JP2011137197A - Desiliconizing and dephosphorizing method for molten iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a desiliconizing and dephosphorizing method for molten iron which improves the dephosphorizing efficiency in a molten iron pre-treating process by a means applicable to the actual operation. <P>SOLUTION: When the desiliconizing and the dephosphorizing treatments are applied in the molten iron pre-treating process, (mass% FeO):(mass% SiO<SB>2</SB>) in slag at the desiliconizing period in the initial period of treatment, is controlled in the range of 90:10-60:40 to improve the liquid-phase ratio of the slag. By this method, the melting speed of sub-raw material and a material-shifting speed in the slag, are increased and thus, the dephosphorizing efficiency is improved. In order to control the (mass%FeO):(mass%SiO<SB>2</SB>) in the slag in the desiliconizing period into the range of 90:10-60:40, the oxygen supplying speed is controlled so that the ratio η of being contributed to the desiliconization by the oxygen supplied in the desiliconizing period becomes in the range of 21 to 62%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an improvement of a hot metal removal Si removal P treatment method in a hot metal preliminary treatment step.

  Conventionally, hot metal preliminary treatment in which a CaO source is introduced into the hot metal before charging the converter and oxygen is blown to remove Si and P is widely performed. Since P remaining in steel has a great influence on steel properties, various efforts have been made in the steel industry to improve the de-P efficiency.

For example, Patent Document 1 relating to the application of the present applicant discloses the knowledge that the oxygen supply rate into the hot metal affects the de-Si removal P treatment, and the oxygen supply rate from the top blowing lance is set to 0.3 Nm. It is described that by maintaining at ³ / min / t or less, hot metal having a Si content of 0.3% or more can simultaneously proceed with de-Si de-P process.

However, it is possible to maintain the oxygen supply rate from the top blowing lance at 0.3 Nm ³ / min / t or less during the entire blowing process in the experimental furnace, but in the actual operation, the hot metal temperature is maintained. Preferably, surplus heat for dissolving the cold iron source needs to be generated, so that oxygen needs to be supplied from the upper blowing lance at a rate higher than 0.3 Nm ³ / min / t. For this reason, it is not easy to improve the de-P efficiency by applying the invention of Patent Document 1 to actual operation.

JP-A-2-93011

  An object of the present invention is to provide a hot metal de-Si de-P treatment method capable of solving the above-mentioned conventional problems and improving the de-P efficiency in the hot metal pretreatment process by means applicable to actual operation. It is.

As a result of repeated researches by the present inventors to solve the above problems, the point of de-P improvement is in the initial slag formation, and the liquid supply rate is high by appropriately controlling the oxygen supply rate in the initial de-Si phase. It has been found that if slag is formed, the dissolution rate of the auxiliary raw material and the mass transfer rate in the slag are improved, and the de-P efficiency can be reliably improved. The present invention has been completed based on this finding. In performing hot metal de-Si removal P treatment in the hot metal preliminary treatment step, (mass% FeO) in the slag in the de-Si stage in the early stage of treatment: (mass% The SiO ₂ ) is controlled in the range of 90:10 to 60:40 to increase the slag liquid phase ratio, and the de-P efficiency is improved by increasing the dissolution rate of the auxiliary material and the mass transfer rate in the slag. It is what.

In the present invention, in performing the hot metal de-Si removal P treatment in the hot metal preliminary treatment step, the operation is performed so that α defined by the formula (a) is 0.17 to 0.49 in the de-Si period of the initial treatment. It is preferable to control the conditions.
α = VO ₂ ÷ [% Si] initial ÷ d ^0.6 ÷ ε ^0.7 × M × ln ([% Si] initial ÷ 0.001) (a)

  In addition, it is preferable to add quick lime or calcium carbonate into the hot metal together with slag generated after the hot metal preliminary treatment step as an auxiliary raw material for adjusting the basicity for de-P. The particle size is preferably 5 mm or less. Furthermore, it is preferable to add the auxiliary raw materials for adjusting the basicity into the hot metal in order of increasing particle size, and the auxiliary raw materials for adjusting the basicity may be added to the hot metal in order of increasing basicity. preferable.

In the present invention, by controlling the (mass% FeO) :( mass% SiO ₂ ) in the slag in the de-Si stage in the early stage of hot metal pretreatment to a range of 90:10 to 60:40, the temperature is around 1300 ° C. In the region, it is possible to form a slag of the surrounding uniform liquid phase region, which is displayed as Fayalite (2FeO · SiO ₂ ) in the CaO—SiO ₂ —FeO ternary phase diagram. This slag has a high liquid phase rate, and can increase the dissolution rate of the auxiliary raw material for de-P and the mass transfer rate in the slag. Can be improved. In the present invention, the oxygen supply rate is controlled so that the ratio η in which oxygen supplied in the Si removal period contributes to the Si removal is in a range of 21% ≦ η ≦ 62%, so that (Mass% FeO): (mass% SiO ₂ ) can be controlled in the range of 90:10 to 60:40, but it is only necessary to control the oxygen supply rate to be higher only during the de-Si period in the initial stage of treatment By adding iron oxide (Fe ₂ O ₃ ) typified by iron ore in addition to top-blown oxygen, it can be sufficiently implemented even in actual operation.

It is 1300 ° C. isothermal sectional view of _CaO-SiO 2 -FeO3 ternary phase diagram. And loading the Si concentration is a graph of oxygen supply rate VO ₂ showed the effects de P ratio of the de Si phase. And loading the Si concentration is a graph showing the relationship between the oxygen supply rate VO ₂ of de Si phase required to achieve the de-P rate goal. The present inventor is a graph showing the range eta is oxygen supply rate VO ₂ comprising in the range of 21% ≦ η ≦ 62% in equipment tested.

The present invention is described in further detail below.
In the present invention, the (mass% FeO) :( mass% SiO ₂ ) in the slag in the de-Si stage in the early stage of hot metal pretreatment is controlled in the range of 90:10 to 60:40. As shown in the 1300 ° C. isothermal sectional view of the CaO—SiO ₂ —FeO ternary phase diagram of FIG. 1, a uniform liquid phase is formed in this range even when CaO is near 0%. As a result, the liquid phase rate of the initial slag formed in the initial stage of the treatment can be increased, and the dissolution rate of the auxiliary raw material for de-P and the mass transfer rate in the slag are also increased. It is possible to improve the P-free rate.

Here, the de-Si period means a time period from the start of the treatment to the end of the de-Si reaction. A time t (min) until the de-Si reaction is completed is represented by t = [% Si] initial ÷ η ÷ VO ₂ ÷ 0.125. However, η is the ratio of the supplied oxygen to de-Si (de-Si oxygen efficiency), VO ₂ is the oxygen supply rate to the system, and in addition to oxygen blowing from the top blowing lance, it is charged in the solid state as oxide The oxygen is also a value added in terms of gaseous oxygen.

Considering the reaction of Fe + 1/2 O ₂ = FeO and the reaction of Si + O ₂ = SiO ₂ and calculating from atomic weight, 4.5 kg of FeO and 1.9 kg of SiO ₂ are generated per 1 kg of O ₂ (mass % FeO): (mass% SiO ₂ ) in the range of 90:10 to 60:40 corresponds to a range of 21% ≦ η ≦ 62% (supplied oxygen reacts only with Si or Fe). Assumption). Therefore, as described above, in order to control the (mass% FeO) :( mass% SiO ₂ ) in the slag in the de-Si phase to the range of 90:10 to 60:40, oxidation is performed together with oxygen blowing from the top blowing lance. What is necessary is just to control so that (eta) may satisfy | fill the range of 21% <= (eta) <= 62% using means, such as iron insertion. When η is less than 21%, (mass% FeO): (mass% SiO ₂ ) shifts to the FeO excess side than 90:10, conversely, when η exceeds 62%, it shifts to the SiO ₂ excess side, This is outside the preferred range. In actual operation, it is unlikely that η will be less than 21%, so it is important how to suppress η to 62% or less.

Here, factors that increase η include an increase in charged Si due to hot metal and an increase in the stirring power in the furnace (an increase in the flow rate of top blowing oxygen), and factors that decrease η include an increase in oxygen supply rate. FIG. 2 is a graph showing the influence of the charged Si and the oxygen supply rate VO ₂ in the de-Si period on the de-P rate. Η increases due to the increase in the charge [Si], and the de-P rate deteriorates. It can be read that by increasing the oxygen supply rate VO ₂ , η decreases and the P removal rate improves.

FIG. 3 is a graph showing the relationship between the charged Si and the oxygen supply rate VO _{2 in the} de-Si period necessary to achieve the target de-P rate. Since SiO ₂ tends to be generated when the amount of charged Si is large, it can be read that the target de-P rate cannot be achieved unless the oxygen supply rate VO ₂ is increased as the charged Si is higher.

In the following, the range in which the oxygen supply rate VO ₂ should be set according to the charged Si% will be described.
In order to generate the slag having the above composition, when the ratio of oxygen supplied in the de-Si period to react with the element X is η _X , as described above, η _Si : η _Fe = 21: 79 to 62:38 Since the range is sufficient, the target is achieved by controlling the oxygen supply rate VO ₂ in the de-Si period to the following range.
VO ₂ max = 0.49 × [% Si] initial × d ^0.6 × ε ^0.7 ÷ M ÷ ln ([% Si] initial ÷ 0.001)
VO ₂ min = 0.17 × [% Si] initial × d ^0.6 × ε ^0.7 ÷ M ÷ ln ([% Si] initial ÷ 0.001)
The calculation basis will be described below. The meanings and units of symbols in each mathematical formula are as shown in Table 1 below.

First, if the FeO concentration in the slag is 40% or more under the hot metal treatment conditions, the reaction is rate-controlled by the movement of Si in the hot metal, so the relationship of the following equation (1) is established.
−ln ([% Si] initial ÷ [% Si]) = k _Si × A ÷ V × t = k _Si × (π ÷ 4 × d ² ) ÷ (M ÷ 7.0) × t = 5.5 × k _Si × d ² ÷ M × t (1)

The mass transfer coefficient in the hot metal is expressed by equation (2) as a function of the stirring power and the inner diameter of the furnace body.
k _Si = 3.9 × 10 ⁻⁵ × (ε ÷ d ² ) ^0.7 Equation (2)

Since 1 Nm ³ / t of oxygen reacts with 0.125% of Si, assuming that all of the supplied oxygen reacts with Si or Fe, the time t until the de-Si is completed is expressed by equation (3). Is done.
t = [% Si] initial ÷ η _Si ÷ (VO ₂ ÷ 60) ÷ 0.125 (3)

Assuming that the Si concentration at the end of the de-Si reaction is 0.001% and rearranging the equations (1), (2), and (3), the relationship of the following equation (4) is derived.
VO ₂ = 0.103 ÷ η _Si × [% Si] initial × d ^0.6 × ε ^0.7 ÷ M ÷ ln ([% Si] initial ÷ 0.001) (4)

Since the appropriate range of η _Si is 21 to 62%, the upper and lower limit values of VO ₂ are calculated as described above when substituted into the equation (4).

Note that ε can be calculated using the following relational expression.
ε = εbottom + εtop
εbottom = 371 × K × Qbottom × T × {ln (1 + 9.8 × 6800 × h ÷ P) + (1−Tn ÷ T)}
εtop = 0.137 × cos θ × Qtop ³ × m ÷ n ² ÷ D ³ ÷ x

A graph of VO ₂ max and VO ₂ min calculated based on the above calculation basis is shown in FIG. However, conditions such as ε, d, and M are based on the numerical values of the equipment tested by the inventor. The oxygen supply rate VO ₂ may be controlled within this range in accordance with the charged Si.

  The auxiliary materials for adjusting basicity for de-P described in claims 3 to 6 will be described below. Also in the present invention, an auxiliary raw material for adjusting the basicity is required for removing P, and it is preferable to use quick lime or calcium carbonate together with slag generated after the hot metal preliminary treatment step. A typical slag generated after the hot metal pretreatment process is the converter slag, which is returned to the hot metal pretreatment process and used for de-P to reduce the amount of quicklime and calcium carbonate used. be able to.

  The particle size of such a basic material for adjusting the basicity is preferably 5 mm or less. This is because if the particle size exceeds 5 mm, it takes time to dissolve, and it becomes difficult to proceed with de-P simultaneously with de-Si.

  In addition, when the auxiliary raw materials for adjusting the basicity are not the same particle size, it is preferable to add them in order from the larger particle size. This is because a large particle size takes time to dissolve. Moreover, it is preferable to add the auxiliary raw materials for adjusting the basicity in order from the lowest basicity. This is because the lower the basicity, the easier it is to dissolve and the initial slag formation is stable.

The hot metal having the composition shown in Table 2 was charged into a converter-type refining furnace (d = 5.3 m, ε = 5.1 × 10 ⁶ W, M = 290 to 305 ton), and subjected to de-Si de-P treatment. It was. The hot metal has a C content of 3.9 to 4.5% and a P content of 0.064 to 0.084%, but the Si content is significantly different from 0.21 to 0.83%. It was. The α represented by the formula (a) of claim 2 is shown in the table by changing the oxygen supply rate from the top blowing lance in the de-Si period in the range of 1.2 to 2.2 Nm ³ / min / t. It was changed as follows. The value of the slag composition in the table is a value obtained by converting the slag composition at the time of de-Si calculated from the operating conditions into a FeO-SiO ₂ binary system.

  No. 1-No. No. 10 is an example in which α falls within the scope of the present invention. 11-No. No. 20 is Comparative Example (1), No. 21-22 is a comparative example (2) which deviated upwards from this range. In any case, the Si content in the hot metal after the treatment was almost zero, but the P content is as shown in the table, calculated as (P before treatment-P after treatment) ÷ P before treatment. It was confirmed that the P removal rate was 25 to 57% in the comparative examples (1) and (2), but significantly improved to 61 to 79% in the examples. Moreover, about the comparative example (2), the slag flowed out from the upper part of the furnace at the initial stage of the process, and it was difficult to continue the process. This is presumably because the oxygen supply rate was too high, so that de-C started and CO gas was generated before the slag with good gas releasing properties was formed, and the slag was lifted.

  The hot metal having the composition shown in Table 3 was charged into a converter-type refining furnace and subjected to de-Si removal P treatment. The hot metal has a C content of 3.8 to 4.8% and a P content of 0.064 to 0.091%, but the Si content is significantly different from 0.17 to 0.67%. It was. Quick lime / calcium carbonate and slag generated after the pretreatment step were used as auxiliary materials at the time of de-P. No. No. 1 to No. 10 are examples of the present invention in which quick lime / calcium carbonate and slag generated after the pretreatment step are used in combination. 11 to No. 20 are comparative examples using only quicklime and calcium carbonate. The P removal rate was 27 to 73% in the comparative example, but it was confirmed that the removal rate was significantly improved to 67 to 85% in the example.

  The hot metal having the composition shown in Table 4 was charged into a converter-type refining furnace and subjected to de-Si de-P treatment. The hot metal has a C content of 3.7 to 4.3% and a P content of 0.065 to 0.105%, but the Si content is significantly different from 0.23 to 0.68%. It was. The auxiliary material at the time of removing P was screened with a sieve to adjust the particle size and tested. No. No. 1 to No. 10 are examples of the present invention in which treatment was performed using only a sieve under a 5 mm mesh sieve. Nos. 11 to 20 are comparative examples using only a sieve under a 50 mm mesh sieve. The P removal rate was 37 to 66% in the comparative example, but it was confirmed that the removal rate was significantly improved to 47 to 79% in the example.

  The hot metal having the composition shown in Table 5 was charged into a converter-type refining furnace and subjected to de-Si de-P treatment. The hot metal has a C content of 3.7 to 4.5% and a P content of 0.064 to 0.087%, but the Si content is significantly different from 0.16 to 0.86%. It was. About the auxiliary material at the time of de-P, the test was conducted by preparing almost the same amount of 0 to 5 mm and 0 to 50 mm, which were adjusted by sieving with a sieve. No. No. 1 to No. 10 are examples of the present invention in which processing was performed in the order of adding an auxiliary material of 0 to 5 mm after adding an auxiliary material of 0 to 50 mm. Nos. 11 to 20 are comparative examples in which processing was performed in the order of adding auxiliary materials of 0 to 50 mm after adding auxiliary materials of 0 to 5 mm. Although the P removal rate was 16 to 64% in the comparative example, it was confirmed that the removal rate was greatly improved to 52 to 84% in the examples.

The hot metal having the composition shown in Table 6 was charged into a converter-type refining furnace and subjected to de-Si removal P treatment. The hot metal has a C content of 3.9 to 4.5% and a P content of 0.064 to 0.082%, but the Si content is significantly different from 0.19 to 0.88%. It was. About the auxiliary materials at the time of de-P, quick lime and calcium carbonate (CaO: SiO ₂ = 1: 0) and converter slag (CaO: SiO ₂ ≈3: 1) were prepared in substantially the same amount and tested. No. Nos. 1 to 10 are examples of the present invention in which processing was performed in the order of charging quick lime and calcium carbonate (high basicity) after charging converter slag (low basicity). Nos. 11 to 20 are comparative examples in which processing was performed in the order of charging converter slag (low basicity) after charging quick lime and calcium carbonate (high basicity). The P removal rate was 9 to 62% in the comparative example, but it was confirmed that the removal rate was significantly improved to 56 to 79% in the examples.

Claims (6)

In performing hot metal de-Si removal P treatment in the hot metal preliminary treatment step, (mass% FeO) :( mass% SiO ₂ ) in the slag in the de-Si stage in the initial stage of the treatment is controlled in the range of 90:10 to 60:40. And improving the de-P efficiency by increasing the slag liquid phase ratio and increasing the dissolution rate of the auxiliary raw material and the mass transfer rate in the slag. In performing hot metal de-Si removal P treatment in the hot metal preliminary treatment step, the operating conditions are controlled so that α defined by the formula (a) is 0.17 to 0.49 in the de-Si period of the initial treatment. The hot metal removal Si removal P treatment method according to claim 1.
α = VO ₂ ÷ [% Si] initial ÷ d ^0.6 ÷ ε ^0.7 × M × ln ([% Si] initial ÷ 0.001) (a)   2. The hot metal de-Si de-P treatment method according to claim 1, wherein quick lime or calcium carbonate is used as a secondary material for adjusting the basicity for de-P, together with slag generated after the hot metal pretreatment step.   4. The hot metal de-Si removal P treatment method according to claim 3, wherein the particle size of the auxiliary raw material for adjusting the basicity is 5 mm or less.   4. The hot metal de-Si removal P treatment method according to claim 3, wherein the auxiliary materials for adjusting the basicity are introduced in the order of increasing particle size.   4. The hot metal de-Si de-P treatment method according to claim 3, wherein the auxiliary materials for adjusting the basicity are introduced in order from the lowest basicity.