JPS59136412A - Injection of gas into molten metal bath - Google Patents

Abstract

PURPOSE:To easily manufacture extra low nitrogen steel by preventing nitrogen from being picked up, by screening the surface of molten metal from the atmosphere by feeding inert gas onto that when inert gas is injected into the molten metal bath from the upper immersion lance. CONSTITUTION:An immersion hood 12 is supported with a support frame body 7 and the lower part of hood 12 is immersed into the molten steel 3 of ladle 2 by hanging the support frame with a wire rope 9 from a drum 8. The hood 12 is composed of a cylinder body 10 and a cover 11, and the cover 11 closed the cylinder body 10 with an oil hydraulic cylinder, a link 14 and a tractive bar 15. An immersion lance 1 is immersed into the molten steel 3 by inserting it from the hole small gap 18 of cover 11 and the molten steel 3 is stinned by injecting inert gas. At the same time, the inert gas is injected via a header 16 from the nozzle 17 equipped on the cylinder body 10. Therefore, the bare steel 6 generated by stirring does not touch the atmosphere and the pickup of nitrogen is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of blowing inert gas into a molten metal bath from an immersion lance, and in particular actively avoids contact between molten metal and air to prevent nitrogen pickup. This is the purpose.

In this case, inert gas injection includes the following cases.

(1) Stirring of the molten metal bath by blowing inert gas (
2) Using an inert gas as a carrier gas, add various additives, and stir and mix. (3) When heating the molten metal bath, add a heat generating agent such as At and supply oxygen. In some cases, the molten metal in the ladle 2, such as the molten steel 3, is removed from the immersion lance 1 as shown in FIG. When an inert gas (Ar gas) is blown into the lance, bubbles 4 rise around the lance as shown in the figure, and the rising flow causes the slag layer 5 to flow outward, exposing the so-called bare hot water 6. This bare water 6 comes into contact with the atmosphere and picks up nitrogen, causing an increase in the nitrogen content in the molten steel. Especially in the treatment of low-nitrogen steel,
It is necessary to avoid pickup of this nitrogen as much as possible.

As one method for preventing nitrogen pick-up, for example, as shown in Figure 1 of Japanese Patent Application Laid-open No. 57-7354, a hollow cylinder surrounding 6 parts of the bare water is immersed in molten steel, and the gas released from the molten steel is removed. A method is disclosed in which a hollow cylindrical body is raised to create a non-oxidizing atmosphere inside the hollow cylindrical body. However, in the case of a hollow cylinder like the one mentioned above, the upper end is open to the atmosphere, so
It took time to convert the atmosphere inside the cylinder into IR with the inert gas blown into it, and the replacement was not complete, so it was difficult to produce ultra-low nitrogen steel using the above method.

The present invention completely eliminates the drawbacks of the conventional method described above, that is, completely prevents the pickup of nitrogen, thereby making it possible to easily produce ultra-low nitrogen steel.

Hereinafter, the apparatus used to carry out the method of this invention will be explained with reference to FIG.

In FIG. 2, the same numbers as in FIG. 1 indicate the same parts. Now, in FIG. 2, 7 is a support frame of the immersion hood, and a wire rope 9 is connected to the upper winding and unwinding drum 8.
(It is suspended so that it can be raised and lowered from two points.

An immersion cylinder (10) is fixed to the center of the frame 7, and an openable/closable lid 11 is provided at the upper end of this cylinder (10), forming an immersion hood 12. This lid 11
The lid 11 is opened and closed by an opening/closing mechanism consisting of a hydraulic cylinder 13, a link 14, and a suspension bar 15 provided on the side of the frame 7. In the illustrated state, the lid 11 is in the closed state, and the lid 11 is in the open state. In case (2), the opening/closing mechanism should be driven in the direction of the arrow.

This opening/closing type lid 11 is opened at C2 when the immersion lance 1 is immersed, and closed when inert gas is blown into the lance. In the figure, 16 is a ladder for supplying inert gas, and 17 is a nozzle for blowing inert gas into the immersion hood 12 connected to this header 16.

An example of the device used in this invention is as described above, and the immersion hood 12 is a closed type (non-open type) consisting of a combination of the immersion cylinder 10 and the openable lid 11, and
The reason why the inert gas is blown into the interior from the nozzle 17 is as follows.

First, although the immersion hood 12 is a closed type, the lid 1
Firstly, it is difficult to completely seal the lance hole in this type of equipment due to the small gap 18 formed in the lance hole.Secondly, from the viewpoint of molten steel contamination due to melted refractory mixed in, and to extend the service life of the immersion hood, it is difficult to completely seal the immersion hood. It is desirable that the immersion depth be shallow, but if the immersion depth is made shallow, a gap may be created between the lower end of the hood and the hot water surface due to fluctuation of the hot water surface due to inert gas injection. However, the amount of inert gas blown into the molten steel was not large enough to rise through the molten steel and accumulate in the hood to completely purge the air entering from the above-mentioned gaps. The naked bath will pick up nitrogen from the air.

In this case, according to the present invention, the nozzle 1 is inserted into the hood 12.
By actively blowing in an appropriate amount of inert gas from step 7,
This completely replaces the air inside the hood with inert gas, completely preventing the pickup of nitrogen from the naked hot water inside the hood.

Further, in order to improve the life of the immersion hood 12 and the immersion lance 1, it is preferable to locate the immersion lance 1 in a shallow place. In this way, the spread of the inert gas blown from the immersion lance 1 is reduced, and therefore the immersion hood 12
It also has the advantage of being able to make the outer diameter smaller. However, in this case, the stirring power becomes insufficient, so it is desirable to use bottom bubbling from the ladle in combination to supplement the stirring power.

Next, an example will be described.

Example 1 1QQ ton of molten steel having the components shown in Table 1 was tapped in a converter at a tapping temperature of 1640°C, and was placed in a ladle, and the shape of the cylinder was circular;
An immersion hood (lid opening/closing type) with a cylinder inner diameter of 2000 ran was immersed in molten steel at a depth of 250 m with A and t of 3. Q
At the same time as introducing Q Kv't-5teel, oxygen was blown in from the immersion lance at 14 Nm 15), and Ar gas was supplied into the hood at Q, 5 Nm 15).
Heat treatment was performed for 12 minutes. At this time, the immersion lance was made into a double pipe, and Ar gas for lance protection was applied from the outer pipe to 3 Nm5.
15) Infused. As a result, the molten steel temperature decreased from 1570℃ to 1
620°C (increased by 2).

The composition of the molten steel after treatment is listed in Table 1, and there was no increase in nitrogen at all.

On the other hand, the molten steel components after treatment when no immersion hood was used are also listed in Table 1, and the nitrogen content increased by 1 part.

Example 2 100 tons of molten steel having the composition shown in Table 2, which was tapped in a converter at a tapping temperature of 1710°C, was placed in a ladle and heated to 1-5 Nm3. /;) A
Using r gas as a carrier gas, first add 1.50% At ash.
K9/1-steel blowing, followed by iteflux (CaO-fluorite 90:10 mixture) at 2.00K
g/1-steel, Oa-Si powder at 0.70 Ky
/1-steel was blown in, and at the same time, Ar gas was supplied into the hood at a rate of 1.0 Nm3/] for 10 minutes.

The molten steel components after treatment are listed in Table 2. Table 2 also shows the composition of the molten steel after the same treatment without using an immersion hood.

Table 2 (wt) As detailed above, according to the method of the present invention, the pickup of nitrogen when performing inert gas blowing treatment from an immersion lance can be greatly reduced compared to the conventional method. This greatly contributed to the production of low-nitrogen steel.

[Brief explanation of drawings]

Fig. m1 is an explanatory diagram of the conventional method, and Fig. 2 is an explanatory diagram of the apparatus used to implement the method of the present invention. l; Immersion lance 12; Immersion hood 17; Inert gas blowing nozzle

Claims (1)

[Claims] In a method of blowing an inert gas from an upper immersion lance into a molten metal bath housed in a container whose upper part is open to the atmosphere, the lance surrounds the exposed part of the molten metal at the lower part of a hood that penetrates the ceiling. A method for blowing gas into a molten metal bath, which comprises immersing the molten metal bath in a molten metal bath, and supplying an inert gas into the hood.