JP2002129219A - Method for dephosphorizing molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for dephosphorizing molten iron without using halogenide, such as fluorite as the typical example. SOLUTION: In dephosphorizing the molten iron with lime and oxygen and/or iron oxide by using a refining furnace having a top-bottom combined-blown function, peculiarly, slag basicity is regulated to 0.8-1.8, (T.Fe) is regulated to 8-20 mass% and slag quantity is regulated to >=25 kg/t.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for performing refining that satisfies both prevention of melting of refractories and improvement of dephosphorization efficiency without using a halide represented by fluorite in hot metal dephosphorization.

[0002]

2. Description of the Related Art A method for dephosphorizing hot metal using quick lime and an oxidizing agent is widely used. When a topped car, which is a transport container, is used as a reaction container, the volume of the upper space (free board) is small, so that it has a high basicity and a low (T ·
In order to suppress slag forming as Fe), dephosphorization is performed in a large amount of lime per unit using hot metal that has been desiliconized in advance (for example, iron and steel, Vol. 69, 19).
1983, p. 1818). In this case, although desiliconization has been performed in advance, there is a problem that there are many dephosphorized slags because there are many lime basic units, and slagification is poor due to high basicity, such as fluorite and calcium chloride. Since it is necessary to use a large amount of halide, the amount of slag increases,
There is a problem that refractory erosion becomes severe.

[0003] Conventionally, attempts have been made to improve the reaction efficiency of hot metal dephosphorization without using a halide.

For example, Japanese Patent Application Laid-Open No. Hei 2-11712 discloses a dephosphorizing agent obtained by mixing iron oxide, CaO and SiO ₂ and melting or sintering them. JP-A-56-938
No. 06 discloses a basicity (CaO / SiO ₂ ) of 1.8.
A dephosphorizing agent is disclosed, which is obtained by sintering a powdery raw material which becomes 2CaO.SiO ₂ by being blended so as to be 2.3 to 2.3. In these cases, the cost required for melting or sintering is high, so that they have not been put to practical use.

[0005] Japanese Patent Application Laid-Open No. 8-157921 discloses a method for dephosphorizing hot metal in a converter mainly containing converter slag and iron oxide.
Basicity = 1.2-2.0, Al ₂ O ₃ = 2-16%, (T
A method of making Fe) = 7 to 30% is disclosed. In this case, since the reaction occurs only by the top slag due to the converter, the basicity of the top slag is reduced, and
There is a problem that a large amount of Al ₂ O ₃ , which is a neutral oxide, is added, so that the dephosphorization ability is greatly reduced. Examples include (T
e) shows only a result of 20% or more, and the slag specific unit calculated from the mass balance of CaO based on the description of the examples is 40 to 65 kg / t. However, although there is no description of the state of refractory erosion, in general, such high concentrations
In the case of (T.Fe), there is a problem that refractory erosion is extremely large. Further, under the condition that (T · Fe) is less than 20%, only 7% is described, but in this case, Al ₂ O ₃ is contained as much as 10.2%. Therefore, this is also a condition in which refractory erosion is large. Further, in this case, even if the phosphorus concentration after the treatment is lowered, (T.Fe)
Is too low, so that there is a problem that the dephosphorization efficiency is poor and the treatment requires a long time. In other words, refractory melting is inherently severe
Since only an example in which (T.Fe) is 20% or more and an example in which (T.Fe) having essentially poor dephosphorization efficiency is 7% or less are described, refractory melting is not performed. No assumption can be made about the conditions that satisfy both the loss and the dephosphorization efficiency.

[0006] By the way, the hot metal phosphorus concentration [%
A mass balance relationship as shown in equation (3) is established between P] ₀ , the concentration of the hot metal phosphorus [% P] _f after the dephosphorization treatment, and the phosphorus concentration (% P) _f in the slag. (% P) _f = 1000 × ([% P] ₀ − [% P] _f ) / SV (3)

[0007] Therefore, when the slag intensity changes, [%
Phosphorus distribution required for dephosphorization from [P] ₀ to [% P] _f (L = (%
P) _f / [% P] _f ) will change, and as can be seen from equation (4), if the slag basic unit SV is doubled, the required L becomes １ ／. L = {1000 × ([% P] ₀ − [% P] _f ) / SV} / [% P] _f ... (4)

However, on the other hand, it is said that the phosphorus distribution is represented by the formula (5) (JP-A-7-70626). logL = 2.51 · log (% T · Fe) + 0.0715 · [(% CaO) + 0.25 (% MgO)] + 7710.2 / T-8.55 + (105.1 / T + 0.0723) · [% C] · · …… (5)

[0009] Based on this formula, (% CaO) for reducing the phosphorus distribution to 1/2 is determined by temperature (T; K), carbon concentration ([% C];%), (% Mg
If the calculation is performed with O) kept constant, the value changes from 41% to 36%. However, this is only a decrease of about 10% as a unit of slag, and from the mass balance of equation (4), the phosphorus distribution is reduced by 1%.
This is inconsistent with the requirement of twice the slag basic unit to achieve / 2. In other words, as long as the slag is designed based on the relationship as in equation (5), the slag intensity cannot be a variable. Therefore, the lime intensity is adjusted based on a constant [Si] concentration in the hot metal before treatment. To control the dephosphorization. In this case, a desiliconization process was required to cope with fluctuations in the blast furnace tapping [Si] concentration, so capital investment was required.

[0010]

SUMMARY OF THE INVENTION According to the present invention, in the case of high basicity, low (T.Fe) treatment, which is a conventional technique, a large amount of lime is required and a large amount of halide is required for slagging. And CaO and S disclosed in JP-A-2-11712 and JP-A-56-93806.
iO In ₂ were mixed melted / sintered dephosphorization agent, a problem of high cost of melting or sintering, JP 8-157
No. 921 discloses a method of controlling the composition of top slag in hot metal dephosphorization in a converter, in which it is impossible to make any assumptions about conditions that satisfy both refractory erosion and dephosphorization efficiency. Based on the idea described in Japanese Patent Application Laid-Open No. 7-70626, the problem that a desiliconization process is required in order to obtain a constant [Si] concentration in the hot metal before treatment is solved, and refractory erosion is suppressed without using a halide. It is another object of the present invention to provide a hot metal dephosphorization method capable of increasing the dephosphorization efficiency.

[0011]

The gist of the present invention resides in the following methods. (1) In hot metal dephosphorization treatment with lime and oxygen and / or iron oxide using a refining furnace having a top and bottom blowing function, the slag basicity is 0.8 or more and 1.8 or less, and Is 8% or more and 19% or less by mass percent, and the slag specific unit is 25 kg / t or more. (2) In (1), [Si] concentration in hot metal before treatment Si
₀ (mass percent)
A hot metal dephosphorization method characterized by controlling t). (3) In (2), [Si] concentration in hot metal before treatment Si
_0. A hot metal dephosphorization method characterized by controlling the relationship between ₀ (mass percent) and the basic unit of slag SV (kg / t) so that α in formula (1) is not less than −15 and not more than 50. SV = α + 75 × Si ₀ (1) (4) In (1) to (3), the slag basicity B is controlled according to the slag basic unit SV (kg / t). Dephosphorization method. (5) In (4), the relationship between the slag basicity B and the slag basic unit SV (kg / t) is expressed by the equation (2) where β is 1.3 or more and 2.
A hot metal dephosphorization method, wherein the method is controlled to be 1 or less. B = β−0.006 × SV (2)

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is based on the finding that slag produced by a dephosphorization treatment has a sufficiently high dephosphorization ability if the composition satisfies certain conditions.

The hot metal dephosphorization treatment is a non-equilibrium system process that occurs between a slag phase having a high (FeO) and a high oxygen activity and a hot metal having a low oxygen activity close to carbon saturation. The equilibrium phosphorus distribution varies greatly depending on the oxygen activity at the slag / hot metal interface. For example, although FIG. 1 shows the results of thermodynamic calculations, oxygen activity of balancing in the slag and (FeO) 10 ^{- 2}
And the oxygen activity equilibrating with the carbon in the hot metal is 10 ^-4 , whereas the equilibrium phosphorus distribution greatly changes from 10 to 1000 by slightly changing the oxygen activity.

According to a detailed study by the present inventors, since the interfacial oxygen activity is close to the slag side, the distribution of phosphorus determined by the equilibrium relationship is very large. It was clarified that it was not determined by a mathematical expression that reflected the equilibrium relationship as represented by the expression.

In other words, the distribution of phosphorus after the hot metal dephosphorization treatment is not in an equilibrium relation, but means only a cross section of the process in which the dephosphorization proceeds. FIG. 2 shows the test result which shows this clearly. When the slag amount is the same, the phosphorus distribution increases linearly as the hot metal phosphorus concentration [% P] _f after the dephosphorization decreases. . When the concentration of hot metal phosphorus [% P] _f after the dephosphorization treatment is the same, the lower the [Si] concentration before the treatment, the higher the phosphorus distribution. In a normal operation in which the basicity is within a certain range, when the [Si] concentration before treatment is low, the amount of lime input is relatively small, so the amount of slag is small. If the hot metal phosphorus concentration [% P] _f after the dephosphorization treatment decreases, the phosphorus distribution shown in equation (4) corresponds to the phosphorus concentration in the slag in addition to the decrease in the denominator ([% P] _f ). ([% P] ₀ -[% P] _f ), which is a mass balance phenomenon in which the distribution of phosphorus is improved. Furthermore, if the amount of slag decreases due to a decrease in hot metal [Si] or the like, the phosphorus concentration in the slag is concentrated, resulting in an improvement in the distribution of phosphorus.

This means that, under the condition that the phosphorus distribution is determined not by the formula (5) but by the mass balance by an appropriate slag composition, the proper securing of the slag amount is the condition that enables the dephosphorization. It is to be.

There are several choices for the proper slag composition and amount.
However, the slag basicity B is 0.8 or more and 1.8 or less, (T · Fe)
8% or more and 19% or less in terms of mass percentage
By setting the SV to 25 kg / t or more, as shown in Table 1, fluorite
Dephosphorization without using halide represented by
Becomes Here, the slag basicity B is determined by CaO and SiO in the slag. _Two
Mass percentage of (CaO) / (SiO_Two). Haloge
By not using sulfides, the amount of slag is reduced,
It is possible to suppress the erosion of the refractory.

Usually, the amount of slag, the concentration of each component, and the basicity are controlled by the amount of auxiliary materials such as lime and iron oxide. The input amount can be adjusted based on the regression formula based on the past data of the refining, taking into account the hot metal component before treatment, the target value of the hot metal component after treatment, the amount and components of slag remaining from pretreatment. Adjustments are also possible.

Here, slag basicity B, (TF
e), the respective values of the slag basic unit SV, (CaO), and (SiO ₂ ) are the values at the end of the dephosphorization treatment. Indicates a value. The value at the end of the dephosphorization treatment is the analysis value after blowing, or
It refers to the value at the time of blow-off estimated from the analysis value before processing and the input amount. The analysis value after blowing is an analysis value of slag after supply of lime and oxygen and / or iron oxide for the purpose of dephosphorization is completed, and is performed by sampling with a sublance or the like. Alternatively, if new refining using the same slag is not performed after this point, sampling at tapping and sampling from a slag pan or slag yard after waste disposal are included. In the present specification, the mass percentage is simply indicated as “%”.

[0020]

[Table 1]

Here, Si ₀ is the Si concentration (mass%) in the hot metal before treatment, W _CaO is the lime basic unit (kg / t), (T.Fe) is the total iron concentration (mass%) in the slag, ( (CaO) and (SiO ₂ ) are CaO and SiO ₂ respectively.
Concentration in slag (mass%), B is basicity calculated by (CaO) / (SiO ₂ ), SV is slag basic unit (kg / t), [% P] _f is hot metal after dephosphorization P concentration (% by mass). Here, the basic unit of lime is calculated in consideration of not only the amount added from lime but also the CaO content entering the furnace from dolomite, decarburized slag, dephosphorized slag, and the like. Tables 2 and 3 are similar.

Table 1 shows the results of a test conducted in a 100 kg scale test bottom-blowing converter. The [P] concentration in the hot metal before treatment was 0.095% to 0.115%, and the temperature after treatment was 133.
It was 0 ° C or higher and 1420 ° C or lower. During the dephosphorization, quicklime and iron ore were added and oxygen was blown upward, but no fluorite was added. Also, the target value of [% P] _f 0.02 (wt
%) Was evaluated by ○ and ×.

From the above, when the slag basicity is lower than 0.8, the phosphoric acid activity increases, so that the phosphorus distribution determined by the equilibrium relationship decreases, and the phosphorus distribution is affected by the equilibrium relationship of the formula (5). If the efficiency decreases and the basicity is higher than 1.8,
Since the melting point of the slag increases and the liquid phase ratio decreases, the mass transfer rate in the slag decreases and the reaction rate decreases.

FIG. 3 shows the relationship between (T.Fe) and dephosphorization efficiency (K) when the basicity is 0.8 or more and 1.8 or less, and FIG. 4 shows the basicity when the basicity is 0.8 or more and 1.8 or less. 8 shows the relationship between (T.Fe) and the refractory erosion rate in the case of 8 or less. Here, the dephosphorization efficiency (K) is shown by equation (6), and the refractory erosion rate is the result of measuring the cross-sectional area of the refractory in contact with the slag before and after the treatment. K = ln (before treatment [% P] / after treatment [% P]) / lime unit consumption (6)

From the above, when (T.Fe) is lower than 8%, the melting point of the slag increases, and the distribution of phosphorus determined by the equilibrium relationship decreases due to the decrease in the interfacial oxygen activity (5). Dephosphorization efficiency is reduced due to the effect of the equilibrium relationship in the equation.
It can be seen that if it is higher than 9%, the refractory erosion rate increases. On the other hand, if it is 19% or more, the operation becomes difficult due to severe slag forming.

By satisfying the above slag condition, the distribution of phosphorus can be determined not by the formula (5) but by the mass balance. Therefore, it is efficient to secure the slag basic unit appropriately at 25 kg / t or more. Dephosphorization becomes possible. Here, the upper limit is not particularly defined, but is preferably 150 kg / t or less from the viewpoint of forming and yield. The effect of slag intensity is based on the following mechanism. First, the dephosphorization reaction mainly proceeds by the reaction between the iron particles suspended in the slag and the slag, so that the reaction interface area is controlled by the amount of the iron particles. Furthermore, since the amount of granular iron suspended in the slag increases in proportion to the slag basic unit, the larger the slag basic unit, the larger the reaction interface area,
As a result, the dephosphorization rate is increased. Slag basic unit is 25kg / t
If the amount is smaller than the above range, the amount of granular iron suspended in the slag is small, so that the reaction interface area decreases and the dephosphorization rate decreases.

The reason that the refining furnace has a top-bottom blowing function is that the iron particles suspended in the slag can be increased, the slag temperature can be made the same as the hot metal temperature, and the slag fluidity can be ensured. This is because the stirring is sufficiently strong and is not limited by the mass transfer rate of [P] in the hot metal. In the case of only top blowing, the stirring of hot metal is insufficient,
If the mass transfer rate of [P] is rate-limiting and the dephosphorization rate cannot be sufficiently increased, and only bottom-blowing is performed, the granular iron suspended in the slag cannot be increased sufficiently, and the slag temperature cannot be increased. Since the temperature is lower than the temperature, the slag fluidity cannot be secured, so that the dephosphorization rate cannot be sufficiently increased. As a refining furnace, a top-bottom blow converter is desirable, but there is no problem even if the ladle is shaped as long as it has a sufficient internal volume that does not overflow with slag. In addition, the top blown gas is desirably pure oxygen, and the bottom blown gas is oxygen, an inert gas,
Hydrocarbon gas is preferred.

As the hot metal dephosphorization treatment, lime and oxygen and / or
Or it was limited to the thing by iron oxide. Since the dephosphorization reaction is an oxidation reaction, both or both of oxygen and iron oxide are required as an oxidizing agent. Further, a basic oxide is required to reduce the activity of the generated phosphoric acid, but lime, which is the least expensive, is advantageous. The lime includes a case where CaO contained in decarburized slag and dephosphorized slag is reused in addition to quick lime and limestone. Iron ore, scale,
In addition to dust, the case where iron oxide contained in decarburized slag or dephosphorized slag is reused is also included. Fluorite and alumina used to lower the melting point of lime are not used because they cause refractory erosion. In particular, from the viewpoint of refractory erosion and the like, it is desirable that the F concentration in the slag be 0.1% or less and the alumina concentration be less than 2%.

The basic unit of slag is calculated by measuring the mass after the waste or by calculating the mass balance of CaO shown in the equation (7). Slag basic unit = (lime basic unit) / (in slag (% CaO) / 100) (7) Here, the lime basic unit is not only the amount added from lime but also dolomite, decarburized slag, It is calculated taking into account all the CaO content that enters the furnace from phosphorus slag and the like.

The [Si] concentration in the hot metal before the treatment is Si ₀
In this method, the slag basic unit SV (kg / t) is controlled according to (%). When the [Si] concentration is high, the supplied oxygen is [Si]
The lime is consumed for oxidation, and the quicklime is consumed for the production of calcium silicate, so that the dephosphorization efficiency decreases. However, as described above, the amount of granular iron suspended in the slag increases in proportion to the slag basic unit, so when the [Si] concentration is high, the slag basic unit is increased by increasing the amount of lime input, etc. Then, even if it is high [Si] hot metal, dephosphorization becomes possible without a decrease in phosphorus efficiency.

Claim 3 discloses the specific control conditions of claim 2, and as shown in FIG.
[Si] concentration in hot metal before treatment Si ₀ (%) and slag basic unit SV
This is a method of controlling the relationship with (kg / t) such that α in the expression (1) is not less than −15 and not more than 50. SV = α + 75 × Si ₀ (1)

Table 2 shows the results of a test carried out in a 100 kg scale test bottom-blowing converter. The [P] concentration in the hot metal before the treatment was 0.095 to 0.115%, and the temperature after the treatment was 1330 to 1430.
20 ° C. During the dephosphorization, quicklime and iron ore were added and oxygen was blown upward, but no fluorite was added. In the comparative example, a test in which silica sand was added together with quick lime to increase the slag basic unit, and a furnace was tilted 1-2 minutes after the start of dephosphorization blowing to reduce the slag basic unit, and a part of the slag was discharged. After slagging, a test in which dephosphorization blowing was restarted was performed. As in Table 1, the target value of [% P] _f 0.02 (wt
%) Was evaluated. Note that the SV lower limit is a calculated value when α is set to −15 in Expression (1), and the SV upper limit is a calculated value when α is set to 50 in Expression (1).

[0033]

[Table 2]

As shown in the comparative example, when silica sand is added to increase the slag basic unit, the dephosphorization does not proceed sufficiently because the dissolving speed of the massive silica sand into the slag is low, and the slag basic unit is reduced. In the case where waste is carried out in the middle to reduce the amount, the amount of iron in the slag is reduced, so that the reaction rate is reduced and adverse effects on dephosphorization due to oxidation of [Si] appear.

A fourth aspect is a method for controlling the slag basicity B according to the slag basic unit SV (kg / t). In the past, based on the concept that reflected the equilibrium relationship as shown in equation (5), phosphorus distribution was adjusted to a constant [Si] concentration before treatment, and lime intensity was adjusted, so slag intensity was a variable. I didn't get it. However, as described above, since the amount of granular iron suspended in the slag increases in proportion to the slag basic unit, the larger the slag basic unit, the more advantageous for dephosphorization. In other words, under the condition that the phosphorus distribution is not determined by the equation (5) but is determined by the mass balance, it means that the slag basicity can be reduced as the slag basic unit increases. Therefore, the dephosphorization treatment for controlling the basicity by the slag basic unit SV can be performed.

Claim 5 discloses specific conditions. The relationship between the basicity of slag B and the basic unit of slag SV (kg / t) is expressed by the formula (2) where β is 1.3 or more and 2. This is a method of controlling so as to be 1 or less. B = β−0.006 × SV (2)

Table 3 shows the results of a test carried out in a 100 kg scale test bottom-blowing converter. The [P] concentration in the hot metal before the treatment was 0.095 to 0.115%, and the temperature after the treatment was 1330 to 1430.
20 ° C. During the dephosphorization, quicklime and iron ore were added and oxygen was blown upward, but no fluorite was added. The lower limit B is a calculated value when β is set to 1.3 in the equation (2), and the upper limit B is a calculated value when β is set to 2.1 in the equation (2). The evaluation is the same as before and the target value of [% P] _f
The test was performed with the degree of reaching 0.02 (wt%).

[0038]

[Table 3]

If the basicity is low even in the same unit of slag, the liquidity of the slag increases and the fluidity increases,
As a result, the residence time in the slag phase of the granular iron generated from the molten iron bulk by the energy of the top blowing and the bottom blowing and suspended in the slag is shortened. Therefore, the dephosphorization rate does not increase sufficiently. Conversely, when the basicity is high even in the same unit of slag, the liquid phase ratio of the slag is reduced, so that the fluidity is reduced. As a result, the composition of the slag tends to be non-uniform.
Due to this, unslagified lime remains and (T.Fe) at the interface
Is reduced from the slag bulk, and the dephosphorization efficiency is not sufficiently increased.

[0040]

EXAMPLES The examples were carried out using a 6 ton scale top and bottom blown converter. A 4-hole lance of 7φ was used as the upper blowing lance, and the oxygen supply rate was 350 Nm ³ / h. The bottom was blown with a small diameter collecting tube tuyere and nitrogen was supplied at 22 Nm ³ / h.

Melted in another melting furnace, C: 4.15%,
Si: 0.45%, Mn: 0.23%, P: 0.11%,
About 6 tons of hot metal at S: 0.012% and a temperature of 1330 ° C. was charged into the converter, and dephosphorization refining was performed for 7 minutes. During the dephosphorization, 13.2 kg / t of quicklime and 16.4 kg / t of iron ore were fed from the upper bunker. After the treatment, C: 3.84%, Si:
0.01%, Mn: 0.08%, P: 0.017%, S:
The temperature was 1365 ° C. at 0.015%. The composition of the resulting dephosphorized slag is T • Fe: 16.3%, CaO: 32.1
%, SiO ₂ : 29.3% (slag basicity B = 1.10), P
₂ O ₅ : 4.97%, MnO: 5.55%, Al ₂ O ₃ : 1.32%,
MgO: 3.13%, CaF ₂ : 0.1% or less, about 41.2 kg / t
Was the amount. At this time, the slag basic unit SV calculated by the formula (1) is 18.8 or more and 83.75 or less, and the slag basicity B calculated by the formula (2) is 1.05 or more and 1.85 or less. According to the present invention, dephosphorization with less erosion of the refractory can be performed as compared with the treatment using a halide.

(Comparative Example) In the comparative example, the same 6-ton scale top-bottom blow converter as used in the example was used. Melted in another melting furnace, C: 4.25%, Si: 0.11%, Mn: 0.13
%, P: 0.105%, S: 0.011% and the temperature is 134.
About 6 tons of hot metal at 0 ° C is charged into the converter, and dephosphorization refining is performed in 7 minutes.
Minutes. During dephosphorization, 5.1 kg / t of quicklime and 15.1 kg / t of iron ore were fed from the upper bunker. After the treatment, C: 4.14%, Si: 0.02%, Mn: 0.18%,
P: 0.036%, S: 0.008%, temperature is 1332 ° C
Met. The composition of the resulting dephosphorized slag is T.Fe: 13.
3%, CaO: 23.5%, SiO 2: 22.1% ( slag basicity _{B = 1.06), PO 2.5:} 7.64%, MnO: 5.15%, Al
₂ O ₃ : 1.53%, MgO: 2.85%, and the specific unit of slag was about 20 kg / t. At this time, the slag basic unit SV calculated by the equation (1) is 6.75 or more and 58.25 or less, and the slag basicity B calculated by the equation (2) is 1.18 or more and 1.98 or less. The slag basic unit was small and dephosphorization was insufficient.

[0043]

According to the present invention, hot metal dephosphorization can be carried out without using a halide represented by fluorite.

[Brief description of the drawings]

FIG. 1 is a thermodynamic calculation result showing the relationship between oxygen activity and phosphorus distribution.

FIG. 2 is an experimental result showing the relationship between the phosphorus concentration after treatment and phosphorus distribution in the dephosphorization treatment.

FIG. 3 is an experimental result showing a relationship between (T.Fe) concentration in slag and dephosphorization efficiency during dephosphorization refining.

FIG. 4 is an experimental result showing the relationship between the (T.Fe) concentration in slag and the refractory erosion rate.

FIG. 5 is an experimental result showing an appropriate relationship between [Si] concentration before treatment and slag basic unit.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shinya Kitamura 20-1 Shintomi, Futtsu-shi Nippon Steel Corporation Technology Development Division F term (reference) 4K002 AB01 AB04 AC07 AD02 AE01 AE02 4K014 AA03 AB03 AB04 AC01 AC16 AC17 AD00 AD27

Claims (5)

[Claims] 1. A smelting furnace having a top-bottom blowing function,
In the hot metal dephosphorization treatment with lime and oxygen and / or iron oxide, the basicity of slag is 0.8 or more and 1.8 or less,
A hot metal dephosphorization method characterized in that Fe) is 8% or more and 19% or less in terms of mass percent, and the slag specific unit is 25 kg / t or more. 2. The hot metal dephosphorization method according to claim 1, wherein the slag basic unit SV (kg / t) is controlled according to the Si concentration Si ₀ (mass%) in the hot metal before treatment. 3. The relationship between the Si concentration Si ₀ (mass%) in the hot metal before treatment and the slag basic unit SV (kg / t) is expressed by
The hot metal dephosphorization method according to claim 2, wherein the control is performed so as to be 15 or more and 50 or less. SV = α + 75 × Si ₀ (1) 4. The slag basicity B is calculated based on the slag basic unit SV (kg).
4. Control according to / t).
The method for dephosphorizing hot metal according to any one of the above. 5. Slag basicity B and slag basic unit SV (kg)
The method of claim 4, wherein the relationship with (/ t) is controlled so that β in equation (2) is 1.3 or more and 2.1 or less. B = β−0.006 × SV (2)