JPH06136405A - Production of high-density pure iron sintered compact - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a dense pure iron powder sintered body without CIP or HIP treatment. [Structure] Carbonyl iron powder having an average particle size of 3 to 40 μm and a carbon content of 0.1 to 1.2% by weight is mixed with a binder, granulated, and injection-molded to remove a sample prepared by injection molding. Was done. Next, in a hydrogen atmosphere, temperature range 2
The sintered body was obtained by heating 00 to 1000 ° C. at a temperature rising rate of 1 to 10 ° C./min, holding at 1000 ° C. or 1300 ° C. for 1 hour, and then cooling.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a high density pure iron sintered product by powder metallurgy.

[0002]

2. Description of the Related Art A high density pure iron sintered product is used as a soft magnetic material for a printer yoke of a dot printer. The higher the density and the higher the magnetic properties and mechanical properties of these materials are, the more dense they are. At the same time, the smaller the amount of non-metallic inclusions, especially the amount of metal oxide, the better the mechanical strength and corrosion resistance.

When a pure iron sintered body having a carbon content of 0.05% or less is produced by powder metallurgy, low carbon iron powder is the main raw material. As this low carbon iron powder, carbonyl iron powder is generally used which is carbonized by hydrogen reduction of carbonyl iron powder. However, this low-carbon carbonyl iron powder contains a large amount of coarse agglomerated powder obtained by sintering a part of the powder during decarburization.

A high-density and dense sintered product could not be obtained only by producing a green compact by a press molding method or an injection molding method using a low carbon carbonyl iron powder containing these agglomerated powders as a main raw material and sintering. In order to obtain a high-density pure iron sintered body, this green compact is subjected to CIP (cold isostatic pressing) to densify it, or a low-density sintered product is subjected to HIP (high temperature). Hydrostatic press) was being processed. However, in these methods, the number of steps for CIP or HIP treatment increases, and the manufacturing cost also increases. In addition, these sintered products have an oxygen content of 0.1.
It is as high as 0.5% by weight and has a large amount of metal oxides.

It is also possible to remove the agglomerated powder in advance by classification, but the amount of the agglomerated powder is large, the yield of using the raw material is poor, and the manufacturing cost becomes high. It is also conceivable to grind the agglomerated powder, but it is difficult to grind it because the particle size of the raw material is small.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to obtain a high density pure iron powder sintered body without performing CIP or HIP treatment.

[0007]

[Means for Solving the Problems] An iron-based powder compact having an average particle size of 3 to 40 μm and containing 0.1% or more of carbon is placed in a reducing atmosphere at a temperature range of 200 to 1000 ° C.
The object can be achieved by heating and sintering at a temperature rising rate of 10 ° C / min.

[0008]

The iron-based powder used in the present invention has a carbon content of 0.
It should be 1 to 1.2% by weight. Carbonyl iron powder, reduced iron powder, atomized iron powder and the like can be used as the iron-based powder. If the carbon content of the iron-based powder is less than 0.1% by weight, the density of the green compact will not be sufficiently high, and the density will not be sufficiently increased by sintering. On the other hand, if it exceeds 1.2% by weight, the density of the green compact is high, but decarburization is insufficient during sintering and a low carbon sintered body cannot be obtained.

The average particle size of the iron-based powder must be 3-40 μm. If the average particle size is less than 3 μm, the sintering rate will be too fast, and the sintering will occur before the decarburization reaction is sufficiently carried out during sintering, resulting in a sintered body having a low carbon content up to the center of the sintered body. I can't get a body. On the other hand, the average particle size is 40μ
If it exceeds m, a high-density molded body cannot be obtained and the sintered body does not have a high density.

The above powder is formed into a green compact by a press molding method or a metal injection molding method. In the press molding method, the raw metal powder is mixed with about 1% by weight of a lubricant such as stearic acid, charged into a press die, and pressed into a green compact. The pressing pressure is preferably 400 to 600 MPa.

In the metal injection molding method, a raw metal powder is mixed with a large amount of an organic binder, granulated, and then injected into a mold by an injection molding machine to form a green body, which is heated at a low temperature in a non-oxidizing atmosphere and then bound. Is decomposed and removed to obtain a green compact. As the organic binder used in the metal injection molding method, a commonly used substance, for example, a thermoplastic resin such as polyvinyl alcohol or wax such as paraffin wax can be used. The organic binder is preferably 5 to 20% by weight. The injection conditions are as follows: injection temperature 80-200 ° C, injection pressure 50
-200 MPa is preferable. The binder is decomposed and removed by heating in a nitrogen stream at 250 to 300 ° C. for about 2 hours.

Sintering of the green compact must be done in a reducing atmosphere. The reducing atmosphere is preferably an atmosphere having a dew point of −20 ° C. or less, such as hydrogen, ammonia decomposition gas, or a mixed gas atmosphere of these and an inert gas. The flow rate and partial pressure of the atmosphere gas may be adjusted according to the amount of the sintered product.

The heating conditions are a temperature range of 200 to 1000 ° C., a heating rate of 1 to 10 ° C., and then heating to 1000 ° C. If it is necessary to further increase the sintered density, 1000
You may heat at -1300 degreeC for 0.5 to 5 hours. After that, it may be gradually cooled or rapidly cooled. If the temperature rising rate is less than 1 ° C./minute, it takes a long time for sintering, which is not preferable. On the other hand, when the heating rate is 10 ° C./minute or more, the sintering is too fast and the central portion of the green compact is not sufficiently decarburized.

[0014]

【Example】

Experiment Nos. 1 to 12: Carbonyl iron powder having an average particle size of 5 μm and carbon contents of 0.40, 0.70 and 0.89 wt%, respectively, was mixed with a binder, granulated, and injection pressure was 1
Injection molding at 00MPa and injection temperature of 160 ℃, size 3
A sample of 0 mm × 10 mm × 5 mm was prepared. The binder is low-density polyethylene, ethylene-vinyl acetate copolymer and reagent grade stearic acid in a weight ratio of 3: 1: 1.
8 parts by weight was added to 92 parts by weight of carbonyl iron powder.

The sample was heated to 450 ° C. in a nitrogen atmosphere at 2
The binder was removed by heating at a temperature rising rate of 0 ° C./min. Next, this was heated in a hydrogen atmosphere having a dew point of −55 ° C. and a flow rate of 5 l / min up to 200 to 1000 ° C. at a heating rate shown in Table 1, held at 1000 ° C. or 1300 ° C. for 1 hour, and then heated to 1100 ° C. in a furnace. After cooling, nitrogen was introduced into the furnace for forced cooling. The carbon content, oxygen content, relative density and microstructure of the obtained sintered body were examined. The results are shown in Table 1.

[0016]

[Table 1]

According to this, not only the relative density of the example is higher than that of the comparative example, but also the carbon content and the oxygen content are very low, and metal oxide inclusions are not recognized, so that excellent low carbon sintering is achieved. Goods have been obtained.

Experiment No. 13: Using low carbon carbonyl iron powder having an average particle size of 5 μm and a carbon content of 0.03% by weight,
Experimental example No. A sintered body was produced in the same manner as in No. 4, and the same evaluation results are shown in Table 1. According to this, it can be seen that high relative density cannot be obtained when low carbon iron powder is used.

[0019]

The average particle size is 3 to 40 μm and 0.1 to
Make a green compact with iron powder containing 1.2% by weight of carbon,
This is placed in a reducing atmosphere at a temperature range of 200 to 1000 ° C.
By heating and sintering at a temperature rising rate of 1 to 10 ° C./minute,
A dense pure iron sintered body can be obtained without CIP or HIP treatment.

Claims (1)

[Claims] 1. An average particle size of 3 to 40 μm and 0.1 to
A powder compact of iron powder containing 1.2% by weight of carbon in a reducing atmosphere in a temperature range of 200 to 1000 ° C. and 1 to 10 ° C.
A method for producing a high-density pure iron sintered body, which comprises heating at a rate of / min and sintering.