JP3381626B2 - Bearings made of free graphite-precipitated iron-based sintered material exhibiting excellent wear resistance under high surface pressure - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention aims at strengthening the base material by precipitating free graphite, which contributes to the improvement of lubricity, in the pores without precipitating it in the base material and by growing it in the pores. As described above, by forming the matrix with no precipitation of free graphite in a fine pearlite phase, excellent wear resistance is exhibited even under high surface pressure. This is a binder bearing).

[0002]

2. Description of the Related Art Conventionally, as described in, for example, Japanese Patent Application Laid-Open No. 8-41610, in% by weight (hereinafter, "%" means "% by weight"), C: 1.1 to 4%, S: 0 0.02 to 0.5%, B: 0.01 to 0.5%, Cu: 0.5 to 4%, with the balance being Fe and inevitable impurities, and substantially the main component being pearlite. Bearings (graphite precipitation) composed of a matrix and a free-graphite-precipitated iron-based sintered material (hereinafter referred to as "graphite-precipitated sintered material") having a structure consisting of fine precipitated free-graphite and pores dispersedly distributed in the matrix Sintered material bearings) are known.

[0003]

On the other hand, in recent years, various drives have been remarkably increased in output and speed, and along with this, the rotary shaft, which is a structural member of the drive, rotates under a high load condition. As a result, the bearing, which is the mating member,
Although it will be exposed to high load friction conditions, that is, high surface pressure, in the case of the above-mentioned conventional graphite precipitation sintered material bearing, wear will progress rapidly when subjected to high surface pressure, and the service life will be relatively short. It is the current situation.

[0004]

Therefore, the present inventors have
From the above viewpoints, as a result of research to develop a graphite precipitation-sintered material bearing that exhibits excellent wear resistance even under high surface pressure, as a result, it was basically Fe as a raw material powder and S as an alloy component. (Sulfur) component, or also Cr and Mn
And an S component, and further an atomized Fe alloy powder containing a predetermined amount of each of the S component and Ni and / or Mo components as necessary, and hexagonal boron nitride (hereinafter, h-BN).
Powder) and / or boric acid powder, and further using Cr powder, Cu powder, Mn powder, S (sulfur) powder, and graphite powder, and optionally Ni powder and Mo powder,
These raw material powders are mixed in a predetermined composition, mixed under normal conditions, and pressed into a green compact, and the green compact has a relatively high sintering temperature in a reducing atmosphere.
After heating to a predetermined temperature within the range of 0 to 1250 ° C. and holding for a predetermined time, a relatively slow cooling rate, that is, 5 to 40 ° C.
/ Min Cooling rate (Martensite phase and bainite phase appear at cooling rates exceeding 40 ° C / min, and the aggressiveness of the opponent increases sharply, while pearlite phase at cooling rates of less than 5 ° C / min. The reason for this is that the sintering is significantly increased), and is preferably sintered at a cooling rate of 10 to 35 ° C./min and cooled to at least 600 ° C., and C: 1 to 3%, S: 0.05 to 1%, B: 0.05 to 1%, Cr: 0.5 to 5%, Cu: 0.5 to 4%, Mn: 0.2 to 1%, and, if necessary, Ni. : 1 to 5%, Mo: 0.5 to 2%, the balance of which is Fe and inevitable impurities, and preferably a density of 6.0 to 7.2 g / cm ³ .
Furthermore, in other words, when an iron-based sintered material having a theoretical density ratio of 80 to 95% is formed, in this iron-based sintered material, the C component ( Graphite powder) forms a solid solution, and this solid solution C component is combined with the B component of the above-mentioned h-BN powder and boric acid powder, together with the effect of suppressing the precipitation of free graphite in the matrix by the Cr component that is also solid solution in the matrix. Due to the action of the solid solution S component in the Fe alloy powder, it precipitates as free graphite in the pores during the cooling process and grows. As a result, the precipitated free graphite exists substantially only in the pores. Since the matrix is not substantially free of precipitated free graphite, it is not only remarkably strengthened, but it is hardened by solid solution Cr and becomes a fine pearlite-based phase, so it is composed of this iron-based sintered material. Bearings have high surface pressure Also coupled with lubricity improving effect due to precipitation of free graphite present in the pores, it is to obtain a finding that comes to exhibit excellent wear resistance.

The present invention was made based on the above-mentioned research results. C: 1 to 3%, S: 0.05 to 1%, B: 0.05 to 1%, Cr: 0. 5 to 5%, Cu: 0.5 to 4%, Mn: 0.2 to 1%, and, if necessary, Ni: 1 to 5% and / or Mo: 0.5 to 2%. , And the balance consisting of Fe and unavoidable impurities , and the free graphite being a pearlite element due to the action of the S and B components.
Precipitates and grows in the pores dispersedly distributed in the ground, and
Precipitated free graphite does not exist in the substrate due to the action of r component
The present invention is characterized by a graphite-precipitated-sintered material bearing formed of a graphite-precipitated-sintered material having a structure and exhibiting excellent wear resistance under high surface pressure.

Next, the reason why the component composition of the graphite precipitating sintered material constituting the graphite precipitating sintered material bearing of the present invention is limited as described above will be explained. (A) C C component has a function of forming a pearlite phase of the base material to improve wear resistance and also a function of coexisting action of B and S components to precipitate as free graphite in pores to improve lubricity. However, if the content is less than 1%, the desired effect cannot be obtained, and if the content exceeds 3%, the strength tends to decrease sharply. It was set to 1-3%.

(B) S and B These components positively precipitate the graphite solid-solved by synergistic action in the pores as fine free graphite in the cooling process,
It has a function of growing, and such a graphitization function has, in principle, Fe, Fe--Cr alloy,
And Fe-Cr-Mn alloy, and optionally Fe
-Ni alloy, Fe-Mo alloy, and Fe-Ni-Mo
Fe alloy powder formed by atomizing a molten metal containing a predetermined amount of S component in the alloy, and for the B component, by using h-BN powder and boric acid powder as the boron source, respectively, as a raw material powder, further. Although it is promoted, if the content of any of the S and B components is less than 0.05%, the above graphitization into the pores cannot be sufficiently exhibited. Not only does the free graphite become precipitated in the matrix and the matrix becomes insufficiently strengthened, but also hard cementite (F
e ₃ C) is precipitated, and the attacking property against the other party is increased. On the other hand, if the content of either S or B exceeds 1%, the sinterability decreases and the desired It is not possible to ensure the strength of the steel, but it becomes impossible to secure the desired wear resistance due to the appearance of the ferrite phase in the base material.
S: 0.05 to 1%, preferably 0.1 to 0.
5%, B: 0.05 to 1%, preferably 0.1 to 0.5
Defined as%.

(C) Cr The Cr component is solid-solved in the base material to increase the hardness of the base material, refines the pearlite phase constituting the base material, and suppresses free graphite from precipitating in the base material. Due to the action of the S and B components, the free graphite that has precipitated and grown in the pores improves the lubricity, and it has the action of exhibiting excellent wear resistance under high surface pressure, but its content is 0.5%. If less than 5%, the desired effect cannot be obtained. On the other hand, if the content exceeds 5%, the precipitation and growth of graphite by S and B components will be suppressed. It was set to 0.5 to 5%, preferably 1 to 3%.

(D) Cu The Cu component is a component necessary for liquid phase sintering which is indispensable for ensuring a predetermined strength, but its content is 0.5%.
If the content is less than the above, sufficient sinterability cannot be obtained, and therefore desired strength cannot be ensured. On the other hand, the desired good sinterability is sufficient if the content is up to 4%. It was set to 0.5 to 4%, preferably 1 to 3%.

(E) Mn The Mn component has the function of forming a solid solution in the matrix to improve the strength, but if its content is less than 0.2%, the desired strength-improving effect cannot be obtained. When the content exceeds 1%, the graphitization by the B component and the S component becomes significantly impaired. Therefore, the content is set to 0.2 to 1%, preferably 0.4 to 0.8%. .

(F) Ni The Ni component has the action of forming a solid solution in the matrix to improve the toughness, so it is contained if necessary, but the content is 1
If the content is less than 5%, the desired effect of improving toughness cannot be obtained. On the other hand, if the content exceeds 5%, the austenite phase appears and the deterioration of wear resistance cannot be avoided. .About.5%, preferably 1 to 4%.

(G) Mo Mo The Mo component has a function of forming a solid solution in the base material to increase the hardness of the base material, and thus contributes to the improvement of wear resistance. Therefore, it is contained if necessary. If the amount is less than 0.5%, the desired effect cannot be obtained, while if the content exceeds 2%, the press moldability (compressibility) of the raw material powder (mixed powder) is deteriorated. Density of sintered material is 6.0g / c
The density is less than m ³ , which is a desirable density of 6.0.
Since the density of 7.2 g / cm ³ cannot be obtained and the desired strength cannot be secured, the content thereof is set to 0.5.
.About.2%, preferably 1 to 1.5%.

The graphite-precipitated sintered material constituting the bearing preferably has a theoretical density ratio of 80 to 95% as described above, in other words, a pore ratio of 2 to 15 area% by microscopic observation with an optical microscope. This is 15% by area
If it exceeds, the strength of the bearing will suddenly decrease. On the other hand, it is technically difficult to reduce the proportion to less than 2 area%, because it is technically difficult only by press molding. 2-10% by area,
The porosity can be adjusted in principle by the press molding pressure of the green compact.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the graphite-precipitated sintered material bearing of the present invention will be specifically described with reference to Examples. As the raw material powder, atomized Fe-S alloy powder (S: 0.3) having a predetermined average particle diameter in the range of 10 to 150 μm
2% content), atomized Fe-Cr-S alloy powder (C
r: 2.1%, S: 0.22% included), atomized Fe
-Cr-Mn-S alloy powder (Cr: 2.2%, Mn:
0.7%, S: 0.21% included), atomized Fe-N
i-S alloy powder (Ni: 4.4%, S: 0.12% content), atomized Fe-Mo-S alloy powder (Mo: 1.
3%, S: 0.15% content), atomized Fe-Ni-
Mo-S alloy powder (Ni: 4.2%, Mo: 1.5%,
S: 0.13% content), Cr powder, Cu powder, Ni powder, Mo powder, S (sulfur) powder, graphite powder, h-BN powder, and boric acid powder are prepared, and these raw material powders are shown in Tables 1 and 2. Blended to the blending composition shown in, and added 0.75% of zinc stearate as a lubricant,
It is mixed for 1 minute and press-formed into a green compact at a pressure of 5 to 7 ton / cm ² , and the green compact is 1100 to 1250 in an ammonia decomposition gas atmosphere in a mesh belt type sintering furnace.
After maintaining at a predetermined temperature in the range of ℃ for 25 minutes, 5-40
By gradually cooling to 550 ° C. at a predetermined cooling rate within the range of ° C./min and then sintering under the conditions of standing cooling, the component composition substantially the same as the above-mentioned composition and an optical microscope (magnification: 100
JIS Z2550, which is composed of a graphite-precipitated sintered material having the structure shown in Tables 1 and 2 [percentage of pearlite phase in the matrix and percentage of pores (free graphite)] measured by micrographs. Tensile test piece with specified dimensions and outer diameter: 18 mm × inner diameter: 8 mm × length: 8 mm
Inventive graphite precipitation sintered material bearings (hereinafter referred to as invented bearings) 1 to 21 having the dimensions of, and Cr as an alloy component
A conventional graphite-precipitated sintered material bearing (hereinafter, referred to as a conventional bearing) containing no graphite and composed of a graphite-precipitated sintered material in which precipitated free graphite is dispersed and distributed in the matrix was manufactured.

Then, an S45C carbon steel shaft having a diameter of 8 mm and a length of 50 mm is inserted into each of the above-mentioned various bearings (clearance between the bearing and the shaft: about 2).
5 μm), and both ends of the shaft are supported at a distance of 5 mm from the end face of the bearing.
Placed under a high load with a surface pressure of 48 kgf / cm ² ,
Grease is used as a lubricant, and the peripheral speed of the shaft is 120
m / min. The wear resistance was evaluated by performing a wear test for 60 minutes under the high surface pressure condition. To evaluate the wear resistance, the bearing after the test was traversed in the longitudinal direction, the amount of wear along the vertical surface of the lower half bearing surface was continuously measured, and the maximum amount of wear and the minimum amount of wear were picked up. . The results are shown in Tables 1 and 2. Further, in Tables 1 and 2, 55 mm × 10 mm × 10
The results of tensile tests (tensile strength) performed using test pieces having a size of mm are also shown.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

From the results shown in Tables 1 and 2, all of the bearings 1 to 21 of the present invention are substantially pearlite-based phase base material strengthened by Cr solid solution and pores dispersedly distributed in the base material. Since free graphite is precipitated and grows on the base metal and is composed of a graphite precipitation sintered material having a structure in which the free graphite does not precipitate due to the solid solution of Cr as well, it does not matter even under wear conditions under high surface pressure. However, the values of the maximum wear amount and the minimum wear amount on the bearing surface are relatively small, and the difference between them is also extremely small, which shows that even wear is excellent in wear resistance. A conventional bearing is a graphite precipitation sintered material having a structure in which the matrix is composed mainly of a pearlite-based phase, but free graphite precipitates and grows in the matrix and no precipitation of free graphite is observed in the pores. Configured so high Not only variation occurs locally worn due to strength reduction of the matrix due to precipitation free graphite in the wear conditions at pressure, wear progresses very fast, it is clear that the inevitable or shortening of the service life. As described above, the graphite-precipitated sintered material bearing of the present invention exhibits excellent wear resistance even under high surface pressure, and exhibits excellent bearing characteristics for a long period of time, so that high output of various drive devices and It has industrially useful properties, such as satisfying high speed and labor saving.

Front page continued (72) Inventor Toru Sakurada 5-3-8 Shiba, Minato-ku, Tokyo Within Mitsubishi Motors Corporation (72) Inventor Toshihide Kawahara 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (56) References JP 64-15350 (JP, A) JP 8-209202 (JP, A) JP 9-49064 (JP, A) JP 8-41610 (JP, A) JP-A-9-41071 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00 304 C22C 37/00 C22C 38/32 F16C 33/10 F16C 33/12

Claims (4)

(57) [Claims] 1. By weight% (mass%), C: 1-3%, S: 0.05-1%, B: 0.05-1%, Cr: 0.5-5%, Cu: 0. 0.5 to 4%, Mn: 0.2 to 1%, the balance consisting of Fe and unavoidable impurities , and free graphite due to the action of S and B components.
Precipitates and grows in the pores dispersedly distributed in the ground, and
Precipitated free graphite does not exist in the substrate due to the action of r component
A bearing made of a free graphite-precipitated iron-based sintered material exhibiting excellent wear resistance under high surface pressure, which is composed of a free graphite-precipitated iron-based sintered material having a structure. 2. In weight% (mass%), C: 1-3%, S: 0.05-1%, B: 0.05-1%, Cr: 0.5-5%, Cu: 0. 0.5 to 4%, Mn: 0.2 to 1%, Ni: 1 to 5%, and the balance of Fe and inevitable impurities, and S and Free graphite is a pearlite element due to the action of the B component.
Precipitates and grows in the pores dispersedly distributed in the ground, and
Precipitated free graphite does not exist in the substrate due to the action of r component
A bearing made of a free graphite-precipitated iron-based sintered material exhibiting excellent wear resistance under high surface pressure, which is composed of a free graphite-precipitated iron-based sintered material having a structure. 3. In weight% (mass%), C: 1-3%, S: 0.05-1%, B: 0.05-1%, Cr: 0.5-5%, Cu: 0. 0.5 to 4%, Mn: 0.2 to 1%, Mo: 0.5 to 2%, and the balance of Fe and inevitable impurities, and Due to the action of the S and B components, free graphite becomes a pearlite element
Deposited in the pores of dispersion distribution in the ground to grow, or One same C
Precipitated free graphite does not exist in the substrate due to the action of r component
A bearing made of a free graphite-precipitated iron-based sintered material exhibiting excellent wear resistance under high surface pressure, which is composed of a free graphite-precipitated iron-based sintered material having a structure. 4. By weight% (mass%), C: 1-3%, S: 0.05-1%, B: 0.05-1%, Cr: 0.5-5%, Cu: 0. 0.5 to 4%, Mn: 0.2 to 1%, Ni: 1 to 5%, Mo: 0.5 to 2%, and the balance of Fe and inevitable impurities. , And by the action of the S and B components, the free graphite becomes a pearlite element.
Precipitates and grows in the pores dispersedly distributed in the ground, and
Precipitated free graphite does not exist in the substrate due to the action of r component
A bearing made of a free graphite-precipitated iron-based sintered material exhibiting excellent wear resistance under high surface pressure, which is composed of a free graphite-precipitated iron-based sintered material having a structure.