JPH02104441A - Vacuum cleaning method of molten metal - Google Patents

Abstract

PURPOSE:To improve the capacity of the cleaning treatment of a molten metal by applying an electromagnetic force to the molten metal during bubbling and stirring and heating the molten metal. CONSTITUTION:The molten steel 2 is put into a vessel 1 and after the atmosphere therein is substd. with gaseous Ar, the molten steel is bubbled by blowing a prescribed gaseous mixture composed of gaseous Ar and gaseous H2 into the vessel 1 from the bottom thereof under the atmosphere pressure. The electromagnetic stirring of the molten steel 2 is executed by simultaneously applying the electromagnetic force to the molten steel by an electromagnetic coil 3 installed around the vessel 1 at this time. The gas bubbling and electromagnetic stirring are thereafter stopped and the pressure in the vessel 1 is rapidly reduced by a control valve, then the molten steel is rested in this state. As a result, the collision of the inclusions against each other is increased by the electromagnetic stirring and the inclusions relatively increased in the size float during the bubbling. The intrusion of these inclusions again into the molten metal due to the reduced pressure 2 is prevented and, therefor, the efficiency of removing the inclusions is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for vacuum cleaning molten metal for removing inclusions floating in the molten metal.

[Conventional technology]

Inclusions floating in molten metal (for example, alumina inclusions in molten steel) cause product quality defects, and various methods have been proposed to reduce and remove them.

The present inventors made the following proposal in view of the requirement that the total amount of oxygen in molten steel should be suppressed to 15 ppm or less for the purpose of producing high-grade materials. That is, pressurized molten metal is bubbled with soluble gas to dissolve the gas in the molten metal, and then the pressure is rapidly reduced to generate fine gas bubbles in the molten metal. . According to this method, normal inclusions in the molten metal are trapped in the gas bubbles and floated to the surface during the initial bubbling.

On the other hand, since this bubbling is performed on pressurized molten metal, a large amount of bubbling gas dissolves into the molten metal. Due to the subsequent rapid depressurization, the gas dissolved in the molten metal becomes fine gas bubbles and is generated from the entire area of the molten metal. At this time, fine inclusions are trapped by the gas bubbles and float up.

Although this is an extremely efficient and excellent method for removing inclusions in molten metal, if the time left after depressurization is short, a large amount of the bubbling gas will remain dissolved in the molten metal. Therefore, it was necessary to further degas after the completion of the treatment.

Therefore, the present inventors found that in the above method, the bubbling gas was the cause of remaining undissolved. We have proposed a new method for cleaning molten metal in which the pressure treatment of the molten metal during bubbling is stopped, the bubbling is performed at atmospheric pressure or lower, and then the depressurization treatment is performed. In this improved method, the vacuum treatment not only generates fine gas bubbles, but also degasses the molten metal.

[Problem that the invention seeks to solve]

However, even with this improved method, the trapped inclusions do not come to the surface completely unless the pressure is reduced and left for a while after bubbling, which takes a long time and reduces processing capacity. There was a problem.

The present invention was devised in view of such problems, and aims to further improve the above-described method and improve its processing performance.

[Means for solving problems]

Therefore, in the method of the present invention, when implementing the above-described vacuum cleaning method for molten metal, electromagnetic force is applied to the molten metal during bubbling to stir and heat the molten metal.

The present inventors conducted various experiments with the aim of improving processing capacity, but found that if the standing time after depressurization was shortened, the removal of minute inclusions did not proceed as expected. Therefore, attempts have been made to improve the efficiency of removing normal inclusions by bubbling, which is performed prior to bubbling.

Based on subsequent experimental results, a configuration was devised to increase the efficiency of removing inclusions through bubbling by applying a low-frequency electromagnetic force to the molten metal during bubbling, mainly to actively stir the molten metal. It was done. This seems to be because collisions between inclusions increase due to stirring, and relatively large inclusions float to the surface during bubbling. In addition, because this forced stirring is expected to increase the amount of bubbling gas dissolved, the amount of fine gas bubbles generated due to pressure reduction will also increase, and it is also expected to improve the removal efficiency of fine inclusions.

Furthermore, as the gas bubbling time progresses, the temperature of the hot water naturally becomes lower, and as a result, the amount of bubbling gas dissolved in the water decreases. Furthermore, since the fluidity of the molten metal also decreases, the stirring effect due to bubbling also gradually decreases. In such cases, the method of the present invention is implemented so that high-frequency electromagnetic force is applied to the molten metal during bubbling, and the molten metal is actively heated mainly by Joule heat generated by the generated induced current. Also good.

The reason why the electromagnetic force is applied is limited to only during bubbling is to prevent inclusions that have surfaced after depressurization from being mixed into the molten metal again due to electromagnetic stirring. .

In the second invention, stirring of the molten metal after the depressurization treatment is performed by bubbling an inert gas. As mentioned above, if electromagnetic stirring is continued even after depressurization treatment, there is a risk that floating inclusions will be reintroduced into the molten metal. There is no need to worry about inclusions.

In addition, in the vacuum cleaning method for molten metal, the deeper the bath depth, the lower the W
Since the weight of the welding metal is applied as static pressure, it becomes difficult to degas the deep part of the bath when the pressure is reduced. Therefore, stirring by gas bubbling as described above also increases the efficiency of degassing by reducing the pressure.

〔Example〕

Specific examples of the present invention will be described below.

FIG. 1 shows an outline of an apparatus configuration for carrying out the method of the present invention. In this example, 50 tons of molten steel (2) is placed in a container (1), and after replacing the internal atmosphere with Ar gas, Ar gas = 70%, 11, l gas: 3 under atmospheric pressure.
200Q/ from the bottom of container (1) using 0% mixed gas
Gas was bubbled for 20 minutes by blowing at a blowing speed of min. At this time, at the same time, the electromagnetic coil (3) installed around the container (1) turns the molten steel (2) into a '+1! Magnetic force was applied and electromagnetic stirring was performed. After this, gas bubbling and fi
Electromagnetic stirring stopper and pressure regulating valve (not shown) inside the container (1)
The pressure was rapidly reduced and the mixture was left as it was for 20 minutes. or,
As a comparative example to this example, 50 tons of molten steel was subjected to the same treatment without electromagnetic stirring during bubbling under the same other conditions.

FIG. 2 shows changes in the total amount of oxygen in molten steel over time according to the present example (a) in the figure) and the comparative example (b) in the figure.

In this example, the total amount of oxygen in the molten steel (2) has already been considerably reduced during mixed gas bubbling due to electromagnetic stirring. This is thought to be because collisions between inclusions increased due to stirring during bubbling, and relatively large inclusions rose to the surface during this bubbling, reducing the total amount of oxygen in the molten steel (2). Furthermore, the total amount of oxygen after all steps were completed was also lower in this example. This is due to the agitation during bubbling, which causes relatively small inclusions to collide to some extent and become larger, becoming gas bubbles. This seems to be due to an increase in the amount.

Therefore, in order to make the molten steel treated in the comparative example have the same total oxygen content as the molten steel (2) treated in the present example, it is necessary to allow the molten steel to stand for a little longer after depressurization, and the processing capacity It can be seen that this example is superior in terms of.

〔Effect of the invention〕

As detailed above, according to the method of the present invention, it is possible to improve the efficiency of removing inclusions by gas bubbling, thereby increasing the throughput of cleaning molten metal by the vacuum cleaning method for molten metal described above. This means that it is possible to do so.

Furthermore, according to the second invention method of the present application, it is possible to stir the molten metal by inert gas bubbling even after the depressurization treatment, and it is expected that the treatment capacity of -m will be improved, especially when the bath depth becomes deep. The improvement in processing power will be significant.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an overview of the configuration of an apparatus for implementing the method of the present invention, and FIG. 2 is a graph diagram showing changes in the total oxygen content in molten steel according to the present example and a comparative example. In the figure, (1) shows the container, (2) shows the molten steel, and (3) shows the electromagnetic coil.

Claims (1)

[Claims] 1. The gas is dissolved in the molten metal by bubbling the molten metal with a gas soluble in the molten metal at atmospheric pressure or lower, and then the pressure is rapidly reduced to form a fine gas in the molten metal. Generating bubbles and degassing the bubbling gas remaining dissolved in the molten metal using this reduced pressure,
In carrying out a vacuum cleaning method for molten metal in which inclusions floating in molten metal are trapped in gas bubbles caused by bubbling and fine gas bubbles generated by depressurization and removed after floating, the molten metal is removed during bubbling. A vacuum cleaning method for molten metal characterized by stirring and heating it by applying electromagnetic force to it. 2. Bubbling the molten metal with a gas soluble in it at atmospheric pressure or lower to dissolve the gas in the molten metal, and then rapidly reducing the pressure to generate fine gas bubbles in the molten metal, At this reduced pressure, the bubbling gas remaining dissolved in the molten metal is degassed,
In carrying out a vacuum cleaning method for molten metal in which inclusions floating in molten metal are trapped in gas bubbles caused by bubbling and fine gas bubbles generated by depressurization and removed after floating, the molten metal is removed during bubbling. A vacuum cleaning method for molten metal, which comprises stirring and heating the molten metal by applying an electromagnetic force to the molten metal, and stirring the molten metal by bubbling an inert gas into the molten metal after the vacuum treatment.