JPH06200316A - Method for refining molten metal, refining vessel therefor and tuyere for the refining vessel - Google Patents

Abstract

(57) [Summary] [Object] The present invention, when refining molten metal by utilizing the reaction occurring at the interface between gas and molten metal, increases the reaction rate to shorten refining time and improve productivity. The purpose is to improve. According to the present invention, in refining a molten metal in a molten metal refining vessel while stirring with bottom blowing gas,
It is characterized in that the gas outlet is blown from the bottom by means of a slit-shaped bottom blowing port. According to the present invention, the generated bubbles are miniaturized, the reaction interface area between the gas and the metal is increased, and the retention time of the bubbles is also increased, so that the molten metal can be refined in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for refining molten metal, a refining vessel and a tuyere for the refining vessel.

[0002]

2. Description of the Related Art When refining molten metal by utilizing a gas-liquid reaction, for example, when decarburizing molten steel in a low carbon region, carbon in molten steel is combined with oxygen in molten steel and CO It becomes a gas and escapes from the gas-liquid interface. In refining utilizing the reaction at such a gas-liquid interface,
By blowing gas from the bottom of the container to increase the gas-liquid interface area, the reaction can be promoted and the processing time can be shortened.

Conventionally, a method of blowing gas into molten steel has been disclosed in, for example, Japanese Patent Laid-Open No. 2-217412 or Japanese Patent Laid-Open No. 3-6.
A method is known in which an inert gas is blown into molten steel in a decompression / vacuum tank as in Japanese Patent No. 1316, and a certain effect can be expected in improving the decarburization rate. At that time, the gas is blown from a porous plug or a circular tube nozzle. When the blowing gas flow rates are the same, the smaller the bubble diameter that is blown, the larger the gas-liquid reaction interfacial area and the shorter the refining reaction time.

Since the bubble diameter depends on the blowing nozzle diameter, it is necessary to make the nozzle diameter as small as possible in order to make the bubbles small. In that case, however, the blowing flow rate per nozzle is limited, so that the same flow rate is maintained. A large number of nozzles are required to secure it. As such a bottom blowing tuyere, a CB tuyere in which thin tubes are gathered is known, but in this case, the distance between the nozzles is short and the air bubbles coalesce, so that small air bubbles are not generated. In order to secure a distance between nozzles that prevents bubbles from merging, a large number of tuyere with one thin tube nozzle must be installed in the refining container, and the cost of tuyere brick, tuyere sleeve brick, etc. Increase. Also,
Even when using a porous plug, even if each pore is small, the distance between the pores is still extremely small, and the wettability between the molten metal and the plug is poor, so the gas spreads on the plug surface and coalesces bubbles. And still small bubbles are not generated.

[0005]

DISCLOSURE OF THE INVENTION The present invention, when refining a molten metal while blowing gas, increases the gas-metal interfacial area by generating small bubbles, accelerates the refining reaction, and shortens the processing time. It is an object of the present invention to provide a method for refining molten metal to be shortened, a refining vessel for carrying out the method, and a tuyere for the refining vessel.

[0006]

The subject matter of the present invention is as follows. (1) Refining molten metal using a molten metal refining vessel, when refining molten metal while stirring with bottom blowing gas, bottom blowing by a bottom blowing tuyere with a gas outlet shape Method.

(2) In a molten metal refining vessel used for refining molten metal while stirring with bottom blowing gas, the gas outlet shape of the bottom blowing tuyere is slit-shaped Refining vessel. (3) A bottom blown tuyere used for a molten metal refining vessel used when refining molten metal while stirring with a bottom blown gas, characterized in that the gas outlet shape is a slit shape. Tuyere for refining container.

A feature of the present invention is that the gas outlet shape of the bottom blowing tuyere is formed into a slit shape so that the diameter of generated bubbles can be reduced without reducing the gas flow rate per nozzle, and the gas-metal The point is that the interfacial area can be increased and the reaction occurring at the gas-liquid interface can be made to proceed faster than before.

[0009]

The operation of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing the shape of tuyere, FIG. 2 is an explanatory view of an example of decarburization of molten steel in the low carbon region using the tuyere, and FIG. 3 is an enlarged view of a portion of FIG. 2A. As shown in FIG. 1, when the slit portion 2 is provided in the middle of the circular tube nozzle 3 inside the tuyere brick 1, the gas outlet shape becomes an elongated rectangle. When this tuyere 7 is installed at the bottom of the refining vessel 4 for the molten metal 5 as shown in FIG. 2 and Ar gas is blown into it, the bubbles 6 become the length of the short side of the rectangular nozzle outlet as shown in FIG. It is defined and blown into the molten metal. Since it is slit-shaped, the length of the short side is very small and the bubbles generated are also small, but the outlet cross-sectional area is considerably larger than that of a circular pipe nozzle whose diameter is the length of the short side, and a large flow rate. The gas of can be blown in. Carbon and oxygen in the molten steel react with each other on the surface of the Ar bubbles blown into the molten metal to form CO gas and the decarburization reaction proceeds, but the reaction interface area increases as the Ar bubbles become smaller. Further, as the bubbles are smaller, the floating speed of the bubbles is also reduced, so that the molten steel residence time of the bubbles is increased. For the above two reasons, the total decarburization reaction rate increases as the bubbles become smaller when the blowing gas flow rates are the same.

For the above reasons, it becomes possible to refine molten metal by utilizing the reaction occurring at the interface between gas and metal in a shorter treatment time than before. We have
The water model and the inside of the small crucible containing the molten metal were observed by X-ray transmission, and it was confirmed that the diameter of the generated bubble was defined by the length of the short side of the nozzle slit portion.

[0011]

EXAMPLE A decarburization experiment of low carbon molten steel was conducted using a cylindrical refining vessel having an inner diameter of 1.1 m and having a bottom blowing stirring function. The nozzle slit of the tuyere has a short side length of 0.5 mm,
The length of the long side was 25 mm. In the experiment, the C concentration was set to 290 to
It was performed using molten steel adjusted to 310 ppm. The molten steel weight was 6 t, the Ar gas blowing amount was 100 Nl / min, and the refining time was 10 minutes. After the start of refining, a metal sample was taken every 2 minutes and C analysis was performed. FIG. 4 shows the change with time of the C concentration in the molten steel during this experiment. As a comparison, the change over time of the C concentration is also shown when using a tuyere having a circular tube nozzle with an inner diameter of 4 mm in which the nozzle outlet cross-sectional areas are almost the same. It was confirmed that the refining method according to the present invention took less time to reach a certain C concentration.

[0012]

According to the present invention, the refining time utilizing the reaction occurring at the gas-metal interface can be shortened and the productivity can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view of a tuyere in which a nozzle outlet shape is a slit shape.

FIG. 2 is an explanatory view of an example in which the present invention is applied to a refining vessel for decarburizing molten steel by blowing Ar gas from the bottom.

FIG. 3 is an enlarged explanatory view of a portion A of FIG.

FIG. 4 is a graph showing changes in C concentration in molten steel during a decarburization experiment.

[Explanation of symbols]

 1: Tuyere brick 2: Nozzle slit part 3: Circular tube nozzle 4: Refining vessel 5: Molten metal 6: Bubble 7: Tuyere

Claims (3)

[Claims] 1. When the molten metal is refined using a molten metal refining vessel while stirring with a bottom blowing gas, the molten metal is blown to the bottom by a bottom blowing tuyere having a slit-shaped gas outlet shape. Refining method. 2. A refining vessel for molten metal used for refining molten metal while stirring with bottom blowing gas, characterized in that the gas outlet shape of the bottom blowing tuyere is slit-shaped. container. 3. A bottom blowing tuyere used for a refining container for molten metal used when refining molten metal while stirring with bottom blowing gas, characterized in that the gas outlet shape is a slit shape. Tuyers for refining molten metal.