JP5874578B2 - High-speed blowing method for converters - Google Patents

Description

  It is a blowing method of an upper bottom blowing converter for producing molten steel from hot metal that has not been subjected to hot metal preliminary dephosphorization treatment. More specifically, the blowing time is a short time of 13 minutes or less, The present invention relates to a high-speed blowing method for a converter, which can efficiently produce molten steel having a P concentration of 0.020% by mass or less in molten steel.

  In recent years, hot metal preliminary dephosphorization has come to be frequently used in order to improve the efficiency and efficiency of steel production methods. In that case, in order to produce molten steel from hot metal, two furnaces are required: a hot metal pretreatment furnace for desiliconizing and dephosphorizing the hot metal and a decarburization furnace for decarburizing the hot metal that has been pretreated with the hot metal. Become. However, by dividing the treatment into two furnaces, the reaction efficiency is remarkably improved, and the hot metal pretreatment furnace and the decarburization furnace are normally subjected to high-speed treatment such as 13 minutes or less.

  However, in order to produce molten steel from hot metal, it is not always necessary to use two furnaces, and there are cases where such two furnaces cannot be used due to operational reasons. Even in such a case, when manufacturing molten steel from hot metal, in order to meet the recent high efficiency and high efficiency, the processing time in the converter (the top blowing for desiliconizing, dephosphorizing and decarburizing the hot metal) There has been a demand for a blowing method capable of performing (oxygen supply time) in a short time such as 13 minutes or less.

  When carrying out blowing in an upper-bottom blowing converter using hot metal that has not been subjected to hot metal preliminary dephosphorization treatment, it is necessary for the converter to advance the dephosphorization reaction as the decarburization reaction proceeds. The dephosphorization reaction proceeds by a reaction between the basic slag formed by melting and hatching CaO charged in the furnace and the molten iron.

  However, pure CaO has a melting point of 2000 ° C. or higher, and it is difficult to melt and hatch in a converter having a steel output temperature of about 1600 to 1700 ° C. If the hatching of CaO is insufficient, the required dephosphorization ability cannot be obtained, resulting in a detrimental effect that removes the components.

  Furthermore, if the blowing time is shortened to increase the efficiency of the converter, the time required for melting and hatching CaO is also shortened, which causes a problem that the dephosphorization rate decreases.

JP2011-038156

I. Fluorite is used for the purpose of promoting CaO hatching and ensuring dephosphorization ability. CaF ₂ which is the main component of fluorite lowers the melting point of CaO and improves the hatching rate. However, in this method, since F is mixed in the discharged slag, it is difficult to recycle the slag from the viewpoint of environmental protection.
II. In Japanese Patent Application Laid-Open No. 2011-38156, using hot metal that has been subjected to hot metal preliminary dephosphorization treatment, the Al ₂ O ₃ concentration in the slag after completion of blowing is 3.5% or less, and the basicity is 4.0 or more and 6. A method of increasing the efficiency of converter blowing to 0 or less is shown. However, this method uses hot metal that has been subjected to hot metal preliminary dephosphorization treatment, and [Si] in the hot metal is 0.01% or less. Therefore, if this method is applied as it is to converter blowing in hot metal that has not been subjected to preliminary hot metal dephosphorization, the amount of CaO necessary to ensure basicity will increase, and the iron yield will deteriorate due to the increase in slag amount, etc. Cost deterioration due to

  The present invention improves the hatching rate without using fluorite that has been used as a conventional hatching accelerator, and further ensures dephosphorization capability in response to shortening the blowing time for higher efficiency. With the goal.

The gist of the present invention is as follows.
(1) Blowing method of an upper bottom blown converter for producing molten steel from molten iron that has not been subjected to hot metal preliminary dephosphorization treatment, and the [Si] concentration in molten metal at 0.40% to 0.60% in molten metal For the following hot metal, the charging basicity calculated by the formula (I) is set to 3.0 or more and 4.0 or less, and CaO—Al ₂ O ₃ double oxidation is added to the Al ₂ O ₃ source to be charged into the furnace. By using the product, adjusting the Al ₂ O ₃ mass concentration in the slag to 4.0% or more and 6.0% or less after the end of blowing , not using fluorite , and after the end of blowing [C] concentration in molten steel = 0.05 mass% or less, molten steel temperature = 1630 ° C or more and 1690 ° C or less, so that the blowing time is 13 minutes or less, and the P concentration in the molten steel after blowing is 0 . High-speed blowing of converters characterized by producing molten steel of less than 0.020 mass% Law.

Charge basicity = (CaO mass charged into the furnace) / (Si mass in hot metal charged into the furnace × 2.14 + SiO ₂ mass charged into the furnace)
... (I)

It is a graph which shows the relationship between blowing time and [P] after completion | finish of blowing.

  Quick lime is generally used for the purpose of causing a dephosphorization reaction at the time of blowing in the converter, but as described above, the melting point of pure CaO is 2000 ° C. or higher, and the highest temperature during the blowing. However, it is not easy to hatch CaO by converter blowing at about 1700 ° C.

  If the CaO hatching is insufficient, the increase in CaO concentration in the slag that contributes to the dephosphorization reaction is suppressed, so the possibility of dephosphorization cannot be ensured and the components may be removed, causing problems in operation. End up.

  Moreover, what is necessary is just to improve an acid-feeding speed | rate in order to shorten the blowing time in converter blowing. If the oxygen supply into the furnace and the dust collection facilities are increased, the acid delivery rate can be increased.

  However, if the blowing time is actually shortened, the time required for the hatching of CaO is also shortened, so the CaO hatching rate is lowered and the dephosphorization ability is lowered.

If Al ₂ O ₃ is added, the melting point of CaO can be lowered from the viewpoint of diversification of the slag constituent components, so that the CaO hatching rate can be improved.

Therefore, the reduction in CaO hatching rate due to the shortening of the blowing time was compensated by lowering the melting point of CaO by adding Al ₂ O ₃ , and the blowing conditions for achieving both short-time blowing and dephosphorization ability were investigated. Went. Hereinafter, each blowing condition for ensuring the dephosphorization ability in the short-time converter blowing using the hot metal not subjected to the preliminary dephosphorization treatment and having a blowing time of 13 minutes or less will be described.

1. [Si] concentration in hot metal In the present invention, hot metal that has not been subjected to preliminary dephosphorization treatment is used, and the Si concentration in the hot metal is 0.40% to 0.60% in mass%.

Although there is a balance with the charging basicity described later, since the amount of slag cannot be secured when the molten iron Si concentration is less than 0.40%, the molten iron Si concentration is equivalent to 0.40% using meteorites or rocks. The SiO ₂ source is charged and adjusted so that When blowing without supplying the SiO ₂ source, the basicity of charging to obtain a P concentration (0.020% by mass or less) in the molten steel becomes too high after completion of the predetermined blowing, and the CaO melting point is remarkably increased. Therefore, it becomes easy to become a hatching defect.

  If the hot metal Si concentration exceeds 0.60%, the amount of CaO necessary to secure the basicity for proceeding with the predetermined dephosphorization will increase even if the reduction in the required basicity is taken into account. Becomes prominent. If CaO is reduced in order to avoid cost deterioration and the basicity is lowered too much, problems that cause adverse effects such as slipping will occur.

2. Charge basicity To obtain a P concentration (0.020% by mass or less) in the molten steel after the completion of predetermined blowing, the charge basicity is set to 3.0 or more and 4.0 or less.

  When the charging basicity is less than 3.0, the CaO hatching rate is easily increased, but the dephosphorization ability is lowered because the CaO concentration in the slag is lowered.

  In addition, if the charging basicity exceeds 4.0, the melting point of slag increases due to the increase in basicity, the CaO hatching rate deteriorates, and the amount of CaO contributing to the dephosphorylation reaction decreases on the contrary. Dephosphorization ability will fall.

The charging basicity in the present invention can be determined by the formula (I).
Charge basicity = (CaO mass charged into the furnace) / (Si mass in hot metal charged into the furnace × 2.14 + SiO ₂ mass charged into the furnace)
... (I)

3. [C] concentration in molten steel after completion of blowing The [C] concentration in molten steel after completion of blowing is 0.05% or less.

In the present invention, in order to set the blowing time (supply time of top blowing oxygen) to 13 minutes or less, it is necessary to set the top blowing oxygen supply rate to 3.0 to 5.0 Nm ³ / min per ton of hot metal. In order to promote the various reactions by stirring the molten steel and slag in such high-speed blowing, it is appropriate that the feed rate of the bottom blowing gas is 0.02 to 0.20 Nm ³ / min per ton of hot metal. is there.

  Under such conditions, when the [C] concentration in the molten steel after completion of blowing exceeds 0.05%, the reaction rate between the top blown oxygen and the molten steel [C] is still relatively high, and the amount of FeO produced is high. It will decrease. FeO in the slag contributes to the oxidation reaction of P in the dephosphorization reaction in addition to the melting point drop of the slag in which a large amount of CaO is added. Therefore, the [C] concentration in the molten steel after the completion of blowing is high. When the medium FeO concentration is low, a predetermined P concentration in molten steel (0.020 mass% or less) cannot be stably obtained by blowing for 13 minutes or less.

4). Steel output (molten steel) temperature The steel output temperature is 1630 ° C or higher and 1690 ° C or lower.

  When the steel output temperature is less than 1630 ° C., there are few heat sources that are carried over to the secondary refining process, which leads to deterioration in heat-up costs and refractory costs in the secondary refining equipment, and the molten steel treatment time becomes long.

When the steel output temperature exceeds 1690 ° C., the equilibrium constant of the dephosphorization reaction is lowered, so that the dephosphorization ability is lowered.
The adjustment of the Al ₂ O ₃ concentration in the slag, which is a feature of the present invention, will be described.

5). Blowing after the end of the slag _(Al 2 _{O 3)} Concentration blowing closes in slag _(Al 2 _{O 3)} concentration is 6.0% or less than 4.0%.

When the concentration of (Al ₂ O ₃ ) in the slag is less than 4.0% after the end of blowing, the hatching of CaO cannot be ensured in the short time blowing of 13 minutes or less, and the dephosphorization ability decreases.

When blowing after the end slag _(Al 2 _{O 3)} is the concentration to 4.0 to 6.0%, since the melting point depression of CaO due to _Al 2 _{O 3} added is significant, slag formation of CaO is promoted dephosphorization The CaO concentration in the slag that contributes to the reaction increases and the dephosphorization reaction is promoted.

However, it varies depending on the shape of the converter, the acid feed rate, the exhaust gas superficial velocity, etc., but if the Al ₂ O ₃ concentration exceeds 6.0%, there is a risk that slipping may occur. In practice, the concentration of (Al ₂ O ₃ ) in the slag after the end of blowing must be 4.0 to 6.0%.

In addition, it is important to use a CaO—Al ₂ O ₃ double oxide for adjusting the Al ₂ O ₃ concentration in the slag according to the present invention. In the present invention, the CaO—Al ₂ O ₃ double oxide means that CaO is 30 to 60% and Al ₂ O ₃ is 30 to 60%, and the ratio of CaO and Al ₂ O ₃ (CaO / Al ₂ O ₃ ) A substance containing 70% or more of a pre-melt compound having a value of 0.5 to 2.0 and MgO, SiO ₂ or the like as other impurity components.

The melting point of Al ₂ O ₃ alone is about 2000 ° C., whereas CaO—Al ₂ O ₃ double oxide has a melting point of about 1200 ° C. and can be easily melted from the initial stage of blowing (about 1300 ° C.). I can do it. Thereby, (% Al ₂ O ₃ ) can be reliably increased.

In addition, taking advantage of the low melting point, by introducing CaO-Al ₂ O ₃ complex oxide at the start of blowing, cover slag formation is promoted from the early stage of blowing, and it can be used to prevent dust and spitting. Can do.

In the conventional knowledge, it is known that the inclusion of the Al ₂ O ₃ concentration in the slag promotes slopping. Slopping is not preferable because it causes slag and hot metal to flow out of the converter, resulting in adverse operations. However, in the present invention, even when the Al ₂ O ₃ concentration in the slag is about 4.0 to 6.0%, there is no slopping. Various factors are involved in the mechanism of slopping, but basically it is considered that whether or not slopping occurs is determined by the balance between CO gas generation rate and slag viscosity accompanying decarburization reaction. ing.

In the present invention, by forming a _CaO-Al 2 _{O 3} composite oxide is rapidly melted liquid phase slag by using a _CaO-Al 2 _{O 3} mixed oxide as _Al 2 _{O 3} source, further oxygen-flow-rate Relatively fast during slag It is considered that the hatching of CaO proceeds faster than the conventional knowledge due to the situation where Fe is likely to rise. Accordingly, it is considered that the occurrence of slopping can be suppressed because it passes through the actual basicity region where the viscosity of the slag, which is likely to cause slopping, is reached faster than before.

The actual basicity can be obtained by the formula (II).
Actual basicity = (CaO weight in molten slag) / (SiO ₂ mass in molten slag)
... (II)

  By the blowing method shown above, it is possible to ensure the dephosphorization ability in the short-time converter blowing using the hot metal that has not been subjected to the preliminary dephosphorization treatment and having a blowing time of 13 minutes or less. If this method is used, since F is not included in the slag component, the exhaust slag can be recycled. Further, the charging basicity of the present invention is the charging basicity shown in JP-A-2011-38156 (because the basicity in the slag component after completion of blowing is 4.0 to 6.0, Therefore, the secondary material cost and the iron yield are prevented from deteriorating.

(1) Hot metal conditions For hot metal preliminary desulfurization treatment, hot metal passed through a mechanical stirring desulfurizer (KR) was used. Before pouring the hot metal into the top-bottom converter, 30 to 50 tons of scrap was put into the furnace, and the main component based on the cant back analysis after KR was mass% [C] = 4.4 to 4.8. %, [Si] = 0.4 to 0.6%, [Mn] = 0.1 to 0.3%, [P] = 0.11 to 0.15%, hot metal temperature = 1300 to 1400 ° C. 240 to 260 tons were poured. However, the scrap and the molten iron are adjusted so as to be 270 to 290 ton.

(2) In-furnace auxiliary materials After charging scrap and hot metal, oxygen blowing from the top blowing lance to the hot metal was started. Immediately after the flow rate was adjusted to 0.04 to 0.10 Nm ³ / min / t using CO ₂ as the bottom blowing gas and the oxygen flow rate was started to be blown at 3.5 to 4.3 Nm ³ / min / t. A small amount of dolomite was charged, and an appropriate amount of quicklime was added so that the charging basicity was 3.0 to 4.0. The balance between heat input into and out of the furnace was adjusted using a scale (iron oxide).

(3) During the concentration of _Al 2 _{O 3} adjusting slag in the concentration of _Al 2 _{O 3} adjusted slag using _CaO-Al 2 _{O 3} composite oxide. The CaO—Al ₂ O ₃ double oxide was weighed so that the Al ₂ O ₃ concentration in the slag was 4.0% or more and 6.0% or less by mass%, and was put into the converter immediately after the start of blowing.

(4) Blowing Oxygen was blown into the molten steel so that the [C] concentration was 0.05% or less, and the steel was discharged at a temperature of 1630 ° C or higher and 1690 ° C or lower, and the molten steel was sampled after transferring the molten steel to the ladle. The molten steel component was measured. Blowing control was performed using both static control based on the charge balance and dynamic control that is measured and corrected using a sublance during blowing.

  As a result of the above treatment, the components in the molten steel were [C] = 0.03 to 0.05%, [Si] = 0.01% or less, and [Mn] = 0.08 to 0.15% in mass%. .

[P] in the molten steel component is shown in FIG. For comparison, the Al ₂ O ₃ source is not actively fed into the converter, and the other conditions satisfy the requirements of the present invention, and the Al ₂ O ₃ concentration in the slag is 1.0-2. The conventional blowing method which became 0.0% and the one which satisfied all the requirements according to the present invention and adjusted the Al ₂ O ₃ concentration in the slag to 4.0 to 6.0% are plotted.

As a whole, it can be seen that [P] becomes higher after the end of blowing as the blowing time is shortened. However, for an example in which the blowing time is about 11 minutes, for example, the conventional example in which the Al ₂ O ₃ concentration in the slag becomes 1.0 to 2.0% after the end of the blowing [P] = 0.020 to 0 In the example in which the present invention was applied to adjust the Al ₂ O ₃ concentration in the slag to about 4.0 to 6.0%, [P] = 0 after completion of the blowing It was reduced to about .015%.

  In this research example, neither the conventional blowing method nor the method of the present invention caused slopping or spitting.

  In this example of the present invention, even if the blowing time is 13 minutes or less, the P concentration in the molten steel after blowing is 0.020% or less, and slopping and spitting are also problems until the blowing time is about 10 minutes. However, it was confirmed that high-efficiency and high-efficiency blowing can be performed.

Claims (1)

A method of blowing an upper-bottom blowing converter for producing molten steel from molten iron that has not been subjected to hot metal preliminary dephosphorization treatment, wherein the molten iron has a [Si] concentration of 0.40% to 0.60% in molten metal. The basicity calculated by the formula (I) is set to 3.0 or more and 4.0 or less, and a CaO—Al ₂ O ₃ double oxide is used as an Al ₂ O ₃ source to be introduced into the furnace. By adjusting the Al ₂ O ₃ mass concentration in the slag to 4.0% or more and 6.0% or less after completion of the blowing , not using fluorite , and in the molten steel after the blowing [C] Concentration = 0.05% by mass or less, Molten steel temperature = 1630 ° C. or more and 1690 ° C. or less, so that the blowing time is 13 minutes or less and the P concentration in the molten steel after the blowing is 0.020 mass. A high-speed blowing method for a converter, characterized by producing molten steel of less than 10%.
Charge basicity = (CaO mass charged into the furnace) / (Si mass in hot metal charged into the furnace × 2.14 + SiO ₂ mass charged into the furnace)
... (I)

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