JP3531480B2 - Hot metal dephosphorization method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dephosphorization treatment carried out as a hot metal pretreatment, in which efficient dephosphorization is carried out by using a solvent mainly composed of CaO containing no F source such as CaF _2. Is about how you can.

[0002]

2. Description of the Related Art Conventionally, a hot metal pretreatment method has been developed in which preliminary dephosphorization is performed at the hot metal stage to remove P in the hot metal to some extent and then converter decarburization blowing is performed. This preliminary dephosphorization treatment is carried out in equipment such as a torpedo, a hot metal ladle and a converter, and is carried out by adding a CaO-based medium solvent and oxygen such as gaseous oxygen or a solid oxygen source. In order to efficiently transfer P from the hot metal to the slag side during this dephosphorization treatment, control of the slag composition, slag amount, etc. is an important factor. In particular, by adding CaF ₂ to the solvent, 1) the meltability of the slag is improved, 2) SiO
Ca ion increases by dividing the network of ₂ , 3)
It has been previously pointed out that an effect such as an increase in the activity of FeO can be obtained, and CaF ₂ is widely used in actual operation to enhance the reactivity of dephosphorization.

For example, in Japanese Patent Publication No. 6-17496, [CaF ₂ + Al ₂ O ₃ ] / CaO and Al ₂ O ₃ / C are used in addition to the CaO / O weight ratio CaO / O to be added.
A technique has been disclosed in which each weight ratio of aF ₂ is specified and CaF _{2 is} added to improve the dephosphorization efficiency. However, recently, from the viewpoint of environmental protection, the regulation standard of the elution amount of F in slag tends to be strengthened, and therefore, it is necessary to reduce the F concentration in the dephosphorized slag to the limit.

[0004]

Therefore, the development of a dephosphorization treatment technique which does not use an F source such as CaF ₂ is strongly desired, but at present, the basicity of slag is made low and the amount of slag is extremely increased. The actual situation is that there are only effective measures such as operations and multiple processing. However, the extreme increase in the amount of dephosphorized slag, as in the former case, runs counter to the need for reducing the amount of slag, which is strongly desired from the perspective of environmental protection. Doing so has a problem of increasing the manufacturing cost of molten steel, and therefore these cannot be drastic measures.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to carry out the hot metal preliminary dephosphorization efficiently by using a medium solvent containing no F source such as CaF _2. To provide.

[0006]

The present inventors have found that CaF ₂
In order to find a hot metal pretreatment method capable of efficiently performing dephosphorization treatment without using an F source such as (fluorite),
Various experiments and studies were carried out using a converter type container. As described above, CaF ₂ plays an important role in ensuring the meltability of slag, and in the experiments conducted by the present inventors,
If CaF ₂ is not added, the added solvent (Ca
The (O source) did not appear to be slagging, and the dephosphorization reaction efficiency also decreased. However, especially when the Si concentration is 0.1% by weight
In the dephosphorization treatment of low-Si hot metal reduced below, from the results of experiments conducted by changing the hot metal temperature before and after the dephosphorization treatment, the dephosphorization treatment of low-Si hot metal without the addition of CaF ₂ was performed. The phosphorus reaction efficiency depends on the hot metal temperature before and after the dephosphorization treatment,
That is, it was found that the hot metal temperatures at the start of the dephosphorization treatment and at the end of the dephosphorization treatment are greatly affected, and that by controlling these temperatures within a specific range, high dephosphorization reaction efficiency can be obtained.

Since the dephosphorization process is an oxidation reaction of P, it has been generally considered that a low hot metal temperature during the dephosphorization process is generally advantageous, but the results of experiments and studies by the present inventors , Low Si hot metal with Si concentration of 0.1 wt% or less is CaF
_In the case of dephosphorization without adding F source such as ₂ ,
In order to promote the dephosphorization reaction, the meltability of the slag is an important factor, and in order to secure the meltability of such slag, hot metal with a higher Si concentration is added with CaF _2. It was found that it is more effective to keep the treatment temperature higher than that of the conventional method in which dephosphorization was performed. Regarding hot metal temperature control, the hot metal temperature during dephosphorization can be calculated from the gas composition analysis value of the exhaust gas and / or the exhaust gas temperature, and the hot metal temperature at the end of the dephosphorization process can be easily controlled based on this. I knew I could do it.

Based on the above findings, the present invention quantifies the hot metal temperature range in which efficient dephosphorization treatment can be carried out from the relationship between the hot metal temperature before and after the dephosphorization treatment and the dephosphorization behavior. Yes, its features are as follows. [1] In the dephosphorization treatment performed as a hot metal pretreatment, S
Hot metal having an i concentration of 0.1% by weight or less was added to C containing no F source.
A solvent mainly composed of aO is added, and the hot metal temperature A (° C.) at the start of the dephosphorization treatment and the hot metal temperature B at the end of the dephosphorization treatment are added.
A method for dephosphorizing hot metal, which comprises performing dephosphorization treatment while controlling the hot metal temperature so that (° C) satisfies the following relationships (1) to (4). (1) In the case of A <1300, 1300 ≦ B <1350 (2) In the case of 1300 ≦ A <1330, [2600-A] ≦ B < 1350 (3) In the case of 1330 ≦ A <1350 , 1270 ≦ B <[2680-A] (4) When A ≧ 1350, 1270 ≦ B ≦ 1330

[2] In the dephosphorization method of the above [1], the hot metal having a Si concentration of more than 0.1% by weight is mixed with S of 0.1% by weight or less.
A method for dephosphorizing hot metal, which comprises desiliconizing to an i concentration and then dephosphorizing. [3] In the dephosphorization method of [1] or [2] above, calculate the hot metal temperature during the dephosphorization process from the gas composition analysis value of the exhaust gas and the exhaust gas temperature, and control the hot metal temperature at the end of the dephosphorization process. A method for dephosphorizing hot metal, which comprises:

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, it has been conventionally considered that a low hot metal temperature during dephosphorization treatment is advantageous, but a low Si content of 0.1% by weight or less is desirable. Hot metal C
When performing the dephosphorization treatment without adding an F source such as aF ₂ , securing the meltability of the slag is an important factor for promoting the dephosphorization reaction, and the meltability of such slag is In order to secure the
It is necessary to keep the treatment temperature higher than that of the method of adding F ₂ or the like to perform the dephosphorization treatment).

FIG. 1 shows that the hot metal temperature A at the start of the dephosphorization process and the hot metal temperature B at the end of the dephosphorization process are depleted when the low Si hot metal is dephosphorized without adding an F source such as CaF _2. The results of examining the effect on the phosphorus reaction efficiency (P concentration in the hot metal after dephosphorization treatment) are shown. In this test, hot metal that has been subjected to desiliconization treatment and desulfurization treatment after being tapped from the blast furnace (P concentration in the hot metal: about 0.1% by weight, Si concentration: tr.
1 wt%) is dephosphorized at various hot metal temperatures (hot metal temperature A at the start of the dephosphorization process, hot metal temperature B at the end of the dephosphorization process) using a 300 ton converter, and P in the hot metal after the process. The concentration was checked.

In this dephosphorization treatment, CaF ₂ is used as a solvent.
CaO-based roasted lime (CaO unit: 9 to 1)
Using only 1 kg / hot metal-T, oxygen (total oxygen unit:
As 8 to 10 Nm ³ / T), gaseous oxygen supplied through a top blowing lance and a solid oxygen source mainly composed of iron ore were used together. In addition, the oxygen transfer rate of gaseous oxygen is 15000 to
25000 Nm ³ / hr, lance height is 1.5 to 2.5
m, and the blowing time for supplying a predetermined amount of gaseous oxygen was 9 to 11 minutes.

In FIG. 1, the P concentration in the hot metal after dephosphorization treatment is [P] ≦ 0.015% by weight, 0.015% by weight <[P].
≤0.025% by weight and [P]> 0.025% by weight are arranged separately. According to this, the highest dephosphorization reaction efficiency is obtained, and the P concentration in the hot metal after the dephosphorization treatment is shown. Is [P] ≦
0.015% by weight means that the hot metal temperature A (° C) at the start of the dephosphorization treatment and the hot metal temperature B (° C) at the end of the dephosphorization treatment are as follows.
It is understood that it is limited to the case where the relationships (1) to (4) are satisfied. (1) In the case of A <1300, 1300 ≦ B <1350 (2) In the case of 1300 ≦ A <1330, [2600-A] ≦ B < 1350 (3) In the case of 1330 ≦ A <1350 , 1270 ≦ B <[2680-A] (4) When A ≧ 1350, 1270 ≦ B ≦ 1330

Therefore, in the present invention, the low Si hot metal having a Si concentration of 0.1% by weight or less is used as C without the F source such as CaF _2.
The dephosphorization treatment is performed by adding a solvent mainly composed of aO. At that time, the hot metal temperature A (° C) at the start of the dephosphorization treatment and the hot metal temperature B (° C) at the end of the dephosphorization treatment are The conditions are that the hot metal temperature is controlled so that the relations of (4) to (4) are satisfied. The hot metal temperature at the start of the dephosphorization treatment varies depending on the hot metal temperature at the time of tapping, the desiliconizing treatment conditions usually performed in the above process, and the like, but is generally about 1200 to 1400 ° C.

The dephosphorization method of the present invention is carried out on hot metal having a Si concentration of 0.1% by weight or less. Therefore, when the Si concentration of tapped hot metal exceeds 0.1% by weight. For this purpose, desiliconization treatment (usually performed by adding oxygen such as a solid oxygen source or gaseous oxygen to the hot metal) in a blast furnace casting floor or a hot metal ladle is performed, and the Si concentration in the hot metal before dephosphorization treatment is set to 0.1. Dephosphorization treatment is performed after adjusting the content to be not more than wt%.

When carrying out the method of the present invention, the hot metal temperature during the dephosphorization treatment is calculated from the gas composition analysis value of the exhaust gas and the exhaust gas temperature, and the hot metal temperature at the end of the dephosphorization treatment is easily calculated based on this. Can be controlled. That is, the combustion C amount in the dephosphorization container is obtained from the gas composition analysis value of the exhaust gas, and the calorific value is obtained from this. In addition, the heat absorption efficiency of C combustion can be obtained from the exhaust gas temperature. Therefore, estimating the heat dissipation loss from the furnace body for these calorific values and heat efficiency,
The hot metal temperature in the furnace can be calculated from the heat balance.

In the dephosphorization treatment according to the present invention, a medium solvent mainly containing CaO that does not contain an F source such as CaF ₂ and an oxygen source are added. Here, in the present invention, the medium solvent does not substantially include the F source if it does not include the F source, and therefore, it is possible that the medium solvent contains a small amount of the F source as unavoidable impurities. Do not disturb Further, gaseous oxygen and / or solid oxygen source can be used as the oxygen source. Usually, a gaseous oxygen source is mainly used, and if necessary, a solid oxygen source such as iron ore and mill scale is used together. Either pure oxygen gas or oxygen-containing gas may be used as the gaseous oxygen.

As a container for carrying out the dephosphorization method of the present invention, a converter type container is the most preferable in that a freeboard can be sufficiently secured, but other than this, any container such as a hot metal ladle and a torpedo can be used. Can be used. Further, there is no particular restriction on the method of supplying gaseous oxygen, and the acid can be fed by any method such as top blowing with a lance, injection into hot metal, or bottom blowing. In the case of using a converter-type container or a hot metal ladle, top blowing with a lance is common, and in the case of using a torpedo, injection into the hot metal with a lance is common.

[0019]

[Examples] The hot metal tapped from the blast furnace was subjected to a desiliconization treatment in a blast furnace cast bed and a hot metal ladle, and then desulfurized in a hot metal ladle using mechanical agitation, followed by dephosphorization treatment in a 300 ton converter . The P concentration in the hot metal before the dephosphorization treatment was approximately 0.1% by weight, which was almost constant, and the Si concentration was in the tr. Was 0.1% by weight.

In this embodiment, C is used as a solvent for dephosphorization.
Using only CaO-based roasted lime that does not contain aF ₂ ,
The unit consumption of O was 9 to 11 kg / hot metal-T. Moreover, the supply of gaseous oxygen is performed by the top blowing lance, and the solid oxygen source mainly consisting of iron ore is also added to reduce the total oxygen unit to 8
It was set to be 10 Nm ³ / T. Gas oxygen transfer rate is 1500
0-25000 Nm ³ / hr, lance height is 1.5-
It was 2.5 m and the blowing time of gaseous oxygen was 9 to 11 minutes.

The hot metal component after the dephosphorization treatment including the P concentration is
Table 1 shows the hot metal components before the dephosphorization treatment, the hot metal temperature at the start of the dephosphorization treatment and at the end of the dephosphorization treatment, and the like. According to the table,
In all the examples of the present invention, the target [P] standard ≦ 0.015
Weight percent has been achieved. On the other hand, in the comparative examples in which the hot metal temperature does not satisfy the conditions of the present invention, the dephosphorization reaction efficiency is low, and the P concentration in the hot metal after the treatment exceeds 0.015% by weight.

[0022]

[Table 1]

[0023]

As described above, according to the method of the present invention, C
It is possible to perform dephosphorization treatment of hot metal with extremely excellent dephosphorization efficiency without using an F source such as aF ₂ .

[Brief description of drawings]

FIG. 1 is a graph showing the influence of the hot metal temperature at the start of dephosphorization treatment and the hot metal temperature at the end of dephosphorization treatment on the dephosphorization reaction efficiency.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Watanabe 1-2, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Shinichi Akai 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Co., Ltd. (72) Inventor Satoshi Kodaira 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihonkokan Co., Ltd. (56) Reference JP-A-11-323419 (JP, A) JP-A-9-249909 (JP , A) JP-A-7-179920 (JP, A) JP-A-62-161908 (JP, A) JP-A-2000-73111 (JP, A) JP-A-2-77513 (JP, A) (58) Survey Areas (Int.Cl. ⁷ , DB name) C21C 1/02

Claims (3)

(57) [Claims] 1. In the dephosphorization treatment performed as a hot metal pretreatment, the hot metal having a Si concentration of 0.1% by weight or less is added to a medium solvent mainly containing CaO containing no F source, and the dephosphorization treatment is started. The hot metal temperature A (° C) at the time and the hot metal temperature B (° C) at the end of the dephosphorization treatment satisfy the following relationships (1) to (4). Method for dephosphorizing hot metal. (1) In the case of A <1300, 1300 ≦ B <1350 (2) In the case of 1300 ≦ A <1330, [2600-A] ≦ B < 1350 (3) In the case of 1330 ≦ A <1350 , 1270 ≦ B <[2680-A] (4) When A ≧ 1350, 1270 ≦ B ≦ 1330 2. The hot metal according to claim 1, wherein the hot metal having a Si concentration of more than 0.1% by weight is subjected to desiliconization treatment to a Si concentration of 0.1% by weight or less and then dephosphorization treatment. Dephosphorization method. 3. The hot metal temperature during the dephosphorization treatment is calculated from the gas composition analysis value of the exhaust gas and the exhaust gas temperature, and the hot metal temperature at the end of the dephosphorization treatment is controlled. Method for dephosphorizing hot metal.