JPS5813602B2 - Reduction sintering method using induction heating of steel powder - Google Patents

Description

Detailed Description of the Invention: The surface of atomized powder produced by the water spray method used to produce iron powder, mill scale, etc. discharged in large quantities during hot rolling, is exposed to water and oxygen in the air during rapid cooling from high temperatures. An oxide film is formed by the reaction with

When this type of powder is used in powder metallurgy, it requires a long reduction process at a temperature of 1000 to 1200° C. in a furnace with a strong reducing atmosphere such as hydrogen gas.

In this method, the dew point also rises due to the reduction reaction of hydrogen gas, so it is necessary to flow a large amount of reducing gas, and there is a risk of explosion in a reduction furnace that uses hydrogen as its main component, so sufficient equipment management is required. .

Industrial reduction furnace production equipment uses a continuous belt conveyor, and a large amount of hydrogen is required for the frame at the furnace inlet to prevent air from entering, and the durability of the mesh belt in the hydrogen stream at high temperatures is also limited. This causes an increase in costs.

In addition, when reducing these oxides, Ni and Mo-based oxides are relatively easy to reduce, but Mn and Cr-based oxides have low free energy and are difficult to reduce, and cannot be reduced in a reduction furnace at a maximum temperature of about 1200°C. It takes several hours.

The purpose of the present invention is to solve or improve these problems, and to shorten the process by using unreduced powder and sintering the compact at the same time as reducing the compact.

In the present invention, a resin coated powder (R.C. P), then 2 to 6 to
Compacting at a pressure of n/cm', then 200 to 400
Cure for about 5-10 minutes at a temperature of .

By heating and hardening the resin, this curing prevents the generation of soot during the resin combustion during induction heating in the next process, and also prevents the green compact from deforming in the direction of the magnetic force due to the softening of the resin in the initial heating stage. This is done to prevent

The drawing shows the Rattler value for the molding pressure after heating the preform, which is the room temperature strength of the molded product after curing, where a is the case without curing and b is 20.
Curing was performed at 0° C. for 5 minutes, C at 300° C. for 5 minutes, and d at 400° C. for 5 minutes.

The steel powder used here contained 0.74% Mn and Cr.
O. It is made by coating the surface of 81% low-alloy steel powder with 2.5% phenolic resin, which leaves 20% residual carbon after burning the resin, and is molded to 7.5 gr with a diameter of 12.25.

In the figure, at a molding pressure of 5 ton/cm', the Rattler value was 2.5% without curing, but at 300°C it was 0.
．． It can be seen that this has improved to 1%.

An induction heating device for vertical conveyance requires a Rattler value that can sufficiently withstand the weight of stacked objects to be heated.

The above phenolic resins are novolac type, novolac +
Either the hexamine type or the resol type may be used, but the novolac type without hexamine is more advantageous than the resol type because it generates less odor gas, the amount of residual carbon can be easily adjusted, and two-stage curing is possible.

The above resin coated powder is made by heating steel powder to 130°C.
It is obtained by heating to ~160°C, adding phenol resin, kneading for about 30 seconds, and then classifying (passing through a sieve) while cooling with air on a vibrating conveyor.

The molded body after the above curing is 100 Hz to 1
An eddy current is generated in the grains by an induction heating device of 0.00 kHz, accelerating the temperature increase rate, and after about 1 to 4 minutes, the temperature rises to 1000 to 1
The reduction sintering reaction is completed by reaching 400° C. and maintaining it for 3 to 5 minutes.

The carbon remaining on the surface of the metal powder after the resin decomposition reacts strongly with the oxide on the surface of the metal powder to generate a CO reducing gas atmosphere inside the particles, and the reduction rate progresses in conjunction with the high temperature heating state.

Between the heated body and the coil is N to discharge the reaction gas.
Flow a non-oxidizing gas atmosphere flow of grade 2.

Conventionally, hydrogen or Ax ammonia decomposition gas is used as the reducing gas, but in the method of the present invention, a non-oxidizing gas is sufficient as it only requires the reaction gas to be quickly discharged, and the flow rate is lower than before and there is no risk of explosion etc. It is simple and easy to manage.

The coated phenolic resin has a reducing effect, and at the same time has a carburizing effect that adjusts the amount of carbon remaining in the powder after reduction. It also has a lubricating effect between particles during compaction, and is a binder during compaction. It has a multipurpose effect that also has the following effects at the same time.

If the amount of phenolic resin coated on the surface layer of the metal powder is less than 1%, chips will easily occur during transportation during curing after compaction, making handling inconvenient; In this case, the molded body collapses due to the gas generated by the decomposition of the phenol resin during curing, which is undesirable.

If the amount of phenolic resin is limited to 1 to 7% as mentioned above, the effective residual carbon content during reduction of this phenolic resin must be in the range of 10 to 60% to deoxidize the oxygen of iron powder. It will be a good thing.

If the residual carbon content is less than 10%, deoxidation may be insufficient, and if it is 60% or more, the carbon content is too large and the strength of the sintered body becomes weak.

Examples of the present invention are shown below. C: 0.03%, Cr
: 0.81%, Mn: 0.74%, MO: 0
．． 2 3%, Si: 0.03% initial oxygen amount 7 2 0
0 ppm unreduced low-alloy steel powder under 70 mesh is coated with 2.5% (wt%) novolac-type phenolic resin containing 20% residual carbon after combustion on the surface of the steel powder using a hot method. After making it into powder, 4t
The inner and outer diameter and height are 23φ x 4 at a molding pressure of on/cm'.
A cylinder of 2φ×14.5mm was formed and cured at 300° C. for 5 minutes, and then set in a 3KC high-frequency induction heating device in a non-oxidizing atmosphere of nitrogen.

The temperature rises to 1300℃ in about 3 minutes after electricity is applied, and this temperature is increased to about 5℃.
After holding for a minute, it was cooled to room temperature and the amount of oxygen was measured.
It was confirmed that the amount was reduced to 0 ppm.

In order to determine the strength of the sintered body, a pressure tube ring test was conducted and it was confirmed that the sintered body had sufficient sintering strength (50 kg/cm').

[BRIEF DESCRIPTION OF THE DRAWINGS] The drawing is a diagram showing the Rattler value after heating the preform.

Claims (1)

[Scope of Claims] 1. A phenolic resin containing 10 to 60% of residual carbon that is effective during reduction is added to unreduced water-atomized low-alloy steel powder.
The surface of the above steel powder is uniformly coated and blended in a range of ~7% to form a resin-coated powder, which is then compacted and cured.
A reduction sintering method by induction heating of steel powder, characterized in that reduction and sintering are performed simultaneously by induction heating to a temperature of 0 to 1400°C. 2 A novolac type phenolic resin containing 10 to 60% residual carbon is uniformly coated on the surface of steel powder in the range of 1 to 7%, and used as a lubricant, binder, and surface oxide reduction agent during molding, and as a metal powder. The reduction sintering method by induction heating of steel powder according to claim 1, which has a carburizing effect on steel powder. 3 Initial oxygen amount 5,
The reduction sintering method by induction heating of steel powder according to claim 1, wherein 0 0 0 to 2 0,0 0 0 ppm is reduced to provide a low oxygen content.