JP2607329B2 - 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 method for dephosphorizing hot metal in a converter.

[0002]

2. Description of the Related Art Regarding minimization of total steelmaking cost and stable hot metal of low phosphorus steel, as a conventional hot metal dephosphorization method, (1) a method of performing preliminary phosphorus removal by injecting a dephosphorizing flux into hot metal in a torpedo car; (2) Preliminary dephosphorization by injecting or spraying a flux for dephosphorization into the hot metal in the ladle, or (3) Dephosphorization using one of two converters and dephosphorization on the other. A method of performing charcoal (for example, see JP-A-63-19521)
No. 0) is used.

[0003] By the way, the dephosphorization reaction proceeds more advantageously as the temperature is lower and the slag contains more basic components. However, in any of the methods (1), (2) and (3), when the dephosphorization step is shifted to the decarburization step, the hot metal needs to be transferred, and the temperature must be lowered. In each case, the temperature was 1300 ° C. or higher, and instead, CaO /
A basic slag having SiO ₂ of 1.5 or more is used.
Therefore, the input CaO basic unit cannot be reduced below a certain value in order to secure basicity.

In the specification of Japanese Patent Application No. 2-181989 (Japanese Patent Application Laid-Open No. 4-72007) , the present applicant concentrated the refining function of the conventional multi-step process in a converter to greatly reduce the energy loss of hot metal. At the same time, we proposed a method that can significantly reduce fixed costs (equipment costs and labor costs) in the process before and after the converter.

FIG. 2 shows this flow. As a first step, hot metal is charged into a converter, and as a second step, dephosphorization and desilicon refining is performed by adding a flux and blowing over oxygen. As a third step, the converter is tilted to discharge the slag generated in the second step, and as a fourth step, decarburization is performed to a predetermined C content by flux addition and O ₂ blowing. As a fifth step, the slag generated in the fourth step is left in the converter, and the steel is returned to the first step, and the steps up to the fifth step are repeatedly performed.

[0006]

In a process in which dephosphorization and decarburization steps are continuously performed using the same converter, the dephosphorization step can be performed in a short time because the dephosphorization end point temperature can be lowered. Can be. Further, since the decarburized slag is reused in the dephosphorization step, the CaO unit consumption can be reduced. The present invention further examines these usefulnesses and provides a method for dephosphorizing hot metal using low-basic slag.

[0007]

SUMMARY OF THE INVENTION The gist of the present invention is that when hot metal is refined to produce molten steel, hot metal is charged into a converter as a first step, and flux addition and oxygen blowing are performed as a second step. Performing dephosphorization and refining to reduce the phosphorus content to a predetermined level, tilting the converter as a third step and discharging the slag generated in the second step, and then performing a decarburization step with the same converter, In the second step of the molten steel manufacturing method in which the slag is left in the converter and the slag is recycled to the first step, acid is sent to aim at CaO / SiO ₂ = 1 of the slag , and P is removed.
A hot metal dephosphorization method characterized by controlling the treatment end point temperature to 1300 ° C. or lower, wherein the top blowing acid transfer rate is 2.5
It can be Nm ³ / min / t or more.

Hereinafter, the present invention will be described in detail. In the present invention, hot metal pretreatment and decarburization are integrated and operated by the same converter.
That is, as shown in FIG. 2, one or a plurality of bottom-blowing tuyeres for blowing a flux for dephosphorization and decarburization into a furnace bottom, and a plurality of bottom-blowing tuyeres for blowing a slag forming gas into a belly facing a tapping hole. Hot metal is charged into a top and bottom blown converter with tuyeres,
A flux based on quicklime powder is blown from the above-mentioned bottom blowing tuyere using an inert gas such as N ₂ as a carrier gas.

At this time, the dephosphorization reaction rate can be increased by mixing iron oxide powder with quick lime powder or by making the tuyere a triple tube structure and blowing O ₂ gas through the same tuyere. Alternatively, dephosphorization is promoted by blowing O ₂ gas from the upper blowing lance and adding flux by adding, blowing, spraying or the like from above to control [Fe 0%] of the generated slag. can do.

At the time when the content of P and C is reduced to a predetermined value, the furnace is tilted toward the counter-ejecting side (the waste side) to discharge only the slag.

Immediately after the waste is finished, the furnace is erected immediately, and a small amount of auxiliary materials (quicklime, dolomite, iron ore, etc. for refractory protection and recovery P prevention) are charged, and normal top-bottom blowing decarburization refining is performed. Do. After blow-off, the molten steel is tapped, but the slag is left in the furnace as it is to be used as a pretreatment slag for the next charge.

In the present invention, since the dephosphorization and decarburization steps are continuously performed using the same converter, the dephosphorization end point temperature is 1300 ° C.
Therefore, even if a low-basic slag having CaO / SiO _{2 of} about 1 is used, a dephosphorization ability equivalent to the conventional one can be obtained. In addition, the problem of a decrease in the dephosphorization rate due to the use of a low-basic slag can be solved by setting the top-blowing acid transfer rate higher than before, for example, 2.5 Nm ³ / min / t.

[0013]

EXAMPLE A dephosphorization experiment was conducted using an 8t test converter. The hot metal containing 4.5% C, 0.1% P, and 0.3% Si was refined for 10 minutes using decarburized slag obtained by recycling hot metal at an initial temperature of 1300 ° C. Slag basicity after the experiment,
Table 1 shows the hot metal temperature, the basic unit of CaO input, and the acid feed rate.

[0014]

[Table 1]

Experiment No. 1-3 are slag CaO / SiO
_In the case of low acid feed rate aiming at around ₂ = 1, experiment No. 4 is Ca
This is the case of a high acid feed rate with the aim of O / SiO ₂ = 1. For comparison, an experiment (No. 5) in the case of a low acid feed rate was also performed aiming at CaO / SiO ₂ = 1.5.

FIG. 1 shows the change over time of the [P] concentration in the hot metal. No. In comparison with No. 5, In case of 1-4, input CaO
It can be seen that the basic unit can be reduced by about 2 to 5 kg / t.
No. No. 1 to 3 for low acid feed rates It was found that although the dephosphorization rate was slightly lower than in the case of No. 5, the target [P] level could be sufficiently reached within a predetermined time. Also,
No. By increasing the acid feed rate as shown in FIG. It was also found that it is possible to increase the number to 5 or more.

Table 2 shows the average unit of CaO in the conventional processes (1), (2) and (3). It can be seen that even in comparison with these processes, the present invention can greatly reduce the CaO unit consumption.

[0018]

[Table 2]

[0019]

According to the present invention, the dephosphorization and decarburization steps are carried out continuously by using the same converter, so that the dephosphorization end point temperature can be lowered, and the CaO / SiO ₂ = 1 in the slag is aimed at to reduce the CaO basic unit. Can be reduced.

[Brief description of the drawings]

FIG. 1 is a table showing the change over time of the [P] concentration in hot metal.

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

Claims (2)

(57) [Claims] 1. When refining molten iron to produce molten steel, the molten iron is charged into a converter as a first step, and a dephosphorization refining is performed by adding a flux and blowing over oxygen as a second step. As a third step, the converter is tilted to discharge the slag generated in the second step, and then a decarburization step is performed by the same converter, and the slag is discharged while remaining in the converter. In the second step of the molten steel manufacturing method in which the slag is steelified and recycled in the first step, CaO / SiO ₂
= 1 and acid sending, de-P treatment end point temperature is 1300 ℃ or less
A method for dephosphorizing hot metal, characterized in that: 2. The top blowing acid transfer rate is 2.5 Nm ³ / min / t.
2. The method for dephosphorizing hot metal according to claim 1, wherein: