JP2009228101A - Method for pre-treating molten iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for pre-treating molten iron by which a dephosphorization is efficiently performed in a less flux unit consumption without using fluorite, and the phosphoric acid concentration in slag can be increased in the molten iron pre-treating method using a converter-type refining vessel. <P>SOLUTION: In a method for applying the dephosphorization to the molten iron by using the converter-type refining vessel, the dephosphorizing material mainly consisting of CaO is added and also an oxygen source is supplied into the molten iron in which either one or both of P concentration and S concentration before dephosphorization are adjusted so that the P concentration [mass% P] and Si concentration [mass% Si] in the molten iron become within the range of the inequality [1], 0.1≤[mass Si]≤1.87([mass% P]-0.05). Then, it is controlled so that the total iron concentration (mass% T.Fe) in the slag produced by the dephosphorization is ≥10 to ≤45 mass%, the P concentration in the molten iron after dephosphorization is ≥0.05 mass%, and the temperature after dephosphorization is 1,350 to 1,400°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hot metal pretreatment method using a converter-type refining vessel.

  The hot metal dephosphorization and decarburization are all performed simultaneously in the same converter. Instead of the converter steelmaking process, the hot metal dephosphorization is performed in a separate vessel from the decarburization prior to decarburization. The method has become widely used. In the hot metal preliminary dephosphorization treatment, a method of performing dephosphorization refining by adding a solid oxide material such as iron oxide and a dephosphorization flux to the hot metal is common.

  Conventionally, hot metal dephosphorization has been carried out by injecting a flux for dephosphorization (solid oxide such as iron oxide and quick lime) into hot metal in a topped car to perform preliminary dephosphorization, or in hot metal in a ladle. On the other hand, a method of injecting a dephosphorization flux is used.

However, in these methods, the total iron concentration in slag (generally, in the fluorescent X-ray analysis method used for component analysis of slag, metallic iron, Since it cannot be analyzed according to the form of FeO, Fe ₂ O _{3 and the} like, and the total value of those Fe is obtained as an analysis value, the total value of Fe is called the total iron concentration. Since it exists mainly in the form of FeO, there is no large error even if the total iron concentration is used.Hereinafter, the total iron concentration in the slag may be described as (T.Fe).) , It must be treated with slag having a high basicity (mass concentration ratio of CaO and SiO _{2 in} the slag, hereinafter sometimes referred to as CaO / SiO ₂ ), and in terms of dephosphorization efficiency. There was a problem.

  In addition, the use of fluorite was indispensable for maintaining slag hatching and reaction efficiency under high basicity conditions. Furthermore, because iron oxide is used as the oxidizing material, its decomposition and heat absorption lower the temperature during the dephosphorization process, reducing the amount of scrap consumed in the next converter, and reducing the amount of molten steel produced. There was a problem.

  Therefore, attempts have been made to use gaseous oxygen instead of iron oxide. However, when gaseous oxygen is used, since the slag (T.Fe) increases, the decarburization reaction is also promoted. There was a problem that forming occurred and dephosphorization could not be continued.

  On the other hand, a hot metal pretreatment method in which dephosphorization is performed using a converter-type refining vessel as a hot metal pretreatment vessel has recently been used. Since strong stirring, which is a feature of the converter type, is used, dephosphorization can be promoted even if slag with low basicity is used, and dephosphorization can be performed without using fluorite.

  Furthermore, since the free board is large, restrictions on slag forming are reduced, and gaseous oxygen can be used as the oxidizing material, so that the hot metal temperature after the pretreatment is kept high compared to the conventional method using only the solid oxide material. It is possible to secure heat tolerance in the entire refining process including decarburization.

  However, even in this method, the phosphoric acid concentration in the slag after the dephosphorization treatment is at most several mass%, which is not sufficient in terms of dephosphorization reaction efficiency.

  On the other hand, phosphorus is a harmful element because of the required properties of steel, but it is one of the elements indispensable for the growth of plants, and slag with high phosphoric acid concentration may be used as a phosphate fertilizer. Furthermore, if a slag containing a high concentration of phosphoric acid is obtained, it is not impossible to recover industrial phosphoric acid therefrom.

  However, as described above, the phosphoric acid concentration in the obtained slag is as low as several mass% at most, even with the converter type preliminary dephosphorization method. It does not lead to the utilization of.

  To increase the phosphoric acid concentration in the slag and increase the reaction efficiency of lime, reduce the amount of slag to be produced by de-Si treatment in advance and dephosphorizing the hot metal with a reduced Si concentration Is effective. When the amount of dephosphorization is the same, if the amount of produced slag decreases, it is obvious that the phosphoric acid concentration in the slag increases. For this reason, for example, a technique for reducing the Si concentration before treatment is disclosed in, for example, a patent. It is shown in Document 1.

  In this method, in order to fix the produced phosphoric acid, it is necessary to produce slag with high refining ability, and generally it is required to increase the basicity of slag. However, simply increasing the basicity of the slag will raise the melting point of the slag, making it impossible to maintain the slag in a molten state and dephosphorization will not proceed, so fluorite should be added as a solvent. Was essential.

  For this reason, the generated dephosphorization slag contains a high concentration of F, and there has been a major problem in its processing due to environmental regulations.

JP 2004-156146 A

  In the hot metal pretreatment method using a converter type refining vessel, the present invention can efficiently remove phosphorous with a small amount of flux basic unit without using fluorite and increase the phosphoric acid concentration in the slag. The object is to provide a possible hot metal preliminary method.

  The gist of the present invention is as follows.

(1) In a method of dephosphorizing hot metal using a converter-type refining vessel, the P concentration [mass% P] in the hot metal and the Si concentration [mass% Si] in the hot metal are expressed by the following formula [1]. Is produced by adding a dephosphorization material mainly composed of CaO and supplying an oxygen source to the hot metal in which either or both of P concentration and Si concentration before dephosphorization treatment are adjusted so as to be in the range of The total iron concentration in the slag (mass% T.Fe) is 10% to 45%, the P concentration in the hot metal after dephosphorization is 0.05 mass% or more, and the temperature after dephosphorization is 1350 to 1400 ° C. A hot metal pretreatment method characterized by controlling the hot water.
0.1 ≦ [mass% Si] ≦ 1.87 ([mass% P] −0.05) [1]

(2) T. added to the hot metal. CaO (CaO basic unit for dephosphorization) is in a range determined by the following formulas [2] to [4], the hot metal preliminary treatment method as described in (1) above.
T.A. CaO (kg / ton-hot metal) = α (1 + k) [mass% Si] × 600/28
... [2]
1.1 ≦ α ≦ 1.5 [3]
k = 0.68 ([mass% P] −0.05) / [mass% Si]... [4]

  (3) The hot metal preliminary treatment method according to (1) or (2), wherein the dephosphorization material mainly composed of CaO is added in two or more times.

  According to the present invention, it is possible to efficiently remove phosphorus without using fluorite and with a small amount of flux unit, and further, it is possible to increase the concentration of phosphoric acid in the slag to be generated. Utilization of slag as a phosphate fertilizer and recovery of phosphoric acid from produced slag can be facilitated. Therefore, the present invention can be expected to have a large industrial effect in terms of utilization of phosphoric acid resources.

  Generally, hot metal dephosphorization is realized by fixing the produced phosphoric acid as a compound with CaO. However, in the process, it is necessary to cause a dephosphorization reaction between the liquid slag and the hot metal. Even if solid lime is simply added to the hot metal, no dephosphorization occurs.

Therefore, it is necessary to control the slag composition so that slag having a liquid composition is generated in the range of 1250 to 1400 ° C. which is the hot metal pretreatment temperature. Conventionally, a generally performed method is a method in which lime is melted by reacting with SiO ₂ or FeO generated by supplying oxygen to generate CaO—SiO ₂ —FeO-based slag. is there.

Here, according to the CaO—SiO ₂ —FeO system phase diagram (see, for example, EMLevin, CRRobbins, HFMcMurdie: Phase Diagram for Ceramists, Vol. 1 (1964), p204 [The American Ceramic Society]), CaO / SiO _Since the upper limit of ₂ is about 1.5 even at 1400 ° C. and FeO = 50 mass%, in this method, in order to obtain liquid slag at the pretreatment temperature, CaO / SiO ₂ is less than 1.5. Need to be low basicity.

  However, since the slag refining ability generally increases with basicity, this method has a limit on the slag refining ability. Therefore, a large amount of slag is required for dephosphorization, and a large amount of dephosphorizing material such as lime is also required.

  Increasing basicity and improving the slag refining capacity will enable efficient dephosphorization with a small amount of slag, but simply increasing the basicity will not only dissolve the added lime, Rather, since the amount of the liquid portion of the slag is reduced, the dephosphorization efficiency is deteriorated.

  In an extreme example, hot metal de-Si treatment is performed in advance, and when only lime is added to the hot metal whose Si concentration is extremely reduced to almost zero, molten slag is not generated, and dephosphorization reaction is also caused. It does n’t happen at all.

Therefore, in de-P under the condition where CaO / SiO ₂ is increased, a solvent material such as fluorite is essential.

  On the other hand, the present inventors thought that phosphoric acid itself produced by the dephosphorization treatment could be used as a solvent, and intensively studied. By controlling to a certain slag composition / metal composition, the basicity was determined. It has been found that even when the content is increased, fluidity and dephosphorization ability can be maintained and slag having a high phosphoric acid concentration can be obtained.

  First, a preliminary experiment was conducted to confirm whether there exists a slag composition that maintains a liquid state at a hot metal pretreatment temperature without adding fluorite. That is, when fluorite is not used, slag can be melted by adding phosphoric acid without using fluorite at a high basicity of 1.5 or more, which exceeds the upper limit of the basicity at which slag can be melted. We investigated whether it could be achieved.

In the experiment, an artificial slag prepared by mixing reagents was charged into an iron crucible, placed in a Tamman furnace, heated to 1400 ° C, the upper limit of dephosphorization reaction, and examined whether the slag was melted. . After confirming the dissolution of the slag, in order to further improve the basicity, 3CaO · P ₂ O ₅ pellets and 2CaO · SiO ₂ pellets, which have been compacted, are added as CaO sources and added at 1400 ° C. for 2 to 4 hours. I held it.

  Thereafter, it was confirmed that at least one of the pellets remained, and then the liquid portion of the slag was collected and rapidly cooled to perform component analysis. Here, the reason why the composite oxide containing CaO is used as the CaO source instead of solid CaO is as follows.

The actual dephosphorization slag is a multi-component system, but the main component is a quaternary system of CaO—SiO ₂ —FeO—P ₂ O ₅ . However, there is no information about the state diagram in the quaternion system. On the other hand, in each ternary phase diagram of CaO—SiO ₂ —FeO and CaO—P ₂ O ₅ —FeO, the solid phase that equilibrates with liquid slag on the high basicity side at 1400 ° C. is not CaO, They are 2CaO · SiO ₂ and 3CaO · P ₂ O ₅ , respectively. Therefore, they were considered to be balanced even in the quaternary system.

The obtained results are shown in Table 1. This composition, a liquid slag, 3CaO · P ₂ O ₅ pellets or because it retention in the state of coexisting with 2CaO · SiO ₂ pellets, 3CaO at 1400 ° C. the experimental temperature · P ₂ O ₅ or 2CaO · SiO ₂ This is considered to correspond to the saturated composition.

Concentration of CaO in slag, concentration of P ₂ O ₅ and concentration of SiO ₂ (hereinafter referred to as (mass% CaO), (mass% P ₂ O ₅ ), and (mass% SiO ₂ ), respectively. May be T.). Although it varies depending on the Fe concentration and other components (Al ₂ O ₃ , MgO, etc.), from the experimental results, changing X as the variable X, from the ratio, (mass% CaO) / (X (mass% P ₂ O ₅ ) + (mass% SiO ₂ )) was calculated by a trial and error method so that the variation was minimized, and when X = 0.64, (mass% CaO) / (X (mass % P ₂ O ₅ ) + (mass% SiO ₂ )) was found to fall within a range of 1 to 1.3 with little variation.

That is, when (mass% CaO) / (0.64 (mass% P ₂ O ₅ ) + (mass% SiO ₂ )) is expressed as C / (P + S) for convenience, C / (P + S) is approximately It was found to be in the range of 1-1.3.

As described above, in the composition coexisting with 3CaO · P ₂ O ₅ or 2CaO · SiO ₂ , CaO, P ₂ O ₅ and SiO ₂ are in a certain relationship (C / (P + S) = 1 to 1.3). I understood that. Therefore, in order to control to this composition, it is necessary to control so that at least CaO, P ₂ O ₅ and SiO ₂ have a certain relationship (C / (P + S) = 1 to 1.3). It is believed that there is.

Here, CaO is added as a dephosphorizing material and can be controlled. On the other hand, P ₂ O ₅ and SiO ₂ are formed by oxidizing and removing P and Si in the hot metal, so that the P concentration and Si concentration in the hot metal before dephosphorization are controlled within a predetermined range. Therefore, it is considered that control is possible.

FIG. 1 shows the relationship between (mass% SiO ₂ ) / (mass% P ₂ O ₅ ) and basicity. From this, in order to set the basicity to 1.5 or more, which exceeds the upper limit at which slag can be melted without fluorite, (mass% SiO ₂ ) / (mass% P ₂ O ₅ ) It turns out that it is necessary to set it as 1.75 or less.

Here, SiO ₂ is produced by oxidation of Si in the hot metal, and more easily oxidized than P. Therefore, after de-P, almost all of the Si in the hot metal is oxidized to SiO ₂ . You can think of it as being done. Therefore, the generation amount of SiO ₂ is determined by the Si concentration in the hot metal.

On the other hand, the difference between P before and after the dephosphorization treatment corresponds to P ₂ O ₅ which is oxidized and removed, but the P concentration after the dephosphorization treatment is not uniquely determined. The P concentration in the hot metal after dephosphorization has a correlation with the P ₂ O ₅ concentration in the slag, and is generally arranged by the phosphorus distribution ratio LP = (mass% P ₂ O ₅ ) / [mass% P]. (Hereinafter, the phosphorus concentration in the hot metal may be referred to as [mass% P].)

Phosphorus distribution ratio LP is represented by temperature (larger as the temperature is lower), oxygen potential ((mass% T.Fe) is often substituted, higher is higher)), slag basicity (represented by CaO / SiO ₂ ). However, in the case of hot metal dephosphorization, the oxygen potential difference between slag and metal is large, so it cannot be obtained in equilibrium, and the concentration after dephosphorization treatment The actual situation is that it is the apparent distribution ratio.

  In this case, the phosphorus distribution ratio LP is not a thermodynamic value, but a value that is affected by the processing conditions such as the acid feed rate and bottom blowing stirring. It is requested by conducting a laboratory experiment.

Therefore, a dephosphorization experiment was conducted aiming at a composition in which C / (P + S) was in the above-mentioned certain range (1 to 1.3). A 1-ton laboratory laboratory furnace was charged with hot metal of 0.10 to 0.15 mass% P and 0.1 to 0.15 mass% Si, and 3CaO · P ₂ O ₅ , 2CaO · SiO ₂ saturated composition The dephosphorization experiment aiming at the slag composition with C / (P + S) of 1 to 1.3 was performed.

In FIG. 2, the phosphorus distribution ratio LP = (mass% P ₂ O ₅ ) / [mass% P], which is the ratio between the phosphoric acid concentration in the slag after dephosphorization and the P concentration in the hot metal, was calculated and plotted. A high LP value is obtained in the temperature range of 1350 to 1400 ° C. after the dephosphorization treatment. However, although mentioned later, (mass% T.Fe) was 10 to 45% of range.

  According to the equilibrium theory, the higher the temperature, the lower the phosphorus distribution ratio LP. In addition, the low temperature is advantageous in terms of equilibrium for dephosphorization. On the other hand, since slag does not melt, dephosphorization does not occur. As a result, when the temperature is lower than 1350 ° C., the phosphorus distribution ratio seems to be decreased. From this, it is considered that the proper temperature range after dephosphorization treatment is 1350 to 1400 ° C.

  The phosphorus distribution ratio LP also changes depending on (mass% T.Fe). As shown in FIG. 3, in the case of this slag composition, when (T.Fe) is less than 10 mass%, the molten state Since it is not obtained, the phosphorus distribution ratio is low. On the other hand, if it exceeds 45 mass%, the CaO content is diluted, and the phosphorus distribution ratio is lowered. From this, the proper (mass% T. Fe) is 10 to 45%.

  As described above, as shown in FIGS. 2 and 3, after dephosphorization treatment, 1350 to 1400 ° C., (mass% T. Fe) is 10 to 45%, and a value of about 200 is obtained as the phosphorus distribution ratio LP. You can see that

Here, as shown in Table 1, in the slag melt composition range, (mass% P ₂ O ₅ ) is in the range of 10 mass% or more. From this, the range of [mass% P] in the hot metal after the dephosphorization treatment may be 0.05 mass% or more from [mass% P] = (mass% P ₂ O ₅ ) / LP. Recognize.

That is, if [mass% P] after dephosphorization is in the range of 0.05 mass% or more, (mass% P ₂ O ₅ ) is 10 mass% or more.

  As for the amount of phosphoric acid produced by the dephosphorization treatment, the P concentration in hot metal before dephosphorization treatment is [mass% P], and the P concentration in hot metal after dephosphorization treatment is 0.05 mass%. , ([Mass% P] -0.05) is formed.

Here, in order to determine the basic unit of phosphoric acid produced when 1 ton of hot metal is dephosphorized (kg / ton-hot metal), the basic unit of removed phosphorus is:
1000 (kg) × ([mass% P] −0.05) × 1/100 (kg / ton-hot metal)
Because
Phosphoric acid basic unit (kg / ton-hot metal) = phosphorus basic unit (kg / ton-hot metal) × (molecular weight of phosphoric acid) / (atomic weight of phosphorus × 2)
Than,
P ₂ O ₅ (kg / ton-hot metal) = 10 × ([mass% P] −0.05) × 142/62
It is.

Similarly, intensity of the resulting SiO _2, when the Si concentration in the hot metal before the dephosphorization treatment with [wt% Si], Si concentration after dephosphorization process, because it is almost zero,
1000 × [mass% Si] × 1/100 × (SiO ₂ molecular weight) / (Si atomic weight)
Than,
SiO ₂ basic unit (kg / ton-hot metal) = 600 [mass% Si] / 28
It is.

Therefore, as described above, the condition of (mass% SiO ₂ ) / (mass% P ₂ O ₅ ) ≦ 1.75 necessary for setting the basicity to 1.5 or more is rewritten using the above relational expression. When,
(Mass% SiO ₂ ) / (mass% P ₂ O ₅ ) = SiO ₂ basic unit / P ₂ O ₅ basic unit =
600 [mass% Si] / 28 / ((10 × ([mass% P] −0.05) × 142/62) ≦ 1.75
That means
[Mass% Si] ≦ 1.75 × 142 × ([mass% P] −0.05) / (62 × 60) ≦ 1.87 ([mass% P] −0.05)
It becomes.

On the other hand, if [mass% Si] is too low, the absolute amount of SiO ₂ produced by the dephosphorization process is insufficient, so that the amount of molten slag cannot be secured, and the dephosphorization reaction stagnates.

  FIG. 4 shows [mass% Si] before dephosphorization and dephosphorization rate (= (before dephosphorization [mass% P] −after dephosphorization [mass% P]) / before dephosphorization [mass% P]. ] Is calculated by x100, an index indicating the ratio of dephosphorization to the P concentration in the hot metal before the dephosphorization treatment). When the Si concentration in the hot metal is less than 0.1 mass%, It can be seen that the phosphorus rate is greatly reduced. For this reason, the lower limit of the Si concentration in the hot metal was set to 0.1% by mass.

  From the above, the following formula [1] is obtained as an appropriate concentration range. If the Si concentration and the P concentration in the hot metal before the dephosphorization satisfy this relationship, it is understood that efficient dephosphorization can be performed in a region with a higher basicity than the conventional method without adding fluorite. It was.

As mentioned above, about the 1st invention in this invention, in the method of dephosphorizing hot metal using a converter type refining vessel, P concentration [mass% P] in hot metal and Si concentration in hot metal A dephosphorization material mainly composed of CaO is added to hot metal in which either or both of the P concentration and the Si concentration before dephosphorization treatment are adjusted so that [mass% Si] falls within the range of the following formula [1]. The total iron concentration (mass% T. Fe) in the slag produced by the dephosphorization process is 10 mass% or more and 45 mass% or less, and the P concentration in the hot metal after the dephosphorization process is 0.05. The hot metal pretreatment method was characterized in that the temperature after dephosphorization treatment was controlled to 1350 to 1400 ° C. by mass% or more.
0.1 ≦ [mass% Si] ≦ 1.87 ([mass% P] −0.05) [1]

  In the present invention, the oxygen source supplied to the hot metal may be either gaseous oxygen or a solid oxide material, or a combination of gaseous oxygen and a solid oxide material. The gaseous oxygen may be pure gaseous oxygen or an oxygen-containing gas, and iron ore, sintered ore, mill scale, or the like can be used as the solid oxide material.

  Further, in the case of gaseous oxygen, the oxygen source supply method may be combined with methods such as injection into hot metal and bottom blowing in addition to top blowing by a lance. In addition, in the case of a solid oxide material, supply into the hot metal can be performed by an arbitrary method such as injection or bottom blowing in addition to charging from above.

  As the refining vessel in which the dephosphorization treatment is carried out, it is possible to use a hot metal transport vessel such as a hot metal ladle or a topped car in addition to the converter type vessel, but in the dephosphorization treatment in the present invention, compared with the conventional method. Since high (mass% T.Fe) is required, a converter type refining vessel that can sufficiently secure a free board is used.

  The dephosphorization material mainly composed of CaO is not particularly defined, and a dephosphorization material used in normal operation can be used. However, the CaO content in the dephosphorization material is 50% by mass or more. Are preferred.

  As described above, the first invention in the present invention can be carried out by appropriately adding a dephosphorizing material mainly composed of CaO.

  Next, the second invention in the present invention will be described.

In the dephosphorization method of the present invention, when the hot metal dephosphorization treatment is performed using a converter-type refining vessel, the T.S. CaO (CaO basic unit) is in a range determined by the following formulas [2] to [4].
T.A. CaO (kg / ton-hot metal) = α (1 + k) [mass% Si] × 600/28
... [2]
1.1 ≦ α ≦ 1.5 [3]
k = 0.68 ([mass% P] −0.05) / [mass% Si]... [4]

As described above, in the slag composition targeted by the present invention, CaO, SiO ₂ and P ₂ O ₅ satisfy a certain relationship (C / (P + S) = 1 to 1.3). In the first invention, the relationship between SiO ₂ and P ₂ O ₅ is defined, but in the second invention, the preferred addition amount of CaO to be added is determined from the relationship between CaO and SiO ₂ , P ₂ O _5. It is characterized by determining.

As shown in Table 1, in the slag composition targeted by the present invention, C / (P + S) = CaO / (0.64 P ₂ O ₅ + SiO ₂ ) is in the range of 1 to 1.3. Therefore, it is considered that the addition amount of CaO is preferably determined so as to satisfy this relationship.

Now, if C / (P + S) = α,
α = C / (P + S) = (mass% CaO) / (0.64 (mass% P ₂ O ₅ ) + (mass% SiO ₂ ))
Because
(Mass% CaO) = α (0.64 (mass% P ₂ O ₅ ) + (mass% SiO ₂ ))
= Α (0.64 (mass% P ₂ O ₅ ) / (mass% SiO ₂ ) +1) (mass% SiO ₂ )

Here, (mass% P ₂ O ₅ ) / (mass% SiO ₂ )
= ((10 × ([mass% P] −0.05) × 142/62) / (600 [mass% Si] / 28)
= 1.07 ([mass% P] -0.05) / [mass% Si]
Therefore,
(Mass% CaO) = α (0.64 (mass% P ₂ O ₅ ) + (mass% SiO ₂ ))
= Α (0.68 ([mass% P] −0.05) / [mass% Si] +1) (mass% SiO ₂ )

here,
CaO basic unit / SiO ₂ basic unit = (mass% CaO) / (mass% SiO ₂ )
Because
CaO basic unit = SiO ₂ basic unit × (mass% CaO) / (mass% SiO ₂ )
= 600 [mass% Si] / 28 × [α (0.68 ([mass% P] −0.05) / [mass% Si] +1)]

The basic unit of CaO If you write and organize CaO,
T.A. CaO = α (0.68 ([mass% P] −0.05) / [mass% Si] +1) [mass% Si] × 600/28
= Α (k + 1) [mass% Si] × 600/28
Thus, the expression [2] is obtained.

  As shown in Table 1, since C / (P + S) = 1 to 1.3, the value of α is ideally in the range of 1 to 1.3, but in actual operation, Since the dissolution rate of CaO is slow, adding excess CaO to the required amount of CaO has been performed.

  Therefore, based on the experimental knowledge of the present inventor, the ideal α value is in the range of 1.1 to 1.5 while the ideal α value is in the range of 1 to 1.3. From this, the formulas [2] to [4] are obtained as the relationship between the added CaO basic unit and the hot metal composition.

  Incidentally, the amount of CaO to be added is determined in advance so that the concentration of CaO in the dephosphorizing material to be added is grasped in advance and the desired amount of CaO is added.

  Finally, the third invention in the present invention will be described.

  The dephosphorization method of the present invention is characterized in that when performing dephosphorization of hot metal using a converter-type refining vessel, CaO added to the hot metal is divided into two or more times.

  When dephosphorization is performed according to the first and / or second invention of the present invention, a dephosphorization material mainly composed of CaO may be added at once in a normal converter type refining facility. However, if it is added all at once, it may sinter in the furnace before it becomes a target slag composition and melts, resulting in a phenomenon that the generation of slag is delayed and dephosphorization does not proceed easily. .

  Therefore, more preferably, it is recommended to add the dephosphorization material mainly composed of CaO at least twice. The degree of division is preferably as it is divided, and it is more preferable if continuous addition or intermittent addition can be performed.

In principle, since it should be added according to the amount of SiO ₂ and P ₂ O ₅ produced, for example, by analyzing the exhaust gas from the dephosphorization furnace, decarburization of hot metal It is more preferable to obtain the amount, estimate the amount of SiO ₂ and P ₂ O ₅ to be generated based on the decarburization amount and the supply amount of the oxygen source, and control the addition rate of CaO based on this amount. .

Example 1
Dephosphorization of the blast furnace hot metal was carried out using a 300-ton converter. In the dephosphorization treatment, oxygen was blown from the top blowing lance, and a mixed gas of oxygen and nitrogen and LPG were blown from the tuyere provided at the bottom of the furnace, and lump lime was added from above. The dephosphorization time was 7 to 9 minutes. Moreover, the amount of iron ore added was adjusted from the hot metal temperature and the amount of scrap before dephosphorization, and the temperature after dephosphorization was adjusted. The results are shown in Table 2.

In the table, Kcao is an index calculated by the following formula [5] derived from the assumption that the dephosphorylation reaction follows the first-order rate equation. Kcao is generally used as an index indicating the reaction efficiency of lime, and the higher the value, the better the efficiency.
Kcao = ln ([mass% P] ₀ / [mass% P]) / T. CaO ... [5]

  Examples 1 and 2 are examples carried out according to the first invention of the present invention, but good dephosphorization was obtained. Examples 3 and 4 are examples in which lime basic units were determined and added within the range of the formula [2] according to the second invention, and higher Kcao was obtained. In Example 5, lime is divided and introduced. The effect of split lime injection is not an improvement in refining capacity, but a reduction in variation, so this alone cannot be understood.

  Therefore, Table 3 shows the average value and σ of Kcao in the case of divided input and Kcao in the case of collective input. From this, it can be seen that by dividing and introducing, the variation becomes smaller, and as a result, the average value of Kcao also increases.

  On the other hand, the results of Comparative Examples 1 to 6 show that the hot metal component is not appropriate (Comparative Examples 1 and 2), (mass% T.Fe) after treatment is not appropriate (Comparative Examples 3 and 4), and the temperature is shifted ( In the case of Comparative Examples 5 and 6), it can be seen that dephosphorization is insufficient and Kcao is low.

It is a figure which shows the relationship of the slag composition ratio obtained by the preliminary experiment. It is a figure which shows the relationship between post-process temperature and phosphorus distribution ratio. It is a figure which shows the relationship between slag (mass% T.Fe) and phosphorus distribution ratio. It is a figure which shows the relationship between [mass% Si] before a dephosphorization process, and a dephosphorization rate.

Claims (3)

In the method of dephosphorizing hot metal using a converter-type smelting vessel, the P concentration [mass% P] in the hot metal and the Si concentration [mass% Si] in the hot metal are within the range of the following formula [1]. In this way, slag produced by dephosphorization treatment by adding a dephosphorization material mainly composed of CaO and supplying an oxygen source to the hot metal prepared by adjusting either or both of P concentration and Si concentration before dephosphorization treatment. The total iron concentration (mass% T.Fe) in the steel is 10 mass% or more and 45 mass% or less, the P concentration in the hot metal after dephosphorization treatment is 0.05 mass% or more, and the temperature after dephosphorization treatment is 1350 to 1400 ° C. A hot metal pretreatment method characterized by controlling the hot water.
0.1 ≦ [mass% Si] ≦ 1.87 ([mass% P] −0.05) [1] T. added to the hot metal. 2. The hot metal preliminary treatment method according to claim 1, wherein CaO (CaO basic unit for dephosphorization) is in a range determined by the following formulas [2] to [4].
T.A. CaO (kg / ton-hot metal) = α (1 + k) [mass% Si] × 600/28
... [2]
1.1 ≦ α ≦ 1.5 [3]
k = 0.68 ([mass% P] −0.05) / [mass% Si]... [4]   The hot metal preliminary treatment method according to claim 1 or 2, wherein the addition of the dephosphorizing material mainly composed of CaO is performed in two or more times.

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