JPH11323420A - Pretreating method for molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the reduction of the amt. of steel making slag to be generated and the recycling of decarburized slag and dephosphorized slag by regulating the basicity of slag to a specified range and regulating the total oxygen feeding rate at the time of desiliconizing to a specified range. SOLUTION: In desiliconizing treatment for molten iron, by regulating the basicity of slag to 1.0 to 3.0 and the total oxygen feeding rate to 0.4 to 2.5 Nm<3> /min/ton, high desiliconizing efficiency can be obtd. even in a low [Si] region. The regulation of the basicity can be executed by using decarburized slag and dephosphorized slag. in the case in which molten iron in the following charge is charged without discharging the decarburized slag in the former charge, and desiliconizing treatment is executed, by controlling the basicity of slag and the total oxygen feeding rate to this proper ranges and executing the operation, rephosphorizing is suppressed, desiliconizing treatment to a low Si region is executed, and at the point of time in which [Si] reaches <=0.2%, at least a part of slag is discharged, and successively, dephosphorizing refining and decarburizing refining are continued, by which the amt. of steel making slag to be generated can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot metal pretreatment method for performing efficient desiliconization down to a low [Si] region.

[0002]

2. Description of the Related Art In recent years, waste regulations have tended to be tightened due to global environmental problems, and the need to reduce the amount of steelmaking slag generated has increased. In order to realize this, it is necessary to strengthen the desiliconization treatment and reduce the hot metal [Si] at the time of shifting to the next step of dephosphorization or decarburization to, for example, 0.15% or less. Furthermore, the high basicity slag generated by the dephosphorization or decarburization treatment is difficult to reuse due to the problem of powder expansion due to the large amount of unslagged CaO, and is converted to low basicity slag and discharged. It is necessary. To this end, it is conceivable to recycle the decarburized slag or dephosphorized slag to a desiliconization treatment to reduce the basicity.
There is a problem that ₂ O ₅ ) returns to hot metal.

[0003] Hot metal desiliconization technology in the pretreatment of the iron making process and / or the steel making process is widely used.
It is widely known that the reaction efficiency decreases as i] decreases. (For example, Iron and Steel, 67th year, 1981
Year, Vol. 16, p. 2675-) In addition, the desiliconization efficiency in the low Si region is reduced, and a decarburization reaction is caused to cause severe slopping.

[0004] For example, Japanese Patent Application Laid-Open No. 57-92117 discloses a desiliconization method in which the basicity of the produced slag is 0.5 to 1.5. This publication discloses that the slag (T.Fe) decreases as the basicity increases, so that the oxidation loss of hot metal [Mn] is suppressed. However, [Si] after the treatment is as high as about 0.3%, and there is no disclosure of behavior in a low Si region.

Japanese Patent Application Laid-Open No. Sho 63-241105 discloses that a high basicity slag having a basicity of 3 or more generated in a hot metal dephosphorization step is stored in a hot metal receiving vessel, and hot metal from a blast furnace is received in this vessel. A technique is disclosed for performing pig iron and desiliconizing the molten iron. This publication discloses that when the basicity of the desiliconized slag increases, the Mn distribution decreases and the hot metal [Mn] increases, and as an example, the basicity is shown to about 2.8. . However, there is no description about [Si] after the treatment, and no description is given of the behavior in the low Si region.

On the other hand, JP-A-8-92614 discloses that
A method is disclosed in which a hot metal that has been subjected to dephosphorization and desulfurization treatment is discharged in a vessel, and then the hot metal that has been subjected to desiliconization treatment in a blast furnace casting bed while leaving slag is received. However, although not described in this publication, this method has a problem in that rephosphorization accompanying a decrease in slag basicity is unavoidable, and the load of the dephosphorization treatment in the next step increases.

[0007]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 57-92 is disclosed.
In the methods disclosed in JP-A-117-117 and JP-A-63-241105, there is no description about the behavior in the low Si region, and there is no known method for improving the reaction efficiency in the low Si region. There is no problem. Also,
The method disclosed in Japanese Patent Application Laid-Open No. 8-92614 has a problem that rephosphorization due to a decrease in basicity cannot be avoided. An object of the present invention is to solve these problems and realize efficient desiliconization up to the low Si region, thereby reducing the amount of steelmaking slag generated and recycling decarburized slag and dephosphorized slag. To provide a way to make it possible.

[0008]

The gist of the present invention for solving the above problems lies in the following methods. (1) In the desiliconization treatment of hot metal, the slag basicity is set to 1.0
To 3.0, and the total oxygen supply rate during desiliconization is 0.4 to
A hot metal pretreatment method characterized by 2.5 Nm ³ / min / ton.

(2) The method for pretreatment of molten iron according to (1), wherein the slag basicity is controlled using decarburized slag. (3) The hot metal pretreatment method according to (1), wherein the slag basicity is controlled using dephosphorized slag. (4) In (2), when performing desiliconization, dephosphorization, and decarburization treatment using a converter, the molten iron of the next charge is charged and desiliconization is performed without discharging the decarburized slag of the previous charge. A hot metal pretreatment method comprising: performing a treatment, discharging at least a portion of the slag when the molten iron [Si] becomes 0.2% or less, and continuing dephosphorization refining and decarburization refining.

(5) In (3), when performing desiliconization and dephosphorization treatment using a converter, the next charge of hot metal is charged and desiliconization is performed without discharging the dephosphorization slag of the previous charge. A hot metal pretreatment method characterized by performing a treatment, discharging at least a part of the slag when the molten iron [Si] becomes 0.2% or less, and continuing the dephosphorization refining. Here, the basicity is defined as (% CaO) and (% SiO ₂ ) in the slag.
(% CaO) / (% SiO ₂ ). If slag analysis is not performed, it can be obtained by calculating the material balance based on the amount of desiliconization and the specific unit of quicklime. The total oxygen supply rate is the sum of all oxygen supplied as oxygen gas or iron oxide.
Seek in terms of Nm ^3. The supply method is the total sum of all of the spraying, regardless of the top blowing, upward addition, injection, and the like. The decarburized slag means slag generated by converter refining, and the dephosphorized slag means slag generated by hot metal dephosphorization using a quicklime-based flux.

In the present invention, decarburized slag is defined as slag basicity (C
The weight ratio of aO to SiO ₂ is 3.0 to 5.0, the slag (T.Fe) is preferably 7 to 30%, the (P ₂ O ₅ ) is preferably 6% or less. Are slag basicity of 1.0 to 5.0, (T.Fe) of 1 to 15%, (P ₂ O
₅ ) is preferably 3 to 8%.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The desiliconization reaction of the present invention will be described. The present inventors have found from a large number of experimental results that it is important to increase the slag basicity and increase the oxygen supply rate in order to efficiently desiliconize up to the low Si region. Generally, the desiliconization reaction is described by the following formula (1), and the reaction rate: K is given by the following formula (2). Also,
When iron oxide or oxygen gas is supplied to hot metal as an oxygen source for desiliconization, a decarburization reaction proceeds simultaneously with desiliconization.

[Si] +2 (FeO) = (SiO ₂ ) + 2Fe (1) K = d [Si] / dt = (kA / V) × ([Si] − [Si] ₀ ) (2) Here, k is the overall mass transfer coefficient, A is the reaction interface area, V is the volume of molten steel, and [Si] ₀ is the equilibrium value of [Si] in the hot metal. it can. Also,
k is the mass transfer coefficient on the metal side; km, the mass transfer coefficient on the slag side; ks, the distribution ratio; L (= (Si) ₀ / [S
i] ₀ ) and is expressed by equation (3). Here, (S
i) ₀ is the equilibrium value of (Si) in the slag.

1 / k = 1 / km + 1 / (L × ks) (3) In the high Si region at the beginning of the desiliconization reaction, [S
i] is large, the reaction is easy to proceed, and (FeO) can be maintained at a high level without being reduced by decarburization because it is thermodynamically prioritized over decarburization. , K are governed by the mass transfer coefficient km on the metal side.

However, in the low [Si] region, decarburization is prioritized thermodynamically, so (FeO) is reduced by decarburization. As a result, L in equation (3) becomes small, and k becomes It becomes dominated by mass transfer on the slag side. The slag-side mass transfer coefficient ks is given by:
It is smaller by one digit or more due to viscosity and diffusion coefficient. For this reason,
The reason why the desiliconization stagnates in the low Si region is not only that the driving force of the reaction decreases, but also that k decreases.

The present inventors have made the present invention as a method for increasing the overall mass transfer coefficient k in the low [Si] region, and have realized this by appropriately controlling the basicity and the total oxygen supply rate. In other words, by appropriately controlling the basicity, the melting point is low, and the viscosity is low.By controlling the total oxygen supply rate, the decarburization reaction can proceed properly, and the CO gas generated during decarburization can be used. The slag is stirred to increase k. 1 and 2 show the experimental results. From these figures, when the basicity is too low, the desiliconization efficiency does not increase because the slag has a high viscosity even if it has a low melting point. on the other hand,
When the basicity is too high, the liquid phase has a low melting point but a high melting point, so that the solid phase is crystallized, so that the slag as a whole becomes highly viscous and the desiliconization efficiency decreases. Furthermore, if the total oxygen supply rate is too low, the decarburization reaction does not proceed, and the slag is not sufficiently stirred, and the desiliconization efficiency decreases.If the total oxygen supply rate is too high, excessive decarburization occurs. As it proceeds, severe slag forming occurs, and processing cannot be continued. Also, the total oxygen supply rate is appropriate,
In addition, when the basicity is appropriate, the (FeO) concentration of the slag is about 3 to 7%, and the activity is large, so that the slag has good reactivity and synergistically favors desiliconization. I do.

The desiliconization efficiencies in FIGS. 1 and 2 are as follows.
The desiliconization oxygen efficiency represented by equation (4) is obtained.
0.35 to 0.45% before treatment [Si], after treatment [Si]
Is a treatment of 0.07 to 0.14%. Desiliconization efficiency = (Before treatment [% Si]-After treatment [% Si]) x 11.42 x 100 / oxygen basic unit (kg / t) ... (4) Means for increasing the basicity of the desiliconized slag As a raw stone
Although the method of adding ash is common, it is expensive.
Use decarburized slag in converter and dephosphorized slag in hot metal dephosphorization
Is advantageous in terms of cost. But these
(P _TwoO_Five) Is included in hot metal during desiliconization
When phosphorus is restored, desiliconization proceeds efficiently, but results and
The dephosphorization width in hot metal dephosphorization and converter decarburization has increased,
As a result, the cost will increase.

However, the proper salt defined by the present inventors
Treatment at a basic and appropriate total oxygen supply rate will reduce phosphorus reversion
And efficient desiliconization becomes possible. Reaction rate of phosphorus reversion reaction;
Kp also has a reaction rate similar to the above formulas (2) and (3).
It is expressed by the following equations (5) and (6). Kp = −d [P] / dt = (kp · A / V) × ([P] − [P]₀) (5) 1 / kp = 1 / kmp + 1 / (Lp × ksp) (6) where kp is the overall mass transfer coefficient, A is the reaction area, and V
Is the volume of molten steel, [P]₀Is the equilibrium value. Also, kmp is
Mass transfer coefficient on metal side, ksp is mass transfer on slag side
The coefficient, Lp, is the distribution ratio. Field of rephosphorization reaction during hot metal desiliconization
In the case, [P] ₀Is higher than [P] and the reaction is minor.
The feature is that it moves in the direction of₀Is the difference
Small and Lp large, so the metal side
Mass transfer rate will have a significant effect. Accordingly
Therefore, the mass transfer on the slag side for desiliconization as shown in the present invention
The operation that promotes movement does not have the effect of promoting phosphorus reversion,
Conversely, hot metal [P] to increase slag (FeO)₀The low
And even dephosphorization is possible.

The reasons for limiting the numerical values of the present invention will be described below. In claim 1, the reason for setting the slag basicity to 1.0 to 3.0 and the total oxygen supply rate to 0.4 to 2.5 Nm ³ / min / ton is as follows.
This is because, as shown in FIGS. 1 and 2, a high desiliconization efficiency can be obtained even in a low [Si] region only when these two conditions are compatible. Claims 2 and 3 are cases where the basicity is adjusted using decarburized slag and dephosphorized slag. As shown in FIG. 3, as shown in claim 1, the total oxygen supply rate is set to 0.4 Nm. ³ / min / to
By making n or more, phosphorus reversion can be suppressed. However, 2.5
If it is larger than Nm ³ / min / ton, processing becomes difficult due to slopping.

The amount of decarburized slag and dephosphorized slag added is determined by the slag basicity after desiliconization according to the hot metal [Si] concentration before treatment and the basicity of the decarburized slag and dephosphorized slag. Is determined by the material balance calculation so as to fall within the range. Claim 4 defines the process conditions when performing desiliconization, dephosphorization, and decarburization using a converter. In other words, in the case where the decharging treatment is carried out by charging the hot metal of the next charge without discharging the decarburized slag of the previous charge, the dephosphorization is suppressed by operating under the conditions described in claim 1 and the low Si region By performing the desiliconization treatment up to [Si] is reduced to 0.2% or less, at least a part of the slag is discharged, and the dephosphorization refining and the decarburization refining are continued. Can be suppressed.

If slag is discharged while [Si] is higher than 0.2%, there is a problem that the amount of slag in dephosphorization refining or decarburization refining increases. The lower limit is not specified, but
If the content of [Si] is less than 0.03%, the desiliconization efficiency starts to decrease, so it is preferable that the content is 0.03% or more. [S
When i] becomes 0.2% or less, the entire amount of slag discharged may be sufficient.

The amount of decarburized slag remaining in the furnace at the time of charging the hot metal of the next charge is determined by the slag basicity after desiliconization according to the hot metal [Si] concentration before treatment and the basicity of the decarburized slag. It is desirable to determine by material balance calculation so that it is within the range,
Hot metal [Si] is 0.3-0.9% and the amount of decarburized slag is 15-
If it is 40 kg / t, there is no problem even if the whole amount is left. Claim 5 defines the process conditions when performing the desiliconization and dephosphorization using a converter. In other words, when the decharging treatment is carried out by charging the hot metal of the next charge without discharging the dephosphorization slag of the previous charge, the dephosphorization is suppressed by operating under the conditions shown in claim 1 to reduce the low Si region. When the [Si] becomes 0.2% or less, at least a part of the slag is discharged, and the dephosphorization refining is continued to suppress the amount of steelmaking slag generated. it can.

If slag is discharged while [Si] is higher than 0.2%, there is a problem that the amount of slag in dephosphorization refining or decarburization refining increases. The lower limit is not specified, but
If the content of [Si] is less than 0.03%, the desiliconization efficiency starts to decrease, so it is preferable that the content is 0.03% or more. [S
When i] becomes 0.2% or less, the entire amount of slag discharged may be sufficient.

The amount of dephosphorized slag remaining in the furnace at the time of charging the hot metal of the next charge is determined by the slag basicity after desiliconization according to the hot metal [Si] concentration before treatment and the basicity of the dephosphorized slag. It is desirable to determine by material balance calculation so that it is within the range,
Hot metal [Si] is 0.3-0.9% and the amount of dephosphorization slag is 25-
If it is 50 kg / t, there is no problem even if the whole amount is left. Hereinafter, the present invention will be described in more detail based on examples.

[0025]

EXAMPLES Example 1 Example 1 was carried out in a test converter. Top blowing lance is 8
A water-cooled Laval nozzle with a single hole of mmφ was used, and 150 Nm ³ / Hr was sprayed. Nitrogen gas was blown at 10 Nm ³ / Hr from the tuyere of the single tube and stirred for bottom blowing. C: 4.3%, Si: 0.35%, Mn:
About 6 tons of hot metal having a temperature of 1450 ° C. and 0.31%, P: 0.105%, and S: 0.032% were charged into the converter, and 2 Nm ³ / t of top-blown oxygen gas was supplied to the converter. 12.2 kg / t of iron ore (2 Nm ³ / t in terms of oxygen) and 1 lime from the bunker
1 kg / t was added. The treatment time was 5 minutes, and the total oxygen supply rate was 0.8 Nm ³ / min / ton. The basicity of the slag after the treatment was 1.7, the [Si] after the treatment was 0.07%, the desiliconization efficiency was as high as 56%, and a stable treatment without slag forming was performed.

Example 2 This Example 2 was carried out in a test converter under the same conditions as in Example 1 described above. While leaving about 25 kg / t of decarburized slag generated by the pre-charge, C: 4.2%, Si: 0.36%,
Mn: 0.30%, P: 0.101%, S: 0.035
% Hot metal about 6t in temperature 1440 ° C. was charged to the converter at while supplying top-blown oxygen gas 2 Nm ³ / t, 2 Nm iron ore from the furnace on the bunker at 12.2 kg / t (oxygen converted ³ / t) Added. The treatment time is 5 minutes, and the total oxygen supply rate is 0.8 Nm ³ /
min / ton. The basicity of the slag after treatment is 2.1,
After treatment [Si] is 0.06%, and after treatment [P] is 0.16%.
At a rate of 05%, the desiliconization efficiency was as high as 60%, there was little phosphorus reversion, and a stable treatment without slag forming could be performed. Further, the produced slag had no unslagged lime and had a property of little powder expansion.

Example 3 Example 3 was carried out in a test converter under the same conditions as in Example 1 described above. C: 4.5%, Si: 0.36%, with about 35 kg / t of dephosphorized slag generated by the pre-charge remaining.
Mn: 0.29%, P: 0.106%, S: 0.030
% Of hot metal at a temperature of 1465 ° C. was charged into the converter, and 2.2 Nm ³ / t of top-blown oxygen gas was supplied, while iron ore was 12.2 kg / t (2 Nm in terms of oxygen) from the furnace bunker. ³ / t) was added. The treatment time is 5 minutes and the total oxygen supply rate is 0.8
It was 4 Nm ³ / min / ton. The basicity of the slag after the treatment is 2.
65, after treatment [Si] is 0.07%, after treatment [P]
Was 0.106%, the desiliconization efficiency was as high as 59%, and stable treatment without phosphorus reversion and without slag forming could be performed. Further, the produced slag had no unslagged lime and had a property of little powder expansion.

Comparative Example 1 This Comparative Example 1 was also performed in a test converter under the same conditions as in Example 1 described above. C: 4.3%, Si: 0.34%, Mn:
About 6 tons of hot metal of 0.32%, P: 0.105%, S: 0.030% and a temperature of 1450 ° C. are charged into the converter, and ³ Nm ³ / t of top-blown oxygen gas is supplied to the converter. 18.3 kg / t of iron ore ( ³ Nm ³ / t in terms of oxygen) and 3 of quicklime from a bunker
kg / t was added. The treatment time was 7.5 minutes, and the total oxygen supply rate was 0.8 Nm ³ / min / ton. The basicity of the slag after the treatment is 0.6, the [Si] after the treatment is 0.15%, and the desiliconization efficiency is low at 25%. Was intensely difficult to operate.

Comparative Example 2 This Comparative Example 2 was also performed in a test converter under the same conditions as in Example 1 described above. C: 4.7%, Si: 0.37%, C: 4.7%
Mn: 0.24%, P: 0.100%, S: 0.025
% Of hot metal at a temperature of 1445 ° C. is charged into a converter, and while supplying top-blown oxygen gas at 3.0 Nm ³ / t, 18.3 kg / t of iron ore (3 Nm in terms of oxygen) is supplied from an on-furnace bunker. ³ / t) was added. The treatment time was 20 minutes, and the total oxygen supply rate was 0.1 minute.
It was ³ Nm ³ / min / ton. The basicity of the slag after the treatment is 2.
61, the treated [Si] was 0.15%, and the desiliconization efficiency was 2%.
It was as low as 9%, and after the treatment, [P] was restored to 0.184%.

[0030]

According to the hot metal pretreatment method of the present invention, low S
By realizing efficient desiliconization up to the i-th region, it was possible to reduce the amount of steelmaking slag generated and to recycle decarburized slag and dephosphorized slag.

[Brief description of the drawings]

FIG. 1 shows a total oxygen supply rate of 0.8 to 1.2 Nm according to the present invention.
It is a figure which shows the relationship between the desiliconization efficiency and slag basicity in the case of ³ / min / ton.

FIG. 2 is a graph showing the relationship between the desiliconization efficiency and the total oxygen supply rate when the basicity is 1.5 to 1.8 according to the present invention.

FIG. 3 is a graph showing the relationship between the amount of reconstituted phosphorus and the total oxygen supply rate when the basicity is 1.5 to 1.8 according to the present invention.

Claims (5)

[Claims] 1. In the desiliconization treatment of hot metal, the slag basicity is set to 1.0 to 3.0, and the total oxygen supply rate at the time of desiliconization is set to 0.4 to 2.5 Nm ³ / min / ton. A hot metal pretreatment method characterized by the following. 2. The hot metal pretreatment method according to claim 1, wherein the slag basicity is controlled using decarburized slag. 3. The hot metal pretreatment method according to claim 1, wherein the slag basicity is controlled using dephosphorized slag. 4. The method according to claim 2, wherein the silicon is desiliconized using a converter.
In the case of performing dephosphorization and decarburization, hot metal of the next charge is charged and desiliconization is performed without discharging the decarburized slag of the previous charge, and the hot metal [Si] is reduced to 0.2% or less. A hot metal pretreatment method, comprising discharging at least a part of the slag at the time when the slag becomes dephosphorized and continuing dephosphorization refining and decarburization refining. 5. The method according to claim 3, wherein the desiliconization is performed using a converter.
When performing the dephosphorization treatment, the hot metal of the next charge is charged without removing the dephosphorization slag of the previous charge and desiliconization treatment is performed, and when the molten iron [Si] becomes 0.2% or less. A method for pretreating molten iron, comprising discharging at least a part of the slag and continuing dephosphorization refining.