JPS5844121B2 - steel refining method - Google Patents

Description

Detailed Description of the Invention This invention is a steel refining process in which gas is blown from a nozzle installed below the bath surface in combination with oxygen top blowing. Concerning a steel refining method that operates while conducting.

In the oxygen top-blown steelmaking method (Togawa gun, scrap, and auxiliary materials are charged, and oxygen is blown into the steel using an oxygen lance, refining is carried out, but in the early and middle stages of refining, there is an active reaction between the molten steel and oxygen. A large amount of carbon oxide Q is generated and the steel bath is sufficiently stirred, but at the final stage of refining, the generation of carbon monoxide gas rapidly decreases and the steel bath is not sufficiently stirred.

Therefore, in the oxygen top-blown steelmaking method, a method has been proposed in which gas is blown into the bath in combination with oxygen top-blowing to strengthen the stirring of the steel bath.

However, there are no reports that have examined in detail the conditions for blowing gas into the bath in combination with oxygen top blowing.

In addition, unless the gas and the steel bath undergo an exothermic reaction, the steel bath is cooled by the gas on the gas outlet side, which can clog the nozzle and prevent gas from being blown in. No reliable conditions have been found regarding the gas blowing pressure or nozzle manufacturing for this purpose.

In view of the current situation, this invention aims to optimize the structure and blowing conditions of the double-pipe nozzle in a steelmaking process in which gas is blown into the bath using a double-pipe nozzle in combination with oxygen top-blowing. This paper proposes a steel refining method that allows stable gas injection over the entire period and ensures sufficient stirring of the steel bath.

This invention uses a double tube nozzle that satisfies the following formula in refining by blowing gas into the bath in combination with oxygen top blowing, and Po/Pe≧
The gist is a steel refining method that operates by supplying gas under the conditions of 1.89.

In the practice of this invention, the gases blown into the bath may be one of the following: oxidizing gases such as carbon dioxide, nitrogen, neutral gases such as carbon oxide, inert gases such as argon, krypton, cannon, etc. Two or more types can be used in combination.

Further, in this invention, the structure of the double tube nozzle and the gas injection conditions were determined for the following reasons.

It is thought that the behavior of the blown gas has a large influence on the clogging of the nozzle installed below the bath surface.

Molten steel enters the nozzle when the gas is blown into the bath at less than the speed of sound, and when the steel bath is stirred, the second
As shown in the figure, it is thought that the gas 2 ejected from the nozzle 1 is cut off discontinuously, and when this gas cut-off occurs, molten steel enters the nozzle.

However, when the gas is blown into the bath at the speed of sound or higher, in the so-called chef 7-ing state where the nozzle diameter do and the air column dg are equal, the gas is continuously blown out as shown in FIG. Molten steel rarely enters the nozzle.

This air column (jet core) becomes more stable as the air column density becomes higher, that is, the flow velocity becomes higher.

The inventors focused on this point and conducted various experiments regarding the structure of the double pipe nozzle and gas injection conditions in order to stably blow gas into the bath without increasing the gas flow rate or gas pressure. That's what I did.

As a result, in order to prevent nozzle clogging, as shown in FIG. 4, the gas flow velocity in the slit 5 of the double tube nozzle 4 is set to the sonic velocity, and a gas jet wall is created to protect the jet or bubble in the inner tube 6. It is necessary.

The nozzle structure for implementing this is such that the ratio of the inner tube cross-sectional area AM to the slit cross-sectional area As is in the range 1≦AM/AS≦3, and the ratio of the inner tube wall thickness t to the slit width t8 is t/
l <, 3. o.

If AM/AS <1, the cross-sectional area of the slit portion is larger than the cross-sectional area of the inner tube, and the nozzle becomes close to a single hole, so there is no point in using a double-tube nozzle.

In addition, in the case of AM/A3>S, 6876M>2 from the following formula
In this case, unless the slit 5 and the inner tube wall thickness t are made thicker, the flow rate cannot be balanced and the effect of the jet wall provided by the slit will be diminished.

Here, when t/dM<1, approximately (1+2t/
dM) 2f-1+α1(tag 0<α1(also x 1st
As shown in the figure, d8: outer diameter of outer tube, dM: inner diameter of inner tube,
t: Inner pipe wall thickness In the above formula, when AS/AM>3 (6876M)
2〉4+α1.6876M〉2+α2 (0×α2<1)
>2.

Therefore, it is desirable that the distance between the inner tube 6 and the slit 5 be as small as possible in order for the effect of the jet wall due to the slit to work effectively.

Then, the ratio between the inner tube wall thickness t and the slit width ts is t/1
When 8>3.0, the effect of the slit jet is reduced as shown in FIG.

Furthermore, in order to prevent blockage of the double pipe nozzle, it is important to create a jet on the slit side.In order to ensure this jet formation using pressure and reduce the pressure condition on the inner pipe side, the gas outlet It is necessary that the ratio of Po (Po - tank pressure - nozzle pressure loss) to the steel bath static pressure Pe around the nozzle satisfies the following conditions.

Gas blowing from the slit Po/Pe≧1.89 Gas blowing from the inner tube 2.5≧Po/Pe≧1.0 Here, if the gas blowing from the slit Po/Pe<1.89, It is not possible to maintain a gas flow rate of Matsuha 1 or higher, and the jet is interrupted and the wall does not function as a wall.

Further, when the gas is blown from the inner tube with Po/Pe=1.0, the gas pressure is balanced, so that no gas flows from the inner tube.

When 1.0<Po/'Pe<1.10, the influence of waving on the bath surface due to stirring of the steel bath appears, and pe substantially fluctuates, making the flow of the main pipe gas unstable.

Also, if the tank pressure pT exceeds 10 kg/ca, the equipment cost for a high-pressure container will increase, so the tank should be pT < 10 k
g/cyst is preferred, in practice 9.5 kg/cr
rt or less.

Nozzle pressure drop, (P is inversely proportional to the inner tube inner diameter dM,
If dM is small, such as when blowing gas into the bath in combination with oxygen top blowing, JP≧1.0, and the gas outlet pressure Po
does not exceed 8.5 kg/crA.

The steel bath surface is approximately 2 kg/c4 or less, and if atmospheric pressure is considered, the steel bath static pressure pe around the nozzle is 3 kg/c4.
vt or less.

Therefore, Po/Pe does not normally exceed 3.

On the other hand, when P o / P e > 2.5, the meaning of the double pipe, which is to create a jet on the slit side and reduce the pressure condition on the inner pipe side, disappears, and when P o / P e > 3.0, gas blow-through is possible. Since gender also comes into play, P o/P e≦2.
5 is desirable.

Regarding the appropriate amount of gas to be blown into the bath in combination with oxygen top-blowing, the inventors have determined through experiments that the uniform mixing time of the steel bath is 2.
It has been found that 0 seconds to 70 seconds is appropriate.

In this case, the amount of zero-order gas is 1/10 to 1/10 of the amount of top-blown oxygen.
/100, so the number and dimensions of the nozzles are unique.

As is clear from FIG. 6, the cross-sectional area n (AM
+As) and the processable steel capacity W is as follows.

The double tube nozzle structure and gas blowing conditions in this invention can be applied not only to the case of blowing gas into a bath in combination with oxygen top blowing, but also to the case of blowing gas into a bath of a refining vessel.

Next, embodiments of the invention will be described.

The melt gun shown in Table 2 was charged at a gun rate of 86.8% into a 300-ton oxygen top-blowing converter having a double tube nozzle with dimensions shown in Table 1 at the bottom of the furnace. Oxygen top-blowing refining was carried out under the conditions shown below while blowing argon gas into the bath.

During refining under the above conditions, there was no clogging of the nozzle (gas could be blown stably throughout the refining period), and steel whose chemical composition is shown in Table 4 was melted.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the symbols of each part of the double pipe nozzle for blowing gas installed at the bottom of the furnace, and Figure 2 is an explanatory diagram showing the phenomenon of gas exhaustion when gas is blown into the bath at a speed below the speed of sound. Figure 3 is an explanatory diagram showing the state when gas is blown into the bath at a speed higher than the speed of sound, Figure 4 is an explanatory diagram schematically showing the gas blowing state that prevents nozzle clogging, and Figure 5 is An explanatory diagram schematically showing a gas blowing state from a double pipe nozzle with a large inner pipe wall thickness,
FIG. 6 is a chart showing the relationship between nozzle capacity and bath completion mixing time. In the diagram, 1... nozzle, 2... gas, 3...
...Steel bath, 4...Double pipe nozzle, 5...
...Slit, 6...Inner tube, PTs...
... Tank pressure of gas on the slit side, PTM ... Tank pressure of gas on the inner tube side, Po ...... Gas outlet pressure,
pe... Steel bath static pressure around the nozzle, t. ...Slit width, t...Inner tube wall thickness, d
s: outer diameter of outer tube, dM: inner diameter of inner tube, H: bath head height, W: steel bath amount,
ρFe... Viscosity of steel bath.

Claims (1)

[Claims] 1. In refining performed by blowing gas into the bath in combination with oxygen top blowing, po/pe ≧1,8 from the slit between the inner tube and the outer tube using a double tube nozzle that satisfies the following formula.
A steel refining method characterized by operating by supplying gas under 90 conditions.