copper-iron-manganese alloy having the lower hardness than the hardness of the structures. Accordingly, running-in ability of the sliding surface with the opposite member such as a rotating shaft is improved, and the tribological property are improved.
In the iron-based sintered sliding member of the present invention, natural graphite or artificial graphite can be used as the carbon.
This carbon is dispersedly contained in the proportion of 1-5 mass % in the structure of the matrix, i.e. the pearlite structure or the structure of the matrix in which pearlite partially coexists with ferrite. The carbon has a solid lubrication action in itself, and functions as a retaining agent for a lubricant oil later. In particular, when the mixing ratio of the carbon is 3 mass % or more, self-lubrication is realized due to the solid lubrication action of carbon.
In the iron-based sintered sliding member of the present invention, lubricant oil is contained in the proportion of 10-15 volume %.
The lubricant oil gives a liquid lubrication action to the iron-based sintered sliding member. At the same time, together with the solid lubrication action of the carbon, the self-lubricating effect is increased.
An iron-based sintered sliding member manufacturing method of the present invention comprises:
blending 3-20 mass % alloy powder which comprises 4-6 mass % manganese, 3-5 mass % iron, and copper as a remaining part, and 1-5 mass % carbon powder to iron powder as a main component, and mixing the alloy powder and the carbon powder, to make powder mixture;
then, filling the powder mixture in a mold and compacting the powder mixture to obtain a green compact of a desired shape; and
sintering the green compact at a temperature of 1000-1100 degrees Celsius for 30-60 minutes in a heating furnace whose inside has been adjusted to be a neutral or reducing atmosphere.
The iron-based sintered sliding member obtained by this manufacturing method comprises 2.67-18.6 mass % copper component, 0.12-1.2 mass % manganese, 1.0-5.0 mass % carbon component, and iron component as a remaining part. The structure of the matrix presents pearlite structure or structure in which pearlite partially coexists with ferrite. No free cementite precipitates in the structure, and the copper-iron-manganese alloy is dispersedly contained in the structure of the matrix.
In the above-described iron-based sintered sliding member manufacturing method, the copper-iron-manganese alloy powder as a component part becomes a liquid phase at a temperature of 1050 degrees Celsius. Thus, at a temperature of 1000 degrees Celsius or higher but under 1050 degrees Celsius, the sintering becomes solid-phase sintering. On the other hand, at a temperature from 1050 degrees Celsius to 1100 degrees Celsius inclusive, the sintering becomes liquid-phase sintering. In the iron-based sintered sliding member obtained by solid-phase sintering, its matrix presents pearlite structure or structure in which pearlite partially coexists with ferrite. No free cementite precipitates in the structures. And, the copper-iron-manganese alloy is dispersedly contained in the structure of the matrix.
On the other hand, in the iron-based sintered sliding member obtained by liquid-phase sintering, its matrix presents pearlite structure or structure in which pearlite partially coexists with ferrite, and no free cementite precipitates in the structures, densifying the sintered sliding member to improve its mechanical strength. And, the copper-iron-manganese alloy is dispersedly contained in net-like forms at grain boundary of the structure of the matrix.
The iron-based sintered sliding member obtained by solid-phase sintering or liquid-phase sintering contains copper and manganese i.e. elements promoting generation of ferrite phase (α phase) structure. Thus, in both types of sintering, the matrix presents pearlite structure or structure in which pearlite partially coexists with ferrite, and no free cementite precipitates in the structures.
The present invention provides an iron-based sintered sliding member made from iron powder, copper-iron-manganese alloy powder, and carbon powder, and a manufacturing method thereof, the iron-based sintered sliding member comprising 2.67-18.6 mass % copper component, 0.12-1.2 mass % manganese component, 1.0-5.0 mass % carbon component, and iron component as a remaining part, wherein its matrix presents pearlite structure or structure in which pearlite partially coexists with ferrite and the copper-iron-manganese alloy is dispersedly contained in the structure of the matrix to shows good running-in ability and excellent tribological property.
Next, embodiments of the present invention will be described in detail, although the present invention is not limited in any way by these embodiments.
An iron-based sintered sliding member of the present invention is one containing iron component, copper-iron-manganese alloy component, and carbon component, and is characterized in that it comprises 2.67-18.60 mass % copper component, 0.12-1.20 mass % manganese component, 1.0-5.0 mass % carbon component, and iron component as the remaining part; its matrix presents pearlite structure or structure where pearlite partially coexists with ferrite; and the structure of the matrix dispersedly contains carbon component and copper-iron-manganese alloy component.
In the iron-based sintered sliding member of the present invention, it is favorable to use, as the main component iron, reduced iron powder or atomized iron powder (water atomized iron powder), each powder having a grain size (177 μm or less) that can sift through an 80 mesh sieve, and apparent density of about 2.4-3.0 Mg/m3. Specific surface areas of these iron powders measured by the gas adsorption method (BET method—ISO 9277) are 60-80 m2/kg in the case of the atomized iron powder and 80-100 m2/kg in the case of the reduced iron powder. The atomized iron powder has a relatively-small number of gas cavities within its powder particles, and thus its specific surface area is small. On the other hand, the reduced iron powder has a relatively-large number of gas cavities, and their surfaces are hubbly. Thus, the specific surface area of the reduced iron powder is larger than that of the atomized iron powder.
Copper component and manganese component, which are blended with the main component iron at predetermined ratios, are used in the form of copper-iron-manganese alloy. These copper and manganese components in this alloy are elements that promote generation of ferrite phase (α phase) structure, and act so as to inhibit the below-described reaction between the iron component as the main component and the carbon component in the process of sintering, and thus to prevent precipitation of free cementite in the structure of the matrix of the sintered compact. Details of this action of the copper and manganese components of inhibiting the reaction between the iron component and the carbon component in the process of sintering have not been made clear. However, it is inferred that this is because previous alloying of these elements leads to preferential solid-state solution of the copper and manganese components into the iron component as the main component, and this prevents solid-state solution of the carbon component into the iron component largely.
The component composition of this copper-iron-manganese alloy component is 89-93 mass % copper component, 3-5 mass % iron component, and 4-6 mass % manganese component. This copper-iron-manganese alloy powder is blended in the proportion of 3-20 mass % with the iron component as the main component. In other words, the copper component is blended in the proportion of 2.67-18.6 mass %, the iron component in the proportion of 0.09-1.0 mass %, and the manganese component in the proportion of 0.12-1.2 mass % with the iron component.
The copper-iron-manganese alloy component mentioned above has its liquid phase point at a temperature of 1050 degrees Celsius, and its sintering is solid-phase sintering at a temperature lower than 1050 degrees Celsius and liquid-phase sintering at a temperature of 1050 degrees Celsius or higher. In the solid-phase sintering at a sintering temperature lower than 1050 degrees Celsius, the copper-iron-manganese alloy component is dispersedly contained in the pearlite structure of the matrix or the structure in which pearlite partially coexists with ferrite. In the liquid-phase sintering at a sintering temperature of 1050 degrees Celsius or higher, the copper-iron-manganese alloy component is dispersedly contained in net-like forms at grain boundaries of the pearlite structure of the matrix or the structure in which pearlite partially coexists with ferrite.
In
Further,
In the microphotographs shown in
Because the copper-iron-manganese alloy which is dispersedly contained in the structure of the matrix where the pearlite partially coexists with ferrite has lower hardness than that of the site of that structure, the running-in ability at the time of sliding on the opposite member becomes better, and the tribological property are improved.
Next, the present invention will be described referring to examples. Of course, the following examples do not limit the present invention.
To atomized iron powder having an average particle size of 70 μm (Atomel 300M manufactured by Kobe Steel, Ltd.), were blended: 12 mass % copper-iron-manganese alloy powder having an average particle size of 75 μm (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) and comprising 90.5 mass % copper component, 4.1 mass % iron component, and 5.4 mass % manganese component; and, as a carbon component, 3 mass % natural graphite powder having an average particle size of 40 μm (CB 150 manufactured by Nippon Graphite Industries, Ltd.). These powders were mixed by a V-type mixer for 20 minutes to obtain powder mixture (10.86 mass % copper component, 0.65 mass % manganese component, 85.49 mass % iron, and 3 mass % carbon component). Then, this powder mixture was filled in a mold and compacted at a compacting pressure of 5 ton/cm2, to obtain a green compact of a rectangular shape.
This rectangular-shaped green compact was placed in a heating furnace whose inside was adjusted to be a hydrogen gas atmosphere, subjected to solid-phase sintering at a temperature of 1000 degrees Celsius for 60 minutes, and then taken out of the heating furnace, to obtain a rectangular-shaped iron-based sintered material. This iron-based sintered material was machined to obtain an iron-based sintered sliding member measuring 30 mm in each side length and 5 mm in thickness. The density of this iron-based sintered sliding member was shown to be 6.2 g/cm3, and, as for its structure, it was ascertained that it presented structure in which pearlite partially coexisted with ferrite as shown in
Powder mixture (10.86 mass % copper component, 0.65 mass % manganese component, 85.49 mass % iron component, and 3 mass % carbon component) similar to that of the Example 1 was obtained, filled in a mold, and compacted at a compacting pressure of 5 ton/cm2, to obtain a green compact of a rectangular shape. This rectangular-shaped green compact was placed in a heating furnace whose inside was adjusted to be a hydrogen gas atmosphere, subjected to liquid-phase sintering at a temperature of 1100 degrees Celsius for 60 minutes, and then taken out of the heating furnace, to obtain a rectangular-shaped iron-based sintered material. This iron-based sintered material was machined to obtain an iron-based sintered sliding member measuring 30 mm in each side length and 5 mm in thickness. The density of this iron-based sintered sliding member was shown to be 6.7 g/cm3, and, as for its structure, it was ascertained that it presented structure in which pearlite partially coexisted with ferrite as shown in
To atomized iron powder having an average particle size of 70 μm (the same iron powder as in the Example 1), were blended: 10 mass % copper-iron-manganese alloy powder having an average particle size of 75 μm (the same alloy powder as in the Example 1) comprising 90.5 mass % copper component, 4.1 mass % iron component, and 5.4 mass % manganese component; and, as a carbon component, 3 mass % natural graphite powder having an average particle size of 40 μm (the same graphite powder as in the Example 1). These powders were mixed by a V-type mixer for 20 minutes to obtain powder mixture (9.05 mass % copper component, 0.54 mass % manganese component, 87.41 mass % iron component, and 3 mass % carbon component). Then, this powder mixture was filled in a mold and compacted at a compacting pressure of 5 ton/cm2, to obtain a green compact of a cylindrical shape.
This cylindrical-shaped green compact was placed in a heating furnace whose inside was adjusted to be a hydrogen gas atmosphere, subjected to liquid-phase sintering at a temperature of 1100 degrees Celsius for 60 minutes, and then taken out of the heating furnace, to obtain a cylindrical-shaped iron-based sintered material. This iron-based sintered material was machined to obtain an iron-based sintered sliding member having an inside diameter measuring 20 mm, an outside diameter measuring 28 mm, and a length measuring 15 mm. The density of this iron-based sintered sliding member was shown to be 6.6 g/cm3, and, as for its structure, it was ascertained that it presented structure in which pearlite partially coexisted with ferrite as shown in
Powder mixture (10.86 mass % copper component, 0.65 mass % manganese component, 85.49 mass % iron, and 3 mass % carbon component) similar to that in the Example 2 was obtained, filled in a mold, and compacted at a compacting pressure of 5 ton/cm2, to obtain a green compact of a cylindrical shape. This cylindrical-shaped green compact was placed in a heating furnace whose inside was adjusted to be a hydrogen gas atmosphere, sintered at a temperature of 1100 degrees Celsius for 60 minutes, and then taken out of the heating furnace, to obtain a cylindrical-shaped iron-based sintered material. This iron-based sintered material was machined to obtain an iron-based sintered sliding member having an inside diameter measuring 20 mm, an outside diameter measuring 28 mm, and a length measuring 15 mm. The density of this iron-based sintered sliding member was shown to be 6.7 g/cm3, and, as for its structure, it was ascertained that it presented structure in which pearlite partially coexisted with ferrite as shown in
An iron-based sintered material similar to the iron-based sintered material of the SMF class 4 prescribed in Japanese Industrial Standards JIS Z2550 was prepared. That is to say, to atomized iron powder having an average particle size of 70 μm (the same iron powder as in the Example 1), were blended: 3 mass % electrolyte copper powder having an average particle size of 100 μm and, as a carbon component, 0.7 mass % natural graphite powder (the same graphite powder as in the Example 1). These powders were mixed by a V-type mixer for 20 minutes, to obtain powder mixture (3 mass % copper component, 0.7 mass % carbon component, and the residual iron component). Then, this powder mixture was filled in a mold and compacted at a compacting pressure of 4 ton/cm2, to obtain a green compact of a cylindrical shape.
This rectangular-shaped green compact was place in a heating furnace whose inside was adjusted to be a hydrogen gas atmosphere, sintered at a temperature of 1120 degrees Celsius for 60 minutes, and then taken out of the heating furnace, to obtain a cylindrical-shaped iron-based sintered material. This iron-based sintered material was machined to obtain an iron-based sintered sliding member having an inside diameter measuring 20 mm, an outside diameter measuring 28 mm, and a length measuring 15 mm. The density of this iron-based sintered member was shown to be 6.5 g/cm3. This iron-based sintered sliding member was subjected to oil impregnation processing, to obtain an iron-based oil impregnated sintered sliding member having the oil content of 15 volume %.
Now, will be described results of evaluation of tribological property with respect to the iron-based oil impregnated sintered sliding members obtained by the above-described Examples and Comparative Example. With respect to the iron-based oil impregnated sintered sliding members obtained in the Examples 1 and 2, their thrust sliding characteristics were evaluated according to the thrust test conditions described below. Further, with respect to the iron-based oil impregnated sintered sliding members obtained in the Examples 3 and 4 and the Comparative Example, journal oscillation characteristics and journal rotation characteristics were evaluated under the below-described journal oscillation test conditions and journal rotation test conditions.
Speed: 1.3 m/min
Load: 800 kgf/cm2
Test time: 8 hours
Opposite member: carbon steel for machine structural use (S45C)
Lubrication condition: application of lithium grease at the start of the test
Test method: As shown in
Speed: 3 m/min
Load: 100 kgf/cm2, 250 kgf/cm2
Oscillation angle: ±45°
Test time: 100 hours
Opposite member: bearing steel (SUJ2 quenched)
Lubrication condition: application of lithium grease to the sliding surfaces at the start of the test
Test method: As shown in
Speed: 10 m/min
Load: 250 kgf/cm2, 300 kgf/cm2
Test time: 100 hours
Opposite member: bearing steel (SUJ2 quenched)
Lubrication condition: application of lithium grease to the sliding surfaces at the start of the test
Test method: As shown in
Results of tribological property evaluations performed under the above-described test conditions were shown in Tables 1-3.
From the test results shown in Table 1, it is shown that the iron-based oil impregnated sintered sliding members of the Examples 1 and 2 remained stable throughout the test times in their friction coefficients even under the high load condition of the load (surface pressure) of 800 kgf/cm2, and their wear losses after the test were extremely small. In the test results shown in Table 2, the * mark in Table 2 shows that, under the load (surface pressure) of 150 kgf/cm2, the wear loss rose rapidly when the friction coefficient rose 19 hours after the start of the test, and accordingly the test was stopped at that point. Further, in the test results shown in Table 3, the ** mark in Table 3 shows that, under the load (surface pressure) of 300 kgf/cm2, the friction coefficient rose rapidly (to 0.3) 11 hours after the start of the test, and accordingly the test was stopped.
As described above, the present invention provides an iron-based sintered sliding member made from iron powder, copper-iron-manganese alloy powder and carbon powder, comprising 2.67-18.60 mass % copper component, 0.12-1.20 mass % manganese component, 1.0-5.0 mass % carbon component, and iron component as the remaining part. The matrix presents pearlite structure or structure in which pearlite partially coexists with ferrite, and the copper-iron-manganese alloy is dispersedly contained in the structure of the matrix. The copper-iron-manganese alloy having lower hardness than the hardness of the structure of the matrix is dispersed in the structure, and thus, as for sliding on the opposite member, the iron-based sintered sliding member of the present invention shows good running-in ability and excellent excellent tribological property. Thus, the iron-based sintered sliding member of the present invention can be applied to a sliding use including for example a bearing, a sliding plate, a washer, and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-190176 | Aug 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/058741 | 5/24/2010 | WO | 00 | 12/30/2011 |
