JP3250131B2 - Free graphite precipitated iron-based sintered body with high strength and high 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 researching to improve the strength and toughness of the free graphite-dispersed iron-based sintered body, it was found that Fe-containing Mo and S or Mo, S, and Cu at a predetermined ratio. Mo-S based alloy or Fe-Mo-S-Cu
A molten alloy is prepared, and the molten alloy is powdered by an atomizing method to obtain a powder of the alloy having a structure in which S is dispersed and precipitated at a crystal grain boundary. Then, a predetermined amount of Ni powder is added to the atomized powder. After mixing, in a hydrogen atmosphere, 7
A partial alloying treatment is performed at a temperature of 50 to 1050 ° C. for a predetermined time, and Ni is added to the surface of the atomized powder.
Is alloyed with a partially alloyed atomized powder of Ni, and a predetermined ratio of graphite powder and hexagonal boron nitride (hereinafter referred to as B
N) is mixed, and if the partially alloyed atomized powder does not contain Cu, Cu powder is also mixed and mixed, and a green compact formed from this mixed powder is relatively produced in a reducing atmosphere. High sintering temperature of 1100-1250 ° C
, And after holding for a predetermined time, desirably 40 ° C /
When sintering under cooling conditions at a cooling rate of not more than min, the graphite powder forms a solid solution with the Ni partially alloyed atomized powder (which constitutes a polycrystalline particle by a sintered body) at the above sintering temperature, and this solid solution C precipitates and grows as free graphite with S as a nucleus dispersed and precipitated at the crystal grain boundaries of the polycrystalline grains during cooling, and this graphitization is present at the mutual interface of the polycrystalline units. BN promotes the BN because it has an action of suppressing the formation of cementite, and at the same time, the Ni
The effect of improving the sinterability by the solid solution contained Cu in the partially alloyed atomized powder or the compounded Cu powder (in the sintered body, uniformly contained in the polycrystal grain unit), and the above polycrystalline grains by partially alloying N contained in high concentration on body surface
Research results have shown that a sintered body having high strength and toughness can be obtained, in combination with the toughness improving effect of i and the strength improving effect of Mo uniformly contained in the polycrystalline grains. It is.

[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%, BN: 0 0.11 to 1.5%, S: 0.02 to 0.5%, the balance being Fe and unavoidable impurities, and polycrystalline grains as shown in the microstructure diagram in FIG. And the polycrystalline particles are Fe-Ni-Mo-
In addition to being composed of a Cu-based alloy, the Ni content has a higher Ni concentration distribution at the surface portion than at the central portion, and furthermore, precipitation S is present at the grain boundary portions of the crystal grains constituting the polycrystalline grains. Free graphite deposited iron-based sintered body with excellent strength and toughness, having a structure in which free graphite deposited and grown as nuclei is distributed and BN is distributed at the interface of the polycrystalline grains. 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%. Desirably, the content is 1 to 4%.

(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 decreases, the density of the sintered body cannot be increased, and the strength and toughness decrease. %. 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) BN BN has a function of dispersing and distributing at the interface of polycrystalline grains to suppress the formation of cementite in the polycrystalline grains, and rather to promote the growth of graphite. The content is 0.0
If the content is less than 1%, the above-mentioned effect is not exerted. As a result, the growth of graphite is suppressed, the formation of cementite is promoted, and the desired high toughness cannot be secured in the sintered body. Exceeds 1.5%, the sinterability decreases,
Since it causes a decrease in strength, its content is 0.5 to
It was determined to be 1.5%. Desirably, the content is 0.1 to 0.7%.

(F) SS The S component is dispersed and precipitated at the crystal grain boundaries during the formation of the atomized powder from the molten metal, and the precipitated S serves as a nucleus when solid solution C is precipitated as free graphite during sintering. And BN have the effect of precipitating and growing free graphite at the crystal grain boundaries of the polycrystalline grains, but if the content is less than 0.02%, the formation of free graphite is insufficient and the cementite Increases the formation of steel and cannot maintain the desired toughness. On the other hand, if the content exceeds 0.5%, the strength decreases, so that the content is set to 0.02 to 0.5%. %. Desirably, the content is 0.05 to 0.3%.

[0012]

Next, the sintered body of the present invention will be described in detail with reference to examples. Various melts containing a predetermined amount of Mo, Cu, and S 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 diameter of 2 μm and BN powder of the same 10 μm were blended, and 1% of zinc stearate was added thereto, followed by mixing with a V-type mixer for 30 minutes to obtain 7 ton / cm ² Pressing into a green compact at a pressure of
By sintering at a temperature of 1130 ° C. for 30 minutes, the component compositions shown in Table 1 and FIG.
The sintered bodies 1 to 13 of the present invention having a structure of the same kind as shown in the micrograph of the structure and having dimensions of 10 mm in length, 10 mm in width, and 55 mm in length were produced. Also, for comparison purposes, Table 2
As shown in Table 2, the comparative sintered bodies 1 to 11 were prepared under the same conditions except that the content of any one of the constituents (marked with * in Table 2) was out of the range of the present invention. Each was manufactured. 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.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

From the results shown in Tables 1 and 2, all of the sintered bodies 1 to 13 of the present invention have high strength and high toughness, while those of the comparative sintered bodies 1 to 11 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% (mass%): C: 0.5 to 2%, Ni: 0.5 to 5%, Mo: 0.1 to 2%, Cu: 0.5 to 4%, cubic The composition contains: 0.01 to 1.5% of crystalline boron nitride, 0.02 to 0.5% of S, and the remainder is composed of Fe and unavoidable impurities; The polycrystalline particles are F
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. In the part, free graphite deposited and grown with the precipitate S as a nucleus is distributed, and at the interface of the polycrystalline grains, high strength and high toughness characterized by having a structure in which hexagonal boron nitride is distributed. Free graphite-precipitated iron-based sintered body.