JP2001026806A - Pre-treatment method of molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molten iron pretreating method with which dephosphorization can be made at the low temp. side profitable to the dephosphorization in molten iron temp. and the metal stuck quantity on a charging ladle with the molten iron discharged into the ladle for charging into a converter after completing the molten iron pre-treatment is reduced as much as possible. SOLUTION: In the molten iron pretreating method executing the dephosphorization and desulfurization in the molten iron completing desiliconization, the molten iron pre-treatment is executed so that the molten iron temp. T2 at the time when the pretreated molten iron completing the molten iron pretreatment, is carried and discharged into the ladle for charging into the converter, becomes in the range of 1,220-1,270 deg.C, and the carbon concn. C1 in the molten iron becomes in the range of 4.0-4.3 mass %. In the case of using ΔT for the dropping temp. of the molten iron till discharging the pretreated molten iron into the ladle for charging into the converter, the temp. target value T1 of the pretreated molten iron is set by T2 value and ΔT value to adjust the molten iron temp. and the carbon concn. is adjusted so that the carbon concn. in the pretreated molten iron becomes the above value C1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot metal pretreatment performed in a steel process prior to refining in a converter,
The present invention relates to a method of hot metal pretreatment for performing dephosphorization and desulfurization on hot metal after desiliconization.

[0002]

2. Description of the Related Art In a steel process, hot metal from a blast furnace is desiliconized in a blast furnace casting bed or the like and then received in a mixed iron wheel, which is a transport container, and the desiliconization is completed. The hot metal is subjected to hot metal pretreatment in a mixed iron wheel. Hot metal pretreatment is a process of performing dephosphorization and desulfurization at the hot metal stage. Hot metal that has completed hot metal pretreatment (preheated hot metal) is transported to a hot metal discharge site by a mixed iron car and refined in a converter. It will be paid out in the converter charging pan.
The representative chemical components of the hot metal from the blast furnace are as follows: C (carbon): 4.0 to 4.6 mass%, Si (silicon): 0.2
To 0.7 mass%, Mn (manganese): 0.2 to 2.5 mass%, P (phosphorus): 0.02 to 0.2 mass%, S (sulfur): 0.01 to 0.1 mass % And the hot metal temperature is 15
It is about 00 to 1550 ° C.

[0003] The main purpose of the hot metal pretreatment is to remove P in the hot metal. In the hot metal dephosphorization treatment, calcined lime powder (CaO) or the like is used as a dephosphorization flux (refining agent). In addition, iron ore powder (Fe ₂ O ₃ ) as an oxidizing agent is used as an oxygen source required for dephosphorization, and gas oxygen blowing from an O ₂ lance is also used to form P in the hot metal into slag. CaO ・ P ₂
Removed as O ₅ . In order to cause the hot metal to react with the calcined lime powder or iron ore powder, an injection method is employed in which a flux lance is inserted to the bottom of the hot metal in the mixed iron wheel, and the calcined lime powder and the like are injected into the hot metal along with nitrogen gas (N ₂ ). ing. Note that S (sulfur) in the hot metal is removed as CaS by using, for example, a mixture of CaO and CaF ₂ (blown by the injection method) as a desulfurization flux.
Desulfurization is performed simultaneously.

The dephosphorization reaction is an oxidation reaction, and the lower the temperature, the greater the affinity for oxygen and the more easily it is promoted. To reduce the amount of flux used for dephosphorization, pretreatment of the hot metal should be performed at a low temperature as much as possible. It is better to do. However, when the hot metal temperature is brought to a low temperature side which is advantageous for dephosphorization and hot metal pretreatment is performed, the hot metal discharged from the converter hot pot after finishing the hot metal pretreatment is used to remove the edge and bottom of the charging pot. The amount of bullion deposited on the surface increases. Further, in the molten iron pretreatment with such a low temperature side, when carrying out the blowing of pure oxygen gas by lance O ₂ in an attempt to reduce the bullion adhesion amount, consideration for the carbon concentration not been made in the molten iron, Although the hot metal temperature rises, C in the hot metal is oxidized and decreases outside the appropriate range, and from the relation of the iron-carbon equilibrium state, conversely, the hot metal tends to solidify and the amount of deposited metal increases. Often occurred.

[0005] As a result, the amount of hot metal that can be received in the converter charging pot is gradually reduced due to the adhesion of metal,
The problem is that the amount of hot metal charged per converter decreases, and it takes a lot of time to remove the deposited metal in the converter charging pan, which lowers the productivity of molten steel in the converter. there were.

Accordingly, an object of the present invention is to perform hot metal pretreatment for dephosphorization and desulfurization of hot metal after desiliconization, so that the hot metal temperature can be dephosphorized at a low temperature that is advantageous for dephosphorization, and An object of the present invention is to provide a hot metal pretreatment method capable of minimizing the amount of metal ingots in the charging pot due to the hot metal discharged into the converter charging pot after finishing the hot metal pretreatment.

[0007]

In order to achieve the above object, a first aspect of the present invention is a hot metal pretreatment method for dephosphorizing and desulfurizing hot metal that has been desiliconized. and hot metal temperature in pretreated molten iron is dispensed into being transported converter instrumentation Nyunabe is T _2: 1,220-1
A method for pre-treating hot metal so as to be in the range of 270 ° C and the carbon concentration of the hot metal is in the range of C ₁ : 4.0 to 4.3% by mass. Assuming that the amount of hot metal temperature drop before being discharged into the pan is ΔT,
The temperature target value T ₁ of the pre-treated hot metal is set to the T ₂ value
Performs settings to adjust the hot metal temperature by T value, a hot metal pretreatment method characterized in that the concentration of carbon pretreatment hot metal to adjust the carbon concentration to a value C ₁ of the.

According to a second aspect of the present invention, in the hot metal pretreatment method according to the first aspect, the carbon concentration of the hot metal is adjusted by injecting carbon powder into the hot metal by an injection method or adding an oxygen source. It is characterized by performing.

In the hot metal pretreatment method of the present invention, hot metal pretreatment (dephosphorization / desulfurization treatment) can be performed on the hot metal M that has been desiliconized at a low temperature that is advantageous for dephosphorization. Finished hot metal M '(pre-processed hot metal) is transported and discharged into the converter charging pan M "
'In order to reduce as much as possible bullion attachment by (hot metal temperature falls below, pretreatment hot metal M pretreatment hot metal M)' carbon concentration of C _1: from 4.0 to 4.3% by weight range The carbon concentration is adjusted to be within. The reason for limiting the carbon concentration is that in hot metal whose carbon concentration is out of this range,
This is because the solidification temperature becomes higher due to the relationship of the carbon-based equilibrium state, and the amount of metal ingot due to the molten iron increases when the molten iron is discharged into the converter charging pan.

Further, the temperature of the molten iron M "when paid out in Tenro instrumentation Nyunabe is T _2: To 1220 to 1270 to be in the range of ℃ the hot metal pre-treatment, pre-treatment the hot metal M '
Assuming that the amount of decrease in the hot metal temperature until the iron is discharged into the converter charging pan is ΔT, the target temperature value of the pretreated hot metal M ′ is T ₁ =
ΔT + (1220 ° C. + 1270 ° C.) / 2 is set to adjust the hot metal temperature. The ΔT is a value that can be preliminarily and accurately estimated and obtained based on past operation data as shown in the following equation.

[0011]

(Equation 1)

In these equations, T ₁ : target temperature value of the pretreated hot metal M ′, T ₂ : temperature of the hot metal M ″ when discharged into the converter charging pan, ΔTa: transport by the mixed iron wheel Hot metal temperature drop (° C), t1: transport time from dephosphorization / desulfurization station to hot metal discharge site (minutes), α: temperature drop coefficient (° C / minute), ΔTb: mixed iron wheel to converter charging pot Of the hot metal temperature due to the transfer of the hot metal (minute).

Here, ΔT is generally a value of about 35 to 45 ° C. Hot metal in the preliminary process, the temperature target value T ₁ of the pretreated hot metal as described above is set by the T ₂ and the [Delta] T, is performed to adjust the hot metal temperature. The reason for this is
When the temperature of the pre-treated hot metal M 'is higher than (ΔT + 1270 ° C. (upper limit of T ₂ )), a high dephosphorizing ability cannot be obtained, while the temperature is lower than (ΔT + 1220 ° C. (lower limit of T ₂ )). If the temperature of the hot metal M "when discharged into the furnace charging pan is lower than 1220 ° C., the amount of metal ingot by the hot metal M" increases.

In the hot metal pretreatment method according to the present invention, when adjusting the carbon concentration, when increasing the carbon concentration in the hot metal, carbon powder or the like is added as a carbon source. As an addition method of the carbon powder, an injection method in which the carbon powder is blown into the hot metal together with nitrogen gas using a flux lance is preferable.
The method of dropping carbon powder from the hopper above the hot metal of the mixed iron wheel and adding it to the hot metal is not preferable because the carbon powder easily burns in the air during the fall, the yield of the carbon powder is poor, and the amount of carbon powder varies widely. On the other hand, when lowering the carbon concentration in the hot metal, an oxidizing agent such as iron ore powder or gaseous oxygen such as pure oxygen is used to oxidize C and separate it from the hot metal as a CO gas to drive out.

The hot metal temperature is controlled by adjusting the supply amounts of gaseous oxygen as an oxygen source required for dephosphorization and a solid oxidant such as iron ore powder. When raising the hot metal temperature, gaseous oxygen such as pure oxygen is used to raise the temperature of the hot metal due to heat generated by an oxidation reaction. On the other hand, when lowering the hot metal temperature, an oxidizing agent such as iron ore powder is used to lower the hot metal temperature by endothermic heat generated by the reduction reaction.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the hot metal pretreatment method according to the present invention, temperature measurement and component measurement are performed on hot metal M after desiliconization, and hot metal temperature T ₀ , carbon concentration C ₀ ,
The measurement data such as the phosphorus concentration P ₀ is obtained, and thereafter, gaseous oxygen (pure water) as an oxygen source required for dephosphorization is obtained from the following equation which is created based on the analysis of the past operation data and input to the computer. The amount OG of oxygen) and the amount OM of iron ore powder as a solid oxidizer are determined, and the injection amount CM of carbon powder used for adjusting the carbon concentration is determined.

[0017]

(Equation 2)

In these equations, P₀: Not pre-treated
Phosphorus concentration of pig M, P₁： Phosphorus of pretreated hot metal M '
Concentration (target phosphorus concentration), T₀: Temperature of unpretreated hot metal M
Degree, T ₁: Target temperature of pretreated hot metal M ', C₀: Not yet
Carbon concentration of hot metal M, C₁: Charcoal of pretreated hot metal M '
Element concentrations, a1, a2, a3, b1, c1, and d1: constants.

[0019]

Embodiments of the present invention will be described below. The value of the hot metal temperature drop amount ΔT from completion of the hot metal pretreatment to being discharged into the converter charging pan is ΔT = ΔTa + ΔTb.
= 100 (min) x 0.17 (° C / min) + 23 ° C = 40 ° C
In order to set the temperature of the hot metal M ”when discharged into the converter charging pan to be in the range of T ₂ : 1220 to 1270 ° C,
The target temperature value of the pre-treated hot metal (hot metal after the hot-metal pre-treatment) M ′ is T ₁ = [ΔT + (1220 ° C. + 1270 ° C.) /
2] = 1285 ° C. In addition, pre-treated hot metal M '
Is the target value C ₁ of the carbon concentration of C ₁ = [(4.0 mass% +
4.3 wt%) / 2] = 4.15 and% by weight, the target value P ₁ of the phosphorus concentration was 0.020 wt%.

Under the conditions of the present invention for each hot metal after the desiliconization was completed, and as a comparative example, hot metal M "when discharged into the converter charging pan was as shown in Table 1 Pre-treatment was performed.

[0021]

[Table 1]

Then, the temperature of the hot metal M "when it was discharged into the converter charging pan and the carbon concentration of the hot metal M" were measured.
In addition, for each hot metal pretreatment, after the completion of charging of the hot metal from the converter charging pan to the converter, the amount of metal ingot in the pan was measured, and the metal adhesion rate was determined from the result. Here, the metal deposition rate =
(Amount of metal ingot / Rated hot metal in converter charging pot). FIG. 1 shows the results of the metal adhesion rate.

FIG. 2 shows the relationship between the measured temperature of the pretreated hot metal M 'and the dephosphorization ability. FIG. 2 shows the dephosphorization ability Lp in the case of basicity = 4, which is a normal basicity value in the hot metal pretreatment. The dephosphorization capacity, so-called slag - distribution value of P between hot metal _{{(% P 2 O 5)} / [% P]}
And the logarithm of this is defined as the dephosphorization capacity Lp.

From FIG. 1 described above, in any of the three hot metal temperature ranges of the hot metal M "when the hot metal is discharged into the converter charging pan, the carbon concentration is defined as 4.0 to 4.0.
In the range of 3% by mass, the metal deposition rate is low (for comparison, the temperature condition T ₂ : 1 of the hot metal M ″ defined in the present invention is 1).
A carbon concentration of 3.8% by mass at 220 to 1270 ° C.,
The gold deposition rates at 3.9% by mass and 4.4% by mass are plotted). In addition, the higher the temperature of the hot metal M ″, the lower the metal adhesion rate, and Comparative Example 2 showed the least metal adhesion. However, regarding dephosphorization, the pretreated hot metal M ′ was used.
The lower the hot metal temperature is, the more dephosphorization is promoted. In Comparative Example 2, the dephosphorization ability Lp is reduced although the amount of deposited metal is significantly small. On the other hand, in the example of the present invention, as shown in FIG. 2, a high dephosphorization ability having an Lp value of 150 or more can be obtained, and as shown in FIG. The amount has been achieved, and both high dephosphorization ability and low metal deposition rate can be optimized.

Next, a comparison was made between the present invention example and the conventional method example. Here, in the present invention, the target temperature T ₁ of the pretreated hot metal M ′ is 1285 ° C., the temperature drop ΔT: 40 ° C., the target carbon concentration C _{1 of the} pretreated hot metal M ′ is 4.15 mass%, And the target value P ₁ of the phosphorus concentration of the hot metal M ′: 0.0
This is a case where the hot metal pretreatment is performed at a setting of 20% by mass. Also, unlike the method of the present invention, the conventional method has a hot metal temperature T ₂ : 1220 when dispensed into the converter charging pan.
The temperature adjustment and the carbon concentration adjustment of the pre-treated hot metal are not performed so that the temperature of the hot metal falls within the range of 1270 ° C. and the carbon concentration of the hot metal falls within the range of C ₁ : 4.0 to 4.3 mass%.

FIG. 3 is a histogram of the carbon concentration of the hot metal M ″ discharged into the converter charging pan according to the present invention and the conventional method. FIG. 4 is a histogram of the present invention and the conventional method. 5 is a histogram of the temperature of the hot metal M ″ discharged into the converter charging pan in FIG. As shown in FIGS. 3 and 4, according to the present invention, the carbon concentration of the hot metal M ″ discharged into the converter charging pan can be controlled within the range of 4.0 to 4.3 mass%, The temperature of the hot metal M "can also be controlled within the range of 1220 to 1270C.

FIG. 5 is a diagram showing an example of a comparison result of the metal adhesion rate and the like between the present invention example and the conventional method example. As shown in the figure, in the conventional method example, the base metal adhesion rate was 2%.
On the other hand, in the present invention example, the ingot adhesion rate becomes 0.8%, which is half that of the conventional case, and the hot metal temperature can be dephosphorized on the low temperature side which is advantageous for dephosphorization. In comparison, the amount of the dephosphorizing flux (refining agent) used was reduced by 3%.

[0028]

As described above, according to the hot metal pretreatment method according to the present invention, in the hot metal pretreatment for dephosphorizing and desulfurizing the hot metal after desiliconization, the pretreated hot metal after the hot metal pretreatment is completed. Is transported and discharged into the converter charging pan, the hot metal temperature is in the range of 1220 to 1270 ° C, and the carbon concentration of the hot metal is in the range of 4.0 to 4.3 mass%. In this way, the hot metal temperature and the hot metal carbon concentration are adjusted to perform hot metal pretreatment, so that the hot metal temperature can be dephosphorized at a low temperature, which is advantageous for dephosphorization. As a result, the amount of flux used for dephosphorization can be reduced and the cost can be reduced. Molten steel productivity It is possible to avoid the deterioration.

[Brief description of the drawings]

FIG. 1 is a graph showing the ingot adhesion rates in the present invention example and a comparative example.

FIG. 2 is a graph showing a relationship between a measured temperature value of pretreated hot metal and a dephosphorization ability.

FIG. 3 is a histogram of the carbon concentration of the hot metal discharged into the converter charging pan in the present invention example and the conventional method example.

FIG. 4 is a histogram of the temperature of hot metal discharged into a converter charging pan in the present invention example and the conventional method example.

FIG. 5 is a diagram illustrating an example of a comparison result of a base metal adhesion rate and the like between the present invention example and the conventional method example.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ikuo Hoshikawa 1 Kanazawacho, Kakogawa-shi, Hyogo Prefecture Kobe Steel Works Kakogawa Works F-term (reference) 4K014 AA01 AA02 AA03 AC16 AD01 AD17

Claims (2)

[Claims] 1. A hot metal pretreatment method for dephosphorizing and desulfurizing a hot metal that has been desiliconized, wherein the preprocessed hot metal that has undergone the hot metal pretreatment is transported and discharged into a converter charging pan. The hot metal temperature of T ₂ is in the range of 1220 to 1270 ° C., and the carbon concentration of the hot metal is C ₁ : 4.0 to 4.0.
This is a method of pre-treating hot metal so as to be in a range of 4.3% by mass, and assuming that the temperature drop of hot metal until the pre-processed hot metal is discharged into the converter charging pan is ΔT, the temperature target of the pre-processed hot metal is defined as ΔT. The value T ₁ is set by the T ₂ value and the ΔT value, and the hot metal temperature is adjusted, and the carbon concentration is adjusted so that the carbon concentration of the pre-treated hot metal becomes the value C _1. Hot metal pretreatment method. 2. The hot metal pretreatment method according to claim 1, wherein the adjustment of the hot metal carbon concentration is performed by blowing carbon powder into the hot metal by an injection method or adding an oxygen source.