JP2018115350A - Refining method of hot metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refining method of hot metal capable of reducing the amount of quicklime newly added for Blow2 blowing after Blow1 blowing and subsequent deslagging.SOLUTION: In the refining method of hot metal according to the present invention, dephosphorized hot metal 14 is produced by Blow1 blowing in which a CaO source is added and oxygen is top-blown into molten pig iron 12 contained in a converter-type vessel 11, and Blow2 blowing is performed after formed slag 15 is discharged, in which oxygen is top-blown into the dephosphorized hot metal 14 with new addition of quicklime. An auxiliary raw material containing one or both of an ingot-making slag with CaO and quicklime is used as the CaO source, concentration of AlOis 3.5 mass% or more and 10 mass% or less, and basicity is 0.8 or more and 1.2 or less in the slag 15 after the Blow1 blowing, and deslagging of the slag 15 is performed after the Blow1 blowing so that a mass of the slag is reduced to the range between 50 mass% or more and 80 mass% or less, provided that a total mass of the slag 15 formed by the Blow1 blowing is 100 mass%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a hot metal refining method in which slag is discharged after blowing (hereinafter also referred to as Blow 1 blowing) and further blown (hereinafter also referred to as Blow 2 blowing).

In the steelmaking process, the reduction in the amount of steelmaking slag generated has become a challenge due to the decrease in recycling applications of the steelmaking slag discharged.
As a measure to reduce the amount of steelmaking slag generation and improve the steelmaking cost, a part of P (phosphorus) concentrated slag is discharged after Blow1 blowing (intermediate waste), thereby reducing the de-P load in Blow2 blowing. It is effective to improve the ratio of hot metal pretreatment (Blow 1 blowing) that enables reduction and quick lime (converter (T.CaO)) reduction.
Furthermore, as a measure to reduce the amount of newly added quicklime (hereinafter also referred to as new quicklime) used during blowing, high phosphoric acid slag generated by Blow 1 blowing is discharged with high efficiency (intermediate) It is necessary to reduce the P concentration brought into Blow 2 blowing and to reduce the amount of new quicklime added in Blow 2 blowing.

For example, in Patent Document 1, by controlling the Al ₂ O ₃ concentration and basicity of slag and carrying out de-P with high efficiency, the de-P load in Blow 2 blowing is reduced and Mn by adding Mn ore is reduced. It is disclosed to reduce costs. Specifically, the basicity of the slag by Blow 1 blowing is in the range of more than 2.2 and 3.5 or less. That is, since Blow 1 blowing is performed at a high basicity, the de-P property can be improved.
Patent Document 2 discloses that de-P and intermediate excretion are carried out with high efficiency by controlling ((Al ₂ O ₃ concentration) + (TiO ₂ concentration)) and basicity of slag. ing. Specifically, the basicity of the slag during Blow 1 blowing is in the range of 1.4 to 2.2.

JP 2007-262576 A JP 2008-63645 A

However, the conventional technique still has the following problems to be solved.
Under the conditions of Patent Document 1, the inventors have clarified that variations occur in the ratio of intermediate waste (intermediate waste rate) and the amount of P brought in as slag to Blow 2 blowing. . Therefore, in Blow 2 blowing, it is necessary to determine the amount of new quicklime added when the amount of brought-in P is large (when the intermediate rejection rate is poor), and this amount cannot be reduced sufficiently.
Moreover, although patent document 2 is low basicity compared with patent document 1, since it blows Blow1 on the conditions of high basicity, the addition amount of the new quick lime in Blow2 blowing from the said reason Cannot be reduced sufficiently.
Thus, since the conventional technology cannot sufficiently reduce the amount of new quick lime added in Blow 2 blowing, the total amount of new quick lime added in both Blow 1 and Blow 2 blowing is also sufficiently reduced. could not.

  The present invention has been made in view of such circumstances, and a hot metal smelting method that can reduce the amount of newly added quick lime when compared with the conventional method when slag is discharged after Blow 1 blowing and Blow 2 blowing is performed. The purpose is to provide.

The hot metal refining method according to the present invention that meets the above-described object is a method of melting a de-P molten metal by Blow 1 blowing (first blowing) in which a CaO source is added to the hot metal in a converter type vessel and the acid is blown upward. After that, in the refining method of hot metal that performs Blow 2 blowing (second blowing) in which the generated slag is discharged, fresh lime is newly added to the de-P molten metal, and the acid is blown upward.
As the CaO source, using an auxiliary material containing either one or both of ingot slag containing CaO and quick lime,
The slag after the Blow 1 blowing, Al ₂ O ₃ concentration: 3.5 mass% or more and 10 mass% or less, basicity: 0.8 or more and 1.2 or less,
The slag after Blow 1 blowing is discharged in the range of 50% by mass to 80% by mass with 100% by mass as the total mass of the slag produced by Blow 1 blowing.

  In the hot metal refining method according to the present invention, it is preferable to further use decarburized slag generated in the past hot metal refining as the CaO source.

In the hot metal refining method according to the present invention, the slag after Blow 1 blowing is Al ₂ O ₃ concentration: 3.5 to 10% by mass and basicity: 0.8 to 1.2. The slag rejection rate (intermediate rejection rate) and the variation in the amount of brought-in P as slag for Blow 2 blowing can be reduced as compared with the conventional case. And since the slag removal after this Blow1 blowing is performed in the range of 50-80 mass% of the total mass of slag, the addition amount of the quick lime newly added by Blow2 blowing can fully be reduced, and Blow1 blowing The amount of new quicklime added in both smelting and Blow 2 blowing can also be reduced as compared with the conventional case.

It is explanatory drawing of the refining method of hot metal. It is explanatory drawing for calculation of an intermediate rejection rate.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
First, the outline of the hot metal refining method will be described with reference to FIG.
Hot metal 12 is charged from the container 10 into the converter-type container 11 (charging process).
A deoxidized P molten metal 14 is melted by Blow 1 blowing, in which a CaO source is added to the molten iron 12 in the converter type vessel 11 and the lance 13 is used to blow and send the acid. In Blow 1 blowing, de-P treatment is mainly performed (Blow 1 process).

Next, the converter-type vessel 11 is tilted, and the slag 15 in the furnace generated by Blow 1 blowing is discharged from the furnace port 16 (intermediate discharge process).
Then, quick lime (hereinafter, also referred to as new quick lime) is newly added to the de-P molten 14 after the intermediate waste, and blow 2 blowing is performed by using the lance 13 to perform top blowing. In Blow 2 blowing, de-C treatment is mainly performed, but de-P treatment is also performed (Blow 2 process).
The converter-type vessel 11 is tilted, and the molten steel 17 that has been subjected to de-P treatment and de-C treatment is produced from the steel exit 18 (steel production step).

  As described above, in the conventional technology, in Blow 1 blowing, the slag is made highly basic and the de-P treatment is made highly efficient, but this high basicity leads to variations in the intermediate rejection rate of slag. In addition, it is necessary to determine the amount of quick lime to be newly added in Blow 2 blowing in accordance with the case where the intermediate waste rate is poor (when the amount of P brought in by slag into Blow 2 blowing is large).

The inventors of the present invention have reduced the slag at the time of Blow 1 blowing to a lower basicity than before (deterioration efficiency of P is slightly lowered), stabilized the intermediate rejection rate of slag, and reduced the P of the slag to Blow 2 blowing. It was conceived that the amount of new quicklime added in Blow 2 blowing could be stably reduced by eliminating variations in the amount brought in.
Thereby, it discovered newly that the total addition amount of the new quicklime added by both Blow1 blowing and Blow2 blowing could be reduced notably compared with the past.

That is, the hot metal refining method according to one embodiment of the present invention is a secondary raw material containing either one or both of ingot slag containing CaO and quick lime as a CaO source to be added in Blow 1 blowing. Slag after Blow 1 blowing, Al ₂ O ₃ concentration: 3.5 mass% to 10 mass%, basicity: 0.8 to 1.2, and slag discharged after Blow 1 blowing In other words, the intermediate rejection rate is a method in which the total mass of the slag produced by Blow 1 blowing is 100% by mass within a range of 50% by mass to 80% by mass. This will be described in detail below.

[1] Suppression of variation in intermediate rejection rate When the slag has a low melting point, the liquid phase rate is improved.
The liquid phase slag has good forming properties at the end of Blow 1 blowing, and the drainage starts from the beginning of the tilting of the converter-type vessel at the time of intermediate dumping, and the end of the tilting (just before the leakage of the molten P molten metal) The evacuation continues stably until. As a result, a stable intermediate rejection rate can be realized.
However, when the melting point of the slag is high, the reproducibility of the liquid phase ratio and the occurrence of forming deteriorates due to the processing charge. Possible causes of this include the added agglomeration slag and the addition of new quicklime, and the state of stirring of the molten metal by acid delivery, but are not clear.
In addition, if the liquid phase ratio and the state of foaming vary, there may be cases in which evacuation is performed only at the end of the tilt, and the intermediate evacuation ratio varies.

Therefore, in order to ensure a low melting point slag composition, as described above, the Al ₂ O ₃ concentration (alumina concentration) and basicity ((CaO mass% in slag) / (SiO in slag) of Blow 1 blown slag. ₂ mass%): hereinafter also simply referred to as C / S).
Here, when the Al ₂ O ₃ concentration of the slag is less than 3.5% by mass, the slag melting point is not sufficiently lowered, which causes variations in forming. Moreover, since the hatching of slag is insufficient, the de-P reaction is difficult to proceed.
On the other hand, even if the Al ₂ O ₃ concentration of the slag is more than 10% by mass, the necessary decrease in the melting point of the slag can be achieved, but since the CaO amount is relatively reduced, the de-P property is lowered.

From the above, the Al ₂ O ₃ concentration of the slag after Blow 1 blowing was set to 3.5% by mass or more and 10% by mass or less (preferably, the upper limit was 8% by mass, and further 5% by mass).
Use of ingot slag is effective for controlling the Al ₂ O ₃ concentration (alumina component) of the slag. This is because the ingot slag generally contains a large amount of an alumina component.
In addition, since the ingot slag is substantially equivalent to the premelt product, the ingot slag is easy to hatch, and also contains CaO and is effective as a CaO source.

Moreover, when the basicity of slag is less than 0.8, the amount of CaO in the slag is reduced with respect to the amount of SiO ₂ , and the de-P property in Blow 1 blowing is significantly deteriorated.
On the other hand, when the basicity of the slag exceeds 1.2, the slag melting point is insufficiently reduced, leading to variations in the forming situation and the intermediate rejection rate.
From the above, the basicity of the slag after Blow 1 blowing was set to 0.8 or more and 1.2 or less (preferably, the lower limit was 0.85).
For controlling the basicity of the slag, quick lime (CaO) can be used as a CaO source.
Further, decarburized slag generated by refining hot metal in the past can also be used as a CaO source. This decarburization slag is a slag obtained after Blow 2 blowing in past hot metal refining, and may be in a molten state or in a solid state (stone-like shape).

[2] About the intermediate rejection rate As described above, even if the Al ₂ O ₃ concentration and basicity of the slag after Blow 1 blowing is regulated to suppress the variation in the intermediate rejection rate, it is added at the time of Blow 2 blowing In order to effectively utilize the new quicklime, the present inventors have revealed that there is an appropriate value for the intermediate excretion rate.
That is, as described above, it is necessary to perform intermediate waste in the range of 50% by mass or more and 80% by mass or less with the total mass of the slag generated by Blow 1 blowing being 100% by mass.
The intermediate rejection rate can be adjusted, for example, by an operator (operator) adjusting the tilt angle of the converter-type container 11 described above.

Here, when the intermediate waste rate is less than 50% by mass, the concentration of P brought into Blow 2 blowing increases and recovery P is generated, so the amount of new quicklime added during de-C is increased.
On the other hand, when the intermediate rejection rate is more than 80% by mass, the amount of slag brought from Blow 1 blowing to Blow 2 blowing decreases, so the amount of SiO ₂ required for hatching of new quicklime added during Blow ₂ blowing The amount of Al ₂ O ₃ is insufficient. As a result, the hatching failure of the new quicklime added at the time of Blow 2 blowing occurs, and the variation of de-P occurs. Therefore, it is necessary to add a lot of new quicklime, and the amount of new quicklime added cannot be reduced.
That is, in order to prevent the hatching failure of new quicklime, it is necessary to carry over an appropriate amount of slag from Blow 1 blowing.

A method for calculating the above-described intermediate rejection rate will be described below.
The intermediate slag rate is the removal of slag (slag) generated after Blow 1 blowing from the total amount of slag generated after Blow 1 blowing without charging (carrying over) Blow 2 blowing. Refers to the percentage of slag. When you do not weighing of the slag, in order to quantify the intermediate drain slag ratio, it may obtained from balance calculations of SiO _2.
Hereinafter, an example of this calculation method will be described with reference to FIG.

The SiO ₂ balance calculation (mass balance calculation) from the Blow 1 process to the Blow ₂ process is performed, and the intermediate rejection rate is quantified.
In the Blow 1 process, Si (existing in hot metal, scrap, etc.) and SiO ₂ (existing in auxiliary materials, etc.) are charged into the converter type vessel (Blow 1 charging in FIG. 2) at the start of refining, and Blow 1 blowing is performed. Executed.
When the Blow 1 process is completed, all of Si and SiO ₂ shift to slag as SiO ₂ ((I) in FIG. 2: after Blow 1 blowing).

The SiO ₂ transferred to the total amount of slag is divided into one that is removed at the time of intermediate evacuation (one that is discharged outside the furnace) and one that is not evacuated (one that remains in the furnace) ((II in FIG. 2). ): After intermediate evacuation), all un-exhausted stuff is charged into the Blow 2 process converter type vessel.
Note that after Blow2 blowing in Figure 2 shows the amount of SiO ₂ of the converter-type vessel after the Blow2 step is completed. That is, the above-mentioned unexcluded one ((III) in FIG. 2) and one newly generated in the Blow 2 process (Blow 2 charging).
From the above, the mass ratio of the above-mentioned undrained SiO ₂ (“B” in FIG. 2) after Blow ₂ blowing and SiO ₂ (“A” in FIG. 2) charged with Blow 1 “{ 1- (B / A)} × 100 ”is defined as the intermediate rejection rate (mass%).

  Therefore, since the slag component is a known value, the intermediate rejection rate is defined as a (= 1− (B / A)), and this a (unit: −) is defined as an unknown number by Equation (1). In addition, the symbols used, including formula (2) and formula (3) described later, are as shown in Table 1 below.

In other words, the intermediate rejection rate a defined by the equation (1) is determined by the amount of SiO ₂ carried over from the Blow 1 step to the Blow ₂ step (left side of the equation (1)) and the SiO _{2 in} the total mass (tons) of slag in the Blow 2 step. The mass obtained by subtracting the mass of SiO ₂ charged with Blow ₂ from the mass (the right side of the formula (1)) can be expressed by an equation with an equivalent amount.
W _SiO2 ^Blow1 × (1-a) = SW ^Blow2 × SC _SiO2 ^Blow2- W _SiO2 ^Blow2 (1)
W _SiO2 ^Blow1 : Amount of SiO ₂ (tons) charged into the converter type vessel in the Blow 1 process. A metal Si contained in terms of SiO ₂ was molten iron and scrap (converted into SiO ₂ amount), the sum of SiO ₂ contained in the auxiliary raw material.
SW ^Blow2 : Mass (ton) of slag in the Blow2 process.
SC _SiO2 ^{Blow2: Blow2} SiO ₂ concentration of the slag after blowing (mass%).
W 2 _{SiO 2} ^{Blow 2} : The amount of SiO ₂ (tons) charged into the converter type vessel in the Blow 2 process. Total value of SiO ₂ contained in auxiliary materials such as slag recycling (ingot slag and decarburized slag) and / or silica stone. The amount of SiO ₂ contained in the slag carried over from the Blow 1 process is excluded.

The mass (SW ^Blow2 ) of the in-furnace slag in the Blow2 process, which is an unknown quantity of the above formula (1), is derived from the formula (3). Note that SW ^Blow1 used in Equation (3) is derived from Equation (2). For this derivation, the CaO concentration and SiO ₂ concentration (unit: mass%) in the slag of the Blow 1 process and Blow 2 process, and the total CaO mass and SiO ₂ total mass (unit: tons) charged from the main raw material and auxiliary raw material Are used respectively.
SW ^{Blow 1} = (W _CaO ^{Blow 1} + W _{SiO 2} ^{Blow 1} ) / (SC _CaO ^{Blow 1} + SC _SiO 2 ^{Blow 1} ) (2)
SW ^Blow2 = {(1-a) × SW ^{Blow 1} × (SC _CaO ^{Blow 1} + SC _{SiO 2} ^{Blow 1} ) + (W _CaO ^Blow 2 + W _{SiO 2} ^{Blow 2} )} / (SC _CaO ^Blow 2 + SC _SiO2 ^{Blow 2} ) (3)
W _CaO ^Blow1 : The amount of CaO (tons) charged into the converter type vessel in the Blow1 process. Total value of CaO contained in the agglomerated slag and / or quick lime auxiliary material.
SC _CaO ^{Blow 1} : CaO concentration (mass%) of slag after Blow 1 blowing.
SC _SiO2 ^Blow1 : SiO ₂ concentration (mass%) of slag after Blow 1 blowing.
SW ^Blow1 : Slag mass in Blow1 process.
W _CaO ^Blow2 : The amount of CaO (tons) charged in the converter vessel in the Blow2 process. Total value of CaO contained in slag recycling and / or auxiliary raw material of quicklime.
SC _CaO ^Blow2 : CaO concentration (mass%) of slag after Blow2 blowing.
SC _SiO2 ^{Blow2: Blow2} SiO ₂ concentration of the slag after blowing (mass%).
From the above calculation, the intermediate rejection rate can be calculated.

Moreover, in order to carry out de-P during Blow 2 blowing, addition of new quicklime in Blow 2 blowing is performed based on the following formula.
The amount of new quicklime introduced in Blow 2 blowing is calculated from the de-P width required for de-P in Blow 2 blowing.
This P removal width is calculated from the “target P” at the end of Blow 2 blowing (for example, equivalent to the component specifications required for the product) and the input “P” hot metal P. From the formulas (4) to (6) shown in Fig. 4, the amount of new quicklime in Blow 2 blowing is determined.

(New quicklime amount in Blow 2 blowing) = {(after intermediate waste [P]) − (target [P])} × α (4)
(After intermediate waste [P]) = (After blow 1 blowing [P]) + {100% − (Intermediate waste rate (%))} × {(molten iron [P]) − (After blow 1 blow [P] ])} (5)
(After blow 1 blowing [P]) = (molten iron [P]) × {100% − (depletion rate of blow 1 blowing (%))} (6)
Here, α is 0.1 to 0.4 (a constant corresponding to the process capability of blowing obtained from past performance values), and [P] is the P concentration (mass%) contained in the molten iron. .

  Next, examples carried out for confirming the effects of the present invention will be described.

Experimental conditions 1) Condition a) amount of main raw material A total of 300 to 400 tons of molten metal was melted in a converter (converter type vessel) using the following charges.
-Hot metal charge: 250-350 tons-Cold iron charge: 0 or more than 0 and 50 tons-Scrap charge: 0 or more than 0 and 100 tons b) Charged to the converter Main components of hot metal-C: 3.0-5.0 (mass%)
・ Si: 10 to 100 (× 10 ⁻² mass%)
・ Mn: 5 to 10 (× 10 ⁻² mass%)
· P: 50~200 (× ^{10 -3} wt%)
S: 1-20 ( ^x10-3 mass%)
2) Sub-raw material (sub-material) conditions and input brands: quicklime, limestone, silica, MgO, charcoal, slag recycling (decarburized slag and ingot slag)
And launch methods: upper adding 3) BOF embodiment, the upper base吹転furnace, the upper spray conditions / oxygen-flow-rate: from 40000 to 95000 ^(Nm 3 / hr)
-Bottom blowing conditions / bottom blowing gas types: O ₂ , CO ₂ , N ₂ , LPG

  Table 2 shows test conditions and test results performed based on the above-described execution conditions.

“%” In Table 2 means “mass%”.
The “De-P ratio (%)” of “Blow 1 blowing” in Table 2 is represented by the following formula.
{1- (Achieved P concentration (% by mass) of molten metal at the time of Blow 1 blowing) / (Mold P concentration (% by mass) before starting blowing (before starting Blow 1))} × 100
The “target P concentration” of “Blow 2 blowing” in Table 2 is the P concentration of molten steel when the “minimum value” of the “intermediate rejection rate” is implemented. The “minimum value” and “maximum value” of the “intermediate rejection rate” are the minimum value and the maximum value of the variation of the intermediate rejection rate when the same operation is performed, respectively.
“Kg / t” which is a unit of “new quicklime” in Table 2 is the amount of new quicklime added per ton of molten metal. “Blow 1 + Blow 2” of “new quick lime” is the total amount of “new quick lime” of “Blow 1 blowing” and “Blow 2 blowing”.
The “evaluation” of “new quicklime” in Table 2 is 28 (kg / t) or less as “low” (addition of new quicklime was sufficiently reduced), and over 28 (kg / t) “high” (The amount of new quicklime added could not be reduced).

First, _Al 2 _{O 3} concentration of the slag after Blow1 blowing is, the effect on the amount of new quicklime will be described with reference to Comparative Examples 1 and 2 Examples 1 and 2. In addition, the basicity (C / S) of the slag after Blow1 blowing of Examples 1 and 2 and Comparative Examples 1 and 2 was set to 1.2.
As shown in Table 2, in Examples 1 and 2, since the Al ₂ O ₃ concentration was within the appropriate range (3.5 to 10%), variation in the intermediate rejection rate could be suppressed. And the amount of new quick lime addition of “Blow 2 blowing” required to achieve the target P concentration of 15 × 10 ⁻³ % by setting the intermediate rejection rate within the appropriate range (50 to 80%) is 26 As a result, the amount of new quicklime added to “Blow1 + Blow2” could be reduced to 26.7 (kg / t).

On the other hand, Comparative Example 1, because it is less than the lower limit of the above-described appropriate range of concentration of Al ₂ O ₃ (3.0 mass%), slag formation of slag is insufficient, the intermediate discharge slag ratio of the above-described appropriate range The lower limit was exceeded (40 to 70%), and the de-P reaction was difficult to proceed (de-P rate: 30%). For this reason, it is necessary to increase the addition amount of new quick lime of “Blow 2 blowing” required to achieve the target P concentration to 29.8 (kg / t). As a result, the amount of new quick lime of “Blow 1 + Blow 2” is also increased. Increased.
In Comparative Example 2, since the upper limit value of the proper range the concentration of _Al 2 _{O 3} greater than (12 wt%), de P of relatively CaO amount is reduced is decreased (de P ratio: 30%) . For this reason, it is necessary to increase the addition amount of new quick lime of “Blow 2 blowing” required to achieve the target P concentration to 28.7 (kg / t). As a result, the amount of new quick lime of “Blow 1 + Blow 2” is also increased. Increased.

Next, the influence which the basicity of the slag after Blow1 blowing has on the addition amount of new quicklime will be described with reference to Examples 1 and 3 and Comparative Examples 3 and 4. Incidentally, _Al 2 _{O 3} concentration of the slag after Blow1 blowing of Comparative Examples 3 and 4 as in Examples 1 and 3 was set to 3.5.
As shown in Table 2, since Examples 1 and 3 set the basicity within an appropriate range (0.8 to 1.2), it was possible to suppress variations in the intermediate rejection rate. And, by setting the intermediate rejection rate within the above-described appropriate range, the amount of new quicklime added to achieve the target P concentration can be reduced to 26.7 (kg / t), As a result, the amount of new quicklime added as “Blow1 + Blow2” could be reduced to 26.7 (kg / t).

On the other hand, in Comparative Example 3, since the basicity was less than the lower limit (0.5) of the appropriate range, the de-P property was significantly deteriorated (de-P rate: 30%). For this reason, it is necessary to increase the addition amount of new quick lime of “Blow 2 blowing” required to achieve the target P concentration to 28.7 (kg / t). As a result, the amount of new quick lime of “Blow 1 + Blow 2” is also increased. Increased.
Further, in Comparative Example 4, since the basicity was over the upper limit (1.5) of the appropriate range, it is necessary to add new quick lime by Blow 1 blowing, and the intermediate rejection rate by setting high basicity Varied (45-90%). Therefore, in order to achieve the target P concentration, it is necessary to add 3 (kg / t) of fresh quicklime in “Blow 1 blowing”, and 26.6 (kg / t) of fresh quick lime in “Blow 2 blowing” As a result, it was necessary to increase the amount of new quicklime of “Blow1 + Blow2” to 29.6 (kg / t).

Finally, the influence of the intermediate slag rejection rate on the amount of new quicklime added will be described with reference to Example 1 and Comparative Examples 5 and 6. Incidentally, _Al 2 _{O 3} concentration of the slag after Blow1 blowing of Comparative Examples 5 and 6 Example 1 was set to 3.5, the slag basicity was 1.2.
As described above, in Example 1, since the Al ₂ O ₃ concentration and the basicity were within the above-described appropriate ranges, variation in the intermediate rejection rate could be suppressed. Then, by setting the intermediate rejection rate within the above-described proper range, the amount of new quicklime added as “Blow1 + Blow2” could be reduced to 26.7 (kg / t) in order to achieve the target P concentration.
On the other hand, in Comparative Example 5, since the intermediate rejection rate was adjusted to a range (90 to 100%) exceeding the upper limit of the appropriate range (because almost all of the slag was discharged after Blow 1 blowing), the target P concentration was achieved. Therefore, it is necessary to increase the amount of new quicklime added to “Blow2 blowing” to 30.7 (kg / t), and as a result, the amount of new quicklime of “Blow1 + Blow2” also increased.
Moreover, since the comparative example 6 adjusted the intermediate rejection rate to the range (40 to 70%) that deviates from the lower limit of the appropriate range, the amount of P brought into Blow 2 blowing increases and the target P concentration is achieved. It was necessary to increase the necessary amount of new quicklime of “Blow2 blowing” to 28.3 (kg / t), and as a result, the amount of new quicklime of “Blow1 + Blow2” also increased.

  From the above, by using the hot metal refining method of the present invention, it is confirmed that the amount of newly added quick lime can be reduced as compared with the conventional method when slag is discharged after Blow 1 blowing and Blow 2 blowing is performed. did it.

  As described above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the configuration described in the above embodiment, and the matters described in the scope of claims. Other embodiments and modifications conceivable within the scope are also included. For example, a case where the molten iron refining method of the present invention is configured by combining a part or all of the above-described embodiments and modifications is also included in the scope of the right of the present invention.

10: Vessel, 11: Converter type vessel, 12: Hot metal, 13: Lance, 14: De-P molten metal, 15: Slag, 16: Furnace port, 17: Molten steel, 18: Outlet port

Claims (2)

After melting the de-P molten metal by Blow 1 blowing, which adds the CaO source to the hot metal in the converter vessel and feeds it with oxygen, the generated slag is discharged, and new quick lime is added to the de-P molten metal In the refining method of hot metal that performs Blow 2 blowing,
As the CaO source, using an auxiliary material containing either one or both of ingot slag containing CaO and quick lime,
The slag after the Blow 1 blowing, Al ₂ O ₃ concentration: 3.5 mass% or more and 10 mass% or less, basicity: 0.8 or more and 1.2 or less,
The refining of hot metal, wherein the slag after Blow 1 blowing is discharged in a range of 50% by mass to 80% by mass, with the total mass of the slag generated by Blow 1 blowing being 100% by mass. Method.   2. The hot metal refining method according to claim 1, wherein decarburization slag generated in the past hot metal refining is further used as the CaO source.

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