JPH07179920A - Production of molten steel - Google Patents

Abstract

PURPOSE:To reduce the unit consumption of a lime by specifying the composi tion of slag on the way of refining process and the temp. at the end point of treatment. CONSTITUTION:Molten iron is decarburize-refined to produce molten steel in the same refining vessel. At this time, in a first process, the molten iron is charged into a refining vessel. In a second process, dephosphorize-refining or desiliconize and dephosphorize-refining are applied to reduce phosphorus in the molten iron to a prescribed content. In a third process, the refining vessel is tilted to remove the slag produced in the second process. Thereafter, in the fourth process, the decarburize-refining is executed in the same refining vessel. In this process, CaO/SiO2 in the slag after the second process is made to be <=2.5, the sum of concns of iron oxide and manganese oxide (T.Fe+MnO) >10%, the concn of MgO <10% and the temp. at the end point of the treatment is made to be 1320-1400 deg.C. By this method, the discharge quantity of the slag after dephosphorizing treatment can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing molten steel in a converter.

[0002]

2. Description of the Related Art As a conventional hot metal dephosphorization method for reducing the total cost of steel making to a minimum and reducing phosphorus, (1)
Preliminary dephosphorization by injecting dephosphorization flux into hot metal in a torpedo car, (2) Preliminary dephosphorization by injecting or spraying dephosphorization flux into hot metal in ladle, or (3)
A method of dephosphorizing on one side and decarburizing on the other side by using two converters (for example, JP-A-63-195210) is used.

However, the above (1), (2),
In any of the methods (3), when the dephosphorization step is transferred to the decarburization step, the hot metal needs to be transferred, the temperature must be lowered, and the energy loss is large. In order to solve this problem, in Japanese Patent Application Laid-Open No. 2-181989, the conventional refining function over multiple steps is integrated in a converter to significantly reduce the energy loss of the hot metal and to fix the steps before and after the converter. A method has been proposed that enables a significant reduction in costs (equipment costs, labor costs).

FIG. 2 shows this flow. As a first step, hot metal is charged into a converter, and as a second step, flux addition and oxygen blowing are performed to perform desiliconization and dephosphorization refining,
The phosphorus content is reduced to a predetermined value, the converter is tilted as a third step to discharge the slag generated in the second step, and then a fourth step is performed in the same converter by adding flux and blowing oxygen to a predetermined value. Decarburization up to the C content, and as the fifth step, steel is tapped while leaving the slag generated in the fourth step in the converter, and the process returns to the first step again, and the fifth step is repeated. To do. Depending on the case, the slag generated in the fourth step may not be returned to the first step, but the entire amount of slag may be discharged after tapping in the fifth step.

[0005]

When the process of continuously performing the dephosphorization and decarburization steps using the same converter described above is used,
It is possible to reduce energy loss when moving from the dephosphorization process to the decarburization process, and it is possible to significantly reduce fixed costs (equipment costs, labor costs). However, if the amount of slag discharged in the third step is small, the phosphorus removed in the slag in the second step returns to the molten steel again in the fourth step (hereinafter referred to as "reconstituted phosphorus"). It becomes necessary to dephosphorize again, and the amount of flux such as quick lime must be increased, leading to an increase in cost. Moreover, since the slag having a high phosphorus concentration in the fourth step is reused in the second step, the dephosphorization load in the second step increases and the cost increases. When the amount of slag discharged in the third step is small as described above, there arises a problem that the dephosphorization load increases and the cost increases.

In the present invention, by optimizing the operating conditions in the second step of the above-mentioned molten steel manufacturing method, the amount of slag discharged in the third step is increased, the amount of reconstituted phosphorus in the fourth step is suppressed, and the quicklime basic unit is reduced. It is an object of the present invention to provide a method for reducing the above.

[0007]

The present invention advantageously solves the above-mentioned problems, and the gist thereof is to perform dephosphorization treatment and decarburization treatment in one refining vessel to remove molten steel from hot metal. During production, C in the slag after dephosphorization treatment
aO / SiO ₂ is 2.5 or less, the sum of iron oxide and manganese oxide concentrations (T.Fe + MnO) is 10% or more, and the MgO concentration is 10% or less, and the treatment end point temperature is 1
A molten steel manufacturing method is characterized in that the temperature is 320 ° C. or higher and 1400 ° C. or lower.

[0008]

The present invention will be described in detail below. The present invention integrates the hot metal pretreatment and decarburization and operates in the same converter. That is, for example, as shown in FIG. 2, one or a plurality of bottom blowing tuyere for blowing flux for dephosphorization and decarburization to the bottom of the furnace, and gas blowing blades for slag forming on the tapping hole and the facing furnace side. The hot metal is loaded into an upper-bottom blowing converter equipped with a port, and a flux based on quicklime powder is blown from the above-mentioned bottom-blowing tuyere using an inert gas such as nitrogen as a carrier gas for dephosphorization treatment.

At this time, the dephosphorization reaction rate can be increased by mixing the iron oxide powder with the quicklime powder or by forming the tuyere with a triple tube structure and blowing oxygen gas through the same tuyere. Alternatively, dephosphorization can be promoted by spraying oxygen gas from the top-blown lance and adding flux from the top by methods such as charging, blowing, and spraying to control the iron oxide concentration of the produced slag. be able to.

When the phosphorus content is reduced to a predetermined level, the furnace is tilted to the side of the unextruded steel (slag side) to discharge only the slag.
However, if the amount of slag discharged at this time is small, the phosphorus removed in the slag is re-phosphorized during the next decarburization treatment, so that it is necessary to add extra quick lime, leading to an increase in cost. The relationship between the slag ratio (amount of discharged slag / amount of generated slag × 100) and the basic unit of quick lime is shown in FIG. It can be seen that when the slag removal rate is less than 60%, the quick lime basic unit rapidly increases. Therefore, the slag removal rate must be at least 60% or more.

The amount of slag discharged decreases as the fluidity of the slag decreases. In addition, the fluidity is slag CaO / SiO ₂ ,
(T. Fe + MnO) concentration, MgO concentration, and temperature. This is because if CaO / SiO ₂ is high,
This is because when the (T.Fe + MnO) concentration is low and when the MgO concentration is high, the melting point of the slag rises, and when the temperature is low, the solid phase precipitates in the slag and the apparent viscosity of the slag rises. So the slag composition before slag discharge,
That is, CaO / SiO ₂ at the end of the dephosphorization treatment is 2.5 or less, and the sum of iron oxide and manganese oxide concentrations (T.Fe +
(MnO) is 10% or higher, the MgO concentration is 10% or lower, and the temperature is 1320 ° C. or higher, whereby the fluidity of the slag can be enhanced and the slag ratio can be 60% or higher.
With respect to the temperature, the higher the temperature, the more advantageous it is. However, since the phosphorus removal reaction is hindered when the temperature rises, it is necessary to keep it at 1400 ° C or lower.

Immediately after the slag is exhausted, the furnace is immediately erected and auxiliary materials (refractory protection, quick lime for preventing phosphorus reversion, dolomite, iron ore, Mn ore, etc.) are put in to carry out ordinary upper bottom blown decarburization refining . After blowing off, the molten steel is tapped, but the slag is left in the furnace as it is and used as the flux for dephosphorization for the next charge.

[0013]

EXAMPLE 4.5% C, 0.1% P, 0.3% S
1350 ° C hot metal containing i was charged into a 300t converter with a pre-charged decarburizing slag left, and while bottom blowing and stirring, quicklime and iron ore were added as a dephosphorizing agent and top blowing acid was carried out. After the dephosphorization treatment, the slag was discharged, and then the decarburization treatment was conducted. CaO / SiO ₂ , (T / Fe + MnO) concentration of slag at the end of dephosphorization treatment, MgO
The concentration and temperature are shown in Table 1.

[0014]

[Table 1]

Test No. 1 to 10 are CaO / SiO ₂
Is 2.5 or less, the sum of iron oxide and manganese oxide concentrations (T.Fe + MnO) is 10% or more, the MgO concentration is 10% or less, and the temperature is 1320 ° C. or more. For comparison, the test No. 11 to 12 are CaO / S
iO ₂ is 2.5 or less, and (T.Fe + MnO) is 10
% Or more and the MgO concentration is 10% or less, but the temperature is less than 1320 ° C., the test No. 13-14 is Ca
O / SiO ₂ is 2.5 or less, and (T.Fe + MnO)
Is 10% or higher and the temperature is 1320 ° C. or higher.
When the concentration is more than 10%, the test No. 15 to 16 are
CaO / SiO ₂ is 2.5 or less and MgO concentration is 10
% Or less and the temperature is 1320 ° C. or higher, but (T.Fe +
MnO) is less than 10%, the test No. 17-1
No. 8 has (T.Fe + MnO) of 10% or more and MgO
Although the concentration is 10% or less and the temperature is 1320 ° C or more, C
This is the case where aO / SiO ₂ exceeds 2.5.

Table 2 shows the slag ratio and quicklime basic unit in each test. CaO / SiO ₂ is 2.5 or less, and the sum of iron oxide and manganese oxide concentrations (T.Fe + MnO) is 10
% Or more and the MgO concentration is 10% or less, and the temperature is 13%.
It can be seen that when the temperature is 20 ° C. or higher, the waste slag ratio is set to 60% or more more stably than in the comparative example, and the quicklime basic unit can be reduced.

[0017]

[Table 2]

The present invention has been described above mainly using the molten steel production method in which desiliconization, dephosphorization and decarburization are performed in the same converter, and the slag after decarburization is used for desiliconization and dephosphorization. However, the present invention is not limited to this, and naturally it does not depart from the scope of the present invention when applied to a molten steel production method in which slag after decarburization is discharged and is not used for desiliconization and dephosphorization. .

[0019]

EFFECTS OF THE INVENTION In the process of performing desiliconization, dephosphorization treatment and decarburization treatment in the same refining vessel, by carrying out the present invention, it is possible to increase the discharge amount of slag after dephosphorization treatment. The unit can be reduced.

[Brief description of drawings]

[Fig. 1] Waste slag ratio (amount of discharged slag / amount of generated slag × 10
It is a figure which shows the relationship between 0) and quicklime basic unit.

FIG. 2 is a schematic explanatory diagram of a refining process using the same converter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noriyuki Mitsuko 12 Nakamachi, Muroran, Hokkaido Stock of Nippon Steel Corporation (72) Inventor Fumio Koizumi 12 Nakamachi, Muroran, Hokkaido Stock of Nippon Steel Muroran Works

Claims (2)

[Claims] 1. When refining hot metal to produce molten steel, the hot metal is charged into a refining vessel as a first step, and dephosphorization refining or desiliconization and dephosphorization refining are performed as a second step to contain a predetermined phosphorus content. In the molten steel manufacturing method in which the amount is reduced to a third step, the refining vessel is tilted as the third step to discharge the slag generated in the second step, and then the fourth step is decarburization refining in the same refining vessel. CaO / SiO _{2 in} the slag after the process is 2.
5 or less and the sum of iron oxide and manganese oxide concentrations (TF
e + MnO) is 10% or higher, the MgO concentration is 10% or lower, and the treatment end point temperature is 1320 ° C. or higher, 140
A method for producing molten steel, characterized in that the temperature is 0 ° C. or lower. 2. When refining hot metal to produce molten steel, the hot metal is charged into a refining vessel as the first step, and the second step is dephosphorization treatment or desiliconization and dephosphorization refining to contain a predetermined phosphorus content. The amount is reduced to the third step, the refining vessel is tilted as the third step to discharge the slag generated in the second step, and then the fourth step is the decarburization in the same refining vessel, and the fifth step is the fourth step. In the second step of the molten steel manufacturing method, in which the produced slag is tapped while remaining in the refining vessel, the process is returned to the first step, and the above steps are repeatedly performed, CaO in the slag is removed.
/ SiO ₂ is 2.5 or less, the sum of iron oxide and manganese oxide concentrations (T.Fe + MnO) is 10% or more, and Mg
O concentration is 10% or less, and the treatment end point temperature is 132
The method for producing molten steel is characterized in that the temperature is 0 ° C. or higher and 1400 ° C. or lower.