JPS61281809A - Ladle refining method for molten steel - Google Patents

Abstract

PURPOSE:To refine a high-purity steel easily and quickly by adding a reforming flux to the slag on the surface of the molten steel in a ladle, heating the slag with a heater and adding a desulfurizing agent together with an inert gas into the molten steel. CONSTITUTION:The reforming flux is added to the slag 3 on the surface of the molten steel 2 in the ladle 1 and the slag is heated with the burner 4 by which the ladle refining of the molten steel is executed. The desulfurizing agent is added together with the inert gas via a lance or bottom blowing nozzle into the molten steel 2 before or after the addition of the reforming flux. The slag 3 is then heat-compensated by the burner heating from above, by which the fluidity thereof is improved and the reforming flux is uniformly melted therein to accelerate the reaction between the slag and flux. Since the slag has a reducing property, the reoxidation of valuable elements such as Al, Si and Mn in the steel is prevented. Inclusions are liable to float on the molten steel as the temp. decrease of the molten steel is prevented by the burner heating. In addition, the desulfurization is remarkably improved.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a method for refining molten steel in a ladle, more specifically, in the ladle refining of molten steel, it modifies floating slag on the surface of the molten steel and removes the presence of intervening particles in the molten steel. This invention relates to a method for suspending substances and adsorbing them to slag and promoting desulfurization of molten steel.

(Conventional technology and its problems) In the secondary refining of molten steel, minute inclusions (
It is extremely important to remove as much as possible the main composition of metal oxides such as Al2O3, SiO2, and MnO. However, this is accompanied by considerable difficulties. This is because these inclusions are continuously generated at the contact interface between the floating slag on the surface of the molten steel and the molten steel. Therefore, it is necessary to modify the floating slag, that is, to reduce the oxidizing composition such as FeO and MnO contained in the slag.

In this case, there is a problem in that the temperature of the molten slag and molten steel decreases due to the addition of the modified 7 lux. In other words, since the modified 7"7x is normally added to the slag at room temperature!!! (solid), it takes away the heat from the slag and molten steel to melt it. This temperature drop causes the slag to lose its fluidity. This leads to an increase in the non-uniformity of the slag composition and a decrease in reactivity with the molten steel due to the residual unmelted 7 lac, which greatly impairs the slag reforming effect.Furthermore, the slag modification effect is greatly impaired. This has an unfavorable effect on the removal of inclusions, in that the floating of inclusions is inhibited due to a decrease in the properties of the inclusions.To avoid this situation, a method of adding modified 7 lux in a molten state is considered, but in this case There are many problems, such as the addition of 9 facilities to install a melting device and the difficulty in handling the reforming 7-fax.

On the other hand, for example, Japanese Patent Application Laid-Open No. 60-3966 discloses that elements contained in molten steel due to FeO%MnO in floating slag are
In order to suppress the increase in inclusions in steel due to oxidation such as AI], [Sil, etc., a coolant (Cabl dolomite, etc.) is added to the slag in the ladle, then A1 dross is added, and then a coolant is added. , a technique for reducing the reactivity of suspended slag has been shown. However, this approach is extremely difficult to completely reform oxidizing slag, so the idea is to harden the slag itself and suppress its reactivity with molten steel. It can be said that it is a thing. In fact, when using this method, the temperature drop of the molten steel due to the added coolant is large, and the reaction with the slag is uneven due to the presence of unmelted parts, making it ineffective despite the use of expensive materials. There are disadvantages such as the fact that the temperature is low, and although the surface in contact with the molten steel still melts and reacts, combined with the non-uniform A1 dross effect, a reliable reforming effect cannot be expected.

On the other hand, Japanese Patent Publication No. 52-23968 discloses a method of refining reduced slag by adding quicklime, fluorite, etc. while heating floating slag in a ladle with electrode arc heat. According to this, the slag reforming effect is recognized and it is predicted that Fe01Mn0 in the slag will be reduced, but if this is actually carried out, equipment costs such as electrodes and energizing equipment will be enormous. Therefore, there are disadvantages and uneconomical effects such as increased consumption of electricity, longer working time, and the need to use only a specific type of steel in order to carry out production on a normal scale. It is not practical.

In this way, from a practical standpoint, no practical means of modifying the oxidizing slag of cram schools has yet been developed.

The present invention solves the above-mentioned problems, effectively modifies slag by simple means, and improves FeO%M in slag.
By reducing nO etc., we aim to reduce inclusions in steel,
It is also an object of the present invention to add a desulfurizing agent to promote desulfurization of molten steel, promote the floating of inclusions, and adsorb them to slag, thereby refining high-purity steel at low cost and in a short time.

(Means for Solving the Problems) The present invention provides a method for adding modified 7 lux to slag on the surface of self-molten steel in a ladle, heating it with a burner, and refining the molten steel in a ladle before or after adding the modified flux. The above objective is achieved by adding a desulfurizing agent together with an inert gas into the molten steel via a lance or a bottom blower/thrower.

(Function) In the method of the present invention, the slag floating on the surface of the molten steel from above the ladle is thermally compensated for by means of burner heating, and the fluidity of the slag is improved, and the added modified flux is The melt easily penetrates into the molten steel, ensuring its uniformity and further promoting the reaction with the slag, resulting in the modification of the slag, that is, the reduction of oxidizing compositions such as FeO and MnO in the slag, and the generation of inclusions in the molten steel. We aim to reduce the factors and promote adsorption to slag. Furthermore, since the slag is reducing, reoxidation of valuable elements such as A1, Si%Mn, and Ti in the steel is prevented. In addition, heating with a burner prevents the temperature of the molten steel from becoming too low, which is preferable for inclusion flotation.In other words, the strong stirring causes the inclusions to float and become adsorbed to the slag, but at the same time, the strong stirring A1, S in steel by
Oxidation of i, Mn, Ti, etc. leads to an increase in some inclusions. Therefore, the adsorption of inclusions floated by heating modification of slag is improved and valuable elements such as AI and Six in steel are increased.
Inclusions are actively reduced by suppressing the formation of inclusions due to re-oxidation of Mn%Ti, etc., and by adsorption and flotation of inclusions to the powder particles during powder injection, and the cleanliness is greatly improved. improves. Furthermore, in addition to the above-mentioned effects as one of the cleaning methods, desulfurization is also greatly improved. This desulfurization process involves the addition of modified flux and the F in the slag formed on the surface by heating.
ed, the desulfurization rate improves due to the reduction of MnO and the reaction progresses actively due to the high temperature, and the surface of the injected desulfurization agent particles easily becomes A 1.0 , SiO
This desulfurization reaction is improved reentrantly by forming a fusion layer such as a and absorbing (S) in the steel. It is also more desirable to carry out slag modification at the same time as the desulfurizing agent is injected, since contact between the modified slag and molten steel is ensured for a long period of time, and desulfurization and inclusions are sufficiently adsorbed.

In addition, in the present invention, the manner of addition and heating of the modified 7 gamma flux includes the case where the modified flux is sprinkled on the floating slag in the ladle and then heated from the top surface of the slag with a burner; When adding modified 7 lux heated with a burner to slag and then heating the slag with a burner from the top surface; Is the modified 7 lux added to the slag that flows out during tapping? When adding Tx and heating the floating slag from above in the ladle with a burner; After heating the floating slag in the ladle, adding modified flux and heating with a burner; When heating the floating slag in the ladle. This is included when adding modified 7 lux heated with a burner and then heating with a burner.

In the present invention, the term "modified flux" refers to 7 fluxes that are effective in making slag reducible.
Examples include Ft, AI%N, and those with added compounds. "Burner heating" refers to burning fuel such as LPG, melted oil, and oxygen as a combustion improver in a burner, and heating it with the flame.Reformed flux is added to the fuel transport system piping, and the fuel is heated at the center of the burner. In some cases, the modified 7 lacs is added separately from the addition port and then heated with a burner from the outside.
A general term for appropriate burner heating methods.

In addition, the desulfurization agent used in the present invention may be CaO alone or partially added with CaF=, or metal Ca, M[r
, a simple substance of Na or a compound containing these, or Ca
There are Cz1 premelt blacks, etc., and the amount added depends on the (S) content of the molten steel subjected to desulfurization and the desired (S) content after treatment.
S) It varies considerably depending on the value, but usually 1.0~
81g/T-molten steel, and the timing of addition to the molten steel is modification 7
FAX may be added to the slag and heated with a burner to melt the slag together, but it is also possible to add 7 FAX before adding 4, then add flux to the slag and heat with a burner. However, either Even in this case, it is preferable to stop the burner heating when adding the desulfurizing agent.

Therefore, if a desulfurizing agent is added to the molten steel before adding the reforming 7 lax, in addition to desulfurization being carried out in the slag reforming process, the reforming 7 lax that also serves as temperature control when supplying the molten steel to the subsequent process can be added.

Furthermore, when added after the addition of modified 7 lux, the desulfurization rate increases. However, no matter what happens, there is no difference in the effect of promoting the floating of inclusions.

The desulfurizing agent may be blown in using a lance or a bottom blowing nozzle. In that case, an inert gas such as Ar or N2 is used as a carrier for the desulfurizing agent.

(Example) Examples of the present invention will be shown below along with comparative examples.

Example 1 In this example, modified flux heated by a burner is sprinkled onto the floating slag on the surface of molten steel poured into a ladle, and then a top-blowing lance is immersed into the molten steel from the top of the slag to desulfurize the slag. Indicates the case where

Referring to FIG. 1, a ladle 1 is covered with a sieve 9, and a reformed flux (here, composed of 90% CaO powder and 10% CaF2 powder) is supplied as fuel (from a heating burner opened in the ladle).
After blowing in a predetermined amount, desulfurization treatment was performed using a desulfurization agent and inert gas supply device (not shown) provided in the top blowing lance 10.

As a desulfurization agent, 90% Cab powder and 10% CaF2 powder are used.
A powder consisting of 400 kg/pan (22 kg/T) was used. After this desulfurization treatment, argon gas 8 was blown into the molten steel from a nozzle provided at the bottom of the ladle to stir the molten steel.

As a result, FeO and MnO in the slag are
% to 0.7%. This is 11% for non-heat reforming and non-desulfurization (general treatment @), 2.9% for desulfurization but no reforming (Comparative Example 1), and , compared to 2.8% in the case without desulfurization (Comparative Example 2) (Comparative Examples 2 to 6 correspond to Examples 1 to 5, respectively, except for the presence or absence of the addition of a desulfurization agent). In fact, it has drastically decreased to 1 ha. In addition, it can be seen that the cleanliness of the molten steel is also greatly improved compared to the comparative example.

In addition, numeral 5 in the figure is a modified flux addition port which is inserted into the outside when the modified 7 lux is added directly from the burner.

Example 2 This example shows a case in which modified 7Lax at room temperature is sprinkled on the upper surface of the slag and heated with a burner from the upper surface of the slag.
is closed. The timing and mode of addition of the desulfurizing agent are as shown in Table 1.

Example 3 In this example, modified flux was added to the inflow and outflow lags during tapping, and the floating slag was heated with a burner from the upper surface in a ladle.

Example 4 In this example, after heating floating slag, modified 7 lux at room temperature was added, followed by heating with a burner.

Example 5 This example shows a case where, after heating floating slag, a modified flux heated with a burner was added, followed by heating with a burner.

It can be seen that in both cases, the degree of slag modification and the cleanliness of molten steel are much improved compared to other comparative examples.

(Effects of the Invention) As explained in detail above, the present invention achieves a rapid and uniform reaction between slag and modified 7 fux using a simple burner heating means without using an electrode arc. This not only makes it possible to effectively remove compositions caused by inclusions such as FeO%MnO in the slag, but also prevents the temperature of the molten steel from decreasing. Adding a desulfurizing agent not only has a desulfurizing effect, but also promotes the floating of inclusions in the molten steel, and the floating inclusions are adsorbed by the slag, making the molten steel even more purified and producing high-purity steel. There are many things that contribute to the economic realization of refining.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating an example of an apparatus for carrying out the method of the present invention. 1... Ladle, 2... Molten steel, 3... Slag, 4...
・Heating burner, 5... modified 7 lux addition port. 58 Paternal Flux Door Carollo BAr Force Voluntary Procedure Amendment June 2, 1985

Claims (1)

[Claims] (1) When refining the molten steel in the ladle by adding modified flux to the slag on the surface of the molten steel in the ladle and heating it with a burner, insert a lance or bottom-blowing nozzle into the molten steel before or after adding the modified flux. A ladle refining method for molten steel, characterized in that a desulfurization agent is added together with an inert gas via a molten steel ladle.