JPH0432510A - Method for raising temperature of molten steel in ladle with oxygen blowing - Google Patents

Abstract

PURPOSE:To prevent erosion of refractory and clogging of a nozzle for casting caused by produced slag from the refractory material by beforehand adjusting Si content in molten steel to high and adding the specific small quantity of Al at the time of raising temp. of molten Si killed steel with oxygen blowing. CONSTITUTION:At the time of continuously cast after charging the Si killed steel 1 already refined with a ladle 2, the temp. of molten steel is raised to the temp. being suitable to casting. For this purpose, inert gas is blown from a bubbling lance 6 and after removing the molten slag 7 floated with rising bubble, a submerged tube 4 is lowered to the position having no molten slag 7 and the tip part is submerged into the molten slag 7. Fe-Si is charged from a charging tube 5 in the submerged tube 4 to adjust Si content in the molten steel 1 at higher than the aimed value. Successively, O2 gas is supplied onto the molten steel surface from a lance 3 and during this period, Al is added into the molten steel 1 at 10-5O% of the theoretical oxidation with supplied oxygen quantity. The temp. of molten Si killed steel 1 is raised with oxidation of Al and Si and also the molten slag composed of 3Al2O3.2SiO2 is generated, and the erosion of the lining refractory of submerged tube 4 and the clogging of nozzle for continuous casting can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method of blowing acid into steel in a ladle after it has been tapped from a refining furnace and deoxidized and refined to raise its temperature.

(Prior Art) Generally, in continuous casting processes from refining furnaces such as converters and electric furnaces, it is necessary to operate with consideration to temperature, composition, and timing of supply of molten steel.

However, in actual operation, continuous casting becomes impossible due to variations in the blow-off temperature of the refining furnace, poor timing of tapping, and fluctuations in the yield of additive alloys.

Therefore, for example, as shown in JP-A-53-149826 or JP-A-59-13331'4, a combustible material such as alloy 81 is added to the upper surface of the steel in the ladle. A method has been proposed in which the temperature of molten steel is raised by blowing acid at the same time.

(Problems to be Solved by the Invention) However, the above-described method for heating solid solution steel in a ladle with acid blowing has the following problems.

First, a common method for heating Si-killed steel is to use an FeSi alloy as a heat generating material, oxidize it with top-blown oxygen, and use the heat generated by the oxidation to heat up molten steel in a ladle. In this method, the refractory lining of the immersion pipe is severely eroded and cannot withstand normal work.

The most effective method to solve this problem and prevent melting loss of the immersion pipe refractories is to use a heat generating material whose oxidation product has a high melting point. That is, this is because the oxidation product does not react with the refractory once solidified.

A heat generating material that meets this condition is AQ, and this oxide l! , O, has a high melting point of 2000° C. or higher, and during normal operation, it solidifies inside the immersion tube, and there is no melting loss of the immersion tube.

The use of Aff as a heating agent for raising the temperature of molten steel in this way is extremely advantageous in terms of operation.

However, if A is used as a heating agent in Si quilted steel, a small amount of A cannot be oxidized and remains in the molten steel. Since the tandate nozzle has a relatively small diameter, if a small amount of AQ remains in the molten steel, this AQ will clog the nozzle and make casting impossible. This is the reason why AQ cannot be used as

In addition, the method of heating molten steel using an Fe-Si alloy has the disadvantage that the immersion tube is severely damaged by erosion as described above, and also has the major disadvantage that Mn in the molten steel is removed by oxidation. Mn also contributes to oxidation heat generation, but its calorific value is 1/1 compared to Si and AQ.
6, which can hardly be called efficient. Further, the amount of Mn removed by oxidation must be replaced by a Fe--Mn alloy, which is undesirable as it increases the cost significantly.

The reason why a large amount of Mn is removed by oxidation is that the oxidation strength of Mn is very similar to that of 81, although it is slightly inferior to that of 81.

The present invention prevents the erosion of the refractory during heating with blown acid, which is a drawback of the conventional heating method for heating steel in a ladle with blown acid, suppresses the loss of valuable elements, and realizes high-speed heating. Another object of the present invention is to provide a heating method that does not cause nozzle clogging during casting.

(Means for Solving the Problems) The present invention involves blowing inert gas into molten steel in a ladle to stir the molten steel, and immersing an immersion tube in the upper part of the molten steel, adding a heat generating agent into the immersion tube, and blowing oxygen into the molten steel. In the method of raising the temperature of molten steel in a ladle, the Si content of the molten steel in the ladle is adjusted to be higher than the target value beforehand when spraying oxygen to the molten steel of killed steel. Alternatively, it is a blown acid heating method for steel in a ladle, which is characterized by adding an alloy and continuously adding 10% to 50% of the amount that the added pure aluminum bottle would theoretically burn with oxygen. .

Hereinafter, Sj Killed II (S i = 0.
10% or more) of molten steel will be described based on the diagram.

The molten steel heating equipment used in the present invention is implemented by installing an immersion pipe 4 on the upper surface of the molten steel as shown in FIG. A heating input pipe and an exhaust gas suction pipe 5 are connected to one side of the dipping tube 4 by a structure that follows the up and down movement of the dipping tube 4. Also, a blown oxygen lance 3 is placed which is raised and lowered independently of the dip tube 4. A bubbling lance 6 is installed for the purpose of stirring the molten steel l from the bottom of the ladle.

1- An actual heating work method using the heating equipment described above will be described.

Prior to immersing the immersion tube 4 into molten steel, the bubbling lance 6 is lowered to remove the slag 7 floating on the surface of the ladle molten steel below the immersion tube 4. Thereafter, the immersion tube 4 is lowered and immersed in the melt 91.

In this state, a Sl-based ferroalloy such as Fe-Si ferroalloy is introduced into the dipping tube 4, and the 81 component of the ladle solid solution 1i+ is adjusted to be higher than its target value.

After that, oxygen is supplied, but during this period, AQ is supplied in an amount equivalent to 10% to 50% of the amount of AQ that theoretically oxidizes with the amount of supplied oxygen.
is continuously supplied during oxygen supply. At this time, a small amount of Si-based alloy may be supplied into the immersion tube 4 at the same time, but the
In order to completely oxidize and burn C in the immersion tube 4 and prevent it from remaining in the molten steel, it is preferable not to supply Si-based alloy iron. In addition, in order to effectively oxidize the molten steel in the immersion tube 4, the stirring condition of the molten steel in the immersion tube 4 is extremely important, and based on the results of various water model tests and actual operations,
The immersion depth is 200 mm or more, and the amount of stirring gas is 1 t of molten steel.
INρ/min per ON, preferably less than or equal to INρ/min.

When heating with blown acid using this method, 8ρ is first oxidized inside the immersion tube 4, and the remaining oxygen after oxidizing 1 simultaneously oxidizes Si in the molten steel.

As described above, the present invention focused on the erosion mechanism of immersion pipe refractories and found that raising the melting point of the oxidation product is effective in reducing 3i and O through the simultaneous oxidation of 80 and Si.

2 S i Oy double salt product is produced.

As shown in Figure 2, this 3A (1203' 2S io, +; The oxidizing ability of 1 is significantly higher than that of Mn, and by supplying a small amount of AC to the oxygen supply point, AQ oxidizes in preference to Mn oxidation.Therefore, the oxidation of Mn is suppressed. .

If the amount of Ag introduced here is less than 10% of the theoretical oxidation amount, high-speed heating can be achieved, and moreover, Si in the molten steel is oxidized in advance and Si in the slag.

The concentration increases and the erosion of refractories progresses rapidly.

Furthermore, if the AQ amount is more than 50%, the octane added to the immersion tube remains in the molten steel, causing nozzle blockage during casting.

In this way, by taking into account the above conditions and continuously adding the A12 to the required ratio at each time, the AQ
Alternatively, we have established a heating method for S quilt steel that is effective in achieving the high-speed heating inherent to AQ gold alloys, suppressing wear on the refractories, and preventing casting inhibition caused by A.

(Example) Next, the case where the heating method of the present invention is applied after tempering and adding extra Si to 81 quilt steel with a Sl content of 0.15% is shown in comparison with the conventional method and a comparative example. Shown in 1.

The heating conditions in Table 1 are as follows: The oxygen delivery rate is 4000 Nm3/lIr.
This is a comparison when the conventional method uses Fe-5i to raise the temperature, and since the amount of oxygen required to oxidize Si is larger than that of AQ, the heating rate is lower.

The amount of erosion of immersion pipe refractories is measured by using a small amount of A (
In the case of the present invention method in which both AQ and Si are oxidized at the same time,
It can be seen that this is a very small and significant improvement compared to the conventional method.

Furthermore, the reduction in Mn in the steel is smaller than in the conventional method, resulting in savings in Mn-based alloys.

In this way, this method provides an effective heating method for Si quilt steel, and is an extremely useful method for heating steel in a ladle for CCs having small-diameter nozzle tundishes.

Table 1 Method of the Invention The amount used was set at 0.1 of the theoretical combustion amount with oxygen.

B Method 2 The amount of Aa used was set to 0.05, which is the amount that can be theoretically burned with oxygen.

Comparative Example - The amount of a used was set to 06, which is the amount that can be theoretically burned with oxygen.

*In order to confirm whether operation is possible when the amount of C used is increased, a confirmation test was conducted using the amount of e used that was theoretically combustible with oxygen (L, S). Very good results were obtained regarding the amount of material corrosion loss, but the amount of residual T, 8, in the molten steel was as high as 0,00%, and nozzle clogging occurred with the small-diameter tundish nozzle, making it unsuitable for normal operation. It turns out there isn't.

(Effects of the Invention) As described above, the heating method of the present invention can achieve high-speed heating of molten steel without causing any nozzle clogging during casting, which is unique to Si-killed sea bream, and prevents melting of refractories. This is an extremely excellent method for heating molten steel by blowing acid.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the ladle content steel heating device used in the present invention, Figure 2 is the melting point diagram of S i Ot-αAL03, and Figure 3 is a diagram of the melting point of S i Ot-αAL03.
Figures (a) and (b) are diagrams showing a comparison of the nozzle blockage during casting and the occurrence index of slab pinholes. l... Molten steel 2... Ladle top-blown oxygen lance immersion tube Total heating material input pipe and flue gas suction pipe bubbling lance slag Applicant Nippon Steel Corporation Figure I & 3 (α) Figure 1N2 5IOrjAl+O+

Claims (1)

[Claims] In a method in which inert gas is blown into the molten steel in the ladle to stir the molten steel, a dipping tube is immersed above the molten steel, a heating agent is added to the dipping tube, and oxygen is blown to raise the temperature of the molten steel in the ladle. When blowing oxygen to molten steel of Si-killed steel, after adjusting the Si content of the molten steel in the ladle to be higher than the target value, at the same time as blowing oxygen, aluminum or aluminum alloy is added, and the added pure A blowing acid heating method for steel in a ladle, characterized by continuously adding 10% to 50% of the amount of aluminum theoretically combustible with oxygen.