JP5438543B2 - Dephosphorization method - Google Patents

Description

  The present invention relates to a dephosphorization method in which gaseous oxygen and a solid oxygen source are supplied in a top bottom blowing converter type refining vessel prior to the decarburization step to perform dephosphorization of hot metal.

Conventionally, as a technique for performing dephosphorization processing of hot metal in an upper bottom blown converter type refining vessel, for example, there are those of Patent Documents 1 to 3.
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 in the 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.

  In Patent Document 2, a refining agent is added to hot metal held in a converter equipped with a gas top-bottom blowing function, and the hot metal is stirred and degassed with a gas blown from the furnace bottom tuyere while topping up oxygen gas. In the hot metal pretreatment method for phosphorous, 20 kg / t or more of sintered ore having a particle size of 2 to 5 mm is used as a part of the refining agent, and the amount of oxygen brought into the hot metal by sintering ore sinters A. When the oxygen content of the ore is used and B is the amount of oxygen gas blown into the hot metal, 30% ≦ A / (A + B) × 100 ≦ 60% is satisfied.

  Patent Document 3 discloses a method of dephosphorizing hot metal having a Si content of 0.3 mass% or more using a iron making agent mainly composed of CaO and oxygen in a converter type furnace, The average particle size is set to 10 mm or less, and the basicity of the slag after dephosphorization is set to 2.0 or less in terms of mass%.

JP 2002-322506 A Japanese Patent No. 3705170 JP 2004-190114 A

In Patent Document 1, when performing the dephosphorization treatment, although the bottom blowing stirring power density and L / L ₀ are disclosed, the amount of oxygen outside desiliconization and the particle size of quicklime are not considered at all. Moreover, in patent document 2 and patent document 3, when performing the dephosphorization process, although the particle size of quicklime is disclosed, the amount of oxygen outside desiliconization and the bottom blowing stirring power density are not considered at all.
That is, even if the techniques of Patent Documents 1 to 3 are used, the stirring power density, the solid oxygen ratio, the amount of oxygen outside desiliconized, the particle size of quicklime, L / L ₀ , and hot metal temperature that affect dephosphorization are determined. Since this is not taken into consideration, it is actually difficult to ensure that the phosphorus concentration [P] of hot metal is not more than a desired value.

Therefore, in view of the above-mentioned problems, the present invention sets the relationship between the parameter Z obtained by multiplying the stirring power density and the solid oxygen ratio, and the amount of oxygen outside desiliconized, the particle size of quicklime, L / L ₀ , and hot metal temperature. It aims at providing the dephosphorization method which can improve dephosphorization efficiency by setting it as an appropriate range.

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 product of X [kw / t] and the solid oxygen ratio Y [%] is defined as parameter Z, and the amount of oxygen supplied during the process is used for the desiliconization reaction. The relationship between the oxygen amount G _O2 other than oxygen and the parameter Z is 0.00065 × Z ² −0.12 × Z + 12.5 ≦ G _O2 , the particle size of the quick lime to be charged is 5 to 40 mm, and gaseous oxygen is blown The ratio of the depth L ₀ of the molten metal to the depth L _{0 of the} bath is set to 0.01 to 0.20, and the hot metal temperature after the dephosphorization treatment is set to 1280 to 1340 ° C. is there.

According to the present invention, the relationship between the parameter Z obtained by multiplying the stirring power density and the solid oxygen ratio and the amount of oxygen outside desiliconization, the particle size of quick lime, L / L ₀ , and the hot metal temperature are within appropriate ranges. The dephosphorization efficiency can be improved.

It is the figure which showed the steelmaking process including the dephosphorization method (dephosphorization process). It is a relationship figure of the parameter Z which multiplied the stirring power density and the solid oxygen ratio, and the amount of oxygen outside desiliconization.

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 10 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), or the molten metal 2 after dephosphorization is charged into the converter-type smelting vessel 3 again after the slag is discharged and decarburized. Degassing and component adjustment are performed on the molten metal 2 that has been decarburized.

Thus, in the dephosphorization method of the present invention, before the decarburization process (decarburization step) is performed in the converter 4, the converter type refining vessel 3 that is different from or the same as the converter 4 that performs the decarburization process. Thus, the dephosphorization process for lowering [P] is mainly performed on the molten metal 2.
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 raw materials [quick lime, a solid oxygen source (for example, iron ore, sintered ore, mill scale), such as 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, it is necessary to slow the supply rate of gaseous oxygen or a solid oxygen source (for example, iron oxide) as compared with the converter-type refining vessel 3 in order to prevent slipping, and the processing time becomes longer. 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.

Hereinafter, the dephosphorization process of the present invention will be described in detail.
[Amount of oxygen input during processing]
Now, when oxygen is supplied during the dephosphorization process, the desiliconization reaction occurs 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. In other words, in the present invention, first, the product of the bottom blowing stirring power density during processing X [kw / t] and the solid oxygen ratio Y [%] is defined as a parameter Z (Z = XY). The defined parameter Z and the amount of oxygen to be supplied during the processing, and the amount of oxygen G _O2 other than oxygen used for the desiliconization reaction (hereinafter referred to as the amount of oxygen outside Si or the amount of oxygen outside Si for descriptive convenience The bottom blowing stirring power density X, the solid oxygen ratio Y, and the desiliconized oxygen amount G _O2 are set so that the relationship with the following relationship is 0.00065 × Z ² −0.12 × Z + 12.5 ≦ G _O2 It is adjusted.

When considering the dephosphorization reaction (dephosphorization process), the bottom blowing stirring power density X is an important factor. For example, if the bottom blowing stirring power density X is too small, the mass transfer of phosphorus to the slag-hot metal bath surface is delayed and the diffusion rate of quick lime in the slag is slow, so that the quick lime hatching is delayed and dephosphorization is performed. May interfere with the reaction.
On the other hand, if the bottom blowing agitation power density X is too large, the reaction between the slag and carbon in the hot metal proceeds too much, and the FeO (oxidation degree) in the slag is lowered to reduce the phosphorus concentration [P]. In addition to the shortage of sources, the dephosphorization reaction may be hindered as in the case where the bottom blown stirring power density X is too low due to the delayed hatching of quicklime.

Thus, bottom-blown agitation power density X, since various affecting dephosphorization reaction, the inventors, the In obtaining the de-Si outside oxygen amount G _O2 was used as an important parameter.
In addition, when considering the dephosphorization treatment, the solid oxygen ratio Y in addition to the bottom blowing power agitation power density X is also an important factor. When gaseous oxygen is blown instead of a solid oxygen source for dephosphorization, for example, when some gaseous oxygen reacts with the CO gas in the converter type refining vessel 3 to become CO ₂ gas and does not contribute to the dephosphorization reaction There is also. Also, at the part where gaseous oxygen collides with the hot metal bath surface, a high temperature region (ignition region) where the oxygen jet and hot metal are in direct contact is formed due to the strong impinging pressure of the oxygen jet. Does not happen. Here, there is a shut-off blowing method as described in Japanese Patent Application Laid-Open No. 2004-115910 as a method that does not create an ignition region. In such a method, the height of the top blowing lance and the oxygen flow rate are strictly controlled. In operation where the amount of hot metal charged and the adhesion state of metal in the converter smelting vessel 3 change every heat, the height of the top lance and the oxygen flow rate are strictly controlled. It can be difficult to do.

  For the reasons described above, when supplying oxygen to the hot metal, it is considered preferable to supply a solid oxygen source instead of gaseous oxygen. However, gaseous oxygen is blown to generate slag entrainment and promote dephosphorization reaction. You can also expect Therefore, in the dephosphorization treatment, it is preferable to supply both a solid oxygen source and gaseous oxygen. In consideration of the action of gaseous oxygen that promotes the dephosphorization reaction, the balance between the solid oxygen source and gaseous oxygen, that is, The solid oxygen ratio Y is also important.

Thus, since the gaseous oxygen and the solid oxygen source have various effects on the dephosphorization reaction, the inventor has determined the solid oxygen ratio Y indicating the supply ratio of the gaseous oxygen and the solid oxygen source as the deoxygenated oxygen. In determining the amount G _O2 , it was used as an important parameter.
The inventor determined the parameter Z to be the product (XY) of both the bottom blowing stirring power density X and the solid oxygen ratio Y that have various effects on the dephosphorization reaction. Since both the bottom blowing stirring power density X and the solid oxygen ratio Y change their values, the degree of slag oxidation changes. Therefore, this parameter Z can also be said to be a “parameter representing the degree of slag oxidation”.

That is, even with the same amount of deoxygenated oxygen _{O 2} , the dephosphorization ability changes depending on the oxidation degree (Z) of the slag, so that the phosphorus concentration [P] after the dephosphorization treatment changes. For this reason, it is very meaningful to define the necessary oxygen amount (the amount of oxygen outside desiliconization) according to the parameter Z indicating the degree of oxidation of slag.
Therefore, the inventor arranges the parameter Z, which can be said to be the degree of oxidation of slag, by various experiments and the like, and in order to reduce the phosphorus concentration [P] of the hot metal after the dephosphorization process to 0.025% by mass or less, It has been found that the relationship between the external oxygen amount G _O2 and Z may be 0.00065 × Z ² −0.12 × Z + 12.5 ≦ G _O2 .

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. When 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. Further, when the amount of oxygen (the amount of oxygen outside Si removal) is too large, slopping is likely to occur in the dephosphorization process, which causes a decrease in yield. Specifically, in a general steel type in which the post-treatment phosphorus target is not low, which is the subject of the present invention, an oxygen removal amount of oxygen G _O2 of 13 Nm ³ / t or less is sufficient. If the amount of oxygen exceeds this value, there is no problem from the viewpoint of dephosphorization, but problems such as a problem of thermal likelihood and an increase in processing time due to an increase in the amount of oxygen increase, and it can no longer be said that dephosphorization is efficient.

Therefore, in this embodiment, the experiment was conducted with the upper limit of the desiliconized oxygen amount G _{O2 set} to 13 Nm ³ / t.
The amount of oxygen- _excluded oxygen G _O2 can be obtained from equation (1). The solid oxygen source amount (V _{02 (i)} ) shown in the formula (1) is the solid oxygen source amount (V _{02 (S)} ) contained in all the auxiliary materials, that is, the solid oxygen source supplied by the dephosphorization process. The total amount is shown, and can be obtained by equation (2). Further, 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 by 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.

The solid oxygen ratio Y described above is the total oxygen supply amount obtained by combining the total amount of solid oxygen source (solid oxygen amount V _{02 (s)} ) represented by the formula (4) and the amount of gaseous oxygen supplied by the top blowing lance 7. Of these, the ratio of the amount of solid oxygen source is shown, and can be obtained by, for example, the equation (5).

  Further, in determining the above-described bottom blowing stirring power density X, the formula proposed by Mori et al. (Iron and Steel 67 (1981), page 672), Nakanishi et al. (Iron and Steel 68 (1982), page A14), In the present invention, the forest formula is used as shown in formula (6).

In equation (6), 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 (6) was measured before and after dephosphorization treatment, and was averaged. In the equation (6), η was set to 0.06 (η = 0.06).
[About the particle size of quicklime]
For the dephosphorization reaction, oxygen and CaO are necessary for the sake of convenience, as indicated by 2 [P] +5 (FeO) +3 (CaO) → 3 (CaO.P ₂ O ₅ ) + 5Fe. In order for this CaO to contribute to the dephosphorylation reaction, it must be melted in the slag, but the melting point of CaO varies depending on the literature, but is about 2600 ° C., which 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 and JP-A-2003-12912, the melting point of quick lime is obtained by using a melting point depressant such as fluorite or alkali metal oxide. To make it easy to melt. 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 quicklime 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.
As a method of supplying quick lime to the molten metal 2, as shown in Japanese Patent Laid-Open No. 63-199815 and Japanese Patent Laid-Open No. 2005-272883, it is not sucked into the dust collector by using injection or blasting. Although quick lime with a small particle size can be introduced, if these facilities are used, it becomes a large-scale and a large-scale capital investment is required. Therefore, in the present invention, quick lime is supplied from above the furnace body. It is intended for the supply device 9 or the like.

[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 can be obtained by the equation (7). This formula (7) is a general formula described in “Iron Metallurgical Reaction Engineering” [Revised New Edition] 2nd edition, Kiyoshi Segawa, Nikkan Kogyo Shimbun, page 94 (5.5).

In addition, the nozzle coefficient k shown by Formula (7) 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 patent 2736555. 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 using the microwave level meter disclosed in Japanese Examined Patent Publication No. 4-81734, etc., by measuring the height of the bottom of the furnace in the empty furnace and the level of the molten metal after charging the molten metal 2. The bath depth was determined.

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 the temperature of molten metal]
When the dephosphorization reaction has the same slag composition, the lower the temperature, the lower the equilibrium phosphorus concentration, and the easier the reaction proceeds. When the hot metal temperature after the dephosphorization process is high, In this invention, since it leads to the fall of dephosphorization efficiency, the upper limit of the hot metal temperature after completion | finish of a dephosphorization process is 1340 degreeC. On the other hand, in the dephosphorization process, when the hot metal temperature is too low and the temperature is low, the saturation solubility of lime (CaO) in the slag is lowered, and as a result, the lime hatching is delayed. In such a case, since the dephosphorization efficiency is lowered, the present invention sets the lower limit of the hot metal temperature after the dephosphorization process to 1280 ° C.

  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. The tuyere 8 into which N ₂ gas is blown is a single-layer tube (where the gas is blown out in a ring shape), and the number thereof is 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%. The HMR (hot metal ratio) was determined by a formula calculation according to a conventional method of those skilled in the art.

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 dephosphorization treatment, the standard upper limit of [P] after blowing was set to 0.010% by mass. The auxiliary raw materials are iron ore (0.191 Nm ³ —O ₂ / kg), sintered ore (0.177 Nm ³ —O ₂ / kg), mill scale (0.145 Nm ³ —O ₂ / kg), It was input as usual by those skilled in the art.

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

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. The lower limit oxygen amount in the table indicates a value of 0.00065 × Z ² −0.12 × Z + 12.5.

In Examples 1 to 18, the amount of oxygen outside desiliconization (oxygen outside Si) exceeds the lower limit oxygen amount, and the relationship between the amount of oxygen outside desiliconization G _O2 and Z is 0.00065 × Z ² −0. .12 × Z + 12.5 ≦ G _O2 is satisfied. That is, as shown in FIG. 2, in Examples 1 to 18, the plot points indicating the oxygen removal-outside oxygen amounts G _O2 and Z are 0.00065 × Z ² −0.12 × Z + 12.5 ≦ G _O2 . It is in the area A to be filled.

Further, in the examples, the particle size of the quick lime to be charged is 5 to 40 mm (the quick lime column), and the ratio between the depth L ₀ of the molten metal and the bath depth L ₀ when blowing gaseous oxygen is 0.01. ˜0.20 (L / L0 column), and the hot metal temperature after dephosphorization treatment is 1280 to 1340 ° C. (post-treatment temperature column). Therefore, [P] required for general-purpose steel after dephosphorization treatment could be reduced to 0.025% by mass or less (Experimental result column, evaluation “◯”). In general-purpose steel, the standard upper limit of [P] after blowing is 0.025 mass%, which is very common as described in JP-A-2001-98314 and the like. is there.

On the other hand, in Comparative Examples 19 to 29, the amount of oxygen outside desiliconization (oxygen outside Si) is below the lower limit oxygen amount, and the relationship between the amount of oxygen outside desiliconization G _O2 and Z is 0.00065 × Z ^2. −0.12 × Z + 12.5 ≦ G _O2 is not satisfied. That is, as shown in FIG. 2, in Comparative Examples 19 to 29, the plot points indicating the oxygen amounts outside of Si removal G _O2 and Z are 0.00065 × Z ² −0.12 × Z + 12.5 ≦ G It is in area B that does not satisfy _O2 .

For this reason, in this comparative example, 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 30 to 32, 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 Example 33 to Comparative Example 34, the particle size of quick lime is larger than 40 mm, so that quick lime is difficult to dissolve and the slag hatchability 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 Example 35, quick lime having a particle size of less than 5 mm or quick lime having a particle size of more than 40 mm was used, and thus [P] after the dephosphorization treatment could not be reduced to a standard value or less (Experimental result column) , Rating "x").

In Comparative Examples 36 to 38, 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 lowered and the dephosphorization treatment is performed. Later [P] could not be made to be below the standard value (experimental result column, evaluation “×”). In Comparative Examples 39 to 41, 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 Example 42 to Comparative Example 43, the hot metal temperature after dephosphorization is less than 1280 ° C., and the hot metal temperature is too low, so that quick lime hatchability deteriorates, and the basicity of slag decreases and slag is reduced. Since the dephosphorization ability was lowered, [P] after the dephosphorization process could not be made to be equal to or less than the standard value (Experimental result column, evaluation “×”).
In Comparative Examples 44 to 47, the hot metal temperature after the dephosphorization treatment is higher than 1340 ° C., so the temperature in the dephosphorization treatment is too high, so the dephosphorization efficiency is lowered, and [P] after the dephosphorization treatment is reduced. It could not be less than the standard value (experimental result column, evaluation “×”).

As described above, in the present invention, the relationship between the parameter Z obtained by multiplying the stirring power density and the solid oxygen ratio and the amount of oxygen outside desiliconized G _O2 is 0.00065 × Z ² −0.12 × Z + 12.5. Dephosphorization efficiency can be improved by setting ≦ G _O2 and setting the quick lime particle size, L / L ₀ , and hot metal temperature within appropriate ranges.
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 product of the bottom blowing stirring power density during processing X [kw / t] and the solid oxygen ratio Y [%] is defined as parameter Z, and is the amount of oxygen supplied during processing and used for desiliconization reaction. The relationship between the oxygen amount G _O2 other than oxygen and the parameter Z is 0.00065 × Z ² −0.12 × Z + 12.5 ≦ G _O2
The particle size of the quicklime to be added is 5 to 40 mm, and 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 0.01 to 0.20, and dephosphorization treatment is performed. A dephosphorization method characterized by performing a dephosphorization treatment at a subsequent hot metal temperature of 1280 to 1340 ° C.