JPH0841526A - Production of high clean steel - Google Patents

Abstract

PURPOSE:To simply improve the product quality of a high clean steel and to stabilize the casting operation by adding CaO and calcium aluminate at the time of tapping the molten steel from a refining furnace, improving flow-out slag and softening the slag. CONSTITUTION:At the time of tapping the molten steel into a ladle from a converter 1 in which oxygen blowing was executed, the CaO for improving the flow-out slag and the calcium aluminate for softening the slag are added. These additives promote the good slag-making by the molten steel heat at the time of tapping and the stirring force of steel tapping flow, and Al2O3 inclusion produced during refining treatment is changed into the slag, and also, the flowability of the slag is improved. Further, deoxidizer such as Al, etc., is added after tapping the molten steel to reduce the low grade oxides in the slag, and oxidizing degree of the slag is stably becomes a low level. By this method, the high clean steel reduced in the content of the Al2O3 inclusion is obtd. and the clogging of a nozzle in the continuous casting is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high-cleanliness steel for reforming outflow slag when tapping steel from a refining furnace using oxygen such as a converter and an electric furnace, and particularly to a cause of product defects. The present invention relates to a method for producing high-cleanliness steel for improving product quality by forming a ladle slag composition that removes alumina inclusions and the like.

[0002]

2. Description of the Related Art Generally, molten steel produced in a converter or the like is subjected to component adjustment and deoxidation adjustment to control the amount of oxygen in the molten steel. However, since the oxidized molten slag existing in the upper portion of the molten steel is not completely deoxidized, an element having a strong affinity with oxygen in the molten steel (such as Al) and the upper portion of the molten steel during the period from the addition of the deoxidizer to the solidification of the molten steel. Reacts with the oxidized molten slag (for example, Fe oxide, Mn, etc.) present in to produce a deoxidized product. As a result, the control of oxygen in the steel is significantly impaired, and the deoxidized product produced causes deterioration of the product quality of the steel.

Therefore, conventionally, various techniques have been proposed for preventing the deterioration of steel quality caused by the deoxidized product.

Japanese Patent Laid-Open No. 61-19723 discloses that when molten steel is tapped from a melting furnace to a ladle, sol. A
A method is described in which oxygen in steel is converted to Al ₂ O ₃ to form slag by adding Al so that 1 is 0.50% or more, and a clean steel having oxygen in steel of 20 ppm or less is produced.

In Japanese Patent Laid-Open No. 61-266170, a silicate modifier is added on the oxide film of slag, and a heat generating agent such as Al or coal is added to enhance the temperature raising effect. There is described a method for reforming steelmaking slag in which the ladle is vibrated to cause the surface-hardened slag to melt and react with the modifier, and after the reforming work is completed, the residue in the ladle is discharged.

Further, in Japanese Patent Laid-Open No. 63-262412, a strong deoxidizing agent is added to molten steel surface slag immediately after refining and gas stirring is performed to reduce FeO and MnO in the slag, and degassing is performed by stirring molten steel gas. A method for cleaning molten steel is described in which acid products are floated and removed.

[0007]

However, in the method described in the above-mentioned Japanese Patent Laid-Open No. 61-19723, Al is added to the tapped steel, and sol. Since Al needs to be a high Al molten steel of 0.50% or more, there is a problem that the alloy cost becomes high. In addition, after this deoxidation treatment, the target A
There is also a problem that a de-Al treatment for reaching the l component is required, which complicates the operation process.

Further, the method described in JP-A-61-266170 aims at reforming including a slag oxide film, but since the slag flowing out of the converter has a high basicity and a high melting temperature, With this method, slag melting is difficult, and for example, there is a problem that nozzle clogging occurs in continuous casting, resulting in lack of operational stability. Also, regarding slag stirring, there is a problem that sufficient stirring and mixing cannot be achieved only by ladle vibration.

Further, in the method described in JP-A-63-262412, a strong deoxidizer is added to reduce the oxidation degree of slag, and Al in the molten steel reacts with oxygen during the secondary refining treatment. To suppress the formation of Al ₂ O ₃ by
Since the slag flowing out of the converter has a high basicity and is difficult to melt, a uniform reaction with the slag is difficult and a large solid phase of slag is generated A
There is a problem that the absorption capacity of l ₂ O ₃ is also small.

Therefore, the object of the present invention is to use a relatively simple process to reduce the inclusions of alumina to improve the quality of the product and to soften the slag to stabilize the casting operation.

[0011]

In the prior art, it is considered that lower oxides such as SiO ₂ and MnO in ladle slag act as an oxygen source for molten steel to form inclusions such as Al ₂ O _3. , The oxygen potential has been reduced and the reaction has been suppressed by slag solidification.

[0012] However, as a result of detailed investigation, it was found that the product defects and the effect of lowering the degree of slag oxidation in the ladle or the chilling effect due to the addition of CaO were scarce and were greatly influenced by the slag composition.

In the present invention, in addition to Al for slag deoxidation and CaO for composition control in the tapping stage, low melting point calcium aluminate is added in order to promote slag formation of slag outflow and added CaO. . Calcium aluminate is added in an amount of 5% or more of the amount of lime added in a weight ratio to accelerate slag slag formation and enhance the absorption capacity of alumina inclusions generated during the refining process.

[0014]

The relationship between the product performance and the contents of lower oxides such as FeO and MnO in the slag has been confirmed as shown in FIG. In the figure, product performance is represented by inclusion index. As can be seen from the figure, the T. Fe +
When the amount of MnO is more than 8 to 10% by weight, the product performance deteriorates sharply. This is due to the reaction between the slag caught during the refining treatment and the Al component in the steel, or the Al ₂ O ₃ -based inclusions generated by the oxidation during addition of the alloy.

In fact, Al ₂ O ₃ type inclusions have been detected as product inclusions, and it is necessary to suppress secondary oxidation by improving the efficiency of slag reforming and forming a complete seal.

FIG. 2 is a schematic diagram for explaining the operating method in the present invention. In the present invention, when steel is tapped from the converter 1 to the ladle 2, the molten steel heat at the tapping and the stirring force due to the tapping flow are used for the purpose of converting slag to C.
aO and low melting point compound calcium aluminate (12
CaO 7 Al ₂ O ₃ ) is added simultaneously. After tapping, a deoxidizer such as Al is added to reduce the slag lower oxide.

In the present invention, calcium aluminate acts as a slag slag formation accelerator, and also slags of high basicity slag. Further, the slag fluidity becomes high, the converter slag and the slag forming agent are made uniform, and the reaction with the slag deoxidizer is made efficient, so that the slag oxidation degree can be stably lowered. Further, the molten steel in the ladle is completely covered by the slag melting and does not come into contact with the atmosphere, so secondary oxidation is suppressed.

[0018]

Example A test was conducted by changing the amount of calcium aluminate with respect to CaO added during tapping. Table 1 shows the test results. However, the amount of CaO added was 6 kg / t. The product performance is indicated by the incidence of inclusion defects.

[0019]

[Table 1] By setting the amount of calcium / aluminate / CaO to 0.02 or more, preferably 0.05 or more, the slag of the ladle slag becomes good, and the (T.Fe) + (of the ladle slag after the secondary refining treatment is obtained. (MnO) is stably reduced to 5 or less, and the product performance is significantly improved.

Further, it was confirmed that the improvement of the molten steel coating effect by the slag slag improves the [N] pickup in the refining process as compared with the normal operation.

[0021]

The present invention has the following effects.

(1) Alumina inclusions in the product were reduced, and the rate of product incompleteness was reduced to about 1/5 due to Al kill tinplate.

(2) Since the ladle slag comes close to a stable calcium-aluminate composition with a low melting point, nozzle clogging in continuous casting is prevented and the operation can be stabilized.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between product performance and the content of lower oxides in slag.

FIG. 2 is a schematic diagram for explaining an operating method according to the present invention.

[Explanation of symbols]

 1 ... Converter, 2 ... Ladle

Claims (2)

[Claims] 1. A method for producing highly clean steel, which comprises adding CaO for improving outflow slag and calcium aluminate for softening slag when tapping from a refining furnace. 2. The method for producing a highly clean steel according to claim 1, wherein a deoxidizing agent is added after tapping.