JP2016079462A - Method for refining hot pig iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for manufacturing a high purity steel from hot pig iron having a silicon concentration of 0.45 mass% or more efficiently at low cost.SOLUTION: A method includes a desiliconization process for conducting a desiliconization treatment by adding a desiliconization agent to a blast furnace molten iron having a silicon concentration of 0.45 mass% to make a silicon concentration of 0.2 mass% to 0.4 mass%, a desulfurization process for conducting a desulfurization treatment by adding a desulfurization agent to the molten pig iron after the desiliconization treatment and a dephosphorization process for conducting a dephosphorization treatment by injecting the molten pig iron after the desulfurization treatment and adding a dephosphorization agent to suppress FeO contained in a desiliconization slag before the desulfurization treatment to 16 mass% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a hot metal refining method suitable for producing high purity steel from hot metal having a silicon concentration of 0.45 mass% or more.

  In recent years, various techniques have been developed for manufacturing technology of high-purity steel in which the contents of P, S, C, and the like are reduced to an extremely low level (for example, Patent Document 1).

  Conventionally, raw materials having a low content such as Si have been used for the production of these high purity steels. However, in recent years, due to severe price competition in the steel industry, there has been a shift to raw materials with a high content such as Si (so-called “poor raw materials”) to control raw material prices. However, there is an increasing demand for technology for producing high-quality high-purity steel as efficiently and at low cost as in the past.

JP2013-127087A

  An object of the present invention is to provide a technique for producing high-purity steel efficiently and at low cost from hot metal having a silicon concentration of 0.45% by mass or more.

  In the present invention, as a means for solving the above-mentioned problem, in the hot metal refining method, “a silicon removal process is performed by adding a silicon removal agent to a blast furnace hot metal having a silicon concentration of 0.45 mass% or more to reduce the silicon concentration to 0”. The desiliconization step of 2 mass% to 0.4 mass%, the desulfurization step of adding a desulfurizing agent to the hot metal after the desiliconization treatment and performing the desulfurization treatment, and the hot metal after the desulfurization treatment into the converter reactor Having a dephosphorization step of inserting, adding a dephosphorization agent and performing a dephosphorization process, and adopting a configuration in which FeO contained in the desiliconized slag before the desulfurization process is suppressed to 16% by mass or less. Yes.

In addition, the degassing process has a decarburization process in which the hot metal after the dephosphorization process is mainly deoxygenated with oxygen gas. It is preferable to include a granulated one, and the desiliconization treatment is performed under conditions where the basicity of the desiliconization slag is (CaO) / (SiO ₂ ) = 0.3 to 1.5. preferable.

  The hot metal refining technology, which includes a desiliconization process, a desulfurization process, a dephosphorization process, and a decarburization process, and is refined in this order, is, for example, “Iron and Steel 74th (1988) No. 2 270-277. Although this is disclosed in “Page”, this technique is a technique in which a treatment for reducing the silicon concentration to 0.15% or less is essential in the desiliconization step. In the case where iron ore having a low content such as Si is used as a raw material as in the prior art, there is no particular problem with this conventional technique, but when a poor material having a high content such as Si is used, the silicon concentration is set to 0. When trying to reduce the amount to less than 15% by mass, a considerable amount of desiliconizing agent (flux containing FeO) is required, and the desiliconizing time increases with the amount of desiliconizing agent used. It takes a long time to reduce productivity. Further, when a large amount of desiliconizing agent is used, the amount of FeO in the desiliconized slag increases. However, when this FeO is carried over to the next process (desulfurization process) together with the desiliconization slag, the problem of inhibiting the desulfurization reaction, In the desiliconization process, when the silicon concentration is reduced to less than 0.15% by mass, the amount of slag produced in the dephosphorization process is reduced because of the lack of Si as the main component of the slag, and the previous process (desulfurization process). Therefore, the sulfur concentration contained in the desulfurized slag carried over cannot be diluted, and there is a problem that the sulfur concentration required for high-purity steel cannot be achieved due to resulfurization in the dephosphorization process.

  On the other hand, according to the present invention, “the silicon concentration after the desiliconization treatment is stopped at 0.2 mass% to 0.4 mass%, and FeO contained in the desiliconization slag before the desulfurization treatment is reduced to 16%. Since it is “suppressed by mass% or less”, the amount of desiliconization agent used can be reduced and the desiliconization processing time, which is a bottleneck process, can be shortened compared to the above-mentioned technology, thereby improving productivity. be able to. In addition, as a result of reducing the amount of desiliconizing agent used, each of the above problems (problems that inhibit the desulfurization reaction, problems that cause desulfurization in the dephosphorization process, or The problem of slopping during desiliconization can be avoided.

  In the above prior art, since it is premised on the dephosphorization process in the hot metal ladle (container having no free board part), from the viewpoint of avoiding the slag forming during the dephosphorization process, the silicon concentration is set in the prior desiliconization process. Although it has been required to reduce to “less than 0.15% by mass”, in the present invention, since the dephosphorization process is performed in the converter reactor, a certain amount of slag forming is acceptable, and prior degassing is possible. The target level of the silicon concentration after the desiliconization process in the silicon process can be increased to “0.2 mass% to 0.4 mass%”.

It is a figure explaining the flow of this invention.

  Preferred embodiments of the present invention are shown below. As shown in FIG. 1, the hot metal refining method of the present embodiment is blast furnace hot metal having a silicon concentration of 0.45% by mass or more through each step in the order of desiliconization step, desulfurization step, dephosphorization step, and decarburization step. This is a method for refining hot metal from high purity steel. Hereinafter, each process is explained in full detail.

<Desiliconization process>
The hot metal discharged from the blast furnace passes through the blast furnace casting floor and is inserted into a kneading wheel for hot metal conveyance. In this embodiment, the silicon carbide is used as a smelting vessel, and silicon removal is performed with a silicon concentration of 0.2 mass% to 0.4 mass%.

In this embodiment, a solid oxygen source and oxygen gas are used as an oxygen source for the desiliconization reaction ([Si] + O ₂ → SiO ₂ ). Here, [Si]: silicon in the molten iron, SiO _2: a SiO ₂ in the slag.

  As the solid oxygen source, at least one of mill scale, iron-making dust, and sintered powder is used, and when the hot metal is dropped from the blast furnace casting floor and inserted into the kneading car, it is put into the falling flow. . Similarly, when introducing the solid oxygen source, it is preferable that other desiliconizing agents are also introduced in the falling flow.

  The shortage of solid oxygen source can be additionally charged by blowing fine powder through a lance. Oxygen gas is blown from above the chaotic vehicle using a lance, or is blown into the chaotic vehicle. From the viewpoint of stirring power, blowing into the kneading vehicle is preferable, but since there is a risk of tuyere melting, it is preferable to select an optimal means as appropriate.

  The flux containing the desiliconizing agent FeO is input as a mixed raw material with a solvent medium (CaO or the like). In this embodiment, the decarburized slag generated in the subsequent decarburizing step is less than 25 mm in this mixed raw material. Is used that contains crushed and sized particles. By using this decarburized slag in combination, it is possible to obtain the effect of reducing the discharge slag outside the system by reusing the decarburized slag, in addition to the effect of suppressing forming associated with the desiliconization process and the effect of reducing the amount of quicklime used.

The above-mentioned solvent solvent adjusts the basicity ([mass% CaO] / [mass% SiO ₂ ]) of the slag generated by the desiliconization process (hereinafter referred to as desiliconized slag) to improve the fluidity of the slag. has the effect of adjusting, in the present embodiment, the basicity of the desiliconization slag, a _{(CaO) / (SiO 2)} = 0.3~1.5 become relatively desiliconization treatment under conditions of low basicity Is going.

  When the basicity of the desiliconized slag exceeds 1.5, the flowability of the slag decreases, and as a result, the reduction reaction of FeO is difficult to proceed, and the desiliconization reaction is inhibited and the FeO concentration in the desiliconized slag is high. It is not preferable because it stays. In addition, since the slag with reduced fluidity is easily separated from the hot metal, the amount of slag carried over with the hot metal is reduced when the hot metal after desiliconization is discharged to the refining vessel for the next process (desulfurization process). If the sulfur concentration in the slag (hereinafter referred to as desulfurization slag) existing in the smelting vessel is increased during the desulfurization treatment, and the desulfurization slag with the increased sulfur concentration is carried over to the next process (dephosphorization process), This is not preferable because sulfur (a phenomenon in which sulfur transferred into the slag by the desulfurization treatment is transferred again into the molten iron) is likely to occur.

  If the basicity of the desiliconized slag is less than 0.3, the reduction rate of FeO becomes slow and the desiliconization efficiency is lowered, which is not preferable. In addition, since the reduction rate of FeO is slowed, the FeO concentration remaining in the desiliconized slag increases when the next process is performed without securing a sufficient desiliconization time. If slag having a high FeO concentration is carried over to the next step (desulfurization step), the progress of the desulfurization reaction, which is a reduction reaction, is hindered, and the desulfurization efficiency is remarkably lowered. The desulfurization reaction proceeds as [S] + CaO → CaS + [O], where [S]: sulfur in hot metal, CaO: CaO in slag, CaS: CaS in slag, [O]: hot metal It is oxygen inside.

  In this embodiment, from the viewpoint of desulfurization efficiency, FeO contained in the desiliconized slag before the desulfurization treatment is suppressed to 16% by mass or less. The amount of FeO in the slag can be controlled by adjusting the amount of desiliconizing agent input, basicity, and stirring conditions.

  Even when the concentration of FeO remaining in the desiliconization slag becomes high, the desiliconization slag is completely removed when the hot metal after the desiliconization process is discharged to the refining vessel for the next process (desulfurization process). For example, theoretically, the desulfurization efficiency does not decrease as described above, but complete waste is time-consuming and time consuming, and the yield deteriorates due to iron loss accompanying waste, so it is practical on an industrial basis. It is not a safe means. On the other hand, according to the method of the present embodiment, adjustment of the basicity of the desiliconized slag and adjustment of the FeO concentration contained in the desiliconized slag, these disadvantages can be avoided.

  In the present embodiment, the desiliconization reaction is performed with stirring until the desiliconization process is completed after the addition of the desiliconizing agent. Since the desiliconization reaction proceeds at the slag / hot metal interface, the reaction interface can be increased by stirring to promote the reaction, and FeO in the desiliconized slag can be efficiently reduced. The stirring means is not particularly limited, and any means such as mechanical stirring and gas blowing stirring can be adopted.

<Desulfurization process>
After discharging the desiliconization slag through the desiliconization step, the hot metal is inserted into a refining vessel for desulfurization treatment, and a desulfurization agent is added to perform the desulfurization treatment. Here, the refining vessel and the stirring means are not particularly limited, and a desulfurization agent injection method in a hot metal ladle or a kneading vehicle, or a mechanical stirring method in a hot metal ladle can be adopted.

  In the present embodiment, as described above, FeO contained in the desiliconized slag before the desulfurization treatment is suppressed to 16% by mass or less to promote the desulfurization reaction ([S] + CaO → CaS + [O]). Yes.

<Dephosphorization process>
The dephosphorization reaction proceeds as 2 [P] +5 [O] + 3CaO → 3CaO · P ₂ O ₅ , where [P]: phosphorus in hot metal, [O]: oxygen in hot metal (oxygen gas) or iron oxide), CaO: CaO in the slag, CaO _· P 2 _{O 5:} a _P 2 _{O 5} which is fixed to the CaO in the slag.

  After discharging the desulfurization slag through the above steps, the hot metal is inserted into a converter reactor for the dephosphorization step, and a dephosphorization process is performed by adding a dephosphorization agent and stirring the top bottom. . When the dephosphorization process is performed in a hot metal pan (a container without a free board portion) as in the prior art, the silicon concentration is set to “0.15” in the prior desiliconization process from the viewpoint of avoiding slag forming during the dephosphorization process. It is required to be reduced to a level of less than “mass%”. However, by adopting a configuration in which the dephosphorization process is performed in a converter reactor as in this embodiment, a certain amount of slag forming is allowed, The target level of the silicon concentration after the desiliconization process in the desiliconization process can be increased to “0.2 mass% to 0.4 mass%”. Si remaining in the hot metal in the desiliconization process is converted into slag and removed from the hot metal in the dephosphorization process.

  In the present embodiment, as described above, the silicon concentration after the desiliconization treatment is kept at “0.2 mass% to 0.4 mass%”, thereby sufficiently securing the slag volume at the initial stage of the dephosphorization process and securing the slag volume. In addition to reducing the amount of secondary materials (fluorite, etc.) used for the purpose of promoting the hatching of lime sources, the dephosphorization efficiency is increased.

<Other processes>
If necessary, a decarburization process in which a decarburizing agent is added to the hot metal after the dephosphorization process to perform a decarburization process, and a subsequent secondary refining (degassing, desulfurization) process may be added.

The results of treating the high Si hot metal 280t by the process of kneading car desiliconization → (slag discharge) → pan desulfurization → converter dephosphorization are shown in Examples 1 to 4 and Comparative Examples 1 to 3 below (Table 1). Yes.
In Examples 2 and 3, fine decarburized soot having a particle size of 25 mm or less was added to the molten iron as a desiliconizing agent during the kneading wheel desiliconization treatment. In Table 1, [% Si] [% P] [% S] indicates the concentration of each element in the hot metal, C / S is the basicity of the desiliconized slag, FeO is the FeO concentration in the desiliconized slag, (% S) indicates the sulfur concentration in the slag. All concentrations in the hot metal or slag in Table 1 are mass%. Moreover, the density | concentration which became out of the range of this invention in Comparative Examples 1-3 is displayed with the underlined bold type.

  As shown in Table 1, the silicon concentration after the desiliconization treatment is 0.2 mass% to 0.4 mass%, and FeO contained in the desiliconization slag before the desulfurization treatment is suppressed to 16 mass% or less. In Examples 1 to 4, it was possible to obtain extremely low sulfur and low phosphorus hot metal through the above process.

  On the other hand, in Examples 1 and 2 where the silicon removal treatment was performed until the silicon concentration after the silicon removal treatment was 0.12% by mass, a significant decrease in the phosphorus removal efficiency was confirmed. Moreover, in Comparative Examples 1-3 in which FeO contained in the desiliconized slag before the desulfurization treatment exceeds 16% by mass, a decrease in the desulfurization efficiency is recognized as compared with Examples 1-3, and even through the above process. It was not possible to obtain ultra-low sulfur and low phosphorus hot metal.

  Specifically, in Comparative Example 1, since [% Si] after desiliconization was low and the FeO concentration was expected to be high from the situation such as the color of slag, the desiliconization slag was discharged for a long time. As a result, the amount of slag carried over to the desulfurization process decreased and the amount of slag generated in the desulfurization process was small, so the sulfur concentration (% S) in the slag was relatively high. Since this desulfurization slag was carried over to the dephosphorization process and the resulfurization in the dephosphorization process became large, it was possible to produce ultra-low sulfur steel with a sulfur concentration of 0.003% by mass or less after the dephosphorization process. I could not do it. In Comparative Example 2, [% Si] after desiliconization was excessively lowered as in Comparative Example 1, but the desulfurization process was carried out at a normal desulfurization step without performing the desulfurization as in Comparative Example 1, and thus desulfurization. The efficiency was low, and it was not possible to melt extremely low sulfur steel. In Comparative Example 3, since the basicity of the desiliconized slag after the desiliconization treatment was excessive, the reduction of FeO did not proceed and the FeO concentration was expected to be high. As a result, as in Comparative Example 1, the sulfur concentration (% S) in the desulfurized slag was excessively high, and the resulfurization in the dephosphorization step was increased, so that the ultra-low sulfur steel was not melted.

Claims (3)

A hot metal refining method for producing high purity steel from a blast furnace hot metal having a silicon concentration of 0.45% by mass or more,
A desiliconization step of adding a desiliconizing agent to the blast furnace hot metal to perform a desiliconization process, and setting the silicon concentration of the hot metal after the desiliconization process to 0.2 mass% to 0.4 mass%;
A desulfurization process in which a desulfurizing agent is added to the hot metal after the desiliconization treatment to perform the desulfurization treatment;
Inserting the hot metal after the desulfurization treatment into a converter type reaction vessel, adding a dephosphorization agent and carrying out a dephosphorization treatment,
A hot metal refining method, wherein FeO contained in desiliconized slag before desulfurization treatment is suppressed to 16% by mass or less. Furthermore, it has a decarburization step of adding a decarburizing agent to the hot metal after the dephosphorization treatment and performing a decarburization treatment,
The hot metal refining method according to claim 1, wherein the desiliconizing agent includes a material obtained by crushing and sizing the decarburized slag produced in the decarburizing step to less than 25 mm. 3. The hot metal according to claim 1, wherein the desiliconization treatment is performed under a condition in which the basicity of the desiliconization slag is (CaO) / (SiO ₂ ) = 0.3 to 1.5. Refining method.