JP2012207248A - Method for dephosphorizing molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for dephosphorizing molten iron that can stably prevent slopping during blowing.SOLUTION: In the method for dephosphorizing molten iron, when a top-blowing oxygen flowing amount is 1.5-4.0 Nm/min/molten iron t and a bottom-blowing Nflowing amount is 0.1-0.6 Nm/min/molten iron t using a top and bottom blown converter-type container, addition of quicklime and iron oxide is performed, slag basicity after treatment is 1.5-2.5, and coke powders are blown from a sublance to the slag during blowing. In the method, the blowing rate of the coke powders is set in a predetermined range specified by the top-blowing oxygen flowing amount and the sum of Si concentration and Ti concentration in the molten iron before treatment, and the blowing amount of the coke powders is set in a predetermined range which is set based on the blowing rate of the coke powders specified by the top-blowing oxygen flowing amount and the sum of the concentrations above.

Description

  The present invention relates to a method for preventing slopping in hot metal dephosphorization processing using gaseous oxygen or iron oxide using a converter-type refining vessel.

  In recent years, a method of melting low phosphorus steel by hot metal dephosphorization has become the mainstream. A method of dephosphorizing in a short time by using a converter-type container capable of top-bottom blowing and blowing gaseous oxygen onto the molten iron at high speed is often employed. Recently, there has been a demand for further shortening of the processing time by increasing the flow rate of gaseous oxygen.

  When the upper blown oxygen flow rate is increased, the amount of CO gas produced by the reaction between the oxygen gas blown up and [C] in the hot metal increases, and this CO gas is trapped in the slag and the slag is foamed. Becomes easier to form. Further, when the flow rate of the top blowing oxygen is increased and the generation rate of the CO gas is increased, the slag forming becomes excessively intense and the slag overflows from the furnace port. This overflow phenomenon is referred to as slopping and causes a decrease in dephosphorization workability, and its occurrence should be avoided.

  Here, when the CO gas generation speed is the same, the slag is more easily formed as the CO gas is more difficult to escape from the slag. Therefore, the composition of the slag produced during the hot metal dephosphorization treatment also has an important influence on the slag forming.

In this regard, the process [Si] in the pre-hot metal is oxidized during dephosphorization process, where incorporated into the slag as SiO _2, slopping is likely to occur when increasing the SiO ₂ concentration in the slag. That is, as the amount of [Si] in the hot metal before processing increases, slopping is likely to occur.

In addition, when increasing the basicity of slag, that is, the CaO / SiO ₂ ratio, in order to maintain the dephosphorization rate at a high value, the amount of quick lime to be added increases as the amount of [Si] in the hot metal before treatment increases, so the amount of slag to be generated also increases. Increase. Then, when the amount of CO gas contained in the slag unit volume is the same, the larger the slag amount, the larger the volume of the formed slag, so that the slag is easily slopped from the furnace port.

  In order to suppress the occurrence of such slopping, Patent Document 1 discloses a method of calming slag forming after dephosphorization blowing by blowing carbonaceous material into the slag using a sub lance.

Japanese Patent No. 3533955

  The method disclosed in Patent Document 1 is a method of calming slag forming after the completion of dephosphorization blowing, and the case where high-flow dephosphorization treatment is performed by increasing the top blowing oxygen flow rate or the hot metal composition before treatment, There is no disclosure of a solution for slopping during blowing, which is a problem when the Si] concentration is high.

  The object of the present invention is to add the sum of [Si] concentration and [Ti] concentration of hot metal composition before treatment under the condition that the slag composition is controlled within a certain range in hot metal dephosphorization using a top-bottom blow converter. It is to present a method capable of avoiding slopping during blowing when the flow rate is high or when the upper blown oxygen flow rate is increased to perform high-speed dephosphorization treatment.

The present inventors diligently studied to solve the above problems.
As a method of calming the slag forming during hot metal dephosphorization, a method of spraying coke powder from the sub lance to the slag during blowing is effective. The degree of calming of the slag forming does not depend only on the spraying speed and amount of the coke powder, but should also vary depending on the ease of forming the slag. Therefore, the present inventors paid attention to the top blowing oxygen gas flow rate and the slag composition as main factors affecting the ease of forming slag.

However, basicity (CaO / SiO ₂ ) in the slag composition has a very close relationship with the dephosphorization rate, and in the range of 1.5 to 2.5 in order to obtain a high dephosphorization rate at low cost. Must be controlled. In order to increase the basicity to more than 2.5, the amount of quick lime input increases, and the processing cost increases. On the other hand, when the basicity is less than 1.5, the dephosphorization ability of the slag is lowered, resulting in poor dephosphorization. In addition, [Si] density | concentration in hot metal is mentioned as a factor which has large influence on the dephosphorization process cost. When the [Si] concentration in hot metal increases, the amount of SiO ₂ produced during hot metal dephosphorization increases, so the higher the [Si] concentration in hot metal, the higher the required amount of quicklime and the higher the processing cost.

  Based on the above examination, when the basicity was set in the range of 1.5 to 2.5 and the hot metal dephosphorization experiment was carried out, even when the top blowing oxygen gas flow rate was the same, slapping occurred. The result that there was a case not to have been obtained. Thus, as a result of detailed investigation of the cause of slopping, it was found that not only the [Si] concentration in the molten iron but also the [Ti] concentration greatly affects the occurrence of slopping.

As described above, when the [Si] concentration in the hot metal increases, the concentration in the slag (SiO ₂ ) increases and the slag is easily formed. Further, if the slag basicity is the same, the amount of slag increases as the [Si] concentration in the hot metal increases, and slopping becomes easier. Furthermore, it has been found that the higher the concentration in the slag (TiO ₂ ) (in the present invention, the oxide produced by oxidizing [Ti] in the hot metal is referred to as “TiO ₂ ”), the easier the slopping.

Therefore, an experimental study described below was further performed in consideration of [Ti] in addition to [Si] as a hot metal component related to slopping.
Hot metal 270t was charged into the top bottom blowing converter, and the top blown oxygen flow rate was 1.3 to 4.2 Nm ³ / min / molten iron t, and the bottom blown N ₂ flow rate was 0.1 to 0.6 Nm ³ / min / molten iron t. Then, hot lime and iron oxide were added to perform hot metal dephosphorization. Here, the slag basicity after the treatment was 1.5 to 2.5, and the hot metal temperature in the pan after the treatment was 1290 to 1350 ° C.

As a result, when the sum R (= [% Si] + [% Ti]) of the [Si] concentration and [Ti] concentration in the hot metal was 0.2 or more, the top blowing oxygen flow rate was 1.5 Nm ³ / When min / molten iron t was exceeded, the result that slopping occurred during hot metal dephosphorization blowing was obtained. However, [Si] was 0.15 mass% or more, and [Ti] was 0.04 mass% or more.

Therefore, when coke powder (particle size of 0.3 mm or less) was sprayed onto the forming slag from the sublance inserted into the furnace during hot metal dephosphorization, slopping could be suppressed.
In addition, since the amount of CO gas produced | generated by a decarburization reaction will increase when a top blowing oxygen flow rate becomes large, slag forming is promoted and it becomes easy to perform a slopping. As a result, the higher the top blow oxygen flow rate, the higher the top blow speed and the top blow amount of coke powder required to suppress slopping. Here, the coke powder top blowing speed means a value obtained by dividing the amount of coke powder top blown by the time over which the coke powder was blown, that is, an average top blowing speed.

  In this way, when the confirmation experiment of the suppression of the slopping by the coke powder top blowing was conducted paying attention to the hot metal composition, the appropriate value of the coke powder blowing speed and the blowing amount is not only the top blowing oxygen flow rate but also the [Si] concentration in the hot metal. And [Ti] concentration were also found to be strongly dependent.

[Si] and [Ti] in the hot metal are oxidized by the top blown oxygen to become SiO ₂ and TiO ₂ , respectively, and are taken into the slag. As a result, the concentration of SiO ₂ and TiO _{2 in} the slag increased, and slag forming was promoted, and slopping was likely to occur. As a result, the higher the sum R of the concentrations of [Si] and [Ti] in the hot metal (= [% Si] + [% Ti]), The amount of top blowing also increased.

  Furthermore, as a result of repeated experimental investigations, when hot metal dephosphorization was performed in the top-bottom blowing converter, the appropriate values for the coke powder spraying speed V and spraying amount W for suppressing slopping from the sublance were determined. It can be quantitatively grasped as a function of the sum R (= [% Si] + [% Ti]) of Q and [Si] concentration and [Ti] concentration in the pre-treatment hot metal (the following formulas (1) to (5)). And the knowledge was obtained.

In addition, appropriate V is the range which satisfy | fills following formula (1)-(4) simultaneously.
W is an appropriate value within the range of four times the lower limit value V _min and the upper limit value V _max of the appropriate range of V described above.

−0.14 + 0.16 × Q ≦ V ≦ 0.27 + 0.82 × Q (1)
−0.25 + 1.75 × R ≦ V ≦ −0.26 + 3.81 × R (2)
1.5 ≦ Q ≦ 4.0 (3)
0.2 ≦ R ≦ 1.0 (4)
V _min ≦ W ≦ 4 × V _max (5)
Here, Q: top blowing oxygen flow rate (Nm ³ / min / molten iron t),
R: Sum (mass%) of [Si] concentration and [Ti] concentration in hot metal before treatment,
V: Coke powder top blowing speed (kg / min / molten iron t),
W: Coke powder top spray amount (kg / molten iron t),
V _min : the minimum value of V that simultaneously satisfies the above formulas (1) to (4), and
V _max : The maximum value of V that satisfies the above expressions (1) to (4) at the same time.

The present invention, which has been completed based on the above knowledge, uses an upper bottom blown converter type vessel, an upper blown oxygen flow rate of 1.5 to 4.0 Nm ³ / min / molten iron, and a bottom blown N ₂ flow rate of 0.1 to 0. Hot metal dephosphorization method in which quick lime and iron oxide are added as 6 Nm ³ / min / molten iron t, slag basicity after treatment is 1.5 to 2.5, and coke powder is blown from sub lance to slag during blowing In the hot metal dephosphorization method, the coke powder spraying speed V and the coke powder spraying amount W are within the ranges defined by the above formulas (1) to (5).

  According to the present invention, even when the sum of the [Si] concentration and the [Ti] concentration in the hot metal composition before processing is high or when the top blown oxygen flow rate is increased to perform high-speed dephosphorization processing, Can be stably avoided.

Hereinafter, the dephosphorization method according to the present invention will be described in detail with reference to examples.
In the dephosphorization method according to the present invention, the top blowing oxygen flow rate is a high flow rate of 1.5 Nm ³ / min / molten iron t or more, and the sum of [Si] concentration and [Ti] concentration in the molten iron before treatment is somewhat high. This is a method of effectively suppressing the occurrence of slopping even under conditions where it is particularly likely to occur. Therefore, the hot metal to be treated is one that satisfies the following compositional conditions.

0.2 ≦ [% Si] + [% Ti] ≦ 1.0
The concentration of other components in the hot metal is not particularly limited.
Carrying out the dephosphorization method according to the present invention, 1.5 Nm ³ / min / hot metal t can be blown over the oxygen in the above flow rate, bottom blowing _{N 2} flow rate of 0.1~0.6Nm ³ / min / hot metal t The equipment configuration is not particularly limited as long as it can be ensured that the coke powder can be sprayed from the sub lance to the slag. It is preferable that powdery quicklime can be supplied from the main lance together with oxygen.

Hot metal 270t was charged into the top bottom blowing converter, and the top blown oxygen flow rate was 1.3 to 4.2 Nm ³ / min / molten iron t, and the bottom blown N ₂ flow rate was 0.1 to 0.6 Nm ³ / min / molten iron t. Then, hot lime and iron oxide (scale) (about 15 kg / molten iron t) were added to perform molten iron dephosphorization treatment.

In some experiments, most of the quicklime was used as powder, and this powder was added by blowing oxygen gas containing 80% by mass or more of N ₂ or O ₂ from the top blowing lance onto the hot metal bath surface.

  The slag basicity after the treatment was 1.5 to 2.5. Further, the [Si] concentration in the hot metal before the treatment was 0.15% by mass or more, the [Ti] concentration was 0.01% by mass or more, and the [P] concentration was about 0.1% by mass.

During hot metal dephosphorization blowing, coke powder (particle size 0.3 mm or less) from sub lance to forming slag at a rate of 0.1 to 3.7 kg / min / molten iron, 0.06 to 14.8 kg / molten metal t Sprayed. Carrier gas of coke powder and _{N 2,} was 0.05~0.4Nm ³ / min / hot metal t. The coke powder spraying speed V (kg / min / molten metal t) / carrier N ₂ flow rate (kg / min / molten metal t) was set to 0 to 15. The case where V is 0 corresponds to the case where only N ₂ gas is sprayed without the coke powder being sprayed (Comparative Example 1). In this case, the N ₂ flow rate was 0.2 Nm ³ / min / molten iron t.

  In the evaluation, when the [P] concentration in the hot metal in the hot pot after treatment was less than 0.02% by mass and slopping did not occur during blowing, the hot metal after treatment was judged as good. The case where the amount of medium [P] was 0.02% by mass or more or slopping occurred during blowing was judged as inappropriate (“×” in the table).

  The results are shown in Tables 1 and 2.

Hereinafter, examples will be described in detail.
(Comparative Example 1)
Even if the top blown oxygen flow rate Q is the desired lower limit of 1.5 Nm ³ / min / molten iron t and the sum R of [Si] concentration and [Ti] concentration in the molten iron is as low as 0.2, during dephosphorization blowing Slapping has occurred. From this, it can be seen that, under the condition that Q is 1.5 Nm ³ / min / molten metal t or more and R is 0.2 or more, slopping will occur during blowing unless coke powder is blown up. It was.

(Invention Examples 1 to 4 and Comparative Example 2)
Even if Q is increased from 1.5 to 4.0 Nm ³ / min / molten iron t, coke powder is fed from the sub lance at a speed V within the range defined by the above formulas (1) to (4), and the above formula (5) By blowing the amount W within the range specified in the above to the forming slag, slopping during blowing can be avoided, and the [P] concentration after the treatment can also be made less than 0.02% by mass.

On the other hand, when Q is increased to 4.2 Nm ³ / min / molten iron t, the amount of coke powder from the sub lance is 1.6 kg / min / molten iron t close to the upper limit within the proper range, and the amount close to the upper limit of the proper range 6.5 kg. / Although hot metal t was sprayed onto the forming slag, slapping occurred during blowing.

As described above, the upper limit of Q for blowing up the coke powder from the sub lance to suppress the slopping during blowing was 4.0 Nm ³ / min / molten iron t.
(Invention Examples 5 to 9 and Comparative Example 3)
When the sum R of the [Si] concentration and [Ti] concentration in the hot metal is 1.0 or less, the coke powder is blown from the sub lance into the forming slag at a speed within the proper range. Slopping during smelting could be avoided, and the [P] concentration after treatment could be less than 0.02% by mass.

  On the other hand, when R is as high as 1.1, the coke powder is formed from the sub lance at a rate of 2.3 kg / min / molten iron t close to the upper limit within the proper range and an amount of 9.0 kg / molten iron t close to the upper limit of the proper range I sprayed it on the slag, but slapping occurred during blowing.

As described above, the upper limit of R for suppressing the slopping during blowing by blowing the coke powder from the sub lance was 1.0.
(Invention Examples 10 and 11 and Comparative Examples 4 and 5)
In the desired operating conditions, the speed is close to the lower limit value in the proper range at Q = 1.5 Nm ³ / min / molten iron t, R = 0.2, which is the most difficult condition for slopping. When hot metal t was sprayed to the forming slag with an amount of 0.11 kg / hot metal t close to the lower limit of the appropriate range (Invention Example 10), slopping during blowing could be avoided, and the [P] concentration after treatment was also It was made less than 0.02% by mass.

On the other hand, in the desired operating conditions, the speed is less than the lower limit value within the proper range at Q = 1.5 Nm ³ / min / molten iron t, R = 0.2, which is the most difficult condition to be slopped. When 0.05 kg / min / molten iron t was sprayed onto the forming slag at an amount in the appropriate range of 0.20 kg / molten iron (Comparative Example 4), slapping occurred during blowing.

  From this, it was found that slopping cannot be avoided unless coke powder is sprayed at an appropriate rate with respect to the CO gas generation rate for forming slag. The appropriate value of the coke powder spraying speed is the increase speed of the CO gas bubbles taken into the slag and the speed at which the CO gas bubbles taken into the slag with the coke powder blown from the sub lance are broken and released to the outside of the slag. It is determined by a balance.

On the other hand, in the desired operating conditions, the speed is close to the upper limit value in the proper range at Q = 4.0 Nm ³ / min / molten iron t, R = 1.0, which is the most easily slopping condition. When the amount of 14.0 kg / molten iron t, which is close to the upper limit of the appropriate range, was sprayed on the forming slag at / min / molten iron t (Invention Example 11), slopping during blowing can be avoided, and after treatment [P] The concentration could be less than 0.02% by mass.

On the other hand, the speed exceeding the upper limit within an appropriate range at Q = 4.0 Nm ³ / min / molten iron t, R = 1.0, which is the most easily slopping condition among the desired operating conditions. When 7 kg / min / molten iron t was sprayed onto the forming slag with an amount in the proper range of 7.4 kg / molten iron (Comparative Example 5), slapping occurred during blowing.

  The reason for this is not clear, but if the coke powder spraying speed is too high, the coke powder will not efficiently disperse into the forming slag and will collide with the hot metal bath surface and furnace wall, making it impossible to exert the effect of suppressing slopping. This is considered to be a cause.

(Invention Examples 12 and 13 and Comparative Examples 6 and 7)
In the desired operating conditions, the most difficult to slip, Q = 1.5 Nm ³ / min / molten iron t, R = 0.2, the speed close to the lower limit within the proper range 0.11 kg / min When hot metal t is sprayed to the forming slag with an amount of 0.11 kg / hot metal t close to the lower limit of the appropriate range (Invention Example 12), slopping during blowing can be avoided, and the [P] concentration after treatment is also It was made less than 0.02% by mass.

On the other hand, in the desired operating conditions, the speed is within the proper range at 0.10 kg / min at Q = 1.5 Nm ³ / min / molten iron t, R = 0.2, which is the most difficult condition to slopp. When 0.06 kg / molten iron t, which is less than the lower limit value of the appropriate range, was sprayed on the forming slag with / molten metal t (Comparative Example 6), slapping occurred during blowing.

  From this, it was found that even if the coke powder was sprayed at an appropriate rate with respect to the CO gas generation rate for forming the slag, slopping could not be avoided unless the coke powder was sprayed in an appropriate amount. In order to destroy the CO bubbles in the slag with the coke powder and suppress the slopping, the coke powder must be dispersed in the slag and stay in the slag for a certain period of time.

  As described above, coke powder reacts with slag (FeO) and is consumed. Therefore, in order to maintain the forming calming effect to some extent, it is necessary to put coke powder into the slag in an appropriate amount.

On the other hand, in the desired operating conditions, the speed is close to the upper limit value in the proper range at Q = 4.0 Nm ³ / min / molten iron t, R = 1.0, which is the most easily slopping condition. When the amount of 14.0 kg / molten iron t, which is close to the upper limit of the appropriate range, was sprayed on the forming slag at / min / molten iron t (Invention Example 13), slopping during blowing can be avoided, and after treatment [P] The concentration could be less than 0.02% by mass.

On the other hand, the speed is 3.5 kg / min within an appropriate range at Q = 4.0 Nm ³ / min / molten iron t, R = 1.0, which is the most easily slopping condition among the desired operating conditions. When 14.8 kg / molt iron of 14.8 kg / molten iron t was sprayed onto the forming slag with / molten iron t (Comparative Example 7), slopping during blowing could be avoided, but the [P] concentration after treatment was 0 It rose to 0.023 mass% and it became poor dephosphorization.

If the coke powder is added in an appropriate amount or more, the concentration in the slag (FeO) is reduced more than necessary with the coke powder, resulting in poor dephosphorization.
(Invention Examples 14 to 16 and Comparative Example 8)
By setting the slag basicity after treatment to 1.5 to 2.5, [P] after treatment was less than 0.02% by mass even when coke powder was blown from the sub lance within appropriate conditions.

  On the other hand, when the slag basicity after the treatment is lowered to 1.4, even if the coke powder is blown up from the sub lance within an appropriate condition, the [P] after the treatment rises to 0.022% by mass and dephosphorization occurs. It became defective. The coke powder blown from the sub lance can suppress the slopping by destroying the CO bubbles in the slag. At that time, (FeO) in the slag reacts with C in the coke, and the (FeO) concentration in the slag is reduced. It will decline.

  In order to obtain a high dephosphorization rate, the basicity of the slag must be increased and the concentration of (FeO) in the slag must also be increased. And when the basicity of slag is low, it is necessary to raise especially the (FeO) density | concentration in slag. Therefore, when the coke powder is sprayed from the sub lance when the slag basicity is low and the (FeO) concentration in the slag is lowered, dephosphorization is poor.

(Invention Examples 17 and 18)
40% by mass or 100% by mass of quick lime used for hot metal dephosphorization blowing is powder (particle size 0.2 mm or less), oxygen gas containing 80% by mass or more of O ₂ is used as carrier gas, and this powder is blown. During the smelting, it was added by spraying from the top blowing lance to the hot metal bath surface. Coke powder was sprayed from the sub lance under conditions within the proper range.

  As a result, it was possible to avoid slopping during blowing and to reduce [P] to 0.01% by mass or less after the treatment. This is because the quick-blown quicklime powder quickly dissolved into the slag and contributed sufficiently to the dephosphorization reaction.

Claims (1)

Using an upper bottom blown converter type vessel, the top blown oxygen flow rate was 1.5 to 4.0 Nm ³ / min / molten iron t, the bottom blown N ₂ flow rate was 0.1 to 0.6 Nm ³ / min / molten iron t, In the hot metal dephosphorization method in which iron oxide is added and the slag basicity after treatment is 1.5 to 2.5 and the coke powder is sprayed from the sub lance to the slag during blowing, the coke powder spraying speed V and the coke powder spraying amount A hot metal dephosphorization method characterized in that W is within a range defined by the following formulas (1) to (5).
−0.14 + 0.16 × Q ≦ V ≦ 0.27 + 0.82 × Q (1)
−0.25 + 1.75 × R ≦ V ≦ −0.26 + 3.81 × R (2)
1.5 ≦ Q ≦ 4.0 (3)
0.2 ≦ R ≦ 1.0 (4)
V _min ≦ W ≦ 4 × V _max (5)
Here, Q: top blowing oxygen flow rate (Nm ³ / min / molten iron t),
R: Sum (mass%) of [Si] concentration and [Ti] concentration in hot metal before treatment,
V: Coke powder top blowing speed (kg / min / molten iron t),
W: Coke powder top spray amount (kg / molten iron t),
V _min : the minimum value of V that simultaneously satisfies the above formulas (1) to (4), and
V _max : The maximum value of V that satisfies the above expressions (1) to (4) at the same time.