JP5772645B2 - Dephosphorization method for hot metal - Google Patents

Description

  The present invention relates to a method for improving the dephosphorization rate while suppressing iron loss without using a halide typified by fluorite in a hot metal dephosphorization method using a top-bottom blow converter. It is.

  In recent years, with the increase in demand for low P steel with low phosphorus (P) content, a steelmaking method of performing decarburization blowing in a converter after preliminary phosphorus removal at the hot metal stage to remove phosphorus in the hot metal Has developed. The preliminary dephosphorization process at this time is performed by using a torpedo car, a hot metal ladle, or a converter, and adding a CaO-based refining agent and an oxygen source.

In this preliminary dephosphorization treatment, it is important to increase the slag basicity (CaO mass% / SiO ₂ mass%) in order to efficiently perform the dephosphorylation reaction. However, when the slag basicity is increased, the melting property of the CaO-based refining agent to be supplied deteriorates. Therefore, in actual operation, a method for ensuring the refining agent melting property by adding fluorite as a part of the refining agent. Has been widely used.

  However, recently, from the viewpoint of environmental issues, the amount and concentration of fluorine are also regulated in steelmaking slag products, and a hot metal dephosphorization method that does not use halides such as fluorite has been developed. ing.

As a hot metal dephosphorization method using no halide, a method using calcium ferrite is known.
In Patent Document 1, including CaO and Fe t _O that compound on at least a part, a method of adding a refining agent to the main component CaO and Fe t _O is disclosed.

In Patent Document 2, so that the actual basicity obtained by analyzing the slag after dephosphorization blowing completion (the ratio of the CaO mass concentration and SiO ₂ mass concentration in the slag) is 1.8 to 2.6 In addition, a hot metal dephosphorization method using a refining agent containing calcium ferrite at least in part is disclosed.

  In these Patent Documents 1 and 2, only the dephosphorization efficiency is described, and no iron loss is disclosed. Therefore, even if molten slag can be formed efficiently using calcium ferrite and dephosphorization efficiency is improved, slag with high basicity is generally poor in fluidity, and granular iron generated by top-blowing oxygen jet is trapped in slag. The problem remains that the iron yield is deteriorated.

On the other hand, attempts have been made to improve the dephosphorization efficiency with a low basicity.
Patent Document 3 discloses a hot metal dephosphorization method in which the slag basicity is set to 0.8 to 1.8 to adjust the slag content (T.Fe) and the slag mass, but the iron content including the slag medium grain iron is disclosed. There is no description about the yield, and the condition that satisfies both the dephosphorization efficiency improvement and the iron yield improvement cannot be inferred from the description.

Furthermore, in Patent Document 4, the slag basicity is relatively low at 1.0 to 2.5, and the supply rate of the top blown oxygen is 1.5 to 5.0 Nm ³ / min / molten iron ton, A method for suppressing a decrease in iron yield while obtaining high dephosphorization efficiency is disclosed. However, the conditions that the slag basicity is 1.0 to 2.5 and the supply rate of the top blown oxygen is 1.5 to 5.0 Nm ³ / min / molten ton are in a wide range including many of the known conditions in recent years. is there. Moreover, the improvement of the iron yield, which is the subject of the invention, is due to the suppression of spitting and dust generation, and no mention is made of granular iron in the slag. Therefore, in such a wide range, suitable conditions that satisfy both the dephosphorization efficiency improvement and the iron yield improvement cannot be inferred from the description.

JP 2005-314760 A JP 2010-001536 A JP 2002-129219 A JP 2008-266666 A

  The present invention, without using a halide typified by fluorite, improves the iron yield by reducing the granular iron that is discharged together with the slag while suspended in the slag after the hot metal dephosphorization treatment, Another object of the present invention is to provide a hot metal dephosphorization method with high dephosphorization efficiency that does not decrease the dephosphorization rate.

  In the hot metal dephosphorization treatment, the present inventors have proposed a method for efficiently removing phosphorus without suppressing the loss of iron content without using a halide typified by fluorite. As a result of investigating the combination of this method and the method of spraying powdered CaO source onto hot metal together with oxygen from a top blowing lance and dephosphorizing the powder, These findings A to D could be obtained.

(A) By reducing the basicity of slag, the fluidity of slag is improved, and as a result, the amount of granular iron in the slag after dephosphorization treatment is significantly reduced.
(B) By appropriately using calcium ferrite, the melt hatching of CaO after the middle stage of the treatment is promoted, and as a result, the necessary dephosphorization rate can be ensured even under relatively low basicity conditions.

  (C) In addition to the above items A and B, by blowing an appropriate amount of powdered CaO together with oxygen from an upper blowing lance, it can be increased to a predetermined basicity without reducing the hatching rate of CaO, Slag forming can be suppressed and grain iron loss can be suppressed.

  (D) The above-mentioned items A to C are such that when normal hot metal containing 0.20% by mass or more of Si is targeted, changes in spitting and dust generation are observed in actual operation. Does not reach.

The above-mentioned knowledge is realized by the present invention having the following invention specific matters, and can solve the above-mentioned problems.
(1) A hot metal dephosphorization method containing 0.2 to 0.6% by mass of Si, which is performed using an upper-bottom blowing converter,
The charge basicity (CaO mass / SiO ₂ mass) during dephosphorization treatment is set to 1.4 to 2.0,
Among the CaO sources supplied to make the range of the basic charge,
Hot iron dephosphorization characterized in that calcium ferrite is supplied as a lump and supplied in an amount of 4 kg or more per ton of hot metal, and CaO is supplied in the form of powder in the range of 2 to 4 kg per 1 ton of hot metal by spraying with hot oxygen along with oxygen. Processing method.

  (2) The above-mentioned calcium ferrite is supplied while the oxygen spraying time is 35% or more and 80% or less of the total oxygen spraying time after the start of oxygen spraying by the top blowing lance ( The method for dephosphorizing hot metal as described in item 1).

  (3) The supply of the CaO in powder form is completed by the time when 80% of the total oxygen spraying time has elapsed after the start of oxygen spraying by the top blowing lance ( The method for removing phosphorus from hot metal as described in item 2).

  According to the present invention, without using a halide typified by fluorite, the iron yield is improved by reducing the granular iron that is discharged together with the slag while being suspended in the slag after the hot metal dephosphorization treatment, In addition, a hot metal dephosphorization method with high dephosphorization efficiency without reducing the dephosphorization rate is provided.

FIG. 1 is a graph showing the relationship between charge basicity and [P] after de-P. FIG. 2 is a graph showing the relationship between charging basicity and iron yield. FIG. 3 is a graph showing the relationship between the amount of calcium ferrite input and [P] after dephosphorization. FIG. 4 is a graph showing the relationship between the amount of powdered CaO spray and the iron yield. FIG. 5 is a graph showing the relationship between the charged basicity and [P] after dephosphorization.

Hereinafter, modes for carrying out the present invention will be described.
(1) General dephosphorization treatment conditions In the present invention, using an upper bottom blowing converter having an upper blowing lance and a bottom blowing tuyere, the charging basicity (CaO mass / SiO ₂ mass) is set to 1.4. The hot metal is preliminarily dephosphorized under the condition of ~ 2.0.

  The hot metal before dephosphorization is usually mass%, C: 4.2-4.7%, Si: 0.2-0.6%, Mn: 0.2-0.5%, P: 0 100 to 0.130%, and the hot metal temperature is 1250 to 1390 ° C. After the dephosphorization of the hot metal, in mass%, C: 3.5 to 3.9%, Si: 0.02% or less, Mn: 0.1 to 0.3%, P: 0.03% The following is contained, and the temperature is set to 1280 to 1350 ° C.

From the top blowing lance, oxygen gas was blown onto the hot metal at a rate of 1.0 to 2.0 Nm ³ / min per 1 ton of hot metal, and stirring gas such as nitrogen or Ar was supplied from the bottom blowing tuyere to 0.15 to 1 t of hot metal. Blow into the hot metal at a rate of 0.45 Nm ³ / min.

(2) Charging basicity Charging basicity refers to the "total amount of CaO contained in the secondary raw material supplied into the converter" as a molecule, and "SiO contained in the secondary raw material supplied into the converter" ₂ mass total "and is Si contained in the" hot metal and scrap is a numerical value of the ratio is calculated the sum of the SiO ₂ mass "in the case of the oxidized to the total SiO ₂ as a denominator. The basicity of slag after dephosphorization is a value obtained by multiplying the charging basicity by the hatching rate of CaO, and the hatching rate depends on the dephosphorization processing conditions such as the auxiliary material supply method and the oxygen supply method. However, conventionally, it fluctuated in the range of 0.7 to 1.0.

In the present invention, the charging basicity is adjusted in the range of 1.4 to 2.0.
FIG. 1 shows the result of dephosphorization treatment of about 240 t of hot metal containing components before dephosphorization treatment under the above-described general dephosphorization treatment conditions by a conventional method using neither calcium ferrite nor powdery CaO. It is a graph which shows.

  As shown in the graph of FIG. 1, when fluorite is used, the P concentration in the hot metal after dephosphorization decreases as the charging basicity increases, and the charging basicity is 1.4 or more. The concentration of P in the hot metal after dephosphorization was about 0.030% by mass or less. However, when fluorite is not used, the P concentration in hot metal after dephosphorization is high as a whole, and even if the charging basicity is increased, the effect of lowering the concentration of P in hot metal after dephosphorization is little. However, in order to make the P concentration in the molten iron after treatment approximately 0.030% by mass or less, it was necessary to increase the charging basicity to a region exceeding 2.0.

FIG. 2 is a graph showing the relationship between the charging basicity and the iron yield when dephosphorization is performed under the same conditions as in FIG.
As shown in the graph of FIG. 2, when fluorite was used, there was no tendency to decrease the iron yield even when the charging basicity was increased. However, when fluorite was not used, the iron yield was low as a whole, and when the charging basicity was increased, the iron yield tended to decrease. The difference between the two was constant at about 0.5% when the charging basicity ranged from 1.4 to 2.0, but when the charging basicity exceeded 2.0, there was a tendency to gradually widen. .

Therefore, in the present invention, the charging basicity is adjusted within the range of 1.4 to 2.0 with the aim of increasing the dephosphorization effect similar to the case of using fluorite without using fluorite. It was.
When the charging basicity is less than 1.4, it is difficult to stably lower the P concentration in the molten iron to 0.030% or less even when fluorite is used. Also, at such a low basicity, slag formation is intense, so that slapping increases and the iron yield decreases.

  On the other hand, when the charging basicity exceeds 2.0, the decrease in the iron yield without using fluorite is large, so it is difficult to recover the decrease in the iron yield due to the absence of fluorite by the new invention. This is because I thought.

  By adjusting the charging basicity to 2.0 or less, the slag basicity after the dephosphorization treatment is surely 2.0 or less. Therefore, with such low basicity slag, the hatching rate of CaO is increased. High and unhatched CaO is low. Therefore, such a slag is advantageous for obtaining a low water expansion coefficient necessary for use as a raw material for roadbed materials.

(3) Use conditions of calcium ferrite and powdered CaO In the present invention, as a CaO source to be supplied to adjust the charging basicity, in addition to quick lime derived from natural minerals, light calcined dolomite, limestone, etc., at the time of steelmaking refining In addition to the converter slag and ladle slag, which are by-products, at least 4 kg of calcium ferrite, which is a synthetic premelt product, is used per 1 ton of hot metal to promote the hatching of the CaO source.

The calcium ferrite in the present invention, there is provided a compound of CaO and _Fe 2 _{O 3,} 4 in a ratio mass ratio of CaO and _Fe 2 _{O 3: 6~3:} 7 refers to the.
Since this calcium ferrite has a low melting point of around 1400 ° C., the hot metal temperature during the treatment according to the present invention is 1250 to 1350 ° C., and oxygen gas is blown from the top blowing lance to make Si, C and Fe in the hot metal. In the method of oxidizing such as a heat source, it has a characteristic that it can be easily melted and hatched. Moreover, since this calcium ferrite contains both CaO and FeO indispensable for the dephosphorization reaction, it is excellent as a dephosphorizing agent. Therefore, when Si etc. contained in the hot metal before processing is oxidized to SiO ₂ etc., when generating molten slag together with CaO source etc. supplied as an auxiliary material in addition to calcium ferrite, the slag generation is promoted. In addition, it is suitable as an auxiliary material for promoting the dephosphorization reaction.

  The amount of calcium ferrite used is 1.4 to 2.0 in charge basicity, and after securing the CaO mass supplied in powder form from the top blowing lance in the range of 2 to 4 kg per 1 ton of hot metal, Increasing the amount in place of other CaO-containing auxiliary materials is advantageous for improving the hot metal dephosphorization rate. However, since it is more expensive than other CaO-containing auxiliary materials, as described below, by using 4 kg or more per 1 ton of hot metal, the P concentration in the hot metal after treatment is stably reduced to 0.03% by mass or less. Since the effect to reduce can be exhibited, it is good to adjust the amount of use while paying attention to it.

  FIG. 3 shows the calcium ferrite per 1 ton of hot metal under the general hot metal dephosphorization conditions described above, in which 2 to 4 kg of powdered CaO is sprayed together with oxygen from an upper blowing lance without using fluorite. It is a graph which shows the result of having investigated the relationship between usage-amount and P% in hot metal after a process.

  As shown in the graph in FIG. 3, in combination with the effect of spraying powdered CaO together with oxygen from 2 to 4 kg per 1 ton of hot metal from an upper blowing lance, supplying calcium ferrite in an amount of 4 kg or more per 1 ton of hot metal, P in the molten iron after treatment It can be seen that the concentration is stably 0.030% or less.

In addition, the use effect of such calcium ferrite is not more than the time when Si is almost absent in the hot metal rather than adding in the initial stage of oxygen supply where Si is present in the hot metal and SiO ₂ is easily generated. That is, it is considered that the oxygen spraying is more suitably performed by adding it on the hot metal after the oxygen spraying time of 35% or more of the total oxygen spraying time has elapsed after the start of the oxygen spraying by the top blowing lance.

  However, even if calcium ferrite is added, it requires a melt hatching time and a dephosphorization reaction time after addition, so that the oxygen spraying time is 80% of the total oxygen spraying time after the start of oxygen spraying by the top blowing lance. It is preferable to carry out before% elapses.

  Further, in order to promote the melt hatching of the CaO-containing auxiliary raw material and increase the hatching rate of CaO, it is effective to supply the CaO-containing auxiliary raw material more finely. However, even if CaO having a fine particle size distribution such that the maximum particle size is 5 mm or less is charged and added from above the converter, the scattering loss increases and the intended effect cannot be improved. As a means for supplying a CaO source having a finer particle diameter, a method in which a powdery CaO source is sprayed onto the hot metal together with oxygen gas from an upper blowing lance is excellent. According to this method, even if a powdery CaO source is used, the scattering loss can be suppressed, and since the CaO is directly supplied to the hot spot region, the hatching rate is expected to be high. .

  Therefore, in the present invention, in addition to the use of calcium ferrite as described above, powdered CaO is further sprayed onto the hot metal together with oxygen through an upper blowing lance to promote the hatching of CaO. Therefore, the powdery CaO source in the present invention is a mixture of CaO sources containing 40 mass% or more of CaO such as quick lime or converter slag, and the CaO content concentration of the entire mixture is 80 mass% or more. , And pulverized so that the maximum particle size is 3 mm or less. Accordingly, a crushed quick lime having a maximum particle size of 1 mm or less is preferable, and a finer particle having a maximum particle size of 0.5 mm or less is more preferable from the viewpoint of speeding up the hatching of CaO. .

  The amount of powdered CaO to be sprayed is such that the basicity of charging is 1.4 to 2.0, and the mass of CaO supplied by calcium ferrite as described above is 4 kg or more per 1 ton of hot metal. It is considered that the larger the number, the better the promotion of the de-P reaction. However, when powdered CaO was used, the tendency for slag forming to be suppressed was recognized as described later with reference to FIG. Accordingly, the low basicity side with a charging basicity close to 1.4 has an effect of suppressing slugging and preventing slopping, but the present invention has a charging basicity of 1.7 to 2.0. It should be noted that under relatively high conditions within the technical scope of the above, the fluidity of the slag is reduced and the granular iron in the slag is increased.

  FIG. 4 shows that, under the above-mentioned general hot metal dephosphorization conditions, without using fluorite, the charging basicity is 1.7 to 2.0, and the amount of calcium ferrite used per 1 ton of hot metal is 4 to 8 kg. It is a graph showing the influence which the quantity of the powdery CaO sprayed from an upper blowing lance with oxygen has on iron content yield on the conditions to be used.

  As shown in the graph of FIG. 4, it can be seen that the iron yield decreases when the amount of powdered CaO used exceeds 4 kg per 1 ton of hot metal. Under conditions where the amount of powdered CaO used is large, the fluidity of the slag after dephosphorization is low, and the situation in which there is a large amount of granular iron was visually confirmed. This decrease in iron yield was caused by the increase in granular iron in the slag. It is thought that there is.

  However, the use of powdered CaO has the effect of increasing the hatching rate of CaO and moderately suppressing slag foaming, so it is appropriate to use 2 kg or more per 1 ton of hot metal.

  Therefore, in the present invention, in addition to the above-described use of calcium ferrite, further, powdered CaO is sprayed on the hot metal together with oxygen through an upper blowing lance in the range of 2 to 4 kg per 1 ton of hot metal, so that CaO is hatched. Promote and control slag forming appropriately.

  In order to improve the spraying effect of the powdered CaO as described above, a certain amount of time is required during the spraying of the top-blown oxygen with respect to both the dephosphorization reaction promotion and the slag foaming suppression. Therefore, it is preferable to complete the spraying of powdered CaO after the start of the oxygen spraying by the top-blowing lance until the oxygen spraying time reaches 80% of the total oxygen spraying time.

Next, the present invention will be described more specifically with reference to examples.
About 240 t of hot metal discharged from the blast furnace was desulfurized with a mechanical stirring desulfurizer (KR), and then charged into an upper bottom blowing converter for dephosphorization. The top lance is used having four oxygen ejection holes, the oxygen supply rate is 20000Nm ³ /h(1.4Nm ³ / min / t therefrom), nitrogen feed rate of bottom-blown are four tuyeres It was performed as ^{5400Nm 3 /h(0.38Nm 3 / min / t} ).

Calcium ferrite has a composition of CaO = 38% by mass, Fe _t O = 60% by mass, and has a maximum particle size of 50 mm. A powdery CaO source sprayed from an upper blowing lance has a composition of CaO = Using quick lime of 94% by mass and a maximum particle size of 3.0 mm, the blowing speed when spraying it was 150 kg / min.

The blowing time was 8 to 10 minutes, and the temperature after the treatment was controlled to 1280 to 1320 ° C.
The results of Examples and Comparative Examples of the present invention are summarized in Table 1 together with the auxiliary raw material supply conditions, including the examples shown in Table 1, the charging basicity and the P concentration in hot metal after dephosphorization treatment. FIG. 5 is a graph showing the relationship.

Hereinafter, No. 1 in Table 1 is used. 1 to 11 will be described. Reference numeral 1 denotes an embodiment that satisfies the conditions specified in claim 1. After the treatment, the P concentration in the molten iron was 0.024%, which was 0.030% or less of the target value, and the iron yield was a good value of 97.4%.

  No. 2 is an embodiment that satisfies the conditions specified in claims 1 and 2. No. Compared to 1, the P concentration in the hot metal after the treatment decreased to 0.019%, and the iron yield was 97.1%.

  No. 3 is an embodiment that satisfies the conditions specified in claims 1 and 2. No. 2 as well. Compared to 1, the P concentration in the hot metal after the treatment decreased to 0.019%, and the iron yield was 96.9%, which was inferior numerical values.

  No. 4 is an embodiment that satisfies the conditions specified in claims 1 to 3. No. Compared with 1 to 3, the P concentration in the hot metal after the treatment decreased to 0.014%, and the iron yield was 98.6%, which was the best value.

  No. 5-7 is a prior art example, and neither calcium ferrite nor powdery CaO spraying is carried out. Although the P concentration in the hot metal after the treatment tended to decrease as the charging basicity was increased, none of the target values could be reduced to 0.030% or less.

No. 8 is a comparative example, and a small amount (2.1 kg / t) of calcium ferrite was used. However, the target value of the P concentration in the hot metal after the treatment could not be achieved.
No. 9 is a comparative example in which calcium ferrite was added to a small amount (1.8 kg / t), and powdered CaO was used in a predetermined amount (3.0 kg / t) that satisfies the conditions defined in claim 1. However, the target value of the P concentration in the hot metal after the treatment could not be achieved.

  No. 10 is a comparative example in which calcium ferrite was added to a small amount (2.2 kg / t), and powdered CaO was used in a large amount (5.8 kg / t) exceeding the conditions defined in claim 1. As a result, the P concentration in the hot metal after the treatment reached the target value of 0.028%, but instead, the iron yield was significantly reduced to 95.4%, and the results were not satisfactory.

  Furthermore, no. 11 is a comparative example, in which powdered CaO is not used, and instead a large amount of calcium ferrite (4.9 kg / t) is used, and the charging basicity is made higher than a predetermined range. As a result, the P concentration in the hot metal after the treatment was 0.015%, which was much lower than the target value. However, the iron yield was significantly reduced to 95.4%, and the results were not satisfactory.

Claims (3)

A hot metal dephosphorization method containing 0.2 to 0.6% by mass of Si using an upper-bottom blowing converter,
The charge basicity (CaO mass / SiO ₂ mass) during dephosphorization treatment is set to 1.4 to 2.0,
Among the CaO sources supplied to make the range of the basic charge,
Supply calcium ferrite in 4kg or more per ton of hot metal in bulk,
And the hot metal dephosphorization processing method characterized by supplying CaO in powder form in the range of 2 to 4 kg per 1 ton of molten iron by spraying the molten metal together with oxygen through an upper blowing lance. The supply of the calcium ferrite is performed while the oxygen spraying time is 35% or more and 80% or less of the total oxygen spraying time after the start of oxygen spraying by the top blowing lance. The hot metal dephosphorization processing method of description. The supply of the CaO in powder form is completed by the time when 80% of the total oxygen blowing time has elapsed after the start of oxygen blowing by the upper blowing lance. The hot metal dephosphorization processing method of description.