JP5803837B2 - Method of desiliconization and dephosphorization of hot metal - Google Patents

Description

  The present invention does not use fluorine-containing auxiliary materials when desiliconizing and dephosphorizing hot metal in a converter, and it realizes high dephosphorization performance in a short time at a low cost by suppressing slopping and spitting. The present invention relates to a desiliconization and dephosphorization method for molten iron.

  In recent years, the ratio of the converter steelmaking process divided into hot metal preliminary dephosphorization and hot metal decarburization has increased in response to the growing need for low phosphatization of steel products and the need to increase the efficiency of its manufacturing process. doing. In addition, reducing the burden on the global environment through the steelmaking process is becoming increasingly important. Therefore, in hot metal preliminary dephosphorization treatment, a technique that has high dephosphorization ability and high dephosphorization treatment efficiency without using a secondary raw material containing fluorine such as fluorite is strongly demanded.

  As a dephosphorization treatment method having a high dephosphorization ability without using an auxiliary raw material containing fluorine such as fluorite, there is an invention of “powder-on-powder dephosphorization method” (Patent Document 1), and an invention that has been further improved in recent years Many have been released. For example, (1) a method of spraying a CaO-containing dephosphorizing agent after generating cover slag to reduce the amount of spitting during the dephosphorization process (Patent Document 2), and (2) suppressing the amount of generated slag Therefore, a dephosphorization method in which the slag basicity after dephosphorization treatment is carried out with hot metal having a Si concentration of 0.20% by mass or less at more than 2.5 and 4.95 or less (Patent Document 3), (3) high speed In order to achieve both dephosphorization treatment and hatching rate maintenance, there is a method (Patent Document 4) in which blowing from a lance of a low basicity and granular solid oxygen source is used.

JP-A-8-311523 Japanese Patent No. 3687433 Japanese Patent No. 3952846 JP 2008-266666 A

  However, (1) is effective in suppressing spitting, and (2) may provide a high dephosphorization ability, but the relationship with increasing the efficiency is unclear. On the other hand, (3) may be capable of high-efficiency dephosphorization, but requires a special device for blowing a granular solid oxygen source and cannot be easily implemented.

  In order to improve the efficiency of hot metal dephosphorization, it is necessary to solve difficult problems such as compatibility of increasing basicity, increasing hatchability and suppressing spitting, and simultaneously increasing FeO in slag and suppressing slopping. Is piled up. In other words, it is difficult for existing inventions alone to achieve sludge and spitting, and to achieve higher processing efficiency than before, without generating extra costs based on the powder top blowing dephosphorization method. It was.

  The object of the present invention is to solve the above-mentioned problems of the prior art and to establish a dephosphorization / dephosphorization technology that ensures high dephosphorization efficiency and high dephosphorization performance at a lower cost.

The present invention is as described below.
(1) In an upper bottom blowing type converter equipped with an upper blowing lance and a bottom blowing nozzle, C: 4.3 to 4.6%, Si: 0.30 to 0.50% and P: It is a method of charging molten iron having 0.090-0.120% and spraying powdered quicklime with oxygen from the upper blowing lance to degassing and dephosphorizing,
A solid oxygen source is added to the hot metal, and 2.0 to 4.0 Nm ³ / t in terms of oxygen flow rate is added within 30 seconds immediately before or immediately after the start of oxygen supply from the top blowing lance,
The top blowing oxygen supply rate from the top blowing lance is 2.0 to 3.0 Nm ³ / min / t,
The bottom blowing gas supply rate from the bottom blowing nozzle is set to 0.2 to 0.3 Nm ³ / min / t during the degassing process period, and 0.4 to 0.4 after the degassing process until the end of the dephosphorization process. 0.5 Nm ³ / min / t,
The charge basicity is CaO / SiO ₂ : 2.5 to 3.0 by mass ratio,
80% or more of the total CaO mass included in the calculation of the charging basicity is adjusted at a blowing rate of 6 kg / min / t or less with powdered quicklime having a maximum particle size of 0.5 mm or less, and the above top blowing Sprayed hot metal with oxygen from the lance,
The supply time of the top blowing oxygen is 6 minutes or less,
A degassing / dephosphorizing method for hot metal, wherein the concentration of C in the hot metal after the treatment is 3.4 to 3.7% by mass.

  However, the degassing treatment period is a period from the start of the supply of the above blown oxygen to the removal of Si in the hot metal, and is a time (min) calculated by the equation (1).

([Si] ₀ × 8−Q _o ′) / Q _o (1)
[Si] ₀ : Si concentration (mass%) of the hot metal charged into the converter
Q _o ′: solid oxygen amount (Nm ³ / t) to be added onto the hot metal within 30 seconds immediately before or after the start of oxygen supply from the top blowing lance
Q _o : Oxygen flow rate supplied from top blowing lance (Nm ³ / min / t)

  According to the present invention, it is possible to realize a dephosphorization process in a short time at a low cost, while suppressing a slopping and spitting while ensuring a high dephosphorization ability without using an auxiliary material containing fluorine. It has become possible to simultaneously achieve environmental load reduction (fluorine-free), high dephosphorization ability (lower [P] after treatment), and high dephosphorization efficiency (high-speed dephosphorization blowing).

1) Basic Embodiment The hot metal discharged from the blast furnace is basically not subjected to hot metal preliminary desiliconization treatment, but is subjected to hot metal preliminary desulfurization treatment as necessary, and in terms of mass concentration, C: 4.3 The hot metal having ˜4.6%, Si: 0.30 to 0.50% and P: 0.090 to 0.120% is converted into an upper bottom blowing type converter equipped with an upper blowing lance and a bottom blowing nozzle. The hot metal supply time is 6 minutes or less and the C concentration in the molten iron after the treatment is 3.4 to 3.7% by mass concentration, and the P concentration in the molten iron after the treatment is 0 in mass concentration. Reduce to .015% or less.

In order to complete the above desiliconization and phosphorus removal treatment in such a short time, it is necessary to set the oxygen supply rate of the top blowing oxygen from the top blowing lance to 2.0 to 3.0 Nm ³ / min per ton of hot metal to be treated. In addition, in order to reduce the burden on the global environment in recent years, no synthetic raw materials containing fluorine such as fluorite are used, and in order to reduce the cost of using a dephosphorization agent, a synthetic synthetic material that is expensive as a CaO source Without using calcium aluminate, calcium ferrite, etc., it is necessary to suppress the occurrence of slopping and spitting and achieve a low phosphorus concentration in the hot metal.

2) Means for ensuring high dephosphorization without using fluorine-containing auxiliary materials A powdered CaO-containing substance (hereinafter referred to as powder CaO) is blown up to hot metal together with top blowing oxygen. This is because the fine CaO-containing material is directly sprayed onto a high-temperature fire point to promote hatching without using a secondary raw material containing fluorine.

  As the powder CaO, it is necessary to make the maximum particle size as fine as 0.5 mm or less, and as the maximum particle size is made as fine as 0.1 mm or less, hatching is faster and more stable. The material is preferably quick lime powder, but may be a mixture of quick lime powder and limestone powder having a CaO concentration of 80% by mass or more.

  In order to use the above-described high-speed hatching mechanism among the mass of CaO supplied into the furnace, the mass ratio supplied with powder CaO must be 80% or more. If this ratio is less than 80%, hatching of the supplied CaO is delayed, and the desired P concentration in the hot metal after the treatment cannot be stably obtained. In addition, the hatching of the supplied CaO is delayed, causing problems in slag basicity control, and the slag forming suppression function described later is not sufficiently exhibited, and slopping is likely to occur.

  The ratio supplied by the powder CaO is preferably as high as possible, and is most preferably 100%.

3) Slopping suppression means in high-speed processing Control of the amount of slag in the furnace and basicity control of the slag in the furnace are important.

  (1) Regarding the amount of slag in the furnace, in addition to preventing spitting due to high-speed acid feeding, it is necessary to ensure a certain amount or more in order to reduce P in the hot metal, but excessive generation induces slopping. Therefore, it becomes an operation impediment factor.

  The amount of slag produced depends on the amount of CaO supplied and the amount of FeO produced, but can basically be controlled by the Si concentration in the hot metal. Therefore, as a result of examining the amount of slag that can stably achieve the prevention of spitting and the dephosphorization ability and suppress the slopping, the Si concentration in the hot metal is 0.30 to 0.50 mass%. I knew that it was necessary to keep it at a certain level.

  For hot metal outside this Si concentration range, even if the other requirements according to the present invention are satisfied, the supply time of the top blown oxygen is 6 minutes or less and the desired low P concentration hot metal cannot be obtained. It is necessary to apply.

  (2) Regarding the slag basicity in the furnace, it must be increased as soon as possible within a range in which the hatching rate of the supplied CaO can be prevented from decreasing after the end of the degassing treatment period. This is because, after the desiliconization period, the top blown oxygen mainly reacts with C in the molten iron, so the amount of generated CO gas increases, the amount of generated slag increases, or the viscosity is high and the CO gas is difficult to escape. This is because slapping tends to occur in the case of slag.

For this purpose, assuming that powder CaO is used, the slag basicity (CaO / SiO ₂ ) is set to 2. at the end of the dephosphorization process where it is necessary to increase the amount of slag to promote dephosphorization. It is necessary to raise it to about 3 to 2.9. Such slag basicity is a device that sets the charging basicity as high as CaO / SiO ₂ : 2.5 to 3.0 by mass ratio and increases the hatching rate of CaO to 90% or more. Is achieved by applying

  As a basic means of the device, it is necessary to spray as much as possible (80% or more) of the total CaO mass included in the calculation of the charging basicity with powdered CaO onto the hot metal together with top blowing oxygen. The ratio of CaO supplied in the form is preferably 100%.

  However, since CaO supplied in powder form needs to be sprayed onto the hot metal together with the upper blowing oxygen, if the supply speed is too fast, the hatching rate at the hot metal surface portion will decrease, and the outside of the furnace will pass through the slag. The ratio of splashing to becomes higher. On the other hand, CaO that has not hatched on the hot metal surface part is useful for breaking bubbles when the slag is forming. Therefore, about several percent of the supplied CaO is preferable, and this bubble breaking function is used. In addition, it is preferable to continue spraying the powder CaO after the desiliconization period ends until the dephosphorization process ends.

However, since the decrease in the hatching rate of the supplied CaO leads to an increase in the cost of using the secondary raw materials required for the dephosphorization treatment, it is preferable that about 90% or more of the molten slag is used. Such hatching of the CaO at the hot metal surface part appropriately controls the supply rate of the powder CaO as long as the supply rate of the top blown oxygen is determined to be 2.0 to 3.0 Nm ³ / min / t. Is achieved. The supply rate of the powder CaO will be described later together with measures for suppressing spitting.

4) Spitting suppression means in high-speed processing It is important to form a certain amount of cover slag from the initial stage of blowing and to keep the formed slag in a molten state.

(1) First, as a cover slag formation measure, there is no out-of-furnace degassing treatment, using hot metal having a Si concentration of 0.30% by mass or more, and SiO ₂ produced by top blowing oxygen from the start of blowing It reacts rapidly with powdered CaO to produce a low melting point slag, and then promotes the hatching of the added CaO.

Here, in order to secure molten slag on the hot metal at the time of starting the supply of top blowing oxygen, a solid oxygen source (preferably a scale) is added immediately before or after the start of oxygen supply from the top blowing lance to partially melt the hot metal. It is necessary to react with middle Si to produce a molten slag mainly composed of iron oxide and SiO ₂ . When 2.0 to 4.0 Nm ^{3 is} added when the solid oxygen source is converted into the top blown oxygen flow rate, assuming that the reaction efficiency of the solid oxygen source with Si in the molten iron is 50%, the generated SiO ₂ is 2.5. It is ˜5.0 kg / t, and a sufficient amount is secured as the initial cover slag.

In the present invention in which the supply rate of top blown oxygen is 2.0 to 3.0 Nm ³ / min / t, assuming that the reaction efficiency between Si in the initial hot metal and top blown oxygen is 100%, SiO 2 _{2 The} production rate is 2.5 to 3.7 kg / min / t. However, since the Si concentration in the hot metal is 0.30 to 0.50% by mass, the total mass of SiO ₂ is only 6.4 to 10.7 kg / t, which is not a level that induces slapping.

(2) Regarding the maintenance of the molten state of the in-furnace slag, it can be handled by controlling the spraying speed of the powder CaO. First, the molten slag to be generated in the initial stage is considered to have a basicity (CaO / SiO 2) so that the molten metal temperature in the converter is a low temperature of about 1300 to 1350 ° C. and can maintain a molten state even at that temperature. ₂ ) is preferably about 1.0. On the other hand, since it is necessary to finally increase the charging basicity by mass ratio to CaO / SiO ₂ : 2.5 to 3.0, 10 to 20 kg / t of CaO is required.

  Since it is assumed that the entire treatment time is within 6 minutes, considering that the period after the desiliconization treatment period is about 4 to 5 minutes, the CaO supply rate is on average 5 kg / min / It is not necessary to increase it to t or more, and 6 kg / min / t or less is considered to be sufficient even in a period in which it is desired to increase the rate of increase in slag basicity for 1 to 2 minutes from the end of the desiliconization treatment. If this speed is too high, the momentum of the powder CaO sprayed together with the top-blown oxygen is increased, and spitting tends to occur, which is not preferable.

  However, although it is a relatively low temperature condition immediately after the start of blowing, if the basicity of the slag is too low, the refractory of the converter refractory may be melted and the slag may be formed. Therefore, the supply rate of the powder CaO during this period is preferably about 3 kg / min / t or more.

In the present invention, the “desiliconization treatment period” is a period from the start of supply of top blowing oxygen to the removal of Si in the hot metal, since 1.0% by mass of Si in the hot metal becomes SiO _2. Since 8.0 Nm ³ / t of oxygen is required, it is defined as the time (min) calculated by the equation (1): ([Si] ₀ × 8−Q _o ′) / Q _o .

5) Dephosphorization promoting means in high-speed treatment Ensuring a certain amount of slag, securing the hatching rate of the supplied CaO, and promoting the slag-metal reaction. As described above, in order to ensure the amount of slag, the hot metal component range is determined and the slag basicity is increased, and in order to ensure the hatching rate, the powder CaO supply rate is mainly limited. The metal reaction is promoted by controlling the bottom blowing gas flow rate and the C concentration in the hot metal at the end of the treatment.

  (1) Regarding the bottom blowing gas, it is desirable to lower the flow rate and relatively weakly stir the hot metal during the period from the start of blowing to the end of degassing. This is because it is preferable that the top blown oxygen mainly reacts with Si in the hot metal, and the remaining oxygen reacts with Fe to produce FeO. Conversely, FeO in the produced slag reacts with C in the hot metal and is reduced. It is not preferable to keep the in-furnace slag in a molten state.

On the other hand, during the period in which the slag generation is promoted while increasing the slag basicity in the furnace after completion of the degassing treatment period, the amount of slag is increased and the molten iron and slag are vigorously stirred, so that C in the molten iron and the slag The reaction between P and slag in the hot metal must be promoted without hesitation that FeO will react. Therefore, the bottom blowing gas flow rate in the present invention is de硅processing period 0.2~0.3Nm ³ / min / t during de-硅processed to dephosphorization process ends 0.4~0.5Nm ³ / min / T.

  (2) Also, after the desiliconization period, the top blown oxygen basically reacts with C in the molten iron to become CO, so the gas flow rate is about 10 times that of the bottom blown gas flow rate. By appropriately utilizing this CO gas, the dephosphorization reaction is greatly accelerated. Since this CO gas generation amount is determined by the amount of oxidation reduction of hot metal C, the hot metal and slag stirring by CO gas can be controlled by managing the hot metal C concentration at the end of the treatment. For this purpose, it is appropriate that the C concentration in the hot metal at the end of the treatment is 3.4 to 3.7% by mass, which is the lower value.

  Since the hot metal after carrying out the present invention is subjected to a decarburization process for producing molten steel using a converter, if the C concentration in the hot metal after the process becomes too low, the heat source during the decarburization process will be insufficient. . Therefore, the hot metal C concentration at the end of the treatment must be 3.4% by mass or more.

  The present invention has been obtained as a necessary requirement to be integrated as a result of a comprehensive study based on the idea of the technical idea described above, and to realize the idea.

Hot metal 78t to 85t (composition: [C] about 4.4% by mass, [Si] 0.30 to 0.50% by mass, [P] 0.090 to 0.120% by mass) to the top bottom blow converter Then, desiliconization and phosphorus removal treatment was performed with up-blowing oxygen of 2.0 to 3.0 Nm ³ / min / t. Twenty to thirty seconds before starting the supply of top-blown oxygen to the hot metal, 2.0 to 4.5 Nm ³ / t of scale (mainly FeO) was added as a solid oxygen source in terms of oxygen amount, and the top-blown oxygen Simultaneously with the start of supply, powdered quicklime containing 92% CaO as powder CaO and having a maximum particle size of 0.1 mm or less was blown at a rate of 3.8 to 6.4 kg / min in terms of pure CaO per ton of hot metal. The dephosphorization and dephosphorization treatment was carried out by spraying on the hot metal bath surface with oxygen at an attaching speed. Moreover, 0 to 7.4 kg / t of CaO was introduced using massive quicklime having a maximum particle size of 60 mm or less immediately before starting the supply of top-blown oxygen or immediately after the start of the supply. No synthetic ironmaking materials such as fluorine-containing auxiliary materials and calcium aluminate were used.

The charge basicity was 2.1 to 3.0, and the relationship with the actual basicity was investigated. The charge basicity is (total amount of CaO in the added CaO-containing auxiliary material) / (the amount of SiO ₂ produced by oxidation of [Si] in the hot metal and the amount of SiO ₂ in the auxiliary raw material charged in the furnace) And the actual basicity is (CaO mass concentration% of slag) / (SiO ₂ mass concentration% of slag).

During the dephosphorization process, N ₂ gas was blown into the hot metal at 0.2 to 0.5 Nm ³ / min / t from the bottom blowing nozzle, and stirring was performed.

  The hot metal temperature after dephosphorization (the hot metal temperature measured in the pan after the hot water from the converter) was 1302 to 1341 ° C., and the hot metal [C] after the treatment was controlled to 3.38 to 3.68% by mass. It was. Table 1 summarizes the specific conditions and results of each dephosphorization treatment in this investigation.

  The object of the present invention is to use no fluorine-containing auxiliary materials, and without using a synthetic iron making material other than powder CaO and lump CaO, (1) hot metal after processing [P] ≦ 0.015 mass %, (2) Sloping and spitting suppression, and (3) Dephosphorization treatment time (supplying time of top blowing oxygen) of 6 minutes or less, and dephosphorization treatment is performed under the conditions specified in the present invention. In this case, it was confirmed that all of (1) to (3) were satisfied (see Invention Examples 1 to 9 in Table 1).

  On the other hand, when the treatment is performed under conditions that do not satisfy even one of the conditions defined in the present invention, [P]> 0.015 mass% after treatment or slopping or spitting occurs, resulting in hindering stable operation. (See Comparative Examples 10 to 16 in Table 1).

  First, examples of the present invention and comparative examples 10 and 11 will be described. Under conditions where the powder blowing speed exceeded 6.0 kg / min / t, spitting became intense during the powder spraying, and adhesion of metal to the oxygen top blowing lance occurred. Moreover, 1 mass% or more of un-hatched CaO (f.CaO) was present in the slag after the treatment, and it was found that the hatching failure of the supplied CaO occurred. As a result, the hot metal [P] after dephosphorization was also 0.015% by mass or more, and a decrease in dephosphorization ability was confirmed.

Next, examples of the present invention and comparative examples 12 to 14 will be described. As a result of continuing strong stirring at a bottom blowing gas flow rate of 0.5 Nm ³ / min / t from the Si removal period, [P] after treatment was 0.015% by mass or more. This is presumably because the generated FeO reacted with [C] in the hot metal by vigorous stirring, and the slag in the furnace was not maintained in a molten state. Moreover, the dephosphorization reaction progressed rapidly, but the hatching of CaO was delayed. As a result, large-scale slopping occurred, and the amount of slag remaining in the furnace decreased. Decline was confirmed. As in Comparative Example 12, there are rare cases where the hot metal after processing [P] ≦ 0.015% by mass is achieved, but since the level of slopping becomes severe and the stable operation is hindered, the continuous operation condition is still Not suitable.

  Finally, examples of the present invention and comparative examples 15 and 16 will be described. As a result of the treatment with the powder CaO ratio being less than 80%, the slag after treatment (f.CaO) becomes 1.5 mass% or more, and in the high-speed treatment where the supply time of the top blowing oxygen is 6 minutes or less, it is a lump. It was confirmed that the CaO supplied in No. 1 did not sufficiently hatch. As a result, it was found that it was difficult to achieve molten iron [P] ≦ 0.015 mass% after the treatment.

  From the above results, in order to achieve high dephosphorization capability without using fluorine-containing auxiliary materials, suppress slopping and spitting, and realize dephosphorization processing in a short time at low cost, The effectiveness of operation within the range of conditions defined in the present invention was confirmed.

Claims (1)

In an upper bottom blowing type converter equipped with an upper blowing lance and a bottom blowing nozzle, by mass concentration, C: 4.3 to 4.6%, Si: 0.30 to 0.50%, and P: 0.090. A method of charging molten iron having ˜0.120%, and spraying powdered quicklime with oxygen from the upper blowing lance to degassing and dephosphorizing,
A solid oxygen source is added to the hot metal, and 2.0 to 4.0 Nm ³ / t in terms of oxygen flow rate is added within 30 seconds immediately before or immediately after the start of oxygen supply from the top blowing lance,
The top blowing oxygen supply rate from the top blowing lance is 2.0 to 3.0 Nm ³ / min / t,
The bottom blowing gas supply rate from the bottom blowing nozzle is set to 0.2 to 0.3 Nm ³ / min / t during the degassing process period, and 0.4 to 0.4 after the degassing process until the end of the dephosphorization process. 0.5 Nm ³ / min / t,
The charge basicity is CaO / SiO ₂ : 2.5 to 3.0 by mass ratio,
80% or more of the total CaO mass included in the calculation of the charging basicity is adjusted at a blowing rate of 6 kg / min / t or less with powdered quicklime having a maximum particle size of 0.5 mm or less, and the above top blowing Sprayed hot metal with oxygen from the lance,
The supply time of the top blowing oxygen is 6 minutes or less,
A degassing / dephosphorizing method for hot metal, wherein the concentration of C in the hot metal after the treatment is 3.4 to 3.7% by mass.
However, the degassing treatment period is a period from the start of the supply of the above blown oxygen to the removal of Si in the hot metal, and is a time (min) calculated by the equation (1).
([Si] ₀ × 8−Q _o ′) / Q _o (1)
[Si] ₀ : Si concentration (mass%) of the hot metal charged into the converter
Q _o ′: solid oxygen amount (Nm ³ / t) to be added onto the hot metal within 30 seconds immediately before or after the start of oxygen supply from the top blowing lance
Q _o : Oxygen flow rate supplied from top blowing lance (Nm ³ / min / t)