JP2002363628A - Hot metal dephosphorizing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot metal dephosphorizing method capable of suppressing generation of slopping when dephosphorizing the hot metal by utilizing a converter slag as a CaO source of a dephosphorizing agent. SOLUTION: (1) A hot metal dephosphorizing method in which the ratio of the converter slag in the CaO source of the dephosphorizing agent to be fed is changed in the increasing direction in the middle of the dephosphorizing process in accordance with an Si concentration in the hot metal before the dephosphorizing process and the oxygen quantity fed from the start of the dephosphorizing process. (2) A hot metal dephosphorizing method in which the time of the change is set after the time of completion of the desiliconization period in the dephosphorizing process and before the time of completion of the dephosphorizing period. (3) A hot metal dephosphorizing method in which the ratio of a CaO feed speed A1 in quicklime, or the like, to a CaO feed speed B1 in the converter slag, A1 /B1 , is set to be 1/3 to 3 by the time of change.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of hot metal dephosphorization, and more specifically, in dephosphorizing hot metal, converter slag and quick lime and / or limestone are used as a CaO source of a dephosphorizing agent. Belongs to the technical field related to the hot metal dephosphorization treatment method.

[0002]

2. Description of the Related Art Generally, in the dephosphorization of hot metal, a slag forming agent such as lime and an oxidizing agent such as iron oxide are injected into the hot metal, and oxygen is blown upward or injected into the hot metal to perform the dephosphorizing process. Is going.

The converter slag generated when the pretreated hot metal is blown in the converter has a low P concentration of about 0.2 to 0.8 in the slag and contains about 50% CaO.
It is known that when used as a hot metal dephosphorizing agent, it again exhibits a dephosphorizing ability. In recent years, a method has been reported in which converter slag generated in a converter is used as a CaO source at the time of dephosphorization to reduce the cost of slag processing and to reduce the amount of quicklime during dephosphorization. For example, JP-A-06-287
No. 615 proposes and reports on a method of adding converter slag to hot metal during hot metal pretreatment or placing it before blast furnace receiving, or injecting and dephosphorizing hot metal. Also, JP-A-07-268431, JP-A-08-00361
No. 1 discloses a technique for performing a dephosphorization treatment using a converter slag mixed with iron oxide or a slag-making agent.

[0004] In actual operation, it has been reported that converter slag (less slag blowing slag) generated by blowing molten dephosphorized hot metal is used as a dephosphorizing agent to improve the phosphorus distribution and to replace quicklime. (Ishizaka, Terada, Yamagami, Hasegawa et al., 19
89 STEEL MAKING CONFEREN-CE PROCEEDINGS, 249 〜25
Five ).

[0005]

At the beginning of the dephosphorization treatment, the oxidation of Si in the hot metal proceeds preferentially prior to the dephosphorization reaction, so that the basicity (CaO / Si
O ₂ ) hardly rises, and a phenomenon called sloping in which slag overflows from the furnace opening of a mixed iron wheel or converter is likely to occur. Furthermore, when converter slag is used as a dephosphorizer, the converter slag is a pre-melt product that has once been melted in a converter, so the slagging speed is high, and therefore slagging becomes excessive during the treatment. There is a problem that slopping is likely to occur. If slopping occurs, troubles such as prolongation of processing time and suspension of equipment failure will occur. Therefore, when converter slag is used as a dephosphorizing agent, it is necessary to control the basicity of the slag and the rate of slagging.

The present invention has been made in view of such circumstances, and has as its object to perform dephosphorization of hot metal using converter slag as a CaO source of a dephosphorizing agent. An object of the present invention is to provide a hot metal dephosphorization treatment method capable of suppressing the occurrence of lopping.

[0007]

In order to achieve the above object, a method for dephosphorizing hot metal according to the present invention is described in claims 1-6.
The hot metal dephosphorization treatment method described above has the following configuration.

That is, the hot metal dephosphorization treatment method according to the first aspect of the present invention is a hot metal dephosphorization treatment method using a converter slag and quick lime and / or limestone as a CaO source of a dephosphorizing agent when dephosphorizing hot metal. S in hot metal before dephosphorization
The hot metal characterized by changing the ratio of the amount of converter slag in the CaO source of the dephosphorizing agent to be supplied in the middle of the dephosphorization process in accordance with the i concentration and the amount of oxygen supplied from the start of the dephosphorization process. This is a phosphorus removal method (first invention).

A hot metal dephosphorization method according to a second aspect of the present invention is a hot metal dephosphorization method using converter slag and quick lime and / or limestone as a CaO source of a dephosphorizing agent when hot metal is dephosphorized. After the end of the desiliconization period in the treatment and before the end of the dephosphorization period, the Ca
This is a hot metal dephosphorization method characterized by changing the ratio of the amount of converter slag in the O source in the increasing direction (second invention).

[0010] hot metal dephosphorization treatment method according to claim 3, wherein the supply amount of oxygen from the dephosphorization process start (Nm ³ / hot metal 1 ton)
= 7 × Since the concentration of Si in the hot metal before the dephosphorization treatment (% by mass) and before the end of the dephosphorization period, C
The hot metal dephosphorization treatment method according to claim 1 or 2, wherein the ratio of the amount of converter slag in the aO source is changed in an increasing direction (third invention).

According to a fourth aspect of the present invention, in the hot metal dephosphorization treatment method, the feed rate A ₁ of the CaO content in the quicklime and / or limestone is changed until the ratio of the amount of the converter slag is changed in the increasing direction. Feed rate B ₁ of CaO in furnace slag
Ratio: A ₁ / B _{1 is set} to 1/3 to 3, and in the subsequent period, the supply rate A ₂ of CaO in quicklime and / or limestone and the supply rate B ₂ of CaO in converter slag The hot metal dephosphorization treatment method according to claim ₁ , wherein the ratio of A ₂ / B ₂ is smaller than the ratio A ₁ / B ₁ (the fourth invention).

According to a fifth aspect of the present invention, in the hot metal dephosphorization treatment method, the feed rate A ₁ of the CaO content in the quicklime and / or limestone is not changed until the ratio of the amount of the converter slag is changed in the increasing direction. Feed rate B ₁ of CaO in furnace slag
Ratio: A ₁ / B _{1 is set} to 1/3 to 3, and in the subsequent period, the supply rate A ₂ of CaO in quicklime and / or limestone and the supply rate B ₂ of CaO in converter slag Ratio of A ₂ / B ₂ to 0 or more and less than 3, more preferably 0 to
The hot metal dephosphorization treatment method according to any one of claims 1, 2, 3 and 4, wherein the second method is (fifth invention).

The hot metal dephosphorization treatment method according to claim 6 is the hot metal dephosphorization treatment method according to claim 1, wherein a part of the converter slag to be supplied is added from above the hot metal. (Sixth invention).

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is embodied in the following manner, for example. Dephosphorization of hot metal is performed using converter slag and quicklime and / or limestone (hereinafter referred to as quicklime) as a CaO source of a dephosphorizing agent. That is, converter slag, quick lime, and the like are added to the hot metal, and the hot metal is dephosphorized.

At this time, the ratio of the amount of converter slag in the CaO source of the dephosphorizing agent to be added (supplied) is determined by the Si concentration in the hot metal before the dephosphorization treatment and the amount of oxygen supplied from the start of the dephosphorization treatment. Change in the increasing direction during the phosphorus treatment. That is, the supply speed (supply amount per unit time) of the converter slag is b,
Assuming that the supply speed of quicklime or the like is a, b / (a + b) is increased during the dephosphorization process.

Alternatively, after the end of the desiliconization period in the dephosphorization treatment, and before the end of the dephosphorization period, the supplied dephosphorizer Ca
The ratio [b / (a + b)] of the amount of converter slag in the O source is changed in the increasing direction.

Regarding the point in time when the ratio [b / (a + b)] is changed in the increasing direction, more specifically, for example, the supplied oxygen amount (Nm ³ / ton of hot metal) from the start of the dephosphorization treatment = 7
X After the time when the Si concentration (mass%) in the hot metal before the dephosphorization treatment is reached and before the end of the dephosphorization period.

Regarding the feed rate b of the converter slag and the feed rate a of quicklime, etc., more specifically, the ratio [b / (a
+ B)] in the period up to the point of change in the increasing direction, for example, the ratio of the supply rate A ₁ of CaO in quicklime or the like to the supply rate B ₁ of CaO in converter slag: A ₁ / B
₁ is a feed rate b and a such that 1/3 to 3, and the feed rate B ₂ of the CaO content in the CaO content supply rate A ₂ and BOF slag in quicklime, etc. in the subsequent period Supply speeds b and a are such that the ratio: A ₂ / B ₂ is smaller than the ratio: A ₁ / B ₁ .

The present invention is implemented in such a form. Hereinafter, the operation and effect of the present invention will be mainly described.

FIG. 1 shows a graph of Ca used for hot metal dephosphorization.
The relationship between the ratio X of the converter slag in the O source and the slopping occurrence rate Y during the dephosphorization treatment is shown. As can be seen from FIG. 1, in the desiliconization stage in the initial stage of the dephosphorization treatment in which the desiliconization reaction proceeds preferentially, the slopping occurrence rate Y increases with an increase in the converter slag ratio X. However, in the dephosphorization period after the end of the desiliconization period, there is no correlation between the converter slag ratio X and the slopping occurrence rate Y, and the slopping occurrence rate Y is low overall. Therefore, when the ratio X of the converter slag in the desiliconization stage at the initial stage of the dephosphorization treatment is reduced, the occurrence of slopping can be suppressed. Further, after the end of the desiliconization period, the ratio X of the converter slag can be increased without hindering the increase of the slopping occurrence rate Y, and accordingly, the supply amount of quicklime and the like is reduced. And the converter slag alone may be used as the CaO source. This is because after the end of the desiliconization period, the basicity of the slag increases, and the treatment becomes stable.

In a hot metal dephosphorization method using converter slag and quick lime as a CaO source of a dephosphorizing agent, in the conventional hot metal dephosphorization method, the supply ratio of converter slag and quick lime etc. is the same through dephosphorization. , Ca from converter slag
The ratio between the supply rate of O and the supply rate of CaO from quicklime is always the same, and the ratio X of the converter slag is several tens%.
It is about . Therefore, as can be seen from FIG. 1, slopping is likely to occur in the desiliconization period at the initial stage of the dephosphorization treatment. In addition, quicklime or the like is wasted after the end of the desiliconization period in which only the converter slag is sufficient as the CaO source.

In the method for dephosphorizing hot metal according to the first invention of the present invention, the Ca of the dephosphorizing agent to be supplied is determined by the concentration of Si in the hot metal before the dephosphorization and the amount of oxygen supplied from the start of the dephosphorization.
The ratio of the amount of converter slag in the O source is changed in an increasing direction during the dephosphorization treatment. That is, to reduce relatively the amount of ratio X ₁ of converter slag in a CaO source is supplied in the early stages of dephosphorization process (as compared to the later ratio X _2), and supplies in the course subsequent dephosphorization treatment CaO
The ratio X ₂ of the amount of converter slag in the source be greater than the ratio X _1. Also, the time of changing from the ratio X ₁ to a ratio X ₂ are determined by the supply amount of oxygen from the Si concentration and the dephosphorization process start during hot metal pre-dephosphorization process (cumulative supply amount of oxygen). Since the Si concentration and the accumulated supply oxygen amount are indicators of the progress of the desiliconization, it is possible to estimate the end point of the desiliconization period. It is also possible to use

Accordingly, the ratio X ₁ of the amount of converter slag is reduced to such an extent that the occurrence of slopping can be suppressed, and the point of change from the ratio X ₁ to the ratio X ₂ is determined at the end of the desiliconization period or thereafter. By doing so, it becomes possible to suppress the occurrence of slopping. Further, after the end of the desiliconization period, the ratio of the amount of converter slag X ₂
Can be increased, and the supply amount of quicklime or the like can be reduced, whereby the economic efficiency can be improved.

Further, in the method for dephosphorizing hot metal according to the second invention of the present invention, the CaO source of the dephosphorizing agent to be supplied is provided after the end of the desiliconization period in the dephosphorization process and before the end of the dephosphorization period. The ratio of the amount of converter slag in the inside is to be changed in the increasing direction. That is, C supplied in the initial stage of the dephosphorization treatment
the ratio X ₁ in the amount of converter slag relatively small in aO source, after the end of the de-珪期in dephosphorization process, before the end of the dephosphorization stage, BOF in the CaO source supplying the ratio X ₂ of the amount of slag is greater than the ratio X _1. Therefore, by reducing the ratio X ₁ in the amount of the converter slag to an extent capable of suppressing the slopping occurs, so it can suppress the occurrence of slopping. Further, the ratio X ₂ of the amount of the converter slag can be increased without increasing the rate of occurrence of slopping.
Can be increased, and accordingly, the supply amount of quicklime or the like can be reduced.

The amount of oxygen supplied from the start of the dephosphorization treatment (Nm ³
/ 1 ton of hot metal) = 7 × the point at which the Si concentration (mass%) in the hot metal before the dephosphorization treatment corresponds to the end point of the desiliconization period in the dephosphorization treatment. Therefore, the point in time when the ratio of the amount of converter slag in the CaO source is changed in the increasing direction is determined by the amount of oxygen supplied from the start of the dephosphorization treatment (Nm ³ / ton of hot metal) = 7 × hot metal before dephosphorization treatment If it is before the end of the dephosphorization period after the time when the medium Si concentration (% by mass) is reached, it will be before the end of the dephosphorization period after the end of the desiliconization period in the dephosphorization treatment.
For this reason, the same operation and effect as in the case of the second invention can be obtained (third invention).

FIG. 2 shows the supply rate A ₁ of CaO in quicklime and the like in the desiliconization period in the dephosphorization treatment and the C rate in the converter slag.
The relationship between the ratio of aO to the supply speed B ₁ : A ₁ / B ₁ and the slopping occurrence rate Y is shown. As can be seen from FIG. 2, when A ₁ / B ₁ is less than ３, the slapping occurrence rate Y is higher than when A ₁ / B ₁ is _１ ／ or more. From this point, it is desirable that A ₁ / B ₁ be 1/3 or more.

However, when the ratio A ₁ / B ₁ is large, the ratio of converter slag which tends to form slag is reduced, so that unslagized lime is generated. FIG. 3 shows the relationship between A ₁ / B ₁ and unslagified lime (F-CaO) in the slag after the dephosphorization treatment. As can be seen from FIG. 3, when A ₁ / B ₁ exceeds 3, the F-CaO (unslagged lime) ratio increases. In this case, in the dephosphorization reaction mainly performed by the permanent reaction, the dephosphorization efficiency decreases, and as a result, the lime intensity decreases. From this point, it is desirable to set A ₁ / B ₁ to 3 or less.

In view of the above, in the hot metal dephosphorization treatment method according to the fourth invention of the present invention, quick lime and / or limestone are not used until the ratio of the amount of converter slag is changed in the increasing direction. Of the supply rate A ₁ of CaO in the converter to the supply rate B ₁ of CaO in the converter slag: A ₁ /
B _{1 is set} to 1/3 to 3, and in the subsequent period, the ratio of the supply rate A ₂ of CaO in quicklime and / or limestone to the supply rate B ₂ of CaO in converter slag: A ₂ / B
₂ was set to be smaller than the above ratio: A ₁ / B ₁ .
According to this hot metal dephosphorization treatment method, the rate of occurrence of slopping can be more reliably reduced, and the ratio of unslagged lime (F-CaO) can be reduced, so that the dephosphorization efficiency can be improved. As a result, lime intensity can be improved.

Here, A ₂ / B ₂ is set to be less than 3. The smaller the ratio, the higher the ratio of converter slag in the CaO source, and accordingly, the smaller the supply amount of quicklime and the like. And can improve economic efficiency. From such a point, it is desirable to set A ₂ / B ₂ to 2 or less (fifth invention). At this time, only the converter slag may be used as the CaO source. In this case, the converter slag can be used effectively to the maximum, and the economy can be improved most.

In supplying the converter slag as a CaO source of the dephosphorizing agent, the method of adding the converter slag is not particularly limited, and various methods can be adopted. A method of adding from above can be adopted (sixth invention).

When the Si concentration of the hot metal to be dephosphorized (Si concentration before the dephosphorization treatment) is extremely low, the desiliconization period in the initial stage of the dephosphorization treatment is short, and slopping is unlikely to occur. Therefore, the hot metal dephosphorization method according to the present invention,
The effect is large and suitable when the Si concentration of the hot metal to be dephosphorized is relatively high, and the effect is particularly large and suitable when the Si concentration of the hot metal to be dephosphorized is 0.10% by mass or more. is there.

[0032]

EXAMPLES Examples and comparative examples of the present invention will be described below.
Note that the present invention is not limited to this embodiment.

Table 1 shows the composition of the converter slag used in the examples and comparative examples. Table 2 shows the operating conditions of the hot metal dephosphorization treatment according to the example and the comparative example (conventional method). Under these operating conditions, the Si concentration: 0.10% by mass or more (0.12 to
(0.24% by mass) was subjected to a dephosphorization treatment.
That is, in the hot metal dephosphorization treatment according to the comparative example, the blowing speed (supply speed) of the converter slag and quick lime of the CaO source in the dephosphorization period and the dephosphorization period after the end of the desiliconization period is the same,
The ratio of the amount of converter slag in the CaO source was kept constant throughout the dephosphorization treatment. On the other hand, in the hot metal dephosphorization treatment according to the example, the ratio of the amount of converter slag in the CaO source was changed in the increasing direction at the end of the desiliconization period.

More specifically, in the hot metal dephosphorization treatment according to the comparative example, the ratio of the supply rate A ₁ of CaO in the quicklime and the supply rate B ₁ of CaO in the converter slag during the desiliconization period: A ₁ / B _{1 is} also the ratio of the supply rate A ₂ of CaO in quicklime and the supply rate B ₂ of CaO in converter slag in the dephosphorization period after the end of the desiliconization period: A ₂ / B ₂ Both were set to 0.28. On the other hand, in the hot metal dephosphorization treatment according to the example, Ca in the quicklime during the desiliconization period
The ratio of the supply rate A _{1 of} O and the supply rate B ₁ of CaO in the converter slag: A ₁ / B _{1 is set} to 1.64, and CaO in quicklime during the dephosphorization period after the end of the desiliconization period. the ratio of the minute feed rate a ₂ and feed rate B ₂ of the CaO content of the converter slag: and the a ₂ / B ₂ and 0.31. Incidentally, the supply amount of oxygen (Nm ³ / hot metal 1 t) = 7 × dephosphorization pretreatment Si concentration (wt%) in molten iron and the time de-珪期termination comprising time from dephosphorization process start.

FIG. 4 shows the rate of occurrence of slopping during the hot metal dephosphorization treatment according to the above Examples and Comparative Examples (conventional method). In the case of the comparative example, the rate of occurrence of slopping is as high as 32%, whereas in the example of the present invention, the rate of occurrence of slopping is as low as 13%. On the other hand, in the dephosphorization stage of de珪期end later, since the slopping incidence is low regardless of the feed rate A ₂ of the CaO content in the quick lime feed rate A of the CaO content in the quick lime in this period ₂ it is possible to suppress the following one third of feed rate B ₂ of the CaO content of the converter slag, it is possible to dephosphorization process operation mainly composed of converter slag as a source of CaO content .

FIG. 5 shows the relationship between quick lime and converter slag in the total CaO used in the dephosphorization treatment. In the case of the embodiment of the present invention, the ratio of converter slag, the ratio of quicklime, and the ratio of total CaO were smaller than those of the comparative example.
The amount is also small. As described above, in the case of the present invention, the ratio of converter slag can be increased, so that the total amount of CaO used for the dephosphorization can be reduced.

In the above embodiment, the point in time when the ratio of the amount of converter slag in the CaO source is changed in the increasing direction is the end point of the desiliconization period, and A ₁ / B ₁ in the desiliconization period is 1.64. A ₂ / B ₂ in the dephosphorization period after the end of the desiliconization period
Was set to 0.31, but A ₁ / B ₁ in the desiliconization period was 1 /
In the case of 3, the rate of occurrence of slopping is low as in the case of the above embodiment, and when A ₁ / B ₁ is made slightly smaller than 1/3, the rate of occurrence of slopping is very slightly lower than in the case of the above embodiment. However, the rate of occurrence of slopping was substantially the same as that of the above example. Also, A ₁ / B
_{When 1 is set} to 3, the rate of occurrence of slopping is low as in the case of the above-described embodiment, and when A ₁ / B ₁ is slightly larger than 3, the rate of occurrence of slopping is also reduced as in the case of the above-described embodiment. It was low.

When the time when the ratio of the converter slag amount in the CaO source was changed in the increasing direction was set after the end of the desiliconization period, the rate of occurrence of slopping was low as in the case of the above embodiment. Also, when the time point of this change was slightly before the time point of the end of the desiliconization period, the rate of occurrence of slopping was almost the same as in the case of the above embodiment.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

According to the method for dephosphorizing hot metal according to the present invention, it is possible to suppress the occurrence of slopping when performing dephosphorizing of hot metal using converter slag as a CaO source of a dephosphorizing agent. become able to.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a converter slag mixing ratio and a slopping occurrence ratio in a dephosphorization treatment.

[2] The ratio of the feed rate B ₁ of CaO content in CaO fraction supply rate A ₁ and BOF slag in lime or the like in de珪期in dephosphorization process: the A ₁ / B _1, slopping It is a figure which shows the relationship with an incidence.

FIG. 3 shows the ratio of the feed rate A ₁ of CaO in quicklime and the like in the desiliconization period in the dephosphorization treatment to the feed rate B ₁ of CaO in converter slag: A ₁ / B ₁ and dephosphorization. It is a figure which shows the relationship with F-CaO (non-slag lime) in slag after a process.

FIG. 4 is a diagram showing the relationship between the time of the dephosphorization treatment (the desiliconization period and the dephosphorization period) and the rate of occurrence of slopping.

FIG. 5 is a diagram showing a relationship between a dephosphorization treatment method (conventional method, an example of the present invention) and a dephosphorization lime index.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K013 BA03 CA04 EA01 EA03 EA12 FA02 4K014 AA01 AA03 AB02 AB03 AB04 AB12 AC01 AC12

Claims (6)

[Claims] In a hot metal dephosphorization method using converter slag and quick lime and / or limestone as a CaO source of a dephosphorizing agent when dephosphorizing hot metal, the concentration of Si in the hot metal before dephosphorization and the dephosphorization are determined. A hot metal dephosphorization treatment method characterized in that the ratio of the amount of converter slag in the CaO source of the supplied dephosphorizer is increased in the middle of the dephosphorization treatment depending on the supplied oxygen amount from the start of the treatment. 2. A hot metal dephosphorization method using converter slag and quick lime and / or limestone as a CaO source of a dephosphorizing agent when dephosphorizing hot metal, after the end of the desiliconization period in the dephosphorization process. A method of dephosphorizing hot metal, wherein the ratio of the amount of converter slag in the CaO source of the dephosphorizing agent to be supplied is increased before the end of the dephosphorization period. 3. The amount of supplied oxygen (Nm) from the start of the dephosphorization treatment.
³ / hot metal 1 t) = 7 × dephosphorization treatment the hot metal in the Si concentration (wt% before) and a point on, before the end of the dephosphorization stage, and supplies the converter slag in a CaO source dephosphorization agent 3. The hot metal dephosphorization treatment method according to claim 1, wherein the ratio of the amounts is changed in an increasing direction. 4. The supply rate A ₁ of CaO in quicklime and / or limestone and the CaO in converter slag during the period until the ratio of the amount of converter slag is changed in the increasing direction.
Ratio of the feed rate B ₁ to the feed rate B ₁ : A ₁ / B _{1 is set} to 1/3 to 3, and in the subsequent period, the feed rate A ₂ of the CaO content in the quicklime and / or limestone and the feed rate AO in the converter slag
Min ratio of the feed rate B ₂ of: the A ₂ / B ₂ the ratio: A ₁ /
Claim 1, 2 or 3 hot metal dephosphorization method according smaller than B _1. 5. The supply rate A ₁ of CaO in quicklime and / or limestone and the CaO content in the converter slag until the ratio of the amount of converter slag is changed in the increasing direction.
Ratio of the feed rate B ₁ to the feed rate B ₁ : A ₁ / B _{1 is set} to 1/3 to 3, and in the subsequent period, the feed rate A ₂ of the CaO content in the quicklime and / or limestone and the feed rate AO in the converter slag
Ratio with supply speed B ₂ per minute: A ₂ / B ₂ is 0 or more and less than 3,
5. The hot metal dephosphorization treatment method according to claim 1, 2, 3, or 4, more preferably 0 to 2. 6. The hot metal dephosphorization treatment method according to claim 1, wherein a part of the converter slag to be supplied is added from above the hot metal.