JP2002327209A - Smelting method in converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blowing method which enables both high refining performance of dephosphorization and a stable operation, in a blowing process for decarbonization in a converter for smelting a high-carbon steel (%C>=0.1 when having stopped the decarbonization and the blowing). SOLUTION: Quantity of T.Fe(FeO) in slag is determined by the balance of formation and annihilation of T.Fe(FeO), where a formation speed of T. Fe(FeO) in slag is assumed to be proportional to a product of an oxygen feeding speed (F02 ) and an area of reaction interface between gaseous oxygen and molten pig iron (an ignition point area: S), and an annihilation speed to be proportional to squares of F02 . The smelting method is characterized by setting the ratio of the formation speed to the annihilation speed, F02 /S, to be in the range of 2,100-26,000 (Nm<3> /hr.m<2> ), to control T.Fe in the slag. Then, a stable operation becomes compatible with high smelting performance of dephosphorization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a refining process (particularly, T.Fe in slag) for decarburization blowing of a converter at the time of melting high carbon steel (mass% C at the time of decarburization blow-off). The present invention relates to a converter refining method with high control accuracy.

[0002]

2. Description of the Related Art In recent years, the LD-ORP method for removing hot metal in a converter for the purpose of reducing fixed costs has become widespread. In this method, after de-P refining in a converter, the molten metal is once discharged into a pot, and then hot metal is charged into the converter again to perform de-C refining. Time will take a long time.

Here, regarding the decarbonization behavior in the converter steelmaking process, the progress of the decarbonization reaction during blowing has been represented by a trapezoidal model as shown in FIG. It is said to be divided into. The features are as follows. Region-I: A region in which oxidation of Si occurs preferentially over oxidation of C. Region-II: A region in which oxidation of C occurs preferentially, and the de-C reaction is controlled by oxygen supply. Region-III: De-C reaction. Is the rate at which the supply of C is controlled and the de-C rate decreases.On the other hand, conventionally, it has been thought that T.Fe in slag, which is an important index for refining control of converter blowing, depends on L / L ₀ . .
Generally, T.Fe in the slag is reduced with increasing L / L _0, L /
It is thought that T.Fe in slag increases with a decrease in L ₀ . Incidentally, L / L ₀ is generally used as an index of the stirring strength of molten steel, L ₀ represents a bath depth, L represents a dent depth of the bath, and L
Is calculated by equation (1). L = L _h0 · exp (−0.78 · h / L _h0 ) ……………… (1) L _h0 = 63.0 (F _O2 / (nd / k)) ^2/3 ……………… ( 2) However, L ₀ : Bath depth (mm) L: Bath dent depth (mm) h:
Lance height (mm) L _h0 : Cavity depth when lance height h = 0 F _O2 : Acid feed rate (Nm ³ / hr.) N: Number of lance holes d: Nozzle diameter (mm) k: Porous Coefficient by nozzle inclination angle

[0004]

Table 1 shows the transition of metal components when high carbon materials are melted by the LD-ORP method. As shown in Table 1, hot metal after de-P C concentration of about
It has a high concentration of 3.7%, and Si is tr.
In the de-C blowing with the D-ORP method, the de-C reaction proceeds under the oxygen supply rate-determining conditions according to Region-II. That is, LD-
In the decarburization blowing period of the ORP method, the decarbonization reaction mainly occurs from the beginning,
Since the reaction is rate-controlled by oxygen supply, it is essential to increase the acid feed rate in order to shorten the time of de-C blowing as part of the time reduction of the LD-ORP method.

[0005]

[Table 1]

[0006] The de-C blowing time can be shortened by increasing the acid feed rate as described above.
(2) L / L ₀ increases due to the increase in acid feed rate,
T. Fe decreases, and as a result, sufficient P removal ability cannot be secured, and it becomes difficult to melt low P steel. On the other hand, if the amount of T.Fe in the slag is excessively increased in order to ensure the removal of P, it is considered that slopping occurs and stable operation becomes difficult.

[0007] As described above, the problem in shortening the time of de-C refining is to control the amount of T.Fe in the slag that is appropriate to ensure both the removal of P and the suppression of slopping.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. That is, the gist is as follows. (1) A method for refining a converter in which the carbon concentration at the end point is 0.1% by mass or more, wherein T.Fe in the slag is controlled based on _FO2 / S.

However, F _O2 ; acid supply rate (Nm ³ / hr.)
S; Fire area (m ² ) (2) The converter according to (1), wherein the FO ₂ / S is refined in a range of 21000 to 26000 (Nm ³ /hr.·m ² ). Refining method.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors increased the acid feeding rate by changing the lance tip, etc. to increase the test level-1 (Table 2).
In the test carried out, L / L ₀ and the results of examining the relationship between T.Fe in the slag, the slag with increasing L / L ₀ as shown in FIG. 2
T.Fe also increased, showing a tendency different from the conventional findings, and accompanying this, slopping also occurred. The present inventors have analyzed the factors that caused the phenomenon different from the conventional knowledge, and the results are as follows.

[0011]

[Table 2]

There are two differences between this test and the conventional operation.
One is that the acid supply rate is increased, and the other is that the lance gap is increased to make L / L ₀ uniform, and the resulting fire area is increased. That is,
Fire point area with oxygen-flow-rate to the L / L ₀ is constant is changed. Therefore, Figure 3 shows the average acid feed rate and the
Figure 4 shows the relationship between T.Fe and the average fire point area and T.Fe in slag.
The relationship was shown. For the fire area, using the average acid feed rate and average lance gap, as shown in FIG. 5, based on a schematic diagram for deriving the fire area, equation (3)
To (6).

L _S = (4.12 × P ₁ −1.86) × R ₀ where | P ₀ −P ₁ | / P ₀ ≦ 0.1 ……………… (3) L _S = (3.52 × P ₁ − 1.26) × R _{0 where, | P 0 - P 1 |} / P 0> 0.1 ..................... (3) 'L G = cosα × (L S + L F) ..................... ( _{4) R 2 = 2.26 × R} 1 ..................... (5) R 3 = R 2 + L F · tan β ..................... (6) However, L _G: lance gap L _S: Supersonic region length L _F : Free jet length R ₀ : Slot diameter R ₁ : Slot outlet diameter R ₂ : Supersonic tip diameter R ₃ : Fire point diameter P ₀ : Lance design pressure P ₁ : Sloat inlet pressure α: Lance throat angle β: Spread angle in free jet From Fig. 3 and Fig. 4, it can be seen that T.Fe in the slag has increased due to the increase in acid feed rate and fire area. I understand. So Fe
The generation behavior of O was examined in consideration of the reactor reaction during converter blowing.

FIG. 6 is a schematic view showing a reaction mechanism in the furnace. Oxygen supplied to the surface of the hot metal reacts with Fe in the molten iron to generate FeO within a flash point. The produced FeO moves to the emulsion phase in which slag and granular iron are mixed, and reacts with C in the molten iron by stirring the emulsion phase of the upper blowing oxygen. These reactions are shown in the following formulas (7) to (9). 2Fe + O ₂ → 2FeO (7) FeO + C → Fe + COC (8) O ₂ + 2C → 2CO ((9) Blowing of high carbon steel Assuming that the reaction inside is mainly represented by the above three formulas, the following hypothesis was made on the mechanism of T.Fe generation and disappearance in slag, and the mechanism of de-C reaction,
This phenomenon will be described. Production of FeO: The reaction represented by the formula (7) occurs at the fire point, and FeO is produced. (1) Considering the ignition point area as the reaction interface area between iron and oxygen, FeO
Is proportional to the fire area. (2) The generation rate of FeO increases with an increase in the acid supply rate. Disappearance of FeO: Most of the FeO generated at the flash point moves to the emulsion phase, and FeO reacts with C in the metal by stirring the bath and is reduced (Equation (8)). The rate of the reduction depends on the stirring power of the bath.

[0015] It is considered that the de-C reaction of the formula (9) occurs near the fire point. In this test, L / L ₀ at the beginning of the strong stirring blowing period and at the end of the weak stirring blowing period were the same as before, and the change timing was changed to the first half, the middle, and the second half of the conventional operation. Therefore, the stirring power is generally equal or slightly stronger, and the reduction reaction of FeO is considered to be about the same or to proceed faster than before. On the other hand, it is conceivable that the FeO concentration is increased as compared with the conventional art due to the increase in the acid transfer rate and the fire area. Here, assuming that the FeO concentration in the slag is determined by the speed difference between its generation and extinction, in this test, the reason for the excess T.Fe in the slag is as follows:
It is considered that FeO generated at the fire point was generated in large amounts due to an increase in the acid supply rate and the fire area, and the generation rate was faster than the disappearance rate of FeO by reduction. Hereinafter, each reaction rate is formulated.

Generally, the kinetic energy-E is represented by the following equation (10). E = 1/2 · m · v ² ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… Corresponds to F _O2 , and the kinetic energy -E _t of the top-blown gas is proportional to the square of F _O2 . Further, the stirring energy because it is necessary to consider the stirring of the slag by the bottom blown gas - when the the E _b, stirring energy of slag - can be represented by the sum of E _t and E _b. However, when smelting high carbon steel, since the bottom blown gas operates at a low flow rate (about 1/10 of the stirring energy of the top blown oxygen), the elimination rate R ( Annihilation) can be expressed by a function of the square of _FO2 as in equation (11). R (extinction) ∝E _t + E _b ∝α · F _O2 ² ……………… (11) where E _t : stirring energy of the top-blown gas E _b : stirring energy of the bottom-blown gas-FeO Since the iron oxidation reaction is represented by equation (7), the formation rate of FeO R (generation) (= d [FeO] / dt)
Is expressed as follows. R (generation) = d [FeO] / dt = S / V ・ k ・ [Fe] ・ [O] …………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… Rate constant [M]: concentration of substance M Here, the concentration of iron and the volume are almost constant
The generation rate of FeO can be approximated as being proportional to the product of S and [O], that is, the flash area S and the acid supply rate F _O2 , and is expressed by equation (12) ′. R (generation) ∝S · F _O2 ……………… (12) 'We thought that the FeO concentration could be expressed by the ratio of the speed of its generation to its extinction, and decided to show the blowing index by these ratios. . R (extinction) / R (generation) ∝α · F _O2 ² / (S · F _O2 ) = F _O2 / S ………………………………………………………………………………………………… (13) (13) F _O2
The relationship between F _O2 / S and T.Fe in the slag is shown in FIG. 7, and it can be seen that T.Fe in the slag increases with decreasing F _O2 / S. Decrease of F _O2 / S is increased production rate of FeO, or means a decrease in the extinction rate, as a result, it is reasonable exhibit a tendency T.Fe in the slag increases. From the above knowledge, high-precision converter refining becomes possible by performing refining control based on F _O2 / S.

[0017]

EXAMPLE A test was conducted in which high carbon steel was melted with various changes in _FO2 / S. The test method was the same as Test Level-1, and the test was performed in the range shown in Test Level-2 (Table 3).

[0018]

[Table 3]

FIG. 8 shows the relationship between the acid feed rate and the C removal rate, and FIG. 9 shows the relationship between the T.Fe in the slag and the P distribution ratio together with the results of Test Level-1. The de-C rate increased with increasing acid-feed rate, as in Test Level-1. Further, the distribution ratio of P depends on T.Fe in slag, and T.Fe in slag ≧
It was found that the P distribution ratio equivalent to the conventional one can be obtained by securing 8.

Next, FIG. 10 shows the relationship between F _O2 / S and T.Fe in the slag, and FIG. 11 shows the relationship between F _O2 / S and the occurrence of slopping. Note that the degree of slopping in FIG. 11 means the magnitude of the occurrence of slopping observed during the test, and Table 4 shows the definition thereof. When the score is ≤1, it is a range in which the operation can be performed stably, and when the score is 2, the slopping is slightly large, so that the frequency must be reduced. Rating = 3
It will be impossible to operate, so it is necessary to avoid it. As shown in FIG. 11, it can be seen that the T.Fe in the slag increases with the decrease in F _O2 / S, and the degree of slopping increases accordingly.

[0021]

[Table 4]

In FIG. 8 to FIG. 11, the term "test" refers to the test result of the test level-2 and the test level-1.
Means that the test results are also shown. First
The mechanism of FeO generation has been described. First, the relationship between the hot spot area and the T.Fe in the slag is shown in Fig. 12 for data in which the acid transfer rate and the stirring force are almost the same as those in the conventional operation. T.Fe is increasing. That is, as described above, it is found that the generation of FeO depends on the area of the fire point.

On the other hand, the relationship between the acid feed rate and the T.Fe in the slag is shown for the case where the fire area is about the same as the conventional operation.
As shown in Fig. 13, the higher the acid transfer rate, the lower the T.Fe in the slag. By the way, FIG. 14 shows the relationship between the acid feeding speed and the stirring power at this time, and it can be seen that the stirring power increases with the acid feeding speed. In other words, when the acid supply rate is increased, the generation rate of FeO is increased, while the disappearance rate of FeO is also increased due to the increase of the stirring force. Under the conditions of this test, the disappearance rate exceeds the production rate. it is conceivable that. If the lance shape is changed and it becomes possible to increase only the acid supply rate under the same fire area and the same stirring force, it can be inferred that T.Fe in the slag increases with the increase. .

As described above, a strong correlation was found between F _O2 / S and T.Fe in the slag, so that it is possible to control T.Fe to a more appropriate value by using this F _O2 / S as an index. Understand. Further, as a blowing design using this F _O2 / S as an index, a study was made on the melting of low-P steel. P distribution ratio required for melting low P steel
Since it is necessary T.Fe ≧ 8 in order to obtain 50, from FIG. 10 F _O2
/ S ≦ 26000 is a necessary condition. On the other hand, from FIG. 11, if the degree of slopping is allowed up to the degree of slopping = 2, the necessary condition is F _O2 / S ≧ 21000. That is, 21000
≦ F _O2 / in a range of from S ≦ 26000, can be obtained T.Fe in the slag necessary for de P with minimal slopping occurred.

[0025]

According to the present invention, the blowing time of de-C blowing when melting high carbon steel is shown in FIG.
5 By applying the method of the present invention, high-speed blowing was enabled, and the time required for de-C blowing was reduced by about 3 minutes.

[Brief description of the drawings]

FIG. 1 is a diagram showing a trapezoidal model of de-C blowing.

FIG. 2 is a diagram showing a relationship between L / L ₀ and T.Fe in slag.

FIG. 3 is a diagram showing a relationship between F _O2 and T.Fe in slag.

FIG. 4 is a view showing a relationship between a fire area and T.Fe in slag.

FIG. 5 is a schematic diagram for deriving a fire area.

FIG. 6 is a schematic view showing a reaction mechanism in a furnace.

FIG. 7 is a view showing the relationship between F _O2 / S and T.Fe in slag.

FIG. 8 is a diagram showing a relationship between F _O2 and a de-C rate.

FIG. 9 is a diagram showing a relationship between T.Fe in slag and a P distribution ratio.

FIG. 10 is a diagram showing the relationship between F _O2 / S and T.Fe in slag.

11 is a diagram showing the relationship between the F _O2 / S and slopping occurrence.

FIG. 12 is a diagram showing a relationship between a fire area and T.Fe in slag.

FIG. 13 is a view showing the relationship between F _O2 and T.Fe in slag.

FIG. 14 is a diagram showing a relationship between F _O2 and a stirring force.

FIG. 15 is a diagram showing blowing times of a conventional operation and a high-speed blowing operation.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keiji Hata 1 Kimitsu, Kimitsu-shi, Chiba F-term in Nippon Steel Corporation Kimitsu Works (reference) 4K070 AB03 AB06 AB13 AB17 AC03 BA05 BA09 BA12 BA13 BB02 BC01 BC04 BD09 EA01 EA02 EA09

Claims (2)

[Claims] 1. A refining process of the converter in which the carbon concentration of 0.1 mass% or more of the end point, in the slag on the basis of the F _O2 / S
A refining method for a converter characterized by controlling T.Fe. However, F _O2 ; acid feed rate (Nm ³ / hr.) S; fire area (m
² ) Wherein said F _O2 / S is, 21000~26000 (Nm ³ / hr.
^{2. The} method for refining a converter according to claim 1, wherein the refining is performed within a range of m2).