JP2001234229A - Method for reforming slag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reforming slag which is capable of surely reducing the MnO and FeO in the slag without the occurrence of slag inclusion and a change in molten steel components. SOLUTION: In the method for reforming the slag which lowers the oxygen concentration of the slag existing on the molten steel in a ladle by a reducing agent, the lower oxide in the slag is reduced by blowing inert gas containing the gas of alkaline earth metals from a lance to the slag surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slag reforming method for obtaining highly clean steel.

[0002]

2. Description of the Related Art In the production of ultra-low carbon steel, molten steel that has been decarburized to about 0.04% C by blowing oxygen in a converter is further subjected to vacuum degassing to react with dissolved oxygen and carbon. The C concentration is reduced to about several tens of PPM. Although the oxygen concentration in the molten steel is greatly increased by the decarburization treatment, Al is added after the decarburization treatment to deoxidize the molten steel, and the molten steel is refluxed at a light vacuum using a vacuum degassing apparatus. Many alumina-based inclusions generated by the acid are removed.

[0003] However, the oxygen concentration in the slag (the concentration of lower oxides such as MnO and FeO) also increases with the decarburization treatment in the converter, so that oxygen in the slag is reduced to Al in the molten steel after Al deoxidation. The reoxidation reaction represented by the following formulas (1) and (2) occurs, and the cleanliness of the molten steel is greatly reduced.
This reoxidation reaction is carried out by spraying a large amount of oxygen in order to lower the C concentration, and is extremely violent in ultra-low carbon steel having a high oxygen concentration in the slag. 3MnO + 2Al = Al ₂ O ₃ + 3Mn (1) 3FeO + 2Al = Al ₂ O ₃ + 3Fe (2)

For this reason, for example, Japanese Patent Application Laid-Open No. Sho 59-70710
In Japanese Unexamined Patent Publication No. Hei. 2-250915, Al or an Al-containing flux is added to a ladle slag after tapping from a converter, and in Japanese Unexamined Patent Publication No. Hei 6-122917, a plurality of launders containing Al or an Al alloy are added. A slag reforming method of immersing a rod-shaped material in slag to reduce lower oxides of MnO and FeO in the slag has been carried out to prevent reoxidation of molten steel by the slag.

[0005]

In the conventional slag reforming method, when adding Al to the slag surface, an inert gas such as Ar gas is blown from a porous plug at the bottom of the ladle to stir the slag. MnO, FeO in slag
Is trying to reduce enough. For this reason, the slag is unnecessarily entrained by the stirring of the bubbling, which has caused inclusion defects caused by the slag.

Furthermore, in the conventional method, Al cannot always be added uniformly to the entire slag, so that the slag is partially unreduced, and the reoxidation of molten steel by the slag cannot be sufficiently prevented. Also, A added to the slag
Since a part of l melts into the molten steel and the Al concentration becomes unnecessarily high, there is also a problem that the reoxidation rate of Al in the molten steel is increased and the cleanliness of the molten steel is reduced.

In view of such a problem, an object of the present invention is to provide a method for reforming slag which can surely reduce MnO and FeO in slag without involving slag and changing molten steel components. I do.

[0008]

Means for Solving the Problems In order to solve the above problems, the present invention has the following features. That is, (1) In a slag reforming method in which the oxygen concentration of slag on molten steel in a ladle is reduced by a reducing agent, an inert gas containing an alkaline earth metal gas is blown from a lance onto the slag surface, A slag reforming method characterized in that lower oxides in slag are reduced. The slag according to claim 1, wherein (2) an inert gas containing a total gas concentration of alkaline earth metal of 10% or more is sprayed on the slag surface to reduce lower oxides in the slag. It is a reforming method.

[0009]

FIG. 1 shows an embodiment of the present invention.
In the figure, a Mg gas 1 previously generated by heating is sprayed through a lance 2 made of a refractory onto a slag 5 on molten steel 4 in a ladle 3. After colliding with the slag 5, the Mg gas 1 spreads circumferentially along the slag 5 and the Mn in the slag 5
O and FeO are reduced by the following equations (3) and (4). MnO + Mg = MgO + Mn (3) FeO + Mg = MgO + Fe (4)

[0010] Since Mg has a stronger reducing power than Al, the reduction of slag proceeds more rapidly than that of Al. Therefore, it is not necessary to agitate the slag unnecessarily, and it is possible to prevent inclusion defects from occurring due to slag entrainment. In the present invention, Mg is not added to the slag as a metal, but Mg is added to the slag.
Since the gas is sprayed on the slag surface as a gas, Mg gas is supplied to the entire slag, and the reduction reaction proceeds uniformly over the entire slag. Further, since the Mg gas comes into contact with the slag at the gas phase interface and the reduction reaction proceeds, the Mg gas does not melt into the molten steel, and there is no change in the molten steel component.

Since the boiling point of Mg is 1097 ° C.,
A method of heating and gasifying metallic Mg at a temperature of 00 ° C. or higher, a method of bringing a heated Ar gas into contact with metallic Mg to form an Mg-Ar mixed gas, and a method of generating a Mg gas by reducing MgO with Al or the like. For example, Mg gas may be generated in the lance and on the upstream side of the lance, and may be sprayed from the lance onto the slag surface. Since Mg is a very strong reducing agent, MnO and FeO in slag can be easily reduced if the concentration of Mg gas in the blown gas is 10% or more. However, the gas for diluting the Mg gas is preferably Ar gas, but may be another inert gas which does not cause contamination of the molten steel.

Although the above description of the present invention has been made by taking Mg gas as an example, the present invention is not limited to Mg gas, but has a boiling point relatively lower than the temperature of molten steel and a strong reducing power. Alkaline earth metals such as Mg, Ca, and Sr may be used.

The present invention has a great effect in an extremely low carbon steel in which re-oxidation from slag is intense, but is not necessarily limited to this. In view of its principle, the present invention can be sufficiently applied to a low carbon steel. In particular, in a Ti-added low-oxygen steel or the like in which an Al alloy is not used as a deoxidizer, or even if it is used in a small amount, the slag reforming method of the present invention can prevent Al from being mixed by slag reforming. It has excellent effects.

[0014]

The present invention will be described below with reference to examples and comparative examples. (Example 1) 280 t of molten steel decarburized in a converter was tapped in a ladle and moved to a slag reforming site. 100kg from lance for 1000kg ladle slag at slag reforming site
% Mg gas was blown at 270 Nm ³ / h for 5 minutes. Thereby, the total Fe in the slag was reduced from 10% to 3% as a whole. After degassing the molten steel by vacuum degassing, the components are adjusted, and the components C: 30 ppm, Si: 0.
015%, Mn: 0.25%, P: 0.02%, S:
0.01% (all by mass%) of molten steel was produced. Thereafter, casting was performed at a casting speed of 1.6 m / min. The obtained cast slab has an Al concentration of 0.04% and a total oxygen concentration (TO) of 1
The content became 5 ppm or less, and a highly clean steel was obtained.

(Example 2) Molten steel 28 decarburized in a converter
0t was tapped into a ladle and moved to a slag reforming site. At a slag reforming site, a 50% Mg-Ar gas is supplied from a lance at 400 Nm ³ / h for 1000 kg of ladle slag at a rate of 5 Nm ³ / h.
Sprayed for minutes. Thereby, the total Fe in the slag was reduced from 7% to 2% as a whole. After deoxidizing the molten steel by vacuum degassing, the components are adjusted, and component C: 30 p
pm, Si: 0.015%, Mn: 0.25%, P:
0.02%, S: 0.01% (all by mass%) molten steel was produced. Thereafter, casting was performed at a casting speed of 1.6 m / min. The resulting cast slab had an Al concentration of 0.04% and a total oxygen concentration (TO) of 14 ppm or less, and a highly clean steel was obtained.

Comparative Example 1 Molten steel 28 decarburized in a converter
0t was tapped in the ladle. This molten steel was subjected to a vacuum degassing process to adjust the components without modifying the slag, and the components C: 30 pp
m, Si: 0.015%, Mn: 0.25%, P: 0.
02%, S: 0.01% (all by mass%) molten steel was produced. The total Fe in the slag in the ladle was 10%. Thereafter, casting was performed at a casting speed of 1.6 m / min. The obtained slab had an Al concentration of 0.035% and (TO) of 3
It became 0 ppm or more, and a high clean steel was not obtained.

Comparative Example 2 Molten steel 28 decarburized in a converter
0t was tapped into a ladle and moved to a slag reforming site. At the slag reforming site, 100 kg of metal Al was added to 1000 kg of ladle slag to reform the slag. The total Fe in the slag varies greatly depending on the measurement position,
In some places, the total Fe showed a high value of about 8% even after the modification. The molten steel is subjected to vacuum degassing to deoxidize and adjust the components. Component C: 30 ppm, Si: 0.015%, Mn:
Molten steel of 0.25%, P: 0.02%, and S: 0.01% (all by mass%) was smelted. Thereafter, the casting speed was 1.6
It was cast at m / min. The Al concentration of the obtained slab is 0.1.
055%, the total oxygen concentration (TO) was 30 ppm or more, and no highly clean steel was obtained.

[0018]

As described above, by applying the slag reforming method of the present invention, the oxygen in the slag can be reliably reduced without causing slag entrainment or changes in the molten steel component, and thus the quality of the slab is improved. Is improved, and the yield is significantly improved. In addition, since the cleanliness is improved and the clogging of the immersion nozzle is suppressed, the unsteady work can be omitted, and the operability is greatly improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

[Explanation of symbols]

 1: Mg gas 2: Refractory lance 3: Ladle 4: Molten steel 5: Slag

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Eiichi Takeuchi 20-1 Shintomi, Futtsu Nippon Steel Corporation Technology Development Division F term (reference) 4K013 BA08 CB04 CC04 CF02 CF13 EA24 EA25 FA05

Claims (2)

[Claims] In a slag reforming method for reducing the oxygen concentration of slag on molten steel in a ladle with a reducing agent, an inert gas containing an alkaline earth metal gas is blown from a lance onto the slag surface, A method for reforming slag, comprising reducing a lower oxide in slag. 2. The total gas concentration of alkaline earth metals is 10%.
The slag reforming method according to claim 1, wherein the inert gas contained above is blown onto the slag surface to reduce lower oxides in the slag.