JP2770736B2 - Free graphite precipitated iron-based sintered material with excellent strength and wear resistance - 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 material having high strength and excellent wear resistance and suitable for use as, for example, various sliding parts.

[0002]

2. Description of the Related Art Conventionally, as described in, for example, JP-A-57-16148 and JP-B-57-8860, free graphite iron-based sintering having a structure in which free graphite is dispersed and distributed in a pearlite base material. It is known that materials are used as sliding parts such as gears for oil pumps, bearings for rotary compressors, and transmission parts for automobiles. Further, the free graphite iron-based sintered material described above, a green compact formed from a mixed powder having a predetermined compounding composition, 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, That is, 90
It is also known that it is manufactured by sintering at a predetermined temperature in the range of 0 to 1000 ° C.

[0003]

On the other hand, in recent years, various types of driving devices have been remarkably increased in output and weight, and accordingly, the use conditions of the above-mentioned sliding parts, which are structural members thereof, have become more severe. Not only that, it is required to be thinner, but the conventional free graphite iron-based sintered material having a structure in which relatively coarse unreacted residual free graphite is dispersed and distributed in the above-described base material is subjected to severe conditions. At present, these requirements cannot be satisfied satisfactorily due to insufficient wear resistance and insufficient strength when used in the above conditions.

[0004]

Means for Solving the Problems Accordingly, the present inventors have
From the above point of view, we focused on the above-mentioned conventional free graphite iron-based sintered material and conducted research to improve its strength and wear resistance. As a result, as a raw material powder, iron powder and graphite powder were basically used. , Fe-S alloy powder, hexagonal boron nitride (hereinafter, referred to as
BN) and a Cu powder are blended in a predetermined blending composition, and a green compact formed from a mixed powder obtained by mixing is mixed at a relatively high sintering temperature in a reducing atmosphere. When the graphite powder is heated to a predetermined temperature in the range of 1100 to 1250 ° C. to sufficiently dissolve the graphite powder, and sintering is preferably performed at a cooling rate of 40 ° C./min or less from this state,
Since the BN and S act so as to remarkably accelerate the precipitation of the solid solution graphite in the matrix at the sintering temperature as free graphite upon cooling, fine free graphite was precipitated on the pearlite matrix. An iron-based sintered material having a structure can be obtained, and the resulting free graphite-precipitated iron-based sintered material has high strength and excellent wear resistance.For example, when used as a sliding part, The research results show that it is possible to satisfactorily cope with thinning and use under severe conditions.

The present invention has been made on the basis of the above-mentioned research results, and is expressed in terms of% by weight (hereinafter,% indicates% by weight), C: 1.1 to 4%, S: 0.1 to 1%,
BN: 0.05 to 1%, Cu: 0.5 to 4%, and, if necessary, P: 0.05 to 0.6%, with the balance being Fe and unavoidable impurities. The present invention is characterized by a free graphite-precipitated iron-based sintered material having high strength and excellent wear resistance, having a structure in which fine free graphite is precipitated on a pearlite base material.

Next, the reason why the component composition of the free graphite-precipitated iron-based sintered material of the present invention is limited as described above will be described. (A) C In the C component, while forming a base pearlite, BN
And S have the effect of improving the strength and wear resistance by precipitating as fine free graphite in the element due to the coexistence of S and S. However, when the content is less than 1.1%, ferrite precipitates in the element. As a result, the desired effect cannot be obtained in the above-mentioned action. On the other hand, if the content exceeds 4%, grain boundary cementite is precipitated and the strength and seizure resistance are reduced.
The content was determined to be 1.1 to 4%. Preferably 1.5
２．５2.5% is good.

(B) S and BN These components have the effect of accelerating the precipitation of graphite coexisting as a solid solution with the base material as fine free graphite during the cooling process. If BN is less than 0.1% and BN is less than 0.05%, not only the desired effect is not obtained but also brittle grain boundary cementite is precipitated. S: 1% and BN: 1% regardless of content
If the content exceeds 0.1%, the sinterability will be impaired and the strength will decrease.
It was determined as 0.05-1%. Preferably, S: 0.1
-0.6%, BN: 0.1-0.6%.

(C) Cu The Cu component has a function of improving the strength by forming a solid solution in the base material, but if its content is less than 0.5%, the desired strength improving effect cannot be obtained. If the amount exceeds 4%, no further effect of improving the strength is exhibited, and in addition, the amount of expansion at the time of sintering becomes large and causes a decrease in dimensional accuracy. It was decided. Desirably 1-3%
Is good.

(D) Since the PP component has a function of forming a liquid phase at the time of sintering to improve sinterability and contributing to improvement of strength, it is contained as necessary. If the amount is less than 0.05%, a desired strength improving effect cannot be obtained, while the content is 0.6%.
, The content becomes determined to be 0.05 to 0.6%. Preferably, 0.2
-0.3% is good.

[0010]

EXAMPLES Next, the free graphite-precipitated iron-based sintered material of the present invention will be specifically described with reference to examples. As raw material powder,
Both iron powder having a particle size of -300 mesh, copper powder,
Graphite powder, FeS powder, and Fe-P alloy (P: 27
%) And BN powder having an average particle size of 10 μm are prepared, and these raw material powders are blended in the composition shown in Tables 1 and 2, and 0.5% of zinc stearate is added as a lubricant to obtain V powder. After mixing in a rotary mixer for 30 minutes, 6 tons
/ Cm ² at a predetermined temperature in the range of 1100 to 1250 ° C. for 25 minutes in an ammonia decomposition gas atmosphere in a mesh belt type continuous sintering furnace. By sintering at a cooling rate of min to room temperature under the condition of cooling to room temperature, it has substantially the same component composition as the above-mentioned composition and the base structure shown in Tables 1 and 2, and the dimensions specified in JIS Z2550 Of the present invention, a free graphite-precipitated iron-based sintered material (hereinafter referred to as a sintered material of the present invention) 1 to 12 comprising a tensile test piece and a bearing having a size of 18 mm in outer diameter, 8 mm in inner diameter, and 10 mm in thickness. Comparative free graphite precipitated iron-based sintered material (hereinafter referred to as comparative sintered material)
1 to 6 were manufactured respectively. The comparative sintered material 1
Nos. 6 to 6 have compositions in which the content of any of the components that affect the precipitation of free graphite is out of the range of the present invention.

[0011]

[Table 1]

[0012]

[Table 2]

Next, for the various sintered materials obtained as a result, an S45C carbon steel shaft was inserted into the above-mentioned bearing for the purpose of evaluating wear resistance.
A wear test was performed under the conditions of rpm, surface pressure: 20 kgf / cm ² , and operation time: 1 hour, and the maximum wear depth of the bearing sliding surface was measured. Further, for the purpose of evaluating the strength, a tensile test was performed using the above tensile test piece, and the tensile strength and elongation were measured.
The results of these measurements are shown in Tables 1 and 2.

[0014]

From the results shown in Tables 1 and 2, all of the sintered materials 1 to 12 of the present invention have a structure in which fine free graphite is dispersed and distributed in a pearlite substrate, and have high strength and excellent wear resistance. As shown in Comparative Sintering Materials 1 to 6, the content of any one of C, S and BN (marked with * in Table 1) is within the scope of the present invention. Obviously, a composition out of the range results in inferior properties of at least one of strength and wear resistance. As described above, the free graphite-precipitated iron-based sintered material of the present invention exhibits excellent abrasion resistance even under severe conditions in a thinned state when used as, for example, sliding parts of various driving devices. It has industrially useful characteristics, such as being able to sufficiently satisfy the demand for higher output and lighter weight.

Claims (2)

(57) [Claims] C .: 1.1 to 4% by weight, S: 0.1 to 1% by weight
%, Hexagonal boron nitride: 0.05-1%, Cu: 0.5-
/ 4%, the balance being Fe and unavoidable impurities, and a free graphite-precipitated iron having excellent strength and wear resistance, characterized by having a structure in which fine free graphite is precipitated on a pearlite base material. Sintered material. 2.% by weight: C: 1.1 to 4%, S: 0.1 to 1
%, Hexagonal boron nitride: 0.05-1%, Cu: 0.5-
4%, P: 0.05-0.6%, the balance being Fe and unavoidable impurities, and a structure in which fine free graphite is precipitated on a pearlite base material. Free graphite-precipitated iron-based sintered material with excellent strength and wear resistance characterized by the following characteristics.