JP2005248218A - Molten iron pretreatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molten iron pretreatment by which desiliconization and dephosphorization rates can be improved at a low cost, and the treatment time can sufficiently be shortened and further, problem of working trouble caused by stickiness of solidified slag to the opening hole part of a treating vessel can easily be solved. <P>SOLUTION: The molten iron pretreatment is provided for the desiliconization and the dephosphorization by blowing oxidizing agent and flux from a lance dipped into the molten iron in the treating vessel, wherein the blowing quantity of the oxidizing agent from the main lance is reduced at the step of dephosphorizing reaction end stage and also, the dipping depth of the main lance is made further deeper and the blowing is continued. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hot metal pretreatment method, in particular, hot metal in a hot metal pretreatment container such as a kneading wheel or a hot metal ladle, by blowing various hot metal pretreatment agents from a lance to desiliconize and dephosphorize the hot metal. The present invention relates to a preliminary processing method.

In recent years, in the steelmaking process, silicon (element symbol Si) and phosphorus (element symbol P) in hot metal are used to reduce the burden of converter blowing and to minimize the cost of steelmaking steel. A so-called “hot metal preliminary treatment”, which is previously removed using an oxidizing agent, is performed.
There are various methods for the hot metal pretreatment depending on the processing vessel to be used (for example, a converter, a hot metal pan, a kneading car, etc.). In particular, the method of blowing an oxidizing agent (iron oxide, gaseous oxygen, etc.) or basicity adjusting agent (lime-based flux, etc.) using a lance immersed in hot metal in a processing vessel such as a kneading car or hot metal ladle is a converter. Compared with desiliconization and dephosphorization, it is advantageous in that the reaction efficiency of the oxidizing agent is high and the processing cost is low.

Conventionally, as shown in the following, hot metal pretreatment techniques using a processing vessel such as a kneading wheel or a hot metal ladle are known.
(1) A method of dephosphorization after removing SiO ₂ rich slag after desiliconization (Patent Document 1)
(2) A method of continuously forcibly removing slag by vacuum suction equipment or the like during processing when degassing, dephosphorizing, or desulfurizing hot metal (Patent Document 2)
(3) A method of discharging slag after desiliconization by tilting a chaotic vehicle (Patent Document 3)
(4) Method of using soda ash when performing dephosphorization without discharging slag after desiliconization (Patent Document 4)
(5) A method of adding iron oxide separately onto hot metal when CaO and an oxidizing agent are blown into the hot metal (Patent Document 5)
(6) A method using a special lance that uses a blown flow as a swirling flow in order to increase the reaction interface area between the slag and metal by dispersing an oxidizing agent in the hot metal (Patent Document 6)
(7) A method of using two injection lances and blowing a dephosphorizing agent from one and a desulfurizing agent from the other (Patent Document 7)
(8) Dephosphorization method using two injection lances and blowing in an oxidizing agent (Patent Document 8)
JP 61-33814 A JP 63-18011 A JP-A-5-5114 JP 59-104412 A JP-A-4-218609 Japanese Patent No. 2856576 JP 58-218311 A Japanese Patent Laid-Open No. 2002-146423

However, among the above prior arts, (1) and (2) require slag removal equipment for removing slag after desiliconization, which requires equipment costs, removes from the desiliconization process, There is a problem that it takes time to shift to the dephosphorization treatment.
Prior art (4) is disadvantageous in terms of cost because the unit price of the treatment agent is high. Furthermore, when the output of the blast furnace [Si] is high, there is a problem that the pre-desiliconization slag must be removed before the treatment, and the treatment becomes difficult due to the slopping during the treatment.
Prior art (3) was developed to solve these problems, but lacks consideration in terms of promoting the reaction itself at the dephosphorization stage and promoting the discharge of slag. Therefore, there is a problem that it is still insufficient for improving the dephosphorization rate.
The prior art (5) has a problem that the added iron oxide remains unreacted on the slag, and the ratio of iron oxide contributing to the reaction is small. In other words, the iron oxide added from above merely raises the oxygen potential of the top slag, and it is difficult to say that an oxygen source that contributes to the dephosphorization reaction is efficiently added. There is a problem that the sex gets worse.
In the prior art (6), there is a problem that the structure of the lance to be used is complicated and the manufacturing cost is higher than that of the single pipe lance.
The prior art (7) has a problem that the dephosphorization reaction is rather inhibited because the dephosphorization agent and the desulfurization agent are injected simultaneously.
The prior art (8) discloses a pretreatment method in which an oxidizing agent is efficiently blown by using two injection lances. However, when this method is applied from the initial stage of desiliconization, slag forming occurs frequently. However, slag calming treatment such as addition of a forming inhibitor or interruption of the treatment is required, and the treatment time is extended. Furthermore, although the oxidizing agent blowing efficiency is good, there is a problem that the reaction efficiency of the oxidizing agent is lowered.

  As described above, when the above-mentioned problems of the prior art are arranged, the desiliconization and dephosphorization rates are not sufficiently improved, and the processing time of the hot metal preliminary processing can be sufficiently shortened. In addition to the problem that there is no such problem, the processing cost is increased.

  In addition, the problems of the prior art include other problems such as work obstacles caused by adhesion of solidified soot to the opening of the processing vessel (for example, the furnace port of a kneading car) as an inhibitor of desiliconization and phosphorus removal efficiency. Can be considered. In particular, when using a chaotic vehicle, this problem tends to occur. In other words, a large amount of solidified soot called gulls adheres to the inner wall surface of the hot metal opening of the kneading wheel and closes this part, making it difficult to put in and out the lance used for hot metal pretreatment. However, there is a problem that the hot metal treatment must be abandoned because the hot metal circulating flow during the processing is hindered and a part of the hot metal sometimes flows out.

  The object of the present invention is to reduce the desiliconization and dephosphorization rate at a low cost in view of the above-mentioned problems of the prior art, and can sufficiently reduce the processing time. An object of the present invention is to propose a hot metal pretreatment method that can easily solve the problem of work obstacles due to adhesion of solidified soot to the opening of the processing vessel.

  The present invention provides a reaction by controlling the immersion depth of the main lance and the sub lance in the hot metal and the blowing amount of the oxidizing agent in accordance with the progress of the dephosphorization reaction during the pretreatment of the hot metal, particularly in the operation of the dephosphorization process. We propose a hot metal pretreatment method that can realize both improvement of efficiency and protection of the processing vessel. Further, according to the present invention, during the dephosphorization treatment, not only the immersion depth of each lance is controlled, but also the amount of oxidizing agent blown into the hot metal is controlled, and further, gaseous oxygen is introduced onto the hot metal bath surface. This is a hot metal pretreatment method that eliminates the problem of defective mouth (opening blockage obstruction) when performing pretreatment of hot metal using a processing container, particularly a kneading vehicle, by spraying.

  The basic idea of the present invention is to prepare a hot metal to be desiliconized and dephosphorized by blowing an oxidizing agent or a flux from a main lance immersed in a hot metal held in a processing vessel such as a kneading vehicle or a sub lance. In the treatment method, when deoxidizing and dephosphorizing by blowing an oxidant into the hot metal from the lance, the amount of oxidant blown from the lance is reduced at the final stage of the dephosphorization reaction, and the lance is immersed. This is a hot metal pretreatment method characterized in that the depth is further increased and blowing is continued.

  In the present invention, the end stage of the dephosphorization reaction is either when P is at a level of 0.008 mass% or less, or for 10 minutes before the end of the dephosphorization process. Performing spraying, injecting oxidant into the hot metal bath surface or hot metal, in addition to the main lance, use a sub lance that is immersed in a position shallower than the main lance or held on the bath surface, and The sub lance is immersed in a position within 1 m below the bath surface of the hot metal and at a position shallower by 0.1 m or more than the immersion depth of the main lance.

  According to the present invention, in the hot metal pretreatment operation, low-cost and high-speed desiliconization / dephosphorization processing can be performed at a level that could not be achieved under the prior art, and the problem of poor processing vessel mouth is inevitable. Also has an excellent effect that it can be easily eliminated.

  Hereinafter, the main lance sunk in the hot metal in the processing container (hereinafter referred to as an example of a “chaotic car”, but of course not limited to this example, may be a hot metal ladle or the like). A hot metal pretreatment method in which an oxidizing agent is blown in using an iron will be described. In the present invention, the blowing of the oxidizing agent is performed mainly using the main lance at the desiliconization and dephosphorization period, particularly at the end of the dephosphorization reaction. At this time, the immersion depth of the main lance in the hot metal is moved to a deeper position. And the point is that the blowing amount of the oxidizing agent at this time is reduced. In other words, blowing the oxidizing agent into the hot metal through desiliconization and dephosphorization is not different from the conventional method, but in order to promote the dephosphorization reaction at the end of the dephosphorization process where stagnation occurs, the reaction site should be expanded. The purpose is to move the immersion depth of the main lance to a deeper position, so that pretreatment for rapid hot metal dephosphorization is performed, and oxidation at the time when the dephosphorization reaction at the end of dephosphorization is stagnant. By suppressing the use amount of the agent (dephosphorizing agent), the hot metal pretreatment is to be realized efficiently at low cost.

  As the oxidizing agent used in the present invention, two types of solid oxygen source such as iron oxide-containing substance and gaseous oxygen can be used. As the gaseous oxygen, either pure oxygen having an oxygen concentration of 99% or more, or pure oxygen added to the carrier gas of the iron oxide-containing substance may be used. The point is that the oxygen concentration is high and it is useful as an oxidizing agent (hereinafter, gaseous oxygen is also simply referred to as “gasic acid”).

In the operation in the dephosphorization period according to the present invention, a soda ash-based flux or a solid oxygen source and a soda ash-based flux may be used in combination with the use of the oxidizing agent as necessary. That is, in the present invention, a basicity adjusting agent (lime or quicklime, lime-based flux such as fluorite as necessary) may be blown together with the oxidizing agent as necessary. As these solid oxygen source and basicity adjusting agent, a method in which a granular material is blown through a carrier gas is preferable. As the carrier gas, air or inert gas can be used.
In addition, when blowing together using a solid oxygen source and a gaseous acid as an oxidizing agent, a gaseous oxygen should just be added and blown into the solid oxygen source sent by the carrier gas conveyance method.

  In general, the oxidizer is blown into the hot metal in the kneading vehicle by a constant method with the main lance being immersed at a constant depth. This is because the reaction efficiency of the oxidant is improved when the lance immersion depth is increased, so that the lance immersion depth is set as deep as possible. However, if the lance immersion depth is too large, the stirring flow of the hot metal due to blowing increases, and the refractory inside the kneading vehicle tends to be damaged, so there is a limit naturally. In addition, when the opening is small like a chaotic car, deposits such as slag are generated in the opening, and the necessary lance immersion depth cannot be maintained (cannot be inserted) due to mutual interference during the insertion of the lance. May occur.

  Therefore, in the present invention, attention is paid to the stagnation time of the reaction that occurs at the end of the dephosphorization reaction during the pretreatment, and at the end of the dephosphorization reaction, even if a large amount of oxidizing agent is blown, the dephosphorization oxygen efficiency deteriorates (reaction efficiency). Therefore, the amount of oxidant blown at this stage is reduced, and the immersion depth of the hot lance is increased by the amount of attenuation of the hot metal stirring flow due to the reduction, while the risk of refractory damage is eliminated while the reaction site is eliminated. As a result, the efficiency of the hot metal pretreatment and the cost reduction can be realized at the same time.

Hereinafter, the present invention will be specifically described based on the drawings.
As shown in FIG. 1, at the start of the desiliconization and dephosphorization processes of the hot metal accommodated in the kneading wheel 2, the blowout port 1 a at the lower end is oriented in the horizontal direction in the hot metal 3 in the kneading wheel 2. The main lance 1 provided is immersed. An oxidizing agent is blown from the main lance 1, and a basicity adjusting agent is mixed and used as necessary. For example, when mixed injection of iron oxide (sintered ore powder) + lime powder (quick lime) + gaseous acid is performed, desiliconization proceeds first by the action of the oxidizing agent (iron oxide + gaseous acid), and the base The basicity of the slag 4 floating on the hot metal 3 is also adjusted by the lime powder which is a degree adjusting agent.

From the main lance 1, an oxidizing agent having an oxygen supply amount (symbol: QO ₂ : solid oxygen source is shown in terms of gas) of 0.05 Nm ³ / min / molten iron or more is blown. This is because if the oxygen supply amount QO ₂ from the main lance 1 is not blown with an oxidizing agent corresponding to 0.05 Nm ³ / min / molten iron t, desiliconization and dephosphorization reactions are significantly delayed. On the other hand, even if the oxidizing agent corresponding to the oxygen supply amount QO ₂ is blown too much, the desiliconization and dephosphorization rates are saturated and the supplied oxygen is wasted, so the upper limit is 0.4 Nm ³ / min / molten iron. t.

Of the desiliconization and dephosphorization treatment periods in which the oxidizing agent is blown, during the desiliconization period, the slag 4 tends to form as the desiliconization progresses, so that slag overflow does not occur from the kneading vehicle opening 2a. The blowing of the oxidizing agent from the main lance 1 preferably takes a blowing pattern in which the oxygen supply amount QO ₂ is gradually increased, but may be quantitative or stepwise. At the stage of entering the dephosphorization period, it is advantageous to cause the dephosphorization reaction by increasing the oxygen supply amount QO ₂ so as to be close to the upper limit.

According to the inventors' research, it is found that the dephosphorization oxygen efficiency defined by the following formula (1) is remarkably lowered in the latter half of the dephosphorization treatment period. In particular, at the final stage of the dephosphorization reaction, the oxygen supply amount QO ₂ is preferably 0.15 Nm ³ / min / molten iron or less. More preferably 0.05 to 0.13 Nm ³ / min / molten iron t. The final stage of the dephosphorization reaction is appropriately determined within the above range from the experiment or the processing pattern, based on the processing container to be used, the amount of molten iron, and the amount of blowing oxidant.
Dephosphorization oxygen efficiency = amount of oxygen used for oxidation of phosphorus in hot metal / (total amount of oxygen blown into hot metal-amount of oxygen used for oxidation of Si) (× 100%) (1)
Here, the unit of each oxygen amount on the right side of the formula (1) is Nm ³ / molten iron t.

In the final stage of the dephosphorization reaction, that is, in the latter half of the dephosphorization process period, in the present invention, the immersion depth h ′ of the main lance 1 is moved to a deeper position h ″. The purpose is to improve the dephosphorization reaction efficiency by adjusting the lance depth to increase the residence time of the dephosphorizing agent in the hot metal when the dephosphorization oxygen efficiency is lowered.
FIG. 2 shows the results of experiments to determine the relationship between the lance immersion depth h ′ (the hot metal depth in a stationary state = H) and the de-P oxygen efficiency. As shown in this figure, it can be seen that the deep lance immersion depth is higher than the shallow lance immersion depth.

  Therefore, in the present invention, the immersion depth h ″ of the main lance 1 is set to a deeper position 0.5H to 0.9 as shown in FIG. 3 when the dephosphorization oxygen efficiency in the latter half of the dephosphorization process is lowered. By moving to H, it was decided to perform an operation to compensate for the decrease in dephosphorization oxygen efficiency.

In addition, this means that even if the immersion depth of the main lance 1 is increased to approach the container bottom in the latter half of the dephosphorization process, the oxygen supply is performed in the latter half of the dephosphorization process as described above. The quantity QO ₂ is 0.15 Nm ³ / min / molten iron or less, which is reduced compared to the first half of the dephosphorization treatment period, so that it is possible to eliminate the influence of refractory wear due to the flow of blowing into the container bottom. This is possible in terms of points.

  It should be noted that the reason why the dephosphorization oxygen efficiency decreases in the latter half of the dephosphorization treatment stage, that is, at the end of the dephosphorization reaction, is that the oxygen potential locally increases due to the blowing of the oxidizing agent, and the excess oxygen causes This is because a decarburization reaction occurs and the amount of oxygen used for dephosphorization decreases. Therefore, in the final stage of the dephosphorization reaction, the amount of oxidant blown from the main lance 1 is reduced.

  Also, from the beginning to the middle of the dephosphorization reaction, as the oxidizing agent is blown from the main lance 1, solidified soot adheres to the kneading wheel 2, particularly around the upper wall portion, particularly the opening 2a. May be invited. For this reason, in the present invention, mainly from the middle of the dephosphorization process, the sub lance 6 is lowered and inserted through the opening 2a and sprayed on the hot metal bath surface in the kneading wheel 2. By this process, it is preferable to perform a process of burning the gas generated in the kneading vehicle to generate heat, compensating for the temperature drop of the molten iron, and removing the molten coagulant by dissolution and adhesion prevention.

Moreover, as to the role of the sublance 6, as shown in FIG. 3, at the end of the dephosphorization reaction, the sublance 6 is immersed shallowly (≦ 1 m) in the hot metal bath and oxidant + flux + gasic acid is blown. Therefore, it is possible to compensate for the stagnation of the overall dephosphorization efficiency. However, the immersion depth of the sub lance 6 is set to be 0.1 m or more shallower than the immersion depth of the main lance 1 so that the reaction site does not compete.
In the present invention, the effect of the sub lance 6 makes it possible to perform hot metal pretreatment at a low total cost without causing a decrease in the dephosphorization speed and without causing a lance operation trouble at the kneading vehicle opening 2a. is there.

  In the present invention, as the oxidant blown into the hot metal from the main lance 1 and the sub lance 6, either a gaseous acid or a solid oxygen source can be used, but it is mainly preferable to use a solid oxygen source. The reason is that the solid oxygen source has an action of accelerating the reaction between the slag and the metal by melting in the molten iron to form slag (gasic acid does not have this hatching action). For this purpose, the main lance 1 is preferably used mainly with a solid oxygen source as an oxidizing agent. As the solid oxygen source, iron oxide is most preferable, but as an alternative, iron oxide-containing substances (room dust; RD) such as blast furnace raw material sintered ore or iron ore powder, iron-making dust, mill scale, etc. ) Can be used.

  Furthermore, in this invention, you may provide the time which blows out only a gaseous acid from the said main lance 1. FIG. In this gas acid alone blowing treatment, solidified soot adheres to and grows in the opening 2a of the mixed iron wheel 2 etc. containing molten iron regardless of any of the silicon removal treatment period or the dephosphorization treatment period. Depending on the circumstances, it is preferable to perform it at an appropriate time when it is necessary to remove it. By this process, the solidified soot adhering to the inner surface of the opening 2a of the kneading vehicle 2 can be surely melted and removed, so that the problem of the kneading vehicle work trouble can be easily solved without adding any additional equipment. it can. In addition, what is necessary is just to determine suitably the amount of gas acid single blowing according to the adhesion size etc. of the coagulation | solidification soot. Further, it is preferable to use pure oxygen among the gas acids because the solidified soot can be melted more rapidly.

  Further, in this process, when at least one of the main lance 1 and the sub lance 6 is raised up to the hot metal at the end of the completion of the hot metal pretreatment, and the gas acid is blown out, the solidification of the opening 2a generated during the pretreatment is performed. It is particularly preferable in that the adhesion of the soot can be removed at the completion stage of the hot metal pretreatment, and the work trouble accompanying the adhesion of the solidified soot at the time of receiving the next hot metal and starting the pretreatment can be solved.

Further, in the present invention, in synchronization with at least a part of the oxidant blowing time, as shown in FIG. The operation of tilting the chaotic wheel 2 may be performed before the oxidant is blown, or may be canceled and restored appropriately. The upper limit of the tilt angle is that the hot metal does not overflow, and preferably 3 ° to 10 °. In this work, the low basicity slag 4 generated at the time of desiliconization is made unnecessary by using the special removal equipment and overflowing from the opening 2a of the kneading vehicle 2 as necessary. The purpose is to allow timely discharge to the fluency bit 7 provided on the side.
Conventionally, at the stage of desiliconization treatment, the slag 4 from the opening 2a due to slag forming overflowed, and the desiliconization treatment was forced to be interrupted. It will be possible to overflow and discharge in a timely manner, and the operation can be continued without interrupting the desiliconization process.
Further, conventionally, a large amount of a basicity adjusting agent has been used to suppress slag forming. However, according to the present invention, the amount of slag on the hot metal 3 can be reduced by overflowing and discharging the slag 4. Therefore, the amount used can be greatly reduced.

Furthermore, when slag forming is actively caused and the formed slag 4 is discharged by the tilting operation of the kneading vehicle 2, the generated SiO ₂ even when the hot metal before desiliconization is high [Si]. However, the desiliconization treatment is not hindered, the desiliconization treatment can be completed easily in a short time, and the dephosphorization treatment can be transferred without delay.
Further, even in the dephosphorization treatment stage, the kneading vehicle 2 can be similarly removed by tilting the kneading vehicle 2 to an appropriate angle at any time, so that the treatment time can be shortened and the usage amount of the basicity adjusting agent can be reduced. .
Although the above is described in the usage example of the kneading wheel 2, the same applies to the case where the hot metal ladle is used, and the same effect can be obtained by setting the processing container to the tilted state by the tilting operation.

  As described above, according to the method of the present invention, it is possible to solve all of the above-mentioned problems of the prior arts (1) to (7), and a low-cost and high-speed desiliconization at a level that cannot be achieved conventionally. Dephosphorization is possible. Examples will be described below.

The hot metal preliminary treatment was performed under the following conditions using a kneading wheel (hot metal (bus) depth H: 2.3 m in a stationary state) with a hot metal amount of 280 t.
(1) Hot metal component: (C): 4.4 mass%, (Si) 0.20 mass%, (P) 0.17 mass%, 1370 ° C
FIG. 5 shows the blowing treatment pattern of the oxidizing agent and basicity adjusting agent for desiliconization and dephosphorization treatment.
In this treatment, as shown in FIG. 5, the main lance 1 is inserted and immersed at an immersion depth of 800 to 11000 mm, and a sintered ore powder (RD <125 μm) which is a solid oxygen source as an oxidizing agent, Blowing was performed at 200 kg / min (gas conversion: 21.6 Nm ³ / min). In addition, in order to reduce the temperature drop in the pretreatment, the main lance 1 was used with 10 Nm ³ / min of gas acid. Then, quick lime as a basicity adjusting agent was blown at 200 kg / min so that the slag basicity was approximately 1.0 during the desiliconization period.
Thereafter, the amount of sintered ore powder (RD) was increased while degassing was promoted while maintaining the blowing of gas acid for preventing temperature drop. That is, at this stage, by increasing the amount of sintered ore powder (RD) by 400 kg / min (at the time when 10 minutes have elapsed), no abnormal slag forming is observed, and (Si) 0.01 mass after treatment for about 12 minutes Until the end of the dephosphorization reaction, blowing was performed with the sintered ore powder amount kept at 400 kg / min (57.6 Nm ³ / min in terms of gas).
After that, about 10 minutes before the completion of the dephosphorization treatment, the sintered ore powder amount (RD) of the main lance 1 and the like is reduced from 400 kg / min to 300 kg / min, while the sub lance 6 is made of iron oxide. Powder injection of 200 kg / min sintered ore was performed. The immersion depth of the sublance 6 was 0.8 m.
As a result, the pretreatment of the hot metal of 280 tons could be completed in 35 minutes. In addition, by the gas-acid injection from the sub lance 6 on the hot metal at the end of the above dephosphorization process, the large solidified soot on the inner surface of the opening of the upper wall of the kneading wheel that was likely to be produced by this preliminary process was successfully removed.
FIG. 6 shows the relationship between the dephosphorization oxygen efficiency (%) and the dephosphorization section. As is clear from this figure, the dephosphorization oxygen efficiency by the hot metal pretreatment method (● mark) according to the present invention is higher over the entire section, and high-speed desiliconization and dephosphorization processes are possible. In other words, it was found that the amount of oxidant used can be reduced by the amount of high dephosphorization oxygen efficiency.

  The present invention can be applied to hot metal pretreatment, particularly desiliconization and dephosphorization treatment, used in the steelmaking process.

It is sectional drawing which shows the manner of desiliconization and dephosphorization based on the method of this invention. It is a graph which shows the relationship between de-P oxygen efficiency and lance immersion depth. It is sectional drawing which shows the state of the implementation state in the dephosphorization reaction last stage in the method of this invention. It is sectional drawing which shows the way of slag removal by chaotic vehicle tilting. It is a schematic diagram which shows an example of the solid oxidizing agent for describing the Example of this invention, and a gas-acid blowing schedule. It is a graph which shows the change of the dephosphorization oxygen efficiency for every de-P section in an Example.

Explanation of symbols

1 Main lance 2 Chaos
1a outlet
2a Chaotic car opening 3 Hot metal 4 Slag 6 Sublance 7 Fluent bit

Claims (5)

In the hot metal pretreatment method of desiliconization and dephosphorization by blowing an oxidizing agent or flux from a lance immersed in the hot metal in the processing vessel,
A hot metal pretreatment method characterized in that the amount of oxidizing agent blown from the main lance is reduced at the final stage of the dephosphorization reaction, and the main lance is further deepened to continue blowing. 2. The hot metal pretreatment method according to claim 1, wherein the end stage of the dephosphorization reaction is either when P is at a level of 0.008 mass% or less or for 10 minutes before the end of the dephosphorization process. . 3. The hot metal pretreatment method according to claim 1 or 2, wherein gaseous oxygen is sprayed onto the hot metal bath surface. In blowing the oxidizing agent into the hot metal bath surface or hot metal, a sub lance which is immersed in a position shallower than the main lance or held on the bath surface is used in addition to the main lance. 4. The hot metal pretreatment method according to any one of 3 above. The hot metal pretreatment method according to claim 4, wherein the immersion depth of the sub lance is set to a position within 1 m below the bath surface of the hot metal and 0.1 m or more shallower than the immersion depth of the main lance.

Images