JPH01215916A - Method for treating dephosphorization of molten iron - Google Patents

Abstract

PURPOSE:To efficiently execute dephosphorizing reaction in molten iron by specifying CaO/O values in refining agent at desiliconizing reaction stage preceding dephosphorization, the dephosphorizing reaction stage following this and the dephosphorizing reaction last stage at the time of dephosphorizing by blowing basic slag making agent and oxidizing agent into molten iron with carrier gas. CONSTITUTION:Before supplying the molten iron tapped from a blast furnace into a steelmaking furnace, dephosphorizing pre-refining is executed. Then, lime series basic flux and dephosphorizing agent composing of oxidizing agent are blown with the carrier gas. In this case, the refining reaction is divided into a first stage, which desiliconizing reaction precedes the dephosphorizing reaction till coming down to about 0.05% Si content in the molten iron, a second stage, which vigorous dephosphorizing reaction develops as following the above stage, and a third stage, which P in the molten iron is decreased in accordance with progress of the dephosphorizing reaction and the dephosphorizing reaction is delayed. By making 2.3-3.0 of the value of CaO/O in the dephosphorizing agent used in the first stage and 1.7-2.2 of the value of CaO/O in the dephosphorizing agent in the second and third stages, O2 efficiency used in the dephosphorizing reaction is improved, and pre-dephosphorizing reaction in the molten iron is executed at extremely efficiently.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for dephosphorizing hot metal.

BACKGROUND OF THE INVENTION It is well known to produce steel by dephosphorizing hot metal to reduce the amount of auxiliary materials used for dephosphorization in the steelmaking process.

For example, in JP-A-58-73709, the silicon content is 0.
．． When injecting a powdered dephosphorization/desulfurization agent together with a carrier gas into a hot metal bath with a concentration of 25% or less, the amount of oxidizing agent consisting of gaseous oxygen or a solid oxygen source that composes the fluid to be injected is adjusted to match the hot metal phosphorus concentration. A method for pretreatment of hot metal is disclosed, which is characterized by controlling according to the transition and promoting dephosphorization.

Problems to be Solved by the Invention The purpose of the above-mentioned conventional technology is to perform dephosphorization and desulfurization while suppressing the consumption of useful components such as decarburization and demanganization. This technology changes the blowing oxygen ratio when the hot metal phosphorus concentration reaches 0.04%, based on the knowledge that the dephosphorization efficiency by the desulfurization agent decreases when the phosphorus concentration reaches 0.04%.

However, since this technique relates to treatment in the latter stage of the dephosphorization treatment process, even if dephosphorization and desulfurization agents can be saved, the effect is not so great.

Means for Solving the Problems As a result of a more detailed study of the entire hot metal dephosphorization process, the present inventors obtained new knowledge regarding the blending conditions of the dephosphorization agent and the timing of its addition, and have developed the present invention. completed.

That is, in the present invention, when dephosphorizing hot metal by injecting a quicklime-based refining flux and an oxidizing agent into a hot metal bath using a carrier gas, desiliconization progresses preferentially and dephosphorization progresses slowly. Initially, the CaO10 ratio in the dephosphorization treatment agent should be within the range of 2.3 to 3.0, and thereafter, the dephosphorization treatment should be performed with the CaO10 ratio in the dephosphorization treatment agent within the range of 1.7 to 2.2. This is a hot metal dephosphorization treatment method characterized by the following.

The dephosphorization treatment process of working hot metal is divided into a dephosphorization reaction stage phase in which desiliconization proceeds preferentially and dephosphorization progresses slowly, and a dephosphorization reaction stage II phase in which desiliconization is completed and dephosphorization proceeds quickly. If the process is divided into dephosphorization reaction stages in which the phosphorus content in the hot metal decreases and dephosphorization progress stalls again, there is an optimum value for the dephosphorization agent compounding ratio (CaO10) in each dephosphorization reaction stage. By optimally controlling the blending ratio of the dephosphorizing agent in each stage, it is possible to shorten the dephosphorizing treatment time and reduce the unit consumption of the dephosphorizing agent.

EXAMPLE FIG. 1 is a diagram showing the relationship between the amount of dephosphorizing agent used and the phosphorus concentration in hot metal, divided by dephosphorization reaction stage. In addition, the first
~2 Symbols in the figures each indicate intermediate sampling data of the same process.

As shown in the figure, the dephosphorization behavior at each stage has the following characteristics.

Construction period: Desiliconization progresses preferentially, and dephosphorization progresses slowly (period until Si in hot metal drops to 0.05%).

Stage II: Desiliconization is completed and dephosphorization progresses rapidly.

■ Stage: [P] decreases and the progress of dephosphorization stagnates again.

Figure 2 is a diagram showing the relationship between the phosphorus concentration in hot metal and the dephosphorization oxygen efficiency, and was obtained from continuous sampling during the hot metal dephosphorization process. As can be seen from this figure, as the phosphorus [P] in the hot metal decreases, the dephosphorization oxygen efficiency ηg changes from low to high to low. This is considered to correspond to the above-mentioned dephosphorization reaction stage, and there is a large difference between the treatments in dephosphorization and oxygen efficiency, especially in the process stage and stage II. Here, the dephosphorization oxygen efficiency (ηP) is defined by the following formula.

Dephosphorization oxygen efficiency (η engineering) - (oxygen consumed for dephosphorization) X1
00/(Oxygen in iron oxide + gaseous oxygen - oxygen consumed in oxidation) (2) ... ■ The inventors further investigated the dephosphorization oxygen efficiency at each dephosphorization stage, and found that It has been found that the phosphorus-oxygen efficiency changes depending on the CaO10 ratio in the dephosphorizing agent, which is determined by the composition of the dephosphorizing agent, and that this Ca0ZO ratio has an optimum value for each dephosphorization reaction stage.

Note that the CaO10 ratio herein refers to the ratio defined by the following formula.

CaO10 = CaO injection amount (kg) / [Oxygen in iron oxide (kg) + gaseous oxygen (N) x 32/22.4]
-Contest-■ Figure 3 is a diagram showing the relationship between the CaO10 ratio and the dephosphorization oxygen efficiency ηP in the 91st stage of the dephosphorization reaction.

As shown in Figure 3, in the first dephosphorization reaction stage, increasing CaO10 increases η8 when the CaO10 ratio is 3.0 or less, but this tendency is particularly strong when the CaO10 ratio is 2.3 or higher. .

FIG. 4 is a diagram showing the relationship between the CaO10 ratio and the dephosphorization oxygen efficiency η: in the dephosphorization reaction stage II.

As shown in the figure, in the dephosphorization reaction stage II,
When the CaO10 content in the dephosphorizing agent increases, 1g improves, but C
There is a bending point at the point where aO10 is 1.8, and beyond this point, 1g shows a decreasing tendency. Therefore, Ga010 in the dephosphorizing agent should be set at 1.8 in the period (2), but in reality there are variations due to operating conditions, etc., and Ga010 is set at 1.8.
It is not a good idea to control the CaO10 ratio to a certain point, but it is effective to control the CaO10 ratio within a range of 1.7 to 2.2 in consideration of variations.

If the CaO10 ratio is less than 1.7, 1g is too low, and conversely 2.
Even if it exceeds 2, η: decreases.

Figure 5 shows CaO in the dephosphorizing agent at the 91st stage of the dephosphorization reaction.
10 is a diagram showing the relationship between the phosphorization and oxygen efficiency η.

As shown in FIG. 5, there is a similar tendency for stage (2) as for stage (2). That is, up to a CaO10 ratio of 1.8, ηg improves as the value of the CaO10 ratio increases;
．． At 8 or higher, there is no improvement in η2, and the CaO10 ratio is 2.2.
When it exceeds , η decreases. Therefore, for stage (2) as well, it is effective to control the cao10 ratio within the range of 1.7 to 2.2. The value of ηg itself is lower than that in Stage II, but this is because as the phosphorus concentration in the hot metal decreases, the dephosphorization reaction shifts from oxygen supply rate-limiting to mass transfer rate-limiting of phosphorus in the hot metal. This is thought to be due to a decrease in phosphorus rate.

In the present invention, the CaO10 ratio in the dephosphorizing agent in the hot metal dephosphorization process is changed between the dephosphorization reaction stages 91 and 2 and before the dephosphorization process. The point of change can be when the Si value in the hot metal is reduced to 0.05%.

Effects of the Invention As described above, according to the present invention, the dephosphorization treatment process of hot metal is divided into each dephosphorization reaction stage, and the composition of the dephosphorization treatment agent is optimized for each stage to perform the dephosphorization treatment. As a result, the efficiency of the dephosphorization reaction can be increased, and remarkable effects can be achieved, such as reducing the unit consumption of the dephosphorizing agent, shortening the treatment time, and preventing a drop in hot metal temperature.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the amount of dephosphorizing agent used and the phosphorus concentration in the hot metal, divided by dephosphorization reaction stage, and Figure 2 shows the relationship between the phosphorus concentration in the hot metal and the dephosphorization oxygen efficiency. Figure 3 is a diagram showing the relationship between CaO10 ratio and dephosphorization oxygen efficiency in dephosphorization reaction stage 91, and Figure 4 is a diagram showing the relationship between CaO10 ratio and dephosphorization oxygen efficiency in dephosphorization reaction stage ■. Figure 5 shows the CaO1 in the dephosphorizing agent at the dephosphorization reaction stage II.
It is a figure showing the relationship between 0 ratio and dephosphorization oxygen efficiency. Representative Patent Attorney I -L Miyabi Figure 3 Ca○/○ Figure 4 Ca○/○

Claims (1)

[Claims] When dephosphorizing hot metal by injecting quicklime-based refining flux and oxidizing agent into the hot metal bath using a carrier gas, dephosphorization takes place preferentially and dephosphorization is slow in the early stages of dephosphorization. The CaO/O ratio in the agent is 2.3 to 3.0.
After that, the CaO/O ratio in the dephosphorization treatment agent should be within the range of 1.
．． A method for dephosphorizing hot metal, characterized in that the dephosphorizing treatment is carried out within the range of 7 to 2.2.