JP2750048B2 - Ladle slag reforming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ladle slag reforming method useful for smelting high cleanliness steel.

[0002]

2. Description of the Related Art Various slag reforming methods have been proposed for improving the cleanliness of molten steel. For example, in Japanese Patent Publication No. 62-39205, at the time of tapping,
It is stated that high cleanliness steel can be melted by adding a slag reducing agent in addition to the deoxidizing agent and the flux.

[0003]

However, the method described in JP-B-62-39205 has the following problems. (1) The amount of slag reducing agent added should be changed according to the amount of slag flowing out of the steelmaking furnace.However, since the amount is not specified in relation to the amount of slag flowing out, sufficient reduction Is not achieved. Figure 1 shows the amount of converter slag outflow and T.C. in slag when the reducing agent was added in a fixed amount of 250 kg. The relationship with Fe% is shown. As shown in the figure, T. in slag was increased with an increase in slag outflow. Fe% is increasing, and therefore, when the slag outflow is large, it can be seen that the reducing agent is insufficient. In addition, T.C. Although the Fe% decreases, the T.C. in slag is less than a certain amount of slag outflow. Fe% is constant. The above results suggest that it is necessary to change the reducing agent input amount according to the slag outflow amount.

(2) The final slag component is CaO: Al ₂ O ₃
The ratio is controlled in the range of 2: 1. However, with such a CaO: Al ₂ O ₃ ratio, the melting point of the slag is high and the slag is solidified, so that sufficient reduction cannot be obtained. For this reason, sufficient cleanliness cannot be obtained.

(3) Furthermore, slag control cannot be performed simply by adding a slag reducing agent, and it is difficult to expect sufficient reduction.

[0006] An object of the present invention is to overcome the above-mentioned problems of the prior art, and the final slag component is Ca depending on the amount of slag flowing out of the converter during tapping.
O: 40-50%, and Al ₂ O _3: achieved such that 40-50%, with adjusting the amount and composition of the slag reductant, by utilizing slag agitation and modification of stable slag What you want to do.

[0007] The present invention developed for such a purpose, when reforming the slag in the ladle prior to the secondary refining, according to the amount of slag flowing into the ladle during tapping from the steelmaking furnace. , collected by adding Al, alumina and CaO in a ladle
Adjust the Al ₂ O ₃ minutes and C aO-component in the slag pot, a slag is stirred by the inert gas continues, a final slag component
CaO: 40-50% at and Al ₂ O _3: a method of modifying the ladle slag and adjusting the 40-50% range.

Further, the present invention, prior to the secondary refining, upon modifying the ladle slag, based on the slag amount and the slag composition flowing out into the ladle upon tapping from the steelmaking furnace below
Al ₂ O ₃ minutes in slag in ladle determined by equations (1) and (2) (A value)
And an amount of the Al source in which the ratio of the CaO content (B value) is 1.0 to 1.3,
An alumina source and a CaO source were charged, and the slag was subsequently stirred with an inert gas, and the final slag component was changed to CaO: 40.
This is a method for reforming ladle slag, characterized in that it is adjusted to be in the range of 5050% and Al ₂ O ₃ : 40-50%.

A = α × [W × ｛(% T.Fe) / 100 × 102/165 + (% MnO) / 100 × 102/213 + (% SiO ₂ ) / 100 × 102/90｝ + W _AL ] ... (1) B = β x [W x (% CaO) / 100 + W _CA ] ... (2) where α, β: Coefficients determined according to the steelmaking furnace W: Outflow slag amount (kg) (% T.Fe): T.Fe concentration in outflow slag (%) (% MnO): MnO concentration in outflow slag (%) (% SiO ₂ ): SiO ₂ concentration in outflow slag (%) (% CaO) : CaO concentration in effluent slag (%) W _AL : Alumina source to be input at tapping (kg) W _CA : CaO source to be input at tapping (kg)

[0009]

The reduction of the slag flowing into the ladle is mainly represented by the following reaction formula. 3 (FeO) + 2Al = ( Al 2 O 3) + 3Fe 3 (MnO) + 2Al = (Al 2 O 3) + 3Mn 3 (SiO 2) + 4Al = 2 (Al 2 O 3) + 3Si Therefore, Al amount required for slag reduction And produce (Al ₂ O
₃ ) The amount can be determined from the amount of slag flowing out into the ladle and the (FeO), (MnO), and (SiO ₂ ) concentrations in the outflowing slag.

Therefore, the amount of alumina added separately (
If W _AL ) is known, the amount of alumina in the ladle (A value)
Is represented by the following equation (1).

(Equation 3)Here, as the alumina source to be added, Al and Al_TwoO_Three With
The mixture aluminum ash is particularly advantageously suitable. To
Al and Al in aluminum ash_TwoO_ThreeAdjusting the ratio of
To adjust the amount of Al required for slag reduction and slag composition
Required amount of Al _TwoO_ThreeIs obtained at the same time.

Hereinafter, a method for determining the amount of slag flowing out into the ladle, and (% FeO), (% MnO) and (% SiO ₂ ) in the slag flowing out will be described. Figure 2 shows the amount of slag flowing into the ladle
The relationship between W (kg / ch) and tapping time t (min) is shown. FIG.
When the relationship was regressed, the following equation (3) was obtained.

(Equation 4)

FIG. 3 shows the tapping slag content (% T.Fe) and tapping.
(% C) × 100. During tapping slag (% T.Fe)
Is the same as that in the slag flowing out into the ladle (% T.Fe), so regression of the relationship in FIG. 3 yielded the following equation (4). (% T.Fe) = 40 / (% C × 100) +5 (4)

[0013] Fig. 4 shows that in the tapping slag (% MnO) and I.Mn (kg /
t) / CaO (kg / t). Where I.Mn (kg / t) is
This is the input Mn during the steelmaking furnace blowing. During tapping slag (%
MnO) is the same as the slag (% MnO) flowing out into the ladle, so regression of the relationship in FIG. 4 yielded the following equation (5). Note that I.Mn (kg / t) is given by equation (6).

(Equation 5)

FIG. 5 shows that (% SiO ₂ ) in tapping slag and (v.v +
1) (where vv is the actual basicity of tapping slag,
vv = as defined in (% CaO) / (% SiO 2). ) When,
It shows the relationship between the components other than (% T.Fe) and (% MnO) in tapping slag, that is, {100 − (% T.Fe) × 71/55 − (% MnO)}. The following equation was obtained by regressing the relationship in FIG. 5 since the inside of the tapping slag (% SiO ₂ ) is the same as the inside of the slag (% SiO ₂ ) flowing into the ladle.

(6) (% SiO ₂ ) × (v.v + 1) = {100 − (% T.Fe) × 71/55 − (% MnO)} − 10 By transforming the above equation, the following equation (7) is obtained. become. The actual basicity (vv) is calculated from the calculated basicity as {vv (Cal) +0.5}.
Which is an empirically required relationship.

(% SiO ₂ ) = {100 − (% T.Fe) × 71/55 − (% MnO) −10} / (v.v + 1) (7)

On the other hand, the CaO content (B value) in the ladle is calculated by the following equation (2) based on the slag (% CaO) flowing into the ladle and the CaO content (W _CA ) charged during tapping. Is shown. B = beta × [W × (% CaO) / 100 + W CA ] ... (2) It should be noted that in the slag flowing out into the ladle (% CaO) is the same as in tapping slag (% CaO), ( From equation 7) and actual basicity (vv)
It is given by equation (8).

(Equation 8)

Next, FIG. 6 shows the results of a study on the relationship between T.Fe% in the slag after the addition of the reducing agent and the ratio A / B of A and B determined as described above. From the figure, A / B is 1 to
It can be seen that T.Fe% in the slag is the lowest in the range of 1.3. However, there is a limit to the lower limit of T.Fe% in slag, and it is still difficult to say that the concentration is sufficiently satisfactory.

Next, the stirring effect was investigated.
FIG. 7 shows histograms when A / B is adjusted to the range of 1 to 1.3 and slag stirring is performed and when it is not performed. As is clear from the figure, the average value of (T.Fe%) was 4% when slag agitation was not performed, but it could be reduced to 2% by performing slag agitation. did it. Therefore, in order to obtain a sufficient reducing effect, it is important to adjust the A / B to be in the range of 1 to 1.3 and then perform the slag stirring.

The slag is stirred by any method such as a method of blowing an inert gas from the bottom of a ladle, a method of blowing from an injection lance, or a method of mechanically stirring with a stirrer or the like. An equivalent effect can be obtained.

By the way, when the slag components when a sufficiently satisfactory reducing effect as described above was obtained were examined, all of them satisfied the ranges of CaO: 40 to 50% and Al ₂ O ₃ : 40 to 50%. Was. Then, in order to investigate the effect of the final slag component on the reduction effect, the composition of the CaO component and Al ₂ O ₃ component in the slag was intentionally shifted from the above-mentioned preferred range, and the reduction effect was degraded. Was. Therefore, in the present invention, per final slag component, CaO: and a 40-50%, Al ₂ O _3: it was limited to 40-50% range.

[0020]

【Example】

Example 1 In a converter with a heat size of 250 ton, after primary refining, and after tapping into a ladle, slag reduction was performed. The tapping time at this time was 6.0 minutes, tapping (% C) was 0.045%, the basic unit of CaO used during converter blowing was 5.0 kg / t, and the Mn used during converter blowing.
The ore unit consumption was 8 kg / t (Mn = 15%), the calculated basicity during converter blowing was 3.5, and the hot metal Mn was 0.15%. Further, as an alumina source, aluminum ash having a composition containing Al: 18% and alumina: 80% was supplied at a rate of 300 kg / ch, and a CaO source was CaO
Was added at a rate of 300 kg / ch. At this time, the A value and the B value were 670 and 782, respectively, and the A / B was 1.17. (α = 1, β = 1) Thereafter, Ar gas was blown from the bottom of the pot, and a stirring process was performed for 5 minutes. The final slag composition is as follows: CaO: 42%, Al ₂ O ₃ :
48%. As a result, T.Fe% in slag before treatment
After treatment, T.Fe% in slag was 3.5%
It could be reduced to 0.5%.

[0021]

Comparative Example In a similar converter, slag was reduced in the same manner after tapping into a ladle. The tapping time was 6.5 minutes, tapping (% C) was 0.042%, the basic unit of CaO used during converter blowing was 6.0 kg / t, and the Mn used during converter blowing was Mn.
Ore intensity is 9 kg / t, calculated basicity at the time of converter blowing is 3.5,
Hot metal Mn was 0.14%. At this time, the input amount of the alumina source was 300 kg / ch, while the input amount of CaO was 150 kg / ch.
ch. The A value and the B value at this time are 695, respectively.
, 870 and therefore the A / B was 0.80. Thereafter, Ar gas was blown from the bottom of the pot, and a stirring process was performed for 7 minutes. The final slag composition is as follows: CaO: 40.0%, Al ₂ O ₃ : 5
1.0%. As a result, T.Fe% in slag before treatment
Was 14.0%, but reached 4.5% after treatment.

[0022]

As described above, according to the present invention,
When tapping from the steelmaking furnace to the ladle during secondary refining, the slag that has flowed out to the ladle along with the tapping flow can be effectively reformed, and as a result, the total oxygen in the molten steel is 25 ppm or less. Stable smelting of clean molten steel is now possible.

[Brief description of the drawings]

FIG. 1 shows the amount of converter slag outflow and T.C. in slag when a fixed amount of a reducing agent is added at 250 kg. 4 is a graph showing a relationship with Fe%.

FIG. 2 is a graph showing the relationship between the amount of slag flowing into a ladle and tapping time.

Fig. 3 During tapping slag (% T.Fe) and tapping (% C) x 100
6 is a graph showing a relationship with the graph.

Fig. 4 In tapping slag (% MnO) and I. Mn (kg / t) / CaO (kg /
12 is a graph showing the relationship with (t).

FIG. 5: The product of (% SiO ₂ ) in tapping slag and actual basicity (v.v + 1), and the fraction of tapping slag other than (% T.Fe) and (% MnO) ｛100− ( It is a graph which shows the relationship with (% T.Fe) * 71/55-(% MnO)}.

FIG. 6 is a graph showing the relationship between A / B and T.Fe% in slag after adding a reducing agent.

FIG. 7 is a histogram when A / B is adjusted to a range of 1 to 1.3 and slag agitation is performed;

Claims (2)

(57) [Claims] 1. Prior to secondary refining, in reforming slag in a ladle, Al, alumina and CaO are introduced into the ladle according to the amount of slag flowing into the ladle during tapping from a steelmaking furnace. added to adjust the Al ₂ O ₃ minutes and C aO-content of ladle slag,
Continuing the slag is stirred by an inert gas, the final slag composition CaO: 40-50% at and Al ₂ O _3: reforming method of ladle slag and adjusting the 40-50% range. (2) Prior to the secondary refining, in reforming the slag in the ladle, the following (1), (2) based on the amount and composition of the slag flowing into the ladle during tapping from the steelmaking furnace. Determined by the formula
An amount of Al source, alumina source and C in which the ratio of Al ₂ O ₃ content (A value) to CaO content (B value) in the slag in the ladle is 1.0 to 1.3
and aO source were charged into a ladle, the slag is stirred by the inert gas continues, a final slag composition CaO: and a 40-50% Al ₂ O _3: characterized in that to adjust the 40-50% range Ladle slag reforming method. A = α × [W × ｛(% T.Fe) / 100 × 102/165 + (% MnO) / 100 × 102/213 + (% SiO ₂ ) / 100 × 102/90｝ + W _AL ] ... (1) B = β x [W x (% CaO) / 100 + W _CA ] ... (2) where α, β: Coefficients determined according to the steelmaking furnace W: Outflow slag amount (kg) (% T.Fe): T.Fe concentration in outflow slag (%) (% MnO): MnO concentration in outflow slag (%) (% SiO ₂ ): SiO ₂ concentration in outflow slag (%) (% CaO) : CaO concentration in effluent slag (%) W _AL : Alumina source to be input at tapping (kg) W _CA : CaO source to be input at tapping (kg)