JPH04221007A - Method for dephosphorizing molten iron - Google Patents

Abstract

PURPOSE:To remove P in molten iron in a short time to a slag while the iron is still melted by using a slag forming agent consisting essentially of iron oxide and quick lime as the dephosphorizing agent. CONSTITUTION:A slag forming agent consisting of the powders of the iron oxide-contg. material and quick lime is blown into the molten iron tapped from a blast furnace and simultaneously sprinkled over the molten iron surface. A slag high in basicity (CaO/SiO2) is formed on the molten iron surface, and the Si and P in the molten iron are oxidized by the iron oxide to SiO2 and P2O5 which are slagged and removed along with the CaO. The addition of the slag forming agent is suspended at the last stage of the desiliconizing and dephosphorizing refining to prevent the waste of the agent. The molten iron is desiliconized and dephosphorized without being slopped.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dephosphorizing hot metal.

0002

[Prior Art] Generally, in the dephosphorization treatment of hot metal in a hot metal storage container such as a topedo, a dephosphorization slag agent containing iron oxide and quicklime as the main components is blown into a hot metal bath to perform the dephosphorization treatment. There is. On the other hand, as a method of adding a dephosphorizing agent,
As in Japanese Patent No. 9-47317, there is also a method in which a dephosphorizing slag agent is blown into a hot metal bath and at the same time iron oxide is added onto the bath surface.

[0003] Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 2-93011, iron oxide and a slag-forming agent mainly composed of CaO are injected into the hot metal at the same time, and the iron oxide is kept on the top surface of the hot metal until the treatment is completed. There is also a method of continuously adding it to the top. However, 1)
In the method of simply injecting a dephosphorizing agent consisting of iron oxide and a slag-forming agent mainly composed of CaO into a hot metal bath, the treatment time becomes long for high-Si hot metal in which a large amount of dephosphorizing agent is used. In addition, if only by blowing, there is a limit to the amount of CaO injected, and it is not possible to increase the basicity of the slag during the desiliconization stage, resulting in operational inhibition due to slopping. Even in low-Si hot metal, if the entire amount of CaO is injected, the injecting time becomes longer.

2) In the method disclosed in JP-A No. 59-47317, iron oxide is supplied onto the hot metal surface by top addition, and only the slag-forming agent is injected, so that iron oxide and iron oxide in the hot metal are injected. Since less CO gas is generated due to the reaction of C, C
Stirring of the hot metal by O gas becomes insufficient, and the dephosphorization reaction cannot proceed sufficiently. 3) In the method disclosed in JP-A-2-93011, iron oxide and a sludge-forming agent mainly composed of CaO are injected, and only iron oxide is added above, so that a sludge-forming agent mainly composed of CaO is not produced. In addition to the long blowing time of the slag agent, when dephosphorizing high-Si hot metal, it is difficult to maintain the basicity of the initial slag (CaO/SiO2) because CaO is supplied only by blowing, and slopping is difficult. This occurs frequently and becomes a factor that hinders operations.

[0005]

[Problems to be Solved by the Invention] In order to solve the above-mentioned drawbacks of the prior art, the present invention provides a novel hot metal that does not cause operational interruption, has a short treatment time, and allows iron oxide to undergo a sufficient dephosphorization reaction. The purpose is to provide a method for dephosphorization.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present invention is directed to injecting a slag-forming agent mainly composed of iron oxide and CaO into a hot metal bath and adding it to the top surface of the hot metal. Furthermore, top addition to the top surface of hot metal can be stopped at the end of the dephosphorization process.

[0007]

[Operation] According to the present invention, when high-Si hot metal is dephosphorized, iron oxide and a slag-forming agent mainly composed of CaO are blown into the hot metal and simultaneously added to the top surface of the hot metal. Therefore, the basicity of the slag (CaO/SiO2) can be increased from the beginning, and the oxidation reaction of Si can proceed quickly.
Since the slag basicity defined by aO/SiO2 can be maintained high at an early stage, it has become possible to shorten the dephosphorization treatment time and prevent slopping by ensuring a high slag basicity. Furthermore, since iron oxide is also injected,
Since a large amount of CO gas can be generated by the decarburization reaction in hot metal and the hot metal can be sufficiently stirred, it is also possible to promote desiliconization and dephosphorization reactions.

[0008]Although the iron oxide and CaO-based slag-forming agent added to the top do not immediately contribute to the reaction, the top addition is stopped at the end of the dephosphorization process and only the blowing is continued. By doing this, it is possible to secure time for the iron oxide added above and the slag-forming agent mainly composed of CaO to fully contribute to the dephosphorization reaction, and the dephosphorization oxygen efficiency is higher than in the case of conventional blowing only. The dephosphorization process time can be shortened.

[0009] The final stage of the dephosphorization process is a period of about 5 to 10 minutes before the end of the dephosphorization process, and is appropriately determined in consideration of the phosphorus concentration in the hot metal. Further, as the iron oxide in the present invention, mill scale, iron ore, steelmaking dust, etc. are used, and fluorite, soda ash, etc. may be added to the slag forming agent.

0010

[Example] A hot metal dephosphorization treatment experiment was carried out by putting 280 tons of hot metal into a 350 tons speed. Table 1 shows the experimental conditions and results, and Table 2 shows the hot metal components (% by weight) before and after the dephosphorization treatment. Note that a small amount of fluorite was added during the experiment.

[0011]

[Table 1] ──────────────────────────
──────────
CaO scale processing time slopping slag
(kg/t) (kg/t) (min)
(kg/t) Blowing only 15.5
37.6 33
18.5 blowing + top addition *8.5
20.6 18
1.2 *7.
0 17.6──────────────
────────────────────── Note
*: Blowing *: Top addition

0012

[Table 2] ──────────────────────────
──────────
C Si Mn
P Before dephosphorization treatment
4.5 0.30 0.20
0.115 0.030 After dephosphorization treatment 4.2
0.01 0.20 0.025
0.020──────────────────
──────────────────With the blowing + top addition method, even if the hot metal Si concentration before dephosphorization treatment is 0.30%, the dephosphorization treatment time is 18 minutes and the slopping slag consumption rate is reduced 1.2kg/t
The treatment time was shortened by 15 minutes and the slopping dregs were reduced by 17.3 kg/t compared to the conventional method using only blowing.

[0013] Also, with the same amount of hot metal, the Si concentration before treatment was 0.
Experiments were also conducted with 0.05% hot metal. Table 3 shows the component concentrations before and after the treatment, and Table 4 shows the experimental conditions and results.

[0014]

[Table 3] ──────────────────────────
──────────
C Si Mn
P Before dephosphorization treatment
4.5 0.05 0.20
0.115 0.030 After dephosphorization treatment 4.2
0.01 0.20 0.025
0.020──────────────────
──────────────────

[0015]

[Table 4] ──────────────────────────
──────────
CaO scale processing time slopping slag
(kg/t) (kg/t) (min)
(kg/t) Blowing 1
0.0 25.8 22
5.0 blowing + top addition *5.0
15.0 12 0
*5.0
10.8────────────────────
────────────────Note *: Voice-over
*: When the Si concentration before top addition treatment is 0.05%, the treatment time is 10 minutes shorter by performing the top addition method, and the treatment time is 12 minutes.
There was no case of blowing + top addition for 0 kg/t.

Next, an experiment was conducted by changing the timing at which the top addition was completed. As shown in Table 5, the experimental conditions were such that the top addition was completed at the end of the dephosphorization treatment by blowing, and 4 minutes and 7 minutes before that.

[0017]

[Table 5] ──────────────────────────
────────── Experiment A Blow-in only Experiment B Blow-in + top addition until the end of treatment Experiment C Blow-in + top addition finished 4 minutes before the end of treatment Experiment D Blow + 7 minutes before end of treatment Top addition completed────────────
──────────────────────── Figure 1 shows the influence of the timing of the end of top addition on the dephosphorization oxygen efficiency.

Compared to Experiment A, which is a conventional method, the oxygen efficiency for dephosphorization is about the same in Experiment B, which is a method of the present invention, but it is improved in Experiments C and D, in which the top addition is stopped at the end of the dephosphorization process. In this example, nitrogen was used as the gas for blowing and blowing onto the hot metal surface, and oxygen was not used. However, the present invention is not limited to this. Spraying may also be used.

[0019]

[Effects of the Invention] According to the present invention, the dephosphorization treatment time can be shortened and slopping can be significantly reduced. Furthermore, since the treatment time could be shortened, not only could the throughput be increased, but the temperature after the dephosphorization treatment could also be increased, and the converter yield could be improved.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the effect of top addition time on dephosphorization oxygen efficiency in Examples.

Claims (2)

[Claims] 1. A hot metal dephosphorization process characterized in that, when dephosphorizing hot metal, a slag-forming agent containing iron oxide and CaO as main components is added to the upper surface of the hot metal while being blown into the hot metal bath. Phosphorus method. 2. The method for dephosphorizing hot metal according to claim 1, wherein the top addition to the top surface of the hot metal is stopped at the end of the dephosphorization process.