JP2001164310A - Refining method in top and bottom blown converter - Google Patents

Abstract

(57) [Abstract] [Problem] In decarburization and dephosphorization refining while making slag in an upper-bottom blowing converter, improve dephosphorization ability and improve iron yield by suppressing slopping. To provide a way to SOLUTION: Si trace hot metal in an upper-bottom blower is
In a refining method of decarburizing and dephosphorizing while adding slag and adding a CaO source such as an O ₂ source and quick lime and calcium carbonate, a part of the CaO source is conveyed together with an oxygen jet blown into hot metal from a top blowing lance. When spraying hot metal, the spraying of the CaO source is 50% of the total oxygen blowing time.
Perform later. At that time, SiO ₂ source such as Ni dregs SiO ₂
It is preferably a low melting point slag containing

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a refining method in a top-bottom blow converter.

[0002]

2. Description of the Related Art Iron-containing cold materials, carbon materials,
A method in which oxygen is supplied to obtain high-carbon molten iron, and the high-carbon molten iron is used as a raw material to perform oxygen blowing in a separate top-bottom blow converter to obtain molten steel of a required component. Japanese Patent Publication No. 3-49964 and Japanese Patent Publication No. 4-1160 describe a method in which a part of the molten carbon iron is left in the furnace and used as seed water.
No. 3 is known.

[0003] In such a melting method of iron-containing cold material,
The produced high-carbon molten iron is a Si trace, and in oxygen blowing in another converter, there is no Si, which is the source of SiO ₂ in the slag in the furnace. Or SiO such as Fe-Si
_{Although two} sources need to be added, the former has a high melting point and cannot be expected to have a slag-making effect at the beginning of refining. The latter was also commercially unsuitable due to its high cost. Therefore, Japanese Patent Application Laid-Open
As described in JP-A-150212, inexpensive and easily soluble Si
Ni refining by-products, which are O ₂ rich premelt by-products, have been used as SiO ₂ sources. However, even in this method, the lump lime charged into the furnace as an auxiliary material for refining remains partially unslagged.

Further, in the case of the above-mentioned iron-containing cold material melting method, the high carbon molten iron to be produced has a high phosphorus concentration, and it is necessary to increase the dephosphorization capacity in a decarburization refining furnace. In general, to increase the dephosphorization capacity, it is necessary to increase the basicity of slag or the iron oxide content of slag, but as described above, the increase in basicity is not significant because massive lime remains as slag. This cannot be expected, and conversely causes an increase in auxiliary material costs. Also,
An increase in the iron oxide content in the slag causes a decrease in iron yield and a decrease in alloy yield, resulting in an increase in cost and is not an appropriate means.

On the other hand, as a method for increasing the dephosphorization capability, while blowing gas from the bottom blowing tuyere of the top-bottom blowing converter, a powdery CaO source is conveyed together with an oxygen jet blown into the hot metal from a top blowing lance to transfer hot metal. The refining and refining method for spraying on a surface is known in Japanese Patent No. 1302973 and Japanese Patent Application Laid-Open No. 58-19432. It is described that by this method, a reduction in iron yield and a reduction in work efficiency due to scattering of molten iron and molten slag outside the furnace, so-called slopping, are prevented, and promotion of dephosphorization is achieved. In particular, in the former publication, a method in which the entire amount of slag forming material is sprayed from an oxygen lance within 3/4 of the oxygen blowing time, while in the latter publication, the basicity of the generated slag is 1.0 to 1.0 in the desiliconization period at the initial stage of refining. A method of controlling so as to be 8.0 is disclosed. However,
No method of blowing the CaO source in the case of high carbon molten iron in Si traces is disclosed. In addition, it does not disclose a method of using a bulk and powdery CaO source in combination.

[0006]

From such a background,
The present inventors have found that Si trace hot metal in the top-bottom
In a refining method in which an O ₂ source and a CaO source such as quicklime and calcium carbonate are added and decarburization and dephosphorization refining is performed while slag is produced, all of the CaO source is transported together with an oxygen jet blown into hot metal from a top blowing lance in powder form. Investigation of a method of spraying hot metal on hot metal revealed that, although the dephosphorization ability was improved, there was a problem that excessive slagging caused frequent slopping, resulting in a decrease in iron yield and a decrease in workability. Therefore, a method was examined in which a part of the CaO source was conveyed in powder form together with an oxygen jet blown into the hot metal from an upper blowing lance and sprayed onto the hot metal.

The present invention has been made on the basis of the results of this study, and decarbonization is performed while adding a SiO ₂ source and a CaO source, such as quicklime and calcium carbonate, to Si trace hot metal in an upper-bottom blowing converter to form slag. It is an object of the present invention to provide a refining method for dephosphorizing and refining, in which the dephosphorizing ability is enhanced and the iron yield is improved by suppressing the slopping to improve the iron yield. In addition, the Si trace hot metal in the present invention is described in
It shows hot metal containing 0.07% or less of Si, as in JP-A-0212.

[0008]

Means for Solving the Problems (1) S in top-bottom blowing converter
In a refining method in which a SiO ₂ source and a CaO source such as quicklime and calcium carbonate are added to i-trace hot metal and decarburization and dephosphorization refining is performed while slag is formed, an oxygen jet that blows a part of the CaO source into the hot metal from an upper blowing lance A refining method in an upper-bottom blowing converter, wherein the CaO source is blown at 50% or more of the total oxygen blowing time when the steel is conveyed and blown to the hot metal. (2) The refining method in the top-bottom blow converter according to (1), wherein the SiO ₂ source is a low melting point slag containing SiO ₂ such as Ni slag.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A source of SiO ₂ and CaO such as quicklime and calcium carbonate are added to Si trace hot metal in a top-bottom blowing converter.
In a refining method in which decarburization and dephosphorization refining is performed while adding a source and making slag, when the entire amount of the CaO source to be added is supplied over the entire time of refining by spraying from a lance,
Although the dephosphorization ability is improved, excessive slagging causes frequent slopping, which causes a decrease in iron yield and a decrease in workability. It is known that in the first half of decarburization refining, almost all of the supplied oxygen is consumed for the combustion of carbon in the molten iron, so the iron oxide concentration in the slag is low,
When the CaO source is sprayed, the CaO source is supplied to the ignition point together with the oxygen gas, so that the CaO-Fe _t
It is known that an O compound is formed, and a slag having a very high oxidizing property and a low melting point is formed. For this reason, slopping is likely to occur during the decarburization and dephosphorization refining.

Therefore, in the method of supplying the CaO source, it is necessary to add a part of the CaO source in a lump. As in the example,
It has been found that when 6.8 kg / t is supplied in powder form, decarburization and dephosphorization refining can be performed without generating slopping. However, the dephosphorization ability greatly changes depending on at which stage of refining the spraying of the limited CaO source is performed.

The present inventors investigated the difference in dephosphorization ability depending on the timing of spraying a CaO source from an upper blowing lance. FIG.
Even if the total quicklime unit is the same, the refining time is 5
It has been found that the more the CaO source is sprayed at 0% or more, the better the dephosphorization ability. As is generally known, as the decarburization refining reaction proceeds, the temperature of the molten iron increases, and phosphorus in the slag returns to the molten iron by an equilibrium reaction, so-called rephosphorus occurs. This time is after 50% of the total oxygen blowing time, and by blowing a CaO source from the upper blowing lance after 50% of the total oxygen blowing time, CaO-
This is because a slag having a high oxidizing property is formed by forming a Fe _t O compound and the dephosphorization reaction is enhanced.

As a result, when the CaO source is sprayed frequently after 50% of the refining time within the supply limit of the powdery CaO source for preventing the occurrence of the slopping, the iron by the slopping is reduced. It was found that the phosphorus concentration in the molten iron at the end of the decarburization and dephosphorization refining was low without lowering the yield and lowering the work efficiency.

[0013]

EXAMPLE In a 100-ton top-bottom blower, powdered CaO
Table 1 shows the results of decarburization and dephosphorization refining performed by changing the spraying time of the source.

[0014]

[Table 1]

No. No. 1 is a case where the whole amount of the CaO source was supplied in powder form from a lance over the entire time of refining. Phosphorus distribution was high, but iron yield decreased significantly due to the occurrence of slopping. No. 2-No. No. 6 is a comparison of the case where the total quicklime unit was constant, the powdery CaO source was 6.8 kg / t or less at which no slopping occurred, and the spraying amount after blowing 50% was changed. As can be seen from FIG. 1, the greater the spraying amount after blowing 50%, the greater the phosphorus distribution and the higher the dephosphorization ability.

In addition, No. 1 to No. 6 is described in JP-A-7-150212 as a SiO ₂ source,
No. Ni slag was used. 7-N
o. Numeral 9 uses silica stone. In this case, when the refining flux is sprayed after 50% of the refining time, the phosphorus distribution is improved, and the effect is recognized. However, as described in JP-A-7-150212, when the Ni slag is used, By comparison, the phosphorus distribution was lower.

[0017]

According to the present invention, in the decarburization and dephosphorization refining of Si trace hot metal, which has a poor slagging property and has a problem in securing dephosphorization ability, the timing of spraying the powdery CaO source together with the massive CaO source. The slag forming property can be controlled by setting the time to 50% or more of the total oxygen blowing time, and it is possible to improve the dephosphorization ability while suppressing the scattering of molten iron and molten slag outside the furnace due to the occurrence of slopping. Become.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between a spraying amount of a refining flux after 50% of a decarburization and dephosphorization refining time and a phosphorus distribution ratio.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuo Onuki 1Fuji-cho, Hirohata-ku, Himeji-shi, Hyogo F-term in Nippon Steel Corporation Hirohata Works (reference) 4K002 AB01 AB04 AC07 AC10 AE02 BE10 4K012 CA00 CA10

Claims (2)

[Claims] 1. An Si trace hot metal in an upper-bottom blower
In a refining method of decarburizing and dephosphorizing while adding and adding CaO source such as O ₂ source and quick lime and calcium carbonate, a part of the CaO source is powdered together with an oxygen jet blown into hot metal from a top blowing lance. A refining method in an upper-bottom blowing converter, wherein the CaO source is blown at 50% or more of the total oxygen blowing time when transported and blown to the hot metal. 2. The refining method according to claim 1, wherein the SiO ₂ source is a low melting point slag containing SiO ₂ such as Ni slag.