JP2635721B2 - How to prevent slag from flowing out of the converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention is a method for solidifying slag in a converter before molten steel tapping and preventing slag in the converter from flowing out accompanying the molten steel during tapping. It is about.

<Conventional Technology> When slag in a converter flows out together with molten steel at the time of tapping, the slag itself becomes an inclusion, and also serves as an oxidizing source of molten steel after deoxidation, thereby lowering the cleanliness of the molten steel.

Therefore conventionally, as proposed in Japanese Patent Application Sho 62-192136, the addition of CaO in accordance with the T.Fe amount of slag to adjust a basicity CaO / SiO ₂ of the slag, solidified the slag However, the above-described method of tapping while preventing outflow during tapping has been adopted.

This method uses T.Fe in the slag in the converter as shown in Fig.3.
And the basicity of the slag CaO / SiO ₂ .

The broken line in the figure is the solidification success / failure line obtained from past results.
The lower right area from this line is the area where solidification is successful.

However, the conditions for solidification differ depending on the composition of the slag other than T.Fe.
_As the concentration of ₂ O _{3 and the} like increases, the basicity required for slag solidification increases, which requires more and more CaO,
As a result, the amount of slag in the converter increases.

To solve this problem, there is a proposal in Japanese Patent Application Laid-Open No. 63-79910.

This proposal uses a phenomenon known per se,
MgO itself is a high melting point oxide, and when MgO is added to a CaO-SiO-FeO-based slag over a certain limit, the slag also increases in melting point, utilizing the fact that the melting point of the slag is increased.
Inject or inject MgO to raise the melting point of the slag in the converter to minimize outflow during tapping, and to set the amount of MgO added to the slag in the furnace to 0.3 to 0.8 weight ratio of the CaO weight in the slag. It is.

<Problems to be Solved by the Invention> According to the conventional slag solidification method described above, slag solidification is not stable, and a large amount of Ca is required to stabilize it.
O is required, and as a result, the amount of slag increases, the slag processing cost increases, and it is difficult to achieve the above-mentioned purpose. To solve these problems, Japanese Patent Application Laid-Open No. 63-79
In the case of using high T.Fe and SiO
_{When 2} is high (when CaO / SiO ₂ is low), the slag in the furnace may not be solidified even if MgO / CaO is 0.8.

Also, when MgO / CaO described in the examples is 0.36, T.Fe
When CaO / SiO ₂ is low, the slag in the furnace may not be solidified, and the solidification of the slag in the furnace may not be stable. In order to stabilize this unstable solidification, it is necessary to increase MgO / CaO ₂ as much as possible. For this reason, when T.Fe is low,
Alternatively, when CaO / SiO ₂ is high, even if it is lower than that, solidification occurs, so that excess MgO is used and the processing cost increases.

An object of the present invention is to provide a method for solidifying slag in a converter stably even when T.Fe, CaO / SiO _2, and even Al ₂ O ₃ change, and significantly reducing the solidification cost of the slag in the furnace. Is the subject.

<Means for Solving the Problems> To solve the above problems, the present invention provides: (1) In the hot metal blowing, the solid phase ratio of the slag in the converter is 30% or more at the end of blowing or after blowing. The basic means is to add a certain amount of MgO into the converter. (2) In the hot metal blowing, at the end of blowing or after blowing, CaO / SiO ₂ and T.Fe MgO according to the amount As a specific means, it is added into the converter.

<Operation> The present inventors conducted various experiments to solve the above-mentioned problems.
The examination was repeated.

As a result, each of the prior arts described above, T.Fe and Ca among the slag components that have an effect on the melting point of the slag in the converter
We focused on only O / SiO ₂ or only MgO / CaO, and found that there was a problem in considering each separately.

The inventors obtained the relationship shown in FIG. 4 through experiments and studies. The figure shows the relationship between the solid fraction of slag and the amount of slag flowing into the ladle.

Here, the solid phase ratio of the slag is a method widely used in this field based on each component value (sampling value) at the reaction point, for example, standard free energy, free energy of formation, activity coefficient and the like. A value obtained by calculating the ratio of crystallized substances (solid phase) generated in the slag at the reaction point using thermodynamic data by equilibrium calculation.

According to the figures, the inventors found that the solidification of the slag in the converter is basically governed by the solid fraction of the slag, and this solid fraction is 30%.
With the above, even if the composition of the slag affecting the melting point of the slag changes, the amount of slag flowing out during tapping is significantly reduced to 6 kg / ton or less, and it has been found that substantially all of the above problems can be solved. .

Next, in establishing the solid phase ratio of 30% of the slag, the present inventors examined the type and amount of the slag solidifying agent required according to T.Fe and CaO / SiO ₂ of the slag. In this study, the present inventors found the relationship shown in FIG.

When assuming the solidification by CaO, relationship between CaO / SiO ₂ and solidifying before content of Al ₂ O ₃ showing a solidification limit shown in Fig. 5,
As is evident from the figure, even when T.Fe was kept constant, the solidification limit significantly changed according to the change in the content of Al ₂ O _{3 in} the general operation range.

Therefore, we investigated a solidifying agent with little effect of Al ₂ O ₃ ,
The findings shown in FIG. 2 were obtained.

The figure shows the results of the investigation in which the relationship between the Al ₂ O ₃ concentration in the slag and the amounts of MgO and CaO added as the slag solidifying agent was determined.

From the figure, it was found that the addition amount of MgO shown by the solid line was little affected by the Al ₂ O ₃ concentration, and was only about 70% of the addition amount of CaO shown by the dotted line.

Therefore, as a result of further study, the required addition amount of MgO was CaO
/ SiO ₂ and the general range of converter blowing is Al ₂
The change in the O ₃ concentration is as small as 1 to 5%, and the solidification by MgO does not substantially change the MgO amount required for the solidification by the change of Al ₂ O _3. It was found that the amount of MgO added for solidification was determined by T.Fe and CaO / SiO ₂ . FIG. 1 shows the relationship.

So based on Figure 1 CaO / SiO ₂ separately organize the addition amount of MgO from the relationship between T.Fe rolling furnace slag, Got a relationship. The present invention has been made based on this finding.

<Examples> Examples of the present invention are shown below together with comparative examples.

(1) Converter used Top and bottom blown converter (340 ton / ch) (2) Converter shutoff temperature 1600 to 1750 ° C (3) Shutoff component [C]: 0.02 to 0.50% [Mn]: 0.2 to 2.0 % (P): 0.005 to 0.030% (S): 0.001 to 0.03% (4) slag component CaO: 35.0~65.0% FeO: 7.0~28.0% SiO 2: 5.0~18.0% MnO: 2.0~35.0% MgO: 5.0 110.0% Al ₂ O ₃ : 1.0 to 5.0% (5) Addition method of solidifying agent.

The solidification temperature of the molten steel was detected from the sample of the molten steel, the carbon content of the molten steel was calculated from this, and the T.Fe was determined from the relationship between the carbon content of the molten steel and T.Fe obtained from the past results shown in FIG.
Seeking Fe, predict CaO / SiO ₂ of SiO ₂ generation amount calculated from the CaO dosages and hot metal and Si components in auxiliary materials, for the solid fraction of the slag at least 30% depending on the value The amount of the slag solidifying agent required for the above was determined by the above relational expression and added.

In order to obtain T.Fe and CaO / SiO ₂ , a method of directly analyzing and detecting may be used in addition to calculation.

 The processing conditions and results are shown in Table 1 together with Comparative Examples.

In Test Nos. 1 to 13 of the examples of the present invention, (1 to 5 represent 3 ≦ Ca
For O / SiO ₂ <4,6-9, 4 ≦ CaO / SiO ₂ <5,10-13 for 5 ≦ CaO / S
In the case of iO ₂ <6), the amount of slag flowing out to the ladle during tapping was stable, and the MgO / CaO became 0.9 kg or less including 6 and 0.2 to 8 kg / ton or less.

In these examples of the present invention, the slag outflow was drastically reduced, and as a result, the Al yield when Al was added to the ladle was stabilized at a high level of 60% or more.
0 also stably decreased to 25 ppm or less. The MgO source is M
Similar effects were obtained using gO grains or crushed MgO bricks.

On the other hand, in Test Nos. 14 to 17 of Comparative Examples in which CaO was added and slag was solidified, 15 to 17 obtained the same effect as that of MgO, but required a large amount of slag solidifying agent. 14 is T.
In the relationship between Fe and CaO, it is in the solidification region, but Al ₂ O ₃
Was as high as 5%, and the amount of slag flowing out increased.

Also, Comparative Examples 19, 21, 23 and MgO to which no MgO was added
In Comparative Examples 18, 20, 22, and 24 in which the slag composition was not included in the solidification region, the slag outflow to the ladle during tapping reached 10 kg / ton or more, and as a result, the Al yield was increased. 50%
The TO decreased to 35 ppm or more, and the cleanliness of the molten steel decreased.

In Comparative Examples 18, 20, 22, and 24, MgO / CaO was in the range of 0.3 to 0.8, but the slag in the furnace did not solidify satisfactorily, and the outflow slag amount exceeded 10 kg / T.

<Effects of the Invention> The present invention relates to the production of slag in a converter at the end of or after the end of hot metal blowing.
T. Fe and CaO / SiO ₂ were determined, and based on this, the slag solid fraction was 30
% Of the required slag solidifying agent is added, so that the slag solidification is stable even though the required amount of solidifying agent is smaller compared to the conventional slag solidification by adding CaO or MgO. The amount of slag flowing into the ladle is greatly reduced. As a result, the yield of the alloy is improved, and the cleanliness of the molten steel is significantly improved.

[Brief description of the drawings]

Fig. 1 shows the amount of MgO and CaO / S to achieve a slag solid fraction of 30% or more.
indicates iO ₂ of relationship, FIG. 2 shows the relationship between the content of MgO and the amount of Al ₂ O ₃ of relationship and the amount of CaO and the amount of Al ₂ O ₃ to achieve 30% or more slag solid phase ratio, FIG. 3 is 4 shows the relationship between T.Fe of slag and basicity. Figure 4 shows the relationship between the outflow amount of slag in the ladle and solid fraction of the slag, FIG. 5 shows the relationship between吹止previous amount of Al ₂ O ₃ and basicity of the slag, FIG. 6 is吹止It is a figure which shows the relationship between hourly carbon amount and T.Fe.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-40308 (JP, A) JP-A-62-37307 (JP, A) JP-B-62-1444 (JP, B2)

Claims (2)

(57) [Claims] Claims 1. In the blowing of hot metal, at the end of blowing or after finishing blowing, the amount of Mg in which the solid phase ratio of slag in the converter becomes 30% or more.
A method for preventing slag from flowing out of a converter, characterized by adding O into the converter to solidify the slag. 2. In the hot metal blowing, at the end of blowing or after blowing, depending on the amount of CaO / SiO ₂ and T.Fe in the slag in the converter, A method for preventing slag from flowing out of a converter, characterized by adding MgO into the converter to solidify the slag.