JP2780342B2 - Vacuum degassing method for molten metal - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a vacuum degassing method for degassing a molten metal using a vacuum degassing device such as VOD, RH, and DH.

[Conventional technology]

Since molten steel smelted in a steelmaking furnace that performs smelting and refining in a converter or the like contains a large amount of gas components, a vacuum degassing method for degassing the steel under vacuum has been implemented. VO
The D method and the VAD method degas by exposing the bath surface to vacuum while holding the molten steel in a ladle, and the molten steel is agitated as necessary to increase its efficiency. DH method and RH
According to the method, molten steel is sucked into a vacuum chamber and the bath surface is degassed by exposing the bath surface to vacuum. The degassing effect is higher than the former two.

[Problems to be solved by the invention]

Although these methods are extremely efficient degassing methods, special-purpose steels may require more stringent gas components present as impurities.

Therefore, the present inventors have found that when degassing is performed with these vacuum degassing devices, a gas soluble in the molten steel is dissolved in the molten steel, and a dissolved gas component is generated and floated as fine gas bubbles by decompression. At this time, a method of promoting vacuum degassing by flapping the bath surface was developed. Since gas bubbles formed in the molten steel by this method are very fine and generated in a large amount, the area of the bath surface exposed to vacuum due to the fluttering of the bath surface increases, and the degassing efficiency becomes extremely high.

The present invention clarifies what kind of gas should be used as the dissolved gas used in the above-mentioned processing, and makes it easier to control the concentration of a specific gas component required in accordance with product quality characteristics. It is assumed that.

[Means for solving the problem]

Therefore, the present invention is based on the premise that when a gas component in a molten metal is to be particularly reduced by the above-mentioned improved vacuum degassing method, a soluble gas different from the gas component is used as a dissolved gas. And

That is, even if the dissolved gas is generated as fine gas bubbles and the degassing efficiency is increased by flapping the bath surface exposed to vacuum, if the dissolved gas is the same as the gas component to be degassed, the gas is removed. Degassing of only the component does not proceed, and degassing of other gas components proceeds. Therefore, what is used as the dissolved gas is to use a soluble gas different from the gas component to be degassed. However,
The gas component may be a gaseous component or a component contained in a solid.

The present inventors applied the above configuration to decarburization of molten steel,
The present invention was invented.

That is, when the ultra-low carbon treatment is performed as a decarburization process of molten steel, it takes a very long time and there is a problem in productivity,
The present inventors have applied the above configuration, the H ₂ gas is added to the molten steel during decarburization, the expansion allowed by decarburization reaction bath surface area exposed to vacuum in a fine H ₂ gas bubbles generated in vacuo Promoted. However, this time, a large amount of H ₂ gas components remained in the molten steel, and it took a long time to remove the H ₂ gas component even with a vacuum degassing apparatus, which caused a problem in the quality of the steel material. Therefore, in order to advance the dehydrogenation reaction at the end of the decarburization, N ₂ gas was dissolved in the molten steel, and fine N ₂
Gas bubbles were generated to accelerate the dehydrogenation reaction. At this time, gas bubbles are generated with the non-metallic inclusions as nuclei, so that the efficiency of removing the inclusions is also improved. Could be lower. Therefore, the present inventors, as a configuration of the present invention,
The present invention proposes a new vacuum degassing method in which the steps of gas dissolution, decompression, and degassing are performed twice and decarburization, dehydrogenation, and deoxidation of molten steel proceed remarkably and efficiently.

Embodiment 1 First, an embodiment which is a premise of the present invention will be described.

The present inventors used a 250 ton RH vacuum degasser to
250 tons were vacuum degassed.

As shown in FIG. 1, the degassing apparatus immerses molten steel (2) in a ladle (1) in a reflux immersion pipe (3a) of an RH vacuum degassing tank (3).
(3b) and Ar gas at 2000Nl / m into one immersion tube (3a)
The molten steel (2) is circulated in the ladle (1) and the degassing tank (3) by blowing at a speed of in, whereby the molten steel (2) is exposed to a vacuum in the degassing tank (3). And is degassed.

On the other hand, the present inventors specifically aimed at accelerating the dehydrogenation of the molten steel (2), and set the immersion lance (4) below the immersion pipe (3a).
The plunging, from which by blowing N ₂ gas at a rate of 1000 Nl / min, and is dissolved.

FIG. 2 is a graph showing changes in [H] in molten steel (2) between an example which is a prerequisite configuration of the present invention (hereinafter referred to as a prerequisite configuration example) and a conventional example in which only Ar gas is injected. is there. In the prerequisite configuration example, [H] can be removed to 0.7 ppm by degassing treatment for 10 minutes and to 0.5 ppm or less in 20 minutes, indicating that the effect is higher than that of the conventional example.

Embodiment 2 Next, an embodiment of the present invention will be described.

The present inventors used a 250 ton RH vacuum degassing apparatus, depressurized the inside of the vacuum chamber to 1 torr or less, and supplied Ar gas as reflux gas.
By blowing at a rate of 600 Nl / min, vacuum degassing of 250 tons of molten steel was performed for 10 minutes. In this case the present invention example, was blown H ₂ gas at a rate of 400 Nl / min together.

Next, the blowing speed of Ar gas was reduced to 1500 Nl / min, and in the present invention example, the dissolved gas was switched from H ₂ gas to N ₂ gas.
Blowing was performed at 500 Nl / min, and vacuum degassing was continued in the same apparatus for 10 minutes.

FIGS. 3 to 5 show the behavior of [C], [H] and T. [O] during melting when the above treatment is performed.

As is apparent from FIG. 3, it takes about 10 minutes after the start of degassing in the present invention until the [C] in the molten steel, which was about 300 ppm at the beginning, becomes 15 ppm or less, and it takes more than 20 minutes in the conventional example. Was.

Thereafter, in the conventional example, the blowing of Ar gas is continued, and in the present invention example, the gas is further switched to the dissolved gas N ₂ gas to perform degassing, and the [H] in the molten steel is as shown in FIG. changed. That is, in the example of the present invention, since H ₂ gas was blown in the immediately preceding step, [H] shows a higher value than the conventional example, but it becomes 1 ppm or less in about 10 minutes after switching the N ₂ gas. Could be lowered. However, in the conventional example, [H]
It takes about 10 minutes more time to reduce the concentration to 1 ppm or less than in the examples of the present invention.

Further, T. [O] in the molten steel changed as shown in FIG. 5, and it was reduced to 30 ppm in the conventional example and 15 ppm in the present invention example 10 minutes after the addition of Al.

〔The invention's effect〕

As described above in detail, in the present invention, in the vacuum degassing method, the dissolved gas is generated and floated as fine gas bubbles under reduced pressure to increase the reaction interface area of the bath surface exposed to vacuum, thereby improving the degassing efficiency. In such a case, the conditions of the dissolved gas to be used are clarified, and thereby, the specific gas component can be reduced to the utmost limit.
In other words, by performing the method of the present invention, decarburization, dehydrogenation, and deoxidation in molten steel proceeded to a considerable extent, and the production efficiency of ultraclean molten steel was greatly improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of an experimental apparatus of a premise configuration example of the present invention, FIG. 2 is a graph showing a change in [H] of molten steel in the above premise configuration example, and FIG. FIG. 4 is a graph showing the behavior of [C] of molten steel in the example, FIG. 4 is a graph showing the behavior of [H] of molten steel in the example,
FIG. 5 shows T. [O] in molten steel in the same embodiment.
It is a graph which shows the change of. In the figure, (1) shows a ladle, (2) shows molten steel, (3) shows an RH vacuum degassing tank, (3a) and (3b) show its reflux immersion pipe, and (4) shows an immersion lance.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshihiko Kawai 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Atsushi Watanabe 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Hideaki Tenma 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-57-194206 (JP, A) JP-A-53-102819 (JP) , A) JP-A-61-295314 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C21C 7/10 C22B 9/04

Claims (1)

(57) [Claims] If 1. A performing degassing of the molten metal using a vacuum degasser, fine H ₂ gas by degassing of dissolved H ₂ gas into the molten metal in the vacuum degassing apparatus perform decarburization while generating bubbles, then the dehydrogenation and deoxidation while generating fine N ₂ gas bubbles by degassing in same vacuum degassing apparatus by dissolving N ₂ gas into the molten metal A vacuum degassing method for molten metal, which is performed.