JP7348519B2 - Method of dephosphorizing hot metal - Google Patents

Description

The present invention relates to a dephosphorization method in which a dephosphorizing agent is sprayed onto hot metal by blowing.

In recent years, a method of performing dephosphorization treatment by top-blowing CaO powder without using fluorite has been adopted due to environmental considerations, and various proposals have been made regarding top-blowing conditions for CaO powder.

Patent Document 1 discloses a technique of increasing basicity without reducing the CaO slag formation rate by top-blowing CaO powder, and suppressing granular iron loss by suppressing slag foaming. Patent Document 2 discloses that the CaO powder supply rate is 3 kg/min/ton of hot metal or less, and that the basicity (CaO/SiO ₂ ratio) of the slag after treatment is in the range of 2 to 3. ing. Further, Patent Document 3 discloses that the CaO powder supply rate is set to 0.5 kg/min/t to 3.0 kg/min/t, and the conditions of blend basicity and powder supply period are specified.

Patent No. 5772645 Patent No. 5553167 Patent No. 5412994

The method described in Patent Document 1 is not a technique aimed at dephosphorization, and there is no description regarding slag volume, so it is unclear whether it is sufficiently effective as dephosphorization. The methods described in Patent Documents 2 and 3 have problems in that the dephosphorization ability is insufficient and the dephosphorization effect varies because the conditions to be considered, such as the Si concentration in the hot metal, are insufficient.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a method for dephosphorizing hot metal that can stably obtain a high dephosphorizing effect.

The present invention is as follows.
(1)
A method for dephosphorizing hot metal,
A step of charging a first dephosphorizing agent and a solid oxygen source containing 50% by mass or more of iron oxide into a refining container;
Next, a step of dephosphorizing and blowing the hot metal by blowing a second dephosphorizing agent together with oxygen from an oxygen supply lance,
During the dephosphorization blowing step, the second dephosphorizing agent is continuously supplied for a period of 50% or more of the entire period of the dephosphorization blowing from the start of the oxygen blowing until the end, When 50% of the period of the dephosphorization blowing has elapsed, the relationship between the supply amount W _deP-II of the second dephosphorizing agent and the amount W _charge of the auxiliary material satisfies the following formula (1), and Hot metal characterized in that the relationship between the supply amount W _deP-II of the second dephosphorizing agent and the auxiliary material charging amount W _charge at the time when the oxygen blowing is finished satisfies the following formula (2). Dephosphorization method.
0.16<W _deP-II /W _charge <0.25...(1)
0.30<W _deP-II /W _charge < 0.44 ...(2)
W _charge =W _deP-I +W _oxide +W _SiO2 ...(3)
W _SiO2 =0.0214×W _iron ×[Si]...(4)
Here, W _deP-I represents the charging amount (t) of the first dephosphorizing agent, W _oxide represents the charging amount (t) of the solid oxygen source, and W _SiO2 is generated by the desiliconization reaction. W _iron represents the _amount (t) of the hot metal charged in the slag, [Si] represents the Si concentration (t) in the hot metal before dephosphorization treatment. mass%).

According to the present invention, it is an object of the present invention to provide a method for dephosphorizing hot metal that can stably obtain a high dephosphorizing effect.

FIG. 3 is a diagram for explaining changes in basicity of slag during dephosphorization blowing. It is a figure for explaining the relationship between the supply amount of the second dephosphorizing agent and the P concentration in hot metal in the first half of blowing. FIG. 3 is a diagram for explaining the relationship between the supply amount of the second dephosphorizing agent and the P concentration in hot metal at the end of blowing.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the present inventors conducted intensive studies on the detailed process of the dephosphorization reaction, particularly in order to find conditions for stably producing ultra-low phosphorus steel.

The point where the oxygen jet collides with the hot metal surface (hereinafter referred to as the fire point) is at a high temperature of 2000°C or higher, and the FeO production reaction shown in equation (5) below and the decarburization reaction shown in equation (6) below occur. occur in parallel.
2[Fe]+O ₂ =2(FeO)...(5)
(FeO) + [C] = [Fe] + CO↑ ... (6)

Here, by supplying fine CaO powder directly from a lance to the fire point together with an oxygen jet, it is possible to promote the melting of CaO itself, and when mixed with FeO, a low melting point calcium ferrite melt (hereinafter referred to as CF) is generated. Therefore, it is extremely useful for promoting slag formation and maintaining a high liquid phase ratio. In addition, the FeO concentration in CF changes depending on the supply speed of CaO powder, and the faster the CaO powder is supplied, the lower the concentration and activity of FeO in CF, which makes it more stable as an oxide and less likely to be reduced to C. , FeO can be stably supplied to the slag.

On the other hand, the dephosphorization reaction generates a dicalcium silicate (2CaO.SiO ₂ , hereinafter referred to as C ₂ S) solid phase in the liquid slag, converting P in the liquid slag into tricalcium phosphate (3CaO.P). It becomes possible to incorporate it into the solid phase as ₂ O ₅ (hereinafter referred to as C ₃ P), and the dephosphorizing ability of the liquid phase slag can be maintained at a high level. In order to generate C ₂ S, it is necessary to quickly increase the basicity of the slag to a certain value or higher. On the other hand, if CaO powder is continued to be supplied in excess at high speed until the final stage of dephosphorization blowing, the basicity of the slag will become too high. If the basicity of the slag is too high, the solid phase ratio of the slag will increase significantly, the fluidity will deteriorate, and the dephosphorization reaction will be greatly inhibited.

FIG. 1 is a diagram for explaining changes in basicity of slag during dephosphorization blowing. As shown in FIG. 1, in the first half of the blowing period (up to 50% of the total blowing period), CaO powder is supplied as fast as possible in order to quickly generate C ₂ S. However, since it is necessary to continue supplying powder during the second half of blowing, if too much CaO powder is supplied during the first half of blowing, the slag may Since the solid phase becomes excessive and the fluidity of the slag deteriorates, it is necessary to suppress the blowing speed in order to control the slag composition to an appropriate level.

As shown in FIG. 1, in the latter half of blowing, the slag basicity is increased as much as possible without reaching the solid phase excess region. At this time, the CaO powder supply rate is ensured to be above a certain level so that FeO can be stably supplied into the slag.

Next, more specific conditions will be described when performing the dephosphorization treatment under the conditions described above. In the dephosphorization treatment, before performing dephosphorization blowing, hot metal, a first dephosphorization agent, and a solid oxygen source are first charged into a refining vessel such as a converter. Then, dephosphorization blowing is performed in a state in which SiO ₂ is generated in the slag by the desiliconization reaction of the hot metal by oxygen feeding.

The brand and particle size of the first dephosphorizer to be charged to the hot metal are not particularly limited as long as it can control the basicity of the slag, but considering the yield at the time of charging, it is better to use a powder of several mm to several It is preferable that the particles be in the form of particles of about 10 mm. Examples of the first dephosphorizing agent include quicklime, limestone , and dolomitic lime.

A solid oxygen source is charged into the hot metal in order to adjust the temperature of the hot metal and promote slag formation. As long as it contains a large amount of iron oxide (approximately 50% by mass or more), the brand, particle size, etc. are not particularly limited. Specific examples include iron ore.

Next, detailed conditions for dephosphorization blowing will be explained. The second dephosphorizing agent is continuously supplied for 50% or more of the entire period of dephosphorizing blowing from the start to the end of oxygen blowing. By continuously supplying CaO powder, it is possible to continue supplying a low melting point CF melt to the slag, making it possible to increase the FeO content of the slag and maintain its meltability. If the continuous supply period is less than 50% of the total period, the supply of CF will be delayed and the liquid phase ratio of the slag will decrease. Note that the oxygen delivery rate of the oxygen jet is basically constant, and the oxygen delivery rate is not particularly limited, but for example, if the hot metal is 300 tons, the oxygen delivery rate during dephosphorization blowing is approximately 400 to 700 Nm. It is often within the range of ³ /min.

Further, the second dephosphorizing agent is directly supplied together with the oxygen jet from the oxygen supply lance to the fire point in order to adjust the slag basicity. The brand is not particularly limited as long as it contains a CaO source, but preferably contains 50% by mass or more of CaO or CaCO ₃ . Furthermore, unlike the first dephosphorizing agent, the second dephosphorizing agent is supplied from the oxygen supply lance, so it is preferably a powder, and more preferably has a particle size of less than 100 μm.

Next, the supply amount of the second dephosphorizing agent will be explained. The present inventors investigated the conditions for supplying the second dephosphorizing agent in order to increase the dephosphorizing ability of slag and obtain a stable and high dephosphorizing effect, and found the conditions through tests, simulations, etc.

Figure 2 is a diagram for explaining the relationship between the supply amount of the second dephosphorizing agent and the P concentration in hot metal in the first half of blowing, and Figure 3 is a diagram for explaining the relationship between the supply amount of the second dephosphorizing agent and the P concentration in hot metal in the first half of blowing. It is a figure for explaining the relationship between supply amount and P concentration in hot metal. From the experimental results shown in Figures 2 and 3, the supply amount of the second dephosphorizing agent is determined to be equal to the supply amount W _deP-II of the second dephosphorizing agent and the Material charging amount W
The relationship with _charge satisfies the following equation (1), and the relationship between the supply amount W _deP-II of the second dephosphorizing agent and the auxiliary material charging amount W _charge at the end of blowing is as shown in (2) below. Make sure that the formula is satisfied.
0.16<W _deP-II /W _charge <0.25...(1)
0.30<W _deP-II /W _charge <0.45...(2)
W _charge =W _deP-I +W _oxide +W _SiO2 ...(3)
W _SiO2 =0.0214×W _iron ×[Si]...(4)

Here, W _deP-I represents the charging amount (t) of the first dephosphorizing agent, W _oxide represents the charging amount (t) of the solid oxygen source, and W _SiO2 represents the charging amount (t) of the first dephosphorizing agent. W _iron represents the amount of _hot metal (t) charged into the refining vessel, and [Si] represents the Si concentration (mass%) in the hot metal before dephosphorization treatment. represent.

As mentioned above, it is important to balance the CaO powder supply rate between the first half of blowing and the second half of blowing. It is necessary to increase the basicity and generate C2S by the first half of the blowing period (up to 50% of the total blowing period). The ratio between the supply amount of auxiliary material and the amount of auxiliary material charged is more than 0.16. However, if excessive CaO powder is supplied during the first half of blowing, the supply rate must be significantly reduced during the second half of blowing in order to keep the final slag composition within an appropriate range, and the supply of CF is delayed. Therefore, in the first half of blowing, the ratio between the amount of second dephosphorizing agent supplied and the amount of auxiliary material charged is set to be less than 0.25, as shown in equation (1).

On the other hand, in the latter half of blowing, it is necessary to increase the basicity of the slag as much as possible within the range of solid-liquid coexistence. Therefore, at the end of blowing, as shown in equation (2), the ratio between the amount of second dephosphorizing agent supplied and the amount of auxiliary material charged is set to exceed 0.30. However, if the slag basicity is increased too much, the slag becomes a complete solid phase, loses fluidity, and dephosphorization reaction no longer occurs. Therefore, at the end of blowing, as shown in equation (2), the ratio between the amount of second dephosphorizing agent supplied and the amount of auxiliary material charged is set to be less than 0.45.

As described above, in dephosphorization blowing, the supply amount of the second dephosphorizing agent is determined in relation to the amount of auxiliary material charged. Since the amount of the auxiliary material charged is determined based on the Si concentration in the hot metal before the desiliconization reaction, it is possible to obtain a stable and high dephosphorization effect without causing variations in the effect.

Next, an example of the present invention will be described. The conditions in the example are examples of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is based on this example of conditions. It is not limited. The present invention can adopt various conditions as long as the purpose of the present invention is achieved without departing from the gist of the present invention.

After blast furnace treatment, 300 tons of hot metal was tapped into a hot metal ladle, and after performing preliminary treatment such as desulfurization, the hot metal was charged into a converter. Thereafter, the first dephosphorizing agent and solid oxygen source were charged into the converter, and oxygen supply was started to start dephosphorizing blowing. Note that the oxygen supply rate during dephosphorization blowing was 400 Nm ³ /min. Note that hot metal samples were taken before the start of dephosphorization blowing and at the end of blowing and subjected to chemical analysis to analyze the P concentration in the hot metal. It is determined that the effects of the invention have been sufficiently achieved when the ratio of the P concentration in hot metal [P] ₀ before the start of blowing to the P concentration [P] in hot metal _{after dephosphorization at the end of blowing} is 0.15. did. Note that the underlines in Tables 1 and 2 indicate conditions outside the scope of the present invention.

As shown in Tables 1 and 2, Ch. No. 1 to 3, the second dephosphorizing agent is continuously supplied for 50% or more of the entire dephosphorizing blowing period, and the conditions of the above-mentioned formulas (1) and (2) are satisfied. Therefore, the effects of the invention were sufficiently obtained.

On the other hand, Ch. No. 4 and Ch. No. No. 5 did not satisfy the conditions of the above-mentioned formula (1), so the dephosphorizing effect was insufficient. Also, Ch. No. 6 and Ch. No. Since Sample No. 7 did not satisfy the condition of the above-mentioned formula (2), the dephosphorizing effect was insufficient. Furthermore, Ch. No. In Sample No. 8, the period during which the second dephosphorizing agent was continuously supplied was less than 50% of the total period of dephosphorizing blowing, so the dephosphorizing effect was insufficient.

Claims (1)

A method for dephosphorizing hot metal,
A step of charging a first dephosphorizing agent and a solid oxygen source containing 50% by mass or more of iron oxide into a refining container;
Next, a step of dephosphorizing and blowing the hot metal by blowing a second dephosphorizing agent together with oxygen from an oxygen supply lance,
During the dephosphorization blowing step, the second dephosphorizing agent is continuously supplied for a period of 50% or more of the entire period of the dephosphorization blowing from the start of the oxygen blowing until the end, When 50% of the period of the dephosphorization blowing has elapsed, the relationship between the supply amount W _deP-II of the second dephosphorizing agent and the amount W _charge of the auxiliary material satisfies the following formula (1), and Hot metal characterized in that the relationship between the supply amount W _deP-II of the second dephosphorizing agent and the auxiliary material charging amount W _charge at the time when the oxygen blowing is finished satisfies the following formula (2). Dephosphorization method.
0.16<W _deP-II /W _charge <0.25...(1)
0.30<W _deP-II /W _charge < 0.44 ...(2)
W _charge =W _deP-I +W _oxide +W _SiO2 ...(3)
W _SiO2 =0.0214×W _iron ×[Si]...(4)
Here, W _deP-I represents the charging amount (t) of the first dephosphorizing agent, W _oxide represents the charging amount (t) of the solid oxygen source, and W _SiO2 is generated by the desiliconization reaction. W _iron represents the _amount (t) of the hot metal charged in the slag, [Si] represents the Si concentration (t) in the hot metal before dephosphorization treatment. mass%).

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