JPH08199219A - Dephosphorizing method of molten iron - Google Patents

Abstract

PURPOSE: To provide the dephosphorizing method in which P hit rate after treatment is improved, flux consumption unit is reduced and lowering of yield of iron is extremely suppressed. CONSTITUTION: In the dephosphorizing method of molten iron in which the bottom agitating power is >=1.0kw/t, the top blowing oxygen supply rate is >=2.5Nm<3> /min/t, CaO/SiO2 in the slag after treatment is >=0.6 to <=2.5, the treatment completing temp. is 1250-1400 deg.C, the top blowing oxygen supply rate, bottom blowing gas flow rate and a height of the top blowing lance are controlled so as to turn the T. Fe concentration in slag, which is calculated by the equation, T. Fe concentration (weight %) in slag = 6.49×(top blowing oxygen supply rate) (Nm<3> /min/t)-15.35×(L/L0 )+9.68|2-CaO/SiO2 |+11.73, (wherein, L: recessed depth of molten steel due to top blowing, L0 : standstill molten steel depth) to 10-20.

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 the minimization of the total cost of steelmaking and the stable hot metal of low phosphorus steel, the conventional hot metal dephosphorization method is as follows.
(1) Method for pre-dephosphorization by injecting flux for dephosphorization into hot metal in torpedo car, (2) Pre-dephosphorization by injecting or spraying flux for dephosphorization on hot metal in ladle Or (3) using two converters for dephosphorization on the one hand and decarburization on the other hand (see, for example, JP-A-63-
195210) is used.

However, when a torpedo car is used, the dephosphorization reaction is far from equilibrium because the stirring is weak, and more flux than necessary is used to achieve the target dephosphorization amount, such as raw coal. There is a problem that the unit is high. Further, when a torpedo car or a hot metal ladle is used as a processing container, if the top blowing acid speed is increased and the processing time is shortened, the freeboard is small, which causes a problem in operation due to foaming of slag. Under the present circumstances, the shortest treatment time of the dephosphorization step is about 20 minutes in the process (1) and about 11 minutes in the process (2). Also, in the process (3), the acid transfer rate is 1.0 N at most.
It is operated at m ³ / min / t and the processing time is about 10
It took a minute.

The present inventors have conducted various dephosphorization experiments in order to solve such problems, and have clarified the following. By ensuring the bottom blowing stirring power of 1 kW / t or more, the dephosphorization reaction progresses to almost equilibrium. As a result, in the range of the post-treatment temperature of 1250 to 1400 ° C, CaO / SiO _{2 in} the slag after the treatment is 0.6 to 2.5 and the target dephosphorization amount is sufficiently reached depending on the temperature.

At a high acid transfer rate of 2.5 Nm ³ / min / t or more, the dephosphorization oxygen efficiency is not significantly reduced, the dephosphorization rate constant is improved, and the dephosphorization treatment time is shortened. Is possible. T. in slag after treatment By adjusting the Fe concentration to 10 to 20% by weight, the dephosphorization reaction can be made more appropriate, and the flux basic unit can be reduced while maintaining the iron yield.

Based on these facts, "When the flux addition and oxygen top blowing and bottom blowing stirring are performed to dephosphorize the hot metal, the bottom blowing stirring power is 1.0 kW / t or more,
Top blowing acid rate is 2.5 Nm ³ / min / t or more, treatment end point temperature is 1250 ° C. or more and 1400 ° C. or less, CaO / SiO _{2 in} the slag after treatment is 0.6 or more and 2.5 or less, T.I.
A method for dephosphorizing hot metal, characterized in that the Fe concentration is 10 to 20% by weight (Japanese Patent Application No. 05-165790), was proposed. The amount of flux basic unit such as quick lime is reduced to the minimum required amount according to the treatment temperature by giving a sufficiently large bottom-blown agitation so that the process proceeds, and (2) shortening the treatment time by increasing the acid transfer rate. Made it possible.

However, in the above-mentioned dephosphorization method, the bottom blowing stirring power can be calculated in advance from the amount of hot metal, the temperature of hot metal, and the flow rate of bottom blowing gas, and the rate of top blowing acid can be calculated in advance from the amount of hot metal. , CaO / SiO _{2 in} the slag after the treatment can be estimated from the flux amount and the hot metal component by a blending calculation, but the T.O. Regarding the Fe concentration, there is no relational expression among bottom-blown stirring power, top-blown acid feed rate / lance height, and slag composition, which is difficult to estimate before treatment, and it is known until the slag after treatment is analyzed. The reality was that there was nothing. Therefore, when changing the acid transfer rate, or when changing the amount of scrap used or the decarburization stop temperature in the converter, the temperature of the hot metal dephosphorization end point is changed from the heat balance, and CaO in the slag is changed accordingly. When changing SiO ₂ / SiO ₂ , the T. Fe is the target 1
It deviates from 0 to 20% by weight, (1) the target [P] level is not reached, (2) extra flux is added to prevent the [P] deviation, and the average value of the flux basic unit increases (3 ) There were often obstacles such as deterioration of iron yield.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a T.S. Predict the Fe concentration in advance, adjust the top-blowing acid feeding rate, lance height, and bottom-blown stirring power so that the concentration will be 10 to 20% by weight, and treat in a state where the dephosphorization reaction is optimized. Is carried out to accurately control the [P] concentration after the treatment, reduce the average flux basic unit, and suppress the reduction of the iron yield as much as possible.

That is, the present invention provides a hot metal dephosphorization method in which the [P] hit ratio after treatment is improved, the flux basic unit is reduced, and the decrease in iron yield is suppressed as much as possible.

[0010]

The gist of the present invention is as follows. When dephosphorizing and refining the hot metal by performing flux addition and oxygen top blowing and bottom blowing stirring,
Bottom blowing stirring power is 1.0 kW / t or more, top blowing acid feeding rate is 2.5 Nm ³ / min / t or more, C in slag after treatment
aO / SiO ₂ is 0.6 or more and 2.5 or less, and the treatment end point temperature is 1250 ° C. or more and 1400 ° C. or less. So that the Fe concentration is 10 to 20% by weight,
A method for dephosphorizing hot metal, which comprises controlling the rate of top blowing acid, the flow rate of bottom blowing gas, and the height of top blowing lance.

Slag T. Fe concentration (wt%) = 6.49 × (the top-blown ^{oxygen-flow-rate) (Nm 3 / min / t} ) -5.73 × ( bottom blowing agitation power) (kW / t) -15.35 × (L / L O) +9.68 | 2-CaO / SiO ₂ | +11.73 (1) The present invention is described in detail below. The present invention, first, after charging the hot metal into the converter with a bottom blowing function, the flux is added by upward or bottom blowing injection, blowing oxygen gas from the top blowing lance, while performing gas stirring from the bottom, Perform dephosphorization refining. At this time, Japanese Patent Application No. 05-1657
As shown in No. 90, the bottom blowing stirring power is 1.0 kW /
t or more, the rate of acid to be blown up is 2.5 Nm ³ / min / t or more, the treatment end point temperature is 1250 ° C. or more and 1400 ° C. or less, CaO / SiO _{2 in} the slag after treatment is 0.6 or more and 2.5 or less, T ． By setting the Fe concentration to 10 to 20% by weight, it becomes possible to perform the dephosphorization treatment in a short time while reducing the flux basic unit and suppressing the iron yield reduction as much as possible.

The present inventors have conducted various dephosphorization experiments and carried out T. The relationship between the Fe concentration, the top-blown acid flow rate, the lance height, the bottom-blown stirring power, and CaO / SiO _{2 in the} slag was investigated, and the relationship shown by the equation (1) was found from multiple regression analysis. T. in slag Fe concentration (wt%) = 6.49 × (the top-blown ^{oxygen-flow-rate) (Nm 3 / min / t} ) -5.73 × ( bottom blowing agitation power) (KW / t) -15.35 × (L / L O) +9.68 │2-CaO / SiO ₂ │ ＋ 11.73 (1) L: Depth of molten steel by top-blown jet (mm) L _O : Stationary molten steel depth (mm) Where, bottom-blown stirring power is formula (2) From (No. 101, 1
02nd Nishiyama Memorial Technical Lecture, Iron and Steel Institute of Japan, 1984,
p. 73) Use the calculated value.

[0013]

[Equation 1]

Further, L is a value calculated from the equation (3) (“Iron Metallurgical Reaction Engineering”, Nikkan Kogyo Shimbun, 1969, p.94). L = L _h · exp (−0.78 _h / L _h ) (3) L _h = 63.0 (kF _O2 / nd) ^2/3 h: Lance height (mm) from stationary surface k: Jet Interference coefficient (−) F _O2 : Top-blown oxygen flow rate (Nm ³ / h) n: Number of holes in lance (−) d: Hole diameter of lance (mm) T.S. in slack after treatment in various dephosphorization experiments. The T.F. calculated from the Fe concentration and the equation (1). The relationship with the Fe concentration is shown in FIG. According to the equation (1), the T. Fe concentration can be estimated very accurately, and Japanese Patent Application No. 05-16579
It has been clarified that it is possible to stably realize the efficient dephosphorization treatment condition in which the flux basic unit is reduced and the iron yield reduction is suppressed as much as shown in No. 0.

[0015]

EXAMPLE A dephosphorization experiment was carried out for 10 charges using an 8t test converter. Initial temperature 1180-130 containing 4.3-4.6% C, about 0.1% P, about 0.3% Si
About 6 tons of hot metal at 0 ° C. was refined for 6 minutes. Quick lime was used as a flux after calculating the blending ratio so that the CaO / SiO ₂ after treatment was 1.5. Top blowing acid rate is 2.5-
3.5 Nm ³ / min / t, bottom blowing is N ₂ gas 200,
Refining was carried out under two conditions of 300 Nm ^{3 /} h (2.0, 3.0 kW / t), and at that time, the T.S. calculated from the formula (1) was used. F
L / L ₀ is determined so that the e concentration becomes 15%, and (3)
The lance height was calculated from the formula. Further, the amount of scrap was appropriately mixed with the hot metal to be treated so that the hot metal temperature after the treatment was constant at 1350 ° C.

Tables 1 and 2 (continued from Table 1) show T.S. in slag calculated from the specifications in this embodiment and the equation (1). F
e Concentration and actual results Fe concentration, target [P] concentration and actual [P] concentration, iron yield, and quick lime basic unit are shown. T. in slag It can be seen that the Fe concentration is controlled to ± 2% of the calculated value. Further, the [P] concentration is less than or equal to the target [P] concentration in all the charges, which shows that the dephosphorization process is efficient with good controllability.

Table 3 shows the hit rate of the [P] concentration in this embodiment, that is, the ratio of achieving the target [P] concentration,
The variation of [P], that is, the average value of the deviation from the target [P] concentration, and the average value of quick lime basic unit and iron yield are shown. For comparison, each value in the conventional method 50 charge when the formula (1) is not used is also shown. Compared with the conventional method, the accuracy rate of [P] concentration is dramatically improved,
It was clarified that the variation in the amount of iron was reduced, the basic unit of quick lime was reduced, and the reduction of iron yield could be suppressed.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

According to the present invention, it is possible to improve the [P] hit rate after the treatment, reduce the flux basic unit, and improve the iron yield.

[Brief description of drawings]

FIG. 1 is a diagram showing T.S. in slag calculated by the equation (1). After the Fe concentration and the actual processing T. It is a figure which shows the relationship of Fe.

Claims (1)

[Claims] 1. When dephosphorizing and refining the hot metal by adding flux and performing oxygen top blowing and bottom blowing stirring, the bottom blowing stirring power is 1.0 kW / t or more, and the top blowing acid feeding rate is 2.5.
Nm ³ / min / t or more, CaO / S in slag after treatment
iO ₂ is 0.6 or more and 2.5 or less, and the treatment end point temperature is 125.
In the method for dephosphorizing hot metal, which is characterized in that the temperature is 0 ° C. or higher and 1400 ° C. or lower, in the slag T.V. calculated by the formula (1). A method for dephosphorizing hot metal, which comprises controlling a top-blown acid flow rate, a bottom-blown gas flow rate, and a top-blown lance height so that the Fe concentration is 10 to 20% by weight. T. in slag Fe concentration (wt%) = 6.49 × (the top-blown ^{oxygen-flow-rate) (Nm 3 / min / t} ) -5.73 × ( bottom blowing agitation power) (kW / t) -15.35 × (L / L O) +9.68 │2-CaO / SiO ₂ │ ＋ 11.73 (1) L: Depth of molten steel by top-blown jet L _O : Depth of stationary molten steel