JPH02111810A - Method for preventing flowing-out of slag in converter - Google Patents

Abstract

PURPOSE:To prevent flowing-out of slag accompanied with molten steel at the time of tapping the molten steel by adding MgO so that solid phase ratio of the slag in a converter at the end period of blowing comes to the specific value in the blowing of molten iron. CONSTITUTION:At the time of blowing the molten iron, the MgO is added into the converter so that the solid phase ratio of the slag in the converter at the end period of the blowing or after completing the blowing comes to <=30%, to solidify the slag. In this purpose, in accordance with CaO/SiO2 and T.Fe content in the slag in the converter, the MgO is added so as to come to MgO (%)>=[T.Fe(%)+39.3]/2.1 in the case of 3<=CaO/SiO2<4, MgO(%)>=[T.Fe (%)+4.4]/0.8 in the case of 4<=CaO/SiO2<5 and MgO(%)>=[T.Fe(%)-4.2]/0.7 in the case of 5<=CaO/SiO2<6. By this method, the flowed-out slag quantity at the time of tapping the molten steel is reduced to <= about 6kg/ton.

Description

[Detailed description of the invention] <Industrial application field> The present invention solidifies the slag in the converter before /8@ steel tapping to prevent the slag in the converter from flowing out along with l8 steel during tapping. It is about how to prevent it.

<Prior Art> When the slag in the converter flows out together with the molten steel during tapping, it not only becomes inclusions but also becomes a source of oxidation of the molten steel after deoxidation, reducing the cleanliness of the molten steel.

For this reason, conventionally, as proposed in Japanese Patent Application No. 1982-192, CaO was added according to the T and Fe contents of the slag to drastically adjust the basicity of the slag, Can/SiO□, and the slag was The method used was to solidify the steel and prevent it from flowing out during tapping as described above.

This method is as shown in Fig. 3.
This is based on the relationship between e and the basicity of the slag, CaO/Sing.

The broken line in the figure is the solidification success/failure boundary line obtained from past results, and the range to the lower right of this line is considered to be the area where solidification is successful.

However, the conditions for solidification differ depending on the composition of the slag other than T and Fe, and even with T and Fe, if the concentration of Ah03, etc., which lowers the melting point of the slag, increases, the basicity required for slag solidification increases, which causes CaO As a result, the amount of slag in the converter increases.

To solve this problem, Japanese Patent Application Laid-Open No. 63-79910
There is a proposal for a publication.

This proposal uses a well-known phenomenon, and M
gO itself is a high melting point oxide, CaO-5iOFen
When MgO is added to the system slag above a certain limit, the slag also has a high melting point. Taking advantage of this fact, MgO is introduced or blown into the converter at the end of refining or immediately after the refining of the converter to make the slag in the converter have a high melting point and then taken out. This is to minimize the outflow during steel production, and the amount of MgO added to the slag in the furnace is set at a weight ratio of 0.3 to 0.8 of the weight of CaO in the slag.

<Problems to be solved by the invention> According to the conventional slag solidification method described above, the slag solidification is not stable, and a large amount of Ca is required to stably solidify the slag.
The need for O as a result increases the amount of slag, increases the slag processing cost, and makes it difficult to achieve the objectives stated at the beginning. In order to solve these problems, JP-A-63-
Even if the proposal of Publication No. 79910 is used, when ■T and Fe are high and when ■SiO□ is high (when CaO/Sing is low), the slag in the furnace may not solidify even if MgO/CaO is 0.8.

Furthermore, when MgO/CaO is 0.36 as described in the examples, when T and Fe are high and Can/SiO□ is low, the furnace slag may not solidify, and the solidification of the furnace slag may not be stable. be. In order to stabilize this unstable solidification, it is necessary to increase MgO/CaO□ as much as possible. Therefore, when T and Fe are low, or when Can/Si
If O□ is high, solidification will occur even if it is less than that, so extra MgO will be used, increasing processing cost.

The present invention uses T, Fe, CaO/SiO2, and A1.0
It is an object of the present invention to provide a method for stably solidifying slag in a converter even if 2 changes, and significantly reducing the cost of solidifying the slag in a converter.

<Means for Solving the Problems> In order to solve the above problems, the present invention has the following objectives: (1) In blowing hot metal, the solid phase ratio of slag in the converter is 30% or more at the end of blowing or after the end of blowing. The basic method is to add MgO into the converter, and (2) in hot metal blowing, after the completion of blowing or blowing, [aO/SiO□ and 1', a specific method is to add MgO into the converter according to the amount of Fe.

Effects> The present inventors have repeatedly conducted various experiments and studies with the aim of solving the above problems.

As a result, each of the above-mentioned conventional technologies focuses only on T, Fe, and CaO/5iOz or only on MgO/CaO among the slag components that affect the melting point of the slag in the converter. I found that there is a problem with considering them separately.

Through experiments and studies, the present inventors obtained the relationship shown in Figure 4. Figure 0 shows the relationship between the solid phase ratio of slag and the amount of slag flowing into the ladle.

Here, the solid phase ratio of slag means the value of each component at the reaction point (
For example, a method widely used in this field is based on the sampled value).
This is the value determined by equilibrium calculation of the proportion of crystallized substances (solid phase) formed in the slag at the reaction point using thermodynamic data such as activity coefficients.

The present inventors have shown that the solidification of slag in the converter is basically controlled by the solid phase ratio of the slag, and this solid phase rate is 30%.
In this case, even if the slag components that affect the melting point of slag change, the amount of slag flowing out during tapping will be 6 kg/lon.
It has been found that substantially all of the above-mentioned problems can be solved.

Next, in establishing a solid phase ratio of 30% in the slag, the present inventors determined that the slag's T, Fe, CaO/SiO□
We investigated the type and amount of slag solidifying agent required. Through this study, the inventors discovered the relationship shown in FIG.

Assuming solidification by CaO, the relationship between Can /SiO□ showing the solidification limit and the pre-solidification hOi content shown in Figure 5 is general even if T and Fe are held constant, as is clear from the figure. Within the operating range, the solidification limit changed significantly as the a content of A1□03 changed.

So A1. We conducted an investigation on solidifying agents with less influence of o and ζ, and obtained the findings shown in Fig. 2.

The figure shows the results of the investigation on the relationship between the temperature in the slag and the amounts of Mgo and CaO added as slag solidifying agents.

It has been found from the figure that the amount of MgO added indicated by the solid line is less affected by the A1□03 concentration, and can be approximately 70% of the amount of CaO added indicated by the dotted line.

After further consideration, we found that the required amount of MgO to be added was C.
It varies depending on the aO/5411K, and in the general range of converter blowing, the change in AI□034 degrees is as small as 1 to 5% (,
In solidification with MgO, this degree of change in A1□O1 does not substantially change the amount of MgO required for solidification, so in general converter blowing, the amount of MgO added for solidification is T,
It was found that it is determined by Fe and CaO/SiO□.

Figure 1 shows the relationship.

Therefore, based on FIG. 1, the amount of MgD added for each Can/Sin□ was organized from the relationship with T and Fe of the slag in the converter.

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

(11 converters used: top-bottom blowing converter (340 ton/c)
h) (2) Converter blow-off temperature 1600°C-1750°C (
3) Blowing component (C): 0.02-0.50% (Mn): 0.2-2.0% <p3: 0.005-0.030% [5): 0
．． 001~0.03% (4) Slag component CaO: 35.0~65.0% FeO: 7.0~28.0% SiO□: 5.0~18.0% 'lnl]: 2.0~ 35.0%! 4. <o
: 5. Q~1O10%Alzc13: t, 0
~5.0% (5) Method of adding solidifying agent.

The solidification temperature of l8 steel is detected from the sample of l8 steel, and the carbon M contained in the molten steel is calculated from this. Figure 6 shows the relationship between the carbon content of the molten steel determined from past results, "I", and Fe. Calculate T and Fl! from the 5iOz generation bed calculated from the amount of CaO input and the Si content in the hot metal and auxiliary raw materials.
7,540 g of aO was predicted, and in accordance with this value, the amount of slag solidifying agent required to make the solid phase ratio of slag 30% or more was calculated from the above relational expression and added.

In order to obtain the above-mentioned T, Fe, and Can/SiO□, a method of direct analysis and detection may be used in addition to calculation.

The processing conditions and results are shown in Table 1 along with comparative examples.

In test numbers 1 to 13 of the examples of the present invention (1 to 5 are 3≦C
aO7540g<4, 6-9 is 4≦CaO/si
o, <5.10-13 is 5≦Can/5iOz<
6), the amount of slag flowing into the ladle during tapping is stable, including 5 with MgO/Can of 0.9 and 8 with 0.2.
kg/lon or less.

In these examples of the present invention, as a result of the drastic reduction in the amount of slag flowing out, the A1 yield when adding AI to the ladle was stabilized at a high level of 60% or more, and T and O were also stably reduced to 25 ρρl or less. Nao M
Similar effects were obtained whether Mg0 grains or crushed MgO bricks were used as the gO source.

On the other hand, in test numbers 14 to 17 of comparative examples in which slag solidification was performed by adding Can, test numbers 15 to 17 obtained the same effect as in the case of MgO, but required a large amount of slag solidifying agent. Further, although No. 14 is in the solidification range in terms of the relationship between T, Fe, and CaO, the amount of slag flowing out increased because the Ah03 content was as high as 5%.

In addition, 19.2I, 2 of comparative example in which Mgfl was not added
In Comparative Example 18.20.22.24 in which the slag composition was not in the solidified region even though 3 and MgO were added, the amount of slag flowing into the ladle during tapping reached 10 kg/lon or more, and as a result, A1 7. Yield decreases to below 50%.
0 was 35 ppm or more, and the cleanliness of the container steel decreased.

Comparative example 18.20.22.24 had MgO/CaO in the range of 0.3 to 0.8, but the indoor slag was not solidified satisfactorily, and the amount of slag flowing out exceeded 10 kg/T.

<Effects of the Invention> The present invention improves the T of slag in the converter at the end of hot metal blowing or after completion
, Fe and CaO / SiO
Since gOl is added, compared to conventional slag solidification by adding UaO or MgO, although the amount of a-solidifying agent required is smaller, slag solidification is stable and the amount of slag flowing out to molten steel is significantly reduced. reduce As a result, the alloy yield is improved, and furthermore, the cleanliness of the (g) steel is greatly improved, and other effects are great.

[Brief explanation of the drawings] Figure 1 shows the relationship between M and gO amounts and CaO/SiO□ stars to achieve a slag solid fraction of 30% or more, and Figure 2 shows the relationship between the slag solid fraction and the slag solid fraction of 30% or more. MgOl and AlzOz It
and the relationship between the amount of CaO and the amount of A1□03, and the third
The figure shows the relationship between T, Fe and basicity of slag. Figure 4 shows the relationship between the solid fraction of slag and the amount of slag flowing into the ladle, Figure 5 shows the relationship between A1□02 amount and basicity of slag before blow-off, and Figure 6 shows the relationship between slag solidity and basicity before blow-off. It is a figure showing the relationship between carbon content, T, and Fe.

Claims (2)

[Claims] (1) In hot metal blowing, MgO in an amount such that the solid phase ratio of the slag in the converter is 30% or more at the end of blowing or after the end of blowing.
A method for preventing the outflow of slag in a converter, which is characterized by adding to the converter to solidify the slag. (2) In hot metal blowing, CaO/SiO_2 and T. Depending on the amount of Fe, when 3≦CaO/SiO_2<4, MgO (%) ≧ (T.Fe (%) + 39.3)/2.1
When 4≦CaO/SiO_2<5, MgO (%) ≧ (T.Fe (%) + 4.4)/0.85
Inside the converter, which is characterized in that when ≦CaO/SiO_2<6, MgO (%) ≧ (T.Fe (%) - 4.2)/0.7, MgO is added into the converter to solidify the slag. Method for preventing slag outflow.