JPH0559420A - Method for pre-treating molten iron - Google Patents

Abstract

PURPOSE:To efficiently and precisely control the aimed component values after treating by deciding the blended quantity of flux so as to satisfy all of molten iron condition before pre-treating, the aimed component values after treating and the treating condition. CONSTITUTION:At the time of removing by priority of P and S in molten iron containing <=0.6wt.% Si and <=0.8wt.% Mn, by using both equations of de-P ratio =K1+f1+f2+f3 and de-S ratio =K2+f4+f5+f6, the pre-treating condition is decided. In the equations, K1, K2: constants, f1, f4: molten iron condition before treating, f2, f5: flux conditions, f3, f6: conditions of de-P and de-S. By this method, standard deviation of the P and S contents after pre-treating is made to <=3.5X10<-3> (%) to each. Oxygen used to removal of P in the molten iron is combined with Si and Mn and de-Si and de-Mn reactions are developed by priority to the de-P reaction and the de-P reaction efficiency is restrained. The produced SiO2 and MnO at this time, lower the basicity of the slag, and de-S reaction is restrained.

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 method, and in particular, in the de-P and de-S treatment, it is possible to accurately and economically control the [P] and [S] component values after the pre-treatment. Related to a pretreatment method capable of

[0002]

2. Description of the Related Art Since the composition of hot metal has a great influence on the refining efficiency in the steel making process such as a converter and the quality of the steel, it is necessary to prepare for the removal of P, S and Si depending on the composition of the hot metal and the type of steel produced. Processing is performed. In this hot metal pretreatment, as a method for removing [P] and [S] in the hot metal, generally, P removal is performed.
It is carried out by injecting the agent and the S-removing agent into the hot metal or utilizing the metal slag reaction while stirring with an impeller or the like. Further, recently, in order to further improve the quality, the demand for low P and low S is expanding, and the hot metal pretreatment process occupies an important position. [P] after pretreatment,
Increasing the accuracy of controlling the [S] component is essential in the steelmaking process.

On the other hand, in the actual operation, various operating conditions are used, which causes a lot of variations in processing reaction. Therefore, in the present situation, the P removal required to control the target post-processing component values ([P], [S])
There is an economical problem because it is necessary to set the composition and amount of the agent and the S-removing agent flux at the upper limit of the variation. On the contrary, if economic efficiency is emphasized, the ability to control the post-treatment component value will be inevitably reduced.

[0004]

SUMMARY OF THE INVENTION In view of the actual situation as described above, the present invention, in order to solve the problems of dispersion of component values after treatment in actual operation and economical problems, hot metal conditions before pretreatment, It is intended to propose a hot metal pretreatment method capable of determining a necessary and sufficient flux blending amount that satisfies all target components and treatment conditions after treatment.

[0005]

Means for Solving the Problems The present inventor investigated the causes of variations in the hot metal pretreatment reaction and analyzed variously. As a result, the behavior of [P] and [S] in the pretreatment (de-P ratio, de-S rate)
The ratio is the hot metal condition before treatment: components (C, Si, Mn, P, S
Etc.), temperature, amount composition of de-P agent and de-S agent added, amount Reaction conditions: close relationship with stirring time, impeller rotation speed, etc. in case of impeller system, blowing speed, blowing time, etc. in case of injection system I found out that there is. Therefore, in order to accurately control the target treatment components ([P] and [S]), it is necessary to determine the composition and amount of the de-P agent and the de-S agent by a method that satisfies all of these conditions. is there.

Based on the above findings, the present invention has found a certain relationship between the P removal rate and S removal rate at the time of hot metal pretreatment and the above-mentioned factors (1) to (3), and arrived at the invention. That is, according to the present invention, P and S are preferentially removed by adding a de-P agent and a de-S agent to hot metal containing Si content of 0.6 wt% or less and Mn content of 0.8 wt% or less. Method, the treatment conditions are determined using the following formula, and the standard deviations of P and S contents after treatment are 3.5 × 10 5
^The gist is to be ^-3 (%) or less and 1.5 x 10 ^-3 (%) or less.

De-P rate = K ₁ + f ₁ + f ₂ + f ₃ De-S rate = K ₂ + f ₄ + f ₅ + f ₆ where K ₁ and K ₂ are constants f ₁ and f ₂ are hot metal conditions before treatment f ₂ , F ₅ is the condition of flux f ₃ and f ₆ is the condition of de-P and de-S reaction

[0008]

In the present invention, the content of [Si] and [Mn] is limited because it is a condition necessary for preferentially removing [P] and [S] over other components. That is, the Si content is 0.6% by weight or less, and the Mn content is 0.
Under the condition of 8% by weight, [O] (solid oxygen or gaseous oxygen) used for removing [P] in the hot metal is [S].
i] [Mn], so that the Si removal and Mn removal reactions occur preferentially over the P removal reaction, and as a result, the P removal efficiency is suppressed. In addition, the SiO ₂ and MnO produced at that time lower the basicity of the slag and also suppress the de-S reaction. For the above reasons, the contents of [Si] and [Mn] are limited.

As a method of promoting the reaction between slag and metal in the de-P and de-S methods, there are an injection method in which a flux is directly blown into the hot metal to cause a reaction, or a method in which the flux is added onto the hot metal and forcedly stirred by an impeller or the like. Either is fine.

The standard deviations of the P and S contents after the treatment are 3.5 × 10 ⁻³ (%) or less and 1.5 × 10 ³ respectively.
^-3 (%) or less is due to the following reasons. That is, the hot metal pretreatment (P removal and S removal) is an essential process for producing low P and low S steels in the current steelmaking process. Therefore, in the actual operation, the fluctuation of the hot metal component after the pretreatment, especially [P] with respect to the target value,
When [S] becomes a higher component, the de-P and de-S pretreatment is performed again, or the de-P and de-S treatment is performed at the time of converter blowing which is the next step of the pre-treatment. It is necessary to break it. When such a case occurs, in actual operation, the schedule will be significantly changed or the processing cost will be significantly increased. Therefore, the above-mentioned upper limit value of the standard deviation is set for the purpose of preventing the operation hindrance and suppressing the cost increase.

The contents of the relational expression for determining the processing conditions are as follows, for example. K ₁ = 185.9 f ₁ = −59.4X ₅ + 283.0X ₇ −253.0X ₈ − with respect to the P removal rate.
0.116X ₉ f ₂ = 0.098X ₃ -2.502X ₄ + 0.177X ₁₀ f ₃ = -0.007X _{2 With} respect to the de-S ratio, K ₂ = 159.7 f ₄ = -18.0X ₅ +17 .2X ₆ -34.0X ₇ -11
_{20X 8 -0.015X 9 f 5 = 0.914X} 3 + 7.12X 4 f 6 = -2.414X 1 -0.016X 2 wherein, X _1: throughput (hot metal by weight) (T / pan) X ₂ : impeller rotational speed X _3: quicklime (Kg / T) X _4: fluorite amount (Kg / T) X _10: de-Si sintered ore weight _{(Kg / T) X 5:} [% Si] in ( pretreatment) X ₆ : [% Mn] in (before treatment) X ₇ : [% P] in (before treatment) X ₈ : [% S] in (before treatment) X ₉ : hot metal temperature before treatment (° C.)

When carrying out the pretreatment of the hot metal according to the present invention, the P removal rate from the target post-treatment component and the target pre-treatment component,
By obtaining the S removal rate and determining the reverse flux condition, it is possible to minimize the variation in the processing reaction and to perform the efficient processing.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view showing an example of the hot metal pretreatment process of the present invention, 1 is a ladle, 2 is an impeller for stirring,
3 is a slag scrap.

That is, in this hot metal pretreatment process, in order to efficiently and preferentially carry out P removal and S removal, a method of performing Si removal treatment with a Si removal agent before the P removal treatment was adopted. It should be noted that the [S
i] When the content is sufficiently low, the Si removal treatment can be omitted. Further, iron oxide-based flux was used as the P-removing agent, quicklime-based flux was used as the S-removing agent, and fluorspar was used as the slag slag formation accelerator.

FIG. 2 shows the relationship between the actual desulfurization rate before and after the treatment and the quicklime-based flux basic unit in this embodiment, and FIG. 3 shows the actual desulfurization rate before and after the treatment and the estimated desulfurization rate obtained by the relational expression of the present invention. The relationship of each is shown. From FIG. 2 and FIG. 3, it was confirmed that the correlation with the S removal rate obtained by the relational expression of the present invention was improved and the variation before and after the treatment was drastically reduced rather than the correlation with only the basic unit of the S removal agent.

Similarly, FIG. 4 shows the relationship between the actual de-P ratio before and after the treatment and the basic unit of the de-P-agent in this embodiment, and FIG. 5 is obtained by the actual de-P ratio before and after the treatment and the relational expression of the present invention. The relationship of the estimated P removal rate is shown respectively. Also in this P removal treatment, as is clear from FIGS. 4 and 5, the P removal determined by the relational expression of the present invention rather than the correlation of the P removal agent basic unit alone.
It was confirmed that the correlation with

Table 1 shows the control accuracy of the components after the treatment of the present invention before and after the application of the present invention, and the P removing agent and S removing agent.
By comparing the actual use of the agents, it can be seen that the application of the present invention enables accurate and economical treatment. Therefore, by grasping the operating condition factors having a high degree of influence as in the relational expressions for obtaining the de-P rate and the de-S rate of the present invention before the treatment and determining the composition and amount of the de-P and de-S agents, the efficiency After treatment, the components can be controlled accurately and accurately.

[0018]

[Table 1]

[0019]

As described above, according to the method of the present invention, when P and S are preferentially removed by the pretreatment, all the hot metal conditions before the treatment, the target components after the treatment and the treatment conditions are satisfied. Since the necessary and sufficient flux blending amount can be determined, it is possible to control the target post-treatment component value efficiently and accurately at low cost, which is a great effect.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a hot metal pretreatment process of the present invention.

FIG. 2 is a record S before and after processing in an embodiment of the present invention.
It is a figure which shows the relationship between a rate and a quicklime-based flux basic unit.

FIG. 3 is a diagram showing the relationship between the actual S / S ratio before and after the processing and the estimated S / S ratio obtained by the method of the present invention in the same embodiment.

FIG. 4 is a diagram showing the relationship between the actual P removal rate before and after the treatment and the P removal agent basic unit in the same example.

FIG. 5 is a diagram showing the relationship between the actual P removal rate before and after the processing and the estimated P removal rate obtained by the method of the present invention in the same embodiment.

[Explanation of symbols]

 1 Ladle 2 Impeller for stirring 3 Slag scratch

Claims (1)

[Claims] 1. A Si content of 0.6% by weight or less, and M
In a method for preferentially removing P and S by adding a P-removing agent and a S-removing agent to hot metal having an n content of 0.8% by weight or less, pretreatment conditions are determined using the following formulas, and pretreatment is performed. The standard deviations of the P and S contents after 3.5 × 10
^-3 (%) or less and 1.5 x 10 ^-3 (%) or less, a hot metal pretreatment method. De-P rate = K ₁ + f ₁ + f ₂ + f ₃ De-S rate = K ₂ + f ₄ + f ₅ + f ₆ where K ₁ and K ₂ are constants f ₁ and f ₄ are hot metal conditions before treatment f ₂ and f ₅ Is the flux conditions f ₃ and f ₆ are the de-P and de-S reaction conditions