JPH05255725A - Method for pre-treating molten iron - Google Patents

Abstract

PURPOSE:To desulfurize molten iron with low unit consumption of Mg by effectively using Mg series flux in a pretreating method of molten iron. CONSTITUTION:The flux is injected into the molten iron and after desiliconizing and dephosphorizing, slag is removed, and after deoxidizing with Al or Al series flux, the Mg series flux is injected or the Al series flux and the Mg series flux are injected at the same time into molten iron to execute the desulfurization in the condition of <=6ppm oxygen in the molten iron. As the other way, after desiliconizing and dephosphorizing in the same way as the above, the slag is removed, and the Al slag, and calcium carbonate are added to the slag, and after reforming the slag to contain <=3% T. Fe in the slag, the Mg series flux is injected into the molten iron to execute the desulfurizing treatment. By this method, while preventing rephosphorization, the desulfurization can be executed with low unit consumption of the Mg series flux.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot metal pretreatment method, and more particularly to a hot metal pretreatment method of desulfurization using Mg flux after desiliconization and dephosphorization, which has excellent desulfurization efficiency.
Widely used in the fields of steelmaking and steelmaking.

[0002]

2. Description of the Related Art Degassing, dephosphorization, desulfurization, etc., in which a lance is immersed in hot metal contained in a container such as a hot metal car from a blast furnace, and a flux is blown into the hot metal through the lance with an inert gas or the like. The pretreatment of is widely practiced. It is generally accepted that Mg-based flux has an excellent effect on desulfurization. However, in the conventional method of simultaneously advancing desulfurization and dephosphorization, it is necessary to increase the oxygen potential in the slag in order to promote the dephosphorization reaction, while Mg reacts violently with oxygen. In this case, Mg cannot be used because it occurs, and it was extremely difficult to produce ultra-low sulfur content.

Further, in the desulfurization of hot metal with Mg-based flux, the produced MgS reacts with a small amount of oxygen in the molten steel or FeO in the slag to easily oxidize Mg in MgS to produce MgO, and a re-sulfurization phenomenon. Occurs. Further, there is a problem in that oxygen in Fe or FeO in slag reacts with Mg in the flux and expensive Mg blown in is not effectively used for desulfurization. That is, although the Mg-based flux has been confirmed to have an excellent effect on desulfurization, the conventional method of simultaneously promoting dephosphorization and desulfurization has two major problems: a rise in cost due to an increase in the basic unit and a re-sulfurization to hot metal. was there.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a pretreatment method for hot metal which prevents vulcanization and effectively causes Mg-based flux to act.

[0005]

The subject matter of claim 1 according to the present invention is as follows. That is, in the hot metal pretreatment method of performing desiliconization, dephosphorization, desulfurization, etc. by injecting flux into the hot metal contained in a container such as a hot metal car, the step of degassing and dephosphorizing by injecting flux And a step of degassing the hot metal by blowing the metal Al powder after the slag removal or a flux containing the metal Al powder into the hot metal, and a flux containing Mg after the deoxidation is blown into the hot metal to obtain 6 ppm of oxygen in the hot metal. And a step of performing a desulfurization treatment in the following state.

According to the second aspect of the present invention, as in the first aspect of the present invention, a step of blowing flux to desiliconize and dephosphorize and then remove slag, and after the slag removal, metal Al powder or metal Al powder is removed. And a flux containing Mg and a flux containing Mg are simultaneously blown into the hot metal to carry out a desulfurization treatment in a state where the oxygen in the hot metal is 6 ppm or less, which is a pretreatment method for hot metal. The subject matter of claim 3 is as follows. That is, in the same manner as in the first and second aspects of the present invention, a step of blowing flux to desiliconize and dephosphorize and then remove the slag, and adding Al slag and calcium carbonate to the slag after the slag to remove the T. Preliminary hot metal preparation comprising the steps of reforming Fe (total iron) to 3% or less, and blowing the flux containing Mg after reforming the slag into the hot metal for desulfurization treatment. It is a processing method.

According to the first and second aspects of the present invention, desiliconization, dephosphorization and desulfurization are separated, slag is removed after desiliconization and dephosphorization, and then the oxygen potential of the hot metal is further reduced or reduced to the limit by Al powder. Inject Mg flux into the
It effectively uses Mg for the desulfurization action. Next, in the present invention, the reason why the oxygen potential of the hot metal when the Mg-based flux is blown for desulfurization is limited to 6 ppm or less will be described. After desiliconizing and dephosphorizing the hot metal and removing the slag, a basic experiment was conducted in which the concentrations of oxygen and Mg in the hot metal were variously changed, and the equilibrium relationship of the components in the hot metal was investigated. 1300
The Mg equilibrium with oxygen in the hot metal at ℃ is shown in FIG. 1, and the S equilibrium with Mg in the hot metal is shown in FIG. It can be seen from FIG. 1 that the solubility of Mg increases when oxygen is lowered. It can be seen from FIG. 2 that the solubility of S decreases with the increase of Mg.

From these results, in order to reduce S in the hot metal to 10 ppm or less, it is necessary to set Mg to 40 ppm or more, and in order to set Mg to 40 ppm or more, oxygen is 6 ppm.
Must be: Therefore, in the present invention,
S: To desulfurize with a target of 10 ppm or less, the oxygen content of the hot metal during Mg injection was limited to 6 ppm or less. However, considering variations in slag composition, temperature and other operations, 3 ppm or less is preferable because a stable result can be obtained. Next, FIG. 3 shows the relationship between oxygen in the hot metal and the Mg basic unit when S in the hot metal after desulfurization is set to 10 ppm or less. From FIG. 2, the Mg unit consumption decreases as the oxygen concentration decreases. If the oxygen concentration is lowered by 1 ppm, the Mg basic unit can be reduced by about 5%.

In the second aspect of the present invention, Al powder and Mg are blown in at the same time, and a part of Mg is consumed in the reduction reaction of Al ₂ O ₃ , so that the basic unit of Mg slightly increases. In order to reduce the amount of expensive Mg used as much as possible, it is important to sufficiently perform deoxidation with an Al-based flux, and to float the separated Al ₂ O ₃ produced, and then blow in the Mg-based flux. The invention of claim 3 removes the Mg-based flux before blowing it, adds Al slag and calcium carbonate, and sufficiently stirs the FeO in the slag and the Al-based flux to combine to form FeO in the slag. It is a method of lowering the slag to modify the slag, and then blowing a flux containing Mg into the hot metal for desulfurization treatment, which is intended to reduce the oxidation loss of Mg.

Next, in the present invention, the reason why the T.Fe (total iron) of the slag is limited to 3% or less when Al slag and calcium carbonate are added after the slag is explained. That is, after slag removal, Al slag and calcium carbonate were added to the slag to change the amount of T.Fe in the slag and the basicity of the slag variously, and in each case, a Mg-based flux was then added for desulfurization. A basic experiment to perform the treatment was performed. The relationship between T.Fe in the slag and the basic unit of magnesium is shown in FIG. 4, and the relationship between the slag basicity and the amount of reconstituted phosphorus is shown in FIG. As is clear from FIG. 4, the T.Fe in the slag increases from around 4% in the Mg basic unit. Therefore, in the present invention, the T.Fe in the slag is increased.
Was limited to 3% or less.

Next, in FIG. 5, the reconstitution amount on the vertical axis is a number obtained by subtracting the P amount in the hot metal before slag reforming from the P amount in the hot metal after slag reforming. As is clear from FIG. 5, when the basicity in the slag is less than 3.0, the amount of recondensation increases, so from this result, the basicity of the slag must be 3.0 or more in order to prevent reconstitution. I was able to find out.
Next, in the invention of claim 3, after the slag is removed, Al slag and calcium carbonate are added, and the calcium carbonate content is Al
The reason for limiting the amount of slag to the range of 20 to 50% will be described. This treatment is for reducing T.Fe in the slag and modifying it in order to perform the desulfurization effect by adding Mg as effectively as possible.
The slag is used and its main composition is as shown in Table 1.

[Table 1] Thus promoting reduction action by Al slag and the Al ₂ O ₃ which is generated to flotation, by adding CaCO ₃ is a gas generating material simultaneously with stirring molten iron, by generating CO ₂ in the hot metal It is intended to separate the Al ₂ O _{3 by} stirring and floating.

The reason why the amount of CaCO ₃ added in this case is limited to 20 to 50% of the amount of added Al slag is as follows. That is, the present inventors, like the converter slag reforming at the time of producing high cleanliness steel by RH treatment, have a CaO / Al ₂ O ₃ ratio of CaO / Al ₂ O ₃ in order to obtain a slag composition having a high absorption capacity for the produced Al ₂ O _3. Is in the range of 1.6 to 1.8, and C
Considering the stirring effect of the hot metal by the CO ₂ gas generated by the decomposition of aCO _{3, if} the amount of added Al is less than 20%, a sufficient stirring effect cannot be obtained, and if it exceeds 50%, the gas generation becomes excessive, On the contrary, since it hinders the floating separation of Al ₂ O ₃ , it was limited to the range of 20 to 50%.

[0013]

【Example】

Example 1 200 tons of hot metal was received in a hot metal wheel, and 28 kg / t of iron oxide was blown into the hot metal according to the method of claim 1 to obtain 20
Slag was removed by performing desiliconization and phosphorus removal for a minute. Then 0.
1 kg / t metal Al powder was blown and refined for 3 minutes to deoxidize the oxygen content to 2 ppm or less, and then a flux containing 0.5 kg / t Mg was blown for desulfurization for 5 minutes. During desulfurization, the oxygen content of the hot metal was 2 ppm or less, and as a result, S in the hot metal could be desulfurized to 10 ppm or less. In this embodiment, since the hot metal was deoxidized to oxygen of 2 ppm or less and the Mg-based flux was blown, a small amount of Mg was effectively used to obtain a low Mg.
It was possible to desulfurize S to 10 ppm or less per unit.

[0014]

Example 2 200 tons of hot metal was received in a hot metal wheel, and 28 kg / t of iron oxide was blown by the method of claim 3 for 20 minutes for desiliconization and desulfurization to remove slag. Then 0.5 Kg / t Al
Slag and 0.2Kg / t calcium carbonate are added to the slag to modify the T.Fe in the slag to 2% and the slag basicity to 3.5.
After that, 0.5 kg / t of Mg-based flux was blown into the hot metal to perform desulfurization treatment for 5 minutes. As a result, S of hot metal before processing
It was possible to desulfurize the content of 200 ppm to 20 ppm.
No recondensing phosphorus was found in the hot metal before and after the desulfurization treatment. In this example, after the slag was removed, T.Fe in the slag was modified to 3% or less and 2%, and at the same time, the slag basicity was 3.0 or more and 3.5.
Then, since a Mg-based flux was blown in, a small amount of Mg
Was used effectively and it was possible to desulfurize with low Mg unit consumption without re-phosphorization.

[0015]

As is apparent from the above-mentioned embodiment, the present invention removes slag after desiliconization and dephosphorization and blows a Mg-based flux after deoxidizing with Al, or a flux containing Al and Mg at the same time. Blow-in to desulfurize the oxygen in the hot metal to 6ppm or less, or remove slag after desiliconization and dephosphorization, and then add Al slag and calcium carbonate to improve T.Fe of slag to 3% or less. At the same time, the basicity of the slag is adjusted to 3.0 or more, and then Mg-based flux is blown to desulfurize to reduce the oxidation loss of Mg and reduce the basic unit of Mg-based flux to prevent re-phosphorus. However, it was able to effectively desulfurize.

[Brief description of drawings]

FIG. 1 is an equilibrium diagram showing Mg equilibrated with oxygen in hot metal in a desulfurization step of a basic experiment for obtaining the present invention.

FIG. 2 is an equilibrium diagram showing S in equilibrium with Mg in hot metal in the desulfurization step of the basic experiment for obtaining the present invention.

FIG. 3 is a correlation diagram showing the relationship between oxygen in the hot metal and Mg basic unit in the desulfurization stage when the desulfurization target is an S content of 10 ppm or less in the hot metal.

FIG. 4 is a correlation diagram showing the relationship between T.Fe in the slag and the Mg basic unit in the desulfurization step of the basic experiment for obtaining the present invention.

FIG. 5 is a correlation diagram showing the relationship between the slag basicity and the amount of reconstituted phosphorus in the desulfurization stage of the basic experiment for obtaining the present invention.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 31, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

[Figure 3]

[Figure 4]

[Figure 5]

Front page continued (72) Inventor Yoshikazu Kurose 1-chome, Kawashima-dori, Mizushima Kurashiki-shi, Okayama (No house number) Kawasaki Steel Co., Ltd.

Claims (5)

[Claims] 1. A method for pretreatment of hot metal in which flux is blown into hot metal contained in a container such as a hot metal car to perform desiliconization, dephosphorization, desulfurization, etc. A slag, a step in which the metal Al powder after the slag removal or a flux containing the metal Al powder is blown into the hot metal to deoxidize the hot metal, and a flux containing Mg after the deoxidation is blown into the hot metal in the hot metal And a step of performing a desulfurization treatment in a state where oxygen is 6 ppm or less, a method for pretreatment of hot metal. 2. In a hot metal pretreatment method in which flux is blown into hot metal contained in a container such as a hot metal car to perform desiliconization, dephosphorization, desulfurization, etc., the flux is blown to desiliconize and dephosphorize and then remove. And a step of performing a desulfurization treatment in which the metal Al powder or the flux containing the metal Al powder and the flux containing Mg are blown into the hot metal at the same time and the oxygen in the hot metal is 6 ppm or less. A pretreatment method for hot metal, characterized in that 3. In a hot metal pretreatment method in which flux is blown into hot metal contained in a container such as a hot metal car to perform desiliconization, dephosphorization, desulfurization, etc., a flux is blown to desiliconize and dephosphorize and then remove. The step of slagging, and adding Al slag and calcium carbonate to the slag after removing the slag to remove the T.Fe in the slag.
A pretreatment of hot metal, which comprises a step of reforming (total iron) to 3% or less, and a step of blowing a flux containing Mg after reforming the slag into the hot metal for desulfurization treatment. Method. 4. The method for pretreatment of hot metal according to claim 3, wherein the amount of calcium carbonate added is in the range of 20 to 50% by weight of the amount of Al slag added. 5. The hot metal pretreatment method according to claim 3, wherein the slag basicity after the reforming in which the flux containing Mg is blown is 3.0 or more.