JPH02270902A - Manufacture of iron sintered product - Google Patents

Abstract

PURPOSE:To manufacture a high density iron sintered product containing little O2 and excellent in productivity at a low cost by executing decarbonizing treatment to pulverized product of white pig iron, kneading with binder, heating in the air after injection-molding, removing the binder and sintering after further executing hydrogen reduction treatment. CONSTITUTION:The high carbon-containing iron as the white pig having brittle material quality by rapid cooling, is finely pulverized and heated, e.g., at 760 deg.C for a 2 hour in the air to execute decarbonization. To this decarbonize-treated iron powder, the binder of paraffine, wax, polyethyrene, etc., is added and kneaded to execute the injection-molding to have the desired shape. This forming product is heated at <=350 deg.C in the air to remove the binder in the forming product, and successively this is heated at 300 - 600 deg.C under hydrogen-containing atmosphere, and after reducing oxide film contained in the forming product into the iron, this is sintered and the high density and high purity iron series sintered product having little oxygen content is manufactured at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a processing method for the sintering of injection molded iron powder compacts.

[Conventional technology]

BACKGROUND ART Conventionally, injection-molded sintered bodies using iron powder as a molding material have been made using iron powder obtained by an atomization method or the like and having a spherical shape or a shape close to the spherical shape.

However, iron powder obtained by the atomization method or the like has a low production capacity and is expensive, making it unsuitable for mass production.

On the other hand, as a method for obtaining fine iron powder at a relatively low cost, there is a method in which a high carbon molten metal having a white pig iron structure is rapidly cooled and crushed, and then this is further mechanically crushed.

During this mechanical crushing, the raw materials to be treated undergo a movement of being crushed against each other, so that the produced fine powder has a flat plate shape. For this reason, compared to injection molded products using spherical powder, long-term heating is required to remove volatile matter from the binder resin material after molding, that is, degreasing work, and if it is incomplete, the molded product will deform. There was a drawback.

In addition, in the fine pulverization process of mechanical crushing, the powder is mixed with water in the form of a slurry, so that an oxide layer is formed on the surface of the fine powder produced.

Therefore, as the IR1m crushing and m crushing process,
As described in Japanese Patent Application No. 3-266002, Japanese Patent Application No. 63-58684, etc., a step is required to remove oxygen by contacting carbon and hydrogen contained in the powder itself. In this oxygen removal process, activation of the powder surface causes sintering and agglomeration, which increases the particle size. Therefore, in order to maintain the powder particle size below the average of 10 μm required for injection molding, the processing temperature must be lowered to some extent. The sintered body using this powder has the disadvantage that the voids with the oxide film become a bottleneck for shrinkage, making it difficult to obtain a molded body with only a low density.

[Problem to be solved by the invention]

The problem to be solved by the present invention is to produce a high-density injection-molded body with low oxygen content using fine powder with an average size of 10 μm or less obtained by crushing high-carbon iron such as white pig iron, which has the above-mentioned drawbacks. The goal is to find a way to obtain it.

[Means to solve the problem]

The present invention involves injection molding using fine iron powder obtained by pulverizing quenched high carbon iron that has been turned into white pig iron and subjecting it to decarburization treatment, and then heating this injection molded product to a temperature of 350°C or less in an atmospheric atmosphere. The binder resin is removed by vaporization, and further
This problem was solved by hydrogen reduction at 00°C followed by sintering.

[Effect]

Injection molding uses around 10% binder, and after molding, most of these binders must be removed in a resin process. Some binders, such as dibryl phthalic acid, evaporate at low temperatures, while others, such as polypropylene, have high evaporation temperatures. The latter binder is a polymeric resin that is difficult to evaporate in an inert atmosphere, but
When heated in the atmosphere, it reacts with oxygen and is converted into a substance with small molecules that evaporates easily, so it can be degreased at low temperatures.

When degreasing in an inert atmosphere, for example nitrogen, 50
Although it is necessary to heat to around 0°C, in atmospheric degreasing, degreasing is almost completed at around 300°C, resulting in a significant reduction in processing time.

On the other hand, the degreasing time is also greatly affected by the shape of the powder. In other words, if it is a spherical object, the gasified binder will come out relatively easily, but if the crushed powder contains a flat plate-like object, the gas passage will be complicated, and if the processing time is insufficient, bulges, cracks, etc. will occur. Prone to defects.

Therefore, if atmospheric degreasing can be applied to crushed powder, which requires a longer degreasing time than atomized powder, one of the factors inhibiting injection molding can be removed.

Atmospheric degreasing applied to oxide-based ceramics also has the problem of oxidation when metal powder is used, but high-carbon crushed iron powder still has some oxygen remaining after decarburization, which causes new oxidation. It's not a big problem just to prevent it.

Generally, in the sintering process of iron powder, it is heated to about 800℃ in an inert atmosphere such as nitrogen, and then heated to about 1200℃ in a hydrogen stream.
Sinter at temperatures above ℃. Moreover, under these conditions, when the iron powder having an oxide film on its surface is changed into a hydrogen-rich atmosphere, the surface is immediately reduced and sintering occurs.

Therefore, if the surrounding sintering progresses before hydrogen permeates and voids with oxide films are left behind, the shrinkage of the compact will not be prevented, the sintered density will not increase, and a good quality compact will not be obtained.

Therefore, as a result of investigating the sintering behavior in a hydrogen-rich atmosphere of a compact made by injection-molding fine iron powder obtained by mechanically crushing the above-mentioned quenched high-carbon ferrous iron and performing the above-mentioned atmospheric degreasing, it was found that in a certain heating temperature range, the entire surface It was found that although deoxidation progressed, sintering hardly occurred.

That is, there is an inflection point in the increase in the progress of deoxidation at approximately 300°C, and below 300°C, substantial sintering does not occur, but deoxidation progresses slowly and the reaction takes too long, making it difficult to apply it industrially. Can not. On the other hand, if the temperature exceeds 600°C, local sintering progresses rapidly, pores are blocked, and a dense sintered body cannot be obtained.

Therefore, if the compact is reacted with hydrogen gas before sintering begins, oxygen on the surface of the iron powder will be completely removed, and a healthy sintered compact will be obtained when the sintering temperature is reached.

[Example] Carbon content 3.1% by weight, oxygen content 8.0% by weight1,
Crushed iron powder with an average particle size of 7.6 μm was heated at 760°C for 2 hours to form a light sintered body, which was loosened using a vortex mill. Carbon content IQ: 0.3% by weight, oxygen content: 0.6
A raw material powder having a weight percent and an average particle size of 8.4 μm was obtained.

A binder composed of paraffin, wax, and polyethylene was kneaded with iron powder in an amount of 10% by weight, and the mixture was injection molded to a size of 3 x 6 x 5 Q mm under normal conditions.

This was charged into a degreasing furnace in an air atmosphere, and heated from 80°C to 300°C.
The temperature was raised to 6°C/hr over 38 hours. The weight change after degreasing was 7.5%. This weight change corresponds to 82.5% of the binder amount.

On the other hand, for comparison, molded bodies made under the same conditions were heated from 80°C to 500°C for 60 hours to 1 hour in a nitrogen atmosphere.
When degreasing was carried out for 00 hours, the swelling and surface cracking after degreasing were significant, and a defect-free degreased molded article was obtained for the first time after 140 hours.

Next, in order to sinter this degreased molded body,
The temperature was raised at a rate of 1300° C./hour and maintained at 1300° C. for 5 hours.

At this time, the density of the sintered body obtained by flowing hydrogen at 100+n 1 /minute from 800° C. was 6.8, and the relative density was 87%.

As a result of observing the internal structure using a microscope, pores with an oxide film on the inner surface were found here and there.

On the other hand, the density of the sintered body in which hydrogen was flowed from 300℃ using the same heat treatment pattern was 7.2, and the relative density was 92%.
Met. When this internal structure was observed under a microscope, it was found that almost no oxide film was present on the inner walls of the pores.

〔Effect of the invention〕

The sintering method of the present invention can provide the following effects.

(1) Rapid degreasing is possible in the atmosphere at low temperatures, increasing work efficiency.

(2) Degreasing can be carried out in a short time even if crushed powder containing irregularly shaped powder is used as the raw material powder.

(3) High-density, high-purity iron sintered bodies can be obtained even with raw iron powder having an oxide film surface.

(4) Therefore, crushed fine iron powder, which itself can be obtained industrially at low cost, can be used to a large extent for injection molding.

Patent Applicant: Yoshikawa Kogyo Co., Ltd. Agent: Kobori Procedural Amendment May 22, 1989, 1999 Patent Application No. 92280 2, Title of Invention: Process for manufacturing iron sintered products 3, Person making the amendment Relationship to the incident Patent applicant 4, agent address ■812 1-1-1 Hakata Ekimae, Hakata-ku, Fukuoka City
1 Hakata Shin-Mitsui Building Dai (092) 451-8781 (Li) Page 5, line 10 of the specification, "Sintered. Moreover, under these conditions," is corrected as follows.

“There is a method of sintering or a method of sintering in a vacuum.

Moreover, under the previous conditions, ``(2) Page 5, line 5 from the bottom cannot be obtained. '', add the following sentence.

``Of course, the latter vacuum sintering method does not remove the oxide layer, so the density does not increase.''

Claims (1)

[Claims] 1. Pulverize quenched high carbon iron, perform injection molding using fine iron powder that has been decarburized, degrease the injection molded product at a temperature of 350°C or less in an air atmosphere, and further
A method for manufacturing iron sintered products, which involves performing hydrogen reduction at 0 to 600°C and then sintering.