JP4979514B2 - Hot metal dephosphorization method - Google Patents

Description

  The present invention relates to a hot metal dephosphorization method for improving the dephosphorization efficiency in the dephosphorization process and producing a low phosphorus hot metal accurately and stably.

In recent years, the demand for steel material quality has further increased, and hot metal dephosphorization has been performed as a method for stably melting low phosphorus steel. Prior to dephosphorization, hot metal dephosphorization is performed by adding a slagging agent into the hot metal and supplying oxygen to the hot metal to oxidize and remove Si to SiO ₂ and then hatch the slag that has floated on the hot metal. Subsequently, FeO is generated at the slag-metal interface, and P in the hot metal is oxidized and removed to P ₂ O ₅ .
In order to improve the dephosphorization efficiency in the hot metal dephosphorization process, it is necessary to supply oxygen sufficiently to the hot metal in order to reliably oxidize and remove Si in the hot metal to SiO ₂ . Moreover, it is necessary to sufficiently stir the hot metal so that P in the hot metal comes into contact with FeO generated at the interface between the slag that has floated and the metal (hot metal).

As described above, it is important to change the flow rate of oxygen from the top blowing lance and the flow rate of bottom blowing stirring (bottom blowing stirring power) in accordance with the progress of blowing, and the dephosphorization processing method in which these are performed For example, those disclosed in Patent Document 1 or Patent Document 2 are known.
In the dephosphorization method of Patent Document 1, oxygen is blown from the top blowing lance to the hot metal and stirring gas is blown into the hot metal from the bottom blowing nozzle. The oxygen flow rate from the top blowing lance, lowered by the blow progress 10% 2.0Nm ³ / min · t to 1.5Nm ³ / min · t, further blow progress 80% slag formation is completed Lower to 1.0 Nm ³ / min · t. Further, the flow rate of bottom blowing stirring is increased from 0.05 Nm ³ / min · t to 0.2 Nm ³ / min · t at a blowing progress of 30%.

The dephosphorization process of Patent Document 2 is such that the oxygen flow rate from the top blowing lance is lowered from 1.75 Nm ³ / min · t to 0.5 Nm ³ / min · t and the bottom at 60% of the blowing progress at which hatching is completed. The flow rate of blowing stirring is increased from 0.04 Nm ³ / min · t to 0.08 Nm ³ / min · t.
On the other hand, in the dephosphorization process, P in the hot metal reacts with FeO generated at the slag-metal interface and is removed as P ₂ O ₅ , so that it is necessary to stably generate FeO at the slag-metal interface. In addition, since the reaction efficiency decreases when the temperature of the hot metal in the dephosphorization process is too high, it is necessary to appropriately control the temperature of the hot metal during or after the dephosphorization process.

As described above, Patent Documents 3 and 4 disclose techniques for supplying iron oxide into hot metal in hot metal dephosphorization and appropriately controlling the hot metal temperature during or after dephosphorization. What is known.
For example, Patent Document 3 discloses that iron ore or iron ore is used to generate FeO necessary for dephosphorization treatment after controlling the height of the top blowing lance, the oxygen flow rate from the top blowing lance, and the flow rate of bottom blowing stirring. A method has been proposed in which the mill scale is charged into the hot metal.
Furthermore, in Patent Document 4, a mill scale or the like determined based on the heat balance after treatment is controlled while controlling the slag components, and the oxygen flow rate from the top blowing lance is adjusted to adjust the oxygen flow rate after treatment. A method of controlling the temperature of the hot metal in a range of 1250 to 1400 ° C. has been proposed.
JP 2006-152426 A JP 2002-275519 A Japanese Patent No. 3486889 JP 2006-265623 A

By the way, in the dephosphorization process of patent document 1, the upper blowing lance height is set as high as 3.0 m until the blowing progressing degree 80% which hatching is complete | finished. In other words, the oxygen flow rate from the upper blowing lance is set numerically as large as 1.25 to 2.0 Nm ³ / min · t, but the effect of blowing oxygen on the hot metal is rather small. Therefore, in the dephosphorization method of Patent Document 1, there is a possibility that oxygen is not sufficiently supplied during hot metal, and there is a possibility that Si and P in the hot metal cannot be removed sufficiently.
Further, in dephosphorization process of Patent Document 1, raised in the blow progress 30% slag formation is not completed the flow of the bottom blowing is agitated 0.04Nm ³ / min · t to 0.08Nm ³ / min · t Therefore, there is a possibility that the slag and hot metal that floated by vigorous stirring of the hot metal will be scattered. The scattered slag and hot metal adhere to the upper blowing lance as a metal, and the productivity is greatly impaired because the adhered metal is removed. Moreover, when adhesion | attachment of a bullion is intense, it will become difficult to raise an upper blowing lance after completion | finish of a dephosphorization process, and it will become a situation which cannot implement operation for a long time.

Furthermore, in the method for melting low phosphorus koji in Patent Document 2, the oxygen flow rate up to 60% of the blowing rate at which hatching is completed is as large as 1.75 Nm ³ / min · t, and oxygen collision from the upper blowing lance As a result, the hot metal surface swells violently. For this reason, when slag hatching is about to end, there is a high possibility that slag and molten iron will scatter, which causes problems such as adhesion of metal to the upper blowing lance as in the dephosphorization method of Patent Document 1.
That is, in order to improve the dephosphorization efficiency, it is necessary to finely adjust the oxygen flow rate from the top blowing lance and the bottom blowing stirring flow rate (bottom blowing stirring power) according to the progress of the dephosphorization process.

On the other hand, in the latter half of the dephosphorization process, the slag rises and covers the hot metal surface of the molten iron. Therefore, even if oxygen is blown from the upper blowing lance, it is difficult for oxygen to reach the molten iron and FeO is not easily generated at the slag-metal interface. Therefore, as disclosed in Patent Document 3, a method of adding iron oxide such as iron ore or mill scale to the hot metal to replenish the iron oxide is also conceivable.
However, when iron oxide is excessively added to the hot metal, a part of oxygen in the iron oxide undergoes a decarburization reaction and also reacts with carbon in the hot metal, so that the carbon concentration of the hot metal decreases. As a result, in the decarburization process performed after the dephosphorization process, there is a possibility that the amount of carbon in the molten iron is insufficient and the molten steel temperature at the time of steel output cannot be stably maintained.

Further, in hot metal dephosphorization treatment, it is preferable to maintain the temperature of the hot metal in a temperature zone where the reaction efficiency of the dephosphorization reaction is high. When is used, the temperature of the hot metal during or after the dephosphorization process may not be accurately controlled.
The present invention has been made in order to solve the above-mentioned problems, and its purpose is to reliably remove Si in the hot metal, to sufficiently hatch the surfaced slag and to improve the hot metal in the dephosphorization process. It is an object of the present invention to provide a hot metal dephosphorization method that can effectively remove P in the hot metal by accurately controlling the temperature and can stably maintain the hot steel temperature at the time of steelmaking.

In order to achieve the object, the present invention takes the following technical means.
That is, the hot metal dephosphorization processing method of the present invention,
In a dephosphorization furnace in which oxygen is blown into the hot metal from the top blowing lance and blown by bottom blowing stirring, a desiliconization period in which Si is removed from the hot metal, and a slag that floats on the hot metal following the desiliconization period. When carrying out the hot metal dephosphorization process through the ironmaking period to be produced and the dephosphorization period following the ironmaking period and removing P in the hot metal,
Before the start of the desiliconization period, the basicity of the hot metal (CaO / SiO ₂ ) is adjusted to 2.5 to 3.5, and the height from the hot metal surface of the hot metal to the outlet of the upper blowing lance is increased. Set to 1.8-2.2m,
In the desiliconization period, the oxygen flow rate from the top blowing lance is set to 3.0 to 4.0 Nm ³ / min · t, and the bottom blowing stirring power calculated by the equation (1) is set to 100 to 300 W / t. Smelt,
In the ironmaking period, the oxygen flow rate from the top blowing lance is 1.3 to 1.6 Nm ³ / min · t, and the bottom blowing stirring power is blown to 100 to 300 W / t,
In the dephosphorization period, the oxygen flow rate from the top blowing lance is 1.3 to 1.6 Nm ³ / min · t, and the bottom blowing stirring power is blown at 500 W / t or more,
After completion of the ironmaking period, a coolant having a pure iron content of 90% or more is introduced so that the temperature of the molten iron after the addition becomes 1350 to 1400 ° C., and after dephosphorization calculated from the total oxygen amount Iron oxide is continuously added to the hot metal at a rate of 1.0 to 10.0 kg / min · t so that the carbon concentration of the hot metal becomes 3.2% or more.

In order to improve the dephosphorization efficiency, the present inventors first surely oxidize and remove Si in the hot metal, and then surely hatch the slag for dephosphorization, and further, the interface between the slag and the hot metal. It was considered necessary to sufficiently produce FeO that reacts with P. For this purpose, the stage of slag hatching is promoted between the desiliconization stage and the dephosphorization stage by weakening both the oxygen flow rate from the top blowing lance and the stirring power of the bottom blowing. As a result, the present invention has been completed.
In the dephosphorization period, the present inventors control the temperature of the hot metal to 1350 to 1400 ° C. at which the dephosphorization reaction proceeds easily, and generate FeO that reacts with P in the hot metal at the slag-metal interface. Therefore, it was considered necessary to supply iron oxide to the hot metal in addition to supplying oxygen from the top blowing lance. Then, the present inventors have found that it is necessary to use a coolant having a high pure iron content capable of obtaining a stable cooling effect in order to more accurately control the temperature of the hot metal, and the present invention has been completed. It was.

By taking the measures described above, Si in the hot metal can be surely removed, the floated slag is sufficiently hatched, and the temperature of the hot metal in the dephosphorization process is accurately controlled, so that P in the hot metal is effective. The molten steel temperature at the time of steel output can be stably maintained.
In addition, the flow rate of oxygen from the top blowing lance and the stirring intensity of the bottom blowing can be appropriately controlled at each stage of the blowing process, and the temperature of the hot metal and the carbon concentration of the hot metal after dephosphorization can be controlled. Low phosphorus steel can be melted with high accuracy.

  According to the hot metal dephosphorization method of the present invention, Si in the hot metal can be surely removed, the slag for dephosphorization is sufficiently hatched, and the temperature of the hot metal in the dephosphorization process is accurately controlled. P can be effectively removed, and the molten steel temperature during steel output can be stably maintained. As a result, low phosphorus steel can be melted stably and with high accuracy.

First, the converter equipment 1 in which the hot metal dephosphorization processing method according to the present invention is performed will be described. However, the hot metal dephosphorization method of the present invention is not limited to the one using this converter facility 1.
The converter facility 1 includes a dephosphorization furnace 2 and a decarburization furnace.
As shown in FIG. 1, the dephosphorization furnace 2 has a furnace port 3 that opens upward, and an upper blowing lance that blows oxygen into the hot metal inserted from the furnace port 3 and charged in the furnace. 4 is provided. Above this furnace port 3 is provided a hopper 7 for charging auxiliary materials. An outlet 9 is formed in the furnace wall 8 of the dephosphorization furnace 2 so that the hot metal can be extracted by tilting the furnace body, and a stirring gas can be supplied to the furnace bottom 5 of the dephosphorization furnace 2 into the hot metal. The tuyere 6 is formed in the bottom.

The upper blow lance 4 is provided with a blower outlet 10 having a plurality of Laval nozzles with nozzle hole diameters of 25φ to 35φ set at an inclination angle of 10 ° to 14 ° at the tip thereof. The upper blow lance 4 is movable up and down so that the height H from the hot metal surface of the hot metal to the blowout port 10 can be changed.
The hopper 7 is provided in the furnace port 3 of the dephosphorization furnace 2. The hopper 7 can be charged with the coolant 12, the iron oxide 13, or the slagging agent 14 in the furnace.
The hot metal refining method in the converter equipment 1 mentioned above is as follows.

First, the hot metal transported from the blast furnace is charged into the tilted dephosphorization furnace 2. Thereafter, the dephosphorization furnace 2 is turned upward, the upper blowing lance 4 is inserted from the furnace port 3 of the dephosphorization furnace 2, and oxygen gas is blown from the blower outlet 10 toward the hot metal. At the same time, a dephosphorization process is performed while nitrogen gas, argon gas, or the like is blown from the furnace bottom 5 and the molten iron is stirred.
When the dephosphorization process is completed, the dephosphorization furnace 2 is tilted, the hot metal is discharged from the tap 9 to an external ladle, and the discharged hot metal is transported together with the ladle to the decarburization furnace. In the decarburization furnace, oxygen gas is blown from an upper blowing lance 4 inserted from the furnace port 3 to the molten iron poured, and the molten iron is stirred from the furnace bottom 5 with stirring gas such as nitrogen or argon. The carbon is reacted with oxygen to perform decarburization.

The molten steel that has been decarburized is tilted through the decarburization furnace, and is then removed from the decarburization furnace and sent to the secondary refining equipment and continuous casting machine.
By the way, in the hot metal dephosphorization method of the present invention, among the above-described hot metal refining methods, the hot metal discharged from the blast furnace is poured into the dephosphorization furnace 2 and dephosphorized in the dephosphorization furnace 2 and discharged. It is related to the process until.
Hereinafter, the hot metal dephosphorization method will be described in more detail.
As shown in FIG. 2 and FIG. 3, when carrying out the hot metal dephosphorization method of the present invention, in order to increase the dephosphorization efficiency, the upper lance 4 is used under appropriate conditions in accordance with the progress of the blowing process. It is necessary to carry out oxygen blowing, bottom blowing stirring, and addition of auxiliary materials.

The progressing stage of the blowing process includes a desiliconization period in which Si is removed from the hot metal, a slagging process in which the slag 11 floating on the hot metal is hatched following the desiliconization period, and a P in the hot metal following the slagging process. There are three processing stages, a dephosphorization period that removes.
First, before explaining the desiliconization period, the ironmaking period, and the dephosphorization period, the preparation stage before the start of blowing (before the desiliconization period) will be described.
As shown in FIG. 1, before the start of the desiliconization period, the hot metal conveyed from the blast furnace is first charged into the furnace of the dephosphorization furnace 2. For the hot metal charged in the dephosphorization furnace 2, a slag-forming agent 14 such as calcined lime (CaO) is introduced from the hopper 7, and the basicity (calculated basicity) of the hot metal becomes 2.5 to 3.5. Adjusted. Further, an upper blowing lance 4 is inserted into the dephosphorization furnace 2 from the furnace port 3, and the height H of the upper blowing lance 4 is 1.8 to from the hot metal surface of the hot metal charged in the dephosphorization furnace 2. 2.2m.

The basicity is the ratio of the CaO concentration to the SiO ₂ concentration in the hot metal. When the basicity is less than 2.5, the dephosphorization ability of the slag 11 is low and the dephosphorization is not sufficiently performed, or the acidic oxide SiO ₂ is excessive and the refractory material of the basic oxide is used. The melting loss of the furnace body mainly comprised becomes large, and the lifetime of the dephosphorization furnace 2 falls. On the other hand, when the basicity is greater than 3.5, a part of the CaO added excessively is not dissolved, and the hatching of the slag 11 during the desiliconization period becomes insufficient, and the dephosphorization efficiency may decrease. . Therefore, in the hot metal dephosphorization method of the present invention, the basicity is set to 2.5 to 3.5.

On the other hand, the upper blowing lance 4 is used for processing from the desiliconization period to the dephosphorization period with the height set in the preparation stage. If the height of the upper blow lance 4 is less than 1.8 m, the distance from the blower outlet 10 to the hot metal surface of the hot metal becomes too close, and the blown oxygen strongly collides with the hot metal. As a result, hot metal splatters (spitting) and yield decreases. In addition, the molten iron that has been scattered adheres to and accumulates at the outlet 10 and the furnace outlet 3 of the upper blowing lance 4 and normal operation cannot be continued.
Furthermore, if the height of the upper blow lance 4 exceeds 2.2 m, the distance from the blower outlet 10 to the hot metal surface of the hot metal is too far, and oxygen is not sufficiently blown into the hot metal. As a result, oxygen supply to the hot metal becomes insufficient, and removal of Si in the hot metal in the desiliconization period and removal of P in the hot metal in the dephosphorization period become insufficient. Therefore, in the hot metal dephosphorization processing method of the present invention, the height of the upper blowing lance 4 is set to 1.8 to 2.2 m.

As shown in FIG. 2A, in the desiliconization period, while stirring gas is blown from the furnace bottom 5 and the hot metal is stirred, oxygen is blown into the hot metal from the upper blowing lance 4 to convert Si in the hot metal into SiO ₂ . This is the period to be removed by oxidation. The desiliconization period is a period in which the total amount of oxygen blown from the upper blowing lance 4 is 3.5 to 4.5 Nm ³ / t from the start of blowing.
As shown in FIG. 3, during the desiliconization period, the oxygen flow rate from the top blowing lance 4 is a hard blow (strong stirring) of 3.0 to 4.0 Nm ³ / min · t, and is calculated by the equation (1). The bottom blowing stirring power is soft blow (weak stirring) of 100 to 300 W / t.

By setting the oxygen flow rate from the top blowing lance 4 to 3.0 Nm ³ / min · t or more, oxygen is sufficiently supplied into the hot metal, and the oxidation of Si in the hot metal to SiO ₂ is efficiently performed. Further, by setting the oxygen flow rate from the upper blowing lance 4 to 4.0 Nm ³ / min · t or less, the molten iron is scattered by the oxygen blowing from the upper blowing lance 4 and is deposited on the outlet 10 of the upper blowing lance 4. As a result, the occurrence of operational hindrance is suppressed or prevented.
The bottom blowing agitation power ε is calculated using a well-known equation (1) (101, 102nd Nishiyama Memorial Technology Course, Japan Iron and Steel Institute, 1984, p. 73). By setting the bottom blowing stirring power to 100 W / t or more, the hot metal is sufficiently stirred and the Si in the hot metal can be reliably oxidized. Further, by setting the bottom blowing stirring power to 300 W / t or less, it becomes possible to stir the molten iron whose surface is not sufficiently covered by the slag 11 so as not to be scattered, and the molten iron is supplied to the outlet 10 of the upper blowing lance 4. It is possible to suppress or prevent the occurrence of the operation hindrance due to the adhesion and deposition.

As shown in FIG. 2 (b), in the slagging period following the desiliconization period, the slag 11 floating on the molten iron is promoted by the slagging agent 14 to form the slag 11 suitable for the dephosphorization reaction. It is a period to do. The ironmaking period is a period in which the integrated amount of oxygen blown from the upper blowing lance 4 is 3.5 to 4.5 Nm ³ / t from the end of the desiliconization period.
As shown in FIG. 3, in the Zokasuki, oxygen flow ^{3.0~4.0Nm 3 / min · t 1.3~1.6Nm 3} / min · t from the hard blow from the top blowing lance 4 Can be switched to soft blow. In addition, the bottom blow stirring power remains soft blow of 100 to 300 W / t.

The meaning that the flow rate of oxygen from the top blowing lance 4 is 1.6 Nm ³ / min · t or less is to suppress the reduction of the hot metal temperature due to excessive blowing of oxygen and to promote the hatching of the slag 11. Further, the meaning that the oxygen flow rate from the top blowing lance 4 is 1.3 Nm ³ / min · t or more means that oxygen is sufficiently blown into the hot metal to cause a decarburization reaction in the hot metal, and the exhaust gas generated by this decarburization reaction. This is because it can be effectively used as fuel.
On the other hand, the meaning that the bottom blowing agitation power in the ironmaking period is 300 W / t or less means that, as in the desiliconization period, the agitation with respect to the molten iron becomes too large and the molten iron adheres to and accumulates on the upper blowing lance 4 and operation hindrance occurs. This is to suppress or prevent this.

As shown in FIG. 2 (c), in the dephosphorization period following the ironmaking period, FeO is generated at the interface between the molten iron and the slag 11 that has floated on the molten iron, and P in the molten iron is oxidized by FeO. Is a period in which P is removed as P ₂ O ₅ . The dephosphorization period is a period in which the integrated amount of oxygen blown from the upper blowing lance 4 is 7.0 to 9.0 Nm ³ / t from the end of the ironmaking period.
As shown in FIG. 3, in the dephosphorization period, the oxygen flow rate from the top blowing lance 4 is a soft blow of 1.3 to 1.6 Nm ³ / min · t, and the bottom blowing stirring power is 100 to 300 W / The soft blow of t is switched to a hard blow of 500 W / t or more.

The reason why the oxygen flow rate from the upper blowing lance 4 in the dephosphorization period is set to 1.3 Nm ³ / min · t or more is that FeO necessary for the dephosphorization reaction can be generated at the slag-metal interface. Further, it is possible to suppress the decarburization reaction in the dephosphorization period and increase the carbon concentration in the hot metal.
The reason why the oxygen flow rate from the top lance 4 is 1.6 Nm ³ / min · t or less is to reduce the ratio of oxygen consumed for decarburization by weakening the collision of oxygen with the molten metal surface. In addition, by increasing the ratio of oxygen consumed for iron oxidation and suppressing hot metal decarburization during the dephosphorization period, the carbon concentration of hot metal is not lowered too much in the decarburization process following the dephosphorization process. It is. By doing in this way, it becomes possible to ensure a sufficient carbon concentration in the hot metal in the decarburization treatment and to stably maintain the molten steel temperature at the time of steel output.

On the other hand, the bottom blowing stirring power in the dephosphorization period was set to 500 W / t or more because the hot metal was sufficiently stirred so that P in the hot metal was in contact with FeO formed at the interface between the slag 11 and the hot metal that had floated up. This is because it is possible to improve the dephosphorization efficiency.
In the dephosphorization period, since the surface of the hot metal is covered with the slag 11, the hot metal does not adhere to the upper blowing lance 4 even if the bottom blowing agitation power is increased to some extent, and the operation inhibition is the desiliconization period. And it doesn't matter as much as the era of construction. Therefore, it is desirable that the bottom blowing stirring power be set to 500 W / t or more, which is larger than that in the desiliconization period or the ironmaking period, to promote the oxidation of P in the molten iron.

In the dephosphorization period, the coolant 12 is introduced and the temperature of the hot metal is controlled to 1350 to 1400 ° C. As the coolant 12, a material such as scrap that has a low iron oxide content and a pure iron content of 90% or more is employed. If a large amount of iron oxide such as a mill scale whose oxidation state is not stable is used as the coolant 12, the cooling capacity of the coolant 12 is likely to fluctuate, and it becomes difficult to control the temperature of the hot metal to 1350-1400 ° C. Because.
In addition, in the dephosphorization period, the iron oxide 13 is added in an amount of 1.0 to 10.0 kg / min · so that the carbon concentration of the hot metal after dephosphorization calculated from the total oxygen amount is 3.2% or more. The molten iron is continuously charged at a rate of t. Note that sintered ore or iron ore is used for the iron oxide 13. The iron oxide 13 is continuously supplied into the hot metal as an FeO source so that oxidation of P in the hot metal by FeO is stably and continuously performed at the interface between the slag 11 and the hot metal.

By setting the charging speed of the iron oxide 13 to 1.0 kg / min · t or more, the concentration of iron oxide in the slag 11 can be increased, and the oxidation of P in the hot metal can be reliably performed. Further, when the charging speed of the iron oxide 13 exceeds 10.0 kg / min · t, the slag 11 is cooled by the iron oxide 13 and the hatching of the slag 11 is inhibited, and the dephosphorization efficiency is lowered.
The input amount of the iron oxide 13 is set so that the total decarburization amount by the oxygen and the iron oxide 13 from the top blowing lance 4 is estimated and the carbon concentration in the hot metal after the treatment is 3.2% or more. For example, as shown in FIG. 4, if the carbon concentration is lower than 3.2%, the liquidus temperature at the same hot metal temperature increases, and the hot metal tends to become solid (the hot metal viscosity increases). As a result, hot metal tends to adhere to the furnace 3 and the ladle, which may hinder productivity.

Therefore, the hot metal temperature is set to liquidus + 50 ° C. to liquidus + 100 ° C. at a carbon concentration of 3.2%, that is, the hot metal temperature is set to 1350 to 1400 ° C. The lower limit of the hot metal temperature is set to the liquidus + 50 ° C. in consideration of the temperature variation of the hot metal.
As described above, in the hot metal dephosphorization processing method of the present invention, the top blowing lance 4 is hard blown and the bottom blowing stirring power is soft blow, and the top blowing lance 4 is soft blow. Between the dephosphorization period in which the bottom blowing agitating power is hard blow, there is provided a steelmaking period in which the top blowing lance 4 is soft blow and the bottom blowing agitating power is soft blow. By controlling the carbon concentration of the hot metal later, low phosphorus steel can be produced stably and with high accuracy.

Hereinafter, the hot metal dephosphorization processing method of the present invention will be described in more detail using Examples and Comparative Examples.
As described above, the present inventors define the period of oxygenation by the amount of accumulated oxygen. First, a preliminary experiment was performed in order to clarify the range of the amount of oxygen accumulated during the period of ironmaking.
In the preliminary experiment, the dephosphorization furnace 2 was discharged as a preparatory stage in order to eliminate the influence of residual slag from the previous charge, and then the dephosphorization furnace 2 after discharge was equipped with 90 t of hot metal having a Si concentration of 0.45%. I entered. Subsequently, calcined lime (slagging agent 14) was poured into the hot metal so that the basicity was 3.0, and the height of the upper blowing lance 4 was set to 2.0 m.

Subsequently, during the silicon removal period, the oxygen flow rate from the top blow lance 4 is set to a hard blow of 3.5 Nm ³ / min · t and the bottom blow stirring power is set to a soft blow of 280 W / t. The amount was blown from the start of blowing to 3.6 Nm ³ / t.
When the silicon removal period is completed at an oxygen accumulation amount of 3.6 Nm ³ / t, the slagging period is started. However, to what extent this slagging period may be set as the slagging period has not been determined. Therefore, with regard to blowing conditions during the ironmaking period, the bottom blowing stirring power is fixed to 280 W / t soft blow, and only the oxygen flow rate from the top blowing lance 4 is set to 1.4 Nm ³ / min · t soft blow. Then, the oxygen accumulated amount from the top blowing lance 4 is blown by 5 charges of 3.4, 3.5, 4.0, 4.5, 4.6 Nm ³ / t from the end of the desiliconization period, respectively. Went.

  Next, after the blowing is completed up to a predetermined oxygen accumulation amount, in order to determine whether or not the slagging period is surely performed, the blowing is temporarily interrupted and the slag 11 hatching status (slag hatching) And the concentration of P in the hot metal was measured to determine the dephosphorization rate when the blowing was interrupted. The results are shown in Table 1.

The “slag hatchability” is evaluated by visually observing the slag 11 in the furnace, and evaluating the hatchability when there is no solid material as ◯, and x when there is a solid material.
The “dephosphorization rate at the time of interruption of blowing” is obtained by (concentration of P in molten iron before treatment−concentration of P in molten iron at the time of interruption of blowing) ÷ (concentration of P in molten iron before treatment). It is done.
When attention is paid to the evaluation result of “slag hatchability” in Table 1, solid substances remain in the furnace at an oxygen cumulative amount of 3.4 Nm ³ / t, and hatching is not completed. On the other hand, when the oxygen accumulation amount is 3.5 Nm ³ / t or more, there is no solid matter in the furnace, and hatching is completed. From this, it is judged that it is preferable to set the accumulated amount of oxygen to 3.5 Nm ³ / t or more in the ironmaking period.

On the other hand, if the dephosphorization treatment is performed to a range of 30% or more in the dephosphorization period, dephosphorization that should be originally performed in the dephosphorization period is performed during the dephosphorization period. This is not preferable because it is performed. In view of this point, paying attention to the evaluation result of “dephosphorization rate at the time of suspension of blowing” in Table 1, even if the blowing of the slagging period is performed up to an accumulated oxygen amount of 4.5 Nm ³ / t, The dephosphorization rate is less than 30%, but the dephosphorization rate at the time of interruption of blowing is 30% when the oxygen accumulation amount is 4.6 Nm ³ / t. From this, the upper limit of the oxygen accumulation amount in the ironmaking period is determined to be 4.5 Nm ³ / t.

The results in Table 1 were comprehensively judged, and the period of the integrated oxygen amount of 3.5 to 4.5 Nm ³ / t from the end of the desiliconization period was determined as the sprouting period of the present invention.
Next, “basicity” and “top blowing lance height” of hot metal before the start of blowing, “top blowing lance oxygen flow rate” and “bottom blowing agitation” in each stage of desiliconization, ironmaking and dephosphorization The evaluation was made by changing various operating conditions of “power”, “iron oxide input rate” in the dephosphorization period, and “refrigerant pure iron”.
The results are shown in Tables 2-5.

[Examples 1 to 3]
As shown in Tables 2 and 3, Examples 1 to 3 are examples in which the slagging agent 14 was added so that the “basicity (calculated basicity)” satisfies 2.5 to 3.5, and Comparative Example 1 2 is an example in which the slagging agent 14 is added so that the “basicity” is 2.4 and 3.7. Other experimental conditions are the same in the examples and comparative examples.
In Examples 1 to 3, when paying attention to “P concentration in hot metal” (hereinafter referred to as “P concentration after treatment”) in “After treatment hot metal conditions” in Table 3, the P concentration after treatment is 0.015 to It is 0.018%, which is lower than the threshold value 0.020% of the P concentration after treatment required in actual operation, and it can be seen that the dephosphorization treatment is properly performed.

However, in Comparative Example 1 where the basicity is 2.4, the “P concentration after treatment” is 0.040%, which is higher than the threshold value 0.020% of the P concentration after treatment required in actual operation. Yes. This is considered to be because when the basicity is less than 2.5, the dephosphorization ability of the slag 11 is lowered and the dephosphorization is not sufficiently performed.
In Comparative Example 2 with a basicity of 3.7, the “P concentration after treatment” is 0.040%, which is higher than the threshold value 0.020%, and the dephosphorization efficiency is lower than in Examples 1-3. This seems to be because when the basicity is greater than 3.5, hatching of the slag 11 becomes insufficient during the desiliconization period.

That is, from Examples 1 to 3 and Comparative Examples 1 and 2 described above, the dephosphorization ability of the slag 11 is improved by starting the dephosphorization process after adjusting the basicity of the hot metal to 2.5 to 3.5. It is possible to carry out dephosphorization treatment with high dephosphorization efficiency without lowering.
[Examples 4 to 6]
As shown in Tables 2 and 3, Examples 4 to 6 are examples in which the dephosphorization treatment was performed by setting the “top blowing lance height” to be 1.8 to 2.2 m, and Comparative Examples 3 and 4 are examples in which the dephosphorization process was performed with the “upper blowing lance height” set to 1.7 m and 2.3 m. Other experimental conditions are the same in the examples and comparative examples.

In Examples 4 to 6, the “P concentration after treatment” is 0.015 to 0.018%, which is lower than the threshold value 0.020% of the P concentration after treatment required in actual operation. It can be seen that the processing is performed properly.
However, in Comparative Example 4 where the “upper lance height” is 2.3 m, the “P concentration after treatment” is 0.039%, and the threshold value of the P concentration after treatment required in actual operation is 0.020%. Higher. This is presumably because the distance from the top blowing lance 4 to the hot metal surface of the hot metal became longer, oxygen was not sufficiently blown into the hot metal, and P in the hot metal was sufficiently removed during the dephosphorization period.

  On the other hand, in Comparative Example 3 where the height of the upper blowing lance is 1.7 m, the “P concentration after treatment” is 0.019%, which is lower than the threshold of 0.020%. Focusing on the evaluation items of “metal adhesion to the furnace” and “metal adhesion to the furnace mouth”, “metal adhesion to the top blowing lance” is 36%, which is higher than the threshold of 12%. The “metal adhesion to the mouth” is 65%, which is higher than the threshold value of 15%. This is presumably because the distance from the upper blowing lance 4 to the hot metal surface of the hot metal became shorter, and the metal (hot metal) scattered by the oxygen adhered to the upper blowing lance 4 and the furnace port 3.

The “bulb adhesion to the upper blowing lance” is indicated by the ratio of the length of the adhesion of the bare metal to the length of the upper blowing lance 4. In addition, “metal adhesion to the furnace port” was measured from the designed area and photograph of the furnace port 3 by tilting the dephosphorization furnace 2 after the dephosphorization process and taking a photo of the furnace port 3. The difference (decrease) from the area of the furnace port 3 is obtained, and this area difference is divided by the designed area of the furnace port 3.
In other words, the upper blowing lance 4 is set at a height of 1.8 to 2.2 m from the surface of the hot metal to perform the dephosphorization process, thereby suppressing the spattering of the hot metal and the bare metal from the upper blowing lance. 4 and the furnace port 3 can be dephosphorized with high dephosphorization efficiency while suppressing or preventing adhesion to the furnace port 3.
[Examples 7 to 9]
As shown in Tables 2 and 3, Examples 7 to 9 are examples in which the dephosphorization treatment was performed so that the “top blowing lance oxygen flow rate” was 3.0 to 4.0 Nm ³ / min · t during the desiliconization period. Comparative Examples 5 and 6 are examples in which dephosphorization was performed at oxygen flow rates of 2.8 Nm ³ / min · t and 4.2 Nm ³ / min · t. Other experimental conditions are the same in the examples and comparative examples.

In Examples 7 to 9, the “P concentration after treatment” is 0.016 to 0.020%, which is lower than the threshold value 0.020% of the P concentration after treatment required in actual operation. It can be seen that the processing is performed properly.
Further, in Comparative Example 5 in which the “top blowing lance oxygen flow rate” is 2.8 Nm ³ / min · t, the “P concentration after treatment” is 0.018%, which is lower than the threshold value 0.020%. There is a tendency for the oxygen flow rate to become too small and to exceed the operation time allowable for operation.
That is, in Example 7, the time required to complete the desiliconization period was 1.1 minutes, in Example 8, 1.0 minute, in Example 9, 1.0 minute, and in Comparative Example 6, 0. .8 minutes, both of which are shorter than the threshold value of 1.2 minutes and satisfy the operation time allowed for actual operation. However, in Comparative Example 5, it takes 1.4 minutes to complete the desiliconization period, which is longer than the threshold value of 1.2 minutes and does not satisfy the operation time allowed for actual operation. For this reason, the operation condition in which the “top blowing lance oxygen flow rate” is 2.8 Nm ³ / min · t is a comparative example.

On the other hand, in Comparative Example 6 in which the “top blowing lance oxygen flow rate” is 4.2 Nm ³ / min · t, the “P concentration after treatment” is 0.017%, which is lower than the threshold value 0.020%. “Body adhesion to top blowing lance” is 35%, which is higher than the threshold of 12% required for actual operation. This is considered to be because the flow rate of oxygen from the upper blow lance 4 was increased and the molten iron was scattered and deposited on the outlet 10 of the upper blow lance 4.
In other words, during the desiliconization period, the oxygen flow rate from the top blowing lance 4 is set to 3.0 to 4.0 Nm ³ / min · t, so that spattering of molten metal (spitting) and adhesion of the metal to the top blowing lance 4 of the molten iron are performed. Blowing can be performed while suppressing or preventing this.
[Examples 10 to 12]
As shown in Tables 2 and 3, Examples 10 to 12 are examples in which dephosphorization treatment was performed with the “bottom blowing stirring power in the desiliconization period” being 100 to 300 W / t, and Comparative Example 7 was “desiliconization period” This is an example in which the dephosphorization treatment was performed with the “bottom blowing agitation power” at 320 W / t. Other experimental conditions are the same in the examples and comparative examples.

In Examples 10 to 12, the “P concentration after treatment” is 0.017 to 0.018%, which is lower than the threshold value 0.020% of the P concentration after treatment required in actual operation. It can be seen that the processing is performed properly.
Further, in Comparative Example 7 in which “bottom blowing stirring power in the desiliconization period” is 320 W / t, “P concentration after treatment” is 0.012%, which is lower than the threshold value 0.020%. “Attachment of bullion to lance” is 34%, which is higher than the threshold of 12% required for actual operation. This is presumably because the hot metal stirring was excessively strong and the molten metal surface waved, and the amount of metal (hot metal) deposited and deposited on the outlet 10 of the upper lance 4 increased.

That is, in the desiliconization period, dephosphorization treatment is performed while suppressing or preventing hot metal splattering (spitting) and adhesion to the upper metal lance 4 by blowing the bottom blowing stirring power at 300 W / t or less. It becomes possible.
[Examples 13 to 15]
As shown in Tables 2 and 3, Examples 13 to 15 were subjected to dephosphorization treatment so that the “upflow lance oxygen flow rate in the slagging period” satisfied 1.3 to 1.6 Nm ³ / min · t. Comparative examples 8 and 9 are examples in which the dephosphorization treatment was performed with the “upper blowing lance oxygen flow rate in the ironmaking period” being 1.2 Nm ³ / min · t and 1.7 Nm ³ / min · t. Other experimental conditions are the same in the examples and comparative examples.

In Examples 13 to 15, the “P concentration after treatment” is 0.015 to 0.016%, which is lower than the threshold value 0.020% of the P concentration after treatment required in actual operation. It can be seen that the processing is performed properly.
Further, in Comparative Example 8 in which the “upflow lance oxygen flow rate in the ironmaking period” is 1.2 Nm ³ / min · t, the “P concentration after treatment” is 0.018%, which is lower than the threshold value 0.020%. However, the “carbon monoxide concentration in the exhaust gas” is 35%, which is lower than the threshold value 50% required in actual operation, and it is difficult to effectively use the exhaust gas. This is because the oxygen from the top lance 4 is not sufficiently blown into the hot metal and the decarburization reaction is less likely to occur in the hot metal, and the carbon monoxide concentration in the exhaust gas becomes low, making it difficult to effectively use the exhaust gas. it is conceivable that.

The “carbon monoxide concentration in the exhaust gas” is evaluated by the average concentration of carbon monoxide in the exhaust gas.
On the other hand, in Comparative Example 9 where the “upflow lance oxygen flow rate in the ironmaking period” is 1.7 Nm ³ / min · t, the “P concentration after treatment” is 0.039%, which is higher than the threshold value of 0.020%. It can be seen that the dephosphorization process is not performed properly. In Comparative Example 9, the evaluation of “slag hatchability” is also “x”, and the slag 11 is not sufficiently hatched. This is considered to be because the hot metal temperature was lowered by excessive blowing of oxygen and the hatching of the slag 11 was not promoted.

Furthermore, in Comparative Example 9, “metal adhesion to the upper blowing lance” is 31%, which is higher than the threshold value 12%, and much metal is attached to the upper blowing lance 4. This is considered to be because oxygen was strongly blown from the upper blowing lance 4 to the molten iron, and the molten iron (metal) was scattered and deposited on the outlet 10 of the upper blowing lance 4.
That is, in the ironmaking period, the exhaust gas can be effectively used by blowing the oxygen flow rate from the top blowing lance 4 to 1.3 to 1.6 Nm ³ / min · t, and spattering of hot metal (spitting) ) And adhesion to the top blowing lance 4 of the bullion can be suppressed or prevented. Then, the slag 11 can be surely hatched, and the dephosphorization process can be performed with high dephosphorization efficiency in the dephosphorization period following the slag formation period.
[Examples 16 to 18]
As shown in Tables 2 and 3, Examples 16 to 18 are examples in which the dephosphorization treatment was performed so that the “bottom blowing stirring power in the ironmaking period” satisfies 100 to 300 W / t, and Comparative Example 10 is This is an example in which the dephosphorization treatment was performed with “bottom blowing stirring power in the ironmaking period” set to 320 W / t. Other experimental conditions are the same in the examples and comparative examples.

In Examples 16 to 18, the “P concentration after treatment” is 0.018 to 0.020%, which is lower than the threshold value 0.020% of the P concentration after treatment required in actual operation. It can be seen that the processing is performed properly.
Further, in Comparative Example 10 in which “bottom blowing stirring power in the ironmaking period” is 320 W / t, “P concentration after treatment” is 0.018%, which is lower than the threshold value 0.020%. The bullion adhesion to the lance is 36%, which is higher than the threshold value of 12%. This is considered to be because the hot metal stirring was strengthened and the hot metal surface was ruffled, and the metal (spray) deposited and deposited on the outlet 10 of the upper blowing lance 4 increased.

  That is, in the ironmaking period, the bottom blowing agitating power is blown at 300 W / t or less, so that spattering of molten iron (spitting) and adhesion to the top blowing lance 4 of the metal can be suppressed or prevented. In addition, the slag 11 can be sufficiently hatched by soft blow, and P in the molten iron can be surely reacted to perform the dephosphorization process with high dephosphorization efficiency.

[Examples 19 and 20]
As shown in Tables 4 and 5, in Examples 19 and 20, the dephosphorization treatment was performed so that the “upflow lance oxygen flow rate in the dephosphorization period” satisfied 1.3 to 1.6 Nm ³ / min · t. The comparative examples 11 to 16 are dephosphorization by setting the “upflow lance oxygen flow rate in the dephosphorization period” to 0.5 to 1.2 Nm ³ / min · t or 1.7 to 1.8 Nm ³ / min · t. This is an example of processing. Other experimental conditions are the same in the examples and comparative examples.
In Examples 19 and 20, the “P concentration after treatment” is 0.017 to 0.019%, which is lower than the threshold value 0.020% of P concentration after treatment required in actual operation. It can be seen that the processing is performed properly.

Further, in Comparative Examples 11 to 14 in which the “upflow lance oxygen flow rate in the dephosphorization period” is 0.5 to 1.2 Nm ³ / min · t, the “P concentration after treatment” is 0.015 to 0.019%. However, the carbon monoxide concentration in the exhaust gas is as low as 21 to 40%, making it difficult to effectively use the exhaust gas. This is thought to be because the oxygen blown into the hot metal was reduced, the decarburization reaction was suppressed, and the carbon monoxide concentration in the exhaust gas was reduced.
On the other hand, in Comparative Examples 15 and 16 in which the “upflow lance oxygen flow rate in the dephosphorization period” is 1.7 to 1.8 Nm ³ / min · t, the “P concentration after treatment” is 0.038 to 0.041%. Both are higher than the threshold value 0.020%, and the dephosphorization process is not properly performed. This is because, as a result of oxygen colliding violently from the upper blowing lance 4 against the surface of the hot metal and pushing the slag 11 so that oxygen easily reaches the hot metal, the ratio of oxygen reacting with C in the hot metal increases and slag This is probably because the ratio of oxygen that contributes to the formation of FeO in 11 decreased, and the dephosphorization efficiency decreased.

In other words, in the dephosphorization period, the upper lance oxygen flow rate is blown at 1.3 to 1.6 Nm ³ / min · t, so that the exhaust gas after blowing can be used effectively and the dephosphorization efficiency is high. Phosphorus treatment can be performed.
[Examples 21 to 23]
As shown in Tables 4 and 5, Examples 21 to 23 are examples where the dephosphorization treatment was performed so that the “bottom blowing stirring power in the dephosphorization period” satisfied 500 W / t or more, and Comparative Example 17 was “ This is an example in which the dephosphorization treatment was performed with the “bottom blowing stirring power in the dephosphorization period” set to 450 W / t. Other experimental conditions are the same in the examples and comparative examples.

In Examples 21 to 23, “P concentration after treatment” is 0.012 to 0.014%, which is lower than the threshold value 0.020% of P concentration after treatment required in actual operation. It can be seen that the processing is performed properly.
On the other hand, in Comparative Example 17 where the “bottom blowing stirring power in the dephosphorization period” is 450 W / t, the “P concentration after treatment” is 0.040%, which is higher than the threshold value of 0.020%. The process is not performed properly. This is considered to be because the stirring of the hot metal in the dephosphorization furnace 2 becomes insufficient, the oxidation of P becomes difficult to proceed at the interface between the slag 11 and the hot metal, and the dephosphorization efficiency is lowered.

That is, in the dephosphorization period, the dephosphorization process can be performed while maintaining high dephosphorization efficiency by blowing the bottom blowing stirring power at 500 W / t or more.
[Examples 24 and 25]
As shown in Tables 4 and 5, Examples 24 and 25 are examples in which the dephosphorization treatment was performed so that the “iron oxide charging rate” satisfies 1.0 to 10.0 kg / min · t. Examples 18 and 19 are examples in which the dephosphorization treatment was performed at a charging rate of 0.8 kg / min · t and 11.0 kg / min · t. Other experimental conditions are the same in the examples and comparative examples.

In Examples 24 and 25, the “P concentration after treatment” is 0.017 to 0.018%, which is lower than the threshold value 0.020% of the P concentration after treatment required in actual operation. It can be seen that the processing is performed properly.
On the other hand, in Comparative Example 18 in which the “iron oxide input rate” is 0.8 kg / min · t, the “P concentration after treatment” is 0.043%, after the dephosphorization treatment required in actual operation. The P concentration threshold of 0.020% is higher, and the dephosphorization efficiency is lower. This is considered to be because the concentration of iron oxide in the slag 11 was lowered, FeO was hardly generated at the interface between the slag 11 and the hot metal, and P in the hot metal was not easily removed.

On the other hand, even in Comparative Example 19 in which “the rate of iron oxide input during the dephosphorization period” is 11.0 kg / min · t, the “P concentration after treatment” is 0.042%, which is the dephosphorization treatment required in actual operation. The latter P concentration threshold is higher than 0.020%, and the dephosphorization efficiency is low. Furthermore, in Comparative Example 19, “slag hatchability” was evaluated as “x”, and the slag 11 was not sufficiently hatched. This is considered to be because the slag 11 was supercooled by the iron oxide 13 and the hatching of the slag 11 was inhibited, and the dephosphorization efficiency was lowered.
That is, in the dephosphorization period, high dephosphorization efficiency is achieved so as not to impair the hatchability of the slag 11 by performing the dephosphorization process while introducing the iron oxide 13 at an input rate of 1.0 to 10.0 kg / min · t. The hot metal dephosphorization process becomes possible.
[Examples 26 to 28]
As shown in Tables 4 and 5, Examples 26 to 28 are examples in which the coolant 12 was introduced during the dephosphorization period so that the “temperature of the molten iron after dephosphorization treatment” satisfied 1350 to 1400 ° C. Examples 20 and 21 are examples in which the coolant 12 was introduced during the dephosphorization period so that the “temperature of the hot metal after the dephosphorization treatment” was 1410 ° C. and 1340 ° C. Other experimental conditions are the same in the examples and comparative examples.

In Examples 26 to 28, the “P concentration after treatment” is 0.018 to 0.020%, which is lower than the threshold value 0.020% of the P concentration after treatment required in actual operation. It can be seen that the processing is performed properly.
On the other hand, in Comparative Example 20 in which the coolant 12 was introduced in the dephosphorization period so that the “temperature of the molten iron after dephosphorization” was 1410 ° C., the “P concentration after treatment” was 0.040%, which is the actual operation. The P concentration threshold after the treatment required above is higher than 0.020%, and the dephosphorization efficiency is lowered. This is presumably because the hot metal temperature after the dephosphorization process became too high, deviating from the temperature range suitable for the dephosphorization reaction, and the dephosphorization efficiency in the dephosphorization period was lowered.

Further, in Comparative Example 21 in which the coolant 12 was introduced in the dephosphorization period so that the “temperature of the molten iron after dephosphorization” was 1340 ° C., the “P concentration after treatment” was 0.016%, and the threshold value was set to 0. Although it is lower than 020%, the “metal adhesion to the furnace opening” is 40%, which is higher than the threshold value of 15%. This is presumably because the hot metal temperature after the dephosphorization process was lowered and the hot metal viscosity was increased and the hot metal became easier to adhere.
In other words, the dephosphorization process is performed while introducing the coolant 12 so that the temperature of the hot metal after the dephosphorization process is 1350 to 1400 ° C., thereby suppressing or preventing the adhesion of the metal to the furnace port and the high dephosphorization efficiency. It is possible to dephosphorize with.
[Examples 29 and 30]
As shown in Tables 4 and 5, Examples 29 and 30 are examples in which the coolant 12 having a pure iron content of 90% or more was added by dephosphorization treatment, and Comparative Examples 22 to 24 had a pure iron content of 78 to 88%. This is an example in which the coolant 12 is added. Other experimental conditions are the same in the examples and comparative examples.

In Examples 29 and 30, the “P concentration after treatment” is 0.018 to 0.019%, which is lower than the threshold value 0.020% of the P concentration after treatment required in actual operation. It can be seen that the processing is performed properly.
On the other hand, in Comparative Examples 22 to 24, the “hot metal temperature difference” fluctuates within a large range such as −35 or 30 ° C. As a result, as in Comparative Example 23, the “P concentration after treatment” is 0.037%, which is higher than the threshold value 0.020%, or as in Comparative Example 22, “bare metal adhesion to the furnace opening” occurs. 42%, exceeding 15% of the threshold. This is because the cooling capacity of the coolant 12 fluctuates and the temperature of the hot metal after the dephosphorization process increases or decreases, resulting in a decrease in the dephosphorization efficiency or the bullion being scattered and adhering to the furnace port 3. It is thought that it was because of.

  That is, by using the coolant 12 having a pure iron content of 90% or more in the dephosphorization period, the coolant 12 can stably exhibit the cooling capacity, and the dephosphorization efficiency is lowered and the furnace port 3 is reduced. It is possible to accurately control the temperature of the hot metal without causing the hot metal to adhere.

It is sectional drawing of the dephosphorization furnace of this invention. It is explanatory drawing which shows the hot metal dephosphorization processing method of this invention. It is explanatory drawing which shows transition of the oxygen flow rate and bottom blowing stirring power in the hot metal dephosphorization processing method of this invention. It is a figure which shows the relationship between the carbon concentration in hot metal, and the temperature of hot metal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Converter equipment 2 Dephosphorization furnace 3 Furnace port 4 Upper blowing lance 5 Furnace bottom 6 Tuyere 7 Hopper 8 Furnace wall 9 Outlet 10 Outlet 11 Slag 12 Coolant 13 Iron oxide 14 Shaking agent

Claims (1)

In a dephosphorization furnace in which oxygen is blown into the hot metal from the top blowing lance and blown by bottom blowing stirring, a desiliconization period in which Si is removed from the hot metal, and a slag that floats on the hot metal following the desiliconization period. When carrying out the hot metal dephosphorization process through the ironmaking period to be produced and the dephosphorization period following the ironmaking period and removing P in the hot metal,
Before the start of the desiliconization period, the basicity of the hot metal (CaO / SiO ₂ ) is adjusted to 2.5 to 3.5, and the height from the hot metal surface of the hot metal to the outlet of the upper blowing lance is increased. Set to 1.8-2.2m,
In the desiliconization period, the oxygen flow rate from the top blowing lance is set to 3.0 to 4.0 Nm ³ / min · t, and the bottom blowing stirring power calculated by the equation (1) is set to 100 to 300 W / t. Smelt,
In the ironmaking period, the oxygen flow rate from the top blowing lance is 1.3 to 1.6 Nm ³ / min · t, and the bottom blowing stirring power is blown to 100 to 300 W / t,
In the dephosphorization period, the oxygen flow rate from the top blowing lance is 1.3 to 1.6 Nm ³ / min · t, and the bottom blowing stirring power is blown at 500 W / t or more,
After completion of the ironmaking period, a coolant having a pure iron content of 90% or more is introduced so that the temperature of the molten iron after the addition becomes 1350 to 1400 ° C., and after dephosphorization calculated from the total oxygen amount A hot metal dephosphorization method characterized by continuously adding iron oxide to the hot metal at a rate of 1.0 to 10.0 kg / min · t so that the carbon concentration of the hot metal becomes 3.2% or more. .

Images