JP3250132B2 - Free graphite precipitated iron-based sintered material with high strength and toughness - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a free graphite precipitated iron-based sintered body having high strength and high toughness.

[0002]

2. Description of the Related Art Conventionally, free graphite-dispersed iron-based sintered bodies have been used as sliding parts such as engine parts and transmission parts of automobiles, gears of oil pumps and bearings of rotary compressors. Further, as described in JP-A-57-16148 and JP-B-57-8860, for example, the free graphite-dispersed iron-based sintered body is compacted from a mixed powder having a predetermined composition. The powder is prepared in a reducing atmosphere at a low temperature at which the graphite powder blended as the raw material powder does not form a solid solution with the substrate, that is, 900 to 1
It is also known to manufacture by sintering at a predetermined temperature in the range of 000 ° C.

[0003]

On the other hand, in recent years, there has been a strong demand for higher output and lighter weight of various types of driving devices, and accordingly, the sliding parts, which are structural members of the driving devices, have become more severe. In addition to being forced to use in, the further thinning is required in the situation, but in the above conventional free graphite dispersed iron-based sintered body, strength and toughness is insufficient, these At present, it is impossible to satisfy the demands satisfactorily.

[0004]

Means for Solving the Problems Accordingly, the present inventors have
From the above-mentioned viewpoints, as a result of conducting research to improve the strength and toughness of the free graphite-dispersed iron-based sintered body, it was found that Fe-containing Mo and B or Mo-B and Cu at a predetermined ratio. Mo-B based alloy or Fe-Mo-B-Cu
A melt of a base alloy is prepared, and this melt is powdered by an atomizing method to obtain a powder of the alloy having a structure in which B is precipitated along a crystal grain boundary. In addition, after mixing, in a hydrogen atmosphere,
A partial alloying treatment is performed at a temperature of 750 to 1050 ° C. for a predetermined time, and the surface of the atomized powder is N
i is alloyed, a predetermined ratio of graphite powder is mixed with the partially alloyed atomized powder of Ni, and if the partially alloyed atomized powder does not contain Cu, Cu powder is also mixed and mixed. A green compact formed from a material having a relatively high sintering temperature of 1100 to 1100 in a reducing atmosphere.
After heating to a temperature of 1250 ° C. and holding for a predetermined time, and then sintering at a cooling rate of desirably 40 ° C./min or less, the graphite powder becomes Ni partially alloyed atomized powder at the above sintering temperature (this is a sintered powder). The solid solution C forms a solid solution and the solid solution C is strongly graphitized by the action of precipitation B existing along the crystal grain boundaries of the polycrystalline material during cooling,
As a result, free graphite precipitates and grows along the crystal grain boundaries, and at the same time, Cu contained as a solid solution in the above-mentioned Ni partially alloyed atomized powder, or mixed Cu powder (in the case of a sintered body, uniformly formed into a polycrystal) ), The effect of improving the toughness by Ni contained at a high concentration on the surface of the polycrystalline grains by partial alloying, and the effect of uniformly solidifying the entire polycrystalline grains. Research results have shown that a sintered body having high strength and toughness can be obtained in combination with the strength improving effect of Mo contained in the molten state.

[0005] The present invention has been made based on the above research results, and is expressed in terms of% by weight (% by mass).
Indicates weight% (mass%)], C: 0.5 to 2%, Ni: 0.5 to 5%, Mo: 0.1 to 2%, Cu: 0.5 to 4%, B: 0 0.1 to 0.5%, the balance being Fe and unavoidable impurities, and as shown in the microstructure diagram in FIG. Is Fe-Ni-Mo-
It is composed of a Cu-based alloy, has a higher Ni concentration distribution at the surface portion than at the central portion, and further has a precipitation B along the grain boundaries of the crystal grains constituting the polycrystalline grains. Is distributed, and has a structure in which free graphite deposited and grown by the precipitation B is dispersed and distributed at the grain boundaries of the crystal grains, characterized by a free graphite precipitated iron-based sintered body having excellent strength and toughness. It is.

Next, the reason why the component composition of the sintered body of the present invention is limited as described above will be described. (A) C The C component has a function of improving the lubricating property by dissolving in the matrix and improving the lubricity by dispersing and distributing as free graphite at the crystal grain boundaries, in addition to improving the strength. If the content is less than 2, a desired improvement effect cannot be obtained in the above operation, while the content is 2%.
If the content exceeds 0.1%, the toughness will decrease, so the content is set to 0.5 to 2%. Desirably 0.7-1.
A content of 5% is good.

(B) Ni The Ni component is partially alloyed on the surface of the atomized powder, which is a raw material powder, and the Ni partially alloyed atomized powder forms polycrystalline grains after sintering. The surface portion of the crystal grains has a high Ni concentration, and the Ni concentration distribution improves the toughness of the sintered body. If the content is less than 0.5%, a desired toughness improving effect can be obtained. On the other hand, if the content exceeds 5%, austenite is excessively generated and the strength is reduced. Therefore, the content is set to 0.5 to 5%. Preferably 1
-4% is good.

(C) Mo The Mo component has the effect of improving the strength of the sintered body by uniformly dissolving in the base material, that is, the polycrystalline grains, but the content of less than 0.1% is desirable. Strength improvement effect cannot be obtained,
On the other hand, if the content exceeds 2%, the compressibility of the powder is reduced, the density of the sintered body cannot be increased, and the strength and toughness are reduced. It was determined to be 2%. Desirably, the content is 0.5 to 1.5%.

(D) Cu The Cu component is an indispensable component for producing a sintered body having excellent strength and toughness because it has an effect of improving sinterability. If the content is less than 5%, the desired effect cannot be obtained, while if the content exceeds 4%, the dimensional change during sintering rapidly increases. It was set at 4%. Desirably, the content is 1 to 3%.

(E) BB The B component precipitates along the crystal grain boundaries when the atomized powder is formed from the molten metal, and the precipitated B forms a solid solution during sintering.
Promotes the precipitation of components as free graphite upon cooling,
When the content is less than 0.01%, the formation of free graphite is insufficient, and on the other hand, the formation of cementite in the base material increases and the desired toughness cannot be secured. If the content exceeds 0.5%, the strength is reduced, so that the content is 0.01 to 0.1%.
It was determined to be 5%. Desirably, the content is 0.05 to 0.3%.

[0011]

Next, the sintered body of the present invention will be described in detail with reference to examples. Various melts containing predetermined amounts of Mo, Cu, and B components in Fe are prepared, and an atomized powder having a particle size of 150 mesh or less is formed from the melt by a water atomizing method. 325
After a predetermined amount of Ni powder below the mesh is blended and mixed,
A partial alloying process was performed in a hydrogen atmosphere at a temperature of 900 ° C. for 60 minutes to hold Ni for alloying on the surface of the atomized powder, and the particle size was adjusted to the Ni partially alloyed atomized powder. In this state, a predetermined amount of graphite powder having an average particle size of 2 μm was compounded, and 1% of zinc stearate was further added thereto, followed by mixing with a V-type mixer for 30 minutes.
A green compact was press-molded at a pressure of 7 ton / cm ² , and this green compact was sintered in a decomposed ammonia gas at a temperature of 1130 ° C. for 30 minutes to obtain a component composition shown in Table 1. , And a structure of the same type as shown in the structure schematic diagram of FIG.
Inventive sintered bodies 1 to 11 of 0 mm × length: 55 mm were produced. In addition, for comparison purposes, as shown in Table 2, the content of any one of the components (marked with * in Table 2)
However, comparative sintered bodies 1 to 9 were produced under the same conditions except that the composition was out of the range of the present invention. Next, the tensile strength and the Charpy impact value of the various sintered bodies obtained as a result were measured for the purpose of evaluating the strength and toughness.
The measurement results are shown in Tables 1 and 2.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

According to the results shown in Tables 1 and 2, the sintered bodies 1 to 11 of the present invention have high strength and high toughness, while those of the comparative sintered bodies 1 to 9 can be seen. In addition, it is clear that, if the content of any one of the constituents is out of the range of the present invention, the desired high strength and high toughness cannot be obtained, and at least one of the properties is inferior. As described above, since the free graphite-precipitated iron-based sintered body of the present invention has high strength and high toughness, it can be used under severe conditions and reduced in thickness even when used as a sliding part of various devices, for example. I can respond satisfactorily.

[Brief description of the drawings]

FIG. 1 is a schematic structural view of a free graphite-precipitated iron-based sintered body of the present invention.

Claims (1)

(57) [Claims] 1. Weight% (% by mass): C: 0.5 to 2%, Ni: 0.5 to 5%, Mo: 0.1 to 2%, Cu: 0.5 to 4%, B : 0.01 to 0.5%, the balance being Fe and unavoidable impurities, and an aggregate of polycrystalline grains.
It is made of an e-Ni-Mo-Cu-based alloy, and has a higher Ni concentration distribution at the surface portion than at the central portion, and further has a grain boundary of crystal grains constituting the polycrystalline body. A precipitate of free graphite having high strength and high toughness, characterized by having a structure in which precipitate B is distributed along the crystal grains and free graphite precipitated and grown by the precipitate B is distributed in the grain boundaries of the crystal grains. Sintered material.