JPH06299226A - Vacuum-degassing method for molten steel - Google Patents

Abstract

PURPOSE:To efficiently execute the degassing in a short time by correlating the inner diameter at the lower end of a vacuum vessel with the inner diameter at the upper end of a ladle and the inner diameter at the upper end of molten steel in the vacuum vessel, in the case of executing the degassing refining by setting the cylindrical vacuum vessel on the upper part of the ladle containing the molten steel. CONSTITUTION:By setting the cylindrical pressure reducing and vacuum vessel 3 on the upper part of the ladle 2 containing the molten steel 1, the pressure reducing and vacuum degassing refining is executed. At this time, the inner diameter (a) at the lower end of the vacuum vessel is larger than the inner diameter (b) at the upper end of the molten steel in the vacuum vessel. Further, this inner diameter (b) is made to be >1/2 of the inner diameter (c) at the upper end of the ladle 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an efficient degassing method for removing carbon, nitrogen and hydrogen contained in molten steel or molten metal under reduced pressure and vacuum.

[0002]

2. Description of the Related Art Carbon, nitrogen or hydrogen contained in steels and alloys is required to be in a very small amount in order to improve workability, prevent aging and improve ductility and further improve low temperature toughness. Generally, in the steel industry, degassing treatment of molten steel or molten metal (hereinafter simply referred to as molten steel) is performed by various methods such as those shown on pages 671 to 685 of the Ironmaking Steelmaking Edition, 3rd Edition Iron and Steel Handbook II. It is carried out using the decompression / vacuum refining equipment. Degassing method using molten steel circulation type decompression / vacuum tank (R
Regarding H degassing method), in order to send the molten steel into the decompression / vacuum tank (hereinafter simply referred to as the vacuum tank), a large amount of gas is blown into the molten steel from one dipping pipe, and the molten steel is decompressed by the gas lift effect.・ Supply it to the vacuum tank and recirculate the molten steel. The degassing rate has a large value when the molten steel recirculation rate is high. However, the size of the dipping pipe for supplying molten steel to the vacuum tank which is the reaction tank is limited by the ladle diameter and the brick thickness,
The molten steel recirculation velocity cannot be extremely increased, and a more efficient degassing method is expected to be presented.

The degassing reaction is a liquid phase that is molten steel and a gas
It progresses at the interface with the gas phase (gas / liquid interface). At this time, each
The rate of the degassing reaction is represented by the equations (1 ') to (3'),
To increase the degassing rate, the reaction rate constant k_xThe value of the
Needs to be increased. k _xIs proportional to the reaction area
At the same time, it greatly depends on the circulation rate of molten steel to the reaction site.
It Therefore, the degassing reaction rate is increased, and the ultra low
To make molten steel with charcoal, extremely low nitrogen and extremely low hydrogen,
At the same time as increasing the gas / liquid interface area, a method for promoting molten steel circulation
Concrete means of law are needed.

Speed of degassing reaction Decarburization treatment: [C] + [O] = CO (1) (d mass% [C]) / dt = -K _c · mass% [C] ... (1 ′) Dehydrogenation treatment: [H] + [H] = H ₂ ... (2) (d mass% [H]) / dt = −K _H · mass% [H] ... (2 ′ ) Denitrification treatment: [N] + [N] = N ₂ ... (3) (d mass% [N]) / dt = −K _N · mass% [N] ² ... (3 ′)

[0005]

There is an urgent need to provide a degassing method for efficiently and rapidly removing carbon, nitrogen or hydrogen contained in molten steel to an extremely low concentration. INDUSTRIAL APPLICABILITY The present invention performs reduced pressure / vacuum treatment of molten steel or molten metal to efficiently and economically produce ultra-low carbon, ultra-low nitrogen in a short time.
It is an object of the present invention to provide a degassing method for producing extremely low hydrogen molten steel.

[0006]

SUMMARY OF THE INVENTION The present invention is to solve the problems of the prior art in an advantageous manner.
When the vacuum tank is installed above the ladle containing molten steel or molten metal and the decompression and vacuum degassing of molten steel or molten metal in the ladle is performed, the inner diameter of the lower end of the vacuum tank is the upper end of the molten steel in the vacuum tank. It is characterized by using a cylindrical decompression / vacuum tank that is larger than the inner diameter and has a molten steel upper end inner diameter that is 1/2 or more of the ladle upper end inner diameter.

The present invention will be described below with reference to the drawings.

1 is a drawing showing a typical example of a method for carrying out the present invention. The lower end of the decompression / vacuum tank 3 is immersed in a ladle 2 containing the molten steel or molten metal 1 to be degassed, and the molten steel is sucked into the vacuum tank 3 while an inert gas plug 4 or lance is applied to the molten steel. Degassing is carried out while injecting through 5 and circulating molten steel. At this time, decompression
The inner diameter a of the lower end is set to be larger than the inner diameter b of the upper end so that the shape of the vacuum chamber does not hinder the circulation of molten steel. Further, the inner diameter b of the upper end portion should be 1/2 or more of the inner diameter c of the ladle so that the gas can be released from the upper end sufficiently quickly.

The inventors of the present invention have found that the size of the inner diameter of the immersion pipe is a controlling factor of the degassing rate, and at the same time, its shape has a great influence on the circulating action of the molten steel. It has been found that the shape of the decompression / vacuum chamber 3 becomes large when it is expanded downward. That is, it was confirmed that a sufficient molten steel free surface can be secured, and efficient degassing treatment can be performed by gas injection, decompression, and shape selection of the vacuum chamber. When denitrifying and decarburizing molten steel by applying the method of the present invention, in order to maintain or increase the oxygen concentration of the molten steel, an oxygen gas or an oxygen-containing gas is directly introduced into the molten steel by the injection nozzle 6. It may be blown through, or may be blown onto the molten steel surface by using the blowing lance 5.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 In a degassing furnace as shown in FIG. 1, 250 tons of molten steel was decarburized using a type I cylindrical vacuum chamber. The inner diameter of the ladle is 3.5 m, the inner diameter of the upper portion of the cylindrical vacuum chamber is 2.0 m, and the inner diameter of the lower end of the vacuum chamber is 2.8 m. The distance between the inner wall of the ladle and the cylindrical dipping tube is 25 cm. A from the plug
The flow rate of r gas injection is 1000 to 1200 (Nl / mi
n), lance blowing Ar flow rate is 1500-2000 (N
1 / min), and Ar was blown in while evacuating. FIG. 2 shows the change over time in the [C] concentration. Compared to the case where the inner diameter of the upper part of the vacuum chamber was 2.8 m, the method of the present invention was able to decarburize to an extremely low carbon concentration in a short time, and was able to produce an extremely low carbon molten steel.

Example 2 In a degassing furnace as shown in FIG. 1, dehydrogenation treatment of 250 tons of killed molten steel was carried out using a cylindrical vacuum chamber as shown in type II. The inner diameter of the ladle is 3.5 m, the inner diameter of the upper part of the cylindrical vacuum chamber is 2.0 m, and the inner diameter of the lower end of the vacuum chamber is 2.8 m.
Is. At this time, the flow rate of Ar gas blown from the plug is 4
The lance blowing Ar flow rate was 1500 (Nl / min) from 00 to 500 (Nl / min), and Ar was blown while vacuum exhausting. FIG. 2 shows the change in [H] concentration with time. Compared with the case where the inner diameter of the upper part of the vacuum chamber was 2.8 m, dehydrogenation was possible to an extremely low concentration in a short time, and an extremely low hydrogen molten steel could be produced.

Example 3 In a degassing furnace as shown in FIG. 1, 250 tons of molten steel was denitrified using a type I cylindrical vacuum chamber for 25 minutes. The inner diameter of the ladle is 3.5 m, the inner diameter of the upper portion of the cylindrical vacuum chamber is 2.0 m, and the inner diameter of the lower end of the vacuum chamber is 2.8 m. The flow rate of Ar gas blown from the plug is 400 (Nl /
min), lance blowing Ar flow rate is 1500-2000
(Nl / min), and Ar was blown in while evacuating. FIG. 4 shows a comparison of [N] concentration before and after degassing. Compared with the conventional method, in the method of the present invention, denitrification was possible to an extremely low concentration in a short time, and an extreme nitrogen molten steel could be melted.

[0012]

EFFECTS OF THE INVENTION The degassing rate of molten steel is increased, and molten steel having ultra-low carbon, ultra-low nitrogen and ultra-low hydrogen concentration can be produced.

[Brief description of drawings]

FIG. 1 is a drawing showing an example of a degassing facility for carrying out the present invention,

FIG. 2 is a drawing showing a change with time of [C] concentration,

FIG. 3 is a drawing showing changes with time of [H] concentration,

FIG. 4 is a drawing showing comparison of [N] concentration before and after degassing treatment.

[Explanation of symbols]

 1 Molten Steel or Molten Metal 2 Ladle 3 Lower Spread Cylindrical Vacuum Tank 4 Gas Injection Plug 5 Gas Injection Lance 6 Gas Injection Nozzle

Claims (1)

[Claims] 1. When a cylindrical decompression / vacuum tank is installed above a ladle containing molten steel or molten metal to carry out decompression / vacuum degassing refining of molten steel or molten metal in the ladle, the inner diameter of the lower end of the vacuum tank Is larger than the inner diameter of the molten steel in the vacuum tank, and the inner diameter of the molten steel in the vacuum tank is 1 of the inner diameter of the ladle.
A degassing method for molten steel or molten metal, which is characterized by using a cylindrical decompression / vacuum tank of ≥2.