JPS58126955A - Sintered material having cast iron structure and its manufacture - Google Patents

Abstract

PURPOSE:To inexpensively manufacture a sintered material having a cast iron structre by a relatively simple operation by molding a composition prepared by adding specified percentages of Si, C and P to Fe and by sintering the molded body under specified conditions. CONSTITUTION:A blended composition consisting of, by weight, 0.8-3.0% as Si of ferrosilicon powder contg. 15-75% Si and having 1-10mum average particle size, 1-5% graphite powder having <=20mum average particle size and 0.02-0.4% as P of Fe-P alloy powder contg. 0.3-28% P as powdered starting materials is uniformly mixed and molded by a conventional powder molding method. This molded body is sintered at 1,050-1,160 deg.C in a reducing atmosphere to obtain a sintered material having a cast iron structure consisting of free graphite, a ferrite phase and a pearlite phase.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sintered material having a cast iron structure obtained by a powder metallurgy method, and a method for producing the same.

At present, ordinary cast iron has excellent properties such as wear resistance, machinability, and vibration absorption ability, and is used in a wide variety of fields as a mechanical component due to its low price. It is known that this excellent property of cast iron is mainly due to the uniformly and abundantly dispersed free graphite. For example, in cast iron sliding materials, free graphite acts as a solid lubricant on the sliding surface to reduce friction, and the remaining pores of free graphite serve as oil reservoirs to retain oil. (1) Also, during cutting, the finely distributed free graphite acts as a chip breaker and plays the role of improving machinability.

Furthermore, since the production of cast iron parts had to rely on the casting method, it also had the essential problem of being inferior in mass productivity compared to the powder metallurgy method.

Until now, various attempts have been made to research sintered materials that have the excellent properties of cast iron and the mass productivity of powder metallurgy, and their manufacturing methods, but none have been successful for the following reasons. It was not possible to do so. That is, (a) when a large amount of graphite is added to an iron-based alloy (approximately 3% by weight, similar to cast iron) and sintered, cementite precipitates, the matrix becomes hard, the mechanical properties deteriorate, and the sintering temperature decreases. If the value is lowered, cementite precipitation can be prevented, but strength cannot be obtained.

(b) It is possible to prevent the precipitation of cementite by adding graphitization-stable elements such as Si, but
The conditions for dispersion into solid solution require heating to approximately 1,200°C or higher, which is much higher than the sintering temperature of ordinary iron-based sintered materials, which increases manufacturing costs. 8, unless the sintering atmosphere is strictly controlled.
1 may be oxidized.

Therefore, from the above-mentioned viewpoint, the present inventors have developed a cast iron structure in which free graphite is dispersed in a matrix consisting of a ferrite phase and a ferrite phase under normal production conditions for iron-based sintered materials. As a result of conducting research to obtain the material by powder metallurgy, the particle size of ferrosilicon powder, which is the Sl source in the iron-based sintering raw material, was adjusted to a specific range, and C and S1
He discovered that the purpose could be achieved by appropriately selecting the composition range of the raw materials, and first filed a patent application in 1164-1983.
No. 69 (hereinafter referred to as prior invention), 15 to 75% (
Ferrosilicon powder containing 81 of
．． 8 to 2.5%, 2 to 5% of graphite powder with an average particle size of 20 μm or less, and iron powder are mixed uniformly, and after molding using a normal powder molding method, We proposed a method for producing sintered materials, which consists of sintering at a predetermined temperature in a reducing atmosphere.

However, the recent demands for this type of material are even more stringent, and the present inventors have also found that it has superior strength and wear resistance than the sintered material having a cast iron structure obtained by the prior invention, and In order to find a sintered material with a cast iron structure that has good rigidity in terms of workability, and a reliable and highly efficient manufacturing method, we conducted further research and found that the composition was almost the same as that used in the prior invention. In the raw materials of
When sintering is performed with the addition of a specific amount of P, the strength and wear resistance of the sintered material itself further improves due to the action brought about by the added P component, that is, the action of strengthening the base and promoting sintering. Despite this, we have come to the conclusion that the rigidity is not impaired in any way.

Therefore, this invention was made based on the above findings, and the sintered material contains Si: 0.8 to 3.0%.

C: 1-5%, P: 0.02-0.4%, F
e and unavoidable impurities: By making the structure a cast iron structure consisting of free graphite, a ferrite phase, and a pearlite phase, it has particularly excellent strength and wear resistance, and has excellent resistance to stiffness. Ferrosilicon powder containing 15 to 75% of 81 and having an average particle size of 1 to 10 μm:
Fe-P alloy powder containing 0.8 to 3.0% sii, graphite powder with an average particle size of 20 μm or less: 1 to 5%, and 0.3 to 28% P: 0.02 in P amount ~0.40%,
By uniformly mixing raw material powders having a composition in which the remainder is iron powder, molding using a normal powder molding method, and then sintering in a reducing atmosphere at a temperature range of 1050 to 1160°C. The present invention is characterized in that it is possible to produce a sintered material having a cast iron structure consisting of free graphite, a ferrite phase, and pearlite.

In other words, the reason why a material having a cast iron structure can be obtained by sintering as described above is that when the particle size of ferrosilicon powder, which is the Si source in the iron-based sintering raw material, is adjusted to a specific range, the sintering raw material iron powder particles 81 components are uniformly distributed on the surface layer, and the S1
is dissolved in Fe without oxidizing during sintering, and the α of Fe is
The fact that C and S1 stabilize the phase and accelerate the diffusion between Fe particles, thus promoting sintering.
By appropriately selecting the composition range of the raw materials, approximately 105
Fe particles that have become γ phase at a heating temperature of 0°C increase the solid solubility limit of C, and by regulating the particle size of C powder below a specific value, C can be easily diffused into Fe rice grains. Become,
Then, during the cooling process, the fine C around these dissolved in Fe precipitates with voids and undissolved graphite as nuclei due to the graphitization promoting effect of 81, and finally, 81 forms around the free graphite. - This is due to the technical reason that a so-called cast iron structure with a ferrite phase and a pearlite phase on the outside is obtained.

The iron powder used in the production of the sintered material is preferably one that is normally used as a raw material for powder metallurgy, and the powder is formed under normal conditions, for example 4 to 6 tons/c
! A molding pressure of about 100 ml is applied, and a suitable reducing atmosphere during sintering is, for example, ammonia decomposition gas. Furthermore, the Fe--P alloy powder added to the raw material may have any particle size as long as uniform mixing is possible.

Next, in the sintered material of the present invention and the manufacturing method thereof, the composition range of the sintered material, the 81 content in the ferrosilicon powder, the blending amount of the ferrosilicon powder, the blending amount of the graphite powder, and the blending amount of the Fe-P alloy. The reason why the P content, the blending amount of the Fe-P alloy powder, the average particle diameter of the ferrosilicon powder and the graphite powder, and the sintering temperature were limited to the above-mentioned values will be explained.

■Si content of sintered material The Si component has the effect of increasing the strength and stiffness of the sintered material, but if its content is less than 0.8%, the desired effect will not be achieved. On the other hand, if it exceeds 3.0 yen, the strength will decrease, so the content should be reduced to 0.
．． It was limited to 8-3.0%.

■C content of sintered material If the content of C component is less than 1 yen, it will not be possible to provide sliding properties comparable to cast iron, while if the content exceeds 5%, it will be difficult to achieve a uniform blend, and Since the strength decreases significantly, the content was limited to 1 to 5%.

■ P content of sintered material The P component has the effect of strengthening the base of the sintered material and promoting sintering, thereby improving strength and wear resistance. If the content is less than 0.40 inch, the desired effect cannot be obtained; on the other hand, if the content exceeds 0.40 inch, the base will harden and the rigidity will deteriorate. Limited.

■ 81 content in the raw material 7Erosilicon powder If the 81 content in the ferrosilicon powder as a source of Sl in the sintered metal is less than 15%, the 7Erosilicon powder becomes soft and difficult to grind. On the other hand, if the amount exceeds 75 cm, the amount as ferrosilicon powder is regulated to 81%, and the total amount of ferrosilicon powder blended is small, and the iron powder surface cannot be sufficiently coated. Its content was limited to 15-75%.

■ P content in raw material Fe-P alloy powder Fe-P alloys with a P content of about 0.3 to 28 inches are commonly available on the market, and in addition, Fe-P alloys with a P content of about 0. If the content is less than 3%, it will be necessary to increase the amount of powder added, making it difficult to adjust the composition, whereas if the content exceeds 28%, it will be extremely difficult to manufacture. , its content was limited to 03-28%.

■ Ferrosilicon powder and graphite powder as raw materials.

and Fe-P alloy powder blending amount During sintering, there is almost no relative loss between the blended raw materials, so the blending amount is adjusted so that a sintered material with the predetermined component composition can be obtained. Silicon powder: S1 amount was limited to 0.8 to 3.0%, graphite powder: 1 to 5%, Fe-P alloy powder: P amount was limited to 0.02 to 0.40%.

■ Particle size of ferrosilicon powder If the average particle size of the ferrosilicon powder to be blended is less than 1 μm, the powder raw material will oxidize too quickly and be difficult to handle.On the other hand, if the average particle size exceeds 1-0 μm, iron powder The average particle size of 1 to 10μ slows down the diffusion into particles, delays the formation of α phase, and reduces mechanical properties.
It was limited to m.

(2) Particle size of graphite powder If the average particle size of the graphite powder to be blended exceeds 20 μm, the specific surface area becomes small and diffusion into the iron powder particles becomes slow, so the average particle size was limited to 20 μm or less. Preferably, this average particle diameter is optimally 15 μm or less.

■ Sintering temperature If the sintering temperature is less than 1050°C, most of the sl remains undiffused, so the resulting sintered material cannot be expected to have sufficient strength.
On the other hand, if the temperature exceeds 1160'C, a liquid phase may begin to appear depending on the composition and deformation of the sintered material may occur.
The temperature was limited to 50-1160°C.

Next, the present invention will be explained in comparison with Examples and Comparative Examples.

For each example, the raw material powders shown in Table 1 were prepared, these raw material powders were blended into the composition shown in Table 1, mixed, and then molded into a green compact at a pressure of 4 ton/i. By sintering these green compacts in an ammonia decomposition bath atmosphere at the temperatures shown in Table 1, they have substantially the same composition as the blended composition, and both have lo
Sintered material 1 of the invention with dimensions of mXlo11X50
-17 and Comparative Sintered Materials 1-5 were produced, as well as molten Fe12 conventional cast iron.

The tensile strength, friction and wear characteristics, and rigidity of each of these materials were measured, and the results were also included in the first
Shown in the table.

The friction and wear characteristics were measured using a bottle-on-disk type tester using pins made from the various sintered materials and conventional cast iron mentioned above, and disks made from 845C Cr-plated material. Speed: 1m 7
1M, load: 6 kgf/d test shift,
- Evaluation was made by measuring the specific wear amount of test i, and the rigidity resistance was expressed as the time required to penetrate a sample with a diameter of 3.2 mm φ through a sample with a thickness of 5.5 mm. Awl material: 2 High-speed steel 9 Rotation speed: 400 rpm, pressing crab 5kl
i! It was measured under the condition of f.

From the results shown in Table 1, it can be seen that the sintered materials 1 to 17 of the present invention have almost the same stiffness and have higher strength and wear resistance than the comparative sintered materials 1 to 5 that do not contain P. It is clear that the sintered materials 1 to 17 of the present invention have substantially the same rigidity as conventional molten cast iron, but have poor strength and wear resistance. is significantly superior.

As described above, according to the present invention, a sintered material having a cast iron structure can be manufactured at a low cost with relatively simple operations, so it is possible to manufacture not only mechanical parts having mechanical properties equivalent to those of cast iron, but also machine parts having the same properties as cast iron. This brings about industrially useful effects, such as the ability to efficiently mass-produce small mechanical parts with complex shapes.

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Claims (2)

[Claims] (1) Si: 0.8 to 30%, C: 1 to 5%, P: 0.02 to 0.40%, Fe and unavoidable impurities: balance (weight%), and A sintered material characterized by having a cast iron structure consisting of free graphite, a ferrite phase, and a pearlite phase. (2) Contains 15-75% of 81 and has an average particle size of 1
~10 μm ferrosilicon powder: 0,8-3 with 81 amount
．． 0chi, graphite powder with average particle size of 20μm or less: 1-5%, 03-2
Fe-P alloy powder containing 8 P: O in P amount, 0
After uniformly mixing raw material powders having a compounding composition of 2 to 0.4%, iron powder: balance (more than 1% by weight) and molding using a normal powder molding method, the mixture is heated to 1050 to 1160% in a reducing atmosphere. A method for producing a sintered material having a cast iron structure consisting of free graphite, a ferrite phase, and a pearlite phase, the method comprising sintering at a temperature range of °C.