JPS5827916A - Desiliconizing method for molten iron - Google Patents

Abstract

PURPOSE:To prevent heat loss occuring in the endothermic reaction by decomposition of iron oxide and to desiliconize molten iron while suppressing the decarburization reaction thereof in the preliminary desiliconizing stage of the molten iron by blowing the powder of iron oxide which is a desiliconizing agent with a specific amt. of gaseous oxygen into the molten iron. CONSTITUTION:Prior to refining of molten iron in a converter to make steel, the molten steel is preliminarily desiliconized to facilitate the succeeding dephosphorization reaction. As a desiliconizing agent, a powdery compsn. consisting essentially of Fe2O3 is blown into the molten iron, whereby the molten iron is desilionized. Here, gaseous oxygen as a carrier gas at 4-200Nl to 1kg of Fe2O3 which is the desiliconizing agent is blown into the molten iron. The temp. drop of the molten iron on account of endothermic reaction by decomposition of Fe2O3 is suppressed by oxidation reaction of Si owing to the presence of the gaseous oxygen. If the amt. of the gaseous oxygen is regulated in the above- mentioned range, the rate of decarburization by oxidation of C serving as a heat source during refining for steel making is decreased and the preliminary refining by desiliconization is effected efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot metal pretreatment method performed prior to refining in a converter or the like, and particularly to a desiliconization method for reducing silicon in hot metal.

As is well known, silicon in hot metal can be very quickly reduced by oxygen during a refining process such as converter blowing. However, if the silicon content in the hot metal is high at the start of converter blowing or at the start of dephosphorization as a preliminary treatment prior to converter blowing, the SiO2 concentration in the slag will increase and the slag will become a base. Degree CaO/Si
As a result, it becomes difficult to remove phosphorus from the hot metal. Therefore, especially when you want to obtain low phosphorus steel,
As a pre-process of converter blowing or a pre-process of dephosphorization treatment,
It is required to perform a so-called desiliconization treatment to reduce silicon.

By the way, various methods for desiliconizing hot metal have been developed in the past, such as adding a desiliconizing agent to the runner in the blast furnace hearth, and adding a desiliconizing agent after charging hot metal into a hot metal ladle. ,
Methods of promoting the reaction by mechanical stirring or gas stirring, and methods of blowing a desiliconizing agent into hot metal together with an inert gas are known. All of the desiliconizing agents used in these desiliconizing treatments are mainly composed of F.203.
・205 is decomposed to produce 02 as shown in the following equation (1).

3...(1) Fe2O5→2Fe+7-02 02 generated by this decomposition is consumed in the desiliconization reaction expressed by the formula (2).

Sl+02→sho.・・・・・・ （
2)7 However, while the desiliconization reaction in equation (2) is an exothermic reaction, the decomposition reaction in equation (1) is an endothermic reaction, so the lower the desiliconization reaction efficiency is, the lower the temperature of the hot metal will be. growing. FIG. 1 shows the amount of temperature drop corresponding to the desiliconization reaction efficiency when iron ore is injected into hot metal tons 13 to 18 together with an inert gas. From Figure 1, the amount of temperature drop in hot metal depends on the desiliconization reaction efficiency, and if the reaction efficiency is less than 80%, the temperature will drop, and if it is less than 50%, the temperature drop will be as much as 30 to 40 degrees Celsius. is clear. Normally, the desiliconization reaction efficiency is about 40 to 90 degrees, so in actual operation, a temperature drop occurs in most cases, and in extreme cases, the temperature drops by 40 to 90 degrees.
Since the temperature can drop by as much as ℃, the reality is that heat loss cannot be ignored in conventional desiliconization treatments.

In order to prevent heat loss during the desiliconization process as described above,
A method of blowing oxygen gas onto the surface of the hot metal bath during the desiliconization process (top blowing) has also been known, but in this method, the decarburization of the hot metal progresses due to the top blown oxygen gas, and as a result, the desiliconization process There is a problem that the C content of the subsequent hot metal decreases. That is, in the subsequent method, the C content decreases, resulting in the problem of insufficient heat source in converter blowing, etc., and it may become impossible to secure the necessary tapping temperature.

This invention was made in view of the above circumstances, and aims to provide a hot metal desiliconization treatment method that efficiently performs desiliconization while preventing heat loss and suppressing decarburization reactions. It is something.

That is, the desiliconization treatment method of the present invention includes F.20 in hot metal.
F・20.1kg of desiliconizing agent mainly composed of 4 to 2
The percentage indicates that it is blown in with a carrier gas having an oxygen content of 0ON-1J.

The hot metal desiliconization treatment method of the present invention will be explained in more detail below.

In the method of this invention, as mentioned above, Fe 203
A desiliconization agent mainly composed of F.203 is blown into hot metal together with a carrier gas containing a predetermined amount of oxygen.

As mentioned above, the F.203 injected into the hot metal decomposes as shown in the above formula (1) and generates 02, and the 02 contributes to the desiliconization in the above formula (2). Here, as shown in the above-mentioned FIG. 1, the amount of temperature drop due to F.203 injection depends on the desiliconization reaction efficiency, and as the desiliconization reaction efficiency increases, the temperature drop is prevented. Therefore, in this invention, a gas containing oxygen gas is used as a carrier gas for injecting the desiliconizing agent, and the desiliconizing reaction of the formula (2) is carried out also by the oxygen gas 02, thereby causing the injected F. The apparent effect of 203 is to improve the desiliconization efficiency and suppress the temperature drop. As a conventional measure to prevent temperature drop, spraying oxygen gas onto the bath surface may be considered, but in this case, as mentioned above, the decarburization reaction will proceed at the same time and the converter blowing process will be delayed. In some cases, this may lead to the problem of insufficient heat source. In contrast, the method of the present invention involves injecting oxygen-containing gas into hot metal, that is, into the hot metal at a certain depth below the hot metal bath surface, and decarburizing by the static iron pressure at that injection position. The reaction is suppressed, and as a result, a decrease in the carbon content of the hot metal after treatment is prevented, making it difficult for the above-mentioned problems to occur.In addition, by suppressing the decarburization reaction, the desiliconization reaction proceeds preferentially, increasing the desiliconization efficiency. Becomes good.

(5) By the way, when blowing oxygen gas into hot metal, the blowing lance tends to melt, and it has been thought that countermeasures for this, such as using a special and expensive lance, are necessary. However, when blowing oxygen together with a desiliconizing agent whose main component is F e 203, if the amount of oxygen gas is less than a certain amount, F
It is thought that the degree of melting loss even in a normal lance is reduced due to the endothermic effect caused by the decomposition of e203 (formula (1) above). Therefore, the present inventors conducted an experiment in which oxygen gas was injected into hot metal together with iron ore by varying the oxygen gas flow - brittleness and iron ore injection speed, and investigated the state of corrosion of the lance, as shown in Figure 2. The results shown are obtained. Second
From the figure, it is clear that when 7717 m1n of oxygen gas is injected, the lance will not be eroded if the iron ore injection rate is 50 kg/min or more. Since this iron ore is considered to be substantially Fe 205, lance erosion can be prevented by limiting the amount of oxygen blown to less than 200 kol of Fe2O31. If the oxygen content exceeds 200-13, there will be problems such as melting of the lance and the decarburization reaction will be accelerated as the temperature rises (6). For these reasons, in the desiliconization treatment method of the present invention, the upper limit of the amount of oxygen in the carrier gas blown together with the desiliconization agent is set at p 200 per kg of Fe2O5 in the desiliconization agent.
It was set as Nff1.

On the other hand, the lower limit of the amount of oxygen is determined as follows from the viewpoint of preventing the hot metal temperature from falling as described above. That is, the above (1)
If 02 is applied externally so that the calorific value due to the reaction of the above equation (2) is greater than the endothermic scene of the reaction of the equation (2), the temperature drop of the hot metal will be prevented, so the temperature drop will be prevented. The amount of oxygen required for
It is determined by the following equation (3) from the heat balance of the reaction in equation 2).

Vo2≧(0,193-0,210η) WF, 2o,
-=-(3) However, Vo2: Oxygen gas injection amount (N@7m
1n) WF@2o5: F・203 injection amount (kg/mi
n) η: Fe2O3 desiliconization reaction efficiency In equation (3), the reaction efficiency η varies depending on the blowing conditions, etc., but mainly depends on the hot metal temperature, the Si content before desiliconization, and the target S1 content, Hot metal temperature is 1250~1
Under normal conditions of 450℃ 40~90% (η-04~
A range of 0.9) is common.

When the reaction efficiency is 90% (η=09), from equation (3), vo
2≧0.004 WF, □. 3, the minimum amount of oxygen gas required to prevent temperature drop is 4N-ey for F(as 1 kg). Figure 3 shows the minimum amount of oxygen gas required to prevent temperature drop ( Compare the relationship between the critical 02 gas (li:) and the reaction efficiency with the theoretical value based on equation (3) and the actual value [
Indicated by ~. In Figure 3, there is a slight difference between the theoretical value and the measured value, but near 90% (η = 09), where the reaction efficiency is considered to be maximum under normal conditions, they almost match, and the critical 02 gas amount is around 4AA9. Therefore, even under actual operating conditions, it is necessary to inject at least 4 7 kg of oxygen gas even if the reaction efficiency is the best.

In carrying out the method of the present invention, the carrier gas to be blown in together with the desiliconizing agent does not need to be oxygen gas alone; nitrogen gas or inert gas and oxygen gas may be used as appropriate depending on the required blowing pressure, etc. It is sufficient to mix and blow in, in which case the oxygen gas in the mixed gas is 4 to 20ON-eAg-Fe2o
All you have to do is determine 3 tonal yōni blowing mikasu 1.

Furthermore, the desiliconizing agent used in the desiliconizing treatment method of the present invention may be a desiliconizing agent containing Fe 205 as a main component and that is used in conventional methods, such as fine powder of iron ore. or mill scale, etc. can be used, and Fe
In addition to 2O5, we also use CaO and CaF2 for slag, etc.
Of course, it may contain Na2CO3 or the like. However, it is desirable that the F@203 content of the desiliconizing agent be 60% or more.

Examples and comparative examples of this invention are described below.

Example: Fe2O390% in a 200 ton hot metal bath in a pig iron mixing car.
A desiliconizing agent containing Cation was blown in using a mixed gas of oxygen gas and nitrogen gas as a carrier gas.

Comparative Example 1 A desiliconizing agent similar to that described above was blown into a bath containing 200 tons of hot metal in a pig iron mixing car using nitrogen alone as a carrier gas.

Comparative Example 2 (9) While oxygen gas was being blown onto the surface of a 200 ton pig iron bath in a pig iron mixing car, nitrogen alone was used as a gas to blow the desiliconizing agent into the bath as described above. .

Other conditions in the above examples and comparative examples, as well as hot metal components and hot metal temperatures before and after the desiliconization treatment are shown in Table 1.

(10) H Mimaki', )8-27! J1G (4) From Table 1, according to the examples according to the present invention, a desiliconization amount of 0.31% was obtained, and the reduction in carbon content (the decrease in jl and the decrease in temperature 1) was extremely small. However, according to Comparison 01 which did not use oxygen gas, the amount of silicon removed was 0.24.
Despite efforts by the authorities, the temperature dropped by as much as 25 degrees Celsius. On the other hand, according to Comparative Example 2 in which oxygen gas was sprayed onto the bath surface, a desiliconization amount of 0.29% was obtained, but the carbon content decreased by as much as 0.19%, and the temperature decreased by 5. It was ℃. Therefore, it is clear that according to the method of the present invention, it is possible to effectively desiliconize while suppressing decarburization and a drop in hot metal temperature.

As described above, according to the desiliconization treatment method of the present invention, it is possible to obtain a high desiliconization efficiency while preventing a temperature drop during the treatment and preventing the progress of decarburization. of#
Since damage is prevented as much as possible, various effects can be obtained, such as being able to use ordinary inexpensive glasses.

[Brief explanation of the drawing]

Figure 1 shows the relationship between hot metal temperature drop and desiliconization reaction efficiency in the desiliconization process of hot metal, and Figure 2 shows the relationship between oxygen gas flow rate and iron ore injection speed on blowing lance erosion FIG. 3 is a graph showing the relationship between the critical oxygen gas flow rate required to prevent a drop in hot metal temperature in the desiliconization process and the desiliconization reaction efficiency. Applicant: Kawasaki Steel Corporation (13) Fig. 1 Private language f-ri9%) Fig. 2 aLl''-Sword/person'y; and 7 de(=n;)−8′

Claims (1)

[Claims] A desiliconizing agent containing Fe2O5 as a main component is
Win 1kg of e2O3! 1. A method for desiliconizing hot metal, which comprises blowing into hot metal together with a carrier gas containing 54 to 20 ONA of oxygen.