JP2018178235A - Pretreatment method of hot metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the utilization efficiency of CaO by promoting slagging of CaO and to enhance the reaction efficiency of oxygen to be input in a pretreatment (desiliconization and dephosphorization) in which a refining agent is blown into hot metal in a refining container. SOLUTION: A refining agent containing an iron oxide source, gaseous oxygen, and quicklime is blown into the hot metal in a refining container from a refining agent blowing lance immersed in the hot metal, and desiliconization treatment and dephosphorization treatment are continuously performed. In the method for pretreating hot metal, the ratio of quicklime blowing rate (kg / min): FCaO to oxygen blowing rate (kg / min): FO defined by the following formula (1): A method for pretreatment of hot metal, which comprises blowing FCaO / FO so as to satisfy the following formula (2). FO ＝ FO_FeOt ＋ FO_O2 ・ ・ ・ (1) FO_FeOt: Oxygen blowing speed by iron oxide source (kg / min) FO_O2: Oxygen blowing speed by gaseous oxygen (kg / min) 1.5 ≦ FCaO / FO ≦ 3.0 ・・ ・ (2) [Selection diagram] Fig. 3

Description

  The present invention relates to a hot metal pretreatment method for efficiently reducing the Si concentration of hot metal and then reducing the P concentration of hot metal in a refining vessel such as a mixing wheel.

  When oxygenating the molten metal in the converter to convert it to molten steel, the load of blowing in the converter is reduced and it is easy to adjust the molten steel to the desired composition. Usually, "hot metal pretreatment" to remove silicon, phosphorus, sulfur and the like is performed.

  That is, while the hot metal discharged from the blast furnace is still present in the hot metal, the decanter or the mixing car, the lime-based flux, the oxidizing agent, and / or the soda ash as a refining agent in the hot metal The system flux or the like is blown with a carrier gas (for example, nitrogen, oxygen) or directly added from above, and silicon, phosphorus, sulfur or the like is transferred to the slag and removed.

Thermodynamically, the desiliconation reaction proceeds prior to the dephosphorization reaction, but in order to efficiently advance the desiliconation reaction, it is necessary to keep the SiO ₂ activity in the slag low (SiO in FIG. 1). ₂ isoactivity diagram (1550 ° C, see). In addition, raising the basicity of the slag (% CaO /% SiO ₂ , hereinafter sometimes referred to as “C / S”) improves the dephosphorization ability of the slag, so it can be used as a CaO source of a refining agent to be added to hot metal. It is common to use quicklime.

However, if the hot metal temperature is 1300 to 1400 ° C., the upper limit of C / S that can dissolve CaO is about 1.5, and CaO exceeding this upper limit is not dissolved (shrink) in slag, so it is useless. (Refer to the ternary phase diagram of the CaO-SiO ₂ -FeO system in FIG. 2).

Therefore, it is necessary to adjust the amount of CaO to be poured into the molten metal so that the ratio (C / S) of CaO to be introduced and SiO ₂ generated by the desiliconization reaction becomes 1.5 or less. If C. is introduced at once, C / S may rise too much at the initial stage of the silicon removal treatment, which may lower the silicon removal efficiency.

  According to Patent Document 1, after receiving molten iron in a container, the basicity of slag is reduced to 1.0 or less while stirring the molten iron in the container, and removal is performed within 10 minutes after completion of the silicon removal treatment. A hot metal desiliconization method is disclosed which is characterized by initiating a crucible. In the method of Patent Document 1, it is considered that the upper limit of the basicity of slag is defined to be 1.0 lower than the theoretical upper limit (1.5) in order to carry out the silicon removal and removal smoothly and efficiently. The improvement of the desiliconization efficiency can not always be expected.

  On the other hand, when lance is immersed in hot metal and CaO and iron oxide source (refining agent) are continuously fed by injection method, the C / S of slag gradually increases and the extreme amount of CaO fed In many cases, a method of injecting a refining agent by an injection method is adopted (refer to, for example, Patent Documents 2 and 3), since the conversion defects are unlikely to occur. However, even in this case, the utilization efficiency of CaO may be maximal when the C / S of the slag is lower than 1.5 (theoretical upper limit), for example, 1.2 or less.

Japanese Patent Laid-Open No. 2000-001712 Japanese Patent Application Publication No. 2004-018941 JP 2005-248218 A

  As described above, when the basicity (C / S) of slag is lower than 1.5 (theoretical upper limit), for example, 1.2 or less, the utilization efficiency of CaO may be maximal Therefore, even when CaO is blown continuously into the hot metal, if the blowing speed of CaO is high, the CaO concentration rises locally, for example, in the blowing area. It was thought that the solid phase (CaO) crystallized out and the blown CaO did not fully hatch and the utilization efficiency of CaO would be reduced.

  In the present invention, based on the above idea, during the pretreatment (desiliconization, dephosphorization) in which the refining agent is blown into the molten metal in the refining vessel, the transformation of CaO is promoted to enhance the utilization efficiency of CaO and to be introduced. It is an object of the present invention to increase the reaction efficiency of oxygen and to provide a hot metal pretreatment method for solving the problem.

The present inventors diligently studied methods for solving the above problems. As a result, when a refining agent (iron oxide source, gaseous oxygen, quick lime, etc.) is blown into the molten metal in the refining vessel, the quick lime blowing rate (kg / min): F _CaO and the oxygen blowing rate (kg / min): When the ratio to F 2 _O : F 2 _{CaO 3} / F 2 _O is controlled to an appropriate range, the quick-boiling lime to be blown in efficiently hatches, the reaction efficiency of the input oxygen is improved, and the desiliconization reaction and the dephosphorization reaction proceed rapidly It turned out to be. This finding will be described later.

  The present invention has been made based on the above findings, and the summary thereof is as follows.

(1) A refining agent containing an iron oxide source, gaseous oxygen and quicklime is blown into a molten metal in a refining vessel from a refining agent blowing lance immersed in the molten metal, and the desiliconization treatment and the dephosphorizing treatment are continuously performed. In the hot metal pretreatment method to be performed,
The ratio of the above refining agent to quick lime injection rate (kg / min): F _CaO and oxygen injection rate (kg / min): F 2 _O defined by the following formula (1): F 2 _{CaO 2} / F 2 _O The pre-processing method of the molten iron characterized by blowing so that following formula (2) may be satisfy | filled.
F _O = F _O ^_ _FeOt + F _O ^_ _{O 2} (1)
F _O ^_ _FeOt : Oxygen injection rate by iron oxide source (kg / min)
F _O ^_ _{O 2} : Oxygen blowing rate by gaseous oxygen (kg / min)
1.5 ≦ F _CaO / F _O ≦ 3.0 (2)

  (2) The method of pre-treating molten metal according to the above (1), wherein the Si content is adjusted to 0.05 to 0.25 mass% by the silicon removal treatment.

  (3) The method for pretreating hot metal according to (1) or (2) above, wherein P: 0.05 to 0.10 mass% is adjusted by the dephosphorization treatment.

  (4) The method according to any one of the above (1) to (3), wherein the refining vessel is a mixing car.

  According to the present invention, in the pretreatment (desiliconization and dephosphorization) of hot metal in the refining vessel, it is possible to effectively utilize quick lime and to enhance the reaction efficiency of the input oxygen.

A SiO ₂ Tokatsu amount diagrams (1550 ° C.). It is a ternary phase diagram of CaO-SiO ₂ -FeO system. It is a diagram showing the relationship between F _CaO / F _O and local basicity C / S _local.

In the method of pre-treating hot metal according to the present invention (hereinafter sometimes referred to as “the method of the present invention”), a smelting agent containing an iron oxide source, gaseous oxygen and quicklime is dipped in the smelter in smelter. In the pre-treatment method of hot metal which blows from a refining agent blowing lance, desiliconizing treatment and dephosphorizing treatment are continuously performed,
The ratio of the above refining agent to quick lime injection rate (kg / min): F _CaO and oxygen injection rate (kg / min): F 2 _O defined by the following formula (1): F 2 _{CaO 2} / F 2 _O It is characterized by blowing so that following formula (2) may be satisfy | filled.
F _O = F _O ^_ _FeOt + F _O ^_ _{O 2} (1)
F _O ^_ _FeOt : Oxygen injection rate by iron oxide source (kg / min)
F _O ^_ _{O 2} : Oxygen blowing rate by gaseous oxygen (kg / min)
1.5 ≦ F _CaO / F _O ≦ 3.0 (2)

  Hereinafter, the method of the present invention will be described.

Conventionally, the basicity (C / S) generally used is the characteristic of the slag when all the CaO input and all the SiO ₂ formed are uniformly present in the refining vessel. It is useful as an indicator to show.

However, in the actual pretreatment, even if the final CaO input amount and the SiO ₂ generation amount are the same, the amount of CaO present in the smelting vessel during the pretreatment is variable depending on the injection rate, and the amount of SiO ₂ generated is The form of progress of the pre-treatment is not uniform as it varies with the production rate.

  Here, consider the reaction when the iron oxide source, gaseous oxygen and quick lime are simultaneously blown into the molten iron as a refining agent.

Iron oxide in the iron oxide source and gaseous oxygen react with Si in the hot metal to form SiO ₂ , and locally, for example, a CaO-SiO ₂ -FeO-based slag is generated in the blowing region. The basicity C / S (hereinafter sometimes referred to as "C / S _local ") of the locally formed slag is the blowing rate F _{CaO of CaO} and the blowing rate F of oxygen which is a generation source of SiO ₂ Ratio to _O : It is considered to be proportional to F _CaO / F 2 _O.

Therefore, a situation may occur where F _CaO / F _O becomes too large, C / S _local exceeds 1.5, and CaO does not hatch, but C / S _local does not exceed 1.5. If formed continuously, it is thought that the hatching of CaO can be promoted.

Therefore, the present inventors do not use the comprehensive basicity generally used conventionally, but locally, for example, the basicity of a CaO-SiO ₂ -FeO-based slag generated in a blowing region. focusing on C / S _local, was adopted F _CaO / F _O which is proportional to the C / S _local as an operation indicator. Then, based on the conditions and results of actual preliminary processing, the optimum range of the operation index F _CaO / F _O for C / S _local was clarified.

That is, a refining agent containing an iron oxide source, gaseous oxygen and quick lime, quick lime injection rate (kg / min): F _CaO, and oxygen injection rate (kg / min) defined by the following formula (1): When the ratio to F 2 _O : F 2 _{CaO 2} / F 2 _O is blown so as to satisfy the following formula (2), the local C / S _local is maintained in an appropriate range, and the infused quicklime efficiently hatches. The desiliconization reaction proceeds efficiently.
F _O = F _O ^_ _FeOt + F _O ^_ _{O 2} (1)
F _O ^_ _FeOt : Oxygen injection rate by iron oxide source (kg / min)
F _O ^_ _{O 2} : Oxygen blowing rate by gaseous oxygen (kg / min)
1.5 ≦ F _CaO / F _O ≦ 3.0 (2)

FIG. 3 shows the relationship between F _CaO / F 2 _O and the local basicity C / S _local . If F _CaO / F _O is 1.5 or more and 3.0 or less, a situation where C / S _local does not exceed 1.5 can be continuously formed to promote the hatching of CaO, The silica reaction can be efficiently promoted. This point is the basic idea of the method of the present invention.

  Hereinafter, the conditions of the method of the present invention will be described.

Hot metal:
The hot metal targeted by the method of the present invention is not particularly limited to the hot metal of a specific component composition, but is a hot metal of a normal component composition. Specifically, for example, a hot metal discharged from a blast furnace or a hot metal melted in an electric furnace can be mentioned.

Refining vessel:
Pretreatment of the hot metal is usually carried out using a mixing car for transferring the hot metal to the refining process as a refining vessel, but the refining container of the method of the present invention is not limited to the mixing car but for transferring the hot metal to the next refining process. It is a container (for example, a hot metal ladle etc.), and should just be a container which can pre-process.

Refiner:
The refining agent blown into the molten metal from the refining agent injection lance immersed in the molten metal is a refining agent containing an iron oxide source, gaseous oxygen and quick lime. Iron oxide is blown into the hot metal using, for example, mill scale, sinter ore, iron ore, sinter dust, etc. as an iron oxide source. Although quick lime is usually blown in the form of a lime-based flux, it may be CaO alone, or may be blown with a mixture of calcium carbonate (CaCO ₃ ), a converter crucible or the like whose main component is CaO.

Operation index F _CaO / F _O : 1.5 or more, 3.0 or less (the above formula (2))
A refining agent containing an iron oxide source, gaseous oxygen and quick lime, quick lime injection rate (kg / min): F _CaO, and oxygen injection rate (kg / min) defined by the above equation (1): F 2 _O The ratio: F _CaO / F 2 _O is blown so as to satisfy 1.5 or more and 3.0 or less (the above formula (2)).

If F _CaO / F _O is less than 1.5, the amount of quick lime injection is insufficient, and the basicity (C / S _local ) of the slag does not reach an appropriate range, and the desiliconation reaction does not proceed, so F _CaO / F _O is 1.5 or more. Preferably it is 1.7 or more.

On the other hand, when F _CaO / F _O exceeds 3.0, the amount of quick lime injected becomes excessive, and the solid phase (CaO) precipitates in the region where the basicity (C / S _local ) exceeds 1.5, Ca The F _CaO / F 2 _O should be less than 3.0 because the utilization efficiency of Preferably it is 2.7 or less.

Oxygen injection rate (kg / min): F _O = F _O ^_ _FeOt + F _O ^_ _{O 2} (above equation (1))
Since oxygen is blown into the hot metal in the form of iron oxide in addition to gaseous oxygen, oxygen injection rate (kg / min): F 2 _O is oxygen injection rate by iron oxide (kg / min): F 2 _O ^_ and _FeOt, oxygen flow rate with gaseous oxygen (kg / min): defined by the sum of F _O ^_ _O2.

Thus, by defining the oxygen injection rate (kg / min): F 2 _O , the total amount of oxygen input to the hot metal is adjusted during pre-treatment of the hot metal to bring F _CaO / F 2 _O within the appropriate range. Can be controlled.

F _O ^_ _FeOt depends on the iron oxide source. For example, when the iron oxide source is mill scale, “iron oxide injection rate × 16/72”, and when the iron oxide source is iron ore, “iron oxide injection rate × 48/160”. F _O ^_ _O2 is oxygen-flow-rate (Nm ³ / h) /60×1.429 (gaseous oxygen density), by changing the oxygen-flow-rate, it is possible to adjust the F _O ^_ _O2.

  According to the method of the present invention, quick lime can be effectively used, the reaction efficiency of input oxygen can be enhanced, and pretreatment of molten iron (refining, dephosphorization) in the refining vessel can be efficiently performed. Si: 0.05 to 0.25 mass%, and / or P: 0.05 to 0.10, in order to reduce the load on converter smelting of aluminum and to make it easier to adjust the molten steel to a desired composition. It is preferable to reduce to mass%.

  Next, although the Example of this invention is described, the conditions in an Example are one condition example employ | adopted in order to confirm the practicability and effect of this invention, and this invention is the one condition example. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the scope of the present invention.

Example 1
Mixing 250 tonnes of molten iron (Si: 0.4 to 0.6 mass%, P: 0.100 to 0.125 mass%, C: 4.4 to 4.7 mass%) out of the blast furnace It was charged and transported to a pretreatment site equipped with a refining agent injection device, and pretreatment of hot metal (silicon removal treatment and phosphorus removal treatment) was performed under the pretreatment conditions shown in Table 1.

The results of the pretreatment were evaluated by the composition of Si and P after pretreatment and the reaction efficiency η ₀ (proportion of oxygen consumed in the desiliconization reaction and the dephosphorization reaction) of the input oxygen defined by the following equation. It was evaluated that η _O > 0.65 was a pass (o).

eta ₀ = consumed oxygen quantity / total oxygen input amount = {(ΔP × 142/62 + ΔSi × 32/28) × 10} / (F O × processing time / 250 (t))
ΔP: P concentration before pretreatment (mass%)-P concentration after pretreatment (mass%)
ΔSi: Si concentration before pretreatment (mass%)-Si concentration after pretreatment (mass%)
F ₀ : F _O ^_ _FeOt + F _O ^_ _{O 2}
10: Coefficient for conversion of unit

  In the comparative example, the Si concentration after pretreatment is 0.25 mass% or more, and the index (the reaction efficiency of input oxygen) is less than 0.70, whereas in the invention example, the Si concentration after pretreatment is 0. It is understood that the index (the reaction efficiency of input oxygen) exceeds 0.70 at 20 mass% or less.

  As described above, according to the present invention, in the pretreatment (desiliconization and dephosphorization) of hot metal in the refining vessel, quick lime can be effectively used to enhance the reaction efficiency of the input oxygen. Thus, the present invention is highly applicable in the steel industry.

Claims (4)

In the hot metal in the refining vessel, a refining agent containing an iron oxide source, gaseous oxygen and quick lime is blown from a refining agent blowing lance dipped in the hot metal, and the desiliconizing treatment and the dephosphorizing treatment are continuously performed. In the pre-processing method,
The ratio of the above refining agent to quick lime injection rate (kg / min): F _CaO and oxygen injection rate (kg / min): F 2 _O defined by the following formula (1): F 2 _{CaO 2} / F 2 _O The pre-processing method of the molten iron characterized by blowing so that following formula (2) may be satisfy | filled.
F _O = F _O ^_ _FeOt + F _O ^_ _{O 2} (1)
F _O ^_ _FeOt : Oxygen injection rate by iron oxide source (kg / min)
F _O ^_ _{O 2} : Oxygen blowing rate by gaseous oxygen (kg / min)
1.5 ≦ F _CaO / F _O ≦ 3.0 (2)   The pre-processing method of hot metal according to claim 1, wherein Si: 0.05 to 0.25 mass% is adjusted by the silicon removal treatment.   The pre-processing method of the molten iron according to claim 1 or 2, wherein P: 0.05 to 0.10 mass% is adjusted by the dephosphorization treatment.   The method for pre-treating molten iron according to any one of claims 1 to 3, wherein the refining vessel is a mixing car.

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