JP3440755B2 - How to add auxiliary raw materials to the converter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for charging an auxiliary raw material into a converter, and more particularly, to a suitable slag forming agent used in refining hot metal after pretreatment in the converter. It is a technology that puts an appropriate amount into a converter at an appropriate time to smoothly and stably slag them.

[0002]

2. Description of the Related Art In recent years, in converter steelmaking, a so-called composite converter having a function of blowing oxygen, nitrogen, CO, CO ₂ , or argon gas from the bottom of the furnace is generally used in addition to the function of blowing oxygen upward. It became so. This combined converter increased the decarburization rate and, consequently, reduced the oxygen usage. Then, from the viewpoint of further enhancing this excellent decarburization property, if the hot metal that has been previously subjected to desiliconization, desulfurization, and dephosphorization treatment (hereinafter referred to as pretreatment) is used, the load on the converter is reduced,
It was expected that the above effects would be further improved. for that reason,
In the recent converter steelmaking, 90% of the hot metal used is subjected to a pretreatment, and so-called dephosphorization hot-melting is often used.

By the way, dephosphorization pig iron has a problem in that the initial slag formation in the converter blowing is slower than that of ordinary hot metal which is not pretreated. Since the Si content in the hot metal is low,
This is because the amount of SiO ₂ that forms the nucleus of initial slag formation is small. Therefore, in the present converter operation, there is a tendency that the slag forming agent (hereinafter, also referred to as an auxiliary material) is excessively added to dephosphorize more than necessary.

Further, in the present converter operation, from the viewpoint of preventing melting damage of the converter refractory, a part of the slag is left in the converter once every several times during tapping, and light burned dolomite is added to the slag. So-called slag coating for tilting the converter is added. Therefore, there is another problem that the presence or absence of the slag left behind has an important influence on the initial slag formation, and the slag formation varies from charge to charge. The reason for adding the light-burned dolomite is that the slag must be constantly supersaturated with MgO during blowing in order to prevent melting of the converter refractory (MgO-based).

Further, in the present converter operation, as shown in FIG. 6, since the absolute amount of the slag 6 covering the molten steel 5 is small,
There is also a tendency that so-called spitting 9 of molten steel occurs or dust 10 is easily generated during blowing. This spitting 9 increases the molten steel loss by increasing the size of the ingot 8 in the converter 1, and dust generation has the same meaning. Therefore, proper slagging and securing of the amount of slag are required in the converter operation. Has become an important issue for

[0006]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention is intended to smoothly perform rapid slag formation from the initial stage of converter blowing, prevent meltdown of converter refractory, and suppress spitting and dust generation. It is an object of the present invention to provide a method for feeding auxiliary raw materials to a converter for improving the hot metal yield.

[0007]

In order to achieve the above object, the inventor has calculated the melting point from the composition of the slag-forming agent based on the equilibrium theory by the conventional method of charging the auxiliary raw material into the converter. It was reviewed by repeating an analysis using a software (which is called “ChemSage”, which is commercially available and which calculates the equilibrium diagram of a multi-component system from the chemical composition of each auxiliary material to be input) and a large number of experiments. And the result was materialized as this invention.

That is , according to the present invention, burnt lime, light burnt dolomite, raw dolomite, serpentine, ingot slag and fluorspar are put into molten pig iron in the converter to form slag, and the slag between the slag and the molten pig iron produced. -When the metal reaction is carried out under oxygen blowing, burnt lime is charged within 20% to 60% of the total blowing time,
And, during the period, the total amount of burnt lime added is equally divided into multiple times and the serpentine is added at the above-mentioned burnt lime loading period.
It is divided into several times and added during the period.
From the beginning of the period, put up to 30%, the light burned dolomite
And the above-mentioned slag will be used up to 10% from the beginning of the entire blowing period.
Inject the raw dolomite from 25% of the total blowing period
It is a method of charging auxiliary raw materials into a converter, which is characterized by charging up to 30% .

[0009]

In addition to the of al, the present invention, the pig iron, is also a sub-material injection method to the converter, characterized in that the hot metal after the pretreatment. In the present invention, since the auxiliary raw material is charged into the converter with the above-described configuration, rapid slaging can be smoothly performed from the initial stage of the blowing of the converter. As a result, not only was it possible to improve the hot metal yield by preventing melting damage of converter refractories and suppressing the generation of spitting and dust, but it was also possible to reduce the amount of auxiliary raw materials and the amount of ferroalloy used.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The contents of the present invention will be described below, including the process leading to the invention. 2. Description of the Related Art Conventionally, when a 200-ton converter is used as a typical example, the charging of the auxiliary raw material in the converter blowing is performed as shown in FIG. 2 (the charging timing is indicated by a mark). That is, the total blowing time is divided into 10%
It is indicated by: Burned lime: Split charging within a period of 5 to 50%, input standard amount of 500 kg per time Light burned dolomite: Period from the beginning of blowing to 15%,
Continuous dosing at 0.7 ton / min Raw dolomite: 25% to 35% period, Continuous dosing at 0.7 ton / min Serpentine rock: Finished by 40% period from the beginning of blowing Slagging agent: Full amount in advance Initially batch-injection by weighing: Fluorite: 10 to 80% dividedly injecting, reference amount of 150kg each time, when the above is applied for dephosphorization hot metal blowing, Chem
The results of the Sage analysis are shown in Table 1. Further, FIG. 3 shows a transition of CaO solubility (also referred to as CaO slagging ratio R ′) (%) during blowing.

From Table 1 and FIG. 3, in the blowing of this dephosphorized hot metal, R'is less than 30% even after 60% of the blowing period. That is, 30% of CaO in the input auxiliary material
% Or less is dissolved. Moreover, this is a calculation result, and it seems to be lower in actual blowing.

[0013]

[Table 1]

In addition, when CaO is dissolved at the time of blowing stop,
The amount of CaO dissolved in the course of blowing was determined as 0 and is shown in FIG. From FIG. 4, in the initial stage of blowing (10 to 30%),
It can be seen that about 35% of dissolved CaO at the time of blowing is the limit of dissolution. That is, at that time, only about 35% of the total CaO input has been slagged. However, in a normal operation, 70% of the total CaO input is added by this time, including the pre-added calcined lime. Therefore, in the conventional operation, CaO is excessively added at the initial stage of blowing.

[0015] Therefore, the inventors have conducted extensive attempt to put the appropriate amount of CaO content to the appropriate time, it was completed the previous Symbol present invention. In the present invention, 20% of the total blowing time
If less than 20%, CaO will be added excessively, and the temperature of the slag produced will be lowered, which will become an obstacle to slag formation, and if more than 60% is added, This is because there are some that remain solid without slagging even when blowing off. Moreover, the input amount per time is 40
Approximately 0 kg / ton of molten steel , it is preferable to divide and input multiple times.
Yes. This is because the input amount and the slagging speed match, and the slagging can be performed appropriately.

Next, in order to accelerate the dissolution of CaO, SiO
_Since the coexistence of ₂ is indispensable, we considered a method of adding serpentinite.
It was This is to make the slag composition necessary for the slag-metal reaction as soon as possible. In addition, when CaO or SiO ₂ is dissolved, it is desirable to dissolve it at a temperature as low as possible from the viewpoint of promoting slag formation. Therefore , in the present invention, in order to lower the melting point of the mixture, fluorite is added from the beginning of the entire blowing period up to 30%, and a slag serving as a base that aids in the dissolution of burnt lime and serpentine is previously prepared. I was allowed to form it. Furthermore, since the melting point of the slag decreases as the multi-component system, for lowering the melting point of the slag to be the base, dolomitic, the Zokatamarikasu so as to put into up to 10% from the initial raw whole blowing period Or, raw dolomite was also introduced at the beginning of blowing. Here, the ingot is
It is the slag collected from the ladle.

The light-burned dolomite and raw dolomite are
Since the refractory lining of the converter is MgO-based, early slagging is preferable from the viewpoint of preventing its melting loss. However, since the raw dolomite has a high cooling ability even when it is charged from the beginning of blowing, it was added from 25% to 30% of the total blowing period as usual. An example of a secondary raw material charging method according to the present invention this and is patterned shown in Fig. That is, it is described as follows. Roasted lime: divided input within a period of 20 to 60 %,
Input standard amount 400kg / ton of molten steel Light burned dolomite: Period from the beginning of blowing to 10%,
Continuous dosing at 0.7 ton / min Raw dolomite: 25% to 30% period, Continuous dosing at 0.7 ton / min Serpentine rock: Divided into multiple times within the above-mentioned burned lime loading period. Fluorite added at a time of 10% from the beginning by pre-weighing: Input at 25% to 30% of the total blowing period, reference amount of 150 kg per addition In addition, as the present invention, the slag remaining at the time of tapping Consideration was also given to changing the amount of auxiliary raw material to be input depending on the presence or absence. In other words, in the charge after the total amount of slag is discharged at the time of tapping, the slag composition in the initial slag formation is different from that in the charge in which slag remains, and CaO slag formation delay and variation,
This is because variations in the slag composition, poor dephosphorization, and unsaturation of MgO in the slag (supersaturation is essential during blowing to prevent refractory meltdown). For example, in FIG.
Depending on the presence or absence of slag left, CaO in the subsequent charge
The difference in solubility R'is shown.

Therefore, in such a case, it is necessary to supplement the substitute for the core of slag formation in the charge after leaving the slag with an auxiliary material . During its, spitting prevented, in view of the refractory protective, the Al ₂ O ₃ in the slag 4 wt%, the initial basicity 3
Consideration is given to ~ 4.

Light-burnt dolomite (kg / t) = calcined lime (kg / t) ×
0.29 Serpentine (kg / t) = Roasted lime (kg / t) x 0.22 Aggregate slag (kg / t) = Roasted lime (kg / t) x 0.39 Fluorite (kg / t) = In addition to the above, the present invention described above can be applied to ordinary hot metal that has not been subjected to hot metal pretreatment, so that the case of blowing hot metal after pretreatment is particularly advantageous . 2 of the present invention.

[0020]

Example 1 The method of introducing the auxiliary raw material according to the present invention shown in FIG. 1 was applied to the so-called dephosphorized hot metal after the hot metal pretreatment to blow it, and an extremely low carbon steel was melted. The converter 1 used is commonly referred to as LD-KGC and has a function (nozzle or lance) 3 lined with MgO refractory 2 to blow oxygen upward and blow inert gas bottom.
(See FIG. 6). This operation was performed as a charge after leaving the slag. The amount of hot metal used was 200 tons, and the flow rate of top-blown oxygen was 450 Nm ^3.
/ Min, bottom blown argon gas flow rate is 4 Nm ³ / mi
n, the hot metal temperature during blowing was 1250 to 1650 ° C. As shown in Table 2, hot metal is usually used.
For this reason, in Example 2, the amount of auxiliary raw material input was increased and other phosphorus was removed.
Maintained at the same level as the example. (Example 2) In the same converter as in Example 1, ordinary hot metal not subjected to pretreatment was blown as a charge after leaving slag. In the same converter as in Example 1, the same dephosphorized hot metal was blown by the charge after the entire amount was discharged. (Conventional Example) In the same converter as in Example 1, blowing of a plurality of charges was performed according to a conventional auxiliary raw material charging method.

The above operating conditions and operating results are collectively shown in Tables 2 and 3. Table 4 shows the chemical composition of the hot metal used.

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

[Table 4]

From Table 3, the following facts were clarified, and the effectiveness of the present invention was confirmed. According to Table 3, reduction of secondary raw materials and improvement of the slag formation yield are observed as compared with the present invention, and the slag formation ratio is improved even when there is no slag residue. In addition,
Even when using normal hot metal, as shown in Table 3, the rate of slag formation
There was no problem above and it was feasible. In addition, although the present invention is applied to the LD-KGC type converter in the above-mentioned embodiment, it goes without saying that the present invention can be applied to other types of converters.

[0026]

As described above, according to the present invention, rapid slag formation can be smoothly performed from the initial stage of converter blowing.
As a result, not only was it possible to improve the hot metal yield by preventing melting damage of converter refractories and suppressing the generation of spitting and dust, but it was also possible to reduce the amount of auxiliary raw materials and the amount of ferroalloy used.

[Brief description of drawings]

FIG. 1 is a pattern diagram showing an example of an auxiliary raw material charging method according to the present invention.

FIG. 2 is a pattern diagram showing a conventional auxiliary raw material charging method.

FIG. 3 is a diagram showing a transition of CaO solubility during dephosphorization hot metal blowing.

FIG. 4 is a diagram showing the CaO solubility at each blowing time, based on the amount of CaO dissolved at the time of blowing stop.

FIG. 5 is a diagram showing a comparison of CaO solubility between the charge after leaving the slag and the charge after discharging the whole amount.

FIG. 6 is a diagram showing a so-called LD-KGC type converter.

Continuation of the front page (56) Reference JP-A-8-325623 (JP, A) JP-A-7-173516 (JP, A) JP-A-8-3616 (JP, A) JP-A-7-179921 (JP , A) JP-A-55-107715 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C21C 1/00-7/10

Claims (2)

(57) [Claims] 1. A slag-metal reaction between the generated slag and the hot metal is performed by adding burned lime, light burned dolomite, raw dolomite, serpentine, slag and fluorite to the hot metal in the converter. upon causing under oxygen blowing, along with the full blowing the burnt lime was charged to 20% of the time to 60% of the time, and to introduce and evenly divided into a plurality of times all turned sintered lime amount within that period , The serpentine is the above-mentioned
It is divided into several times during the entry period and put in.
Add up to 30% from the beginning of the smelting period, and light burn doloma
Ito and the agglomerate of slag are 10% from the beginning of the whole blowing period.
The raw dolomite is 25% of the total blowing period.
To 30% from 30 to 30% . 2. The pig iron is used as hot metal after pretreatment.
The method of charging the auxiliary raw material to the converter according to claim 1, wherein
Law.