JPS61130414A - Method for dephosphorizing refined molten steel in ladle - Google Patents

Abstract

PURPOSE:To oxidize and remove the phosphorus contained in a molten steel subjected to refining by decarburization by putting the molten steel into a ladle, if the content of P therein is above the specified value, then inserting an immersion pipe into the part from which molten slag is removed by blowing an inert gas, adding a dephosphorizing flux to the molten steel and subjecting the molten steel to oxygen blowing. CONSTITUTION:The molten steel 3 is put into the ladle 1 if the content of P in the molten steel after refining is above the specified value and is not accepted in terms of compsn. The inert gas is then blown through a bottom tuyere 2 of the ladle and the molten slag 3a on the surface of the molten steel in raised part is removed as the inert gas rises. The immersion pipe 4 made of refractories is immersed partly into the molten steel 3 in the part where the molten steel surface is exposed after the removal of the molten slag. Oxygen is blown to the molten steel from a lance 5 provided in the upper part of the immersion pipe and at the same time a basic flux such as quicklime or fluorite is added from a storage tank 7 to the molten steel surface by a chute 8. The basic dephosphorized slag contg. iron oxide of >=15% T, Fe is formed to oxidize the phosphorus in the molten steel and to fix the same into basic slag. The molten steel is thus dephosphorized and refined.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for simply refining molten steel in a ladle that has been refined in a refining furnace.

(Conventional technology) With the spread of continuous casting and speeding up, time constraints on supplying molten steel from steelmaking furnaces to continuous casting equipment have become extremely severe, and operational forms that do not have the luxury of shortening steelmaking time, etc. It can't be helped.

One way to shorten the steelmaking time is to make judgments based on the analysis results of samples taken at the end of the work without checking the analysis results at the end of work in the steelmaking furnace, but in this case, the composition is only based on predictions. Since the steel is unconfirmed, the phosphorus content of specially refined molten steel may not meet the standard value. Furthermore, it is impossible to bring this component within the specifications even with the use of secondary refining equipment, and because the specifications cannot be met, it is not possible to supply hot water to continuous casting in the subsequent process, and casting operations are interrupted. This may lead to serious situations such as

Therefore, as described in Japanese Patent Application Laid-Open No. 53-149826, gas is injected from the gas injection hole at the bottom of the ladle to stir the molten steel while a protective wall is provided, and oxidation is carried out inside the protective wall through a supply pipe. A method of heating molten steel by blowing oxygen gas from an oxygen blowing pipe while adding a reactant (hereinafter simply referred to as the ladle oxygen blowing heating method), or JP-A-56-15011
As shown in Publication No. 8, a method of desulfurizing and deoxidizing the molten steel by heating the molten steel with electricity, adding flux such as lime, and stirring an inert gas (hereinafter simply referred to as the energization inert gas method) Numerous refining methods have been proposed, such as (named).

However, in these conventional methods, for example, in the ladle oxygen-blown heat raising method, the temperature of the molten steel is increased by oxidation of the oxidizing reactant, which makes it impossible to dephosphorize refined molten steel. The addition At.

This oxidation is not limited to mere oxidation of Sl, Ti, Mn, etc., but also leads to a rapid oxidation loss of valuable elements originally contained in the molten steel or of the molten iron itself.Furthermore, with this oxidation, a large amount of oxides such as At203 are added to the steel. The number of system inclusions increases, which also impairs the quality of the steel. Further, in the energized inert gas method, even if a flux such as lime is added, only desulfurization is performed, and dephosphorization of molten steel cannot be expected. Moreover, since it involves energized heating, equipment costs and operating costs are extremely high. Furthermore, in order to prevent the above-mentioned refined molten steel from exceeding the phosphorus standard during normal operation, it is necessary to select raw materials for the refining furnace of the converter TT electric furnace or to perform sufficient dephosphorization and refining by adding more refining flux than necessary. The load on converters, electric furnaces, etc. has increased rapidly, and refining flux,
It has drawbacks such as large economic losses in terms of refractories, molten steel yield, etc.

(Problems to be Solved by the Invention) The present invention is not limited to simply raising the temperature of refined molten steel or adjusting the components of C, Mn, Si, S, etc., which are the drawbacks of the conventional method as described above, but also increases the temperature of refined molten steel. This is a refining method that enables the dephosphorization of phosphorus, which is an impurity, and does not cause quality deterioration due to the increase in inclusions associated with dephosphorization refining, and is extremely simple and inexpensive compared to conventional methods. Our objective is to provide a ladle phosphorization method for regenerating refined molten steel.

(Means to Solve Problem Z) The in-ladle dephosphorization method for refined molten steel according to the present invention will be described below. As mentioned above, the present invention is not just for molten steel, but for molten steel in a refining furnace such as a converter or an electric furnace. When the crude molten steel is poured into a ladle, etc., a deoxidizing agent such as Fe-St I Fe-MntAL is added to adjust the molten steel to the composition specifications.As a result, the refined molten steel has no phosphorus content. Since this is known just before casting, it is possible to easily dephosphorize and regenerate the stratified steel. By spraying the contained oxidizing gas under specific conditions to perform dephosphorization and refining, it is possible to perform dephosphorization and regeneration without increasing inclusions or causing large losses of valuable elements such as iron. I discovered something.

Dephosphorization refining of purified molten steel is carried out within a limited area isolated by a dipping pipe, etc., without forming oxidizing slag that has dephosphorizing ability on the wide surface of the purified molten steel, and by effectively spraying oxidizing gas. The high T, Fe (iron oxide) containing slag 7 is formed locally and circulated by bottom-blowing inert gas in the immersion tube.

Through this circulation, the phosphorus in the refined molten steel is rapidly formed by the dephosphorization flux such as quicklime, fluorite, calcium ferrite, etc. added in the immersion tube and the above-mentioned spraying of the oxidizing gas. It is removed by the dephosphorization slag into the dephosphorization slag. Furthermore, after dephosphorization and refining, the dephosphorization slag is sufficiently chilled by adding limestone, raw dolomite, cold quicklime, whiskers (iron grains), etc. inside the dipping tube or on the surface of the ladle from which the dipping tube has been removed. Prevents rephosphorization.

In addition, in order to effectively refining such purified molten steel, it is necessary to spray oxidizing gas to increase the amount of oxygen that does not directly reach the molten steel surface at the bottom of the lance, and in particular to reduce the amount of inert gas supplied from the bottom of the ladle. It is more preferable to suppress weak stirring to form a high concentration of T and Fe-containing slag on the inner surface of the immersion tube at an early stage.

Therefore, the refined molten steel that has been dephosphorized and refined has some of the necessary components such as Si t Mn r At that were previously adjusted to the required components of the molten steel removed, and in particular, there are a lot of inclusions in the molten steel. Since the inclusions are mixed in, an inert gas such as argon or nitrogen is continuously supplied from the bottom of the ladle to float and remove the inclusions, and the necessary deoxidizer or alloy is added to the molten steel in the immersion tube. (Example) Next, an example of the dephosphorization method according to the present invention will be described.

Figure 1 is a cross-sectional view of the in-ladle dephosphorization of refined molten steel according to the present invention! In the diagram shown, the bottom of the ladle 1 is provided with a fine hole or a supply port 2 for inert gas made of a gas permeable substance, and floating slag 3a'f! of refined molten steel 3 is provided. : The immersion tube 4 is immersed into the molten steel 3 to a suitable depth. A lance 5 for spraying oxidizing gas is attached to the immersion tube 4 so as to be able to move up and down, and a chute 8 is installed at one end of the tank 6 for deoxidizing agent or ferroalloy and the storage tank 7 for dephosphorizing slack. They are connected via the

Here, the refined molten steel is one that has already been adjusted to the desired specification in a tapping ladle or secondary refining furnace, such as At-guild ([At:l=o, o 104 or more).
, At-8t-killed ([:Si]=0
．． 15 to 0.3%) steel, etc., and if it is found that phosphorus is removed as a result of analysis inside the ladle, inert gas is added from the bottom to 350% (350%).
After removing the floating slag 3a, the dipping tube 4 is lowered and dipped into the ladle.
The inert gas at the bottom was reduced to 100 to 20,017 minutes, and the oxidizing gas was sprayed onto the surface of the molten steel using a lance 5, and 500 kg of quicklime per pot and 100 kg of fluorite were added as flux from the storage tank 7. /additional pot to form a dephosphorizing slag with -Fe of 15 or more.

The result of refining in this way is simply the oxidizing gas in the immersion tube using the conventional method! This is shown in comparison with the case of spraying.
It is clear that the method of the present invention is extremely effective for dephosphorization, and is also an excellent dephosphorization method that can regenerate refined molten steel in a short time without deteriorating its quality due to interference with inclusions, etc.

(Effects of the Invention) As described above, by using the method for dephosphorizing refined molten steel according to the present invention, it is possible to dephosphorize the refined molten steel without causing quality deterioration, and moreover, the loss of valuable elements such as iron can be suppressed. This is an extremely excellent dephosphorization method that effectively and easily regenerates refined molten steel.

In addition, since it is possible to easily regenerate unqualified molten steel by dephosphorization, it is possible to supply purified molten steel without interrupting the subsequent casting process, which has an extremely large economic effect.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a mode of dephosphorization of purified molten steel in a ladle according to the present invention. 1: Ladle, 2: Inert gas supply port, 3: Refined molten steel, 4:
Immersion tube, 5: Lance, 6: Ferroalloy storage tank, 7: Dephosphorization flux storage tank, 8: Chute. 2 Furu 4'u Sui Daishin Keiguchi

Claims (1)

[Claims] While stirring the purified molten steel by blowing inert gas from the bottom of the ladle, a dipping tube is inserted into the ladle, and oxidizing gas is sprayed onto the surface of the purified molten steel in the dipping tube, and dephosphorization flux is added. A method for dephosphorizing purified molten steel in a ladle, characterized in that the refining is completed in a ladle, and then the purified molten steel is stirred by blowing inert gas from the bottom of the ladle.