JPS5848603B2 - Manufacturing method of atomized iron powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing atomized iron powder, and in particular to a method devised to reduce the amount of nonmetallic inclusions as much as possible and obtain high quality atomized iron powder. It is.

In the present invention, atomized iron powder is a general term for pure iron, carbon steel, alloy steel, cast iron, etc., which are finely pulverized by a spraying method.

Atomized iron powder is a relatively new material for powder metallurgy, and has recently attracted attention because it has advantages such as being suitable for mass production and having stable quality.

There are two manufacturing methods: the gas atomization method and the water atomization method.The former is a method in which high-pressure gas such as nitrogen gas is applied to the molten steel as it flows down from a tundish nozzle, and the molten steel is atomized and then rapidly solidified, while the latter is a method in which the molten steel is rapidly solidified after being atomized. This is a method in which high-pressure water is applied to the molten steel while flowing it from a tundish nozzle, and the molten steel is atomized and then rapidly cooled and solidified.
They are common in that molten steel is placed in a ladle and atomized while flowing down through a tundish.

The solvent used as a raw material for these atomized iron powders is melted in a converter or an electric furnace, and the present invention relates to a method for producing high-quality atomized iron powder using molten steel melted in an electric furnace as a raw material.

Molten steel production using an electric furnace is carried out by sequentially performing a melting stage process, an oxidizing stage process, a slag removal process, and a reducing stage process. In the oxidizing stage process, quicklime etc. are added to the molten iron raw material to adjust the basicity of slag. After adding , oxygen is blown in to decarburize and oxidize and refine, removing harmful oxidizing impurities as sludge.

In addition, in the reduction stage process, smelting is carried out in the presence of basic reducing slag,
This process removes the oxygen enriched in the molten steel during the oxidation stage and also performs desulfurization, etc., and is the final process in electric furnace melting. After the reduction process, the molten steel is taken out into a ladle and sent to the spraying process. It will be done.

By the way, the treatment temperature during the reduction period in electric furnace molten steel is usually 1
Although 600 to 1660°C is considered to be optimal, if this molten steel is subsequently subjected to a spraying process, the molten steel may cool and solidify at the tundish nozzle, causing the nozzle to close.

For this reason, in the past, molten steel was heated to 1730-1750 just before tapping.
By raising the temperature to about ℃, the tundish nozzle is prevented from closing.

However, during this temperature rising process, the slag on the surface of the molten steel partially decomposes and the amount of gas in the molten steel increases, causing boiling in the ladle, which is extremely dangerous to work with. It is customary to add a strong deoxidizing agent such as A7 or FSi.

In other words, the oxygen remaining in the molten steel is removed as much as possible by reacting with strong deoxidizers such as Al and FSi, so the boiling phenomenon of the molten steel is almost prevented, and at the same time, the oxygen remaining in the reduction stage process is also removed. be done.

However, if Al203, S102, etc. generated in this process are injected into the tundish together with molten steel without being floated and separated, they will become non-metallic inclusions and mix into the atomized iron powder, significantly impairing the quality of the iron powder. It will be done.

Therefore, from the standpoint of improving the quality of atomized iron powder,
It is preferable not to use the strong deoxidizing agent.

The present invention was made in view of the above-mentioned circumstances, and its purpose is to produce high-quality atomized iron powder with few nonmetallic inclusions using molten steel melted in an electric furnace as a raw material. As a concrete measure, we aim to prevent the boiling phenomenon during tapping without adding a strong deoxidizing agent to the ladle, and to prevent the contamination of non-metallic inclusions caused by the strong deoxidizing agent. We are trying to provide a method that can prevent this from happening.

The structure of the present invention that effectively achieves this purpose is to inject molten steel treated in an electric furnace into a tundish, and drop atomized iron powder through the tundish nozzle. The gist of this manufacturing method is that the treatment temperature during the reduction period in an electric furnace is set at 1,700 to 1,750°C to ensure sufficient reduction.

In the present invention, the temperature in the reduction period, which is the final step during electric furnace melting, is raised from the beginning to 1700 to 1750° C., which is the appropriate temperature for tapping, so that the reduction reaction sufficiently proceeds due to the high temperature effect.

If this melting method is adopted, decomposition of slag due to temperature rise just before tapping as in conventional methods is prevented, and the increase in gas amount in the molten steel is suppressed as much as possible, so the steel can be tapped directly into the ladle. No boiling phenomenon occurs.

Moreover, in the reduction stage process, the molten steel is sufficiently reduced due to the high temperature effect, so there is no fear that the molten steel will be insufficiently deoxidized.

In this way, the addition of a deoxidizing agent to the molten steel in the ladle can be omitted, and as a result, the contamination of non-metallic inclusions caused by the deoxidizing agent can be completely eliminated.

Naturally, reducing agents such as coal powder are used in the reduction stage process along with slag-forming agents such as CaO and CaF2, but since these are separated and removed from the molten steel during the tapping process, they can cause non-metallic inclusions to be mixed in. This is not the case, and the main cause of inclusions is the deoxidizing agent (or reducing agent) added after tapping.

In addition to the above, other causes of nonmetallic inclusions in the atomized iron powder include entrainment of slag suspended in the tundish.

That is, in order to prevent air oxidation of the molten steel in the tundish and to keep it warm, it is customary to leave a layer of slag floating on the surface of the molten steel in the tundish. When this slag flows out of the tundish nozzle together with the molten steel, the slag is mixed into the atomized iron powder as non-metallic inclusions.

Therefore, in order to further enhance the effects of the present invention, it is desirable not to involve the slag in the surface layer when pouring molten steel into the tundish.

The present inventor has also carried out experiments on measures to prevent entrainment, and as a result, a cylinder was installed upright inside the kundish to prevent surface slag from flowing into the cylinder, and molten steel was prevented from flowing into the cylinder. It was found that the purpose could be easily achieved by injecting the liquid into the tundish through the cylinder.

This can be easily understood from the examples in FIGS. 1 and 2.

That is, FIG. 1 is a schematic longitudinal cross-sectional view showing the conventional injection method.
The molten steel 2 melted in the electric furnace 1 is once taken out into the ladle 3 and then injected into the tundish 4, and falls from the tundish nozzle 5, and is injected with high pressure water or high pressure gas from the injection device 6. to atomize the molten steel 2, and add it to the water tank 1 if necessary.
Proceed with cooling and solidification to obtain atomized iron powder 8 ≦Here, it is customary to suspend slag 9 on the surface of the molten steel in the tundish 5 for both oxidation prevention and heat retention, and the molten steel 2 is poured from the top of this slag 9. When injected, the slag 9 is caught up in the molten steel flow and dispersed deep, and a part of it flows out from the nozzle 5 together with the molten steel 2.

As a result, slag is mixed into the atomized iron powder 8 as a nonmetallic inclusion, making it difficult to obtain high quality atomized iron powder.

On the other hand, in the example shown in FIG. 2, a cylindrical body 10 is set upright in the tundish 4, and the molten steel 2 is injected through the cylindrical body 10 while preventing the slag 9 from flowing into the cylindrical body 10.

By doing this, there is no danger that the slag 9 will be blocked by the cylinder 10 and caught in the molten steel flow, and will always float to the surface layer due to the difference in specific gravity, so that only the molten steel 2 will selectively flow out from the tundish nozzle 5. .

In this way, non-metallic inclusions due to slag entrainment can be prevented as much as possible.

However, even if the method shown in Fig. 2 is adopted, if the injected molten steel 2 itself contains non-metallic inclusions caused by the reducing agent, these will be mixed into the nozzle 5 along with the molten steel 2 regardless of the presence or absence of a cylinder. However, in the present invention, the molten steel melted in the electric furnace is directly poured into the tundish 4 through the ladle (without adding a reducing agent), so the amount of non-metallic inclusions is minimized. can.

The effects of the present invention described above can be confirmed by the following experimental series.

That is, by adopting the reducing period conditions and hotpot conditions shown in Table 1,
Ladle and tundish. After that, atomized iron powder is obtained by spraying, and using the atomized iron powder as a raw material powder, a true density powder forging material is produced using a normal powder forging process, and the cleanliness and inclusions of the powder material are evaluated. We compared the size and number.

The results are summarized in Table 2.

As is clear from the results in Table 2, the value of the cleanliness of the atomized iron powder obtained by the conventional method is extremely high, and the amount of inclusions is also extremely large.

On the other hand, in Example 1 (an example in which the ladle deoxidizing agent was omitted), the cleanliness value could be reduced by about 40%, and the reduction in inclusions was also remarkable.

In particular, in Example 2, in which a cylindrical body was installed upright in the tundish to prevent slag from being entrained, the cleanliness was further reduced.
The amount of inclusions has also been further reduced.

In particular, there are no large inclusions of 21μ or more.

The present invention is roughly configured as described above, but the point is that the temperature during the reduction period is set to a high enough temperature to prevent nozzle closure from the beginning and to achieve sufficient reduction, so that when tapping molten steel from an electric furnace, Or no boiling phenomenon occurs in the ladle.

Therefore, there is no need to add strong deoxidizing agents such as Al or FSi to prevent boiling, so the amount of non-metallic inclusions mixed into the molten steel is reduced as much as possible, making it possible to obtain high-quality atomized iron powder. can.

In other words, if nonmetallic inclusions are mixed into atomized iron powder, the impact strength and fatigue strength of high-density sintered materials made from the same powder will be extremely reduced. significantly contributes to improving the mechanical strength of

In this case, by using the cylinder to prevent tundish slag from being mixed in when pouring molten steel from the ladle into the tundish, the amount of inclusions mixed into the atomized iron powder can be further reduced.

[Brief explanation of the drawing]

Figures 1 and 2 are process explanatory diagrams illustrating the process of pouring molten steel melted in an electric furnace from a ladle into a tundish. Figure 1 is a conventional method, and Figure 2 is a cylindrical body advantageously used in the present invention. This shows an injection method using 1... Electric furnace, 2... Molten steel, 3...
... Ladle, 4... Tongue tissue, 5...
Tundish nozzle, 6... Injection device, 1.
...Aquarium, 8...Atomized iron powder, 9.
... Slag, 10 ... Cylindrical body.

Claims (1)

[Scope of Claims] 1. A method for producing atomized iron powder by injecting molten steel produced in an electric furnace into a tundish and dropping the molten steel from a tundish nozzle, the method comprising: processing during the reduction period in the electric furnace; A method for producing high-quality atomized iron powder, characterized by sufficiently reducing the temperature at 1,700 to 1,750°C. 2. A manufacturing method according to claim 1, in which molten steel is transferred from an electric furnace to a ladle without using a forced deoxidizing agent. 3 A method of producing atomized iron powder by injecting molten steel produced in an electric furnace into a tundish and letting the molten steel fall from a tundish nozzle, the process temperature being set at 1700 to 1750°C during the reduction period in the electric furnace. The atomized iron powder is characterized in that the molten steel is sufficiently reduced in the tundish by erecting a simple body in the tundish to prevent tundish slag from flowing into the cylindrical body, and the molten steel is injected into the tundish through the cylindrical body. manufacturing method.