JP2011058053A - Dephosphorizing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the slag forming property, and to protect the refractory when executing the dephosphorization by using recycled slag of decarburization slag. <P>SOLUTION: When executing the dephosphorization of molten iron by feeding gaseous oxygen and solid oxygen source in a top and bottom blown converter type refining vessel prior to the decarburization process, the amount of oxygen to be fed during the dephosphorization and oxygen other than oxygen used for desiliconization is set to be ≥10 Nm<SP>3</SP>/t, the grain size of quick lime to be charged is set to be 5-40 mm. The decarburization slag containing MgO is fed so that the ratio of the recess depth L of a molten metal to the bath depth L<SB>0</SB>when blowing gaseous oxygen is set to be 0.01-0.20, the bottom blown stirring power density ε is set to be 0.5-3.5kw/t, and the amount of MgO to the amount of slag after dephosphorization is set to be ≤4.5 mass%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a dephosphorization method for performing dephosphorization of hot metal in an upper bottom blown converter type refining vessel prior to the decarburization step, for example.

Conventionally, as a technique for performing dephosphorization of hot metal in an upper bottom blowing converter type refining vessel using recycle slag, for example, there is one of Patent Document 1.
In Patent Document 1, hot metal containing Si is dephosphorized in a top-blown converter using slag having a basicity (CaO / SiO ₂ ; weight ratio) in the range of 1.5 to 3.0. In refining, the value of bottom blowing stirring force ΣεBottom is set to a range of 1.5 to 3.4 (Kw / ton), and the oxygen blowing rate QO2 ore by the top blowing acid rate QO2 gas and iron ore supply. sum of ΣQO2 the value of (Nm ³ / min / ton), depending on the value of the stirring force, determined by the top-blown oxygen-flow form, the average value of (L / L ₀₎ in blowing period (L / L ₀₎ Is set to 0.25 or less.

Moreover, there exist patent document 2 and patent document 3 as a technique which performs the dephosphorization process of hot metal in a top bottom blowing converter type | mold refining container.
In Patent Document 2, while performing gas stirring from the bottom of the reaction processing vessel charged with hot metal, a majority amount of quick lime is added in the form of a lump, and gaseous oxygen is blown from an upper blowing lance to perform hot metal dephosphorization treatment. A granulated quick lime granulated from powdered quick lime is added as a quick lime source, and the basicity after the dephosphorization treatment is 1.5 to 2.0.

  In Patent Document 3, when performing a hot metal dephosphorization treatment with lime and oxygen and / or iron oxide using a smelting furnace lined with a refractory mainly composed of MgO and having an upper bottom blowing function, the slag basicity is determined. 0.8 to 1.8, T · Fe in the slag is adjusted to 8 to 19% by mass percent, and MgO in the slag is adjusted to 0.3 to 6%.

JP 2002-322506 A JP 05-302109 A JP 2002-146422 A

In Patent Document 1, although the bottom blowing agitation force and L / L ₀ are controlled when performing dephosphorization treatment using recycled slag, the particle size of quicklime and MgO in the slag are not considered.
The technology of Patent Document 2 discloses the particle size of quicklime, and Patent Document 3 discloses that dephosphorization treatment is performed by controlling MgO in the slag. However, these technologies are based on cycle slag. Since dephosphorization is not performed, even if the techniques of Patent Documents 1 to 3 are combined, it is very difficult to improve the slag hatchability.

  Therefore, in view of the above problems, the present invention provides a dephosphorization method capable of improving the slag hatchability and protecting refractories when performing dephosphorization treatment using recycled slag of decarburized slag. The purpose is to do.

In order to achieve the above object, the present invention has taken the following measures.
That is, the technical means for solving the problems in the present invention is that when performing dephosphorization of hot metal by supplying gaseous oxygen and a solid oxygen source in an upper bottom blown converter type refining vessel prior to the decarburization step. The amount of oxygen to be introduced into the chamber and the amount of oxygen other than oxygen used in the desiliconization reaction is set to 10 Nm ³ / t or more, the particle size of the input quicklime is set to 5 to 40 mm, and the molten metal at the time of blowing in gaseous oxygen The ratio of the dent depth L to the bath depth L ₀ is set to 0.01 to 0.20, and the bottom blowing stirring power density ε is set to 0.5 to 3.5 kw / t, and the slag after the dephosphorization treatment The decarburization slag containing MgO is supplied so that the amount of MgO relative to the amount is 4.5% by mass or less.

  ADVANTAGE OF THE INVENTION According to this invention, even in the dephosphorization process using recycling slag like decarburization slag, a dephosphorization process can be performed efficiently, without reducing a dephosphorization efficiency.

It is the figure which showed the steelmaking process including the dephosphorization method (dephosphorization process).

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a steel making process including the dephosphorization method (dephosphorization process) of the present invention. In the following description, hot metal or molten steel will be described as molten metal.
As shown in FIG. 1, in general, in the steelmaking process, first, the molten metal 2 is discharged from the blast furnace 1, and then the molten metal 2 is subjected to a desulfurization process (desulfurization process) in a pan 7 or the like. Thereafter, the molten metal 2 is charged into the converter-type smelting vessel 3 and the molten metal 2 is dephosphorized (dephosphorization process). The molten metal 2 is charged into the converter 4 and decarburized (decarburized). Step). Degassing and component adjustment are performed on the molten metal 2 that has been decarburized. In the following description, hot metal or molten steel will be described as molten metal.

  As described above, the dephosphorization method of the present invention is performed by the converter-type refining vessel 3 different from the converter 4 that performs the decarburization process prior to performing the decarburization process (decarburization process) in the converter 4. Primarily, a dephosphorization process for lowering [P] is performed on the molten metal 2. By separating the dephosphorization process and the decarburization process and reusing (recycling) the slag (decarburized slag) generated during the decarburization process, the total slag discharge amount in both processes is reduced. Yes.

The converter 4 that performs the decarburization treatment may be an upper blowing converter that blows gaseous oxygen from the upper blowing lance 5 into the molten metal 2 or the like, or a bottom blowing converter that blows gaseous oxygen from the tuyere 6 at the bottom of the furnace. Alternatively, it may be an upper bottom blowing converter in which gaseous oxygen is blown from the top blowing lance 5 and gaseous oxygen or inert gas is blown from the tuyere 6.
The converter-type smelting vessel 3 for performing the dephosphorization process is an upper bottom blowing type provided with an upper blowing lance 7 for blowing gaseous oxygen into the molten iron 2 and a tuyere 8 for blowing oxygen or inert gas into the molten iron 2 from the furnace bottom. Then, oxygen is supplied by gaseous oxygen from the top blowing lance 7, and the molten metal 2 is stirred by oxygen from the tuyere 6 or inert gas. The converter type refining vessel 3 includes a supply device 9. The supply device 9 supplies auxiliary materials [quick lime, solid oxygen source (for example, iron oxide), decarburized slag)], and is, for example, a hopper or a chute.

  In addition, in performing the dephosphorization process of the molten metal 2, it is possible to use a kneading car and a ladle, but since a free board is small in a kneading car and a ladle, slopping tends to occur. In such a case, in order to prevent slopping, it is necessary to slow down the supply rate of gaseous oxygen or a solid oxygen source as compared with the converter-type refining vessel 3, and the dephosphorization process may take time. Therefore, in this invention, it does not use a kneading car and a ladle, but targets what performs the dephosphorization process with the converter-type refining vessel 3. The refractories provided in the converter type refining vessel 3 and the converter 4 are mainly magnesia refractories and contain MgO.

Hereinafter, the dephosphorization process of the present invention will be described in detail.
[Amount of oxygen input during processing]
In the present invention, when performing the dephosphorization process, gaseous oxygen or a solid oxygen source is supplied as an oxygen source, but the amount of oxygen supplied during the dephosphorization process (as will be described later, the amount used in the desiliconization reaction). Is 10 Nm ³ / t or more.

Now, when oxygen is supplied during the dephosphorization treatment, the desiliconization reaction takes place preferentially before the dephosphorization reaction. Therefore, in the present invention, desiliconization reaction takes precedence over dephosphorization reaction and oxygen is used in the dephosphorization reaction. Therefore, it is used in such desiliconization reaction (desiliconization treatment). The amount excluding oxygen is taken into consideration. That is, in the present invention, the amount of oxygen supplied during the dephosphorization treatment and the amount of oxygen other than oxygen used for the desiliconization reaction (hereinafter, sometimes referred to as the amount of oxygen outside de-Si for convenience of explanation) is 10 Nm ^3. / T or more.

In the dephosphorization treatment, oxygen is required. If the amount of oxygen outside the de-Si is less than Nm ³ / t, the dephosphorization efficiency is lowered and the desired [P] cannot be ensured. Here, although the upper limit value of the oxygen amount outside de-Si is not stipulated, if the amount of oxygen (the amount of oxygen outside de-Si) is too large, [C] after dephosphorization is too low, and decarburization is performed. There is a risk that the heat likelihood in the process is lost. If the heat likelihood in the decarburization process is lost, a heat-up material such as carbon or FeSi must be input in the decarburization process, and the cost increases. In addition, if the amount of oxygen (the amount of oxygen outside de-Si) is too large, slopping is likely to occur in the dephosphorization process, resulting in a decrease in yield. Therefore, the amount of oxygen outside de-Si is 25 Nm ³ / t or less. It is preferable to make it.

The amount of oxygen- _excluded oxygen G _O2 can be obtained from equation (1). The solid oxygen amount (V _{02 (i)} ) shown in the formula (1) is the solid oxygen amount (V _{02 (S)} ) contained in all the auxiliary materials, that is, the total amount of the solid oxygen source supplied by the dephosphorization process. This can be obtained by the equation (2). In addition, since the solid oxygen source includes divalent iron oxide (FeO) and trivalent iron oxide (Fe ₂ O ₃ ), the trivalent iron oxide in the total iron oxide is expressed by the formula (3). The total amount of the solid oxygen source is determined by substituting the value into the equation (2).

In addition, the analysis method of FeO and Fe ₂ O ₃ , that is, how to obtain it, first, in the ICP emission analysis method, the total iron concentration (% T. Fe) was obtained, and the metal iron concentration (% M .Fe) is obtained by the method of JISM8713. Moreover, (% FeO) was calculated | required by the method of JISM8712 with the EDTA2Na solution from the residue of the bromine methanol method. Here, the method for obtaining FeO and Fe ₂ O ₃ is described, but this method is in accordance with ordinary methods of those skilled in the art.
[About the particle size of quicklime]
The dephosphorization reaction requires oxygen and CaO as indicated by 2 [P] +5 (FeO) +3 (CaO) → 3 (CaO.P ₂ O ₅ ) + 5Fe for convenience. In order for this CaO to contribute to the dephosphorization reaction, it must be melted in the slag. The treatment temperature during the dephosphorization treatment is 1250 to 1400 ° C., whereas the melting point of CaO varies depending on the literature, but it is about 2600 ° C. It is much higher than the processing temperature. As a supply source of CaO, quick lime is generally used. However, quick lime is mostly made of CaO, so it is difficult to melt. In the prior art, for example, as shown in JP-A-03-122209, JP-A-2003-12912, etc., a melting point depressant such as fluorite or alkali metal oxide is used to lower the melting point of quicklime and melt it. It was easy to do. When fluorite is used in this way, the slag produced by the dephosphorization process contains a lot of fluorine, which is restricted by environmental standards. When used for building materials, etc., there is a problem that the reuse destination of slag is limited.

  Therefore, according to the present invention, the particle size of quick lime is reduced so that quick lime can be easily melted without using a melting point depressant containing fluorine, which is restricted by environmental standards. ing. Specifically, the particle size of quick lime such as quick lime serving as a CaO source is 5 mm or more and 40 mm or less. In addition, the particle size of quicklime was discriminate | determined using the sieve based on JISZ8801.

When the lime particle size is less than 5 mm, when quick lime is charged, it is scattered by the rising air flow from the converter-type refining vessel or sucked into the dust collector for gas recovery provided on the furnace body. There is. That is, if the particle size of quicklime is less than 5 mm, the amount of quicklime reaching the bath surface of the molten metal 2 is reduced, and the yield of quicklime is reduced.
When the particle size of quick lime exceeds 40 mm, quick lime becomes difficult to melt, so the particle size of quick lime is set to 40 mm or less.

  In addition, as a method of supplying quick lime to the molten metal 2, as shown in JP-A-63-199815 and JP-A-2005-272883, the particle size is small without being sucked into the dust collector by using injection or blasting. Although quick lime can be thrown in, if these facilities are used, it will become large-scale, and since large-scale capital investment is required, in this invention, supply of quick lime is the supply apparatus 9 etc. from the upper direction of a furnace body. Targeted by.

[Ratio between the depth L of the molten metal and the depth L _{0 of the} bath]
The ratio between the depth L ₀ of the molten metal and the depth L _{0 of the} bath is an index indicating the strength of gaseous oxygen, and is often used as an index of the blowing condition in dephosphorization treatment and the like. In other words, L is the depth of the dent of the molten metal when blowing, that is, when oxygen is blown from the top blowing lance 4 toward the molten metal 2, and L ₀ is during non-blowing, that is, the top blowing lance. This is the bath depth when oxygen is not blown from 4 toward the molten metal. The relationship between the depth L of the molten metal and the oxygen flow rate when oxygen is blown from the upper blowing lance 4 is obtained by the equation (4). This formula (4) is a general formula described in “Iron Metallurgical Reaction Engineering” [revised edition] 2nd edition written by Kiyoshi Segawa, Nikkan Kogyo Shimbun, page 94 (5.5).

In addition, the nozzle coefficient k shown by Formula (4) was calculated | required from the relationship between the nozzle hole angle of the top blowing lance 4 and the number of nozzle holes using FIG. 10 of the patent 2736555 gazette. In this embodiment, the upper blow lance 7 has 6 holes and 15 °, and the nozzle coefficient k is 1.31. L ₀ is measured by measuring the height of the bottom of the furnace in the empty furnace and the surface height of the molten metal after charging 2 using a microwave level meter disclosed in Japanese Patent Publication No. 4-81734. Depth was sought.

If L / L ₀ is large and the collision pressure of gaseous oxygen against the molten metal 2 is too strong, the hot spot region where the dephosphorization reaction is unlikely to occur becomes large, and the dephosphorization efficiency decreases. Moreover, when the collision pressure of gaseous oxygen is too strong, the reaction shown by [C] + 1 / 2O ₂ → CO becomes dominant and the dephosphorization efficiency is lowered.
Therefore, in the present invention, when supplying gaseous oxygen, gaseous oxygen is blown by soft blow with a small collision pressure of gaseous oxygen so that dephosphorization efficiency does not decrease.
Specifically, the soft blow described above is performed by supplying gaseous oxygen in a range where L / L ₀ is 0.01 or more and 0.20 or less. Here, when L / L ₀ is larger than 0.20, it cannot be said that soft blow is any longer, and the collision pressure of gaseous oxygen becomes strong, so that the dephosphorization efficiency is lowered for the reason described above.
When L / L ₀ is less than 0.01, the blowing of gaseous oxygen is too weak. For example, a large amount of gaseous oxygen reacts with the CO gas in the furnace before reaching the bath surface of the molten metal 2 (so-called 2 Secondary combustion), the amount of iron oxide in the slag decreases, and the dephosphorization efficiency decreases. Further, if L / L ₀ is less than 0.01, the blowing of gaseous oxygen is too weak, so that the mixing of slag and molten metal due to the collision pressure of gaseous oxygen is reduced, and the reaction interface area is reduced, resulting in desorption. Phosphorus efficiency decreases.

[About bottom blowing stirring power density]
In the dephosphorization process, the stirring power density for bottom blowing to stir the hot metal is also important. Formulas for calculating the stirring power density are formulas proposed by Mori et al. (Iron and Steel 67 (1981), p. 672), Nakanishi et al. (Iron and Steel 68 (1982), p. A14), and so on. However, in the present invention, the Mori equation is used as shown in equation (5) in determining the bottom blowing stirring power density.

In equation (5), the steel bath depth h ₀ is the same as the bath depth L ₀ (h ₀ = L ₀ ). Moreover, the hot metal temperature of the formula (5) was measured before and after dephosphorization treatment, and was taken as an average.
If the bottom blowing agitation power density is less than 0.5 kw / t and is too weak, the mass transfer of phosphorus to the slag-hot metal bath surface will be delayed, and the diffusion rate of CaO in the slag will be slow. As a result, the hatching delays, delaying the dephosphorylation reaction and dephosphorization efficiency. Further, the heat supply to the slag by stirring is reduced, the FeO concentration in the slag is increased, and the dephosphorization efficiency is lowered.

If the bottom blowing agitation power density is larger than 3.5 kw / t and too strong, FeO in the slag decreases due to the active reaction between the slag and molten iron, and the oxidation source for dephosphorization is insufficient. At the same time, hatching of quicklime is delayed, and the dephosphorization efficiency is reduced as in the case where the stirring power is low.
[About decarburization slag]
In the dephosphorization process of the present invention, decarburization slag is always supplied as a part of the CaO source in addition to the above-mentioned quicklime, but the supplied decarburization slag is slag after dephosphorization process (dephosphorization). The amount of MgO is sometimes 4.5% or less.

  Here, the decarburized slag is slag generated by the decarburization process, and the amount of quick lime used in the dephosphorization process is reduced by using the slag generated by the decarburization process for the dephosphorization process. It is possible to reduce the amount of total slag generated in the dephosphorization process and the decarburization process. This decarburization slag usually contains 5 to 10% by mass of MgO from the viewpoint of protecting the furnace body during the decarburization treatment (protection of refractory). By using such decarburization slag containing MgO for the dephosphorization process, the furnace body of the converter-type refining vessel 3 that performs the dephosphorization process can be protected.

  In the decarburization slag, since the dephosphorization process is 1250 to 1400 ° C. and lower than the decarburization process, the saturation solubility of MgO is as low as 2 to 3%, and hatching defects may occur. In using the decarburized slag, the MgO amount was set to 4.5% (mass%) or less based on the slag amount after the treatment. That is, if a large amount of decarburized slag is supplied so that the amount of MgO in the dephosphorized slag exceeds 4.5% (mass%), the liquid phase rate of the slag in the dephosphorization process decreases and the dephosphorization is performed. In the present invention, since the efficiency is decreasing, the amount of MgO in the dephosphorization slag does not exceed 4.5% even when the decarburization slag is used for the dephosphorization treatment.

  In setting the supply amount of decarburization slag (the amount of decarburization slag to be input), the amount of decarburization slag to be input is obtained using Equations (6) to (8).

Specifically, first, the amount of CaO to be added (W _(CaO) ) is obtained by equation (6). Then, the minimum amount W _{s (min)} of the dephosphorization slag is obtained from the amount of CaO to be added and the maximum value (maximum concentration) of the CaO amount contained in the dephosphorization slag (slag after treatment ₎ . Thus, when the amount of dephosphorization slag is minimum, the MgO concentration in the dephosphorization slag is considered to be the highest. Therefore, as shown in equation (7), when decarburization slag is introduced, The case where phosphorus slag is minimum is considered as a standard.

Next, it is considered that the amount of MgO contained in the amount of decarburized slag to be input (W _LDslag ) [(% MgO) _LDslag ] is equal to the amount of MgO [(% MgO) _call ] when the dephosphorization slag is minimum. The amount of decarburization slag (W _LDslag ) is determined in the range where the MgO amount [(% MgO) _LDslag ] does not exceed 4.5% according to the equation (8). In addition, (% CaO) _max in Formula (7) was 48 mass% from the analysis result of the dephosphorization slag processed as usual by those skilled in the art.

The amount of decarburized slag (W _LDslag ) determined in this way is the amount of decarburized slag that is input during the dephosphorization process.
Table 1 shows the implementation conditions.

As shown in Table 1, the dephosphorization treatment was performed in a 250-ton class top-bottom blowing type converter-type refining vessel. In top blowing, an upper blowing lance having 6 holes, a hole diameter of 55 mm, and a hole angle of 15 ° was used. The bottom blowing gas was N ₂ gas, a single-layer annular tube (where the gas is blown out has a ring shape), and the number of single-layer annular tubes was four.
In the molten metal (molten metal) charged into the converter type refining furnace, [C] = 4.2 to 4.6% by mass, [Si] = 0.2 to 0.4% by mass, [Mn] = 0.2 -0.4 mass%, [P] = 0.100-0.130 mass%, and HMR = 90-100%.

The HMR was determined by blending calculation according to a conventional method of those skilled in the art so that the temperature after dephosphorization was 1290 to 1310 ° C., depending on the hot metal Si and the temperature before treatment. The auxiliary material was charged in its entirety by the supply device 9 after hot metal and scrap were charged into the converter-type refining vessel. The amount of CaO required for the dephosphorization treatment was determined by the auxiliary raw material control of those skilled in the art, and the basicity was set to 1.5 to 2.5. In the decarburization slag, (T.Fe) = 15-22 mass%, (CaO) = 42-48 mass%, (SiO ₂ ) = 10-14%, (MnO) = 3-5 mass%, (MgO ) = 5 to 9% by mass, and (P ₂ O ₅ ) = 0.5 to 2.5% by mass. Moreover, what generate | occur | produced when the decarburization process was performed with respect to the hot metal made into [P] <= 0.025 mass% by dephosphorization process was used for the decarburization slag. The particle size of the decarburized slag was also set to 5 mm or more and 40 mm or less. Moreover, quick lime was used for CaO sources other than decarburization slag. In the dephosphorization treatment, the standard upper limit of [P] after blowing was set to 0.025 mass%. In addition, it is very general that the standard upper limit of [P] after blowing is 0.025 mass% as described in JP-A-2001-98314 and the like.

  Tables 2 to 5 summarize examples and comparative examples in which dephosphorization treatment was performed based on the implementation conditions of Table 1. Tables 2 and 3 summarize examples in which the treatment was performed by the dephosphorization method of the present invention, and Tables 4 and 5 were treated by a method different from the dephosphorization method of the present invention. The comparative examples are summarized.

  When the maximum particle size is 40 mm and the minimum particle size is 5 mm, the particle size of the quicklime is 37.5 mm below the nominal size of 40 mm and close to 40 mm (all particles pass through). And a nominal size above 5 mm and on a 5.6 mm sieve closest to 5 mm (all particles do not pass). That is, in Examples and Comparative Examples, the particles remaining in the column of 5.6 mm sieving ratio were expressed in%, and the particles remaining in the column of 37.5 mm sieving ratio were expressed in%. In Examples and Comparative Examples, the amount of gaseous oxygen was shown as the amount of gaseous acid, and the amount of solid oxygen source was shown as the amount of solid acid.

In Examples 1 to 18, the amount of oxygen removed from Si (the value in the column of oxygen removed from Si) was 10 Nm ³ / t, and the particle size of quick lime to be added was 5 to 40 mm (1 + 2 in the column of quick lime particle size). The value is 0%).
In Examples 1 to 18, the ratio of the depth L ₀ of the molten metal and the depth L _{0 of the} bath when gaseous oxygen is blown is set to 0.01 to 0.20 (in the column of the depth of the molten metal recess). L / L0 is within a range of 0.01 to 0.20), and bottom blowing stirring power density ε is 0.5 to 3.5 kw / t (the value of ε in the stirring power density column is 0.5 to 0.5). Decarburization slag is supplied in a range where the amount of MgO to be added is 4.5% or less of the amount of slag after dephosphorization treatment (decarburization in the column of decarburization slag recycling). The value of charcoal slag input is lower than the decarburized slag limit).

That is, in Examples 1 to 18, since all the conditions in the dephosphorization method of the present invention are satisfied, even if decarburized slag is used for dephosphorization, [P] after dephosphorization is less than the standard value. (Experimental result column, evaluation “◯”).
On the other hand, in Comparative Examples 19 to 24, the amount of oxygen outside de-Si was less than 10 Nm ³ / t, and since the supply amount was small, the dephosphorization efficiency was lowered, and [P] after dephosphorization treatment was below the standard value (Experimental result column, evaluation “×”).

  In Comparative Examples 25 to 27, the particle size of quick lime is less than 5 mm, so that the amount of quick lime reaching the bath surface of the molten metal 2 is small, so that the dephosphorization efficiency is reduced. P] could not be reduced to the standard value or less (Experimental result column, evaluation “×”). In Comparative Examples 28 to 30, the particle size of quick lime is larger than 40 mm, so that quick lime is difficult to melt and the hatchability of slag is lowered, so that the dephosphorization efficiency is reduced, and [P] after the dephosphorization treatment Could not be less than the standard value (Experimental result column, evaluation “×”).

In Comparative Examples 31 to 33, the ratio of the dent depth L of the molten metal to the bath depth L ₀ is less than 0.01 and the blowing of gaseous oxygen is too weak, so the dephosphorization efficiency is reduced, and the dephosphorization treatment is performed. Later [P] could not be made to be below the standard value (experimental result column, evaluation “×”). In Comparative Example 34 to Comparative Example 36, the ratio of the dent depth L of the molten metal to the bath depth L ₀ is larger than 0.2 and the blowing of gaseous oxygen is too strong. It is. For this reason, the dephosphorization efficiency was lowered, and [P] after the dephosphorization treatment could not be reduced to the standard value or less (experimental result column, evaluation “×”).

  In Comparative Examples 37 to 39, since the bottom blowing stirring power density ε is less than 0.5 kw / t and the stirring power is too small, the dephosphorization efficiency is lowered, and [P] after the dephosphorization treatment is the standard value. The following could not be made (Experimental result column, evaluation “×”) In Comparative Examples 40 to 42, since the bottom blowing stirring power density ε exceeds 3.5 kw / t and the stirring power is too strong, the dephosphorization efficiency is lowered as a result. P] could not be reduced to the standard value or less (Experimental result column, evaluation “×”).

In Comparative Example 43 to Comparative Example 46, too much decarburized slag was added and the MgO content in the slag after the dephosphorization process exceeded 4.5%, so the slag hatched during the dephosphorization process As a result, the dephosphorization efficiency was lowered, and as a result, [P] after the dephosphorization treatment could not be reduced to the standard value or less (Experimental result column, evaluation “×”).
As described above, when decarburization slag is supplied to a converter type refining vessel and dephosphorization is performed, decarburization is performed so that the amount of MgO is 4.5% or less with respect to the amount of slag after dephosphorization. The slag must be supplied, and the ratio of the solid oxygen source, the particle size of the quick lime to be added, the ratio of the dent depth L to the bath depth L _0, and the bottom blowing agitation power density ε according to the present invention. Need to be set like Thereby, even in the dephosphorization process using the recycle slag such as the decarburization slag, the dephosphorization process can be performed efficiently without reducing the dephosphorization efficiency.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Blast furnace 2 Molten metal (molten metal, molten steel)
3 Converter type refining vessel 4 Converter 5 Upper blowing lance 6 Tuyere 7 Upper blowing lance 8 Feather 9 Feeding device

Claims (1)

Prior to the decarburization process, when supplying the gaseous oxygen and solid oxygen source in the top bottom blowing converter type refining vessel,
The amount of oxygen to be supplied during the treatment, and the amount of oxygen other than oxygen used in the desiliconization reaction is 10 Nm ³ / t or more, the particle size of the quick lime to be charged is 5 to 40 mm, and the molten metal at the time of blowing gaseous oxygen The ratio of the dent depth L to the bath depth L ₀ is set to 0.01 to 0.20, and the bottom blowing stirring power density ε is set to 0.5 to 3.5 kW / t. A dephosphorization method comprising supplying decarburized slag containing MgO so that the amount of MgO relative to the amount of slag is 4.5 mass% or less.

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