JPS58126959A - Sintered material with cast iron structure and method for producing the same - Google Patents

Abstract

PURPOSE:To obtain a sintered material having a cast iron structure by mixing ferrosilicon powder with graphite powder, copper powder and iron powder so that specified amounts of Si, C and Cu are contained and by sintering the mixture at a specified temp. in a reducing atmosphere after molding. CONSTITUTION:A composition consisting of, by weight, 0.8-3% Si, 1-5% C, 1-4% Cu and the balance Fe with inevitable impurities is prepared by mixing ferrosilicon powder contg. 15-75% Si and having 1-10mum average particle size with graphite powder, copper powder and iron powder each having <=20mum average particle size. The composition is molded by a conventional powder molding method and 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 the excellent properties of cast iron are primarily due to the uniformly and highly 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 9 for oil retention. Furthermore, during cutting, the finely distributed free graphite acts as a chip breaker and plays the role of improving rigidity.

However, although cast iron has such excellent properties as a material for machine parts, on the other hand, if the casting capacity is small, the cooling rate after casting is fast, resulting in white pig iron, and for small parts, cast iron's original properties There was a problem in that it was not possible to obtain products with specific characteristics.

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. In other words, (a) When a large amount of graphite (approximately 3% by weight, equivalent to cast iron) is added to an iron-based alloy and sintered, cementite precipitates and the base becomes hard9, mechanical properties decrease, 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 developed a powder material having a cast iron structure in which free graphite is dispersed in a matrix consisting of a pearlite phase and a ferrite phase under normal manufacturing conditions for iron-based sintered materials. As a result of research aimed at obtaining the desired results using metallurgical methods, the particle size of ferrosilicon powder, which is the 81 source in the iron-based sintering raw material, was adjusted to a specific i range, and C and S
I discovered that the objective could be achieved by appropriately selecting the composition range of the raw materials, and first filed a patent application in 1983-116.
469 (hereinafter referred to as prior invention), 15 to 75%
Ferrosilicon powder containing Si (hereinafter referred to as % by weight) and having an average particle size of 1 to 10 μm, with a Si content of 0.0 μm.
8 to 2.5% of graphite powder with an average particle size of 20 μm or less
Sintering, which consists of uniformly mixing raw material powder with a composition of ~5% and iron powder, molding it using a normal powder molding method, and then sintering it at a predetermined temperature in a reducing atmosphere. A method for manufacturing the material was proposed.

However, the recent demands for this type of material are even more stringent, and the present inventors have also found that the sintered material with a cast iron structure obtained by the prior invention has superior strength and wear resistance. Furthermore, 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 it is almost the same as that used in the prior invention. In the raw materials of the composition,
When a specific amount of Cu is added and sintered, the added C
Even though the strength and wear resistance of the sintered material itself are further improved by the action brought about by the u component, that is, the action of strengthening the matrix and stabilizing pearlite, the rigidity is not impaired in any way. We have come to this conclusion.

Therefore, this invention was made based on the above knowledge, and the sintered material contains Si: 0.8 to 30%.

C: 1 to 5%, Cu: 1 to 4%, Fe and unavoidable impurities: the remainder, and by making the structure a cast iron structure consisting of free graphite, a ferrite phase, and a pearlite phase, It is characterized by particularly excellent strength and abrasion resistance, as well as excellent properties such as rigidity and vibration absorption ability, and furthermore, it contains 15 to 75% of 81, and ferrosilicon powder with an average particle size of 1 to 10 μm: 0 in sii
Graphite powder with 8-3°0% and average particle size of 20 μm or less: 1
After uniformly mixing raw material powders having a composition of ~5%, copper powder: 1~4%, and the balance consisting of iron powder, and molding using a normal powder molding method, in a reducing atmosphere, 1050-1
The present invention is characterized in that a sintered material having a cast iron structure consisting of free graphite, a ferrite phase, and pearlite can be produced by sintering in a temperature range of 160°C.

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 the ferrosilicon powder, which is the Sl source in the iron-based sintering raw material, is adjusted to a specific range, the surface layer of the sintering raw material iron powder particles 81 components are uniformly distributed in the sintering process, and the S1 is solid-dissolved in Fe without being oxidized during sintering, stabilizing the α phase of Fe, and accelerating the diffusion between Fe particles, thus promoting sintering. 1050 by appropriately selecting the composition range of the C and S1 raw materials.
The Fe particles that have become r-phase at the heating temperature of ℃ increase the solid solubility limit of C, and by regulating the particle size of the C powder to below a specific value, C can be easily diffused into the 20 particles. Then, during the cooling process, the fine C around these dissolved in Fe is precipitated by the graphitization promoting effect of 81, with the vacancies and undissolved graphite as nuclei, and finally, free carbon is formed. Graphite mawashi 9 to 8
This is due to the technical reason that a so-called cast iron structure with a 1-ferrite phase and a pearlite phase on the outside can be obtained.

It should be noted that the iron powder used for producing the above-mentioned sintered material is preferably one that is normally used as a raw material for powder metallurgy, and the powder is formed under normal conditions, such as 4 to 6 tb. For example, ammonia decomposition gas is suitable as the reducing atmosphere. Furthermore, the copper powder added to the raw material is preferably one normally used for powder metallurgy, but any particle size can be used 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 Si content in the ferrosilicon powder, the amount of ferrosilicon powder, the amount of graphite powder, and the amount of copper powder. , the reason why the average particle diameters of the ferrosilicon powder and graphite powder, and the sintering temperature were limited as described above will be explained.

■ 81 content of sintered material The Si component has the effect of increasing the strength of the sintered material and improving its machinability, but if its content is less than 0.8%, the desired effect will not be achieved. On the other hand, its content is 30
If it exceeds 0.9%, the strength will decrease, so the content was limited to 0.8 to 3.0%.

■ C content of sintered material If the content of C component is less than 1%, it is not possible to maintain the sliding properties normally found in cast iron, while if the content exceeds 5%, it becomes difficult to achieve a uniform blend. Also, since the strength decreases significantly, its content was limited to 1 to 5%.

■ Cu content of sintered material The Cu component has the effect of strengthening the base of the sintered material and stabilizing pearlite, thereby improving strength and wear resistance, but if the content is less than 1%, The effect is not clearly manifested, and on the other hand, even if the content exceeds 4%, no further improvement in the effect is observed and it is also uneconomical, so the content was limited to 1 to 4%.

■ 81 content in ferrosilicon powder as a raw material If the 81 content in ferrosilicon powder as a source of Si in the sintered metal is less than 15%, the ferrosilicon powder becomes soft and difficult to grind. On the other hand, if it exceeds 75%, the amount as ferrosilicon powder, that is, the amount added is restricted to 81%, and the total amount of ferrosilicon powder blended decreases, making it impossible to sufficiently coat the surface of the iron powder.
Its content was limited to 15-75%.

■ Ferro silicon powder and graphite powder as raw material powders.

Since there is almost no relative loss in the blended raw materials themselves during sintering, the blended quantities of copper powder and copper powder should be adjusted so that a sintered material having the above-mentioned composition range can be obtained. Powder = 0.8 to 3.0% in Sl amount, graphite powder: 1 to 5%, copper powder: 1 to 4
It was limited to chi.

■ Particle size of ferrosilicon powder When the average particle size of the ferrosilicon powder used in the blend is less than 1 μm, the raw material powder oxidizes quickly and becomes difficult to handle.On the other hand, when the average particle size exceeds 10 μm, it becomes iron powder particles. The average particle size should be reduced from 1 to 10 μm because the diffusion of α phase is delayed and the mechanical properties are deteriorated.
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, much of the Si remains undiffused, so the resulting sintered material cannot be expected to have sufficient strength.
On the other hand, if the temperature exceeds 1160°C, depending on the composition, a liquid phase may begin to appear and deformation of the sintered material may occur.
The temperature was limited to 0 to 1160°C.

Next, the present invention will be explained using examples and comparing with comparative examples.

For each example, 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/cnL. These green compacts are then sintered in an ammonia decomposition gas atmosphere at the temperatures shown in Table 1 to obtain a powder that has substantially the same composition as the blended composition and is lcl++aX101++11X5011! Inventive sintered materials 1-15 and comparative sintered materials 1-5 having dimensions of IE were manufactured, and conventional cast iron of molten Fe12 was also prepared.

The tensile strength, friction and wear characteristics, and rigidity of each of these materials were measured, and the results are also shown in Table 1.

The friction and wear characteristics were measured using a pin-on-disk type tester using pins made of the various sintered materials and melted conventional cast iron, and a disk made of 545C Cr-plated material. Speed: 14n/sec.

Load: 6 IKgf/(Tested under 7 conditions and evaluated by measuring the specific wear amount after the test, and the stiffness performance!
5. The time required to penetrate a 5111-thick sample with a 3.2 mm diameter aperture. Material of the aperture: High-speed steel. Measured under the conditions of 2 revolutions: 400 rpm, and a pressing force of 5 kgf. This is what I did.

From the results shown in Table 1, it can be seen that the sintered materials 1 to 15 of the present invention have almost the same rigidity and have higher strength and wear resistance than the comparative sintered materials 1 to 5 that do not contain Cu. It is clear that there has been further improvement.6. ? In addition, the characteristics of the sintered materials 1 to 15 of the present invention are as follows, compared to conventional cast iron made of ingots:
The machinability is almost the same, but the strength and wear resistance are 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.

Applicant: Mitsubishi Metals Corporation Agent Tomi 1) Kazuo

Claims (2)

[Claims] (1) Si: 0.8-3.0%. It has a composition consisting of C: 1 to 5%, Cu: 1 to 4%, Fe and unavoidable impurities: balance P (more than % by weight), and has a cast iron structure consisting of free graphite, a ferrite phase, and a pearlite phase. A sintered material characterized by: (2) Contains 15-75% of 81 and has an average particle size of 1
~10 μm ferrosilicon powder: Sii fo, 8
~3.0%, graphite powder with average particle size of 2oμm or less: 1-5%, copper powder = 1
Raw material powders having a composition of ~4%, iron powder: balance (more than % by weight) are mixed uniformly, molded using a normal powder molding method, and then heated at a temperature of 1050 to 1160°C in a reducing atmosphere. 1. 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 within a range of 100 to 100 mm.