JPH05295417A - Treatment of molten steel - Google Patents

Abstract

PURPOSE:To prevent reduction of MnO in molten slag from being reduced and entering molten steel and to easily produce a low-Mn steel by adding a specific quantity of boron oxide into the molten steel at the time of tapping the molten steel from a converter. CONSTITUTION:At the time of tapping the molten steel from the converter after making the molten steel by decarburize-refining molten iron in the converter, the boron oxide is added at 0.5-3kg/ton of the molten steel. Reducing agents such as A, Si, etc., are added at the time of tapping the molten steel because of deoxidation of the molten steel and the adjustment of components, but as MnO in the molten slag has an intense affinity with B2O3 and is combined with B2O3, activity of MnO is rekmarkably lowered. Therefore, Mn reduced with Al and Si do not go into the molten steel, and rather, Mn in the molten steel is oxidized to MnO and removed into the molten slag, and the low-Mn steel is easily and stably obtd.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a low Mn steel, which is intended to efficiently produce a low Mn steel by suppressing Mn reduction from slag to molten steel or removing Mn from the molten steel in the production of low Mn steel. Regarding

[0002]

2. Description of the Related Art In recent years, in the production of ultra-low sulfur steel and ultra-low phosphorus steel,
The control of chemical components in steel is becoming more and more strict. It is difficult to remove sulfur efficiently in a converter, which is an oxidative refining process, and hot metal desulfurization has been performed for a long time, in which desulfurizing agents such as quick lime are put in a pan or the like. Also, since it is a great burden to remove silicon and phosphorus only by blowing in the converter, iron oxide is added to the hot metal to desiliconize it, and the slag generated is separated and removed, and then a flux for dephosphorization is added. Then, dephosphorization treatment is performed, and the obtained treated hot metal is blown in a converter (Japanese Patent Publication No. 60-59962).

According to these methods, phosphorus and sulfur can be removed efficiently, but the fact that the hot metal treatment slag is basic and that the phosphorus concentration decreases in the converter blowing of the hot metal after the hot metal pretreatment causes a decrease in the phosphorus concentration. Since the amount of slag is small, it is difficult to reduce Mn. In addition, as known from Japanese Examined Patent Publication No. 3-77245, positively increasing the Mn concentration in the hot metal stage, increasing the blow-off Mn of the converter, and reducing the amount of Mn alloyed iron used is toughness and toughness. It is useful when manufacturing thick plate materials and bar steel products. However, in a thin plate material that requires workability, it is necessary that Mn is as low as 0.15% or less. In this case, it is difficult to reduce Mn by the conventional hot metal pretreatment, and the amount of slag is increased in the converter to reduce Mn. However, after tapping the converter, mainly Mn in the slag flowing out of the converter is reduced to molten steel by deoxidation during tapping or reduction refining of secondary refining, and M in molten steel
n increases, and it is not an efficient method for producing a low Mn steel.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for suppressing the reduction of Mn from slag to molten steel and further removing Mn from the molten steel to efficiently produce a low Mn steel. And

[0005]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems, in which 1 t of molten steel is mixed with boron oxide at the time of tapping the converter.
The molten steel treatment method is characterized by adding 0.5 to 3 kg per ton to suppress the reduction of Mn from the slag or remove Mn from the molten steel.

[0006]

The function of suppressing Mn reduction from slag to molten steel or removing Mn from molten steel will be described below. In the converter, oxygen is supplied to remove C in molten steel and oxidize Mn.
The slag absorbs the Mn oxide. In this case, when the amount of slag is large, the amount of Mn contained in the slag increases, so that the Mn of molten steel decreases. Next, an alloy such as Al or Si is added for deoxidizing and adjusting the composition when the molten steel that has been blown in the converter is tapped into a ladle. At this time, a part of the slag generated in the converter inevitably flows out into the pan together with the molten steel, and the molten steel is deoxidized and deoxidized and reduced by the deoxidizing agent such as Al and Si. Mn
Occurs in the molten steel.

Therefore, when manufacturing low Mn steel, it is necessary to suppress this Mn reduction. In order to solve this problem, in the present invention, an additive having a strong binding force with MnO in the slag and reducing the activity of MnO is added to the tapping steel. Boron oxide is suitable as an additive because it has a strong binding force with MnO and reduces the activity of MnO. Table 1 shows the results of an experiment in which boron oxide was added at the time of tapping the converter.

[0008]

[Table 1]

As shown in Table 1, it has been found that addition of boron oxide makes it possible to suppress Mn reduction from slag and to remove Mn from molten steel depending on the amount added. Further, the boron oxide content has an appropriate range, and the range is as shown below. That is, when the amount of boron oxide added is less than 0.5 kg per 1 ton of molten steel (hereinafter referred to as 0.5 kg / t), the reduction inhibiting effect of Mn is hardly recognized. On the other hand, when 0.5 kg / t or more is added, reduction of Mn from slag to molten steel can be suppressed,
Further, Mn may be removed from the molten steel. However, if the addition amount exceeds 3 kg / t, the viscosity of the slag is significantly reduced and the slag foams (slag forming).
Becomes noticeable, and the phenomenon of blowing out from the reaction container occurs.
This causes production problems and loss of iron contained in the slag to the outside of the system, which is a serious problem in productivity and economy. Therefore, the amount of boron oxide to be added is 0.5 to 0.5 per amount of molten steel.
3 kg / t is suitable. The additive may be a substance containing boron oxide.

[0010]

EXAMPLE The graph shown in FIG. 1 shows the relationship between the Mn content at the end of the converter blowing (blown-out) and the Mn content of the molten steel in the ladle by adding boron oxide during tapping of the converter. . In the case where there is no addition of boron oxide or the amount is less than 0.5 kg / t, the Mn value in the ladle is often above the straight line showing no change in the Mn amount, and the Mn amount is increased. On the other hand, in the case of adding 0.5 kg / t or more, there is no change in the Mn content, or there is a decrease. It is also understood that slag foaming may occur when the amount of addition exceeds 3.0 kg / t.

[0011]

As described above, according to the present invention, reduction of Mn from slag can be suppressed, and efficient removal in combination with converter blowing enables stable production of low Mn steel with good workability. Became. Further, when manufacturing ultra-low phosphorus low Mn steel, which is required to reduce the phosphorus content in the steel material (for example, P ≦ 0.010%) due to material needs, hot metal pretreatment and conversion that mainly consist of dephosphorization treatment are performed. By combining with furnace blowing, it has become possible to stably produce ultra low phosphorus low Mn steel.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of boron oxide added at the time of tapping and Mn in molten steel.

Claims (1)

[Claims] 1. 1 ton of molten steel containing boron oxide when the converter is tapped
A molten steel treatment method, which comprises adding 0.5 to 3 kg per unit to suppress reduction of Mn from slag or remove Mn from molten steel.