JP2743090B2 - How to control the carbon content of metal injection products - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling the carbon content of a metal injection product.

(Prior art) In producing general iron-based sintered parts, cast iron powder
A technique in which Fe ₂ O ₃ is added to improve sinterability and improve mechanical properties is disclosed in Japanese Patent Publication No. 61-3863, which aims to use cast iron cuttings. It is the invention which was completed.

On the other hand, when sintering metal powders, there is a method in which a binder is added to these powders and then molded into a predetermined shape, followed by sintering. A method of adding a large amount of a binder and performing injection molding has been attempted. Some have already been put to practical use.

In the latter case, a desired shape is injection-molded by mixing a metal powder, an organic substance mainly composed of resin and wax, and utilizing the fluidity of the organic substance.

The molded body is heated at a relatively low temperature while maintaining its shape, so that most of the organic matter is decomposed and removed.

The molded body after the binder removal is usually from 4% by weight to 15% by weight of the initially input binder amount so as not to be destroyed by handling, transfer and the like until the process proceeds to the subsequent main sintering step. %.

In the subsequent main sintering, most of the remaining binder is decomposed and removed, but part of it becomes carbon and remains in the metal sintered body.

(Problems to be Solved by the Invention) However, since the debinding step is usually performed in an inert gas atmosphere such as N ₂ , Ar or the like or in the air, if degreasing is performed in an inert gas atmosphere, Depending on the type of binder to be used and the mixing ratio with the metal powder, as an example, the amount of carbon remaining in the sintered body using an average 4 μm iron powder when the binder usage ratio is 45 vol% is shown in Table 1. As shown.

If the desired amount of carbon in the sintered body is not sufficient with the amount of carbon entering from these binders, the amount of carbon may be increased by further adding graphite powder, and there is no problem in the production method.

However, when the amount of carbon larger than the desired amount of carbon enters the sintered body from the binder, the amount of carbon must be accurately reduced by some method, and in reality, such a case is overwhelmingly more problematic. there were.

In view of this, the present invention oxidizes carbon remaining unnecessarily in the sintered body with the binder serving as a supply source,
The object of the present invention is to provide a method for controlling the carbon content of a metal injection-molded product capable of accurately reducing to a desired carbon content and obtaining a uniform structure without carbon segregation, and to solve the disadvantages of the prior art. It was done.

(Means for Solving the Problems) In order to achieve the above object, the invention of claim 1 of the present application is directed to an injection molded product comprising 55 to 65% by volume of iron powder for sintering and 35 to 45% by volume of an organic binder. When sintering after passing through the binder removal process, Fe ₂ O ₃ ,
By adding one or more metal oxides such as Fe ₃ O ₄ , Cu ₂ O, NiO, CoO, Cr ₂ O ₃ , MnO, V ₂ O ₃ and sintering in a reducing or non-oxidizing atmosphere, The binder serves as a supply source to control carbon remaining more than necessary to a desired carbon amount. According to a second aspect of the present invention, in the first aspect, the metal oxide has an average particle size of 1 to 2.5 μm.

(Function) According to the first aspect of the present invention, the amount of carbon remaining in the sintered body more than necessary with the binder as a supply source for the iron powder for sintering can be accurately reduced to a desired amount of carbon, and can be uniformly controlled. Therefore, a uniform structure without carbon segregation can be obtained.

According to the invention of claim 2, the average particle size of the metal oxide is 1
Since the size of the metal oxide is reduced to 2.5 μm to prevent the metal oxide particle size from becoming fine, during injection molding and cooling in the mold, even if the thermal conductivity of the metal oxide is poor, Since a compact having a small internal stress is produced without hindering heat conduction, cracks do not occur during degreasing.

(Examples) Hereinafter, the present invention will be described with reference to Comparative Examples and Examples.

Comparative Example To 4290 g of spherical iron powder having an average particle size of 4 μm, a carbon content of 0.01% and an oxygen content of 0.2%, (1). A binder mainly composed of microcrystalline wax; (2). (3) a binder mainly composed of a mixture of microcrystalline wax and low molecular weight acrylic (molecular weight: 55,000) in equal proportions; 391.5g (8.36% by weight) of a binder containing polyamide as a main component was added, and 140
The mixture was kneaded at 2 ° C. for 2 hours, and the kneaded product was pulverized and put into an injection molding machine.

Then, a rod-shaped test piece of φ5 × 501 was injection-molded at a molding pressure of 1 ton / cm ² .

Next, the molded product was heated to 500 ° C. at a rate of 10 ° C./hr in an N ₂ atmosphere, and was held for 2 hours and then cooled in a furnace. Then in a vacuum furnace 1
Sintering was performed at 250 ° C for 1 hour to obtain a sintered product having a relative density of 95 to 97%.

Table 1 shows the analysis results of the carbon content of each of the 20 sintered products at this time.

Example 1. 4 μm iron powder used in Comparative Example and Fe ₂ O having an average particle size of 2 μm
_{The three} powders were mixed in a V-type mixer for 30 minutes according to the composition shown in Table 2.

Then, 391.5 g (8.36% by weight) of a binder containing polyamide as a main component was added to 4290 g of each mixture, and kneaded at 140 ° C. for 2 hours by a pressure kneader. This kneaded product was pulverized and put into an injection molding machine.

A rod-shaped test piece of φ5 × 501 was injection molded at a molding pressure of 1 ton / cm ² .

Next, each of the 5 molded products is 10 ° C / hr up to 500 ° C in N ₂ atmosphere.
The temperature was raised at the rate described above, the temperature was maintained for 2 hours, and then the furnace was cooled. Thereafter, each of the five degreased samples was sintered in a vacuum furnace at 1250 ° C for 1 hour to obtain a sintered product having a relative density of 95 to 97%.

The relationship between the amount of Fe ₂ O ₃ added and the residual carbon is shown in the figure. According to this, it can be seen that the amount of residual carbon can be controlled according to the amount of addition.

The variation was within the range of 0.1% C at maximum with high accuracy.

Example 2. To 4035 g of the 4 μm iron powder used in the comparative example, 2% Ni-1.5%
The average particle diameter is 1 μm, with Cu-0.2% C as the target value of the component.
109 g of NiO powder, 73 g of Cu ₂ O powder having an average particle size of 2.5 μm, and 73 g of Fe ₂ O ₃ powder having an average particle size of 2 μm were added.
The mixture was mixed for 30 minutes with a shape mixer. To 4290 g of the mixed powder, 391.5 g (8.36% by weight) of a binder containing polyamide as a main component was added and kneaded at 140 ° C. for 2 hours by a pressure kneader, and the kneaded powder was pulverized into a rod-shaped test piece of φ5 × 501. Was injection molded at a molding pressure of 1 ton / cm ² .

Next, the molded article was heated to 500 ° C. at a rate of 10 ° C./hr in an N ₂ atmosphere, kept for 2 hr, and then cooled in a furnace. Then in a vacuum furnace 125
After sintering at 0 ° C. for 1 hour, the analysis of each element of Ni, Cu, and C was carried out. As a result, an iron-based sintered product almost at the target value of 2.04% Ni-1.52% Cu-0.22% C was obtained. Thus, a sintered alloy having a target component can be obtained by appropriately combining metal oxides.

In this example, when the particle size of the metal oxide is 1 to 2.5 μm, the average particle size of the iron powder for sintering is 4 μm, and the ratio of the particle size of (metal oxide / iron powder for sintering) is as follows: It becomes 0.25 to 0.625.

Of course, if the amount of carbon is insufficient due to the configuration of the metal oxide, the required amount of graphite may be added.

(Effect of the Invention) As described above, according to the first aspect of the present invention,
(1) By accurately reducing the amount of carbon remaining in the sintered body to a desired amount of carbon, a sintered body containing the desired amount of carbon can be obtained. Therefore, even when a binder having a large residual carbon content is used, the present invention can be applied to a low carbon component.

(2) Since the carbon remaining in the sintered body can be uniformly controlled, there is no segregation of carbon and a uniform structure can be obtained, so that the material strength is improved.

According to the second aspect, (3) the metal oxide is coated at the time of molding by suppressing the increase in the specific surface area of the metal oxide by setting the particle diameter of the metal oxide to 1 to 2.5 μm in the first aspect. By reducing the amount of the binder, the manufacturing cost can be reduced.

[Brief description of the drawings]

The drawing is a graph showing the relationship between the amount of added Fe ₂ O _{3 and} the amount of residual carbon by the method for controlling the amount of carbon in a metal injection product according to the present invention.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshikiyo Tanaka 3-1-1 Ueno, Hirakata-shi, Osaka Komatsu Manufacturing Co., Ltd. (56) References JP-A-2-57607 (JP, A)

Claims (2)

(57) [Claims] 1. An injection molded product comprising 55 to 65% by volume of iron powder for sintering and 35 to 45% by volume of an organic binder is sintered after passing through a binder removing step. Fe ₂ O ₃ , Fe ₃ O ₄ , Cu ₂ O, NiO, CoO, Cr ₂ O ₃ , MnO, V ₂ O ₃
By adding one or more metal oxides, etc., and sintering in a reducing or non-oxidizing atmosphere, the binder serves as a supply source to control unnecessarily remaining carbon to a desired amount of carbon. Characteristic method for controlling carbon content of metal injection products. 2. The metal oxide has an average particle size of 1 to 2.5 μm.
2. The method for controlling the carbon content of a metal injection product according to claim 1, wherein