JPS58221219A - Dephosphorization method of molten steel - Google Patents

Abstract

PURPOSE:To dephosphorize molten steel inexpensively with high efficiency by discharging the slag formed in a steel making furnace together with the molten steel tapped therefrom into a ladle and stirring the slag and the molten steel in the ladle. CONSTITUTION:The slag formed in a steel making furnace is discharged without much dephosphorization although it has dephophorization power at a high temp. of about >=1,600 deg.C in the steel making furnace. The molten steel cools down by about 50-100 deg.C when it is transferred into a ladle. Gaseous Ar is blown into such cooled steel in the ladle to stir the slag discharged from the steel making furnace together with the molten steel, whereby the dephosphorization power of said slag is activated and the steel can be dephosphorized effectively. Since the slag itself has large degree of oxygen potential, there is no need for replenishing the source for oxygen, and since there is not need for any flux, the steel is dephosphorized inexpensively, and the problems such as the decrease in the temp. of the molten steel and the generation of white smoke are eliminated.

Description

[Detailed description of the invention] The present invention relates to a method for dephosphorizing molten steel.

Conventionally, as a molten steel dephosphorization method, CaO-FeO-Fe, 0.
- A method of adding 7 lux of CaF, -5iO1-1110, system to the tapping flow when steel is tapped from a steelmaking furnace to a ladle, or a method of adding CaF, -5iO1-1110, system 7 lux to the tapping stream when tapping steel from a steelmaking furnace to a ladle, or a method in which Cab > 551, (FeO + Fe, O,)
> 2 Charge 7 lux of F196 into the ladle,
In addition, a method is known in which molten steel is tapped from a steelmaking furnace and dephosphorized. However, these methods have low dephosphorization rates and cause problems in terms of cost and operation because the temperature of the molten steel is often lowered. For example, even if the above flux is added at 11 to 12 kg/ton of molten steel at the time of tapping, 40 to 50
%, and the molten steel temperature at that time drops by as much as 75-95%.Another method is the dephosphorization method using N, Co, etc. This method has a better dephosphorization rate than the above-mentioned dephosphorization method, but the temperature drop of the molten steel is as large as the normal temperature drop plus 50 to 60°0.
The problem is that a large amount of white smoke is generated. Also,
All of the above methods require the use of a large amount of 7 lux, which is a cost problem.

The present invention was devised in view of these circumstances, and it is possible to perform dephosphorization treatment with high efficiency without having to suffer from the problems of the above-mentioned nine conventional methods and without using expensive flux. The purpose is to provide a method.

For this reason, the present invention provides a method for dephosphorizing slag produced in a steelmaking furnace by discharging it into a ladle together with molten steel when tapping molten copper, and stirring the slag and molten steel in the ladle. Its basic characteristic is the benevolence it possesses.

It has long been known that the dephosphorization reaction is accelerated when molten steel is heated to a low temperature, but the blow-off temperature in a steelmaking furnace is generally set at 1600° or higher, taking into account the temperature drop during tapping. Temperature may inhibit the dephosphorization reaction. FIG. 1 shows an example of this, with CaO451-8i0. ton-T, Fa
20%-MnO with Mg06q6 as the main component, A40
3, Ti01.

It shows the relationship between the dephosphorization ability of slag composed of 0, , and s and the temperature of molten steel. For this reason, even though the slag in the steelmaking furnace still has sufficient dephosphorizing ability, [P] is reduced to 1.
Normally, it is discharged without containing much 0.

On the other hand, the temperature of molten steel in the ladle is always lower than the temperature in the steelmaking furnace, and the difference therebetween is as much as 50 to 100 degrees. The present inventor, Hiro, took note of the dephosphorization ability of the slag discharged from the steelmaking furnace as described above, and the molten steel temperature in the ladle, which is lower than the temperature inside the steelmaking furnace. It was discovered that the dephosphorization ability of lithium slag can be activated, and that by flowing out the slag produced in a steelmaking furnace together with molten steel into the ladle and stirring them, efficient dephosphorization can be carried out. It is something.

In addition, the steelmaking furnace produced slag does not need to supply a large amount of metals having a 0*m potential, such as iron oxide, as a III source necessary for the dephosphorization reaction.

The dephosphorization process in the ladle is performed by stirring the steelmaking furnace produced slag and molten copper, and for this reason, for example, stirring is performed while supplying a stirring gas (for example, Ar gas) into the ladle. .

〔Example〕

Using the 250 TON converter, the molten copper that had been blown at a temperature of 9,1680"0 was tapped into the ladle, and the converter slag was also discharged into the ladle, followed by a gas flow of -Jio, 5 Nm.
By stirring the slag and molten f14 for 20 minutes using Ar gas/min (Ar gas), the flow rate of converter slag into the ladle was varied from 2.5 to 60 o'clock per molten steel TON, and after stirring, The Om phosphorus rate was investigated. The temperature of the molten steel in the ladle is 1610'0 before stirring and 1580°C after stirring.
In addition, the CP) concentration in molten steel before treatment is 0.007~
It was 0.020 well. The results are shown in Fig. 2, which shows that the dephosphorization reaction was activated in the ladle, and effective dephosphorization was carried out.In particular, the slag was more than 20 times larger than the molten steel TON. It can be seen that a high dephosphorization rate of 60% or more was obtained in this case.

According to the present invention as described above, dephosphorization can be carried out efficiently without the problems of conventional methods such as a large drop in surface temperature or generation of white smoke, and without using any flux. It has excellent effects.

[Brief explanation of the drawing]

FIG. 1 shows the relationship between the slag dephosphorization ability and the molten copper temperature. FIG. 2 shows the relationship between the outflow amount of converter slag and the dephosphorization rate in an example of the present invention. Special fraud applicant Nippon Kokan Co., Ltd. Figure 1 1600 1640 1680 1720 17
60 blowing i's deep &('c) Fig. 2 10 2030 4050 60

Claims (1)

[Claims] A molten steel dephosphorization method characterized by discharging slag generated in the steelmaking furnace into the ladle when tapping molten steel into the ladle (steelmaking furnace), and then stirring the slag and molten steel in the ladle.