JP5493911B2 - Hot metal dephosphorization method - Google Patents

Description

  The present invention relates to a method for dephosphorizing hot metal with high efficiency using a top-bottom blowing converter type reaction vessel.

  Conventionally, in the hot metal pretreatment process in which hot metal dephosphorization processing is performed using a converter, scrap and hot metal are charged into the converter and dephosphorization blowing is performed by adding massive quicklime, limestone, etc. as a dephosphorizing agent. I was refining. However, in order to promote the dephosphorization of the hot metal, it is necessary to melt the dephosphorizing agent (incubation), and since the hot metal temperature during dephosphorization blowing is usually as low as 1300 to 1400 ° C., this temperature range In order to quickly hatch the dephosphorizing agent, hatching accelerators such as fluorite were used.

  However, in recent years, since it has become impossible to use fluorite substantially, a new technique for hatching a dephosphorizing agent has become necessary. As an example, Patent Document 1 discloses a hot metal dephosphorization method in which powdered quicklime is sprayed on hot metal together with top-blown oxygen without using a hatching accelerator such as fluorite. Further, even in such a method, it is considered preferable to increase the slag basicity after the dephosphorization treatment in order to efficiently produce the low phosphorus hot metal, as shown in Patent Document 2, There is also an example in which the later slag basicity is processed to be 2.5 to 5.0.

However, the top blowing oxygen flow rate of the invention described in Patent Document 1 is 0.7 to 2.0 Nm ³ / min / ton, and the oxygen supply time is about 10 minutes. Although the flow rate of the top blown oxygen in the invention described in Patent Document 2 is unknown, its dephosphorization processing time is described as 8 to 12 minutes, so it is estimated that it is the same level as the invention described in Patent Document 1. The The reason why the upper blown oxygen flow rate is about 2.0 Nm ³ / min / ton or less is described in Patent Document 1 as avoiding an increase in spitting, but the conventional dephosphorization time is about 10 minutes. It is also related to the fact that was enough.

However, in recent years, the necessity for increasing the efficiency of the dephosphorization process has increased, and there has been a demand for shortening the treatment time to about 6 to 10 minutes. In order to meet this requirement, it is necessary to increase the flow rate of the top blown oxygen, prevent the dephosphorization rate from decreasing, and suppress the increase in spitting. For example, in Patent Document 3, after generating a cover slag having a relatively low basicity, a CaO-containing dephosphorizing agent is sprayed onto the molten iron together with the top-blown oxygen, so that the top-blown oxygen flow rate is 0.5 to 2.5 Nm ^3. Disclosed is a method capable of reducing the amount of spitting even if it is increased to / min / ton.

Further, Patent Document 4 discloses an invention in which the supply rate of gaseous oxygen from the top blowing lance is increased to 1.5 to 5.0 Nm ³ / min / ton. However, it is necessary to lower the slag basicity to 1.0 to 2.5 in order to suppress spitting and dust generation, and in order to prevent the dephosphorization ability from being lowered at the low basicity, the oxygen potential of the slag Trying to increase.

  However, when the flow rate of the top blown oxygen is increased, spitting increases, and the iron oxide concentration in the slag becomes unexpectedly high, which may cause slopping. In addition, as a result of shortening the dephosphorization time, the dephosphorization ability may be lowered. With respect to these fears, Patent Document 4 does not disclose any specific means other than spraying a powdered solid oxygen source from the top blowing lance, and the powdered solid from the top blowing lance is not disclosed. Since oxygen source spraying requires special equipment, a simpler method is desired.

JP-A-8-311523 JP 2003-328025 A JP 2001-64713 A JP 2008-266666 A

  An object of the present invention is to provide a highly efficient dephosphorization treatment in a method for removing phosphorus (P) from hot metal without using an auxiliary raw material containing substantially fluorine as a dephosphorizing agent using an upper bottom blowing converter. And to provide a method of performing it with high efficiency. More specifically, the dephosphorization rate of the molten iron is 80% or more even when the supply time of the top blowing oxygen is 6 to 8 minutes, and the occurrence of spitting and slopping is suppressed to a level that is practically no problem. It is to provide a way that can be done.

In order to reduce the oxygen supply time in the top-bottom blown converter from the conventional 8-12 minutes to 6-8 minutes, the supply flow rate of the top blown oxygen is 0.7-2.0 Nm ³ / min / It can be increased from ton, etc., and it can be suppressed to the same level of spitting and slopping as usual even at 2.0 to 4.0 Nm ³ / min / t, and [P] concentration is 0.020% or less after conventional processing It is necessary to establish a blowing method capable of maintaining (dephosphorization rate of 80% or more).

When the top blowing acid speed is 2.0 Nm ³ / min / t or more, slopping easily occurs. The reason for this is that since the amount of oxygen supplied per hot spot area increases, iron oxide is easily generated. This is because when the Fe concentration is set, it easily becomes 15% by mass or more. T. in this slag. The Fe concentration can be reduced by increasing the bottom blowing gas flow rate. There is also a circumstance that a higher Fe concentration is better. Therefore, dephosphorization treatment was performed at an appropriate bottom blowing gas flow rate for a high top blowing acid rate, and slag T.I. By adjusting the Fe concentration to a higher appropriate range, it is considered that a treatment for maintaining the dephosphorization rate while suppressing the slopping during blowing is possible. However, the T.P. The adjustment of the Fe concentration has a difficulty in the adjustment range, and only by the adjustment, after dephosphorization treatment under the condition that the upper blowing acid rate is 2.0 Nm ³ / min / t or more, [P] ≦ 0.02 mass% It is difficult to achieve steadily.

  Therefore, T. In addition to adjusting the Fe concentration to a higher level, it was considered useful to increase the oxygen potential of the hot metal. Since the dephosphorization reaction depends on the basicity of the slag and the oxygen potential at the slag / hot metal interface, the idea is that a high dephosphorization rate can be achieved by increasing each. A method for increasing the oxygen potential of the hot metal may be to lower [C] after the treatment. For example, it is reliable and effective to blow down [C] to 3.2 mass% or less.

  However, if [C] is 3.4% by mass or less, the solidification start temperature (liquidus temperature) of the hot metal becomes high, and when the processed hot metal is transported to the decarburization furnace of the next step, etc., to the hot metal ladle. There is a risk that the amount of bullion will increase and the production will decrease. As a countermeasure against this fear, during dephosphorization blowing, [C] is once blown down to 3.2 mass% or less to increase the hot metal dephosphorization rate, and then a carbon source is added to the hot metal to add [C] If the concentration is increased to 3.4% by mass or more, hot metal dephosphorization treatment can be performed which has a high hot metal dephosphorization rate and can prevent adhesion of metal to the hot metal pan.

  Furthermore, if the above idea is applied to a method of dephosphorizing a CaO-containing dephosphorization agent disclosed in Patent Documents 1 to 4 by spraying it on hot metal together with top-blown oxygen, the object of the present invention is more easily and reliably achieved. It will be possible to achieve.

Therefore, in the present invention, massive quicklime having a particle size of 30 mm or less (CaO content: 92 to 95% by mass, residual CO ₂ and impurities) is mainly used as the massive CaO source. However, converter slag or ladle slag may be used in combination up to an amount of CaO mass ratio of less than 50% in the bulk CaO source. Table 1 shows an example of the composition (unit: mass%) of ladle slag. This is because these slags contain SiO ₂ and Al ₂ O _{3 in} addition to CaO and have a low melting point, and are suitable for initial cover slag generation. In particular, ladle slag can be used as an Al ₂ O ₃ source in the present invention.

  However, in the present invention, since the basicity after the dephosphorization blowing is adjusted with emphasis on the ability to dephosphorize hot metal, among the bulk CaO sources used before blowing or at the beginning of blowing, the conversion of CaO purity is low. The amount of furnace slag and ladle slag used is limited. This is because if they are used frequently, the amount of slag after dephosphorization will increase and there will be cases where the basicity adjustment will be hindered.

  The bulk CaO source is introduced into the converter by weighing and feeding the required amount from a bunker installed on the converter before starting the supply of top-blown oxygen or within 2 minutes after the start, And put it in the chute together with the scrap. Therefore, in order to reduce the scattering loss at the time of charging, it is preferable to sieve to a particle size of 5 mm or more.

In addition, as the powdered CaO source, quick lime powder having a particle size of 60 mesh under (CaO content: 92 to 95 mass%, residual CO ₂ and impurities) is mainly used. It may be used.

  The powdered CaO source is added by spraying toward the molten iron together with the top blowing oxygen, and the spraying is started simultaneously with the start of the top blowing oxygen supply or within 2 minutes from the start of the top blowing oxygen supply. Therefore, it is natural that the powdered CaO source is hatched faster than the bulk CaO source and the dephosphorization reaction efficiency is higher. Therefore, the present invention does not necessarily require the use of a powdered CaO source, but the mass ratio of the powdered CaO contained in the total CaO source used is the mass ratio of the powdered CaO source that is sprayed onto the hot metal together with the top-blown oxygen. A ratio of 40% or more is preferable because the [P] concentration in the hot metal after the dephosphorization treatment is stabilized at 0.020% by mass or less. Since the [P] concentration after the treatment also depends on the [P] concentration in the hot metal before the treatment, a dephosphorization rate of 80% or more may be used as a measure of the effect of the present invention.

The present invention has been completed based on the above findings and is as follows.
(1) Using an upper bottom blowing converter, only a secondary material that does not contain fluorite is used as a dephosphorizing agent, and an upper blowing oxygen flow rate is 2.0 Nm ³ / min / t or more and 4.0 Nm ³ / min / t. a method for dephosphorization process molten iron under the following conditions, bottom blowing flow rate of 0.15Nm ³ / min / t or more 1.5Nm ³ / min / t or less in the slag T. after dehydration phosphorus treated as The Fe mass concentration is adjusted so as to be 3% by mass or more and 15% by mass or less, and the mass concentration of carbon contained in the molten iron during the dephosphorization treatment is 2.8% by mass or more and 3.2% by mass or less. And then, after supplying the carbon source to the hot metal and adjusting the mass concentration of carbon contained in the hot metal after the dephosphorization treatment to 3.4% by mass or more and 3.8% by mass or less. And a dephosphorization method for hot metal.

(2) Of the CaO source used as a dephosphorizing agent, by spraying 40 mass% or more in a mass ratio of CaO as a powdered CaO source having a particle size of 60 mesh or less to the hot metal from the upper blowing lance together with the upper blowing oxygen, The pot immediately after the dephosphorization treatment has a mass concentration ratio of CaO and SiO ₂ (% CaO /% SiO ₂ ) of 2.3 or more and 3.2 or less, and after the dephosphorization treatment, the hot water is discharged from the converter to the hot metal ladle. The hot metal dephosphorization method according to (1) above, wherein the temperature of the hot metal in the hot metal is adjusted to 1320 ° C. or higher and 1380 ° C. or lower.

(3) The Al ₂ O ₃ source is charged before blowing or within 2 minutes after the start of blowing so that the concentration of (Al ₂ O ₃ ) in the slag at the end of blowing is 3% by mass or more and 10% by mass or less. The method for dephosphorizing hot metal as described in (1) or (2) above.

According to the present invention, using an upper bottom blow converter, the upper blowing oxygen flow rate is set to 2.0 to 4.0 Nm ³ / min / t without using a secondary material substantially containing fluorine as a dephosphorizing agent. A low phosphorus hot metal in which the [P] in the hot metal after the dephosphorization treatment is 0.020% or less can be produced in an upper blowing oxygen supply time of 6 to 8 minutes.

It is a graph which shows the relationship between [P] during dephosphorization blowing and [P] during dephosphorization blowing. It is a graph which shows the relationship between [P] after a dephosphorization process, and [P] after a dephosphorization process. It is a graph which shows the relationship between the variation | change_quantity ((DELTA) [C]) of carbon concentration based on having been carburized during dephosphorization blowing, and the amount of dephosphorization ((DELTA) [P]).

  In the method of operating a dephosphorization furnace according to the present invention, it is not necessary to use an auxiliary material substantially containing fluorine for performing the dephosphorization treatment. The auxiliary material substantially containing fluorine is one containing high concentration of fluorine such as fluorite. For example, even if a substance such as slag containing less than 1% by mass of fluorine is used as a secondary raw material, the fluorine concentration in the slag after dephosphorization is less than 0.4 ppm. In the practice of the present invention, it does not fall under “use of a sub-raw material substantially containing fluorine”.

In the present invention, the top blowing oxygen supply time is performed in a short time of 6 to 8 minutes without using a sub-material substantially containing fluorine. In particular, even in such short-time blowing, this is a high-efficiency, low-phosphorus hot metal production method in which the amount of [P] in the molten iron after treatment is 0.020% or less. In such a highly efficient method, the supply flow rate of the top blown oxygen must basically be 2.0 Nm ³ / min / ton or more. Basically, the blowing with a low oxygen flow rate period of 1.0 to 2.0 Nm ³ / min / ton for only a short time such as less than 1 minute during the supply time of the top blowing oxygen, It is meant to be included within the equivalent scope of the present invention. However, it is obvious that the dephosphorization time is shortened as the upper oxygen flow rate is increased. Instead, it is well known that increased spitting / sloping and poor dephosphorization are problematic. Naturally, there is an upper limit to the possible top-blown oxygen flow rate. In the present invention, the upper limit is set to 4.0 Nm ³ / min / ton, and basically even if oxygen of 2.0 Nm ³ / min / ton or more is sprayed on the hot metal during the supply period of the top-blown oxygen, the speed is increased. Established with the aim of developing a technology that does not cause sloping and slopping to be an operational problem, and that [P] in the molten iron after treatment can be 0.020% or less.

When the top blowing oxygen flow rate is 2.0 Nm ³ / min / ton or more, the T.I. Fe concentration tends to increase. In the present invention, the top blown oxygen flow rate is in the range of 2.0 to 4.0 Nm ³ / min / ton, and the bottom blow gas flow rate is 0.15 to 1.5 Nm ³ / min, so that T. in slag The Fe concentration is adjusted to 15% by mass or less, and the occurrence of slopping is suppressed through this adjustment. If it is 15% by mass or more, there is a problem of cost increase due to deterioration of the iron yield, so it is necessary to make it 15% by mass or less in order to prevent it.

On the other hand, T. in the slag. Spitting decreases with increasing Fe concentration. T. in slag When Fe is 3% by mass or less, spitting increases, and undenitrated CaO (f.CaO) is 3% by mass or more, which reduces the above-described reduction of exhaustability and increase of furnace body adhesion slag. Therefore, it is necessary to be 3% by mass or more. The T.O. in the slag under a high acid feed rate of 2.0 to 4.0 Nm ³ / min / ton at the top blowing oxygen flow rate. The Fe concentration can be adjusted to the range of ^{3 to} 15% by mass by adjusting the flow rate of the bottom blowing gas in the range of 0.15 to 1.5 Nm ³ / min.

  In the dephosphorization method according to the present invention, the mass concentration [C] of carbon contained in the hot metal during the dephosphorization treatment is temporarily reduced to 2.8 to 3.2 mass%. By blowing down [C] to 3.2 mass% or less during dephosphorization, it is possible to ensure the dephosphorization ability required in the present invention. However, if [C] is blown down too much, the subsequent carburizing load becomes large, so [C] during dephosphorization blowing is controlled to 2.8% by mass or more.

  In the dephosphorization processing method according to the present invention, [C] during dephosphorization blowing is once reduced to 2.8 to 3.2% by mass as described above, and then a carbon source is supplied to the hot metal to remove the dephosphorization. After the phosphorus treatment, the mass concentration [C] of carbon contained in the hot metal is adjusted to 3.4 to 3.8 mass%. When the hot metal [C] after the treatment is 3.4% by mass or less, the liquidus temperature of the hot metal becomes high. For this reason, the amount of bullion attached to the hot metal pan increases and the production volume decreases. On the other hand, if it is 3.8% by mass or more, the carbonization yield (C yield) of the carbon source is remarkably lowered. In order to control the [C] concentration during blowing while securing a high carburization yield, it is necessary to suppress contact between the carbon source and slag. It can be said that the method of spraying the source is effective. Alternatively, a carbon source such as coal powder may be blown into the hot metal from a tuyere provided at the bottom of the converter.

  In the dephosphorization processing method according to the present invention, it is preferable to adjust the temperature of the hot metal in the pan immediately after discharging from the converter to the hot metal pan after the dephosphorization treatment so that the temperature is 1320 ° C. or higher and 1380 ° C. or lower. Under conditions where the temperature in the pan after the dephosphorization treatment, specifically, the temperature of the hot metal in the pan immediately after discharging from the converter to the hot metal pan after dephosphorization treatment is less than 1320 ° C. Is hindered, the fluidity of the slag is lowered, and there is a risk of dephosphorization failure and increased spitting. Further, when the temperature of the hot metal exceeds 1380 ° C., the temperature may be high, resulting in poor dephosphorization. As a method of adjustment, based on the hot metal composition and temperature information before the start of dephosphorization, the amount of cold material corresponding to the temperature rise calculated from the amount of oxygen sprayed on the hot metal is calculated and put into the converter. The method to do is common.

Further, the dephosphorization treatment method according to the present invention, adjusted to slag CaO and SiO ₂ in a mass concentration ratio after dephosphorization (% CaO /% SiO ₂₎ is 2.3 or more 3.2 or less It is preferable. If the slag basicity after blowing (the mass concentration ratio of CaO and SiO _{2 in} the slag after dephosphorization treatment (% CaO /% SiO ₂ )) is excessively larger than 3.2 for the purpose of ensuring high dephosphorization ability There is a concern that the unreacted CaO content also increases by the method of the present invention, leading to a decrease in the evacuation property of the treated slag and an increase in the furnace body-attached slag. Moreover, when the slag basicity after blowing is excessively smaller than 2.3, there is a risk that the dephosphorization ability is lowered and dephosphorization is poor.

These requirements were investigated and confirmed as follows.
First, the investigation conditions will be described. About 270 t of molten iron subjected to desulfurization treatment and about 20 t of scrap were charged into an upper bottom blowing converter. Table 2 shows examples of main components of the hot metal (unit: mass%).

The top blown oxygen is 2.0 to 4.0 Nm ³ / min / t, the bottom blown gas is N ₂ is 0.15 to 1.5 Nm ³ / min / t, and the dephosphorizer is massive quicklime (particle size 0.5 ~ 30mm) is used in the range of 2 to 15kg / t, powdered quicklime (particle size of 60 mesh or less) in the range of 5 to 20kg / t, and the ratio of CaO supplied in powder form is based on 40 to 80% by mass. . However, only a lump quick lime was used for a part.

For carburizing, the tip of the lance was lowered to a position 1.5 m above the hot metal bath surface, and graphite powder was sprayed from the tip toward the hot metal for 2 to 4 minutes at a speed of 800 to 1100 kg / min.
Regarding the carburizing treatment, [C] during blowing is estimated using a static model, and then blown down until the estimated [C] reaches 2.8 to 3.2% by mass. After spraying and dephosphorization, the [C] was adjusted to 3.4 to 3.8% by mass. T. after dephosphorization treatment Fe was adjusted to 3 to 15% by mass, and the basicity was adjusted to 2.3 to 3.2.

  FIG. 1 shows the relationship between [C] and [P] obtained by sampling hot metal using a sub lance during dephosphorization blowing and analyzing off-line. From FIG. 1, it was found that [P]% can be lowered as [C]% is lower.

  FIG. 2 shows the relationship between [C] and [P] after the dephosphorization treatment. [C] is once blown down to 2.8 to 3.2% by mass during dephosphorization blowing, and then the change in mass concentration of carbon in molten iron (Δ [C]) is 0.3 to 0.8. In the examples of the present invention in which [C] was increased to 3.4 to 3.8% by mass by performing carburization so as to be mass%, [P] after the treatment was 0.01 to 0.02% by mass. It was settled in.

This was a good result that [P] was 0.005 to 0.015% by mass lower than the conventional dephosphorization treatment in which [C]% was not blown down and carburized.
In addition, the dispersion | variation in [P] after this process was smaller when powdered quicklime was used.

  FIG. 3 shows the relationship between the amount of change in carbon concentration (Δ [C]) and the amount of dephosphorization (Δ [P]) based on carburization during dephosphorization blowing. When carburizing was performed, a certain amount of rephosphorus had occurred, although not so much that the effect of lowering the hot metal [C]% was lost.

  Summing up the above results, [P]% in the hot metal after the treatment can be lowered as the [C]% is blown down during the treatment. Therefore, it can be said that it is optimal to set the [C] in the range of 2.8 to 3.2% by mass and then carburize to set the [C] to 3.4 to 3.8% by mass. .

  The control of [C] during the dephosphorization blowing is a so-called static control using data such as [C] and [Si] components and the amount of oxygen supplied to the hot metal before starting the dephosphorization blowing. However, other methods such as collecting hot metal samples and analyzing [C] quickly may be used.

Further, in the slag _(Al 2 _{0 3)} concentration spitting was suppressed by charging the _Al 2 _{0 3} source before blowing so that 3-10 wt%. When the concentration in the slag (Al ₂ O ₃ ) is 3 to 10% by mass, the slag is easily formed and the reduction rate in the slag (FeO) is decreased. It is thought that Fe increased, hatching was promoted, and cover slag was easily formed. On the other hand, when the concentration in the slag (Al ₂ O ₃ ) increases, the viscosity of the slag increases. As a result, slag forming occurred with an increase in the concentration of (Al ₂ O ₃ ) in the slag, and slopping increased. If the concentration in the slag (Al ₂ O ₃ ) exceeds 10% by mass, excessive forming will cause slag overflowing to the outside of the furnace, slag overflow from the furnace outlet during hot water, etc., making operation difficult. It was confirmed.

In order to confirm the stable production effect of the low phosphorus hot metal under high speed blowing of the present invention, the following test was conducted.
(1) Test conditions The hot metal components before dephosphorization were [C]: 4.2 to 4.8% by mass, [Si]: 0.15 to 0.45% by mass, [P]: 0.095 to 0.120% by mass, [Mn]: 0.20 to 0.35% by mass, about 264t of hot metal and about 29t of scrap having a temperature before dephosphorization of 1300 to 1370 ° C., and about 29t of scrap are used as an upper bottom blowing converter. Note that mainly, the top blowing oxygen flow rate is 2.4 to 3.0 Nm ³ / min / t, N ₂ is used as the bottom blowing gas, and the bottom blowing flow rate is 0.30 to 0.50 Nm ³ / min / t. Blowed with. However, as a comparative example, processing was partially performed under conditions other than those described above.

The hot metal ratio of the dephosphorization furnace was 89 to 91% by mass. As quicklime, a pure CaO content of about 92% by mass, a lump with a particle size of 0.5 to 30 mm and a powder of 150 μm or less were used.
As the dephosphorizing agent, massive quicklime was used in a range of 2 to 15 kg / t and powdered quicklime was used in a range of 5 to 20 kg / t, and the ratio of CaO supplied in powder form was basically 40% by mass or more.

Further, the arrival [C] during dephosphorization was estimated using a static model based on the hot metal component and blowing conditions.
As a method of adding the carburizing agent, the tip of the sub lance is lowered to a position 1.5 m above the hot metal bath surface, and graphite powder having a [C] concentration of 90 mass% is directed from the tip to the hot metal at a rate of 1000 kg / min. Sprayed for 1-4 minutes. Regarding the carburizing treatment, [C] during blowing is estimated using a static model, and then blown down until the estimated [C] reaches 2.8 to 3.2% by mass. After spraying and removing P, [C] was adjusted to 3.4 to 3.8% by mass.
In many examples and comparative examples, before starting the blowing of top-blown oxygen, ladle slag 4.0 to 7.0 kg / t described in Table 1 was added to the converter to remove phosphorus. Processed.

(2) Evaluation method Evaluation is performed after de-P [P], T.P. Fe, iron yield, pouring hot metal adhesion, and C powder yield were performed. The evaluation of the pouring pot metal adhesion was based on the difference between the weight of the pouring pan before de-P pouring and the weight of the pouring pan after de-C pouring.

  Table 3 shows test conditions and test results of the examples.

The top blowing oxygen flow rate, bottom blowing flow rate, T. In the present invention examples 1 to 9 that satisfy the conditions of claim 1 for Fe, reached during dephosphorization process [C], and after dephosphorization process [C], as shown in Table 3, after dephosphorization [P] ≦ 0 Good results were obtained with 0.020% by mass. Further, in addition to the above-described conditions, Examples 6 to 9 of the present invention satisfying the conditions shown in claim 2 for the slag basicity after dephosphorization, the powder ratio of the CaO source, and the temperature in the pan after dephosphorization, Even better results were obtained with [P] ≦ 0.015 mass% after dephosphorization. In all cases, spitting and slopping were minor, and there were no occurrences that would hinder operations. In addition to the above-described conditions, it was confirmed that the present invention examples 8 and 9 in which the concentration of (Al ₂ O ₃ ) in the slag after the dephosphorization treatment was 7 to 9% by mass showed large slag forming. However, slopping has not occurred, and T. Even better Fe removal results were obtained with high Fe concentration and [P] ≦ 0.011 mass% after treatment.

  On the other hand, in Comparative Example 1 in which the flow rate of the top blown oxygen is lower than the conditions specified in the present invention, there is no problem with [P] and the slopping / spitting after the dephosphorization treatment, but the supply time of the top blown oxygen is 10 Productivity was low because it exceeded the minute. Further, in Comparative Example 2 in which the flow rate of the top blown oxygen is higher than the conditions defined in the present invention, not only slopping occurred, but also the [P] concentration after treatment cannot reach the target value of 0.023% by mass. It was. Further, slopping occurred in Comparative Example 3 with a low bottom blowing flow rate, and spitting was severe in Comparative Example 4 with a high bottom blowing flow rate, and the [P] concentration after treatment was also poor at 0.033 mass%. .

  On the other hand, in Comparative Examples 5 to 8 in which the top blow oxygen flow rate and the bottom blow flow rate satisfy the scope of the present invention, in Comparative Example 5 in which the [C] concentration during the dephosphorization treatment was blown down to 2.71% by mass, The carburizing treatment load was large, and the target of the present invention in which the supply time of top blowing oxygen was 8 minutes or less could not be achieved. On the contrary, in Comparative Example 6 in which the [C] concentration during the dephosphorization process was blown down only to 3.34% by mass, the supply time of the top blowing oxygen was about 7 minutes, and the object of the present invention was achieved. However, the [P] concentration after treatment was 0.039% by mass, which was the worst dephosphorization result. Further, in Comparative Example 7 in which [C] after the dephosphorization treatment was lowered, the dephosphorization result itself was not a problem, but the hot metal after the treatment partially solidified in the pan, and the object of the present invention is to increase productivity. The result was against. On the other hand, in Comparative Example 8 in which [C] after dephosphorization was increased, the decarburization process cost was increased more than necessary because the carburization yield was low.

Claims (3)

Using an upper-bottom blow converter, using only auxiliary materials that do not contain fluorite as a dephosphorization agent,
A method in which the hot metal is dephosphorized under a condition that the flow rate of top blown oxygen is 2.0 Nm ³ / min / t or more and 4.0 Nm ³ / min / t or less,
Bottom-blown flow rate of 0.15Nm ³ / min / t or more 1.5Nm ³ / min / t or less in the slag T. after dehydration phosphorus treated as Adjust so that the Fe mass concentration is 3 mass% or more and 15 mass% or less,
In addition, the mass concentration of carbon contained in the hot metal during the dephosphorization treatment is temporarily reduced to 2.8 mass% or more and 3.2 mass% or less, and then a carbon source is supplied to the hot metal to supply the dephosphorization. A method for dephosphorizing hot metal, which comprises adjusting the mass concentration of carbon contained in the hot metal after the treatment to 3.4% by mass or more and 3.8% by mass or less. Of the CaO source used as a dephosphorizing agent, by spraying 40 mass% or more in a mass ratio of CaO as a powdered CaO source having a particle size of 60 mesh or less to the hot metal from the upper blowing lance together with the upper blowing oxygen,
The slag CaO and SiO ₂ in a mass concentration ratio after dephosphorization (% CaO /% SiO ₂₎ is 2.3 or more 3.2 or less,
The hot metal desorption according to claim 1, wherein the temperature of the hot metal in the pan immediately after discharging from the converter to the hot metal pan after dephosphorization is adjusted to 1320 ° C or higher and 1380 ° C or lower. Phosphorus treatment method. The Al ₂ O ₃ source should be charged before blowing or within 2 minutes after the start of blowing so that the concentration of (Al ₂ O ₃ ) in the slag at the end of blowing is 3% by mass or more and 10% by mass or less. 3. The hot metal dephosphorization method according to claim 1, wherein the hot metal is dephosphorized.

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