JPH08283817A - Operation for obtaining high mn yield at the time of blowing in converter - Google Patents

Abstract

PURPOSE: To provide a method by which high Mn yield is obtd. and the consumption of Fe-Mn alloy can drastically be reduced at the time of decarburization- refining dephosphorized molten iron in a converter. CONSTITUTION: In the refining method charging the dephosphorized molten iron into a converter and adding sintered Mn ore, the composition of the added sintered Mn ore is controlled to >=3 CaO/SiO2 and 2-10% Al2 O3 , and at the time of (C) <=0.5%, coke powder having <=5mm in grain size is blown into slag in a ratio of 1.5-5.0kg/t, and at the time of (C) >=0.10%, the blowing is stopped to obtain the high Mn yield in the molten steel. Thus, the Fe-Mn alloy is drastically reduced due to high Mn yield and the unit consumption of lime in the converter is reduced to obtain extremely large merit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the addition of Mn sinter ore into a converter such as top-blown, top-bottomed or bottom-blown with the hot metal that has been dephosphorized in the hot metal pretreatment and discharged. The present invention relates to an operating method for obtaining a high Mn yield when decarburizing and refining.

[0002]

2. Description of the Related Art With the recent development of hot metal pretreatment technology,
The mainstream of refining in converters is decarburization blowing with less slag. Among them, the method for adding Mn to molten steel is to perform an smelting reduction by adding an inexpensive Mn ore into the smelting instead of the conventional method of using an expensive Fe-Mn-based alloy after the smelting. Methods have become popular. This M
As a measure for improving blown Mn using n-ore, for example, as described in JP-A-60-9813, Mn in a converter is used.
In the method of refining by adding ore, in the final stage of refining, a powdery or lumpy C-containing substance is added from above to the slag produced by adding Mn ore, and MnO in the produced slag is forced. The method of reducing to is proposed. Further, as another example, as described in JP-A-62-33709, powdery Mn ore, which is cheaper than lumpy Mn ore, is sintered in advance and oxygen in the ore is sintered. A method has also been proposed in which high blown Mn is obtained by decomposing and releasing by heating and increasing the amount of Mn sinter added by the difference in the amount of decomposition heat.

[0003]

However, in the method described in JP-A-60-9813, since the melting point of Mn ore is as high as 1550 ° C. or higher, the Mn ore itself cannot be melted or dissolved in slag. Since the slag produced after adding Mn ore is not sufficient, the reaction does not proceed sufficiently even if the slag is reduced by the C-containing substance, and the Mn yield is greatly improved. I can't. Also in the method described in JP-A-62-33709, even if the Mn ore is sintered in advance, the Mn yield improving effect corresponding to the increase in the reaction area is recognized, but the Mn sintered ore Since the melting point itself is as high as that of Mn ore, a dramatic improvement in Mn yield cannot be expected. Therefore, there has been a strong demand for a converter operating method that solves these problems and significantly improves the Mn yield.

[0004]

The gist of the present invention is as follows. The hot metal dephosphorized by the hot metal pretreatment and the slag that had been discharged were charged into a converter, and Mn was added at the initial stage of refining.
In the decarburizing refining method of adding sinter, the CaO / SiO ₂ content of the Mn sinter is 3 or more, and the Al ₂ O ₃ concentration is 2 to ₃ .
At the end of the refining process, the coke powder having a particle diameter of 5 mm or less was blown into the slag produced in the furnace at 1.5 to 5.0 kg / t at the end of refining when the concentration of [C] became 0.5% or less. , [C] ≧ 0.10% to stop blowout, high blow-off Mn operating method in converter.

[0005]

Next, the operation will be described. As a method for solving the above problems at once, the inventors of the present invention use Mn sintered ore that has good slag forming property and excellent reactivity, and the Mn sintered ore is sufficiently melted to generate slag (slag at the time of previous refining). It was noted that coke powder was blown into the slag to efficiently reduce MnO in the slag in the state where the reactivity of the slag was slightly increased). That is, even if the slag is forcibly reduced with a carbonaceous material such as coke as in the conventional method, the slag containing an undissolved portion of the Mn ore or the Mn sintered ore is in an unsmelted state, or the slag has a composition of MnO. If the reduction is not appropriate from a thermodynamic point of view (poor reactivity), the reduction effect of the carbonaceous material cannot be sufficiently exerted. This problem is solved by the means of the present invention.

First, CaO / SiO ₂ is 3 or more as a Mn source having good slag-forming property and excellent thermodynamic reactivity.
It was experimentally found that Mn sinter obtained by firing Al ₂ O ₃ to 2 to 10% is effective. The present Mn sinter is obtained by mixing limestone with Mn ore powder and / or iron Mn ore powder and firing it with a sintering machine. When sinter is prepared by mixing limestone with Mn ore or iron Mn ore, the CaO content contained in the limestone is the melting point of Mn sinter as expected from the CaO-Mn ₃ O ₄ system phase diagram. Lower. In particular, when the CaO / SiO ₂ of the Mn sintered ore is set to 3 or more, the effect is remarkable, and the melting point becomes 1400 ° C. or less.

Further, this CaO / SiO ₂ has an M content of 3 or more.
It was also found that the melting point lowering effect is further promoted when the Al ₂ O ₃ content of the n sinter contains 2% or more.
However, if the Al ₂ O ₃ content exceeds 10%, the reactivity of the Mn sinter decreases (the activity of MnO decreases), which is not preferable. The Mn sinter having CaO / SiO ₂ of 3 or more and Al ₂ O ₃ of 2 to 10% is easily melted in the converter because of its low melting point as described above, and is slightly melted during the previous refining. It fuses with the remaining amount of slag (CaO / SiO ₂ is adjusted to around 3) to greatly promote the slag formation of the produced slag. Furthermore, the Mn sintered ore itself has a high Ca content.
Since it has an O / SiO ₂ composition, it dissolves and has high CaO.
A molten slag of / SiO ₂ is generated and its reactivity, that is, the activity of MnO in the slag is increased, and the reduction of MnO is promoted.

Usually, in order to secure the basicity of the slag,
Although quick lime is added before or during blowing, when the high basicity Mn sintered ore of the present invention is used, this is completely unnecessary. Normally used CaO / SiO ₂ is 2
When the following low basicity Mn sinter is used, it is necessary to add quick lime to increase the reactivity of the slag, as in the case of adding quick ore of Mn ore. Since it takes time to dissolve, MnO in slag
However, the reduction of Mn is delayed, and a high Mn yield at the time of blowing cannot be expected. In addition, SiO ₂ content and Al ₂ O ₃ in the Mn sintered ore
The component is contained as a gang component in Mn ore or iron Mn ore, and by utilizing this, the deficiency may be added as a sintering raw material.

Next, regarding the method of forcibly reducing the MnO-containing slag by blowing coke powder into the slag, the coke blowing timing is such that the high bath temperature can be secured and the slag slag state is the best. Is to select M
It is preferable in promoting the reduction reaction of nO. In particular, it is most effective to start blowing coke at the time when the oxygen potential of slag starts to rise after the peak of decarburization. That is, at that time, it is desirable to start the blowing after the time when the [C] concentration of the molten steel becomes 0.50% or less and finish the blowing immediately after the end of the blowing.

Further, the smaller the coke powder is, the more advantageous it is from the viewpoint of increasing the surface area. However, the size of the coke powder is 5 mm or less in consideration of the loss amount sucked together with the exhaust gas and the crushing cost being high. Anything is appropriate. The effect of the present invention can be obtained by applying it to any of a top blowing converter, a top bottom blowing converter, or a bottom blowing converter, but it is possible to secure strong stirring conditions advantageous for promoting the slag-metal reaction. A larger effect can be obtained in a bottom blow converter or a bottom blow converter.

FIG. 1 shows that the hot metal dephosphorized by the hot metal pretreatment is charged into an upper-bottom blowing converter having a good decarburizing reaction efficiency due to the stirring effect, and the Mn sinter having the above-mentioned proper composition is added. FIG. 3 is a diagram showing a relationship between a coke basic unit (blown amount) and a Mn yield in blowing stop when the coke powder is refined by refining and [C] concentration becomes 0.5% or less and coke powder is blown into the slag. As is clear from the figure, the more the basic unit of coke,
The Mn yield is high, and in order to obtain a high yield of 75% or more, the coke basic unit needs to be 1.5 kg / t or more.

However, the basic unit of coke is 5.0 kg / t.
Even if the amount is increased, the Mn yield becomes almost constant, the coke is wasted, and there is a variation in [C] due to the [C] pickup after the blow stop. Therefore,
The basic unit of coke is appropriately in the range of 1.5 to 5.0 kg / t. The coke is blown into the slag by inserting a nozzle through the tap hole, by blowing it through a nozzle provided in the furnace belly, or by making the main lance piping into two systems and using a nozzle different from oxygen gas. You may blow up. In the figure, as a comparison, the result of using the raw ore of Mn ore as it is instead of the Mn sintered ore is also indicated by a broken line, but the Mn yield remains low.

FIG. 2 shows that the hot metal dephosphorized in the hot metal pretreatment is charged into an upper-bottom blowing converter, and the above-described Mn sinter having the proper composition is added for refining to obtain a [C] concentration of 0. It shows the relationship between the blowing stop [C] concentration and the blowing stop Mn yield when the coke powder is blown into the slag at 0.5% or less. As can be seen from the figure, if the blow stop [C] is set to 0.10% or more, a high Mn yield of 75% or more can be obtained. On the contrary, if the blow stop [C] is lower than 0.10%, the Mn yield will be reduced correspondingly. This is because the oxygen potentials of the molten steel and the slag become too large, the equilibrium [Mn] becomes significantly low, and the reoxidation reaction of [Mn] proceeds. Therefore, it is necessary to stop blowing before the oxygen potential of the slag rapidly increases, that is, in the region where the [C] concentration is 0.1% or more. In the figure, Mn sinter that was fired to a proper composition was used as a comparison, but the result when coke blowing was not performed at the final stage of blowing is also indicated by a broken line, but the Mn yield remained low. There is.

[0014]

【Example】

1. Hot metal components (hot metal dephosphorized by hot metal pretreatment) are shown in Tables 1 and 2. 2. Amount of hot metal 350t 3. Top-bottom blow converter blowing method Top-blowing acid feed rate: 75,000 (Nm ³ / hr) Bottom-blowing acid feed rate: 0.2 (Nm ³ / min · t) Bottom-blowing gas species: O ₂ gas and CO Mixed gas of ₂ gases 4. Blowing powder coke size: ≤ 5.0 mm 5. Timing of charging Mn sinter ore Total amount charging at the beginning of blowing 6. Operating conditions and results Tables 1 and 2 are also summarized in the same manner.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

According to the present invention, during decarburization blowing (less phosphorus demolition hot metal blowing) with less slag in a converter, Mn sintered ore adjusted to an appropriate composition is added, and at the end of blowing. By blowing coke powder into the slag and stopping it before the reoxidation of [Mn] occurs, a high Mn yield can be obtained.
In addition to enjoying the benefits of a large reduction in Fe-Mn alloys, it also leads to a reduction in the basic unit of quick lime in the converter.
The effect of the present invention on this kind of industrial field is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a basic unit of coke and a Mn yield in blowing stop.

FIG. 2 is a diagram showing a relationship between blow stop [C] and Mn yield in blow stop.

Claims (1)

[Claims] 1. A decarburization refining method in which the hot metal dephosphorized by the hot metal pretreatment and slag is charged into a converter, and Mn sintered ore is added in the initial stage of the refining, in the Mn sintered ore. CaO /
Coke powder with a particle size of 5 mm or less is generated in the furnace at the final stage of refining with SiO ₂ of 3 or more and Al ₂ O ₃ concentration of 2 to 10% and [C] concentration of 0.5% or less. Blow 1.5-5.0 kg / t into the slag, [C] ≧
A high blow-out Mn operating method in a converter characterized in that the blow-off is stopped at 0.10%.