JPS5919967B2 - Vacuum degassing method for molten steel - Google Patents

Description

[Detailed description of the invention] The present invention relates to a vacuum degassing method for molten steel.

In recent years, quality requirements for steel have become stricter, and vacuum degassing treatment is increasingly being applied to meet these quality requirements.

There are various processing methods for this vacuum degassing method, but recently, inert gas is injected into the molten steel in a reduced pressure tank, and the combined effect of the gas lift pump effect and depressurization effect of this inert gas is used to degas the steel. It is effective in removing harmful gases and inclusions.

On the other hand, injecting gas into the tank significantly shortens the life of the tank refractories and increases the cost of furnace materials.

This furnace cost now accounts for about 35% of the vacuum degassing treatment cost.

The present invention relates to a vacuum degassing method that enables an efficient gas injection effect without comparably reducing the life of the vacuum chamber refractories when injecting inert gas into molten steel.

Figures 1 and 2 show a degassing method generally called the RH method.
1 is a ladle, 2 is molten steel, and 3 is an immersion pipe, which is divided into an ascending pipe 3a with a built-in inert gas blowing pipe 4 and a descending pipe 3b without gas injection.

5 is a lower tank, and 6 is an upper tank, which are connected to a vacuum pump.

When the pressure inside the tank is reduced with a vacuum pump and inert gas is blown into the tank through the blowing pipe 4, the molten steel is drawn into the pressure reducing tank, and the gas blowing through the blowing pipe 4 causes the rising pipe 3a and the descending pipe 3 to
The density of the molten steel with 3a changes, and the molten steel continuously circulates from 3a to 3b.

On the other hand, at the bottom of the lower tank 5 of the immersion pipe 3 and directly above the gas inlet 4 of the reflux pipe, the refractory tends to be locally eroded by the rapid cooling reaction of the gas and the turbulent flow of the molten steel.

For this reason, this part becomes a bottleneck, and the dipping tube and lower tank often need to be replaced.

In order to solve this problem, the present invention was made to inject an inert gas from the bottom of the ladle as shown in Fig. 3 to eliminate the spalling of the refractory caused by the gas and the local melting loss caused by the turbulent flow of molten steel caused by the gas. It is something.

The apparatus used for carrying out the method of the present invention is explained with reference to FIG. 8.
-1 is a porous plug provided at the bottom of the ladle and communicated with a gas generator (not shown) via a blow pipe 8.

6 is an upper tank connected to a conventional vacuum pump, and 7 is a lower tank opened at the bottom.

When inert gas is blown into molten steel through a porous plug, the spread of the molten steel surface due to the inert gas varies depending on the slag thickness and bath depth, but according to the experience of the present inventors, the slag thickness is 100 mm and the bath depth is 2500 mm. ~2800mm, Porous plug diameter 200φmm, molten steel spread is 100° ~ 120°
It is approximately 0 mmφ.

Therefore, considering the influence of gas refractories, the inner diameter of the lower tank 7 is set to 1.
If it is about 200+600=1800φmm, the lower tank 7
It was found that the lifespan of was significantly improved.

The ability to stir the molten steel during treatment according to the present invention was investigated by water model experiments, and it was found that the molten steel was stirred almost uniformly as indicated by the arrow flow in Figure 3.

However, the stirring capacity is small compared to the conventional RH method, and to compensate for this, a nitrogen gas leak valve (
Nitrogen gas is rapidly blown into the vacuum tank from a source (not shown) to restore pressure, and the molten steel in the tank is periodically pushed back into the ladle.

After discharging the molten steel, the nitrogen gas is removed, the pressure inside the tank is reduced again, and the molten steel is sucked up.

By repeating this pressure reduction and pressure reduction operation several times, it was possible to obtain stirring performance comparable to that of the RH method.

FIG. 4 shows an example of a processing pattern of the method of the present invention.

Argon gas is used as an inert gas at 3001/min, and nitrogen gas is used at 6 kg/cr? I tried to become an L.

As a result, the refractory costs compared with the conventional method are as shown in Table 1.

From the table above, both construction costs and running costs have been significantly reduced.
It was confirmed that it is extremely effective.

The present invention, configured as described above, can reduce the cost of equipment such as refractories without impairing the degassing function, and greatly contributes to improved productivity and equipment maintenance.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing the schematic configuration of the RH vacuum degassing tank;
FIG. 2 is a sectional view showing the bottom of the degassing tank in FIG. 1, FIG. 3 is a schematic diagram of an apparatus used for the vacuum degassing method of the present invention, and FIG. 4 is a diagram of an embodiment of the processing pattern of the method of the present invention. . 1... Ladle, 2... Molten steel, 3...
...Dipping pipe, 3a...Rising pipe (dipping pipe), 3b
...Down pipe (immersion pipe), 4...Gas blowing pipe, 5...Lower tank, 6...Upper tank,
7...Immersion pipe, 8...Gas blowing pipe, 8
-1・・・Porous plug.

Claims (1)

[Claims] 1- An upper tank having a vacuum device system communication port on the side and an opening at the bottom; an upper tank formed with the same or approximate diameter as the inner diameter of the upper tank, and connected to the upper tank and in which the lower body part is immersed; When degassing molten steel using a vacuum degassing tank consisting of a bottom-open immersion tube, the molten steel is stored in a ladle with an inert gas inlet at or near the center of the bottom, and the vacuum degassing tank is A part of the steel is immersed in the molten steel, and an inert gas is passed through the bottom of the ladle, and the vacuum chamber is repeatedly depressurized and depressurized several times during the refining period to suck up the molten steel in the ladle. Or a vacuum degassing method for molten steel, which is characterized by degassing the molten steel while discharging it.